PATENT Attorney Docket No.081906-1391247-252410PC Client Ref. No.2023-543-2 IDEAL STRUCTURE AND SCALABLE FABRICATION METHODS STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT [0001] This invention was made with government support under Grant No.2020-67017- 31275 awarded by the United States Department of Agriculture. The government has certain rights in the invention. CROSS-REFERENCE TO RELATED PATENT APPLICATIONS [0002] The present patent application claims benefit of priority to U.S. Provisional Patent Application No.63/424,590, filed November 11, 2022, the entirety of which is hereby incorporated by reference for all purposes. BACKGROUND OF THE INVENTION [0003] Perishable food requires strict cooling conditions to prevent the rapid growth of pathogenic organisms. Currently, to control temperature, traditional ice in different shapes (chunks, cubes, or slurries) is the most approachable and common cooling media for customers and retailers. The general preference towards ice is due to its affordability, cooling efficiency, and convenience of use. The high cooling efficiency of ice comes from its considerable heat capacity and latent enthalpy. However, the meltwater of ice is drawing concerns over food cross-contamination. [0004] Microbial cross-contamination caused by meltwater has been a serious food safety and quality concern. A small piece of bacterial-contaminated food is enough to cause the contamination of a widespread area through meltwater. Commercially available icepacks are widely used and available in the market. However, the thick plastic shell decreases the cooling efficiency and introduces environmental concerns. The non-biodegradable cooling contents in the packs are environmental concerns. Thus, the demand is high for efficient, reusable, scalable and safe coolant substitutes for ice. The present disclosure satisfies this need and offers other advantages as well. BRIEF SUMMARY OF THE INVENTION [0005] In one embodiment, the present disclosure provides a method for making a crosslinked jelly ice cube (JIC), the method comprising: dissolving a biodegradable polymer in water to produce a homogenous solution; placing the homogenous solution in a mold; chilling the homogenous solution in the mold to form a JIC; and exposing the JIC to a crosslinking agent to produce a crosslinked JIC. [0006] In certain aspects, the chilling occurs between about 20°C to about -25°C. In certain aspects, the chilling occurs between about 0°C to about -50°C. [0007] In certain aspects, exposing the JIC to the crosslinking agent is by immersion, misting, a gaseous atmosphere or including in the homogenous biodegradable polymer solution. [0008] In certain aspects, the surface layer of the JIC comprising the biodegradable polymer is crosslinked by immersion. [0009] In certain aspects, the surface layer of the JIC comprising the biodegradable polymer is crosslinked by misting. [0010] In certain aspects, the JIC comprising the biodegradable polymer is crosslinked by including in the homogenous solution. [0011] In certain aspects, the crosslinking of the biodegradable polymer is spontaneous after contacting to the crosslinking agent. [0012] In certain aspects, the crosslinking of the biodegradable polymer is induced by a member selected from the group consisting of heat, radio waves, infrared, visible light, UV, and X-rays. [0013] In certain aspects, the biodegradable polymer is a plant-based polymer or animal- based polymer. [0014] In certain aspects, the polymer is a protein. [0015] In certain aspects, the polymer is a member selected from the group consisting of collagen, gelatin, soy protein, whey protein, zein protein, elastin, laminin, fibrin, silk fibroin lysozyme, bovine serum albumin, ovalbumin, alginate, starch, cellulose, modified proteins, carbohydrates, and combinations thereof. [0016] In certain aspects, the biodegradable polymer is gelatin. In certain instances, using gelatin from different sources, it may be possible to obtain hydrogels with a variety of distinct and diverse physical, chemical, and biological properties. For example, gel strength and rigidity may change with gelatin from different sources. In certain instance, the biodegradable polymer is “water-swellable” or forms a “hydrogel,” which indicates that the polymer takes on and retains water within a network. [0017] In certain aspects, the biodegradable polymer content of the JIC is between about 1% to about 60% w/w. In certain aspects, the biodegradable polymer content of the JIC is between about 5% to about 20% w/w. [0018] In certain aspects, the crosslinking agent is a member selected from the group consisting of menadione sodium bisulfate (MSB), glutaraldehyde (GTA), 1-ethyl-3-(3- dimethylaminopropyl)carbodiimide (EDC), photosensitizers, water soluble vitamin, transglutaminase, genepin, sulfonates, malemide, polyethylene glycol dendrimeric systems, dendritic polymers, hyper-branced dendritic polymers, formaldehyde, enzymatic cross-linker, glycation, glyceraldehydes, cyanamide, diimide, diisocyante, dimethyl adipimidate, carbodiimide and N,N’-carbonyldiimidazole (CDI), N,N’-dicyclohexylcarbonylimide (DCC), N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ), 4-(4,6-dimethoxy-1,3,5-triazine)- 4-methylmorpholium (DMT-MM), 2-benzotriazole-1,1,3,3-tetramethyluronium tetrafluoroborate (TBTU), 3,4-dihydro-3-hydroxy-4-oxo-1,2,3-benzotriazine (HODhbt), benzotriazol-1-oxy-tris-pyrrolidone-phosphonium hexafluorophosphate (PyBOP), benzotriazol-1-yl-oxy-tris-dimethylamino-phosphonium hexafluorophosphate (BOP), 1- ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), N-hydroxysuccinimide (NHS), papain, bromelain, ficin, laccase, peroxidase, and a physical crosslinking agent such as low temperature. A physical crosslinking agent can be low temperature such as about 4°C to about -200°C. In certain instances, low temperature physical crosslinking is by chilling the hydrogel to its phase transition temperature to generate a sol-gel. [0019] In certain aspects, crosslinking is photo-induced. [0020] In certain aspects, the photoinduced crosslinking occurs with UV light at 280-600 nm under an inert atmosphere. [0021] In certain aspects, the disclosure provides a jelly ice cube (JIC) made by the scalable methods described herein. [0022] In yet another embodiment, the present disclosure provides, a method for making a crosslinked jelly ice cube (JIC), the method comprising: dissolving a biodegradable polymer and crosslinking agent, in water to produce a homogenous solution; placing the homogenous solution in a mold; chilling the homogenous solution in the mold to form a JIC; and exposing the JIC to a condition to induce crosslinking reaction. [0023] In certain aspects, the chilling occurs between about 20°C to about -200°C. [0024] In certain aspects, the JIC comprising the biodegradable polymer is crosslinked by chemical crosslinking. [0025] In certain aspects, the crosslinking of the biodegradable polymer is induced by a member selected from the group consisting of heat, radio waves, infrared, visible light, UV, and X-rays. [0026] In certain aspects, the biodegradable polymer is a plant-based polymer or animal- based polymer. [0027] In certain aspects, the polymer is a protein. [0028] In certain aspects, the polymer is a member selected from the group consisting of collagen, gelatin, soy protein, whey protein, zein protein, elastin, laminin, fibrin, silk fibroin lysozyme, bovine serum albumin, ovalbumin, alginate, starch, cellulose, modified proteins, carbohydrates, and combinations thereof. [0029] In certain aspects, the biodegradable polymer is gelatin. [0030] In certain aspects, the biodegradable polymer content of the JIC is between about 1% to about 60% w/w, or about 5% to about 20% w/w. [0031] In certain aspects, the crosslinking agent is a member selected from the group consisting of menadione sodium bisulfate (MSB), glutaraldehyde (GTA), 1-ethyl-3-(3- dimethylaminopropyl)carbodiimide (EDC), photosensitizers, water soluble vitamin, transglutaminase, genepin, sulfonates, malemide, polyethylene glycol dendrimeric systems, dendritic polymers, hyper-branced dendritic polymers, formaldehyde, enzymatic cross-linker, glycation, glyceraldehydes, cyanamide, diimide, diisocyante, dimethyl adipimidate, carbodiimide and N,N’-carbonyldiimidazole (CDI), N,N’-dicyclohexylcarbonylimide (DCC), N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ), 4-(4,6-dimethoxy-1,3,5-triazine)- 4-methylmorpholium (DMT-MM), 2-benzotriazole-1,1,3,3-tetramethyluronium tetrafluoroborate (TBTU), 3,4-dihydro-3-hydroxy-4-oxo-1,2,3-benzotriazine (HODhbt), benzotriazol-1-oxy-tris-pyrrolidone-phosphonium hexafluorophosphate (PyBOP), benzotriazol-1-yl-oxy-tris-dimethylamino-phosphonium hexafluorophosphate (BOP), 1- ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), N-hydroxysuccinimide (NHS), papain, bromelain, ficin, laccase, peroxidase, and a physical crosslinking agent such as low temperature. A physical crosslinking agent can be low temperature. [0032] In certain aspects, crosslinking is photo-induced. [0033] In certain aspects, the photoinduced crosslinking occurs with UV-vis light at 280- 600 nm under an inert atmosphere. [0034] In certain aspects, the disclosure provides a jelly ice cube (JIC) made by the method described herein. [0035] In yet another embodiment, the present disclosure provides a 3-D printing method for making a crosslinked jelly ice cube (JIC), the method comprising: chilling a dissolved biodegradable polymer in water to produce a sol-gel homogenous solution; extruding the sol-gel homogenous solution layer-by-layer in a mold to produce a JIC; and exposing the JIC to a crosslinking agent to produce a crosslinked JIC. [0036] In certain aspects, exposing the JIC to the crosslinking agent is by immersion, misting, a gaseous atmosphere or including in the homogenous solution. [0037] In certain aspects, the surface layer of the JIC comprising the biodegradable polymer is crosslinked by immersion. [0038] In certain aspects, the surface layer of the JIC comprising the biodegradable polymer is crosslinked by misting. [0039] In certain aspects, the JIC comprising the biodegradable polymer is crosslinked by including in the homogenous solution. [0040] In certain aspects, the crosslinking of the biodegradable polymer is spontaneous after contacting to the crosslinking agent. [0041] In certain aspects, the crosslinking of the biodegradable polymer is induced by a member selected from the group consisting of heat, radio waves, infrared, visible light, UV, and X-rays. [0042] In certain aspects, the biodegradable polymer is a plant-based polymer or animal- based polymer. [0043] In certain aspects, the polymer is a protein. [0044] In certain aspects, the polymer is a member selected from the group consisting of collagen, gelatin, soy protein, whey protein, zein protein, elastin, laminin, fibrin, silk fibroin lysozyme, bovine serum albumin, ovalbumin, alginate, starch, cellulose, modified proteins, carbohydrates, and combinations thereof. [0045] In certain aspects, the biodegradable polymer is gelatin. [0046] In certain aspects, the biodegradable polymer content of the JIC is between about 1% to about 60% w/w. In certain aspects, the biodegradable polymer content of the JIC is between about 5% to about 20% w/w. [0047] In certain aspects, the crosslinking agent is a member selected from the group consisting of menadione sodium bisulfate (MSB), glutaraldehyde (GTA), 1-ethyl-3-(3- dimethylaminopropyl)carbodiimide (EDC), photosensitizers, water soluble vitamin, transglutaminase, genepin, sulfonates, malemide, polyethylene glycol dendrimeric systems, dendritic polymers, hyper-branced dendritic polymers, formaldehyde, enzymatic cross-linker, glycation, glyceraldehydes, cyanamide, diimide, diisocyante, dimethyl adipimidate, carbodiimide and N,N’-carbonyldiimidazole (CDI), N,N’-dicyclohexylcarbonylimide (DCC), N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ), 4-(4,6-dimethoxy-1,3,5-triazine)- 4-methylmorpholium (DMT-MM), 2-benzotriazole-1,1,3,3-tetramethyluronium tetrafluoroborate (TBTU), 3,4-dihydro-3-hydroxy-4-oxo-1,2,3-benzotriazine (HODhbt), benzotriazol-1-oxy-tris-pyrrolidone-phosphonium hexafluorophosphate (PyBOP), benzotriazol-1-yl-oxy-tris-dimethylamino-phosphonium hexafluorophosphate (BOP), 1- ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), N-hydroxysuccinimide (NHS), papain, bromelain, ficin, laccase, peroxidase, and a physical crosslinking agent such as low temperature. A physical crosslinking agent can be low temperature, (e.g., 0°C or at its phase transition temperature). [0048] In certain aspects, the disclosure provides a jelly ice cube (JIC) made by the scalable methods described herein. [0049] In still another embodiment, the present disclosure provides a jelly ice cube (JIC), the JIC comprising: a biodegradable crossed-linked polymeric hydrogel network, wherein the network comprises a plurality of isolated chambers or cell-like cavities, creating a lattice. [0050] In certain aspects, the lattice is substantially honeycombed. [0051] In certain aspects, each chamber or cell-like cavity of the lattice entraps water. [0052] In certain aspects, the shape of the JIC is a member selected from the group consisting of free form, a cube, a pyramid, a sphere, a cylinder, a prism, and cone. As it is possible to 3-D print the JIC, it can take on any free form shape. In certain instances, a customized or tailored design and/or geometry can be generated for cooling various-sized items and commodities. [0053] In certain aspects, the plurality of isolated chambers or cell-like cavities comprises a dense matrix of uniformly sized, durable water-retaining cells within the biopolymer network. [0054] In certain aspects, each isolated chamber or cell-like cavity of at least a portion of the plurality of isolated chambers or cell-like cavities has a pore to imbibe water. [0055] In certain aspects, each pore is about 0.1 nm to about 100 µm or 0.1 nm to about 20 nm is diameter. In one aspect, smaller pores