The present invention relates to a gel casting device, preferably for three dimensional gels, and a method of production of gels using such a device.

Three dimensional cell culture scaffolds have been recognized to allow patterns of gene expression and other cellular activities that more closely mimic living organisms than the conventional two dimensional cell cultures in dishes.

This has led to the development of novel families of synthetic polymer hydrogels, which are often termed artificial ECMs

(aECM) , since they mimic many aspects of the extracellular matrix. Casting of such aECM gel systems has to proceed in a way as to provide a three dimensional scaffold. One major difficulty is to provide a system, which allows ease of use and a high reproducibility of the cast gels.

One approach is to use standard gel casting methods with two glass plates and spacers. Usually, it is convenient to place multiple drops of a gel precursor liquid on a first glass plate. Arranging a second glass plate on the first glass plate at a certain distance allows for the formation of three dimensional gel matrices .

While this method allows casting of gels with more or less reproducible results, the assembly of the different parts is cumbersome and requires a multitude of auxiliary material, such as clamps. Moreover, while positioning and affixing of the two glass plates, lateral motion might occur, causing torsion or shear forces on the gel. Disassembly of the casting arrangement is also difficult, as a relatively thin glass plate has to be lifted. The said glass plate is fragile and easily breaks under the pressure of the makeshift clamps.

One objective of the present invention is to provide a gel casting device, especially for the casting of three dimensional gels, which avoids the disadvantages of the known devices and which specifically provides for an easy to use device allowing casting of gels with highly reproducible results. This problem is solved by a device as claimed in claim 1.

The Device for casting of three dimensional gels comprises:

- a first part with a casting surface; and

- a second part with a cover surface.

The second part is removably fixable on the first part in such a way as to provide a casting area with a defined height D between the casting surface and the cover surface.

Preferably, the first part is in the form of a rectangular or generally rectangular plate. More preferably, the first part has a rectangular shape with at least one, but preferably four rounded corners. Both parts of the device are removably fixable together, preferably by fixation means provided on the first and/or the second part. This allows for an easy assembly of the device, since only two parts must be assembled.

The first part preferably comprises at least two raised areas bordering the casting surface. At least one shoulder is arranged adjacent of each of said raised areas on said casting surface. These shoulders define a supporting surface at a defined distance D from said casting surface. The at least two raised areas are arranged such that they are at the edges of the casting surface, preferably on two opposite ends of the first part of the device. If the first part is of rectangular shape, the at least two raised areas are arranged on the two ends of the plate which are further apart from each other .

Distance D may be smaller than the height of the raised areas, such that the supporting areas are arranged closer to the casting surface than the top surfaces of the raised areas. Alternatively, distance D may be as big as the height of the raised areas, such that the supporting surfaces are on level with the top surfaces of the raised areas.

The supporting surfaces offer a seating for the cover surface of the second part . By placing the cover surface on the supporting surfaces, the cover surface is kept at distance D from the casting surface .

In the assembled state, the casting surface and the cover surface are facing each other, thereby defining a casting area in- between. The casting area has a defined height D, which may vary depending on the configuration of the casting device.

Preferably, guide pins are located on the side of the cover surface of said second part which are insertable in matching openings on the side of the casting surface of said first part. Further, the cover surface of said second part is insertable between the raised areas of the first part to be seated on the supporting surfaces of said shoulders, thereby defining a casting space with a defined height D. The guide pins avoid lateral movements of the first and the second part against each other once assembled, which almost eliminates the generation of shear or torsion forces on any cast gel in the casting area. Moreover, the pins act as guidance to assemble both parts together in correct spatial arrangement .

Further, the cover surface is preferably provided such that it may be inserted between the raised areas to be placed on the support surfaces of the shoulders. Such a configuration additionally reduces the amount of movement of the two parts against each other once the two parts are assembled, since at least torsion motions will be avoided by abutment to the raised areas.

The guiding pins and the matching openings preferably additionally comprise means for a form- fit connection of said pins in said openings.

Hence, the pins and the openings also serve as fixation means to removably fix the first and the second part together. The form- fit connection may be of any suitable configuration, but preferably is a snap fit connection. The fixation means tightly hold the second part on the first part, thereby keeping the cover surface at distance D from the casting surface, even if the device is moved.

