A modular instrument for exploring the mechanics of cardiac myocytes

The cardiac ventricular myocyte is a key experimental system for exploring the mechanical properties of the diseased and healthy heart. Millions of primary myocytes, which remain viable for 4-6 h, can be readily isolated from animal models. However, currently available instrumentation allows the mechanical properties of only a few physically loaded myocytes to be explored within 4-6 h. Here we describe a modular and inexpensive prototype instrument that could form the basis of an array of devices for probing the mechanical properties of single mammalian myocytes in parallel. This device would greatly increase the throughput of scientific experimentation and could be applied as a high-content screening instrument in the pharmaceutical industry. The instrument module consists of two independently controlled Lorentz force actuators-force transducers in the form of 0.025 x 1 x 5 mm stainless steel cantilevers with 0.5 m/N compliance and 360-Hz resonant frequency. Optical position sensors focused on each cantilever provide position and force resolution of <1 nm/ radicalHz and <2 nN/ radicalHz, respectively. The motor structure can produce peak displacements and forces of +/-200 mum and +/-400 microN, respectively. Custom Visual Basic.Net software provides data acquisition, signal processing, and digital control of cantilever position. The functionality of the instrument was demonstrated by implementation of novel methodologies for loading and attaching healthy mammalian ventricular myocytes to the force sensor and actuator and use of stochastic system identification techniques to measure their passive dynamic stiffness at various sarcomere lengths.