Irritations caused by the reaction of skin to textiles and other materials are a general concern in health care. Nevertheless, mechanical contact between the skin of patients and medical textiles and devices are inevitable or might be essential, e.g. for the monitoring of body functions through fabric sensors. Numerous factors influence the mechanical interaction, such as surface texture of skin and material, pressure or interfacial liquids. There is a lack in experimental investigations related to the in situ observation of the interface.

In this SNSF funded project we investigated the interaction of skin with textiles and reference material surfaces on different scales down to 50 μm lateral resolution and 10 μm height resolution appropriate for the hierarchical surface structure of the skin. Terahertz imaging can directly access the skin-textile interface, even under contact pressure. While THz radiation penetrates relevant materials, it is reflected by the skin and partially absorbed by interfacial water. To attain the required spatial resolution we applied THz holography and developed synthetic aperture and ptychographic techniques to devise a high-resolution THz imaging set-up for assessing hidden material interfaces and to apply it to the interface between human skin and THz transparent textile materials during mechanical contact. The THz technique was developed beyond the state of the art, including reflection holography; procedures to separate surface topography of skin and textile and to identify water content; and synthetic aperture techniques based on multiple viewing angles.

The measurement of interfacial parameters, in particular of microscopic skin surface deformations and mechanical interactions with textiles as a function of interfacial moisture will improve the understanding of the mechanical behaviour of the skin and mean a major advancement in the physiological and medical field, e.g. by providing clues for optimising the surfaces of future smart textiles for health monitoring. 

Our PhD-student Lorenzo Valzania was supervised by Prof Thomas Feurer, Institute of Applied Physics, University of Berne. He left us in 2019 to work at the Laboratoire Kastler Brossel in Paris.