Microengineered platforms for characterizing the contractile function of in vitro cardiac models

Abstract

Emerging heart-on-a-chip platforms are promising approaches to establish cardiac cell/tissue models in vitro for research on cardiac physiology, disease modeling and drug cardiotoxicity as well as for therapeutic discovery. Challenges still exist in obtaining the complete capability of in situ sensing to fully evaluate the complex functional properties of cardiac cell/tissue models. Changes to contractile strength (contractility) and beating regularity (rhythm) are particularly important to generate accurate, predictive models. Developing new platforms and technologies to assess the contractile functions of in vitro cardiac models is essential to provide information on cell/tissue physiologies, drug-induced inotropic responses, and the mechanisms of cardiac diseases. In this review, we discuss recent advances in biosensing platforms for the measurement of contractile functions of in vitro cardiac models, including single cardiomyocytes, 2D monolayers of cardiomyocytes, and 3D cardiac tissues. The characteristics and performance of current platforms are reviewed in terms of sensing principles, measured parameters, performance, cell sources, cell/tissue model configurations, advantages, and limitations. In addition, we highlight applications of these platforms and relevant discoveries in fundamental investigations, drug testing, and disease modeling. Furthermore, challenges and future outlooks of heart-on-a-chip platforms for in vitro measurement of cardiac functional properties are discussed.

Keywords: Biosensors.

Fig. 1. Schematic overview showing the assessment of contractile functions of in vitro cardiac models and the corresponding applications.

Cell sources of in vitro cardiac models include adult cardiomyocytes, neonatal animal cardiomyocytes and cardiomyocytes derived from human embryonic stem cells (hESCs) and from induced pluripotent stem cells (iPSCs). In vitro cardiac models are established in the forms of single cardiomyocytes, 2D cell monolayers and 3D cardiac models. The assessment of contractile functions of in vitro cardiac models can facilitate research applications for fundamental cardiac physiology studies, disease modeling and therapeutic discoveries. Reproduced with permission^,,,. Copyright 2014 the American Physiological Society, Copyright 2017 Springer Nature, Copyright 2019 Elsevier, Copyright 2015 Royal Society of Chemistry. Figure created with BioRender.com.

Fig. 2. Contractile function measurement of single cardiomyocytes.

a Carbon fiber force-length measurement system for mechanical manipulation and force measurement of intact cardiomyocytes. Cell passive/active forces are calculated from carbon fiber bending. Reproduced with permission. Copyright 2007 American Physiological Society. b MEMS force transducer system for the contraction measurement of isolated cardiomyocytes. The right image demonstrates a single cell attached to the clamp. Reproduced with permission. Copyright 2014 American Physiological Society. c Determination of cardiomyocyte contraction with atomic force microscopy (AFM). Reproduced with permission. Copyright 2016 American Chemical Society. d Micropillar arrays that are 10 µm high and 10 µm in diameter. Micropillar deformation is measured to calculate cell contractility. Reproduced with permission. Copyright 2018 Elsevier. e InGaN/GaN nanopillar arrays used for contraction measurement at a spatial resolution of 800 nm. Reproduced with permission. Copyright 2021 American Association for the Advancement of Science. f Traction force microscopy used to measure contractile stress based on the movement of fluorescent beads embedded in a deformable gel substrate. Reproduced with permission. Copyright 2014 American Physiological Society. g Video-based analysis of single-cell beating displacement or strain magnitude using brightfield microscopy. h Video-based analysis of sarcomere shortening by tracking of the movement of fluorescently labeled myofibrils (actin). g, h Reproduced with permission. Copyright 2017 American Heart Association

Fig. 3. Contractile function measurement of 2D cardiomyocyte monolayers.

