FIGURE 2.

Human skin keratinocytes (HaCaT) were purchased from AddexBio (San Diego, CA, USA). HaCaT cells were cultured in DMEM, along with 10% fetal bovine serum (FBS) and 1% antibiotic‐antimycotic (AA) solution in a 37°C, 5% CO₂ incubator. Every 48 to 72 h, fresh DMEM was used to replenish the cell culture media. The cytotoxicity of the fibroblast‐derived exosomes was assessed using 3‐(4,5‐dimethylthiazol‐2‐yl)−2,5‐diphenyltetrazolium bromide (MTT; Sigma‐Aldrich, St. Louis, MO, USA). HaCaT cells were distributed into 96‐well plates (1×10⁴ cells/well) and incubated for 24 h under cell culture conditions (37°C, 5% CO₂). Then, the medium was replaced with a supplement‐free medium, and different exosome concentrations of 1×10⁴, 1×10⁵, 1×10⁶, and 1×10⁷ particles/ml were added to the cells and incubated for 24 and 48 h. Post‐exosome addition, the cells were treated with 5 mg/ml MTT solution (Sigma‐Aldrich, St. Louis, MO, USA; M5655) and incubated in a 37°C incubator for 4 h. After incubation, the supernatant was removed, and the formazan formed by MTT reduction was lysed by adding dimethyl sulfoxide (DMSO; MilliporeSigma, Billerica, MA, USA, 1.02952). The absorbance was then measured at 540 nm using a spectrophotometer (Molecular Devices, San Jose, CA, USA).