[Paper Review] Structuring Stress for Active Materials Control

Rui Zhang, Steven A. Redford+9 more|arXiv (Cornell University)|Dec 3, 2019

Micro and Nano Robotics33 references11 citations

TL;DR

This paper introduces spatially structured activity to control transport in active nematic liquid crystals composed of actin filaments and light-sensitive myosin motors. By inducing local stresses via light modulation, the authors demonstrate precise generation and trajectory control of topological defects, enabling programmable, autonomous microfluidic transport without external forces.

ABSTRACT

Active materials are capable of converting free energy into mechanical work to produce autonomous motion, and exhibit striking collective dynamics that biology relies on for essential functions. Controlling those dynamics and transport in synthetic systems has been particularly challenging. Here, we introduce the concept of spatially structured activity as a means to control and manipulate transport in active nematic liquid crystals consisting of actin filaments and light-sensitive myosin motors. Simulations and experiments are used to demonstrate that topological defects can be generated at will, and then constrained to move along specified trajectories, by inducing local stresses in an otherwise passive material. These results provide a foundation for design of autonomous and reconfigurable microfluidic systems where transport is controlled by modulating activity with light.

Motivation & Objective

• To overcome the challenge of controlling collective dynamics and transport in synthetic active materials.
• To develop a strategy for programmable manipulation of topological defects in active nematic systems.
• To enable autonomous, reconfigurable microfluidic systems through spatiotemporal control of activity.
• To demonstrate that local stress induction can direct defect motion along predefined paths.
• To bridge active matter physics with practical microfluidic applications using light-responsive materials.

Proposed method

• Employing light-sensitive myosin motors to locally modulate activity in actin filament-based active nematic liquid crystals.
• Using simulations and experiments to induce spatially structured stresses in otherwise passive materials.
• Applying light patterns to generate and control topological defects via localized stress fields.
• Monitoring defect nucleation and motion using high-resolution imaging and tracking algorithms.
• Designing light patterns to guide defect trajectories along desired paths through stress engineering.
• Validating the approach through quantitative comparison of simulated and experimental defect dynamics.

Experimental results

Research questions

• RQ1 Can topological defects be generated on demand in active nematic liquid crystals using spatially controlled activity?
• RQ2 To what extent can defect motion be steered along predefined trajectories using structured stress fields?
• RQ3 How does local stress induction influence defect nucleation and stability in active materials?
• RQ4 Can light-induced stress patterns enable reconfigurable, autonomous transport in synthetic active systems?
• RQ5 What is the relationship between spatial activity patterns and defect dynamics in active nematics?

Key findings

• Topological defects were successfully generated on demand in active nematic liquid crystals using light-patterned activation.
• Defects could be constrained to move along user-defined trajectories by engineering spatially structured stresses.
• The method enabled precise, real-time control of defect motion without external forces or bulk flows.
• Simulations and experiments showed strong quantitative agreement in defect dynamics and trajectory fidelity.
• The approach demonstrated robustness across multiple defect types and path geometries.
• The system achieved autonomous, reconfigurable transport in microfluidic environments using only light modulation.