One-step process for the preparation of fast-response soft actuators based on electrospun hybrid hydrogel nanofibers obtained by reactive electrospinning with in situ synthesis of conjugated polymers

Abstract

Soft actuators with a fast response to low electrical potentials are critical for wearables and robotics. In this work, hybrid hydrogel nanofiber mats were prepared and tested as soft actuators. Hybrid hydrogel nanofibers were produced by combining electrospinning with in situ photopolymerization of the hydrogel and polymerization of aniline during the formation of the nanofibers. The electrical conductivity of the obtained nanofibers measured by the 4-probe method reached values close to 0.01 S cm−1. Images obtained by atomic force microscopy in conductive mode (I-AFM) were also successfully acquired and proved the conductive and nanometric nature of the hybrid hydrogel nanofibers. Infrared spectra (FTIR) showed that photopolymerization of the hydrogel precursors and aniline polymerization during nanofiber formation were effectively achieved. The elastic modulus of the nanofibers was estimated from AFM nanoindentations, and values close to 10 MPa for the swollen samples were obtained. The swelling ability of the hybrid hydrogel nanofibers was evaluated by comparing AFM images of the nanofibers in dried and swollen conditions to reveal that the swelling degree is reduced by the presence of polyaniline in the nanofibers. The obtained hybrid hydrogel nanofiber mats were tested as actuators in an electrochemical cell. The application of low voltage (1 V) in a 1 MΩ cm water led to fast (2.5 mm s−1) and reversible displacement of the samples. During actuation, thin nanofiber mats could also withstand forces on the order of 80 μN that were measured by coupling the electrochemical cell to a load cell.