Shape anisotropy-governed locomotion of surface microrollers on vessel-like microtopographies against physiological flows

Abstract

Surface microrollers are promising microrobotic systems for controlled navigation in the circulatory system thanks to their fast speeds and decreased flow velocities at the vessel walls. While surface propulsion on the vessel walls helps minimize the effect of strong fluidic forces, three-dimensional (3D) surface microtopography, comparable to the size scale of a microrobot, due to cellular morphology and organization emerges as a major challenge. Here, we show that microroller shape anisotropy determines the surface locomotion capability of microrollers on vessel-like 3D surface microtopographies against physiological flow conditions. The isotropic (single, 8.5 µm diameter spherical particle) and anisotropic (doublet, two 4 µm diameter spherical particle chain) magnetic microrollers generated similar translational velocities on flat surfaces, whereas the isotropic microrollers failed to translate on most of the 3D-printed vessel-like microtopographies. The computational fluid dynamics analyses revealed larger flow fields generated around isotropic microrollers causing larger resistive forces near the microtopographies, in comparison to anisotropic microrollers, and impairing their translation. The superior surface-rolling capability of the anisotropic doublet microrollers on microtopographical surfaces against the fluid flow was further validated in a vessel-on-a-chip system mimicking microvasculature. The findings reported here establish the design principles of surface microrollers for robust locomotion on vessel walls against physiological flows.

High‐Performance Magnetic FePt (L10) Surface Microrollers Towards Medical Imaging‐Guided Endovascular Delivery Applications

“…[ 2 ] Surface rolling magnetic microrobots or surface microrollers have emerged as a promising microrobotic platform for controlled navigation in the circulatory system, which takes advantage of decreased flow velocities at the vessel walls. [ 3,4 ] So far, the locomotion ability of the cell‐sized microrobots is limited to the vessels with relatively low flow velocities, such as post‐capillary venules. [ 3,5 ] The magnetic material used in the microrollers is one of the main limiting factors for locomotion against stronger fluid flows.…”

Hemodynamics Challenges for the Navigation of Medical Microbots for the Treatment of CVDs

“…The size and lack of flexibility may damage the walls of the vessels and limit the size of the vessels in applications.

Figure 3 Some of the most recent microbots designed for the vasculature system: ( a ) ciliary microbot [ 35 ]; ( b ) soft attractor wall microbot [ 36 ]; ( c ) self-folding microbot [ 38 ]; ( d ) sperm-shaped microbot [ 40 ]; ( e ) snake-shaped microbot [ 41 ]; ( f ) scallop-shaped microrobot [ 42 ]; ( g ) microrocket robot [ 43 ]; ( h ) surface microrollers [ 45 ]; ( i ) helical microbots [ 46 ]. All images have been reproduced with permission from the corresponding publishers, therefore further requests for permission related to the material excerpted should be directed to them.

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A Practical Guide to Analyzing and Reporting the Movement of Nanoscale Swimmers

“…For externally powered nanoswimmers, identifying the mechanism is more straightforward than for their chemical counterparts. Typically, a magnetically powered nanoswimmer twists its body or rolls on a surface in a rotating magnetic field; [161][162][163][164] an electrically powered Janus nanoswimmer moves on a 2D plane sandwiched between two conductive electrodes by a mechanism known as induced charge electrophoresis (ICEP); 165 and an acoustically powered nanorod moves in a levitation plane created by resonating ultrasonic waves, 166,167 or by resonant oscillation of an on-board bubble. 168,169 There are certainly variations and caveats to each of these mechanisms, but in general there is some consensus as to how they work.…”