Photo-guided azopolymer hydrogel actuators

Source: Light, Science & Applications, by David Urban; Ryota Toyohara; Marcel Rey; Daniele Martella; Dag Roar Hjelme; Andrea Alessandrini; Toshiro Ohashi; Emiliano Descrovi (September 17, 2026). AI-generated summary by biochip.com, published October 3, 2026. Not independently reviewed.

Researchers from the Norwegian University of Science and Technology, Politecnico di Torino, Hokkaido University, and partner institutions have built azopolymer-hydrogel composite actuators that change shape in water when illuminated with polarized green light. The micrometer-scale structures can repeatedly stretch in different directions as the light polarization changes, addressing a long-standing limitation of azopolymer materials: their tendency to retain past deformations. The team also formed closeable microwells that act as light-controlled microvalves. The work points toward reconfigurable components for lab-on-a-chip systems, biotechnology, and controlled drug release.

Using Light to Direct a Soft Material

Azopolymers contain light-responsive dye molecules called azobenzenes. Under polarized light, these materials soften and flow preferentially along the light's polarization direction, much as bristles might bend when combed in one direction. That behavior makes azopolymers useful for reshaping tiny structures, but conventional versions deform plastically: once their shape changes, they do not easily return or switch cleanly to a new configuration.

This lack of reversibility is a practical problem for micro-actuators, which are tiny devices designed to move or change shape on command. Previous deformations accumulate over time, while larger structures can be difficult to deform and may become sticky or mechanically unstable in water. Those drawbacks have limited the use of azopolymers in biological and microfluidic settings.

Nanoparticles Inside a Hydrogel

The team addressed those problems by embedding azopolymer nanoparticles in a water-swollen polymer network, creating an azoGel composite. The nanoparticles provide the directional response to polarized light, while the hydrogel matrix distributes their movement through the overall structure. Crucially, the elastic gel also supplies restoring forces that help the material overwrite earlier light-induced changes.

To make the structures, the researchers prepared nanoparticles of poly(Disperse Red 1 methacrylate-co-methyl methacrylate), a photo-deformable azopolymer. They combined the particles with polyvinyl alcohol and high-molecular-weight polyvinylpyrrolidone, molded the mixture into microstructured templates, annealed it at 135 degrees Celsius, and re-swollen the resulting composites in water.

Microposts Stretch Along Polarized Light

The researchers tested cubic azoGel microposts measuring about 10 by 10 by 10 micrometers. When illuminated from above with a linearly polarized green laser at 532 nanometers, the water-swollen cubes elongated in parallel with the polarization direction. Confocal microscopy showed that the deformation extended through the composite, indicating that the particles were dispersed well enough to produce a coordinated response.

Under 90 seconds of illumination, the structures kept elongating in the chosen direction. Sequential illumination using perpendicular polarization directions produced alternating linear deformations, reaching up to twice the side length of the original cubes. The team reported operation with illumination intervals as short as five seconds.

Light type also changed the resulting geometry. Linear polarization stretched the structures along a single in-plane direction, while circularly polarized illumination produced flattened, mushroom-like forms that expanded in both in-plane directions. The researchers also observed less deformation farther from the illuminated surface, reflecting light absorption through the cube and attachment to the substrate.

From Moving Posts to Microvalves

The group extended the material concept to printed microwells, small cavities that can be closed and reopened by controlling light polarization. These structures function as potential microvalves, meaning they could regulate access to a small compartment without mechanical pumps or physical contact. Such control could be valuable where fluid handling must occur at microscopic scales.

Unlike hydrogel actuators that rely mainly on light-driven heating, swelling, or chemical reactions, azoGel composites use the polarization direction itself as the control signal. The direction of local movement is therefore not permanently fixed during fabrication. Instead, the same structure can be directed along different orientations during use.

Why This Matters

Microfluidic devices often need valves, barriers, and moving parts that work reliably in water. AzoGel actuators combine a light-responsive material with a soft, water-compatible matrix, offering a route to remotely controlled components that can be reshaped repeatedly. The approach may be especially relevant for lab-on-a-chip platforms, where small volumes and compact device footprints make conventional mechanical hardware difficult to integrate.

The next steps will be to establish how these actuators perform in more complex microfluidic designs and biological environments. Their ability to close microwells repeatedly suggests a foundation for light-addressable control of microscopic compartments, but practical systems will need to balance optical intensity, speed, durability, and geometry for specific applications.

Topics: Lab-on-a-chip · Microfluidics

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