Researchers at the Massachusetts Institute of Technology (MIT; Cambridge, USA) wished to create a chemically defined, xeno-free, feeder-free synthetic substrate that could support robust self-renewal of fully dissociated human embryonic stem and induced pluripotent stem cells. To do so, they first created about 500 polymers that differed in the physical properties of their surfaces--including roughness, stiffness, and affinity for water--to find an appropriate material that might play a role in stem-cell growth. The researchers then grew stem cells on each of them and analyzed each polymer's performance. After correlating surface characteristics with performance, they found that there was an optimal range of surface hydrophobicity (water-repelling behavior), but that varying roughness and stiffness did not seem to have much effect on cell growth.

The researchers also adjusted the composition of the materials, including proteins embedded in the polymer, and found that the best polymers contained a high percentage of acrylates (a common ingredient in plastics), had a moderate wettability, and employed integrin αvβ3 and αvβ5 engagement with adsorbed vitronectin to promote proliferation colony formation. Using their best-performing material, the researchers induced both embryonic and pluripotent stem cells to continue growing and dividing for up to three months. They were also able to generate large quantities of cells, numbering in the millions. The study was published in the August 22, 2010, issue of Nature Materials.

"For therapeutics, you need millions and millions of cells,” said lead author Krishanu Saha, Ph.D., of the department of chemical engineering. "If we can make it easier for the cells to divide and grow, that will really help to get the number of cells you need to do all of the disease studies that people are excited about.”

Both human embryonic stem cells and induced pluripotent stem cells can self-renew indefinitely in culture; however, present methods to clonally grow them are inefficient and poorly defined for genetic manipulation and therapeutic purposes, since a layer of mouse cells or proteins are used to stimulate the stem-cell growth; however, these same cells are likely cause an immune reaction if injected into a human patient.

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