Theoretical and experimental study of 2D conformability of stretchable electronics laminated onto skin

Smoothly attaching the stretchable epidermal electronic devices (EEDs) onto the skin surface is highly desired to improve the measurement accuracy of electrophysiological signal. The paper presents an analytical approach to study interfacial mechanics of the 2D planar EEDs on the checkerboard buckling patterns of human skin. Energy variation method is proposed to determine a criterion whether EEDs laminate conformally onto the skin surface under undeformed and stretched cases. EEDs with low bending stiffness (thin, soft devices/backing layer), smooth and soft skin, and strong adhesion promote conformal contact. Furthermore, the adhesion energy at the EED/skin interface is measured by the homemade peeling experiment platform with different substrate thicknesses and areal coverages. The upper limit of the areal coverage for EED conformal contact with the skin is proposed with given EED/skin properties. Conformability of EEDs are validated by experiments with different substrate thickness, areal coverage and external loadings. It provides a design guideline for EED to conformally contact with the skin surface for more accurate biological signal monitoring.