Design of Transparent Conducting Electrodes and Surface Relief Gratings for Plasmonic Polymer Solar Cells

As the concept of renewable energy becomes increasingly important in the modern society, a considerable amount of research has been conducted in the field of organic photovoltaics in recent years. Although organic solar cells generally have had lower efficiencies compared to silicon solar cells, they have the potential to be mass produced via solution processing. A common polymer solar cell architecture relies on the usage of P3HT (electron donor) and PCBM (electron acceptor) bulk heterojunction. One of the main issues with this configuration is that in order to compensate for the high exciton recombination rate, the photoactive layer is often made very thin (on the order of 100 $%). This results in low solar cell photocurrents due to low absorption. This thesis investigates a novel method of light trapping by coupling surface plasmons at the electrode interface via surface relief gratings, leading to EM field enhancements and increased photo absorption. Experimental work was first conducted on developing and optimizing a transparent electrode of the form &'()/+,/&'() to replace the traditional ITO electrode since the azopolymer gratings cannot withstand the high temperature processing of ITO films. It was determined that given the right thickness profiles and deposition conditions, the MAM stack can achieve transmittance and conductivity similar to ITO films. Experimental work was also conducted on the fabrication and characterization of surface relief gratings, as well as verification of the surface plasmon generation. Surface relief gratings were fabricated easily and accurately via laser interference lithography on photosensitive azopolymer films. Laser diffraction studies confirmed the grating pitch, which is dependent on the incident angle and wavelength of the writing beam. AFM experiments were conducted to determine the surface morphology of the gratings, before and after metallic film deposition. It was concluded that metallic film deposition does not significantly alter the grating morphologies.

Nanotechnology in food industry II: risk assessment and legislation

Currently, there is increasing use of nanomaterials in the food industry thanks to the many advantages offered and make the products that contain them more competitive in the market. Their physicochemical properties often differ from those of bulk materials, which require specialized risk assessment. This should cover the risks to the health of workers and consumers as well as possible environmental risks. The risk assessment methods must go updating due to more widespread use of nanomaterials, especially now that are making their way down to consumer products. Today there is no specific legislation for nanomaterials, but there are several european dispositions and regulations that include them. This review gives an overview of the risk assessment and the existing current legislation regarding the use of nanotechnology in the food industry.

Andrienne Pauline Macaire (1796-1855): una artista en los márgenes

Durante el siglo XIX diversos artistas europeos emprendieron el viaje hacia diferentes puntos del continente americano. Entre ellos, mucho se dedicaron a la litografía, logrando en ciertos casos un amplio éxito comercial. Este artículo examina la trayectoria de la artista ginebrina Andrienne Pauline Macaire (1796-1855), dueña junto a su esposo de un temprano emprendimiento litográfico en la ciudad de Buenos Aires. Macaire puede ser considerada la primera artista profesional de renombre activa en esa ciudad. En efecto, es posible diferenciar su trayectoria de las de otras artistas contemporáneas, de las cuales se dispone de menos información y de las que han sobrevivido menos obras. En una primera parte del texto se analiza su inscripción en la literatura artística nacional. A continuación, se describe su formación en Ginebra y se estudia su importante actividad en Buenos Aires, estableciendo conexiones con el panorama artístico local. A lo largo del artículo se presentan obras y fuentes inéditas, o insuficientemente exploradas, a fin de justipreciar su carrera artística y de brindar elementos para futuras investigaciones.

Fabrication and Characterization of Efficient Optical Filter Arrays Implemented by 3D Nanoimprint

