*3.11. MTS Metabolic Activity Assay*

Codfish collagen in 20 mM acetic acid with increasing concentration (0–1000 μg/mL) were added to a 48-well plate and evaporated at room temperature in an orbital shaker. Plates were sterilized by 15 min exposure to a 1.2 W UV lamp Omnicure series 2000 EXFO S2000-XLA (Omnicure, Bleichenbach, Germany). MRC-5 cells were seeded at 5 × 104 cells/mL in the collagen containing wells. Wells without collagen or containing 5% DMSO were used as negative and positive controls of cytotoxicity, respectively. Cells were cultured for 24 h at 37 ◦C in a humidified 5% CO2 atmosphere. Metabolic activity was measured using a CellTiter 96® kit (Promega Corporation Madison, USA) according to the manufacturer's instructions. Absorbance was recorded at 490 nm in a Microplate Reader-Gen 5 2.0 SYNERGY HT (Biotek, Luzern, Switzerland).
