<div><div><div><div><p>Insects are the most successful animal on the planet, undergoing evolutionary adaptions in size and the development of flight that have allowed access to vast ecological niches and enabled a means by which to both prey and escape predation. Possessing some of the fastest visual systems on the planet, powerful sets of flight muscles, and mechanosensors tuned to perceive complex environments in high-fidelity, they are capable of performing acrobatic maneuvers at speeds that far exceed that of any engineered system. In turn, stable flight requires the coordinated effort of these highly specialized flight systems while performing activities ranging from evasive flight maneuvers to long-distance seasonal migrations in the presence of adverse flow conditions. As a result, the exceptional flight performance of flying insects has inspired a new class of aerial robots expressly tailored to exploit the unique aerodynamic mechanisms inherent to flapping wings. Over the course of three research studies, I explore new actuation techniques to address limitations in power and scalability of current robot platforms, develop new analytical techniques to aid in the design of insect-inspired robot flapping wings, and investigate attributes of flapping wing aerodynamics that allow insects to overcome the difficulties associated with flight in turbulent flow conditions, in an effort to advance the science of animal locomotion.</p><p>Recent advancements in the study of insect flight have resulted in bio-inspired robots uniquely suited for the confined flight environments of low Reynolds number flow regimes. Whereas insects employ powerful sets of flight muscles working in conjunction with specialized steering muscles to flap their wings at high frequencies, robot platforms rely on limited sets of mechanically amplified piezoelectric actuators and DC motors mated with gear reductions or linkage systems to generate reciprocating wing motion. As a result, these robotic systems are typically underactuated - with wing rotation induced by inertial and aerodynamic loading - and limited in scale by the efficiency of their actuation method and the electronics required for autonomous flight (e.g., boost converters, microcontrollers, batteries, etc.). Thus, the development of novel actuation techniques addressing the need for scalability and use of low-power components would yield significant advancements to the field of bio-inspired robots. As such, a scalable low-power electromagnetic actuator configurable for a range of resonant frequencies was developed. From physics-based models capturing the principles of actuation, improvements to the electromagnetic coil shape and a reconfiguration of components were made to reduce weight and increases overall efficiency. Upon completion of a proof-of-concept prototype, multiple actuators were then integrated into a full-scale robot platform and validated through a series of free flight experiments. Design concepts and modeling techniques established by this study have since been used to develop subsequent platforms utilizing similar forms of actuation, advancing the state-of-art in bio-inspired robotics.</p><p>With the ability to make instantaneous changes in mid-flight orientation through subtle adjustments in angle-of-attack, the maneuverability of flying insects far exceeds that of any man-made aircraft. Yet, studies on insect flight have concluded that the rotation of insect wings is predominately passive. Coincidentally, bio-inspired flapping wing robots almost universally rely on passive rotational mechanisms to achieve desired angles-of-attack - a compromise between actuator mass and the controllable degrees-of-freedom that results in underactuated flight systems. For many platforms, the design of passive mechanisms regulating the rotational response of the wing is determined from either simulations of the wing dynamics or empirically derived data. While these approaches are able to predict the wing kinematics with surprising accuracy, they provide little insight into the effects that wing parameters have on the response or the aerodynamic forces produced. Yet, these models establish a means by which to both study insect flight physiology and explore new design principles for the development of bio-inspired robots. Using a recent model of the passively rotating insect wing aerodynamics, a novel design principle used to tune the compliance of bio-inspired robot wings is developed. Further, through the application of nonlinear analysis methods, parameters optimizing lift production in flapping wings is identified. Results from this analysis are then validated experimentally through tests preformed on miniature flapping wings with passive compliant hinges. This work provides new insight into the role passive rotational dynamics plays in insect flight and aids in the development future flapping wing robots.