In dieser Arbeit werden optische Filterarrays für hochqualitative spektroskopische Anwendungen im sichtbaren (VIS) Wellenlängenbereich untersucht. Die optischen Filter, bestehend aus Fabry-Pérot (FP)-Filtern für hochauflösende miniaturisierte optische Nanospektrometer, basieren auf zwei hochreflektierenden dielektrischen Spiegeln und einer zwischenliegenden Resonanzkavität aus Polymer. Jeder Filter erlaubt einem schmalbandigem spektralen Band (in dieser Arbeit Filterlinie genannt) ,abhängig von der Höhe der Resonanzkavität, zu passieren. Die Effizienz eines solchen optischen Filters hängt von der präzisen Herstellung der hochselektiven multispektralen Filterfelder von FP-Filtern mittels kostengünstigen und hochdurchsatz Methoden ab. Die Herstellung der multiplen Spektralfilter über den gesamten sichtbaren Bereich wird durch einen einzelnen Prägeschritt durch die 3D Nanoimprint-Technologie mit sehr hoher vertikaler Auflösung auf einem Substrat erreicht. Der Schlüssel für diese Prozessintegration ist die Herstellung von 3D Nanoimprint-Stempeln mit den gewünschten Feldern von Filterkavitäten. Die spektrale Sensitivität von diesen effizienten optischen Filtern hängt von der Genauigkeit der vertikalen variierenden Kavitäten ab, die durch eine großflächige ‚weiche„ Nanoimprint-Technologie, UV oberflächenkonforme Imprint Lithographie (UV-SCIL), ab. Die Hauptprobleme von UV-basierten SCIL-Prozessen, wie eine nichtuniforme Restschichtdicke und Schrumpfung des Polymers ergeben Grenzen in der potenziellen Anwendung dieser Technologie. Es ist sehr wichtig, dass die Restschichtdicke gering und uniform ist, damit die kritischen Dimensionen des funktionellen 3D Musters während des Plasmaätzens zur Entfernung der Restschichtdicke kontrolliert werden kann. Im Fall des Nanospektrometers variieren die Kavitäten zwischen den benachbarten FP-Filtern vertikal sodass sich das Volumen von jedem einzelnen Filter verändert , was zu einer Höhenänderung der Restschichtdicke unter jedem Filter führt. Das volumetrische Schrumpfen, das durch den Polymerisationsprozess hervorgerufen wird, beeinträchtigt die Größe und Dimension der gestempelten Polymerkavitäten. Das Verhalten des großflächigen UV-SCIL Prozesses wird durch die Verwendung von einem Design mit ausgeglichenen Volumen verbessert und die Prozessbedingungen werden optimiert. Das Stempeldesign mit ausgeglichen Volumen verteilt 64 vertikal variierenden Filterkavitäten in Einheiten von 4 Kavitäten, die ein gemeinsames Durchschnittsvolumen haben. Durch die Benutzung der ausgeglichenen Volumen werden einheitliche Restschichtdicken (110 nm) über alle Filterhöhen erhalten. Die quantitative Analyse der Polymerschrumpfung wird in iii lateraler und vertikaler Richtung der FP-Filter untersucht. Das Schrumpfen in vertikaler Richtung hat den größten Einfluss auf die spektrale Antwort der Filter und wird durch die Änderung der Belichtungszeit von 12% auf 4% reduziert. FP Filter die mittels des Volumengemittelten Stempels und des optimierten Imprintprozesses hergestellt wurden, zeigen eine hohe Qualität der spektralen Antwort mit linearer Abhängigkeit zwischen den Kavitätshöhen und der spektralen Position der zugehörigen Filterlinien.

3D nanoimprint technology for NIR Fabry-Pérot filter arrays

Im Rahmen dieser Arbeit wird die Herstellung von miniaturisierten NIR-Spektrometern auf Basis von Fabry-Pérot (FP) Filter Arrays behandelt. Bisher ist die kostengünstige Strukturierung von homogenen und vertikal erweiterten Kavitäten für NIR FP-Filter mittels Nanoimprint Technologie noch nicht verfügbar, weil die Qualität der Schichten des Prägematerials unzureichend ist und die geringe Mobilität der Prägematerialien nicht ausreicht, um die vertikal erweiterten Kavitäten zu füllen. Diese Arbeit konzentriert sich auf die Reduzierung des technischen Aufwands zur Herstellung von homogenen und vertikal erweiterten Kavitäten. Zur Strukturierung der Kavitäten wird ein großflächiger substratkonformer UV-Nanoimprint Prozess (SCIL - Substrate Conformal Imprint Lithoghaphy) verwendet, der auf einem Hybridstempel basiert und Vorteile von harten und weichen Stempeln vereint. Um die genannten Limitierungen zu beseitigen, werden alternative Designs der Kavitäten untersucht und ein neues Prägematerial eingesetzt. Drei Designlösungen zur Herstellung von homogenen und erweiterten Kavitäten werden untersucht und verglichen: (i) Das Aufbringen des Prägematerials mittel mehrfacher Rotationsbeschichtung, um eine höhere Schichtdicke des Prägematerials vor dem Prägeprozess zu erzeugen, (ii) die Verwendung einer hybriden Kavität bestehend aus einer strukturierten Schicht des Prägematerials eingebettet zwischen zwei Siliziumoxidschichten, um die Schichtdicke der organischen Kavität zu erweitern und (iii) die Optimierung des Prägeprozesses durch Verwendung eines neuen Prägematerials. Die mit diesen drei Ansätzen hergestellten FP-Filter Arrays zeigen, hohe Transmissionen (beste Transmission > 90%) und kleine Linienbreiten (Halbwertsbreiten <5 nm).

