Exosomes are cell-derived structures packaged with lipids, proteins, and nucleic acids. They exist in diverse bodily fluids and are involved in physiological and pathological processes. Although ...their potential for clinical application as diagnostic and therapeutic tools has been revealed, a huge bottleneck impeding the development of applications in the rapidly burgeoning field of exosome research is an inability to efficiently isolate pure exosomes from other unwanted components present in bodily fluids. To date, several approaches have been proposed and investigated for exosome separation, with the leading candidate being microfluidic technology due to its relative simplicity, cost-effectiveness, precise and fast processing at the microscale, and amenability to automation. Notably, avoiding the need for exosome labeling represents a significant advance in terms of process simplicity, time, and cost as well as protecting the biological activities of exosomes. Despite the exciting progress in microfluidic strategies for exosome isolation and the countless benefits of label-free approaches for clinical applications, current microfluidic platforms for isolation of exosomes are still facing a series of problems and challenges that prevent their use for clinical sample processing. This review focuses on the recent microfluidic platforms developed for label-free isolation of exosomes including those based on sieving, deterministic lateral displacement, field flow, and pinched flow fractionation as well as viscoelastic, acoustic, inertial, electrical, and centrifugal forces. Further, we discuss advantages and disadvantages of these strategies with highlights of current challenges and outlook of label-free microfluidics toward the clinical utility of exosomes.
Isolation of circulating tumor cells (CTCs) from blood has long been a challenge due to the rarity and heterogeneity of these cells. Detection technologies have predominantly focused on different ...molecular or physical properties of CTCs. Size‐based isolation approach using microfilters have been widely used to capture CTCs because of the difference in size and stiffness of the cells compared to other hemocytes. Isolation of rare cells based on their size was the original CTC enrichment technique and it demonstrated a simple yet rapid method that enhanced the recovery of cells with high throughput. In this review, we highlight key technical aspects of filter‐based isolation, detection, and characterization of CTCs, and compare the clinical performance of filter‐based devices with the approved platforms and immunoassays used for the analysis of CTCs. We have also discussed future prospective and incorporation of advances in immunochemistry technique into the filter‐based platforms for enhancing the utility in clinical settings.
Isolation of circulating tumor cells (CTCs) from blood has long been a challenge due to the rarity and heterogeneity of these cells. Detection technologies have predominantly focused on different molecular or physical properties of CTCs. Size‐based isolation approach using microfilters have been widely used to capture CTCs because of the difference in size and stiffness of the cells compared to other hemocytes.
Extracellular vesicles (EVs) are cell-derived vesicles present in body fluids that play an essential role in various cellular processes, such as intercellular communication, inflammation, cellular ...homeostasis, survival, transport, and regeneration. Their isolation and analysis from body fluids have a great clinical potential to provide information on a variety of disease states such as cancer, cardiovascular complications and inflammatory disorders. Despite increasing scientific and clinical interest in this field, there are still no standardized procedures available for the purification, detection, and characterization of EVs. Advances in microfluidics allow for chemical sampling with increasingly high spatial resolution and under precise manipulation down to single molecule level. In this review, our objective is to give a brief overview on the working principle and examples of the isolation and detection methods with the potential to be used for extracellular vesicles. This review will also highlight the integrated on-chip systems for isolation and characterization of EVs.
•An overview on the working principle of isolation and detection methods is provided.•Integrated systems for extracellular vesicles (EVs) characterization are highlighted.•Future challenges of on-chip systems for EVs characterization are summarized.
Microfluidic devices have been used progressively in biomedical research due to the advantages they offer, such as relatively low-cost, rapid and precise processing, and an ability to support highly ...automated analyses. Polydimethylsiloxane (PDMS) and polymethylmethacrylate (PMMA) are both biocompatible materials widely used in microfluidics due to their desirable characteristics. It is recognized that combining these two particular materials in a single microfluidic device would enable the development of an increasingly in-demand array of new applications, including those requiring high flow rates and elevated pressures. Whereas complicated and time-consuming efforts have been reported for bonding these two materials, the robust adhesion of PDMS and PMMA has not yet been accomplished, and remains a challenge. In this study, a new, simple, efficient, and low-cost method has been developed to mediate a strong bond between PMMA and PDMS layers at room temperature in less than 5 min using biocompatible adhesive tape and oxygen plasma treatment. The PDMS-PMMA bond was hydrolytically stable, and could tolerate a high influx of fluid without any leakage. This study addresses the limitations of existing approaches to bond these materials, and will enable the development of highly sought high-pressure and high-throughput biomedical applications.
