Magnetic microposts as an approach to apply forces to living cells

TLDR

Cells respond to mechanical forces whether applied externally or generated internally via the cytoskeleton. The study applied external forces to cells using microfabricated magnetic posts with cobalt nanowires among elastomeric posts to isolate cellular traction responses. A magnetic field generated torque on the cobalt nanowires, deflecting the posts and delivering controlled forces to individual cell adhesions on the elastomeric array. Step forces increased focal adhesion size locally, repeated actuations further enhanced recruitment, and traction recordings revealed either an immediate loss or gradual decay of contractility occurring at discrete peripheral sites, demonstrating a dynamic link between external and internal forces.

Abstract

Cells respond to mechanical forces whether applied externally or generated internally via the cytoskeleton. To study the cellular response to forces separately, we applied external forces to cells via microfabricated magnetic posts containing cobalt nanowires interspersed among an array of elastomeric posts, which acted as independent sensors to cellular traction forces. A magnetic field induced torque in the nanowires, which deflected the magnetic posts and imparted force to individual adhesions of cells attached to the array. Using this system, we examined the cellular reaction to applied forces and found that applying a step force led to an increase in local focal adhesion size at the site of application but not at nearby nonmagnetic posts. Focal adhesion recruitment was enhanced further when cells were subjected to multiple force actuations within the same time interval. Recording the traction forces in response to such force stimulation revealed two responses: a sudden loss in contractility that occurred within the first minute of stimulation or a gradual decay in contractility over several minutes. For both types of responses, the subcellular distribution of loss in traction forces was not confined to locations near the actuated micropost, nor uniformly across the whole cell, but instead occurred at discrete locations along the cell periphery. Together, these data reveal an important dynamic biological relationship between external and internal forces and demonstrate the utility of this microfabricated system to explore this interaction.