172 research outputs found

    Micromachined Magnetoelastic Sensors and Actuators for Biomedical Devices and Other Applications.

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    Magnetoelastic materials exhibit coupling between material strain and magnetization; this coupling provides the basis for a number of wireless transducers. This thesis extends past work on microfabricated magnetoelastic sensors in three ways. First, a new class of strain sensors based on the ΔE effect are presented. Two sensor types are described – single and differential. The single sensor has an active area of 7×2 mm2 and operates at a resonant frequency of 230.8 kHz with a sensitivity of 13×103 ppm/mstrain and a dynamic range of 0.05-1.05 mstrain. The differential sensor includes a strain-independent 2×0.5 mm2 reference resonator in addition to a 2.5×0.5 mm2 sensing element. The sensor resonance is at 266.4 kHz and reference resonance is at 492.75 kHz. The differential sensor has a dynamic range of 0-1.85 mstrain, a sensitivity of 12.5×103¬¬ ppm/mstrain, and is temperature compensated in the 23-60°C range. Second, fluidic actuation by resonant magnetoelastic devices is presented. This transduction is performed in the context of an implantable device, specifically the Ahmed glaucoma drainage device (AGDD). Aspherical 3D wireless magnetoelastic actuators with small form factors and low surface profiles are integrated with the AGDD; the fluid flow generated by the actuators is intended to limit cellular adhesion to the implant surface that ultimately leads to implant encapsulation and failure. The actuators measure 10.3×5.6 mm2 with resonant frequencies varying from 520 Hz to 4.7 kHz for the different actuator designs. Flow velocities up to 266 μm/s are recorded at a wireless activation range of 25-30 mm, with peak actuator vibration amplitudes of 1.5 μm. Finally, detection techniques for improving the measurement performance of wireless magnetoelastic systems are presented. The techniques focus on decoupling of the excitation magnetic signal from the sensor response to improve measurement sensitivity and noise immunity. Three domains – temporal, frequency, and spatial – are investigated for signal feedthrough. Quantitative results are presented for temporal and frequency domain decoupling. Temporal decoupling is used to measure strain sensors with resonant frequencies in the 125 kHz range, whereas frequency domain decoupling is implemented to measure 44 kHz magnetoelastic resonators.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/116647/1/venkatp_1.pd

    Strategies for ocular administration of antiviral and antioxidant agents

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    A tese consistiu no deseño e desenvolvemento de novas formas de administración ocular de fármacos antivirais e antioxidantes. En particular, a tese centrouse no deseño de micelas poliméricas para a administración de fármacos antivirais (aciclovir), e o deseño de lentes blandas de contacto cargadas con axentes antivirais (aciclovir e valaciclovir) e axentes antioxidantes (ácido transferúlico). O obxectivo foi lograr unha liberación controlada do fármaco na superficie ocular, prolongando o seu tempo de residencia na zona precorneal, así como a vectorización do fármaco a estruturas máis profundas do ollo

    Developing Implants for Ophthalmic Drug Delivery and Flow Modulation

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    Glaucoma is the leading cause of irreversible blindness worldwide. Surgical interventions are frequently necessary to lower the intraocular pressure (IOP) and do so by creating a new channel for aqueous humour to drain into the subconjunctival space. This channel can be formed by performing a glaucoma filtration surgery (GFS) or by implanting a glaucoma drainage device (GDD). However, excessive scarring at the surgical site blocks aqueous outflow, elevates IOP, and results in treatment failure. Drugs injected locally to control scarring rapidly clear from the subconjunctiva, and current implants are susceptible to a foreign body response. This work investigated strategies that could improve the outcomes of these current glaucoma interventions. First, drug-eluting spacers were formulated using established biocompatible materials to prolong drug release in conditions representing the subconjunctival space post-GFS or GDD implantation. Of these formulations, the spacer containing non-ionic surfactant, Brij 98, at a concentration of 1.25% w/v was able to prolong the release of dexamethasone from poly(2-hydroxyethyl methacrylate) pHEMA hydrogels significantly longer (>30 days) than hydrogels containing no surfactant (<7 days) at therapeutically relevant drug concentrations in vitro. Next, engineering principles were applied to inflated elastomeric membranes, which provided novel insights into considerations needed to design a novel ophthalmic drug delivery pump. Pocket geometry and material properties had a significant impact on internal pressure and subsequent pump function. Modelling data supports the feasibility of elastomeric pumps for prolonged subconjunctival drug delivery. Finally, an alternative mechanism of IOP control was investigated. Novel and established hydrogel formulations were evaluated for aqueous permeability and mechanical integrity. Despite evidence to suggest the feasibility of hydrogels to modulate aqueous flow, the in vitro permeability of hydrogel candidates was determined to be too low to maintain optimal IOP. Furthermore, hydrogel permeability tended to negate its mechanical integrity, making them unsuitable candidate materials for GDD development

