2.3. AlamarBlue® Cell Proliferation Assay

For the quantification of chondrocyte proliferation within one week of cultivation, an AlamarBlue^® (Bio-Rad, Feldkirchen, Germany) assay was performed as previously described [30,31]. After 24 h adherence on culture, plastic culture medium was removed and AlamarBlue^® solution (5% in cultivation medium) was added. After 3 h incubation at 37 °C, fluorescence was measured at 555 nm excitation and 590 nm emission by a microplate reader (Infinite M200, Tecan Deutschland, Crailsheim, Germany). This time point was defined as t0 and the AlamarBlue^® solution was replaced by the cultivation medium. After a further 1, 4 and 7 days of cultivation, the analysis was repeated and proliferation activity was calculated in relation to t0.