Air-Deflected Microfluidic Chip for Characterization of Fluid-Structure Interactions

Millions of people suffer from dentinal pain each year caused by a pressure change and fluid shear in the dentin tubule and nerve pulp system. Dentin is made up of mostly hydroxyapatite, a hard and opaque material. In-situ characterization is extremely challenging because of the tubules that run through are high-aspect ratio micropores with a feature size of 1-2 µm. Current studies have proven that various methods can be deployed to fabricate microscale geometry using PDMS. The most used methods are three-dimensional stereolithography, fused deposited material (FDM), 3D printed sacrificial mold, FDM 3D printed molds and soft lithography molding from the existing literature. This study simplifies dentin tubules by enlarging and creating a planar case for analysis. The chip geometry investigated consist of three 2 mm by 2 mm by 50 mm parallel channels separated by thin walls of 500 µm, 750 µm, and 1000 µm. The central channel is fitted with a glass capillary and holds liquid. The two outer channels are air pressure channels. The fabrication process is highlighted in this study and utilizes 3D FDM and 3D stereolithography (SLA) printing, negative molding of polydimethylsiloxane (PDMS), spin coating PDMS to create a 1 mm layer, and PDMS-PDMS bonding for chip completion. Pressure is applied to the completed chips in known increments and the dynamic response of the chip is recorded through image capture and processing. The experiments show a sequential, three process response. A strong linear correlation was found between steady state liquid surface height and applied pressure. The theoretical model can fit well the second and third processes of the response by ascertaining the initial height of the second process. The oversimplification and theoretical simulation results lay the groundwork for microfluidic devices that more closely model dentin tube structure, such as the polyvinyl alcohol (PVA) fibers positioned in an array to be tested in a similar fashion to the device in this study

Properties characterization of PDMS/Beeswax composite

Mestrado de dupla diplomação com a UTFPR - Universidade Tecnológica Federal do ParanáPolydimethylsiloxane (PDMS) is one of the elastomers belonging to the polymers that has received the most attention, as it is a material with good thermal stability, biocompatibility, flexibility, low cost and hyperplastic characteristics. As well as PDMS, beeswax, too, has attracted the attention of researchers, as it is a biodegradable material, thermally stable and of natural origin. These materials can be used in areas such as microfluidic systems, medical devices, electronic components, among others. PDMS mixed with beeswax is able to improve hydrophobic properties, abrasion and corrosion resistance, thermal stability and high temperature transparency. However, the manufacturing process used to mix PDMS and waxes requires some steps, such as heating, mixing and degassing, however, conventional methods do not follow a standardized process, resulting in products with low repeatability. To overcome this limitation, a vacuum chamber was developed and built with the objective of optimizing the manufacturing process. Another important factor is the use of beeswax, as it is a natural product, the composition is different depending on the climate and region. For this reason, in this study, the chemical characterization of beeswax was performed. Subsequently, experimental tests were carried out with the composite of PDMS and beeswax. Samples were manufactured using the multifunctional vacuum chamber developed in this dissertation. The samples were submitted to tensile, hardness, DMA, TGA, spectrometry and wettability tests in order to analyze the mechanical, optical and wettability properties. The manufacture of the multifunctional vacuum chamber allowed the production of samples with more uniform properties and made the process more efficient. In the DMA test, the composite showed thermal stability up to 200°C, together with high transparency at 80°C, when compared to pure PDMS. In the wettability test, the composite proved to increase the contact angle close to 150°C, presenting a super-hydrophobic surface.O polidimetilsiloxano (PDMS) é um dos elastómeros pertencente aos polímeros que mais tem recebido atenção, por ser um material com boa estabilidade térmica, biocompatibilidade, flexibilidade, baixo custo e características hiperplásticas. Assim como o PDMS, a cera de abelha, também, tem atraído a atenção dos investigadores, por se tratar de um material biodegradável, termicamente estável e de origem natural. Esses materiais podem ser utilizados em áreas como sistemas microfluídicos, dispositivos médicos, componentes eletrónicos, entre outros. O PDMS misturado com cera de abelha, mostra-se capaz de melhorar as propriedades hidrofóbicas, resistência à abrasão e corrosão, estabilidade térmica e transparência a alta temperatura. Porém, o processo de fabricação utilizado para misturar PDMS e ceras requer algumas etapas, como aquecer, misturar e desgaseificar, contudo, os métodos convencionais não seguem um processo normalizado, originando produtos com baixa repetibilidade. Para contornar esta limitação, desenvolveu-se e construiu-se uma câmara de vácuo com o objetivo de otimizar o processo de fabricação. Outro fator importante é a utilização da cera de abelha por ser um produto natural, a composição é diferente dependendo do clima e da região. Por esse motivo, neste estudo foi realizado a caracterização química da cera de abelha. Posteriormente, foram realizados testes experimentais com o compósito de PDMS e cera de abelha. O fabrico das amostras foi efetuado utilizando a câmara de vácuo multifuncional desenvolvida nesta dissertação. As amostras foram submetidas a ensaios de tração, dureza, DMA, TGA, espectrometria e de molhabilidade com o intuito de analisar as propriedades mecânicas, óticas e de molhabilidade. A fabricação da câmara de vácuo multifuncional permitiu a produção das amostras com propriedades mais uniformes e tornou o processo mais eficiente. No ensaio de DMA, o compósito mostrou uma estabilidade térmica até os 200°C, juntamente com a alta transparência a 80°C, quando comparado ao PDMS puro. No ensaio de molhabilidade, o compósito provou aumentar o ângulo de contacto perto dos 150°C, apresentado uma superfície super-hidrofóbica

