Este trabalho foi patrocinado pela camada de fundo de pesquisa acadêmica (AcRF) 1 (RG171/15), Ministério da educação, Singapura.

1. preparação do canal microfluídicos
<ol><li>Misture o poli-dimetilssiloxano (PDMS) com base na proporção de 10:1 um elastômero.</li>
	<li>Desgaseificar a mistura em um forno a vácuo e despeje-o em uma bolacha de silício com um padrão de fotorresiste Tom negativo na parte superior.</li>
	<li>Desgaseificar a bolacha de silício modelado novamente e aqueça-a 70 ° C por 3 h na incubadora para solidificação.</li>
</ol>2. fabricação de transdutores interdigitais
<ol><li>Depósito 20 nm de Cr e 400 nm de Al em uma bolacha de3 LiNbO; padrão de 20 tiras com uma largura de 150 µm e uma abertura de 2 cm em uma máscara de plástico para fotolitografia depositando o fotorresiste positiva sobre o substrato.</li>
	<li>Remova a camada de Cr-Al na área não-expostos com acetona.</li>
	<li>Tratar a superfície deles com plasma de oxigênio (com uma proporção de nitrogênio e oxigênio de 2:1) com a potência de 30 W para 60 s.</li>
	<li>Alinhar o microchannel PDMS e relacionar isso ao substrato de3 LiNbO pressionando com o polegar por alguns segundos.</li>
	<li>Coloque o dispositivo integrado na câmara de aquecimento a 60 ° C por 3 h.</li>
</ol>3. dual-frequência excitação
<ol><li>Aplicar simultaneamente duas componentes de frequência (f1 e f3, a frequência fundamental e seu terceiro harmônico da IDT fabricado, respectivamente) com a diferença de fase φ entre eles para o par de IDTs, para que a serra produzida pode ser expressos como segue. <img alt="Equation 1" src="/files/ftp_upload/58085/58085eq1.jpg"> Aqui, <img alt="Equation 2" src="/files/ftp_upload/58085/58085eq2.jpg">e <img alt="Equation 3" src="/files/ftp_upload/58085/58085eq3.jpg"> = as pressões acústicas.</li>
	<li>Sintetizar a forma de onda de dupla frequência usando o Equation Editor do software aplicativo de ArbExpress com a frequência de amostragem de 100 MS/s e depois armazená-lo para o gerador de função como entrada arbitrária para a excitação de serra no experimento através um cabo USB.</li>
	<li>Variar o poder da frequência fundamental para a potência total emitida <img alt="Equation 4" src="/files/ftp_upload/58085/58085eq4.jpg"> de 100% (excitação na frequência fundamental puramente) para 0% (excitação na terceira puramente harmônica); para uma boa comparação, mudar, mas mantenha o poder total da mesma.</li>
	<li>Varia a diferença de fase de excitação dupla frequência de 0° a 360°.</li>
</ol>4. simulação numérica
<ol><li>Descrever o movimento do fluxo incompressível laminar com baixo Reynolds (ou seja, Re = 0,55) e Mach os seguintes números35. <img alt="Equation 5" src="/files/ftp_upload/58085/58085eq5.jpg"> <img alt="Equation 6" src="/files/ftp_upload/58085/58085eq6.jpg"> Aqui, <img alt="Equation 7" src="/files/ftp_upload/58085/58085eq7.jpg">= a velocidade do fluido, <img alt="Equation 8" src="/files/ftp_upload/58085/58085eq8.jpg">= a viscosidade dinâmica, <img alt="Equation 9" src="/files/ftp_upload/58085/58085eq9.jpg">= a densidade do fluido, <img alt="Equation 10" src="/files/ftp_upload/58085/58085eq10.jpg">= a pressão sobre o fluido, <img alt="Equation 11" src="/files/ftp_upload/58085/58085eq11.jpg">= a matriz de identidade, e <img alt="Equation 12" src="/files/ftp_upload/58085/58085eq12.jpg">= uma força externa.</li>
	<li>Descreva a força de arrasto do Stoke produzida no objeto como segue36. <img alt="Equation 13" src="/files/ftp_upload/58085/58085eq13.jpg"> Aqui, <img alt="Equation 14" src="/files/ftp_upload/58085/58085eq14.jpg">= raio das micropartículas, <img alt="Equation 15" src="/files/ftp_upload/58085/58085eq15.jpg">= a velocidade do fluido, e <img alt="Equation 16" src="/files/ftp_upload/58085/58085eq16.jpg">= a velocidade da micropartículas.</li>
	<li>Derivar a força de radiação acústica aplicada a micropartículas nos microcanais ao longo do x-eixo (em toda a largura do microchannel) em uma única frequência como segue16 . <img alt="Equation 17" src="/files/ftp_upload/58085/58085eq17.jpg"> Aqui, <img alt="Equation 18" src="/files/ftp_upload/58085/58085eq18.jpg">= volume das micropartículas, <img alt="Equation 19" src="/files/ftp_upload/58085/58085eq19.jpg">= a densidade das micropartículas, <img alt="Equation 20" src="/files/ftp_upload/58085/58085eq20.jpg">= a densidade do meio, <img alt="Equation 21" src="/files/ftp_upload/58085/58085eq21.jpg">= a compressibilidade das micropartículas, e <img alt="Equation 22" src="/files/ftp_upload/58085/58085eq22.jpg">= a compressibilidade do meio.</li>
	<li>A força de radiação acústica resultante da excitação de dupla frequência derivam da seguinte maneira. <img alt="Equation 23" src="/files/ftp_upload/58085/58085eq23.jpg">
</li>
	<li>Expressar o movimento transversal a toda a largura do canal (ao longo do y-axis) sob a força de radiação acústica e o Stokes arraste vigor regida pela segunda lei de Newton como segue. <img alt="Equation 24" src="/files/ftp_upload/58085/58085eq24.jpg">
</li>
	<li>Resolva as equações diferenciais ordinárias (EDOs) acima usando a método de Runge-Kutta de quarta ordem em um computador pessoal. Definir o passo do tempo e duração total como 1 µs e 20 s, respectivamente.</li>
</ol>5. observação experimental
<ol><li>Girar a solução na concentração de 5,9 x 107 com 4 µm verde fluorescentes esferas de poliestireno por 1 mL por vórtice por cerca de 2-3 min e em seguida, mergulhe-a em um sonicador de ultra-som por 10 min para interromper qualquer aglomeração antes de cada teste.</li>
	<li>Preencher a mistura em uma seringa de 3 mL e depois jogá-la com uma bomba de seringa com um caudal de 3 a 5 µ l/min.</li>
	<li>Dirigir o IDT com o sinal de dupla frequência de um gerador de função, seguido de um amplificador de potência.</li>
	<li>Observar as micropartículas estabilizadas na jusante microchannel sob um microscópio de luz em uma ampliação de 40 X e gravar a imagem com uma câmera digital.</li>
	<li>Medir a localização das micropartículas acumuladas em imagens capturadas Digitas usando o ImageJ e a escala estabelecida e determinar quantitativamente a concentração de micropartículas a acumulado com o brilho da fluorescência normalizados no cada nó de pressão.</li>
</ol>

