Soft responsive actuators

Soft responsive actuators, which combine tissue-like softness with high performance, offer significant advantages such as flexibility for various applications. However, their design and fabrication pose challenges. Utilizing Poly(N-isopropylacrylamide) (PNIPAm) hydrogels as the matrix leverages their inherent thermoresponsivity and versatility. These hydrogels can be designed with additional responsivities through copolymerization or nanoparticle integration. This thesis explores various strategies to develop multiresponsive soft actuators by incorporating additional stimuli-responsive elements into PNIPAm hydrogels. Key advancements in this work include the fabrication of anisotropic magnetic and thermoresponsive hydrogels that can be magnetically actuated, swell into out-of-plane deformations, and respond to light. Another notable finding was the oscillatory motion in magnetic bilayer arcs, driven by temperature fluctuations near the VPTT. This behavior, analyzed through a combination of experimental data and theoretical models, revealed the intricate interplay between hydrogel mechanics and magnetic alignment. Significant progress was also made in creating magnetic microswimmers that navigate using photothermal heating and magnetic fields. Their tapered geometry and out-of-equilibrium actuation facilitated movement at low Reynolds numbers, demonstrating directional control and varying swimming behaviors under different magnetic field conditions, as well as interactions with obstacles. Further investigations led to the fabrication of PNIPAm-silica composites with monolayers of silica particles to induce bending, and the exploration of pH-responsive hydrogels with incorporated acidic groups. The latter exhibited shifts in VPTT and pH- and temperature-dependent swelling behaviors, enabling precise control over the curvature in gold-coated hydrogels. Despite these advancements, challenges remain, including enhancing the magnetic response, scalability, and reproducibility of these actuators. Future research should focus on improving biocompatibility and interactions with cells, potentially paving the way for exciting mechanobiological applications.