Resistive coupled microwave sintering - A promising technique to fabricate bioceramics with improved properties

Enhancing the mechanical properties of biocompatible hydroxyapatite is one of the major challenges in the fabrication of bone implants. In this work, phase pure samples of nano-hydroxyapatite with an average crystallite size of 22 nm, were synthesized by a modified single-step combustion technique. The samples were sintered by a novel resistive coupled microwave sintering technique to 98.4% of theoretical density at 1030 °C for a soaking duration of 20 min. The new method yielded pellets with an average grain size of 0.12 ± 0.01 μm, that showed an improved Vickers microhardness of 7.1 GPa, enhanced young's modulus of 110.51 ± 1.8 GPa, and better compressive strength of 172 ± 10 MPa compared to those pellets sintered via conventional resistive heating. The sintered samples showed better cell viability, cell adhesion, proliferation, differentiation, and osteogenic potential. The enhanced mechanical properties achieved by resistive coupled microwave sintering without compromising the biological properties is a remarkable result that can effectively be used in the fabrication of high-quality bone substitutes.