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Despite significant advancements in in vitro cardiac modeling approaches, researchers still lack the capacity to obtain in vitro measurements of a key indicator of cardiac function: contractility, or stroke volume under specific loading conditions—defined as the pressures to which the heart is subjected prior to and during contraction. This work puts forward a platform that creates this capability, by providing a means of dynamically controlling loading conditions in vitro. This dynamic tissue loading platform consists of a thin magnetoresponsive hydrogel cantilever on which 2D engineered myocardial tissue is cultured. Exposing the cantilever to an external magnetic field—generated by positioning magnets at a controlled distance from the cantilever—causes the hydrogel film to stretch, creating tissue load. Next, cell contraction is induced through electrical stimulation, and the force of the contraction is recorded, by measuring the cantilever's deflection. Force–length‐based measurements of contractility are then derived, comparable to clinical measurements. In an illustrative application, the platform is used to measure contractility both in untreated myocardial tissue and in tissue exposed to an inotropic agent. Clear differences are observed between conditions, suggesting that the proposed platform has significant potential to provide clinically relevant measurements of contractility. [ABSTRACT FROM AUTHOR]

Shape‐morphing active networks of mesoscale filaments are a common hierarchical feature in biology for applying forces, transporting materials, and inducing motility with microscale resolution. Synthetic morphing systems of similar dimensions and capabilities hold potential for a range of technological applications, from micro‐muscles to shape‐morphing optical devices. Here, the fabrication of highly‐ordered 2D networks hierarchically constructed of thermoresponsive mesoscale polymeric fibers, which can exhibit morphing with microscale resolution, is presented. It is demonstrated both experimentally and computationally that the morphing of such networks strongly depends on the physical attributes of the single fiber, in particular on two intrinsic length scales—the fiber diameter and mesh size, which stems from network's density. It is shown that depending on these parameters, such fiber‐networks exhibit one of two thermally driven morphing behaviors: i) the fibers stay straight, and the network preserves its ordered morphology, exhibiting a bulk‐like behavior; or ii) the fibers buckle and the network becomes messy and highly disordered. Notably, in both cases, the networks display memory and regain their original ordered morphology upon shrinking. This hierarchically induced phase transition, demonstrated here on a range of networks, offers a new way of controlling the shape‐morphing of synthetic materials with mesoscale resolutions. [ABSTRACT FROM AUTHOR]