are made with a chemical cross-linking agent and a larger pore is made with a physical agent. [0056] In certain aspects, the plurality of isolated chambers or cell-like cavities are nanometer-micrometer scaled. [0057] In certain aspects, the plurality of isolated chambers or cell-like cavities are substantially heterogeneously sized. [0058] In certain aspects, the polymer is a member selected from the group consisting of collagen, gelatin, soy protein, whey protein, zein protein, elastin, laminin, fibrin, silk fibroin lysozyme, bovine serum albumin, ovalbumin, alginate, starch, cellulose, modified proteins, [0059] In certain aspects, the biodegradable polymer content of the JIC is between about 1% to about 60% w/w or about 5% to about 20% w/w or about 1% to about 10% w/w. [0060] These and other aspects, objects and embodiments will become more apparent when read with the following figures and detailed description that follows. BRIEF DESCRIPTION OF THE DRAWINGS [0061] Figure 1 shows a process embodiment of the present disclosure (a) immersing solidified hydrogels in solutions containing chemical crosslinking agents that can induce crosslinking reactions within or among polymer (e.g., protein) molecules; (b) immersing solidified hydrogels in solutions containing crosslinking agents which require additional triggers to generate the crosslinks. The additional triggers include, but are not limited to, photo-irradiation, heat, and X-rays; (c) applying sufficient amount of chemical crosslinking agents on solidified hydrogels to induce spontaneous crosslinking reactions within or among protein molecules on surface of the gels via mist or gaseous environment; and (d) applying mist or gaseous form of crosslinking agents, which requires additional conditions to induce the crosslinking reactions, to surface of solidified hydrogels, then exposing the gels to the adequate conditions, such as but not limited to photo-irradiation, heat, and X-rays, to complete the crosslinking reaction on the surfaces of the gels. [0062] Figure 2 shows a process embodiment of the present disclosure, (a) fabricating hydrogel precursor solutions containing both polymers and chemical crosslinking agents, which can spontaneously induce crosslinking reactions within or among polymers (protein molecules) in controlled reaction rates, and then quickly injecting the solutions to molds in any shapes to form hydrogels. Crosslinking reaction will complete after the shaped hydrogels are made; (b) fabricating hydrogel precursor solutions containing both polymers and chemical crosslinking agents, which requiring additional triggers to induce the crosslinking reactions, and then injecting the solutions to molds in any shapes to form hydrogels. Afterward, exposing the hydrogels to adequate conditions, such as photo-irradiation, heat, and X-rays, to initiate the chemical crosslinking step. [0063] Figure 3 shows the mechanical strengthening effect of immersing gelatin hydrogels (10×10×10 mm) in 5 mg/mL or 10 mg/mL EDC solutions, (a). The compressive strength (b) and strain at break (c) of Gel/EDC[S]-JICs at AFTC0 and after AFTC1, 5, or 10. Images of Gel/EDC[S]-JICs at AFTC0 and after AFTC1, 5, or 10, (d). The compressive strength (e) and strain at break (f) of Gel-JICs at AFTC0 and after AFTC1, 5, or 10. The compressive strength (g) and strain at break (h) of Gel/MSB-JICs at AFTC0 and after AFTC1, 5, or 10. [0064] Figure 4 shows the latent heat of fusion of Gel/EDC[S]-JICs (a), Gel-JICs (b), and Gel/MSB-JICs (c) at AFTC0 and after AFTC1, 5, or 10. The total water content of Gel/EDC[S]-JICs (d), Gel-JICs (e), and Gel/MSB-JICs (f) at AFTC0 and after AFTC1, 5, or 10. The ratio of freezable water of Gel/EDC[S]-JICs (g), Gel-JICs (h), and Gel/MSB-JICs (i) at AFTC0 and after AFTC1, 5, or 10. [0065] Figure 5 shows the compressive stress (a) and strain (b) at break of Gel/EDC[E]- JICs constructed by mixing EDC in different concentrations with gelatin in the precursor solution. Images of Gel/EDC[E]-1-JICs and Gel/EDC[E]-2-JICs before AFTC (AFTC0), (c). The compressive stress (d) and strain (e) at break of Gel/EDC[E]-1-JICs at AFTC0 and after AFTC1, 5, or 10. The compressive stress (f) and strain (g) at break of Gel/EDC[E]-2-JICs at AFTC0 and after AFTC1, 5, or 10. [0066] Figure 6 shows the compressive stress (a) and strain (b) at break of Gel/TA[E]-JICs constructed by mixing TA in different concentrations with 10% gelatin in the precursor solution. The compressive stress (c) and strain (d) at break of Gel/TA[E]-JICs constructed by mixing TA in different concentrations with 8% gelatin in the precursor solution. Images of Gel/TA[E]-1-JICs and Gel/TA[E]-2-JICs before AFTC (AFTC0), (e). The compressive stress (f) and strain (g) at break of Gel/TA[E]-1-JICs at AFTC0 and after AFTC1, 5, or 10. The compressive stress (h) and strain (i) at break of Gel/TA[E]-2-JICs at AFTC0 and after AFTC1, 5, or 10. [0067] Figure 7 shows the latent heat of fusion of Gel/TA[E]-1-JICs (a) and Gel/TA[E]-2- JICs (d) at AFTC0 and after AFTC1, 5, or 10. The total water content of Gel/TA[E]-1-JICs (b) and Gel/TA[E]-2-JICs (e) at AFTC0 and after AFTC1, 5, or 10. The ratio of freezable water of Gel/TA[E]-1-JICs (c) and Gel/TA[E]-2-JICs (f) at AFTC0 and after AFTC1, 5, or 10. [0068] Figure 8 shows the compressive stress and strain at break of Gel/AQS[E]-JICs prepared with 10% gelatin and AQS (anthraquinone sulfate) in different concentrations and photo-irradiated under UVA (365 nm) for 30 min, (a). The compressive stress and strain at break of Gel/AQS[E]-JICs made with 10% gelatin and 0.01% AQS and photo-irradiated under UVA (365 nm) for various durations, (b). Images of Gel/AQS[E]- JICs before AFTC (AFTC0) and after AFTC1, 5, or 10, (c). The compressive stress (d) and strain (e) at break of Gel/AQS[E]- JICs at AFTC0 and after AFTC1, 5, or 10. The latent heat of fusion (f), total water content (g), and the ratio of freezable water (h) of Gel/AQS[E]-JICs at AFTC0 and after AFTC1, 5, or 10. [0069] Figure 9 shows schematics of an embodiment of a surface crosslinked JIC. [0070] Figure 10 shows schematics of an embodiment of an entirely crosslinked JIC. [0071] Figure 11 shows schematics highlighting the distinct 3D biopolymer network structures: nanometer-scaled enclosed chambers ideal for hydrogel cooling media (a) versus open-cell structures seen in hydrogels less suited for repeated cooling applications (b). Visuals produced using OpenAI’s DALL ^E model. [0072] Figure 12 shows structural representation of hydrogel polymeric skeletons. (a) schematic of Gel/EDC and (b) Gel/GTA. Crosslinking mechanisms of gelatin using (c) EDC and (d) GTA. [0073] Figure 13 shows hydrogel fabrication methods. (a) The one-step entirety crosslinking approach, which involves integrating the crosslinking agent directly into the hydrogel precursor solutions. (b) Surface-crosslinking method, where solidified gelatin hydrogels are immersed in diluted solutions of chemical crosslinking agents. (c) A hybrid crosslinking technique that utilizes rapid-freezing-slow-thawing to induce physical crosslinks, complemented by MSB-induced photo-crosslinks. [0074] Figure 14 shows (a) CryoEM image of an 8% gelatin hydrogel (Gel [8]) taken on a glow-discharged holey carbon grid with a resolution of 3.5 Å. The image underwent processing via ImageJ, incorporating a bandpass filter spanning 20 – 30 Å. Within the image, black regions represent protein skeletons, whereas white regions signify water present as ice. (b) Pore size distribution for the Gel [8] sample, encompassing a dataset of 100 points. [0075] Figure 15 shows (a) SEM images showcasing the internal structures of the hydrogel sampled prior to AFTC (A0), dehydrated using CPD; yellow scale represents 50 µm. (b) Effects of electron beam etching. Rectangular-shaped dents and additional morphology features arise from electron beams, especially when observed using 5 kV or 10 kV beams in areas less than 30 µm x 20 µm. [0076] Figure 16 shows evaluating the impact of EDC concentration on crosslinking 10% gelatin hydrogels using the mixing method. (a-b) Compressive mechanical properties of Gel/EDC samples obtained through a one-step integrated entirety crosslinking approach. (c) Compressive properties of Gel/EDC [10-S] samples achieved via surface crosslinking. (d) Total water content, (e) ratio of freezable water, and (f) latent heat of fusion for Gel/EDC samples produced using the one-step entirety crosslinking technique. Gel/MSB [10-F1] and Gel/GTA [10-S] are presented as reference benchmarks, illustrated with pink and yellow dashed lines, respectively. (g) Comparative analysis of the compressive mechanical properties between virgin and crosslinked 10% gelatin hydrogel samples. (h-i) Swelling behavior of both virgin and crosslinked 10% gelatin hydrogel samples. Plotted data are expressed as means ± SD of three replicates. [0077] Figure 17 shows (a) The appearance of prepared samples. (b – c) in vitro enzymatic biodegradability of virgin or crosslinked 10% gelatin hydrogel samples. Compressive mechanical strength (d – h) and strain at break (i – m) of Gel [10] (d and i), Gel/EDC [10-0.2] (e and j), Gel/EDC [10-0.5] (f and k), Gel/MSB [10-F1] (g and l), and Gel/GTA [10-S] (h and m) specimens after various AFTCs. Plotted data are expressed as means ± SD of three replicates. [0078] Figure 18 shows cross-sectional images of Gel [10] (a), Gel/EDC [10-0.2] (b), Gel/EDC [10-0.5] (c), Gel/MSB [10-F1] (d) and Gel/GTA [10-S] (e) hydrogels before AFTC (A0), and after 1 (A1), 5 (A5), 10 (A10) and 15 (A15) cycles of AFTCs, with white scale bars of 2 mm. [0079] Figure 19 shows SEM images of CPD-dehydrated samples: Gel [10], Gel/EDC [10- 0.2], Gel/EDC [10-0.5], and Gel/GTA [10-S] hydrogels before AFTC (A0), and after 1 (A1) application freezing-thawing cycle, with white scale bars of 200 µm and yellow scale bars of 50 µm. [0080] Figure 20 shows total water content (a – e), ratio of freezable water (f – j), and latent heat of fusion (k – o) of Gel [10] (a, f and k), Gel/EDC [10-0.2] (b, g and l), Gel/EDC [10-0.5] (c, h and m), Gel/MSB [10-F1] (d, i and n), and Gel/GTA [10-S] (e, j and o) specimens after various AFTCs. Plotted data are expressed as means ± SD of three replicates. [0081] Figure 21 shows (a) Compressive mechanical properties of EDC-crosslinked 8% gelatin hydrogels using mixing method. (b) The swelling ratio of Gel [8], Gel/EDC [8-0.5], and Gel/EDC [8-2.0] specimen at AFTC0. (c) In vitro enzymatic biodegradability of virgin or crosslinked 8% gelatin hydrogel samples. Compressive mechanical strength (d – g) and strain at break (h – k) of Gel [8] (d and h), Gel/EDC [8-0.5] (e and i), Gel/EDC [8-2.0] (f and j), and Gel/MSB [10-F1] (g and k) specimens after various AFTCs. Plotted data are expressed as means ± SD of three replicates. [0082] Figure 22 shows cross-sectional images of Gel [8] (a), Gel/EDC [8-0.5] (b), and Gel/EDC [8-1.0] (c) hydrogels before AFTC (A0), and after 1 (A1), 5 (A5), 10 (A10) and 15 (A15) cycles of AFTCs. [0083] Figure 23 shows SEM images of CPD-dehydrated samples: Gel [8], Gel/EDC [8- 0.5], and Gel/EDC [8-1.0] hydrogels before AFTC (A0), and after 1 (A1) application freezing-thawing cycle, with white scale bars of 200 µm and yellow scale bars of 50 µm. [0084] Figure 24 shows total water content (a – d), ratio of freezable water (e – h), and latent heat of fusion (i – l) Gel [8] (a, e and h), Gel/EDC [8-0.5] (b, f and j), Gel/EDC [8-1.0] (c, g and k), and Gel/MSB [10-F1] (d, h and l) hydrogel specimens after various AFTCs. Plotted data are expressed as means ± SD of three replicates. DETAILED DESCRIPTION OF THE INVENTION [0085] The present disclosure provides a coolant material or “jelly ice cube” (JIC) and methods of making using a biodegradable polymer such as a protein. The JIC diminishes meltwater while still possessing high cooling efficiency of traditional ice. The JICs contain zero-plastic and can prevent meltwater-caused cross-contamination with high affordability, recyclability, sustainability, and biodegradability. I. Biodegradable Polymer [0086] In one aspect, the biodegradable polymer is a member selected from the group consisting of collagen, gelatin, soy protein, whey protein, zein protein, elastin, laminin, fibrin, silk fibroin lysozyme, bovine serum albumin, ovalbumin, alginate, starch, cellulose, modified proteins, carbohydrates, and combinations thereof. [0087] In one aspect, the biodegradable polymer is gelatin. Gelatin is a product of partial hydrolysis of collagen. During gelatin preparation, collagen is pre-treated under acidic conditions to produce type A gelatin or alkaline conditions to produce type B gelatin. More carboxylic groups are present in type A gelatin than type B gelatin. Either type A or type B is suitable for use in the present disclosure. [0088] The sources of gelatin include bovine skin, bovine hides, cattle, and pork bones, as well as fish and poultry gelatins. Gelatin is a heterogeneous mixture of water-soluble proteins of high average molecular masses, present in collagen. The proteins are extracted by boiling skin, tendons, ligaments, bones, etc. in water. [0089] In certain aspects, the average molecular mass (Da) of the gelatin is about 20,000 to about 100,000 such as 20,000−25,000 (Da), 40,000−50,000 (Da) or 50,000−100,000 (Da). The Bloom number is proportional to MW such as 50-125 (low Bloom) 175-225 (medium Bloom) and 225-325 (high Bloom). These Bloom numbers correspond to 20,000−25,000 (Da), 40,000−50,000 (Da) or 50,000−100,000 (Da), respectively. [0090] Proteins suitable for use in the present disclosure include, for example, natural proteins such as collagen, gelatin, elastin, laminin, fibrin, silk fibroin and globular proteins such as lysozyme, BSA and ovoalbumin and combinations of the foregoing. [0091] In certain aspects, the biodegradable polymer such as a protein (e.g., gelatin) is at a concentration of about 1% to about 60% w/w such as about 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, and/or 60% w/w. In certain instances, the biodegradable polymer