The present invention relates to a composition for laser tissue soldering .

Almost every surgical intervention requires some type of j oining of adj acent sections of tissue . Technologies such as sutures , staples , clips , and adhes ives have been used for many years to close surgical incisions and wounds .

When suturing, the surgeon passes the needle through the tissues close to their edges , pulling them together and thereby relying on tissue and suture strength to hold them tight . Thus , suturing is a delicate , demanding, and time-consuming procedure which requires technical skills . Sutured sites are at an increased risk for leaks , infections , and scarring .

Stapling is appropriate in some cases , but it also relies on the original tissue strength and may be limited by the shape and si ze of the speci fic stapler since a poorly adapted stapler may result in bonding failure . Adhesives also have their limitations since they may exhibit insuf ficient tensile strength and may be toxic .

Methods of wound closure have been continuously evolved, and newer and better techniques have been developed . One of these methods is laser tissue bonding . Broadly, laser tissue bonding is divided into three types , namely laser tissue welding, laser tissue soldering and dye-enhanced laser tissue soldering .

Laser tissue soldering is a technique that is able to form strong bonds. Thermal control is of utmost importance in laser tissue soldering. Temperatures below the target temperature do not allow the formation of strong bonds, while temperatures above the target temperature will damage the surrounding tissues and hinder the healing process.

Infrared thermal cameras and sensors have been used for thermal sensing (for example Gerasimenko et al. "Laser System with Adaptive Thermal Stabilization for Welding of Biological Tissues" in Biomed Eng 49, pages 344-348 (2016) ) . However, the radiation used for temperature sensing is not within the biological window. Therefore, it is only possible to get information of the surface of the tissue. Non-superf icial wounds cannot be controlled. Moreover, optics for their wavelength are expensive.

Dong et al. "Terahertz three-dimensional monitoring of nanoparticle-assisted laser tissue soldering", Vol. 11, Issue 4, pages 2254-2267 (2020) disclose the investigation of the thermal damage during the soldering process by terahertz radiation. However, this method is based on the water content in the tissue and is not able to give information about the temperature during the soldering process.

Khosroshahi et al. "Application of Albumin Protein and Indocyanine Green Chromophore for Tissue Soldering by Using an IR Diode Laser: Ex Vivo and In Vivo Studies" Photomedicine and Laser Surgery 28 (6) , pages 723-33 (2010) disclose the colour change of indocyanine green during soldering process as indicator for the end of the soldering process. However, said method is not very precise.

The problem of the present invention is therefore to provide a composition for laser tissue soldering that allows precise temperature control during the soldering process .

The problem is solved by the composition according to claim 1 . Further preferred embodiments are subj ect of the dependent claims .

The composition according to the present invention comprises a temperature sensitive biocompatible solder and at least one type of nanoparticles . Said first type of nanoparticles is a fluorescent nanothermometer exhibiting an excitation maximum and a temperature dependent emission spectrum each in the range of between 650 and 1350 nm .

The expression "temperature sensitive solder" is known in the art . Temperature sensitive solders are for example protein solders or chitosan solders . Protein solders are preferably selected from the group consisting of albumin, fibrinogen, collagen and gelatin, which denature upon exposure to locali zed heating and which are further capable of cross-linking to each other and to the adj acent tissue to which the composition of the present invention is contacted . Moreover, since the temperature sens itive solder is used in biological tissue soldering processes , it has to be biocompatible as well , thus , it does not produce a toxic or immunological response when exposed to the body .

Within the context of the present invention, the expression " fluorescent nanothermometer" stands for nanoparticles and structures which exhibit an excitation maximum and temperature dependent emission spectrum each in the range of between 650 and 1350 nm . Said nanothermometers are capable of fluorescence , i . e . they absorb electromagnetic radiation ( excitation process ) followed by the spontaneous emission of electromagnetic radiation ( emission process ) . As both the excitation maximum and the emission maximum are in the range of between 650 and 1350 nm, fluorescent nanothermometers according to the present invention work within the biological window, i . e . the biological cells are not negatively impacted by the electromagnetic radiation . When applying the composition according to the invention, the ratio of the excitation maximum and the emission maximum of the fluorescent nanothermometer is used to calculate the temperature of the temperature sensitive solder . Band-shape fluorescent nanothermometry is a preferred method as said method is robust and flexible . However, other methods such as intensity, spectral , polari zation, bandwidth and li fetime luminescence nanothermometry are possible . Said methods are known to the skilled person . The fluorescent nanothermometers have a particle si ze that allows an easy dispersion . Typically, they have a mean crystal si ze of 10 to 200 nm (measured by x-ray di f fraction or electron microscopy) . The temperature sensitivity of the fluorescent nanothermometers can be optimi zed for example by doping at particular percentages in a particular host or by coupling more dyes .

