LAUSR

With cardiovascular diseases representing a leading cause of death worldwide, several biological aspects of heart physiology and pathology remain open and therapeutic needs widely unmet. The attention of biomedical research has been directed toward the development and exploitation of meaningful in vitro models of the myocardium, in both health and disease. Indeed, an increasing need has risen for advanced platforms able to investigate heart pathological mechanisms or development of drug treatments with low impact on cardiac function. An ideal in vitro heart model should be capable of tailoring environmental cues provided to human cells or tissues (biochemical signals, physical stimulations) while also providing means to analyze functional readouts (e.g., contractility of the tissue, electrical activity). These specifics are the key to conduct both basic research investigations (e.g., cellular mechanisms of cardiac pathologies) and translational studies (effects of candidate drug compounds on heart functions). A class of culture platforms recently acknowledged as prospective to meet these needs and advance these fields are organson-chips. Exploiting photo and soft-lithography microfabrication techniques, organs-onchip provide microstructured arrangements of cells recapitulating key organ/tissue functions and supplied by microfluidic channels [1]. The relatively low volume of fluids required to culture cells within these devices makes it possible to focus the use of organson-chip toward human cells (primary cells or derived from pluripotent stem cells), thus stepping away from animal sources. These concepts have been applied to heart-derived cells in order to more finely recapitulate the cardiac environment in vitro within socalled heart-on-chips. To date, this rapidly growing field accounts for several reports describing heart-on-chip designs [2], which in some instances were validated for carrying out relevant drug screening studies [3]. Heart-on-chip models therefore hold concrete potential for advancing the field of cell culture platform. However, they still require improvements and directions in order to attain meaningful biological models for robustly serving pharmaceutical screenings or basic research. We here comment on existing heart-on-chip microfluidic devices, with an outlook on unmet requireTailoring cardiac environment in microphysiological systems: an outlook on current and perspective heart-on-chip platforms