is made from about 1% to about 30% w/w or about 1% to about 20% w/w. In certain aspects, the biodegradable polymer content is about 5% to about 16% such as 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16% w/w. In certain aspects, the biodegradable polymer such as a protein (e.g., gelatin) is at a concentration of about 60% to about 90% w/w. [0092] In certain aspect, the biodegradable polymer, biopolymer or protein is crosslinked. [0093] In certain aspect, the biopolymer is a protein that forms a protein hydrogel matrix. The biopolymer matrix can be strengthened to reduce the destructive impact of temperature variations and ice crystal formations, by crosslinking the polymer matrix or polymer hydrogel matrix. To make robust JIC systems, the degree of crosslinking is well-controlled to generate stable hydrogels or cryogels. [0094] In certain aspects, the present methods for forming a JIC includes crosslinking of all or a portion of the biopolymer. In various aspects, crosslinking can occur by a chemical agent, radiation crosslinking, physical crosslinking, photo induced cross-linking or combinations thereof. [0095] In certain aspects, the amount of cross-linking of the biopolymer is about 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, and/or 100%, based on the total amount of biopolymer. II. Crosslinking [0096] Various chemical cross-linkers are suitable for the present invention. The cross- linkers can be homobifunctional having two reactive ends that are identical or heterobifunctional having two different reactive ends. Cross-linkers include a chemical cross- linking agent, which is a member selected from the group consisting of menadione sodium bisulfate (MSB), glutaraldehyde (GTA), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), photosensitizers, water soluble vitamin, transglutaminase, genepin, sulfonates, malemide, polyethylene glycol dendrimeric systems, dendritic polymers, hyper-branced dendritic polymers, formaldehyde, enzymatic cross-linker, glycation, glyceraldehydes, cyanamide, diimide, diisocyante, dimethyl adipimidate, carbodiimide and N,N’- carbonyldiimidazole (CDI), N,N’-dicyclohexylcarbonylimide (DCC), N-ethoxycarbonyl-2- ethoxy-1,2-dihydroquinoline (EEDQ), 4-(4,6-dimethoxy-1,3,5-triazine)-4-methylmorpholium (DMT-MM), 2-benzotriazole-1,1,3,3-tetramethyluronium tetrafluoroborate (TBTU), 3,4- dihydro-3-hydroxy-4-oxo-1,2,3-benzotriazine (HODhbt), benzotriazol-1-oxy-tris- pyrrolidone-phosphonium hexafluorophosphate (PyBOP), benzotriazol-1-yl-oxy-tris- dimethylamino-phosphonium hexafluorophosphate (BOP), 1-ethyl-3-(3- dimethylaminopropyl) carbodiimide (EDC), and N-hydroxysuccinimide (NHS). A physical crosslinking agent can be low temperature. [0097] Other cross-linkers include, transglutaminase, genepin, papain, bromelain, ficin, laccase, peroxidase, sulfonates, malemide, polyethylene glycol dendrimeric systems, dendritic polymers, hyper-branced dendritic polymers, formaldehyde, enzymatic cross-linker, glycation, glyceraldehydes, cyanamide, diimide, diisocyante, dimethyl adipimidate, carbodiimide and epoxy. [0098] Examples of radiation cross-linking includes exposing the hydrogel to at least one of visible light radiation, infrared radiation, ultraviolet radiation, electron beam radiation, gamma radiation, or x-ray radiation. An example of physical crosslinking is exposing the hydrogel article to freezing and thawing. [0099] Crosslinking may be carried out before and/or after forming the hydrogel structure, after shaping the hydrogel into a desired shape, after in situ formation, or at any other suitable point during processing. [0100] Crosslinking of proteins or macromolecules in hydrogels achieves both desired mechanical properties and maximum amount of freezable water in the system. While crosslinking of polymers can be accomplished by using radical, photo-induced radical reactions or reactive groups of proteins with crosslinking agents, chemical, enzymatically or photo-chemical crosslinking approaches are mostly applicable in the hydrogels. [0101] In certain aspects, the biodegradable polymer content of the JIC is between about 1% to about 60% w/w. In certain aspects, the biodegradable polymer content of the JIC is between about 1% to about 20% w/w, or about 1% to about 10% w/w. [0102] In certain aspects, the amount of crosslinker is at a concentration of about 0.1% to about 15% w/w such as about 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15% w/w. [0103] In certain aspects, the amount of polymer to crosslinker is about 100:1, 90:1; 80:1, 70:1, 60:1, 50:1, 40:1, 30:1; 20:1; 15:1, 10:1, 5:15, 4:1, 3:1, 2:1, or 1:1. [0104] In certain aspects, the longer amount of time the solidified hydrogel is in contact with the crosslinker, the stronger the mechanical strength of the JIC. [0105] In certain aspects, a 10 mm x 10 mm x 10 mm cube of the present disclosure has a compressive strength of about 5 kPa to about 1 MPa, such as about 5 kPa, 25 kPa, 50 kPa, 75 kPa, 100 kPa, 125 kPa, 150 kPa, 175 kPa, 200 kPa, 225 kPa, 250 kPa, 275 kPa, 300 kPa, 325 kPa, 350 kPa, 375 kPa, 400 kPa, 425 kPa, 450 kPa, 475 kPa, 500 kPa, 525 kPa, 550 kPa, 575 kPa, 600 kPa, 625 kPa, 650 kPa, 675 kPa, 700 kPa, 725 kPa, 750 kPa, 775 kPa, 800 kPa, 825 kPa, 850 kPa, 875 kPa, 900 kPa, and/or 1MPa. In certain instances, the compressive strength is about 10 kPa to about 25 kPa, such as about 10 kPa to 20 kPa. [0106] In certain aspects, the physically crosslinking is performed by one or more freeze- thaw cycles. [0107] In certain aspects, the crosslinking is performed while the biodegradable polymer is in a frozen state or a thawed state. [0108] There are various scalable methods to incorporate the chemical crosslinkers into the hydrogel and induce the chemical crosslinking reaction: For example, 1) establishing a physical-crosslinked hydrogel first (by chilling or freezing the solution), then achieving surface crosslinking of JICs by applying and inducing the chemical crosslinking reaction only on the surface of JICs; 2) establishing hydrogel network structures with uniform physical and chemical crosslinking in the entirety of JICs by mixing the chemical crosslinker in the precursor solutions of JICs. In certain instances, the methods disclosed herein can be used to make kilogram quantities of JICs. [0109] In certain aspects, the biodegradable polymer is crosslinked in multiple steps. The first goal is a physically crosslinking (by chilling the hydrogel to its phase transition temperature to generate a sol-gel) and the second goal is chemically or photochemically inducing covalent crosslinking. For example, the photo-induced cross-linking agent MSB, on top of physical cross-linking, introduces robust mechanical properties to a JICs that act against the temperature variations and phase changes. III. Surface Crosslinking [0110] Various methods achieve surface crosslinking of JICs. For example, with reference to Figure 1a, a solidified or sol-gel hydrogel 101 can be immersed in a solution containing a chemical crosslinking agent 110 that can induce crosslinking reactions within or among protein molecules 112. Figure 1b shows solidified hydrogels 120 being immersed in solutions containing crosslinking agents 125, which require additional triggers (e.g., heat or photoinduced) to generate the crosslinks 129. The triggers include, but not limited to, photo- irradiation, heat, and X-rays. [0111] In certain other aspects, Figure 1c shows applying or exposing sufficient amount of chemical crosslinking agents 135 on solidified hydrogels 132 to induce spontaneous crosslinking reactions within or among protein molecules on surface of the gels via mist or gaseous environment and generating a crosslinked structure 138. [0112] Figure 1d shows providing a solidified hydrogel 152 and applying mist or gaseous form of crosslinking agents 153, which requires additional conditions to induce the crosslinking reactions 155, to surface of solidified hydrogels, then exposing the gels to the adequate conditions, such as, but not limited to, photo-irradiation, or heat, or X-rays, to complete the crosslinking reaction 159 on the surfaces of the gels. [0113] The surface crosslinked hydrogels are strong and have excellent performance for repeated cooling uses. [0114] In an example of the described process in Figure 1a, in no way limiting, two stock solutions, 30% gelatin and 1% EDC, were prepared in water. The 10% gelatin solution was prepared by diluting gelatin stock solutions at 50 °C, pipetted into the 10 mm × 10 mm × 10 mm cubic molds, and chilled at 4 °C overnight for gelation (e.g. a sol-gel or solidified hydrogel). Once solidified, gelatin hydrogels were immersed in diluted EDC solutions (e.g., 5 mg/mL or 10 mg/mL) for various durations to achieve the chemically crosslinked surface layer. The prepared samples were evaluated directly (AFTC0) or after 1, 5, or 10 application freeze-thaw cycles (AFTC1, AFTC5, or AFTC10). Each AFTC consists of 18 hours of freezing at – 20 °C and 6 hours of thawing at 21°C; 4 °C for sample preservations. [0115] Figure 13b shows a schematic of a surface-crosslinking method, where solidified gelatin hydrogels are immersed in diluted solutions of chemical crosslinking agents. IV. Uniform Hydrogel Crosslinking [0116] In certain other aspects, hydrogels can also be chemically crosslinked uniformly as an entirety. The uniform crosslinking reaction can be achieved by incorporating crosslinking agents into polymer (e.g., protein) solutions. The solutions can be injected into any shaped containers and chilled below their gelling point to solidify. These hydrogels are thereafter subjected to two methods to realize the entirety crosslinking of the gels. For example, Figure 2a shows fabricating hydrogel precursor solutions containing polymers and chemical crosslinking agent(s) 202, which can spontaneously induce crosslinking reactions within or among protein molecules in controlled reaction rates, reducing the temperature 207 and then quickly injecting the solutions into molds 210 in any shapes to form hydrogels. Crosslinking reaction will complete 212 after the shaped hydrogels are made. [0117] In still other aspects, Figure 2b shows fabricating hydrogel precursor solution containing polymer and chemical crosslinking agent(s) 220, wherein the crosslinking agents require additional triggers to induce the crosslinking reactions. The combined solution is injected into to molds 230 in any shapes to form hydrogels. Afterward, exposing the hydrogels to adequate conditions 235, such as photo-irradiation, heat, and X-rays, the chemical crosslinking step is initiated. In certain aspects, both chemical and photo-induced chemical crosslinking reactions can occur after formation of shaped hydrogels, which determines the polymer network structures in the gel. The chemical crosslinking reactions occur at the sites where the reactive groups on polymer (e.g. gelatin) and the crosslinking agents contact one another. [0118] Figure 13a shows a schematic of a one-step entirety crosslinking approach, which involves integrating the crosslinking agent directly into the hydrogel precursor solutions. V. Hybrid Crosslinking Technique [0119] In certain instances, a hybrid crosslinking technique can be used. As shown in Figure 13c, a hybrid crosslinking technique utilizes rapid-freezing-slow-thawing to induce physical crosslinks, and then complemented by for example, MSB-induced photo-crosslinks. In example 5-9, a physical and chemical crosslinking approach was taken wherein a 1% MSB solution in the precursor solution was used. First the JIC was physically crosslinked by 1 fabrication freeze-thaw cycle (F1), then photo-irradiated under UVA for 10 min. Detailed steps shown in Figure 13c. VI. 3D Printing and Formation of JICs [0120] Based on the method discussed above, JICs can be fabricated via 3D printing techniques. Hydrogel precursor solutions can be either extruded layer-by-layer and crosslinked by photo-induced crosslinking methods post the extrusion of each layer, or directly crosslinked by chemical crosslinking agents. Via 3D printing, JICs can be crosslinked either as entirety or generate crosslinks on the surface. [0121] During extrusion printing, the hydrogel material should have a suitable viscosity, extrudability and be easily extruded out of a nozzle. After printing, the hydrogel maintains its shape (i.e. post-printing stability) and provide adequate mechanical structural support. VII. Jelly Ice Cube (JIC) Structure [0122] In one embodiment, the disclosure provides a jelly ice cube (JIC), the JIC comprising: a biodegradable crossed-linked polymeric hydrogel network, wherein the network comprises a plurality of isolated chambers or cell-like cavities, creating a lattice. [0123] In certain aspects, the lattice is substantially honeycombed. Each cell-like cavity of the substantially honeycombed structure can be any shape such as a circular or a round chamber, a hexagonal, a square, or tubular. [0124] In one aspect, each chamber or cell-like cavity of the lattice entraps water. [0125] In one aspect, the shape of the JIC is a member selected from the group consisting of a free form, a cube, a pyramid, a sphere, a cylinder, a prism, and cone. [0126] In one aspect, the plurality of isolated chambers or cell-like cavities comprises a dense matrix of uniformly sized, durable water-retaining cells within the biopolymer (e.g., protein) network. [0127] In one aspect, each isolated chamber or cell-like cavity of at least a portion of the plurality of isolated chambers or cell-like cavities has a pore to imbibe water. [0128] In one aspect, each pore is about 0.1 nm to about 100 µm in diameter. Alternatively, each pore is between about 0.1 nm to about 100 nm or about 0.1 nm to about 20 nm in diameter. [0129] In one aspect, the plurality of isolated chambers or cell-like cavities are nanometer- or micrometer-scaled. [0130] In one aspect, the plurality of isolated chambers or cell-like cavities are substantially heterogeneously sized. [0131] In one aspect, the biodegradable