This video segment adapted from NOVA scienceNOW examines the work of medical researchers who are developing new techniques to repair and replace failing human organs by growing them from a patient’s own cells, thus preventing organ rejection. Organs can be grown on both synthetic scaffolds and the nonliving protein skeleton of an existing organ. If perfected, the techniques could save the lives of thousands of people who die before donor organs become available.
More than 110,000 people in the United States are waiting for a life-saving organ transplant. Each day, nearly 20 of them will die. Those who do receive transplants face the risk of rejection, as the immune system attacks the foreign tissue, prompting the lifelong need for immunosuppressant drugs.
Transplantation also raises a number of bioethical concerns: how to define when a donor has died, who can give consent for organ donation, when and how consent can be given, the medical treatment of donors, and organ trafficking.
The field of regenerative medicine holds the promise of solving these problems through the repair or replacement of organs or tissues, ideally, by using a patient’s own cells. Regenerative techniques include stem cell therapies, in which cells are injected into an organ or tissue to help it repair itself, and transplantation of organs or tissues grown in a laboratory. An organ grown from a patient’s own cells is less likely to be rejected because the immune system will recognize the tissue and not attack it.
In the 1990s, researchers at Massachusetts General Hospital in Boston successfully grew cartilage from cow cells on synthetic biodegradable material shaped like a human ear. The scaffold was seeded with the cartilage cells and implanted under the skin of a mouse, where it had the necessary nutrients and blood supply to grow. The goal of the experiment was not to grow human ears on mice, but to prove that new tissue engineering techniques could successfully grow a viable organ. Researchers are working to grow human ears by seeding a similar synthetic biodegradable scaffold with a patient’s own cartilage cells and using the patient’s blood supply.
Unlike the ear, which is made of cartilage, most organs have much more complex internal structures—including intricate circulatory systems, valves, and chambers. Since synthetic scaffolds for organs are very difficult to engineer, Doris Taylor and Harald Ott at the University of Minnesota found a way to start with existing organs.
Working with rat, pig, and cadaver organs, Ott discovered a way to strip all of the cells from an organ's extracellular matrix. The extracellular matrix is a "skeleton" made of fibronectin protein that internally supports an organ. Through trial and error, Ott discovered that a chemical called sodium dodecyl sulfate (SDS) dissolves the cells but leaves the underlying protein matrix intact. SDS is a detergent that dissolves cells by disrupting the lipid (fat) bilayer in the cell membrane. The cells are then washed away. In lower concentrations, SDS is used in shampoo to break down and wash away oil and dirt while leaving hair, which is made of a protein called keratin, intact.
Ott and Taylor next seeded a matrix from a mouse heart with a mixture of heart cells and stimulated it with an electrical signal. The matrix retained the original structures of the blood vessels, which the researchers used to deliver oxygen to the cells. After eight days, the laboratory heart began to beat. The technique was repeated with rat lungs, which were transplanted into a rat and functioned. If the new technique is perfected, doctors may one day be able to extract cells from a patient and grow whatever organ that patient needs.
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