Vladimir Tsukruk, Professor, School of Materials Science and Engineering, Georgia Institute of Technology.
Dr. Tsukruk defined adaptive materials and structures as comprising the ability to sense external stimuli (ideally with low detection limit and large dynamic range) and actuate a calibrated reaction (e.g., change in organization) governed by a feedback loop to achieve a desired state (e.g. shape, compliance, appearance). He noted that many examples of adaptive and other uniquely beneficial materials and systems exist in nature, including:
• Adaptive colors in butterflies, octopi – photonic, sensing, camouflaging
• Dynamic adhesion in gecko feet – climbing, holding
• Self-healing biological parts – self-healing materials
• Reptilian locomotion – movement on complex terrains
• Dog canine – remote trace chemical sensing
• Silk materials – tough lightweight nanocomposites
• Night vision in some species – thermal sensors
• Wave tracking in seals and fish – underwater monitoring
• Spider hair air flow receptors – mechanical sensors
Devices with unique functionality and performance can be developed by characterizing the mechanisms underlying biological materials and recapitulating them synthetically. Using an example from his own laboratory, Dr. Tsukruk stated that the unique ability of snakes to detect small temperature changes as part of their infrared detection capabilities was traced to a special organ in which thermal expansion of air pockets leads to deformation of a membrane, which is detected in downstream cell signaling. Synthetic nanostructures with such a membrane arrangement were created and exhibited temperature sensitivity of 10 mK, with a spatial resolution of 30 µm when used in an array. Dr. Tsukruk said that at the time they were developed, these sensors showed unique performance compared to state-of-the-art bolometers. Importantly, these sensors are a passive material: temperature changes deform membranes so as to produce changes in reflectivity, which can be assayed as needed. He pointed out that a similar approach was used to mimic the ability of spiders to detect sound waves using unique hair structures, and to mimic the ability of fish to sense fluid velocity. In the latter case, a biomimetic structure had an unprecedented fluid motion detection limit of 2 µm/sec.
Dr. Tsukruk noted that the development of bio-inspired materials requires close multidisciplinary collaboration involving biologists and engineers. There are no comprehensive catalogs of useful mimicable biological materials/structures, and most are identified through word of mouth. Productive collaborations between engineers and biologists are rare and are usually initiated in the United States (sometimes with goal-driven introductions made by, e.g., DARPA). He stated that foreign biologists, who may not have previously thought about potential bioinspired applications, are drawn into collaborations with US engineers. In several cases they have subsequently established similar collaborations closer to home (examples were provided for Europe). A rough estimate is that fewer than 30% of engineers developing bioinspired materials have biomedical end-goals. Most are pursuing consumer product, defense or energy objectives.
While most of the work described by Dr. Tsukruk was carried out in the United States and Europe, he believed China would also make advances in this area. He provided the example of Peking University, which established a materials science program only ~5 years ago, but has managed to recruit a group of top scientists, most of whom previously held academic positions in the United States. Its graduate program was copied from Georgia Tech. In addition, Russia’s SkyTech and Saudi