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O movimento de micropartículas no microchannel por um SSAW com a excitação de dupla frequência foi extensivamente investigado neste estudo, e uma técnica de padronização efetivamente sintonizável variando os sinais de excitação de dupla frequência foi desenvolvida e testada. A produção de uma forma de onda é facilmente realizada pela maioria dos geradores de função, e a abordagem de ajuste é muito conveniente. O S12- e S11-respostas de frequência dos IDTs fabricados ilustram vário...

Tecnologia LOC integra uma ou várias funções em um microchip para biologia, química, biofísica e processos biomédicos. LOC permite uma configuração de laboratório em uma escala menor do que o sub milímetros, taxas de reação rápida, um tempo de resposta curto, um controle de processo de alta, um consumo de baixo volume (menos reagentes desperdício, menor custo e menos volume de amostra necessário), uma alta taxa de transferência devido à paralelização, um baixo custo no futuro da produção em massa e cost-effective descartáveis, uma segurança elevada para estudos químicos, radioativos ou biológicos e as vantagens de um dispositivo compacto e portátil,1,2. Manipulação de célula precisa (ou seja, acumulação e separação) é fundamental num LOC-com base em análise e diagnóstico3,4. No entanto, a precisão e a reprodutibilidade da manipulação de micropartículas têm uma variedade de desafios. Muitas técnicas, tais como electro-osmose5, Dieletroforese (DEP)6, magnetophoresis7, thermophoresis8,9, uma abordagem óptico10, um optoelectronic abordagem11 , uma abordagem hidrodinâmico12e acoustophoresis13,14,15, foram desenvolvidos. Em comparação, abordagens acústicas são apropriadas para um aplicativo LOC porque, teoricamente, muitos tipos de micropartículas/células podem ser manipulados de forma eficaz e canaliza com um suficientemente alto contraste (densidade e compressibilidade) comparados com o fluido circundante. Portanto, comparado a suas contrapartes, abordagens acústicas são inerentemente elegíveis para a maioria das micropartículas e objetos biológicos, não importa suas propriedades ópticas, elétricas e magnéticas de16.
Ondas acústicas superficiais (serras) dos IDTs propagam principalmente na superfície de um substrato piezoelétrico na espessura de vários comprimentos de onda e, em seguida, vazamento no ângulo Rayleigh no fluido no microchannel, de acordo com a lei de Snell, o17, 18,19,20,21,22. Eles têm as vantagens técnicas de uma alta eficiência de energia ao longo da superfície devido a sua localização de energia, uma flexibilidade excelente design em alta frequência, um bom sistema de integração com o canal microfluídicos e miniaturização usando tecnologia de sistema de microeletrônica-mecânica (MEMS) e um elevado potencial de produção em massa23. Neste protocolo, serras são geradas a partir de um par de idênticos IDTs e propagadas na direção oposta para gerar uma onda estacionária, ou SSAW, em microchannel, onde as micropartículas suspensas são empurradas para nós de pressão, principalmente pela acústica aplicada força de radiação24. A amplitude de tal força resultante é determinada pelo seu fator de contraste acústico22,25, microparticulado tamanho e a frequência de excitação.
Tal acoustophoresis tem a limitação de padrões de manipulação predeterminados que não são facilmente ajustáveis. A frequência de excitação dos IDTs é determinada pela sua distância periódica, assim a largura de banda é bastante limitada. Várias estratégias foram desenvolvidas para aumentar a capacidade de manipulação e pré-definido. Os primeiros e segundo modos de ondas acústicas em pé, aplicados em diferentes partes do microchannel poderiam separar micropartículas mais eficazmente, de acordo com velocidades diferentes de movimento em direção a linhas nodal26. Estes dois modos também podem ser aplicados a toda a parte do microchannel e trocou como alternativa de28,de27,29. No entanto, para isso, um grande número de equipamentos (ou seja, três geradores de função, duas unidades de impedâncias e um relé eletromagnético) é necessário, com o aumento de custo e controle complexidade a montagem experimental devido a diferentes impedâncias elétricas na frequência fundamental e terceira harmônica do piezoceramic placa30. Além disso, dedos inclinados transdutores interdigitais (SFITs) poderiam ser aplicadas para ajustar as células e as micropartículas padronização excitando um período dos dedos inclinados para uma certa ressonância de20,31. No entanto, em seguida, a largura de banda é inversamente proporcional ao número de dedos inclinados. Várias linhas de pressão nodal têm uma maior eficiência de separação e sensibilidade em comparação com a única linha nodal no separador convencional baseada em SSAW micropartículas. Alternativamente, a localização de nós de pressão também pode ser alterada simplesmente ajustando a diferença de fase aplicada para os dois IDTs no projeto de32,33.
A frequência fundamental e a terceira harmônica de IDTs tem respostas semelhantes de frequência para que eles podem ser um pouco excitados ao mesmo tempo, que fornece mais pré-definido para a manipulação de micropartículas34. Em comparação com a excitação de IDT convencional em uma única frequência, ajustar as pressões acústicas de fases entre eles e a excitação de dupla frequência fornece exclusividade técnica, tais como o de até ~ 2 dobras reduziu o tempo de movimento à pressão nodal linha ou o centro da microchannel, variado número e localização das linhas nodal pressão e as concentrações de micropartículas.

