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ADDING tiny particles that release the appropriate chemical signals could
help cell implants repair or replace damaged tissue. The technique has already
helped fetal brain cells survive and thrive.

鈥淚t鈥檚 a significant advance in tissue engineering,鈥� says Robert Langer, a
tissue engineer at the Massachusetts Institute of Technology in Cambridge.

Getting the right biochemical environment around implanted cells is vital.
Without it, they will die or develop into the wrong kind of cell. For instance,
nerve growth factor (NGF) has to be supplied to the experimental cell
transplants intended to treat spinal cord injuries, Parkinson鈥檚 and Huntington鈥檚
diseases.

But taking NGF as a drug can cause extreme side effects such as burning
sensations. To avoid this, researchers have tried injecting NGF directly into
the brain. 鈥淭he problem is that it doesn鈥檛 last for very long,鈥� says biochemist
Mark Saltzman of Cornell University in Ithaca, New York.

Instead, Saltzman鈥檚 team made microscopic particles containing NGF from the
slow-dissolving material used for surgical sutures and mixed them with fetal
brain cells containing cholinergic neurons. When the researchers implanted this
mix into the brains of healthy adult rats, they found that levels of NGF around
the implant peaked after seven days and dropped back to normal levels by three
weeks.

Higher levels of a brain enzyme called choline acetyltransferase suggested
that the implanted cholinergic neurons were thriving. 鈥淚t鈥檚 pretty convincing
evidence that indeed it was working,鈥� says Jeffrey Kocsis, a neurobiologist at
Yale University.

Langer agrees. 鈥淚t鈥檚 the first time that cells, synthetic elements and
controlled release have been combined and programmed to aid cell
transplantation,鈥� he says. 鈥淭his approach could be used to affect any type of
cell or tissue.鈥�

The microparticles could also be tailored to deliver any protein or drug,
says Saltzman. And if coated with molecules that attract particular cells, the
drug could be delivered only to those cells.