1,720,972 research outputs found
Light-Fueled Liquid Crystal Networks for Aquatic Soft Robotics
No full textThe field of soft robotics has developed in response to the need for mechanisms that can operate safely in interaction with humans. Within the field of soft robotics, there is a growing demand for the development of small-scale soft devices capable of non-invasive medical interventions in a variety of technologies, including medical microrobotics, biosensing, and biomedical engineering. Among the many materials used for small-scale soft robotics, liquid crystal networks (LCNs) are of particular interest. LCNs are molecularly anisotropic and demonstrate reversible, programmable shape change upon exposure to external stimuli such as light or heat. However, the actuation of LCNs is often triggered by light, either photochemically or photothermally, which is typically less efficient when operating in flooded environments. Actuation in confined and flooded environments is an important challenge that must be overcome for the implementation of LCNs in real-world biomedical applications. Decoupling the mechanisms of powering, locomotion, and control from robotic functions is a strong solution for achieving efficient operation in flooded media. This work showcases two examples of decoupling locomotion and robotic function for the efficient use of small-scale devices at the air-water interface. This is done through the use of LCNs for control in conjunction with protein motors for powering. An LCN that responds to visible light, rather than UV, is also fabricated and characterized, and will be used for underwater robotic applications in future studies.
In the first case study, protein motors and LCNs are used to power and control a multi-component mechanical device. A milli-scale gear train with integrated motor and clutch functionalities is fabricated and operated at the air-water interface. The driving gear has a protein motor coating and generates propulsive force using the Marangoni effect. This force is transmitted through the gear train unless the clutch gear is activated. The clutch gear is fabricated from a photothermally responsive LCN that has been plasticized through the addition of a nematogenic solvent to improve actuation efficiency. The teeth of the clutch gear bend downwards to disengage from the gear train upon exposure to light, halting the chain of motion on demand. The second case study utilizes photochemical LCNs with applied protein motor coating to construct a V-shaped swimmer that moves across the surface of the water. Photochemical LCNs are used for their meta-stable state that allows for deformations to be held without constant exposure to stimuli. The protein motors are integrated directly onto the LCN swimmer for a single device with orthogonal mechanisms for powering and control. The protein motors generate force that propels the swimmer forward while deformation of the LCN is used for directional control.
In both case studies, UV light is required for shape-change. Looking forward to biomedical applications, a photochemical LCN that is responsive to visible light is also developed and characterized in both air and water. The design of LCN-based small-scale devices with a focus on safe and efficient operation in wet environments will open up new and exciting applications
The Effect of Liquid Crystal Inclusions on the Mechanical Properties of Liquid Crystal Elastomers
No full textThe synergy between materials with differing mechanical properties is an evolutionary adaptation for survival that pervades all of biology. Recognizing these masterstrokes of the natural world has inspired composite materials that enhance all aspects of quality of life. Composite design is particularly important for soft robots, which have advantages over their rigid-bodied counterparts for precision medicine, aquatic locomotion, and human interaction broadly. The relatively inferior mechanical properties of contemporary soft robots are not yet sufficient to replace hard-bodied robots and must be enriched for high load-bearing situations. Liquid Crystal Elastomers (LCEs) hold much promise as a candidate material for soft robotic bodies due to their rapid and reversible stimuli-responsive shape change. Solid fillers, interpenetrating polymer networks, and microstructural modulation have been employed to stiffen and toughen LCEs, yet these strategies substantially hinder extensibility or the liquid crystalline (LC) order. Liquid metal inclusions have recently been harnessed to profoundly increase the elastic modulus and toughness, though the isotropic droplets still compromise LC order. Ever elusive is a method for amplifying mechanical properties that elevate LC order without substantially compromising extensibility.
In this thesis, a stiffened and toughened LCE composite is developed by doping with low molecular weight liquid crystal solvents. First, the influence of the nematogen 4-cyano-4'-pentylbiphenyl, 5CB, is studied. Through miscibility, thermal, and crystallographic studies, the enhanced mechanical properties are shown to emanate from strain-induced short-range smectic order (i.e., cybotacticity) and nanoscale phase separation of the LC solvent from the matrix. Uniquely, cybotacticity arises from components possessing no individual smectic ordering. Improvements of 570% and 370% in stiffness and toughness are conferred and extensibility only decreases by 20%. The first study is built upon by examining LCE modification with the smectogen 8CB (4-cyano-4′-octylbiphenyl). Markedly larger improvements are displayed in the stiffness (760%) and toughness (415%) while retaining 90% of the neat LCE’s elasticity. Strain-induced charge transfer is discovered as another factor responsible for the improved mechanical properties. Designing a stiffer, tougher, and lighter LCE with anisotropic liquids will facilitate the development of more effective soft actuators and attract more interest to the theory and application of liquid inclusion stiffening
Programmable stimuli-responsive zwitterionic hydrogels for soft robotic applications
No full textAs a prominent class of actuators, stimuli-responsive hydrogels have attracted significant interest in the
soft robotics community for biomedical applications. Key features of hydrogels, including high water
content and similar physicochemical properties to that of tissues, make them excellent materials to be
used in a wide range of biomedical applications such as drug delivery, and tissue engineering.
