Brownian fluctuations and hydrodynamics of a microhelix near a solid wall

Silvio Bianchi,Viridiana Carmona Sosa,Roberto Di Leonardo,Gaszton Vizsnyiczai

doi:10.1038/s41598-020-61451-y

Abstract

We combine two-photon lithography and optical tweezers to investigate the Brownian fluctuations and propeller characteristics of a microfabricated helix. From the analysis of mean squared displacements and time correlation functions we recover the components of the full mobility tensor. We find that Brownian motion displays correlations between angular and translational fluctuations from which we can directly measure the hydrodynamic coupling coefficient that is responsible for thrust generation. By varying the distance of the microhelices from a no-slip boundary we can systematically measure the effects of a nearby wall on the resistance matrix. Our results indicate that a rotated helix moves faster when a nearby no-slip boundary is present, providing a quantitative insight on thrust enhancement in confined geometries for both synthetic and biological microswimmers.

Highlights

We combine two-photon lithography and optical tweezers to investigate the Brownian fluctuations and propeller characteristics of a microfabricated helix
The combination of drag anisotropy in slender bodies and a chiral shape gives rise to a net hydrodynamic thrust on helical bodies that rotate around their axis[3]
In this respect very little has been done for chiral objects: Brownian diffusion of colloidal particles with regular shapes such as spheres, ellipsoids or rods, has been largely studied[13,14,15,16,17,18]

Summary

Introduction

We combine two-photon lithography and optical tweezers to investigate the Brownian fluctuations and propeller characteristics of a microfabricated helix. The absence of inertial effects is a very important ingredient in the description of dynamical phenomena at the micron scale, but what is really peculiar of the microscopic world is the unavoidable presence of Brownian fluctuations In this respect very little has been done for chiral objects: Brownian diffusion of colloidal particles with regular shapes such as spheres, ellipsoids or rods, has been largely studied[13,14,15,16,17,18]. Exploiting the high degree of spatial control provided by optical tweezers, we can systematically study wall effects on the roto-translational coupling Based on these findings we conclude that a rotating helical propeller would move faster when a no-slip boundary is closer

Methods

Results

Conclusion