The researchers began by studying the factors influencing the formation of hierarchical structures.
"We noticed how collagen is secreted in confined spaces, and how its assembly into tissues can be influenced by its environment," said study lead author Woo-Jae Chung, a post-doctoral researcher in Lee's lab. "Unfortunately, collagen is a difficult material to study because it is hard to tune its physical and chemical structures. We needed a convenient model system to solve this problem."
That system was a soup of saline solution containing varying concentrations of a common bacteria-attacking virus, the M13 bacteriophage. The researchers chose the M13 virus harmless to humans and a model organism in research labs because its long, "chopstick-like" shape with a helical groove on its surface closely resembles collagen fibers.
The technique the scientists developed entails dipping a flat sheet of glass into the viral bath, then slowly pulling it out at precise speeds. The sheet emerges with a fresh film of viruses attached to it. At a pulling rate ranging from 10-100 micrometers per minute, it could take 1-10 hours for an entire sheet to be processed.
By adjusting the concentration of viruses in the solution and the speed with which the glass is pulled, the researchers could control the liquid's viscosity, surface tension, and rate of evaporation during the film growth process. Those factors determined the type of pattern formed by the viruses. The researchers created three distinct film patterns using this technique.
With a relatively low viral concentration of up to 1.5 milligrams per milliliter, regularly spaced bands containing filaments oriented at 90 degree angles to each other were formed.
With a slower pulling rate came increased physical constraints to the movement and orientation of the viruses.
|Contact: Sarah Yang|
University of California - Berkeley