Tiny seal holds great promise

Engineers at Ohio State University have mastered a technique for sealing plastic casings in a development that 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, called resin-gas injection assisted bonding, aids the flow of medicine and other fluids through biomedical microelectromechanical systems (BioMEMS). The researchers add that they 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.’

BioMEMS are microscopic medical devices under development around the world. One day these devices could deliver medicine directly to tumours 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 blocked the tiny channels found in microdevices.

Then they hit upon a method for using traditional liquid adhesive in a non-traditional way.

For this initial work, Lee and his colleagues moulded a plastic device about the size of a small matchstick. The device consisted of a 100-micrometer wide channel with a fluid reservoir at each end.

They moulded the device in two pieces – a bottom platform containing the channel and reservoirs, and a lid. They then coated both parts with hydroxyethyl methacrylate (HEMA), and fit the two together. While sticky in its liquid form, HEMA cures to a smooth surface under ultraviolet (UV) light.

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 travelled 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. By changing additives in the adhesive, Lee said the researchers can make coating of the device water-friendly or waterproof.

Similarly, 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.