Active Polymer Gel Actuators

Many kinds of stimuli-responsive polymer and gels have been developed and applied to biomimetic actuators or artificial muscles. Electroactive polymers that change shape when stimulated electrically seem to be particularly promising. In all cases, however, the mechanical motion is driven by external stimuli, for example, reversing the direction of electric field. On the other hand, many living organisms can generate an autonomous motion without external driving stimuli like self-beating of heart muscles. Here we show a novel biomimetic gel actuator that can walk spontaneously with a worm-like motion without switching of external stimuli. The self-oscillating motion is produced by dissipating chemical energy of oscillating reaction. Although the gel is completely composed of synthetic polymer, it shows autonomous motion as if it were alive

Molecular Design and Functional Control of Novel Self-Oscillating Polymers

If we could realize an autonomous polymer system driven under biological conditions by a tailor-made molecular design, human beings could create unprecedented biomimetic functions and materials such as heartbeats, autonomous peristaltic pumps, etc. In order to achieve this objective, we have investigated the molecular design of such a polymer system. As a result, we were the first to demonstrate a self-oscillating polymer system driven in a solution where only malonic acid existed, which could convert the chemical energy of the Belousov-Zhabotinsky (BZ) reaction into a change in the conformation of the polymer chain. To cause the self-oscillation in solution, we have attempted to construct a built-in system where the required BZ system substrates other than the organic acid are incorporated into the polymer itself. That is, the novel polymer chain incorporated the metal catalyst of the BZ reaction, a pH-control site and an oxidant supply site at the same time. As a result of introducing the pH control and oxidant supply sites into the conventional-type self-oscillating polymer chain, the novel polymer chain caused aggregation-disaggregation self-oscillations in the solution. We clarified that the period of the self-oscillation of the novel self-oscillating polymer chain was proportional to the concentration of the malonic acid. Therefore, the concentration of the malonic acid can be determined by measuring the period of the novel self-oscillating polymer solution. In this review, we introduce the detailed molecular design of the novel self-oscillating polymer chain and its self-oscillating behavior. Moreover, we report an autonomous self-oscillating polymer gel actuator that causes a bending-stretching motion under the constant conditions

