Click-crosslinked hydrogels and methods of use

1. An injectable hydrogel comprising a first polymer and a second polymer, wherein the first polymer and the second polymer are the same polymer and are both alginate, and 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 Young's modulus of the hydrogel is about 500 Pa to about 50,000 Pa.

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 —CO—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):

formula (II):

and 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 (a) comprises the amino acid sequence RGD; (b) comprises the amino acid sequence RGDC; and/or (c) is covalently linked to the polymer via a thiol-ene reaction.

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

8. The hydrogel of claim 7 , wherein the cell is a mammalian cell; wherein the biological factor is a protein, nucleic acid, lipid, or carbohydrate; and/or wherein the protein is a growth factor or fragment thereof or an antibody or fragment thereof.

9. 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 7 , 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.

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

a) providing a first polymer comprising a tetrazine moiety and a second polymer comprising a norbornene moiety;

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

11. The method of claim 10 , 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.

12. The method of claim 10 , wherein the first polymer comprising a tetrazine moiety is generated by reacting the first polymer with a) benzyl amine tetrazine, benzyl alcohol tetrazine, or benzoic acid tetrazine, and b) a coupling agent.

13. The method of claim 10 , wherein the second polymer comprising a norbornene moiety is generated by reacting the second polymer with a) norbornene methanamine, norbornene methanol, or norbornene carboxylic acid, and b) a coupling agent.

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