A novel remote-sensing isometric force transducer for micromechanics studies.

We have developed an innovative transducer for measuring force with femtonewton-to-micronewton resolution in biological systems. A magnetic microsphere is attached to the specimen being studied and is positioned between two electromagnets. Video microscopy and edge detection are used to monitor small movements of the microsphere that occur when the specimen generates force. An automatic control system adjusts the current through the electromagnets to keep the microsphere stationary. Measured force is a linear function of this current. This transducer is unique in its combination of sensitivity and isometric properties and its ability to measure force without direct connections to the specimen. That is, the transducer is "remote sensing" and can measure force through intervening membrane or tissue. The transducer is isometric at steady state to the limit at which displacement of the microsphere can be resolved, which can be as low as 19 nm. The completed system is being used to study the mechanics of interstitial connective tissue but may also be used to study molecular generation of force.