A new effect makes it possible to permanently bond metals to soft gels and even biological tissue. Previously, gluing soft water-based materials to hard surfaces was very complicated or even impossible. But actually there is a simple solution, Reports from a working group led by Srinivasa Raghavan of the University of Maryland. A wide range of soft materials can be firmly attached to metal or graphite surfaces. All you have to do is apply a voltage of a few volts between them for a short period, and then the materials stick together permanently. This mechanism could enable new machines inspired by biology.
In biology, rigid connections between hard and soft materials – for example bones and tendons – are widespread, but such connections pose an enormous problem for human technology. To do this, the surfaces in question must be chemically treated, and this does not always work either. What's even more surprising is how simple and versatile the effect is that experts have recently discovered. The resulting adhesive effect between materials is often so strong that the soft material tears rather than detaching itself from the surface. How the connection takes place is still largely unclear.
The group first placed graphite electrodes on either side of an acrylamide gel cylinder and applied a voltage of five volts. After three minutes, the gel was firmly attached to the positively charged anode. Further experiments show that this also works with metals on the one hand – and on the other hand with all kinds of biological materials: potatoes, apples, bananas, tomatoes, garlic, chicken breasts… and the compound even holds up under water, as it turns out. What they all have in common is that the hard material must be electrically conductive, while the soft material must be ionic conductive so that charged particles dissolved in water can move freely.
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