Fig. 3: Biocompatibility and long-term test of TPP electrodes.

a Photographs of arm skin of the subject for the biocompatibility test. Scale bar: 2 cm. b Skin condition after wearing of 3, 6, and 24 h. Scale bar: 1 cm. After 6 hours’ attachment, glue came off from Ag/AgCl electrodes and sticked tightly on the skin, which was very hard to wash off. However, with TPP electrode, the PPA shows very little glue left on the skin after 24 hours’ adhesion. c A photograph of the electrodes for long-term test, and a schematic diagram to illustrate activities of the subject during the test. Scale bar: 2 cm. d sEMG signals recorded by TPP and Ag/AgCl electrodes during the long-term test (n = 3 samples for each measurement). Data are presented as mean values ± SD. e Fluorescent images of endothelial cells grown on PPA and TPP films to show their biocompatibility. Scale bar: 100 μm. Micrographs (×3) were collected independently with similar results.