Preparation and in vitro characterization of graphene-containing bioactive glass scaffolds

Bone tissue engineering is a field containing studies on the repair and regeneration of the damaged bone tissue. Bioactive glasses have crucial effect in bone regeneration due to their ability to make strong bonding with the bone tissue. In this study, graphene-containing, electrically conductive, borate-based 13-93B3 bioactive glass composite scaffolds were prepared for bone tissue applications. Graphene was incorporated to the bioactive glass structure using two different approaches. In the first method (Method I), graphene nanopowders (1, 3, 5, 10 wt. %) were added to the bioactive glass suspension and bioactive glass composite scaffolds were manufactured using polymer foam replication method. It was observed that the addition of graphene did not adversely affect the mechanical properties and increased the electrical conductivity of the glass scaffolds. In the X-ray diffraction analysis, the peak corresponding to the hydroxyapatite crystal was observed in all samples, indicating that all the samples were bioactive after 30 days of immersion into the simulated body fluid. However, Fourier transform infrared spectroscopy analysis and scanning electron microscope observations have shown that the rate of hydroxyapatite formation decreases with increasing graphene concentration, especially in samples incubated in short periods in simulated body fluid. Based on cytotoxicity assay findings, pre-osteoblastic MC3T3-E1 cell growth was significantly inhibited by scaffolds containing a higher amount of graphene compared to the bare bioactive glass scaffold. The best performance was obtained for samples containing 5% graphene, which provides an increase in electrical conductivity with moderate cellular response and the ability to form hydroxyapatite in vitro. In the second approach (Method II), bare 13-93B3 bioactive glass scaffolds were prepared by polymer foam replication method using the same conditions with Method I. After sintering they were coated with the graphene-containing (1, 3, 5, 10 wt. %) polycaprolactone (PCL) solution. Results revealed that electrical conductivity and compression strength of the samples increased with increasing concentration of graphene nanopowders. Based on SEM analysis a noticeable difference was not observed in HA forming ability of the bare and the graphene- coated scaffolds immersed in simulated body fluid. In vitro cytotoxicity experiments showed that pre-osteoblastic MC3T3-E1 cell viability of the graphene- containing samples was higher than control group samples after 7 days of incubation. However, a decrease in cell viability was obtained after 14 days for samples coated with graphene starting from 3 wt. %. Additionally, a higher ALP activity was detected in cells cultured on the graphene-containing borate glass scaffolds than those on the bare PCL coated 13-93B3 scaffolds suggested the presence of graphene nanopowders stimulated an early stage of osteoblastic differentiation. The results of the study showed that electrically conductive 13-93B3 bioactive glass composite scaffolds produced by both approaches have potential to be used in bone tissue engineering applications.