Introduction
Ceramic-based bone graft substitutes such as hydroxyapatite (HA), β-tricalcium phosphate, and bioactive glasses have been widely studied for bone tissue engineering, due to their biocompatibility and osteoconductivity[i] Moreover, several studies have shown how graphene and its derivatives, due to their unique properties, can strongly promote cell adhesion, by enhance cellular adherence, proliferation, and osteoblast differentiation, and how the high elastic modulus of graphene-based materials can be a driving force for spontaneous osteoblastic differentiation[ii].
 
Objective
Previous study in our laboratory reported that mesenchymal stem cells derived from adult human bone marrow (ahMSCs) can be seeded and grow on SiCaP2O5 ceramic[iii]. The aims of this study was to optimize the scaffold function by rGO coating, obtaining scaffolds totally covered by a thin layer of rGO.
 
Results and discussion
The starting ceramic material (SiCaP2O5) was prepared by a solid-state reaction, and then uniformly coated with reduced graphene oxide (rGO), a graphene derivative obtained through chemical or thermal reduction of graphene oxide (GO).
Morphological analysis of the rGO-SiCaP2O5 scaffold was realized by SEM showing a uniformly and continuous coating of the ceramic disc with a thin sheet of rGO, presenting an irregular surface with undulations to form wrinkles, confirming the expected high surface area to cause the cells attached to be stretched, resulting in physical stimulation.
Scaffold’s bioactivity was studied in vitro by immersion in SBF until 14 days, showing how up to 3 days appear some isolated spheres that grow by time until cover the entire surface at 7 days. Cross-section analysis at 14 days soaking’ time, showed a uniform and continuous precipitate layer above the rGO coating sheet, reaching thickness of 8.6 mm, identified as carbohydroxyapatite.
The in vitro cell culture study confirmed that rGO-SiCaP2O5 scaffold increased the ahMSCs proliferation rate with any sign of cytotoxicity.
The morphological changes of ahMSCs cultured on bioactive samples after 3 and 7 days were determined by SEM. It is worth mentioning that rGO-SiCaP2O5 scaffold appeared completely cover of cells after 7 days what confirmed a better environment for growing and proliferation cells expected after rGO coating.

Acknowledgements: This work is part of the project PID2020-116693RB-C21  and PID2020-116693RB-C22, funded by MCIN/AEI/10.13039/501100011033 Spain. Grant CIAICO/2021/157 funded by Generalitat Valenciana Spain.

[i] Díaz-Arca, A.; Velasquez, P.A.; Mazón, P; De Aza, P.N. Mechanism of In Vitro Reaction of a New Scaffold Ceramic Similar to Porous Bone. J. Eur. Ceram. Soc. 2020, 40, 2200-2206.
[ii] Wu, M.; Zou, L.; Jiang, L.; Zhao, Z.; Liu, J. Promising Graphene-Based Nanomaterials and Their Biomedical Applications and Potential Risks: A Comprehensive Review. ACS Biomater. Sci. Eng. 2021, 7, 5363−5396.
[iii] Rabadán-Ros, R.; Mazón, P.; Serena, S.; Sainz, M.A.; Meseguer-Olmo, L.; De Aza, P.N. In Vitro Behaviour of Nurse’s Ass-Phase: A New Calcium Silicophosphate Ceramic. J. Eur. Ceram. Soc. 2017, 37, 2943-2952