polymer content of the JIC is between about 1% to about 60% w/w. [0132] In one aspect, the biodegradable polymer content of the JIC is between about 1% to about 10% w/w, or between about 5% to about 20% w/w. [0133] In certain aspects, the idealized structure of the hydrogel-based cooling media or “Jelly Ice Cube” (JIC) as imaged is shown in FIG.11a. The comprehensive schematic representation of one aspect the JIC shows a reusable hydrogel-based, resilient hydrogel network replete with an extensive 3D network of nano/micro-meter-scaled isolated chambers. In certain instances, this structure, created from hydrophilic biopolymers, entraps significant volumes of freezable water within these chambers or cavities. [0134] The 3D structure is highly porous and when crosslinked by using crosslinking agents, can hold >80% wt of water inside with less than 20 % wt of gelatin in the closed cell network structures. In certain instances, the weight of water is between about 80% to about 99%, such as about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, and/or 99%. In certain instances, the weight of biodegradable polymer (e.g., gelatin) is between about 1% to about 20%, such as about 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, and/or 20%. [0135] Advantageously, a closed cell chamber or cell-like cavity in the 3D structure holds water in a small volume that cannot produce large ice crystal when frozen, preventing damages to the network and prolong repeated uses (thawing-freezing). The hydrophilic gelatin network allows water molecules to diffuse and penetrate through cells but may not allow them to flow. [0136] The significance of crosslinking in sculpting the structure is underscored, emphasizing its pivotal role in enhancing the effectiveness and efficiency of the resulting hydrogel. [0137] The schematic in FIG.11a highlights certain fundamental structural attributes characterizing the hydrogel materials to excel as efficient, reusable cooling mediums. The reusable hydrogel-based coolant is a resilient hydrogel network replete with an extensive network of nanometer-scaled isolated chambers or cell-like cavities. This structure, created from hydrophilic biopolymers, entraps significant volumes of freezable water within the chambers. [0138] In certain aspects, to yield maximum efficacy, the hydrophilic polymeric lattice embodies several key characteristics. The hydrogel maintains an appropriate biopolymer concentration to form closed cells or cavities, which has at least one pore, or only one pore. If the concentration dips, the hydrogel exhibits open cell structures, rendering it fragile (See, figure 11b). Such a structure would struggle to retain significant water content, particularly after freeze-thaw cycles. Figure 11b does not contain a plurality of cell-like cavities of chambers. Conversely, an excessively high biopolymer concentration compromises the total water content in the hydrogel, which also limits the heat-absorbing ability. Therefore, in certain aspects, a balance in biopolymer concentration is desired. In certain aspects, biodegradable polymer content of the JIC is between about 1% to about 60% w/w. [0139] In certain aspects, resilience against repeated freeze-thaw cycles requires that the hydrogel is well crosslinked. This crosslinked network is robust enough to resist damaging effects of ice crystal formation during freezing. However, if the gel is overly crosslinked, it can diminish its hydrophilic nature, thereby reducing its ability to retain freezable water during thawing. [0140] To efficiently achieve a rapid, one-step fabrication and crosslinking of JICs, chemical crosslinking emerges as a superior method due to its cost-effectiveness and quick reaction rate. Both (1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride) (EDC) and glutaraldehyde (GTA) are useful as chemical crosslinking agents. The methods disclosed herein can employ various agents and these two are merely representative crosslinking agents with different characteristics that can be used in fabricating crosslinked JICs. Figure 12a-d depict the anticipated hydrogel structures, highlighting the crosslinking density and underlying reaction mechanisms. [0141] For example, two crosslinking agents EDC and GTA, in no way limiting, can be used. The distinction between EDC and GTA in crosslinking gelatin hydrogels primarily revolves around their reaction and conversion rates. EDC interacts with the gelatin molecule’s carboxyl groups, particularly those in the amino acid side chains (e.g., aspartic and glutamic acid) or C-termini, resulting in the formation of an o-acylisourea intermediate, as depicted in Figure 12c. This intermediate is inherently unstable in aqueous solutions and easily undergoes hydrolysis. If this intermediate meets a primary amine group (e.g., lysine, arginine) before hydrolyzing, it forms an amide bond, achieving crosslinking. However, if it hydrolyzes, it becomes non-reactive to primary amines, limiting crosslinking efficiency. Since EDC works as a zero-length crosslinker, gelatin network can only be “stappled” where a carboxylic group is extremely close to an amine group. An advantage of EDC is its potential of forming homogeneous crosslinked structure of the gelatin network, as shown in Figure 12a. With EDC, the gelatin network can be uniformly reinforced, retaining its inherent 3D structure and maintaining abundant hydrophilic groups for freezable water retention. [0142] Conversely, GTA reacts swiftly with gelatin’s amine groups, as highlighted in Figure 12d. [1] GTA crosslinks through the formation of Schiff’s base linkages with the gelatin’s amino groups. As a short spacer crosslinking agent, GTA can introduce a slight spatial distortion in the polymer network. Coupled with the rapid crosslinking speed of GTA, during mixing, gelatin molecules can be fixed quickly upon encountering GTA, leading to potential clustering. Therefore, the resultant hydrogel might exhibit variable crosslinking density, as visualized in Figure 12b, with bundled gelatin molecules causing concentration disparities throughout the mixture. [0143] As-fabricated JICs can be subjected to a variety of dehydration methods, including lyophilization, critical point drying (CPD), oven drying, or room-temperature drying, to enhance their preservation and facilitate efficient shipping. Upon dehydration, the material achieves a lightweight and stable state under ambient conditions. Rehydration of the dehydrated material can be accomplished by immersing the dry hydrogel form in water, either at ambient conditions or chilled temperatures (0 – 20°C), until the original water content is fully restored. [0144] The freezing temperature of the hydrogel is not particularly limited, so long as it is suitable to freeze or solidify the biopolymer. For example, temperatures of 0° C or lower may be suitably employed. In one aspect, a temperature of 0 to -20° C is employed to freeze the hydrogel. In one aspect, a temperature of -20° C is used. [0145] Once thawed, it is better to handle JICs with a minimum exposure time of temperatures above 0 °C. After each use, freezing temperature, i.e., -20 °C, is suitable for storage to retain water content in JICs. [0146] The time of freezing, i.e., time of storage at freezing temperature, is not particularly limited and may range from a few hours or less to 24 hours or more. This range includes all values and subranges therebetween, including 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, and 24 hours. Generally, overnight storage at freezing temperature is suitable, but other times may also be suitable. [0147] After each freeze-thaw cycle, JICs can be effectively rehydrated, cleaned or sanitized with brief water or diluted bleach rinse. The application of JICs can reduce water consumption in the food supply chain and food waste by controlling microbial contaminations. [0148] In another embodiment, the present disclosure provides a method for cooling an object using a jelly ice cube (JIC), the method comprising: providing a chilled or frozen jelly ice cube (JIC); and contacting the object with the JIC. [0149] In certain aspects, the JIC is chilled before contacting the object. [0150] In certain aspects, the cooling material or JIC is suitable for maintaining temperature-sensitive items, e.g., medicinal, or unstable compounds, cell or tissue samples, or other biologically or chemically active substances, at reduced temperatures. [0151] In certain instances, the JIC possesses biocidal functionality. Advantageously, in order to address concerns regarding biological contamination and/or microbial growth of JICs during use, a photosensitizer can be used to provide light-induced antimicrobial functions under store lighting conditions. Biocidal reactive oxygen species (ROS), including hydroxyl radicals, hydrogen peroxide, and singlet oxygen, produced by the JICs containing different amounts of photosensitizer (e.g., MSB) can be used to eliminate microorganisms. [0152] The idealized structure of the reusable hydrogel-based cooling media or “Jelly Ice Cube” (JIC) can be formulated either with or without the use of a food-grade crosslinking agent, such as transglutaminase, papain, bromelain, ficin, laccase, peroxidase, genipin, yielding an edible cooling medium. When crosslinked with a food-grade crosslinking agent, the resulting JIC is edible. For example, a gelatin solution, with concentrations ranging from 5% to 20%, is combined with transglutaminase, with concentrations ranging from 0 – 100 U/g, according to the procedure depicted in Figure 13A. For effective crosslinking, this precursor solution undergo an incubation at temperatures between 20°C and 70°C for a duration ranging from 1 minute to 24 hours. This incubation can occur either before or after the solution is dispensed into molds. After crosslinking, the enzyme can be inactivated by a temperature above 70°C. Following this step, the solution is cooled to a temperature range of 0°C to 20°C to facilitate a sol-gel transition. It is expected that the resulting hydrogel will exhibit an internal configuration akin to that illustrated in Figure 11a. The reusable hydrogel- based coolant is a resilient hydrogel network replete with an extensive network of nanometer- scaled isolated chambers or cell-like cavities. This structure, created from hydrophilic biopolymers, entraps significant volumes of freezable water within the chambers. [0153] Once frozen, the cooling material or JIC is suitable for maintaining temperature- sensitive items, e.g., drinks, food, medicinal, or unstable compounds, cell or tissue samples, or other biologically or chemically active substances, at reduced temperatures. VIII. Examples [0154] Chemically crosslinking the surface of the JICs effectively improves their mechanical stability and reusability. The thickness of the surface crosslinked layer of JICs is related to the amount of crosslinking agent adsorbed or absorbed, as well as the number of crosslinkers effectively reacted with the polymer (e.g., protein) chains. It is hypothesized that with a thicker crosslinked surface layer, JICs show more robust performances. [0155] The disclosure provides at least four (4) subcategories of methods to achieve surface crosslinking of JICs. 1. 1-A) immersing solidified JICs in solutions with chemical crosslinking agents which induces spontaneous crosslinking reactions with or among protein molecules; 2. 1-B) first immersing solidified JICs in solutions containing crosslinking agents which requires additional conditions to generate the crosslinks, then exposing the JICs to the adequate conditions, which includes but not limited to photo-irradiation, heat, and X- rays; 3. 1-C) applying sufficient amount of chemical crosslinking agents, which induce spontaneous crosslinking reactions with or among protein molecules, on surface of JICs via mist or gaseous environment; 4. 1-D) first applying mist or gaseous form of crosslinking agents, which requires additional conditions to induce the crosslinking reactions, to surface of JICs, then exposing the JICs with crosslinking agent to the adequate conditions, which includes but not limited to photo-irradiation, heat, and X-rays, to complete the crosslinking reaction. Example 1 illustrates the surface modification method 1-A: Gel/EDC[S]-JICs [0156] Two stock solutions, 30% Gelatin and 1% EDC, were prepared in water.10% gelatin solution was prepared by diluting gelatin stock solutions at 50 °C, pipetted into the 10 mm × 10 mm × 10 mm cubic molds, and chilled at 4 °C overnight for gelation. Once solidified, gelatin hydrogels were immersed in diluted EDC solutions (e.g., 5 mg/mL or 10 mg/mL) for various durations to achieve the chemically crosslinked surface layer. The prepared samples were evaluated directly (AFTC0) or after 1, 5, or 10 application freeze- thaw cycles (AFTC1, AFTC5, or AFTC10). Each AFTC consists of 18 hours of freezing at – 20 °C and 6 hours of thawing at 21 °C.4 °C for sample preservations. [0157] The mechanical strengthening effect induced by the surface crosslinked hydrogels by using EDC is characterized and shown in Figure 3 (a). The compressive strength of the Gel-EDC[S]-JICs increased rapidly in the initial period of immersion before reaching equilibrium, as shown in Figure 3 (a). Within a specific range, the higher concentration of EDC showed a higher speed of enhancing strength due to quick chemical crosslink reactions. Before equilibrium, a longer immersion time resulted in a better mechanical strengthening effect. With a cubic sample of 10x10x10 mm, immersing in 5 mg/mL for 30 min resulted in JICs with compressive strength of 160.62 kPa, which is beyond the strength criteria (10 kPa) of JICs. Thus, for the reusability test, 10% gelatin immersed in 5 mg/mL for 30 min was used to represent the performance of Gel/EDC[S]-JICs. [0158] Figure 3 (b-d) show the mechanical performance and appearances of Gel/EDC[S]- JICs before AFTC (AFTC0) and after 1, 5, and 10 AFTCs. According to previous research results, if a JIC survives a normal pressure of 10 kPa, it will not be crushed by a food load as tall as 1 m. Though it might be a harsh requirement for the general use of JICs, 10 kPa was used as the criteria to evaluate the compressive strength of JICs in this research. It can be observed that the mechanical stability of Gel/EDC[S]-JICs was much better than that of Gel- JICs (Figure 3 (e-f)) and similar to Gel/MSB-JICs (Figure 3 (g-h)). Besides, as shown in Figure 4, compared to Gel-JICs, the stabilities of Gel/EDC[S]-JICs in water content and heat- absorbing ability were much improved. The reduction of fusion heat of Gel/EDC[E]-JICs was also less than 5% after AFTC 10 compared to the initially produced (AFTC0). Within 10 AFTCs, the total water and freezable water contents of Gel/EDC[S]-JICs remained in the range of 86.5% – 88.5% and 87.1% – 91.2%, respectively. Entirety Crosslinking of the JICs JICs can also be chemically crosslinked uniformly as an entirety. Uniform crosslinking from the inner to the surface can be achieved by incorporating the crosslinking agent into precursor solutions of JICs. There are two major categories of methods to realize the entirety crosslink of JICs: 1. 