Alternatively, the fixation means might also have any other configuration than a form-fit connection. For example, the guiding pins might be fixed within their matching openings by means of a thread, an additional connection member or the like.

The matching openings may additionally comprise guiding means to guide said guiding pins in a straight movement . Such guiding means may be of different shape, such as a T-slot or the like. Preferably the guiding means are in the form of at least one longitudinal slot and at least one matching protrusion. The guiding means allow the insertion of the pins and hence the placement of the second part on the first part in a straight movement. This ensures that during assembly of the device, the cover surface approaches the casting surface in a unidirectional movement. This further reduces the possibility of torsion or shear forces on the gel. It further ensures the placement of the casting and the cover surfaces parallel to each other .

Preferably, the gel casting surface is hydrophobic.

As understood herein, hydrophobic means that if a drop of water is applied to the surface, the contact angle between said water drop and the casting surface is 80° or more.

The gel precursor formulation should not be attracted to the material of the casting surface. If the liquid is very strongly attracted to the casting surface the gel precursor formulation will completely flatten or spread out on the surface. The contact angle between the casting surface and the formulation will be close to 0° .

The material of the casting surface should be chosen such as to provide a contact angle of not less than 80° to a water drop. More preferably the material is chosen such that the contact angle is between 90° and 170°. Most preferably the material is chosen such that the contact angle is 150°.

If the casting surface was hydrophilic it would promote the attachment of the gel to the casting surface, thus making the removal of any gel difficult. This could further cause damage to or even destroy the shape of the gel thus leading to a gel shape which is not ideal for use, especially for visualisation of the substances or cells entrapped within the gel.

Preferably said casting surface is structured. The structure may comprise a multitude of slots and/or protrusions, especially of rectangular and/or of circular shape.

A structured surface allows the casting of a multitude of gels at the same time, the protrusions thereby hindering the different gels of sticking together. Slots may serve as moulds for casting of gels. The slots may be provided in specific shapes, such as circular and/or rectangular. Alternatively, the spheres and/or the protrusions may be provided in any suitable geometrical form. Such protrusions may also be designed to allow for channels throughout the gel structure; such channels may allow for a flow of cell culture and/or tissue growth media or the like to provide nutrients to any cells which may be encapsulated within the gel formulation. Such irrigation channels are especially advantageous to nourish cells if the volume of the cast gel is large.

The device is preferably made of or comprises a polymer material. The preferred polymer material should be easily machine- able and also be able to undergo injection moulding. The preferred polymer may be a thermoplastic, an elastomeric and/or a thermosetting polymer. Preferably, the device is made of or comprises a polymer selected from: Acrylonitrile butadiene styrene

(ABS) ; Poly (methyl methacrylate) (PMMA) ; Celluloid Cellulose acetate; Cycloolefin Copolymer (COC) ; Ethylene-Vinyl Acetate

(EVA) ; Ethylene vinyl alcohol (EVOH) ; Fluoroplastics like poly (tetrafluor ethylene) (PTFE) , Fluorinated ethylene propylene

(FEP) , Perfluoroalkoxy (PFA) , Chlorotrifluoroethylene (CTFE) , Ethylene chlorotrifluoroethlyene (ECTFE) , Ethylene tetrafluoro- ethylene (ETFE) ; Ionomer; Liquid crystal polymers like Kydec™ (Kydex LLC); Polyacetal (POM); Polyacrylates ; Polyacrylonitrile (PAN) ; Polyamide (PA) ; Polyamide-imide (PAI) ; Polyaryletherke- tone (PAEK) ; Polybutadiene (PBD) ; Polybutylene (PB) ; Polybuty- lene terephthalate (PBT) ; Polycaprolactone (PCL) ; Polyethylene terephthalate (PET) ; Polycyclohexylene dimethylene terephthalate (PCT) ; Polycarbonate (PC) ; Polyhydroxyalkanoates (PHAs) ; Polyke- tone (PK) ; Polyester; Polyethylene (PE) ; Polyetheretherketone (PEEK) ; Polyetherketoneketone (PEKK) ; Polyetherimide (PEI) ;

