Fig. 2: In vitro characterization results for f-PCB.

a, Stress–strain curve of the whole serpentine interconnect used in this study. b, Photograph of the serpentine interconnect under mechanical stretching with various strains. c, Numerical simulation results of uniaxial stretching of the whole serpentine interconnect at 0.3 N. d, Photographs of the cMaSK under various mechanical deformations including twisting and crumpling. e, Optical microscopy image of the adhesion layer used in the cMaSK. f, Measured lap shear strength value between the adhesion layer and various face masks. The data are presented as mean values ± standard deviation (s.d.) (n = 3 different face mask specimens examined in independent measurements). g, Photograph of the cMaSK detached from the surgical face mask. h, Photograph of the mask fit test setup. The device compares with the particle concentration of the environment and inside the face mask. i, Mask fit quantity values of various types of face mask with and without the attached cMaSK. The data are presented as mean values ± s.d. (n = 60 from continuous mask fit quantity measurement; Supplementary Fig. 12). j, Fit factor (FF) value calculated from the capacitance sensor pads as a function of distance between the sensor pad and conductive plate. The data are presented as mean values ± s.d. (n = 6 from independent measurements).