College of Aerospace Engineering, Chongqing University, Chongqing 400044, China.
State Key Laboratory of Power Transmission Equipment and System Security and New Technology, Chongqing University, Chongqing 400044, China.
ACS Appl Mater Interfaces. 2021 Jul 14;13(27):32084-32093. doi: 10.1021/acsami.1c05661. Epub 2021 Jun 30.
Transparent e-skin that can fully mimic human skin with J-shaped mechanical-behavior and tactile sensing attributes have not yet been reported. In this work, the skin-like hydrogel composite with J-shaped mechanical behavior and highly transparent, tactile, soft but strong, flexible, and stretchable attributes is developed as structural strain sensing element for e-skin. Piezo-resistive polyacrylamide (PAAm) hydrogel is used as supporting matrix to endow high transparency, softness, flexibility, stretch-ability and strain sensing capability desired for e-skin. Ultrahigh molecular weight polyethylene (UHMWPE) fiber with a wavy configuration is designed as reinforcement filler to provide the tunable strain-limiting effect. As a result, the as-prepared UHMWPE fiber/PAAm composite e-skin presents unique "J-shape" stress-strain behavior akin to human skin. And the PAAm composite can switch from supersoft to highly stiff in the designed strain range up to 100% with a prominent tensile strength of 48.3 MPa, which enables it to have the high stretch-ability and excellent load-bearing ability, simultaneously. Moreover, finite element model is developed to clarify the stress distribution and damage evolution for the UHMWPE fiber/PAAm composite during the tensile process. The PAAm composite exhibits not only an excellent strain sensing performance with a long-term reliability up to 5000 loading-unloading cycles but also an extraordinary softness and mechanical strength with a low initial modulus of 6.7 kPa, which is matchable with soft human epidermis. Finally, the e-skin is used for demonstrations in monitoring various human activities and protecting structural integrity in designed strain ranges. The strategy for reinforcing piezo-resistive hydrogel with wavy-shaped UHMWPE fibers proposed here is promising for the development of transparent, flexible, soft but strong e-skin with a tunable strain-limiting effect akin to human skin.
尚未有报道称，有一种透明的电子皮肤，它可以完全模拟人类皮肤的 J 形机械行为和触觉感知属性。在这项工作中，开发了具有 J 形机械行为和高透明性、触觉、柔软但坚固、灵活、可拉伸等属性的类皮肤水凝胶复合材料，用作电子皮肤的结构应变传感元件。压阻性聚丙烯酰胺（PAAm）水凝胶用作支撑基质，赋予电子皮肤所需的高透明度、柔软性、灵活性、拉伸性和应变传感能力。设计了具有波浪形结构的超高分子量聚乙烯（UHMWPE）纤维作为增强填料，以提供可调节的应变限制效果。因此，所制备的 UHMWPE 纤维/PAAm 复合电子皮肤呈现出类似于人类皮肤的独特“J 形”应力-应变行为。并且 PAAm 复合材料可以在设计的应变范围内从超软切换到高刚性，应变高达 100%，拉伸强度高达 48.3 MPa，使其具有高拉伸性和优异的承载能力。此外，还开发了有限元模型来阐明 UHMWPE 纤维/PAAm 复合材料在拉伸过程中的应力分布和损伤演化。PAAm 复合材料不仅具有出色的应变传感性能，长期可靠性可达 5000 次加载-卸载循环，而且具有出色的柔软性和机械强度，初始模量低至 6.7 kPa，与柔软的人类表皮相匹配。最后，该电子皮肤用于在设计的应变范围内监测各种人体活动和保护结构完整性的演示。这里提出的用波浪形 UHMWPE 纤维增强压阻水凝胶的策略有望开发出具有类似于人类皮肤的可调节应变限制效果的透明、灵活、柔软但坚固的电子皮肤。