Enzyme Powered Nanomotors Towards Biomedical Applications

[eng] The advancements in nanotechnology enabled the development of new diagnostic tools and drug delivery systems based on nanosystems, which offer unique features such as large surface area to volume ratio, cargo loading capabilities, increased circulation times, as well as versatility and multifunctionality. Despite this, the majority of nanomedicines do not translate into clinics, in part due to the biological barriers present in the body. Synthetic nano- and micromotors could be an alternative tool in nanomedicine, as the continuous propulsion force and potential to modulate the medium may aid tissue penetration and drug diffusion across biological barriers. Enzyme-powered motors are especially interesting for biomedical applications, owing to their biocompatibility and use of bioavailable substrates as fuel for propulsion. This thesis aims at exploring the potential applications of urease-powered nanomotors in nanomedicine. In the first work, we evaluated these motors as drug delivery systems. We found that active urease- powered nanomotors showed active motion in phosphate buffer solutions, and enhanced in vitro drug release profiles in comparison to passive nanoparticles. In addition, we observed that the motors were more efficient in delivering drug to cancer cells and caused higher toxicity levels, due to the combination of boosted drug release and local increase of pH produced by urea breakdown into ammonia and carbon dioxide. One of the major goals in nanomedicine is to achieve localized drug action, thus reducing side-effects. A commonly strategy to attain this is the use moieties to target specific diseases. In our second work, we assessed the ability of urease-powered nanomotors to improve the targeting and penetration of spheroids, using an antibody with therapeutic potential. We showed that the combination of active propulsion with targeting led to a significant increase in spheroid penetration, and that this effect caused a decrease in cell proliferation due to the antibody’s therapeutic action. Considering that high concentrations of nanomedicines are required to achieve therapeutic efficiency; in the third work we investigated the collective behavior of urease-powered nanomotors. Apart from optical microscopy, we evaluated the tracked the swarming behavior of the nanomotors using positron emission tomography, which is a technique widely used in clinics, due to its noninvasiveness and ability to provide quantitative information. We showed that the nanomotors were able to overcome hurdles while swimming in confined geometries. We observed that the nanomotors swarming behavior led to enhanced fluid convection and mixing both in vitro, and in vivo within mice’s bladders. Aiming at conferring protecting abilities to the enzyme-powered nanomotors, in the fourth work, we investigated the use of liposomes as chassis for nanomotors, encapsulating urease within their inner compartment. We demonstrated that the lipidic bilayer provides the enzymatic engines with protection from harsh acidic environments, and that the motility of liposome-based motors can be activated with bile salts. Altogether, these results demonstrate the potential of enzyme-powered nanomotors as nanomedicine tools, with versatile chassis, as well as capability to enhance drug delivery and tumor penetration. Moreover, their collective dynamics in vivo, tracked using medical imaging techniques, represent a step-forward in the journey towards clinical translation.[spa] Recientes avances en nanotecnología han permitido el desarrollo de nuevas herramientas para el diagnóstico de enfermedades y el transporte dirigido de fármacos, ofreciendo propiedades únicas como encapsulación de fármacos, el control sobre la biodistribución de estos, versatilidad y multifuncionalidad. A pesar de estos avances, la mayoría de nanomedicinas no consiguen llegar a aplicaciones médicas reales, lo cual es en parte debido a la presencia de barreras biológicas en el organismo que limitan su transporte hacia los tejidos de interés. En este sentido, el desarrollo de nuevos micro- y nanomotores sintéticos, capaces de autopropulsarse y causar cambios locales en el ambiente, podrían ofrecer una alternativa para la nanomedicina, promoviendo una mayor penetración en tejidos de interés y un mejor transporte de fármacos a través de las barreras biológicas. En concreto, los nanomotores enzimáticos poseen un alto potencial para aplicaciones biomédicas gracias a su biocompatibilidad y a la posibilidad de usar sustancias presentes en el organismo como combustible. Los trabajos presentados en esta tesis exploran el potenical de nanomotores, autopropulsados mediante la enzima ureasa, para aplicaciones biomédicas, y investigan su uso como vehículos para transporte de fármacos, su capacidad para mejorar penetración de tejidos diana, su versatilidad y movimiento colectivo. En conjunto, los resultados presentados en esta tesis doctoral demuestran el potencial del uso de nanomotores autopropulsados mediante enzimas como herramientas biomédicas, ofreciendo versatilidad en su diseño y una alta capacidad para promover el transporte de fármacos y la penetración en tumores. Por último, su movimiento colectivo observado in vivo mediante técnicas de imagen médicas representan un significativo avance en el viaje hacia su aplicación en medicina

Biomimetic Based Applications

The interaction between cells, tissues and biomaterial surfaces are the highlights of the book "Biomimetic Based Applications". In this regard the effect of nanostructures and nanotopographies and their effect on the development of a new generation of biomaterials including advanced multifunctional scaffolds for tissue engineering are discussed. The 2 volumes contain articles that cover a wide spectrum of subject matter such as different aspects of the development of scaffolds and coatings with enhanced performance and bioactivity, including investigations of material surface-cell interactions

