Cross-linked chitosan improves the mechanical properties of calcium phosphate-chitosan cement.

Calcium phosphate (CaP) cements are highly applicable and valuable materials for filling bone defects by minimally invasive procedures. The chitosan (CS) biopolymer is also considered as one of the promising biomaterial candidates in bone tissue engineering. In the present study, some key features of CaP-CS were significantly improved by developing a novel CaP-CS composite. For this purpose, CS was the first cross-linked with tripolyphosphate (TPP) and then mixed with CaP matrix. A group of CaP-CS samples without cross-linking was also prepared. Samples were fabricated and tested based on the known standards. Additionally, the effect of different powder (P) to liquid (L) ratios was also investigated. Both cross-linked and uncross-linked CaP-CS samples showed excellent washout resistance. The most significant effects were observed on Young's modulus and compressive strength in wet condition as well as surface hardness. In dry conditions, the Young's modulus of cross-linked samples was slightly improved. Based on the presented results, cross-linking does not have a significant effect on porosity. As expected, by increasing the P/L ratio of a sample, ductility and injectability were decreased. However, in the most cases, mechanical properties were enhanced. The results have shown that cross-linking can improve the mechanical properties of CaP-CS and hence it can be used for bone tissue engineering applications.

The effect of graphene substrate on osteoblast cell adhesion and proliferation.

Understanding the effect of graphene substrate on graphene-cell interaction is important for considering graphene as a potential candidate for biomedical applications. In this article, biocompatibility of few layers of graphene film transferred to different substrates was evaluated using osteoblasts. The substrates were oxidized silicon wafer (SiO2/Si stack), soda lime glass, and stainless steel. Chemical vapor deposition method was employed to synthesize graphene on copper substrate using methane and hydrogen as precursors. The quality and the thickness of graphene films on different substrates were estimated by Raman spectra, whereas the thickness of graphene film was confirmed by reflectance and transmittance spectroscopy. The study was also focused on cell attachment and morphology at two time points. The results show that graphene does not have any toxic effect on osteoblasts. The cell adhesion improves with graphene coated substrate than the substrate alone. It seems that graphene substrate properties play a dominant role in cell adhesion. The result of this study suggests that a layer of graphene on bone implants will be beneficial for osteoblast attachment and proliferation.