Mesenchymal stem cell spheroid, generated from rat mesenchymal stem cell lines. (A) Parental cell line grown permanently as a monolayer culture. (B) and (C) The generation of mesenchymal stem cell (MSC) spheroids. Cellular aggregation of MSCs was observed 2 h after a microplate culture (B). A cell aggregation formed a compact spheroid at 24 h (C). Scale bars = 100 μm (a and c) and 1 mm (B).