*2.2. Human Bone Marrow-Derived Mesenchymal Stromal Cells*

The study was approved by the Ethics Committee of the Saarland Physicians Council (*Ärztekammer des Saarlandes*, reference number Ha06/08). All patients provided informed consent before being included in the study, which was performed in accordance with the Helsinki Declaration. Bone marrow aspirates (~15 mL; 0.4–1.2 <sup>×</sup> <sup>10</sup><sup>9</sup> cells/mL) were prepared from the distal femurs of patients undergoing total knee arthroplasty (n = 12, age 75 ± 3 years). Bone marrow-derived human mesenchymal stromal cells (hMSCs) were isolated by washing and centrifuging the aspirates in Dulbecco's modified Eagle's medium (DMEM) and resuspending the pellet in red blood cell lysing buffer with DMEM (1:1) [44,45]. The mixtures were washed and resuspended in DMEM, 10% fetal bovine serum, 100 U/mL penicillin, and 100 μL/mL streptomycin (growth medium) for cell plating and maintenance in T75 flasks at 37 ◦C under 5% CO2. A medium change was performed after 24 h using growth medium with recombinant FGF-2 (1 ng/mL) for expansion [44,45], followed by changes every 2–3 days and replating when the cells reached a density of 85%, using cells at no more than passage 1–2.
