A tactile display made from a watery gel that changes shape to show objects on its surface has been developed by German electrical engineers. It uses a hydrogel, the type of material used to make soft contact lenses, which consist mainly of water bound up within a polymer. Some hydrogels can swell or shrink in response to changing conditions like temperature or acidity. Andreas Richter and Georgi Paschew from the Technical University of Dresden turned to those abilities when trying to develop a new tactile display for blind people. "We use smart hydrogels, which can significantly change their volume and mechanical strength," Richter told New Scientist. Light control The two scientists created a square array of 4225 blobs of temperature-sensitive hydrogel, each approximately 300 microns across and separated from its neighbours by a similar amount. Just one square centimetre of the array contains 297 of the gel "pixels". They sit on a black polyester backing that heats up when hit by a beam of light that is narrow enough to warm individual blobs. Below 29 °C the pixels are 0.5 millimetres tall, but if heated to 35 °C they expel some of their water and become half as tall. They also become opaque and much harder to the touch. Rapidly scanning the light beam across the black backing makes it possible to display high-resolution, tactile images (see image, top right) that change twice a second. Once the light beam moves away from a pixel, its temperature quickly drops and the gel swells back to its previous size, sucking up its lost water. To bring the shape changes into sharper relief and also prevent water from escaping, the gel is sealed beneath a plastic membrane. Surgery tool Richter says this system could be used to make tactile displays that communicate information at a person's touch. Such displays could be for blind people, or built into the interfaces of robotic surgery equipment to let human surgeons feel what is at a robot's fingertips. Some improvements are needed before this can become reality, such as reducing the temperatures at which the gel responds, but the team's prototype can already do most of what a display would require. Richter is also exploring how shrinking and swelling gels could act as tiny pumps and valves for microscale lab-on-a-chip devices. "This is a remarkable demonstration – the first – designing, engineering and optimising an integrated complex surface and an important step forward," says João Cabral, head of the polymers and microfluidics group at Imperial College, London.