传统基于水凝胶的驱动器面临诸多限制，例如低输出力（约2 kPa）和缓慢的驱动速率，因而导致其功密度低（约0.01 kJ/m3）的问题长期存在。此外，在水凝胶合成和应用中，实现低滞后和高强度也面临重大挑战。
近日，日本秋田县立大学邱建辉教授等人在Science China Materials发表研究论文，开发了一种稀疏交联且高纠缠的聚丙烯酸水凝胶（PAAc），有效解决了上述问题。
本文要点
1) 受到哺乳动物肌肉纤维能量转换机制的启发，该水凝胶被用于储存和释放聚合物网络中的弹性势能。2) 实现了60.6 kPa的强收缩力、30.8 kJ/m3的超高功密度，以及高达53.8%的能量转换效率。3) 该水凝胶展现出独特的双态功能，能够在弹性和塑性之间无缝转换，为可调节和精准控制能量释放机制奠定了基础。上述特性使得该水凝胶驱动器有望实现多样化实际应用。Figure 1. Conceptual scheme of contractive materials. (a) Muscle fibers of mammalian. (b) In biological systems, muscle fibers consume ATP to store elastic potential energy, which is then rapidly converted into kinetic energy upon release, generating movement. (c) Inspired by biological systems, elastic potential energy is stored in hydrogels through mechanical stretching, stabilized by reversible bonds formed in response to an external stimulus. When a secondary stimulus is applied, these bonds dissociate, allowing the hydrogel to rapidly contract and release the stored energy, generating substantial force.Figure 2. Mechanism diagram of the preparation process of highly entangled hydrogels (a) and the corresponding crosslinking reaction (b).Figure 3. Conceptual scheme for energy storage and release using highly entangled hydrogel. (a) Pre-stretched hydrogel can be locked by forming new –COO-Fe coordination bond (middle) and unlocked by protonation of carboxylic acid (right). (b) Image of unstretched hydrogel (left), fixed hydrogel after Fe3+ (middle), and shrunk hydrogel after acid treatment (right). Stress-strain curves of hydrogel treated with 0.01 M Fe3+ (c) and 1 M acid at different stretching ratios (d). (e) Stress-strain curves of hydrogel during Fe3+ treatment and after five loading-unloading cycles (holding for 3 min).![]()
Figure 4. Elastic potential energy storing and releasing. Elastic potential energy density (WE) of hydrogels as function of strain under different φi (a) and I/C (b). Length ratio (L/L0) as a function of time and C (Fe3+) (c). (d) The relationship between the concentration of Fe3+ in hydrogel locked and strain. Contraction strength over time is compared in 0.1, 0.25 and 1.0 M hydrochloric acid (e) and UV irradiation (h), under various Fe3+ concentration used for fixation (f). (g) The force-displacement curve during energy storing and releasing. (i) Comparison of contraction strength and tensile strength of the highly entangled and reported hydrogels. For (c) to (h), the highly entangled hydrogels were prepared using a precursor of φi = 100% and I/C = 0.308.Bin Zhang, Jianhui Qiu, Xuefen Meng, Eiichi Sakai, Huixia Feng, Liang Zhang, Jianhua Tang, Guohong Zhang, Hong Wu, Shaoyun Guo. Enhancing energy conversion efficiency in entangled hydrogel actuators. Sci. China Mater. (2024).https://doi.org/10.1007/s40843-024-3112-y
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