Self-assembly of a swollen chitosan/chondroitin sulfate hydrogel by outward diffusion of the chondroitin sulfate chains

A hydrogel constituted of chitosan (CT) and chondroitin sulfate (CS) was synthesized. In previously reported works the stochiometric ratio has been used, but in this paper an excess of CS (40% CT and 60% CS) was used because the hydrogel could be applied as a CS carrier. The hydrogel properties were investigated by differential scanning calorimetry, wide-angle X-ray scattering (WAXS), scanning electron microscopy, and high-performance liquid chromatography. Changes in the pH of the gel-surrounding liquid had a considerable effect on both the release and the molecular reorganization of CS. Furthermore, the formed hydrogel exhibited interesting parameters for use in biotechnology, such as water affinity, thermal properties and morphology upon sequential pH variation. The protonation or deprotonation of the different groups that participate in the complex formation and the coiling or uncoiling of like or unlike chains concomitant to the release of CS are believed to be the main factors affecting the hydrogel properties. CS was released mainly at pH higher than 6.5, the value of pKaCT, and the released CS maximum fraction was approximately 0.5. The WAXS data demonstrated that the CT/CS complex in the hydrogel presented macromolecular reorganization at pHs ranging from 6 to 12.