Deposition of calcium hydroxyapatite on negatively charged polyphosphazene surfaces

A number of polyphosphazenes with negatively charged β-alanine (β-Ala) and γ-amino butyric acid (GABA) side groups were synthesized and studied for their ability to initiate the growth of hydroxyapatite (HAp) during exposure to simulated body fluid (SBF). All the polymers were hydrolytically sensitive, with the final hydrolysis rate dependent on the specific active side groups (GABA>β-Ala). These systems also underwent extensive mineralization, with calcium phosphate deposited across their entire surface during exposure to SBF (up to 115 wt % gain after 4 weeks). This degree of deposition is a major advance over previously reported polyphosphazene systems, which underwent a maximum of 27 wt % gain after immersion in SBF for 4 weeks. The extent of mineralization over the surface was monitored using environmental scanning electron microscopy (ESEM) coupled with energy dispersive X-ray spectroscopy (EDS). In addition, X-ray diffraction (XRD) was used to determine the identity of the mineralized material.