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

Bucky gel actuator for morphing applications

Since the demonstration of Bucky Gel Actuator (BGA) in 2005, a great deal of effort has been exerted to develop novel applications for electro-active morphing materials. Three-layered bimorph nanocomposite has become an excellent candidate for morphing applications since it can be easily fabricated, operated in air, and driven with few volts. There has been limited published study on the mechanical properties of BGA. In this study, the effect of three parameters: layer thickness, carbon nanotube type, and weight fraction of components, on the mechanical properties was investigated. Samples were characterized via nano-indentation and DMA. It was found that BGA composed of 22 wt% single-walled carbon nanotubes and 45 wt% ionic liquid exhibited the highest hardness, adhesion, elastic and storage moduli. Most of BGA potential applications would require control over one BGA output: displacement. In this study, various sets of experiments were designed to investigate the effect of several parameters on the maximum lateral displacement of BGA. Two input parameters: voltage and frequency, and three material/design parameters: carbon nanotube type, thickness, and weight fraction of constituents, were selected. A new thickness ratio term was also introduced to study the role of individual layers on BGA displacement. In addition, an important factor in the design of BGA-based devices, lifetime, was investigated. Finally, possible degradation of BGA was studied by repeating displacement measurements after several weeks of being stored. Based on displacement studies, a new model was established utilizing nonlinear regression to predict BGA maximum displacement based on the effect of these parameters. This model was verified by comparing its predictions with other reported results in the literature. The model displayed a very good fit with various reported cases of BGA samples made with different types of CNT and ionic liquid. Microfluidics is a promising field of application for BGA. A brief literature review on the electroactive mechanisms used in microfluidics is presented. Preliminary force studies proved that BGA has the capability to be employed as a microvalve. A flow regulator utilizing a BGA microvalve was designed and fabricated. Flow rate measurements showed the capability of BGA-valve in manipulating the flow rate in different ranges

A review of hemorheology : measuring technologies and recent advances

Significant progress has been made over the years on the topic of hemorheology, not only in terms of the development of more accurate and sophisticated techniques, but also in terms of understanding the phenomena associated with blood components, their interactions and impact upon blood properties. The rheological properties of blood are strongly dependent on the interactions and mechanical properties of red blood cells, and a variation of these properties can bring further insight into the human health state and can be an important parameter in clinical diagnosis. In this article, we provide both a reference for hemorheological research and a resource regarding the fundamental concepts in hemorheology. This review is aimed at those starting in the field of hemodynamics, where blood rheology plays a significant role, but also at those in search of the most up-to-date findings (both qualitative and quantitative) in hemorheological measurements and novel techniques used in this context, including technical advances under more extreme conditions such as in large amplitude oscillatory shear flow or under extensional flow, which impose large deformations comparable to those found in the microcirculatory system and in diseased vessels. Given the impressive rate of increase in the available knowledge on blood flow, this review is also intended to identify areas where current knowledge is still incomplete, and which have the potential for new, exciting and useful research. We also discuss the most important parameters that can lead to an alteration of blood rheology, and which as a consequence can have a significant impact on the normal physiological behavior of blood

Analysis of conjugated heat transfer in micro-heat exchangers via integral transforms and non-intrusive optical techniques

The purpose of this paper is to employ the Generalized Integral Transform Technique in the analysis of conjugated heat transfer in micro-heat exchangers, by combining this hybrid numerical-analytical approach with a reformulation strategy into a single domain that envelopes all of the physical and geometric sub-regions in the original problem. The solution methodology advanced is carefully validated against experimental results from non-intrusive techniques, namely, infrared thermography measurements of the substrate external surface temperatures, and fluid temperature measurements obtained through micro Laser Induced Fluorescence. The methodology is applied in the hybrid numerical-analytical treatment of a multi-stream micro-heat exchanger application, involving a three-dimensional configuration with triangular cross-section micro-channels. Space variable coefficients and source terms with abrupt transitions among the various sub-regions interfaces are then defined and incorporated into this single domain representation for the governing convection-diffusion equations. The application here considered for analysis is a multi-stream micro-heat exchanger designed for waste heat recovery and built on a PMMA substrate to allow for flow visualization. The methodology here advanced is carefully validated against experimental results from non-intrusive techniques, namely, infrared thermography measurements of the substrate external surface temperatures and fluid temperature measurements obtained through Laser Induced Fluorescence. A very good agreement among the proposed hybrid methodology predictions, a finite elements solution from the COMSOL code, and the experimental findings has been achieved. The proposed methodology has been demonstrated to be quite flexible, robust, and accurate. The hybrid nature of the approach, providing analytical expressions in all but one independent variable, and requiring numerical treatment at most in one single independent variable, makes it particularly well suited for computationally intensive tasks such as in optimization, inverse problem analysis, and simulation under uncertainty.Indisponível

On the design and simulation of an airlift loop bioreactor with microbubble generation by fluidic oscillation

Microbubble generation by a novel fluidic oscillator driven approach is analyzed, with a view to identifying the key design elements and their differences from standard approaches to airlift loop bioreactor design. The microbubble generation mechanism has been shown to achieve high mass transfer rates by the decrease of the bubble diameter, by hydrodynamic stabilization that avoids coalescence increasing the bubble diameter, and by longer residence times offsetting slower convection. The fluidic oscillator approach also decreases the friction losses in pipe networks and in nozzles/diffusers due to boundary layer disruption, so there is actually an energetic consumption savings in using this approach over steady flow. These dual advantages make the microbubble generation approach a promising component of a novel airlift loop bioreactor whose design is presented here. The equipment, control system for flow and temperature, and the optimization of the nozzle bank for the gas distribution system are presented. (C) 2009 The Institution of Chemical Engineers. Published by Elsevier B.V All rights reserved

A Quantitative study of the dynamic response of soft tubing for pressure-driven flow in a microfluidics context

Microfluidics typically uses either a syringe pump that regulates the flow rate in microchannels or a pressure pump that controls the inlet pressures to drive the flow. In the context of pressure-driven flow, a reservoir holder containing liquid samples is normally used to interface the pressure pump with the microfluidic chip via soft tubing. The tubing connecting the pump and holder transports the pressurized air while the tubing connecting the holder and chip transports the liquid samples. The pressure output from the pump is usually assumed to be stable and the same as that applied to the liquid in the chip; however, in practice this assumption is often incorrect and may negatively impact chip performance. This assumption is critically challenged when applied to microfluidic chips involving dynamic control of fluids since the pressures are constantly varied (at > 10 Hz). This study presents a method for investigating, quantifying and modelling the pump stability and the dynamics of the air tubing using two pressure sensors. The relationship between the pressure output from the pump and the reservoir holder pressure is generalized as a first-order linear system. This relationship allows the software that controls the pressure pump to output the required pressure to the reservoir holder and thus to the microfluidic chip. These results should significantly improve the performance of microfluidic chips using active fluid control, and may also benefit passive fluid control applications. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature