To improve those odds, tissue engineers are trying to harness the power of stem cells by designing three-dimensional plastic molds, called scaffolds or matrices, that resemble organs or body parts. When a soup of nutrients and stem cells is squirted over a matrix, stem cells may grow into a hunk of tissue that can later be transplanted into a waiting patient. Somehow, the matrix imparts critical organizing information to the cells.
Researchers have successfully created simple tissues such as skin, cartilage, and bone. More complex structures—an ear and teeth—have also been grown. But the hope is that a complex organ, like a kidney or a heart, can be built.
Customized hearts, arteries, or valves would be a boon because substitutes leave much to be desired. Prosthetic devices can’t grow with young patients. Donor valves, whether from cadavers or pigs, fail after 10 to 15 years and sentence the recipient to a lifetime of immunosuppressive drugs to combat rejection. A heart, artery, or valve built from a patient’s own cells may never be rejected.
In what are among the earliest clinical trials, German researchers have created hybrid replacement valves. They started by removing valves from donor cadavers. Then they stripped the valves of rejection-provoking cells, leaving only an elastin-and-collagen matrix, and seeded the valves with stem cells taken from a vein in the leg or arm. The stem cells knit themselves into this donor matrix and, when the valve was transplanted, functioned well for more than three years. Critics of the protocol say it’s not ideal, because donor heart valves are still in short supply. So researchers are hammering away on two fronts: nailing down how stem cells work—and constructing better matrices.
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