Synthesis and Characterization of Nanostructured Electro-active Materials

Thesis (Ph.D.)--University of Washington, 2016-08

Investigating wetting characteristics on microstructured surfaces for superhydrophobicity and metal microcasting

The engineering of liquid behavior on surfaces is important for infrastructure, transportation, manufacturing, and sensing. Surfaces can be rendered superhydrophobic by microstructuring, and superhydrophobic devices could lead to practical corrosion inhibition, self-cleaning, fluid flow control, and surface drag reduction. To more fully understand how liquid interacts with microstructured surfaces, this dissertation introduces a direct method for determining droplet solid-liquid-vapor interfacial geometry on microstructured surfaces. The technique performs metrology on molten metal droplets deposited onto microstructured surfaces and then frozen. Unlike other techniques, this visualization technique can be used on large areas of curved and opaque microstructured surfaces to determine contact line. This dissertation also presents measurements and models for how curvature and flexing of microstructured polymers affects hydrophobicity. Increasing curvature of microstructured surfaces leads to decreased slide angle for liquid droplets suspended on the surface asperities. For a surface with regularly spaced asperities, as curvature becomes more positive, droplets suspended on the tops of asperities are suspended on fewer asperities. Curvature affects superhydrophobicity because microscopic curvature changes solid-liquid interaction, pitch is altered, and curvature changes the shape of the three phase contact line. This dissertation presents a model of droplet interactions with curved microstructured surfaces that can be used to design microstructure geometries that maintain the suspension of a droplet when curved surfaces are covered with microstructured polymers. Controlling droplet dynamics could improve microfluidic devices and the shedding of liquids from expensive equipment, preventing corrosion and detrimental performance. This dissertation demonstrates redirection of dynamic droplet spray with anisotropic microstructures. Superhydrophobic microstructured surfaces can be economically fabricated using metal embossing masters, so this dissertation describes casting-based microfabrication of metal microstructures and nanostructures. Low melting temperature metal was cast into flexible silicone molds which were themselves cast from microfabricated silicon templates. The flexibility of the silicone mold permits casting of curved surfaces, which this dissertation demonstrates by fabricating a cylindrical metal roller with microstructures. The metal microstructures can be in turn used as a reusable molding tool. This dissertation also describes an industrial investment casting process to produce aluminum molds having integrated microstructures. Unlike conventional micromolding tools, the aluminum mold was large and had complex curved surfaces. The aluminum was cast into curved microstructured ceramic molds which were themselves cast from curved microstructured rubber. Many structures were successfully cast into the aluminum with excellent replication fidelity, including circular, square, and triangular holes. This dissertation demonstrates molding of large, curved surfaces having surface microstructures using the aluminum mold. This work contributes a more full understanding of the phenomenon of superhydrophobicity and techniques for the economic fabrication of superhydrophobic microstructures.

Design and development of distributed feedback transistor lasers

The transistor laser is a unique three-port device that operates simultaneously as a transistor and a laser. With quantum wells incorporated in the base regions of heterojunction bipolar transistors, the transistor laser possesses advantageous characteristics of fast base spontaneous carrier lifetime, high differential optical gain, and electrical-optical characteristics for direct “read-out” of its optical properties. These devices have demonstrated many useful features such as high-speed optical transmission without the limitations of resonance, non-linear mixing, frequency multiplication, negative resistance, and photon-assisted switching. To date, all of these devices operate as multi-mode lasers without any type of wavelength selection or stabilizing mechanisms. Stable single-mode distributed feedback diode laser sources are important in many applications including spectroscopy, as pump sources for amplifiers and solid-state lasers, for use in coherent communication systems, and now as TLs potentially for integrated optoelectronics. The subject of this work is to expand the future applications of the transistor laser by demonstrating the theoretical background, process development and device design necessary to achieve singlelongitudinal- mode operation in a three-port transistor laser. A third-order distributed feedback surface grating is fabricated in the top emitter AlGaAs confining layers using soft photocurable nanoimprint lithography. The device produces continuous wave laser operation with a peak wavelength of 959.75 nm and threshold current of 13 mA operating at -70 °C. For devices with cleaved ends a side-mode suppression ratio greater than 25 dB has been achieved.