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microparticle manipulation by standing surface acoustic waves with dual-frequency excitations

Vamos demonstrar um método para aumentar a capacidade de sintonia de uma pé onda acústica de superfície (SSAW) para manipulação de micropartículas num sistema lab-on-a-chip (LOC). A excitação simultânea de frequência fundamental e sua terceira harmônica, que é denominada como excitação de dupla frequência, para um par de transdutores interdigitais (IDTs) poderia gerar um novo tipo de ondas acústicas em um canal microfluidic de pé. Variar o poder e a fase da excitação de dupla frequência sinais resulta em um campo reconfigurável da força de radiação acústica aplicada as micropartículas através do microchannel (por exemplo, o número e a localização de nós de pressão e o concentrações de micropartículas em nós de pressão correspondente). Este artigo demonstra que é possível reduzir o tempo de movimento das micropartículas de nó único pressão ~ 2 vezes para a relação de poder da frequência fundamental superior a 90%. Em contraste, existem três nós de pressão na microchannel se menos do que este limiar. Além disso, ajustar a fase inicial entre a frequência fundamental e terceiros harmônicos resultados em taxas diferentes do movimento dos três nós SSAW pressão, bem como no percentual de micropartículas em cada nó de pressão na microchannel. Existe um bom acordo entre a observação experimental e as previsões numéricas. Este método de excitação romance pode facilmente e de forma não-invasiva integrar o sistema LOC, com uma ampla tenability e apenas algumas alterações para a montagem experimental.

As distribuições da pressão acústica e a força de radiação acústica de um SSAW com a excitação de dupla frequência (6.2 e 18,6 MHz) são mostrados na Figura 1. Aqui, a excitação de dupla frequência ocorre em micropartículas de poliestireno (4 µm de diâmetro) em um microchannel com uma largura de 300 µm com uma potência acústica de 146 mW. A pressão acústica resultante é sempre na fase quando P1 > 90% que somente um ...

Watch this Scientific Journal Video about Microparticle Manipulation by Standing Surface Acoustic Waves with Dual-frequency Excitations at JoVE.com

Microparticle Manipulation by Standing Surface Acoustic Waves with Dual-frequency Excitations

É apresentado um protocolo para manipular as micropartículas em um canal de microfluidic com uma excitação de dupla frequência.

Manipulação de micropartículas de ondas acústicas de superfície com dupla frequência excitações de pé

We demonstrate a method for increasing the tuning ability of a standing surface acoustic wave (SSAW) for microparticles manipulation in a lab-on-a-chip ...

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6.9K visualizações.  Nanyang Technological University. É apresentado um protocolo para manipular as micropartículas em um canal de microfluidic com uma excitação de dupla frequência.

Vídeo: Microparticle Manipulation by Standing Surface Acoustic Waves with Dual-frequency Excitations

Activating Molecules, Ions, and Solid Particles with Acoustic Cavitation

The chemical and physical effects of ultrasound arise not from a direct interaction of molecules with sound waves, but rather from the acoustic cavitation: the nucleation, growth, and implosive collapse of microbubbles in liquids submitted to power ultrasound. The violent implosion of bubbles leads to the formation of chemically reactive species and to the emission of light, named sonoluminescence. In this manuscript, we describe the techniques allowing study of extreme intrabubble conditions and chemical reactivity of acoustic cavitation in solutions. The analysis of sonoluminescence spectra of water sparged with noble gases provides evidence for nonequilibrium plasma formation. The photons and the "hot" particles generated by cavitation bubbles enable to excite the non-volatile species in solutions increasing their chemical reactivity. For example the mechanism of ultrabright sonoluminescence of uranyl ions in acidic solutions varies with uranium concentration: sonophotoluminescence dominates in diluted solutions, and collisional excitation contributes at higher uranium concentration. Secondary sonochemical products may arise from chemically active species that are formed inside the bubble, but then diffuse into the liquid phase and react with solution precursors to form a variety of products. For instance, the sonochemical reduction of Pt(IV) in pure water provides an innovative synthetic route for monodispersed nanoparticles of metallic platinum without any templates or capping agents. Many studies reveal the advantages of ultrasound to activate the divided solids. In general, the mechanical effects of ultrasound strongly contribute in heterogeneous systems in addition to chemical effects. In particular, the sonolysis of PuO2 powder in pure water yields stable colloids of plutonium due to both effects.