Fabrication and Characterization of Magnetic Nanoparticle Composite Membranes

To effectively and accurately deliver drugs within the human body, both new designs and components for implantable micropumps are being studied. Designs must ensure high biocompatibility, drug compatibility, accuracy and small power consumption. The focus of this thesis was to fabricate a prototype magnetic nanoparticle membrane for eventual incorporation into a biomedical pump and then determine the relationship between this membrane deflection and applied pneumatic or magnetic force. The magnetic nanoparticle polymer composite (MNPC) membranes in this study were composed of crosslinked polydimethylsiloxane (PDMS) and iron oxide nanoparticles (IONPs). An optimal iron oxide fabrication route was identified and particle size in each batch was approximately 24.6 nm. Once these nanoparticles were incorporated into a membrane (5 wt. %), the nanoparticle formed agglomerates with an average diameter of 2.26 ±1.23 µm. Comparisons between the 0 and 5 wt. % loading of particles into the membranes indicated that the elastic modulus of the composite decreased with increasing particle concentration. The pressure- central deflection of the membranes could not be predicated by prior models and variation between magnetic and pneumatic pressure-deflection curves was quantified. Attempts to fabricate membranes with above 5 wt. % nanoparticles were not successful (no gelation). Fourier Transform Infrared (FTIR) spectroscopy results suggest that excess oleic acid on the nanoparticles prior to mixing might have prevented crosslinking

Microfluidic system for cell separation and deformation assessment by using passive methods

