Studying monogenic mitochondrial cardiomyopathies may yield insights into mitochondrial roles in cardiac development and disease. Here, we combine patient-derived and genetically engineered iPSCs with tissue engineering to elucidate the pathophysiology underlying the cardiomyopathy of Barth syndrome (BTHS), a mitochondrial disorder caused by mutation of the gene Tafazzin (TAZ). Using BTHS iPSC-derived cardiomyocytes (iPSC-CMs), we defined metabolic, structural, and functional abnormalities associated with TAZ mutation. BTHS iPSC-CMs assembled sparse and irregular sarcomeres, and engineered BTHS “heart on chip” tissues contracted weakly. Gene replacement and genome editing demonstrated that TAZ mutation is necessary and sufficient for these phenotypes. Sarcomere assembly and myocardial contraction abnormalities occurred in the context of normal whole cell ATP levels. Excess levels of reactive oxygen species mechanistically linked TAZ mutation to impaired cardiomyocyte function. Our study provides new insights into the pathogenesis of Barth syndrome, suggests new treatment strategies, and advances iPSC-based in vitro modeling of cardiomyopathy.

Biomedical research has relied on animal studies and conventional cell cultures for decades. Recently, microphysiological systems (MPS), also known as organs-on-chips, that recapitulate the structure and function of native tissues in vitro, have emerged as a promising alternative1. However, current MPS typically lack integrated sensors and their fabrication requires multi-step lithographic processes2. Here, we introduce a facile route for fabricating a new class of instrumented cardiac microphysiological devices via multi-material 3D printing. Specifically, we designed six functional inks, based on piezo-resistive, high conductance, and biocompatible soft materials that enable integration of soft strain gauge sensors within micro-architectures that guide the self-assembly of physio-mimetic laminar cardiac tissues. We validated that these embedded sensors provide non-invasive, electronic readout of tissue contractile stresses, inside cell incubator environments. We further applied these devices to study drug responses, as well as the contractile development of human stem cell derived laminar cardiac tissues over four weeks.

Inspired by the relatively simple morphological blueprint provided by batoid fish such as stingrays and skates, we create a biohybrid system that enables an artificial animal, a tissue-engineered ray, * Correspondence to: K.K.P. 29 Oxford Street, Pierce Hall Cambridge, MA 02130. kkparker@seas.harvard.edu. Phone: 617-495-2850, 617-835-5920. Fax: 617-496-1793 Bioinspired design, as applied to robotics, aims at implementing naturally occurring features such as soft materials, morphologies, gaits, and control mechanisms in artificial settings to improve performance (1-4). For example, recent soft-robotics studies raised awareness on the importance of material properties (3, 4), shifting the focus from rigid elements to soft materials, while other investigations report successful mimicry of gaits or morphological features inspired by insects (5, 6), fish (7,8), snake (9), salamanders (10) and cheetahs (11). While recent advances have the promise of bridging the performance gap with animals, the current soft-robotic actuators based on, for instance, electroactive polymers, shape memory alloys or pressurized fluids, are yet to mature to the point of replicating the high-resolution complex movements of biological muscles (3, 4).In this context, biosensors and bioactuators (12) are intriguing alternatives, since they can intrinsically respond to a number of control inputs (such as electric fields and optical stimulation). Thanks to recent advances in genetic tools (13) and tissue engineering (12), these responses can be altered and tuned across a wide range of time and length scales. Some pioneering studies have exploited these technologies for self-propulsion, developing miniaturized walking machines (14-16), and flagellar (17) or jellyfish inspired (18) swimming devices. These biohybrid systems operate at high energy efficiency and harvest power from energy dense, locally available nutrients, although at present they require specialized environments (physiological solutions) that may limit their applicability. Moreover and most importantly, these biohybrid locomotors lack of the reflexive control (9, 19) necessary to enable adaptive maneuvering and thus of the ability to respond to spatiotemporally varying external stimuli.Here, we design, build and test a tissue-engineered analog of a batoid fish such as stingrays and skates. By combining soft materials and tissue engineering with optogenetics, we created an integrated sensory-motor system that allowed for coordinated undulating fin movement and phototactically controlled locomotion, that is guided via light stimuli. We drew from fish morphology, neuromuscular dynamics and gait control to implement a living, bio-hybrid system that leads to robust and reproducible locomotion and turning maneuvers. Batoid fish are ideal biological models in robotics (8) because their nearly planar bauplan is characterized by a broad dorsoventral disk, with a flattened body and extended pectoral fins, that enhances stability against roll (20). They swim with high energy efficien...

We have developed a detailed mathematical model for Ca handling and ionic currents in the human ventricular myocyte. Our aims were to: 1) simulate basic excitation-contraction coupling phenomena; 2) use realistic repolarizing K current densities; 3) reach steady-state. The model relies on the framework of the rabbit myocyte model previously developed by our group, with subsarcolemmal and junctional compartments where ion channels sense higher [Ca] vs. bulk cytosol. Ion channels and transporters have been modeled on the basis of the most recent experimental data from human ventricular myocytes. Rapidly and slowly inactivating components of I to have been formulated to differentiate between endocardial and epicardial myocytes. Transmural gradients of Ca handling proteins and Na pump were also simulated. The model has been validated against a wide set of experimental data including action potential duration (APD) adaptation and restitution, frequencydependent increase in Ca transient peak and [Na] i . Interestingly, Na accumulation at fast heart rate is a major determinant of APD shortening, via outward shifts in Na pump and Na-Ca exchange currents. We investigated the effects of blocking K currents on APD and repolarization reserve: I Ks block does not affect the former and slightly reduces the latter; I K1 blockade modestly increases APD and more strongly reduces repolarization reserve; I Kr blockers significantly prolong APD, an effect exacerbated as pacing frequency is decreased, in good agreement with experimental results in human myocytes. We conclude that this model provides a useful framework to explore excitationcontraction coupling mechanisms and repolarization abnormalities at the single myocyte level.

Laboratory studies of the heart use cell and tissue cultures to dissect heart function yet rely on animal models to measure pressure and volume dynamics. Here, we report tissue-engineered scale models of the human left ventricle, made of nanofibrous scaffolds that promote native-like anisotropic myocardial tissue genesis and chamber-level contractile function. Incorporating neonatal rat ventricular myocytes or cardiomyocytes derived from human induced pluripotent stem cells, the tissue-engineered ventricles have a diastolic chamber volume of ~500 μL (comparable to that of the native rat ventricle and approximately 1/250 the size of the human ventricle), and ejection fractions and contractile work 50–250 times smaller and 104–108 times smaller than the corresponding values for rodent and human ventricles, respectively. We also measured tissue coverage and alignment, calcium-transient propagation and pressure/volume loops in the presence or absence of test compounds. Moreover, we describe an instrumented bioreactor with ventricular-assist capabilities, and provide a proof-of-concept disease model of structural arrhythmia. The model ventricles can be evaluated with the same assays used in animal models and in clinical settings.