Preparation and characterization of a novel bioactive restorative composite based on covalently coupled polyurethane–nanohydroxyapatite fibres

Nanohydroxyapatite (n-HAp) was prepared using a sol–gel method. n-HAp powder was obtained from the gel form by heat treatment followed by grinding using ball milling. A novel polyurethane composite material was prepared by chemically binding the hydroxyapatite to the diisocyanate component in the polyurethane backbone through solvent polymerization. The procedure involved the stepwise addition of monomeric units of the polyurethane and optimizing the reagent concentrations. The resultant composite material was electrospun to form fibre mats. The fibres were less than 1 μm in thickness and contained no beads or irregularities. Chemical structural characterization of both the ceramics and the novel polymers were carried out by Fourier transform infrared and Raman spectroscopy. X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy and Brunauer–Emmett–Teller surface area analysis were also employed to observe the crystal lattice and size and surface area of the n-HAp. Further characterization (by energy-dispersive X-ray analysis and SEM) of the spun fibres revealed the presence of elements associated with hydroxyapatite and polyurethane without the presence of any loose particles of hydroxyapatite, indicating the formation of the covalent bond between the ceramics and the polymer backbone.