Bioanalytical applications of microfluidic devices

The first part of the thesis describes a new patterning technique--microfluidic contact printing--that combines several of the desirable aspects of microcontact printing and microfluidic patterning and addresses some of their important limitations through the integration of a track-etched polycarbonate (PCTE) membrane. Using this technique, biomolecules (e.g., peptides, polysaccharides, and proteins) were printed in high fidelity on a receptor modified polyacrylamide hydrogel substrate. The patterns obtained can be controlled through modifications of channel design and secondary programming via selective membrane wetting. The protocols support the printing of multiple reagents without registration steps and fast recycle times. The second part describes a non-enzymatic, isothermal method to discriminate single nucleotide polymorphisms (SNPs). SNP discrimination using alkaline dehybridization has long been neglected because the pH range in which thermodynamic discrimination can be done is quite narrow. We found, however, that SNPs can be discriminated by the kinetic differences exhibited in the dehybridization of PM and MM DNA duplexes in an alkaline solution using fluorescence microscopy. We combined this method with multifunctional encoded hydrogel particle array (fabricated by stop-flow lithography) to achieve fast kinetics and high versatility. This approach may serve as an effective alternative to temperature-based method for analyzing unamplified genomic DNA in point-of-care diagnostic.

MICROSCALE DIELECTRIC ANTI-REFLECTION COATINGS FOR PHOTOVOLTAICS

In order to power our planet for the next century, clean energy technologies need to be developed and deployed. Photovoltaic solar cells, which convert sunlight into electricity, are a clear option; however, they currently supply 0.1% of the US electricity due to the relatively high cost per Watt of generation. Thus, our goal is to create more power from a photovoltaic device, while simultaneously reducing its price. To accomplish this goal, we are creating new high efficiency anti-reflection coatings that allow more of the incident sunlight to be converted to electricity, using simple and inexpensive coating techniques that enable reduced manufacturing costs. Traditional anti-reflection coatings (consisting of thin layers of non-absorbing materials) rely on the destructive interference of the reflected light, causing more light to enter the device and subsequently get absorbed. While these coatings are used on nearly all commercial cells, they are wavelength dependent and are deposited using expensive processes that require elevated temperatures, which increase production cost and can be detrimental to some temperature sensitive solar cell materials. We are developing two new classes of anti-reflection coatings (ARCs) based on textured dielectric materials: (i) a transparent, flexible paper technology that relies on optical scattering and reduced refractive index contrast between the air and semiconductor and (ii) silicon dioxide (SiO2) nanosphere arrays that rely on collective optical resonances. Both techniques improve solar cell absorption and ultimately yield high efficiency, low cost devices. For the transparent paper-based ARCs, we have recently shown that they improve solar cell efficiencies for all angles of incident illumination reducing the need for costly tracking of the sun’s position. For a GaAs solar cell, we achieved a 24% improvement in the power conversion efficiency using this simple coating. Because the transparent paper is made from an earth abundant material (wood pulp) using an easy, inexpensive and scalable process, this type of ARC is an excellent candidate for future solar technologies. The coatings based on arrays of dielectric nanospheres also show excellent potential for inexpensive, high efficiency solar cells. The fabrication process is based on a Meyer rod rolling technique, which can be performed at room-temperature and applied to mass production, yielding a scalable and inexpensive manufacturing process. The deposited monolayer of SiO2 nanospheres, having a diameter of 500 nm on a bare Si wafer, leads to a significant increase in light absorption and a higher expected current density based on initial simulations, on the order of 15-20%. With application on a Si solar cell containing a traditional anti-reflection coating (Si3N4 thin-film), an additional increase in the spectral current density is observed, 5% beyond what a typical commercial device would achieve. Due to the coupling between the spheres originated from Whispering Gallery Modes (WGMs) inside each nanosphere, the incident light is strongly coupled into the high-index absorbing material, leading to increased light absorption. Furthermore, the SiO2 nanospheres scatter and diffract light in such a way that both the optical and electrical properties of the device have little dependence on incident angle, eliminating the need for solar tracking. Because the layer can be made with an easy, inexpensive, and scalable process, this anti-reflection coating is also an excellent candidate for replacing conventional technologies relying on complicated and expensive processes.