Bioinspired Light Robots from Liquid Crystal Networks

Bioinspired material research aims at learning from the sophisticated design principles of nature, in order to develop novel artificial materials with advanced functionalities. Some of the sophisticated capabilities of biological materials, such as their ability to self-heal or adapt to environmental changes, are challenging to realize in artificial systems. Nevertheless, many efforts have been recently devoted to develop artificial materials with adaptive functions, especially materials which can generate movement in response to external stimuli. One such effort is the field of soft robots, which aims towards fabrication of autonomous adaptive systems with flexibility, beyond the current capability of conventional robotics. However, in most cases, soft robots still need to be connected to hard electronics for powering and rely on complicated algorithms to control their deformation modes. Soft robots that can be powered remotely and are capable of self-regulating function, are of great interest across the scientific community.In order to realize such responsive and adaptive systems, researches across the globe are making constant efforts to develop new, ever-more sophisticated stimuliresponsive materials. Among the different stimuli-responsive materials, liquid crystal networks (LCNs) are the most suited ones to design smart actuating systems as they can be controlled and powered remotely with light and thereby obviate the need for external control circuitry. They enable pre-programable shape changes, hence equipping a single material with multiple actuation modes. In addition to light, they can also be actuated by variety of stimuli such as heat, humidity, pH, electric and magnetic fields etc., or a combination of these. Based on these advantages of LCNs, we seek inspiration from natural actuator systems present in plants and animals to devise different light controllable soft robotic systems.In this thesis, inspired from biological systems such as octopus arm movements, iris movements in eyes, object detection and capturing ability of Venus flytraps and opening and closing of certain nocturnal flowers, we demonstrate several light robots that can be programmed to show pre-determined shape changes. By employing a proper device design, these light robots can even show the characteristics of selfregulation and object recognition, which brings new advances to the field of LCNbased light robots. For instance, octopod light robot can show bidirectional bending owing to alignment programming using a commercial laser projector; artificial iris is a fully light controllable device that can self-regulate its aperture size based on intensity of incident light; the optical flytrap can not only autonomously close on an object coming into its ‘‘mouth’’ but it can also distinguish between different kinds of objects based on optical feedback, and finally, integration of light and humidity responsiveness in a single LCN actuator enables a nocturnal flower-mimicking actuator, which provides an opportunity to understand the delicate interplay between different simultaneously occurring stimuli in a monolithic actuator.We believe that besides providing a deeper understanding on the photoactuation in liquid crystal networks, at fundamental level, our work opens new avenues by providing several pathways towards next-generation intelligent soft microrobots

Micro/nanoscale magnetic robots for biomedical applications

Magnetic small-scale robots are devices of great potential for the biomedical field because of the several benefits of this method of actuation. Recent work on the development of these devices has seen tremendous innovation and refinement toward ​improved performance for potential clinical applications. This review briefly details recent advancements in small-scale robots used for biomedical applications, covering their design, fabrication, applications, and demonstration of ability, and identifies the gap in studies and the difficulties that have persisted in the optimization of the use of these devices. In addition, alternative biomedical applications are also suggested for some of the technologies that show potential for other functions. This study concludes that although the field of small-scale robot research is highly innovative ​there is need for more concerted efforts to improve functionality and reliability of these devices particularly in clinical applications. Finally, further suggestions are made toward ​the achievement of commercialization for these devices

Towards autonomous DNA-based Nanodevices

Molecular recognition, programmability, self-assembling capabilites and biocompatibility are unique features of DNA. The basic approach of DNA nanotechnology is to exploit these properties in order to fabricate novel materials and structures on the nanometer scale. This cumulative dissertation deals with three aspects of this young research area: fast analysis, autonomous control of functional structures, and biocompatible autonomous delivery systems for nanoscale objects. 1. At low temperatures and under favorable buffer conditions, two complementary DNA strands will form a double-helical structure in which the bases of the two strands are paired according to the Watson-Crick rules: adenine bases bind with thymine bases, guanine bases with cytosine bases. The melting temperature TM of a DNA duplex is defined as the temperature at which half of the double strands are separated into single strands. The melting temperature can be calculated for DNA strands of known sequences under standard conditions. However, it has to be determined experimentally for strands of unknown sequences and for applications under extreme buffer conditions. A method for fast and reliable determination of DNA melting temperatures has been developed. Stable gradients of the denaturing agent formamide were generated by means of diffusion in a microfluidic setup. Formamide lowers the melting temperature of DNA and a given formamide concentration can be mapped to a corresponding virtual temperature along the formamide gradient. Differences in the length of complementary sequences of only one nucleotide as well as a single nucleotide mismatch can be detected with this method, which is of great interest for the detection of sequence mutations or variations such as single nucleotide polymorphisms (SNPs). 2. Knowledge of the stability of DNA duplexes is also of great importance for the construction of DNA-based nanostructures and devices. Conformational changes occuring in artificially generated DNA structures can be used to produce motion on the nanometer scale. Usually, DNA devices are driven by the manual addition of fuel molecules or by the periodic variation of buffer conditions. One prominent example of such a conformational change is the formation of the so-called i-motif, which is a folded four-stranded DNA structure characterized by noncanonical hemiprotonated cytosine-cytosine base-pairs. In order to achieve controlled autonomous motion, the oscillating pH-value of a chemical oscillator has been employed to drive the i-motif periodically through its conformational states. The experiments were conducted with the DNA switch in solution and attached to a solid substrate and constitute the first example of DNA-based devices driven autonomously by a chemical non-equilibrium reaction. 3. Finally, a DNA-crosslinked and switchable polyacrylamide hydrogel is introduced, which is used to trap and release fluorescent colloidal quantum dots in response to externally applied programmable DNA signal strands. Trapping and release of the nanoparticles is demonstrated by studying their diffusion properties using single molecule fluorescence microscopy, single particle tracking and fluorescence correlation spectroscopy. Due to the biocompatibility of the polymerized acrylamide and the crosslinking DNA strands, such gels could find application in the context of controlled drug delivery, where the autonomous release of a drug-carrying nanoparticle could be triggered by naturally occurring, potentially disease-related DNA or RNA strands