2-A) fabricating JICs with precursor solutions infused with both polymers and the chemical crosslinking agents, which induces spontaneous crosslinking reactions with or among protein molecules; 2. 2-B) first solidifying JICs with precursor solutions including both polymers and the chemical crosslinking agents, which requiring additional conditions to induce the crosslinking reactions, then exposing the JICs to the adequate conditions, which includes but not limited to photo-irradiation, heat, and X-rays, to initiate the chemical crosslinking step. Here both chemical and photo-induced chemical crosslinking reactions occur after gel formation, which also will determine the polymer network structures in the gel. The chemical crosslinking reactions occur at the sites where the reactive groups on gelatin and the agents colloid together. Example 2 illustrates the Uniform Crosslinking Method 2-A-1. Gel/EDC[E]-JICs [0159] Two stock solutions, 30% Gelatin and 10 mg/mL EDC, were prepared in water. The precursor solution Gel/EDC[E]-JICs was prepared by diluting and mixing the two stock solutions at 50 °C. Different concentration of EDC was added to the protein solution while the concentration of gelatin remained at 10% for all samples. The precursor solutions were pipetted into the 10 mm × 10 mm × 10 mm cubic molds and chilled at 4 °C overnight for gelation, and the achieved samples were referred to as Gel/EDC[E]-JICs. The prepared samples were evaluated directly (AFTC0) or after 1, 5, or 10 application freeze-thaw cycles (AFTC1, AFTC5, or AFTC10). Each AFTC consists of 18 hours of freezing at – 20 °C and 6 hours of thawing at 21 °C for sample preservations. [0160] Figure 5 (a-b) shows the mechanical strengthening effect of mixing EDC into the precursor solution of hydrogels. It can be observed that with the increase of EDC in the precursor solution, the resulting Gel/EDC[E]-JICs were stronger with both higher compressive strength and compressive strain at break. All Gel/EDC[E]-JICs prepared before AFTC showed the properties reached beyond the mechanical criteria of JICs. Later, JICs fabricated with two representative concentrations of EDC were selected for the test of reusability of JICs, 0.2% EDC out of gelatin content (0.02 wt.% of the total JICs) and 0.5% out of gelatin content (0.05 wt.% of the total JICs), which are labeled as Gel/EDC[E]-1-JICs and Gel/EDC[E]-2-JICs, respectively. The appearances and stability of the mechanical performances are shown in Figure 5 (b-g). After AFTC5 and AFTC10, the average compressive strengths were 14.92 kPa and 12.08 kPa, respectively, for Gel/EDC[E]-1-JICs, and 20.80 kPa and 16.01 kPa, respectively, for Gel/EDC[E]-2-JICs, which are much improved compared to Gel-JICs and succeeded the strength criteria of JICs. Example 3 illustrates Crosslinking Method Example 2-A-2. Gel/TA[E]-JICs [0161] Two stock solutions, 30% Gelatin and 100 mg/mL tannic acid (TA) were prepared in water, respectively. The precursor solution Gel/EDC[E]-JICs was prepared by diluting or mixing the two stock solutions at 50 °C. Different concentration of TA was added to the protein solution, and the final concentration of gelatin in the precursor solutions was diluted to either 10% or 8%. The pH condition of each precursor solution was adjusted to pH 7 or 8 by 1M sodium hydroxide solutions. The adjusted precursor solutions were pipetted into the 10 mm × 10 mm × 10 mm cubic molds and chilled at 4 °C overnight for gelation. The prepared samples were evaluated directly (AFTC0) or after 1, 5, or 10 application freeze- thaw cycles (AFTC1, AFTC5, or AFTC10). Each AFTC consists of 18 hours of freezing at – 20 °C and 6 hours of thawing at 21 °C.4 °C for sample preservations. [0162] Figure 6 (a-b) shows the mechanical strengthening of Gel/TA[E]-JICs prepared by the precursor solutions containing a homogeneous mixture of 10% gelatin and different concentrations of TA. It can be observed that with the increase of TA in the precursor solution, the resulting Gel/TA[E]-JICs were becoming stronger with both higher compressive strength and compressive strain at break. A similar tendency was also observed with Gel/TA[E]-JICs containing 8% gelatin, as shown in Figure 6 (c-d). For Gel/TA[E]-JICs containing either 10% gelatin or 8% gelatin, the ones fabricated at pH 8 showed slightly better mechanical strength, though the mechanical properties of all Gel/TA[E]-JICs prepared before AFTC met beyond the mechanical criteria of JICs. Thus, two representative Gel/TA[E]-JICs were selected for the test of reusability. Gel/TA[E]-JICs fabricated with 1% TA (out of gelatin content) and 10% gelatin content (0.1 wt.% TA mixed with 10% gelatin in JICs, pH 8) and Gel/TA[E]-JICs fabricated with 1% TA (out of gelatin content) with 8% gelatin content (0.08 wt.% TA mixed with 8% gelatin in JICs, pH 8), were labeled as Gel/TA[E]-1-JICs and Gel/TA[E]-2-JICs, respectively. [0163] The appearances and stability of mechanical performances of both Gel/TA[E]-1- JICs and Gel/TA[E]-1-JICs are shown in Figure 6 (e-i). After AFTC5 and AFTC10, the average compressive strength was 23.88 kPa and 18.31 kPa, respectively, for Gel/TA[E]-1- JICs, and 14.41 kPa and 15.02 kPa, respectively, for Gel/TA[E]-2-JICs, which all met beyond the strength criteria of JICs. Besides, the latent heat of fusion, total water content, and the ratio of freezable water of Gel/TA[E]-JICs before AFTC (AFTC0) after 1, 5, and 10 AFTCs are shown in Figure 7. As can be seen, compared to Gel-JICs shown in Figure 4, the stabilities of Gel/TA[E]-JICs in water content and heat-absorbing ability were much improved. The reduction of fusion heat of Gel/TA[E]-1-JICs was negligible after AFTC 10 compared to before use (AFTC0). The total water content and freezable water content remained in the range of 87.9% – 88.6% and 84.8% – 88.3%, respectively for Gel/TA[E]-1- JICs, and 88.1% – 91.4% and 83.4% – 93.9%, respectively for Gel/TA[E]-2-JICs in 10 AFTCs. Example 4 illustrates uniform crosslinking Method 2-B: Gel/AQS[E]-JICs-Photo-induced crosslinking [0164] Two stock solutions, 30% Gelatin and 10 mg/mL AQS were prepared in water. The precursor solution Gel/AQS[E]-JICs was prepared by diluting gelatin stock solutions at 50 °C to a final concentration of 10%. The prepared precursor solutions were pipetted into the 10 mm × 10 mm × 10 mm cubic molds and chilled at 4 °C overnight for gelation. Once solidified, the hydrogels were exposed to UV irradiation under various conditions (UVA, 365 nm, in the air or N ₂ ; UVB, 312 nm, in the air or N ₂ ) for different durations, resulting in the entirely photo-crosslinked Gel/AQS[E]-JICs. The prepared samples were evaluated directly (AFTC0) or after 1, 5, or 10 application freeze-thaw cycles (AFTC1, AFTC5, or AFTC10). Each AFTC consists of 18 hours of freezing at – 20 °C and 6 hours of thawing at 21 °C.4 °C for sample preservations. [0165] Figure 8 (a) shows the mechanical strengthening effect of Gel/AQS[E]-JICs prepared by the precursor solutions containing 10% gelatin and different concentrations of AQS after photoirradiation under UVA (365 nm) for 10 min. It can be observed that with the increase of AQS in the precursor solution, the resulting Gel/AQS[E]-JICs were stronger with both higher compressive strength and compressive strain at break, where the mechanical properties of all Gel/TA[E]-JICs prepared met beyond the mechanical criteria of JICs. Figure 8 (b) illustrates that in a hydrogel containing 10% gelatin and 0.01% AQS, the AQS-induced photo-crosslinking reaction had a relatively fast speed of response and reached equilibrium within 1 min of UVA (365 nm) irradiation. [0166] Thus, JICs fabricated with 10% gelatin and 0.01% AQS, and photo-irradiated under UVA (365 nm) for 10 min were selected to represent the performance of Gel/AQS[E]-JICs. The appearances and stability of mechanical performances are shown in Figure 8 (c-e). After AFTC5 and AFTC10, the average compressive strength was 13.72 kPa and 11.41 kPa, respectively, all of which met beyond the strength criteria of JICs. Besides, the latent heat of fusion, total water content, and the ratio of freezable water of Gel/AQS[E]-JICs before AFTC (AFTC0) after 1, 5, and 10 AFTCs are shown in Figure 8 (f-h). As can be seen, compared to Gel-JICs shown in Figure 4, the stabilities of Gel/AQS[E]-JICs were much more improved. The total and freezable water content remained in the range of 86.5% – 89.5% and 78.0% – 91.4%, respectively, in 10 AFTCs. [0167] As disclosed herein, in certain aspects, the process of making a JIC can lead to a structural difference in the JIC. One process described herein is a surface crosslinking by immersing hydrogels in a solution containing a chemical crosslinking agent, and the crosslinking reaction can be triggered by temperature, time, light, or irradiation. Under this condition, the crosslinking reaction only occurs on the shell of the hydrogel not inside (See, Figure 9). [0168] In another process, a homogeneously crosslinked hydrogel is made by mixing gelatin and a crosslinking agent together in solution and then form a hydrogel solid shape at for example, 4°C. Crosslinking reaction can occur by controlling temperature, time, light, or irradiation. The entire hydrogel is crosslinked. (See, Figure 10). [0169] In another process, 3D printing technology is used to inject a viscous hydrogel solution containing both protein and crosslinking agent. The crosslinking reaction can be triggered by temperature and photo irradiation. [0170] Based on the method discussed above, JICs can also be fabricated via 3D printing techniques. JICs can be either extruded layer-by-layer and crosslinked by photo-induced crosslinking method post to the extrusion of each layer, or directly crosslinked by chemical crosslinking agents. Via 3D printing, JICs can be crosslinked either as entirety or generate crosslinks on the surface. Example 5 illustrates evidence of the structure of crosslinked hydrogel cooling media Materials and Methods [0171] Materials. Gelatin from porcine skin (gel strength 300, Type A), glutaraldehyde (grade I, 8% aqueous solution) and ethanol (anhydrous, ACS grade) were purchased from Sigma Aldrich (Milwaukee, WI).1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) was purchased from Spectrum Chemical MFG Corp (Gardena, CA). MatTek glass bottom dishes, P50G-1.5-30-F, were purchased from MatTek Corporation (Ashland, MA). Milli- Deionized (Milli-DI) and Milli-Q water was used in the materials fabrication and tests. 3.1.2 Fabrication of a series of examples. To validate the proposed models and structural features, a series of examples with various crosslinking methods and gelatin concentrations were prepared and characterized, as detailed in Table 1, and Figure 13. Four primary stock solutions—30% Gelatin, 10 mg ^mL ^-1 EDC, 8% GTA, and 75 mg ^mL ^-1 MSB—were individually prepared in water. The samples mentioned in Table 1 below were derived by the stock solutions. Three different crosslinking method were used for comparison purpose: one- step entirety crosslinking method (Figure 13 a), two-steps surface crosslinking method (Figure 13 b), and multiple-step crosslinking employing both rapid-freezing-slow-thawing and photo-crosslinking reaction (Figure 13 c). Although the JICs has the customizable feature in shape and size, for testing purpose, most of the samples were prepared in size of 10 mm × 10 mm × 10 mm. Table 1. List of examples (gelatin-hydrogel-based JIC samples prepared and characterized). E ^xample N _{ame Crosslinking method} -1 Gel [10] Non-crosslinked, virgin 10% gelatin hydrogel The entire gelatin was crosslinked in a single step by mixing 10% _-2 ^Gel/EDC gelatin with 0.1% EDC (relative to the total gelatin content) in the [ _10-0.1] precursor solution at 50-60°C. The specific procedure is illustrated in Figure 13a. The entire gelatin was crosslinked in a single step by mixing 10% ^{-3 Gel/EDC} gelatin with 0.2% EDC (relative to the total gelatin content) in the [ _10-0.2] precursor solution at 50-60°C. The specific procedure is illustrated in Figure 13a. The entire gelatin was crosslinked in a single step by mixing 10% _-4 ^Gel/EDC gelatin with 0.4% EDC (relative to the total gelatin content) in the [ _10-0.4] precursor solution at 50-60°C. The specific procedure is illustrated in Figure 13a. The entire gelatin was crosslinked in a single step by mixing 10% ^{-5 Gel/EDC} gelatin with 0.5% EDC (relative to the total gelatin content) in the [ _10-0.5] precursor solution at 50-60°C. The specific procedure is illustrated in Figure 13a. The entire gelatin was crosslinked in a single step by mixing 10% ^{-6 Gel/EDC} gelatin with 0.6% EDC (relative to the total gelatin content) in the [ _10-0.6] precursor solution at 50-60°C. The specific procedure is illustrated in Figure 13a. The solidified 10% gelatin hydrogel was surface crosslinked by immersing ^{-7 Gel/EDC} in EDC aqueous solutions with concentrations of either 5 [ _10-S] mg/mL or 10 mg/mL. The immersion lasted for 30 minutes for most samples, while AFM specimens were soaked for 18 hours. The detailed procedure is depicted in Figure 13b. G ^e The solidified 10% gelatin hydrogel was surface crosslinked by _-8 ^l/GTA [ _10-S] immersing in a 5 mg/ml GTA aqueous solution for a duration for 18 h. Detailed steps shown in Figure 13b. Physical and chemical crosslinking. Incorporated 1% MSB the ^{-9 Gel/MSB} precursor solution. First physically crosslinked by 1 fabrication [ _10-F1] freeze-thaw cycle (F1), then photo-irradiated under UVA for 10 min. Detailed steps shown in Figure 13c. -10 Gel [8] Non-crosslinked, virgin 8% gelatin hydrogel. The entire gelatin was crosslinked in a single step by mixing 8% _-11 ^Gel/EDC gelatin with 0.1% EDC (relative to the total gelatin content) in the [ _8-0.1] precursor solution at 50-60°C. The specific procedure is illustrated in Figure 13a. The entire gelatin was crosslinked in a single step by mixing 8% ^{-12 Gel/EDC} gelatin with 0.2% EDC (relative to the total gelatin content) in the [ _8-0.2] precursor solution at 50-60°C. The specific procedure is illustrated in Figure 13a. The entire gelatin was crosslinked in a single step by mixing 8% ^{-13 Gel/EDC} gelatin with 0.5% EDC (relative to the total gelatin content) in the [ _8-0.5] precursor solution at 50-60°C. The specific procedure is illustrated in Figure 13a. The entire gelatin was crosslinked in a single step by mixing 8% _-14 ^Gel/EDC gelatin with 0.8% EDC (relative to the total gelatin content) in the [ _8-0.8] precursor solution at 50-60°C. The specific procedure is illustrated in Figure 13a. The entire gelatin was crosslinked in a single step by mixing 8% ^{-15 Gel/EDC} gelatin with 1.0% EDC (relative to the total gelatin content) in the [ _8-1.0] precursor solution at 50-60°C. The specific procedure is illustrated in Figure 13a. [0172] Application Freezing-Thawing Cycles (AFTCs). The fabricated hydrogels were tested against 0 (A0, before application cycles), 1 (A1), 5 (A5), or 10 (A10) cycles of AFTCs. Each AFTC consisted of 18 h of freezing at −20 °C and 6 h of thawing at 21 °C to evaluate the performance of engineered hydrogels under commonly encountered freeze−thawing conditions. The AFTC conditions in this study were also consistent with the testing conditions for JICs in previous studies, enabling a performance comparison between one-step crosslinked JICs and the earlier JICs. Material Characterizations [0173] Native Hydrogel Structures Observations by CryoEM. The intricate structures of freshly prepared hydrogel samples were analyzed using Cryogenic electron microscopy (CryoEM) according to the methods described by Mastronarde. [2] 4uL 8% gelatin solution was applied to a glow-discharged (30 mA, 30 s) holey carbon grid (300 mesh Quantifoil 1.2/1.3) for plunge freezing in liquid nitrogen using Leica EM GP2 plunger at 60°C. Cryo- EM images was captured at 200 kV using a Thermofisher Glacios electron microscope, which was equipped with a Gatan K3 direct electron detector. Micrographs were recorded at 56,818x (0.88 Å ^pixel ^-1 ) magnification using K3 with dose of 40 e ^A ^-2 . Parallel beam illumination and coma-free alignment was applied using SerialEM. The obtained images were processed using ImageJ, applying a bandpass filter ranging from 20 – 30 Å. Pore size analysis was performed using the acquired images. For determining pore size distribution, the cryoEM image underwent binary thresholding. Contours were then drawn around each identified pore, and measurements were taken based on these contours’ diameters. A set of 100 pores was analyzed to ensure a statistically representative sample. [0174] Internal Structure Examination via Dino-Lite and SEM. The cross-sectional structures of specimens (hydrated) after various AFTCs were visualized using a Dino-Lite digital microscope (Dunwell Tech. Inc., Torrance, CA). To delve deeper into the internal micro-structure, select samples post various AFTCs were dehydrated using the critical point drying (CPD) method and subsequently examined with a Quattro environmental scanning electron microscope (ESEM, Thermo Fisher Scientific, US). Hydrogel samples, whether in their virgin state or after specific AFTCs, were initially sectioned to reveal their inner surface using a surgical blade. These small 3 × 3 × 2 mm samples were then subjected to a solvent exchange through an incremental ethanol-water series (10%, 30%, 50%, 70%, 90%, 100%, 100%, 100%). Upon complete replacement of water with ethanol, the specimens were processed with supercritical CO ₂ in a Tousimis 931 critical point drier to remove the ethanol. Before undergoing ESEM analysis, a thin gold layer (around 10 nm) was applied to these CPD-prepared samples. During the imaging process, electron beams of either 5 kV or 10 kV were utilized, paired with an ETD detector in a high vacuum setting. [0175] Swelling Ratio. The swelling ratio was tested at 23°C by immersing a hydrogel specimen in size of 10 mm × 10 mm × 10 mm in 45 mL of Milli-DI water. The mass of each specimen at different immersion time was weighed after blotting excess water with a filter paper, and the swelling ratio (%) was calculated according to Equation 1, where ^^ is the weight of the specimen in g after immersed in the water bath for a certain time, and ^^ _^ is the initial weight of the specimen in g. ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ൌ ^ ^^– ^^ _^ ^/ ^^ _^ ൈ 100% Equation 1 [0176] Compressive Mechanical Properties. As described in earlier studies, the static compression test was performed using an Instron 5566 tester (Norwood, MA) with a 5 kN or 10 kN static load cell. [3] Specifically, sample sizes of hydrogels for all tests were 10 mm × 10 mm × 10 mm, and the compressive rate was 1 mm ^min ^-1 . Compressive stress (σ, kN) and strain (ε, %) at break were obtained at the breaking point from the static compressive curves. [0177] Latent Heat of Fusion and Water Profiles. The latent heat of different frozen hydrogels was measured using a differential scanning calorimeter (DSC-60, Shimadzu Corporation, Pleasanton, CA) using the method described in Zou et al.[4] The heat flow (W ^g ^-1 ) – time (s) curves were recorded in the temperature range of -20°C to 10°C, supported by liquid nitrogen with a 1°C ^min ^-1 heating rate under 30 mL/min protective nitrogen flow. The latent heat of fusion was reported with the integrated heat values of the phase change peak near 0°C normalized by the mass of the specimen in J ^g ^-1 . Ice-water phase transition heat (334.5 J ^g ^-1 ) was used as the reference. The total water content of fabricated hydrogels was tested using a thermogravimetric analyzer (TGA, SDT-Q600, TA Instrument, New Castle, DE). The total water content (%) and the ratio of freezable water (%) were calculated according to Equation 2 and Equation 3, where ^^ is the weight of specimen in g where the 1 ^st derivative of mass changes against time is below 0.01 g ^s ^-1 , ^^ _^ is the initial weight of specimen under the ambient condition in g, and H is the fusion heat of specimen in J ^g ^-1 . ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ൌ ^ ^^ _^ – ^^^/ ^^ _^ ൈ 100% Equation 2 ^^ℎ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ൌ ^ ^^/334.5^ ൊ ൫^ ^^ _^ – ^^^/ ^^ _^ ൯ ൈ 100% Equation 3 biodegradability tests of engineered hydrogels were conducted by the same protocol described in Zou et al. [5] In a glass tube, a hydrogel specimen in size of 10 mm × 10 mm × 5 mm was immersed in 5 mL 0.5 mg ^mL ^-1 proteinase K solution (≥15 U ^mL ^-1 ) in PBS buffer (pH 7.4, 10 mM). The glass tube was kept at 23°C in a shaking bed to avoid hydrogel melting while realizing high enzymatic digestion activity. The mass of the specimen was recorded at different time point, and the weight count in % was calculated according to Equation 4, where ^^ is the weight of the specimen in g after immersed in the proteinase K solution for a certain time, and ^^ _^ is the initial weight of the specimen in g. ^^ ^^ ^^ ^^ℎ ^^ ^^ ^^ ^^ ^^ ^^ ൌ ^^/ ^^ _^ ൈ 100% Equation 4 Results and Discussions [0179] To validate the proposed structures of hydrogel-based cooling media, two imaging methods were employed. Given the limitations of each imaging technology, samples underwent varied preparation processes before observation. Both untreated and crosslinked gelatin hydrogel samples of 10% and 8% concentrations were studied using appropriate techniques, based on their hydration status or underwent critical point drying (CPD). In this research, hydrated specimens were imaged using cryoEM in a frozen state, while dehydrated samples prepared with the CPD method were imaged via SEM. This approach ensured optimal preservation of the hydrogel samples’ inherent micro-features. [7-8] [0180] Initially, the inherent micro-morphology of different hydrated hydrogel samples was analyzed using cryoEM. However, only the virgin 8% gelatin hydrogel sample (Gel [8]) was successfully prepared to the appropriate thickness for observation on the glow- discharged holey carbon grid. The high viscosity of the virgin 10% gelatin solution hindered the production of slender cryoEM specimens. This resulted in excessively thick 10% gelatin specimens, which subsequently promoted ice crystal formation during plunging, and rendered the images completely black and unsuitable for analysis. As a result, 8% gelatin (Gel [8]) was chosen for cryoEM imaging, as illustrated in Figure 14. Unfortunately, due to viscosity constraints, cryoEM imaging could not be achieved for any crosslinked samples. The obtained cryoEM images were processed using ImageJ, applying a bandpass filter ranging from 20 – 30 Å and shown in Figure 14 a, where the black areas denote protein skeletons, while the white areas correspond to water (in the form of ice). Extremely homogenous distribution of gelatin and water was observed. The interpenetrating gelatin molecules formed a dense water-restraining network with pore (water droplet) size of 2.93 nm ± 2.77 nm. The observed pattern supported out proposed model of efficient hydrogel cooling media, with features of biopolymers forming countless nanometer-scaled closed cells, wherein each cell has at least one pore to retain large amount of freezable water within the network. [0181] Prior research has highlighted the efficacy of critical point drying (CPD) in preserving the inherent structures of biological and hydrogel specimens, making them suitable for scanning electron microscopy (SEM) observation. [7-8] CPD, in contrast to lyophilization, prevents the formation of ice grains within hydrogel samples, a primary cause of structural damage of JICs. [3-6] CPD facilitated a comprehensive analysis of all prepared samples, including Gel [10], Gel/EDC [10-0.2], Gel/EDC [10-0.5], Gel [8], Gel/EDC [8-0.5], Gel/EDC [8-1.0], and Gel/GTA [10-S], with SEM images depicted in Figure 15 a. In contrast to previously obtained SEM images using lyophilization, all CPD-dried virgin gelatin hydrogels (Gel [10] and Gel [8]) and EDC-crosslinked specimens (Gel/EDC [10-0.2], Gel/EDC [10-0.5], Gel/EDC [8-0.5], and Gel/EDC [8-1.0]) exhibited a smooth surface morphology. At 1000x magnification, no distinct porous structure was evident. However, at higher magnifications, damage from the electron beam became prominent, leading to artifact generation, as seen in Figure 15 b. Based on the observations, we infer that the inherent pore sizes of the polymer networks in Gel [10], Gel/EDC [10-0.2], Gel/EDC [10-0.5], Gel [8], Gel/EDC [8-0.5], and Gel/EDC [8-1.0] are all sub-micrometer. This is consistent with the findings presented in Figure 11 and Figure 14, which indicate that the intrinsic porous structure of either virgin or appropriately crosslinked hydrogels comprises nanometer-scaled enclosed water-retaining cells. Given that these nanometer-scaled features fall below the detection threshold of our SEM experimental settings, no discernible features were identified. On the other hand, GTA-crosslinked samples exhibited a multifaceted, uneven cross-sectional surface characterized by micrometer-scaled wave-like, interconnected ridges and valleys, aligning with our theoretical assumptions in Figure 12. The swift crosslinking reaction mediated by GTA led to a heterogeneous polymer network, inducing pronounced gelatin aggregation. It’s plausible that Gel/GTA [10-S] possesses a dual-structured nature, comprising both nanometer and micrometer-scaled features. However, based on our current experimental setup, we can only confirm the micrometer-scaled impact of GTA. [0182] Based on the visual assessment of the structural attributes, two conclusions can be drawn: First, before undergoing any freeze-thaw cycles, the inherent structure of the biopolymer matrix that constitutes an efficient hydrogel cooling media, termed JIC, should predominantly feature a vast array of homogenous nanometer-scaled water-retention pores; second, the one-step entirety crosslinking method with EDC effectively maintains the intrinsic homogeneous polymer network of gelatin hydrogels at concentrations of 8% and 10%. [0183] Additional data were gathered to substantiate the proposed structural attributes of effective hydrogel cooling media and the efficacy of the suggested crosslinking method. Hydrogel properties were analyzed immediately after fabrication (prior to AFTC, A 0) and post various AFTCs (A1, A5, and A10). The evaluations covered compressive mechanical properties, water profile, latent heat of fusion, swelling behavior, and in vitro biodegradation, illustrated in Figure 16 through Figure 20. [0184] Figure 16 illustrates the impact of diverse crosslinking techniques, comparing the efficacy of the one-step scalable method using EDC (examples include Gel/EDC [10-0.1] to Gel/EDC [10-0.6]) against the two-step surface crosslinking with EDC (Gel/EDC [10-S]) or GTA (Gel/GTA [10-S]), and the JICs created via a complex method that combines rapid- freezing-slow-thawing and