Click-crosslinked hydrogels and methods of use

1. A hydrogel comprising a first polymer and a second polymer, wherein the first polymer and the second polymer are the same polymer and are both gelatin, wherein the first polymer is connected to the second polymer by linkers of formula (A):

wherein

bond is a single or a double bond;

R 1 is —C 0 -C 6 alkyl-NH—, —C 0 -C 6 alkyl-O—, or —C 0 -C 3 alkyl-C(O)—;

R 2 is a bond, aryl, or heteroaryl, wherein aryl and heteroaryl are optionally substituted with halogen, hydroxy, C 1 -C 6 alkyl, C 1 -C 6 alkoxy, (C 1 -C 6 alkyl)amino, or di(C 1 -C 6 alkyl)amino;

R 3 is —C 0 -C 6 alkyl-NH—, —C 0 -C 6 alkyl-O—, or —C 0 -C 3 alkyl-C(O)—; and

R 4 is hydrogen, C 1 -C 6 alkyl, aryl, or heteroaryl, wherein aryl and heteroaryl are optionally substituted with halogen, hydroxy, C 1 -C 6 alkyl, C 1 -C 6 alkoxy, (C 1 -C 6 alkyl)amino, or di(C 1 -C 6 alkyl)amino;

wherein the hydrogel is capable of being generated in the presence of a cell or a biological factor without damaging the cell or the biological factor.

2. The hydrogel according to claim 1 , wherein:

bond is a single bond;

R 1 is —C 0 -C 6 alkyl-NH—, or —C 0 -C 3 alkyl-C(O)—;

R 2 is a bond or aryl optionally substituted with halogen, hydroxy, C 1 -C 6 alkyl, C 1 -C 6 alkoxy, (C 1 -C 6 alkyl)amino, or di(C 1 -C 6 alkyl)amino;

R 3 is —C 0 -C 6 alkyl-NH—, or —C 0 -C 3 alkyl-C(O)—; and

R 4 is hydrogen, C 1 -C 6 alkyl, or heteroaryl, wherein heteroaryl is optionally substituted with halogen, hydroxy, C 1 -C 6 alkyl, C 1 -C 6 alkoxy, (C 1 -C 6 alkyl)amino, or di(C 1 -C 6 alkyl)amino.

3. The hydrogel according to claim 2 , wherein R 1 and R 3 are both -methyl-NH—; or R 1 and R 3 are both —C(O)—.

4. The hydrogel according to claim 1 , wherein the linkers of formula (A) are selected from the group consisting of formula (I):

or formula (II):

or formula (III):

5. The hydrogel of claim 1 , wherein the first polymer or the second polymer further comprises a cell adhesive peptide.

6. The hydrogel of claim 5 , wherein the cell adhesive peptide comprises the amino acid sequence arginine-glycine-aspartic acid (RGD).

7. The hydrogel of claim 6 , wherein the cell adhesive peptide comprises the amino acid sequence arginine-glycine-aspartic acid-cysteine (RGDC) (SEQ ID NO: 1).

8. The hydrogel of claim 1 , wherein the Young's modulus of the hydrogel is 50 to 50,000 Pa.

9. The hydrogel of claim 1 , wherein the hydrogel further comprises a cell, a biological factor, and/or a small molecule.

10. The hydrogel of claim 9 , wherein the cell is a mammalian cell.

11. The hydrogel of claim 9 , wherein the biological factor is a protein, nucleic acid, lipid, or carbohydrate.

12. The hydrogel of claim 11 , wherein the protein is a growth factor or fragment thereof or an antibody or fragment thereof.

13. A method for preparing a hydrogel of claim 1 , comprising,

a) providing a first polymer comprising a tetrazine moiety and a second polymer comprising a norbornene moiety wherein the first polymer and the second polymer are the same polymer and are both gelatin;

b) contacting the second polymer with the first polymer to form the hydrogel of claim 1 .

14. The method of claim 13 , wherein: (i) each molecule of the first polymer comprises 1-50,000 tetrazine moieties; (ii) each molecule of the second polymer comprises 1-50,000 norbornene moieties; and/or (iii) step b) comprises contacting a second polymer with a first polymer at a ratio of about 1:10 to about 10:1.

15. The method of claim 13 , further comprising reacting the first polymer with a) benzyl amine tetrazine, benzyl alcohol tetrazine, or benzoic acid tetrazine, and a b) coupling agent to provide the first polymer comprising a tetrazine moiety.

16. The method of claim 15 , wherein the coupling agent is 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC).

17. The method of claim 13 , further comprising reacting the second polymer with a) norbornene methanamine, norbornene methanol, or norbornene carboxylic acid, and b) a coupling agent to provide the second polymer comprising a norbornene moiety.

18. The method of claim 17 , wherein the coupling agent comprises 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and optionally N-Hydroxysuccinimide (NHS).

19. A method of regenerating a tissue in a subject in need thereof, the method comprising contacting the tissue with the hydrogel of claim 1 .

20. A method of delivering a cell, a biological factor and/or a small molecule to a subject, the method comprising administering to the subject the hydrogel of claim 9 , wherein after administration of the hydrogel, the cell, the biological factor and/or the small molecule is released from the hydrogel into a surrounding tissue of the subject, thereby delivering the cell, the biological factor and/or the small molecule to the subject.