Graphene Oxide Finely Tunes the Bioactivity and Drug-Delivery of Mesoporous ZnO Scaffolds

Mesoporous zinc oxide (ZnO) scaffolds coated by drop-casted graphene oxide (GO) flakes are proposed as a novel bilayer system featuring bioactivity, biocompatibility and promising loading/release properties for controlled drug-delivery systems. The high-surface area ZnO scaffolds shows clear apatite deposition but the particular surface chemistry and topography prevent the formation of a continuous coating, resulting in micrometric crystalline apatite aggregates after 28 days in simulated body fluid (SBF). When gentamicin sulfate (GS) is considered as a model molecule, the pure ZnO scaffolds also show functional GS loading efficiency, with fast in vitro release kinetics driven by simple diffusion mechanism. Strikingly, the bioactivity and GS delivery properties of mesoporous ZnO are efficiently triggered by drop-casting GO flakes atop of the mesoporous scaffold surface. The resulting ZnO@GO bilayer scaffolds show the formation of a uniform apatite coating after 28 days in SBF. A biocompatible behavior of the ZnO@GO bilayer scaffolds is also observed, supporting the culture of SaOS-2 osteoblast-like cells. Moreover, the GO coating also leads to a barrier-layer effect, preventing fast GS release especially in the short-time range. This barrier effect, coupled to the existence of nanopores within the GO structure, sieves drug molecules from the mesoporous ZnO matrix and allows for a delayed release of the GS molecule. We thus demonstrated a new-generation ZnO@GO bilayer system as effective multifunctional and biocompatible scaffold for bone tissue engineering.