Now, a dynamic way to control shape, size of 'smart' materials

Washington, July 4 : Researchers at The University of Texas at Austin have developed a dynamic way to alter the shape and size of microscopic three-dimensional structures built out of proteins.

Biological chemist Jason Shear and his former graduate student Bryan Kaehr have shown that hydrogels - detailed three-dimensional microstructures that are currently being used as parts in biology-based microdevices and medical diagnostic technologies for drug delivery, and in tissue engineering - can be expanded and bent by altering the chemistry of the environment in which they were built.

This work lays the foundation for more precise control of hydrogels, which is important for the future utility of these "smart materials". Shear reckons that, among many applications, hydrogels may help better grow bacteria with the aim of understanding disease.

"This provides a significant new way of interacting with cultured cells. The microstructures can be used to capture individual cells, and once isolated, clonal colonies of those cells can be grown and studied," says Shear, an associate professor of chemistry and biochemistry.

As a proof of concept, the researchers made a rectangular house-like structure with a roof wherein they trapped E. coli bacteria, and later released it.

The group revealed that the bacteria blundered into the house through a funnel shaped door, and were trapped in a ring-shaped chamber.

The funnel made it difficult to get out of the house, they added.

"(Once inside) they moved around the space like they were running around a racetrack," says Shear.

The researchers later increased the pH of the cell culture, which changed the volume of the chamber, causing the house to pop off its foundation and release the bacteria.

Shear believes that increasing or decreasing the volume of microstructures dynamically may help gain a better understanding of a phenomenon known as quorum sensing, where bacteria coordinate their gene expression according to the density of their population.

Quorum sensing is important in the pathology of some disease-causing bacteria, like Pseudomonas aeruginosa.

The researchers have revealed that they used photofabrication, a process wherein protein molecules are chemically bound together using a focused laser beam, to create the hydrogels.

The laser causes amino acid side chains to link en masse, which builds a solid protein matrix. The protein scaffold is built layer by layer, much like a raster scanner.

"It's a little bit like a three-dimensional Etch-a-Sketch," says Shear.

Among other high resolution structures developed by the research team are tethers that connect microspheres to surfaces, flower- and fern-like structures, and micro-hands that are less than a quarter the diameter of a hair, pinky to thumb.

Shear and Kaehr experimented with various chemical changes, and found that changing pH caused hydrogel bands to bow out at specific points along their length, and caused shapes like the micro-hands and bacterial chamber to expand.

The researchers also observed that altering ion concentrations caused the fern-like structures to coil and unfurl like fiddleheads emerging from the ground in spring.

Adding ions caused contraction of the tether holding the microsphere, they said.

According to them, such structures may help create better micro- and nano-valves, motors and optics.

The research has been published in the journal Proceedings of the National Academy of Sciences.

ANI