Sep. 25, 2001 COLUMBUS, Ohio - Engineers at Ohio State University have mastered a critical step for manufacturing tiny medical devices. This new technique for sealing plastic casings could bring medical nanotechnology closer to reality.
Led by L. James Lee, professor of chemical engineering at Ohio State, the researchers found that their technique aids the flow of medicine and other fluids through such devices, and can even alter the material on the surface of a device to suit different medical applications.
"Plastics have great potential for use in these devices, because they are inexpensive and easy to shape into individual parts, but sealing a tiny casing poses a special challenge," Lee said. "So does altering the characteristics of the plastic to suit different medical tasks. Our method allows someone to do both in one shot."
Lee and his colleagues described the method, called "resin-gas injection assisted bonding," on September 23 at the BioMEMS and Biomedical Nanotechnology World 2001 conference in Columbus, Ohio.
The research team included Kurt Koelling, associate professor of chemical engineering at Ohio State, graduate student Siyi Lai, and undergraduate student Yeny Hudiono. The researchers collaborated with Sylvia Daunert, associate professor of chemistry at the University of Kentucky, and Marc Madou, formerly a professor of materials science and engineering at Ohio State. Madou is now vice president of advanced technology for Nanogen, Inc., a biotech company in San Diego.
BioMEMS, or biomedical microelectromechanical systems, are microscopic medical devices under development around the world. The tiny devices can be smaller than the width of a human hair. Nanotechnology concerns devices even smaller than bioMEMS.
One day these devices could deliver medicine directly to tumors or other sites of disease in the body.
Lee and his colleagues investigated several different techniques for sealing such devices, including welding, gluing, and even sticking parts together with double-sided adhesive tape. Gluing seemed the most promising, but traditional adhesives only gummed up the tiny channels found in microdevices.
Then they hit upon a method for using traditional liquid adhesive in a nontraditional way.
For this initial work, Lee and his colleagues molded a plastic device about the size of a small matchstick. The device consisted of a 100-micrometer wide channel -- about as wide as a human hair -- with a fluid reservoir at each end.
They molded the device in two pieces -- a bottom platform containing the channel and reservoirs, and a lid. They coated both parts with few drops of a commercially-available adhesive called hydroxyethyl methacrylate (HEMA), and fit the two together.
HEMA is often used as a bonding agent for dental appliances. While sticky in its liquid form, HEMA cures to a smooth surface under ultraviolet (UV) light, just as exposed glue on a model airplane dries smooth and shiny.
After coating and filling the device with HEMA, the researchers blew a short burst of nitrogen gas in one end of the device and out the other, forcing the adhesive to coat the inner surfaces on its way out. Finally, they cured the entire device under UV light.
Tests revealed that liquid traveled successfully through the tiny channel between the two reservoirs, with no leaks, so the device appeared to be sealed successfully inside and outside.
With an electron microscope, the researchers saw that most of the HEMA had flowed cleanly throughout the device, but some of it remained behind in the corners of the reservoirs. As a result, the sharp corners were all smoothed out, which promotes good fluid flow, Lee said.
"The effect is almost like hanging wallpaper. When you come to a corner of the room, you smooth the wallpaper over the corner, rounding out the joint," he explained.
Inside a microdevice, the rounded corners enable fluids to flow smoothly, the way racing cars flow around a curved, banked track.
By changing additives in the adhesive, Lee says the researchers can make coating of the device water-friendly or waterproof. Likewise, they could make the surface bind with certain proteins in the body, or reject proteins. In the future, he and his colleagues will investigate how to make the coating conduct light or electricity, which could come in handy for devices that might one day perform some kind of chemical reaction.
NASA Ames Research Center funded this work.
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