photo-crosslinking (Gel/MSB [10-F1]). All the analysis shown in Figure 16 focused on the intrinsic properties of hydrogels prior to AFTCs (A0). The crosslinking effect of incorporating EDC in the precursor solution can be observed in Figure 16 a-b. Both compressive strength and the strain at break increased with the increased concentration of EDC incorporated in the 10% gelatin hydrogels, as Gel [10], Gel/EDC [10- 0.2] and Gel/EDC [10-0.5] have compressive strength of 68.0 kPa ± 7.3 kPa, 141.6 kPa ± 36.6 kPa and 324.3 kPa ± 15.8 kPa, respectively. The crosslinking effect of EDC on gelatin hydrogels agrees with the pattern described by Adamiak et al. [9]Yet, it should be noted that the elevated reaction temperature (50°C) in the entirety crosslinking process restricted further elevation of EDC concentration due to the risk of gelatin aggregation. [0185] Compared to the one-step entirety crosslinking method, EDC was utilized in a surface crosslinking bath for the solidified 10% gelatin hydrogels (Gel [10]), as depicted in Figure 16 c. Two EDC concentrations, 5 mg/mL and 10 mg/mL, were employed to immerse Gel [10] for various duration at room temperature. Longer reaction times yielded hydrogels with enhanced compressive strength. Surface crosslinking produced hydrogels with superior compressive strength than the one-step entirety method. While surface crosslinking exhibited efficient crosslinking, it had its challenges, especially for scalable production of JICs. For instance, with larger sample sizes and limited crosslinking time, surface crosslinking method might yield a very rigid outer layer and an un-crosslinked core. Moreover, given the potential variable size and shape of JICs, samples with non-standard shapes can introduce complex diffusion patterns, hindering the efficiency of large-scale production. Additionally, surface crosslinking demanded a greater quantity of crosslinking agent in the reaction bath, which can be very difficult to recycle, leading to potential wastage, especially in large-scale productions. [0186] The design of JICs leverages the high latent heat of fusion in the ice-water transition of freezable water. The water profile within the JICs determines the overall cooling efficiency. Given the potential effects of one-step entirety crosslinking with EDC on the hydrophilicity of the polymer network, we studied the water profile, which encompasses the total water content and the ratio of freezable water in the hydrogels. These findings are presented in Figure 16 d-e, with the resulting latent heat of fusion illustrated in Figure 16 f. Incorporating EDC into the JICs via one-step entirety crosslinking did not alter the total water content, while slightly increased the percentage of freezable water and the subsequent latent heat of fusion in the hydrogels. In a prior study, it was established that crosslinking a 10% gelatin hydrogel through both physical and chemical means (Gel/MSB [10-F1])—initiating with a rapid-freeze-slow-thaw cycle, followed by a photo-crosslinking reaction using the photosensitizer, menadione sodium bisulfite (MSB)—boosted the fraction of freezable water in the hydrogel. This enhancement led to considerably better performance relative to virgin hydrogels (Gel [10]). [3, 5] The water profiles and latent heat of fusion of Gel/MSB [10-F1] are delineated with pink dashed lines in Figure 16 d-f, serving as a reference for the Gel/EDC samples. As indicated in Figure 16 e-f, Gel/EDC [10-0.5] and Gel/EDC [10-0.6] exhibit water profiles and thermal absorption capacities akin to Gel/MSB [10-F1]. Additionally, Gel/GTA [10-S] was examined as the most intense crosslinking scenario, achieving the overly high crosslinking degree for 10% gelatin hydrogels. Gel/GTA [10-S] serves as another benchmark, represented by yellow dashed lines in Figure 16 d-f. Consistent with our hypothesis, excessive crosslinking diminishes the material’s heat-absorbing capability. This reduction is attributed to the drastic decrease in the hydrophilicity of the polymer networks, as hydrophilic groups are replaced by non-hydrophilic covalent bonds, as illustrated in Figure 12 b. Given the intended use of JICs and findings from prior research indicating that JICs with a compressive strength of 10 kPa can withstand the pressure from 1m-tall, stacked goods, Gel/EDC [10-0.2] and Gel/EDC [10-0.5] were selected for comprehensive examination. These samples represent two distinct crosslinking degrees achieved using the one-step entirety crosslinking method and were contrasted with samples prepared through alternative crosslinking approaches. [4] [0187] Figure 16 g compares the compressive strength of representative virgin and crosslinked samples. Notably, both Gel/EDC [10-0.2] and Gel/EDC [10-0.5] exhibited a moderate crosslinking degree. Figure 16 h-g further elucidates the degree of crosslinking of various samples by tracking their swelling behavior in ambient water bath. It’s evident that while the polymer network of Gel/EDC [10-0.2] and Gel/EDC [10-0.5] was reinforced, there was not markedly change in the polymer network’s interaction with water, which contrasts starkly with that of Gel/GTA [10-S]. [0188] The employment of EDC as a crosslinking agent offered an added advantage in preserving the material’s transparency and colorless nature, as illustrated in Figure 17 a. Additionally, despite being crosslinked, both Gel/EDC [10-0.2] and Gel/EDC [10-0.5] retained their biodegradability, as depicted in Figure 17 b. The in vitro enzymatic degradation test further affirms the moderate crosslinking degree achieved through the one-step entirety crosslinking method, in contrast to the extensive crosslinking seen in Gel/GTA [10-S]. [0189] In summary, numerous findings demonstrate the effective strengthening and preservation of water profiles using the one-step entirety crosslinking method with EDC at optimal concentrations. The performance of the resultant specimens aligns closely with the benchmark Gel/MSB [10-F1] and significantly surpasses that of the excessively crosslinked sample, Gel/GTA [10-S]. One-step entirety crosslinking method by incorporating EDC in the hydrogel precursor solution stands out as a solution that achieves both efficient and controllable crosslinking. Unlike the process for creating Gel/MSB [10-F1], this approach eschews stringent conditions, offering simplicity, affordability and scalability. In the large- scale production, the crosslinking degree can be finely tuned by adjusting the EDC concentration, and precursor solution’s blending temperature and duration. [0190] For a more comprehensive understanding of the performance of different samples in the real-world application of JICs, selected specimens underwent AFTCs. Each AFTC consisted of 18 h of freezing at −20 °C and 6 h of thawing at 21 °C, which are designed to mimic the conditions the JICs would face in actual use, providing valuable insights into their durability, efficiency, and overall performance. [0191] Figure 17 (d-m) showcases the mechanical stability performances of hydrogels, both virgin (Gel [10]) and crosslinked using various methods (Gel/EDC [10-0.2], Gel/EDC [10-0.5], Gel/MSB [10-F1], Gel/GTA [10-S]). The evaluations were conducted before (A0) and after multiple AFTCs (A1, A5, A10). Irrespective of their crosslinking status, all samples demonstrated a decline in mechanical strength post-AFTCs. This decline was most pronounced after the first AFTC. Specifically, the strength of Gel [10] diminished from 68.0 kPa ± 7.3 kPa (A0) to 11.2 kPa ± 0.2 kPa (A1), Gel/EDC [10-0.2] reduced from 141.8 kPa ± 36.7 kPa (A0) to 13.9 kPa ± 4.1 kPa (A1), Gel/EDC [10-0.5] decreased from 324.3 kPa ± 15.8 kPa (A0) to 20.9 kPa ± 3.8 kPa (A1), and Gel/GTA [10-S] descended from 824.5 kPa ± 133.5 kPa (A0) to 47.6 kPa ± 4.2 kPa (A1). The reduction in strength after A1 for Gel/MSB [10-F1] was less pronounced. This can be attributed to the fact that Gel/MSB [10-F1] underwent one fabrication freeze-thaw cycle prior to photo-crosslinking. During this process, detrimental and irreversible damage from ice grains had already occurred, which is evident from its initial strength value at A0 (39.8 kPa ± 2.4 kPa). The introduction of crosslinking to JICs was necessitated by the observation that, prior to crosslinking, the strength of Gel [10] decreased to barely meet the critical threshold of 10 kPa (registering 11.2 kPa ± 0.2 kPa after A1, 8.7 kPa ± 1.0 kPa after A5, and 11.9 kPa ± 2.8 kPa after A10) as shown in Figure 7 d. As illustrated in Figure 7 g, Gel/MSB [10-F1] exhibited remarkable stability as a JIC, consistently maintaining a strength high above the critical threshold of 10 kPa through a minimum of 10 AFTCs with recorded values of 24.0 kPa ± 4.2 kPa after A1, 26.0 kPa ± 1.4 kPa after A5, and 19.8 kPa ± 1.7 kPa after A10. It is desirable for Gel/EDC [10-0.2] and Gel/EDC [10-0.5] to achieve stability on par with or slightly less than that of Gel/MSB [10- F1], but they should still sustain a strength exceeding 10 kPa. This expectation is underscored by the fact that the fabrication methods for Gel/EDC [10-0.2] and Gel/EDC [10-0.5] are considerably more cost-effective and scalable compared to that of Gel/MSB [10-F1]. For Gel/EDC [10-0.2], the observed strengths were 14.0 kPa ± 4.1 kPa after A1, 12.1 kPa ± 3.8 kPa after A5, and 12.1 kPa ± 3.8 kPa after A10 shown in Figure 17 e. Similarly, for Gel/EDC [10-0.5], the values were 20.9 kPa ± 3.8 kPa after A1, 20.8 kPa ± 3.2 kPa after A5, and 16.0 kPa ± 2.2 kPa after A10 shown in Figure 17 f. Notably, both hydrogels demonstrated greater stability than Gel [10] and consistently surpassed the 10 kPa benchmark. Besides, elevating the concentration of EDC enhanced the mechanical stability of the hydrogel. Gel/GTA [10- S], on the other hand, also reached above the 10 kPa benchmark, providing a good mechanical stability across multiple AFTCs. [0192] The alterations in mechanical properties can be attributed to the ice grains that formed within the hydrogel’s core. [3-6]To visualize these structural changes, two imaging techniques were employed. Initially, surgical blades were utilized to section the hydrogels, thereby revealing a cross-sectional surface on a 5 mm thick halved hydrogel. Figure 18 presents images captured using Dino digital microscopy of the hydrogel cross-sectional surfaces. In line with our proposed model for hydrogel-based cooling mediums, the hydrogels displayed remarkable homogeneity with a smooth surface before AFTCs when observed in micrometer-scale. Consistent with the patterns observed in Figure 17, the inherent uniform structure of all hydrogels was significantly disrupted post-A1, and additional features exceeding the nanometer scale became prominently noticeable. Among the evaluated samples, Gel/MSB [10-F1] exhibited the least structural damage due to ice grain formation, supporting the findings in Figure 17. While Gel/GTA [10-S] demonstrated impressive mechanical strength even after A10 in Figure 17, its internal structure was detrimentally destructed as seen in Figure 18. This suggests that the robust compressive strength of Gel/GTA [10-S] was primarily due to the crosslinked polymer skeleton. However, this crosslinked network of Gel/GTA [10-S] did not offer significant resistance against ice grain formation during freezing and could not counteract the structural changes during thawing. [0193] Figure 19 presents SEM images of CPD-dehydrated samples, elucidating the micro-scale internal structural changes in the above-mentioned specimens due to the first freeze-thaw cycle (A1). As water were fully removed by solvent exchange and CPD, the SEM images indicate the structural change of polymer networks supporting the hydrogels. When contrasted with Gel [10], both Gel/EDC [10-0.2] and Gel/EDC [10-0.5] effectively preserved the hydrogel’s inherent homogeneous structure, namely the homogenous nanometer-scaled water retaining enclosed cells. Notably, the internal surfaces of Gel/EDC [10-0.2] and Gel/EDC [10-0.5] exhibited fewer damages than Gel [10], even though some cracks were still evident post-A1. Elevating the EDC concentration appeared to enhance structural stability, with Gel/EDC [10-0.5] outperforming Gel/EDC [10-0.2] in maintaining structural integrity. Conversely, Gel/GTA [10-S] displayed a multitude of pronounced ditches and cracks, suggesting an even-less stable structure than Gel [10]. [0194] Post to freeze-thaw cycles, the 3D biopolymer matrix exhibited dual-scale features. It’s plausible to infer that the inherent homogeneous nanometer-scale porous structure persisted as the primary feature. The efficacy of the crosslinking methods determined the extent to which this nano-porous structure was preserved. Overlaying this nano-structure, a secondary feature emerged due to the ice grains formed during freezing. Under the specific experimental conditions employed in this study, these additional features induced by ice grains can span from micrometer to millimeter scales. [0195] As explained in our proposed model shown in Figure 11, alterations in the polymer network structures directly influence their capacity to retain freezable water content within the hydrogels. This, in turn, affects their heat absorption capabilities by modifying their latent heat of fusion around 0°C, as depicted in Figure 20. Figure 20 a and f depicts that for Gel [10], there’s a marked decline in both the total water content and the ratio of freezable water, moving from 89.4% and 81.2% at A0 to 85.0% and 57.4% after A10, respectively. In contrast, Gel/GTA [10-S] consistently retained its total water content around 85.5% ± 1.3% throughout the 10 AFTCs. However, its ratio of freezable water showed a decline from 83.2% at A0 to 63.8% post-A10. Similar to the trends observed in Gel/MSB [10-F1], both Gel/EDC [10-0.2] and Gel/EDC [10-0.5] displayed minimal reductions in total water content and the ratio of freezable water. Specifically, the total water content values for Gel/EDC [10- 0.2] and Gel/EDC [10-0.5] were 88.9% and 87.3% at A0, and 87.5% and 88.1% after