Magnetic Control of Tubular Catalytic Microbots for the Transport, Assembly, and Delivery of Micro‐objects

Abstract

Recently a significant amount of attention has been paid towards the development of man‐made synthetic catalytic micro‐ and nanomotors that can mimic biological counterparts in terms of propulsion power, motion control, and speed. However, only a few applications of such self‐propelled vehicles have been described. Here the magnetic control of self‐propelled catalytic Ti/Fe/Pt rolled‐up microtubes (microbots) that can be used to perform various tasks such as the selective loading, transportation, and delivery of microscale objects in a fluid is shown; for instance, it is demonstrated for polystyrene particles and thin metallic films (“nanoplates”). Microbots self‐propel by ejecting microbubbles via a platinum catalytic decomposition of hydrogen peroxide into oxygen and water. The fuel and surfactant concentrations are optimized obtaining a maximum speed of 275 µm s−1 (5.5 body lengths per second) at 15% of peroxide fuel. The microbots exert a force of around 3.77 pN when transporting a single 5 µm diameter particle; evidencing a high propulsion power that allows for the transport of up to 60 microparticles. By the introduction of an Fe thin film into the rolled‐up microtubes, their motion can be fully controlled by an external magnetic field.

Hierarchical nanoporous microtubes for high-speed catalytic microengines

“…The nanoporous microengine with large pores enables a faster transportation rate and a higher reaction rate compared with the smooth microengines and nanoporous microengines with small pores. The high production rate correspondingly causes fast accumulation of O 2 and the formation of microbubbles, 18 which are then expelled from the back end of the microtubular channel, generating a recoiling force. A quantitative analysis of this motion is challenging at the present stage, but our experimental results undoubtedly prove that the nanoporous structures on the microtube walls enhance the reaction rate and motion speed by increasing the reactant transfer rate and the surface area.…”

“…For microtubular engines, the microchannel serves both as the chemical reaction chamber and as the oxygen-collecting cavity, where H 2 O 2 is pumped into the tubular reactor from the front end and bubbles are expelled from the back end. 14,18 This liquid flow feeds the catalytic reaction, leading to the continuous motion of the microengine. 14 For smooth microengines, the chemical fuel can only be pumped in from the front opening, and the reaction may actually be limited by an H 2 O 2 shortage, especially during fast decomposition (Supplementary Figure S2).…”

“…Preliminary demonstrations of multi-functional engines performing complex tasks, such as dynamic target transportation and isolation under remote control using an external field, have been reported so far. [18][19][20] The mobility of catalytic micro-/nanomotors was found to be intrinsically determined by the kinetics of the catalytic reaction and intimately related to factors such as the temperature and electrical potential, the concentration of the chemical fuel and the geometry of the motors. 21,22 Various approaches have been employed to boost the catalytic reaction rate and in turn increase the motor's speed.…”

Efficient bubble propulsion of polymer-based microengines in real-life environments

“…1,7,8 Such bubble-propelled microengines thus display efficient propulsion in salt-rich environments due to electrocatalytic decomposition of hydrogen peroxide fuel. [9][10][11] Previous studies have also indicated the facile motion of polymer-based micromotors or rolled up microjets in various diluted (3-4 fold diluted) real-life media. [12][13][14][15][16][17][18] However, recent reports claimed that the movement of bubble-propelled Cu-Pt microengines is greatly hindered in various diluted real samples, and even completely stopped in highly diluted serum or seawater.…”

Design of a UV-responsive microactuator on a smart device for light-induced ON-OFF-ON motion

“…One is to apply an external field as the driving force, 7,8 which is limited by the specific properties of the materials and is strongly dependent on manual control. The other solution is to introduce an external material flow to provide chemical power, such as the decomposition of hydrogen peroxide 4,[9][10][11][12][13][14][15][16][17][18][19] or the reduction of protons by zinc 20,21 for bubble propulsion or other propelling mechanisms, the Marangoni effect caused by a surface tension gradient [22][23][24] or biomotors such as myosins, kinesins and dyneins via the hydrolysis of adenosine triphosphate. 25 As a branch of material flow research, the Marangoni effect is a facile, environmentally benign and rapidly responsive method for driving small objects automatically.…”