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Whitesides, G.M. The origins and the future of microfluidics. Nature 442, 368-373
Abstract
The manipulation of fluids in channels with dimensions of tens of micrometres--microfluidics--has emerged as a distinct new field. Microfluidics has the potential to influence subject areas from chemical synthesis and biological analysis to optics and information technology. But the field is still at an early stage of development. Even as the basic science and technological demonstrations develop, other problems must be addressed: choosing and focusing on initial applications, and developing strategies to complete the cycle of development, including commercialization. The solutions to these problems will require imagination and ingenuity.
... Microfluidics devices are commonly called Lab-On-a-Chip (LoC), where micro channels can incorporate multiple unit operations [6][7][8], that to some extent, replace benchtop laboratory equipment, performing different tasks such as mixing [9], separation, heating and detection. Benefits of microfluidics technology are based on small volume of liquid samples [10], that enables faster chemical reactions process [11,12] due to acceleration of the mass and heat transfer in the microscale [13,14] and integrated micro actuators [15][16][17]. In the last decades, a microfluidics droplet-based approach has been fast evolved [14,[18][19][20][21], largely employed for biomedical applications [16,22,23], especially leading to studies with cells and antibody development [20,24,25], where microfluidics devices have enabled a creation of new tools and protocols [16,[26][27][28], for example, for single-cell encapsulation, co-encapsulation, cellsorting, droplet recovery/extraction (de-oiling) and pico-injection [14,22,24]. ...
... Optical detection [9], impedance detection [10], and capacitive detection [11] emerge as the predominant sensing techniques utilized for droplet size control and detection. However, it is important to mention that optical-based droplet detection often demands a considerably intricate setup external to the device, involving the introduction of laser light and the subsequent detection of scattered light using optical elements positioned within a microfluidic channel or chamber, as evidenced by studies [12,13]. Optics-based interrogation dependence of external equipment does not allow the fabrication of portable point-of-care (POC) [18,34]. ...
Droplet-based microfluidics has revolutionized numerous fields such as biomedical research, pharmaceuticals, drug discovery, food engineering, flow chemistry, and cosmetics. This paper presents a comprehensive study focusing on the detection and characterization of droplets with volumes in the nanoliter range. Leveraging the precise control of minute liquid volumes, we introduced a novel spectroscopic On-Chip microsensor equipped with integrated microfluidic channels for droplet generation, characterization, and sensing, simultaneously. The microsensor, designed with Interdigitated-Ring-Shaped Electrodes (IRSE) and seamlessly integrated with microfluidic channels, offers enhanced capacitance and impedance signal amplitudes, reproducibility, and reliability in droplet analysis. We were able to make analyses of droplets length in the range 1.0-6.0 mm, velocity 0.66-2.51 mm/s, droplet volume 1.07nL-113.46nL. Experimental results demonstrated that the microsensor's has a great performance in terms of droplet size, velocity, and length, with a significant signal amplitude of capacitance and impedance, and real-time detection capabilities, thereby highlighting its potential for facilitating microcapsule reactions and enabling on-site real-time detection for chemical and biosensor analyses on-chip.
... Microfluidics devices are commonly called lab-on-a-chip (LoC), where microchannels can incorporate multiple unit operations [6][7][8] that, to some extent, replace benchtop laboratory equipment, performing different tasks such as mixing [9], separation, heating, and detection. The benefits of microfluidics technology are based on the small volume of liquid samples [10], which enables faster chemical reactions [11,12] due to the acceleration of mass and heat transfer at the microscale [13,14] and integrated micro actuators [15][16][17]. In the last decades, a microfluidics droplet-based approach rapidly evolved [14,[18][19][20][21], largely employed for biomedical applications [16,22,23], especially leading to studies with cells and antibody development [20,24,25], where microfluidics devices have enabled the creation of new tools and protocols [16,[26][27][28], for example, for single-cell encapsulation, co-encapsulation, cell-sorting, droplet recovery/extraction (de-oiling), and picoinjection [14,22,24]. ...
... Optical detection [9], impedance detection [10], and capacitive detection [11] emerge as the predominant sensing techniques utilized for droplet size control and detection. However, it is important to mention that optical-based droplet detection often demands a considerably intricate setup external to the device, involving the introduction of laser light and the subsequent detection of scattered light using optical elements positioned within a microfluidic channel or chamber, as evidenced by studies [12,13]. Optics-based interrogation dependence on external equipment does not allow for the fabrication of portable point of care (POC) [18,37]. ...
This paper presents a comprehensive study focusing on the detection and characterization of droplets with volumes in the nanoliter range. Leveraging the precise control of minute liquid volumes, we introduced a novel spectroscopic on-chip microsensor equipped with integrated microfluidic channels for droplet generation, characterization, and sensing simultaneously. The microsensor, designed with interdigitated ring-shaped electrodes (IRSE) and seamlessly integrated with microfluidic channels, offers enhanced capacitance and impedance signal amplitudes, reproducibility, and reliability in droplet analysis. We were able to make analyses of droplet length in the range of 1.0–6.0 mm, velocity of 0.66–2.51 mm/s, and volume of 1.07 nL–113.46 nL. Experimental results demonstrated that the microsensor’s performance is great in terms of droplet size, velocity, and length, with a significant signal amplitude of capacitance and impedance and real-time detection capabilities, thereby highlighting its potential for facilitating microcapsule reactions and enabling on-site real-time detection for chemical and biosensor analyses on-chip. This droplet-based microfluidics platform has great potential to be directly employed to promote advances in biomedical research, pharmaceuticals, drug discovery, food engineering, flow chemistry, and cosmetics.
... While biosensor enhancement and biological analysis have been some of the main targeted applications for these systems, their widespread implementation in practical use settings is still limited, as is the case with many lab-on-a-chip systems [170][171][172]. Further work to simplify and lower the cost of these systems, especially with respect to their ease of use, may allow for their broad commercial realization. ...
Particle trapping and enrichment into confined volumes can be useful in particle processing and analysis. This review is an evaluation of the methods used to trap and enrich particles into constrained volumes in microfluidic and nanofluidic systems. These methods include physical, optical, electrical, magnetic, acoustic, and some hybrid techniques, all capable of locally enhancing nano- and microparticle concentrations on a microscale. Some key qualitative and quantitative comparison points are also explored, illustrating the specific applicability and challenges of each method. A few applications of these types of particle trapping are also discussed, including enhancing biological and chemical sensors, particle washing techniques, and fluid medium exchange systems.
... 21 This technology, facilitated by droplet-based microfluidics, enables manipulation of miniscule volumes (fL-aL) within these droplets. 22 Acting as microreactors, the droplets are encapsulated by an immiscible phase, providing protection and facilitating manipulation. Specialized variants, such as evaporating or dissolving droplets, concentrate the analyte for detection using electrochemical techniques. ...
The ability to detect and positively identify molecules under extremely dilute conditions is important for the health of both humankind and the environment. At present, few measurement science techniques can...
... Initially used for biochemical analysis and detection, microfluidic or lab-on-chip systems have more recently been found to be applicable in diagnosis. These devices facilitate the study of some parameters, conditions, and biological mechanisms in vitro, while consuming minimal quantities of reagents and cells, yielding highly sensitive results in a short period of time, distinguishing them from conventional cell cultures [57]. Microfluidic systems complement in vivo strategies and demonstrate their value in drug development and biological research, offering opportunities for evaluating and developing novel biocompatible materials [58]. ...
This review outlines the evolutionary journey from traditional two-dimensional (2D) cell culture to the revolutionary field of organ-on-a-chip technology. Organ-on-a-chip technology integrates microfluidic systems to mimic the complex physiological environments of human organs, surpassing the limitations of conventional 2D cultures. This evolution has opened new possibilities for understanding cell–cell interactions, cellular responses, drug screening, and disease modeling. However, the design and manufacture of microchips significantly influence their functionality, reliability, and applicability to different biomedical applications. Therefore, it is important to carefully consider design parameters, including the number of channels (single, double, or multi-channels), the channel shape, and the biological context. Simultaneously, the selection of appropriate materials compatible with the cells and fabrication methods optimize the chips’ capabilities for specific applications, mitigating some disadvantages associated with these systems. Furthermore, the success of organ-on-a-chip platforms greatly depends on the careful selection and utilization of cell resources. Advances in stem cell technology and tissue engineering have contributed to the availability of diverse cell sources, facilitating the development of more accurate and reliable organ-on-a-chip models. In conclusion, a holistic perspective of in vitro cellular modeling is provided, highlighting the integration of microfluidic technology and meticulous chip design, which play a pivotal role in replicating organ-specific microenvironments. At the same time, the sensible use of cell resources ensures the fidelity and applicability of these innovative platforms in several biomedical applications.
... Microfluidics involves the application of microfabricated devices that precisely manipulate minuscule volumes of fluids, often on the order of 10 À15 -10 À9 l, within microchannels scaled to the dimensions of individual cells. 17 This unique capability renders microfluidics particularly suitable for the manipulation and analysis of single cells. ...
In the context of microfluidic technology, investigating the encapsulation of single cells is of great importance, providing valuable insight into cellular behavior and contributing to advancements in single-cell analysis. This paper presents a computational investigation into the dynamics of single-cell encapsulation within a flow-focusing microfluidic system, with a specific emphasis on addressing the challenges associated with high-efficiency encapsulation. This study utilizes a combined lattice Boltzmann and immersed boundary method to provide an accurate simulation of a three-phase system. This allowed for an in-depth exploration of various critical parameters, including cell injection frequency, cell size, and inlet position. This study identifies optimal conditions for maximizing single-cell encapsulation efficiency, emphasizing the impact of the ratio between cell injection and droplet generation frequencies on encapsulation outcomes. This study investigates the effects of cell-induced changes on droplet formation characteristics. It explains the generation of larger droplets and the occurrence of additional satellite droplets. These findings provide insight into the microfluidic platforms designed for single-cell assays, which have potential applications in various fields such as drug development and personalized therapies. Published under an exclusive license by AIP Publishing. https://doi.
... 9 Droplet-based microfluidic experiments represent a powerful tool for studying supramolecular systems. [10][11][12][13] Not only do they provide greater control than bulk experiments, but they also allow evaluation in confined spaces of the behavior of fibril-like structures as mimetics of natural cytoskeleton. As a result, they are an ideal complement to experiments in solution. ...
In this protocol, we describe how to perform the photo-isomerization of cyclic peptides containing an unsaturated β-amino acid. This process triggers the formation or disassembly of cyclic peptide nanotubes under appropriate light irradiation. Specifically, we start by describing the solid-phase synthesis of the cyclic peptide component. We also present a technique for performing isomerization studies in solution and how to extend it to microfluidic aqueous droplets.
For complete details on the use and execution of this protocol, please refer to Vilela-Picos et al.¹
... The injection of Na 2 SO 4 and a mixed solution of RaBr 2 and BaCl 2 at a flow rate of 1 µL min −1 induces a fluid velocity of about 4 × 10 -3 m s −1 (Fig. 1b). The Reynolds number defined by the ratio of inertial forces to viscous forces is 3.75, indicating a laminar flow whereby the reacting fluids flow in parallel (Fig. 1c-e), without turbulence, and the only mixing that occurs is the result of the diffusion of molecules across the interface (green region of the microfluidic channel in Fig. 1c-e) between the reacting fluids 65 . The concentrations of the reacting solutes for the experiment with 1.5 mM Na 2 SO 4 across lines 1-3 ( Fig. 1b) are plotted in Fig. 2a, b. ...
