Preparation of graphene/polymer composites for biomedical applications

Although bone has its own ability to repair, the defects caused by injury or diseases could not be treated easily. As an alternative to the traditional biological grafts, bone tissue engineering approach uses scaffolds to provide required mechanical and biological supports to the cells that take place in tissue regeneration process. In this study, porous biodegradable bone scaffolds that are reinforced with graphene oxide were prepared by using a blend of poly(L-lactic asid)/poly(ε-caprolactone). The ratio of PLLA/PCL was selected as 50/50 (w/w) considering both degradation rates and mechanical properties of the polymers. In order to obtain porous structure, particle leaching and supercritical cabondioxide methods were carried out. Sodium cloride cyristals having diameter between 150-250 µm were used to keep the pore size under control. Two different methods and two different solvents were utilized for the purpose of dispersing graphene oxide homogeneously in the polymeric phase. In the first method, to achieve exfoliated form, graphene oxide was subjected to lyophilization, and chloroform was used as solvent to fabricate the scaffolds. In the second method, initially graphene oxide was dispersed in 1,1,1,3,3,3-hexaflouro-2-propanol (HFIP) and then the scaffolds were fabricated. 2-5-7 wt% of graphene oxide loaded scaffolds were prepared by each methods and the properties of these scaffolds were compared to unloaded scaffolds. Morphological properties of the scaffolds were investigated by scanning electron microscopy (SEM) and micro-computed tomography (micro-CT). The results obtained showed that the scaffolds have high porosity and interconnectivity. The effect of graphene oxide on cyristallinity of the polymer phase was characterized by X-ray diffraction (XRD) method, and from the XRD data it was seen that an increase in the amount of graphene oxide in the composite, increased the cyrstal peak intensities of the polymers. The thermal properties of the scaffold were examined by differantial scanning calorimetry (DSC) and the results obtained showed that the thermal properties of the polymers are independent of graphene oxide amount in the composite. Finally, the mechanical properties of the scaffolds were investigated by an uniaxial compression test. It was seen that while the mechanical properties of the lyophilized graphene oxide loaded scaffolds decreased with graphen oxide amount, those increased for the scaffolds that were prepared by HFIP with increasing graphene oxide .