Polyethersulfone (PES) ; Polysulfone Polyethylenechlorinates (PEC) ; Polyimide (PI) ; Polylactic acid (PLA) ; Polymethylpentene (PMP) ; Polyphenylene oxide (PPO) ; Polyphenylene sulfide (PPS) ; Polyphthalamide (PPA) ; Polypropylene (PP) ; Polystyrene (PS) ; Polysulfone (PSU) ; Polytrimethylene terephthalate (PTT) ; Poly- urethane (PU) ; Polyvinyl acetate (PVA) ; Polyvinyl chloride

(PVC) ; Polyvinylidene chloride (PVDC) ; Styrene-acrylonitrile (SAN) ; Ethylene propylene rubber (EPR); Ethylene propylene diene rubber (EPDM rubber) ; Epichlorohydrin rubber (ECO) ; Polyacrylic rubber (ACM, ABR) ; Silicone rubber (SI, Q, VMQ) ; Fluorosilicone Rubber (FVMQ) ; Fluoroelastomers (FKM) ; Perfluoroelastomers

(FFKM) ; Polyether Block Amides (PEBA) ; Chlorosulfonated Polyethylene (CSM) and/or mixtures and/or co-polymers thereof.

More preferably, the at least one polymer is a thermoplastic polymer selected from the group comprising of: polypropylene (PP) ; polystyrene (PS) ; Acrylonitrile butadiene styrene (ABS) ; Polyethylene (PE) ; Polyetheretherketone (PEEK) ; Styrene- acrylonitrile (SAN) and/or mixtures and/or co-polymers thereof.

The polymer may be selected depending on the properties of the liquid to be applied to the casting surface. Preferably, the device is made of or comprises a hydrophobic polymer, such that any surface treatment of the casting surface may be avoided. Any hydrophobic polymeric material may be used. But most preferably the device comprises or is made of polypropylene or polystyrene, since these thermoplastics are readily available and straightforward to mould by injection moulding.

Accordingly, the casting device is preferably produced by injection moulding, alternatively followed by further finishing steps, such as surface treatment or the like.

The distance D may be between 1mm and 4mm, preferably between 1.5mm and 3mm, but more preferably distance D is 1.5mm or alternatively 2.5mm. This range offers advantageous gel mechanics integrity when handling the gel as well as good gas and nutrient diffusion allowance, which is favourable for cells growth and viability .

The maximum height D is mainly dictated by the volume of the gel precursor formulation applied on the casting surface and the contact angle between the formulation and the surface. A greater angle provides for a more spherical drop, such that the distance D can be increased.

Preferably, the length L ₂ and width W ₂ of the second part match the length L _c and with _c of the casting surface. This allows the insertion of the second part between the raised areas of the first part. Alternatively, a portion of the cross section of the guiding pins may slightly protrude from the second part, thus making the second part partially slightly longer than the casting surface . Preferably, at least one writing surface is provided on an upper surface of at least one of the raised areas. This allows labelling of the device.

Further preferably, the first part comprises at least one but more preferably four generally arc-shaped recesses on its outer contour. These recesses allow a user to easily grasp the second part for removal .

A further object of the present invention is to provide a method of production of three dimensional gels which is quick and easy. This problem is solved by a method as claimed in claim 13.

The method comprises the steps of:

- providing a gel precursor formulation in a liquid state;

- applying at least once an amount of said gel precursor formulation on the casting surface of a casting device as described herein;

- positioning the cover surface parallel to the casting surface at a distance D;

- polymerizing and/or gelling of said gel precursor composition; and

- removing of said at least one gel from said device.

A suitable gel precursor may be a hydrogel precursor formulation. Alternatively, a more classic gel precursor formulation might also be used, such as a polyacrylamide gel formulation or an agarose solution. The gel precursor is preferably applied using a pipette. The volume of the applied precursor formulation may vary depending on the dimensions of the gel needed. Only one amount of precursor formulation may be applied on the casting surface. Alternatively and depending on the number of gels needed, more than one amount of precursor formulation might be applied .

Preferably, a cell culture is added to the precursor solution prior to its application on the casting surface. This allows a more even distribution of the cells within the three dimensional matrix of the gel compared to the distribution of cells applied on the matrix after polymerization and/or gellation.