Tese de doutoramento em Biomedical EngineeringOs sistemas microfluídicos têm sido usados com sucesso em muitas aplicações biomédicas. As principais vantagens destes sistemas consistem na utilização de volumes de amostras reduzidos e com tempos de ensaios curtos. Além disso, os sistemas microfluídicos possibilitam a execução de várias tarefas em paralelo numa única plataforma microfluídica, como por exemplo a separação e medição da deformabilidade de células/partículas. Em dispositivos microfluídicos, existem dois métodos principais para separar células: métodos passivos, baseados em microestruturas e escoamentos laminares, e métodos ativos, baseados em campos de forças externos. Muitos estudos têm sido realizados com métodos passivos, pois estes não necessitam de forças externas. Nesta tese serão apresentadas diferentes geometrias passivas para um dispositivo microfluídico, constituído por vários filtros de fluxo cruzado e multiníveis com o intuito de separar células/partículas em função do seu tamanho. Outra característica importante é a implementação de microcanais hiperbólicos a montante das saídas por forma a criar um escoamento extensional homogéneo e consequentemente medir a deformabilidade das células de forma controlada. Após a separação e avaliação da deformação, a quantidade de glóbulos vermelhos será quantificada por um método de espectrofotometria. Os resultados indicam que várias geometrias mostraram uma boa taxa de separação, confirmada pelas medidas de camada livre de células e pela espectrofotometria. Verificou-se também que os sistemas microfluídicos testados são capazes de separar amostras patológicas de sangue, demostrando assim o seu potencial em realizar simultaneamente a separação e deformação de células patológicas, como por exemplo células provenientes de pacientes diagnosticados com malária e/ou diabetes.Microfluidic systems have been successfully used at many biomedical applications. Their great advantages allow working with minimal sample volumes and with short assays times. Additionally, microfluidic systems allow parallel operations in a single microfluidic platform such as separation and measurement of single cell/particles deformability. In microfluidic devices, there are two main methods for cells separation: passive methods, based on microstructures and laminar flow, and active methods, based on external force fields. Many studies have been made using passive methods because they do not require external forces. In this thesis it will be presented different geometrical passive approaches for a microfluidic device, that will have crossflow filters and multilevel steps that will separate the cells/particles by their size. Another important feature is the implementation of hyperbolic microchannels upstream the outlets in order to create a homogeneous extensional flow and consequently to measure the cells deformability in a controlled way. After the separation and deformation assessment, the amount of RBCs will be quantified by a spectrophotometry method. The results indicate that several geometries have shown a good separation rate, confirmed by the cell free layer and spectrophotometry measurements. It was also verified that the tested microfluidic systems are able to separate pathological blood samples, showing its potential to perform simultaneously separation and deformation assessments of blood diseases, such as malaria and diabetes.I want to acknowledge the financial support provided by scholarship SFRH/BD/99696/2014 from FCT (Science and Technology Foundation), COMPETE 2020, Portugal 2020 and POCH, that allow the successful development of this PhD project

Micro/nano devices for blood analysis

[Excerpt] The development of microdevices for blood analysis is an interdisciplinary subject that demandsan integration of several research fields such as biotechnology, medicine, chemistry, informatics, optics,electronics, mechanics, and micro/nanotechnologies.Over the last few decades, there has been a notably fast development in the miniaturization ofmechanical microdevices, later known as microelectromechanical systems (MEMS), which combineelectrical and mechanical components at a microscale level. The integration of microflow and opticalcomponents in MEMS microdevices, as well as the development of micropumps and microvalves,have promoted the interest of several research fields dealing with fluid flow and transport phenomenahappening at microscale devices. [...

A Customer Programmable Microfluidic System

Microfluidics is both a science and a technology offering great and perhaps even revolutionary capabilities to impact the society in the future. However, due to the scaling effects there are unknown phenomena and technology barriers about fluidics in microchannel, material properties in microscale and interactions with fluids are still missing. A systematic investigation has been performed aiming to develop A Customer Programmable Microfluidic System . This innovative Polydimethylsiloxane (PDMS)-based microfluidic system provides a bio-compatible platform for bio-analysis systems such as Lab-on-a-chip, micro-total-analysis system and biosensors as well as the applications such as micromirrors. The system consists of an array of microfluidic devices and each device containing a multilayer microvalve. The microvalve uses a thermal pneumatic actuation method to switch and/or control the fluid flow in the integrated microchannels. It provides a means to isolate samples of interest and channel them from one location of the system to another based on needs of realizing the customers\u27 desired functions. Along with the fluid flow control properties, the system was developed and tested as an array of micromirrors. An aluminum layer is embedded into the PDMS membrane. The metal was patterned as a network to increase the reflectivity of the membrane, which inherits the deformation of the membrane as a mirror. The deformable mirror is a key element in the adaptive optics. The proposed system utilizes the extraordinary flexibility of PDMS and the addressable control to manipulate the phase of a propagating optical wave front, which in turn can increase the performance of the adaptive optics. Polydimethylsiloxane (PDMS) has been widely used in microfabrication for microfluidic systems. However, few attentions were paid in the past to mechanical properties of PDMS. Importantly there is no report on influences of microfabrication processes which normally involve chemical reactors and biologically reaction processes. A comprehensive study was made in this work to study fundamental issues such as scaling law effects on PDMS properties, chemical emersion and temperature effects on mechanical properties of PDMS, PDMS compositions and resultant properties, as well as bonding strength, etc. Results achieved from this work will provide foundation of future developments of microfluidics utilizing PDMS

