EAGER:(Early-Concept Grant for Exploratory Research)- Loss-Free Energy Storage and Transition Due to Nature's Miracle Protein Resilin
Mechanical systems with programmable elastic properties to permit loss-free transmission or storage of mechanical energy are the ultimate dream of engineers. Nature offers readily available model systems found in the cuticle of insects. It is assumed that the highly elastic protein resilin- in specific cuticle places leads to optimal energy storage. The central hypothesis is that not only the material itself but also the positioning of elastic elements result in a nearly loss-free energy transport. The objective of the proposed project is to explore the static and dynamic properties of highly elastic cuticle with advanced nanomechanical testing methods. The local probing of the individual elastic elements inside the cuticle under various conditions is original and will reveal fundamentally new information that is not accessible with any other method.
Understanding the mechanical behavior of resilin and the optimal positioning in the insect cuticle will lead to the design of new rubberlike polymers and novel micromechanical spring-systems with extraordinary low energy loss. The expected findings will result in a new quality of micro and nanomechanical systems, which will be superior to any other existing solutions and have a wide range of applications. Energy efficient locomotor systems are of high interest in the construction of minuscule robots for operational use in areas dangerous for human safety and health. Engineering systems based on the example of the excellent flight maneuver of the dragonfly or the efficient jumping mechanism of grasshoppers will have, without any doubt, similar impact as surfaces designed after the LOTUS effect.
This project was focused on two aspects associated with natural and synthetic protein-based biocomposites. The natural biocomposite research examined the mechanical properties of sand field cricket (Grillus firmus) leg joints using advanced nanomechanical testing methods. These joints were shown for the first time (see Fig. 1) to contain a protein called resilin that has been shown by others to have very low energy loss during deformation. Nanoindentation was used to detect significant changes in the mechanical properties of joints (with a layered structure as shown in Fig. 2) from different morphs and genders. In particular, long-winged females exhibit higher elasticity and resilience than short-winged females. This result reflects a trade-off between dispersal ability by walking and reproduction for males and females of the two morphs. It is believed that highlighting the relationship between the structure and mechanical property of the trochanteral-femoral joint of different morphs and genders provides important data so that new composite materials can be developed with improved mechanical properties. Inspired by this natural biocomposite, a synthetic protein-based composite was made from the elastomeric protein elastin in which polycaprolactone fibers were embedded. Nanoindentation testing was used to investigate the differences in the mechanical properties of this biocomposite between materials crosslinked for different time periods (2, 4, and 6 hours). Furthermore, the characterization of the viscoelastic properties by nanoindentation revealed the composite crosslinked for 4 hours as an optimized strain energy storage material when employed at low frequency load cycles. In addition, the poroviscoelastic properties of these protein-based composites were studied using computational models of the indentation measurements. With this approach, it was possible to quantify measurements of the poroviscoelastic properties of these biocomposites. Such techniques are expected to find broader applications for quantifying the influence of crosslinking density and environmental factors on the nanoscale mechanical properties of many other similar materials. In summary the intellectual merit of this research provides an understanding of the development of materials in nature so that synthetic materials can be designed for optimum performance. The broader impacts of this work were related to the expansion of research activities to others. In particular, the PI was involved with the UNL UCARE (undergraduate creative activity and research experiences) program and the NSF REU program, "Undergraduate Research Opportunities in Functional Nanomaterials and Nanoscience at UNL." A distinctive feature of this project was its interdisciplinary nature, thereby encouraging students from both engineering and biology to participate. The PI has also been active in the recruitment of women into the PhD program at UNL. This NSF project supported Ms. Céline Hayot to completion of her PhD. The PI currently supports 3 other women PhD students and plans to continue to recruit highly-qualified individuals from diverse backgrounds for on-going and future research projects.
