Reversible Speed Regulation of Self‐Propelled Janus Micromotors via Thermoresponsive Bottle‐Brush Polymers

Abstract

This work reports a reversible braking system for micromotors that can be controlled by small temperature changes (≈5 °C). To achieve this, gated‐mesoporous organosilica microparticles are internally loaded with metal catalysts (to form the motor) and the exterior (partially) grafted with thermosensitive bottle‐brush polyphosphazenes to form Janus particles. When placed in an aqueous solution of H2O2 (the fuel), rapid forward propulsion of the motors ensues due to decomposition of the fuel. Conformational changes of the polymers at defined temperatures regulate the bubble formation rate and thus act as brakes with considerable deceleration/acceleration observed. As the components can be easily varied, this represents a versatile, modular platform for the exogenous velocity control of micromotors.

Molecular bases for temperature sensitivity in supramolecular assemblies and their applications as thermoresponsive soft materials

“…For pendant polymers, ether-pendant, including ones with OEG sidechains, can also cause LCST-type response in polymers regardless of their backbone chemistry. [81][82][83] Similar to the previous examples, the LCST behavior of polymers with OEG sidechain originates from the combination of hydrophobic alkyl backbones and hydrophilic OEG sidechain. The LCST of these polymers are also influenced by OEG length alteration.…”

“…Moreover, PEO-PPO-pendant polyphosphazene could be grafted onto mesoporous silica NPs for pH-and thermoresponsive drug delivery systems. 81 Many more thermoresponsive polymer-grafted porous silica nanoparticles has been reviewed. 229 Additionally, one study revealed an interesting photothermal system with temperaturecontrolled release by covalently modifying a thermoresponsive OEGMA and MEO 2 MA-based copolymer on to the surface of hollow gold nanoparticles (AuNPs).…”

“…The subtle change in temperature could precisely turn on and off the catalysis. 81 Another example of gate-controlled catalysis was shown by Guo and coworkers, whose work evolved around attaching thermoresponsive polymers and DNAzymes onto AuNPs. The accessibility of DNAzymes depended on the morphology of the polymers, whether shrinking or expanding.…”

Shape Engineering of TiO2 Microrobots for “On‐the‐Fly” Optical Brake

“…[4,18,19,20] However, the research related to on-demand slowing or halting, i.e., braking, the motion of microrobots using light has been limited. [3,18,21,22,23] It was demonstrated that by designing TiO 2 / Au/Pt Janus microrobots, one can obtain "on-the-fly" optical brake together with the reversal of motion direction. [18] The research group found that an intermediate Au layer can be the underlying reason to observe this behavior by switching propulsion mechanism in the presence of UV light and H 2 O 2 fuel.…”

Reversible speed control of one-stimulus-double-response, temperature-sensitive asymmetric hydrogel micromotors

“…Inspired by this, scientists are trying to design artificial, intelligent, and well-adapted motors with functionalities that resemble those of cells and microorganisms. Several geometries of micro-swimmers that convert chemical energy into autonomous motion have already been reported, including Janus particles [1][2][3][4][5][6] and catalytic rods, 7 asymmetric shapes 8 and tubular structures. 9,10 These motors can be powered with different strategies resulting in self-propelling behaviours based on bubbles formation, 11 interfacial tension gradients, 12 self-electrophoresis, 13 or selfdiffusiophoresis induced by asymmetrical chemical reactions.…”