Full Text (PDF)
Because endothelial cells (ECs) line the insides of all blood vessels, they are exposed to shear stress, the tangential force component from flowing blood. Shear stress causes endothelial cells to modify their expression of adhesive molecules, secrete vasodilators and anticoagulants, and rearrange their cytoskeletons. Our laboratory investigates the biophysical properties of cells to understand their force-sensing mechanisms by employing new engineering analyses and experimental studies of single EC mechanotransduction. This research requires the characterizing of cell shape, mechanics, intracellular force distribution, and readouts of force sensation through the use of multimodal microscopy, including differential interference contrast (DIC), total internal reflection fluorescence microscopy (TIRFM), confocal fluorescence imaging, time-resolved fluorescence, and photonic-force microscopy. Through advanced 3-D image processing algorithms, computational fluid dynamics solvers, and finite element (FE) solid mechanics models, we hope to directly correlate time- and position-dependent cell stresses with signal transduction. Results will point to new molecular level interventions for vascular dysfunction and provide the basis for intelligent development of novel biomaterials and tissue-engineered blood vessels.
www.bioe.psu.edu/mechlab
The Technique
To characterize cell mechanics, we use particle tracking microrheology. This technique entails high-speed nanometer-scale tracking of endogenous organelles in live cells cultured on glass coverslips. Analysis of particle trajectories using models for viscoeoastic materials reveals spatial and temporal changes in mechanical properties. Unfortunately, errors in the tracking related to stage drift, system vibration, and electronic noise can lead to errors in interpreting viscoelasticity. We have developed a simple method to mitigate these errors by microfabricating tall posts onto coverslips. These fiduciary posts reveal glass coverslip motion, which, when subtracted from the apparent particle trajectories, results in high-precision tracking of subcellular organelles, even under conditions of excessive stage drift and system vibration. These coverslips permit more accurate representation of cellular mechanics—information that is necessary to interpret the role of forces in vascular health and disease.
Improved nanometer-scale particle tracking in optical microscopy using microfabricated fiduciary posts, p. 437.
