2.1. Cell culture
Primary human cells HDFn (Gibco; Thermo Fisher Scientific, Waltham, MA, USA), HDMEC (PromoCell, Heidelberg, Germany), and NHEK (Lonza, Basel, Switzerland) were cultured in standard incubator conditions (37 ?C, 5%CO2, and 95% humidity). NHEK were expanded inside T75 culture flasks (Sarstedt, Nu¨mbrecht, Germany) coated with laminin 511 (Biolamina, Sundbyberg, Sweden) according to the manufacturer´s instructions, whereas for HDFn and HDMEC, uncoated flasks of the same type were used. HDFn were cultured in DMEM/F-12 (Gibco; Thermo Fisher Scientific, Waltham, MA, USA) supplemented with 5% heat inactivated fetal bovine serum and 1% penicillin and streptomycin. HDMEC were grown in complete microvascular endothelial cell growth medium MV2 (PromoCell, Heidelberg, Germany), completed with 1% antibiotic–antimycotic. Finally, NHEK were cultured in keratinocyte cell basal medium, KBMGoldTM supplemented with the KGM-GOLD TM Bullet Kit TM (Lonza, Basel, Switzerland). HDFn and HDMEC were used between passages 5 and 6, and NHEK were used in passage 2. When 80% confluence was reached, the cells were enzymatically harvested after 8 min of incubation with TrypLE (Thermo Fisher Scientific, Waltham, MA, USA) at 37 ?C. Thereafter, they were used for 3D culture.