Effect of Silane A-174 Modifications in the Structure, Chemistry, and Compressive Strength of PLA-HAP and PLA-β-TCP Biocomposites: Toward the Design of Polymer–Ceramic Implants with High Performance

Abstract

The effect of silane A-174 (3-(trimethoxysilyl)propyl methacrylate (methacryloxypropyl trimethoxysilane)) modifications of the ceramic surface on the structural characteristics and mechanical performance of hydroxyapatite (HAP)–polylactic acid (PLA) and β-tricalcium phosphate (β-TCP)–PLA composite systems was investigated employing a combination of Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), compressive strength measurements, and statistical models constructed via projection to latent structures (PLS) analysis. The composites were synthesized by solvent casting method at ambient conditions employing ceramic/PLA ratios of 60/40 and 50/50, and silane A-174 percentages of 0, 1, and 3 wt %. Peak positions of O 1s, Ca 2p, P 2p, Si 2p, and C 1s in XP spectra of ceramics, surface-modified ceramics, and the corresponding composites and compressive strength values were used as the predictors and response variables in PLS models. It was found that Ca 2p, P 2p, and Si 2p binding energies of the ceramic component employed in composite synthesis played the most significant role in determining compressive strength. PLA-HAP composite with a ceramic/PLA ratio of 50/50, synthesized employing 3 wt % silane A-174 treated HAP (HAP50PLA50Si3), resulted in enhancement of the compressive strength up to 365 MPa, which is the highest compressive strength value reported in the literature to the best of our knowledge. Additional P 2p, Ca 2p, and C 1s features positioned at 129.64, 350.08, and 280.74 eV in the XP spectra of this specimen together with significant shifts of Si 2p and C 1s bands toward lower binding energies and polymer-bridge-like surface characteristics signaled improved polymer–ceramic interaction in this composite. Attaining mechanical performance comparable with and even higher than that of cortical bone upon silane A-174 modifications might provide opportunities for clinical applications toward developing bioresorbable PLA-HAP-based implants that can be employed in load-bearing applications such as knee and hip replacements.