*3.12. Cytotoxicity In Vitro*

The collagen samples were cut into disks sized for a 48-well plate and sterilized by 60Co for 18 h with an accumulative dose of 20 kGy before using. The cells were seeded a concentration of <sup>1</sup> × <sup>10</sup><sup>4</sup> cells/well and cultured with a specific medium. After seeding for 48 h, 50 <sup>μ</sup>L of thiazolyl blue tetrazolium bromide (MTT) solution was added to the wells and incubated for four hours at 37 ◦C/5% CO2. Wells with collagen were used as negative controls of cytotoxicity. We dissolved the formazan salts using DMSO with shaking for 10 min and replaced the solution with blank wells. The absorbance was measured using a 96-well microplate reader at 490 nm [76].
