The overarching goal of our research program is the development of new technologies to interrogate and manipulate biological systems at the cellular scale. Our work is enabled by advances in fabrication, measurement, and computation across multiple domains and lengths scales. Our core capabilities include microfabrication, microfluidics, instrumentation, data analytics, and product development. Our current research interests could be grouped under the following themes:
Image Cytometry and Machine Learning
Cytometry is the quantitative assessment of cells based on morphological characteristics such as size, shape, internal structure, as well as the presence and location of markers identified using fluorescence labels. Advances in microscopy imaging has been steadily improving the quality and quantity of images that could be acquired on cellular samples. We are applying recent advances in machine learning to analyze and derive meaning from vast quantities of image data. Currently, we are developing methods to classify cells based on morphology in order to enable rapid identification of rare pathological (diseased) cells.
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 particularly problematic for cell separation where discriminating properties of target cells must be translated into forces that act against viscous forces imposed by the carrier fluid. To overcome this problem and enable highly selective cell separation, we developed the microfluidic ratchet mechanism that overcomes kinematic reversibility using the deformation of single cells through tapered constrictions with micrometer-scale openings. Deforming cells along the direction taper requires less force than against the direction of taper. Therefore, an oscillatory flow through such constrictions 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 filtration-based separation mechanism. This mechanism enables deformability-based cell separation of high-density cell samples (e.g. whole blood) with significantly improved selectivity over previous methods.
Circulating Tumor Cells and Single Cell Sequencing
Circulating tumor cells (CTCs) are cancer cells shed into the bloodstream where they have the potential to seed metastatic tumors. We showed that these cells are structurally and morphologically distinct from hematological cells (Park 2014), and are therefore separable based on cell deformability. This approach resolves a key challenge in existing technologies, which separate CTCs using cell surface markers that are known to disappear as part of invasion and metastasis. Using the microfluidic ratchet mechanism, we could efficiently enrich for CTCs from the peripheral blood of cancer patients with significantly greater yield (~25X) compared to established methods while keeping the cells in fluid suspension (Park 2016). Our current work focuses on the isolation of individual CTCs for genome and transcriptome sequencing (Park 2018).
Cell Biomechanics in Malaria and Transfusion Medicine
The deformability of individual cells has long been recognized as a potential physical biomarker to evaluate the status of certain diseases and their response to treatment. We developed the microfluidic plunger mechanism to measure the pressure required to deform single cells through micrometer scale constrictions. This process mimics the deformation of circulatory cells through the microvasculature, and is extremely sensitive to morphological changes resulting from disease pathologies. We developed several iterations of this mechanism and used it to interrogate questions in malaria and transfusion medicine (Guo 2012, Myrand-Lapierre 2015, Santoso 2015). In malaria, we showed that the loss of deformability in P. falciparum infected red blood cells is a potential biomarker for antimalarial drug efficacy (Deng 2015). We are currently using this approach to expediate target identification during antimalarial drug development. In transfusion medicine, we are currently using red blood cell deformability as a measure of blood quality in order to improve practices in blood processing and storage.
We are generally interested in the question of how cells make decisions based on input from their local environment. There are many parallels between this process and decision-making in electronic circuits, where amplification and precision sensing of continuous signals leads to discretized outcomes. Our current work explores cellular decision-making during chemotaxis, where cells sense gradients of chemo-attractants in order to trigger a migratory response.