Particularly, hydrogels with stimuli-responsiveness, self-healing, shape-morphing, low cytotoxicity,
and tunable physiochemical properties can be used as functional building blocks in biomedical devices
and robots, enabling minimally invasive medical procedures.
Introducing programmability to the shape-morphing of hydrogels opens up new opportunities,
especially, in the fabrication of remotely controllable biomedical robots. In this work, we synthesized
responsive hydrogel nanocomposites and bilayers with preprogrammed shape transformations that
enable desirable robotic functionalities. For this, we used zwitterionic/acrylate chemistries that impart
self-healing, stimuli-responsiveness, and biocompatibility to our hydrogel system. Introducing
heterogenous physiochemical properties, at the microscale, and employing a multilayering approach,
at the macroscale, rendered differential swelling to the hydrogels, which were then employed as a
programming strategy to facilitate 2D-to-3D shape-morphing of the hydrogel upon exposure to
environmental cues.
As a proof-of-concept, we demonstrated tethered and untethered soft robotic functionalities, such as
actuation, magnetic locomotion, and targeted transport of soft and light cargo in confined and flooded
media. Our future direction includes developing novel bio-inks from this hydrogel system for extrusion
additive manufacturing given their excellent tunability of mechanical properties coupled with the shear thinning rheology of the hydrogel. We believe that the proposed hydrogel formulation will expand the
portfolio of functional materials for fabricating miniaturized soft actuators for biomedical applications
Functional microrobotic systems
No full textMalí roboti schopní pohybu, detekce a interakce mohou mít zásadní vliv na biomedicínské a environmentální aplikace. Aby však bylo možné úspěšně dokončit stanovené úkoly, vyžadují malí robotí funkční komponenty kompatibilní s provozními podmínkami. V této práci vyvíjíme různé chemicky a externě napájené mikroroboty s funkčními součástmi pro sanaci vody a cílené zobrazování. Nejprve zkoumáme vliv vlastností částic na pohon hybridních mikrorobotů poháněných chemicky/světlem—demonstrujeme řízení rychlosti na vyžádání pomocí vestavěné optické brzdy. Poté využíváme samohybné mikroroboty k odstraňování kontaminantů, jako jsou antibiotika a nitroaromatické sloučeniny, překonáním reakcí omezených difuzí. Výsledky ukazují, že schopnost mikrorobotů odstraňovat kontaminanty lze zvýšit pomocí zabudovaných funkčních komponent, například fotoaktivních materiálů a enzymů. Jako další typ procesu sanace vody studujeme kolektivní chování povrchově funkčních magnetických mikrorobotů k zachycování volně plovoucích bakterií a mikroplastů za působení vnějších magnetických polí. Poté, co tuto kapitolu uzavřeme diskusí o klíčových výzvách směřujících k využití mikrorobotů pro sanaci vody, představíme magneticky řízené systémy pro cílené zobrazovací aplikace. Ukazujeme, že konvenční kontrastní látka může být vybavena magnetickými vlastnostmi, které umožňují vnější kontrolu v různých scénářích. Pokusy na zvířatech ukazují na lokalizaci robotických kontrastních látek v gastrointestinálním traktu myší za účelem vizualizace jeho trojrozměrné struktury pomocí rentgenové mikropočítačové tomografie. Kromě toho vyvíjíme organické mikroroboty reagující na pH s magnetickou odezvou a vlastní multifluorescencí. Za fyziologicky relevantních podmínek tito mikroroboti vykazují jedinečnou schopnost přepínání fluorescence při různých hodnotách pH, což umožňuje sledování kyselosti žaludku v cílových místech. Tyto výsledky naznačují, že inteligentní zobrazovací prostředky lze upravit tak, aby umožňovaly nevázanou ovladatelnost s cílem rozšířit možnosti běžných diagnostických přístupů založených na zobrazování. Po diskusi o klíčových výzvách, které je třeba řešit před převedením mikrorobotů do klinické praxe, shrnujeme v poslední kapitole hlavní poznatky práce. Celkově funkční mikrorobotické systémy představené v této práci naznačují slibné vlastnosti pro aplikace v dynamických a komplexních scénářích jako aktivní systémy
Functional microrobotic systems
