Influence of heating rate and soak time on microwave sintered hydroxyapatite and β-tricalcium phosphate ceramics for bone applications

Abstract

Abstract Calcium phosphate-based bio-ceramics, particularly hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP), have gained prominence in biomedical engineering due to their biocompatibility and resemblance to natural bone mineral. However, the non-degradability of HA and the rapid resorption of β-TCP pose challenges for bone scaffold applications. Biphasic calcium phosphate (BCP) composites, combining HA and β-TCP, offer a promising solution by achieving a controlled degradation profile. In this study, HA-TCP ceramics were fabricated using a novel microwave sintering technique to investigate the influence of ramp temperature rate and soak time on the microstructural and mechanical properties of sintered pellets. A ceramic composite with an 80:20 weight ratio of TCP and HA was prepared, and a polyvinyl alcohol (PVA) binder was used to optimize pellet formation. The sintering process was conducted at 1200 °C under varying heating rates (15 °C/min, 25 °C/min, and 35 °C/min) and soak times (30, 45, and 60 min). Results revealed that a ramp temperature rate of 35 °C/min with a soak time of 45 min achieved optimal outcomes, including reduced porosity (26.158%) and increased compressive strength (39.15 MPa). Higher heating for a longer time leads to phase change from β-TCP to α-TCP. Additionally, prolonged soak time during slow cooling resulted in phase transformations from α-TCP to β-TCP, which impacted the mechanical properties. Microwave sintering demonstrated significant advantages, including reduced processing time, energy efficiency, and enhanced densification. This study establishes optimized parameters for the fabrication of HA-TCP ceramics with tailored porosity and mechanical properties, providing a foundation for the development of advanced bone scaffolds in biomedical engineering.