The composition according to the present invention allows a sensitive and accurate measurement of the temperature at the interface between temperature sensitive solder and tissue in real time . Since the composition according to the present invention allows to work in the biological window, it can provide information about the temperature even when applied in wounds at tens of millimetres below the surface . Thus , it can be used for both, superficial and non-superf icial wounds and can therefore greatly improve the soldering process .

The composition according to the present invention allows a soldering process resulting in a tissue bond with suf ficient surgical tensile strength but only minimal immediate and longterm denaturation of the surrounding tissue .

In addition, the composition according to the present invention requires a less expensive setup equipment than systems used in the prior art .

In a preferred embodiment , the composition according to the present invention can additionally comprise a photothermal agent , wherein said photothermal agent is preferably selected from the group consisting of plasmonic nanoparticles ( as a second type of nanoparticles ) and photothermal dyes .

Within the context of the present invention the expression "photothermal agent" stands for agents that can convert laser light into heat in the biological window, i . e . , in a wavelength range of 650 to 1350 nm . Due to their high absorption coef ficient and photothermal energy conversion ef ficiency, both, plasmonic nanoparticles and photothermal dyes can ef ficiently convert light to heat in the biological window . Thus , the photothermal agent has a heating function, while the fluorescent nanothermometer has a thermal sensing function . Fluorescent nanothermometers do not typically provide plasmonic properties .

Within the context of the present invention near IR absorbing dyes of the present disclosure can absorb optical radiation within the near IR spectrum and convert the absorbed radiation to thermal energy . A laser is a device that emits light through a process of optical ampli fication based on the stimulated emission of electromagnetic radiation . A laser di f fers from other sources of light in that it emits light which is coherent . I f the electromagnetic radiation of a laser source has a wavelength range of 650 to 1350 nm, the photothermal agents can selectively absorb incident light in the biological window and convert it to locali zed heat .

The presence of the two types of particles , namely the fluorescent nanothermometers and the photothermal agents , has a synergistic ef fect . The addition of the fluorescent nanothermometers increases the scattering coef ficient of the material which in turn increases its extinction coef ficient . Thus , the increased scattering favours the absorption of laser light by the photothermal agents and consequently its heat production . This allows to reduce the amount of photothermal agents needed in the composition of the present invention .

Preferably, the fluorescent nanothermometers are selected from the group consisting of quantum dots , nanodiamonds , gold nanoclusters , hosted rare earth ions , upconverting nanoparticles , transition metal ions , luminescent organic dyes , luminescent organic polymers and luminescent gels .

Within the context of the present invention the expression "quantum dots" refers to particles which have a three- dimensional si ze in nanoscale ( less than 100 nm) , and are composed of finite number of atoms . Preferably, said quantum dots are selected from the group consisting of carbon dots , CdSe , CdS , Ag2S and PbS , preferably CdSe , CdS , Ag2S and PbS .

Within the context of the present invention the expression "upconverting nanoparticles" refers to nanoparticles that when excited with light emit light that has a wavelength that is shorter than the excitation wavelength. Typically, the comprise a host crystal which is doped with one or several types of lanthanide ions. Typical host materials are metal fluorides (NaYF-i) , oxides (Y2O3) , phosphates (YPO4) , and vanadates (GdVCh) . The lanthanide ions are preferably selected from the group consisting of Er ³⁺ , Yb ³⁺ , Ho ³⁺ , Gd ³⁺ , Tm ³⁺ or combinations thereof.

Within the context of the present invention the expression "hosted rare earth ions" refers to host lattice materials containing dopant rare earth ions. Examples for such hosts are LaFs, Ba3(PO4)2 and BiVCh. The rare earth ions are preferably selected from the group consisting of Eu ³⁺ , Nd ³⁺ , Mn ³⁺ , Er ³⁺ and Dy ³⁺ .

Within the context of the present invention the expression "nanodiamonds" refers to truncated semioctahedral carbonaceous architecture ranging from 5 to 50 nm in diameter.

Within the context of the present invention "gold nanoclusters" refers particles with sizes of less than 2 nm, comprising up to hundreds of gold atoms. Gold nanoclusters may optionally be protected by ligands such as sulfonic thiolate ligands or by thiolated peptides. Examples of gold nanoclusters are Aug, AU13, AU20, AU24, AU32 and AU39.

Examples for fluorescent organic dyes having nanothermometer properties are (E) -2-chloro-N- (4- (5, 5-dif luoro-3- (2-hydroxy- 5- (trifluoromethoxy) styryl) -l-methyl-5H-4X4 , 5X4- dipyrrolo [l,2-c:2',l'-f] [1,3,2] diazaborinin-10- yl ) phenyl ) acetamide (ER thermo Yellow) , Rhodamine 800 and N, N-dibutyl-6-imino-9- ( 3-piperidin-l-ylphenyl ) xanthen-3-amine

(Mito thermo yellow) .

