Biophysical isolation and identification of circulating tumor cells

The integrated on-chip isolation and detection of circulating tumour cells

Circulating tumour cells (CTCs) are cancer cells shed from a primary tumour which intravasate into the blood stream and have the potential to extravasate into distant tissues, seeding metastatic lesions. As such, they can offer important insight into cancer progression with their presence generally associated with a poor prognosis. The detection and enumeration of CTCs is, therefore, critical to guiding clinical decisions during treatment and providing information on disease state. CTC isolation has been investigated using a plethora of methodologies, of which immunomagnetic capture and microfluidic size-based filtration are the most impactful to date. However, the isolation and detection of CTCs from whole blood comes with many technical barriers, such as those presented by the phenotypic heterogeneity of cell surface markers, with morphological similarity to healthy blood cells, and their low relative abundance (∼1 CTC/1 billion blood cells). At present, the majority of reported methods dissociate CTC isolation from detection, a workflow which undoubtedly contributes to loss from an already sparse population. This review focuses on developments wherein isolation and detection have been integrated into a single-step, microfluidic configuration, reducing CTC loss, increasing throughput, and enabling an on-chip CTC analysis with minimal operator intervention. Particular attention is given to immune-affinity, microfluidic CTC isolation, coupled to optical, physical, and electrochemical CTC detection (quantitative or otherwise).

Circulating Nucleic Acids in Colorectal Cancer: Diagnostic and Prognostic Value

Colorectal cancer (CRC) is the third most prevalent cancer in the world and the fourth leading cause of cancer-related mortality. DNA (cfDNA/ctDNA) and RNA (cfRNA/ctRNA) in the blood are promising noninvasive biomarkers for molecular profiling, screening, diagnosis, treatment management, and prognosis of CRC. Technological advancements that enable precise detection of both genetic and epigenetic abnormalities, even in minute quantities in circulation, can overcome some of these challenges. This review focuses on testing for circulating nucleic acids in the circulation as a noninvasive method for CRC detection, monitoring, detection of minimal residual disease, and patient management. In addition, the benefits and drawbacks of various diagnostic techniques and associated bioinformatics tools have been detailed.

Precision Isolation of Circulating Leukemia Cells in Chronic Myelogenous Leukemia Patients Using a Novel Microfluidic Device and Its Clinical Applications

Chronic Myelogenous Leukemia (CML) is a prevalent hematologic malignancy characterized by the malignant transformation of myeloid cells and their proliferation in the peripheral blood. The management of CML poses significant challenges, particularly in detecting and eradicating minimal residual disease, which is crucial for preventing relapse and improving survival outcomes. Traditional minimal residual disease detection methods, such as bone marrow aspiration, are invasive and have limitations which include the potential for sampling errors and false negatives. This study introduces a novel label-free microfluidic chip designed for the segregation and recovery of circulating leukemia cells, offering a non-invasive liquid biopsy approach with potential applications in precision medicine. Over July 2021 to October 2023, we recruited 56 CML patients across various disease stages and collected blood samples for analysis using our microfluidic device. The device demonstrated high efficacy in isolating circulating leukemia cells, with an optimal capture efficiency of 78% at a sample flow rate of 3 mL/h. Our results indicate that the microfluidic device can efficiently segregate and quantify circulating leukemia cells, providing a detailed understanding of CML progression and treatment response. The significant reduction in circulating leukemia cell counts in patients in complete remission highlights the device's potential in monitoring treatment efficacy. Furthermore, the device's sensitivity in detecting minimal residual disease could offer a more reliable prognostic tool for therapeutic decision-making in CML management.

A novel dual-function SERS-based identification strategy for preliminary screening and accurate diagnosis of circulating tumor cells

Non-specific adsorption of bioprobes based on surface-enhanced Raman spectroscopy (SERS) technology inevitably endows white blood cells (WBC) in the peripheral blood with Raman signals, which greatly interfere the identification accuracy of circulating tumor cells (CTCs). In this study, an innovative strategy was proposed to effectively identify CTCs by using SERS technology assisted by a receiver operating characteristic (ROC) curve. Firstly, a magnetic Fe3O4-Au complex SERS bioprobe was developed, which could effectively capture the triple negative breast cancer (TNBC) cells and endow the tumor cells with distinct SERS signals. Then, the ROC curve obtained based on the comparison of SERS intensity of TNBC cells and WBC was used to construct a tumor cell identification model. The merit of the model was that the detection sensitivity and specificity could be intelligently switched according to different identification purposes such as accurate diagnosis or preliminary screening of tumor cells. Finally, the difunctional recognition ability of the model for accurate diagnosis and preliminary screening of tumor cells was further validated by using the healthy human blood added with TNBC cells and blood samples of real tumor patients. This novel difunctional identification strategy provides a new perspective for identification of CTCs based on the SERS technology.

Recent Developments in Inertial and Centrifugal Microfluidic Systems along with the Involved Forces for Cancer Cell Separation: A Review

The treatment of cancers is a significant challenge in the healthcare context today. Spreading circulating tumor cells (CTCs) throughout the body will eventually lead to cancer metastasis and produce new tumors near the healthy tissues. Therefore, separating these invading cells and extracting cues from them is extremely important for determining the rate of cancer progression inside the body and for the development of individualized treatments, especially at the beginning of the metastasis process. The continuous and fast separation of CTCs has recently been achieved using numerous separation techniques, some of which involve multiple high-level operational protocols. Although a simple blood test can detect the presence of CTCs in the blood circulation system, the detection is still restricted due to the scarcity and heterogeneity of CTCs. The development of more reliable and effective techniques is thus highly desired. The technology of microfluidic devices is promising among many other bio-chemical and bio-physical technologies. This paper reviews recent developments in the two types of microfluidic devices, which are based on the size and/or density of cells, for separating cancer cells. The goal of this review is to identify knowledge or technology gaps and to suggest future works.

Multichannel impedance cytometry downstream of cell separation by deterministic lateral displacement to quantify macrophage enrichment in heterogeneous samples

The integration of on-chip biophysical cytometry downstream of microfluidic enrichment for inline monitoring of phenotypic and separation metrics at single-cell sensitivity can allow for active control of separation and its application to versatile sample sets. We present integration of impedance cytometry downstream of cell separation by deterministic lateral displacement (DLD) for enrichment of activated macrophages from a heterogeneous sample, without the problems of biased sample loss and sample dilution caused by off-chip analysis. This required designs to match cell/particle flow rates from DLD separation into the confined single-cell impedance cytometry stage, the balancing of flow resistances across the separation array width to maintain unidirectionality, and the utilization of co-flowing beads as calibrated internal standards for inline assessment of DLD separation and for impedance data normalization. Using a heterogeneous sample with un-activated and activated macrophages, wherein macrophage polarization during activation causes cell size enlargement, on-chip impedance cytometry is used to validate DLD enrichment of the activated subpopulation at the displaced outlet, based on the multiparametric characteristics of cell size distribution and impedance phase metrics. This hybrid platform can monitor separation of specific subpopulations from cellular samples with wide size distributions, for active operational control and enhanced sample versatility.

