*2.4. Prestoblue Assay*

A Prestoblue® working solution was prepared in a growth culture medium without phenol red according to the manufacturer's instructions. Briefly, the culture medium was removed from cell culture wells and a Prestoblue working solution was added and incubated at 37 ◦C, 5% CO2. After 3 h, the well volumes were collected in a new 96-well plate and the absorbance was read at λ = 570 nm (experimental) and λ = 600 nm (reference wavelength for normalization) using a Victor Multilabel plate-reader (Perkin-Elmer, Wellesley USA).

## *2.5. Reduced Glutathione (GSH) Level Measurement*

A monochlorobimane (MCB) fluorescent probe (Sigma-Aldrich, St. Louis, MO, USA) was used to determine relative intracellular GSH levels as previously reported [34] with some modifications. After 24 h of treatment, the cell culture medium was removed from 3D samples and the scaffolds were transferred to 1.5 mL tubes. The cells were incubated for 15 min in DMEM with 1% FBS containing 50 μM MCB, and for a further 15 min in DMEM with 0.5 mg/mL collagenase I and 50 μM MCB (Sigma-Aldrich). Cells collected by digestion of the scaffold were centrifuged at 250× *g*. Cells were resuspended in phosphate-buffered saline (PBS) and plated on black 96-well plates. The fluorescence was measured at 355 nm (excitation) and 460 nm (emission) using a Victor Multilabel plate-reader (Perkin-Elmer, Wellesley USA). GSH levels were normalized on the base of the Crystal Violet (CV) assay.
