L929 Cell Line Culture

The L929 cells (National Collection of Authenticated Cell Culture, Shanghai, China) were cultured in DMEM containing 10% FBS and 1% penicillin/streptomycin. After 24-hour incubation in a 96-well plate, the L929 cells were attached to the bottom of the well. The Fe₃O₄ NPs and Fe₃O₄@PDA NPs were diluted into suspensions of 20 μM, 50 μM, 0.1 mM, and 0.2 mM. The original medium in each well was discarded, and the cells were incubated in different nanoparticle concentrations according to the experimental design for 24 hours. The same amount of fresh medium was used as a control. After 24-hour culture, CCK-8 solution (10 μL/well) was added into the wells, followed by incubation in a constant temperature incubator for 2 h. The absorbance value (OD) was then measured at a wavelength of 450 nm using a microplate reader (Infinite 200 Pro, Tecan, Austria). The formula used for calculating cell viability was:

Where OD treated, blank, and control represent the OD values of treated, blank, and negative control groups, respectively.