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Over a million stroke survivors in the United States have significant disabilities even after rehabilitation–and this number is expected to rise as the baby-boom generation ages.

But there’s hope that lost abilities can one day be restored, thanks to a collaboration between chemical and biomedical engineering professor Robert Langer, ScD ‘74, and neuroscience professor Mriganka Sur. The team, which is funded as part of the $60 million MIT-DuPont Alliance, has made significant progress toward creating implants to replace stroke-damaged areas of the brain.

“The goal is to make things the way they were in the beginning [before the stroke],” Langer says. To replace the damaged areas, the team intends to grow brain cell networks on a scaffold that they will surgically implant in the affected region. Drugs embedded in the scaffold will encourage the cells to grow, make connections with the native cells nearby, and, the researchers hope, restore lost abilities to the stroke patient.

Researchers so far have demonstrated the ability to coax nerve cells to form networks in vitro. Before the brain cells can be implanted, however, they must be prepared for their new roles, in much the way that high school students must learn calculus if they hope to succeed in an MIT engineering course, says Nathan Wilson, a project collaborator and a postdoc in brain and cognitive sciences who works with Sur. Cells intended to replace visual-processing areas of the brain, for example, need to be trained with signals similar to those sent by the eyes. In an important step in the research, Wilson showed that cells grown in a dish and exposed to electrical impulses roughly similar to those from the eyes will respond to these signals by forming networks.

In another important step, Paul George, a graduate student in Langer’s lab, has demonstrated that an electrically conductive plastic the team hopes to use as a
scaffold is biocompatible. When it was implanted for six weeks in living rats, neurons grew around and even through it, via holes in the material.
Sur says a neural implant containing networked cells for stroke patients is probably 20 years away from completion, since the researchers still must learn how best to make the scaffolds, to pair them with drugs that encourage nerve growth, and to train the neurons. Perhaps most important, they need to find cells the brain will not reject. This might mean modifying stem cells or altering a person’s own mature cells so that they grow like young neurons.

Intermediate achievements may be much closer, though. The process of learning how to make an implant–which Sur says is “like making a piece of the brain in a dish”–should lead to many basic science breakthroughs about the way brains work and repair themselves. For example, the electrode grids used to train the cell networks can also be used to read the signals sent through the networks as they form, revealing what connections are being made, says Wilson.

The work may lead to other new therapies. For instance, the conductive plastic might function as an electric splice, bridging gaps caused by spinal injury. It might also be loaded with drugs and implanted to encourage neurons around an injury to rewire themselves more extensively, promoting stroke recovery. Such advances would go far toward improving people’s lives, as the researchers move nearer their ultimate goal. – By Kevin Bullis, SM ‘05

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