Cell Speedometer

We discovered that cells immobilized on adhesive islands (righthand heat map) output two-fold stronger traction stress than cells migrating freely (lefthand heat map). The inverse relationship between force generation and migration speed reflects cell's ability to sense its speed of migration, and may serve as a tool for a cell to determine if it is traveling or has arrived at the destination for tissue formation.



Machine Learning for Traction Force Microscopy

Since its introduction 20 years ago, Traction force microscopy has served as a critical tool for understanding mechanical activities of adherent cells. However its resolution and accuracy have been challenged by the mathematical nature as an ill-posed inverse problem. We have now deployed deep learning, which is known for the power for solving ill-posed problems, for traction force microscopy to obtain stress maps at a high resolution, accuracy, and speed. The new method also proves highly versatile with respect to cell shape, size, traction output, and substrate stiffness.



3D Printing Polyacrylamide

In addition to the extensive use in mechanobiology since 1997, polyacrylamide has been used in many other biomedical applications thanks to its many favorable properties such as adjustable stiffness over the physiological range, optical transparency, low fouling, and biological inertness. To allow the creation of complex shapes for widening its applications such as artificial organs, we have now developed a simple method for 3D printing polyacrylamide using stereolithography, and we are exploring ways to increase the permeability of small molecules across the hydrogel.



How Cells Reorient Perpendicularly to Cyclic Stretching

Many adherent cells reorient upon cyclic stretching perpendicularly to the direction of stretching. The underlying mechanism remains poorly understood. Using an on-stage stretching device that allowed synchronous imaging, we found that the reorientation of NRK epithelial cells took place primarily during the relaxation phase when cells underwent rapid global retraction followed by slow extension transverse to the direction of stretching. Inhibition of myosin II caused cells to orient along the direction of stretching, whereas disassembly of microtubules enhanced transverse reorientation. The importance of relaxation phase explains the puzzling difference between the responses to cyclic and static stretching,