Examples for luminescent organic polymers having nanothermometer properties are thermosensitive polymer such as NIPAM (poly (N-isopropylacrylamide ) , OEGMA (oligo (ethylene glycol) methyl ether methacrylate) , NNPAM (N-n- propylacrylamide ) , PDA (perf luoralkoxy polymere) , PMMA (poly (methyl-2-methylpropenoate ) ) which are linked with a dye (e.g. DBD-AA (N- (2- { [ 7- (N, N-dimethylaminosul f onyl ) -2 , 1 , 3- benzoxadiazol-4-yl ] - (methyl) aminojethyl) -N-methylacrylamide ) , ICG (indocyanine green) , AMC ( 7-amino-4-methyl-cumarine ) , NBD ( 4-chlor-7-nitro-benzofurazane ) .

Examples for luminescent gels are cationic nanogels of N- isopropylacrylamide (NIPAM) , including NIPAM-based cationic fluorescent nanogel thermometers.

The expression "doped with a specific cation" means the replacement of a host cation with said specific cation. Typically, 0.05 to 5 at%, preferably 0.05 to 2 at% of the host cation is replaced with the specific cation. The unit at% is defined as the atomic fraction of the total metal ion concentration. These nanoparticles provide a high chemical-, thermal- and photo-stability. Furthermore, they exhibit no blinking. The absence of blinking significantly improves signal-to-noise ratio. In addition, they do not exhibit bleaching, so that the signal does not disappear over time.

Preferred fluorescent nanothermometers are selected from the group consisting of neodymium-doped BiVCh, manganese (V) doped Ba3(PO4)2, LiNdP40i2, neodymium-doped CaF2, and neodymium-doped LaFs. Said fluorescent nanothermometers , and in particular neodymium-doped BiVCh , exhibit excellent reproducibility while showing negligible dependence on experimental parameters and surroundings , which is of utmost importance for biological tissue application .

The composition according to the present invention can comprise plasmonic nanoparticles having a broad absorption range or plasmonic nanoparticles with steep absorption peeks . In one embodiment , the composition of the present invention comprises a mixture of di f ferent plasmonic nanoparticles . The plasmonic nanoparticles can be in the shape of spheres , core-shell structures , Janus-particle structure , rods , stars , triangles or cubes .

Preferably, the plasmonic nanoparticles are selected from the group consisting of plasmonic metal nanoparticles , plasmonic carbon nanotubes , plasmonic organic nanoparticles , plasmonic conductive oxides and plasmonic conductive transition metal nitrides , hybrids , silica coated nanoparticles or mixtures thereof , preferably plasmonic metal nanoparticles , wherein the metal is selected from the group consisting of Au, Al , Ag, Cu, Pt and Pd, most preferably Au . Gold nanostructures include gold nanoparticles , gold nanorods , gold nanospheres and gold nanostars . Typically, the plasmonic nanoparticles are present in a concentration of about 0 . 005 to 1 mg/ml .

In particular, conductive transition metal nitrides selected from the group consisting of TiN, ZrN, TaN and HfN are very ef ficient light-to-heat converter . They have a broad absorption range and can be produced easily . Furthermore , TiN is inexpensive and already being used as a coating for biomedical implants and many other biological applications , which allows a safe application in humans .

Conductive oxides are preferably selected from the group consisting of RuCh , Al-doped ZnO, Ga-doped ZnO, HfCh , I-doped SnO2 and F-doped SnCh .

A gold nanorod is defined as nanometer-si zed gold particles that are rod shaped . Typically, it has a diameter ranging from a few nanometers to hundreds nanometers with aspect ratios ( length/ diameter ) larger than 1 but typically smaller than 6 . 5 . Such gold nanorods have a steep absorption peak at about 1064 nm . Gold nanorods have the advantage that their steep absorption can be tuned by changing their aspect ratio . Furthermore , depending on their aspect ratio , they are able to absorb selectively at the required wavelength, including the ones in the range 900- 1300 nm .

The composition according to the present invention can also comprise photothermal dyes . Said photothermal dyes are preferably are near-infrared absorbing dyes , preferably selected from the group consisting of indocyanine green, brilliant blue green, bromophenol blue , 4- [ 2- [ 2-chlor-3- [ ( 2 , 6- diphenyl-4H-thiopyran-4-yliden) -ethyliden] - 1-cyclohexen- l- yl ] ethenyl ] -2 , 6-diphenylthiopyrylium-tetraf luoroborat ( IR- 1061 ) , diimminium dye and cyanine dyes .

