Traction force microscopy: Force measurement determines the direction of cell migration

Cell migration is responsible for positive responses in one’s body in aid of healing of wounds, or infamously, invasion of cancer cells through the connective tissues. To better understand these major physiological phenomena, quantification of traction forces is necessary. The most common method to use is Traction Force Microscopy (TFM). Here, we have employed fluorescent superparamagnetic beads as detection markers. During the polymerization process of the polyacrylamide gel, an external magnetic field is applied and a single layer of superparamagnetic beads formed along the surface of the substrate. Such configuration reduces background noise, improving the spatial resolution to 50-nm with 40x magnification for the XY plane. Since the magnetic beads are located at the surface, marker positions are directly influenced by traction forces. Polyacrylamide gels of 1 through 30 kPa stiffness were used for the traction force measurement. The maximum traction force through the 48-hour cellular phase is measured to be 3.7 nN in 2 kPa, while the average traction force is registered to be 1.2 nN in 2 kPa. Increasing stiffness doesn’t change the maximum traction force, but increases the average force. The directions of the traction force exerted on the cell were analyzed for comparison.