No full textMalí roboti schopní pohybu, detekce a interakce mohou mít zásadní vliv na biomedicínské a environmentální aplikace. Aby však bylo možné úspěšně dokončit stanovené úkoly, vyžadují malí robotí funkční komponenty kompatibilní s provozními podmínkami. V této práci vyvíjíme různé chemicky a externě napájené mikroroboty s funkčními součástmi pro sanaci vody a cílené zobrazování. Nejprve zkoumáme vliv vlastností částic na pohon hybridních mikrorobotů poháněných chemicky/světlem—demonstrujeme řízení rychlosti na vyžádání pomocí vestavěné optické brzdy. Poté využíváme samohybné mikroroboty k odstraňování kontaminantů, jako jsou antibiotika a nitroaromatické sloučeniny, překonáním reakcí omezených difuzí. Výsledky ukazují, že schopnost mikrorobotů odstraňovat kontaminanty lze zvýšit pomocí zabudovaných funkčních komponent, například fotoaktivních materiálů a enzymů. Jako další typ procesu sanace vody studujeme kolektivní chování povrchově funkčních magnetických mikrorobotů k zachycování volně plovoucích bakterií a mikroplastů za působení vnějších magnetických polí. Poté, co tuto kapitolu uzavřeme diskusí o klíčových výzvách směřujících k využití mikrorobotů pro sanaci vody, představíme magneticky řízené systémy pro cílené zobrazovací aplikace. Ukazujeme, že konvenční kontrastní látka může být vybavena magnetickými vlastnostmi, které umožňují vnější kontrolu v různých scénářích. Pokusy na zvířatech ukazují na lokalizaci robotických kontrastních látek v gastrointestinálním traktu myší za účelem vizualizace jeho trojrozměrné struktury pomocí rentgenové mikropočítačové tomografie. Kromě toho vyvíjíme organické mikroroboty reagující na pH s magnetickou odezvou a vlastní multifluorescencí. Za fyziologicky relevantních podmínek tito mikroroboti vykazují jedinečnou schopnost přepínání fluorescence při různých hodnotách pH, což umožňuje sledování kyselosti žaludku v cílových místech. Tyto výsledky naznačují, že inteligentní zobrazovací prostředky lze upravit tak, aby umožňovaly nevázanou ovladatelnost s cílem rozšířit možnosti běžných diagnostických přístupů založených na zobrazování. Po diskusi o klíčových výzvách, které je třeba řešit před převedením mikrorobotů do klinické praxe, shrnujeme v poslední kapitole hlavní poznatky práce. Celkově funkční mikrorobotické systémy představené v této práci naznačují slibné vlastnosti pro aplikace v dynamických a komplexních scénářích jako aktivní systémy.Small-scale robots capable of locomotion, sensing, and interaction can have a profound impact on biomedical and environmental applications. Nevertheless, to enable the successful completion of defined tasks, small-scale robots require functional components compatible with the operating conditions. In this thesis, we develop a variety of chemically and externally powered microrobots having functional components for water remediation and targeted imaging. We initially investigate the effect of particle properties on the propulsion of chemical/light-driven hybrid microrobots—demonstrating on-demand speed control by a built-in optical brake. Then, we utilize self-propelled microrobots to remove contaminants, i.e., antibiotics and nitroaromatic compounds, by overcoming diffusion-limited reactions. The results indicate that the microrobots’ removal capacity for target contaminants can be enhanced by the embedded functional components, e.g., photoactive materials and enzymes. As another type of water remediation process, we study the collective behavior of surface-functionalized magnetic microrobots to capture free-swimming bacteria and microplastics under the influence of external magnetic fields. After concluding this chapter with a discussion on key challenges regarding the utilization of microrobots for water remediation, we introduce magnetically controlled systems for targeted imaging applications. We demonstrate that a conventional contrast agent can be equipped with magnetic properties to enable external controllability under different scenarios. Animal experiments indicate the localization of the robotic contrast agents in the gastrointestinal tract of mice to visualize the three-dimensional structure via X-ray micro-computed tomography. Moreover, we develop pH-responsive organic microrobots with magnetic response and intrinsic multi-fluorescence. Under physiologically relevant conditions, these microrobots exhibit a unique fluorescence switching behavior at different pH values to enable the monitoring of gastric acidity at target locations. These results indicate that smart imaging agents can allow untethered controllability with the aim of enhancing the capabilities of conventional imaging-based diagnosis approaches. After discussing key challenges that require interest before the translation of microrobots to the clinic, we summarize the main findings of the thesis in the last chapter. Overall, the functional microrobots presented in this thesis indicate promising features for applications in dynamic and complex scenarios as active systems.
