Poly(ethylene terephthalate)/hydroxyapatite biomaterials: preparation, characterization, and in vitro bioactivity

Poly(ethylene terephthalate)/hydroxyapatite (PET/HAp) composites were prepared by mixing HAp powder with a mixture solution of cyclic oligo(ethylene terephthalate) (C-OET) and dibutyl tinoxide catalyst in dichrolomethane, and then shaping the precomposites in cylindrical pellets. The C-OET in the precomposites was ring-opening polymerized (ROP) to PET under vacuum at 250 degrees C for 24 h. The PET/HAp composites were formulated with HAp to PET ratios of 60:40 (H6P4) and 50:50 (H5P5). The ROP-PET in the composites was present as a thin-layer coating on the HAp grains and evenly distributed throughout the samples. Compressive strength of the PET/HAp composites was significantly increased from 8 MPa of the H10P0 to 17 and 29 MPa for H6P4 and H5P5, respectively. In vitro bioactivity of the PET/HAp composites was studied by soaking in simulated body fluid (SBF) at 36.5 degrees C for 7-28 days. After prolonged soaking, the HAp nanocrystals precipitated from the SBF solution and formed as a layer of globular aggregates, coated on the composite surfaces. The H6P4 composite showed faster formation rate of nano-HAp than the H5P5 composite, indicating that the bioactivity of PET/HAp composites depended on the amount of HAp.