Zheng Haiyan, Lin Nan, He Yanyi, Zuo Baoqi
College of Textile and Clothing Engineering, Soochow University, Suzhou, Jiangsu 215100, China.
National Engineering Laboratory for Modern Silk, Soochow University, Suzhou 215123, China.
ACS Appl Mater Interfaces. 2021 Aug 25;13(33):40013-40031. doi: 10.1021/acsami.1c08395. Epub 2021 Aug 10.
Flexible and wearable hydrogel strain sensors have attracted tremendous attention for applications in human motion and physiological signal monitoring. However, it is still a great challenge to develop a hydrogel strain sensor with certain mechanical properties and tensile deformation capabilities, which can be in conformal contact with the target organ and also have self-healing properties, self-adhesive capability, biocompatibility, antibacterial properties, high strain sensitivity, and stable electrical performance. In this paper, an ionic conductive hydrogel (named PBST) is rationally designed by proportionally mixing polyvinyl alcohol (PVA), borax, silk fibroin (SF), and tannic acid (TA). SF can not only be a reinforcement to introduce an energy dissipation mechanism into the dynamically cross-linked hydrogel network to stabilize the non-Newtonian behavior of PVA and borax but it can also act as a cross-linking agent to combine with TA to reduce the dissociation of TA on the hydrogel network, improving the mechanical properties and viscoelasticity of the hydrogel. The combination of SF and TA can improve the self-healing ability of the hydrogel and realize the adjustable viscoelasticity of the hydrogel without sacrificing other properties. The obtained hydrogel has excellent stretchability (strain > 1000%) and shows good conformal contact with human skin. When the hydrogel is damaged by external strain, it can rapidly self-repair (mechanical and electrical properties) without external stimuli. It shows adhesiveness and repeatable adhesiveness to different materials (steel, wood, PTFE, glass, iron, and cotton fabric) and biological tissues (pigskin) and is easy to peel off without residue. The obtained PBST conductive hydrogel also has a wide strain-sensing range (>650%) and reliable stability. The hydrogel adhered to the skin surface can monitor large strain movements such as in finger joints, wrist joints, knee joints, and so on and detect swallowing, smiling, facial bulging and calming, and other micro-deformation behaviors. It can also distinguish physical signals such as light smile, big laugh, fast and slow breathing, and deep and shallow breathing. Therefore, the PBST conductive hydrogel material with multiple synergistic functions has great potential as a flexible wearable strain sensor. The PBST hydrogel has antibacterial properties and good biocompatibility at the same time, which provides a safety guarantee for it as a flexible wearable strain sensor. This work is expected to provide a new way for people to develop ideal wearable strain sensors.
柔性可穿戴水凝胶应变传感器在人体运动和生理信号监测应用中引起了极大关注。然而，开发一种具有特定机械性能和拉伸变形能力、能与目标器官紧密贴合且具有自愈性能、自粘能力、生物相容性、抗菌性能、高应变敏感性和稳定电学性能的水凝胶应变传感器，仍然是一项巨大挑战。本文通过按比例混合聚乙烯醇（PVA）、硼砂、丝素蛋白（SF）和单宁酸（TA），合理设计了一种离子导电水凝胶（命名为PBST）。SF不仅可以作为增强剂，将能量耗散机制引入动态交联的水凝胶网络，以稳定PVA和硼砂的非牛顿行为，还可以作为交联剂与TA结合，减少TA在水凝胶网络上的解离，改善水凝胶的机械性能和粘弹性。SF与TA的组合可以提高水凝胶的自愈能力，并在不牺牲其他性能的情况下实现水凝胶粘弹性的可调性。所制备的水凝胶具有优异的拉伸性（应变>1000%），并与人体皮肤表现出良好的紧密贴合性。当水凝胶受到外部应变破坏时，无需外部刺激即可快速自我修复（机械性能和电学性能）。它对不同材料（钢、木材、聚四氟乙烯、玻璃、铁和棉织物）和生物组织（猪皮）表现出粘附性和可重复粘附性，且易于剥离无残留。所制备的PBST导电水凝胶还具有宽应变传感范围（>650%）和可靠稳定性。附着在皮肤表面的水凝胶可以监测手指关节、腕关节、膝关节等的大应变运动，并检测吞咽、微笑、面部鼓起和放松等微变形行为。它还可以区分轻微微笑、大笑、呼吸快慢、呼吸深浅等生理信号。因此，具有多种协同功能的PBST导电水凝胶材料作为柔性可穿戴应变传感器具有巨大潜力。PBST水凝胶同时具有抗菌性能和良好的生物相容性，为其作为柔性可穿戴应变传感器提供了安全保障。这项工作有望为人们开发理想的可穿戴应变传感器提供一条新途径。