Acoustic cavitation in liquids submitted to power ultrasound creates transient extreme conditions inside the collapsing bubbles, which are the origin of unusual chemical reactivity and light emission, known as sonoluminescence. In the presence of noble gases, nonequilibrium plasma is formed. The "hot" particles and the photons generated by collapsing bubbles are able to excite species in solution.

Ativando moléculas, íons e partículas sólidas com Acústico cavitação

The chemical and physical effects of ultrasound arise not from a direct interaction of molecules with sound waves, but rather from the acoustic ...

Química

Fabrication, Operation and Flow Visualization in Surface-acoustic-wave-driven Acoustic-counterflow Microfluidics

Surface acoustic waves (SAWs) can be used to drive liquids in portable microfluidic chips via the acoustic counterflow phenomenon. In this video we present the fabrication protocol for a multilayered SAW acoustic counterflow device. The device is fabricated starting from a lithium niobate (LN) substrate onto which two interdigital transducers (IDTs) and appropriate markers are patterned. A polydimethylsiloxane (PDMS) channel cast on an SU8 master mold is finally bonded on the patterned substrate. Following the fabrication procedure, we show the techniques that allow the characterization and operation of the acoustic counterflow device in order to pump fluids through the PDMS channel grid. We finally present the procedure to visualize liquid flow in the channels. The protocol is used to show on-chip fluid pumping under different flow regimes such as laminar flow and more complicated dynamics characterized by vortices and particle accumulation domains.

In this video we first describe fabrication and operation procedures of a surface acoustic wave (SAW) acoustic counterflow device. We then demonstrate an experimental setup that allows for both qualitative flow visualization and quantitative analysis of complex flows within the SAW pumping device.

Fabricação, Operação e Visualização de Fluxo em superfície acústico de ondas orientadas Microfluidics acústico contrafluxo

Surface acoustic waves (SAWs) can be used to drive liquids in portable microfluidic chips via the acoustic counterflow phenomenon. In this video we ...

Engenharia

Fabrication and Operation of Acoustofluidic Devices Supporting Bulk Acoustic Standing Waves for Sheathless Focusing of Particles

Acoustophoresis refers to the displacement of suspended objects in response to directional forces from sound energy. Given that the suspended objects must be smaller than the incident wavelength of sound and the width of the fluidic channels are typically tens to hundreds of micrometers across, acoustofluidic devices typically use ultrasonic waves generated from a piezoelectric transducer pulsating at high frequencies (in the megahertz range). At characteristic frequencies that depend on the geometry of the device, it is possible to induce the formation of standing waves that can focus particles along desired fluidic streamlines within a bulk flow. Here, we describe a method for the fabrication of acoustophoretic devices from common materials and clean room equipment. We show representative results for the focusing of particles with positive or negative acoustic contrast factors, which move towards the pressure nodes or antinodes of the standing waves, respectively. These devices offer enormous practical utility for precisely positioning large numbers of microscopic entities (e.g., cells) in stationary or flowing fluids for applications ranging from cytometry to assembly.

Acoustofluidic devices use ultrasonic waves within microfluidic channels to manipulate, concentrate and isolate suspended micro and nanoscopic entities. This protocol describes the fabrication and operation of such a device supporting bulk acoustic standing waves to focus particles in a central streamline without the aid of sheath fluids.

Fabricação e operação de Acoustofluidic dispositivos que suportam a granel ondas acústicas pe para Sheathless Focando de Partículas

Acoustophoresis refers to the displacement of suspended objects in response to directional forces from sound energy. Given that the suspended objects must ...

