The unique physicochemical properties of graphene and its derivatives enable their application in the diagnostics and therapy of central nervous system (CNS) diseases. However, the potential impacts of surface properties of functionalized graphene on microglia remain poorly understood. Herein, we used graphene oxides (GO), polyethylene glycol (PEG)- and polyethylenimine (PEI)-functionalized GO, which possess different surface charges, to investigate their effects on microglia by focusing on mitochondrial dynamics. The positively charged GO-PEI was found to promote mitochondrial fission as observed in BV-2 cells with mitochondria labeled by DsRed2-mito, indicating that alterations in mitochondrial dynamics depend on the surface properties of graphene. Concurrent to mitochondrial fragmentation, treatment with positively charged GO-PEI induced an increase in mitochondrial recruitment of dynamin-related protein (Drp1). Additionally, GO-PEI treatment also led to apoptotic and autophagic cell death. However, Drp1 silencing by small interfering RNA (siRNA) could effectively attenuate GO-PEI-induced apoptotic and autophagic cell death, indicating that mitochondrial fragmentation occurs upstream of GO-PEI-mediated toxicity in microglia. Overall, our study indicated that positively charged GO-PEI might cause deleterious influence on the central immune homeostasis by Drp1-dependent mitochondrial fragmentation, and provide the strategies for the rational design of graphene-based materials in neuroscience.Keywords: Drp1; functionalized graphene; microglia; mitochondrial dynamics; neurotoxicity

Biodegradable poly(lactic-co-glycolic acid) (PLGA)/carboxyl-functionalized multi-walled carbon nanotube (c-MWCNT) nanocomposites were successfully prepared via solvent casting technique. Rat bone marrow-derived mesenchymal stem cells (MSCs) were employed to assess the biocompatibility of the nanocomposites in vitro. Scanning electron microscopy (SEM) observations revealed that c-MWCNTs gave a better dispersion than unmodified MWCNTs in the PLGA matrix. Surface properties were determined by means of static contact angle, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analysis. The presence of c-MWCNTs increased the mechanical properties of the nanocomposites. Seven-week period in vitro degradation test showed the addition of c-MWCNTs accelerated the hydrolytic degradation of PLGA. In addition, SEM proved that the cells could adhere to and spread on films via cytoplasmic processes. Compared with control groups, MSCs cultured onto PLGA/c-MWCNT nanocomposites exhibited better adhesion and viability and also displayed significantly higher production levels of alkaline phosphatase (ALP) over 21 days culture. These results demonstrated that c-MWCNTs modified PLGA films were beneficial for promoting cell growth and inducing MSCs to differentiate into osteoblasts. This work presented here had potential applications in the development of 3-D scaffolds for bone tissue engineering.Graphical abstractResearch highlights▶ The carboxyl acid groups of acid-treated MWCNTs can form hydrogen bond with polymer matrix to enhance the dispersion of c-MWCNTs in the PLGA matrix. ▶ The incorporation of c-MWCNTs enhanced the mechanical strength of the nanocomposites due to the homogeneous distribution of c-MWCNTs in PLGA matrix. ▶ Addition of c-MWCNTs allowed a better hydrophilicity in the polymer matrix. ▶ The PLGA/c-MWCNT nanocomposites promoted the attachment, proliferation, and differentiation of rat MSCs, which would provide new insights in the PLGA/c-MWCNT nanocomposites for bone tissue engineering.