14 January 2008

The Quest for Replacement Body Parts

Since 1967, when Christiaan Barnard successfully performed the first successful human to human heart transplant, it has been painfully obvious that there are not enough human hearts available to meet the demand. Surgeons have tried various approaches to replacing damaged and worn out hearts--including baboon hearts, refrigerator sized machine replacement hearts, and most reacently, the AbioCor totally implantable artificial heart system. While the AbioCor's batteries can be rechared through the skin, they will eventually have to be replaced. Machine hearts are subject to failure of various types, and experience with them is still only short term.

Eventually, hearts will be "printed", along with other replacement organs. Other organs, such as the urinary bladder, have already been synthetically produced and implanted. But the heart's fibrous skeleton is too complex for scientists to mimic in the lab--to this point.

So lab scientists are learning how to scavenge heart skeletons wherever they can. University of Minnesota scientists have taken dead animal hearts and removed the dead cells--leaving the fibrous infrastructure. By injecting immature heart cells into the scaffolding--in a stepwise manner--they were able to revitalize the heart to the point of beating.
The team took a whole heart and removed cells from it. Then, with the resulting architecture, chambers, valves and the blood vessel structure intact, repopulated the structure with new cells.

"We just took nature's own building blocks to build a new organ," says Dr Harald Ott, a co-investigator who now works at Massachusetts General Hospital. "When we saw the first contractions we were speechless."

The work has huge implications: "The idea would be to develop transplantable blood vessels or whole organs that are made from your own cells," said Prof Doris Taylor, director of the Centre for Cardiovascular Repair, Minnesota, principal investigator.

The method could be used to grow liver, kidney, lung and pancreas, indeed virtually any organ with a blood supply.

In the meantime, researchers continue to work on alternatives--including artificial hearts that spin like a turbine, producing a constant blood pressure rather than a pulse. Such turbine hearts are said to be efficient in small sizes, making it easier to fit size constraints. Such hearts would still have the problem of requiring a power supply.

Rather than replacing the heart, methods of regenerating the existing heart are being developed. Techniques of injecting stem cells into the patient's heart have already produced positive results in some cases. Likewise, procedures that attach "sheets of muscle blasts" to the patient's heart have been successful in Japan. Clearly, it would be preferable if the patient's own heart can serve as a scaffold for cell replacement.

In several pathological processes, however, the underlying structure of the patient's heart has been rendered dysfunctional. Without extensive remodeling surgery, the heart's infrastructure has to be replaced.

In approaching heart replacement, patients, physicians, and families have to weigh the benefits and risks. With the rapid growth in viable choices for replacement, this process will necessarily become more detailed and informed.

Bioprinting organs, and other ways of synthetically reproducing human organs, will be very expensive for a long time. That expense will push experimentation in different directions.

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