In one embodiment of the present invention, the excitation maximum of the fluorescent nanothermometer di f fers from the absorption maximum of the plasmonic nanoparticle by at least 200 nm . This allows to control the laser soldering process by two lasers . One laser is tuned at the wavelength of the fluorescent nanothermometer, and the second laser is tuned at the wavelength of the plasmonic nanoparticles . Thus , one laser is for thermal sensing, while the other is for heating . This allows to interrupt the heating process but to continue the temperature control .

In another embodiment of the present invention, only one laser is used during the soldering process . Said laser is tuned for nanothermometer excitation and photothermal agent absorption which allows a cost-ef fective equipment .

Best results can be obtained with a composition according to the present invention comprising neodymium-doped BiVCh as fluorescent nanothermometers and TiN and/or gold nanorods as plasmonic nanoparticles .

Preferably, the temperature sensitive solder contained in the composition according to the present invention comprises of serum albumin, chitosan, collagen, fibrinogen and gelatin or a mixture thereof , preferably bovine serum albumin (BSA) , human serum albumin (HAS ) and gelatin or a mixture thereof , most preferably a mixture of bovine serum albumin (BSA) and gelatin or human serum albumin (HAS ) and gelatin . The presence of albumin improves the bonding strength of the bond . Gelatin has the advantage that it is j elly-like at room temperature and liqui fies at temperatures above 35 ° C . The presence of gelatin allows for example the formation of strips and patches of the desired geometry as well as the formation of strong bonds . Chitosan provides very good bond strengths and/or burst pressures . In addition, chitosan is hemostatic, mucoadherent and biodegradable which all makes it well suited for use in tissue repair applications . Chitosan is preferably present in combination with serum albumin .

In one embodiment of the present invention, the temperature sentitive solder additionally comprises a biodegradable polymer selected from the group consisting of poly (L-lactic acid) ( PLA) , poly ( glycolic acid) , poly (L-lactic-co-glycolic acid) (PGA) , poly ( [ epsilon] -caprolactone ) (PLGA) and polyortho esters, polyanhydrides or combinations thereof. Said biodegradable polymers work as scaffold and allow the formation of strips of the desired geometry as well as the formation of a strong bond.

In one embodiment of the present invention the fluorescent nanothermometers and the plasmonic nanoparticles are present in a ratio of 1:1 to 5000:1 % by weight. Due to increased scattering coefficient given by the fluorescent nanothermometers , the concentration of the plasmonic nanoparticles can be significantly reduced.

Preferably, the composition comprises 0.01 to 100 mg/ml, preferably 0.1 to 50 mg/ml, most preferably 1 to 10 mg/ml of the fluorescent nanothermometers. This concentration guarantees an optimal sensitivity, and in some applications, it can even eliminate the need for further calibrations after conducting the initial calibration.

In a further embodiment, the composition according to the present invention additionally comprises a therapeutic agent selected from the group consisting of antimicrobial agents, anti-inflammatory agents and angiogenic agents. Antimicrobial agents are antibiotics, antibacterials, antifungals, antivirals and antiprotozoans. Anti-inflammatory agents are compounds that reduce inflammation or swelling. Possible antiinflammatory agents are in particular nonsteroidal antiinflammatory drugs and/or radical scavengers (such as vitamins, metal oxides, including iron oxide, cerium oxide, manganese oxide and cobalt oxide) . As part of the composition according to the present invention, the therapeutic agent is directly applied to the surgical site resulting in a rapid wound healing. Furthermore, a lower dose of said therapeutic agents is possible since no systemic administration is needed. These optionally added therapeutic elements can give rise to synergistic properties and enable photodynamic or photothermal therapy using the solder material.

Preferably, the composition according to the present invention is formulated as paste, gel, strip, patch or viscous fluid having a viscosity of at least 2'000 centipoises at 25°C and can be applied directly on the wound. A patch may be customized to desired size and shape by the surgeon and is particularly suitable for large wounds, whereas pastes, gels and strips are preferably used for small wounds.

In another embodiment, the composition of the present invention is in lyophilised form. The term "lyophilise" with regard to the composition according to the present invention is intended to refer to the freeze-drying of an aqueous solution of the composition. The term "lyophilisate" refers to the product of lyophilisation. According to one embodiment of the invention, the lyophilised composition further comprises a suitable buffering agent for maintaining a pH of about 5.5 to 7.5, preferably of about 6.0 to 7.0, and more preferably about 6.3 to 6.7 after reconstitution of the lyophilisate. The term "reconstitution" refers to immersion of the lyophilisate in an aqueous medium for achieving a hydrated form. A buffering agent of the composition according to the invention may be selected from a group comprising of disodium phosphate dihydrate, sodium dihydrogen phosphate dihydrate, trisodium citrate dihydrate or combination thereof. The lyophilised form of the composition according to the present invention results in an improved longterm stability. In addition, the lyophilised form of the composition according to the present invention can be stored at room temperature or in the fridge. Storage in the fridge is preferred .

