Scaffolds based on tricalcium phosphate and polyhydroxyalkanoates as biodegradable and bioactive bone substitutes with enhanced physicochemical properties

Polyhydroxyalkanoates (PHAs) are biocompatible and biodegradable bacterial-origin polyesters, which have recently emerged as a potential prosperous coating for bioceramic scaffolds. However, biopolymers often have properties inferior to commercially available polymers, and thus blending seems to be an efficient method to tailor their characteristics. In our study poly(3-hydroxybutyrate) (P(3HB)) and medium chain length PHA (mcl-PHA) blends were used as coatings on beta tricalcium phosphate (beta TCP) scaffolds. The influence of the coating type on the physicochemical properties of composites was investigated using various techniques such as X-ray diffraction (XRD), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis with differential scanning calorimetry (TG/DSC), scanning electron microscopy (SEM), atomic force microscopy (AFM), wettability measurements, ultra high-performance liquid chromatography with and mass spectrometry (UHPLC-MS) and in vitro studies. It has been demonstrated that blends with various amounts of brittle P(3HB) and viscous mcl-PHA can serve as coatings on beta TCP scaffolds, modulating their physicochemical properties. Macroporous scaffolds covered with blends possessed high open porosity (similar to 65 vol%) and improved compressive strength (up to 4.9 +/- 0.9 MPa). It has been shown that their wettability can be tailored by modifying composition of blends, making the surface more hydrophobic with increasing amount of mcl-PHA. The highest amount of mcl-PHA was shown to significantly influence the degradation of the composites which may be a valuable feature in the case of customized scaffolds for the controlled release of bioactive substances. Moreover, UHPLC-MS analysis revealed that PHAs degrade to hydroxy acids and their oligomers, which may serve as potentially nourishing compounds for surrounding tissues. According to in vitro biocompatibility tests on mouse preosteoblasts, all evaluated scaffolds were nontoxic. The greater the surface hydrophilicity, the better cell adhesion and proliferation were observed.