Caltech scientists develop first microscopic system of pumps and valves made from soft materials

PASADENA—Researchers at the California Institute of Technology have developed a pump that is less than one-half the width of a human hair. The device is a breakthrough in the 3-D microfabrication of soft materials and could be applied to revolutionize and simplify many technologies, including drug discovery and delivery, according to Caltech applied physics professor Stephen R. Quake and his colleagues, who report their findings in the April 7 issue of Science.

Unlike the silicon-based micromachining techniques used for computer chips, this team has developed a technique called multilayer soft lithography, which is essentially an intricate casting of soft rubber. The work is an extension of soft lithography casting, originally developed by George Whitesides at Harvard University.

"Basically, it's plumbing on a very small scale," says Quake. "We are trying to show that it is useful to make microdevices out of soft rubber for certain applications, rather than the hard materials like glass or silicon used in traditional micromachining. In order to make a valve, one needs to figure out how to make it seal, which is usually done with a rubber washer. We made the entire valve out of the sealing material."

The pump is made possible because of the material's softness and pliability. Embedded in a small clear rubber chip the size of a postage stamp, the pump is actually a series of tiny, multilayer channels that each measure 50 by 30 by 10 microns. By contrast, a human hair is about 100 microns wide.

Operation of the pump is similar to the peristaltic motions that make human digestion possible. By applying pressure in one of the channels, another channel above it or below it in the 3-D matrix can be closed off, thereby allowing the channel to act either as a pump or as a valve.

While the research is basic and mainly aimed at demonstrating the feasibility of the technique, Quake says the pump could have a number of practical applications, including drug delivery, one day possibly enabling doctors to implant a biocompatible device about the size of a postage stamp into a patient's body to deliver drugs for chronic disorders such as allergies, pain, diabetes and cancer.

The device may allow the drug to be delivered in a time-released manner customized for each patient. In addition to delivering the drug, the device could also contain a microsized component that would enable regular monitoring of the patient's condition.

Quake's own lab intends to use the microfabricated valves and pumps in two devices: a DNA sizer, which is a replacement for the current technique known as gel electrophoresis; and a cell sorter, a machine that physically separates microscopic materials such as bacteria or viruses. Both devices originated from research in Quake's lab. Caltech has licensed this technology to Mycometrix Corporation of South San Francisco, which will apply it to develop a variety of commercial products.

In addition to Quake, the others involved in the research are Axel Scherer, a professor of electrical engineering, applied physics, and physics at Caltech; Marc Unger, a postdoctoral scholar in applied physics; Hou-Pu Chou, a graduate student in electrical engineering; and Todd Thorsen, a graduate student in biochemistry.