The osteoconductive properties of graphene-based material surfaces are finely tuned by the conditioning layer and surface chemistry

The molecular layer that adsorbs on the biomaterial surface upon contacting body tissues and fluids, termed the conditioning layer (CL), influences cell behavior regulating scaffold integration and resilience in a patient-specific fashion. To predict and improve the clinical outcome of 3D-printed scaffolds, graphene coatings are employed in bone tissue engineering, due to the possibility to functionalize its chemical/physical properties. In this study, we investigated the composition and the influence of the CL on three different graphene oxide-based coatings of 3D-printed polycaprolactone (PCL) implants: graphene oxide (-GO), carboxylated GO (-GO-COOH) and reduced GO (-rGO). The effects of surface features and CL were evaluated in vitro using bone marrow-derived mesenchymal stromal cells (hBM-MSC). Our results showed that the CL formed on negatively charged PCL-GO-COOH and PCL-rGO scaffolds reduced cell adhesion, while simultaneously enhancing cell cluster formation and proliferation by a fivefold increase. The quantification of bone mineralized matrix highlighted that CL on both PCL-GO-COOH and PCL-rGO coatings sustained the osteogenic potential of these two types of GO. The analysis of CL components adsorbed on the scaffolds revealed that the PCL-GO-COOH and PCL-rGO coatings tend to entrap specific patterns of serum proteins (e.g. anti-adhesive and osteogenic modulators) and ions (carbonate and phosphate), suggesting a correlation between these enriched components and the observed biological outcomes of conditioned scaffolds. Lastly, PCL-rGO coatings maintained unique antibacterial properties after in vitro simulated CL formation, representing a suitable promising strategy to improve bone grafting capable of shaping CL formation while preserving the favorable osteoinductive properties of scaffolds.