Cell viability. A commercial LIVE/DEAD Viability/Cytotoxicity Kit (Invitrogen, Thermo Fisher, Sweden) was used to evaluate cell viability according to instructions from the manufacturer. Cell viability was evaluated after 1 and 7 days of culture. Briefly, culture medium was aspirated and the hydrogels were washed with 1X sterile PBS and the then incubated with 0.5 μL/ mL of calcein AM and 2 μL/mL of ethidium homodimer in PBS for 45 min in dark at 37 °C. Live cells were stained green, whereas dead cells were stained red. The cell-carrying hydrogels were imaged with a Zeiss LSM700 confocal microscope (Germany) and 3-D stacking and Z-sectioning was performed using LSM700 software. For each sample, at least five independent z-stacks at 10x magnification were analyzed. Cell viability was calculated as the ratio of live cells to the total number of cells using ImageJ software (n = 3).