A cell-based sensor of fluid shear stress for microfluidics

Abstract

Microsystems designed for cell-based studies or applications inherently require fluid handling. Flows within such systems inevitably generate fluid shear stress (FSS) that may adversely affect cell health. Simple assays of cell viability, morphology or growth are typically reported to indicate any gross disturbances to cell physiology. However, no straightforward metric exists to specifically evaluate physiological implications of FSS within microfluidic devices, or among competing microfluidic technologies. This paper presents the first genetically encoded cell sensors that fluoresce in a quantitative fashion upon FSS pathway activation. We picked a widely used cell line (NIH3T3s) and created a transcriptional cell-sensor where fluorescence turns on when transcription of a relevant FSS-induced protein is initiated. Specifically, we chose Early Growth Factor-1 (a mechanosensitive protein) upregulation as the node for FSS detection. We verified our sensor pathway specificity and functionality by noting induced fluorescence in response to chemical induction of the FSS pathway, seen both through microscopy and flow cytometry. Importantly, we found our cell sensors to be inducible by a range of FSS intensities and durations, with a limit of detection of 2 dynes/cm2 when applied for 30 minutes. Additionally, our cell-sensors proved their versatility by showing induction sensitivity when made to flow through an inertial microfluidic device environment with typical flow conditions. We anticipate these cell sensors to have wide application in the microsystems community, allowing the device designer to engineer systems with acceptable FSS, and enabling the end-user to evaluate the impact of FSS upon their assay of interest.

Recent advances in lab-on-a-chip for biosensing applications

“…In microfluidic systems designed for cell-based studies, this FSS may adversely affect cell health. Varma and Voldman (2015) developed and tested genetically encoded cell sensors that fluoresce in a quantitative fashion upon FSS pathway activation. These cell sensors could allow microfluidic device designers and end-user to evaluate the impact of FSS upon their assay of interest.…”

Microfluidic Device for On-Chip Immunophenotyping and Cytogenetic Analysis of Rare Biological Cells

“…Shear rate distributions across a section of the device can be found in Figures S3D and E. The shear stress experienced by cells in physiological conditions as they travel through capillaries and arterioles ranges between 40 and 55 dynes/cm 2 [38][39][40][41]. Interestingly, even though the shear stress at a flow rate of 10 L/min was 10 times higher than the average shear stress of cells traveling through arterioles, we did not observe obvious damage of RPMI-8226 or SUP-B15 cells when contained at the entrance of any microtrap within the device.…”

Merging orthogonal microfluidic flows to generate multi-profile concentration gradients

“…In a typical microuidic device, cell may experience uid shear stresses of the order of 0.001-10 dynes per cm 2 for extended durations. 27 The maximum uid shear stress in a microuidic channel, 27 which occurs at the walls, can be determined using:…”