Carbon Nanotube Functionalization Decreases Osteogenic Differentiation in Aluminum Oxide Reinforced Ultrahigh Molecular Weight Polyethylene

Abstract

Ultrahigh molecular weight polyethylene (UHMWPE) is one of the most preferred materials as an acetabular cup-liner for bone implant applications. The current work develops a correlation between wettability, protein adsorption with osteogenic differentiation upon reinforcement of functionalized carbon nanotube (f-CNT) and 10 wt % aluminum oxide (Al₂O₃) in compression molded UHMWPE composites. Phase characterization has confirmed the retention of CNTs after compression molding. The loading of 2 wt % f-CNT in UHMWPE has shown to increase the contact angle (CA, from 88.9° to ∼97.3°), decrease the surface free energy (SFE, 23.20 to ∼20.85 mJ/m²) and elicit enhanced adsorbed protein density (PD, from ∼0.26 to ∼0.32 mg/cm²) in comparison to that of virgin polymer. Similar trend also has observed with 5 and 10 wt % f-CNT reinforcement. Initially, a high density of L929 mouse fibroblast cells is observed for 10 wt % unfunctionalized CNT (u-CNT) loading (48 h of incubation) with high values of dispersion fraction of surface free energy (σ_d), i.e., 0.967, whereas a decrease in cell density after 48 h is attributed to significant apatite mineralization and low dispersion fraction (σ_d) of CNT-Al₂O₃-UHMWPE biocomposites. Interestingly, gene expression studies have corroborated low osteogenic differentiation (i.e., weaker intensity osteopontin and β-actin) in 2-10 wt % f-CNT reinforced Al₂O₃-UHMWPE biocomposites in comparison to that of similar wt % reinforcement of u-CNT. Thus, implant material can be engineered, (bulk or surface-modified), possessing osteoanalogous and cytocompatible properties based on f-CNT-Al₂O₃-reinforced UHMWPE nanocomposites.