Shape-Programmable Architectured Hydrogels Sensitive to Ultrasound.

On-demand motion of highly swollen polymer systems can be triggered by changes in pH, ion concentrations, or by heat. Here, shape-programmable, architectured hydrogels are introduced, which respond to ultrasonic-cavitation-based mechanical forces (CMF) by directed macroscopic movements. The concept is the implementation and sequential coupling of multiple functions (swellability in water, sensitivity to ultrasound, shape programmability, and shape-memory) in a semi-interpenetrating polymer network (s-IPN). The semi-IPN-based hydrogels are designed to function through rhodium coordination (Rh-s-IPNH). These coordination bonds act as temporary crosslinks. The porous hydrogels with coordination bonds (degree of swelling from 300 ± 10 to 680 ± 60) exhibit tensile strength σmax up to 250 ± 60 kPa. Shape fixity ratios up to 90% and shape recovery ratios up to 94% are reached. Potential applications are switches or mechanosensors.