Optimization of Injectable Thermosensitive Scaffolds with Enhanced Mechanical Properties for Cell Therapy.

Strong injectable chitosan thermosensitive hydrogels can be created, without chemical modification, by combining sodium hydrogen carbonate with another weak base, namely, beta-glycerophosphate (BGP) or phosphate buffer (PB). Here the influence of gelling agent concentration on the mechanical properties, gelation kinetics, osmolality, swelling, and compatibility for cell encapsulation, is studied in order to find the most optimal formulations and demonstrate their potential for cell therapy and tissue engineering. The new formulations present up to a 50-fold increase of the Young's modulus after gelation compared with conventional chitosan-BGP hydrogels, while reducing the ionic strength to the level of iso-osmolality. Increasing PB concentration accelerates gelation but reduces the mechanical properties. Increasing BGP also has this effect, but to a lesser extent. Cells can be easily encapsulated by mixing the cell suspension within the hydrogel solution at room temperature, prior to rapid gelation at body temperature. After encapsulation, L929 mouse fibroblasts are homogeneously distributed within scaffolds and present a strongly increased viability and growth, when compared with conventional chitosan-BGP hydrogels. Two particularly promising formulations are evaluated with human mesenchymal stem cells. Their viability and metabolic activity are maintained over 7 d in vitro.