9: Stability of Polysaccharide Complexes: The Effect of Media and Temperature on the Physical Characteristics and Stability of Chitosan-Triphosphate/ Alginate Nanogels

Ionic polysaccharides such as chitosan and sodium alginate (Na-alg) form complexes by electrostatic interactions. Hydrophilic spherical nanogels obtained from these have an enormous potential in biomedical and pharmaceutical applications. However, the application conditions frequently vary from those of the preparation and storage. This concerns in particular the quality of the medium and the temperature.

Nanogels have been produced from two types of chitosan, from animal and fungal sources, by complex formation with pentasodium triphosphate (TPP). Coating with Na-alg provided a negatively charged surface enabling sufficient colloidal stability. The animal and fungal chitosan yielded similar spherical nanogels in terms of formation, size distributions, and zeta potential, with a hydrodynamic diameter in the range of 450-600 nm and a zeta potential of approx. −65 mV in water. Upon transferring the nanogels into PBS or cell culture media, the hydrodynamic diameter significantly decreased while the zeta potential shifted to less negative values. Applying repeated alternating temperature modifications in the range of 4°C to 37°C revealed changes but reversibility of the hydrodynamic diameter and zeta potential as a function of the temperature. In contrast to uncoated chitosan-TPP complexes, which showed a strong aggregation tendency immediately after preparation, the chitosan-TPP/alginate nanogels are highly and reversibly deformable as well as stable in cell culture media and under physiological conditions. These findings demonstrate the importance of the knowledge of the characteristics of therapeutic nanomaterials as a function of both preparation and application conditions.