Opto-Fluidically Multiplexed Assembly and Micro-Robotics

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Written by | Zhao Yixin

Abstract

Recently, Moritz Kreysing and others from the Karlsruhe Institute of Technology in Germany demonstrated that laser-induced local flow fields can be iteratively used for the relative positioning of multiple micro-particles. The researchers showed that multiplexing stimulated by temperatures below the thermal diffusion limit can accelerate the precise manipulation of micro-particles, resulting in flow fields with rich topological structures and mathematical predictability. They represent unprecedented microfluidic control capabilities, exemplified by driving micro-robots with up to 30 degrees of freedom. This article was published in Light: Science & Applications, titled “Opto-fluidically multiplexed assembly and micro-robotics.” Elena Erben is the first author, and Moritz Kreysing is the corresponding author.

Background Introduction

Precise manipulation of microscopic particles in solutions is an important research area with applications in life sciences, biomedical sciences, nanoscience, engineering, and physics research. Contemporary micro-manipulation methods include optical tweezers, magnetic robots, and photo-actuated micro-pushers. These techniques typically require micro-particles or auxiliary probes to have specific material properties, must use high-intensity laser irradiation, or lack optical control capabilities for multiplexing and manipulating multiple micro-particles.

In addition to these established micro-manipulation methods, performing microfluidic operations in multi-pump driven microfluidic chambers is considered a solution for handling micron-sized particles and assembling complex structures. Although this approach is theoretically feasible, the complexity of its methods is inversely proportional to the number of particles. The physical properties of the flow field in pump-driven chambers severely limit the potential of microfluidic technology to handle physics, making the development of hydraulic-driven micro-robots with degrees of freedom comparable to contemporary macroscopic robots seem unattainable.

M. Kreysing and others from the Max Planck Institute for Molecular Cell Biology and Genetics in Dresden proposed another opto-fluidic method for precise micro-manipulation of particles. This method overcomes previous limitations without requiring any hardware changes when transitioning from manipulating single particles to multiple particles. It shows unexpected speed enhancements during multiplexing and is expected to enable analytically high-definition robotic technologies with a large number of degrees of freedom.

Innovative Research

Utilizing optically generated thermoviscous flows, this flow can be used to move and confine individual colloidal particles. In brief, these laminar flows arise from the complex interactions between thermal expansion and the temperature-dependent viscosity, making them second-order physical effects. By using standard acousto-optic modulators and high-definition fluorescence microscopy (Figure 1b), the weakly heated single-mode infrared laser beam (Figure 1a) is directed in spatial scanning at a low kHz repetition rate, allowing these directed flows to be induced optically at any position in the fluid. Analysis indicates that under two-dimensional constraints, the induced flow field is strongly localized near the laser scanning path, decaying at a distance squared inverse rate in the far field. The researchers complemented these laser scanning and imaging optics with an extended closed-loop feedback scheme (Figure 1c) to gradually reduce particle positioning errors over time. Due to the local characteristics of the optically induced flow fields, this method can easily position more particles, assembling quasi-static structures at the micron scale, surpassing the practical and theoretical limits of the number of particles that pump-driven chambers can handle.

Figure 1 Concept of achieving multi-particle positioning through feedback-controlled multiplexed thermoviscous flows

Currently, the most advanced robots can achieve numerous degrees of freedom, dynamic motion, and high precision. In fact, humanoid robots have developed to a level where they can demonstrate complex movements and replicate emotional body language. The method proposed by the researchers can achieve relative positioning of a large number of particles, as these particles do not need to be fixed in their relative positions to reduce the number of degrees of freedom, allowing the particles to remain mobile at all times.

In micro-robots, closely spaced particles may exhibit significant but solvable crosstalk; however, transitioning from flow fields that match the particle positions with the highest flow rates to slightly offset flow fields, thereby combining high-speed flows with significant velocity gradients, creates additional flexibility. Drawing inspiration from humanoid robot research and motion pattern perception studies, the researchers ultimately created a walking humanoid robot animation, weighing about 10-15 times that of a human-scale hydraulic-driven robot, by using hundreds of multiplexed and continuously varying optical and context-generating flow fields to drive individual “body parts.” These robots possess over 30 degrees of freedom, and their dynamics are clearly defined, reliably conveying human attributes such as gender, happiness, and even tension through body language displayed while walking.

Figure 2 Humanoid robot capable of expressing emotional body language, employing context-aware dynamic arrangement strategies to minimize fluid dynamic coupling

Paper Information

Erben, E., Liao, W., Minopoli, A. et al. Opto-fluidically multiplexed assembly and micro-robotics. Light Sci Appl 13, 59 (2024). https://doi.org/10.1038/s41377-024-01406-4

Editor | Sun Tingting

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Highly Cited Article Statistics

The following data comes from Web of Science, and the number of highly cited articles in Light: Science & Applications ranks first among similar journals in the country. As of now:

There is 1 article with over 2000 citations

https://doi.org/10.1038/lsa.2014.99

There are 3 articles with over 1000 citations

https://doi.org/10.1038/s41377-019-0194-2

https://doi.org/10.1038/lsa.2014.30

There are 4 articles with over 800 citations

https://doi.org/10.1038/lsa.2016.133

There are 5 articles with over 700 citations

There are 9 articles with over 600 citations

https://doi.org/10.1038/lsa.2017.141

https://doi.org/10.1038/lsa.2013.28

https://doi.org/10.1038/lsa.2017.168

https://doi.org/10.1038/s41377-020-0341-9

There are 10 articles with over 500 citations

https://doi.org/10.1038/lsa.2015.67

There are 24 articles with over 400 citations

https://doi.org/10.1038/lsa.2013.26

https://doi.org/10.1038/lsa.2014.42

https://doi.org/10.1038/lsa.2016.17

https://doi.org/10.1038/lsa.2015.97

https://doi.org/10.1038/lsa.2014.46

https://doi.org/10.1038/lsa.2014.60

https://doi.org/10.1038/lsa.2015.30

https://doi.org/10.1038/lsa.2012.1

https://doi.org/10.1038/lsa.2016.76

https://doi.org/10.1038/s41377-018-0078-x

https://doi.org/10.1038/lsa.2015.131

https://doi.org/10.1038/s41377-020-0326-8

https://doi.org/10.1038/lsa.2017.39

https://doi.org/10.1038/s41377-018-0060-7

There are 43 articles with over 300 citations

There are 99 articles with over 200 citations

There are 292 articles with over 100 citations

There are 571 articles with over 50 citations

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