Supplementary Online Material.

Supplementary Table 1.Comparison of representative electrode fabrication methods highlighting the versatility of aerosol-jet printing (AJP). Supplementary Table 2. The average cross-sectional areas of different electrodes Supplementary Figure 1 - Optical micrograph of collagen dendrites within the contact pad of a cured collagen sample. Supplementary Figure 2 - Average width of the main printed lines, and thicker regions (collagen) or overspray (silver, co-prints). Supplementary Figure 3. (a) the printing layer mismatch, leaving a large gap in the central area inn one of the UA32 electrodes (scale bar: 1 mm), (b) the cracks in the UA04 electrode centre (Scale bar: 100um). Supplementary Figure 4 - Optical micrographs following the degradation of dendritic regions within collagen samples over time in PBS solution. Supplementary Figure 5 - Optical micrographs highlighting the surface finish of silver samples before and after 12 weeks of incubation in PBS solution. Supplementary Figure 6. The cross-sectional area of UA04 to UA32 electrodes. With increasing collagen content, the electrode width becomes broader, and the central area is lower than sides. Supplementary Figure 7 - Resistance per unit length of silver and co-print samples over time in PBS solution. Supplementary Figure 8 - The flexibility test model. Left: When the electrode is bending. Right: when the electrode is compressed. Supplementary Figure 9. The resistivity changes under different tension and compression conditions in the flexibility test. In each figure, two columns indicate the resistivity measured under tensions and compression with various cylinder diameters (10mm, 20mm, 30mm, and 40 mm). The resistivity was also measured before and after the flexibility test on a flat surface. Plots (a), (c), (e), (g), (i), (k), (m), (o), (q) present the resistivity measured on horizontal directions of UA04 to UA32 electrodes, and PA500 electrodes. Plot (b), (d), (f), (h), (j), (l), (n), (p), (r) present the resistivity measured on vertical direction of UA04 to UA32 electrodes, and PA500 electrodes. Supplementary Figure 10. The SEM image of UA24 electrodes (a) before flexibility test, (b) after flexibility test (Scale bar: 1 mm). The electrodes recover to a flat state in the SEM imaging process. There were no obvious cracks and defects after the flexibility test in SEM images. Supplementary Figure 11 - UV-vis spectra of supernatant solutions from collagen, silver and co-print samples after (a) 4 weeks and (b) 12 weeks.