en Research Paper Research Paper The optimization of biomaterials biodegradation rate similar to tissue regeneration, is one of the main<br> goals in the field of tissue engineering. However, the necessity to assess their possible toxicity is always considered.<br> The aim of this study was cytotoxicity and genotoxicity evaluation of fluorapatite/bioactive glass (FA/BG)<br> nanocomposite foams with two various weight ratios to determine the optimal composition. Nanocomposite foams<br> were made by gel-casting method with FA and BG as precursors in two weight ratios (A and B). Nanocomposite<br> foam extracts (CFEX) were prepared by shaking 100 mg/mL of each foam in a complete culture medium for 72 h in<br> a shaker incubator at 120 rpm/37&ordm;C. Saos-II cells were exposed to different concentrations of CFEXs for 24 and<br> 48 h and then cytotoxicity and genotoxicity were evaluated by MTT and comet assay, respectively. Based on the MTT<br> assay results after 24 h exposure, CFEX A at concentrations &ge;75% and CFEX B at concentrations &ge;50% had a<br> cytotoxic effect, while after 48 h, both CFEXs showed similar cytotoxicity at concentrations &ge;25%. According to the<br> result of the comet assay, DNA damage increased with the increase of CFEXs concentration and exposure time.<br> Both CFEXs showed significantly higher comet tails elongation scores at concentrations &ge;50% and &ge;25% after 24<br> and 48 h exposure, respectively. Both composite foams could be considered as a non-toxic candidate for tissue<br> engineering at concentrations <25% which was less than FA50%/BG50% composite. Therefore, the composite with<br> equal FA/BG proportion has priority if similar results are obtained in in vivo complementary experiments. Cytotoxicity and Genotoxicity, Fluorapatite, Bioactive glass, MTT assay, Comet assay 1 10 http://ijmse.iust.ac.ir/browse.php?a_code=A-10-4058-2&slc_lang=en&sid=1 Ebrahim Zabihi e_zabihi@yahoo.com 1800319475328460016483 1800319475328460016483 No Cellular and Molecular Biology Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, Iran Roghayeh Pourbagher r.pourbagherbio@gmail.com 1800319475328460016484 1800319475328460016484 No Cellular and Molecular Biology Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, Iran Seyedali Seyedmajidi s.majidi.dvm@gmail.com 1800319475328460016485 1800319475328460016485 Yes Dental Materials Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, Iran