Quantifying Cell Adhesion Strength with a Novel Flow Assay

Quantifying the level of adhesion of cells to the extracellular matrix (ECM) is vital in efforts to understand complex biological functions. Cell adhesion to the ECM involves multiple cell surface proteins binding to components of the ECM. The ECM consists of collagen fibers, proteoglycans, and other matrix components, all of which are produced by cells themselves. Fluid flow in microfluidic channels has previously been used to quantify the fluid shear forces required to disrupt cell-ECM adhesion. Enzymatic digestion of cell-ECM adhesion components by the enzyme trypsin has also been used qualitatively. Here, we combine elements of these two methods to develop an accessible alternative. We flowed 0.25% trypsin through a microfluidic channel to rupture the adhesion between single Madin-Darby Canine Kidney (MDCK) cells and collagen I. The fraction of cells that stayed adherent to the collagen surface precipitously dropped at higher flow rates. The channel allowed cell adhesion rupture events to be spatially resolved via time lapse imaging. Our setup enables the use of different extracellular matrix properties as well as cells in different biochemical states to model cell adhesive states relevant to healthy and diseased tissues. Our approach has a large dynamic range – i.e., the assay can quantify the adhesion strength of very weak as well as very strong cell adhesive contacts. Thus, it is of relevance to the study of cell physiology in a multitude of normal as well as diseased states like cancer.