The incidence of bone tissue damage as a necessitates the need for a bone-like implant to facilitate healing and regeneration. Magnesium and its alloys have been explored as promising candidates for temporary biological implants in medical applications due to their resemblance to bone in terms of mechanical properties, biocompatibility, and biodegradability. Moreover, the utilization of magnesium alloys obviates the requirement for subsequent surgeries. However, the rapid degradation rate poses a challenge in clinical applications, leading to issues such as hydrogen gas formation, local pH increase surrounding the implant, compromised mechanical stability, immune system activation, and adverse effects on nearby tissues. This research aims to develop and assess a bilayer coating consisting of microarc oxidation/polycaprolactone-hydroxyapatite biocomposite on AZ31 magnesium alloy. The objective is to regulate the degradation rate, enhance bioactivity, and improve biocompatibility. To this end, the AZ31 substrate was subjected to micro-arc oxidation coating at 70 V for 30 minutes. Subsequently, hydroxyapatite particles were prepared from calf bone to fabricate the polycaprolactone-hydroxyapatite composite. X-ray diffraction and Fourier transform infrared spectroscopy confirmed the successful production of hydroxyapatite. Following this scaffolds with varying proportions (15, 30, 45, and 60% by weight) of hydroxyapatite were generated alongside pure polycaprolactone scaffolds using a 3D printer, aiming for over 58% porosity. The printed biocomposite scaffolds underwent secondary coating with a thin polymer layer on the micro-arc oxidation coating. The characterization of the coatings involved tests like diffraction, Fourier transform infrared spectroscopy, roughness, wettability, scanning electron microscopy, mechanical properties assessment, degradability eva‎luation, bioactivity analysis, and cell culture. The bilayer coatings of micro-arc oxidation/polycaprolactone-hydroxyapatite scaffold on AZ31 demonstrated augmented physical and biological surface properties. The application of micro-arc oxidation coating resulted in an increase in surface roughness from 0.4 μm to 16.3 μm, while the pure polycaprolactone scaffold coating decreased roughness to 1.4 μm. The addition of 60% by weight hydroxyapatite brought the roughness back up to 6.9 μm. The wetting angles of all samples ranged from 0 to 90 degrees, with a decreasing trend observed from 90.1 to 67.4 degrees in the pure polycaprolactone scaffolds to the polycaprolactone composite scaffolds containing 60% by weight of hydroxyapatite. The compressive strength test revealed that incorporating hydroxyapatite in the secondary coating up to 45% by weight improved the mechanical properties of the coatings. The bilayer coating of micro-arc oxidation/polycaprolactone scaffold with 45% by weight of hydroxyapatite displayed a compressive strength of 226.3 MPa at 75% strain, a compressive modulus of 76.6 MPa, a yield strength of 16.4 MPa, and a toughness of 51079.9 kJ/m3. The degradation behavior assessment in phosphate-buffered solution over 56 days demonstrated that the presence of polycaprolactone-hydroxyapatite scaffolds as a secondary coating improved the degradation rate of both the AZ31 substrate and the microarc oxidation coating. Furthermore, the bilayer coating of micro-arc oxidation/polycaprolactone scaffold with 60% by weight of hydroxyapatite exhibited the most bioactive behavior. Investigation of the interaction between bone-like MG63 cells and the double-layer coating showed that not only did the composite coatings have no toxic effects on the cells but also promoted cell growth and proliferation. Coatings containing 45% and 60% by weight of hydroxyapatite displayed favorable biocompatibility. These findings suggest that the two-layer microarc oxidation-polycaprolactone-hydroxyapatite scaffold coating has significant potential in orthopedic implant applications.

مسعود عطاپور , رحمت اله عمادي

فرنوش پهلوان زاده

مهشيد خرازيهاي اصفهاني , عباس بهرامي