Skin-Inspired Hierarchical Polymer Architectures with Gradient Stiffness for Spacer-Free, Ultrathin, and Highly Sensitive Triboelectric Sensors

Abstract

The gradient stiffness between stiff epidermis and soft dermis with interlocked microridge structures in human skin induces effective stress transmission to underlying mechanoreceptors for enhanced tactile sensing. Inspired by skin structure and function, we fabricate hierarchical nanoporous and interlocked microridge structured polymers with gradient stiffness for spacer-free, ultrathin, and highly sensitive triboelectric sensors (TESs). The skin-inspired hierarchical polymers with gradient elastic modulus enhance the compressibility and contact areal differences due to effective transmission of the external stress from stiff to soft layers, resulting in highly sensitive TESs capable of detecting human vital signs and voice. In addition, the microridges in the interlocked polymers provide an effective variation of gap distance between interlocked layers without using the bulk spacer and thus facilitate the ultrathin and flexible design of TESs that could be worn on the body and detect a variety of pressing, bending, and twisting motions even in humid and underwater environments. Our TESs exhibit the highest power density (46.7 μW/cm), pressure (0.55 V/kPa), and bending (∼0.1 V/°) sensitivities ever reported on flexible TESs. The proposed design of hierarchical polymer architectures for the flexible and wearable TESs can find numerous applications in next-generation wearable electronics.

Mimicking Human and Biological Skins for Multifunctional Skin Electronics

“…c) Hierarchical and interlocked e‐skins with gradient stiffness. Reproduced with permission . Copyright 2018, American Chemical Society.…”

“…In addition to microridge structures at the epidermal–dermal junction, a gradient of elastic modulus between the epidermis (140–600 kPa) and dermis (2–80 kPa) enables effective stress concentration and transmission to underlying mechanoreceptors . Inspired by the stiff epidermis and soft dermis layers, triboelectric e‐skins based on interlocked geometry with gradient stiffness were developed (Figure c) . Poly(vinylidene fluoride‐ co ‐trifluoroethylene) (P(VDF‐TrFE)) with a high elastic modulus (≈1 GPa) and PDMS with a low elastic modulus (≈3 MPa) were selected as materials for the top and bottom layers and designed as interlocked microdome‐structured e‐skins.…”

“…Human skin: Dermal–epidermal structure. Reproduced with permission . Copyright 2014, Elsevier, Copyright 2018, American Chemical Society.…”

Interfacial Phenomena of Advanced Composite Materials toward Wearable Platforms for Biological and Environmental Monitoring Sensors, Armor, and Soft Robotics

“…Ha et al created a skin‐like triboelectric wearable sensor utilizing interlocking of microridge polymers for variations in gap distance without using spacers. The interface using interlocking layered poly(vinylidenefluoride‐ co ‐trifluoroethylene) (P(VDF‐TrFE)) and PDMS, similar to the rigid epidermis and soft dermis respectively, with silver nanowire electrodes.…”

Using Artificial Skin Devices as Skin Replacements: Insights into Superficial Treatment

“…These methods can be further considered for the powering of devices as well. While externally powered modules, such as subcutaneously implanted solar cells or wireless charging platforms, and self‐powered electronic skins for tactile sensing have been developed, the body itself is a viable option for a power source. Body motion or heat can be used to power devices .…”