Mesoporous zinc oxide
(ZnO) scaffolds coated with drop-cast graphene
oxide (GO) flakes are proposed to be a novel bilayer system featuring
bioactivity, biocompatibility, and promising loading/release properties
for controlled drug-delivery systems. The high-surface-area ZnO scaffolds
show clear apatite deposition, but their 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, pure ZnO scaffolds also show functional GS loading
efficiency, with fast in vitro release kinetics driven by a simple
diffusion mechanism. Strikingly, the bioactivity and GS delivery properties
of mesoporous ZnO are efficiently triggered by drop-casting GO flakes
atop the mesoporous scaffold surface. The resulting ZnO@GO bilayer
scaffolds show the formation of a uniform apatite coating after 28
days in SBF and demonstrate a biocompatible behavior, supporting the
culture of SaOS-2 osteoblast-like cells. Moreover, the GO coating
also leads to a barrier-layer effect, preventing fast GS release,
particularly in the short time range. This barrier effect, coupled
with 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.