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An in vitro model for assessing potential bone toxicity of Bone Graft Substitutes

Advances in bone research have allowed the development of inorganic calcium- and phosphate-based bone graft substitutes (BGSs). These BGSs are combined with other ingredients to form a paste that is surgically implanted by injection and subsequently hardens in situ. The advantage of these self-setting BGSs is that they are able to fill irregular shaped bone defects prior to hardening into apatites, allowing for bone resorption and substitution. Historically, testing for biocompatibility of BGSs has been performed using in vivo models, however, advances in cell-based models now allow for the substitution of animal-based testing using in vitro techniques.

Our recent research focused on testing the biocompatibility of numerous proprietary BGSs using primary human osteoblasts (hOBs) as well as human mesenchymal stem cells from bone marrow (hMSC-BM), the precursor cells to hOBs. Both cells types were individually plated over strips of hardened BGS. The hOB cells were assessed for cell viability, proliferation, morphology/growth patterns and alkaline phosphatase activity (a classical biomarker for osteoblast function). The precursor cells (hMSC-BM) were assessed for viability, proliferation and morphology/growth patterns, in addition to their ability to differentiate into hOB cells and produce alkaline phosphatase. The mineralisation capacity of the hOB cells was also evaluated.

The results from the study indicate that the newer proprietary formulations exhibit less initial cell death and greater proliferation of hOB and hMSC-BM cells and an increase in alkaline phosphatase activity of hOB, compared to an existing currently available BGS formulation. The multi-cell based in vitro model chosen for this study appears to be a highly effective non-animal method for assessing biocompatibility of BGSs.

Our research into in vitro cell-based models for testing BGS biocompatibility was co-presented with LaunchPad Medical at the SOT conference in Baltimore in March 2017.

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