Micro Electromechanical Systems (MEMS) Based Microfluidic Devices for Biomedical Applications

Micro Electromechanical Systems (MEMS) based microfluidic devices have gained popularity in biomedicine field over the last few years. In this paper, a comprehensive overview of microfluidic devices such as micropumps and microneedles has been presented for biomedical applications. The aim of this paper is to present the major features and issues related to micropumps and microneedles, e.g., working principles, actuation methods, fabrication techniques, construction, performance parameters, failure analysis, testing, safety issues, applications, commercialization issues and future prospects. Based on the actuation mechanisms, the micropumps are classified into two main types, i.e., mechanical and non-mechanical micropumps. Microneedles can be categorized according to their structure, fabrication process, material, overall shape, tip shape, size, array density and application. The presented literature review on micropumps and microneedles will provide comprehensive information for researchers working on design and development of microfluidic devices for biomedical applications

Accelerating micro-scale PCR (polymerase chain reactor) for modular lab-on-a-chip system

The polymerase chain reaction (PCR) is a powerful technique used to exponentially amplify specific DNA sequences of interest through repetitive temperature cycling. The temperatures used in PCR are typically 90°C - 94°C for denaturation, 50°C - 70°C for renaturation, and 70°C - 75°C for extension. The double-stranded helix of nucleotides, carrying the genetic information, is separated during denaturation, reacts with chemical primers during renaturation, and becomes a complete, replica, double-stranded DNA helix structure during extension. The primary drawback of current commercial benchtop PCR machine is its cycle time due to its large thermal capacitance, and micro PCR is under developing using microfabrication technology; smaller and faster in different types of PCR are the primary goal in this study. Continuous flow PCR is one of the primary types of micro PCR and it relies on a continuous flow through three temperature zones to achieve rapid thermal cyclings. To understand its biological performance, an experiment was carried out to study its limiting dynamic performance at different flow velocities from 1 mm/s to 15 mm/s and a thermal and fluidic numerical simulation was realized to give ideas of thermal performance and explain the experimental results. A 5.2 s/cycle for 500 bp and a 9.7 s/cycle for 997 bp were accomplished in this experiment. Thermal management was critical in PCR since the biological performance was primarily dependent on precise temperature control. Liquid crystal is a common tool in investigating thermal performance using its optical properties, which will have different color based on its local temperature. A liquid crystal was realized on renaturation zone of CFPCR chip and post image process was used to help interpret the experimental results. A non-uniform temperature distribution was observed due to the low thermal conductivity of substrate, polycarbonate, and non-uniform temperature supply. Another goal in this research was to develop another type of PCR using different driving mechanism to search other possibilities and compare results with CFPCR. An electrokineitc shuttle PCR was developed and its basic idea was using electrokinetic force to drive DNA fragment through three static temperature zones in a single microchannel. The flow velocities realized in this experiment were 1mm/s to 3mm/s and lower amplification yields were observed. The reasons were unintentional flows such as siphoning flow and hydrodynamic flow, which made the DNA fragment move in a chaotic temperature sequences and result in a lower yield

Towards rapid 3D direct manufacture of biomechanical microstructures

The field of stereolithography has developed rapidly over the last 20 years, and commercially available systems currently have sufficient resolution for use in microengineering applications. However, they have not as yet been fully exploited in this field. This thesis investigates the possible microengineering applications of microstereolithography systems, specifically in the areas of active microfluidic devices and microneedles. The fields of micropumps and microvalves, stereolithography and microneedles are reviewed, and a variety of test builds were fabricated using the EnvisionTEC Perfactory Mini Multi-Lens stereolithography system in order to define its capabilities. A number of microneedle geometries were considered. This number was narrowed down using finite element modelling, before another simulation was used to optimise these structures. 9 × 9 arrays of 400 μm tall, 300 μm base diameter microneedles were subjected to mechanical testing. Per needle failure forces of 0.263 and 0.243 N were recorded for the selected geometries, stepped cone and inverted trumpet. The 90 μm needle tips were subjected to between 30 and 32 MPa of pressure at their failure point - more than 10 times the required pressure to puncture average human skin. A range of monolithic micropumps were produced with integrated 4 mm diameter single-layer 70 μm-thick membranes used as the basis for a reciprocating displacement operating principle. The membranes were tested using an oscillating pneumatic actuation, and were found reliable (>1,000,000 cycles) up to 2.0 PSIG. Pneumatic single-membrane nozzle/diffuser rectified devices produced flow rates of up to 1,000 μl/min with backpressures of up to 375 Pa. Another device rectified using active membrane valves was found to self-prime, and produced backpressures of up to 4.9 kPa. These devices and structures show great promise for inclusion in complex, fully integrated and active microfluidic systems fabricated using microstereolithography alone, with implications for both cost of manufacture and lead time