This work develops a robust classifier for a COVID-19 pre-screening model from crowdsourced cough sound data. The crowdsourced cough recordings contain a variable number of coughs, with some input ...sound files more informative than the others. Accurate detection of COVID-19 from the sound datasets requires overcoming two main challenges (i) the variable number of coughs in each recording and (ii) the low number of COVID-positive cases compared to healthy coughs in the data. We use two open datasets of crowdsourced cough recordings and segment each cough recording into non-overlapping coughs. The segmentation enriches the original data without oversampling by splitting the original cough sound files into non-overlapping segments. Splitting the sound files enables us to increase the samples of the minority class (COVID-19) without changing the feature distribution of the COVID-19 samples resulted from applying oversampling techniques. Each cough sound segment is transformed into six image representations for further analyses. We conduct extensive experiments with shallow machine learning, Convolutional Neural Network (CNN), and pre-trained CNN models. The results of our models were compared to other recently published papers that apply machine learning to cough sound data for COVID-19 detection. Our method demonstrated a high performance using an ensemble model on the testing dataset with area under receiver operating characteristics curve = 0.77, precision = 0.80, recall = 0.71, F1 measure = 0.75, and Kappa = 0.53. The results show an improvement in the prediction accuracy of our COVID-19 pre-screening model compared to the other models.
Gelatin‐based hydrogels have been widely used in tissue engineering, three‐dimensional cell culture, drug delivery, and cell therapy. The mechanical behaviour of hydrogels combined with their ...chemical properties determines their functionality and efficacy. With respect to the mechanical behaviour of hydrogels, the vast majority of publications have reported their linear viscoelastic response. However, for practical conditions in the body, these materials experience large deformations beyond the linear viscoelastic limit. Herein, to mimic practical conditions and to evaluate the mechanical response of the hydrogels subjected to large deformations, we report inter‐ and intra‐cycle nonlinear viscoelastic behaviour of a gelatin methacryloyl (GelMA) hydrogel with different concentrations of the hydrogel precursor (10%–20% w/v) under large amplitude oscillatory shear deformation. To achieve this, we used a novel technique by chemically bonding the hydrogels to treated glass slides, which were attached to the oscillating metal plates using a double‐sided tape to alleviate any error arising from wall slip during rheological measurements. The results show that the elasticity of the covalently cross‐linked hydrogels at large deformations obeys a nonlinear force‐extension law and that the viscous intra‐cycle nonlinearity at moderate deformations stems from the dual cross‐linked (DC; i.e., physical and chemical) nature of the GelMA hydrogel. It was also shown that viscoelastic parameters can be tuned by the concentration of the hydrogel precursor, that is, yield stress increased from 2.6–7.1 kPa, critical strain amplitude decreased from γ0 = 100%–70%, and the onset of inter‐cycle nonlinearity shifted from γ0 = 50%–20% upon increasing the concentration of the hydrogel precursor. These insights have important implications for the rational development of hydrogel‐based biomaterials to design biocompatible scaffolds in tissue engineering applications.
The true nonlinear viscoelastic response of a chemically cross‐linked hydrogel was studied employing a novel technique to completely eliminate the effect of wall slip under large deformations.
Organ-on-a-chip systems are miniaturized microfluidic 3D human tissue and organ models designed to recapitulate the important biological and physiological parameters of their in vivo counterparts. ...They have recently emerged as a viable platform for personalized medicine and drug screening. These in vitro models, featuring biomimetic compositions, architectures, and functions, are expected to replace the conventional planar, static cell cultures and bridge the gap between the currently used preclinical animal models and the human body. Multiple organoid models may be further connected together through the microfluidics in a similar manner in which they are arranged in vivo, providing the capability to analyze multiorgan interactions. Although a wide variety of human organ-on-a-chip models have been created, there are limited efforts on the integration of multisensor systems. However, in situ continual measuring is critical in precise assessment of the microenvironment parameters and the dynamic responses of the organs to pharmaceutical compounds over extended periods of time. In addition, automated and noninvasive capability is strongly desired for long-term monitoring. Here, we report a fully integrated modular physical, biochemical, and optical sensing platform through a fluidics-routing breadboard, which operates organ-on-a-chip units in a continual, dynamic, and automated manner. We believe that this platform technology has paved a potential avenue to promote the performance of current organ-on-a-chip models in drug screening by integrating a multitude of real-time sensors to achieve automated in situ monitoring of biophysical and biochemical parameters.
