Tuning the Rigidity of Silk Fibroin for the Transfer of Highly Stretchable Electronics

Abstract

The transfer of stretchable electrodes or devices from one substrate to another thin elastomer is challenging as the elastic stamp often yields a huge strain beyond the stretchability limit of the electrodes at the debonded interface. This will not happen if the stamp is rigid. However, a rigid material cannot be used as the substrate for stretchable electrodes. Herein, silk fibroin with tunable rigidity (Young's modulus can be changed from 134 kPa to 1.84 GPa by controlling the relative humidity) is used to transfer highly stretchable metal networks as highly conformable epidermal electrodes. The silk fibroin stamp is tuned to be rigid during peeling, and then be soft and highly stretchable as a substrate when laminated on moisturized human skin. In addition, the epidermal electrodes exhibit no skin irritation or inflammation after attaching for over 10 d. The high compliance results in a lower interface impedance and lower noises of the electrode in measuring electromyographic signals, compared with commercial Ag‐AgCl gel electrodes. The strategy of tuning the rigidity at different stages of transfer is a general method that can be extended to the transfer of other stretchable electrodes and devices for epidermal electronics, human machine interfaces, and soft robotics.

Robotic Manipulation under Harsh Conditions Using Self‐Healing Silk‐Based Iontronics

“…Silk is one of the strongest natural polymers, and it has demonstrated promising applications in skin electronics and wearable sensors. [16][17][18][19][20] The facile modifications of silk allow robust strong adhesion to various materials and uneven surfaces, enabling usage on human skin and machine surfaces in this work. [19] Notably, Ca(II) ions and glycerol have been used separately with silk in previous works, but the performance in both cases was limited (Table 1).…”

“…RT stands for room temperature. Transfer of stretchable electronics [20] Silk/Glycerol ≈200% RT NA NA Biomedical applications [21] Silk/Graphene/Ca(II) 70-90% 0-50 Yes Yes (by Graphene) Epidermal electronics [23] Silk/Ca(II) >600% −30-80 Yes Yes (0.02-6.66 mS cm −1 ) Temperature sensing [24] Silk/Ca(II) 600% (RH 50%) NA Yes Yes (0.97-1.96 mS cm -1 ) Flame-retardant [25] Silk/Ca(II) 400% RT NA Yes (by Au coating) Stretchable Electrodes [38] Silk/Glycerol/Ca(II) 1000% (RH 50%) −40-120 Yes Yes (0.01-11.1 mS cm −1 ) Gesture/objects recognition under harsh conditions This work are suitable for both human and robotic facets, including highfidelity sensing, human-friendly, and flexible composition, ease of mounting on robotics, robustness in harsh environments, while being environmentally friendly and cost-competitive for broad fabrication.…”

Ionic Flexible Sensors: Mechanisms, Materials, Structures, and Applications

“…The performance of the electrode prepared using the first strategy mainly depends on the properties of the electrode material, such as, high conductivity, excellent flexibility, low cost, and good stretchability. [161] Recently, several high-performance conducting materials have been developed, including CNTs, [162,163] graphene, [164,165] metal nanowires, [166][167][168] percolating networks of nanowires (NWs), [169][170][171][172] conducting polymers, [173] and conducting composites. [174][175][176][177] Compared to conventional metal electrodes, these conducting materials exhibit excellent flexibility and stretchability, and many are soluble or dispersed in various solvents, thereby providing preparation conditions for stretchable electrodes using some classic preparation methods, such as, coating, 3D printing, template-assisted assembly, vacuum filtration, and electrospinning techniques.…”

Stretchable and Conductive Composite Structural Color Hydrogel Films as Bionic Electronic Skins

“…[ 5 ] Benefitting from these advantages, silk fibroin has been widely developed in various biomedical fields such as drug delivery, tissue engineering, medical dressings, and even simple electronic skins. [ 6 ] On the other hand, structural color, resulting from the interaction of light and periodically arranged nanostructures, has received extensive attention in optical devices. [ 7 ] Particularly, when structural color is combined with soft hydrogels, the change of volume or shape under different stimuli can lead to visual color variation.…”