Development of a PDMS Based Micro Total Analysis System for Rapid Biomolecule Detection

The emerging field of micro total analysis system powered by microfluidics is expected to revolutionize miniaturization and automation for point-of-care-testing systems which require quick, efficient and reproducible results. In the present study, a PDMS based micro total analysis system has been developed for rapid, multi-purpose, impedance based detection of biomolecules. The major components of the micro total analysis system include a micropump, micromixer, magnetic separator and interdigitated electrodes for impedance detection. Three designs of pneumatically actuated PDMS based micropumps were fabricated and tested. Based on the performance test results, one of the micropumps was selected for integration. The experimental results of the micropump performance were confirmed by a 2D COMSOL simulation combined with an equivalent circuit analysis of the micropump. Three designs of pneumatically actuated PDMS based active micromixers were fabricated and tested. The micromixer testing involved determination of mixing efficiency based on the streptavidin-biotin conjugation reaction between biotin comjugated fluorescent microbeads and streptavidin conjugated paramagnetic microbeads, followed by fluorescence measurements. Based on the performance test results, one of the micromixers was selected for integration. The selected micropump and micromixer were integrated into a single microfluidic system. The testing of the magnetic separation scheme involved comparison of three permanent magnets and three electromagnets of different sizes and magnetic strengths, for capturing magnetic microbeads at various flow rates. Based on the test results, one of the permanent magnets was selected. The interdigitated electrodes were fabricated on a glass substrate with gold as the electrode material. The selected micropumps, micromixer and interdigitated electrodes were integrated to achieve a fully integrated microfluidic system. The fully integrated microfluidic system was first applied towards biotin conjugated fluorescent microbeads detection based on streptavidin-biotin conjugation reaction which is followed by impedance spectrum measurements. The lower detection limit for biotin conjugated fluorescent microbeads was experimentally determined to be 1.9 x 106 microbeads. The fully integrated microfluidic system was then applied towards immuno microbead based insulin detection. The lower detection limit for insulin was determined to be 10-5M. The total detection time was 20 min. An equivalent circuit analysis was performed to explain the impedance spectrum results

System optimization for realizing a miniaturized gas chromatograph sensor for rapid chemical analysis

Rapid and comprehensive on-site analysis of chemicals in applications ranging from industrial process control to homeland security is of significant importance to improve the environment and save human life. The need for sensors that are fast, reliable, and portable has never been greater. For the challenging task of on-site instrumentation, where power sources can be limited, shrinking the size of the device is the most effective way to conserve power. Although gas chromatography is a mature technique well suited for these applications, current instrumentation has deficiencies that limit its usage. Speed of analysis and non portability are severe hindrances to using the bench top and portable instruments for on-site applications. This focus of this research is to provide a transition from a portable gas chromatograph (GC) instrument to a handheld GC sensor. The significant issues for realizing a handheld GC sensor were addressed. One important design criterion was that the sensors have the same analytical capability as a commercial GC instrument. Of the many components of a GC, the separation column primarily defines the resolution and the analysis time. Thorough theoretical analysis led to the conclusion that high aspect ratio, rectangular cross-section columns have a distinct advantage over capillary columns. A column including an on-chip sample loop and a makeup gas manifold were designed. Previously reported attempts to fabricate rectangular columns have focused on low aspect ratio or square cross-section columns. Contrasting all prior efforts, significant strides in process development were made to realize nickel GC columns using the LiGA technology with aspect ratios as high as 20. Through process control, a device yield of over 90% was achieved. Tests on these columns yielded more than 20,000 plates for unretained species. Four hydrocarbons were separated in less than 2 s at 100 °C on a 50 μm wide by 600 μm tall by 0.5 m long coated LiGA column. For the first time reported, 2-D GC was implemented using MEMS columns

