Magnetically Actuable Complex-Shaped Microgels for Spatio-Temporal Flow Control

Complex-shaped microgels are promising building blocks for soft metamaterials. Their active and remote orientational control provides significant potential in architecting them in time and space. This work describes the use of magnetically actuable microgels of complex shape for spatio-temporal flow control and showcases the concept for microfluidic impellers. First, the fabrication of complex-shaped magnetically actuable poly(ethylene glycol) diacrylate based microgels via stop-flow lithography is presented. The microgels comprise a pre-programmed magnetic moment set by pre-aligned maghemite nanospindles during the fabrication step. This feature allows the microgels to be positioned in a static magnetic field and rotate under application of a rotating external field. The dependence of the magnetic field rotation rate and strength, maghemite content, and microgel shape on the magnetic response of the microgels is comprehensively quantified. Finally, the magnetic complex-shaped microgels are integrated as actuable impellers in a microfluidic chip. The microgels are positioned in space by polymerizing them around fixed poly(dimethylsiloxane) (PDMS) pillars. Free rotation around the PDMS pillar is achieved due to the oxygen inhibition layer at the chip and pillar surface. The versatility of the fabrication methodology is showcased by the investigation of in-chip mixing in a microfluidic device consisting of soft responsive impellers.

Automated summary

Complex-shaped microgels with active and remote orientational control have great potential in the field of soft metamaterials. This work introduces a method for spatio-temporal flow control using magnetically actuable microgels of complex shape, and demonstrates the concept in microfluidic impellers. The fabrication of these microgels is achieved through stop-flow lithography, and their magnetic response is comprehensively quantified. These complex-shaped microgels are then integrated as actuable impellers in a microfluidic chip, showcasing the versatility of the fabrication methodology.