Small business innovation research. Abstracts of 1988 phase 1 awards

Non-proprietary proposal abstracts of Phase 1 Small Business Innovation Research (SBIR) projects supported by NASA are presented. Projects in the fields of aeronautical propulsion, aerodynamics, acoustics, aircraft systems, materials and structures, teleoperators and robots, computer sciences, information systems, data processing, spacecraft propulsion, bioastronautics, satellite communication, and space processing are covered

Synthèse et étude de nouveaux actionneurs polymères cristallins liquides à chaîne latérale

Abstract: Liquid crystalline elastomers (LCEs) have aroused much scientific interest for applications as soft robots, artificial muscles and energy generators, to name only a few, due to their reversible shape changes in response to diverse stimuli such as heat, light, humidity, and electric field. Such a shape-changing LCE is considered as a device called actuator, which is the topic of this thesis. The stimulated actuation behavior of LCE is attributed to the coupling interplay between liquid crystalline (LC) order and rubber elasticity of a crosslinked polymer network. Up to date, most research effort has been devoted to developing main-chain LCEs, in which the mesogens are part of the chain backbone. Their actuators generally display large reversible shape changes, because the mesogens are aligned in the same direction as chain backbone, a change in LC order causes necessarily a change in polymer chain conformation and thus in network strain. By contrast, side-chain LCEs, in which mesogens are side groups tethered to chain backbone through a flexible spacer, have been much less explored for actuator applications. The lack of interest is largely due to the generally less prominent actuation behaviors resulting from the more or less decoupled side-chain mesogens and chain backbone. Another reason, which is more technical, is that the films of side-chain LCEs are generally brittle owing to a lack of chain entanglement and, consequently, cannot be mechanically stretched to induce alignment of mesogens that is required for actuators. Given the above, in order to conduct original research and make new discoveries, the objective of this thesis is to synthesize novel side-chain LCEs whose films are readily stretchable, to study their reversible shape changes related to order-disorder phase transition, and to investigate their use as actuators. Our hope is that by revisiting this type of LCEs, we can discover new phenomena and unveil new useful properties. As reported in the thesis, we have achieved the main goal, because our research outcomes are significant and represent an advancement of fundamental knowledge in the field. Firstly, we have developed a synthetic method for obtaining side-chain LCEs whose films can easily be prepared and mechanically stretched. Our strategy consists in using a styrene-bytadiene-styrene (SBS) triblock copolymer and functionalizing the central polybutadiene (PB) block with mesogenic side groups. The rationality of our material choice resides in the fact that SBS is a commercially available thermoplastic elastomer whose films, which can readily be preprared through solution casting or compressing molding, have excellent stretchability due to microphase-separated rigid polystyrene (PS) nanodomains acting as physical crosslinking points. Using efficient thiol-ene “click” reaction and esterification reaction, azobenzene mesogens can be grafted on the rubbery PB block, leading to novel family of side-chain LCEs. This synthetic method using post-functionalization of SBS is general and effective for attaching side-group mesogens of choice to PB. For our side-chain LCEs used for actuation studies, in addition to azobenzene mesogens, methacrylate moieties are also linked to PB to realize photocrosslinking of the elastomer, which is indispensable for reversible shape change. After the synthesis and characterization of our side-chain LCEs, we investigated their actuation properties and made discovery of some interesting phenomena unknown in the literature. In an actuator