MICROFLUIDICS INTERFACING TO MASS SPECTROMETRY

Polymer-based microfluidic systems have received considerable attention for high throughput chemical analysis. Recently, the ongoing development of microfluidics interfacing to high-accuracy mass spectrometry to identify large molecules had an important impact on biochemistry. A primary goal of this dissertation is the development of a microfluidic apparatus for performing microscale gel electrophoresis, coupled with integrated electrospray tips for either direct interfacing to mass spectrometry through ESI-MS, or coupling to MALDI-MS through the deposition of separated analyte onto a MALDI target for offline analysis. In this dissertation, microfabrication techniques for polymer-based microchip are developed. A novel electrospray interface is demonstrated with good performance. The optimization of multi-channel electrospray tips for multiplexed analysis from a single microfluidic chip was demonstrated. Gas-phased electrophoretic protein/peptide concentration on a pre-structured MALDI target was further demonstrated via theoretical and experimental analysis. The results for developing μGE-ES using linear polymer gel validate the underlined principles and specify challenges involved in coupling μGE to MS. Finally, cross-linked polyacrylamide gel was explored and characterized using in-situ photo- polymerization method in microchannels

A modular approach to high throughput microsystems

A modular high throughput microsystem was developed using microfabrication technology and nucleic acid analysis. The purpose of developing this microsystem is to identify acute infectious disease and prevent contagious outbreak in a matter of time. This microsystem included three major components, a reagent distribution device, a 96 CFPCR array, and a multi-zone thermal system, to efficiently amplify specific DNA fragments to determine the disease status or precisely pinpoint a disease from multiple patients. Polymerase chain reaction (PCR) is the key component in the nucleic acid analysis for disease because it can be used to amplify interested DNA fragments by repeatedly thermal cycles. Temperature distribution is critical to the PCR reaction, and thermal management was studied; the approaches which reached good biochemical results were applied to the design of a 96 CFPCR array and a multi-zone thermal system. Protein adsorption is another issue when PCR is realized in a micro device because of the increased surface-to-volume ratio, which might terminate the biochemical reaction. A series of experiments were carried out to understand the protein adsorption in the microchannels with different geometries. A disposable 96 CFPCR was designed and fabricated on a polycarbonate substrate by double-sided hot embossing and its requirement of multiple temperature zones was fulfilled by building a multi-zone thermal system. Their thermal performance was characterized by numerical simulations and validated by infrared camera experiments. To evenly distribute the analyte with reducing pipetting steps, a reagent distribution device was designed to assemble with the 96 CFPCR array by using passive alignment structures to perform a systematic performance. The passive alignment structures including three pairs of v-groove and hemisphere-tipped post was studied and modified to ensure a smooth passage for mass, momentum, and energy of chemical analyte. Biochemical experiments demonstrated parallel amplifications of both identical and different DNA fragments from the multiple CFPCRs on the multi-zone thermal system, which implied the potential to detect acute infectious disease with acceleration, accuracy, specificity, and high throughput

Design of a microfabricated device for Ligase Detection Reaction (LDR)

The Ligase Detection Reaction (LDR) is a mutation detection technique used to identify point mutations in deoxyribonucleic acid (DNA). Developed by Francis Barany and associates at Cornell University it is used to find specific low abundant point mutations that may lead to colorectal cancer in the early stages of disease development. The research objective was to design and manufacture a microscale Ligase Detection Reaction (LDR) device in polycarbonate. The LDR module will be incorporated with other microdevices such as: Continuous Flow Polymerase Chain Reaction (CFRCR) and Capillary Electrophoresis (CE) in modular lab-on-a-chip technology. In making the microdevice, the duration of original reaction had to be scaled down from the current 2½ hours for 20 cycles for the macroscale reaction. It was found that an excess of primers in relation to PCR product was needed for efficient ligation. By changing the concentrations, volumes and time for the process the current time is down to 40 minutes for 20 cycles with indications that further time reductions are possible on the microscale. There are two mixing stages involved in the reaction. Micromixers were simulated in Fluent (v5.4, Lebanon, NH) and several test geometries selected for fabrication. Passive diffusion mixing was used based on obtaining high aspect ratios, 7 to 20. The mixers were made by SU-8 lithography, LIGA, laser ablation, and micromilling to characterize each fabrication method. It was found that LIGA was best for making the micromixers, but was the longest process. The micromixers are fabricated and tested using chemi-luminescence technique. For a successful reaction, temperatures of 0°C, 95°C and 65°C were needed. A stationary chamber was used for thermal cycling in which the sample sits while the temperature is cycled. Finite element analysis showed uniform temperatures in the rectangular 1.5μl chambers and that air slits can effectively separate the thermal cycle zone from the 0°C cooling zone and also isolate the mixing region. A test device was laid out and micromilled with the temperature zones maintained and fluid flow controlled. A commercial thin film heater and a thermoelectric module were used with PID controls to obtain the required process temperatures. Heating from 65°C to 95°C took 10 seconds, while cooling from 95°C to 65°C also took 10 seconds. The residence times at the required temperatures can be adapted to changes in the LDR