Scientists enlist viruses to help build biomaterials
It's one of those enduring mysteries of nature - how can one biological substance end up becoming several different types of material? One example is collagen, a fibrous protein that can be made into body parts such as corneal tissue, cartilage, bone, and skin. In an effort to better understand such processes, scientists at the University of California at Berkeley decided to see if they could manipulate another biological building block into forming itself into different materials. They succeeded, using viruses known as M13 phages.
The study was led by bioengineer Seung-Wuk Lee and his student and lead author Woo-Jae Chung. They chose the E. coli-hunting M13 virus due to its filamentous, collagen-like structure and chiral (asymmetric) twist, which allows multiple viruses to assemble into complex arrangements. The virus is harmless to humans.
The scientists suspended the viruses in a buffered salt solution, into which they dipped a thin glass substrate, which the viruses adhered to. By varying the concentration of the viruses, the ionic concentration, and the rate at which the substrate was pulled from the solution, they were able to create three distinct thin-film materials.
By using a relatively low viral concentration and a repeated "stick-slip" withdrawal motion, a film consisting of alternating bands of viruses was created. The viruses in each band were oriented perpendicular to those in the band adjacent to it.
When the pull speed was reduced, the viscosity, surface tension and rate of evaporation during the film growth process were increased. This placed more physical constraints upon each virus's movements, resulting in a film composed of helical (spiral-shaped) ribbons.
Finally, by increasing the viral concentration (and in some cases increasing the withdrawal speed), a film was created out of "complex yet ordered bundles of filaments," which the researchers referred to as "ramen-noodle-like." It was discovered that this particular film could bend light in ways never before observed in natural or man-made materials.
In fact, all three films differed not only in appearance, but also in factors such as their color, iridescence, and polarity. These factors could be precisely tweaked, as the films were being created. The scientists were also able to grow cells on the films, with the cellular material taking on the texture of the substrate - in one instance, a biomaterial similar to tooth enamel was created using calcium and phosphate.
"This novel, self-templating, biomaterials assembly process could be used in many other organic and inorganic materials to build hierarchical structures to tune optical, mechanical and even electrical properties from nano to macro scales," stated Joseph Akkara of the National Science Foundation, which helped fund the project. "The reported approaches could be used to investigate mechanisms for diseases such as Alzheimer's, which is caused by amyloid aggregation in our brain tissues. More broadly, the breakthroughs could potentially yield scientific impacts in the area of tissue regeneration and repair."
The video below shows one of the thin film materials being withdrawn from the saline solution - sped up 900 times.