Lab-on-a-chip systems for cancer biomarker diagnosis

Lab-on-a-chip (LOC) or micro total analysis system is one of the microfluidic technologies defined as the adaptation, miniaturization, integration, and automation of analytical laboratory procedures into a single instrument or "chip". In this article, we review developments over the past five years in the application of LOC biosensors for the detection of different types of cancer. Microfluidics encompasses chemistry and biotechnology skills and has revolutionized healthcare diagnosis. Superior to traditional cell culture or animal models, microfluidic technology has made it possible to reconstruct functional units of organs on chips to study human diseases such as cancer. LOCs have found numerous biomedical applications over the past five years, including integrated bioassays, cell analysis, metabolomics, drug discovery and delivery systems, tissue and organ physiology and disease modeling, and personalized medicine. This review provides an overview of the latest developments in microfluidic-based cancer research, with pros, cons, and prospects.

Label-free microfluidic cell sorting and detection for rapid blood analysis

Blood tests are considered as standard clinical procedures to screen for markers of diseases and health conditions. However, the complex cellular background (>99.9% RBCs) and biomolecular composition often pose significant technical challenges for accurate blood analysis. An emerging approach for point-of-care blood diagnostics is utilizing "label-free" microfluidic technologies that rely on intrinsic cell properties for blood fractionation and disease detection without any antibody binding. A growing body of clinical evidence has also reported that cellular dysfunction and their biophysical phenotypes are complementary to standard hematoanalyzer analysis (complete blood count) and can provide a more comprehensive health profiling. In this review, we will summarize recent advances in microfluidic label-free separation of different blood cell components including circulating tumor cells, leukocytes, platelets and nanoscale extracellular vesicles. Label-free single cell analysis of intrinsic cell morphology, spectrochemical properties, dielectric parameters and biophysical characteristics as novel blood-based biomarkers will also be presented. Next, we will highlight research efforts that combine label-free microfluidics with machine learning approaches to enhance detection sensitivity and specificity in clinical studies, as well as innovative microfluidic solutions which are capable of fully integrated and label-free blood cell sorting and analysis. Lastly, we will envisage the current challenges and future outlook of label-free microfluidics platforms for high throughput multi-dimensional blood cell analysis to identify non-traditional circulating biomarkers for clinical diagnostics.

Microfluidic technologies for cell deformability cytometry

Microfluidic detection methods for cell deformability cytometry have been regarded as powerful tools for single-cell analysis of cellular mechanical phenotypes, thus having been widely applied in the fields of cell preparation, separation, clinical diagnostics and so on. Featured with traits like easy operations, low cost and high throughput, such methods have shown great potentials on investigating physiological state and pathological changes during cellular deformation. Herein, a review on the advancements of microfluidic-based cell deformation cytometry is presented. We discuss several representative microfluidic-based cell deformability cytometry methods with their frontiers in practical applications. Finally, we analyze the current status and propose the remaining challenges with future perspectives and development directions.

Greatly Enhanced CTC Culture Enabled by Capturing CTC Heterogeneity Using a PEGylated PDMS-Titanium-Gold Electromicrofluidic Device with Glutathione-Controlled Gentle Cell Release

The circulating tumor cells (CTCs, the root cause of cancer metastasis and poor cancer prognosis) are very difficult to culture for scale-up in vitro, which has hampered their use in cancer research/prognosis and patient-specific therapeutic development. Herein, we report a robust electromicrofluidic chip for not only efficient capture of heterogeneous (EpCAM+ and CD44+) CTCs with high purity but also glutathione-controlled gentle release of the CTCs with high efficiency and viability. This is enabled by coating the polydimethylsiloxane (PDMS) surface in the device with a 10 nm gold layer through a 4 nm titanium coupling layer, for convenient PEGylation and linkage of capture antibodies via the thiol-gold chemistry. Surprisingly, the percentage of EpCAM+ mammary CTCs can be as low as ∼35% (∼70% on average), showing that the commonly used approach of capturing CTCs with EpCAM alone may miss many EpCAM- CTCs. Furthermore, the CD44+ CTCs can be cultured to form 3D spheroids efficiently for scale-up. In contrast, the CTCs captured with EpCAM alone are poor in proliferation in vitro, consistent with the literature. By capture of the CTC heterogeneity, the percentage of stage IV patients whose CTCs can be successfully cultured/scaled up is improved from 12.5% to 68.8%. These findings demonstrate that the common practice of CTC capture with EpCAM alone misses the CTC heterogeneity including the critical CD44+ CTCs. This study may be valuable to the procurement and scale-up of heterogeneous CTCs, to facilitate the understanding of cancer metastasis and the development of cancer metastasis-targeted personalized cancer therapies conveniently via the minimally invasive liquid/blood biopsy.

Raman spectroscopy reveals phenotype switches in breast cancer metastasis

The accurate analytical characterization of metastatic phenotype at primary tumor diagnosis and its evolution with time are critical for controlling metastatic progression of cancer. Here, we report a label-free optical strategy using Raman spectroscopy and machine learning to identify distinct metastatic phenotypes observed in tumors formed by isogenic murine breast cancer cell lines of progressively increasing metastatic propensities. Methods: We employed the 4T1 isogenic panel of murine breast cancer cells to grow tumors of varying metastatic potential and acquired label-free spectra using a fiber probe-based portable Raman spectroscopy system. We used MCR-ALS and random forests classifiers to identify putative spectral markers and predict metastatic phenotype of tumors based on their optical spectra. We also used tumors derived from 4T1 cells silenced for the expression of TWIST, FOXC2 and CXCR3 genes to assess their metastatic phenotype based on their Raman spectra. Results: The MCR-ALS spectral decomposition showed consistent differences in the contribution of components that resembled collagen and lipids between the non-metastatic 67NR tumors and the metastatic tumors formed by FARN, 4T07, and 4T1 cells. Our Raman spectra-based random forest analysis provided evidence that machine learning models built on spectral data can allow the accurate identification of metastatic phenotype of independent test tumors. By silencing genes critical for metastasis in highly metastatic cell lines, we showed that the random forest classifiers provided predictions consistent with the observed phenotypic switch of the resultant tumors towards lower metastatic potential. Furthermore, the spectral assessment of lipid and collagen content of these tumors was consistent with the observed phenotypic switch. Conclusion: Overall, our findings indicate that Raman spectroscopy may offer a novel strategy to evaluate metastatic risk during primary tumor biopsies in clinical patients.

Isolation of Circulating Tumor Cells

Circulating tumor cells (CTCs) enter the vasculature from solid tumors and disseminate widely to initiate metastases. Mining the metastatic-enriched molecular signatures of CTCs before, during, and after treatment holds unique potential in personalized oncology. Their extreme rarity, however, requires isolation from large blood volumes at high yield and purity, yet they overlap leukocytes in size and other biophysical properties. Additionally, many CTCs lack EpCAM that underlies much of affinity-based capture, complicating their separation from blood. Here, we provide a comprehensive introduction of CTC isolation technology, by analyzing key separation modes and integrated isolation strategies. Attention is focused on recent progress in microfluidics, where an accelerating evolution is occurring in high-throughput sorting of cells along multiple dimensions.

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Circulating tumor cells (CTCs) spread cancer through the bloodstream (metastasis)

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CTC-based liquid biopsy enables minimally invasive sampling of cancer cells in blood

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Their extreme rarity requires all CTC types to be enriched from large blood volumes

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CTC isolation technology is analyzed, with a focus on high-throughput microfluidics

Recent Advances in Microfluidic Platform for Physical and Immunological Detection and Capture of Circulating Tumor Cells

CTCs (circulating tumor cells) are well-known for their use in clinical trials for tumor diagnosis. Capturing and isolating these CTCs from whole blood samples has enormous benefits in cancer diagnosis and treatment. In general, various approaches are being used to separate malignant cells, including immunomagnets, macroscale filters, centrifuges, dielectrophoresis, and immunological approaches. These procedures, on the other hand, are time-consuming and necessitate multiple high-level operational protocols. In addition, considering their low efficiency and throughput, the processes of capturing and isolating CTCs face tremendous challenges. Meanwhile, recent advances in microfluidic devices promise unprecedented advantages for capturing and isolating CTCs with greater efficiency, sensitivity, selectivity and accuracy. In this regard, this review article focuses primarily on the various fabrication methodologies involved in microfluidic devices and techniques specifically used to capture and isolate CTCs using various physical and biological methods as well as their conceptual ideas, advantages and disadvantages.