One aspect of the present invention relates to the use of the composition according to the present invention in the treatment of biological tissue repair by laser soldering. The composition of the present invention can be used for any tissue repair in individuals, and in particular for anastomosis (vessels, tissues and nerves) ; repair surgeries for skull base, cerebrospinal fluid leak (e.g. endoscopic endonasal surgical repair) , nerve, tendon, muscle, fascia, vessel, lungs, diagphram, and esophagus (e.g. iatrogenic esophageal perforation) ; surgeries (possibly also for repairs) in urologic, gynecologic, orofacial, aerodigestive, gastrointestinal, ophthalmological and cerebrospinal fields (e.g. urologic/gynecologic endoscopic pelvic repairs, repairs after fibroidectomies, uterine closure, dental replacement, skin closure, bladder surgery, laparoscopic abdominal surgical repairs) .

In a preferred embodiment of the present invention, the composition of the present invention is used in the treatment of biological tissue repair by laser soldering, wherein the tissue is selected from the group consisting of cornea, blood vessels, fascia, diaphragm, anastomosis of vessels and tissues, dura mater leaks, gastrointestinal tissues and nerves. Said tissues are complex and delicate and would be damaged by conventional suturing . In addition, it could be shown that the compositions according to the present invention are able to avoid bacteria leakage from intestinal defects .

A further aspect of the present invention relates to the use of composition according to the present invention in the treatment of deep tissue wounds ( also called deep tissue inj ury) . Within the context of the present invention the term "deep tissue wounds" means wounds that are more than 2 millimeters , pre ferably more than 5 millimeters below the tissue surface and typically involve soft tissue . Examples are puncture wounds , bullet wounds , or wounds that result from the surgical removal of a substantial amount of tissue , such as in debridement procedures or removal of tumors , and skin or ( engineered) tissue transplantation wounds . It was shown that the composition according to the present invention allows to control the temperature in the deep tissue resulting in a fast and strong bonding of the tissue without negatively impacting the surrounding tissue .

A further aspect of the present invention relates to the use of a composition according to the present invention in the treatment of wound of an individual , wherein the individual is selected from the group consisting of elderly, diabetics , immunosuppressed individuals and immobili zed individuals . Said individuals develop wounds that are slow to heal , do not heal well , or even never heal . Sometimes , an infection might develop . An infection can spread to tissue and bone near the wound or more distant areas of the body . In some cases , and without emergency care , an infection can be li fe-threatening or may even be fatal . Due to the composition according to the present invention, it is possible to obtain a fast and strong bonding of the tissue . In addition, the inflammatory response and the post-surgical recovery period is signi ficantly reduced .

The composition according to the present invention may be used as follows : first the composition is placed on the wound . Then, the composition is irradiated with a laser light having a wavelength of 650 nm to 1350 nm . The laser light activates the fluorescent nanothermometer, and if present , the plasmonic nanoparticles . The composition of the present invention heats up the underlying ti ssue, and thus creates a continuous bond . The result is a waterproof seal along the entire wound which prevents access to external pathogens and does not require suture removal . Accordingly, the present invention also relates to a method for treating wounds involving the steps of placing the composition on the wound and irradiated the composition with a laser light having a wavelength of 650 nm to 1350 nm .

The present invention also includes the use of a laser to facilitate wound healing . Lasers are known to be used in wound healing and can be used with the compositions comprising a temperature sensitive solder . While any suitable laser can be used, a near IR laser ( e . g . , IR-A) , such as from about 650 nm to 1350 nm may be advantageously used . The laser can be , for example , a single-wavelength laser, tuned for nanothermometer excitation and plasmonic particle absorption . Advantageously, two lasers are simultaneously used, one for thermal sensing, the other for heating ( see Figure 8A) . A spectrometer or a NIR camera is preferably used to measure the fluorescence. The resulted data are needed to calculate the temperature of the solder . Further, also water- filtered near infrared light can be used which has higher penetration in tissue due to the elimination of water-absorbed wavelengths and is therefore, especially suitable for deep tissue wound treatments which has lower absorption and higher penetration.

Figures

Figures 1A and IB show the temperature increase in the composition with different compositions (all containing BSA and gelatin as temperature sensitive solder) under laser light irradiation at 750 nm.

Figure 2 shows a scheme of the laser tissue soldering setup.