Cell-cell communication in three dimensional microenvironments

Cellular behavior is dependent on a variety of extracellular cues required for normal tissue function, wound healing, and activation of the immune system. Removed from their in vivo microenvironment and cultured in vitro, cells lose many environmental cues and that may result in abberant behavior, making it difficult to study cellular processes. In order to mimic native tissue environments, optical tweezer and microfluidic technologies were used to place cells within defined areas of the culture environment. To provide three dimensional supports found in natural tissues, hydrogel scaffolds of poly (ethylene glycol) diacrylate and the basement membrane matrix Matrigel were used. Optical tweezer technology allowed precision placement and formation of homotypic and heterotypic arrays of human U937, HEK 293, and porcine mesenchymal stem cells. Alternatively, two microfluidic devices were designed to pattern Matrigel scaffolds. The first microfluidic device utilized laminar flow to spatially pattern multiple cell types within the device. Gradients of soluble molecules were then be formed and manipulated across the Matrigel scaffolds. Patterning Matrigel using laminar flow techniques require microfluidic expertise and do not produce consistent patterning conditions, limiting their use difficult in most cell culture laboratories. Thus, a buried Matrigel polydimethylsiloxane (PDMS) device was developed for spatial patterning of biological scaffolds. Matrigel is injected into micron sized channels of PDMS fabricated by soft lithography and allowed to thermally cure. Following curing, a second PDMS device was placed on top of the buried Matrigel channels to support media flow. In order to validate these systems, a cell-cell communication model system was developed utilizing LPS and TNFα signaling with fluorescent reporter systems to monitor communication in real time. We demonstrated the utility of microfluidic devices to support the cell-cell communication model system by co culturing three cell types within Matrigel scaffolds and monitoring signaling activity via fluorescent reporters.

