Two-step modification process to improve mechanical properties and bioactivity of hydroxyfluorapatite scaffolds

Porous ceramic scaffolds are synthetic implants, which support cell migration and establish sufficient extracellular matrix (ECM) and cell-cell interactions to heal bone defects. Hydroxyapatite (HA) scaffolds is one of the most suitable synthetic scaffolds for hard tissue replacement due to their bioactivity, biocompatibility and biomimetic features. However, the major disadvantages of HA is poor mechanical properties as well as low degradability rate and apatite formation ability. In this study, we developed a new method to improve the bioactivity, biodegradability and mechanical properties of natural hydroxyfluorapatite (HFA) by applying two-step coating process including ceramic and polymer coats. The structure, morphology and bioactivity potential of the modified and unmodified nanocomposite scaffolds were evaluated using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and energy dispersive spectroscopy (EDS). The scaffold with optimized mechanical properties was HFA-30 wt%HT (HT stands for hardystonite) with a total porosity and pore size of 89 ± 1 and 900-1000 µm, respectively. The compressive modulus and strength of HFA (porosity ~ 93 ± 1) were improved from 108.81 ± 11.12-251.45 ± 12.2 MPa and 0.46 ± 0.1-1.7 ± 0.3 MPa in HFA-30 wt%HT sample, respectively. After applying poly(ε-caprolactone fumarate) (PCLF) polymer coating, the compressive strength and modules increased to 2.8 ± 0.15 and 426.1 ± 15.14 MPa, respectively. The apatite formation ability of scaffolds was investigated using simulated body fluid (SBF). The results showed that applying the hardystonite coating improve the apatite formation ability; however, the release of ions increased the pH. Whereas, modified scaffolds with PCLF could control the release of ions and improve the apatite formation ability as well.