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Microfluidic chemotaxis assay using hydrogel-stabilised gradients Azam, Iftikhar


Chemotaxis is the migration of cells in response to a chemical stimulus. This phenomenon is a part of many physiological and pathological processes, such as the neutrophilic response to bacterial invasion, as well as tumour invasion and metastasis. Since the 1960s, assays have been developed to study cell chemotaxis. Early assays mostly measured the number of cells migrating across a membrane, but do not allow tracking of individual cells. Recently, microfluidic assays have enabled single-cell tracking, but they are only able to maintain a stable chemical gradient for a limited time, or require continuous perfusion to maintain a chemical gradient. Here, we developed a microfluidic chemotaxis assay which is capable of maintaining a stable chemical gradient for an extended period of time without the need for a fluid flow system. This capability is achieved by forming a linear chemoattractant gradient in a hydrogel prepolymer in a microchannel, then polymerising the hydrogel by exposure to UV light, thereby fixing the gradient in place. Cells are dispensed on top of the polymerised hydrogel and the cell response to the chemoattractant gradient is observed. Compared to many existing chemotaxis assays, this device requires significantly less time and user expertise to operate. Two versions of the hydrogel-stabilized chemotaxis assay have been developed. Version 1 is manufactured using polydimethylsiloxane (PDMS), while Version 2 is manufactured using 3D printing of translucent epoxy resin. For both versions, the manufacturing methods and operation protocol have been optimised to achieve a device reliability of 80%. Version 2 dramatically reduced the number of failure modes and simplified device operation. A simulation study was conducted to better understand the diffusion process that forms the chemical gradient, and verify the gradient profile applied to the cell sample.

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