A10, respectively; the ratio of freezable water content for Gel/EDC [10-0.2] and Gel/EDC [10-0.5] were 81.7% and 89.2% at A0, and 86.8% and 77.7% after A10, respectively. [0196] In the case of Gel [10], during freezing, phase separation transpires as freezable water crystallizes into ice. Given that the polymer network lacks adequate fortification, the expansive force exerted by the forming ice grains leads to the disruption of a portion of the native water-retaining cells within the polymer networks that illustrated in Figure 11. Absent these intrinsic finely structured enclosed water-retaining cells, when the phase-separated ice melts back into water, these water molecules are readily released from the hydrogel structure, culminating in a reduction of the total water content. On the other hand, in Gel/GTA [10-S], the polymer network is intensely crosslinked, particularly on the exterior due to the surface crosslinking technique employed. This tightly crosslinked outer layer preserves the overall water content, barring the separated water from escaping the hydrogel matrix. However, Nonetheless, due to the diminished hydrophilicity of the polymer chains and the larger inherent water-retaining cells within the polymer networks, the water isn’t effectively managed as freezable water. Gel/EDC [10-0.2], Gel/EDC [10-0.5] and Gel/MSB [10-F1], instead, achieved fine balances that resulted with formations of robust and homogenous refined-sized enclosed water-trapping cells during crosslinking, as depicted in Figure 12. [0197] In this section, we have presented comprehensive evidence supporting the conceptual model of optimal hydrogel cooling media, as depicted in Figure 11. Meanwhile, we have elucidated the ideal crosslinking approach that yields the desired hydrogel structure, as illustrated in Figure 12. We employed three primary crosslinking methods to fabricate a series of hydrogel samples intended for cooling applications. The one-step entirety crosslinking method was utilized to create samples such as Gel/EDC [10-0.1], Gel/EDC [10- 0.2], Gel/EDC [10-0.4], Gel/EDC [10-0.5], and Gel/EDC [10-0.6]. The two-step surface crosslinking approach was applied in the fabrication of Gel/EDC [10-S] and Gel/GTA [10-S]. Meanwhile, the multi-step crosslinking method, which integrates physical crosslinking (triggered by rapid-freezing-slow-thawing) and chemical crosslinking (induced by MSB- mediated photo-crosslinking reactions), was used to produce Gel/MSB [10-F1]. Upon evaluating their mechanical performances, swelling behavior, water profiles and in vitro biodegradability performances, and heat-absorbing capacities, it emerged that the hydrogel cooling media created through the one-step entirety crosslinking method, particularly Gel/EDC [10-0.5], exhibited performance metrics on par with those crafted using the multi- step approach, such as Gel/MSB [10-F1]. However, the advantage of the one-step crosslinking method lies in its enhanced efficiency, scalability, cost-effectiveness, and sustainability, requiring minimal energy, labor and time investment. Most importantly, Gel/EDC [10-0.5] exemplified the significance of engineering resilient, intricately structured polymeric networks with nanometer-scaled enclosed water-retention cells during the manufacturing phase, ensuring a consistent ability to retain freezable water across extended freeze-thaw cycles. Additionally, we presented compelling evidence highlighting the balance needed in the crosslinking reaction. The polymeric nano-cells should be sufficiently robust to withstand damage from ice grains during the freezing process. At the same time, the polymer skeleton should retain a high degree of hydrophilicity, allowing for the retention of a significant amount of freezable water within the cells after thawing. Furthermore, we provided visual evidence with SEM images as examples of adequate crosslinking (Gel/EDC [10-0.2] and Gel/EDC [10-0.5]) versus inadequate crosslinking (Gel/GTA [10-S]) to support the conceptual crosslinking model proposed in Figure 12. [0198] Delving deeper into the benefits of the one-step entirety crosslinking method, we investigated if employing EDC in this process could successfully produce the desired hydrogel cooling media structure using a reduced polymer concentration, specifically 8% gelatin. Decreasing the polymer concentration could potentially lead to a cooling media with a heightened water content. Thus, a series of samples including Gel/EDC [8-0.1], Gel/EDC [8-0.2], Gel/EDC [8-0.5], Gel/EDC [8-0.8], and Gel/EDC [8-1.0] were fabricated with the method described in Figure 13. Representative characteristics are shown in Figure 21. [0199] Compared with 10% gelatin hydrogel systems, the 8% gelatin formulation allowed for the inclusion of a greater concentration of EDC before witnessing aggregation in the precursor solution mixed at 50°C. As depicted in Figure 21 a, we were able to incorporate up to 1.0% EDC. As the concentration of EDC increased, the resulting hydrogels displayed progressively higher compressive strength and strain at break. For a comprehensive evaluation, Gel [8], Gel/EDC [8-0.5], and Gel/EDC [8-1.0] were chosen as representative samples, each reflecting different degrees of crosslinking. The swelling behavior and in vitro enzyme degradation tests are depicted in Figure 21 b-c, respectively. Consistent with the varying degrees of crosslinking indicated by their mechanical properties, Gel/EDC [8-1.0] exhibited the highest degree of crosslinking, while Gel [8] had the lowest. Given that both Gel/EDC [8-1.0] and Gel/EDC [8-0.5] showcased mechanical properties comparable to hydrogels already established as efficient cooling media (e.g., Gel/MSB [10-F1]), both were subjected to extensive AFTCs to evaluate their potential as cooling media, using Gel [8] (negative control) and Gel/MSB [10-F1] (positive control) as benchmarks. [0200] Figure 21 d and h demonstrates that the initial 8% gelatin hydrogel (Gel [8]) was not robust enough for repeated use as a cooling medium, with a compressive strength of 48.5 kPa ± 5.8 kPa, 10.9 kPa ± 0.2 kPa, 6.7 kPa ± 1.5 kPa and 6.6 kPa ± 1.0 kPa at A0, A1, A5 and A10, respectively. In contrast, the Gel/EDC [8-0.5] and Gel/EDC [8-1.0] hydrogels showcased a marked improvement in both absolute compressive strength and its stability over repeated cycles. Specifically, Gel/EDC [8-0.5] displayed strengths of 141.5 kPa ± 14.7 kPa at A0, 17.2 kPa ± 7.0 kPa at A1, 10.0 kPa ± 1.9 kPa at A5, and 9.0 kPa ± 3.5 kPa at A10, while Gel/EDC [8-1.0] exhibited strengths of 470.9 kPa ± 9.4 kPa, 18.1 kPa ± 4.9 kPa, 16.7 kPa ± 8.7 kPa, and 13.9 kPa ± 2.3 kPa at the same respective stages, as shown in Figure 21 e and f, respectively. [0201] The mechanical resilience of the hydrogels was intrinsically tied to internal structural alterations, as depicted in Figures 22 and 23. Drawing parallels with our prior observations on virgin and crosslinked 10% gelatin hydrogels, the virgin 8% gelatin hydrogel (Gel [8]) demonstrated vulnerability to AFTCs. This vulnerability manifested as pronounced long and deep cracks, both at a visible scale (millimeter scale, as seen in Figure 22 a) and on a micrometer scale (as shown in Figure 23). With the introduction of 0.5% EDC crosslinking (Gel/EDC [8-0.5]), the damages inflicted by ice grain formation during freezing were somewhat mitigated. However, visible damage remained evident at both the millimeter (Figure 22 b) and micrometer scales (Figure 23). A more pronounced improvement in structural stability was observed in the hydrogel crosslinked with 1.0% EDC (Gel/EDC [8- 1.0]). This hydrogel exhibited diminished damage on the millimeter scale (Figure 22 c) and even more reduced impairments on the micrometer scale (Figure 23). [0202] Incorporating the nanometer-scale porous insights from cryoEM depicted in Figure 14, we can conclude that before undergoing AFTC, Gel [8], Gel/EDC [8-0.5], and Gel/EDC [8-1.0] consisted of a uniform nanometer-scaled network of water-retaining cells formed by gelatin molecules. After the AFTCs, this nanometer-scale network was somewhat compromised, with the degree of disruption being inversely related on the extent of crosslinking. Among all fabricated 8% gelatin hydrogels, Gel/EDC [8-1.0] exhibited the least disruption, while Gel [8] underwent the most. Superimposed on this nanometer-scaled cellular network, the biopolymer matrix acquired a secondary characteristic: irregular, randomly distributed cracks that are typically above micrometers, induced by ice grains formed under the condition of AFTCs. The frequency of these larger-scale features increased with successive AFTCs. [0203] The water profiles and the consequent heat-absorbing capacity around 0°C of both the virgin (Gel [8]) and crosslinked variants (Gel/EDC [8-0.5] and Gel/EDC [8-1.0]) were characterized, as depicted in Figure 24, using Gel/MSB [10-F1] as a reference standard. All three of the 8% gelatin hydrogel samples maintained a high total water content across 10 AFTCs, with 90.7% ± 0.5% for Gel [8] (Figure 24 a), 89.9% ± 0.8% for Gel/EDC [8-0.5] (Figure 24 b), and 90.1% ± 0.4% for Gel/EDC [8-1.0] (Figure 24 c). As Figure 24 e illustrates, the ratio of freezable water in Gel [8] decreased over time, dropping from 91.3% at A0 to 73.5% after A10. Gel [8-0.5] demonstrated an improved stability, maintaining 88.8% of freezable water at A0 and 81.9% after A10. Gel [8-1.0] exhibited even greater stability, with 94.5% ratio of freezable water at A0 and 83.9% after A10. The latent heat of fusion around 0°C mirrored the pattern observed in the ratio of freezable water, as showcased in Figure 24 i – k. Specifically, the latent heat of fusion values for Gel [8] were 279.0 ± 7.8 J ^g ^-1 at A0, transitioning to 222.8 ± 2.5 J ^g ^-1 after A10. For Gel/EDC [8-0.5], these values spanned from 267.9 ± 8.6 J ^g ^-1 at A0 to 245.0 ± 4.1 J ^g ^-1 after A10, while for Gel/EDC [8- 1.0], they ranged from 286.2 ± 6.6 J ^g ^-1 at A0 to 245.0 ± 4.1 J ^g ^-1 after A10. The efficacy of Gel [8-1.0] was not only comparable to, but in some aspects surpassed, the benchmark set by the positive control, Gel/MSB [10-F1], which positions Gel [8-1.0] as a superior heat- absorbing material with enhanced scalability, sustainability, and cost-effectiveness. [0204] The findings from our experiments using both virgin and crosslinked 8% gelatin hydrogels validate our proposed ideal model for hydrogel cooling media, as illustrated in Figure 11. Additionally, these results corroborate the structural model for employing EDC in the one-step entirety crosslinking method, as depicted in Figure 12. The virgin 8% gelatin hydrogel (Gel [8]) displayed vulnerabilities in its mechanical properties and inconsistent heat absorption capabilities, stemming from an absence of a sturdy polymeric 3D network with resilient enclosed water-retaining chambers. While it was feasible to construct these chambers using an 8% gelatin concentration, their walls remained thin and delicate prior to additional crosslinking. Leveraging EDC in a one-step entirety crosslinking approach significantly enhanced the structural integrity of these chambers, yielding homogeneous, delicate, yet durable water-restraining cell walls. This structural reinforcement endowed Gel/EDC [10-1.0] with formidable mechanical resilience and consistent water retention and heat absorption capacities. The efficacy of a reusable hydrogel cooling media is intrinsically tied to the successful construction of a 3D polymeric network characterized by enclosed water-retaining cells. Conclusions [0205] In this study, we fabricated a series of hydrogel samples, both in their native and crosslinked states, to validate our proposed model for an optimal hydrogel cooling medium, JICs. We identified that the essence of an efficient hydrogel cooling system lies in the successful fabrication of numerous, resilient, uniformly sized, nanometer-scaled enclosed water-retaining cells within a three-dimensional biopolymer matrix during the fabrication process. After undergoing application freezing-thawing cycles, the nanometer-scale uniformity is partially disrupted, giving rise to larger features, ranging from micrometers to millimeters, induced by ice grain formation. To fabricate resilient hydrogel with high potentials as cooling media, we investigated three distinct crosslinking methods: one-step entirety crosslinking, two-step surface crosslinking, and a multi-step approach that combines both physical and chemical crosslinking techniques. Of these, the one-step entirety crosslinking emerged as the most sustainable, scalable, and cost-effective strategy. EDC, used as a representative crosslinking agent, demonstrated an ideal crosslinking rate and reaction speed. Leveraging the EDC-supported one-step crosslinking technique, we not only enhanced the sustainability, scalability, and cost-efficiency of producing reusable hydrogel cooling media with a 10% gelatin concentration but also successfully reduced the polymer concentration to 8% gelatin, thereby achieving a new generation of JICs with superior heat- absorbing capabilities. References [1] Farris, S.; Song, J.; Huang, Q. Alternative Reaction Mechanism for the Cross-Linking of Gelatin with Glutaraldehyde. Journal of Agricultural and Food Chemistry 2010, 58 (2), 998–1003. https://doi.org/10.1021/jf9031603. [2] Mastronarde, D. N. Automated Electron Microscope Tomography Using Robust Prediction of Specimen Movements. J. Struct. Biol.2005, 152 (1), 36–51. https://doi.org/10.1016/j.jsb.2005.07.007. [3] Zou, J.; Sbodio, A. O.; Blanco‐Ulate, B.; Wang, L.; Sun, G. Novel Robust, Reusable, Microbial‐Resistant, and Compostable Protein‐Based Cooling Media. 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The scope of the invention should, therefore, be determined not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. The disclosures of all articles and references cited in this application, including patent applications, patents, and PCT publications, are incorporated herein by reference for all purposes.