Hydrolysis of Ca-deficient hydroxyapatite precursors in the presence of alanine-functionalized polyphosphazene nanofibers

Hard tissues are made of nanoapatite crystallites grown on a nanofibrous collagen matrix. The mechanical interlocking and the chemical bonding between both phases provide the unique properties of hard tissues. A biodegradable alanine-substituted polyphosphazene nanofibrous scaffold was prepared by an electrospinning technique. Scaffolds were loaded with precursors that form Ca-deficient hydroxyapatite upon hydrolysis in aqueous media. Composite scaffolds containing 30, 60, and 90wt% were subjected to hydrolysis in a phosphate buffer solution for up to 10 days, and was followed by pH measurements, x-ray diffraction and scanning electron microscopy. Results showed a delayed conversion of the precursors into Ca-deficient apatite, which was proven to be attributed to the encapsulation of the precursors within the polymer nanofibrous scaffold and the slow introduction of water of hydrolysis to the precursors. This was accompanied by an increasing swelling of the nanofibers. An overall buffering effect took place within the system as a result of the degradation of the polymeric nanofibers, maintaining pH of the media within physiologic pH values.