With the rapid development of flexible electronics, wearable devices, medical monitoring, and robotics technology, the demand for flexible pressure sensors is constantly increasing, and the performance requirements are becoming increasingly stringent. Among the various working mechanisms of pressure sensors, resistive pressure sensors are highly favored due to their high sensitivity, simple structure, stable signal, and ease of manufacturing. Related studies have shown that using microstructure designs such as pyramids, cylinders, and cones can effectively optimize sensor performance. Many organisms in nature have evolved efficient pressure sensing mechanisms, providing valuable inspiration for sensor design. For example, surface structures such as lotus leaves, rose petals, frog skin, and cockroach antennae exhibit excellent pressure sensitivity. However, existing sensors based on single microstructures often only exhibit advantages within specific pressure ranges, making it difficult to balance high sensitivity and strong pressure resistance over a wide pressure range.

1. Source of inspiration for biomimetic structures

The micro scale structure of shark skin and the macro multi-level dome structure of crocodile skin provide structural design inspiration for sensors at the micrometer and millimeter levels, respectively. The skin structure of fish sharks helps to rapidly increase friction and contact points under low pressure, improving sensitivity. The structure of crocodile skin helps to evenly distribute pressure, enhance stability and overload resistance.

2. Sensor design and preparation

The research team proposed a cross scale complementary composite flexible pressure sensor combination strategy and developed three bio inspired sensor architectures: shark shark (S-S), crocodile crocodile (C-C), and crocodile shark (C-S). Using polydimethylsiloxane (PDMS) as a flexible substrate and graphene as a sensitive material, a biomimetic microstructure surface is fabricated through micro imprinting technology. The performance of three combination mode sensors (S-S, C-C, C-S) was tested through experiments, with a focus on evaluating key indicators such as sensitivity, operating range, stability, and dynamic response. Sensitivity is defined as the ratio of the relative resistance change of a sensor to the applied pressure.

1. Performance of biomimetic sensors

S-S sensor: Utilizing a microscale ridge like scale structure, it achieves an exceptional sensitivity of 32 kPa-1 in the low-pressure range (0-2.5 kPa), making it suitable for high-precision applications such as acoustic monitoring. It exhibits a rapid increase in relative resistance change under low pressure, with a sensitivity of 32 kPa-1 in the linear range of 0-2.5 kPa, but the resistance change tends to saturate above 5 kPa.

C-C sensor: Adopting a millimeter scale multi-stage dome structure, it achieves stable deformation and signal output under high pressure of about 100 kPa, suitable for gait analysis and other scenarios. Sensitivity is 5.86 kPa-1 within the pressure range of 0-20 kPa; Sensitivity drops to 0.90 kPa-1 within the range of 20-30 kPa; The sensitivity is 0.30 kPa-1 within the linear range of 30-100 kPa.

C-S sensor: By synergistically integrating two biological structures, it provides a wide working range from 1 Pa to 80 kPa, high sensitivity (18.2 kPa-1), excellent stability (20000 cycles), and fast dynamic response (21/28 milliseconds response/recovery time). Its sensitivity is 18.20 kPa-1 in the range of 0-10 kPa, 1.10 kPa-1 in the range of 10-40 kPa, and 0.12 kPa-1 in the range of 40-80 kPa.

2. Analysis of C-S Sensor Mechanism

The resistance change of the cross scale complementary composite sensor C-S is mainly caused by the pressure induced change in the contact area between the upper and lower graphene sensitive layers, which in turn changes the number of graphene conductive pathways. The deformation characteristics of C-S devices at different pressure stages can be divided into three stages, corresponding to the three-stage linear response of the hierarchical structure inspired by shark skin and crocodile skin in cross scale complementary composite pressure sensors:

(1) Low pressure stage (0-10 kPa): The micro ridges and scale structures of shark skin first undergo significant elastic deformation, forming discrete micro point contacts, significantly increasing the rate of change in contact resistance per unit pressure and endowing the sensor with ultra-high initial sensitivity.

(2) Medium pressure stage (10-40 kPa): As the pressure increases, the deformation of the shark skin microstructure gradually saturates, and the contact points begin to merge to form a contact surface. At the same time, the multi-level dome structure of crocodile skin participates in deformation, creating new contact points. This stage presents a synergistic effect of point contact and surface contact.

(3) High pressure stage (40-80 kPa): The microstructure of shark skin almost loses its ability to deform, while the multi-level dome structure of crocodile skin dominates sensor deformation, transforming the contact interface into a predominantly surface contact mode. Due to its structural characteristics, the hierarchical dome structure can continue to deform without immediately saturating, despite its sensitivity