    Aerospace medicine and biology. A continuing bibliography, supplement 207

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    This bibliography lists 184 reports, articles, and other documents introduced into the NASA scientific and technical information system in May 1980

    Aerospace medicine and biology: A continuing bibliography with indexes

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    This bibliography lists 180 reports, articles and other documents introduced into the NASA scientific and technical information system in February 1985

    Bioinspired Light Robots from Liquid Crystal Networks

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    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

    Making FACES: The facial animation, construction and editing system

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    Optimisation of corneal biomechanical characteristics in orthokeratology for myopia control

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    The rapid increase in myopia prevalence has escalated a wealth of research interest in the prevention mechanisms of myopia. Orthokeratology (ortho-k) is among the most promising approaches. A reluctance to employ this modality has been observed, owing to the selective treatment outcome and the long-term effects to the corneal tissue. This thesis investigates the attitudes of clinicians towards various myopia control interventions, including ortho-k within a cross-sectional internet-based survey; long-term effects of ortho-k lens wear on corneal biomechanical properties in myopic school-children over a two year period; short-term corneal biomechanical changes over the first 7 nights of lens wear; and the influence of factors (age, ethnicity, eye/body size and nutrition) on corneal biomechanical properties in healthy adults. The aim of this thesis is to aid a deeper understanding of the role of corneal biomechanical properties in ortho-k lens wear,specifically for myopia control. The findings within the thesis demonstrate that surveyed eye-care practitioners are aware of the scientific findings within the field of myopia control; two thirds would still prescribe single vision glasses to their patients, owing to a lack of clear guidelines and the selective treatment outcome. Results of the ortho-k studies suggest that the corneal biomechanical characteristics are affected by long term ortho-k wear, having a stabilising effect to the components of the anterior eye in progressing myopia. Short term ortho- k lens wear study reveals marked changes in corneal biomechanical parameters within the first seven nights of lens wear. Ortho-k itself and the anterior segment changes observed cannot explain all the variation in treatment response. The final study demonstrates the relationship between corneal biomechanical parameters and nutrition, ocular biometry and body size, suggesting that individual factors, although non-substantially, contribute towards the treatment outcome. It, is therefore, suggested to establish an internationally acknowledged guideline for myopia control. Further studies should be designed to understand the complex mechanisms underlying ortho-k in myopia control

    Model-based quantification of systolic and diastolic left ventricular mechanics

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    Het linker ventrikel (LV) is de meest gespierde kamer van het hart. Door het gecoördineerd samentrekken van de spiercellen in de LV-wand wordt zuurstofrijk bloed in de aorta gepompt (systolische fase). Daarna ontspannen de spiercellen zich snel waardoor het LV opnieuw met bloed wordt gevuld (diastolische fase). In de kliniek en de onderzoekswereld bestaat er een waaier van modelgebaseerde methoden en concepten om de performantie en de mechanische eigenschappen van het LV te kwantificeren. Invasief bekomen druk- en volumedata laten toe om de systolische en diastolische mechanica van het LV met grote nauwkeurigheid te kennen. In de klinische praktijk wordt echter vaker gebruik gemaakt van (Doppler-) echocardiografie, een snelle en veilige niet-invasieve beeldtechniek. In een eerste deel van dit doctoraatsonderzoek werd een originele methode voorgesteld om, op basis van echocardiografie en klassieke bloeddrukmetingen, de intrinsieke krachtontwikkeling (contractiliteit) van het LV te schatten. De methode werd toegepast bij 2524 mensen die deelnemen aan de Asklepios-studie. De onderzoeksresultaten verschaften ons nieuwe informatie over hoe de evolutie van de krachtontwikkeling verschilt tussen gezonde mannen en vrouwen. De mechanische en vloeistofdynamische fenomenen tijdens de diastole vormden het onderwerp van het tweede deel van het onderzoek. Met behulp van een hydraulisch model van het LV werd nagegaan welke factoren een belangrijke invloed uitoefenen op het gedrag van het LV tijdens de isovolumetrische ontspanningsfase. In dit deel werd eveneens een uitgebreid overzicht gegeven van de meest recente echocardiografische methoden om de diastolische LV-mechanica te begroten. Daarbij werden de bloedstroming, de wandbeweging en de interactie tussen beiden gedetailleerd behandeld
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