Accumulation of magnetically labeled rat mesenchymal stem cells using an external magnetic force, and their potential for bone regeneration.

We evaluated the effect of a novel mesenchymal stem cell (MSC) delivery system using magnetic beads and an external magnetic force, and investigated the osteogenic potential of MSCs coupled with magnetic beads in vitro. MSCs were isolated from the bone marrow of 8-week-old Sprague Dawley green fluorescent protein rats, and expanded in a monolayer culture system. Magnetic beads (Ferri Sphere 100C) with carboxyl groups on the surface were conjugated to anti-rat CD44 mouse monoclonal antibodies by an amide linkage. Expanded MSCs were then combined with the magnetic beads and the MSC-magnetic bead complexes were seeded onto phi100 mm dishes at low density (5 x 10(3) cells/dish) with or without the influence of an external magnetic force provided by a neodymium magnet and supplemented with osteogenic differentiation medium. The complexes could be accumulated effectively by the influence of the external magnetic force. Moreover, the complexes could also differentiate into the osteogenic lineage in the monolayer culture system, as verified by alizarin red staining and RT-PCR for alkaline phosphatase and osteocalcin expression. These findings clearly demonstrate the possibility of a novel cell delivery system using MSCs with magnetic beads and an external magnetic force for bone regeneration. If this treatment option is established, it will be minimally invasive when compared to conventional treatments. Copyright 2007 Wiley Periodicals, Inc.