A gel that shrinks in the heat and swells in the cold has been used as a valve in a microchip drug delivery system by Japanese researchers.

Stimuli-responsive gels have previously been incorporated into microchips, but their manufacture often involves several stages and specialist equipment. The approach of Ryo Yoshida and colleagues at the University of Tokyo, Japan, offers a simple alternative fabrication route using standard laboratory apparatus.

The gel is based on a polymer that is dissolved in methanol and placed on the microchip. By narrowly focusing UV light onto the solution using a microscope, the team controlled gelation on a scale of tens of micrometres. By mounting the chip on a mobile stage, the shape and layout of the gel can be varied.

The researchers built a trial microchip containing a dummy drug, and monitored the flow by UV spectroscopy. The gel, which swells and de-swells according to the temperature, restricted the flow of the drug at lower temperatures but shrank when warmed, allowing the drug to be administered.

Other gels that may be incorporated into such chips include acid- and glucose-sensitive compounds, and the researchers are currently trying to integrate a rhythmic self-oscillating gel.

The simple UV lamp and microscope system offers many benefits, including convenience and adaptability, but Yoshida believes that this approach will complement current techniques. 'I don't think it will completely supersede the other methods in the future, but it will contribute greatly to microchip fabrication,' he said.

Paul O'Sullivan