</p><div>Insect flight is remarkably robust, enabling myriad species to routinely endure adverse flow environments while undergoing common foraging activities and long-distance migratory flights. In contrast to the laminar (or smooth) flow conditions of high-altitude flights by commercial aircraft, insect flight occurs within the lower atmosphere where airflows are unsteady, and often turbulent. Yet despite the substantial challenge these conditions pose to an insect's physiology, flights spanning entire continents are common for numerous migratory species. To investigate how insects sustain stable flight under fluctuating flow conditions, the aerodynamic forces and flows produced by a dynamically scaled robotic insect wing immersed in a specially devised turbulence tank were examined. Despite variation in aerodynamic forces generated between wing strokes, results show that the averaged force from flapping remains remarkably steady under turbulent conditions. Furthermore, measurements of the flows induced by the wing demonstrated that unsteady aerodynamic forces generated by flying insects actively buffer against external flow fluctuations. These results provide mechanistic evidence that insect flight is resilient to turbulent conditions, and establishes principles that aid in the development of insect-inspired robots tailored for flight in adverse flow environments.<br></div></div></div></div></div>

Concrete is the most widely used construction material in the world and is responsible for 7% of global carbon emissions. It is inherently brittle, and it requires frequent repair or replacement which is economically expensive and further generates large volumes of carbon dioxide. Current methods of repair by agents such as mortar, epoxies, and bacteria result in structures with reduced strength and resiliency. Recent advances in the design of structural composites often mimic natural microstructures. Specifically, the structure of abalone nacre with its high stiffness, tensile strength, and toughness is a source of inspiration from the process of evolution. The inspiration from nacre can lead to design of a new class of architected structural materials with superb mechanical properties. This body of work first presents a method to reinforce concrete with an architected polymer phase. Second is presented how a ubiquitous enzyme, Carbonic anhydrase (CA), can be used to repair and strengthen cracked concrete, and how it can be used as an additive in fresh concrete. The first study presents an experimental and computational study on a set of bioinspired architected composites created using a cement mortar cast with brick-and-mortar and auxetic polymer phases. The impact of this unit-cell architected polymer phase on the flexural and compressive strengths, resilience, and toughness is studied as a function of microstructural geometry. All mechanical properties of the architected composite samples are found to be greater than those of control samples due to prevention of localized deformation and failure, resulting in higher strength. The microstructurally designed composites showed more layer shear sliding during fracture, whereas the control samples showed more diagonal shear failure. After initial cracking, the microstructurally designed composites gradually deformed plastically due to interlocking elements and achieved high stresses and strains before failure. Results also show that microstructurally designed composites with the architected polymer phase outperform control samples with equal volume fraction of a randomly oriented polymer fiber phase. Computational studies of the proposed unit cells are also performed, and the results suggest that the orientation of cells during loading is critical to achieve maximum performance of a cementitious composite. The implications of these results are immense for future development of high performing construction materials. The second study outlines methods for repair of concrete and lays the groundwork to develop a self-healing concrete that uses trace amounts of the CA enzyme. The CA catalyzes the reaction between calcium ions and carbon dioxide to create calcium carbonate that naturally incorporates into concrete structures with similar thermomechanical properties as concrete. The reaction is safe, actively consumes carbon dioxide, generates low amounts of heat, and avoids using unhealthy reagents, resulting in a strong structure. This repair method results in concrete samples with similar strength and water permeability as the intact materials. These results offer an inexpensive, safe, and efficient method to create self-healing concrete structures. The science underlying the creation of self-healing concrete is described, producing a material intrinsically identical to the original using the CA enzyme. Using this strategy, a preliminary self-healing concrete mix is able to self-repair fractures via hydration. This body of work addresses a major issue: Is there an efficient and ecological repair for decaying concrete infrastructure? These methods propose alternative reinforcement, alleviates high monetary and energy costs associated with concrete replacement, and consume the greenhouse gas, carbon dioxide.

