Self-adaptive enzyme-powered micromotors with switchable propulsion mechanism and motion directionality

Abstract

Switchable chemotaxis is vital for motile microorganisms seeking benefits or to avoid harm. Inspired by nature, and for the first time, we demonstrate an artificial enzyme-powered micromotor that can autonomously regulate the propulsion mechanism, as well as motion directionality, by solely sensing the change of fuel concentration (Cf) in its surroundings. The as-designed micromotors have a pot-like microstructure with ureases immobilized on the inner surface. With the confined effect of the pot-like microstructure and unique features of the urease catalytic reaction, the molecular products are further reacted into ions, and their propulsion mechanism can be reversibly adjusted between ionic diffusiophoresis and microbubble recoils when Cf changes. Consequently, the as-developed micromotors under magnetic field are able to self-turn back if the local Cf differs greatly in their surroundings, indicating the achievement of positive and negative chemotaxis by sensing local Cf. Meanwhile, the micromotors also show highly enhanced migration speed by microbubble ejection, up to 60 μm/s, around 30 body lengths per second at physiological urea concentrations. Furthermore, they have an outer surface of mesoporous silica which is easily functionalized for applications such as stimuli-responsive delivery-associated therapies. This work will promote “smart” artificial micro/nanomotors for in vivo biomedical applications.

The control effort to steer self-propelled microswimmers depends on their morphology: comparing symmetric spherical versus asymmetric L -shaped particles

“…The basis for our models were active synthesized particles with a photophoretic self-propulsion mechanism [9,20,37]. However, the control approach (on-off strategy) and the evaluation (control effort) would also be applicable to systems with other propulsion mechanisms which allow online on/off switching of the active propulsion [38][39][40][41]. It may even be feasible to design a morphology (and diffusion matrix) to optimize for a specific movement goal.…”

“…The model represents actively self-propelled microswimmers with the possibility to turn the propulsion mechanism on and off. We used models representing microswimmers which achieve propulsion by selfdiffusiophoresis [15,37], but the principle remains identical also for other switchable propulsion mechanisms [38][39][40][41]. The simulation thus represents partly coated particles that under propulsion experience a force in a fixed direction referring on the particle's shape and are redirected by diffusion, neglecting hydrodynamic interactions.…”

Untethered Microrobots for Active Drug Delivery: From Rational Design to Clinical Settings

“…demonstrated an artificial enzyme‐driven micromotor that can automatically adjust the propulsion mechanism and direction of movement by sensing individually changes in the surrounding fuel concentration. [ 130 ] Luo et al. significantly enhanced the propulsive force of enzyme‐driven micromotors by multilayer assembly of enzymes, providing a new approach for the design of efficient enzyme‐driven microrobots, thus promoting their biomedical applications.…”

Artificial nanomotors: Fabrication, locomotion characterization, motion manipulation, and biomedical applications

“…Artificial micro‐/nanomotors (MNMs) are microscale and nanoscale machines that can convert diverse other energy into mechanical movement and forces. [ 1–5 ] Owing to the autonomous movement property, MNMs display significant potentials in various biomedical applications, [ 6–20 ] such as active drug delivery, [ 6–10 ] precision surgery, [ 11,12 ] medical diagnosis, [ 13–16 ] and detoxification. [ 17–19 ] The existence of biological barriers in vivo environments generally requires biomedical MNMs to have a size comparable to the application scenarios.…”