Graphene oxide/multi-walled carbon nanotubes as nanofeatured scaffolds for the assisted deposition of nanohydroxyapatite: characterization and biological evaluation

Abstract

Nanohydroxyapatite (nHAp) is an emergent bioceramic that shows similar chemical and crystallographic properties as the mineral phase present in bone. However, nHAp presents low fracture toughness and tensile strength, limiting its application in bone tissue engineering. Conversely, multi-walled carbon nanotubes (MWCNTs) have been widely used for composite applications due to their excellent mechanical and physicochemical properties, although their hydrophobicity usually impairs some applications. To improve MWCNT wettability, oxygen plasma etching has been applied to promote MWCNT exfoliation and oxidation and to produce graphene oxide (GO) at the end of the tips. Here, we prepared a series of nHAp/MWCNT-GO nanocomposites aimed at producing materials that combine similar bone characteristics (nHAp) with high mechanical strength (MWCNT-GO). After MWCNT production and functionalization to produce MWCNT-GO, ultrasonic irradiation was employed to precipitate nHAp onto the MWCNT-GO scaffolds (at 1–3 wt%). We employed various techniques to characterize the nanocomposites, including transmission electron microscopy (TEM), Raman spectroscopy, thermogravimetry, and gas adsorption (the Brunauer–Emmett–Teller method). We used simulated body fluid to evaluate their bioactivity and human osteoblasts (bone-forming cells) to evaluate cytocompatibility. We also investigated their bactericidal effect against Staphylococcus aureus and Escherichia coli. TEM analysis revealed homogeneous distributions of nHAp crystal grains along the MWCNT-GO surfaces. All nanocomposites were proved to be bioactive, since carbonated nHAp was found after 21 days in simulated body fluid. All nanocomposites showed potential for biomedical applications with no cytotoxicity toward osteoblasts and impressively demonstrated a bactericidal effect without the use of antibiotics. All of the aforementioned properties make these materials very attractive for bone tissue engineering applications, either as a matrix or as a reinforcement material for numerous polymeric nanocomposites.

Keywords:

• nanohydroxyapatite
• multi-walled carbon nanotubes
• graphene oxide
• in vitro
• bactericidal effect
• bioactivity
• bone cells
• tissue engineering

Acknowledgments

Regarding the financial support to this work, the authors would like to thank the Coordination for the Improvement of Higher Education Personnel (PVEs-CAPES, 88887.095044/2015-00), the National Council for Scientific and Technological Development (CNPq grant 474090/2013-2), the Sao Paulo Research Foundation (FAPESP, grants 2011/17877-7, 2011/20345-7 and 2013/20054-8), and the Brazilian Innovation Agency (FINEP; 0113042800). BVMR would also like to thank the FAPESP for the postdoctoral fellowship (2015/08523-8). The authors would also like to thank the Northeastern University for sponsoring this study.

Disclosure

The authors report no conflicts of interest in this work.