Ra,Ba)SO4 solid solutions are commonly encountered as problematic scales in subsurface energy-related applications, e.g., geothermal systems, hydraulic fracturing, conventional oil and gas, etc. Despite its relevance, its crystallization kinetics were never determined because of radium (226), high radioactivity (3.7 × 10¹⁰ Bq g⁻¹), and utilization in contemporary research, therefore constrained to trace amounts (< 10⁻⁸ M) with the composition of BaxRa1-xSO4 commonly restricted to x > 0.99. What if lab-on-a-chip technology could create new opportunities, enabling the study of highly radioactive radium beyond traces to access new information? In this work, we developed a lab-on-a-chip experiment paired with computer vision to evaluate the crystal growth rate of (Ba,Ra)SO4 solid solutions. The computer vision algorithm enhances experimental throughput, yielding robust statistical insights and further advancing the efficiency of such experiments. The 3D analysis results of the precipitated crystals using confocal Raman spectroscopy suggested that {210} faces grew twice as fast as {001} faces, mirroring a common observation reported for pure barite. The crystal growth rate of (Ba0.5Ra0.5)SO4 follows a second-order reaction with a kinetic constant equal to (1.23 ± 0.09) × 10⁻¹⁰ mol m⁻² s⁻¹.
... With the rapid development of computer technology, machine learning has demonstrated powerful data analysis capabilities, which have made great contributions to the development of many industries. Droplets of different sizes, physical properties, and concentrations are produced in processes involving droplet generation, such as microfluid [5,6], ink-jet printing [7], and spraying [8]. The study of droplet dynamics will generate a large number of valuable but complex droplet datasets. ...
In recent years, machine learning has made significant progress in the field of micro-fluids, and viscosity prediction has become one of the hotspots of research. Due to the specificity of the application direction, the input datasets required for machine learning models are diverse, which limits the generalisation ability of the models. This paper starts by analysing the most obvious kinetic feature induced by viscosity during flow—the variation in droplet neck contraction with time (hmin/R∼τ). The kinetic processes of aqueous glycerol solutions of different viscosities when dropped in air were investigated by high-speed camera experiments, and the kinetic characteristics of the contraction of the liquid neck during droplet falling were extracted, using the Ohnesorge number (Oh=μ/(ρRσ)1/2) to represent the change in viscosity. Subsequently, the liquid neck contraction data were used as the original dataset, and three models, namely, random forest, multiple linear regression, and neural network, were used for training. The final results showed superior results for all three models, with the multivariate linear regression model having the best predictive ability with a correlation coefficient R2 of 0.98.
... Microfluidics is the science and technology associated with the manipulation of fluids on the micron scale. [12] Here, capillary forces and surface tension dominate over inertia, and viscosity dominates over momentum. The resulting laminar flow regime is essential for precisely controlling mass transport within microfluidic channels. ...
From energy-related transformations to organic syntheses, single-atom heterogeneous catalysts (SACs) are offering new prospects to tackle sustainability challenges. However, scarce design guidelines and poor mechanistic understanding due to a lack of discovery and operando characterization tools impede theirbroader development. This perspective offers a glimpse into how droplet-based microfluidic technologies mayhelp solve both of these issues, and provides technical considerations for platform design to systematically fabricate SACs and study them under operational conditions during liquid-phase organic syntheses.
... 14 Microfluidics is a technology that manipulates fluids in the scale range from submicron to hundreds of microns. 15 Microfluidic technology is implemented through a microfluidic chip, also known as lab-on-a-chip. Microfluidic channels, microvalves, and micropumps can be created on the chip through micro-nano processing to achieve highly precise microfluid control. ...
Biological particle separation has wide applications in medical diagnosis, bioengineering, and various other domains. Traditional methods, such as filtration, density gradient centrifugation, and size exclusion chromatography, face many challenges, including low separation resolution, low purity, and the inability to be seamlessly integrated into continuous processes. The development of microfluidics has paved the way for efficient and precise biological particle separation. Microfluidic chip‐based methods can generally be performed continuously and automatically, and microfluidic chips can integrate multilevel operations, including mixing, separation, detection, and so forth, thereby achieving continuous processing of particles at various levels. This review comprehensively investigates biological particle separation techniques based on microfluidic chips. According to the different sources of force effect on the particles during the separation process, they can be divided into active separation, passive separation, and affinity separation. We introduce the principles and device design of these methods respectively, and compare their advantages and disadvantages. For the introduction of each method, we used the most classic and latest research cases as much as possible. Additionally, we discussed the differences between experimental standard particles and biological particles. Finally, we summarized the current limitations and challenges of existing microfluidic separation techniques, while exploring future trends and prospects.
... The term "organ" refers to the miniature tissues cultivated within these microfluidic chips, which can mimic the functions of one or more specific tissues. While these systems are less complex than actual organs and tissues, researchers have found that they often provide reliable representations of human physiology and disease (Whitesides 2006). OoCs incorporate advanced in vitro technology, allowing the study of biological cells and tissues outside the body. ...
Safety Pharmacology (SP) plays a critical role in assessing the potential adverse effects of drugs on vital organ systems during the early stages of drug discovery and development. The field of SP has evolved to incorporate various methodologies and testing strategies. In the era of Precision Medicine (PM), SP contributes to the development of PM drugs by ensuring their safety in specific subpopulations. However, it is noted that the SP considerations for PM therapies differ from those for conventional drug candidates. For cell therapies, SP studies must consider the unique characteristics of these products. SP in gene therapies focuses on the safety of genetic material transfer using viral vectors, while CAR-T cell therapies pose the challenges of human cellular products and genome editing vectors. PM also plays a role in SP by identifying robust biomarkers that aid in safety assessment, monitoring, and predicting toxicity. The PM-inspired biomarkers enhance our understanding of how a drug works, help select the right patients for clinical trials, and guide regulatory decisions. Moreover, PM enables the invention of new modalities for SP experiments, such as spheroids, organoids, and organ-on-a-chip models, which provide biologically relevant and stable in vitro systems. Personalized organ-on-a-chip models hold promise for individually assessing drug efficacy and safety, supporting personalized disease prevention and treatment strategies. Experts in both SP and PM recognize the importance of updating SP guidelines to incorporate the advancements of PM. Multidisciplinary efforts are expected to lead to remarkable advances in drug development, ultimately benefiting healthcare.
... Microfluidics attempts to apply fluid mechanics on an extremely microscale, ranging from micrometers to nanometers. [1][2][3] The remarkable performance of microfluidic devices in biology, [4][5][6][7] chemistry, 8,9 medicine, 10,11 and cell engineering [11][12][13] has drawn increasing attention from scientists toward customized microfluidic devices. Acoustohydrodynamic micromixers hold a paramount position in microfluidics on account of their efficient mixing performance and effective controllability. ...
Acoustohydrodynamic micromixers offer excellent mixing efficiency, cost-effectiveness, and flexible controllability compared with conventional micromixers. There are two mechanisms in acoustic micromixers: indirect influence by induced streamlines, exemplified by sharp-edge micromixers, and direct influence by acoustic waves, represented by surface acoustic wave micromixers. The former utilizes sharp-edge structures, while the latter employs acoustic wave action to affect both the fluid and its particles. However, traditional micromixers with acoustic bubbles achieve significant mixing performance and numerous programmable mixing platforms provide excellent solutions with wide applicability. This review offers a comprehensive overview of various micromixers, elucidates their underlying principles, and explores their biomedical applications. In addition, advanced programmable micromixing with impressive versatility, convenience, and ability of cross-scale operations is introduced in detail. We believe this review will benefit the researchers in the biomedical field to know the micromixers and find a suitable micromixing method for their various applications.
Microfluidic devices have become a vastly popular technology, particularly because of the advantages they offer over their traditional counterparts. They have such a wide range of uses and can make complex tasks quite efficient. One area of research or work that has benefited greatly from the use of microfluidics is biosensing, where microfluidic chips are integrated into biosensor setups. There are growing numbers of applications of microfluidics in this area as researchers look for efficient ways to tackle disease diagnostics and drug discovery, which are critical in this era of recurring pandemics. In this work, the authors review the integration of microfluidic chips with biosensors, as well as microfluidic applications in biosensing, food security, molecular biology, cell diagnostics, and disease diagnostics, and look at some of the most recent research work in these areas. The work covers a wide range of applications including cellular diagnostics, life science research, agro-food processing, immunological diagnostics, molecular diagnostics, and veterinarian diagnostics. Microfluidics is a field which combines fundamental laws of physics and chemistry to solve miniaturization problems involving fluids at the nanoscale and microscale, and as such, the authors also examine some fundamental mathematical concepts in microfluidics and their applications to biosensing. Microfluidics has relatively new technologies with great potential in terms of applications.
Infectious pathogens, such as the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), are a threat to global health and prosperity, with the coronavirus disease 2019 (COVID-19) pandemic causing deaths and negative economic impacts worldwide. Pathogens continuously mutate, evading vaccines and treatments; monitoring is therefore crucial to preventing future outbreaks. But there are still many shortcomings in available diagnostic technologies, and scalable and convenient point-of-care technologies are highly demanded. In this work, we demonstrate the application of injection molded centrifugal microfluidic chips with integrated optical pH sensors for multiplexed detection of SARS-CoV-2, influenza A, and influenza B RNA.
The optical pH sensors generated sensitive fluorescent readouts from diagnostic reverse transcription loop-mediated isothermal amplification (RT-LAMP) reactions; limits of detection for influenzas A and B, and SARS-CoV-2 of 89, 245, and 38 RNA copies per reaction, respectively, were attained. Results were obtainable within 44 minutes for SARS-CoV-2 and influenza A, and 48 minutes for influenza B. We implemented a data processing strategy that allowed for reliable, quantitative thresholds for deciding reaction outcomes based on numerical derivatives of the fluorescence curves, enabling 100% specificity. This work demonstrates the utility of optical pH sensors and injection molded centrifugal microfluidics for multiplexed infectious disease diagnostics with point-of-care applications.
Liquid biopsy has emerged as a promising non-invasive strategy for cancer diagnosis, enabling the detection of various circulating biomarkers, including circulating tumor cells (CTCs), circulating tumor nucleic acids (ctNAs), circulating tumor-derived small extracellular vesicles (sEVs), and circulating proteins. Surface-enhanced Raman scattering (SERS) biosensors have revolutionized liquid biopsy by offering sensitive and specific detection methodologies for these biomarkers. This review comprehensively examines the application of SERS-based biosensors for identification and analysis of various circulating biomarkers including CTCs, ctNAs, sEVs and proteins in liquid biopsy for cancer diagnosis. The discussion encompasses a diverse range of SERS biosensor platforms, including label-free SERS assay, magnetic bead-based SERS assay, microfluidic device-based SERS system, and paper-based SERS assay, each demonstrating unique capabilities in enhancing the sensitivity and specificity for detection of liquid biopsy cancer biomarkers. This review critically assesses the strengths, limitations, and future directions of SERS biosensors in liquid biopsy for cancer diagnosis.
