Using Music to Guide the Construction of Better Biomaterials
Spider silk, relative to its size, is stronger than steel and has a higher tensile strength than Kevlar, while being less dense and significantly lighter. Some types of silk can stretch up to several times their length without breaking (one pound of spider silk could stretch around the equator) and remains flexible even in extreme cold. Naturally, these qualities have scientists interested in the possibilities of using spider silk in a broad array of applications—from aircrafts, to body armor, and even prosthetic limbs. (Related article: Silk-based Vaccine and Antibiotics Stabilizer).
Three NIBIB funded researchers, Dr. Markus Buehler PhD., from the Massachusetts Institute of Technology, David Kaplan, PhD, from Tufts University, and Joyce Wong, PhD, from Boston University, have been collaborating to modify the natural structure of spider silk in order to increase its potential uses. These researchers, however, are looking in unexpected places for guidance in creating new synthetic structures namely, art. With the help of mathematician David Spivak, PhD, and composer John McDonald, they attempting to identify what different musical interpretations of successful and unsuccessful synthetic protein structures could teach them about how to construct and reverse engineer new varieties of silk fiber structures.
Their method is based on the theory that all compositions, be it architecture, language, or even music, have underlying structures and that these structures can be optimized to produce the most effective, efficient, pleasing in other words, the best outcome. The researchers decided to ask an unconventional question: Instead of the painstaking trial and error process of randomly combining various protein structures and only determining their effectiveness afterward, could, for example, musical theory and composition provide hints to guide the design of these proteins before they were ever synthesized?”
Spider silk is made almost completely from liquid proteins that the spiders form into fibers. The basic building blocks (i.e. peptides) in and of themselves are not strong, but together, based on their combinations, they can form incredibly robust bonds. Buehler’s team used two major protein building blocks: “A” which is hydrophobic, (repelling water), giving silk its strength, and “B” which is hydrophilic (attracted to and often dissolved by water), enabling flexibility. Using these two fundamental structures in different sequences, scientists have learned about how they interact to form the various attributes of silk that are important for biological function.
Alternating A and B into the sequence ABABAB imitates silk’s natural structure—an equal amount of both hydrophobic and hydrophilic protein structures. The A building block forms strong interactions with each other while the B forms much weaker connections. As in baking, the silk produced is greatly affected by the amount of each ingredient added to the mixture. But while scientists may know what each individual building block contributes, they don’t know how the final product will be affected by changing the quantities of the ingredients.
Buehler, Wong, and Kaplan decided to test two new combinations, AAAB and ABBB, to see how it would affect the characteristics of the silk produced. Kaplan, a chemical and biomedical engineer, altered the genes that produce the liquid silk proteins and Wong, a materials scientist and bioengineer, created a spinneret device that mimics a spider’s ability to spin the liquid into fibers from the raw material.
They discovered, perhaps contrary to what might be expected, that an abundance of the A building block in the AAAB combination actually hindered the formation of fibers and was unsuccessful in forming silk. In the ABBB combination, the abundance of B’s, which alone rarely form organized structures, combined with a smaller amount of A allowed enough freedom for the structures to successfully form strong fibers.
Buehler, Wong, and Kaplan then asked McDonald to write music based on the different silk sequences. They found that the music written for the unsuccessful sequence with more A was much harsher than the more “gentle” B composition.
Not only was the composition of the new protein structure recognizable in the musical pieces, the music based on the more successful ABBB structure could, subjectively, be called “friendlier” and “smoother.”
“So can [McDonald] now create a new piece of music with the same basic A and B building blocks but playing on this theme and essentially emphasize the features that we now know make a better fiber?” asked the team. “And the question is—can he actually come up with a design that we wouldn’t come up with?”
-- Jessica Meade
Wong, Joyce Y., John Mcdonald, Micki Taylor-Pinney, David I. Spivak, David L. Kaplan, and Markus J. Buehler. "Materials by Design: Merging Proteins and Music." Nano Today 7.6 (2012): 488-95. Web.