Hydrolysis of ester bonds in amide crosslinked glycosaminoglycans
A method of preparing a hydrogel product comprising crosslinked glycosaminoglycan molecules, said method including: i) providing a glycosaminoglycan crosslinked by amide bonds, wherein the crosslinked glycosaminoglycans include ester crosslinks formed as byproducts during the amide crosslinking; and ii) subjecting the crosslinked glycosaminoglycans to alkaline treatment to hydrolyze ester crosslinks formed as byproducts during the amide crosslinking.
1. A method of preparing a hydrogel product comprising crosslinked glycosaminoglycan molecules, the method comprising:
(a) acylating crosslinked glycosaminoglycans comprising residual amine groups to form acylated crosslinked glycosaminoglycans; and wherein
(i) the hydrogel product comprises the acylated crosslinked glycosaminoglycan,
(ii) the crosslinked glycosaminoglycan comprises amide bonds between activated carboxyl groups of an activated glycosaminoglycan and 2′amino groups of an at least partially deacetylated glycosaminoglycan with a coupling agent, and
(iii) the residual amine groups are amino groups of the at least partially deacetylated glycosaminoglycan; and
(b) subjecting the glycosaminoglycan crosslinked by amide bonds and further comprising ester crosslinks to alkaline treatment to hydrolyze the ester crosslinks.
2. The method according to claim 1 , further comprising preparing the crosslinked glycosaminoglycans by:
(a) providing a solution comprising the at least partially deacetylated glycosaminoglycan;
(b) activating carboxyl groups on the at least partially deacetylated glycosaminoglycan with a coupling agent, to form activated glycosaminoglycans;
(c) crosslinking the activated glycosaminoglycans via their activated carboxyl groups using a di- or multiamine functional crosslinker to provide the glycosaminoglycans crosslinked by amide bonds.
3. The method according to claim 1 , wherein the at least partially deacetylated glycosaminoglycan is selected from the group consisting of hyaluronic acid, chondroitin and chondroitin sulfate, and mixtures thereof.
4. The method according to claim 1 , further comprising preparing the crosslinked glycosaminoglycan by:
(a) providing a solution comprising the at least partially deacetylated glycosaminoglycan and optionally a second glycosaminoglycan;
(b) activating carboxyl groups on the at least partially deacetylated glycosaminoglycan and/or the optional second glycosaminoglycan with a coupling agent, to form activated glycosaminoglycans;
(c) crosslinking the activated glycosaminoglycans via their activated carboxyl groups using amino groups of the at least partially deacetylated glycosaminoglycans to provide glycosaminoglycans crosslinked by amide bonds.
5. The method according to claim 4 , wherein the at least partially deacetylated glycosaminoglycan is selected from the group consisting of deacetylated hyaluronic acid, deacetylated chondroitin and deacetylated chondroitin sulfate, and mixtures thereof.
6. The method according to claim 4 , wherein the at least partially deacetylated glycosaminoglycan has a degree of acetylation of 99% or less, and a weight average molecular weight of 0.1 MDa or more.
7. The method according to claim 4 , wherein the second glycosaminoglycan is selected from the group consisting of hyaluronic acid, chondroitin and chondroitin sulfate, and mixtures thereof.
8. The method according to claim 2 , wherein the coupling agent is a peptide coupling reagent.
9. The method according to claim 8 , wherein the coupling reagent is 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride.
10. The method according to claim 1 , wherein the alkaline treatment comprises contacting the crosslinked glycosaminoglycans with an alkaline solution for 0.5-4 hours.
11. The method according to claim 1 , wherein the alkaline treatment is performed at a temperature in the range of 0-60° C.
12. The method according to claim 1 , wherein after the alkaline treatment at least 95% of the bonds between the glycosaminoglycans are amide bonds.
13. The method according to claim 10 , wherein the alkaline treatment comprises contacting the crosslinked glycosaminoglycans with an alkaline solution for 0.5-2 hours.
14. The method according to claim 11 , wherein the alkaline treatment is performed at a temperature in the range of 10−30° C.
15. The method according to claim 1 , wherein the alkaline treatment comprises contacting the crosslinked glycosaminoglycans with an alkaline solution with a pH in the range of 12-14.
16. The method according to claim 1 , wherein the alkaline treatment comprises contacting the crosslinked glycosaminoglycans with a solution of sodium hydroxide or potassium hydroxide.
17. The method according to claim 1 , wherein the alkaline treatment comprises contacting the crosslinked glycosaminoglycans with an alkaline solution with a pH in the range of 12-14 for 0.5-4 hours at a temperature in the range of 10−30° C.
18. The method according to claim 1 , wherein acylating the crosslinked glycosaminoglycans comprises acetylating residual amine groups of the crosslinked glycosaminoglycans to form acetylated crosslinked glycosaminoglycans.