Controlling a Stem Cell's Form Can Determine Its Fate

Tissue engineering seeks to repair or re-grow damaged body tissues, often using some form of stem cells. Stem cells are basic repair units in the body that have the ability to develop into any of several different forms. The NIST experiments looked at primary human bone marrow stromal cells, adult stem cells that can be isolated from bone marrow and can "differentiate" into bone, fat or cartilage cells, depending.

"Depending on what?" is one of the key questions in tissue engineering. How do you ensure that the stem cells turn into the type you need? Chemical cues have been known to work in cases where researchers have identified the proper additives—a hormone in the case of bone cells. Other research has suggested that cell differentiation on flat surfaces can be controlled by patterning the surface to restrict the locations where growing cells can attach themselves.

The experiments at NIST are believed to be the first head-to-head comparison of five popular tissue scaffold designs to examine the effect of architecture alone on bone marrow cells without adding any biochemical supplements other than cell growth medium. The scaffolds, made of a biocompatible polymer, are meant to provide a temporary implant that gives cells a firm structure on which to grow and ultimately rebuild tissue. The experiment included structures made by leaching and foaming processes (resulting in microscopic structures looking like clumps of insect-eaten lettuce), freeform fabrication (like microscopic rods stacked in a crisscross pattern) and electro spun nanofibres (a random nest of thin fibres). Bone marrow stromal cells were cultured on each, then analyzed to see which were most effective at creating deposits of calcium—a telltale of bone cell activity. Microarray analysis also was used to determine patterns of gene expression for the cultured cells.

The results show that the stem cells will differentiate quite efficiently on the nanofibre scaffolds—even without any hormone additives—but not so on the other architectures. The distinction, says NIST biologist Carl Simon, Jr., seems to be shape. Mature bone cells are characteristically long and stringy with several extended branches. Of the five different scaffolds, only the nanofibre one, in effect, forces the cells to a similar shape, long and branched, as they try to find anchor points. Being in the shape of a bone cell seems to induce the cells to activate the genes that ultimately produce bone tissue.

COMPAMED.de; Source: National Institute of Standards and Technology (NIST)