Effects of wall compliance on pulsatile flow attenuation in microchannels.

The attenuation of pulsatile flow through highly compliant microchannels has been investigated. The expansion of a compliant microchannel subjected to pulsatile flow is able to store fluid temporarily and thereby reduce the peak-to-peak magnitude of flow fluctuation. In a highly compliant microchannel, the microchannel expansion reduces its hydraulic resistance and its associated pressure drop. For a similar inlet pressure condition, the pressure drop along the length of a more compliant microchannel is lower than a rigid microchannel. Therefore, greater net pressure is available to deform the microchannel wall. So the hypothesis of this study is the coupled relationship between higher pressure and greater wall compliance which will achieve more effective flow stabilization, because both contribute synergistically to greater volumetric expansion. To investigate this hypothesis, a soft elastomer, polydimethylsiloxane was used to compare plain microchannels and microchannels with a series of laterally deformable membranes, which vary in terms of wall compliance. In a 6 Hz pulsatile flow experiment, a membrane microchannel is able to achieve a better pulsatile flow attenuation ratio of 16 when compared to a plain microchannel pulsatile flow attenuation ratio of 10. The hypothesis was also investigated with a 2-D fluid-structure interaction numerical model and the prediction is in agreement with experimental results. The results indicate that higher compliance microchannels have better pulsatile flow attenuation abilities

Convective intracellular macromolecule delivery for cell engineering applications

Efficient intracellular delivery of target macromolecules remains a major obstacle in cell engineering, cell labeling, and other biomedical applications. Current standard methods of intracellular delivery, such as viral transduction and electroporation, do not meet the growing needs in the cell engineering field for cost-effective, scalable, and efficient delivery that maintains cell viability. This thesis work has discovered the cell biophysical phenomenon of convective intracellular macromolecule delivery using mechanically-induced, transient cell volume exchange. Ultrafast microfluidic cell compressions (2 MDa) and particles (>30 nm), while maintaining high cell viability (>95%). Successful experiments in CRISPR-Cas9 gene editing and intracellular gene expression analysis demonstrate potential to overcome the most prohibitive challenges in intracellular delivery for cell engineering.Ph.D