Cell migration is an essential process in a number of physiological and pathological events, and known to be modulated by external microenvironment because cells may sense physical and chemical signals from the microenvironment and collectively respond to these signals. Over the past two decades, a lot of efforts have been made to study how external microenvironment can affect cell migration behaviors. Cells often migrate through confined environments in vivo, such as extracellular matrices in tissues and capillary vessels. Understanding how cells move in these constrained spaces is crucial to clarify various biological processes. For instance, during embryonic development, cells migrate through specific pathways to form tissues and organs. In wound healing, cells migrate to repair damaged tissues. In cancer, tumour cells migrate to invade surrounding tissues and metastasize to distant sites. Recent advances of bio-MEMS technologies have enabled to characterize cell mechanics and to control local cellular environment at micro-scale. In order to study cell migration under confinement, microchannels have been widely fabricated and used due to their directionality and compatibility. Thus, this study reviews recent work on fabrication of microchannels and their applications to investigate cell migration behaviors, ranging from straight channels to tortuous structures. Challenges and limitations associated with studying cell migration in microchannels are also discussed. Reviewing cell migration in confined environments may provide valuable insights into the underlying mechanisms of cell migration and aid in developing strategies for therapeutic interventions.
Microdroplet formation has been widely used in 3D printing, additive manufacturing, chemical synthesis and other fields. Comprehensive understanding for the microdroplet formation is necessary for process optimization of the above-mentioned fields. In this paper, the Giesekus (GK) model is used to simulate the formation of viscoelastic droplet in T-type microchannels based on OpenFOAM. The effects of liquid phase elasticity, viscosity and channel wall wettability on the formation of viscoelastic droplet were investigated by changing the relaxation time of the dispersed phase, polymer viscosity and wall contact angle. The pressure characteristics, droplet final lengths and detachment time were compared under different operating conditions. The simulation results describe the effect of fluid parameters on droplet formation in the form of pressure, which is used to supplement the shortcomings of existing experiments in stress. The results show that the elasticity hinders droplet breakup during the stretching stage. As the polymer viscosity increases, there is a significant increase in the elasticity of the droplet, which prevents the droplet filaments from stretching and breaking, resulting in a slower frequency of droplet formation. Moreover, the influence of wall contact angle and fluid flow rate on the formation of viscoelastic droplets in T-shaped microchannel is also observed. It is found that the wall contact angle also has an impact on the final droplet length, which cannot be ignored.
Ovarian cancer accounts for more deaths than any other female reproductive tract cancer. The major reasons for the high mortality rates include delayed diagnoses and drug resistance. Hence, improved diagnostic and therapeutic options for ovarian cancer are a pressing need. Extracellular vesicles (EVs), that include exosomes provide hope in both diagnostic and therapeutic aspects. They are natural lipid nanovesicles secreted by all cell types and carry molecules that reflect the status of the parent cell. This facilitates their potential use as biomarkers for an early diagnosis. Additionally, EVs can be loaded with exogenous cargo, and have features such as high stability and favorable pharmacokinetic properties. This makes them ideal for tumor-targeted delivery of biological moieties. The International Society of Extracellular Vesicles (ISEV) based on the Minimal Information for Studies on Extracellular Vesicles (MISEV) recommends the usage of the term “small extracellular vesicles (sEVs)” that includes exosomes for particles that are 30–200 nm in size. However, majority of the studies reported in the literature and relevant to this review have used the term “exosomes”. Therefore, this review will use the term “exosomes” interchangeably with sEVs for consistency with the literature and avoid confusion to the readers. This review, initially summarizes the different isolation and detection techniques developed to study ovarian cancer-derived exosomes and the potential use of these exosomes as biomarkers for the early diagnosis of this devastating disease. It addresses the role of exosome contents in the pathogenesis of ovarian cancer, discusses strategies to limit exosome-mediated ovarian cancer progression, and provides options to use exosomes for tumor-targeted therapy in ovarian cancer. Finally, it states future research directions and recommends essential research needed to successfully transition exosomes from the laboratory to the gynecologic-oncology clinic.
Recently, field‐effect transistors (FETs) have emerged as a novel type of multiparameter, high‐performance, highly integrated platform for biochemical detection, leveraging their classical three‐terminal structure, working principles, and fabrication methods. Notably, graphene materials, known for their exceptional electrical and optical properties as well as biocompatibility, serve as a fundamental component of these devices, further enhancing their advantages in biological detection. This review places special emphasis on recent advancements in graphene field‐effect transistor (GFET)‐based biosensors and focuses on four main areas: i) the basic concepts of FETs and the specific electrical properties of GFETs; ii) various state‐of‐the‐art approaches to enhance the performance of GFET‐based biosensors in terms of operating principles and the “3S”—stability, sensitivity, and specificity; iii) multiplexed detection strategies for GFET‐based biosensors; and iv) the current challenges and future perspectives in the field of GFET‐based biosensors. It is hoped that this article can profoundly elucidate the development of GFET biosensors and inspire a broader audience.
This chapter focuses on a series of further sustainable and/or unconventional wet-chemical methods to prepare single metal, alloys, oxides, chalcogenides and other inorganic compounds in the form of nanoparticles (NPs) at low temperature (<200 °C). In particular, the aim of the chapter is to provide the reader with an overview of further methods not specifically addressed by other chapters of the book, such as hydrothermal, polyol-assisted, continuous-flow and sonochemical methods, as well as radiochemistry and laser ablation in liquid media. A theoretical background of each method, a description of the synthetic procedure and a discussion of the synthetic parameters involved, and their influence on the final features of the products, are given, with the pros and cons of the presented synthetic approaches also outlined. In addition, a description of the state-of-the-art of the compounds obtainable through each approach is presented.
Multiomics studies at single-cell level require small volume manipulation, high throughput analysis, and multiplexed detection, characteristics that droplet microfluidics can tackle. However, the initial step of molecule bioseparation remains challenging. Here, we describe a unique magnetic device to trap and extract magnetic particles in sub-nanoliter droplets, for compartmentalisation of detection steps. Relying on electrodeposition of NiFe structures and microfluidic manipulation, the extraction of 1 μm diameter magnetic particles was achieved at high throughput (20 droplets per second) with an efficiency close to 100% in 450 pL droplets. The first demonstration of its adaptability to single-cell analysis is demonstrated with the extraction of mRNA. Using a purified nucleic acid solution, this unique magnetic configuration was able to reach a RNA extraction rate of 72%. This is the first demonstration of a physical separation in droplets at high throughput at single-cell scale.
The use of nanomaterials in medicine offers multiple opportunities to address neurodegenerative disorders such as Alzheimer's and Parkinson's disease. These diseases are a significant burden for society and the health system, affecting millions of people worldwide without sensitive and selective diagnostic methodologies or effective treatments to stop their progression. In this sense, the use of gold nanoparticles is a promising tool due to their unique properties at the nanometric level. They can be functionalized with specific molecules to selectively target pathological proteins such as Tau and α-synuclein for Alzheimer’s and Parkinson’s disease, respectively. Additionally, these proteins are used as diagnostic biomarkers, wherein gold nanoparticles play a key role in enhancing their signal, even at the low concentrations present in biological samples such as blood or cerebrospinal fluid, thus enabling an early and accurate diagnosis. On the other hand, gold nanoparticles act as drug delivery platforms, bringing therapeutic agents directly into the brain, improving treatment efficiency and precision, and reducing side effects in healthy tissues. However, despite the exciting potential of gold nanoparticles, it is crucial to address the challenges and issues associated with their use in the medical field before they can be widely applied in clinical settings. It is critical to ensure the safety and biocompatibility of these nanomaterials in the context of the central nervous system. Therefore, rigorous preclinical and clinical studies are needed to assess the efficacy and feasibility of these strategies in patients. Since there is scarce and sometimes contradictory literature about their use in this context, the main aim of this review is to discuss and analyze the current state-of-the-art of gold nanoparticles in relation to delivery, diagnosis, and therapy for Alzheimer’s and Parkinson’s disease, as well as recent research about their use in preclinical, clinical, and emerging research areas.
Graphical Abstract
Mechanical stimuli such as forces, fluid shear stresses and pressures play a role in the migration of cancer cells through the endothelial monolayer of blood vessels. In the metastatic step of transendothelial migration (entry into the blood vessels), endothelial dissemination and second transendothelial migration (exit from the blood vessels), forces can originate from four main sources: the cancer cells themselves, the endothelial cells and the cells associated with the cancer such as macrophages, neutrophils, platelets and fibroblasts as well as the surrounding extracellular matrix. Mechanical signals and biochemical stimuli may interact synergistically to guide the transmigration of cancer cells through the endothelium. In this chapter, the hypothesis of synergy is tested as the impact of synergistic effects between cancer cells, such as the clustering of cells, is analyzed during transmigration to migrate more effectively, to better oppose immune attacks, and to resist mechanical forces, such as fluid shear stress in vessels. The most important aspects of cancer cell transmigration are the combination of biochemical factors with mechanical factors that can emanate from at least four different sources and the dynamic transition of cancer cells as well as the clustering of cancer cells. Possible perspectives for cancer metastasis and potential targets for tumor-mitigating drugs can be derived from a better understanding of the interplay between the different cell types and their microenvironment, where mechanical signals in particular seem to be at the forefront. The scientists in the field of cancer research can therefore redefine their position and work synergistically by combining mechanical comprehension with biological knowledge. Finally, the interplay of the different parties involved in the transmigration of cancer cells through the endothelium of blood vessels, with emphasis on the interactions between cancer cells and neighboring cells, is dependent not only on the respective biological and mechanical signals, but also on their synergistic interplay, which effectively contributes to the metastasis of cancer cells.
Microfluidics is an interdisciplinary topic of research that draws inspiration from other areas such as fluid dynamics, microelectronics, materials science, and physics. Microfluidics has made it possible to create microscale channels and chambers out of a broad variety of materials by borrowing ideas from a number of different fields. This has opened up exciting possibilities for the development of platforms of any size, shape, and geometry using a variety of approaches. One of the most significant advantages of microfluidics is its versatility in applications. Microfluidic chips can be used for a variety of purposes, such as incorporating nanoparticles, encapsulating and delivering drugs, targeting cells, analyzing cells, performing diagnostic tests, and cultivating cells. This adaptability has led to the development of several device-like systems for use in a range of settings. In this study, we explore cutting-edge novel applications for microfluidic and nanofabrication technologies. We examine current developments in the area of microfluidics and highlight their potential for usage in the medical industry. We pay special attention to digital microfluidics, a recently developed and very useful technique for illness diagnosis and monitoring. The originality of microfluidics is found in the fact that it allows for the miniaturization of complex systems and processes, paving the way for the creation of cutting-edge gadgets with wide-ranging practical applications. Microfluidics has the potential to transform various fields, including medicine, biotechnology, environmental monitoring, and more. The development of novel microfluidic platforms, coupled with advancements in digital microfluidics, promises to revolutionize the way we diagnose, treat, and monitor diseases.
Rare diseases pose complex challenges to individuals, families, and the healthcare system. Collaborative research efforts are essential to improving diagnosis, treatment, and overall quality of life for those affected by these conditions. Animal models stand as indispensable tools in rare disease research, offering insights into disease mechanisms, treatment efficacy, and potential interventions that ultimately improve the lives of those affected by these conditions. Animal models across various species have significantly advanced our knowledge of rare diseases, accelerating the development of therapies and treatment strategies.