PillarX: A Microfluidic Device to Profile Circulating Tumor Cell Clusters Based on Geometry, Deformability, and Epithelial State

Circulating tumor cell (CTC) clusters are associated with increased metastatic potential and worse patient prognosis, but are rare, difficult to count, and poorly characterized biophysically. The PillarX device described here is a bimodular microfluidic device (Pillar-device and an X-magnetic device) to profile single CTCs and clusters from whole blood based on their size, deformability, and epithelial marker expression. Larger, less deformable clusters and large single cells are captured in the Pillar-device and sorted according to pillar gap sizes. Smaller, deformable clusters and single cells are subsequently captured in the X-device and separated based on epithelial marker expression using functionalized magnetic nanoparticles. Clusters of established and primary breast cancer cells with variable degrees of cohesion driven by different cell-cell adhesion protein expression are profiled in the device. Cohesive clusters exhibit a lower deformability as they travel through the pillar array, relative to less cohesive clusters, and have greater collective invasive behavior. The ability of the PillarX device to capture clusters is validated in mouse models and patients of metastatic breast cancer. Thus, this device effectively enumerates and profiles CTC clusters based on their unique geometrical, physical, and biochemical properties, and could form the basis of a novel prognostic clinical tool.

Folic Acid-Modified Fluorescent-Magnetic Nanoparticles for Efficient Isolation and Identification of Circulating Tumor Cells in Ovarian Cancer

Ovarian cancer (OC) is a lethal disease occurring in women worldwide. Due to the lack of obvious clinical symptoms and sensitivity biomarkers, OC patients are often diagnosed in advanced stages and suffer a poor prognosis. Circulating tumor cells (CTCs), released from tumor sites into the peripheral blood, have been recognized as promising biomarkers in cancer prognosis, treatment monitoring, and metastasis diagnosis. However, the number of CTCs in peripheral blood is low, and it is a technical challenge to isolate, enrich, and identify CTCs from the blood samples of patients. This work develops a simple, effective, and inexpensive strategy to capture and identify CTCs from OC blood samples using the folic acid (FA) and antifouling-hydrogel-modified fluorescent-magnetic nanoparticles. The hydrogel showed a good antifouling property against peripheral blood mononuclear cells (PBMCs). The FA was coupled to the hydrogel surface as the targeting molecule for the CTC isolation, held a good capture efficiency for SK-OV-3 cells (95.58%), and successfully isolated 2–12 CTCs from 10 OC patients’ blood samples. The FA-modified fluorescent-magnetic nanoparticles were successfully used for the capture and direct identification of CTCs from the blood samples of OC patients.

An Immunological Perspective of Circulating Tumor Cells as Diagnostic Biomarkers and Therapeutic Targets

Immune modulation is a hallmark of cancer. Cancer-immune interaction shapes the course of disease progression at every step of tumorigenesis, including metastasis, of which circulating tumor cells (CTCs) are regarded as an indicator. These CTCs are a heterogeneous population of tumor cells that have disseminated from the tumor into circulation. They have been increasingly studied in recent years due to their importance in diagnosis, prognosis, and monitoring of treatment response. Ample evidence demonstrates that CTCs interact with immune cells in circulation, where they must evade immune surveillance or modulate immune response. The interaction between CTCs and the immune system is emerging as a critical point by which CTCs facilitate metastatic progression. Understanding the complex crosstalk between the two may provide a basis for devising new diagnostic and treatment strategies. In this review, we will discuss the current understanding of CTCs and the complex immune-CTC interactions. We also present novel options in clinical interventions, targeting the immune-CTC interfaces, and provide some suggestions on future research directions.

Advance of microfluidic constriction channel system of measuring single-cell cortical tension/specific capacitance of membrane and conductivity of cytoplasm

This paper reported a microfluidic platform which realized the characterization of inherent single-cell biomechanical and bioelectrical parameters simultaneously. Individual cells traveled through a constriction channel with deformation images and impedance variations captured and processed into cortical tension T_c , specific membrane capacitance C_sm , and cytoplasmic conductivity σ_cy based on an equivalent biophysical model. These properties of thousands of individual cells of K562, Jurkat, HL-60, HL-60 treated with paraformaldehyde (PA)/cytochalasin D (CD)/concanavalin A (ConA), granulocytes of Donor 1, Donor 2, and Donor 3 were quantified for the first time. Leveraging T_c , C_sm , and σ_cy , (1) high accuracies of classifying wild-type and processed HL-60 cells (e.g., 93.5% of PA treated vs. CD treated HL-60 cells) were realized, revealing the effectiveness of using these three biophysical parameters in cell-type classification; (2) low accuracies of classifying normal granulocytes from three donors (e.g., 56.4% of Donor 1 vs. 2), indicating comparable parameters for normal granulocytes. In conclusion, this platform can characterize single-cell T_c , C_sm , and σ_cy concurrently and quantify multiple parameters in single-cell analysis.

State-of-the-arts techniques and current evolving approaches in the separation and detection of circulating tumor cell

Circulating tumor cells (CTCs) are cancer cells that shed from the primary tumor and then enter the circulatory system, a small part of which may evolve into metastatic cancer under appropriate microenvironment conditions. The detection of CTCs is a truly noninvasive, dynamic monitor for disease changes, which has considerable clinical implications in the selection of targeted drugs. However, their inherent rarity and heterogeneity pose significant challenges to their isolation and detection. Even the "gold standard", CellSearch™, suffers from high expenses, low capture efficiency, and the consumption of time. With the advancement of CTCs analysis technologies in recent years, the yield and efficiency of CTCs enrichment have gradually been improved, as well as detection sensitivity. In this review, the isolation and detection strategies of CTCs have been completely described and the potential directions for future research and development have also been highlighted through analyzing the challenges faced by current strategies.

Progress and application of circulating tumor cells in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) has the highest morbidity and mortality worldwide among malignant tumors. NSCLC is a great threat to health and well-being. Biopsy is the gold standard to diagnose lung cancer, but traditional biopsy methods cannot fully reflect the true condition of tumors. There is growing evidence that a single-point biopsy fails to reveal the complete landscape of the tumor due to intratumor heterogeneity, but it is impractical to complete multiple biopsies that are separated both spatially and temporally. Liquid biopsy heralds that a new era is coming. Circulating tumor cells (CTCs) are tumor cells that circulate in the peripheral blood after being shed from primary or metastatic tumors. CTCs constitute a considerable portion of a liquid biopsy, which contributes to the diagnosis, assessment of prognosis, and therapy of NSCLC. Herein, this review discusses the technologies for detection and enrichment of CTCs as well as clinical applications involving CTCs.

