Mechanical phenotyping of single cells using shear and inertial microfluidics

Disease induced changes to subcellular components leads to measurable changes in whole cell deformability. Thus, mechanical phenotyping offers potential as a diagnostic tool. Cells undergo physical and biological changes during cancer progression and understanding these changes is a major challenge in developing new diagnosis and treatment methods.
High-throughput mechanophenotyping methods are required to account for cell heterogeneity, which arise due to cell-cycle stage and biological noise. Here, a high-throughput microfluidic technique called deformation cytometry was used to deform cells in an extensional flow using a cross-slot geometry. Cells are viscoelastic and their mechanical response to an applied stress depends on the magnitude and timescale of application. Two distinct flow regimes were studied where either shear or inertial forces dominated the system. In the inertia-dominant regime cell response showed yield stress behaviour and subsequent cell structural failure at high stresses, whilst the shear-dominant regime required lower applied stress to achieve high cell strains. The different regimes proved able to expose subtle changes attributed to specific subcellular changes, tested by treating cells with drugs to disrupt the actin, microtubule, and nuclear structure. Deformation and recovery were tracked as a function of time, with various deformation and relaxation parameters found to be useful markers to distinguish cell types.
Deformation cytometry was also applied to studying colorectal cancer progression. Colorectal cancer is the third most common cancer in the UK and the five year survival rate drops from ~93% with early stage diagnosis to ~7% for late stage diagnosis. The deformability of three colorectal cancer cell lines was investigated using both flow regimes. SW480, HT29 and SW620 cell lines offered a model of metastatic progression from primary to metastatic and were compared to the leukaemia cell line HL60. Results indicated increased deformability associated with metastatic progression, and relaxation parameters showed significant changes between different cell types. Additional work showed that hydrodynamic deformation can be used to increase non-endocytic uptake of quantum dots into cells, due to the applied shear force forming transient pores in the cell membrane. Successful delivery of quantum dots into the cytosol will allow them to be used to measure the cell redox environment, which is a marker of disease state including metastatic progression.
Results showed the potential for deformation cytometry as a cell mechanophenotying tool with high sensitivity, including multiparameter characterisation for improved accuracy in detecting disease stage. This work shows that mechanical measurements on a single cell level offer insight into heterogeneity, allowing distinctions to be made between different phenotypes. Future work could use the method for detection of rare events or subpopulations, particularly those arising during disease progression.