Having already produced biocompatible nanofibers from synthetic peptides, chemists at Rice University in Houston, TX are using an amino acid found in the sticky feet of mussels to make those fibers line up into strong hydrogel strings.
The hydrogel strings can be picked up and moved with tweezers, and the researchers expect they will help labs gain better control over the growth of cell cultures.
“Usually when cells grow on a surface, they spread randomly,” said graduate student I-Che Li. “There are a 
Nanoscale multi-domain peptide fibers that are prompted to self-assemble into macroscale fibers are tough enough to be handled with tweezers. (Courtesy of the Hartgerink Research Group) lot of biomaterials we want to grow in a specific direction. With the hydrogel scaffold aligned, we can expect cells to grow the way we want them to. One example would be neuron cells, which we want to grow head-to-tail to aid nerve regeneration. Basically, this could allow us to direct cell growth from here to there -- that’s why this material is so exciting.”
Previously the team had developed synthetic hydrogels that could be injected into the body to serve as scaffolds for tissue growth. The hydrogels contained hydrophobic peptides that self-assembled into fibers about 6 nm wide and up to several microns long. However, because the fibers did not interact with one other, they generally appeared in microscope images as a tangled mass.
Experiments showed the fibers could be coaxed into alignment with the application of shear forces, in the same way that playing cards are aligned during shuffling by pushing on both the top and bottom of the deck. The researchers tried pushing the fibers through a needle to force them into alignment, a process that would be easier if the material was water soluble. So they added a chain of amino acids known as DOPA (3,4-dihydroxyphenylalanine) to the sides of the fibers to allow them to remain water-soluble in the syringe. DOPA is the compound that lets mussels stick to just about anything. Combining DOPA and shear stress from passing through the needle prompted the fibers to form visible, rope-like bundles.
DOPA also promoted chemical cross-linking reactions that helped the bundles hold their shape, and the aligned fibers also proved to have a curious and useful optical property called “uniform birefringence,” or double-refraction. This could allow researchers to use polarized light to see exactly where the aligned fibers are, even if they’re covered by cells.
The aligned fibers might be used for macroscale medical applications but with nanoscale control over the structures.
