1,720,953 research outputs found
Ionic electroactive polymer for organs-on-chip applications
No full textAn organ-on-chip (OoC) is a microelectromechanical (MEMS) device that aims to recapitulate in-vitro the physiology of the smallest functional unit of an organ in order to perform drug analysis or study disease models. OoCs are very complex systems that require actuation and sensing capabilities within controlled and delicate environment. The research presented in this thesis focuses on a transductive material that offers promising properties for organ-on-chip. The objective of the thesis is to demonstrate the potential of using ion-based electroactive materials to tackle current OoC limitations. An ionic electroactive material, called ionic polymer metal composite (IPMC) is proposed, characterized and developed in order to increase the ease of use, integrability, and scalability of OoC. The IPMC consists of a soft polymer, doped with ions naturally present in standard culture media, flanked by platinum electrodes on opposite sides. This biocompatible material shows good actuation and sensing capabilities, requires low driving voltage and has been herein investigated as a potential transducer for several organ-on-chip applications. A first version of the IPMC with a thickness of 180 𝜇m (called thick IPMC) showing good actuation capabilities has been adopted to implement a micropump and a tissue stretcher. The cells strecher could exhibit biologically relevant strain (0.1 %) while showing no toxicity, and the micropump achieved biologically relevant wall shear stress (0.008 Pa) through liquid flow within microchannels. Furthermore, in this thesis, this moisture-sensitive material has been investigated in the context of wafer-level process flow using state-of-the-art microfabrication tools to demonstrate its compatibility with silicon-based technology. A second version of the IPMC has been developed based on a thinner polymer (50 𝜇m, called thin IPMC), as well as an adjusted manufacturing recipe in order to explore the material potential as a sensor for OoC. A comparative study has been performed between the manufacturing of thick and thin IPMC, evidencing different dynamics of the electroless deposition reaction depending on the thickness of the polymer used. The developed thin IPMC shows superior sensing capabilities by virtue of lower flexural rigidity and higher electrodes conductivity. The applications explored with the thin IPMC are microfluidics flow sensing and strain sensing. The microfluidic flow sensor exhibits good sensing capabilities with a sensitivity of 4.78 mV/(uL/s) and a linear behavior in the studied range. In addition, soft lithography and patterning of hydrogel have been investigated on top of the thin IPMC, to further assess the material as a smart substrate for tissue engineering. The present thesis anticipates a potentially significant impact of smart materials as a new tool to engineer multi-functional culture substrates for OoC as well as develop electronically-controllable flexible membranes for micro pumping
Characterization of an Electroactive polymer actuator in diaphragm micropump for organ-on-chip application
No full textThe existing drug development process is economically and scientifically challenging. It fails to efficiently emulate human physiology in-vitro with the current pre-clinical studies which includes in-vitro cell culture models and animal testing. Organ-on-Chip (OoC) technology aims to recreate an in-vivo like micro environment to investigate drug response more effectively. There are ongoing attempts to fabricate OoC technology as a single-platform microdevice to minimize its reliance on external components. In this perspective, the functionality and throughput of this technology can be improved. One such novel approach is addition of an ionic electroactive polymer (iEAP) actuated diaphragm micropump. The primary aim of this thesis project was to determine the suitable dimensions of a micro cantilever iEAP, specifically Ionic polymer metal composite (IPMC) to generate appropriate flow rate for the projected diaphragm micropump. In addition to that, dynamics of the IPMC cantilever actuator was examined in dry environment. To achieve this the actuator tip - force, tip-displacement and longevity tests were performed. The results at macroscopic scale were tentatively explained with molecular characteristics of the material. As a result, it was shown that an IPMC cantilever actuator of millimetric size possesses viscoelastic properties and classical mechanical theories cannot be used to validate the experimental results. Secondly, the actuation results for 0.1 and 1 Hz align with the input driving frequency. The IPMC cantilever of length 7 mm generates the maximum tip-force of 0.138 mN and it is suggested to be used as a diaphragm actuator for the upcoming micropump
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Ionic polymer metal composite-based microfluidic flow sensor for bio-MEMS applications
No full textSensing flow rates in structured microenvironments like lab-on-chip (LOC) and organ-on-chip (OoC) is crucial to assess important parameters such as transport of media and molecules of interest. So far, these micro-electromechanical systems for biology (bio-MEMS) mostly rely on flow sensing systems based on thermal sensors. However, thermal flow sensing has limitations, since the measurement principle, which is based on generation of heat, can negatively affect the biological system by increasing the fluid temperature above physiological conditions. To overcome this issue, we propose a novel electro-mechanical flow sensor centered around the deformation of a cantilever made of a thin and biocompatible ionic electroactive polymer. The polymer, called ionic polymer metal composite (IPMC), is doped with ions naturally present in most cell media for LOC and OoC devices. Unlike already existing cantilever-based systems which rely on piezo sensitive materials, our IPMC-based flow sensor shows durability in wet environment. We were able to successfully measure pulsatile flow induced by pipetting with flowrate gradually increasing from 10μL/s to 40μL/s. The proposed flow sensor shows good sensing capabilities (4.78 mV/(μL/s)) with a linear behavior in the studied range. This work sets a milestone for using flexible, electroactive materials for sensing applications in delicate biological microenvironments.</p
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Manufacturing thin ionic polymer metal composite for sensing at the microscale
No full textIonic polymer metal composites (IPMCs) are a class of materials with a rising appeal in biological micro-electromechanical systems (bio-MEMS) due to their unique properties (low voltage output, bio-compatibility, affinity with ionic medium). While tailoring and improving actuation capabilities of IPMCs is a key motivator in almost all IPMC manufacturing reports, very little efforts have been dedicated to sensing using IPMC thinner than 100 µm. Most reports on IPMC manufacturing and utilization rely on 180 µm-thick Nafion with platinum electrodes, too stiff for bio-MEMS applications. The same fabrication process on thinner membranes does yield in very poor electrodes and performance, and needs to be studied to increase flexibility and sensitivity in the microscale range. This study demonstrates an electroless Pt deposition method for fabricating bio-MEMS-suitable 50 µm-thick IPMC samples. First, we perform a comparative study on the platinum distribution within the Nafion backbone as well as on the surface for the standard electroless deposition recipe for thin (50 µm) and thick (180 µm) Nafion. We report strong differences in platinum distribution for thick and thin IPMC that experienced the same manufacturing process. By varying chemical concentrations from the standard recipe we obtain convenient platinum distribution on thin Nafion, with platinum mainly localized in proximity of surface, as well as electrodes with lower sheet resistance. We could measure the flexural rigidity as 3.43 × 10 − 8 N·m2, 46 times lower than standard 180 µm-thick IPMC. The calculated sensitivity is 0.476 ± 0.02 mV mm−1 and the limit of detection for our sensor is 500 ± 20 µm. This procedure sets a milestone for manufacturing 50 µm-thick IPMC for transducers and sensors in bio-MEMS applications.Electronic Components, Technology and MaterialsMicro and Nano Engineerin
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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