Sol-gel coatings doped with graphene nanoplatelets for improving the degradation rate and the cytocompatibility of AZ31 alloy for biomedical applications

SiO coatings doped with four different functionalized graphene nanoplatelets (COOH-GNPs) concentrations (from 0.005 to 1 wt%) were deposited on AZ31 magnesium substrates to control the corrosion rate and to increase the cytocompatibility of this alloy for MC3T3 pre-osteoblastic cells, to develop biodegradable implants for bone fracture and orthopedic applications. The results show that the highest nanoplatelets concentration promoted the generation of nanoparticle aggregates acting as crack-nucleation points embedded in the coating, decreasing the protective behavior of these coatings. Nanoplatelets concentrations of 0.005 wt% and 0.05 wt% led to obtaining crack-free coatings that provided an improved barrier effect. Cytocompatibility tests show that all the conditions, even the bare AZ31, led to cell proliferation. However, low cell adhesion was found in the bare substrate, contrary to the coated substrates. The coatings with the highest nanoplates concentrations augmented the metabolic activity of cell cultures. The sol-gel coating doped with 0.05 wt% COOH-GNPs presented the best corrosion rate control behavior and improved cytocompatibility, with the generation of a confluent preosteoblastic monolayer on its surface after one week of cell culture.The authors would like to acknowledge the financial support from the Ministerio de Ciencia e Innovación for FPI grant (MAT2015-66334- C3-1-R), Agencia Estatal de Investigaci ́on (Project RTI2018-096391-B- C31), and the Comunidad de Madrid (Project ADITIMAT-CM S2018/ NMT-4411