With the capacity to store and release elastic energy, shape memory hydrogels are promising candidates to construct artificial muscles but usually suffer from low power density due to the slow contraction process and lack real-time sensing function. Inspired by the collaboration of biological muscles and neural systems in nature, we developed poly(acrylic acid-co-acrylamide)/calcium acetate (P(AA-co-AM)/CaAc) shape memory hydrogel with improved actuating speed and integrated sensing performance. The shape memory hydrogel undergoes phase separation at elevated temperatures and stores the elastic energy, generating movement at low temperatures, and releases the stored energy. The energy releasing process could be accelerated by introducing hydrophilic amide groups into the polymer network, thereby improving the power density of the hydrogel based artificial muscles. Moreover, the shape memory hydrogel exhibits excellent conductive performance with a stable output signal and fast responsiveness, enabling the integration of actuating and real-time sensory performance. This strategy could inspire the design and fabrication of intelligent actuating materials and expand their applications in artificial muscles and soft robots.
Herein, a series of electrically conductive polyurethane composites with multi-walled carbon nanotubes (PU/MWCNTs) were in-situ polymerized according to tailoring the segmented PU molecules. The ultralow percolation threshold of MWCNTs (0.057 wt%) in the composites was achieved and the electrically conductive properties were markedly enhanced. The conductivity in PU@MWCNTs1-0.5 % and PU@MWCNTs2-0.5 % was lower than 1.0 × 10 −1 ° S m -1 . While PU@MWCNTs3-0.5 % had the conductivity of over 1.0 × 10 -6 S m -1 , almost 4 orders of significance, which was attributed to the increasing of hard segments on the PU molecule. Furthermore, the high piezoresistive properties of the composites were also observed. Therefore, this work had the important sense in decreasing the low percolation thresholds of conductive polymer composites.
Hydrogels present attractive opportunities as flexible sensors due to their soft nature and tunable physicochemical properties. Despite significant advances, practical application of hydrogel-based sensor is limited by the lack of general routes to fabricate materials with combination of mechanical, conductive, and biological properties. Here, a multi-functional hydrogel sensor is reported by in situ polymerizing of acrylamide (AM) with N,N′-bis(acryloyl)cystamine (BA) dynamic crosslinked silver-modified polydopamine (PDA) nanoparticles, namely PAM/BA-Ag@PDA. Compared with traditional polyacrylamide (PAM) hydrogel, the BA-Ag@PDA nanoparticles provide both high-functionality crosslinks and multiple interactions within PAM networks, thereby endowing the optimized PAM/BA-Ag@PDA hydrogel with significantly enhanced tensile/compressive strength (349.80 kPa at 383.57% tensile strain, 263.08 kPa at 90% compressive strain), lower hysteresis (5.2%), improved conductivity (2.51 S m −1 ) and excellent near-infrared (NIR) light-triggered self-healing ability. As a strain sensor, the PAM/BA-Ag@PDA hydrogel shows a good sensitivity (gauge factor of 1.86), rapid response time (138 ms), and high stability. Owing to abundant reactive groups in PDA, the PAM/BA-Ag@PDA hydrogel exhibits inherent tissue adhesiveness and antioxidant, along with a synergistic antibacterial effect by PDA and Ag. Toward practical applications, the PAM/BA-Ag@PDA hydrogel can conformally adhere to skin and monitor subtle activities and large-scale movements with excellent reliability, demonstrating its promising applications as wearable sensors for healthcare.
危险品化学品经营许可证（带存储）