Drug delivery: Wet or dry
By Felix Cheung

AbstractSmart surfaces can be switched between water-loving and water-repelling states in response to temperature, pH and glucose changes

Materials with surfaces that attract (superhydrophilic) and repel (superhydrophobic) water have many applications, especially in drug delivery. Now, Guangzhao Zhang at the University of Science and Technology of China in Hefei, Lei Jiang at the Chinese Academy of Sciences in Beijing and co-workers1 have prepared a 'smart' surface that can switch between these extreme states in response to temperature, pH and glucose changes.

The researchers coated a silicon wafer with a copolymer consisting of a temperature-sensitive block and a block sensitive to changes in pH and glucose. They then studied the contact angle that a water droplet makes on the wafer when one of the standard conditions (26 °C; pH7.4; glucose concentration of 8.6 gram per litre) is varied.

The researchers found that the coating on the wafer becomes hydrophilic at low temperatures and hydrophobic at high temperatures. An increase in the pH or glucose concentration shifts the 'equilibrium temperature' — the temperature of the balance between hydrophilic and hydrophobic properties — to a higher value. Furthermore, the water repellence of the coating can be greatly enhanced by using a rough wafer instead of a flat one.

The coating is durable and its ability to switch remains even after being laid aside without special protection for two months or longer. The technology could find application in glucose-responsive drugs that control the release of insulin to treat diabetes.