2.3 Mechanical properties
The effect of the agarose concentration on the Young’s modulus of the agarose-collagen hydrogels was evaluated by uniaxial compression test. The correlation with time and temperature was also investigated. Briefly, the hydrogel samples were incubated in PBS at 37 °C in a humidified atmosphere with 5% CO2. At fixed time points (0, 1, 4, and 8 days), cylinders of 8 mm were punched out and loaded into the testing chamber. All tests were performed with a universal testing machine ZwickiLine (Zwick Roell, Germany) fitted with 10 N load cell. Loaded samples were hydrated in PBS at 37 °C and subjected to compression with a displacement rate of 0.01 mm/s, until 80% strain (L. C. Gallo et al., 2018; Monaco, Cholas, Salvatore, Madaghiele, & Sannino, 2017). The compressive modulus was calculated by linear fitting between 2 and 10% of strain of the stress-strain curve. The test was performed in triplicate for each sample type and time point.