Biological Sensor Inspired by a Worm's Strength

By Benedette Cuffari, M.Sc.Mar 24 2017

Image Credit: Shutterstock.com/

The Nereis virens is a burrowing marine polychete that is common to the North Atlantic region of the world. One of the most impressive characteristics about this worm is its incredibly strong fang-like jaws, which play a primary role in its feeding and defense mechanisms.

With a hardness and stiffness strength comparable to that which is shown in human dentin, the bony tissue present beneath the enamel of the tooth, the jaw of the Nereis virens exhibits properties that are superior to those that are present in synthetic polymers¹. With a reported hardness within the range of 0.4-0.8 gigapascals (GPa)², the presence of metals, particularly zinc (Zn), in its molecular structure makes the material much stronger as a result of its ability to bond with the proteins. These dynamic protein-metal bonds allow this complex molecular network of the jaw to be capable of rapidly responding to changing environmental conditions through its expansion and contraction behavior.

Comprised of approximately 90% protein constituents, the jaw structure has inspired researchers to develop novel materials that demonstrate similar physical attributes to resemble its architecture, composition and mechanical properties. As such, researchers at the Massachusetts of Technology’s Department of Civil and Environmental Engineering (CEE) were able to draw from previous protein structural studies of the Nereis jaw and develop a multiscale model that is able to predict the mechanical behavior of materials containing the Nvjp-1 protein, which is predominantly present in this worm². With this model, the research team led by Zhao Qin successfully visualized the atomic arrangements and molecular conformations that represent the supreme mechanical capabilities of this protein material. This predictive model allowed researchers to more fully understand how the protein forms and adjusts to different pH levels, in which this information has been speculated to guide designs for sensor and soft robot devices¹.

The Nvjp-1 protein is chiefly composed of histidine-rich Zn binding proteins. The presence of the histidine amino acids in this molecular bond results in a strong attraction to ions present in the environment, which could account for the overall chemical reaction that takes place between the amino acids and metal ions present within this protein¹. As the environmental conditions change, the histidine-Zn protein interactions follow this change through ensuing protein conformational changes that therefore affect the way in which the protein material responds.

As a result of not only its ability to maintain its structure in varying acidic environments, the flexible nature of this material makes it ideal for use in environments that exhibit a constant flux in pH. The stomach, for example, is one of the primary biological systems that exhibit varying pH levels. When empty, a normal human stomach will maintain a pH within the range of 1-3, which is extremely acidic in order to maintain the presence of gastric acid that is responsible for food digestion³. Upon food consumption, the pH levels in the stomach raise to as high as 4-5.

As a result of the constant acidity fluctuations that take place not only in the stomach, but also in the small intestine and various other biological systems, the application of the protein in the Nereis jaw could pave the way for multifunctional materials to resemble its structure and exude these properties for a wide variety of appropriate electronic devices¹. Current research trends have become increasingly popular in finding methods to develop ingestible sensors that are capable of resisting the acidic environment in the stomach in order to monitor a variety of biological conditions such as bacterial infections, disease diagnosis, medication monitoring and much more⁴. The Nvjp-1 protein could therefore hold a promising future if implemented in these ingestible sensors, as well as a variety of other biological applications.

References

1. Broomell, Chris C., Sue F. Chase, Tom Laue, and J. Herbert Waite. "Cutting Edge Structural Protein from the Jaws of Nereis Virens." Biomacromolecules 9.6 (2008): 1669-677. Web.
2. Schmitt, Carolyn. "Worm-inspired Material Strengthens, Changes Shape in Response to Its Environment." MIT News. 20 Mar. 2017. Web. http://news.mit.edu/2017/bio-inspired-material-changes-shape-and-strengthens-in-response-to-environment-0320.
3. Loomis, Howard F., D.C. "Digestion in the Stomach." Food Enzyme Institute. Web. http://www.foodenzymeinstitute.com/articles/digestion-in-the-stomach.aspx?list=bydate.
4. Staedter, Tracy. "Edible Sensors Powered by Stomach Acid." Seeker.com. 22 Sept. 2015. Web. http://www.seeker.com/edible-sensors-powered-by-stomach-acid-1770264729.html.
5. Shutterstock.com/

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