Facile synthesis and characterization of chitooligosaccharides for biomedical applications

Abstract

Chitooligosaccharides (COS) are depolymerized chains produced from the natural polymer chitosan, which has been determined to exhibit enhanced biological activities relative to the native polymer, in addition to high solubility in neutral to slightly alkaline pH because of the low molecular weight (MW). These aspects make COS more attractive than chitosan in biomedical applications. In this study, a convenient two-stage technique was developed and optimized, where gamma radiation and oxidative degradation with H2O2 was used to depolymerize chitosan to produce COS for biomedical applications. The gamma radiation dose level, H2O2 degradation reaction’s temperature, time and H¬2O2 concentration were optimized in a manner such that depolymerization could be achieved using the mildest combination of conditions. Solubility at a range of pH values (from 2-11) was tested for all the reaction products to determine which reactions yielded COS soluble at physiological pH 7-8.5. The mildest set of conditions was determined to be a dose rate of 15 kGy, and overnight reaction using 2% H2O2 at a temperature of 25oC. The COS product obtained from this reaction was then fully characterized. MW, FTIR analysis, thermogravimetric and differential scanning calorimetric studies, SEM and XRD tests were carried out; the COS was found to have a MW of 12.8±1.6 kDa, a degree of deacetylation of 62.3% and a crystallinity index of 33%. SEM images revealed that the COS had noticeable cracks. Using this COS, a biocompatible photopolymerized hydrogel was developed, where the COS was cross-linked with polyethylene glycol diacrylate and carboxymethyl cellulose. FTIR data showed peaks corresponding to all three components, indicating that the cross-linking was successful. The hydrogel exhibited high swelling characteristics, a porous morphology, had mechanical strength similar to soft tissues (compression modulus of 14.7 kPa) and when cells were incubated in the hydrogel’s solution, a cell viability of more than 95% was observed.