Research

The overarching goal of our research is the development of new technologies for medical research and treatment. Our work is enabled by advances in fabrication, measurement, and computation across a wide range of domains and length scales. Our core capabilities include microfabrication, microfluidics, instrumentation, product development, and data analytics and visualization. Current research areas include 1) the development of new technologies for cell sorting, cell biomechanics, single cell sequencing, chemotaxis, and drug screening; as well as 2) the application of these technologies to study circulating tumor cells, personalize cancer therapies, evaluate blood quality, and expedite antimalarial drug development.

Microfluidic Ratchet for Deformability based Cell Sorting

One of the most interesting and frustrating characteristics of low-Reynolds number flow is its kinematic reversibility, which prevents efficient mixing of reagents and constrains particles along streamlines of its carrier fluid. This characteristic is particular problematic for cell separation where discriminating properties of target cells must be translated into forces that must act against overwhelmingly large viscous forces imposed by the carrier fluid. To overcome this problem and enable highly selective cell separation, we developed the microfluidic ratchet mechanism that enables selective cells to overcome kinematic reversibility of its carrier fluid based on the deformation of single cells through micrometer-scale funnel constrictions where the opening at one end is larger than the diameter of cells, while the opening at the opposing end is smaller than the diameter of the cell. Deforming cells along the direction of taper requires less force than against the direction of taper. Therefore, an oscillatory flow through such a constriction enables selective unidirectional transport of cells based on a combination of size and deformability. The oscillatory flow simultaneously prevents cells from accumulating and adsorbing onto the funnel microstructures that would normally degrade the selectivity of other filtration-based cell separation systems. This mechanism enables deformability based cell separation of high-density cell samples (e.g. whole blood) with significantly improved selectivity over previous methods.

Relevant Publications

Guo Q, Duffy SP, Matthews K, Deng X, Santoso AT, Islamzada E, Ma H, Deformability based Sorting of Red Blood Cells Improves Diagnostic Sensitivity for Malaria Caused by Plasmodium Falciparum, Lab on a Chip (Communication), 16, 645-654, 2016. (PMID: 26768227) [pdf]

McFaul SM, Lin BK, Ma H, Cell separation based on size and deformability using microfluidic funnel ratchets, Lab on a Chip, 12 (13), 2369-2376, 2012. (PMID: 22517056[pdf]

Guo Q, McFaul SM, Ma H, Deterministic Microfluidic Ratchet Based on the Deformation of Individual Cells, Physical Review E, 83, 051910, 2011. [pdf]

Separation and Analysis of Circulating Tumor Cells

Circulating tumor cells (CTCs) are malignant cells shed into the bloodstream where they have the potential to establish metastases in anatomically distant tissues. The capture and enumeration of CTCs has gathered considerable attention because of the potential to use the number and status of these cells (1) as a prognostic marker for tailoring therapies to the needs of individual cancer patients, (2) as a rapid surrogate for evaluating the clinical benefit of new drugs, and (3) as a fluid biopsy of a particularly invasive subpopulation of the original solid tumor. The key challenge in working with CTCs has been their extreme rarity. Existing technologies overcome this problem by first enriching the concentration of CTCs by using the cell surface maker, EpCAM to select for cells with epithelial characteristics. The effectiveness of this selection technique has come into question since one of the key steps of invasion and metastasis is epithelial-to-mesenchymal transition where tumor cells initiate a phenotype switch that is accompanied by a loss of epithelial antigens (e.g. EpCAM). As a result, the aggressively metastatic CTCs are actually the most likely group to evade capture by current methods.

Based on microfluidic cell separation technologies developed by our group, we are developing mechanical means to enrich for CTCs from the blood of cancer patients. CTCs released from solid tumors are mechanically distinct from hematological cells. Our microfluidic device is designed to separate cells based on differences in cell size and cell rigidity with a high degree of selectivity. Our hypothesis is that after this mechanical selection step, the concentration of CTCs is sufficiently enriched to be identified and analyzed using various low-throughput methods. Key advantages of this approach over existing methods are the preservation of relevant CTCs that may have lost their expression for EpCAM due to epithelial-to-mesenchymal transition and the recovery of live CTCs.

Relevant Publications

Park ES, Jin C, Guo Q, Ang RR, Duffy SP, Matthews K, Azad A, Abdi H, Todenhöfer T, Chi KN, Black PC, Ma H, Continuous Flow Deformability-Based Separation of Circulating Tumor Cells Using Microfluidic Ratchets, Small, 12(14), 1909-1919, 2016. (PMID: 26917414) [pdf]

Todenhöfer T, Park S, Jin C, Ang RR, Duffy SP, Matthews K, Abdi H, Ma H, Black PC, Microfluidic enrichment of circulating tumor cells in patients with clinically localized prostate cancer, Urologic Oncology, 16, 30121, 2016. (PMID: 27658563)

Park S, Ang RR, Bazov J, Chi KN, Black PC, Ma H, Morphological Differences Between Circulating Tumour Cells from Prostate Cancer Patients and Cultured Prostate Cancer Cells, PLoS ONE, 9(1), e85264, 2014. (PMID: 24416373) [Link to Article] [pdf]

