Bio-sensing & Bio-actuation Technologies Pioneered At the Micro/Nano-scales

With the rapid advancements in micro- (e.g., MEMS) and nano-scale (e.g., carbon nanotubes) manufacturing, new generations of sensing and actuation technologies that are bio-inspired can be proposed. Specifically, nature bottom-up design paradigm can be mimicked in the laboratory so as to encode sensing and actuation functionality in a new-generation of multifunctional materials intentionally structured at the nano- and sub-nano-scales. Furthermore, biological actuation concepts can inspire a new generation of micro-scale devices fabricated in silicon substrates and using novel material electro-deposition techniques. Specific topics of collaborative interest include:

• Development of multifunctional thin film materials designed at the nano-scale for distributed sensing in civil and mechanical infrastructure systems. Here, the sensing concepts of human skin, which is inherently multi-modal and distributed, are mimicked.
• Exploration of next-generation power-harvesting technologies inspired by the process of photosynthesis naturally occurring in plants.
• Development of next-generation large load and large motion actuation technologies inspired by the nastic action in plants.
• Creation of advanced signal processing techniques based on artificial intelligence and cognitive reasoning common to intelligent life forms.
• Development of fault-tolerant sensors and sensor networks that can self-identify faults through reinforced learning and autonomously repair or work-around the failed sensors.
• Exploration of innovative piezoelectric thin films structured at the nano-scale to behave like muscles in animals.
• Develop hearing capabilities in untraditional frequency bands for hearing damage. Here, the hearing mechanisms that provide some animals like bats and inspects with hearing capabilities that are extremely accurate, of high fidelity and with excessive range, will be mimicked to yield listening devices for damage at the micro-scale.

Dragonfly's compound eye for surveillance systems

A dragonfly's compound eye is made up of 30,000 or so individual lenslets, called omnitidia, each offering a different viewing angle, and giving the insect 360-degree vision. Currently, an artificial compound eye has been developed. Each hemisphere of the eye contains 8,700 microlenses and has a viewing range of 180 degrees [University of California at Berkeley].

Bio-inspired Materials

The realm of bio-inspiration and bio-mimicking can revolutionize the materials that we use in the design and construction of civil or mechanical structural systems. For example, concrete materials are inherently brittle and are prone to cracking and spalling. New materials exhibiting incredible strength, resilience to extreme loads and endowed with self-sensing and even self-healing capabilities would be a core focus of this thrust. Some specific topics of collaborative interest include:

• Creation of ductile materials designed at the macro- and nano-scales that are extremely durable yet offer similar levels of strength as ordinary concrete. For example, the brick and mortar configuration nature uses to create ultra-strong nacre (i.e., mother of pearl) could be mimicked to make new cementitious materials.
• Mimicking of biological healing is a fertile area that would revolutionize the creation of civil and mechanical engineering materials. For example, the biological reactions that occur in animal wounds (e.g., cuts) to regenerate new skin can be explored to inspire means of having cracks self-heal in civil and mechanical structures. In the cementitious material domain, special chemical additives that react to moisture from rain or humidity could induce regeneration of the cement matrix in cracks.
• Creating multi-functional, smart composite structures that can utilize the circulation features of animals and plants for actuation (e.g., nastic motion in plants) and self healing.

Sustainable / green construction materials

Three MIT designers - Mitchell Joachim, Lara Greden and Javier Arbona - created this living treehouse in which the dwelling itself merges with its environment and nourishes its inhabitants. Fab Tree Hab dissolves our conventional concept of home and establishes a new symbiosis between the house and its surrounding ecosystem. The house is constructed by green materials-tree branches which can conform itself to desired shape. Besides, this specific structure can provide sustenance for the inhabitants and other living creatures who interact with the structure.

Bio-inspired Monitoring and Warning Systems for Earthquakes

Earthquakes are extremely lethal in part because they cannot be predicted. Furthermore, early warning systems for earthquakes remain a difficult technology to implement in practical settings. To save human lives, new sensors for development of bio-inspired early detection system for warning of eminent earthquakes are a primary interest for future Taiwan-US collaborations.

The biological structures and mechanisms that contribute to the exceptional hearing and sensing abilities of animals such as frogs, fish, lizards and snakes, among others, will be explored to create novel sensors that can be used for early detection systems for earthquakes. For example, it is widely known that animals exhibit unusual activities proceeding major earthquakes. Ultimately, we hope that an understanding of animal detection and recognition mechanisms will eventually help in the development of bio-inspired sensors for earthquake monitoring and warning. We will emphasize mechanisms and modeling of biological detection of information that can be used in warning of eminent seismic events in lieu of (and as a complement to) research on prediction of seismic events. Collaborative topics include:

• Studying and mimicking exceptional hearing mechanism of animals to provide insight into the design of a sensor to detect infrasound for frequency below 20 Hz. For example, elephants use infrasound waves for communication over extremely long distances (e.g., over hundreds of kilometers). Frogs and fish are also endowed with impressive low frequency detection mechanisms.
• Other animals such as lizards, snakes, and birds will likely provide clues for mimicking their abilities to sense and detect a major earthquake and to provide a few extra seconds (perhaps minutes) warning people to seek safety from the arriving earthquake.

Fish-Inspired Acoustic Detection

It has been illustrated by many researchers that fishes have an acute sensitivity to infrasound, even down to below 1Hz. The otoligh organs are the sensory system responsible for this ability [O. Sand]. Utricle as one of the two otolith organs located in the vertebrate inner ear has an array of hair cell filaments, which is shown in the upper image[Wikipedia]. Hair cell is the basic unit for flow or acoustic sensing system of fishes. Dr Change Liu's group has developed an artificial hair cell (AHC) for flow sensing inspired by fish. Their AHC model is shown in the lower image.