Circulating Tumor Cells: Technologies and Their Clinical Potential in Cancer Metastasis

Circulating tumor cells (CTCs) are single cells or clusters of cells within the circulatory system of a cancer patient. While most CTCs will perish, a small proportion will proceed to colonize the metastatic niche. The clinical importance of CTCs was reaffirmed by the 2008 FDA approval of CellSearch^®, a platform that could extract EpCAM-positive, CD45-negative cells from whole blood samples. Many further studies have demonstrated the presence of CTCs to stratify patients based on overall and progression-free survival, among other clinical indices. Given their unique role in metastasis, CTCs could also offer a glimpse into the genetic drivers of metastasis. Investigation of CTCs has already led to groundbreaking discoveries such as receptor switching between primary tumors and metastatic nodules in breast cancer, which could greatly affect disease management, as well as CTC-immune cell interactions that enhance colonization. In this review, we will highlight the growing variety of isolation techniques for investigating CTCs. Next, we will provide clinically relevant context for CTCs, discussing key clinical trials involving CTCs. Finally, we will provide insight into the future of CTC studies and some questions that CTCs are primed to answer.

Flow of Non-Newtonian Fluids in a Single-Cavity Microchannel

Having a basic understanding of non-Newtonian fluid flow through porous media, which usually consist of series of expansions and contractions, is of importance for enhanced oil recovery, groundwater remediation, microfluidic particle manipulation, etc. The flow in contraction and/or expansion microchannel is unbounded in the primary direction and has been widely studied before. In contrast, there has been very little work on the understanding of such flow in an expansion-contraction microchannel with a confined cavity. We investigate the flow of five types of non-Newtonian fluids with distinct rheological properties and water through a planar single-cavity microchannel. All fluids are tested in a similarly wide range of flow rates, from which the observed flow regimes and vortex development are summarized in the same dimensionless parameter spaces for a unified understanding of the effects of fluid inertia, shear thinning, and elasticity as well as confinement. Our results indicate that fluid inertia is responsible for developing vortices in the expansion flow, which is trivially affected by the confinement. Fluid shear thinning causes flow separations on the contraction walls, and the interplay between the effects of shear thinning and inertia is dictated by the confinement. Fluid elasticity introduces instability and asymmetry to the contraction flow of polymers with long chains while suppressing the fluid inertia-induced expansion flow vortices. However, the formation and fluctuation of such elasto-inertial fluid vortices exhibit strong digressions from the unconfined flow pattern in a contraction-expansion microchannel of similar dimensions.

Inertial microfluidics in contraction-expansion microchannels: A review

Inertial microfluidics has brought enormous changes in the conventional cell/particle detection process and now become the main trend of sample pretreatment with outstanding throughput, low cost, and simple control method. However, inertial microfluidics in a straight microchannel is not enough to provide high efficiency and satisfying performance for cell/particle separation. A contraction-expansion microchannel is a widely used and multifunctional channel pattern involving inertial microfluidics, secondary flow, and the vortex in the chamber. The strengthened inertial microfluidics can help us to focus particles with a shorter channel length and less processing time. Both the vortex in the chamber and the secondary flow in the main channel can trap the target particles or separate particles based on their sizes more precisely. The contraction-expansion microchannels are also capable of combining with a curved, spiral, or serpentine channel to further improve the separation performance. Some recent studies have focused on the viscoelastic fluid that utilizes both elastic forces and inertial forces to separate different size particles precisely with a relatively low flow rate for the vulnerable cells. This article comprehensively reviews various contraction-expansion microchannels with Newtonian and viscoelastic fluids for particle focusing, separation, and microfluid mixing and provides particle manipulation performance data analysis for the contraction-expansion microchannel design.

A weak shear stress microfluidic device based on Viscoelastic Stagnant Region (VSR) for biosensitive particle capture

Particle manipulation in microfluidic devices is of great significance in biological research. However, currently available inertial capture methods require relatively high flow rates, which will cause damage to biological particles, especially for single-celled organisms that are sensitive to environments. Herein, we demonstrate a label-free, size-based, low shear stress manipulation method using the Viscoelastic Stagnant Region (VSR) to capture sensitive bioparticles. This method uses the deformation of molecular chains in the polymer solution which can generate elastic stresses to form vortices which is called VSR because of the extremely low velocity in the contraction-expansion array (CEA) microchannel. Formation and evolution of VSR was observed experimentally using the Micro-PIV system in polyethylene oxide (PEO) solutions with different concentrations. On this basis, 20 μm and 5 μm polystyrene (PS) particles were confined to a certain area in the microchamber and the trajectory of particles motion in VSR was observed. Both the inertial lift force and the viscoelastic force are affected by the particle size, so the method also presented size selectivity. By quantitatively studying the velocity distribution of the particles on the orbit of motion, it was found that the maximum velocity of the particles in the VSR was about 0.02 m s^-1, which is only about 1/100 of that in inertial vortices. Moreover, the spiral motion of particles captured by VSR with variable trajectories was first observed, which is different from the equilibrium orbit in inertial vortices and can provide more motion paths for the particles. This method was further applied to the research of Crypthecodinium cohnii (C. cohnii), which is vulnerable but has high nutritious value. We found that the activity of the C. cohnii decreased slightly after being processed by VSR, but was lost after being processed by the inertial vortices. This research, as a simple and low shear stress particle manipulation method, will provide useful guidance for the manipulation, capture and separation of sensitive biological cells under higher biocompatibility, which is of great significance for the study of cellular and molecular biology.

Rapid isolation of circulating cancer associated fibroblasts by acoustic microstreaming for assessing metastatic propensity of breast cancer patients

We demonstrate a label free and high-throughput microbubble-based acoustic microstreaming technique to isolate rare circulating cells such as circulating cancer associated fibroblasts (cCAFs) in addition to circulating tumor cells (CTCs) and immune cells (i.e. leukocytes) from clinically diagnosed patients with a capture efficiency of 94% while preserving cell functional integrity within 8 minutes. The microfluidic device is self-pumping and was optimized to increase flow rate and achieve near perfect capturing of rare cells enabled by having a trapping capacity above the acoustic vortex saturation concentration threshold. Our approach enables rapid isolation of CTCs, cCAFs and their associated clusters from blood samples of cancer patients at different stages. By examining the combined role of cCAFs and CTCs in early cancer onset and metastasis progression, the device accurately diagnoses both cancer and the metastatic propensity of breast cancer patients. This was confirmed by flow cytometry where we observed that metastatic breast cancer blood samples had significantly higher percentage of exhausted CD8+ T cells expressing programmed cell death protein 1 (PD1), higher number of CD4+ T regulatory cells and T helper cells. We show for the first time that our lateral cavity acoustic transducers (LCATs)-based approach can thus be developed into a metastatic propensity assay for clinical usage by elucidating cancer immunological responses and the complex relationships between CTCs and its companion tumor microenvironment.

Inertial Microfluidics Enabling Clinical Research

Fast and accurate interrogation of complex samples containing diseased cells or pathogens is important to make informed decisions on clinical and public health issues. Inertial microfluidics has been increasingly employed for such investigations to isolate target bioparticles from liquid samples with size and/or deformability-based manipulation. This phenomenon is especially useful for the clinic, owing to its rapid, label-free nature of target enrichment that enables further downstream assays. Inertial microfluidics leverages the principle of inertial focusing, which relies on the balance of inertial and viscous forces on particles to align them into size-dependent laminar streamlines. Several distinct microfluidic channel geometries (e.g., straight, curved, spiral, contraction-expansion array) have been optimized to achieve inertial focusing for a variety of purposes, including particle purification and enrichment, solution exchange, and particle alignment for on-chip assays. In this review, we will discuss how inertial microfluidics technology has contributed to improving accuracy of various assays to provide clinically relevant information. This comprehensive review expands upon studies examining both endogenous and exogenous targets from real-world samples, highlights notable hybrid devices with dual functions, and comments on the evolving outlook of the field.