Figure 3 shows a calibration curve that relates temperature and spectra at different temperatures (through the Fluorescence Intensity Ratio FIR) .

Figure 4 shows a temperature during laser tissue soldering measured using a thermal camera ("Reference temperature") and the fluorescent nanothermometers ("Computed temperature") (using Nd-doped BiVCh at 2.5 mg/ml and TiN at 0.02 mg/ml; BSA 0.250 g/ml and gelatin 0.065 g/ml solution dissolved in PBS (phosphate-buff ered saline) ) .

Figure 5 shows a typical stress-strain graph of a laser soldered tissue (BSA 60%, TiN at 1%.) .

Figure 6 shows histological images with and without the composition on top.

Figure 7A shows the stability of the composition in digestive fluids . Figure 7B shows that the composition is able to avoid bacteria leakage from intestinal defects.

Figure 7C shows that the composition increases the burst pressure if applied on sutures.

Figure 7D shows the bond strength of the composition.

Figure 8A shows lasering with a two-laser setup.

Figure 8B shows the performance of the composition on a surface-near wound and on a deep tissue wound.

Examples

Preparation of the composition

First, the fluorescent nanothermometers need to be prepared. Luminescent Nd-doped BiVCh particles were prepared by flame spray pyrolysis (FSB) . Bismuth (III) nitrate pentahydrate (Bi (NO3) 3*5H ₂ O) and stoichiometric amounts of vanadium (ammonium metavanadate, NH4VO3) were dissolved separately in a 2:1 volumetric mixture of 2-ethylhexanoic acid and acetic anhydride under magnetic stirring for two hours at 100 °C. The Nd ³⁺ is added by dissolving neodymium nitrate hexahydrate (Nd (NO3) 3* 6H2O) . The Nd ³⁺ concentration was defined as atomic fraction (at%) of the total metal ion concentration resulting in the formula Bio.99 Ndo.oiVCh, which has been shown to lead to the highest luminescence intensity. The total metal concentration was kept constant at 0.4 M. All chemicals were supplied by Sigma-Aldrich. The resulting precursor solution was fed at a constant rate (8 ml/min) through a nozzle and dispersed by 3 1/min of oxygen resulting in a fine spray that was ignited and sustained by a surrounding premixed oxygen/methane (1.5/3.2 1/min) flamelet. The particles were collected on a glass microfibre filter (Whatman GF) with the aid of a vacuum pump (Busch Mink MM 1202 AV) . The collected particles were sieved (standard mesh size of 250) and annealed for 6 h at 600 °C (Carbolite Gero 30-3000 °C) .

When the nanothermometers are ready, the fabrication of the composition can begin. Various final concentrations of BSA (Sigma-Aldrich, lyophilised powder, > 96%) , gelatin (Sigma- Aldrich, from Porcine Skin, type-A, strength 300) , BiVCh and TiN (PlasmaChem, 20 nm) can be selected. In this case the final concentrations (w/v) are BSA 25%, Gelatin 6.5%, Nd-doped BiVCh 0.2%, and TiN 0.003%. The composition is made from four starting solutions. A solution of 50% BSA was prepared by dissolving BSA in PBS. The dissolution speed can be increased using a mixer. A solution of 26% gelatin was prepared by adding gelatin to PBS. The solution was mixed and heated in a heated shaker (LLG Labware, uniTHERMIX 1) at 400 rpm and 60 °C until the solution was completely dissolved (usually in less than 30 min) . A 1% solution of Nd-doped BiVCh in water and a 0.1% solution of TiN were prepared and put in an ultrasonicator . Then, 0.5 ml of 26% gelatin were brought to 42 °C and 1.224 mL of 50% BSA were added to it. The mixture was vortexed for about 10 seconds and put in the shaker at 42 °C. Then, 0.349 ml of Nd-doped BiVCh solution were added and the obtained solution quickly vortexed for a few seconds. The process was repeated using instead of the BiVCh solution 52.4 pl of TiN solution. Before the solution cooled down, it was poured into the desired mould, making sure that no bubbles were present. The composition was put in the fridge until gelation.

The presented protocol can be used to prepare compositions with other concentrations.

For example, compositions comprising only fluorescent nanothermometers can be created by using distilled water instead of solutions comprising plasmonic nanoparticles.

Results and discussion

Heating of the composition

The temperature that can be reached by shining a laser on the composition depends on the optical properties of the solder, mainly given by the nanothermometers and in particular by the plasmonic nanoparticles that are added. Whether a certain mix of nanoparticles can be used for laser tissue soldering depends on its ability to convert laser light into heat efficiently.

