Inspired by the overlapping scales of snakes that can slide to conform to deformation, researchers from the Bioinspired Engineering and Biomechanics Center (BEBC) of Xi'an Jiaotong University (XJTU) developed a malleable bionic laminated scale structure with a view to designing mechanical and flexible structural devices.

Under normal circumstances, the fracture failure of rigid materials under deformation is a problem in the development of flexible devices. However, the scale structure "does the opposite", in that it forms by the fracture and overlap of the rigid film on the flexible substrate when under deformation.

The relative sliding between adjacent laminated scales is used to comply with the external deformation, which significantly reduces the strain borne by the rigid scale itself, thereby improving the ductility of the structure and resulting in more than 100 percent strain capacity.

The researchers took the conductive polymer PEDOT:PSS as an example, and realized strain sensing by using the overall resistance change caused by the PEDOT:PSS scale slip under deformation.

The detection range and sensitivity of the sensor can be flexibly adjusted by changing the pre-stretching amplitude of the substrate to achieve high sensitivity and wide range (1 percent~100 percent) strain sensing. Compared with previous research results, the strain sensing range has been further expanded.

Furthermore, the sensors were attached to different parts of the human body surface to realize effective sensing of the skin strain of different amplitudes generated by the normal physiological activities of the human body such as pulse, vocalization, swallowing, facial expression and limb movement, demonstrating the potential for use in wearable physical exercise monitoring and mental state assessment. 

Bionic superimposed scale structure wide-area strain sensor

(A) Staggered and overlapping scales on the surface of snake skin; (B) Deformation mechanism of PEDOT:PSS with overlapping scales; (C) Laminated scale structure PEDOT:PSS is used for strain sensing: (D) Advantages of the developed superimposed scale structure PEDOT:PSS in wide-area sensing; (E) Sensor structure; (F) The developed sensor is used for wearable pulse monitoring (small strain); (G) The developed sensor is used for wearable limb movement monitoring (large strain).

The research results were published in Matter, the top journal in the field of international materials, under the title of Harnessing the wide-range strain sensitivity of bilayered PEDOT: PSS films for wearable health monitoring.

The first author of the paper is Liu Hao, a distinguished researcher of the BEBC. Professor Xu Feng of the BEBC, Assistant Professor Zhang Shiming of the University of Hong Kong and Professor Ali Khademhosseini of the University of California, Los Angeles are corresponding authors. XJTU is the first unit and the communication unit.

The research result is another important progress made by the BEBC in developing embedded three-dimensional spiral sensing structures, rigidity space control hydrogel material, room temperature molding conductive polymer hydrogel material, and environmentally adaptive gel sensors in the field of soft matter mechanics and intelligent flexible sensing.

Link to the paper: https://www.cell.com/matter/fulltext/S2590-2385(21)00304-0

Homepage of the BEBC: http://bebc.xjtu.edu.cn/