Researchers have demonstrated a simple, one-step process in which genetically engineered viruses arrange themselves into extremely ordered patterns with distinctive properties, such as color or strength. The technique could be used to make novel optical devices or biological scaffolds to grow soft tissue, teeth, and bone.
The researchers, led by Seung-Wuk Lee, a bioengineering professor at the University of California, Berkeley, used the technique to make structured films. "We want to mimic nature and create many different types of functional structures with a very simple building block," Lee says.
Viral films: Complex, highly structured films made using viruses could be used as optical devices and as templates for engineering tissue, bone, and teeth.
This work is part of a broader effort to make new types of materials using viruses as microscopic building blocks. Researchers at MIT, led by Angela Belcher, a biological engineering and materials science professor, have previously engineered viruses to bind to inorganic materials—something they would never do naturally—and have them assemble into battery components.
Lee and his colleagues have found a way to fine-tune the arrangement of individual viruses to create sophisticated structures with complex designs all on their own. Using a single virus as a building unit is "pretty exquisite," says Belcher, because its traits can be genetically modified and you can attach many different useful materials to its surface. What's even more important about the new work, which was published in the journal Nature last week, is the precise control over viral self-assembly, resulting in large-scale structures with multiple levels of organization. "This is very beautifully laid out," she says. "They can do so much with a single virus."
The researchers used a rod-shaped bacterial virus, called M13, for their work. First, they dip a flat glass sheet into a saline solution containing the viruses. As they pull the glass out slowly at a controlled speed, the viruses spontaneously configure themselves on the glass surface into orderly patterns. This assembly happens as the solvent evaporates. "Self-assembly is hard to achieve in a systematic way, but what the authors have come up with shows a potentially powerful route to do this," says George Schatz, a chemistry professor at Northwestern University.
By changing the virus concentration in the solution and the pulling speed, the researchers were able to create different structured films. One has regularly placed stripes made of virus bundles in which the viruses are aligned and twisted like corkscrews.
The most complex film has a "ramen-noodle-like" structure that bends light in certain ways. Various pulling speeds change the spacing and width of the viruses in this wavy structure, so that it shows distinct colors. Such films could be used as light reflectors and filters found in displays and photography. The technique could also be used to fabricate photonic crystals and organic photovoltaics.
The researchers also showed that the material could be made into a scaffold to engineer complex tissues. To do this, they genetically tweaked the virus to make it express certain proteins on its surface, which influence the growth of the tissue. They cultured cells on top of the films and found that the cells aligned themselves with the microstructure. What's more, when the films were dipped in a solution of calcium and phosphate ions, the ions mineralized on the film to form a tough material similar to tooth enamel.
"Developing a system like this that could regenerate bone or could be used for growth of materials for teeth is a very possible application," says Belcher.
By Prachi Patel
From Technology Review