# A Microfluidic Digital Shutter of Liquid–Liquid Interface for Fabrication of Multifaceted Hydrogel Microfiber Structure

## TL;DR

A new microfluidic device creates hydrogel microfibers with precise, programmable shapes for use in bioengineering and robotics.

## Contribution

A programmable digital shutter mechanism for fabricating anisotropic hydrogel microfibers with tunable geometries is introduced.

## Key findings

- The digital shutter toggles between liquid bridge maintenance and breakup to control microfiber geometry.
- Microfibers in diverse shapes like linear, helical, and spherical are fabricated with high resolution.
- The platform supports fabrication of cell-laden and magnetically responsive microfibers for biomedical applications.

## Abstract

The digital logic elements based on microfluidic devices are proposed for complex fluidic control. However, there is no logic microfluidic device for fabrication. Moreover, the precise fabrication of anisotropic hydrogel microparticles with programmable geometries has long remained a central challenge in soft matter physics, materials science, and biomedical engineering. Here, a programmable passive digital shutter mechanism based on multiphase liquid–liquid interface dynamics is introduced for the precise fabrication of hydrogel microfibers in a microfluidic platform. There are three fluids in the devices, where two immiscible phases are designed for creating a digital shutter and two aqueous phases for hydrogel formation. It is found that the liquid bridge of hydrogel solution at the liquid–liquid interface has a critical stable length, and the digital shutter is achieved by toggling between liquid bridge maintenance and breakup. By modulating the digital shutter, deterministic control over geometry in terms of length, aspect ratio, curvature, and torsion, and produce microfibers in diverse shapes, including linear, helical, tadpole‐like, and spherical is achieved. To highlight its potential for tissue engineering, active materials, and soft microrobotics, the platform is utilized to generate cell‐laden microfibers with high resolution and viability, and magnetically responsive microfibers.

A programmable passive digital shutter based on multiphase liquid–liquid interface dynamics is introduced for precise fabrication of hydrogel microfibers. By modulating the shutter operation, microfibers with tunable geometry—including linear, helical, tadpole‐like, and spherical forms—are produced. The platform enables the creation of cell‐laden and magnetically responsive microfibers for advanced biofabrication and soft microrobotics.