Light Can Mold and Move Hydrogels


Photo-morphing of initially flat gel sampleUsing only light, hydrogels and be moved around and re-shaped, computer simulations done at the University of Pittsburgh have shown.

Animals like the octopus and cuttlefish that transform their shape depending on their environment have long been the subject of interest for researchers. This is because mimicking similar biological responses in non-living organisms would have considerable implications in the medical arena.

Using hydrogels, which are the materials that constitute most contact lenses and microfluidic or fluid-controlled technologies, such a biomimetic response has now been demonstrated.

“Imagine an apartment with a particular arrangement of rooms all in one location,” said Professor Anna Balazs, lead author of the newly published paper. “Now, consider the possibility of being able to shine a particular configuration of lights on this structure and thereby completely changing not only the entire layout, but also the location of the apartment. This is what we’ve demonstrated with hydrogels.”

Tailored Spirobenzopyran Hydrogels

Balazs and her team experimented with a newer type of hydrogel containing spirobenzopyran molecules. Such materials had been previously shown to form distinct 2-D patterns on initially flat surfaces when introduced to varying displays of light and are hydrophilic, “attracted to” water, in the dark but become hydrophobic, “disliking” water, under blue light illumination. Balazs and Kuksenok expected that light could be a useful stimulus for tailoring the gel’s shape.

With computer modeling, the researchers showed that the gels ran away when exposed to the light, using direct, sustained motion. The team also factored in heat, combining the light and local variations in temperature to further control the samples’ motions.

Microfluidic and Other Applications

Controlling a material with light and temperature could be applicable, Balazs said, in terms of regulating the movement of a microscopic “conveyor belt” or “elevator” in a microfluidic device.

“This theoretical modeling points toward a new way of configuring the gels into any shape, while simultaneously driving the gels to move due to the presence of light,” said researcher Olga Kuksenok.

“Consider, for example, that you could take one sheet of hydrogel and, with the appropriate use of light, fashion it into a lens-shaped object, which could be used in optical applications”, Balazs said. “You don’t need to construct a new device for every new application. By swiping light over the system in different directions, you can further control the movements of a system, further regulating the flow of materials.”

According to Balazs, this type of dynamic reconfiguration in response to external cues is particularly advantageous in the realm of functional materials. Such processes, she said, could have a big impact on sustainability of manufacturing, since the same sample could be used and reused for multiple applications.

Reference:

Kuksenok, O. and Balazs, A. C. (2013), Modeling the Photoinduced Reconfiguration and Directed Motion of Polymer Gels. Adv. Funct. Mater.. doi: 10.1002/adfm.201203876

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