A benign virus could help researchers create materials with biomedical, mechanical, and optical properties that can be tuned, similar to collagen, chitin and cellulose basic building blocks. Collagen is the same material used in corneas, teeth, and skin, and the pattern of its fibers determines its hardness and texture. However, researchers haven’t been able to manipulate these structures, but a team at the University of California, Berkeley has created a model system to study growth patterns similar to collagen, which they developed out of the harmless M13 virus.
By creating virus soups with varying concentrations of bacteria-attacking M13 in saline solutions, they could see how the virus patterns form on a flat sheet of glass slowly pulled out of the viral bath. M13 has a similar shape to collagen, with a long, chopstick-like shape and a helical groove on its surface. And at a pulling rate ranging from just 10-100 micrometers per minute, the researchers could control the surface tension, evaporation rate, and the liquid’s viscosity during the film growth, which determined the type of pattern formed by the viruses.
With a lower concentration of the virus of 1.5 mg/mL in the saline, the virus formed regularly spaced bands with filaments oriented at 90-degree angles. And with a slower pulling rate, the viruses bunched together and twisted into helical ribbons. To create the most complex pattern resembling ramen noodles, a higher viral concentration of 4-6 mg/mL was used, and by using an advanced light source, the noodle-like structure could bend light in ways never before observed in engineered materials or in nature.
Study lead author Woo-Jae Chung says that the levels of order, direction of the twist, and the spacing, width, and height of the film patterns can be controlled by fine-tuning factors that influence kinetics and thermodynamics of the assembly process. And taking it a step further in showing how the virus assembly process could be used in biomedical applications, the team genetically engineered the virus to express specific peptides to influence the growth of soft and hard tissue. The resulting viral films were used as tissue-guiding templates for the biomineralization of calcium phosphate. This formed a composite similar to tooth enamel that could be applied as a regenerative tissue material in the future.
By letting the process run overnight, trillions of viral filaments formed in patterns on the substrate. The work was described in the journal Nature, and this virus model has led researchers to help understand how nature creates complex structures out of basic building blocks like collagen, while developing a way to mimic and extend the process.