Synthesis, characterization, and osteocompatibility evaluation of novel alanine-based polyphosphazenes

This study deals with the synthesis and in vitro osteocompatibility evaluation of two novel alanine-containing biodegradable ester polyphosphazenes as candidates to form self-setting composites with hydroxyapatite (HAp) precursors. The two novel biodegradable polyphosphazenes synthesized were poly[(ethyl alanato)1.0(ethyl oxybenzoate)1.0 phosphazene] (PN-EA/EOB) and poly[(ethyl alanato)1.0(propyl oxybenzoate)1.0 phosphazene] (PN-EA/POB). The polymers were characterized by multinuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). Biodegradability and percentage water absorption of the polymers were evaluated by following the mass change in phosphate buffer (pH 7.4) at 37 degrees C. PN-EA/POB underwent faster degradation and showed higher water absorption compared to PN-EA/EOB. Both polymers became insoluble in common organic solvents following hydrolysis presumably due to crosslinking reactions accompanying the degradation process. Osteoblast cell adhesion and proliferation on PN-EA/EOB and PN-EA/POB was followed by scanning electron microscopy (SEM) and by using a biochemical assay. Both PN-EA/EOB and PN-EA/POB supported the adhesion and proliferation of primary rat osteoblast cells in vitro. Furthermore, the enzymatic activity of the osteoblast cells cultured on the polymers was confirmed by the alkaline phosphatase activity. Thus, these biodegradable amino-acid-based polyphosphazenes are promising new materials for forming self-setting bone cements.