Development of Injectable Thermogelling Chitosan–Inorganic Phosphate Solutions for Biomedical Applications

Thermosetting polymers are attractive candidates for biomedical applications as noninvasive therapeutic delivery vehicles. In the present study, the feasibility of developing a neutral physiological temperature setting injectable formulation based on chitosan and an inorganic phosphate salt have been demonstrated. The in situ gelling system was developed by adding different concentrations of ammonium hydrogen phosphate (AHP) to chitosan solution. The resulting solutions have pH in the range of ∼7–7.2. The gelling time of the chitosan–AHP solution was determined by incubating the solutions at 37 °C. Depending on the concentrations of AHP added, the gelling time varied from 5 min to 30 h at 37 °C. Addition of various diluents to chitosan–AHP solution did not significantly change the gelling time of the solutions. The gels were found to be cytocompatible as evidenced from in vitro cytocompatibility evaluation using MC3T3-E1 mouse osteoblast like cells. The feasibility of using the gels as a stem cell carrier vehicle as well as a macromolecular delivery vehicle has been demonstrated.