Biomimetic mineralization of acid polysaccharide-based hydrogels: towards porous 3-dimensional bone-like biocomposites

Biomimetic synthesis of bone-like composite materials is a promising strategy for the development of novel biomaterials for bone engineering applications. Most research efforts have focused on collagen or peptide-based scaffolds for bone biomineralization. Inspired by recent findings about the important role of polysaccharides in bone biomineralization, we report the use of an acid polysaccharide-based hydrogel (maleic chitosan/PEGDA hybrid hydrogel) for in vitro growth of carbonated apatite in a modified simulated body fluid (SBF) mineralization environment. The resulting mineralized porous hydrogel composites had reduced pore sizes due to direct deposition of minerals onto the wall of pores. The level of mineralization in the hydrogel composites could be controlled by mineralization time, with mineral amounts equal to 21.4 ± 0.3%, 32.5 ± 0.4% and 44.9 ± 0.6% (weight percentages) for the 3, 7 and 17-day mineralized samples, respectively. At 3 days, the mineral phase comprises spherical amorphous nanoparticles embedded within organic layers, and transformed into plate-like calcium-deficient, carbonated-substituted crystalline hydroxyapatite after 7 days. In contrast, a very small amount of mineral phase was found randomly deposited inside a pure PEGDA hydrogel even after 17-day mineralization. We suggest that acid polysaccharide-based hydrogel could not only provide reactive sites for the binding of the mineral phase (due to the functionalized carboxyl moieties in maleic chitosan), but also play an important role in stabilizing the amorphous inorganic phase at the early stage of crystallization. The porous mineralized polysaccharide-based hydrogel composites can serve as viable scaffolds for bone tissue engineering.