Tailoring the Trajectory of Cell Rolling with Cytotactic Surfaces
Cell separation technology is a key tool for biological studies and medical diagnostics that relies primarily on chemical labeling to identify particular phenotypes.
An emergent method of sorting cells based on differential rolling on chemically patterned substrates holds potential benefits over existing technologies, but the underlying mechanisms
being exploited are not well characterized. In order to better understand cell rolling on complex surfaces, a microfluidic device with chemically patterned stripes of the cell
adhesion molecule P-selectin was designed. The behavior of HL-60 cells rolling under flow was analyzed using a high resolution visual tracking system. This behavior was then
correlated to a number of established predictive models. The combination of computational modeling and widely available fabrication techniques described herein represents a crucial step
toward the successful development of continuous, label-free methods of cell separation based on rolling adhesion.
Microfluidic Cell Sorter
This is an artistic rendition of the microfluidic device used in this study. The device was designed with the capability to sort cells using patterned
stripes of P-selectin, although sorting effectiveness has not yet been studied. Angled stripes on either side of the channel direct rolling cells
(blue) toward the center pathway where they are collected as they exit the device. Cells that do not interact with the surface or do not express
P-selectin glycoprotein ligand-1 (red) follow the direction of flow and exit through the two side channels.
(A)Cartoon view of the sorter design showing sample and buffer inlets and sorted and unsorted cells outlets. (B)Photograph of the sorter as currently configured. (C)Photomicrograph of the stripes region of the sorter.
Detecting Interactions Between Cells and Modified Surfaces
Introduction
A recent computational model suggests that label-free cell sorting can be accomplished using a patterned substrate with diagonal stripes of sticky material.
As a cell under laminar flow rolls over these stripes, the interaction between the cell and modified surface can cause a slight change in the cell's path.
In order to test this model, we have developed a tracking program that captures the cell paths and analyzes their motion relative to the stripes.
Tracking
The program utilizes background subtraction and Laplacian filters of varying standard deviation to track cells at resolution of 0.5 µm.
One-to-one assignment algorithm is used to connect cells across multiple frames (tolerance of up to 5 dropped frames).
Analysis
Many cells of interest showed behavior consistent with the model's predictions, showing downward deflection on gap-to-stripe and upward deflection on stripe-to-gap.
Net positive lateral displacement w.r.t. non-interacting "control" cells.
Tracking HL-60 cells rolling under flow for analysing the interation between cells and modified surfaces.