Rodent models are widely used in rare disease research, where mice and rats are used. Rat models and mouse models offer a complementary approach, providing insights into the pathogenesis, treatment strategies, and potential biomarkers of rare diseases. On the other hand, non-rodent animal models also provide diverse opportunities to study rare diseases and contribute unique insights that complement rodent models. Primate models stand as indispensable tools for unraveling the complexities of rare diseases, bridging the gap between laboratory findings and clinical applications. Canine models offer a unique perspective on rare diseases, contributing to our understanding of disease mechanisms, treatment strategies, and translational research. Porcine models offer valuable insights into various rare diseases, benefiting our understanding of disease mechanisms and potential treatments. Zebrafish models have transformed rare disease research by offering unique insights into disease mechanisms, drug screening, and genetic pathways. Feline models provide a unique perspective on rare diseases, offering insights into genetic disorders, metabolic conditions, and more. Drosophila models provide a unique and efficient platform for studying rare diseases, uncovering key insights into disease mechanisms, potential treatments, and therapeutic targets.
Advancements in genetic engineering, especially driven by CRISPR-Cas9 technology, have transformed our ability to create accurate and relevant animal models for rare diseases. These techniques enable researchers to uncover disease mechanisms, test potential therapies, and contribute to the development of personalized medicine approaches. CRISPR-Cas9 technology has transformed the creation of animal models for rare diseases, enabling precise genetic modifications that facilitate the study of disease mechanisms and potential therapies.
Gene knockout and knock-in techniques have revolutionized our ability to investigate gene function and the molecular basis of rare diseases, paving the way for potential therapeutic strategies. Conditional and tissue-specific gene expression systems offer precision and flexibility in creating animal models that closely mimic the genetic and physiological complexities of rare diseases. Induced pluripotent stem cells (iPSCs) have transformed disease modeling, offering a platform to study rare diseases with unprecedented accuracy. Their potential for understanding disease mechanisms and drug screening holds promise for advancing the field of rare disease research. Characterizing and phenotyping rare disease models provide essential insights into disease mechanisms and potential therapeutic strategies. These processes contribute to bridging the gap between basic research and clinical applications, ultimately improving our understanding and management of rare diseases.
Behavioral and physiological assessments offer critical insights into the impact of rare diseases on an organism’s function and well-being. These assessments contribute to a comprehensive understanding of disease mechanisms and aid in the development of targeted interventions. Molecular and histopathological analyses are essential components of characterizing and phenotyping rare disease models, shedding light on the molecular basis and structural changes associated with these conditions. Modeling specific rare diseases serves as a critical tool for deepening our understanding of disease pathology and developing targeted therapeutic approaches. These models contribute to unraveling the complexities of rare disorders and ultimately hold the potential to improve patient care and outcomes.
Developing animal models for neurologically rare diseases offers a valuable platform for gaining insights into disease mechanisms and evaluating potential treatments. These models play a pivotal role in bridging the gap between bench research and clinical applications, ultimately improving the lives of patients with these disorders. Animal models for genetic metabolic disorders offer a powerful tool for understanding disease mechanisms and developing targeted therapies. These models contribute to bridging the gap between basic research and clinical applications, ultimately benefiting patients affected by these disorders. Animal models for rare cancers offer a vital tool for investigating disease mechanisms and evaluating potential therapies. These models contribute to bridging the gap between laboratory research and clinical applications, ultimately improving the prognosis and treatment options for patients with these rare malignancies.
In vivo imaging and analysis offer a transformative approach to understanding the intricacies of biological processes within living organisms. These techniques continue to evolve, enhancing our ability to explore dynamic interactions and providing valuable information for both basic research and clinical applications. Noninvasive imaging techniques for longitudinal studies offer a powerful tool for understanding the dynamic nature of biological processes. These methods continue to evolve, enhancing our ability to observe and analyze changes over time and providing valuable information for both basic research and clinical applications. Imaging modalities for tracking disease progression offer a critical means to visualize and understand the dynamic changes occurring within the body. As these techniques continue to advance, they will play an increasingly vital role in guiding diagnosis, treatment decisions, and the development of novel therapies.
Therapeutic approaches and testing are essential components of medical progress, driving the development of effective treatments for a wide range of diseases. As research methods and technologies continue to advance, the potential for more targeted and personalized therapies becomes increasingly promising. Preclinical drug testing using animal models remains a cornerstone of drug development, providing critical data that informs decisions regarding the progression of potential therapies into human trials. As technology advances, the integration of various approaches will continue to refine and improve the accuracy of preclinical testing. Gene therapy trials in rare disease models represent a transformative approach to addressing genetic disorders at their root causes. As ongoing research continues to refine techniques and expand the scope of treatable conditions, the potential for improving the lives of patients with rare diseases becomes increasingly promising.
Ethical considerations in animal research remain a complex and evolving topic. As the field progresses, it is crucial to continually reassess and adapt ethical standards to ensure responsible and compassionate treatment of animals while advancing medical knowledge. Ethical guidelines are essential for maintaining the integrity of animal research and upholding the welfare of research subjects. As the field progresses, adherence to these guidelines remains crucial to ensuring responsible and ethically sound scientific practices. In vitro and computational models are revolutionizing research by providing effective alternatives to animal studies. As technology advances, these models will continue to play a crucial role in advancing our understanding of diseases and developing new treatments. Case studies underscore the transformative potential of in vitro and computational models in various research domains. As these models continue to evolve and become more sophisticated, their widespread adoption promises to reshape the landscape of biomedical research and contribute to improved healthcare outcomes.
Model-based insights are driving transformative changes in therapeutic development, enabling researchers to uncover new avenues for treatment and refine existing strategies. As technology evolves and our understanding of complex diseases deepens, model-based approaches will continue to play a central role in shaping the future of medicine. Collaborative efforts between researchers and clinicians drive the translation of scientific discoveries into tangible benefits for patients. As medicine becomes increasingly personalized and innovative, the synergy between these two groups will continue to shape the landscape of healthcare and lead to more effective and targeted therapies.
Collaborative research between researchers and clinicians offers immense potential to drive scientific advancements and improve patient care. By addressing challenges and implementing strategies for effective collaboration, the future of medical research holds promise for more innovative and impactful outcomes. Bridging the gap between animal models and human therapies requires a multifaceted approach that integrates advanced models, translational strategies, and a comprehensive understanding of the limitations of animal research. By addressing these challenges and leveraging innovative approaches, researchers can enhance the translation of scientific discoveries into effective treatments for human diseases. Emerging technologies have transformed rare disease modeling, enabling more accurate representations of disease mechanisms and accelerating the development of targeted therapies. As these technologies continue to evolve, they hold the promise of revolutionizing our approach to understanding and treating rare diseases.
Successfully navigating the regulatory landscape and translating rare disease research into clinical trials requires a comprehensive understanding of regulatory pathways, ethical considerations, and strategic approaches to maximize the potential for therapeutic breakthroughs. Regulatory guidelines from the FDA and EMA provide a framework for developing safe and effective therapies for rare diseases. Navigating these guidelines requires a deep understanding of the regulatory landscape and a commitment to patient-centered approaches. Conducting clinical trials for rare diseases requires careful consideration of patient recruitment, trial design, ethical concerns, and patient engagement to ensure the successful development of effective therapies.
Collaborative networks and data sharing are essential for advancing rare disease research, leveraging collective knowledge and resources to accelerate discoveries and therapeutic breakthroughs. Rare disease research consortia demonstrate the power of collaborative efforts, driving advancements in understanding rare diseases, identifying therapeutic targets, and ultimately improving the lives of patients. Data repositories and open science initiatives drive rare disease research forward by enabling broad data sharing, collaboration, and fostering a culture of transparency and innovation.
In closing, the contributions of animal models to rare disease research are profound and far-reaching. By unraveling the mysteries of rare diseases, advancing therapeutic approaches, and ultimately improving patient outcomes, animal models stand as instrumental tools that continue to drive innovation and pave the way for a brighter future in the realm of rare disease research. With this comprehensive exploration, we are sure that the use of animal models in rare disease research, recognizing their invaluable role in reshaping the medical landscape and offering hope to those affected by rare diseases, paves a way for finding new paths and means to combat rare diseases. As we stand on the precipice of future research, it is evident that the potential for discovery is vast. The synergy between cutting-edge technologies, collaborative endeavors, ethical considerations, and patient-centered approaches will shape a new era of rare disease research. This chapter serves as a testament to the progress made so far and an inspiration for the breakthroughs yet to come.
A lattice Boltzmann method is used to explore the effect of surfactants on the unequal volume breakup of a droplet in a T-junction microchannel, and the asymmetry due to fabrication defects in real-life microchannels is modelled as the pressure difference between the two branch outlets ( $\Delta {P^\ast }$ ). We first study the effect of the surfactants on the droplet dynamics at different dimensionless initial droplet lengths ( $l_0^\ast $ ) and capillary numbers ( Ca ) under symmetric boundary conditions ( $\Delta {P^\ast } = 0$ ). The results indicate that the presence of surfactants promotes droplet deformation and breakup at small and moderate $l_0^\ast $ values, while the surfactant effect is weakened at large $l_0^\ast $ values. When the branch channels are completely blocked by the droplet, a linear relationship is observed between the dimensionless droplet length ( $l_d^\ast $ ) and dimensionless time ( ${t^\ast }$ ), and two formulas are proposed for predicting the evolution of $l_d^\ast $ with ${t^\ast }$ for the two systems. We then investigate the effect of the surfactants on the droplet breakup at different values of $\Delta {P^\ast }$ and bulk surfactant concentrations ( ${\psi _b}$ ) under asymmetric boundary conditions ( $\Delta {P^\ast } \ne 0$ ). It is observed that, as $\Delta {P^\ast }$ increases, the volume ratio of the generated droplets ( ${V_1}/{V_2}$ ) decreases to 0 in both systems, while the rate of decrease is higher in the clean system, i.e. the presence of surfactants could cause a decreased pressure difference between the droplet tips. As ${\psi _b}$ increases, ${V_1}/{V_2}$ first increases rapidly, then remains almost constant and finally decreases slightly. We thus establish a phase diagram that describes the ${V_1}/{V_2}$ variation with $\Delta {P^\ast }$ and ${\psi _b}$ .