Solid-liquid interactions in microscale structures and devices

Liquid-solid interactions become important as dimensions approach mciro/nano-scale. This dissertation focuses on liquid-solid interactions in two distinct applications: capillary driven self-assembly of thin foils into 3D structures, and droplet wetting of hydrophobic micropatterned surfaces. The phenomenon of self-assembly of complex structures is common in biological systems. Examples include self-assembly of proteins into macromolecular structures and self-assembly of lipid bilayer membranes. The principles governing this phenomenon have been applied to induce self-assembly of millimeter scale Si thin films into spherical and other 3D structures, which are then integrated into light-trapping photovoltaic (PV) devices. Motivated by this application, we present a generalized analytical study of the self-folding of thin plates into deterministic 3D shapes, through fluid-solid interactions, to be used as PV devices. This study consists of developing a model using beam theory, which incorporates the two competing components — a capillary force that promotes folding and the bending rigidity of the foil that resists folding into a 3D structure. Through an equivalence argument of thin foils of different geometry, an effective folding parameter, which uniquely characterizes the driving force for folding, has been identified. A criterion for spontaneous folding of an arbitrarily shaped 2D foil, based on the effective folding parameter, is thus established. Measurements from experiments using different materials and predictions from the model match well, validating the assumptions used in the analysis. As an alternative to the mechanics model approach, the minimization of the total free energy is employed to investigate the interactions between a fluid droplet and a flexible thin film. A 2D energy functional is proposed, comprising the surface energy of the fluid, bending energy of the thin film and gravitational energy of the fluid. Through simulations with Surface Evolver, the shapes of the droplet and the thin film at equilibrium are obtained. A critical thin film length necessary for complete enclosure of the fluid droplet, and hence successful self-assembly into a PV device, is determined and compared with the experimental results and mechanics model predictions. The results from the modeling and energy approaches and the experiments are all consistent. Superhydrophobic surfaces, which have unique properties including self-cleaning and water repelling are desired in many applications. One excellent example in nature is the lotus leaf. To fabricate these surfaces, well designed micro/nano- surface structures are often employed. In this research, we fabricate superhydrophobic micropatterned Polydimethylsiloxane (PDMS) surfaces composed of micropillars of various sizes and arrangements by means of soft lithography. Both anisotropic surfaces, consisting of parallel grooves and cylindrical pillars in rectangular lattices, and isotropic surfaces, consisting of cylindrical pillars in square and hexagonal lattices, are considered. A novel technique is proposed to image the contact line (CL) of the droplet on the hydrophobic surface. This technique provides a new approach to distinguish between partial and complete wetting. The contact area between droplet and microtextured surface is then measured for a droplet in the Cassie state, which is a state of partial wetting. The results show that although the droplet is in the Cassie state, the contact area does not necessarily follow Cassie model predictions. Moreover, the CL is not circular, and is affected by the micropatterns, in both isotropic and anisotropic cases. Thus, it is suggested that along with the contact angle — the typical parameter reported in literature quantifying wetting, the size and shape of the contact area should also be presented. This technique is employed to investigate the evolution of the CL on a hydrophobic micropatterned surface in the cases of: a single droplet impacting the micropatterned surface, two droplets coalescing on micropillars, and a receding droplet resting on the micropatterned surface. Another parameter which quantifies hydrophobicity is the contact angle hysteresis (CAH), which indicates the resistance of the surface to the sliding of a droplet with a given volume. The conventional methods of using advancing and receding angles or tilting stage to measure the resistance of the micropatterned surface are indirect, without mentioning the inaccuracy due to the discrete and stepwise motion of the CL on micropillars. A micronewton force sensor is utilized to directly measure the resisting force by dragging a droplet on a microtextured surface. Together with the proposed imaging technique, the evolution of the CL during sliding is also explored. It is found that, at the onset of sliding, the CL behaves as a linear elastic solid with a constant stiffness. Afterwards, the force first increases and then decreases and reaches a steady state, accompanied with periodic oscillations due to regular pinning and depinning of the CL. Both the maximum and steady state forces are primarily dependent on area fractions of the micropatterned surfaces in our experiment. The resisting force is found to be proportional to the number of pillars which pin the CL at the trailing edge, validating the assumption that the resistance mainly arises from the CL pinning at the trailing edge. In each pinning-and-depinning cycle during the steady state, the CL also shows linear elastic behavior but with a lower stiffness. The force variation and energy dissipation involved can also be determined. This novel method of measuring the resistance of the micropatterned surface elucidates the dependence on CL pinning and provides more insight into the mechanisms of CAH.

Fabrication et caractérisation de cellules solaires organiques nanostructurées par la méthode de nanoimpression thermique

La morphologie des couches actives des cellules solaires organiques joue un rôle important sur l’efficacité de conversion de l’énergie solaire en énergie électrique de ces dispositifs. Les hétérojonctions planaires et les hétérojonctions en volume sont les plus communément utilisées. Cependant, la morphologie idéale pour l’efficacité se situerait à mis chemin entre celles-ci. Il s’agit de l’hétérojonction nanostructurée qui augmenterait la surface entre les couches actives de matériaux tout en favorisant le transport des porteurs de charge. L’objectif de ce projet de maîtrise est d’étudier l’impact de l’implantation de nanostructures dans les cellules solaires organiques sur leurs performances photovoltaïques. Pour ce faire, on utilise la méthode de nanoimpression thermique sur le matériau donneur, le P3HT, afin que celui-ci forme une interface nanostructurée avec le matériau accepteur, le PCBM. Pour effectuer les nanoimpressions, des moules en alumine nanoporeuse ont été fabriqués à l’aide du procédé d’anodisation en deux temps développé par Masuda et al. Ces moules ont subi un traitement afin de faciliter leur séparation du P3HT. Les agents antiadhésifs PDMS et FTDS ont été utilisés à cette fin. Les résultats obtenus témoignent de la complexité d’exécution du procédé de nanoimpression. Il a été démontré que la pression appliquée durant le procédé, la tension superficielle des éléments en contact et les dimensions des nanopores des moules sont des paramètres critiques pour le succès des nanoimpressions. Ceux-ci ont donc dû être optimisés de manière à réussir cette opération. Ainsi, des cellules à interface nanostructurée à 25% avec des nanobâtonnets de 35 nm de hauteur ont pu être fabriquées. Les cellules nanostructurées ont démontré une efficacité 2,3 ± 0,6 fois supérieure aux cellules sans nanostructures, dites planaires. D’autre part, un solvant a été proposé pour diminuer l’interdiffusion entre les couches de P3HT et de PCBM pouvant altérer les nanostructures. Ce phénomène bien connu survient lors du dépot de la couche de PCBM avec le dichlorométhane, un solvant orthogonal avec ces matériaux. Des mesures au TOF-SIMS ont démontré que le limonène permet de diminuer l’interdiffusion entre les couches de P3HT et de PCBM, ce qui en fait un meilleur solvant orthogonal que le dichlorométhane.

