The Real Action
Baker’s efforts may or may not pay off in a breakthrough for gene therapy (the field is littered with promising strategies that never panned out). But whether this specific approach is successful or not, it reflects an extremely important development in medicine on the very smallest scale. A typical human cell, like the red blood cells that course through your veins, is five micrometers in diameter. But much of the real action in biology occurs at a considerably smaller level. DNA, for example, is less than three nanometers in diameter-about 100 times smaller than the cell. Many common proteins are only a few nanometers across.
Biomedical researchers have never been able to play effectively on a field this small. To do so now, they are importing techniques and expertise from other areas. Semiconductor manufacturers have been making features on silicon chips only a few hundred nanometers across for several years. Mauro Ferrari, among others, is taking these fabrication techniques and applying them to medicine. A professor of internal medicine and mechanical engineering at Ohio State and director of the university’s new biomedical engineering center, Ferrari has made tiny silicon capsules that can hold healthy cells to replace ones that are not functioning; if, say, the pancreatic cells of a diabetes patient are not working, capsules containing replacement cells can be implanted beneath the patient’s skin. Supplying new cells to the body could be a very valuable way to treat certain diseases such as those caused by enzyme or hormone deficiencies, and various medical researchers have been wrestling with the strategy for years. But as in gene therapy, immune reactions are a major problem. Replacement cells are foreign to the body and are therefore attacked by the body’s immune system, with disastrous results.
But Ferrari has come up with a scheme to swindle the immune system using the tools of nanotechnology. When the immune system sees something foreign, it dispatches antibodies to attack it. If, reasoned Ferrari, you could block the antibodies using an artificial barrier, the immune system wouldn’t be able to see the transplanted cells. Ferrari fabricated his silicon capsules to include membranes with pores small enough to screen out antibodies-but large enough to let desirable molecules flow in and out. “The biological recognition molecules don’t know what the hell is inside,” says Ferrari.
The concept is elegant. But in practice, it’s not easy to make nanoholes small enough to keep antibodies out. It turns out that antibodies can get through anything larger than about 18 nanometers (the exact size is still uncertain). Photolithography tools for making state-of-the-art integrated circuits are good for making features only as small as a few hundred nanometers. By adapting these methods used in the semiconductor industry, however, Ferrari managed to create holes only a few nanometers wide.