Three different compositions were used in order to investigate the temperature reached during soldering: two with either only TiN or only Nd-doped BiVCh, and one with both types of nanoparticles (same concentrations described in the Materials section) . A composition comprising 25% BSA, 6.5% Gelatin, 0.3% Nd-doped BiVCh, and 0.01% GNR with a thickness of 0.5 mm was used. A 750 nm multimode GW laser (Laser Century, RLM750TA) is coupled to a fibre and used with a collimator. Laser power of 0.886 ± 0.001 W was used. The laser was shined diagonally, leading to an elliptical beam spot size of 1.5x1.0 cm (area of 2.36 cm ² ) . The temperature is measured using a thermal camera (Fluke TillO) .

The aforementioned experiment was repeated with GNR (Gold NanoRods) instead of TiN using a composition comprising 25% BSA, 6.5% Gelatin, 0.3% Nd-doped BiVCd and 0.01% GNR and a 1064 nm multimode CW laser (Ventus 1064, Laser Quantum Ltd) instead of the 750 nm laser. In this case the laser had a power of 1.29 W and a spot size of 0.4x0.3 cm.

Results and discussion

The measurements of temperature increase for the various compositions are shown in Fig. 1. The increase in temperature from the sample with only Nd-doped B1VO4 is very low, while the temperature increase in the samples that contain TiN is much more pronounced. The increase in temperature for the compositions with the mix of nanoparticles is higher than the one for the compositions with only one type of nanoparticle. Not only that, but it is also higher than the sum of the temperature increases of the two other compositions. This can be attributed to the increased scattering coefficient given by Nd-doped B1VO4 that allows more light to be absorbed by TiN. The same applies when using GNR (Gold NanoRods) instead of TiN.

Temperature measurements through fluorescent nanothermometers

In order to retrieve temperature information from the fluorescent nanothermometers , they need to be calibrated. The nanothermometer powder was placed on a heating plate. A thermal camera is used for reference temperature measurement. The fluorescent spectrum is acquired by a spectrometer (Ocean Insight, STS-NIR) . The signal is collected by a collimator and goes to the spectrometer through an optical fibre. A bandpass filter (Thorlabs, FB750-10) is placed in front of the laser source and two longpass filters at 780 nm (Edmund Optics) are placed in front of the spectrometer. The same setup (without the heating plate in the bottom) is also used for the soldering process. A scheme of the setup is shown in Fig. 2. A laser beam (1) comes out of a fibre collimator and bandpass filter and hits the sample (2) . The light emitted by the sample passes through a longpass filter (3) and is finally focussed by a collimator (4) into a fibre connected to a spectrometer.

A calibration curve (see Fig. 3) is obtained from the spectra at different temperatures, using the same method explained by Gschwend et al. (P. M. Gschwend, F. H. L. Starsich, R. C. Keitel, and S. E. Pratsinis, "Nd ³⁺ -Doped BiVO ⁴ luminescent nanothermometers of high sensitivity," Chem. Commun., vol. 55, no. 50, pp . 7147-7150, 2019) . In order to validate the effectiveness of the temperature measurements, the temperature during laser tissue soldering has been measured using both a thermal camera and the nanothermometers (see Fig. 4) , using 10 seconds as integration time for the spectrometer.

Tensile strength

Preliminary data on the soldering strength have been taken using a solder that contained only TiN. A universal testing machine (Zwick) was used to measure the tensile strength of the samples. Pig small intestine was retrieved from a local slaughterhouse, cleaned with distilled water and frozen. Samples of around 5 x 4 cm ² were cut. Another side-to-side cut was placed in the middle of the sample, parallel to the short side. The composition 25% BSA, 6.5% Gelatin, 0.3% Nd-doped BiVCh and 0.01% TiN was placed on this cut and the soldering process was carried out: laser light with a circular spot size of 0.8 cm ² and intensity of 2.5 W/cm ² was shined on the solder and the sample moved when a temperature of 80 °C was measured with a thermal camera. The tensile properties of the samples were measured soon after. Tensile strengths of about 5 N were measured (a typical stress-strain graph is shown in Fig. 5) .

Water-filtered near infrared light

Water-filtered near infrared light (wIRA) , which has higher penetration in tissue due to the elimination of water-absorbed wavelengths, can also be used for soldering. Porcine small intestine and pig liver were retrieved from a local slaughterhouse the same day of the experiment. Samples were cut into pieced of the desired shape using a surgical scissor or a scalpel. Pieces of intestine were kept at low temperature and hydrated spraying PBS when necessary. A composition containing TiN and BiVO4:Nd (25% BSA, 6.5% Gelatin, 0.3% Nd- doped BiVCh and 0.01% TiN) with a thickness of 0.5 mm was placed on the tissue. Hydrosun 750, a medically approved device that produces wIRA illumination, was used as a source of illumination at 5 cm from the samples. Illumination of 4 min was carried out. Histological samples were prepared, stained, and imaged according to standard practice. Histological images show no visible damage under wIRA irradiation for both intestine and liver tissues, with or without the solder paste on top. Moreover, histological images (Figure 6) show good adhesion of the paste to the tissue, hinting to a strong adhesion .