In the realm of microfluidics, a critical issue prevails: The commercially available flow sensors are situated external to the microfluidic chip, resulting in an inherent deficiency of precise operational insights. Applications such as biochemistry, drug development, single cell analyses, gradient generators, biomedical devices and proactive healthcare demand dependable data for broader utilization. In the present work, we introduce a microfluidic flow sensor designed to gauge electrolyte flow rates on-chip inside a microchannel by measuring electrochemical resistance of electrolytic bubbles within a circuit comprising electrolytic fluid and inter-digitated electrodes. This sensor design features a Si wafer substrate with micropatterned Ti/Pt electrodes bonded to a polydimethylsiloxane (PDMS) microchannel using oxygen plasma. The sensor has been characterized for electrolytic fluid (0.1 M NaCl), 600 μ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu$$\end{document}m wide microchannel, 0–500 μ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu$$\end{document}l/min range of flow, 3V dc power input, and 25 ∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^\circ$$\end{document}C room temperature conditions. Sensor response has been compared for electrolyte concentrations (0.1 M to 0.4 M NaCl), channel width (400–1200 μ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu$$\end{document}m), and input power (1–5 V) corresponding to a given flow rate. The sensor 3σ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sigma$$\end{document} resolution calculated from calibration curve is observed to be 5 μ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu$$\end{document}l/min for lower flow rates (0–100 μ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu$$\end{document}l/min) and 100 μ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu$$\end{document}l/min for higher flow rates (100–500 μ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu$$\end{document}l/min). The limit of detection (LoD) of the sensor is 1 μ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu$$\end{document}l/min. An algorithm based on the trapezoidal rule enabling flow rate prediction within 5 s has been implemented. The proposed flow sensor works over a broad range of flow rates, although with different sensitivity, presenting a novel method employing the electrolysis bubble size and volume for flow rate detection.
Microfluidic devices showcase miniature technology to transform industries and promote sustainability by precisely manipulating small fluid volumes. Laser micromachining is widely used to create precise microchannels for various applications, including microfluidic devices. The present work aims to investigate the surface quality of the microchannel fabricated on polymethylmethacrylate substrate using a CO2 laser. The laser parameters, such as power, machining speed, number of pass and laser focus distance, were varied to create the microchannel and the quality is investigated in two different stages. The first stage was performed with the help of an optical microscope, and further investigations with the aid of confocal and scanning electron microscope. A novel approach of rating the microchannels by visual inspection is introduced in the first stage of investigation. A visual rating is given for all the microchannels considering the edge bulge and surface quality of the microchannel at valley and side wall. Selected microchannels are further investigated in detail to understand the causes of various surface defects. The highest surface quality of 0.675 µm was obtained with laser power 12 W, machining speed 25 mm/s, number of pass 2 and the Z value is 17 mm. The findings will help attain the optimum process parameters for the laser micromachining of polymethylmethacrylate to develop various microfluidics devices. The novel approach of visual rating of the microchannels can shorten the time for the surface quality analysis and fasten the production.
Development of rapid analytical systems utilizing 3D printing is an emerging area of interest with the potential to provide efficient solutions by integrating multidisciplinary technology without compromising the quality of the system. In this study we report the fabrication of a 3D printing assisted microfluidic based absorbance measurement system, leveraging 3D printing along with integrating miniature optical components for the accurate measurement of biological assays. The developed system is rapid, affordable, and compact, through set of computer-aided design models and fusion deposition modeling 3D printing along with relevant electronic circuitry involving optical components like surface mounting devices. The handheld device features a capacitive touchscreen display, programmed to seamlessly perform MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. The device was employed for assessing the cell viability using Michigan cancer foundation-7 (MCF-7) cell lines over varying concentrations of tamoxifen, reciprocating the MTT assay analysis conducted by using spectrophotometer. The device achieved excellent results which upon comparison with the conventional spectrophotometer-based results have shown a correlation coefficient of 0.98. This compact and rapid absorbance measurement system holds significant potential for evaluating the cytotoxicity of drugs, and further development of innovative analytical devices.
This chapter first evokes the objects of chemistry and the role played by experimentation in the constitution of its objects. It then studies how chemists set up experimental protocols to deal with the dependence of chemical bodies on the inert or living environments in which they are found. To this end, its pays particular attention to the preparation of reference matrices for measurement and for the validation of results. In so doing, it stresses the fact that chemists use a dizzying pluralism of instruments, procedures, reasonings, and methods in order to characterize and quantify substances, which are never truly detachable, except in the case of approximations satisfying particular objectives, from the empirical complex {apparatus-methods-chemical substances-associated medium} in which they are scrutinized.
As described in the previous chapter, tip streaming can be produced by accelerating the fluid in the tip of a mother drop. Stresses of hydrodynamic or electrohydrodynamic nature drive this acceleration to the extent of overcoming the resistance offered by the capillary and viscous forces. This phenomenon has modest practical (technological) applications due to the intrinsic unsteady character of the process. Besides, the experimenter has limited control over the flow outcome (for instance, the size of the emitted droplets), which can be achieved only by fixing the flow rate at which the dispersed phase is ejected.
When the droplet is attached to a capillary and fed at the appropriate flow rate, the system eventually adopts either the microdripping or microjetting mode. Microdripping periodically emits tiny droplets of almost equal size from the droplet tip, while microjetting steadily ejects a thin, long, fluid thread. Microdripping and microjetting can produce droplets with the desired morphology, size, and electrical charge.
This chapter describes the axisymmetric microfluidic configurations used to produce microdripping and microjetting. Specifically, we consider the cone-jet mode of electrospray and the coflowing, flow focusing, and confined selective withdrawal configurations. The characteristics of the selective withdrawal and electrified films are also discussed. We introduce and explain the meaning of the dimensionless numbers characterizing the corresponding flows. The numerical and experimental results will be discussed in the following chapters.
The objective of this work is to create a finite element model of different magnetic actuator topologies using COMSOL Multiphysics software. The aim is to simulate and improve the magnetic field generated by different planar microcoil topologies while minimising energy dissipation. The magnetic field generated by square and circular spiral planar microcoils was compared with that produced by serpentine meander planar microcoils. It has been found that the trapping efficiency in a magnetic manipulation microfluidic system for biological applications is closely linked to the geometry and electrical parameters of the planar microcoils. In addition, the location of these microcoils within the microfluidic channel intended for the circulation of the paramagnetic microbeads also play a crucial role. The obtained results show that bu reducing the inter-turn spacing using a thinner conductor cross-section and injected a higher electrical intensity in the actuator, both the magnetic field strength and its gradient can be increased, and therefore cause a higher magnetic actuation force.
Liquid marbles are non-wetting, particle-covered microdroplets with a core-shell structure that are used in sample transport, material synthesis, and real-time sensing. Optimizing the distribution of shell particles remains a challenge, due to a tendency for aggregation via spontaneous assembly, which often leads to multilayered structures. Here, we outline a simple method for fabricating water-filled, monolayer liquid marbles with adjustable particle coverage rates, greatly reducing particle consumption. The soft liquid marbles are enclosed by a small quantity of modified polystyrene microspheres and display good atmospheric stability. The rolling behavior of flexible liquid marbles with wide coverage rates is then characterized. Contrary to common perception, the marbles with transparent openings exhibit high maneuverability on hydrophilic surfaces, and also excel in fusion, reaction and surface cleaning, with an elongated operational duration and a wide visualization range. The study provides new insights into the implementation of liquid marble-based miniaturized platforms.
Micro/nanoscale structure fabrication is an important process for designing miniaturized devices. Recently, three-dimensional (3D) integrated circuits using SiO2 via-holes interlayer filling by copper have attracted attention to extend the lifetime of Moore’s law. However, the fabrication of vertical and smooth-sidewall via-hole structures on SiO2 has not been achieved using the conventional dry etching method due to the limitation of the selective etching ratio of SiO2 and hard mask materials. In this study, we developed a unique method for the deep anisotropic dry etching of SiO2 using atmospheric gas-phase HF and a patterned photoresist. The hydroxyl groups in the photoresist catalyzed the HF gas-phase dry etching of SiO2 at high-temperature conditions. Therefore, fabrication of vertical with smooth-sidewall deep microstructures was demonstrated in the photoresist-covered area on SiO2 at a processing rate of 1.3 μm/min, which is 2–3 times faster than the conventional dry etching method. Additionally, the chemical reaction pathway in the photoresist-covered area on SiO2 with HF gas was revealed via density functional theory (DFT) calculations. This simple and high-speed microfabrication process will expand the commercial application scope of next-generation microfabricated SiO2-based devices.
The rapid evolution of healthcare and technology has given rise to advancements in the fields of bioprinting, tissue engineering, and regenerative medicine. 3D bioprinting has emerged as an alternative to traditional practices by offering the potential to create functional tissues. Traditional tissue engineering has faced challenges due to irregular cell distribution on scaffolds, limited cell density, and the difficulty of manufacturing patient‐specific tissues, which 3D bioprinting overcomes through layer‐by‐layer fabrication. This has immense significance for addressing organ shortages and enhancing transplant options for the future. 3D printing fully functional organs is a far‐sighted dream; however, the field is moving in the right direction, and research is being done to shorten the gap between the dream and reality. Notably, bioprinting's precision and compatibility with complex geometries have fueled its demand for lab‐grown tissue constructs. Computational Fluid Dynamics (CFD), a cornerstone of engineering, finds relevance in diverse sectors, including bioengineering. Its cost‐effectiveness and accurate simulation capabilities have drawn attention to its application in bioprinting research. CFD plays a pivotal role in optimizing 3D bioprinting by testing parameters like shear stress, diffusivity, and cell viability. This reduces the need for repetitive experiments, curbing costs and time. CFD simulations also enable the analysis of flow behaviors and material deformation under stress, aiding in material selection and bioprinter nozzle design. This review delves into recent applications of CFD in 3D bioprinting, shedding light on its potential to enhance the performance of this technology. Through this integration, CFD offers a pathway to advancing bioprinting, thus contributing to the evolution of regenerative medicine and healthcare.
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Fluid-based triboelectric nanogenerators (F-TENGs) represent a cutting-edge technology that leverages fluids as a contact medium to harness renewable energy through contact electrification (CE) and electrostatic induction.
The fabrication of microfluidic devices has progressed from cleanroom manufacturing to replica molding in polymers, and more recently to direct manufacturing by subtractive (e.g., laser machining) and additive (e.g., 3D...
Protein-based fibers combine unique mechanical properties with biocompatibility and biodegradability, and often outperform polymer-based fibers. Furthermore, a growing need for sustainable materials has triggered a revival in the study of protein fibers, including keratin, collagen, elastin, and silk, which do not require environmentally damaging petrochemicals for their synthesis. Nowadays, bioinspired research intends to mimic the underlying proteins as well as their natural assembly or spinning processes, to achieve fibers with properties equivalent to those of their natural counterparts. Protein-based fibers can also be used to mimic functions in nature, which can otherwise not be achieved with synthetic polymer-based fibers. Here, we review promising protein fibers, their synthesis, and applications, such as air and water filtration, energy conversion, smart textiles, and in biosensoring and biomedical fields.
Producing robust and scalable fluid metering in a microfluidic device is a challenging problem. We developed a scheme for metering fluids on the picoliter scale that is scalable to highly integrated parallel architectures and is independent of the properties of the working fluid. We demonstrated the power of this method by fabricating and testing a microfluidic chip for rapid screening of protein crystallization conditions, a major hurdle in structural biology efforts. The chip has 480 active valves and performs 144 parallel reactions, each of which uses only 10 nl of protein sample. The properties of microfluidic mixing allow an efficient kinetic trajectory for crystallization, and the microfluidic device outperforms conventional techniques by detecting more crystallization conditions while using 2 orders of magnitude less protein sample. We demonstrate that diffraction-quality crystals may be grown and harvested from such nanoliter-volume reactions.
Microfluidic devices for manipulating fluids are widespread and finding uses in many scientific and industrial contexts. Their design often requires unusual geometries and the interplay of multiple physical effects such as pressure gradients, electrokinetics, and capillarity. These circumstances lead to interesting variants of well-studied fluid dynamical problems and some new fluid responses. We provide an overview of flows in microdevices with focus on electrokinetics, mixing and dispersion, and multiphase flows. We highlight topics important for the description of the fluid dynamics: driving forces, geometry, and the chemical characteristics of surfaces.