Encapsulation of Local Anesthetic Bupivacaine in Biodegradable Poly(DL-lactide-co-glycolide) Nanospheres: Factorial Design, Characterization and Cytotoxicity Studies

Local anesthetic agents cause temporary blockade of nerve impulses productiong insensitivity to painful stimuli in the area supplied by that nerve. Bupivacaine (BVC) is an amide-type local anesthetic widely used in surgery and obstetrics for sustained peripheral and central nerve blockade. in this study, we prepared and characterized nanosphere formulations containing BVC. To achieve these goals, BVC loaded poly(DL-lactide-co-glycolide) (PLGA) nanospheres (NS) were prepared by nanopreciptation and characterized with regard to size distribution, drug loading and cytotoxicity assays. The 2(3-1) factorial experimental design was used to study the influence of three different independent variables on nanoparticle drug loading. BVC was assayed by HPLC, the particle size and zeta potential were determined by dynamic light scattering. BVC was determined using a combined ultrafiltration-centrifugation technique. The results of optimized formulations showed a narrow size distribution with a polydispersivity of 0.05%, an average diameter of 236.7 +/- 2.6 nm and the zeta potential -2.93 +/- 1,10 mV. In toxicity studies with fibroblast 3T3 cells, BVC loaded-PLGA-NS increased cell viability, in comparison with the effect produced by free BVC. In this way, BVC-loaded PLGA-NS decreased BVC toxicity. The development of BVC formulations in carriers such as nanospheres could offer the possibility of controlling drug delivery in biological systems, prolonging the anesthetic effect and reducing toxicity.

Design, Fabrication, and Mechanical Property Analysis of 3D Nanoarchitected Materials

Recent developments in micro- and nanoscale 3D fabrication techniques have enabled the creation of materials with a controllable nanoarchitecture that can have structural features spanning 5 orders of magnitude from tens of nanometers to millimeters. These fabrication methods in conjunction with nanomaterial processing techniques permit a nearly unbounded design space through which new combinations of nanomaterials and architecture can be realized. In the course of this work, we designed, fabricated, and mechanically analyzed a wide range of nanoarchitected materials in the form of nanolattices made from polymer, composite, and hollow ceramic beams. Using a combination of two-photon lithography and atomic layer deposition, we fabricated samples with periodic and hierarchical architectures spanning densities over 4 orders of magnitude from ρ=0.3-300kg/m³ and with features as small as 5nm. Uniaxial compression and cyclic loading tests performed on different nanolattice topologies revealed a range of novel mechanical properties: the constituent nanoceramics used here have size-enhanced strengths that approach the theoretical limit of materials strength; hollow aluminum oxide (Al₂O₃) nanolattices exhibited ductile-like deformation and recovered nearly completely after compression to 50% strain when their wall thicknesses were reduced below 20nm due to the activation of shell buckling; hierarchical nanolattices exhibited enhanced recoverability and a near linear scaling of strength and stiffness with relative density, with E∝ρ^1.04 and σy∝ρ^1.17 for hollow Al₂O₃ samples; periodic rigid and non-rigid nanolattice topologies were tested and showed a nearly uniform scaling of strength and stiffness with relative density, marking a significant deviation from traditional theories on “bending” and “stretching” dominated cellular solids; and the mechanical behavior across all topologies was highly tunable and was observed to strongly correlate with the slenderness λ and the wall thickness-to-radius ratio t/a of the beams. These results demonstrate the potential of nanoarchitected materials to create new highly tunable mechanical metamaterials with previously unattainable properties.