Direct Force Measurement of the PANC-1's Traction Force

Abstract

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). Polystyrene fluorescent beads were embedded in the substrate as markers, traction force is then recovered from particle displacements. However, such setup has no control over marker positions and often introduce background noise, e.g. loss of spatial resolution. In addition, beads usually aren’t in direct contact with the cells, hence the measurement has a higher degree of estimation due to extrapolations and modeling. Thus, 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 5-nm for XY plane. Since the magnetic beads are located at the surface, marker (magnetic beads) positions are directly influenced by traction forces, improving the accuracy of measurements too. Polyacrylamide gels of 1, 2, 4, through 25 kPa stiffness were used for the traction force measurement. The maximum traction force through the 12-hour cellular phase is measured to be 3.7 nN in 2kPa, 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.