Toward CNT-reinforced chitosan-based ceramic composite coatings on biodegradable magnesium for surgical implants

Biomaterials containing carbon nanotubes (CNTs) represent a class of composites, which have generally been underexploited in the medical field. However, recognition of the potential utility of this class of composite materials may form the basis to develop new CNT biomaterials for implants and regenerative medicine scaffolds. Nanocomposite coatings containing chitosan matrix (CHI) reinforced with multiwall CNTs and CaHPO4 (DCPA) were deposited on pure magnesium substrates using a flexible chemical conversion approach. Field emission scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy were applied to characterize the morphological, chemical, and physical changes that occurred in the composite coatings. The in vitro degradation behavior of the composite-coated samples was evaluated using electrochemical impedance spectroscopy in Hank's solution. Results showed that the tri-phasic composite coating (CHI/CNTs/DCPA) exhibits the highest electrochemical corrosion resistance in comparison with the bi-phasic composite coating (CHI/CNTs and CHI/DCPA) and monophasic CHI-coated magnesium. Potentiodynamic polarization results in Hank's solution indicate that the corrosion potential of the tri-phasic coated Mg is - 1.5 V, while the corrosion current density reaches 0.36 mu A/cm(2). Functionalization of the Mg surface by activation at 75 degrees C produces a rough surface that triggers a combination of chemical and physical interactions between the three phases and Mg ions present in the reaction medium. The bi-phasic (CHI/CNTS) and tri-phasic (CHI/CNTs/CaHPO4) composite coatings revealed high antibacterial performance against Staphylococcus aureus. These corrosion results and the successful deposition of CNT-reinforced CHI/DCPA on pure Mg substrate suggest that the conversion coating approach is effective for the production of new composite coatings for either regenerative medicine or functional implants. As such, the present research might lay the groundwork for a new generation of uses for this versatile class of composite coating materials.