Post-crosslinking partial degradation of amide crosslinked hydrogels

1. A method of preparing a hydrogel product comprising crosslinked glycosaminoglycan molecules at a concentration C final (mg/mL), the method comprising:

(a) crosslinking a glycosaminoglycan having a molecular weight of above 700 kDa in conditions so as to provide a glycosaminoglycan hydrogel crosslinked by amide bonds and having a C min (mg/mL) that is above C final /2, wherein C min is the concentration of gel-form glycosaminoglycan in the gel when fully swollen in physiological buffer;

(b) subjecting the hydrogel from (a) to post-crosslinking degradation of the glycosaminoglycan backbone in 1.0 M to 3.0 M NaOH for 24-48 hours, thereby reducing the C min of the hydrogel to a value that is below C final /2, wherein the post-crosslinking degradation decreases the apparent molecular weight (Mw app ) of the glycosaminoglycan backbone by 15% to 90%; and

(c) formulating the partially degraded hydrogel obtained from (b) to form an injectable hydrogel composition having a concentration of glycosaminoglycan molecules of C final (mg/mL).

2. The method according to claim 1 , wherein the C min of the hydrogel is reduced to below 15 mg/mL.

3. The method according to claim 1 , wherein the C min of the hydrogel is reduced to 0.5-15 mg/mL in (b).

4. The method according to claim 1 , wherein C final is above 10 mg/mL.

5. The method according to claim 1 , wherein C final is between 10-30 mg/mL.

6. The method according to claim 1 , wherein the crosslinking of (a) is performed at a GAG concentration of above 60 mg/mL.

7. The method according to claim 1 , wherein the post-crosslinking degradation of (b) decreases the apparent molecular weight (Mw app ) of the crosslinked glycosaminoglycan with at least 25%.

8. The method according to claim 1 , wherein the hydrogel in (a) is crosslinked to an extent such that it is phase-separated when diluted to 20 mg/ml at pH 6.0-8.0 in 1.0 mM-20 mM phosphate buffer and wherein the post-crosslinking degradation of (b) is to an extent such that the hydrogel is not phase-separated when diluted to 20 mg/ml at pH 6.0-8.0 in 1.0 mM-20 mM phosphate buffer.

9. The method according to claim 1 , wherein the crosslinking of (a) is performed at a pH of 5.0-9.0.

10. The method according to claim 1 , wherein the crosslinking of (a) is performed at a pH of 6.0-8.0.

11. The method according to claim 1 , wherein the crosslinking (a), comprises:

(i) providing a solution of glycosaminoglycan molecules;

(ii) activating carboxyl groups on the glycosaminoglycan molecules with a coupling agent to form activated glycosaminoglycan molecules; and

(iii) crosslinking the activated glycosaminoglycan molecules via their activated carboxyl groups using a di- or multinucleophile functional crosslinker comprising a spacer group selected from the group consisting of di-, tri-, tetra-, and oligosaccharides to obtain crosslinked glycosaminoglycan molecules.

12. The method according to claim 11 , wherein the crosslinker is diaminotrehalose (DATH).

13. The method according to claim 11 , wherein the post-crosslinking degradation comprises reducing the effective crosslinking ratio (CrR) of the glycosaminoglycan less than 10%.

14. The method according to claim 1 , wherein the crosslinking comprises crosslinking an at least partially N-deacetylated glycosaminoglycan by amide bonds between carboxyl groups and free amine groups on the glycosaminoglycan backbone to provide the glycosaminoglycan hydrogel crosslinked by amide bonds.

15. The method according to claim 14 , wherein the post-crosslinking degradation comprises reducing the effective crosslinking degree (CrD) of the glycosaminoglycan less than 10%.

16. The method according to claim 1 , wherein the glycosaminoglycan is hyaluronic acid.

17. The method according to claim 1 , wherein the post-crosslinking degradation decreases the apparent molecular weight (Mw app ) of the glycosaminoglycan backbone by 25% to 80%.