Stability in digestive fluids

Soldered and unsoldered pastes (of the composition 25% BSA, 6.5% Gelatin, 0.3% Nd-doped BiVCh and 0.01% TiN) were immersed in PBS or fasted state simulated intestinal fluid (FaSSIF) for up to seven days. Weight measurements showed that the composition is resistant to digestive fluids (Figure 7a) .

Bacteria leakage

Porcine small intestine and pig liver were retrieved from a local slaughterhouse the same day of the experiment. Three categories of samples were prepared: intact, defected and soldered. For defected and soldered samples, a cut of 5 mm was created and for the soldered samples soldering was performed using a composition with TiN and BiVO4:Nd (25% BSA, 6.5% Gelatin, 0.3% Nd-doped BiVCh and 0.01% TiN) . All intestines were placed in flasks containing 100 mL of LB broth. 6 mL of broth containing E. Goli modified to express green Fluorescent Protein were placed inside the intestines. Absorbance at 492 nm of the surrounding broth was measured by a plate reader (Infinite F200 PRO, Tecan) at different times. Triplicates were used for all categories. Three measurements of absorption were performed for each sample. Absorbance of soldered and intact intestine are in good agreement with each other, indicating the effectiveness of soldering against bacterial leakage (Figure 7B) . Influence on burst pressure

Porcine small intestine was retrieved from a local slaughterhouse the same day of the experiment . To measure the burst pressure the intestine was cut open and flat and a cut of 1 cm parallel to the intestine length was created with surgical scissors . The intestines were sutured using polypropylene sutures (Ethicon Prolene 5- 0 , the standard type and thickness of suture used for small bowel anastomoses in clinical practice ) . The intestines were soldered using a composition with TiN and BiVO : Nd ( 25% BSA, 6 . 5% Gelatin, 0 . 3% Nd-doped BiVCh and 0 . 01 % TiN) and a 750 nm laser . The intestine was mounted on a 3D-printed burst pressure setup . A pump ( Lambda VIT-FIT ) was used to fill the intestines with DI water with a rate of 1 ml/min and a pressure sensor (ABPDANV060PGSA3 , Honeywell ) was used to measure the burst pressure . Triplicates were used for each sample group . Figure 7C shows that the composition according to the present invention results in an increasing of the burst pressure after being applied on sutures .

Bond strength

Porcine small intestine and pig liver were retrieved from a local slaughterhouse the same day of the experiment . A waterbased gravimetric tensile strength setup was used for tensile strength measurements . Intestine samples are cut into pieces with hal f cm width and an additional full-width cut was placed in the middle . Samples were soldered with solder pastes of various BSA, Gelatin and TiN concentrations within the defined ranges and using the 750 nm laser for up to 4 minutes at full or variable power . Soldering was performed either in surface- near wound configuration, with the paste on top of the wound, or in deep tissue wound configuration, with the paste below the wound . Figure 7D shows that the composition according to the present invention is able to form strong bonds .

Two-laser setup

Soldering can be performed using one single laser, in the case of TiN, or with a two-laser setup, as in the case of GNR . Using GNR with a two-laser system allows for decoupling of heating and temperature measurement ( see Figure 8A) . A 750 nm laser can be used for temperature measurement without increasing the temperature of the solder signi ficantly . A 1064 nm laser can be used to heat the solder paste to the desired temperature .

Surface-near wound / deep tissue wound

The solder performance based was investigated in two di f ferent configurations ; soldering of i ) a surface-near wound ( e . g . solder paste on top of the wound) and ii ) a deep tissue wound ( e . g . solder paste below the wound) , and benchmarked against the state-of-the-art temperature measurements using a thermal camera . After validation of the nanothermometry method in comparison to reference temperature , soldering performance was assessed . The composition is able to reach the necessary target temperatures in both its formulations and in both configurations . While in the surface-near configurations the temperatures measured by the thermal camera and the nanothermometry are in good agreement , in the deep tissue configuration the thermal camera dangerously underestimates the temperatures reached during soldering (Figure 8B) . The composition according to the present invention ensures heating only in the regions of the photothermal agent (i.e. the composition) and nanothermometry accurately measures the temperature exclusively of the most relevant area, namely the fluorescent nanothermometer in the two compositions. Thus, the compositions according to the present invention can be used for soldering beyond superficial wounds, for example, for deep tissue wounds.