Tip-growing cells have the unique property of invading living tissues and abiotic growth matrices. To do so, they exert significant penetrative forces. In plant and fungal cells, these forces are ...generated by the hydrostatic turgor pressure. Using the TipChip, a microfluidic lab-on-a-chip device developed for tip-growing cells, we tested the ability to exert penetrative forces generated in pollen tubes, the fastest-growing plant cells. The tubes were guided to grow through microscopic gaps made of elastic polydimethylsiloxane material. Based on the deformation of the gaps, the force exerted by the elongating tubes to permit passage was determined using finite element methods. The data revealed that increasing mechanical impedance was met by the pollen tubes through modulation of the cell wall compliance and, thus, a change in the force acting on the obstacle. Tubes that successfully passed a narrow gap frequently burst, raising questions about the sperm discharge mechanism in the flowering plants.
Manipulation of micro‐ and nanoparticles in complex biofluids is highly demanded in most biological and biomedical applications. A significant number of microfluidic platforms have been developed for ...inexpensive, rapid, accurate, and efficient particle manipulation. Due to the enormous potential of viscoelastic fluids (VEFs) for particle manipulation, various emerging microfluidic‐based VEFs techniques have been presented over the last decade. This review provides an intuitive understanding of VEF physics for particle separation in different microchannel geometries. Besides, active and passive VEF methods are critically reviewed, highlighting the potential and practical challenges of each technique for particle/cell focusing, sorting, and separation. The outcome of this study could enable recognizing deliverable VEF technology with the promising prospect in the manipulation of submicron biological samples (e.g., exosomes, DNA, and proteins).
Manipulation of micro‐ and nanoparticles in complex biofluids is highly demanded in most biological and biomedical applications.
Highlights
1.
The state of the art of viscoelastic fluid (VEF) flow in microfluidics for micro‐ and nano‐(bio)particle manipulation is discussed.
2.A comprehensive critical review of active and passive methods for particle manipulation in viscoelastic flows within microfluidic is provided, and the pros and cons of each method are explained.
3.The promising viscoelastic microfluidic methods for particle sorting and separation are highlighted and potential future applications are presented.
4.This review is intended to facilitate recognizing deliverable VEF technology with unprecedented functionality for next generation of VEF microfluidics with the application in biological sample processing and particle manipulation.
Abstract
Droplets produced within microfluidics have not only attracted the attention of researchers to develop complex biological, industrial and clinical testing systems but also played a role as a ...bit of data. The flow of droplets within a network of microfluidic channels by stimulation of their movements, trajectories, and interaction timing, can provide an opportunity for preparation of complex and logical microfluidic circuits. Such mechanical-based circuits open up avenues to mimic the logic of electrical circuits within microfluidics. Recently, simple microfluidic-based logical elements such as AND, OR, and NOT gates have been experimentally developed and tested to model basic logic conditions in laboratory settings. In this work, we develop new microfluidic networks, control the shape of channels and speed of droplet movement, and regulate the size of bubbles in order to extend the logical elements to six new logic gates, including AND/OR type 1, AND/OR type 2, NOT type 1, NOT type 2, Flip-Flop, Synchronizer, and a parametric model of T-junction as a bubble generator. We further designed and simulated a novel microfluidic Decoder 1 to 2, a Decoder 2 to 4, and a microfluidic circuit that combines several individual logic gates into one complex circuit. Further fabrication and experimental testing of these newly introduced logic gates within microfluidics enable implementing complex circuits in high-throughput microfluidic platforms for tissue engineering, drug testing and development, and chemical synthesis and process design.
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