Synthesis, Mechanical Properties, and in Vitro Biocompatibility with Osteoblasts of Calcium Silicate−Reduced Graphene Oxide Composites Mehdi Mehrali, †,‡ Ehsan Moghaddam, § Seyed Farid Seyed Shirazi,* ,† Saeid Baradaran, ∥ Mohammad Mehrali, † Sara Tahan Latibari, † Hendrik Simon Cornelis Metselaar,* ,† Nahrizul Adib Kadri, ‡ Keivan Zandi, § and Noor Azuan Abu Osman ‡ † Department of Mechanical Engineering and Center of advanced Material, University of Malaya, 50603, Kuala Lumpur, Malaysia ‡ Department of Biomedical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia § Tropical Infectious Diseases Research and Education Centre (TIDREC), Department of Medical Microbiology, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia ∥ Department of Engineering Design and Manufacture, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia ABSTRACT: Calcium silicate (CaSiO 3 , CS) ceramics are promising bioactive materials for bone tissue engineering, particularly for bone repair. However, the low toughness of CS limits its application in load- bearing conditions. Recent findings indicating the promising biocompat- ibility of graphene imply that graphene can be used as an additive to improve the mechanical properties of composites. Here, we report a simple method for the synthesis of calcium silicate/reduced graphene oxide (CS/rGO) composites using a hydrothermal approach followed by hot isostatic pressing (HIP). Adding rGO to pure CS increased the hardness of the material by ∼40%, the elastic modulus by ∼52%, and the fracture toughness by ∼123%. Different toughening mechanisms were observed including crack bridging, crack branching, crack deflection, and rGO pull-out, thus increasing the resistance to crack propagation and leading to a considerable improvement in the fracture toughness of the composites. The formation of bone-like apatite on a range of CS/rGO composites with rGO weight percentages ranging from 0 to 1.5 has been investigated in simulated body fluid (SBF). The presence of a bone-like apatite layer on the composite surface after soaking in SBF was demonstrated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The biocompatibility of the CS/rGO composites was characterized using methyl thiazole tetrazolium (MTT) assays in vitro. The cell adhesion results showed that human osteoblast cells (hFOB) can adhere to and develop on the CS/rGO composites. In addition, the proliferation rate and alkaline phosphatase (ALP) activity of cells on the CS/rGO composites were improved compared with the pure CS ceramics. These results suggest that calcium silicate/reduced graphene oxide composites are promising materials for biomedical applications. KEYWORDS: calcium silicate, reduced graphene oxide, biocompatibility, bioactivity, mechanical properties 1. INTRODUCTION Graphene, a flat monolayer of carbon atoms in a two- dimensional (2D) honeycomb lattice with a high aspect ratio layer geometry and a very high specific surface area, has attracted tremendous attention in recent years due to its exceptional thermal, mechanical, and electrical properties. 1−4 Graphene sheets have been applied in various biotechnologies such as bacteria inhabitation, 5,6 biosensing, 7 drug delivery, 8 cellular imaging, 9 cancer targeting, 10 antiviral materials, 11 tissue engineering, 12−14 and so forth, due to its extremely large surface area, good biocompatibility, biostability, and ease of chemical functionalization. Much of the work on graphene composites has been focused on polymer matrix composites. The addition of graphene has resulted in the improvement of electrical and mechanical properties of the polymer matrix composites. 13,15,16 In recent years, there has been great interest in using graphene-based nanofillers, such as graphene oxide (GO), graphene nanoplatelets (GNPs), and reduced graphene oxide (rGO), to improve the mechanical performance of ceramics and bioceramics such as Si 3 N 4 , 17,18 zirconia/alumina composites, 19 Al 2 O 3 , 20 hydroxyapatite (HA), 21,22 and biphasic calcium phosphate composites. 23 All graphene-reinforced ceramic matrix composites were found to exhibit a decreased tendency to fracture, mainly due to crack bridging, crack Received: November 19, 2013 Accepted: March 3, 2014 Published: March 3, 2014 Research Article www.acsami.org © 2014 American Chemical Society 3947 dx.doi.org/10.1021/am500845x | ACS Appl. Mater. Interfaces 2014, 6, 3947−3962