BIOENGINEERING
The organ donor shortage has become a critical problem as transplant waiting lists grow longer. Each year, fewer than 10 percent of the 40,000 or so Americans who need a new heart get one. But instead of recruiting more organ donors, why not grow new organs? That's what a team at the Draper Laboratory in Cambridge, Massachusetts, is working to do, by creating a rudimentary circulatory system on a silicon chip. Working under the direction of Joseph Vacanti, a surgeon and tissue engineering researcher at Massachusetts General Hospital, the lab microfabricates a system that may one day lead to producing a functioning human organ.
Tissue engineers have been able to grow the cells of complex organs in the laboratory for some time. But getting those cells to assemble themselves into functioning kidney or liver tissue has proved elusive, because organs require lots of plumbing - capillaries, arteries, and veins - to deliver nutrient-rich blood and to remove wastes.
The Draper Lab's circulatory-system-on-a-chip creates a crude version of that vital plumbing. The team used photolithography to etch a pattern of arteries, veins, and capillaries 10 to 20 microns deep onto 4-inch-diameter silicon wafers. Tissue engineers then seeded the chip with cells taken from the lung of a rat. The cells grew to coat the etched pattern, forming a network of blood vessels. The eventual goal is to create a biodegradable structure that would be implanted into a patient. After the structure degraded, it would leave behind a three-dimensional scaffolding upon which new tissue could grow that mimics the functions of an organ.
The next step for the Draper team is to place successive layers of liver cells onto this circulatory system until it has built a multilayer "wedding cake" of blood vessels and liver cells. Draper hopes to be able to use this technique to generate a complex human organ within a decade.
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