Les cytochromes P450 sont des enzymes mononucléaires de fer qui catalysent l’oxydation de liaisons C-H en utilisant le dioxygène de l’air. L’activation de O2 nécessite sa réduction partielle par l'apport de deux protons et deux électrons. Ces derniers sont fournis par le réducteur naturel NADPH par l'intermédiaire d'une flavoprotéine qui permet de convertir l’adduit fer(II)-O2 en un intermédiaire de type fer(III)-peroxo dont les protonations successives permettent la rupture hétérolytique de la liaison O—O et l’obtention d’un intermédiaire de type fer-oxo responsable de l’oxydation du substrat.1 Ce projet s’inscrit dans le cadre de la chimie bio-inspirée, il a pour objectif de développer des catalyseurs de fer non-hémiques afin de réaliser l’oxydation de petites molécules organiques en utilisant le dioxygène de l’air. L’activation du dioxygène est assurée par le biais d’une électrode qui sert de source d’électrons mais également de sonde mécanistique. Pour comprendre le mécanisme de l’activation du dioxygène il est nécessaire (i) de générer les intermédiaires réactionnels oxydants (fer-oxo, fer-(hydro)peroxo) par le biais d’oxydants chimiques comme le PhIO et H2O2 puis (ii) de les caractériser par spectroscopie et électrochimie à basse température. Enfin (iii) l’étude expérimentale par voltampérométrie cyclique de la réaction du complexe de Fe(II) en présence de dioxygène couplée à des simulations de voltampérogrammes de cette même réaction (à l’aide de données thermodynamiques et cinétiques obtenues en (ii)) permettent ainsi de valider le mécanisme de l’activation réductrice du dioxygène de ce système. Ce travail a démontré que les complexes de FeII avec des ligands amines/pyridine peuvent activer le dioxygène à la surface d’une électrode en suivant un mécanisme proche de celui du cytochrome P450. A présent, la difficulté principale est de s’affranchir de la réduction prématurée des intermédiaires lorsqu’ils sont générés à l’électrode. En se basant sur ces résultats, l’essentiel du travail est à présent ciblé sur la compréhension des différents paramètres (première sphère de coordination, conditions expérimentales, …) qui peuvent modifier la stabilité des intermédiaires et donc l’efficacité de la catalyse. / Cytochrome P450 is a mononuclear iron enzyme, which catalyzes the oxidation of robust C-H bonds using O2. Activation of O2 is achieved at the Fe(II) center and requires an electron transfer to convert the iron(II)-dioxygen adduct into an iron(III)peroxo intermediate. After protonation, this latter may directly oxidize substrates or evolves to yield a powerful high valent iron-oxo moiety. In such natural systems, the necessary electrons are provided by a co-substrate NAD(P)H and are conveyed through a reductase.1The aim of this project is to develop non-heme iron(II) complexes as catalysts for the oxidation of small organic molecules by O2. Our objective is to use an electrode to deliver the electrons while providing mechanistic information at the same time thanks to a combined experimental/simulation approach using cyclic voltammetry. This work has shown that simple Fe(II) complexes bearing amine/pyridine ligands can activate O2 at an electrode surface following a mechanism that is reminiscent of the one of P450. However, the main scientific lock is to avoid the fast reduction of the reaction intermediates when they are generated at the electrode. We are currently studying how alterations of the first coordination sphere of the metal center and experimental conditions modulate the formation and the stability of these intermediates and thus, the efficiency of the catalysts.

In this study, the teeth of the Carcharodon carcharias (Great White) and the Galeocerdo cuvier (Tiger) sharks were analyzed to examine their optimized structure-property relationships and edge serrations with regards to shearing. Structure-property analysis was conducted using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy, X-ray diffraction, and optical microscopy to study the teeth using parametric optimization. Quantifying the structural properties also focused on the tooth serrations, which were captured in SEM and micrographs and were analyzed for geometric parameters using ImageJ software. Nanoindentation was performed to determine the material's mechanical properties. Further, finite element analysis (FEA) of the sharks' teeth serrations were carried out to quantify the optimum shearing performance of each serration type – zeroth (no serrations), first (a single array of serrations), and second (a secondary array of serrations upon the first array) order serration. Here, serration order, bite velocity, and angle-of-impact for ascertaining sharks' teeth shearing performance were analyzed. FEA results showed that serrated edges reduced the energy required to pierce and shear materials as the angle of penetration moved away from perpendicular to the surface. These bioinspired findings will help advance the design and optimization of engineered cutting tools.

