School of Materials Science and Engineering, Nanyang Technological University, Singapore, 639798, Singapore.
Robotic Materials Department, Max Planck Institute for Intelligent Systems, 70569, Stuttgart, Germany.
Adv Mater. 2023 Jun;35(22):e2300487. doi: 10.1002/adma.202300487. Epub 2023 Apr 21.
Polymer hydrogels mimic biological tissues and are suitable for future lifelike machines. However, their actuation is isotropic, so they must be crosslinked or placed in a turgor membrane to achieve high actuation pressures, severely impeding their performance. Here, it is shown that organizing cellulose nanofibrils (CNFs) in anisotropic hydrogel sheets leads to mechanical in-plane reinforcement that generates a uniaxial, out-of-plane strain with performance far surpassing polymer hydrogels. These fibrillar hydrogel actuators expand uniaxially by 250 times with an initial rate of 100-130% s , compared to <10 times and <1% s in directional strain rate for isotropic hydrogels, respectively. The blocking pressure reaches 0.9 MPa, similar to turgor actuators, while the time to reach 90% of the maximum pressure is 1-2 min, compared to 10 min to hours for polymer hydrogel actuators. Uniaxial actuators that lift objects 120 000 times their weight and soft grippers are showcased. In addition, the hydrogels can be recycled without a loss in performance. The uniaxial swelling allows adding channels through the gel for local solvent delivery, further increasing the actuation rate and cyclability. Thus, fibrillar networks can overcome the major drawbacks of hydrogel actuators and is a significant advancement towards hydrogel-based lifelike machines.
聚合物水凝胶模仿生物组织，适合未来逼真的机器。然而，它们的致动是各向同性的，因此必须交联或放置在肿胀膜中以实现高致动压力，这严重阻碍了它们的性能。在这里，研究表明将纤维素纳米纤维（CNF）组织在各向异性水凝胶片中会导致机械面内增强，从而产生单轴、面外应变，其性能远远超过聚合物水凝胶。这些纤维状水凝胶致动器可单向膨胀 250 倍，初始速率为 100-130%/s，而各向同性水凝胶的定向应变率分别为<10 倍和<1%/s。阻断压力达到 0.9 MPa，与肿胀致动器相当，而达到最大压力 90%的时间为 1-2 分钟，而聚合物水凝胶致动器的时间为 10 分钟至数小时。展示了可单向致动重达自身重量 120000 倍的物体的致动器和软夹爪。此外，水凝胶可以回收而不会损失性能。单向溶胀允许在凝胶中添加通道以局部输送溶剂，进一步提高致动速度和可循环性。因此，纤维状网络可以克服水凝胶致动器的主要缺点，是朝着基于水凝胶的逼真机器迈出的重要一步。