Fluidic Plunger Mechanism for Cell Deformability Characterization

The deformability of single cells has been extensively studied and recognized as a potential biomarker for the status of various diseases (e.g. cancer and malaria), as well as their response to treatment. Existing methods in for measuring cell deformability, such as micropipette aspiration and ektacytometry, involve complex processes that require sophisticated equipment and skilled personnel. In order enable sensitive and robust measurement of cell deformability that could be used as physical biomarkers for diseases, we developed the fluidic plunger mechanism, which measures cell deformability using the pressure required to deform single cells through micrometer scale constrictions. This process mimics single cell deformation through the microvasculature, and is therefore extremely sensitive to morphological changes resulting from disease pathologies. The fluidic plunger mechanism is similar in principle as micropipette aspiration, but show dramatically improved accuracy, repeatability, and ease-of-use because of the use of an encapsulated microchannel. A key difference between this technique and other microfluidic methods is the use of pressure rather than spatial separation to measure cell deformability, which provide significantly improved sensitivity since the result does not rely on precise imaging.

Relevant Publications

Guo Q, Reiling SJ, Rohrbach P, Ma H, Microfluidic Biomechanical Assay for Red Blood Cells Parasitized by Plasmodium falciparum, Lab on a Chip, 12 (6), 1143-1150, 2012. (PMID: 22318405[pdf]

Guo Q, McFaul SM, Park S, Ma H, Microfluidic micropipette aspiration for measuring the deformability of single cells, Lab on a Chip, 12(15), 2687-95, 2012. (PMID: 22622288[pdf]

Microfluidic Cell-phoresis for High-throughput Cell Deformability Characterization

We developed a simple, sensitive, and multiplexed RBC deformability assay based on the spatial dispersion of single cells in structured microchannels. This mechanism is analogous to gel electrophoresis, but instead of transporting molecules through nano-structured material to measure their length, RBCs are transported through micro-structured material to measure their deformability. After transport, the spatial distribution of cells provides a readout similar to intensity bands in gel electrophoresis, enabling simultaneous measurement on multiple samples. We used this approach to study the biophysical signatures of falciparum malaria, for which we demonstrate label-free and calibration-free detection of ring-stage infection, as well as in vitro assessment of antimalarial drug efficacy.

Relevant Publications

Santoso AT, Deng X, Lee JH, Matthews K, Duffy SP, Islamzada E, Myrand-Lapierre M, McFaul SM, Ma H, Microfluidic Cell-phoresis Enabling High-throughput Analysis of Red Blood Cell Deformability and Biophysical Screening of Antimalarial Drugs, Lab on a Chip, 15(23), 4451-4460, 2015. (PMID: 26477590) [pdf]

Myrand-Lapierre M, Ang RR, Deng X, Matthews K, Santoso AT, Ma H, Multiplexed Fluidic Plunger Mechanism for High-Throughput Analysis of Red Blood Cell Deformability, Lab on a Chip, 15(1), 159-167, 2015. (PMID: 25325848[pdf] [SI Video]

A Physical Biomarker for Antimalarial Drug Efficacy

Malaria, caused by the parasite P. falciparum, remains one of the greatest challenges in human health with ~200 million infections resulting in ~600,000 deaths per year. Central to the pathology of this disease is the reduced deformability of infected red blood cells (iRBCs), which arises primarily from the metabolism of hemoglobin by the parasite, generating the toxic byproduct heme that induces oxidative stress. Interestingly, this rigidification of iRBC is unfavorable to the persistence of the parasite, as rigid iRBCs are rapidly removed from circulation through splenic clearance. Consequently, parasites actively prevent rigidification through biocrystalization of heme into hemozoin. Antimalarials, such as chloroquine, disrupt this process to kill the parasite through accumulation of toxic heme, as well as through increased host-mediated clearance. Recently, we showed that iRBC rigidification is actually a common property of all clinical antimalarials, which suggests its potential as a biophysical marker for antimalarial drug-efficacy, as well as a way to separate iRBCs containing drug-sensitive and drug-resistant parasites.

Relevant Publications

Deng X, Duffy SP, Myrand-Lapierre M, Matthews K, Santoso AT, Du Y, Ryan KS, Ma H, Reduced Deformability of Parasitized Red Blood Cells as a Biomarker for Antimalarial Drug Efficacy, Malaria Journal, 14(1), 428, 2015. (PMID: 26520795) [Link to Article] [pdf]

Matthews K, Duffy SP, Myrand-Lapierre M, Ang RR, Li L, Scott MD, Ma H, Microfluidic analysis of red blood cell deformability as a means to assess hemin-induced oxidative stress resulting from Plasmodium falciparum intraerythrocytic parasitism, Integrative Biology, 2017. (Accepted 2017-05-12) [pdf]

Matthews K, Myrand-Lapierre M, Ang RR, Duffy SP, Scott MD, Ma H, Microfluidic Deformability Analysis of the Red Cell Storage Lesion, Journal of Biomechanics, 48(15), 4065-4072, 2015. (PMID: 26477408) [pdf]