Evaluation of <scp>HAp</scp> ‐Dimethacrylate Composites: Influence of Monomer Chain Length on Mechanical, Thermal, and Ion‐Monomer Release Properties

ABSTRACT There is a growing demand for bioactive composite materials in hard tissue applications. Hydroxyapatite (HAp)‐based composites have emerged as promising candidates due to their chemical similarity to natural bone. However, the influence of dimethacrylate monomer structure and composition ratio on the thermal, mechanical, and degradation properties of HAp composites remains underexplored. In this study, three dimethacrylate monomers (DEGDMA, TEGDMA, and TEeGDMA) were combined with HAp at different weight ratios (50/50, 60/40, and 70/30; Monomer/HAp) to fabricate composite systems via free‐radical polymerization using BPO as thermal initiator. The crystalline structure and particle morphology of synthesized HAp were confirmed by XRD and FT‐IR analyses. Thermal characterization (TG/DTA, DSC) revealed that thermal stability increased with monomer chain length, as reflected by higher T 5% and T 10% values in TEeGDMA systems. Mechanical tests were conducted to evaluate the effect of monomer structure on the compressive strength of 50/50 composites, where H‐50DM exhibited the highest average strength (11.89 MPa) among the tested groups. Degradation and release (Ca 2+ ion and monomers) studies revealed that TEeGDMA‐based composites exhibited the highest weight loss (1.958%) while maintaining the lowest monomer release (0.0009%), both remaining below reported cytotoxic thresholds. The study introduces a novel perspective on how dimethacrylate chain architecture modulates HAp composite performance. These results emphasize the influence of monomer structure on the performance of HAp composites and support their potential in regenerative bone therapies.