In vitro, evaluation of bioactive and biodegradable composites based on polyhydroxybutyrate

Two particulate bioceramics, hydroxyapatite (HA) and tricalcium phosphate (TCP), have been incorporated into polyhydroxybutyrate (PHB) to form new composites for tissue replacement and regeneration applications. HA/PHB and TCP/PHB composites containing 10, 20 and 30 vol% of the bioceramics were produced through an established manufacturing process. In vitro studies were conducted using an acellular simulated body fluid (SBF). Composite specimens were immersed in SBF at 37degreesC for various periods of time prior to surface analyses. Scanning electron microscopic (SEM) examination showed that the earliest: nucleation of mineral crystals occurred on HA/PHB composites only after 1 day immersion in SBF. The mineral crystals were composed of microflakes and completely covered the composite surfaces within a few days. The formation of mineral crystals was slower on TCP/PHB composites than on HA/PHB composites. Thin film X-ray diffraction (TF-XRD) analysis showed that the mineral crystals had the apatite structure with poor crystallinity and an apatite layer formed and grew on composites with an increase in immersion time. Fourier transform infrared (FTIR) spectra revealed that the apatite formed in vitro contained carbonate groups. The formation of a carbonated apatite layer on composite surfaces indicated the in vitro bioactivity of HA/PHB and TCP/PHB composites. Dynamic mechanical analysis (DMA) showed that storage moduli of HA/PHB and TCP/PHB composites increased with immersion time within the duration of in vitro experiments, which was attributed to the formation of the apatite layer on composites.