A Microfluidic Platform for Precision Small-volume Sample Processing and Its Use to Size Separate Biological Particles with an Acoustic Microdevice

A major advantage of microfluidic devices is the ability to manipulate small sample volumes, thus reducing reagent waste and preserving precious sample. However, to achieve robust sample manipulation it is necessary to address device integration with the macroscale environment. To realize repeatable, sensitive particle separation with microfluidic devices, this protocol presents a complete automated and integrated microfluidic platform that enables precise processing of 0.15&#8211;1.5 ml samples using microfluidic devices. Important aspects of this system include modular device layout and robust fixtures resulting in reliable and flexible world to chip connections, and fully-automated fluid handling which accomplishes closed-loop sample collection, system cleaning and priming steps to ensure repeatable operation. Different microfluidic devices can be used interchangeably with this architecture. Here we incorporate an acoustofluidic device, detail its characterization, performance optimization, and demonstrate its use for size-separation of biological samples. By using real-time feedback during separation experiments, sample collection is optimized to conserve and concentrate sample. Although requiring the integration of multiple pieces of equipment, advantages of this architecture include the ability to process unknown samples with no additional system optimization, ease of device replacement, and precise, robust sample processing.

This protocol describes a system architecture for performing automated small volume (0.15&#8211;1.5 ml) particle separations using a microfluidic device, and discusses methods to optimize acoustofluidic device performance and operation.

Uma plataforma microfluídica para processamento de precisão de pequeno volume de amostra e respectiva utilização para Tamanho partículas biológicas separadas com um microdispositivos Acústico

A major advantage of microfluidic devices is the ability to manipulate small sample volumes, thus reducing reagent waste and preserving precious sample. ...

Bioengenharia

Multiplexing Focused Ultrasound Stimulation with Fluorescence Microscopy

By focusing low-intensity ultrasound pulses that penetrate soft tissues, LIPUS represents a promising biomedical technology to remotely and safely manipulate neural firing, hormonal secretion and genetically-reprogrammed cells. However, the translation of this technology for medical applications is currently hampered by a lack of biophysical mechanisms by which targeted tissues sense and respond to LIPUS. A suitable approach to identify these mechanisms would be to use optical biosensors in combination with LIPUS to determine underlying signaling pathways. However, implementing LIPUS to a fluorescence microscope may introduce undesired mechanical artefacts due to the presence of physical interfaces that reflect, absorb and refract acoustic waves. This article presents a step-by-step procedure to incorporate LIPUS to commercially-available upright epi-fluorescence microscopes while minimizing the influence of physical interfaces along the acoustic path. A simple procedure is described to operate a single-element ultrasound transducer and to bring the focal zone of the transducer into the objective focal point. The use of LIPUS is illustrated with an example of LIPUS-induced calcium transients in cultured human glioblastoma cells measured using calcium imaging.

Low-Intensity Pulsed Ultrasound Stimulation (LIPUS) is a modality for non-invasive mechanical stimulation of endogenous or engineered cells with high spatial and temporal resolution. This article describes how to implement LIPUS to an epi-fluorescence microscope and how to minimize acoustic impedance mismatch along the ultrasound path to prevent unwanted mechanical artefacts.

Multiplexação focada a estimulação de ultra-som com microscopia de fluorescência

By focusing low-intensity ultrasound pulses that penetrate soft tissues, LIPUS represents a promising biomedical technology to remotely and safely ...

Fabrication of Nanoheight Channels Incorporating Surface Acoustic Wave Actuation via Lithium Niobate for Acoustic Nanofluidics

Controlled nanoscale manipulation of fluids is known to be exceptionally difficult due to the dominance of surface and viscous forces. Megahertz-order surface acoustic wave (SAW) devices generate tremendous acceleration on their surface, up to 108 m/s2, in turn responsible for many of the observed effects that have come to define acoustofluidics: acoustic streaming and acoustic radiation forces. These effects have been used for particle, cell, and fluid manipulation at the microscale, although more recently SAW has been used to produce similar phenomena at the nanoscale through an entirely different set of mechanisms. Controllable nanoscale fluid manipulation offers a broad range of opportunities in ultrafast fluid pumping and biomacromolecule dynamics useful for physical and biological applications. Here, we demonstrate nanoscale-height channel fabrication via room-temperature lithium niobate (LN) bonding integrated with a SAW device. We describe the entire experimental process including nano-height channel fabrication via dry etching, plasma-activated bonding on lithium niobate, the appropriate optical setup for subsequent imaging, and SAW actuation. We show representative results for fluid capillary filling and fluid draining in a nanoscale channel induced by SAW. This procedure offers a practical protocol for nanoscale channel fabrication and integration with SAW devices useful to build upon for future nanofluidics applications.

