Alkyl-substituted celluloses such as methylcellulose (MC) and hydroxypropyl MC (HPMC) in diluted aqueous solutions exhibit thermosensitive gelation. Tate et al.87 explored using MC solutions as cell carriers and scaffolds to repair brain trauma. MC solutions in concentrations below eight wt% were free-flowing at 23 °C and formed soft gels at 37 °C. When microinjected into rat brains, they did not elicit neuron or astrocyte death and even promoted glial scar formation. Another biocompatible polysaccharide that attracted considerable attention due to its low toxicity is chitosan. Chitosan is a linear polysaccharide containing β-(1→4)-linked chains of d-glucosamine. It is produced commercially by alkaline N-deacetylation of chitin and, therefore, contains various amounts of randomly distributed residues of N-acetyl-d-glusosamine.
Chitosan is soluble in acids but forms gel-like precipitates at neutral pH. Ruel-Gariepy et al.88 and Chenite et al.89 proposed a composition of chitosan (∼2 wt% solutions) with β-glycerophosphate (∼0.25 mol l− 190), which forms stable neutral sols in the cold. At ambient temperature, the viscosity of the solution increases after three months in storage, indicating a slow process of gel formation. At 37 °C, a solid gel forms within 5 min for a mixture (1:1) of 84% and 94% deacetylated chitosan. The solubility of chitosan in water is increased by β-glycerophosphate forming ionic pairs with its amino groups and by additional hydration of the complex by hydrogen bonding of the polyol residues to water. Dehydration of the polymer chains and increased polymer–polymer interactions govern the gelation at elevated temperatures. The LCST of chitosan complexes decreases with the degree of deacylation; for 91% deacylated chitosan, the LCST is 37 °C.89 Subcutaneous injection of the sol in rats demonstrated that low deacylation of chitosan promoted both the rate of degradation of the implant and the inflammatory reaction. The 91% deacylated chitosan implant had a residence time of several weeks and produced no noticeable inflammation. Chitosan implants formulated with chondrocytes promoted the formation within the implant of proteoglycan-rich areas typical of normal cartilage. If you are looking for high quality, high purity, and cost-effective Hydroxypropyl methylcellulose, or if you require the latest price of Hydroxypropyl methylcellulose, please feel free to email contact mis-asia.