prepared using an SBS-based side-chain LCE, i.e., in a film stretched for orientation of mesogens and exposed to UV light for polymer chain crosslinking, the mesogens are aligned perpendicularly with respect to the stretching direction. When a strip actuator is heated to the isotropic state and then cooled back to the LC phase, it displays a reversible shape change that is anomalous. The strip shrinks both in length and width in the isotropic phase, and elongates along the two directions in the LC phase. Our study suggests that this thermally induced anomalous behavior may be caused by subtle interplay between two competing effects arising from the relaxation of chain backbone oriented along the stretching direction and the disordering of side-group mesogens aligned perpendicularly to the stretching direction. This thermally induced unusual behavior of side-chain LCEs, which is reminiscent of auxetic effect of certain polymers under deformation, can be exploited for actuator applications. In another study of our synthesized side-chain LCEs, of which some mesogens bear a chiral group in their structure, we made another interesting discovery. A polydomain strip or ribbon cut directly from a solution-cast film without mechanical stretching for orientation of mesogens, can reversibly twist upon thermally or photothermally induced heating to the isotropic phase and, subsequently, untwist on cooling to the chiral nematic (cholesteric) phase. The rotation direction of the macroscopic helical twisting is specific to the molecular chirality (R or S) of the chiral group (dopant) in the polymer, and the twisting degree is influenced by a number of parameters including the length/width aspect ratio and the thickness of the strip as well as the content of the chiral dopant. This finding is interesting, given that all known methods of preparation for LCE actuators capable of twisting deformation and motion require preset alignment of mesogens at the macroscopic scale. We proposed a mechanism based on the generation of an actuating “chiral” force upon the cholesteric-isotropic phase transition.Les élastomères cristallins liquides (LCEs) ont suscité un grand intérêt scientifique en vue de leurs applications dans les domaines de robots souples, muscles artificiels et générateurs d'énergie, pour n’en nommer que quelques-uns. La base de ces applications est une propriété fascinante de ce type de polymères : ils peuvent changer leurs formes de façon réversible en réponse à des stimuli tels que chaleur, lumière, humidité, champ électrique et champ magnétique. Un tel LCE est considéré comme un dispositif dit actionneur. C’est le sujet de cette thèse. Le comportement d'actionnement stimulé est attribué à un effet de couplage entre l'ordre cristallin liquide (mésophase formée par mésogènes dans un LCE) et l'élasticité du caoutchouc (réseau polymère réticulé). Jusqu’à maintenant, la plupart des efforts ont été consacrés au développement de LCEs à chaîne principale, c’est-à-dire des polymères ayant les mésogènes dans le squelette de chaîne. Leurs actionneurs montrent généralement un changement de forme important en raison du fait que les mésogènes alignent dans la même direction que la chaîne et un changement d’ordre entraîne nécessairement un changement de la conformation de chaîne. Par contre, les LCEs à chaîne latérale, dans lesquels les mésogènes sont des groupements latéraux liés à la chaîne principale par un segment flexible, ont été peu explorés étant donné que les mésogènes sont plus au moins découplés de la chaîne principale. Une autre raison, plus technique, est que les films de LCEs à chaîne latérale sont généralement cassants à cause d’un manque d’enchevêtrements de chaînes et, par conséquent, difficiles à étirer pour induire l’alignement des mésogènes requis pour actionneurs. Le but de cette thèse est donc de synthétiser de nouveaux LCEs à chaîne latérale faciles à étirer, d’étudier leurs comportements en changement de forme, et d’investiguer leurs utilisations en tant qu’actionneurs. Notre espoir est qu’un nouveau regard sur ces polymères relativement inexploités nous permettrait de découvrir