Abstract Microfluidic devices for manipulating fluids are widespread and finding uses in many scientific and industrial contexts. Their design often requires unusual geometries and the interplay of multiple physical effects such as pressure gradients, electrokinetics, and capillarity. These circumstances lead to interesting variants of well-studied fluid dynamical problems and some new fluid responses. We provide an overview of flows in microdevices with focus on electrokinetics, mixing and dispersion, and multiphase flows. We highlight topics important for the description of the fluid dynamics: driving forces, geometry, and the chemical characteristics of surfaces.
Devices for handling nanoliter quantities of fluids are creating new fabrication challenges and finding new applications in biology, chemistry, and materials science.
This letter describes a method for generating monodisperse gaseous bubbles in a microfluidic flow-focusing device. The bubbles can be obtained in a range of diameters from 10 to 1000 μm. The volume Vb of the bubbles scales with the flow rate q and the viscosity μ of the liquid, and the pressure p of the gas stream as Vb∝p∕qμ. This method allows simultaneous, independent control of the size of the individual bubbles and volume fraction of the dispersed phase. Under appropriate conditions, bubbles self-assemble into highly ordered, flowing lattices. Structures of these lattices can be adjusted dynamically by changing the flow parameters.
This letter describes a method for producing chaotic transport trajectories in planar, microfluidic networks prepared by standard, single-step lithography and operated with a steady-state inflow of the fluids into the device. Gaseous slugs flowing through the network produce temporal variation of pressure distribution and lead to stretching and folding of the continuous fluid. Stabilization of the bubbles by surface-active agents is not necessary, and the method is compatible with the wide range of reactions performed in on-chip bioassays.
We fabricated nanofluidic channels that have elliptical cross sections with major and minor radii of less than 100 nm, without the use of electron-beam or other high-resolution lithography. The channels were formed by thermal removal of sacrificial polymer nanofibers. The sacrificial template fiber was deposited on a target substrate by electrospinning and encapsulated by a spin-on glass. The elliptical shape of the channels eliminates sharp corners, at which fluid flow is hindered, and provides convenient boundary conditions for theoretical modeling of fluid flow in the channels. Also, the spin-on glass is optically transparent and compatible with chemical analysis, thereby opening up application in biomolecular separation and single molecule analysis. Hundreds of parallel channels have also been formed by the oriented spinning process. © 2003 American Institute of Physics.
This review reports the progress on the recent development of
micromixers. The review first presents the different micromixer types
and designs. Micromixers in this review are categorized as passive
micromixers and active micromixers. Due to the simple fabrication
technology and the easy implementation in a complex microfluidic system,
passive micromixers will be the focus of this review. Next, the review
discusses the operation points of the micromixers based on
characteristic dimensionless numbers such as Reynolds number Re, Peclet
number Pe, and in dynamic cases the Strouhal number St. The fabrication
technologies for different mixer types are also analysed. Quantification
techniques for evaluation of the performance of micromixers are
discussed. Finally, the review addresses typical applications of
micromixers.
We survey progress over the past 25 years in the development of microscale devices for pumping fluids. We attempt to provide both a reference for micropump researchers and a resource for those outside the field who wish to identify the best micropump for a particular application. Reciprocating displacement micropumps have been the subject of extensive research in both academia and the private sector and have been produced with a wide range of actuators, valve configurations and materials. Aperiodic displacement micropumps based on mechanisms such as localized phase change have been shown to be suitable for specialized applications. Electroosmotic micropumps exhibit favorable scaling and are promising for a variety of applications requiring high flow rates and pressures. Dynamic micropumps based on electrohydrodynamic and magnetohydrodynamic effects have also been developed. Much progress has been made, but with micropumps suitable for important applications still not available, this remains a fertile area for future research.
The fabrication and testing of Teflon AF-coated channels on silicon and bonding of the same to a similarly coated glass wafer are described. With water or aqueous solutions in such channels, the channels exhibit much better light conduction ability than similar uncoated channels. Although the loss is greater than extruded Teflon AF tubes, light throughput is far superior to channels described in the literature consisting of [110] planes in silicon with 45 sidewalls. Absorbance noise levels under actual flow conditions using an LED source, an inexpensive photodiode and a simple operational amplifier circuitry was 1 10 4 ab-sorbance units over a 10-mm path length (channel 0.17-mm deep 0.49-mm wide), comparable to many commercially available macroscale flow-through absorbance detectors. Adherence to Beer's law was tested over a 50-fold concentration range of an injected dye, with the linear 2 relating the concentration to the observed absorbance being 0.9993. Fluorescence detection was tested with fluorescein as the test solute, a high brightness blue LED as the excitation source and an inexpensive miniature PMT. The concentration detection limit was 3 10 9 M and the corre-sponding mass detection limit was estimated to be 5 10 16 mol.
We describe a class of active, tunable optical fiber that incorporates multiple microfluidic plugs into interior fiber microchannels. The propagation characteristics of certain optical modes of these fiber waveguides can be usefully manipulated by controlling the positions and optical properties of these plugs, using actuators and pumps formed on the fiber surface. These hybrid microfluidic/silica structures offer versatile tuning capabilities in a format that preserves the advantages of conventional, passive optical fiber. As an example, we report an all-fiber, narrowband filter, whose transmission wavelength and attenuation are independently adjustable via microfluidic tuning. © 2002 American Institute of Physics.
A 2×2 microfluidic-based optical switch is proposed and demonstrated. The switch is made of an optically clear silicon elastomer, Polydimethylsiloxane (PDMS), using soft lithography. It has insertion loss smaller than 1 dB and extinction ratio on the order of 20 dB. The device is switching between transmission (bypass) and reflection (exchange) modes within less than 20 ms
Spatiotemporal pattern formation occurs in a variety of nonequilibrium physical and chemical systems. Here we show that a microfluidic device designed to produce reverse micelles can generate complex, ordered patterns as it is continuously operated far from thermodynamic equilibrium. Flow in a microfluidic system is usually simple-viscous effects dominate and the low Reynolds number leads to laminar flow. Self-assembly of the vesicles into patterns depends on channel geometry and relative fluid pressures, enabling the production of motifs ranging from monodisperse droplets to helices and ribbons.
Here we report a simple microfluidics phenomenon which allows the efficient mass production of micron size gas bubbles with a perfectly monodisperse and controllable diameter. It resorts on a self-excited breakup phenomenon (which locks at a certain frequency) of a short gas microligament coflowing in a focused liquid stream. In this work, we describe the physics of the phenomenon and obtain closed expressions for the bubble diameter as a function of the liquid and gas properties, geometry, and flow parameters, from a large set of experimental results.
Fluid flow at the microscale exhibits unique phenomena that can be leveraged to fabricate devices and components capable of performing functions useful for biological studies. The physics of importance to microfluidics are reviewed. Common methods of fabricating microfluidic devices and systems are described. Components, including valves, mixers, and pumps, capable of controlling fluid flow by utilizing the physics of the microscale are presented. Techniques for sensing flow characteristics are described and examples of devices and systems that perform bioanalysis are presented. The focus of this review is microscale phenomena and the use of the physics of the scale to create devices and systems that provide functionality useful to the life sciences.
We developed high-density microfluidic chips that contain plumbing networks with thousands of micromechanical valves and hundreds of individually addressable chambers. These fluidic devices are analogous to electronic integrated circuits fabricated using large-scale integration. A key component of these networks is the fluidic multiplexor, which is a combinatorial array of binary valve patterns that exponentially increases the processing power of a network by allowing complex fluid manipulations with a minimal number of inputs. We used these integrated microfluidic networks to construct the microfluidic analog of a comparator array and a microfluidic memory storage device whose behavior resembles random-access memory.
This review describes the design and fabrication of microfluidic systems in poly(dimethylsiloxane) (PDMS). PDMS is a soft polymer with attractive physical and chemical properties: elasticity, optical transparency, flexible surface chemistry, low permeability to water, and low electrical conductivity. Soft lithography makes fabrication of microfluidic systems in PDMS particularly easy. Integration of components, and interfacing of devices with the user, is also convenient and simpler in PDMS than in systems made in hard materials. Fabrication of both single and multilayer microfluidic systems is straightforward in PDMS. Several components are described in detail: a passive chaotic mixer, pneumatically actuated switches and valves, a magnetic filter, functional membranes, and optical components.
This review describes the design and fabrication of microfluidic systems in poly(dimethylsiloxane) (PDMS). PDMS is a soft polymer with attractive physical and chemical properties: elasticity, optical transparency, flexible surface chemistry, low permeability to water, and low electrical conductivity. Soft lithography makes fabrication of microfluidic systems in PDMS particularly easy. Integration of components, and interfacing of devices with the user, is also convenient and simpler in PDMS than in systems made in hard materials. Fabrication of both single and multilayer microfluidic systems is straightforward in PDMS. Several components are described in detail: a passive chaotic mixer, pneumatically actuated switches and valves, a magnetic filter, functional membranes, and optical components.
Microfluidic devices are finding increasing application as analytical systems, biomedical devices, tools for chemistry and biochemistry, and systems for fundamental research. Conventional methods of fabricating microfluidic devices have centered on etching in glass and silicon. Fabrication of microfluidic devices in poly(dimethylsiloxane) (PDMS) by soft lithography provides faster, less expensive routes than these conventional methods to devices that handle aqueous solutions. These soft-lithographic methods are based on rapid prototyping and replica molding and are more accessible to chemists and biologists working under benchtop conditions than are the microelectronics-derived methods because, in soft lithography, devices do not need to be fabricated in a cleanroom. This paper describes devices fabricated in PDMS for separations, patterning of biological and nonbiological material, and components for integrated systems.
This review describes the design and fabrication of microfluidic systems in poly(dimethylsiloxane) (PDMS). PDMS is a soft polymer with attractive physical and chemical properties: elasticity, optical transparency, flexible surface chemistry, low permeability to water, and low electrical conductivity. Soft lithography makes fabrication of microfluidic systems in PDMS particularly easy. Integration of components, and interfacing of devices with the user, is also convenient and simpler in PDMS than in systems made in hard materials. Fabrication of both single and multilayer microfluidic systems is straightforward in PDMS. Several components are described in detail: a passive chaotic mixer, pneumatically actuated switches and valves, a magnetic filter, functional membranes, and optical components.
Microfabrication techniques and scale-up by replication promise to transform classical batch-wise chemical laboratory procedures into integrated systems capable of providing new understanding and control of fundamental processes. Such integrated microchemical systems would enable rapid, continuous discovery and development of new products with the use of fewer resources and the generation of less waste. Additional opportunities exist for on-demand and on-site synthesis, with perhaps the first applications emerging in portable energy sources based on the conversion of hydrocarbons to hydrogen for miniaturized fuel cells.
Microchemical systems can be realized in a wide range of materials including stainless steel, glass, ceramics, silicon, and polymers. The high mechanical strength, excellent temperature characteristics, and good chemical compatibility of silicon combined with the existing fabrication infrastructure for microelectromechanical systems (MEMS) offer advantages in fabricating chemical microsystems that are compatible with strong solvents and operate at elevated temperatures and pressures. Furthermore, silicon-based microsensors for flow, pressure, and temperature can readily be integrated into the systems.
