Piezo-bending actuators for isometric or auxotonic contraction analysis of engineered heart tissue

Engineered heart tissue (EHT) has proven as valuable tool for disease modelling, drug safety screening, and cardiac repair. Especially in combination with the stem cell technology, these in vitro models of the human heart have generated interest not only of basic cardiovascular researchers but also of regulatory authorities responsible for drug safety. A main limitation of 3D-based assays for evaluating cardiotoxicity is their limited throughput. We integrated piezo-bending actuators in a 24-well system for the generation of strip-like rat and human EHT attached to hollow, elastic silicone posts. Muscle contractions of EHTs induced a measurable electrical current in the piezo-bending actuators that could be analysed for contraction amplitude, frequency, and contraction and relaxation kinetics. Compared with the standard video-optical analysis of contractile activity, the new system allows for (a) the analysis of several tissues in parallel, (b) switching between auxotonic and isometric contractions by inserting a stiff metal post in the silicone post opposing the piezo actuator, (c) continuous measurement over days with low data volume (megabyte), (d) automated measurement without the necessity of adjustment of tissue position for video-optical analysis, (e) reduced complexity and costs, (f) high sensitivity of contraction detection, (g) calculation of absolute contraction force, and (h) suitability for variable tissue geometries. The new set-up for contraction analysis based on piezo-bending actuators is a promising new method for the parallel screening of EHT for pharmacological drug effects and other applications of muscle tissue engineering (e.g., skeletal muscle engineering or cardiac repair).