Leather‐Based Strain Sensor with Hierarchical Structure for Motion Monitoring

Abstract

Flexible and wearable strain sensor has drawn a great deal of attention owing to its wide applications in health monitoring, human–machine interfaces, soft robotics, etc. Microstructural design on the conductive layer of strain sensor effectively improves its performance in linearity and hysteresis effect, yet the process of achieving microstructure is complicated. Leather, a kind of conventional flexible materials to manufacture clothes, shoes, etc., possesses natural hierarchical structure that consists of collagen fiber. Herein, leather is used as a substrate to fabricate a strain sensor by filtration of conductive nanomaterials aqueous dispersion. It is found that 0D conductive nanomaterials can be adsorbed in leather to form conductive pathway with leather‐like microstructure. The as‐prepared sensor with such microstructure not only inherits the air permeability, mechanical property, and biocompatibility from leather, but also displays linearity performance within three regions, low hysteresis effect, short response time, high stability, stretchability, as well as good durability. Kirigami is introduced to endow the leather‐based sensor with stretchability. Such a sensor is applicable to human motion monitoring and shape perception of robotic arm.

Maskless Formation of Conductive Carbon Layer on Leather for Highly Sensitive Flexible Strain Sensors

“…Collagen fibers (Figure 1b; Figure S1, Supporting Information) are the main components for leather deriving from animal skin, [ 32 ] which is able to serve as the precursor for the carbon synthesized via the LDW microprocessing. In contrast to the work that prepares devices by vacuum filtration of functional materials on leather, [ 13 ] the LDW fabricates wearable sensors on leather in a scalable, highly efficient, and maskless manner. Figure 1c shows a schematic of a designed sensor array with nine sensing units to be fabricated by the LDW on leather.…”

“…The sensitivity of the device is much higher than the commercial metal based strain sensor [7] and other recently reported devices. [13,[40][41][42] But its stretchability is inferior to the gold nanowire based strain sensors [43][44][45] (Table S1, Supporting Information). For resistive strain sensors using nanoparticles, [46] carbon nanotube, [10] graphene, [47] and nanowires [41] as the active materials, the electrical conductive pathway is formed by the overlapping of the nanomaterials.…”

“…[ 16 ] An alternative solution for the fabrication of wearable electronic devices is to directly load the textile and leather substrates with functional materials, since they are generally composed of hierarchical porous structures. [ 11,13 ] Sun and co‐workers fabricated a textile based wearable strain sensor by a simple dip‐coating process. [ 18 ] Huang and co‐workers successfully fabricated wearable strain and pressure sensors on leather by vacuum filtration of carbon black and carbon nanotubes on leather for human motion and health monitoring.…”

“…Due to the flexibility and breathability, textile [ 10–12 ] and leather [ 13,14 ] are the best carriers for diverse sensors. However, in contrast to rigid substrates (e.g., silicon), [ 15 ] the textile and leather might not survive the long exposure to high temperature, chemical agents or solvents involved in the procedures for the fabrication of conventional electronic devices.…”

“…[ 19 ] A screen‐printing method was developed by Wu's group to prepare silver nanowire patterned textile for strain sensors. [ 20 ] Although the dip‐coating [ 18 ] and vacuum filtration [ 13 ] are simple and highly efficient, they are difficult to realize mass production and lack of patterning capability. While the transfer‐printing [ 19 ] and screen‐printing [ 20 ] have the patterning capability and can realize the mass production of textile based sensors, the inks to be printed on textiles should has suitable viscoelasticity, which takes time‐consuming optimization processes.…”