Reconfigurable artificial microswimmers with internal feedback

AbstractSelf-propelling microparticles are often proposed as synthetic models for biological microswimmers, yet they lack the internally regulated adaptation of their biological counterparts. Conversely, adaptation can be encoded in larger-scale soft-robotic devices but remains elusive to transfer to the colloidal scale. Here, we create responsive microswimmers, powered by electro-hydrodynamic flows, which can adapt their motility via internal reconfiguration. Using sequential capillary assembly, we fabricate deterministic colloidal clusters comprising soft thermo-responsive microgels and light-absorbing particles. Light absorption induces preferential local heating and triggers the volume phase transition of the microgels, leading to an adaptation of the clusters’ motility, which is orthogonal to their propulsion scheme. We rationalize this response via the coupling between self-propulsion and variations of particle shape and dielectric properties upon heating. Harnessing such coupling allows for strategies to achieve local dynamical control with simple illumination patterns, revealing exciting opportunities for developing tactic active materials.

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Triply-responsive OEG-based microgels and hydrogels: Regulation of swelling ratio, volume phase transition temperatures and mechanical properties

Polymer Chemistry ◽

10.1039/d1py00695a ◽

2021 ◽

Author(s):

Dongdong Lu ◽

Mingning Zhu ◽

Jing Jin ◽

Brian R. Saunders

Keyword(s):

Phase Transition ◽

Biomedical Engineering ◽

Volume Phase Transition ◽

Swelling Ratio ◽

Transition Temperatures ◽

Ph Responsive ◽

Network Systems ◽

Volume Phase ◽

Phase Transition Temperatures ◽

Volume Swelling

Thermally- and pH-responsive microgels (MGs) and hydrogels are fascinating network systems that have been applied in biomedical engineering and sensing. The volume-swelling ratio (Q) and the volume-phase transition temperatures (VPTTs)...

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Accounting for Cooperativity in the Thermotropic Volume Phase Transition of Smart Microgels

Gels ◽

10.3390/gels7020042 ◽

2021 ◽

Vol 7 (2) ◽

pp. 42

Author(s):

Simon Friesen ◽

Yvonne Hannappel ◽

Sergej Kakorin ◽

Thomas Hellweg

Keyword(s):

Phase Transition ◽

Interaction Parameter ◽

Quantitative Description ◽

Water Molecules ◽

Volume Phase Transition ◽

Network Chain ◽

Solvent Interaction ◽

Volume Phase ◽

The Cross ◽

Interaction Parameter Χ

A full quantitative description of the swelling of smart microgels is still problematic in many cases. The original approach of Flory and Huggins for the monomer–solvent interaction parameter χ cannot be applied to some microgels. The reason for this obviously is that the cross-linking enhances the cooperativity of the volume phase transitions, since all meshes of the network are mechanically coupled. This was ignored in previous approaches, arguing with distinct transition temperatures for different meshes to describe the continuous character of the transition of microgels. Here, we adjust the swelling curves of a series of smart microgels using the Flory–Rehner description, where the polymer–solvent interaction parameter χ is modeled by a Hill-like equation for a cooperative thermotropic transition. This leads to a very good description of all measured microgel swelling curves and yields the physically meaningful Hill parameter ν. A linear decrease of ν is found with increasing concentration of the cross-linker N,N′-methylenebisacrylamide in the microgel particles p(NIPAM), p(NNPAM), and p(NIPMAM). The linearity suggests that the Hill parameter ν corresponds to the number of water molecules per network chain that cooperatively leave the chain at the volume phase transition. Driven by entropy, ν water molecules of the solvate become cooperatively “free” and leave the polymer network.

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