We demonstrate fabrication of nanoheight channels with the integration of surface acoustic wave actuation devices upon lithium niobate for acoustic nanofluidics via liftoff photolithography, nano-depth reactive ion etching, and room-temperature plasma surface-activated multilayer bonding of single-crystal lithium niobate, a process similarly useful for bonding lithium niobate to oxides.

Fabricação de canais de nanoaltura incorporando atuação de onda acústica superficial via Niobate de lítio para nanofluidos acústicos

Controlled nanoscale manipulation of fluids is known to be exceptionally difficult due to the dominance of surface and viscous forces. Megahertz-order ...

Fabrication of Surface Acoustic Wave Devices on Lithium Niobate

Manipulation of fluids and particles by acoustic actuation at small scale is aiding the rapid growth of lab-on-a-chip applications. Megahertz-order surface acoustic wave (SAW) devices generate enormous accelerations on their surface, up to 108 m/s2, in turn responsible for many of the observed effects that have come to define acoustofluidics: acoustic streaming and acoustic radiation forces. These effects have been used for particle, cell, and fluid handling at the microscale&#8212;and even at the nanoscale. In this paper we explicitly demonstrate two major fabrication methods of SAW devices on lithium niobate: the details of lift-off and wet etching techniques are described step-by-step. Representative results for the electrode pattern deposited on the substrate as well as the performance of SAW generated on the surface are displayed in detail. Fabrication tricks and troubleshooting are covered as well. This procedure offers a practical protocol for high frequency SAW device fabrication and integration for future microfluidics applications.

Two fabrication techniques, lift-off and wet etching, are described in producing interdigital electrode transducers upon a piezoelectric substrate, lithium niobate, widely used to generate surface acoustic waves now finding broad utility in micro to nanoscale fluidics. The as-produced electrodes are shown to efficiently induce megahertz order Rayleigh surface acoustic waves.&#160;

Fabricação de dispositivos de onda acústica de superfície no niobato de lítio

Manipulation of fluids and particles by acoustic actuation at small scale is aiding the rapid growth of lab-on-a-chip applications. Megahertz-order ...

Fabrication and Characterization of Thickness Mode Piezoelectric Devices for Atomization and Acoustofluidics

We present a technique to fabricate simple thickness mode piezoelectric devices using lithium niobate (LN). Such devices have been shown to atomize liquid more efficiently, in terms of &#64258;ow rate per power input, than those that rely on Rayleigh waves and other modes of vibration in LN or lead zirconate titanate (PZT). The complete device is composed of a transducer, a transducer holder, and a &#64258;uid supply system. The fundamentals of acoustic liquid atomization are not well known, so techniques to characterize the devices and to study the phenomena are also described. Laser Doppler vibrometry (LDV) provides vibration information essential in comparing acoustic transducers and, in this case, indicates whether a device will perform well in thickness vibration. It can also be used to &#64257;nd the resonance frequency of the device, though this information is obtained more quickly via impedance analysis. Continuous &#64258;uid atomization, as an example application, requires careful &#64258;uid flow control, and we present such a method with high-speed imaging and droplet size distribution measurements via laser scattering.

Fabrication of piezoelectric thickness mode transducers via direct current sputtering of plate electrodes on lithium niobate is described. Additionally, reliable operation is achieved with a transducer holder and &#64258;uid supply system and characterization is demonstrated via impedance analysis, laser doppler vibrometry, high-speed imaging, and droplet size distribution using laser scattering.

Fabricação e caracterização de dispositivos piezoelétricos do modo de espessura para atomização e acoustofluidos

We present a technique to fabricate simple thickness mode piezoelectric devices using lithium niobate (LN). Such devices have been shown to atomize liquid ...

