As biodegradability of polylactide-polycaprolactone materials has been examined it is important to examine the cytotoxicity effects of the BNNTs. This is of significant importance, as upon disintegration of the scaffold in the body the BNNTs may not be internalized completely by the macrophages (phagocytosis). Experiments have shown that maintaining a fiber length that is below the macrophage diameter [33] can allow for complete phagocytosis and prevent cytotoxocity to occur. In examining the cytotoxicity of BNNTs upon the polymer scaffold degradation murine macrophages (with a diameter of 20 ^m) macrophages and human osteoblasts (ATCC CRL-11372) were seeded in culture medium and allowed to attach on the plastic well surface for 24 h. Then new solution was added which contained a concentration of 1 ^g ml-1 of pure BNNTs (which would correspond to the case of complete PLA-PCL degradation). For comparison purposes control cultures were also performed without the addition of BNNTs. After 60 h cytotoxicity tests were performed on all cell cultures (with and without BNNTs for both macrophages and osteoblasts) using the Cyto-Tox 96 Non-Radioactive Cytotoxicity Assay kit. It was found that the cultures containing the BNNTs did not show an increase in dead cells, either for the osteoblast or the macrophage cultures. Hence, upon complete degradation of polymer scaffolds containing BNNT this study [26] suggested that there will be no toxic effects from the free standing BNNTs that will be released. This could be due to the structural stability and chemical inactivity of these types of fiber reinforcements.

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