<p>Structures with inherent shape change capabilities enable adaptive, efficient designs without the weight and complexity of external actuators and sensors. Morphing structures are found in nature: plants are able to achieve fast motion without muscular or nervous systems. For example, the Venus flytrap snaps to a closed state with spatially distributed curvatures in less than one second. In contrast, synthetic shape change has been limited by a trade-off between complexity and speed. Shape memory polymers (SMPs) can remember complex shapes, but morphing is slow and one-way. Multistability due to mechanical buckling is fast and reversible, but it has been limited to simple shapes. Furthermore, many examples of biological shape change follow logical patterns with mechanisms that selectively respond to environmental stimuli. This suggests that synthetic morphing structures may also lend themselves to alternative forms of sensing, memory, and logic.</p> <p><br></p> <p>In this research, we introduce a new method of using SMPs in combination with the hierarchical architectures of pre-strained multistable laminates to create switchable multistable structures (SMS). An SMS can remember multiple permanent shapes and reversibly snap between them. We use extrusion-based 3D printing to encode contrasting shape memory-based pre-strain fields in a bilayer. Above the SMP’s glass transition temperature, the SMS becomes compliant and remembers multiple encoded permanent shapes with fast snap-through between them. Below the transition temperature, the SMS regains its stiffness and is fixed in a single state. The geometric freedom of 3D printing enables the design and manufacture of bioinspired structures with complex pre-strain fields and deflections. The developed printing method is applied in multiple subsequent studies, including mechanical pixels, self-folding spring origami structures, and multistable structures printed with thermoset composite inks. </p> <p><br></p> <p>The highly nonlinear behavior of bistable, pre-strained structures makes their design difficult and nonintuitive. Generally, these structures are designed using a slow, iterative process with finite element analysis (FEA). We aim to solve the inverse optimization problem: start with target stable states and solve for the necessary pre-strain distributions. To this end, we develop and implement the switching tunneling method (STM) to design pre-strained,</p> <p>multistable structures. Instead of FEA, we leverage analytical solutions for gradient-based optimization. Tunneling allows for the efficient search of a design space which may contain multiple local and global minima. Switching enables us to take advantage of two different function transformations, depending on if the search is far from or close to a minimum. The STM is validated through FEA and experiments for both conventional and variable</p> <p>pre-strain bistable structures.</p> <p><br></p> <p>Structures designed to react to external conditions or events offer the opportunity to directly integrate sensing, memory, and computation into a structure. This concept is explored using metasheets composed of locally bistable unit cells, which display spatiotemporal mechanical sensing (mechanosensing) and memory. A unit cell consists of a bistable dome with a piezoresistive strip at the base; the resistance indicates the state of the dome. The mechanics of bistability offer inherent filtering and nonlinear signal amplification capabilities, tunable via geometric parameters. Metasheet arrays of these unit cells display distributed sensing capabilities, as well as hierarchical multistability.</p> <p><br></p> <p>We explore the use of time-dependent material properties combined with the mechanics of multistability to encode many unique values within a single mechanosensor unit cell, beyond binary memory. When the piezoresistive material is viscoelastic, cyclic loading causes cumulative changes in both the ground and inverted state resistances. Effectively, the metamaterial is able to count how many times an external force has been applied; this count is stored in the metamaterial’s intrinsic, measurable properties.</p> <p><br></p> <p>This work demonstrates the importance of incorporating memory concepts into structural design, which enables multistability with complex stable shapes, as well as spatiotemporal sensing and memory capabilities. Engineered systems require increasingly adaptive and responsive structures to improve efficiency. The incorporation of inherent memory and sensing enables the complex behaviors needed to interact with unstructured environments</p> <p>and biological features, a pressing issue for aerospace, soft robotics and biomedical devices. The methodology developed here to manufacture, design, and analyze multistable structures advances the state of the art and makes their implementation more practical.</p>

<p>  </p> <p>Many engineering structures are designed to withstand a critical mechanical load before failure. When a load greater than the critical load is encountered, the manner of structural failure is important. Nature has been a source of technical inspiration for centuries, and the power of modern scientific investigative techniques has enhanced engineers’ abilities to learn from millennia of evolutionary mechanical refinement. </p> <p>Chitons, a family of marine mollusks, feed on algae attached to rocky substrates, and parts of their feeding organs are subjected to varied loads in the process. In this work, the manner of failure of a chiton’s tooth and supporting structure is investigated, and it is suggested that mechanical details of the structure enable load-limiting and fail-safe performance that protects the animal from potentially dangerous overloading.</p>

