Hagfish make a unique material with remarkable properties. When provoked or attacked, the animal releases a small volume of biopolymer/biofilament material that unfolds, assembles, and expands in water by a factor of 10,000. The resulting gel is cohesive, forming a clogging network used for defense. If analogous engineering materials could be developed to mimic this behavior, numerous practical applications could result, as noted in the Broader Significance and Impact section of this abstract.
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The research objective of this proposal to understand the structure-property mechanics of hagfish defense gel and to articulate this understanding in a way that will enable future work to design bioinspired soft materials with novel functionality. Our approach is to develop rheological measurement techniques for ultra-soft materials generally, pushing the experimental limits of current rheometers by using techniques such as inertio-elastic ringing for linear and nonlinear rheology. With these techniques we will measure the rheology of various hagfish gel composite systems with varying mass fractions and ratios of mucin and thread components, including those not found in nature. The mathematical modeling approach will start with transient network theory, based on strain-stiffening nonlinear elastic elements connected with reversible crosslinks that weaken under stress and provide stress-softening. We will then test these structure-property hypotheses by comparing with experiment, refining, and iterating the mathematical models. The structure-property relationships developed here will be applicable beyond hagfish gel, and generically include other physical gels based on polymeric and/or fibrous components. This would include keratin filament networks, collagen networks, mucin gel networks, and gluten networks, which have all displayed a similar nonlinear rheological behavior to that observed with the hagfish gel.
Broader Significance and Importance:
Hagfish defense gel starts as a small volume of material which then undergoes dramatic volumetric expansion, producing an ultra-dilute, super-elastic gel that blocks the flow of liquid through it. This behavior is unmatched by current engineering materials. The understanding developed by the research here could therefore bring about radical changes in materials available for applications including but not limited to (i) Oil-drilling safeguards, to plug or slow oil leaks with a small amount of material that is pre-deposited in the system or delivered to the system as needed; (ii) Defense, to tangle or clog engine intakes, respiratory air intakes, or water-cooling intakes by delivering a small packet of material with big expansion at destination; (iii) Cell cultures, to provide a sparse network of fibrous thread elements which may offer a unique architecture and lengthscale for tissue scaffolds and 3D cell cultures, complementing smaller lengthscale and denser collagen fiber scaffolds; (iv) Manufacturing non-woven materials with new paradigms of unraveling threads, complementing melt blowing, melt spinning, and electro-spinning processes. The hagfish gel material is unique, yet its components are of general interest, since they are composed of the building blocks of many other soft biological materials.
Broadening Participation of Underrepresented Groups in Engineering:
The research will be integrated into the educational and outreach objective, which is to encourage diversity and broad participation of underrepresented groups in engineering. This will be achieved through the development of The Rheology Zoo, a hands-on curated library of rheologically interesting materials that will serve as a platform for outreach, engagement, and undergraduate research opportunities. Students will, for the first time, see the remarkable behavior of seemingly simple materials, see how that behavior is so important in their daily lives, and be encouraged to think creatively about new engineering opportunities for soft materials. The Zoo will be a venue for part of a six-week summer program to help incoming students transition to college, including a large number of students from underrepresented groups. Students will study interesting viscoelastic materials from The Zoo, make simple measurements, and present their work to pre-college students outside the university to further broaden exposure and recruitment to engineering. Student projects will be integrated into The Zoo, providing a self-sustaining mechanism for the collection beyond the funding life of this proposal.
This research has been funded through the Broadening Participation Research Initiation Grants in Engineering solicitation, which is part of the Broadening Participation in Engineering Program of the Engineering Education and Centers Division.
