MTT Assay

The biocompatibility was performed by MTT test (tetrazolium salt, [3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide]; Sigma-Aldrich, Milan, Italy). Briefly, MTT was solubilized at 2.5 mg/mL in PBS (phosphate buffer solution, Sigma-Aldrich, Milan, Italy). At prefixed days, the medium in each well was removed and 50 μL of MTT solution plus 100 μL of PBS were added and subsequently put in contact with the cell substrates at 37 ◦C for 3 h in the incubator. Then, MTT solution was removed from each well and 100 μL of dimethylsulfoxide (DMSO, Sigma-Aldrich, Milan, Italy) was added. The absorbance was read using an ELISA Plate Reader at L = 570 nm (with reference L = 690 nm).

#### SEM Analysis

The substrates were then washed three times with PBS and dehydrated with ethanol solutions at increasing concentrations (50–75–100% *v*/*v*). The scaffolds were then removed from culture wells, applied onto stubs, sputtered with graphite and analyzed by SEM, as previously described.