Microsystems for broad chemical applications should be discovery tools that can easily be applied by chemists and materials scientists while also having a convincing “scale-out” to at least small production levels. The interplay of both these capabilities is important in making microreaction technology successful. Perhaps the largest impact of microchemical systems will ultimately be the ability to explore reaction conditions and chemistry at conditions that are otherwise difficult to establish in the laboratory. Case studies are selected to illustrate microfluidic applications in which silicon adds advantages, specifically, integration of physical sensors and infrared spectroscopy, highthroughput experimentation in moisture-sensitive organic synthesis, controlled synthesis of nanoparticles (quantum dots), multiphase and heterogeneous catalytic reactions at elevated temperatures and pressures, and thermal management in the conversion of hydrocarbons to hydrogen.
We present studies of drop formation in liquid-liquid systems using a
flow focusing geometry integrated into a microfluidic device. Here, one
liquid flows into two inlet channels surrounding a center channel
containing a second immiscible liquid. The two liquids are forced to
flow through a small orifice downstream. Pressure and viscous stresses
from the outer fluid force the inner fluid into a narrow thread, which
breaks downstream of the orifice. A phase diagram illustrating drop size
as a function of flow rates and flow rate ratios of the two liquids
includes one regime where drop size is comparable to orifice width and a
second regime where drop size is dictated by the diameter of a thin
``focused'' thread, so drops much smaller than the orifice are formed.
Surfactants present in the continuous phase liquid strongly influence
the observed drop patterns. Finally, we demonstrate that nanometer-sized
droplets can be formed. The flow-focusing configuration was inspired by
the work of Ganan-Calvo (PRL 1998).
A flow-focusing geometry is integrated into a microfluidic device and used to study drop formation in liquid–liquid systems. A phase diagram illustrating the drop size as a function of flow rates and flow rate ratios of the two liquids includes one regime where drop size is comparable to orifice width and a second regime where drop size is dictated by the diameter of a thin “focused” thread, so drops much smaller than the orifice are formed. Both monodisperse and polydisperse emulsions can be produced.
Until now, microreaction devices designed for a specific type of reaction were used mainly for highly exothermic, very fast reactions. Described is a modular microreaction system and its application to representative homogeneous and heterogeneous reactions important in organic synthesis. The modular microreaction system allows continuous flow processes to be optimized and employed effectively in the chemical laboratory. The modular microreaction systems proved also versatile for syntheses requiring moderate reaction times, thus extending their application to a large fraction of organic reactions. The use of the modular and cleanable microreaction systems to rapidly develop optimized reaction conditions provides an excellent basis for the development of many chemical transformations scalable from milligram to ton production quantities.
We demonstrate periodic refractive index gratings in optical waveguides formed by microfluidic plugs that are infused into the airholes of a microstructured optical fibers. The periodic microfluidic plugs, created in the cladding, cause resonant coupling between copropagating optical fiber modes, which results in wavelength-dependent attenuation. We also demonstrate the ability to tune the resonant wavelength by compressing the microfluidic structure. These microfluidic resonant structures provide an alternative method for creating and tuning long-period gratings in optical fibers. This also represents an example of a resonant microfluidic structure and establishes potential strategies for enhanced tunable photonic crystal devices. © 2003 American Institute of Physics.
Electrostatic interactions play an important role in nanofluidic channels when the channel size is comparable to the Debye screening length. Electrostatic fields have been used to control concentration and transport of ions in nanofluidic transistors. Here, we report a transistor-reservoir-transistor circuit that can be used to turn “on” or “off” protein transport using electrostatic fields with gate voltages of ±1 V. Our results suggest that global electrostatic interactions of the protein were dominant over other interactions in the nanofluidic transistor. The fabrication technique also demonstrates the feasibility of nanofluidic integrated circuits for the manipulation of biomolecules in picoliter volumes.
We have developed a novel microfluidic device constructed from poly(dimethylsiloxane) using multilayer soft lithography technology for the analysis of single cells. The microfluidic network enables the passive and gentle separation of a single cell from the bulk cell suspension, and integrated valves and pumps enable the precise delivery of nanoliter volumes of reagents to that cell. Various applications are demonstrated, including cell viability assays, ionophore-mediated intracellular Ca2+ flux measurements, and multistep receptor-mediated Ca2+ measurements. These assays, and others, are achieved with significant improvements in reagent consumption, analysis time, and temporal resolution over macroscale alternatives.
Microfluidic devices are finding increasing application as analytical systems, biomedical devices, tools for chemistry and biochemistry, and systems for fundamental research. Conventional methods of fabricating microfluidic devices have centered on etching in glass and silicon. Fabrication of microfluidic devices in poly(dimethylsiloxane) (PDMS) by soft lithography provides faster, less expensive routes than these conventional methods to devices that handle aqueous solutions. These soft-lithographic methods are based on rapid prototyping and replica molding and are more accessible to chemists and biologists working under benchtop conditions than are the microelectronics-derived methods because, in soft lithography, devices do not need to be fabricated in a cleanroom. This paper describes devices fabricated in PDMS for separations, patterning of biological and nonbiological material, and components for integrated systems.
Herein we describe a versatile new strategy for producing monodisperse solid particles with sizes from 20 to 1000 mm. The method involves the formation of monodisperse liquid droplets by using a microfluidic device and shaping the droplets in a microchannel and then solidifying these drops in situ either by polymerizing a liquid monomer or by lowering the temperature of a liquid that sets thermally. This method has the following features: 1) It produces particles with an exceptionally narrow range of sizes. [1] 2) A new level of control over the shapes of the particles is offered. 3) The mechanism for droplet formation allows the use of a wide variety of materials including gels, metals, polymers, and polymers doped with functional additives. 4) The procedure can be scaled up to produce large numbers of particles. A number of methods exist for making inorganic and organic particles with narrow polydispersity. Inorganic col-loids are typically prepared by precipitation reactions from organometallic precursors. [2, 3] Polymer colloids with sizes from 20 nm to approximately 1 mm are usually prepared by a variation of emulsion polymerization techniques. [4] Larger beads are accessible through miniemulsion polymerization, [5] [*] Dr.
Microreactors as a novel concept in chemical technology enable the introduction of new reaction procedures in chemistry, molecular biology and pharmaceutical chemistry. Today, microreactors are realized as miniaturized continuous flow systems or reaction vessels with typical channel or chamber widths in the range of 10–500 μm. The reduction of characteristic dimensions resulting in a small volume of the reaction zone allows an application of high temperature or reactant concentration gradients, as well as a significantly enhanced process control and heat management. Thereby, the unique advantages of microreaction systems are to carry out chemical reactions in unusual process regimes or under isothermal conditions. In addition, microreactors offer the production of toxic or explosive chemicals onsite or ondemand with an inherent safety.Recently, microreactors gain more and more relevance in process development and industrial research. One example for a successful application is the synthesis of a vitamin precursor by a homogeneously catalyzed liquid/liquid-phase reaction. Some other classes of chemical reactions, e.g. gas phase reactions (formation of ethylene oxide) or two phase systems (gas/liquid), are under investigation.
Miniaturization of already existing techniques in on-line analytical chemistry is an alternative to compound-selective chemical sensors. Theory on separation science predicts higher efficiency, faster analysis time and lower reagent consumption for microsystems. Micromachining, a well known photolithographic technique for structures in the micrometer range, is introduced. A first capillary electrophoresis experiment using a chip-like structure is presented.
A method of generating electrospray from solutions emerging from small channels etched on planer substrates in described. The fluids are delivered using electroosmotically induced pressures and are sprayed electrostatically from the terminus of a channel by applying an electrical potential of sufficient amplitude to generate the electrospray between the microchip and a conductor spaced from the channel terminus. No major modification of the microchip is required other than to expose a channel opening. The principles that regulate the fluid delivery are described and demonstrated. A spectrum for a test compound, tetrabutylammonium iodide, that was continuously electrophoresed was obtained by coupling the microchip to an ion trap mass spectrometer. 35 refs., 6 figs.
This paper describes and characterizes a novel microfabricated neuronal culture device. This device combines microfabrication, microfluidic, and surface micropatterning techniques to create a multicompartment neuronal culturing device that can be used in a number of neuroscience research applications. The device is fabricated in poly(dimethylsiloxane), PDMS, using soft lithography techniques. The PDMS device is placed on a tissue culture dish (polystyrene) or glass substrate, forming two compartments with volumes of less than 2 μL each. These two compartments are separated by a physical barrier in which a number of micron-size grooves are embedded to allow growth of neurites across the compartments while maintaining fluidic isolation. Cells are plated into the somal (cell body) compartment, and after 3-4 days, neurites extend into the neuritic compartment via the grooves. Viability of the neurons in the devices is between 50 and 70% after 7 days in culture; this is slightly lower than but comparable to values for a control grown on tissue culture dishes. Healthy neuron morphology is evident in both the devices and controls. We demonstrate the ability to use hydrostatic pressure to isolate insults to one compartment and, thus, expose localized areas of neurons to insults applied in soluble form. Due to the high resistance of the microgrooves for fluid transport, insults are contained in the neuritic compartment without appreciable leakage into the somal compartment for over 15 h. Finally, we demonstrate the use of polylysine patterning in combination with the microfabricated device to facilitate identification and visualization of neurons. The ability to direct sites of neuronal attachment and orientation of neurite outgrowth by micropatterning techniques, combined with fluidically isolated compartments within the culture area, offers significant advantages over standard open culture methods and other conventional methods for manipulating distinct neuronal microenvironments.
Microfabricated integrated circuits revolutionized computation by vastly reducing the space, labor, and time required for calculations. Microfluidic systems hold similar promise for the large-scale automation of chemistry and biology, suggesting the possibility of numerous experiments performed rapidly and in parallel, while consuming little reagent. While it is too early to tell whether such a vision will be realized, significant progress has been achieved, and various applications of significant scientific and practical interest have been developed. Here a review of the physics of small volumes (nanoliters) of fluids is presented, as parametrized by a series of dimensionless numbers expressing the relative importance of various physical phenomena. Specifically, this review explores the Reynolds number Re, addressing inertial effects; the Péclet number Pe, which concerns convective and diffusive transport; the capillary number Ca expressing the importance of interfacial tension; the Deborah, Weissenberg, and elasticity numbers De, Wi, and El, describing elastic effects due to deformable microstructural elements like polymers; the Grashof and Rayleigh numbers Gr and Ra, describing density-driven flows; and the Knudsen number, describing the importance of noncontinuum molecular effects. Furthermore, the long-range nature of viscous flows and the small device dimensions inherent in microfluidics mean that the influence of boundaries is typically significant. A variety of strategies have been developed to manipulate fluids by exploiting boundary effects; among these are electrokinetic effects, acoustic streaming, and fluid-structure interactions. The goal is to describe the physics behind the rich variety of fluid phenomena occurring on the nanoliter scale using simple scaling arguments, with the hopes of developing an intuitive sense for this occasionally counterintuitive world.
