*2.6. Cytotoxicity Test*

Cytotoxicity of films was determined by the MTT assay [34,35]. The conditioned cell culture medium was obtained by immersing films in 1 mL cell culture medium, which was applied to assay the effect of the films on cultured cells. L929 cells were seeded into 96-well plates (7000 cells per well) and cultured in an incubator with 5% CO<sup>2</sup> at 37 ◦C for 24 h before they were incubated with 200 µL conditioned cell culture medium for 24 h. A total of 200 µL MTT reagent was added to each well for a further 4 h incubation at 37 ◦C. Then, the formazan precipitate was extracted by 150 µL DMSO, and the absorbance (492 nm) was recorded using a Multiskan MK3 ELISA reader (Thermo Fisher, Waltham, MA, USA).
