Method of preparing a hydrogel network encapsulating cells
The present invention is directed to a hydrogel network comprised of a physically cross-linked polymer and a chemically cross-linked polymer or physically entangled copolymer containing living cells, such as chondrocytes, encapsulated therein. In a preferred aspect, the physically cross-linked polymer is selected from the group consisting of thermally gelling polysaccharides and proteins, such as agarose or gelatin, and the chemically cross-linked or physically entangled polymer is synthesized from a water-soluble vinyl monomer, either as a homopolymer or copolymer, such as polyethylene glycol diacrylate (“PEG-DA”) and 2-hydroxyethyl methacrylate (“HEMA”).
1. A method for preparing a hydrogel network having living cells encapsulated therein comprising the steps of:
forming a solution of a thermally gelling polysaccharide or protein at a temperature in which the living cells are viable and dispersing the cells therein;
cooling the thermally gelling polysaccharide or protein solution down to or below its gelation temperature in which the living cells are also viable to cause gelation and form a polysaccharide or protein gel and to encapsulate the cells in said gel;
contacting the polysaccharide or protein gel having the living cells encapsulated therein with a solution comprising one or more water-soluble vinyl monomers for a sufficient period of time to disperse the one or more water-soluble vinyl monomers within the gel; and then
polymerizing and/or cross-linking the one or more water-soluble vinyl monomers within said gel.
2. The method of claim 1 wherein said thermally gelling polysaccharide or protein is selected from the group consisting of agarose, gelatin, kappa-carrageenan, iota-carrageenan, elastin-mimetic polymers, and silk-elastin block copolymers.
3. The method of claim 1 wherein said thermally gelling polysaccharide or protein solution is an agarose or gelatin solution having a gelation temperature of about 20° C. to 60° C., and wherein said cooling step forms an agarose or gelatin gel.
4. The method of claim 3 wherein said contacting step comprises soaking said agarose or gelatin gel in a solution comprising polyethylene glycol diacrylate (“PEG-DA”) or polyethylene dimethacrylate (“PEG-DMA”) or 2-hydroxyethyl methacrylate (“HEMA”) as said one or more water-soluble vinyl monomers.
5. The method of claim 1 wherein said living cells are chondrocytes.
6. The method of claim 1 wherein said thermally gelling polysaccharide or protein solution further comprises a photoinitiator or said solution comprising the one or more water-soluble vinyl monomers further comprises a photoinitiator.
7. The method of claim 1 wherein said thermally gelling polysaccharide or protein solution further comprises a chemically or enzymatically degradable monomer or said solution comprising the one or more water-soluble vinyl monomers further comprises a chemically or enzymatically degradable monomer.
8. The method of claim 3 further comprising a crosslinker which is a multifunctional vinyl monomer in the agarose or gelatin solution.
9. The method of claim 8 wherein said multifunctional vinyl monomer comprises N,N′-methylenebisacrylamide.
10. The method of claim 1 wherein said thermally gelling polysaccharide or protein is selected from the group consisting of agarose, gelatin, kappa-carrageenan, iota-carrageenan, elastin-mimetic polymers, and silk-elastin block copolymers; and further comprising polymerizing and/or cross-linking said vinyl monomers within said gel by irradiating said gel for less than ten minutes.
11. The method according to claim 1 wherein said one or more water soluble vinyl monomers comprises a bi-functional polyethylene glycol component and wherein said thermally gelling polysaccharide comprises agarose.
12. The method according to claim 11 , wherein the bi-functional polyethylene glycol component is selected from the group consisting polyethylene glycol diacrylate (“PEG-DA”) or polyethylene dimethacrylate (“PEG-DMA”).
13. The method according to claim 11 , wherein the polyethylene glycol component of the bi-functional polyethylene glycol component has a molecular weight between 200 and 50,000 Daltons.
14. The method according to claim 11 wherein the hydrogel network has a water content of 10% or more.
15. The method according to claim 11 wherein the hydrogel network has a compression stress at failure of at least 1 MPa.
16. The method according to claim 11 wherein the hydrogel network has a tensile stress at failure of at least 1 MPa.
17. The method according to claim 11 in which the one or more water soluble vinyl monomers is PEG-DA, and wherein said PEG-DA:agarose ratio is between about 20:1 and 2:1.
18. The method of claim 1 wherein said one or more water-soluble vinyl monomers comprises PEG-DA or HEMA.
19. The method according to claim 1 , wherein said one or more water-soluble vinyl monomers comprises PEG-DA, and wherein said polyethylene glycol component of the PEG-DA has a molecular weight between 200 and 50,000 Daltons.
20. The method according to claim 1 wherein said living cells are encapsulated within said hydrogel network at a density ranging between about 1,000,000 cells/cm 3 and 50,000,000 cells/cm 3 .
21. The method of claim 1 wherein said solution comprising said one or more water-soluble vinyl monomers further comprises a cross-linker.