Sorting of human mesenchymal stem cells by applying microfluidic chip filtration combined with inertial focusing

Abstract

Human bone marrow-derived mesenchymal stem cells (hMSCs) are promising cell sources for stem cell therapy because of their low immunogenicity, multipotency and self-renewal capacity. In the recent study, it has been reported that hMSCs consist of heterogeneous subpopulations: rapidly self-renewing (RS) cells, spindle-shaped (SS) cells, and flattened and large (FL) cells. Furthermore, RS and SS subpopulations of hMCSs show higher multipotent capacities than cells in the FL group. Because each subpopulation has different proliferative and multipotent capacities, sorting out a specific subpopulation of cells from total cell population is a significant approach for stem cell researches including cell therapy. In this study, to improve separation efficiency, a channel design combining inertial focusing with microfluidic chip filtration was attempted and applied to the size-dependent separation of hMSCs. The channel networks were designed based on the precise calculations of a model for the fluid flow and cut-off width of the hMSCs to be separated. Polydimethylsiloxane (PDMS)-glass chip was fabricated by means of microelectromechanical system (MEMS) process, and the chip had a main channel for the input of an hMSC suspension, a side channel for cell-free media focusing of cells to the opposite sidewall and several multi-branched channels. Multi-branched channels converged on a seven-turn spiral channel where the hMSCs were focused on certain equilibrium positions. Focused hMSCs can be collected from the outlets by size. In addition, the end of the main channel was converted into a spiral channel where the hMSCs experienced further focusing and exited through the outlets. Eventually, the efficiencies of cell separation were 83% and 98% for the small cells (RS and SS) with high differentiation potential and the large cell (FL) group with low differentiation potential for recovery, respectively. The purities were confirmed to be 99% and 76%, respectively. These result showed higher efficiency and throughput than the result of previous microfluidic chip filtration. Thus, size-dependent sorting of hMSCs by microfluidic chip filtration combined with inertial focusing is expected to hold promise for stem cell research.