de nouveaux phénomènes et de nouvelles propriétés. Comme rapporté dans cette thèse, les résultats obtenus nous donnent raison, étant significatifs et représentant un avancement des connaissances fondamentales dans le domaine. Dans un premier temps, nous avons développé une méthode de synthèse permettant l’obtention de LCEs à chaîne latérale dont les films possèdent une excellente extensibilité lors d’un étirement uniaxial. Notre stratégie consiste à utiliser un copolymère tribloc de styrène-butadiène-styrène (SBS) comme le matériau de départ et à fonctionnaliser le bloc polybutadiène (PB) avec les mésogènes comme groupements latéraux. Le rationnel de ce choix réside dans le fait que le SBS est un élastomère thermoplastique commercialement disponible, et que ses films préparés par coulée de solution ou par moulage, peuvent facilement être étirés en raison des nanodomaines rigides de polystyrène agissant comme points de réticulation. En utilisant une réaction “clic” thiol-ène et une réaction d'estérification, les mésogènes à base d’azobenzène peuvent être greffés sur le bloc caoutchouteux du PB, conduisant à une nouvelle famille de LCEs à chaîne latérale. Cette méthode de synthèse par post-fonctionnalisation du SBS est générale et efficace pour fonctionnaliser le bloc PB avec les groupements latéraux au choix. Pour nos LCEs à chaîne latérale, en plus des mésogènes, des unités de méthacrylate sont aussi introduites afin de réaliser la réticulation de chaînes, une condition indispensable pour obtenir un changement de forme réversible. Après la synthèse et la caractérisation de nos LCEs à chaîne latérale, nous avons étudié leurs propriétés d’actionnement. Notre étude a révélé des phénomènes intéressants qui ne sont pas connus dans la littérature. Dans un actionneur préparé avec les LCEs synthétisés, c’est-à-dire dans un film étiré pour l’orientation des mésogènes et exposé à la lumière ultraviolet (UV) pour réticulation de chaînes, les mésogènes sont alignés perpendiculairement par rapport à la direction d’étirement. Lorsqu’un actionneur sous forme d’une bande rectangulaire est soumis à un chauffage à l’état isotrope puis à un refroidissement à l’état cristallin liquide (CL), il montre un changement de forme réversible qui est particulier et différent de ce qui est connu à date. En effet, il rétrécit en longueur et en largeur en même temps lors du chauffage à l’état isotrope, et s’étend dans ces deux directions en refroidissement à la phase CL. Notre étude montre que ce comportement anormal induit thermiquement peut être attribué à un couplage d’interaction subtil entre la relaxation ou l’alignement de la chaîne principale orientée dans la direction d’étirement et le désordre ou l’ordre des groupements mésogènes alignés perpendiculairement à la direction d'étirement lors de la transition de phase CL-isotrope. Ce comportement thermique manifesté par LCEs à chaîne latérale, qui ressemble à un effet auxétique en déformation mécanique, peut être exploité dans le développement d’actionneurs. Dans une autre étude, nous avons synthétisé de nouveaux LCEs à chaîne latérale dont certaines mésogènes portent un groupement chiral. En investiguant leurs comportements en actuation, nous avons fait une découverte. À partir d’un film préparé par coulée de solution et sans étirement pour induire l’alignement des mésogènes, un ruban ou une fibre peut tourner pour former une hélice lors du chauffage à l’état isotrope, et ensuite peut se dérouler pour récupérer la forme plate lors du refroidissement à l’état CL. Le sens d’hélice macroscopique dépend de la chiralité moléculaire (R ou S) du dopant chiral, tandis que le degré de torsion est influencé par des paramètres tels que le rapport de longueur/largueur, l’épaisseur du ruban et la teneur en dopant chiral dans le LCE. Ce phénomène est intéressant, car toutes les méthodes de préparation connues pour réaliser une déformation de torsion nécessitent l’obtention d’un alignement des mésogènes bien organisé à l’échelle macroscopique. Nous avons proposé un mécanisme qui est basé sur la génération d’une force chirale générée lors de la transition de phase