NANOCHANNEL-ASSISTED ACTIVE CONTROL OF MASS TRANSPORT IN POLYDIMETHYLSILOXANE-BASED MICRO- /NANOFLUIDIC SYSTEMS

Department of Mechanical EngineeringNanofluidic devices have been extensively studied due to a fascinating nature of their small size which facilitates biosensing, bio-chemical separations, seawater desalination, nanofluidic transistors, protein, and preconcentration for a Lab-on-a-Chip (LOC). Such applications could be achieved by a control of electrokinetic transport in a nanochannel produced by sophisticated nanofabrication technique. However, it has been a challenge from a fabrication to the control of electrokinetic phenomena in nanochannel because of the cost, time, incompatibility, and addressability issues. Therefore, an innovative method is required to achieve simple fabrication and versatile operations of micro/nanofluidic device with limited resources. This dissertation proposes a new method for nanochannel-assisted active manipulation of mass transport by switching physicochemical environment. In the early chapters of this dissertation, unconventional fabrication methods for hybrid-scale micro-/nanofluidic devices is described by using both crack-photolithography and polydimethylsiloxane (PDMS) based soft lithography. The late chapters introduce the mechanism of the mass transport in micro/nanofluidic device using solutes gradient and humidity for manipulation of colloidal motion and molecule valves, respectively. These studies can be introduced as follows. First, crack-photolithography is employed to facilitate large-scale reproducible channel fabrication through a single molding process and thus enable the fabrication of hybrid-scale micro-/nanofluidic devices at a wafer level with advantages seen in the throughput, cost-effectiveness, reliability, and reproducibility. In addition, modified soft lithography process is developed to fabricate stable nanochannel which is free from the collapse and the crumbling. Second, crack-assisted nanochannel is introduced to manipulate physicochemical environment of neighboring microchamber. Diffusion-controlled ion transport produces solutes gradient inducing spontaneous electric field which affects the motion of colloidal particles. Since the single nanochannel allows the production of concentration gradient in a long-term and stable manner, least source is required to maintain the spontaneous electric field without any external power source, which is appropriate for a portable and self-containable LOC. As a practical application, integrated micro/nanofluidic device facilitates concentration, on-demand extraction, and separation of the colloidal particles. Third, gas permeable PDMS nanochannel with high hydraulic resistance is employed to develop humidity-based gating nanochannel. The rate of mass transport can be manipulated by humidity due to the evaporation of water and the adsorption of solutes to the wall of channel. To demonstrate functionality of humidity for liquid gating or capacitor of molecules, the effect of humidity on mass transport was investigated. This new concept of manipulation of nanofluidic transport made it possible to successfully perform individual mass transport control in a nanochannel array, which is difficult with conventional technique using electricity. It further facilitated on-demand addressable bio/chemical assay using humidity-based molecule valves and pumps. The role of nanochannel as a passage for mass transfer is essential to allow stable and precise control of transport of ions and molecules in the microchannel. It provides wide range of applications using a diffusion-based control of microfluidic environment to induce not only solute gradient for production of electric field but also liquid gating for a valve at molecular level. Thus, achievements of this dissertation contribute to raise the insight about nanochannel-assisted system for simple and precise control of mass transport in hybrid-scale micro-/nanofluidic devices, which is facilitated by the help of the cracking-assisted micro-/nanofabrication technologies.clos

Extensional flow-based microfluidic device: deformability assessment of red blood cells in contact with tumor cells

Red blood cell (RBC) deformability has become one of the important factors to assess blood and cardiovascular diseases. The interest on blood studies have promoted a development of various microfluidic devices that treat and analyse blood cells. Recent years, besides the RBC deformability assessment, these devices are often applied to cancer cell detection and isolation from the whole blood. The devices for cancer cell isolation rely mainly on size and deformability of the cells. However, the examination of deformability of the RBCs mixed with cancer cells is lacking. This study aims at determining the deformation index (DI) of the RBCs in contact with cancer cells using a hyperbolic microchannel which generates a strong extensional flow. The DIs of human healthy RBCs and human RBCs in contact with a tumor cell line (HCT-15, colon carcinoma) were compared by analyzing the flowing RBCs images captured by a high speed camera. The results reveal that the RBCs that were in contact with HCT-15 cells have lower deformability than the normal RBCs.The authors acknowledge the financial support provided by: Student Mobility Placements with the program Lifelong Learning (Erasmus Program), 2007 Global COE Program “Global Nano-Biomedical Engineering Education and Research Network”, Japan. Grant-in-Aid for Science and Technology (PTDC/SAU-BEB/105650/2008, PTDC/EME-MFE/099109/2008 and PTDC/SAU-ENB/116929/2010) from the Science and Technology Foundation (FCT) and COMPETE, Portugal. The authors are also very grateful to Professor Mónica S.N. Oliveira (Strathclyde University), Professor Geyong M. Kim (University of Navarra) and Professor Sergio Arana (University of Navarra) for their discussion and suggestions to this research work