Process for the production of multiple cross-linked hyaluronic acid derivatives
The present invention relates to a process for the production of cross-linked hyaluronic acid (HA) derivatives, in particular multiple, e.g. double cross-linked hyaluronic acid derivatives. The invention also provides novel cross-linked HA derivatives, products containing them and their uses in medical and pharmaceutical and cosmetic applications.
1. A process for the preparation of multiple cross-linked hyaluronic acid (HA), which process comprises cross-linking HA via two or more different functional groups, wherein the cross-linking is effected by contacting HA with a first chemical cross-linking agent so as to form a first type of functional bond and sequentially contacting a second chemical cross-linking agent so as to form a second type of functional bond between HA molecules, and wherein at least one of the first or second type of functional bond is an ester bond.
2. A process according to claim 1 wherein the functional groups are selected from hydroxyl, carboxyl and amino.
3. A process according to claim 1 or claim 2 wherein the crosslinking is effected by means of two or more different bonds selected from ether, ester, sulfone, amine, imino and amide bonds.
4. A process according to claim 1 wherein the cross-linking agent is selected from formaldehyde, glutaraldehyde, divinyl sulfone, a polyanhydride, a polyaldehyde, a polyhydric alcohol, carbodiimide, epichlorohydrin, ethylene glycol diglycidylether, butanediol diglycidylether, polyglycerol polyglycidylether, polyethylene glycol diglycidylether, polypropylene glycol diglycidylether, or a bis- or poly epoxy cross-linker.
5. A process according to claim 1 wherein an ether bond is formed using a crosslinking agent selected from bis and poly epoxides under alkaline conditions.
6. A process according to claim 1 wherein an ester bond is formed using a crosslinking agent selected from bis and poly epoxides under acidic conditions.
7. A process according to claim 5 or claim 6 wherein the crosslinker is selected from 1,2,3,4-diepoxybutane and 1,2,7,8-diepoxyoctane.
8. A process according to claim 1 wherein an ether bond is formed using a glutaraldehyde cross-linking agent under acidic conditions.
9. A process according to claim 1 wherein the crosslinking of each type of functional group is effected sequentially.
10. A process according to claim 9 which comprises cross-linking HA via a first functional group and subsequently further cross-linking the product via a second functional group, wherein said first and second functional groups represent different chemical entities.
11. A process according to claim 9 or claim 10 wherein HA is first cross linked via the hydroxyl groups by formation of ether bonds and subsequently cross-linked via the carboxyl groups by formation of ester bonds.
12. A process according to claim 1 for preparing double crosslinked HA.
13. A process according to claim 12 which comprises: (a) cross-linking HA via a first functional group and (b) subsequently further cross-linking the product of (a) via a second functional group, wherein said first and second functional groups represent different chemical entities.
14. Multiple cross-linked HA obtainable by a process according to claim 1 .
15. Cross-linked HA according to claim 14 wherein the crosslinking bonds are selected from two or more of ether, ester, sulfone, amine, imino and amide bonds.
16. Multiple cross-linked HA according to claim 14 in the form of a film.
17. Multiple cross-linked HA according to claim 1 in the form of a gel.
18. HA according to claim 14 which is double cross linked HA.
19. A product comprising multiple cross-linked HA according to claim 14 .