Mesenchymal stem cells (MSCs), which can differentiate into multiple mesodermal tissues, may be useful for autologous cell transplantation, if MSCs, which are isolated from bone marrow in small numbers, can be expanded in vitro. We developed a combined methodological approach to enrich and proliferate MSCs in vitro using magnetic nanoparticles. Our magnetite cationic liposomes (MCLs), which have a positive surface charge in order to improve adsorption, accumulated in MSCs at a concentration of 20 pg of magnetite per cell. The MCLs exhibited no toxicity against MSCs in proliferation and differentiation to osteoblasts and adipocytes. The MSCs magnetically labeled by MCLs were enriched using magnets and then cultured, resulting in much higher density (seeding density, 1000 cells/cm2) than in ordinary culture (seeding density, 18 cells/cm2). When MSCs were seeded at high density using MCLs, there was a 5-fold increase in the number of cells, compared to culture prepared without MCLs. Our results suggest that this novel culture method using magnetic nanoparticles can be used to efficiently expand MSCs for clinical application.
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