a Picture and schematic of an impedance-based sensor to record contraction of cardiomyocytes grown on interdigitated electrodes. R and C in the simplified equivalent circuit model represent the resistance and capacitance of the cardiomyocyte monolayer. Beating activities are reflected by the dynamic changes in impedance signals. Reprinted with permission. Copyright 2017 Royal Society of Chemistry. b CellDrum used to measure the contraction-dependent membrane deflection by using a laser sensor or the oscillating differential pressure change by using a pressure sensor. Replotted based on. Copyright 2016 Elsevier. c Flexible membrane device integrated with CNT composite strain sensors for the measurement of cardiac contractility. The data plot reveals contraction development with increasing culture days. Reprinted with permission. Copyright 2018 American Chemical Society. Muscular thin-film (MTF) platforms are developed by seeding anisotropic cardiomyocyte monolayers on d micromolded gelatin hydrogel cantilevers, e biohybrid structural color hydrogel cantilevers, f 3D-printed flexible cantilevers with embedded carbon black strain gauges, or g microfabricated silicone cantilevers with embedded high-sensitivity crack sensors. The contraction of cardiomyocyte monolayers is measured by d optically tracking the cantilever curvature change, e imaging the hydrogel color shift from diastole to peak systole and f, g recording the resistance change of embedded strain sensors. Reproduced with permission^,,,. Copyright 2014 Elsevier, Copyright 2018 American Association for the Advancement of Science, Copyright 2017 Springer Nature, and Copyright 2020 Springer Nature

Fig. 4. Contractile function measurement of 3D engineered heart tissues (EHTs).

a EHT bridge across parallel rigid rods on the I-Wire platform. Tissue contraction is measured by an external force probe. Reproduced with permission. Copyright 2016 Elsevier. b Photograph and schematic of the cardiac tissues attached at the tips of two flexible silicone posts and bending the flexible post with force. Contractile force is calculated based on the post length, stiffness and deflection. Reproduced with permission. Copyright 2018 Springer Nature. c The Biowire II platform enables growth of thin cylindrical tissues suspended between two flexible wires that allow quantification of active force, passive tension, and contractile dynamics. Reproduced with permission. Copyright 2019 Elsevier. d EHT developed in a confined microfluidic channel. Tissue contraction is evaluated by tracking the beating motion in the brightfield. Reproduced with permission. Copyright 2015 Springer Nature. e Video-based contraction measurement of 3D cardiac spheroids. Contraction magnitude is represented as the fractional area change of cardiac spheroids between contraction and relaxation. Reproduced with permission. Copyright 2017 Elsevier. f Representative images of an engineered human ventricular cardiac organoid chamber (hvCOC). Changes in the lumen pressure and volume of the hvCOC are separately recorded via a pressure catheter and high-speed video camera. Reproduced with permission. Copyright 2018 Elsevier

Fig. 5. Platform applications in drug testing and disease modeling.

a Schematic diagram showing physiological mechanisms related to cardiomyocyte contraction, including propagation of action potentials, calcium dynamics, sliding of sarcomere filaments, and intercellular communication. b Sample of a high-throughput platform for drug screening based on SU-cantilever arrays. Reproduced with permission, Copyright 2019 Elsevier. c Inherited cardiac tissue model with titin-truncating variants (TTNtvs) established on a flexible microcantilever platform. The representative force curves indicate the diminished contractile performance of patient-derived (pP22582fs^+/−) iPS-CM tissues. Compared with wild-type (pWT) cells, pP22582fs^+/− iPS-CMs have fewer myofibrils and abnormal sarcomeres. Reproduced with permission. Copyright 2015 American Association for the Advancement of Science. d Acquired cardiac fibrosis model with a local scarred region established by 3D printing and self-fusion of healthy and scarred cardiac spheroids in the support hydrogel. The ratios of iPSC-CMs and fibroblasts are 4:1 for healthy and 1:4 for scarred cardiac spheroids. Reduced contraction amplitudes are observed for scarred microtissues compared to healthy controls. Reproduced with permission, Copyright 2021 Springer Nature