Induction of Microstreaming by Nonspherical Bubble Oscillations in an Acoustic Levitation System

When located near biological barriers, oscillating microbubbles may increase cell membrane permeability, allowing for drug and gene internalization. Experimental observations suggest that the temporary permeabilization of these barriers may be due to shear stress that is exerted on cell tissues by cavitation microstreaming. Cavitation microstreaming is the generation of vortex flows which arise around oscillating ultrasound microbubbles. To produce such liquid flows, bubble oscillations must deviate from purely spherical oscillations and include either a translational instability or shape modes. Experimental studies of bubble-induced flows and shear stress on nearby surfaces are often restricted in their scope due to the difficulty of capturing shape deformations of microbubbles in a stable and controllable manner. We describe the design of an acoustic levitation chamber for the study of symmetry-controlled nonspherical oscillations. Such control is performed by using a coalescence technique between two approaching bubbles in a sufficiently intense ultrasound field. The control of nonspherical oscillations opens the way to a controlled cavitation microstreaming of a free surface-oscillating microbubble. High-frame rate cameras allow investigating quasi-simultaneously the nonspherical bubble dynamics at the acoustic timescale and the liquid flow at a lower timescale. It is shown that a large variety of fluid patterns may be obtained and that they are correlated to the modal content of the bubble interface. We demonstrate that even the high-order shape modes can create large-distance fluid patterns if the interface dynamics contain several modes, highlighting the potential of nonspherical oscillations for targeted and localized drug delivery.

A fast and reliable technique is proposed to control the shape oscillations of a single, trapped acoustic bubble that is based on coalescence technique between two bubbles. The steady-state, symmetry-controlled bubble shape oscillations allow analysis of the fluid flow generated in the vicinity of the bubble interface.

Indução de Microstreaming por Oscilações de Bolhas Não Esféricas em um Sistema de Levitação Acústica

When located near biological barriers, oscillating microbubbles may increase cell membrane permeability, allowing for drug and gene internalization. ...

Assembly and Characterization of an External Driver for the Generation of Sub-Kilohertz Oscillatory Flow in Microchannels

Microfluidic technology has become a standard tool in chemical and biological laboratories for both analysis and synthesis. The injection of liquid samples, such as chemical reagents and cell cultures, is predominantly accomplished through steady flows that are typically driven by syringe pumps, gravity, or capillary forces. The use of complementary oscillatory flows is seldom considered in applications despite its numerous advantages as recently demonstrated in the literature. The significant technical barrier to the implementation of oscillatory flows in microchannels is likely responsible for the lack of its widespread adoption. Advanced commercial syringe pumps that can produce oscillatory flow, are often more expensive and only work for frequencies less than 1 Hz. Here, the assembly and operation of a low-cost, plug-and-play type speaker-based apparatus that generates oscillatory flow in microchannels is demonstrated. High-fidelity harmonic oscillatory flows with frequencies ranging from 10-1000 Hz can be achieved along with independent amplitude control. Amplitudes ranging from 10-600 &#181;m can be achieved throughout the entire range of operation, including amplitudes &#62; 1 mm at the resonant frequency, in a typical microchannel. Although the oscillation frequency is determined by the speaker, we illustrate that the oscillation amplitude is sensitive to fluid properties and channel geometry. Specifically, the oscillation amplitude decreases with increasing channel circuit length and liquid viscosity, and in contrast, the amplitude increases with increasing speaker tube thickness and length. Additionally, the apparatus requires no prior features to be designed on the microchannel and is easily detachable. It can be used simultaneously with a steady flow created by a syringe pump to generate pulsatile flows.

The protocol demonstrates a convenient method to produce harmonic oscillatory flow from 10-1000 Hz in microchannels. This is performed by interfacing a computer-controlled speaker diaphragm to the microchannel in a modular manner.

Montagem e Caracterização de um Driver Externo para a Geração de Fluxo Oscilatório Sub-Kilohertz em Microcanais

Microfluidic technology has become a standard tool in chemical and biological laboratories for both analysis and synthesis. The injection of liquid ...