The study on PLLA-nanodiamond composites for surgical fixation devices

Biopolymers have a great potential in biomedical engineering, having been used as scaffolds for hard and soft tissues, such as bone and blood vessels for many years. More recently biopolymers have also found applications in surgical fixation devices. Compared with conventional metal fixation devices, bone grafts and organ substitutes, biopolymer products have advantages of no long-term implant palpability or temperature sensitivity, predictable degradation to provide progressive bone loading and no stress shielding, all of which leads to a better bone healing, reduced patient trauma and cost, elimination of second surgery for implant removal, and fewer complications from infections. However lack of initial fixation strength and bioactivity are two major concerns which limited more widespread applications of biopolymers in orthopedic surgery. Nanodiamond is attractive for its use in reinforcement of composite materials due to their outstanding mechanical, chemical and biological properties. Nanotechnology shows us many innovations and it is generally accepted view that many could be further developed and applied in tissue engineering. In this work, we conduct poly(L-lactic acid) (PLLA) and octadecylamine functionalized nanodiamond (ND-ODA) composite research to optimize the polymer/ND interface, thus to reinforce the mechanical strength. Composites comprising PLLA matrix with embedded ND-ODA were prepared by mixing PLLA/chloroform solution with chloroform suspension of nanodiamonds at concentrations of 0-10 by weight percent. The dispersion of ND-ODA was observed by transmission electron microscopy (TEM). TEM micrographs show that ND-ODA can disperse uniformly in PLLA till 10% wt. Nanoindentation result shows the mechanical strength of ND-ODA/PLLA composites improving following increasing the concentration of ND-ODA in composites. The noncytotoxicity of ND-ODA was demonstrated on 7F2 Osteoblasts. To test the usefulness of ND-ODA/PLLA composites as scaffolds for supporting cell growth, 7F2 Osteoblasts were cultured on scaffolds for 6 days. The attachment and proliferation of 7F2 on all scaffolds were assessed by fluorescent nuclear staining with Hoechst 33258 and Alamar BlueTM assay. The results showed that the adding ND-ODA does small influence cell growth, which indicates the composites have good biocompatibility. The morphology of 7F2 cells growing on all ND-ODA/PLLA composite scaffolds was determined by SEM, which confirms the Osteoblasts spread on the scaffolds. All these results combined suggest that ND-ODA/PLLA might provide a novel composite suitable for surgical fixation devices.