A constriction channel analysis of astrocytoma stiffness and disease progression

Studies have demonstrated that cancer cells tend to have reduced stiffness (Young's modulus) compared to their healthy counterparts. The mechanical properties of primary brain cancer cells, however, have remained largely unstudied. To investigate whether the stiffness of primary brain cancer cells decreases as malignancy increases, we used a microfluidic constriction channel device to deform healthy astrocytes and astrocytoma cells of grade II, III, and IV and measured the entry time, transit time, and elongation. Calculating cell stiffness directly from the experimental measurements is not possible. To overcome this challenge, finite element simulations of the cell entry into the constriction channel were used to train a neural network to calculate the stiffness of the analyzed cells based on their experimentally measured diameter, entry time, and elongation in the channel. Our study provides the first calculation of stiffness for grades II and III astrocytoma and is the first to apply a neural network analysis to determine cell mechanical properties from a constriction channel device. Our results suggest that the stiffness of astrocytoma cells is not well-correlated with the cell grade. Furthermore, while other non-central-nervous-system cell types typically show reduced stiffness of malignant cells, we found that most astrocytoma cell lines had increased stiffness compared to healthy astrocytes, with lower-grade astrocytoma having higher stiffness values than grade IV glioblastoma. Differences in nucleus-to-cytoplasm ratio only partly explain differences in stiffness values. Although our study does have limitations, our results do not show a strong correlation of stiffness with cell grade, suggesting that other factors may play important roles in determining the invasive capability of astrocytoma. Future studies are warranted to further elucidate the mechanical properties of astrocytoma across various pathological grades.

Coarse Raman and optical diffraction tomographic imaging enable label-free phenotyping of isogenic breast cancer cells of varying metastatic potential

Identification of the metastatic potential represents one of the most important tasks for molecular imaging of cancer. While molecular imaging of metastases has witnessed substantial progress as an area of clinical inquiry, determining precisely what differentiates the metastatic phenotype has proven to be more elusive. In this study, we utilize both the morphological and molecular information provided by 3D optical diffraction tomography and Raman spectroscopy, respectively, to propose a label-free route for optical phenotyping of cancer cells at single-cell resolution. By using an isogenic panel of cell lines derived from MDA-MB-231 breast cancer cells that vary in their metastatic potential, we show that 3D refractive index tomograms can capture subtle morphological differences among the parental, circulating tumor cells, and lung metastatic cells. By leveraging its molecular specificity, we demonstrate that coarse Raman microscopy is capable of rapidly mapping a sufficient number of cells for training a random forest classifier that can accurately predict the metastatic potential of cells at a single-cell level. We also perform multivariate curve resolution alternating least squares decomposition of the spectral dataset to demarcate spectra from cytoplasm and nucleus, and test the feasibility of identifying metastatic phenotypes using the spectra only from the cytoplasmic and nuclear regions. Overall, our study provides a rationale for employing coarse Raman mapping to substantially reduce measurement time thereby enabling the acquisition of reasonably large training datasets that hold the key for label-free single-cell analysis and, consequently, for differentiation of indolent from aggressive phenotypes.

Engineering confining microenvironment for studying cancer metastasis

The physical microenvironment of cells plays a fundamental role in regulating cellular behavior and cell fate, especially in the context of cancer metastasis. For example, capillary deformation can destroy arrested circulating tumor cells while the dense extracellular matrix can form a physical barrier for invading cancer cells. Understanding how metastatic cancer cells overcome the challenges brought forth by physical confinement can help in developing better therapeutics that can put a stop to this migratory stage of the metastatic cascade. Numerous in vivo and in vitro assays have been developed to recapitulate the metastatic processes and study cancer cell migration in a confining microenvironment. In this review, we summarize some of the representative techniques and the exciting new findings. We critically review the advantages, as well as challenges associated with these tools and methodologies, and provide a guide on the applications that they are most suited for. We hope future efforts that push forward our current understanding on metastasis under confinement can lead to novel and more effective diagnostic and therapeutic strategies against this dreaded disease.

Microfluidic detection of human diseases: From liquid biopsy to COVID-19 diagnosis

Microfluidic devices can be thought of as comprising interconnected miniaturized compartments performing multiple experimental tasks individually or in parallel in an integrated fashion. Due to its small size, portability, and low cost, attempts have been made to incorporate detection assays into microfluidic platforms for diseases such as cancer and infection. Some of these technologies have served as point-of-care and sample-to-answer devices. The methods for detecting biomarkers in different diseases usually share similar principles and can conveniently be adapted to cope with arising health challenges. The COVID-19 pandemic is one such challenge that is testing the performance of both our conventional and newly-developed disease diagnostic technologies. In this mini-review, we will first look at the progress made in the past few years in applying microfluidics for liquid biopsy and infectious disease detection. Following that, we will use the current pandemic as an example to discuss how such technological advancements can help in the current health challenge and better prepare us for future ones.

Biostable Double-Strand Circular Aptamers Conjugated Onto Dendrimers for Specific Capture and Inhibition of Circulating Leukemia Cells

Background/Objective

Circulating tumor cells (CTCs) are known as the root of cancer metastasis. Capture and inhibition of CTCs may prevent metastasis. Due to the rarity of CTCs in vivo, the current technology about CTCs capture is still challenging. The aim of our study was to conjugate the enhanced biostable double-strand (ds) circular aptamer (dApR) with dendrimers for capturing and restraining CTCs in vitro and in vivo.

Methods

CEM-targeting aptamer (Ap) was looped by ligation after phosphorylation to form circular ds aptamer dApR, which was then conjugated to dendrimers by biotin-streptavidin affinity reaction and named as G-dApR. The physicochemical properties of G-dApR were characterized by using PAGE gel electrophoresis, UV, DLS, AFM, fluorophotometer and laser confocal microscope. Biostability of G-dApR was also analyzed by gel electrophoresis. Confocal microscopy and flow cytometry were then performed to determine the binding specificity of G-dApR to CEM cells and the captured CTCs in mice and in human blood. Apoptosis of the captured cells was finally evaluated by using MTT assay, DAPI staining, AO/EB staining, cell cycle analysis and Annexin V-FITC/PI staining.

Results

Physicochemical characterization demonstrated the entity of dApR and G-dApR, and the nano-size of G-dApR (about 180 nm in aqueous phase). G-dApR exhibited the excellent biostability that confers their resistance to nuclease-mediated biodegradation in serum for at least 6 days. In our established CTCs model, we found that G-dApR could specifically and sensitively capture CTCs not non-target cells even in the presence of millions of interfering cells (10⁸), in mice and in human blood. Finally, the activity of captured CTCs was significantly down-regulated by G-dApR, resulting in apoptosis.

Conclusion

We created the enhanced biostable dApR-coated dendrimers (G-dApR) that could specifically capture and restrain CTCs in vitro and in vivo for preventing CTC-mediated cancer metastasis.