<p dir="ltr">The goal of this thesis is to design nature-inspired biomimetic materials that recapitulate essential features of tissues for biomedical applications including tissue modeling of drug transport and surgical adhesion.</p><p dir="ltr">The first part of this thesis utilizes collagen and glycosaminoglycans to mimic tissues for preclinical modeling of large-molecule drug transport. We first utilize hydrazone crosslinking chemistry with hyaluronic acid to form interpenetrating networks with collagen at different concentrations. The interpenetrating networks enabled a wide range of mechanical properties, including stiffness and swellability, and microstructures, such as pore morphology and size, that can better recapitulate diverse tissues. The mechanical and microstructural differences translated into differences in transport of the macromolecules of different sizes and charges from these matrices. Large macromolecules were impacted by mesh size, whereas small macromolecules were influenced primarily by electrostatic forces. The tunable properties demonstrated by the collagen and crosslinked hyaluronic acid hydrogels can be used to mimic different tissues for early-stage assays to understand drug transport and its relationship to matrix properties.</p><p dir="ltr">We then explore how the glycosaminoglycans hyaluronic acid, chondroitin sulfate, and heparin in collagen hydrogels influence drug transport via glycosaminoglycan-drug interactions and network development. Incorporating different types and concentrations of glycosaminoglycans led to glycosaminoglycan-collagen hydrogels with a range of collagen networks and negative charge densities to recapitulate different tissue compositions. Hyaluronic acid increased the overall viscosity of the hydrogel matrix, and chondroitin sulfate and heparin altered collagen fibrillogenesis. All three GAGs formed concentration-dependent polyelectrolyte complexes with positively charged macromolecules. Transport of positively charged macromolecules through collagen gels with chondroitin sulfate and high concentrations of heparin was inhibited due to complexation and charge effects. Conversely, collagen with low concentrations of heparin hastened the transport of macromolecules due to the limited collagen network resulting from fibrillogenesis inhibition. Overall, the addition of different GAGs into tissue models can better recapitulate native tissue to accurately predict therapeutics transport through a variety of tissues.</p><p>17</p><p dir="ltr">The second part of this thesis investigates the impact of pH and oxidation on an elastin- and mussel-inspired surgical sealant. We combined sodium periodate, an oxidizer, with an L-3,4-dihydroxyphenylalanine-modified elastin-like polypeptide to elucidate how the crosslinking mechanism and intermediate formation impacted adhesion, cure time, and stiffness. Formulations resisted burst pressures greater than physiological internal pressures. They did not swell and had stiffnesses similar to those of soft tissues, and their gelation times varied from seconds to hours. Small increases in the formulation pH led to the formation of α,β-dehydrodopamine intermediates which facilitated the development of multiple crosslinking networks. The mussel-inspired elastin-like adhesive can serve as a model of mussel proteins to further improve our understanding of mussel chemistry. This study exemplifies the importance of pH and oxidation on the performance of mussel-inspired adhesives in surgical sealing within physiological environments.</p><p dir="ltr">The final part of this thesis explores using biomimetic designs in an outreach activity aimed at engaging high school women in chemical engineering. The design and application of the activity led to increased interest in chemical engineering among the participants. There was greater alignment between students' aspirations and the field of chemical engineering, highlighting the potential for such outreach initiatives to inspire future generations of chemical engineers.</p>

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The needle-based procedures are usually considered minimally invasive. However, in insertion into soft tissues such as brain and liver, the tissue damage caused by needle insertion can be very significant. From the literature, it has been known that reduction in needle insertion and extraction forces as well as tissue deformation during the insertion results in less invasive procedure. This work aims to design and develop a new bioinspired design for surgical needles which reduce the insertion and extraction forces of the needle, and its damage to the tissue. Barbs in honeybee stinger decrease its insertion force significantly. Inspired by that finding, a new honeybee-inspired needle was designed and developed, and its insertion mechanics was studied. To study the insertion mechanics of honeybee-inspired needle, insertion tests into artificial and biological tissues were performed using both honeybee-inspired and conventional