Abstract
The nucleation of apatite nanoparticles on exfoliated graphene nanoflakes has been successfully carried out by the sitting drop vapor diffusion method, with the aim of producing cytocompatible hybrid nanocomposites of both components. The graphene flakes were prepared by the sonication-assisted, liquid-phase exfoliation technique, using the following biomolecules as dispersing surfactants: lysozyme, L-tryptophan, N-acetyl-D-glucosamine, and chitosan. Results from mineralogical, spectroscopic, and microscopic characterization (X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman, Variable pressure scanning electron microscopy (VPSEM), and transmission electron microscopy (TEM)) indicate that flakes were stacked in multilayers (> 5 layers) and most likely intercalated and functionalized with the biomolecules, while the apatite nanoparticles were found forming a coating on the graphene surfaces. It is worthwhile to mention that when using chitosan-exfoliated graphene, the composites were more homogeneous than when using the other biomolecule graphene flakes, suggesting that this polysaccharide, extremely rich in –OH groups, must be arranged on the graphene surface with the –OH groups pointing toward the solution, forming a more regular pattern for apatite nucleation. The findings by XRD and morphological analysis point to the role of “functionalized graphene” as a template, which induces heterogeneous nucleation and favors the growth of apatite on the flakes’ surfaces. The cytocompatibility tests of the resulting composites, evaluated by the 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay in a dose–dependent manner on GTL-16 cells, a human gastric carcinoma cell line, and on m17.ASC cells, a murine mesenchymal stem cell line with osteogenic potential, reveal that in all cases, full cytocompatibility was found.
Highlights
In the last decade there has been increasing interest in the preparation of graphene/apatite hybrid nanocomposites and their derivatives, combining the bioactive properties of the nanocrystalline apatite with the mechanical strength of graphene for uses in load-bearing applications in bone tissue engineering [1]
We reported for the first time a new methodology to precipitate biomimetic apatite nanoparticles [19] and other calcium phosphates [20] in microliter droplets by the vapor diffusion sitting drop (VDSD) micromethod
We propose to extend this precipitation micromethod to induce the heterogeneous nucleation of nanocrystalline apatites on exfoliated graphene flakes, as the model of a bidimensional material scaffold
Summary
In the last decade there has been increasing interest in the preparation of graphene/apatite hybrid nanocomposites and their derivatives, combining the bioactive properties of the nanocrystalline apatite with the mechanical strength of graphene for uses in load-bearing applications in bone tissue engineering [1]. For applications in dental and orthopedic surgery, they are usually employed as a bioactive coating on a metallic support, combining the biological properties of the apatite with the mechanical strength of the support, promoting a fast fixation within the surrounding bony tissue. To this end, different calcium phosphate (CaP) coating methods, employing biocompatible titanium and titanium alloy supports, were developed in the past [3,4,5,6,7]
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