Amino Acid Functionalization of Multi-Walled Carbon Nanotubes for Enhanced Apatite Formation and Biocompatibility

The limitation in bone tissue engineering is the lack of available natural or synthetic biomaterials to replace bone tissue under need. Carbon nanotubes have great potential as bone tissue scaffolds because of their remarkable mechanical and electrical properties combined with high aspect ratio. In this work, we demonstrated for the first time a novel approach based on the sol-gel technique for functionalization of multi-walled carbon nanotubes (MWCNTs) with two amino acids: L-arginine, L(+) Arg and L-aspargine, L(+) Asp. We have examined the effect of both functionalities on physico-chemical properties of MWCNTs, cytotoxicity in osteosarcoma MG63 and normal fibroblastic BJ cells and the ability to induce nucleation and growth of hydroxyapatite (HA) crystals in vitro under physiological concentrations of Ca²⁺ and PO⁴⁺ (SBF). The scaffolds were characterized using Fourier transform infrared spectroscopy (FTIR-ATR), dynamic light scattering technique (DLS), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The results showed that both functionalized MWCNTs have a particle size of 269 and 411 nm, a zeta potential of –12.8 and –8.8 mV, respectively, high colloidal stability, enhanced biocompatibility, and enhanced formation of an apatite layer on the scaffolds surface in comparison to ox-MWCNTs. Altogether, the results confirmed the important role of the amino acids L(+) Arg and L(+) Asp in ox-MWCNTs-based composites for bone tissue engineering applications.