For polymerization and/or gelling, the device may be placed to rest either on the top surface of the first part or on the bottom surface of the second part. The device may be alternated between these two positions during polymerization and/or gelling either manually or automatically to promote a homogeneous distribution of the gel precursor formulation or any cells enclosed therewith .

The positioning of the cover surface parallel to the casting surface at a distance D applies a force on the at least one amount of precursor formulation, thus pressing it generally into a tablet shape with height D. Depending on the applied volume of precursor formulation, the diameter of this tablet shape will vary. After polymerization or gelling, the device is disassembled and the gel or gels removed.

In a preferred embodiment of the present method, an aqueous solution, preferably a buffer solution, is applied into the casting space between said casting surface and said cover surface prior the disassembly of the device and the removal of the gel or gels. The buffer solution may be any suitably solution, such as e.g. phosphate buffered saline (PBS). Alternatively, the solution may be a cell culture solution, such as Dulbecco's Modified Eagle Medium (DMEM) . In an alternative embodiment, the casting device comprising polymerized gels with embedded cells may be transferred without disassembly to a cell culture medium for cell growth. The gels may then subsequently be removed from the casting device for analysis and/or further steps.

A further objective of the present invention is to provide the use of a casting device as described herein for casting gels, preferably hydrogels .

A gel casting device as described is preferably used for the casting of three dimensional hydrogels, especially for cell culture. But it is evident that such a device might also be used to cast other type of gels, e.g. electrophoresis gels.

Further aspects and details of the present invention will become apparent from the following figures and examples.

Fig. 1A: A perspective view of a first embodiment of a casting device according to the present invention in disassembled state;

Fig. IB: A perspective view of the embodiment of a casting device according to Fig. 1A in assembled state;

Fig. 2: A bottom view of the embodiment of a casting device according to Fig. 1 in assembled state;

Fig. 3A: A top view of the first part of the casting device according to Fig. 1; A cross section along the line A-A of the first part of the casting device as shown in Fig. 3B;

A bottom view of the second part of the casting devic according to Fig. 1 ;

A side view of the second part as shown on Fig. 4A;

A detailed view of one embodiment of a guiding pin from top;

A detailed cross - section view of the guiding pin as shown on Fig. 5A

A detailed cross section of an embodiment of an opening 6 ;

A detailed cross-section of an embodiment of a snap fit connection of the guiding pin according to Fig. 5 in a matching opening according to Fig. 6;

A second embodiment of a casting device according to the present invention in assembled state viewed from top;

A side view of the embodiment as shown on Fig. 7A;

A bottom view of the embodiment as shown on Fig. 7A;

A third embodiment of a casting device according to the present invention viewed from top;

Fig. 9B: A side view of the embodiment as shown on Fig. 8A; Fig. 9C: A bottom view of the embodiment as shown on Fig. 8A; and

Fig. 10: An embodiment of a method of use of a casting device according to the present invention.

Figure 1 shows a first embodiment of a casting device of the present invention. Figure 1A is an isometric view of the casting device 1 in disassembled state. The device 1 comprises first part 2 with casting surface 9 and second part 3 with cover surface 10. The first part 2 generally is of rectangular shape with rounded ends. Raised areas 7 and 8 are located adjacent to the casting surface 9. Shoulders 14 are between the raised areas 7,8 and the casting surface 9, thereby defining support areas 25 at a distance D from the casting surface 9. Openings 6 matching pins 4 are arranged such as to overlap a part of supporting surfaces 25 as well as a part of raised areas 7,8. The first part 2 also comprises four circular recesses 12 on its contour. Second part 3 comprises two guide pins 4, which feature two longitudinal protrusions 5 as additional guiding means. To form a snap fit connection with the first part 2, the guiding pins 4 additionally comprise a nose 13. See also Figs. 5 and 6 for details.

On figure IB the first embodiment of a casting device is shown in assembled state. Both parts 2,3 are removably fixed together by means of the snap fit connection between guiding pins 4 in the matching openings 6. The cover surface 10 of the second part 3 abuts on the supporting surfaces 25 of shoulders 14, such that a casting area 11 with height D is formed between the casting surface 9 and the cover surface 10. In this embodiment, the second part 3 has the same dimensions as the casting surface 9, such that the second part may be completely inserted between the raised areas 7,8.

