Beijing Key Laboratory of Lignocellulosic Chemistry , Beijing Forestry University , Beijing 100083 , China.
ACS Appl Mater Interfaces. 2019 Oct 23;11(42):39228-39237. doi: 10.1021/acsami.9b15817. Epub 2019 Oct 2.
As a promising functional material, hydrogels have attracted extensive attention, especially in flexible wearable sensor fields, but it remains a great challenge to facilely integrate excellent mechanical properties, self-adhesion, and strain sensitivity into a single hydrogel. In this work, we present high in strength, stretchable, conformable, and self-adhesive chitosan/poly(acrylic acid) double-network nanocomposite hydrogels for application in epidermal strain sensor via in situ polymerization of acrylic acid in chitosan acid aqueous solution with tannic acid-coated cellulose nanocrystal (TA@CNC) acting as nanofillers to reinforce tensile properties, followed by a soaking process in a saturated NaCl solution to cross-link chitosan chains. With addition of a small amount of TA@CNC, the double-network nanocomposite hydrogels became highly adhesive and mechanically compliant, which were critical factors for the development of conformable and resilient wearable epidermal sensors. The salt-soaking process was applied to cross-link chitosan chains by shielded electrostatic repulsions between positively charged amino groups, drastically enhancing the mechanical properties of the hydrogels. The obtained double-network nanocomposite hydrogels exhibited excellent tunable mechanical properties that could be conveniently tailored with fracture stress and fracture strain ranging from 0.39 to 1.2 MPa and 370 to 800%, respectively. Besides, the hydrogels could be tightly attached onto diverse substrates, including wood, glass, plastic, polytetrafluoroethylene, glass, metal, and skin, demonstrating high adhesion strength and compliant adhesion behavior. In addition, benefiting from the abundant free ions from strong electrolytes, the flexible hydrogel sensors demonstrated stable conductivity and strain sensitivity, which could monitor both large human motions and subtle motions. Furthermore, the antibacterial property originating from chitosan made the hydrogels suitable for wearable epidermal sensors. The facile soaking strategy proposed in this work would be promising in fabricating high-strength multifunctional conductive hydrogels used for wearable epidermal devices.
作为一种有前途的功能材料，水凝胶引起了广泛的关注，特别是在柔性可穿戴传感器领域，但将优异的机械性能、自粘性和应变敏感性轻易地集成到单个水凝胶中仍然是一个巨大的挑战。在这项工作中，我们通过在壳聚糖酸性水溶液中就地聚合丙烯酸，同时用单宁酸包覆的纤维素纳米晶体（TA@CNC）作为纳米填料来增强拉伸性能，然后在饱和 NaCl 溶液中浸泡以交联壳聚糖链，制备了高强度、高拉伸、高贴合和自粘性壳聚糖/聚丙烯酸双网络纳米复合水凝胶，用于表皮应变传感器。加入少量 TA@CNC 后，双网络纳米复合水凝胶变得高度粘性和机械柔顺，这是开发贴合和弹性可穿戴表皮传感器的关键因素。盐浸泡过程通过屏蔽带正电荷的氨基之间的静电斥力来交联壳聚糖链，从而显著提高水凝胶的机械性能。所得到的双网络纳米复合水凝胶具有优异的可调机械性能，可以方便地调节断裂应力和断裂应变，范围分别为 0.39 至 1.2 MPa 和 370 至 800%。此外，水凝胶可以紧密地附着在各种基底上，包括木材、玻璃、塑料、聚四氟乙烯、玻璃、金属和皮肤，表现出高附着力和柔顺的附着力行为。此外，得益于强电解质中的丰富游离离子，柔性水凝胶传感器表现出稳定的导电性和应变敏感性，可监测大人体运动和细微运动。此外，壳聚糖的抗菌性能使水凝胶适用于可穿戴表皮传感器。本工作中提出的简单浸泡策略有望在制备用于可穿戴表皮器件的高强度多功能导电水凝胶方面具有广阔的前景。
