School of Materials and Chemical Engineering, Ningbo University of Technology, Ningbo 315211, China.
Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China.
J Mater Chem B. 2020 Nov 4;8(42):9679-9685. doi: 10.1039/d0tb02029j.
Rapid and reversible actuation and shape memory effects are critical for biomimetic soft actuators based on polymer hydrogels. However, most conventional hydrogel actuators show very slow actuation or deformation rates in water. It remains a challenge to realize rapid actuations, particularly for hydrogels to actuate in air. Here, a novel strategy to create diverse hydrogel devices with shape memory effects and rapid reversible actuations even in air was demonstrated. This strategy relies on a precise definition of local crosslinking by using multivalent metal ion coordination. This is demonstrated by infiltrating Fe3+ ions into stretchable nanocomposite polyacrylamide hydrogels with the amide groups converted into primary amine groups for multivalent coordination and crosslinking. The Fe3+ coordination with amine groups enhanced the crosslink density and modulus, leading to deswelling. By using an iron rod electrode, the Fe3+ coordination and crosslinking were precisely controlled to generate hydrogels with heterogeneous local crosslinking, including Janus hydrogels, S-shaped hydrogels, and cross-shaped hydrogel grippers. These soft devices were reversibly actuated in tens of seconds when cyclically dehydrated in ethanol and rehydrated in water. Most interestingly, very rapid reversible actuations of a hydrogel device in air were demonstrated by using electro-redox reaction of Fe3+ and Fe2+ in the hydrogel, where the reversible local coordination crosslinking and decomposition served as a hinge to actuate the hydrogel. This strategy based on reversible local coordination and crosslinking may open an avenue for rapid fabrication of hydrogel devices with well-defined structures and actuation properties.
快速且可还原的致动和形状记忆效应对于基于聚合物水凝胶的仿生软致动器至关重要。然而，大多数传统的水凝胶致动器在水中的致动或变形速度非常慢。实现快速致动，特别是对于在空气中致动的水凝胶，仍然是一个挑战。在这里，展示了一种创建具有形状记忆效应和快速可逆致动的各种水凝胶器件的新策略，即使在空气中也是如此。该策略依赖于通过多价金属离子配位精确定义局部交联。这是通过将 Fe3+离子渗透到具有酰胺基团转化为多价配位和交联的可拉伸纳米复合聚丙烯酰胺水凝胶中来实现的。Fe3+与胺基的配位增强了交联密度和模量，导致溶胀。通过使用铁棒电极，可以精确控制 Fe3+的配位和交联，以生成具有不均匀局部交联的水凝胶，包括 Janus 水凝胶、S 形水凝胶和十字形水凝胶夹具。这些软设备在数十秒内循环脱水在乙醇中和再水合在水中时可实现可逆致动。最有趣的是，通过在水凝胶中使用 Fe3+和 Fe2+的电氧化还原反应，演示了水凝胶器件在空气中的非常快速的可逆致动，其中可逆的局部配位交联和解体用作致动水凝胶的铰链。这种基于可逆局部配位和交联的策略可能为快速制造具有明确定义结构和致动特性的水凝胶器件开辟了一条途径。