Evaluation of the Significance of Constant Laser Therapy, 532 nm, in Various Exposure Times on the Healing Process of Wounds Infected by Acinetobacter baumannii

Many considerable investigations focused on the stimulation of therapeutic manners of infected injuries in mice. The exaggerated pathogens that induced wounds were gram-positive like staphylococcal and gram-negative, for example, Pseudomonas aeuroginosa and Acinetobacter baumannii. Acinetobacter can generate a scale range of an infection that may be received in a hospital or any wellness concern facility. In order to know the significance of laser 532 nm with a constant irradiance at various exposure times on the healing process of wounds infected by Acinetobacter baumannii, this study was performed on the BALB/C mice. An elliptical full-thickness skin injury was made on the backside of 45 adult female (BALB/C) mice. Injuries were affected via Acinetobacter baumannii and were randomly assigned into 3 groups. Semiconductor diode continuous wave laser, λ = 532 nm, with output power 40 mW was used. The power density was 5.71 mW/cm², while the fluencies were 1.7 J/cm² and 5.14 J/cm². Fifteen mice were classified according to the times of irradiation. The first group was infected and presented as control, without irradiation. The second group was infected and irradiated for 5 minutes. The third group, likewise, was infected but irradiated for 15 minutes. All groups were subdivided according to the following period, 3, 5, and 10 days, after irradiation and the animals were killed after the treatment. Wound healing was made by measuring the rate of wound closure and histopathological evaluation. The study determined that 532 nm laser therapy had an obvious and positive influence on the healing of infected wounds with fluence (5.14 J/cm²).

Single Cell Mechanotype and Associated Molecular Changes in Urothelial Cell Transformation and Progression

Cancer cell mechanotype changes are newly recognized cancer phenotypic events, whereas metastatic cancer cells show decreased cell stiffness and increased deformability relative to normal cells. To further examine how cell mechanotype changes in early stages of cancer transformation and progression, an in vitro multi-step human urothelial cell carcinogenic model was used to measure cellular Young's modulus, deformability, and transit time using single-cell atomic force microscopy, microfluidic-based deformability cytometry, and quantitative deformability cytometry, respectively. Measurable cell mechanotype changes of stiffness, deformability, and cell transit time occur early in the transformation process. As cells progress from normal, to preinvasive, to invasive cells, Young's modulus of stiffness decreases and deformability increases gradually. These changes were confirmed in three-dimensional cultured microtumor masses and urine exfoliated cells directly from patients. Using gene screening and proteomics approaches, we found that the main molecular pathway implicated in cell mechanotype changes appears to be epithelial to mesenchymal transition.

A Multifunctional Platform for the Capture, Release, And Enumeration of Circulating Tumor Cells Based on Aptamer Binding, Nicking Endonuclease-Assisted Amplification, And Inductively Coupled Plasma Mass Spectrometry Detection

Inductively coupled plasma mass spectrometry (ICP-MS) combined with element tags has been well designed and extensively applied in cell enumeration. It possesses superior quantitative capability, strong resistance to matrix interference, multiplex detection capability but destructive characteristic. Herein, we constructed an ICP-MS based multifunctional platform for capture, nondestructive enumeration, and release of circulating tumor cells (CTCs). Aptamer on capture probe recognized Mucin 1 (MUC1) on membrane of MCF-7 cells specifically, thus the cells were captured by probe and the Initiator originally hybridized with Aptamer was substituted by MUC1 and released into solution. Then the released Initiator was separated from the captured cells and hybridized with Tb labeled Substrate on detection probe to release a large amount of nicked Tb fragments through the nicking endonuclease assisted amplification for subsequent ICP-MS detection. Meanwhile, cells captured by probe were released by nuclease digestion for further reculture. Such a strategy effectively avoids CTCs destruction resulted from ICP-MS enumeration, increases the detection sensitivity of ICP-MS by involving nicking endonuclease assisted amplification, and realizes cell recovery for further analysis. A limit of detection of 87 MCF-7 cells and a linear range of 250-10 000 MCF-7 cells were realized for ICP-MS enumeration. A cell recovery of 52.7% (with capture and release efficiency of 63.9 and 82.5%, respectively) and a viability of 74.3% were obtained, meanwhile the released cells exhibited strong proliferation ability. This multifunctional platform for CTCs capture, enumeration, and release has great applicable potential in early diagnosis and individual treatment for cancer.

Microfluidic-Based Approaches in Targeted Cell/Particle Separation Based on Physical Properties: Fundamentals and Applications

Cell separation is a key step in many biomedical research areas including biotechnology, cancer research, regenerative medicine, and drug discovery. While conventional cell sorting approaches have led to high-efficiency sorting by exploiting the cell's specific properties, microfluidics has shown great promise in cell separation by exploiting different physical principles and using different properties of the cells. In particular, label-free cell separation techniques are highly recommended to minimize cell damage and avoid costly and labor-intensive steps of labeling molecular signatures of cells. In general, microfluidic-based cell sorting approaches can separate cells using "intrinsic" (e.g., fluid dynamic forces) versus "extrinsic" external forces (e.g., magnetic, electric field, etc.) and by using different properties of cells including size, density, deformability, shape, as well as electrical, magnetic, and compressibility/acoustic properties to select target cells from a heterogeneous cell population. In this work, principles and applications of the most commonly used label-free microfluidic-based cell separation methods are described. In particular, applications of microfluidic methods for the separation of circulating tumor cells, blood cells, immune cells, stem cells, and other biological cells are summarized. Computational approaches complementing such microfluidic methods are also explained. Finally, challenges and perspectives to further develop microfluidic-based cell separation methods are discussed.

EMT-Associated Heterogeneity in Circulating Tumor Cells: Sticky Friends on the Road to Metastasis

Epithelial-mesenchymal transitions (EMTs) generate hybrid phenotypes with an enhanced ability to adapt to diverse microenvironments encountered during the metastatic spread. Accordingly, EMTs play a crucial role in the biology of circulating tumor cells (CTCs) and contribute to their heterogeneity. Here, we review major EMT-driven properties that may help hybrid Epithelial/Mesenchymal CTCs to survive in the bloodstream and accomplish early phases of metastatic colonization. We then discuss how interrogating EMT in CTCs as a companion biomarker could help refine cancer patient management, further supporting the relevance of CTCs in personalized medicine.

Genome‑wide copy number analysis of circulating tumor cells in breast cancer patients with liver metastasis

The genome‑wide copy number analysis of circulating tumor cells (CTCs) provides a promising prognostic biomarker for survival in breast cancer liver metastasis (BCLM) patients. The present study aimed to confirm the prognostic value of the presence of CTCs in BCLM patients. We previously developed an assay for the genome‑wide pattern differences in copy number variations (CNVs) as an adjunct test for the routine imaging and histopathologic diagnosis methods to distinguish newly diagnosed liver metastases and recurrent liver metastases. Forty‑three breast cancer patients were selected for this study in which 23 newly diagnosed and 20 recurrent liver metastases were diagnosed by histopathology and 18F‑FDG PET/CT imaging. CTCs were counted from all patients using the CellSearch system and were confirmed by cytomorphology and three‑color immunocytochemistry. Genomic DNA of single CTCs was amplified using multiple annealing and looping based amplification cycles (MALBAC). Then, we compared the CTC numbers of newly diagnosed and recurrent BCLM patients using Illumina platforms. A high CTC frequency (>15 CTCs/7.5 ml blood) was found to be correlated with disease severity and metastatic progression, which suggests the value for CTCs in the diagnosis of BCLM in comparison with pathohistology and PET/CT imaging (P>0.05). Moreover, CTCs isolated from BCLM patients remained an independent prognostic detection factor associated with overall survival (P=0.0041). Comparison between newly diagnosed and recurrent liver metastases revealed different frequencies of CNVs (P>0.05). Notably, the CNV pattern of isolated CTCs of recurrent BCLM patients was similar to recurrent liver metastases (nearly 82% of the gain/loss regions). Functional enrichment analysis identified 25 genes as a CNV signature of BCLM. Among them, were defensin and β‑defensin genes, which are significantly associated with anti‑angiogenesis and immunomodulation signaling pathways. High CTC frequencies are effective in the evaluation and differentiation between newly diagnosed liver metastases from recurrent liver metastases. Future clinical studies will be necessary to fully determine the prognostic potential of CTC cluster signatures in patients with BCLM.

