New high-tech electrodes
Researchers at ETH Zurich have developed novel electrodes for health monitoring that adhere optimally to the skin and can record high-quality signals. Two young spin-off founders want to bring the product to market this year.
Anyone who has ever had an electrocardiogram performed, for example to check their Heart Fitness to check, knows the electrodes that the doctor attaches to your chest. However, conventional electrode models have considerable disadvantages: Hard metal electrodes are uncomfortable to wear and therefore not reasonable for measurements over longer periods of time. With gel electrodes, as they are most frequently used in everyday clinical practice, patients more often suffer skin irritations or even allergic reactions.
ETH researchers led by Janos Vörös, Professor of Bioelectronics, and Christopher Hierold, Professor of Micro- and Nanosystems, have now succeeded in remedying this situation. They developed an electrode that is similarly elastic to the skin and which the wearer thus hardly feels. Thanks to the special surface structure, signals from the heart and brain can be recorded in high quality. The researchers recently published their work in the scientific journal Advanced Healthcare Materials published.
Inspired by nature
The researchers used a soft material for the new electrode, a skin-compatible mixture of silicone rubber and conductive silver particles, which goes back to an earlier research work from Janos Vörös' group. For the structuring of the surface, the scientists took inspiration from nature: They took advantage of the mechanism that enables grasshoppers to walk even on vertical surfaces. The soles of these insects' feet are covered with countless tiny platelets that look like mushroom heads under the microscope and are arranged in a mosaic pattern. When they come into contact with another surface, an adhesive effect occurs, known in technical jargon as Van der Waals interaction.
The researchers transferred this microstructure to their material, creating an electrode surface that adheres to the skin. The special geometry at the micro level also maximizes the contact area between the skin and the electrode, which allows signals to be recorded in very high quality.
From the clean room to the swimming pool
The researchers produced the prototypes in a specially developed fabrication process in a clean room. They coated a substrate with two different varnishes and covered it with a precisely perforated mask. They then irradiated the whole thing with light, which made the upper, light-sensitive varnish detachable just below the perforated areas. They then immersed everything in a chemical solution. This first attacked the soluble areas of the upper coating and then worked its way to the second coating. There, the researchers stopped the degradation at exactly the right moment, so that the desired mold with all the inverted mushroom heads was created. The cast then produced the specially structured, adhesive electrode surface.
In order to test whether the electrodes also work under heavy stress, the researchers tested them on a female swimmer. Because of the water resistance and vigorous movements, swimming is considered a particularly difficult discipline for performance monitoring using electrodes. The results were convincing: the quality of the signals recorded by the new electrodes was significantly better than that of the gel electrodes that the swimmer also wore. In the meantime, the lake rescue service in Zurich has already shown interest in the new electrodes and is using them as part of an ongoing study.
