Chemically modifed gellan-and xanthan-based hydrogels for biomedical applications
Résumé
Many gels are able to change in volume and/or form in response to external stimuli or solicitations such as changes in temperature, pH electric or magnetic field. These systems are currently drawing increasing interest related to the applications they can offer. In the biomedical domain, such gels would allow controlled and progressive release of active matter. In this context, hydrogels based on polysaccharides are used more and more owing to their specific properties such as biocompatibility and biodegradability. Bacterial polysaccharides, gellan and xanthan, have been chemically modified in order to elaborate temperature-sensitive hydrogels. The elaboration of such hydrogels involves two steps: the first is to functionalize the polymer through the esterification reaction with acrylic derivatives or maleic anhydride. The second step is a grafting-crosslinking reaction in aqueous solution using Nisopropylacrylamide (NIPAm) as a free-radical polymerizable monomer through a radical way and N,N′-methylenebisacrylamide or β-cyclodextrin acrylate as a crosslinking agent. Thus, grafted or crosslinked hydrogels may be elaborated using homogeneous or heterogeneous processes. Optimal reaction conditions were defined from the study of the influence of parameters such as nature of solvent, temperature and reaction time. According to the experimental conditions and the composition of the reaction medium, semi- or full Interpenetrated Polymer Networks (IPN) were obtained. The morphology and swelling properties of these hydrogels will be discussed and compared according to the following media conditions: pH, ionic strength, and temperature. In particular, swelling is of major importance in relation to the desired applications. Swelling kinetics is typical of a limited swelling network. Moreover, biocompatibility, biodegradability and toxicity properties of such derivatives and hydrogels were evaluated. Inclusion and release of drugs were successfully tested. These phenomena are controlled by diffusion processes depending on the drug concentration, the crosslinking density, and the porous morphology. In most cases, the drug transport displays a Fickian behaviour. Hydrogels based on gellan derivatives, with a higher swelling behaviour than xanthan ones, have the best inclusion performance. Release kinetics curves demonstrate a quick initial release of active matter ("burst effect") when it is anchored in superficial layers of the hydrogel. As an example, potential applications were considered for treating ophthalmic diseases. A positive clinical answer was obtained even at a low concentration of the used drug (adrenaline) without any complications. This technique demonstrates its interest due to a gradual release of the required quantity of the drug as compared to instillation. © 2009 by Nova Science Publishers, Inc. All rights reserved.