Hyaluronic acid/chitosan hydrogels

Tan HP, Chu CR et al (2009) Injectable in situ forming biodegradable chitosan-hyaluronic acid based hydrogels for cartilage tissue engineering. Biomaterials 30 2499-2506... 

In situ cross-linkable chitosan-hyaluronic acid based hydrogels for preventing postoperative adhesion has been developed [153]. Hyalmonic acid was oxidized with sodium periodate which cleaves carbon-carbon bonds to create aldehyde groups in D-glucuronic acid units of the molecular chain. The solubility of chitosan in neutral aqueous solution was improved by incorporating carboxymethyl... 

Many naturally occurring polymers, such as collagen, fibrinogen, hyaluronic acid, chitosan and heparin, have been used to make hybrid hydrogels with synthetic polymers, such as PEG, PNIPAm and PVA [31-35]. The hybridization can be performed by covalent bonding or physically interactions. For example, the IPN hydrogel composed of sodium alginate (SA) and poly(diallyldimethylammonium chloride) (PDADMAC) exhibited pH and electrical sensitive behavior [36]. 

To mimic the macromolecular-based ECM in biological tissue, the cell adhesion and proliferation properties of hydrogels are critical parameters. However, various hydrogels that originate from natural resources, such as alginate [87], chitosan [88, 89], and hyaluronic acid [90], and that are synthetically created, such as poly (7V-isopropylacrylamide) (PNIPAAm) [91], PEO [92], PVA [93], and poly(ethylene glycol) (PEG) [94], show a poor cellular viability without modification with cell adhesive proteins or peptides, such as collagen, laminin, fibronectin, and the RGD (Arg-Gly-Asp) sequence. 

Another approach to improve the properties of chitosan hydrogels is via the preparation of polymer composites. Porous hydrogels of N-carboxymethyl chitosan/polyvinyl alcohol were prepared by Lee et al. [99]. Hydroxypropyl chitosan was combined with sodium alginate for the formation of biodegradable hydrogels [100]. Chitosan-hyaluronic acid composite was prepared by Tan et al. [101]. 

Fang JY, Chen JP, Leu YL, Hu JW. Temperature-sensitive hydrogels composed of chitosan and hyaluronic acid as injectable carriers for drug delivery. Eur J Pharm Biopharm 2008 68 626-636. 

Grafts of poly(NIPAAm) have also been used to impart temperature responsive behavior to natural biomaterials for drug delivery, converting them into physically crosslinking hydrogels above the LCST of the poly(NIPAAm) portions. For example, poly(NIPAAm) grafted onto hyaluronic acid formed a gel upon injection which had a 12-hour burst release of riboflavin followed by sustained release (Ha et al. 2006). Similarly, chitosan with grafted poly(NIPAAm) was shown to release 5-fluorouracil at a controlled rate (J.W. Bae et al. 2006). 

MODIFICATION OF CHITOSAN AND HYALURONIC ACID TO OBTAIN SUSTAINABLE HYDROGELS... 

Thus the modification of chitosan and hyaluronic acid allowed to obtain sustainable hydrogels on their basis it is permeable to water phase. Received hydrogels have bioeompatibility ant it is not toxic. In addition the introduction of functional groups in the used biopolymers contributes to the solution of the task immobilization of the MMC on the polymeric matrix that provides prolongation of this release from polymer witch is necessary the medical use in ophthalmology. 

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