Daily news

1 March 2010

Star and flower-shaped moulds tell stem cells what to be

Growing cells in star and flower-shaped moulds may sound frivolous. But this difference is enough to dictate whether human cells become fat or bone.

It’s the first time geometry alone has been shown to shape a cell’s fate, and could lead to new ways of coaxing stem cells into becoming specific tissues for transplant into patients, using physical, not chemical, cues.

Milan Mrksich at the University of Chicago in Illinois and colleagues created moulds, 50 micrometres wide, rather like miniature cookie cutters, in shapes including stars, flowers, squares, pentagons and circle. Into each, they placed a single, human bone marrow cell. A type of stem cell, these immature cells are precursors to blood, bone and fat. The moulds were bathed in a broth of chemicals that encourage cells to become fat and bone.

Despite experiencing identical chemical conditions, 70 per cent of cells sitting in angular moulds, such as stars or thin rectangles, matured into bone. However, cells grown in more curvy moulds, such as circles or flower shapes, were more likely to become fat.


From flower to fat

Mrksich’s team conclude that the deciding factor is the availability of corners, which provide points for cells to push against and sprout internal “stress filaments”. These springy nanocables span cells and form their inner skeletons.

In star-shaped moulds, the sharp corners trigger the growth of long strong filaments, leading to hard bone cells, says Mrksich. By contrast, the rounded edges of flower-shaped moulds encourage the cells to grow short soft filaments, leading to fat cells.

Geometry almost certainly influences the fate of cells in their natural setting in the body. “Cells change their geometries and mechanics throughout development and as they move through the body,” says bioengineer Christopher Chen of the University of Pennsylvania, Philadelphia. Cells may have evolved to use these changes as triggers for switching on genes that guide their development.

Physical forces such as pressure from moving fluid or air are also known to alter cells’ fate.


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