Plasticizing Silk Protein for On‐Skin Stretchable Electrodes

Abstract

Soft and stretchable electronic devices are important in wearable and implantable applications because of the high skin conformability. Due to the natural biocompatibility and biodegradability, silk protein is one of the ideal platforms for wearable electronic devices. However, the realization of skin-conformable electronic devices based on silk has been limited by the mechanical mismatch with skin, and the difficulty in integrating stretchable electronics. Here, silk protein is used as the substrate for soft and stretchable on-skin electronics. The original high Young's modulus (5-12 GPa) and low stretchability (<20%) are tuned into 0.1-2 MPa and > 400%, respectively. This plasticization is realized by the addition of CaCl and ambient hydration, whose mechanism is further investigated by molecular dynamics simulations. Moreover, highly stretchable (>100%) electrodes are obtained by the thin-film metallization and the formation of wrinkled structures after ambient hydration. Finally, the plasticized silk electrodes, with the high electrical performance and skin conformability, achieve on-skin electrophysiological recording comparable to that by commercial gel electrodes. The proposed skin-conformable electronics based on biomaterials will pave the way for the harmonized integration of electronics into human.

A Highly Stretchable, Real‐Time Self‐Healable Hydrogel Adhesive Matrix for Tissue Patches and Flexible Electronics

“…It is notable that all groups have high extensibility (Video S1, Supporting Information), such as Group FT‐6/4 demonstrated high extension ratio of 32 000% from 5.5 mm to around 1760 mm in length (Figure 1g); this was determined by measuring the length before and after stretching the hydrogel by hand. This ratio is much higher than that for other previously reported SF materials 9a,15. The rearrangement and/or reconfiguration of SF structures can be facilitated by the gluing action of the TA molecules between the SF molecules, which might be the cause of the observed high extensibility .…”

“…As shown in Figure 2g, the Hbond interactions within silk proteins were substantially weakened in water, and approximately 40% of the Hbonds completely broke. As noted by Chen et al,9a water tends to form strong Hbonds with silk protein molecules. The number of Hbonds between water and silk was 1808 in this study, which is approximately seven times that formed within the silk proteins.…”

“…However, the formed hydrophobic β‐sheets may yield SF materials without adhesive ability and/or stretchability 6a,8. An alternative method is the inhibition of the formation of β‐sheets in the SF, which can produce materials with flexibility and stretchability, e.g., a calcium‐modified plasticizing SF substrate with high stretchability (>400%) was fabricated by the addition of calcium chloride and ambient hydration, and has been further investigated to develop a highly stretchable (>100%) electrode 9a. Additionally, developing SF‐based adhesives that are, e.g., convenient for synthesis, injection, and safety, which are highly desired for biomedical purposes, remains to be a challenge .…”

“…To better understand the mechanism responsible for the high extensibility of SF, AAMD simulations were performed ( Figure ). The mechanical strength of SF is mainly dictated by the crystalline domain, whereas the stretchability is determined by the amorphous domain 9a,18. Therefore, we simulated the amorphous domain to explore how water and TA molecules influence the stretchability of SF.…”

Patterning Vertically Grown Gold Nanowire Electrodes for Intrinsically Stretchable Organic Transistors

“…[15][16][17][18] Metal nanowires (gold, silver, copper, etc.) [32][33][34] For example, the conductivity of gold is two orders higher than carbon based materials. [32][33][34] For example, the conductivity of gold is two orders higher than carbon based materials.…”