A planar structure sensitive to out-of-plane forces for the force-controlled injection of suspended and adherent cells

We present a novel force sensor for the injection of both suspended and adherent cells. Unlike most configurations, this force sensor is independent of the tool interacting with the cells. It is a planar structure that provides a surface sensitive to out-of-plane forces where living cells can be placed for manipulation. It also integrates two beam resonators. Forces perpendicular to the sensor´s plane are estimated via frequency shifts of the resonators. In this paper, we develop a theoretical study for predicting and optimizing the structure´s sensitivity. As a proof of concept, we report the fabrication and characterization of a first prototype designed for the injection of spherical cells with a diameter of ~100-600 μm. In air, our prototype presently offers a quality factor of 700, and a linear force sensitivity of ~2.6 Hz/mN. The measurement of forces applied upon lobster eggs is also experimentally demonstrated.