Tailoring Microwave-Sintered Zinc Hybrid Nanocomposites for Orthopaedic Implants: Insights into Mechanical Strength, Microstructure, and Biocorrosion Resistance

Abstract

The current study focuses on developing Zn–1.5Mg-based hybrid nanocomposites with varying concentrations of graphene (1–2.5 wt%) and hydroxyapatite (0.5–2 wt%) via microwave sintering. The objective of the work is to improve the mechanical strength, corrosion resistance, and microstructural uniformity for potential biodegradable orthopaedic implants. Five unique compositions (MC1–MC5) with a constant Mg content (1.5 wt%) were developed and evaluated for microstructure using XRD and SEM-EDX, mechanical properties via compression and microhardness testing, and in vitro corrosion in simulated body fluid. Among the composites, Zn-1.5Mg-2Gr-1HA(MC3) exhibited superior performance, with a compressive strength of 147.86 MPa (36.63% increase), 45.5 HV microhardness (20.37% increase), and the lowest corrosion rate of 0.08 mm/year (27.86% decrease) compared to Zn–1.5Mg. These enhancements are attributed to the synergistic effects of uniformly dispersed reinforcements, which promote grain refinement and the formation of a stable passive layer. Optimal concentrations of graphene and hydroxyapatite in 1.5Mg-2Gr-1HA (MC3) and Zn–1.5Mg–1.5Gr–1.5HA (MC4) significantly enhanced the mechanical and biocorrosion properties; however, beyond these optimal levels, the reinforcement content led to agglomeration and performance degradation. All samples exhibited corrosion rates within the clinically acceptable range (0.5 mm/year) for biodegradable implants. The findings validate the feasibility of tailored Zn-based composites via microwave sintering as promising candidates for low- to moderate-load-bearing orthopaedic applications, including bone screws, plates, and scaffolds.