A high throughput, low volume microfluidic device has been designed to decouple the physical processes of protein crystal nucleation and growth. This device, called the Phase Chip, is constructed out of poly(dimethylsiloxane) (PDMS) elastomer. One of the Phase Chip's innovations is to exploit surface tension forces to guide each drop to a storage chamber. We demonstrate that nanoliter water-in-oil drops of protein solutions can be rapidly stored in individual wells thereby allowing the screening of 1000 conditions while consuming a total of only 10 mug protein on a 20 cm(2) chip. Another significant advance over current microfluidic devices is that each well is in contact with a reservoir via a dialysis membrane through which only water and other low molecular weight organic solvents can pass, but not salt, polymer, or protein. This enables the concentration of all solutes in a solution to be reversibly, rapidly, and precisely varied in contrast to current methods, such as the free interface diffusion or sitting drop methods, which are irreversible. The Phase Chip operates by first optimizing conditions for nucleation by using dialysis to supersaturate the protein solution, which leads to nucleation of many small crystals. Next, conditions are optimized for crystal growth by using dialysis to reduce the protein and precipitant concentrations, which leads small crystals to dissolve while simultaneously causing only the largest ones to grow, ultimately resulting in the transformation of many small, unusable crystals into a few large ones.
We present a single-mode, single-polarization, distributed feedback liquid dye laser, based on a short high-order Bragg grating defined in a single polymer layer between two glass substrates. In this device we obtain single-mode operation in a multimode structure by means of transverse-mode discrimination with antiguiding segments. The laser is fabricated using microfabrication technology, is pumped by a pulsed frequency-doubled Nd:YAG laser, and emits narrow-line-width light in the chip plane at 577 nm. The output from the laser is coupled into integrated planar waveguides defined in the same polymer _lm. The laser device is thus well suited for integration, for example, into polymer based lab-on-a-chip microsystems.
We have designed, built, and tested microfluidic systems capable of transporting individual, preimplantation mouse embryos (100-microm to 150-microm diameter) through a network of channels. Typical channels are 160 to 200 microm deep, 250 to 400 microm wide at the top, and narrower at the bottom (0 to 250 microm wide) due to the fabrication process. In these channels, a pressure gradient of 1 Pa/mm causes the medium to flow on the order of 10(-10) m3/s (100 nl/s), with an average speed of 1 to 2 mm/s. Under these flow conditions the embryos roll along the bottoms of the channels, traveling at 1/2 the speed of the fluid. By manipulating the pressure at the wells connected to the ends of the channels, the embryos can be transported to (and retained at) specific locations including culture compartments and retrieval wells.
Emerging microfluidic systems have spurred an interest in the study of electrokinetic flow phenomena in complex geometries and a variety of flow conditions. This paper presents an analysis of the effects of fluid inertia and pressure on the velocity and vorticity field of electroosmotic flows. In typical on-chip electrokinetics applications, the flow field can be separated into an inner flow region dominated by viscous and electrostatic forces and an outer flow region dominated by inertial and pressure forces. These two regions are separated by a slip velocity condition determined by the Helmholtz-Smoulochowski equation. The validity of this assumption is investigated by analyzing the velocity field in a pressure-driven, two-dimensional flow channel with an impulsively started electric field. The regime for which the inner/outer flow model is valid is described in terms of nondimensional parameters derived from this example problem. Next, the inertial forces, surface conditions, and pressure-gradient conditions for a full-field similarity between the electric and velocity fields in electroosmotic flows are discussed. A sufficient set of conditions for this similarity to hold in arbitrarily shaped, insulating wall microchannels is the following: uniform surface charge, low Reynolds number, low Reynolds and Strouhal number product, uniform fluid properties, and zero pressure differences between inlets and outlets. Last, simple relations describing the generation of vorticity in electroosmotic flow are derived using a wall-local, streamline coordinate system.
This review describes the design and fabrication of microfluidic systems in poly(dimethylsiloxane) (PDMS). PDMS is a soft polymer with attractive physical and chemical properties: elasticity, optical transparency, flexible surface chemistry, low permeability to water, and low electrical conductivity. Soft lithography makes fabrication of microfluidic systems in PDMS particularly easy. Integration of components, and interfacing of devices with the user, is also convenient and simpler in PDMS than in systems made in hard materials. Fabrication of both single and multilayer microfluidic systems is straightforward in PDMS. Several components are described in detail: a passive chaotic mixer, pneumatically actuated switches and valves, a magnetic filter, functional membranes, and optical components.
Producing robust and scalable fluid metering in a microfluidic device is a challenging problem. We developed a scheme for metering fluids on the picoliter scale that is scalable to highly integrated parallel architectures and is independent of the properties of the working fluid. We demonstrated the power of this method by fabricating and testing a microfluidic chip for rapid screening of protein crystallization conditions, a major hurdle in structural biology efforts. The chip has 480 active valves and performs 144 parallel reactions, each of which uses only 10 nl of protein sample. The properties of microfluidic mixing allow an efficient kinetic trajectory for crystallization, and the microfluidic device outperforms conventional techniques by detecting more crystallization conditions while using 2 orders of magnitude less protein sample. We demonstrate that diffraction-quality crystals may be grown and harvested from such nanoliter-volume reactions.
There are many experiments in which it would be useful to treat a part of the surface or interior of a cell with a biochemical reagent. It is difficult, however, to achieve subcellular specificity, because small molecules diffuse distances equal to the extent of the cell in seconds. This paper demonstrates experimentally, and analyzes theoretically, the use of multiple laminar fluid streams in microfluidic channels to deliver reagents to, and remove them from, cells with subcellular spatial selectivity. The technique made it possible to label different subpopulations of mitochondria fluorescently, to disrupt selected regions of the cytoskeleton chemically, to dislodge limited areas of cell-substrate adhesions enzymatically, and to observe microcompartmental endocytosis within individual cells. This technique does not require microinjection or immobilization of reagents onto nondiffusive objects; it opens a new window into cell biology.
Microfluidic chip platforms for manipulating liquid volumes in the nanoliter range are slowly inching their way into mainstream genomic and proteomic research. The principal challenge faced by these technologies is the need for high-throughput processing of increasingly smaller volumes, with ever higher degrees of parallelization. Significant advances have been made over the past few years in addressing these needs through electrokinetic manipulation, vesicle encapsulation and mechanical valve approaches. These strategies allow levels of integration density and platform complexity that promise to make them into serious alternatives to current robotic systems.
A microfluidic device is reported that integrated cell handling, rapid cell lysis, and electrophoretic separation and detection of fluorescent cytosolic dyes. The device function was demonstrated using Jurkat cells that were loaded with the fluorogenic dyes - carboxyfluorescein diacetate, Oregon green carboxylic acid diacetate, or Calcein AM. The loaded cells were hydrodynamically transported from the cell-containing reservoir to a region on the microfluidic device where they were focused and then rapidly lysed using an electric field. Complete lysis was accomplished in <33 ms. The hydrolyzed, fluorescent dyes in the cell lysate were automatically injected into a separation channel on the device and detected 3 mm downstream of the injection point. The total separation time was approximately 2.2 s with absolute migration time reproducibilities of <1% and efficiencies ranging from 2300 to 4000 theoretical plates. Results from 139 cells are reported. A small fraction of these cells, approximately 9%, were found to enzymatically hydrolyze the loaded dyes in a manner significantly different from the majority of the cells. Cell analysis rates of 7-12 cells/min were demonstrated and are >100 times faster than those reported using standard bench-scale capillary electrophoresis.
We have evaluated double-stranded DNA separations in microfluidic devices which were designed to couple a sample preconcentration step based on isotachophoresis (ITP) with a zone electrophoretic (ZE) separation step as a method to increase the concentration limit of detection in microfluidic devices. Developed at ACLARA BioSciences, these LabCard trade mark devices are plastic 32 channel chips, designed with a long sample injection channel segment to increase the sample loading. These chips were designed to allow stacking of the sample into a narrow band using discontinuous ITP buffers, and subsequent separation in the ZE mode in sieving polymer solutions. Compared to chip ZE, the sensitivity was increased by 40-fold and we showed baseline resolution of all fragments in the PhiX174/HaeIII DNA digest. The total analysis time was 3 min/sample, or less than 100 min per LabCard device. The resolution for multiplexed PCR samples was the same as obtained in chip ZE. The limit of detection was 9 fg/microL of DNA in 0.1xpolymerase chain reaction (PCR) buffers using confocal fluorescence detection following 488 nm laser excitation with thiazole orange as the fluorescent intercalating dye.
This review describes microfluidic systems in poly(dimethylsiloxane) (PDMS) for biological studies. Properties of PDMS that make it a suitable platform for miniaturized biological studies, techniques for fabricating PDMS microstructures, and methods for controlling fluid flow in microchannels are discussed. Biological procedures that have been miniaturized into PDMS-based microdevices include immunoassays, separation of proteins and DNA, sorting and manipulation of cells, studies of cells in microchannels exposed to laminar flows of fluids, and large-scale, combinatorial screening. The review emphasizes the advantages of miniaturization for biological analysis, such as efficiency of the device and special insights into cell biology.
This paper describes the compatibility of poly(dimethylsiloxane) (PDMS) with organic solvents; this compatibility is important in considering the potential of PDMS-based microfluidic devices in a number of applications, including that of microreactors for organic reactions. We considered three aspects of compatibility: the swelling of PDMS in a solvent, the partitioning of solutes between a solvent and PDMS, and the dissolution of PDMS oligomers in a solvent. Of these three parameters that determine the compatibility of PDMS with a solvent, the swelling of PDMS had the greatest influence. Experimental measurements of swelling were correlated with the solubility parameter, delta (cal(1/2) cm(-3/2)), which is based on the cohesive energy densities, c (cal/cm(3)), of the materials. Solvents that swelled PDMS the least included water, nitromethane, dimethyl sulfoxide, ethylene glycol, perfluorotributylamine, perfluorodecalin, acetonitrile, and propylene carbonate; solvents that swelled PDMS the most were diisopropylamine, triethylamine, pentane, and xylenes. Highly swelling solvents were useful for extracting contaminants from bulk PDMS and for changing the surface properties of PDMS. The feasibility of performing organic reactions in PDMS was demonstrated by performing a Diels-Alder reaction in a microchannel.
We report the first fabrication of a solvent-compatible microfluidic device based on photocurable "Liquid Teflon" materials. The materials are highly fluorinated functionalized perfluoropolyethers (PFPEs) that have liquidlike viscosities that can be cured into tough, highly durable elastomers that exhibit the remarkable chemical resistance of fluoropolymers such as Teflon. Poly(dimethylsiloxane) (PDMS) elastomers have rapidly become the material of choice for many recent microfluidic device applications. Despite the advantages of PDMS in relation to microfluidics technology, the material suffers from a serious drawback in that it swells in most organic solvents. The swelling of PDMS-based devices in organic solvents greatly disrupts the micrometer-sized features and makes it impossible for fluids to flow inside the channels. Our approach to this problem has been to replace PDMS with photocurable perfluoropolyethers. Device fabrication and valve actuation were accomplished using established procedures for PDMS devices. The additional advantage of photocuring allows fabrication time to be decreased from several hours to a matter of minutes. The PFPE-based device exhibited mechanical properties similar to those of Sylgard 184 before and after curing as well as remarkable resistance to organic solvents. This work has the potential to expand the field of microfluidics to many novel applications.