Biomimetic Micro/nano-Structured Surfaces: A Potential Tool for Tuning of Adhesion and Friction
Full text linkEffects of biomimetic micro-patterning of polymeric materials on their interfacial properties were studied experimentally. Micropillars of PDMS and SU-8 epoxy were fabricated through soft lithography and UV lithography techniques, respectively. PDMS pillars were topped by thin terminal films of the same material through dipping method with different thicknesses and viscosities. Adhesion and frictional properties of biomimetic microstructures were examined in two modes of contact, i.e. laid and conformal contact. In the first mode of contact, i.e. laid contact, the contact between adhesive and adherent is laid on top of the micro-protrusions or is in contact with side wall of micropillars. Adhesion properties of the smooth and patterned PDMS were characterized through micro-indentation test. Moreover, the friction properties of the smooth PDMS sample and PDMS micropillars with different aspect ratios were examined in unidirectional friction testing. JKR theory of continuum contact mechanics was utilized to interpret the obtained data. To study the effect of second mode of contact, peeling behaviour of a conformal contact between solidified liquid PDMS and SU-8 micropillars was monitored. Kendall’s model of elastic peeling was used to interpret the peeling data. It was found that patterning of the materials would decrease the real area of contact and accordingly adhesion and friction to the mating surface. Termination of the micropillars with a thin layer of the same material result in increment of adhesion as reduction of the real contact area could be compensated and the compliance of the near surface increases. Elastic energy dissipation as a result of enhanced compliance and crack trapping and crack propagation instabilities are the main reasons behind increment of adhesion of thin film terminated structures. Viscoelasticity of the terminal thin film remarkably increased the adhesion as a result of coupling mentioned mechanisms and viscoelastic loss on the surface. Decline of the overall friction could be tailored through use of different aspect ratios. Higher aspect ratios pillars show higher friction comparing to lower aspect ratio pillars. 550 folds enhancement of adhesion was observed for peeling of the PDMS tape from rigid micropillars with aspect ratio ranging from 0 to 6. It is concluded that for the lower aspect ratio micropillars, the elastic energy dissipation is playing the key role in adhesion enhancement. This role shifts toward side-wall friction during separation by increase in aspect ratio. These all give in hand a versatile tool to control and fine tune the interfacial properties of materials, whether they are concerned with adhesion or friction
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Liquid Crystal Networks for Smart Biomimetic Micro/nano Structured Adhesives
No full textAs modern technology demands for miniaturized structures with higher surface area to the volume ratio, the design and synthesis of materials with tailored surfaces is becoming more important. Moreover, some emerging technologies require materials with smart surface properties that can be controlled remotely, and work adaptively in “on” and “off” states when stimulated externally. Fascinating surface structures and adaptive functionalities that can be found in biological systems have provided great inspirations to researchers for fabrication of synthetic biomimetic assemblies. While the fabrication of materials with non-smart bio-inspired surface structures has been greatly accomplished, the mimicking of adaptive functionalities of the living systems is less investigated. Thus, there is a great zeal in developing materials with smart and adaptive biomimetic structured surfaces. The objective of this dissertation is to design and develop materials with smart biomimetic micro/nanostructured surfaces that can show desirable responses when remotely stimulated.
First, an experimental study on the integration of a dissipative material (resembling the dissipative and wet nature of the tree frog toe pads) to an elastic fibrillar interface (resembling the dry and fibrillar nature of the gecko foot pads) is carried out. Accordingly, a new type of functionally graded adhesive is developed, which is composed of an array of elastic micropillars at the base, a thin elastic intermediate layer and a viscoelastic top layer. The results showed that the new proposed graded structure has remarkable adhesive properties in terms of pull-off force, work of adhesion, and structural integrity (i.e., inhibited cohesive failure). Second, muscle-driven actuation of biomimetic microfibrillar structures is achieved using integrative soft-lithography on a backing splayed liquid crystal elastomer or networks (LCEs/LCNs). Variation in the backing LCE layer thickness yields different modes of thermal deformation from a pure bend to a twist-bend. The muscular motion and dynamic self-cleaning of gecko toe pads are mimicked via this mechanism. Finally, the self-peeling of gecko toes is mimicked by the integration of film-terminated fibrillar adhesives to hybrid nematic LCN cantilevers. A soft gripper is developed based on the gecko-inspired attachment/detachment mechanism. Performance of the fabricated gripper for transportation of thin delicate objects is evaluated by the optimum mechanical strength of the LCN and the maximum size of the adhesive patch
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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