The synergistic antioxidant effect of polydopamine coating with amino-functionalized graphene quantum dots on osteoblast protection against oxidative stress

Oxidative stress is a major pathological feature in patients with metabolic bone diseases and isn't conducive to postoperative osseointegration of implants. Although the free-radical scavenging activities of polydopamine (PDA) have been reported, its antioxidant-active catechol structure is susceptible to oxidation. Here, amino-functionalized graphene quantum dots (GQDs) were introduced into PDA to protect catechol structure from oxidation and expand its free-radical scavenging capacity. Compared to the clinically used hydroxyapatite (HAp) coating and the PDA-HAp coating, the GQD/PDA-HAp coating exhibited higher capacity to scavenge ABTS.+, DPPH and O-2(-). The enhanced antioxidant effect of the GQD/PDA-HAp coating was ascribed to the combined effects of the sp(2)-hybridized carbon in GQDs and more catechol groups in PDA, indicating the synergistic antioxidant relationship between GQDs and PDA. In addition, the amino-functionalized GQDs increased the catechol content and the reducibility of the GQD/PDA coating as confirmed by Folin-Ciocalteu colorimetric assay and mediated electrochemical probing. In vitro studies showed that the GQD/PDA-HAp coating minimized intracellular reactive oxygen species production and protected osteoblast viability against H2O2-induced oxidative stress. Taken together, introducing amino groups in PDA is an efficient approach to preserve its structural related antioxidant properties which may broaden its application in treating oxidative stress-related diseases.