The researchers working on the "Like a second skin" project reckon using the human body to directly operate mobile devices has the potential to be faster and more intuitive than multi-touch displays. As no one had yet worked out how different materials change the perception of stimuli to our skin and thus also influence how comfortable they are to wear, the team set about examining how flexible special films need to be for our skin to feel various sensations. The paper revealing their findings received major acclaim at the prestigious "Conference on Human Factors in Computing Systems".

"Epidermal input devices open up possibilities for a wide range of important applications," explains Professor Jürgen Steimle from the Department of Computer Science at Saarland University. For example, sensors could be attached anywhere on the body to monitor someone's health without any discomfort. Steimle says prostheses could also be improved using this technology to make them feel like a natural body part, as already demonstrated with numerous prototypes - some developed by his own research group under the names "Tactoo", "SkinMarks" and "iSkin". "However, so far this left the key question unanswered as to how sticking-plaster-like input and output films alter dermal perception," Steimle points out. To try to find out, IT specialists from Saarland University teamed up with scientists at the neighboring INM - Leibniz Institute for New Materials and the Korea Advanced Institute of Science and Technology.

Together, they developed multilayered, sticking-plaster-like, silicone-based materials that bond very well to the skin without the need for adhesives and are apparently even reusable. "Adhesives can feel unpleasant, and in some cases even cause an allergic reaction, so we wanted to avoid using them," explains Klaus Kruttwig, head of the "Biointeractions" research group at the INM. Besides experimenting with "tattoo paper", which is already commonly used in many existing systems, the scientists also tested two different silicone-film plasters on the skin of 16 trial participants (average age 27). The differing flexural rigidity of the three materials was used as the comparative measuring parameter. "You normally measure thickness and elasticity, but we chose bending stiffness to be able to draw comparisons based on a single value," reveals Professor Roland Bennewitz, Head of Nanotribology at the INM.

"Till now, it has been difficult to pinpoint the best material for use in designing such applications, as we knew so little about tactile perception," adds Aditya Shekhar Nittala, a PhD student being supervised by Professor Steimle and the paper's main author. "Our work is now helping designers find the best balance between material properties, mechanical robustness and tactile perception."

INM - Leibniz Institute for New Materials gGmbH (66123 Saarbrücken, Germany)
Website: https://www.leibniz-inm.de/en/