*2.3. Sterilization and Cell Culture*

The samples were first placed in 12-well plates and then immersed in 1 mL of ethanol for 30 min. The plates were then placed in a sterile hood where they were exposed to UV for 30 min. To ensure perfect sterilization, the samples were then cleaned with bleach and then autoclaved for 4 h at 120 ◦C.

For each sample (P, S and S + P), the tests were performed three times with MSCs from three different donors. The cells were thawed one week before seeding and all manipulations were performed under hood using sterile equipment. The inoculated samples were placed in an incubator at 37 ◦C, 5% CO2 and 90% humidity. After 45 min, 1 mL of α MEM (Minimum Essential Medium) was added per well and the plates were put back into the incubator. The culture medium was changed twice a week.

The viability of the cells was checked after 3, 7, 14 and 21 days. For this, an Alamar Blue test (a resazurin blue colored indicator which transforms into pink resorufin thanks to the reducing power of mitochondria) was used. The percent difference in reduction is proportional to the metabolic activity of the cells, and, thus, to their viability. The tests were done in a dark sterile hood and the color change was detected using a spectrometer.
