Comparative study on the effects of negatively-charged biopolymers on chitosan-based gels for the development of instantaneous gels

Polymeric electrolytic complexes are solutions of charged/ionized chains. These solutions of positive and negative charge can be combined to make instantaneous networks bonded by electrostatic interactions, a gel network. These electrostatic interaction allows for easy application in injectable gels as the network can be temporarily distributed with the application of force and reformed on the relief of it. Possible applications for these injectable gels include drug delivery and wound-healing. κ-Carrageenan, dextran sulfate, alginate, and chitosan are polyelectrolytic biocompatible polymers which are widely studied and used for a variety of biomedical applications. Gel networks are made by combining a negatively-charged (κ-Carrageenan, dextran sulfate, or alginate) and positively charged (chitosan) solutions. The strong electrostatic interaction between the opposite charges from the gel network and the inherent biocompatibility of the polymers allow future biomedical applications. Quat 188-modified chitosan has additional sites for electrostatic bonding, can be dissolved in neutral, basic, and acidic pH, and has shown inherent antibacterial activity. The objectives of this study are the following: to formulate chitosan-based gels mixing solutions of chitosan with solutions of either κ-Carrageenan, dextran sulfate, or alginate, study the gelation of the gels as function of time and pH (4, 7, and 9) using UV-Vis, characterize the chitosan-based gels through DSC and DMA, characterize the physiological degradation of the chitosan-based gels, and compare results with those from Quat 188-modified chitosan-based gels. Polyelectrolytic solutions of chitosan and negatively-charged biopolymer of similar viscosities were mixed. It was determined from the UV-Vis spectroscopy of the chitosan-carrageenan gels under pH7 buffer that the increase of concentration by a factor of 5 for 0.006M-0.0095M and 1.25 for 0.0095M-0.0150M Chitosan-Carrageenan gels improved gelation by the increase of absorbance however, complete gelation and settling of the gel did not occur even past 3 hours. Similar results were seen in the same gels under pH4 and pH9 buffer. Gelation was almost instantaneous for the modified chitosan-carrageenan gels of similar concentrations. Simulated physiological degradation of chitosan-dextran sulfate gels immersed in pH7.4 PBS-0.01% lysozyme PBS buffer for 1-30 days showed increased degradation of gel as time lapses. DSC, DMA, results of simulated physiological degradation of all chitosan-carrageenan and chitosan-alginate gels are to follow. (author)