*2.8. Scanning Electron Microscopy*

The seven-day spheroids of HepG2 and HEK 293 cells were fixed with a 4% paraformaldehyde at 4 ◦C for 24 h. Fixed spheroids were rinsed with PBS (Sigma-Aldrich, St. Louis, MO, USA), dehydrated using a graded ethanol series (50%, 70%, 80%, 90%, 96% and 100%) and then immersed to mixture of ethanol and hexamethyldisilazane (HMDS; Sigma-Aldrich, St. Louis, MO, USA) in a ratio 1:1 for 10 min, and then to 100% HMDS for 10 min. Spheroids were fixed on a sample stand using double-sided carbon tape and dried overnight in air. Spheroids were sputter coated with 10 nm gold/palladium and analyzed using a scanning electron microscope EVO 10 (Carl Zeiss AG, Oberkochen, Germany) at an accelerating voltage of 10 kV.
