Tissue engineering is the art of taking a sample of cells and “growing” them under the right conditions to form tissue-even whole organs. Skin, bone, and cartilage products based on the technology are already on the market, and engineered bladders and heart valves are showing promise in the lab (see “The Human Body Shop,” TR April 2001).
The driving force behind tissue engineering is the shortage of human organs for transplantation. But that isn’t the only factor. Transplants are expensive and technically difficult, and patients are bound to lifelong drug regimes to prevent their bodies from rejecting the organs. A patent based on the work of Jay and Charles Vacanti, siblings who are pioneers in the field, could begin to change all that.
The challenge researchers face is getting cells to grow into tissue with the same shape and properties as native tissue. One common method involves adding cells to a biodegradable polymer scaffold, which is then implanted in the body. The problem is that it’s hard to keep the cells attached to the polymer. “You need to make sure they’re evenly distributed throughout the scaffold, or else they fall and clump together,” says Linda Griffith, a tissue engineer at MIT. Another approach is to mix cells in a hydrogel, a Jell-O-like polymer, to keep them in place; the hydrogel, however, can’t hold a three-dimensional shape.
The Vacantis decided to combine these two techniques. The first part of their patented method involves taking a polymer scaffold and molding it into the shape of a tissue, like a blood vessel or a piece of liver; the scaffold is then immersed in a liquid hydrogel containing tissue-precursor cells. When implanted in the body, the hydrogel hardens, keeping the cells in place. “It’s like reinforced concrete,” says Jay Vacanti, based at Massachusetts General Hospital. “And the new tissue looks just like the one it was replacing.”
Charles Vacanti’s lab at the University of Massachusetts Medical Center tested the system on rats by removing a section of the spinal cord to simulate a spinal cord injury. They then implanted a polymer scaffold that had been seeded with a hydrogel mixture containing neural precursor cells. After a couple of months, not only did new tissue form, but the precursor cells developed into both regular nerve cells and the insulating glial cells that facilitate transmission of nerve impulses. As a result, most of the animals regained the ability to move their lower limbs.
In the future, the technique could also be used to repair birth defects or replace lost joint cartilage in people with arthritis. And, further down the road, the Vacantis hope to use the technology for growing whole organs.