Figure 2 is a bottom view of the first embodiment of the casting device 1 as shown on figure 1. As can be seen, openings 6 are configured as through borings from the top surface of the raised areas 7,8 and the supporting surfaces 25 to the bottom surface of the first part 3. Guiding pins 4 snugly fit in openings 6 with almost no clearance between their lateral sides and the wall of the openings 6. Noses 13 are engaged with fitting portions of the second part 2 thereby fixing both parts 2,3 together. Release of these connections may be achieved by pressing both noses inwardly, thereby disconnecting the noses 13 from the fitting portions of the first part 2. Two arc shaped recesses 12 are placed on either side of the first part 2. The recesses 12 allow for an easy grasping of the second part 3 by a user of the device for disassembly, since they provide additional space for the user's fingers.

Figure 3A shows the first part 2 from top. Raised areas 7,8 are both arranged on opposite ends of the first part 2. In between the raised areas 7,8 the casting surface 9 is arranged. Shoulders 14 provide a supporting surface 25 between the casting surface 9 and the raised areas 7,8. The casting surface 9 has a width W _c and a length L _c . The length L _c of the casting surface 9 is smaller than the length Li of the first part 2. The width W _c of the casting surface is the same as the width Wi of the first part, with the exception of the four circular recesses 12. Writing surfaces 15 are provided on raised areas 7,8. Alternatively, one of the writing surfaces 15 may be replaced with a logo of a manufacturer or an ordering number. Openings 6 are arranged partly on support surfaces 25 and partly on raised areas 7,8. Preferably, the length Li of the first part 2 is between 100mm and 200mm, more preferably between 110mm and 160mm, most preferably between 120mm and 140mm. The width Wi of the first part 2 is between 10mm and 50mm, more preferably between 15mm and 40mm, most preferably between 20mm and 30mm.

The length L _c of the casting surface 9 is preferably between 50mm and 90mm, more preferably between 60mm and 80mm, most preferably between 70mm and 75mm. The width c of the casting surface is between 10mm and 50mm, more preferably between 15mm and 40mm, most preferably between 20mm and 30mm.

Figure 3B shows a cross section of the first part 2 as shown on figure 3A along the line A-A. To reduce the amount of material and thus also the weight and production costs of the device, recesses 16 may be provided on the bottom side of raised areas 7,8. As can be readily seen on this figure, openings 6 are configured as through bores through the entire thickness of the first part 2. In this embodiment, openings 6 are arranged partly on raised areas 7,8 and partly on support surfaces 25 of shoulders 14. Support surfaces 25 are spaced apart from casting surface 9 by distance D. The first part 2 has a maximal height Hi. In this embodiment, both raised areas have the same height, which corresponds to the maximal height ¾ . Other embodiments may provide for raised areas with different heights.

The maximal height HI of the first part 2 preferably is between 5mm and 15mm, more preferably between 7mm and 12mm, most preferably between 8mm and 10mm.

Figure 4A is a bottom view of the second part 3 of the first embodiment of the casting device 1 as shown on figure 1. The second part 3 comprises a cover surface 10 and two guiding pins 4. The second part 3 has a length L ₂ and a width W ₂ . The guiding pins 4 are arranged such that they slightly protrude from the second part 3 in the longitudinal direction.

The length L ₂ of the second part is preferably between 50mm and 90mm, more preferably between 60mm and 80mm, most preferably between 70mm and 75mm. The width W2 of the second part 3 is between 10mm and 50mm, more preferably between 15mm and 40mm, most preferably between 20mm and 30mm.

Each guiding pin 4 preferably does not protrude from the second part 3 in a direction away of the cover surface more than 15mm, more preferably not more than 10mm, most preferably not more than 8mm .

Figure 4B is a side view of the second part 3 as shown on figure 4A. The guiding pins 4 have a height H ₂ and the cover surface a height H _s . In this embodiment, pins 4 are shorter as the maximal height H _x of the first part 2. Other embodiments may provide for guide pins 4 which are as height as the maximal height ¾ of the first part 2.

