Cellular force measurements using single-spaced polymeric microstructures: isolating cells from base substrate

Mechanical force is one of the most important parameters in cellular physiological behavior. To quantify the cellular force locally and more precisely, soft material probes, such as bulk polymeric surfaces or raised individual polymeric structures, have been developed which are deformable by the cell. The extent of deformation and the elastic properties of the probes allow for calculation of the mechanical forces exerted by the cell. Bulk polymeric surfaces have the disadvantage of requiring computational intensive calculations due to the continuous distortion of a large area, and investigators have attempted to address this problem by using raised polymeric structures to simplify the derivation of cellular mechanical force. These studies, however, have ignored the possibility of formation of local adhesions of the cell to the underlying base substrate, which could result in inaccurate cellular force measurements. Clearly, there is a need to develop polymeric structures that can efficiently isolate the cells from the underlying base substrate, in order to eliminate the continuous distortion problem. In this paper, we demonstrate the measurement of cellular force in isolated cardiac myocytes using single-spaced polymeric microstructures. Each structure is 2 mu m in diameter and single-spaced packed. This geometry of the structures successfully isolates the cells from the underlying substrate. Displacement of the structures was measured in areas underneath the attached cell and at areas in close proximity to the cell. The results show that the individual structures underneath the cell were significantly displaced whereas no substantial strain in the underlying base substrate was detected. The mechanical force of the cell was derived from the displacements of individual structures upon multiplication with the locally determined spring constant. The force distribution reveals a parallel alignment as well as a periodic motion of the contractile units of the myocyte. The flexible fabrication methodology of the polymeric substrate and straightforward determination of minute forces provide a useful way to study cellular mechanical force.