Optimization of human mesenchymal stem cell isolation from synovial membrane: Implications for subsequent tissue engineering effectiveness

Synovium-derived mesenchymal stem cells (SDMSCs) are one of the most suitable sources for cartilage repair because of their chondrogenic and proliferative capacity. However, the isolation methods for SDMSCs have not been extensively characterized. Thus, our aim in this study was to optimize the processes of enzymatic isolation followed by culture expansion in order to increase the number of SDMSCs obtained from the original tissue. Human synovium obtained from 18 donors (1.5 g/donor) was divided into three aliquots. The samples were minced and subjected to collagenase digestion, followed by different procedures: Group 1, Tissue fragments were removed by filtering followed by removing floating tissue; Group 2, No filtering. Only floating fragments were removed; Group 3, No fragments were removed. Subsequently, each aliquot was sub-divided into two density subgroups with half. In Group 1, the cell-containing media was plated either at high (5000 cells/cm²) or low density (1000 cells/cm²). In Groups 2 and 3, the media containing cells and tissue was plated onto the same number of culture dishes as used in Group 1, either at high or low density. At every passage, the cells plated at high density were consistently re-plated at high and those plated at low density were likewise. The expanded cell yields at day 21 following cell isolation were calculated. These cell populations were then evaluated for their osteogenic, adipogenic, and chondrogenic differentiation capabilities. The final cell yields per 0.25 g tissue in Group 1 were similar at high and low density, while those in Groups 2 and 3 exhibited higher when cultured at low density. The cell yields at low density were 0.7 ± 1.2 × 10⁷ in Group 1, 5.7 ± 1.1 × 10⁷ in Group 2, 4.3 ± 1.2 × 10⁷ in Group 3 (Group 1 vs Groups 2 and 3, p < 0.05). In addition, the cells obtained in each low density subgroup exhibited equivalent osteogenic, adipogenic, and chondrogenic differentiation. Thus, it was evident that filtering leads to a loss of cells and does not affect the differentiation capacities. In conclusion, exclusion of a filtering procedure could contribute to obtain higher number of SDMSCs from synovial membrane without losing differentiation capacities.