Preparation of chitosan-threonic acid and chitosan-xylonic acid conjugates gellable by freeze-thawing and evaluation of their biological properties

Chitosan, an aminopolysaccharide, has been used in biomedical fields due to its high biocompatibility, non-toxicity and biodegradability. Conventional chitosan gels contain toxic chemicals such as chemical crosslinkers. The characteristic of the chitosan gels limit their applications to biomedical fields. To overcome the limitation, we previously developed a novel chitosan hydrogel containing no additives (Takei et al., 2012). The hydrogels are formed by freeze-thawing the precursor solution (cryogelation). The cryogel material is chitosan-gluconic acid conjugate. In this study, we examined (i) whether chitosan derivatives containing chemically-incorporated aldonic acid with different molecular weight from gluconic acid formed gels through freeze-thawing process, and (ii) whether the resultant hydrogels possessed similar biological properties to chitosan-gluconic acid conjugate cryogels. We selected threonic acid and xylonic acid as aldonic acid incorporated into chitosan. Aqueous solutions with dissolved chitosan-threonic acid or chitosan-xylonic acid conjugates formed gels by freeze-thawing as that of the chitosan-gluconic acid conjugate did. Chitosan-threonic acid conjugate had low cytotoxicity, and the cryogels had low cellular adhesiveness.