Effects of physical and chemical treatments on the molecular weight and degradation of alginate-hydroxyapatite composites.

Degradation of alginate remains a critical issue to allow predictable biological performance upon implantation of alginate-based materials. Therefore, the objective of the current study is to compare the effects of γ-irradiation (dry state, 20-80 kGy), partial (1 and 4%) periodate oxidation (aqueous solution), and autoclaving (dry state) on the molecular weight of alginate, as well as the degradation behavior of alginate-based composites. The results show that γ-irradiation is by far the most destructive technique characterized by strongly reduced molecular weights and rapid loss of composite integrity upon soaking in simulated body fluid. Partial periodate oxidation is less destructive as characterized by more moderate decreases in molecular weight, but the production of hydrolytically labile bonds compromises the integrity of the resulting composites. Autoclaving is shown to be a powerful tool to reduce the molecular weight of alginate in a controllable and mild manner without compromising the integrity of the resulting alginate-hydroxyapatite composites, simply by increasing the number of repetitive autoclaving cycles.