Issue Date: June 16, 2010
Fiber Bundles Line Up
Scientists at Northwestern University have discovered a mechanism for forming peptide-based liquid crystals that can be drawn by hand into long, highly aligned, gel-like nanofiber bundles with the shapes of noodles (Nat. Mater., DOI: 10.1038/nmat2778). These soft and pliable materials could be useful as scaffolds for growth of cells in biomedical applications.
To make the new material, team leader Samuel I. Stupp and coworkers start with amphiphilic small molecules consisting of peptides with long alkyl chains. When heated in solution, these molecules organize themselves into two-dimensional plaques. As the solution cools, those plaques break into bundles of highly aligned nanofibers. These, in turn, form a liquid crystal that, when drawn through a salt solution, forms long noodlelike "monodomain" gels in which all the bundles are aligned in a single direction.
The drawing process occurs at "an extremely small shear rate that can be delivered by human hands," Stupp explains, whereas in a comparable process, electrospinning of polymers, strong mechanical and electrical forces are required to create oriented fibers.
The gel structures are robust enough to stand up to mechanical manipulations without breaking. For example, Stupp and coworkers showed they could make knots and spirals with them.
And the process is gentle enough that biological cells can be incorporated before forming the gel and drawing it into strings. "Normally, if you put cells in the liquids that people align by electrospinning, the mechanical and electrical forces can kill the cells," Stupp says.
Only certain peptides attached to alkyl tails can form these monodomain gels, Stupp says. The peptide sequence must promote the formation of β-sheets, a type of protein secondary structure. In addition, the sequence must include charged amino acids to make it soluble in water.
Stupp and his coworkers hope to use the materials as scaffolds in biomedical repair applications for tissues such as nerves, blood vessels, and spinal cord. Stupp is particularly excited about the prospect of introducing the liquid directly into tissue. "The natural salts in tissue would cause the monodomain gel to form in place," he says.
Liquid crystals like those in the new material—called "lyotropic"—have been difficult to orient over large areas, says Douglas L. Gin, a materials chemist at the University of Colorado, Boulder. Calling the work groundbreaking, Gin says that Stupp's success in a biomedical application "gives hope to researchers in the field that it should be possible to do for other types of lyotropic liquid crystal materials for other applications."
- Chemical & Engineering News
- ISSN 0009-2347
- Copyright © American Chemical Society