Nanopropellers and Their Actuation in Complex Viscoelastic Media

Abstract

Tissue and biological fluids are complex viscoelastic media with a nanoporous macromolecular structure. Here, we demonstrate that helical nanopropellers can be controllably steered through such a biological gel. The screw-propellers have a filament diameter of about 70 nm and are smaller than previously reported nanopropellers as well as any swimming microorganism. We show that the nanoscrews will move through high-viscosity solutions with comparable velocities to that of larger micropropellers, even though they are so small that Brownian forces suppress their actuation in pure water. When actuated in viscoelastic hyaluronan gels, the nanopropellers appear to have a significant advantage, as they are of the same size range as the gel's mesh size. Whereas larger helices will show very low or negligible propulsion in hyaluronan solutions, the nanoscrews actually display significantly enhanced propulsion velocities that exceed the highest measured speeds in Newtonian fluids. The nanopropellers are not only promising for applications in the extracellular environment but small enough to be taken up by cells.

Structured light enables biomimetic swimming and versatile locomotion of photoresponsive soft microrobots

“…These challenges mean that most artificial microrobots actually have no actuators. Rather, they are in most cases rigid monolithic structures, either pushed by chemical reactions 15 or directly manipulated by torques or forces applied by external magnetic fields [16][17][18][19][20] .…”

“…These challenges mean that most artificial microrobots actually have no actuators. Rather, they are in most cases rigid monolithic structures, either pushed by chemical reactions 15 or directly 4 manipulated by torques or forces applied by external magnetic fields [16][17][18][19][20] .Alternatively, they consist of flexible materials embedding, at best, a small number of passive degrees of freedom (DOFs) 21,22 .In macroscale robots, one approach to increase the number of DOFs has been to adopt soft bodies, capable of biomimetic actuation [23][24][25][26][27][28] . However, these approaches have resisted miniaturization.…”

Nanomotors

“…Mechanisms (i) and (ii) directly affect the propulsion speed, but not the directionality; (iii) affects the directionality or steerability. All of the above mechanisms are characterized by their respective Péclet numbers (Pe) [42]. The criterion for the minimal size of a propeller can be derived from the condition that Pe = 1, at which point diffusion becomes equal to the rate of directed motion.…”

Tubular microjets: Fabrication, factors affecting the motion and mechanism of propulsion

“…Catalytic motors were first reported independently by the teams from Penn State [1] and Toronto university [2] after which, the field of catalytic motors has significantly grown in several areas [3]. Catalytic motors are used to study the fundamentals of motion at the nanoscale where viscosity and Brownian motion makes swimming a challenging task [4,5]. Moreover, a number of applications ranging from drug delivery to water treatment and different methods to control their motion are reported [6].…”