Bovine serum albumin (bsa)

For the transfection, 3 × 10⁵ EA.hy926 cells, BJ fibroblasts, or WB_MSCs were seeded per well of a six-well plate, and the cells were cultivated overnight at 37°C in a 5% CO₂ atmosphere. To generate transfection complexes, called lipoplexes, we incubated 2.5 μg TE mRNA with 4 μL Lipofectamine 2000 in 500 μL OptiMEM I reduced serum-free media (Invitrogen, Carlsbad, CA, USA) for 20 min at RT. Cell medium was discarded and cells were washed once with 1 mL DPBS. Afterward, 500 μL OptiMEM was added to each well of the six-well plate. Subsequently, 500 μL OptiMEM containing lipoplexes was added to the wells. Additionally, 500 μL OptiMEM containing only 4 μL Lipofectamine 2000 was added as a control. After 4 hr of incubation at 37°C, transfection mixtures were removed and 1 mL cell culture medium without phenol red was added to each well. Cells were cultivated at 37°C and 5% CO₂ overnight. The supernatant was collected and stored at −80°C. Cells were detached using 0.05% Trypsin-EDTA (Life Technologies) and 0.05% TNS in 0.1% BSA (PromoCell, Heidelberg, Germany).

For the 2D culture, primary UCMSCs (PromoCell, cat. No. C-12971) were cultured in petri dishes at 37 °C, 5 % CO₂, and 95 % humidity. The cells were kept in an MSC growth medium (Promo Cell, Heidelberg, Germany) with 10 % (v/v) FBS (Life, NY, USA) and a 1 % (v/v) antibiotic-antimycotic solution. The medium was changed every three days. Cells were passaged with Hepes BSS (Promo Cell, Heidelberg, Germany), 0.04 % (w/v) trypsin-EDTA (Promo Cell, Heidelberg, Germany), 0.05 % Trypsin inhibitor 0.1 % BSA (Promo Cell, Heidelberg, Germany) when they reached 80–90 % confluency. For the 3D culture of UCMSCs (second passage), the culture material was prepared by adding 0.05 % (v/v) Cellhesion® (Nissan Chemical Co., Ltd., Tokyo, Japan) to the above medium, in accordance with the manufacturer's instructions. The material was then seeded in 100 ml non-adherent flasks (Corning, NY, USA) at a density of 1 × 10⁶ UCMSCs/flask. This 3D cell system was cultured at 5 % CO₂ and 37 °C, and the medium was changed every three days by centrifugation (cells along with materials, 100 g/min for 5 min) and resuspension.