Münstermann Nils, Weichold Oliver
Institute of Building Materials Research, RWTH Aachen University, Schinkelstraße 3, 52062 Aachen, Germany.
Gels. 2025 Apr 29;11(5):333. doi: 10.3390/gels11050333.
The formation of self-crosslinking chitosan hydrogels using carboxylic acids has a number of limitations. Chitosan dissolves in oxalic, malonic, and succinic acids at a ratio of 1 amino group to 2 carboxyl groups into viscous solutions (G' < G''), but does not dissolve with lower amounts of the acid. Mixing chitosan hydrochloride with disodium carboxylates does not afford gels, but only a coacervate in the case of disodium oxalate, which dissolves upon dialysis. In the homologous series of -carboxyalkyl derivatives (alkyl = methyl, ethyl, propyl), all members form gels (G' > G''). At approx. 50% of substitution, the storage modulus increases from 40 Pa (methyl) to 30,000 Pa (propyl) indicating the increasing strength of intermolecular interactions with the increasing length of the alkyl spacer. This could indicate that a sufficiently long spacer is required to properly connect the chitosan helices. -succinyl chitosan, where the spacer is attached to the backbone as an amide, also forms polymer gels across all degrees of -acylation. When compared to -carboxypropyl chitosan, the latter forms significantly stiffer gels that swell less. This indicates that one covalent bond, a sufficient length, and the conformational flexibility of the spacer are important for gelation.
使用羧酸形成自交联壳聚糖水凝胶存在一些局限性。壳聚糖以1个氨基对2个羧基的比例溶解于草酸、丙二酸和琥珀酸中形成粘性溶液（G' < G''），但在酸量较低时不溶解。将壳聚糖盐酸盐与羧酸钠混合不会形成凝胶，对于草酸钠而言，只会形成一种凝聚层，透析时会溶解。在一系列β-羧基烷基衍生物（烷基 = 甲基、乙基、丙基）中，所有成员都能形成凝胶（G' > G''）。在约50%的取代度下，储能模量从40 Pa（甲基）增加到30,000 Pa（丙基），这表明随着烷基间隔基长度的增加，分子间相互作用强度增强。这可能表明需要足够长的间隔基来正确连接壳聚糖螺旋。β-琥珀酰壳聚糖，其中间隔基作为酰胺连接到主链上，在所有β-酰化程度下也能形成聚合物凝胶。与β-羧丙基壳聚糖相比，后者形成的凝胶明显更硬，溶胀程度更小。这表明一个共价键、足够的长度以及间隔基的构象灵活性对于凝胶化很重要。
