Inductively Expandable Supraparticles as Microscopic Force Generators for Remote Mechanical Actuation.

Abstract

Generating strong mechanical forces at the microscale is central to emerging technologies like soft microrobotics and adaptive materials. However, delivering energy remotely and converting it into mechanical work within confined environments remains challenging. Magnetic nanoparticles enable rapid, contactless heat generation through induction heating under alternating magnetic fields, yet this is typically exploited only for thermal effects. Here, we introduce micrometer-scaled supraparticle additives that convert induction-generated heat directly into mechanical work through confined expansion. These supraparticles are fabricated by spray-drying magnetic nanoparticles with functional blowing agents, enabling actuation by rapid gas release using azodicarbonamide or volumetric expansion via vaporization-induced volume expansion within a superabsorbent poly(acrylamide-co-acrylic acid) network. Upon magnetic excitation, heating generates pressure within the supraparticles, yielding power densities up to 5 kW kg^-1 and lifting capabilities of up to 25 000 times their own mass, exceeding the typical limit of conventional materials (∼10 000x). Actuation is achieved with heating times of ≤5 s and total energy consumption below 3 Wh, remaining reproducible over multiple actuation cycles without failures. Generated stresses are sufficient to disrupt mechanically stable matrices, including rigid epoxies. These results establish supraparticles as versatile platforms for remotely powered mechanical actuation, enabling localized stress generation and material disruption in interactive materials.