needles. The barb design parameters effects on needle forces were studied through multiple insertion and extraction tests into PVC gels. The design parameters values of the barbs were experimentally modified to further reduce the ultimate insertion and extraction forces of the needle. Bioinspired needle with modified barb design parameters values reduces the insertion force by 35%, and the extraction force by 20%. To show the relevance, the insertion tests into bovine liver and brain tissue were performed. Our results show that there was a 10-25% decrease in the insertion force for insertions into bovine brain, and a 35-45% reduction in the insertion force for insertions into the bovine liver using the proposed bioinspired needles. The bioinspired and conventional needles were manufactured in different scales and then used to study the size scale effect on our results. To do so, the insertion tests into tissue-mimicking PVC gels and liver tissues were performed. The results obtained for different sizes of the needle showed 25-46% decrease in the insertion force. The tissue deformations study was conducted to measure tissue deformation during the insertion using digital image correlation. The tissue deformation results showed 17% decrease in tissue deformation using barbed needles. A histological study was performed to accurately measure the damage caused by needle insertion. Our results showed 33% less tissue damage using bioinspired needles. The results of the histological study are in agreement with our hypothesis that reducing needle forces and tissue deformation lead to less invasive percutaneous procedures. / Mechanical Engineering

Biological systems offer novel and efficient solutions to many engineering applications, including marine propulsion. It is of interest to determine how fish interact with the water around them, and how best to utilize the potential their methods offer. A stingray-like fin was chosen for analysis due to the maneuverability and versatility of stingrays. The stingray fin was modeled in 2D as a sinusoidal wave with an amplitude increasing from zero at the leading edge to a maximum at the trailing edge. Using this model, a parametric study was performed to examine the effects of the fin on surrounding water in computational fluid dynamics (CFD) simulations. The results were analyzed both qualitatively, in terms of the pressure contours on the fin and vorticity in the trailing wake, and quantitatively, in terms of the resultant forces and the mechanical power requirements to actuate the desired fin motion. The average thrust was shown to depend primarily on the relationship between the swimming speed and the frequency and wavelength (which both are directly proportional to the wavespeed of the fin), although amplitude can be used to augment thrust production as well. However, acceleration was shown to significantly correlate with a large variation in lift and moment, as well as with greater power losses. Using results from the parametric study, the potential for power regeneration was also examined. Relationships between frequency, velocity, drag, and power input were determined using nonlinear regression that explained more than 99.8% of the data. The actuator for a fin was modeled as a single DC motor-shaft system, allowing the combination of the energetic effects of the motor with the fin-fluid system. When combined, even a non-ideal fin model was able to regenerate more power at a given flow speed than was required to swim at the same speed. Even in a more realistic setting, this high proportion of regenerative power suggests that regeneration and energy harvesting could be both feasible and useful in a mission setting. / Master of Science / Animals interact with the world much differently than engineered systems, and can offer new and efficient ways to solve engineering problems, including underwater vehicles. To learn how to move an underwater vehicle in an environmentally conscious way, it is useful to study how a fish’s movements affect the manner in which it moves through the water. Through careful study, the principles involved can be implemented for an efficient, low-disturbance underwater vehicle. The particular fish chosen for in-depth study was the stingray, due to its maneuverability and ability to travel close to the seafloor without disturbing the sediment and creatures around it. In this work, computational analysis was performed on a model of a single stingray fin to determine how the motion of the fin affects the water around it, and how the water affects the fin in turn. The results were analyzed both in terms of the wake behind the fin and in terms of how much power was required to make the fin move in a particular way. The speed of the fin motion was found to have the strongest effect in controlling swimming speed, although the lateral motion of the fin also helped with accelerating faster. Additionally, the potential for a robotic stingray fin to harness power from the water around it was examined. Based on results from simulations of the fin, a mathematical model was formulated to relate energy harvesting with the flow speed past the fin. This model was used to determine how worthwhile it was to use energy harvesting. Analysis of the model showed that harvesting energy from the water was quite efficient, and would likely be a worthwhile investment for an exploration mission.