Non-contact microfluidic mechanical property measurements of single apoptotic bodies

BACKGROUND

Cells exchange information by secreting micro- and nanosized extracellular vesicles (EVs), ranging from exosomes (30-100 nm) to apoptotic bodies (ABs, 1-5 μm). There is still much to understand about fundamental EV biological, physical, and chemical properties before clinical applications can be developed. EV mechanical properties have only been measured with atomic force microscopy (AFM) with its problematic adhesion and hard substrate effects. To understand EV mechanical behavior in less extreme mechanical conditions relevant to blood flow and many soft tissue environments, a non-contact measurement technique is needed.

METHODS

We measured the mechanical properties of single microscale ABs derived from human blood plasma using non-contact microfluidics. EVs were gently stretched in extensional flow, similar to a traditional tensile test, and a linear mechanical model was applied to estimate mechanical stiffnesses from the observed stretching.

RESULTS

The effective shear elastic modulus of ABs in non-contact flow conditions is approximately 5.6 ± 0.5 Pa, 7 orders of magnitude lower than previously reported AFM-measured biological exosome stiffnesses and 200 times smaller than suspended cells.

CONCLUSIONS

Apoptotic bodies are very soft in fluid environments and exhibit lower effective stiffnesses than suspended cells. By measuring ABs in a natural fluid environment and low-force regime without hard probes and surfaces, we achieved closer agreement with linear mechanical theory and therefore more accurate stiffness measurements.

GENERAL SIGNIFICANCE

AFM manufacturers and users should consider implementing new mechanical models to interpret AFM force indentation curves so that accurate extracellular vesicle mechanical properties can be extracted.

Liquid Biopsy in Colorectal Carcinoma: Clinical Applications and Challenges

Colorectal carcinoma (CRC) is characterized by wide intratumor heterogeneity with general genomic instability and there is a need for improved diagnostic, prognostic, and therapeutic tools. The liquid biopsy provides a noninvasive route of sample collection for analysis of circulating tumor cells (CTCs) and genomic material, including cell-free DNA (cfDNA), as a complementary biopsy to the solid tumor tissue. The solid biopsy is critical for molecular characterization and diagnosis at the time of collection. The liquid biopsy has the advantage of longitudinal molecular characterization of the disease, which is crucial for precision medicine and patient-oriented treatment. In this review, we provide an overview of CRC and the different methodologies for the detection of CTCs and cfDNA, followed by a discussion on the potential clinical utility of the liquid biopsy in CRC patient care, and lastly, current challenges in the field.

Microfluidic applications on circulating tumor cell isolation and biomimicking of cancer metastasis

The prognosis of malignant tumors is challenged by insufficient means to effectively detect tumors at early stage. Liquid biopsy using circulating tumor cells (CTCs) as biomarkers demonstrates a promising solution to tackle the challenge, because CTCs play a critical role in cancer metastatic process via intravasation, circulation, extravasation, and formation of secondary tumor. However, the effectiveness of the solution is compromised by rarity, heterogeneity, and vulnerability associated with CTCs. Among a plethora of novel approaches for CTC isolation and enrichment, microfluidics leads to isolation and detection of CTCs in a cost-effective and operation-friendly way. Development of microfluidics also makes it feasible to model the cancer metastasis in vitro using a microfluidic system to mimick the in vivo microenvironment, thereby enabling analysis and monitor of tumor metastasis. This paper aims to review the latest advances for exploring the dual-roles microfluidics has played in early cancer diagnosis via CTC isolation and investigating the role of CTCs in cancer metastasis; the merits and drawbacks for dominating microfluidics-based CTC isolation methods are discussed; biomimicking cancer metastasis using microfluidics are presented with example applications on modelling of tumor microenvironment, tumor cell dissemination, tumor migration, and tumor angiogenesis. The future perspectives and challenges are discussed.

Applications of machine learning for simulations of red blood cells in microfluidic devices

Background

For optimization of microfluidic devices for the analysis of blood samples, it is useful to simulate blood cells as elastic objects in flow of blood plasma. In such numerical models, we primarily need to take into consideration the movement and behavior of the dominant component of the blood, the red blood cells. This can be done quite precisely in small channels and within a short timeframe. However, larger volumes or timescales require different approaches. Instead of simplifying the simulation, we use a neural network to predict the movement of the red blood cells.

Results

The neural network uses data from the numerical simulation for learning, however, the simulation needs only be run once. Alternatively, the data could come from video processing of a recording of a biological experiment. Afterwards, the network is able to predict the movement of the red blood cells because it is a system of bases that gives an approximate cell velocity at each point of the simulation channel as a linear combination of bases.In a simple box geometry, the neural network gives results comparable to predictions using fluid streamlines, however in a channel with obstacles forming slits, the neural network is about five times more accurate.The network can also be used as a discriminator between different situations. We observe about two-fold increase in mean relative error when a network trained on one geometry is used to predict trajectories in a modified geometry. Even larger increase was observed when it was used to predict trajectories of cells with different elastic properties.

Conclusions

While for uncomplicated box channels there is no advantage in using a system of bases instead of a simple prediction using fluid streamlines, in a more complicated geometry, the neural network is significantly more accurate. Another application of this system of bases is using it as a comparison tool for different modeled situations. This has a significant future potential when applied to processing data from videos of microfluidic flows.

Physical Biomarkers of Disease Progression: On-Chip Monitoring of Changes in Mechanobiology of Colorectal Cancer Cells

Disease can induce changes to subcellular components, altering cell phenotype and leading to measurable bulk-material mechanical properties. The mechanical phenotyping of single cells therefore offers many potential diagnostic applications. Cells are viscoelastic and their response to an applied stress is highly dependent on the magnitude and timescale of the actuation. Microfluidics can be used to measure cell deformability over a wide range of flow conditions, operating two distinct flow regimes (shear and inertial) which can expose subtle mechanical properties arising from subcellular components. Here, we investigate the deformability of three colorectal cancer (CRC) cell lines using a range of flow conditions. These cell lines offer a model for CRC metastatic progression; SW480 derived from primary adenocarcinoma, HT29 from a more advanced primary tumor and SW620 from lymph-node metastasis. HL60 (leukemia cells) were also studied as a model circulatory cell, offering a non-epithelial comparison. We demonstrate that microfluidic induced flow deformation can be used to robustly detect mechanical changes associated with CRC progression. We also show that single-cell multivariate analysis, utilising deformation and relaxation dynamics, offers potential to distinguish these different cell types. These results point to the benefit of multiparameter determination for improving detection and accuracy of disease stage diagnosis.

Insights into brain metastasis: Recent advances in circulating tumor cell research

Background

How tumor cells disseminate to brain and establish brain metastasis remains partly an unsolved problem. This devastating complication of many cancers is initiated by a rare subset of the circulating tumor cells (CTCs) shed into the blood stream. Thus, the profiling of the molecular properties in these brain metastasis‐initiating CTCs is essential to uncover the mechanisms underlying brain metastasis.

