*4.2. Modification of the Surface of Culture Plates*

The surface of the well on plates was modified using type I collagen (Sigma-Aldrich, St. Louis, MO, USA) and dissolved in 0.1 M acetic acid to a stock concentration of 0.1% (*w/v*). Before using type I collagen, a solution was dissolved in water to a final concentration of 0.01% (*w/v*), which was added to cover the surface of the wells. The 96-well plates were left at 4 ◦C overnight. After removing the solution, the surface was washed 3 times for 5 min with PBS (300 μL). The plates so prepared were stored at 4 ◦C for up to 1 month. The plates in the biological assays were irradiated with UV for 30 min before use.
