One of the key challenges in engineering neural tissues for cell-based therapies is to develop a biocompatible scaffold material to direct neural stem cell (NSC) behaviors. One great advantage for a scaffold would be to induce NSC migration toward pathological sites during regeneration and repair. In particular, the inflammatory responses in the pathological zone, which are mainly mediated by microglia in the central nervous system, affect the repair capacity of NSCs through NSC migration. Recently, graphene was used as a neural interface and scaffold material, but few studies have addressed the relationship between microglia and NSCs in a graphene culture system. In this study, we used a combination of immunofluorescence, Western blotting, enzyme-linked immunosorbent assays, and scanning electron microscopy to investigate how conditioned medium (CM) produced from microglia grown on two-dimensional graphene (2D-G) films or three-dimensional graphene (3D-G) foams govern NSC migration. The results revealed that the CM produced by microglia grown in 3D-G cultures could promote neurosphere formation, facilitate NSC migration from the neurospheres, and increase single cell polarization by activating the stromal cell-derived factor 1 α (SDF-1α)/CXC chemokine receptor 4 (CXCR4) signaling pathway and enhancing cell adhesion on the substrate. By contrast, the 2D-G CM failed to achieve these results. Our study suggests the great potential of 3D-G as a neural scaffold for NSC-based therapy in tissue engineering and regenerative medicine.

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Calcium carbonate whisker (CCW) particles were surface modified by grafting of poly(L-lactide) (PLLA) chains in order to improve their affinity to a poly(L-lactide-trimethylene carbonate-glycolide) (PLTG) terpolymer matrix. Composites of the PLTG matrix with CCW and PLLA-g-CCW of various contents were prepared by mixing in solution followed by solvent evaporation. The structure and properties of pure CCW, surface modified PLLA-g-CCW and PLTG/PLLA-g-CCW composites were investigated using Fourier transfer-infrared spectrometry (FT-IR), mechanical testing, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), contact angle measurement, thermal gravity analysis (TGA) and differential scanning calorimetry (DSC). Data show that PLLA chains were successfully grafted on the CCW surface. The PLTG/PLLA-g-CCW composites exhibit a higher tensile strength and elongation at break than neat PLTG. Optimal values are obtained with a PLLA-g-CCW content of 2 wt%. It is assumed that PLLA-g-CCW particles present both reinforcing and toughening effects on the PLTG matrix. The cytocompatibility of the materials was evaluated from cell morphology and MTT assay using the L929 mouse fibroblast cell line. The results indicate that the composite presents very low cytotoxicity. Therefore, PLTG/PLLA-g-CCW composites with improved mechanical properties and good cytocompatibility could be promising as a potential bone substitute material.

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