Bio-inspired acousto-magnetic microswarm robots with upstream motility

TL;DR

This paper introduces biocompatible acousto-magnetic microswarm robots capable of upstream motility in fluid flows, inspired by natural microswimmers, with potential applications in targeted drug delivery and minimally invasive surgery.

Contribution

It presents a novel design of self-assembled microswarms that utilize combined acoustic and magnetic fields for upstream navigation, overcoming limitations of single actuation methods.

Findings

Quantitative agreement between experimental data and the model of rolling behaviour.

Demonstrated upstream motility in fluid flows using combined acoustic and magnetic actuation.

Potential for targeted therapeutics and navigation against blood flow.

Abstract

The ability to propel against flows, i.e., to perform positive rheotaxis, can provide exciting opportunities for applications in targeted therapeutics and non-invasive surgery. To date, no biocompatible technologies exist for navigating microparticles upstream when they are in a background fluid flow. Inspired by many naturally occurring microswimmers such as bacteria, spermatozoa, and plankton that utilize the non-slip boundary conditions of the wall to exhibit upstream propulsion, here, we report on the design and characterization of self-assembled microswarms that can execute upstream motility in a combination of external acoustic and magnetic fields. Both acoustic and magnetic fields are safe to humans, non-invasive, can penetrate deeply into the human body, and are well-developed in clinical settings. The combination of both fields can overcome the limitations encountered by single actuation methods. The design criteria of the acoustically-induced reaction force of the microswarms, which is needed to perform rolling-type motion, are discussed. We show quantitative agreement between experimental data and our model that captures the rolling behaviour. The upstream capability provides a design strategy for delivering small drug molecules to hard-to-reach sites and represents a fundamental step toward the realization of micro- and nanosystem-navigation against the blood flow.