Recent Findings

Important efforts to improve the enrichment and detection of CTCs enabled the detailed molecular and functional analysis of CTCs that drive brain metastasis. In this review, we highlight key findings on existing preclinical studies that provide insights toward a comprehensive picture of brain metastasis‐precursors in CTCs and the potential clinical implications.

Conclusion

A deeper understanding of the brain metastasis precursors should help to stratify high‐risk patients and improve preventive therapeutic strategies. Although all these preclinical evidences have yet to be translated into patients, they provide considerable hope to benefit patients with brain metastases in the future.

Toward Microfluidic Label-Free Isolation and Enumeration of Circulating Tumor Cells from Blood Samples

The isolation, analysis, and enumeration of circulating tumor cells (CTCs) from cancer patient blood samples are a paradigm shift for cancer patient diagnosis, prognosis, and treatment monitoring. Most methods used to isolate and enumerate these target cells rely on the expression of cell surface markers, which varies between patients, cancer types, tumors, and stages. Here, we propose a label-free high-throughput platform to isolate, enumerate, and size CTCs on two coupled microfluidic devices. Cancer cells were purified through a Vortex chip and subsequently flowed in-line to an impedance chip, where a pair of electrodes measured fluctuations of an applied electric field generated by cells passing through. A proof-of-concept of the coupling of those two devices was demonstrated with beads and cells. First, the impedance chip was tested as a stand-alone device: (1) with beads (mean counting error of 1.0%, sizing information clearly separated three clusters for 8, 15, and 20 um beads, respectively) as well as (2) with cancer cells (mean counting error of 3.5%). Second, the combined setup was tested with beads, then with cells in phosphate-buffered saline, and finally with cancer cells spiked in healthy blood. Experiments demonstrated that the Vortex HT chip enriched the cancer cells, which then could be counted and differentiated from smaller blood cells by the impedance chip based on size information. Further discrimination was shown with dual high-frequency measurements using electric opacity, highlighting the potential application of this combined setup for a fully integrated label-free isolation and enumeration of CTCs from cancer patient samples. © 2019 International Society for Advancement of Cytometry.

Microfluidics for studying metastatic patterns of lung cancer

The incidence of lung cancer continues to rise worldwide. Because the aggressive metastasis of lung cancer cells is the major drawback of successful therapies, the crucial challenge of modern nanomedicine is to develop diagnostic tools to map the molecular mechanisms of metastasis in lung cancer patients. In recent years, microfluidic platforms have been given much attention as tools for novel point-of-care diagnostic, an important aspect being the reconstruction of the body organs and tissues mimicking the in vivo conditions in one simple microdevice. Herein, we present the first comprehensive overview of the microfluidic systems used as innovative tools in the studies of lung cancer metastasis including single cancer cell analysis, endothelial transmigration, distant niches migration and finally neoangiogenesis. The application of the microfluidic systems to study the intercellular crosstalk between lung cancer cells and surrounding tumor microenvironment and the connection with multiple molecular signals coming from the external cellular matrix are discussed. We also focus on recent breakthrough technologies regarding lab-on-chip devices that serve as tools for detecting circulating lung cancer cells. The superiority of microfluidic systems over traditional in vitro cell-based assays with regard to modern nanosafety studies and new cancer drug design and discovery is also addressed. Finally, the current progress and future challenges regarding printable and paper-based microfluidic devices for personalized nanomedicine are summarized.

Visual Quantitative Detection of Circulating Tumor Cells with Single-Cell Sensitivity Using a Portable Microfluidic Device

Immunocytological technologies, molecular technologies, and functional assays are widely used for detecting circulating tumor cells (CTCs) after enrichment from patients' blood sample. Unfortunately, accessibility to these technologies is limited due to the need for sophisticated instrumentation and skilled operators. Portable microfluidic devices have become attractive tools for expanding the access and efficiency of detection beyond hospitals to sites near the patient. Herein, a volumetric bar chart chip (V-Chip) is developed as a portable platform for CTC detection. The target CTCs are labeled with aptamer-conjugated nanoparticles (ACNPs) and analyzed by V-Chip through quantifying the byproduct (oxygen) of the catalytic reaction between ACNPs and hydrogen peroxide, which results in the movement of an ink bar to a concentration-dependent distance for visual quantitative readout. Thus, the CTC number is decoded into visually quantifiable information and a linear correlation can be found between the distance moved by the ink and number of cells in the sample. This method is sensitive enough that a single cell can be detected. Furthermore, the clinical capabilities of this system are demonstrated for quantitative CTC detection in the presence of a high leukocyte background. This portable detection method shows great potential for quantification of rare cells with single-cell sensitivity for various applications.

Cells Under Stress: An Inertial-Shear Microfluidic Determination of Cell Behavior

The deformability of a cell is the direct result of a complex interplay between the different constituent elements at the subcellular level, coupling a wide range of mechanical responses at different length scales. Changes to the structure of these components can also alter cell phenotype, which points to the critical importance of cell mechanoresponse for diagnostic applications. The response to mechanical stress depends strongly on the forces experienced by the cell. Here, we use cell deformability in both shear-dominant and inertia-dominant microfluidic flow regimes to probe different aspects of the cell structure. In the inertial regime, we follow cellular response from (visco-)elastic through plastic deformation to cell structural failure and show a significant drop in cell viability for shear stresses >11.8 kN/m2. Comparatively, a shear-dominant regime requires lower applied stresses to achieve higher cell strains. From this regime, deformation traces as a function of time contain a rich source of information including maximal strain, elastic modulus, and cell relaxation times and thus provide a number of markers for distinguishing cell types and potential disease progression. These results emphasize the benefit of multiple parameter determination for improving detection and will ultimately lead to improved accuracy for diagnosis. We present results for leukemia cells (HL60) as a model circulatory cell as well as for a colorectal cancer cell line, SW480, derived from primary adenocarcinoma (Dukes stage B). SW480 were also treated with the actin-disrupting drug latrunculin A to test the sensitivity of flow regimes to the cytoskeleton. We show that the shear regime is more sensitive to cytoskeletal changes and that large strains in the inertial regime cannot resolve changes to the actin cytoskeleton.

Size Distribution Analysis with On-Chip Multi-Imaging Cell Sorter for Unlabeled Identification of Circulating Tumor Cells in Blood

We report a change of the imaging biomarker distribution of circulating tumor cell (CTC) clusters in blood over time using an on-chip multi-imaging flow cytometry system, which can obtain morphometric parameters of cells and those clusters, such as cell number, perimeter, total cross-sectional area, aspect ratio, number of nuclei, and size of nuclei, as "imaging biomarkers". Both bright-field (BF) and fluorescent (FL) images were acquired at 200 frames per second and analyzed within the intervals for real-time cell sorting. A green fluorescent protein-transfected prostate cancer cell line (MAT-LyLu-GFP) was implanted into Copenhagen rats, and the blood samples of these rats were collected 2 to 11 days later and measured using the system. The results showed that cells having BF area of 90 μm² or larger increased in number seven days after the cancer cell implantation, which was specifically detected as a shift of the cell size distribution for blood samples of implanted rats, in comparison with that for control blood. All cells with BF area of 150 μm² or larger were arranged in cell clusters composed of at least two cells, as confirmed by FL nucleus number and area measurements, and they constituted more than 1% of all white blood cells. These results indicate that the mapping of cell size distribution is useful for identifying an increase of irregular cells such as cell clusters in blood, and show that CTC clusters become more abundant in blood over time after malignant tumor formation. The results also reveal that a blood sample of only 50 μL is sufficient to acquire a stable size distribution map of all blood cells to predict the presence of CTC clusters.