Bio-inspired and Nano Sensing Medical Devices

Sensors of micro and nano scales can be embedded and integrated to render an embedded system for sensing, and possibly also actuation. For example, the carbon nanotube (CNT) was found to display strain-gage like sensing capability, with a larger gage factor than semiconductor gages. Such nano sensors can be integrated to form artificial skins for biomedical sensing and possibly also actuation. The development of such biosensors can also empower the intelligence at the contact interface (esp. viscoelastic behavior) typical of biomedical tissues. In addition, CNT forest, grown in meso scale with millions of CNT weaved together, can also find novel applications as a nano-machining tool, utilizing the ductile regime of materials removal on brittle materials in micro/nano scales, similar to those found in the diamond single- point cutting tool. This will involve the modeling of nanomechanics, micro/nano tribology, and process optimization in an integrated modeling of manufacturing process and control.

Bio-sensing and bio-actuation are natural mechanisms inside human bodies after millions of years of evolution. As a result, biosensors (e.g., humanears) have extremely high sensitivity, whereas bioactuators (e.g., tracheae during coughing) have extremely high efficiency. One potential application for these bio-inspired mechanisms is medical devices. Bio-inspired medical devices have several advantages over traditional medical devices. First, bio-inspired medical devices have much better performance, because they adopt the mechanisms and functions of human bodies that have evolved for millions of years. Second, bio-inspired medical devices will integrate better with human bodies, because they are bio-mimetic.

Recent advances in microfabrication and nanotechnology provide an excellent platform to develop bio-inspired medical devices. For example, nanorods resemble cilia in human bodies with enormous surface areas. Possible collaborative topics include:

• Advanced hearing implants simulating hair cells in human inner ears.
• Bio-inspired locomotives to position endoscopes.
• Bio-mimetic membranes for kidney dialysis.
• Bio-conformable and degradable catheter.
• Smart hip joints or knee joints with wear monitoring capability.

Cricket-Inspired Hearing Aid

Adult crickets have around 1000 or more hairs, 100 to 1500 microns long on organs called cerci, which allows them to detect air movements down to 1mm/s or less, indicating the possible approach of predators. The high sensitivity comes about because the tilting hairs apply pressure to neurons at their bases, greatly enhanced by mechanical lever amplification [CICADA, Netherlands-based University of Twente].

Civil Infrastructure System

The past two decades have witnessed an explosive growth of sensor and smart structure technologies for infrastructure management (Liu, Tomizuka and Ulsoy, 2006). For example, many new sensor technologies have been proposed including wireless sensors (Spencer, et al., 2004; Lynch and Loh 2006), active piezoelectric sensors (Wu and Chang, 2001; Lee and Sohn, 2006), MEMS sensors (Judy 2001), fiber optic sensors (Kim and Feng, 2006; Glisic and Inaudi 2007), among many others. Similarly, actuators and control systems have been proposed for structures prone to damage during excessive loading such as that presented by earthquakes (Chu, et al., 2005). While great technological advances have been made in the smart structure field, practical field implementation of these technologies has been lagging behind technology development in the laboratory (DeRisso, et al., 2007). This can be due in part to fundamental flaws in the current approach to sensing and actuation proposed for infrastructure systems. First, existing sensors do not directly detect damage (Adams 2007); rather, sensors make measurement of structural responses with physics-based models necessary to correlate measurements to damage. The complexity inherent to this inverse problem makes damage detection incredibly difficult to implement in a generic/black-box manner (Doebling, et al., 1996). Furthermore, damage is inherently a distributed phenomena occurring on the local-scale. As such, the traditional use of point-based sensors (e.g., strain gauges, accelerometers) only provides information at a given point in the structure; it is probabilistically likely damage will not occur directly beneath the sensor. Hence, dense networks of point-based sensors are necessary to provide sufficient data to analytically model the continuum behavior of the structure. The sensor densities necessary are not only costly to an infrastructure owner, but the traditional tethered monitoring systems necessary to collect measurements from the sensors become increasingly labor-intensive to install. While wireless sensors have emerged as promising alternatives to tethered sensors (Spencer, et al., 2004; Lynch and Loh, 2006), the absence of power sources offering decades of life expectancy severely limits their adoption.

Mechanical System

Aside from civil infrastructures, smart structures and materials have found wide applications in various mechanical systems for the last 20 years. Various sensors are used to monitor health of aging aircraft and turbine engines hoping to detect cracks at their earliest stage to prevent catastrophic failures. Energy harvesting systems are considered for future aircraft to reduce weight and costs of wiring. Biomedical devices, such as piezoelectric forceps, have been developed to conduct minimally invasive surgery. Semi-active and active vibration control is instrumented to make transportation vehicles more comfortable. Acoustic noise control systems have been commercialized to offer individual quiet zones. These smart mechanical systems appear in strategically important applications that have potential impact to the well being of our societies, such as transportation, power generation and health care. Despite the progress in many smart mechanical systems, they often face similar challenges and limitations in sensors and actuators as those encountered in smart civil infrastructures (e.g., point-based and indirect sensing).

The current mode of smart structure technology development yields incremental improvements in the functionality and performance of sensors and actuators due to the aforementioned limitations of current technologies (e.g., point-based, indirect damage sensing). When this slow pace of technology development is compared against the backdrop of the rapidly growing demand for greater infrastructure management and advanced mechanical systems, it is clear that entirely new sensing and actuation paradigms are necessary to accelerate the development of smart structure technologies tailored for the complex task of monitoring and controlling infrastructure systems. One promising new paradigm is bio-inspired sensing and actuation. Our fundamental understanding of nature and its evolutionary approach to the design of highly-optimized biological systems can be brought to bear upon the vexing and complex problems facing the current generation of civil and mechanical systems.