The height H ₂ of the pins 4 is preferably between 5mm and 15mm, more preferably between 7mm and 12mm, most preferably between 8mm and 10mm. The height H _s of the cover surface 10 preferably is between 0.5mm and 5mm, more preferably between 1mm and 4mm, most preferably between 2mm and 3mm.

Figure 5A shows a detailed view of an exemplary embodiment of a guide pin 4 viewed from top. The guide pin 4 comprises nose 13 and two longitudinal protrusions 17 as additional guide means. The protrusions 17 are configured such as to be fittingly in- sertable in corresponding guiding recesses in openings 6 of the first part 2.

Figure 5B shows a cross-section of the embodiment of the quide pin 4 as shown on Fig. 5A. Nose 13 is configured as latch slightly protruding from the guide pin 4. In this embodiment, nose 13 protrudes in a direction diametrically away from cover surface 10. Other embodiments may provide for a nose 13 protruding in the direction of the cover surface 10. Nose 13 might also be configured in any suitable shape, such as pulling ring or the like. Guiding pin 4 slightly protrudes from the second part 3 by means of trusses 28. This allows to place the guiding pins 4 outside of the casting surface 9.

Figure 6 shows a cross sectional detail view of an embodiment of an opening 6. The opening 6 is partially arranged on raised area 7 and partially on shoulder 14. A Fitting area 26 for the accommodation of a snap-fit connection means, such as nose 13, is provided on an inner wall of the opening 6. The fitting area 26 is bordered by a bulge 27, which acts as an additional retaining means for the snap-fit connection. As may be seen, trusses 28 form surfaces alongside the guiding pin 4 which ensure a good and secure fit of guiding pins 4 in openings 6.

Figure 7 is a cross sectional detail view of an embodiment of a snap fit connection between a guide pin 4 according to Fig. 5 and an opening 6 according to Fig. 6. Second part 3 is assembled on first part 2. Cover surface 10 of the second part 3 is seated on the support surface 25 of shoulder 14. This leads to the formation of casting area 11 with height D between casting surface 9 and cover surface 10. Guiding pin 4 is inserted in opening 6. The nose 13 is reversibly engaged with fitting area 26 provided on an inner wall of opening 6. Other embodiments may provide for other means of snap fit connection, such as e.g. a recess in the fitting area 26.

Figure 8 shows a second exemplary embodiment of a casting device 1 according to the present invention. Figure 7A is a top view of this second embodiment. Contrary to the first exemplary embodiment as shown on figure 1, the casting device 1 of the second embodiment does not provide rounded ends of the first part 2. Figure 8B is a side view and figure 8C is a bottom view of the second embodiment.

Figure 9 shows a third exemplary embodiment of a casting device 1 according to the present invention. In this embodiment, one end of the first part 3 is rounded, while the second end has two slightly rounded corners and a straight stretch in between. By this configuration, raised area 7 has a bigger surface than raised area 8. Figure 9A is a top view, Figure 9B is a side view and Figure 9C is a bottom view of the casting device according to the third exemplary embodiment .

Figure 10 is a schematical representation of a method for casting of gels using a gel casting device according to the present invention. In step (a) , a multitude of defined amounts 20 of a gel precursor formulation 19 is applied on the casting surface 9 of the first part 2 of the casting device 1. Application is preferably done using a pipette, represented here schematicaly by a pipette tip 18. After application of the gel precursor formulation 20, the casting device 1 is assembled by positioning the second part 3 on the first part 2 and removably fixing of the two parts 2,3 together by fixation means, especially by a snap fit connection of the guiding pins 4 in openings 6. The casting device is then placed in an incubator, e.g. at 37°C, or a heating chamber for polymerization of the gel. To remove the gels after polymerization, a buffer solution 22, such as phosphate buffered saline, is added into the casting area 11 by means of a pipette 18. This facilitates subsequent disassembly of the second part 3 from the first part 2. The two parts 2,3 may be removed by hand or with the aid of a tool 23, such as a spatula. After the device 1 has been disassembled, the gels 24 may be removed with a spatula 23 or any other suitable tool, such as tweezers .