Spatiotemporal Characterizations of Spontaneously Beating Cardiomyocytes with Adaptive Reference Digital Image Correlation

A Novel non-invasive optical framework for simultaneous analysis of contractility and calcium in single-cell cardiomyocytes

The use of a video method based on the Digital Image Correlation (DIC) algorithm from experimental mechanics to estimate the displacements, strain field, and sarcolemma length in a beating single-cell cardiomyocyte is proposed in this work. The obtained deformation is then correlated with the calcium signal, from calcium imaging where fluorescent dyes sensitive to calcium Ca2+ are used. Our proposed video-based method for simultaneous contraction and intracellular calcium analysis results in a low-cost, non-invasive, and label-free method. This technique has shown great advantages in long-term observations because this type of intervention-free measurement neutralizes the possible alteration in the beating cardiomyocyte introduced by other techniques for measuring cell contractility (e.g., Traction Force Microscopy, Atomic Force Microscopy, Microfabrication or Optical tweezers). Three tests were performed with synthetically augmented data from cardiomyocyte images to validate the robustness of the algorithm. First, a simulated rigid translation of a referenced image is applied, then a rotation, and finally a controlled longitudinal deformation of the referenced image, thus simulating a native realistic deformation. Finally, the proposed framework is evaluated with real experimental data. To validate contraction induced by intracellular calcium concentration, this signal is correlated with a new deformation measure proposed in this article, which is independent of cell orientation in the imaging setup. Finally, based on the displacements obtained by the DIC algorithm, the change in sarcolemma length in a contracting cardiomyocyte is calculated and its temporal correlation with the calcium signal is obtained.

Dual-Modal Sensing Skin Adaptive to Daylight, Darkness, and Ultraviolet Light for Simultaneous Full-Field Deformation Measurement and Mechanoluminescence Responses

Mechanoluminescence (ML) and digital image correlation (DIC) have emerged as promising optical methods to visualize and measure deformation fields. In this study, a dual-modal sensing skin, called the ML-DIC skin is introduced, that is capable of emitting ML and facilitating DIC measurements under various lighting conditions, including daylight, night or darkness, and UV irradiation. Four ML-DIC skins are fabricated with or without carbon nanotubes (CNTs) using a composite powder consisting of SrAl2O4: Eu,Dy (SAO), and acrylic resin, with CNT milling times of 48, 72, and 96 h for three of four skins, respectively. DIC measurements are performed under multiple lighting conditions for measuring photoluminescence, persistence luminescence, and reflection. Uniaxial tension tests demonstrate the superior performance of ML-DIC skins with CNTs compared with pristine SAO skins, with the skin subjected to 48 h of CNT dispersion exhibiting optimal performance. Further investigations focus on ML emission and DIC measurements near the crack-tip vicinity of static and propagating cracks as well as on surfaces above subsurface cracks. The integration of ML and DIC techniques offers a versatile approach for comprehensive deformation analysis applicable to diverse environments, with implications for materials science, engineering, and structural health monitoring.

Characterizing collagen scaffold compliance with native myocardial strains using an ex-vivo cardiac model: The physio-mechanical influence of scaffold architecture and attachment method

Applied to the epicardium in-vivo, regenerative cardiac patches support the ventricular wall, reduce wall stresses, encourage ventricular wall thickening, and improve ventricular function. Scaffold engraftment, however, remains a challenge. After implantation, scaffolds are subject to the complex, time-varying, biomechanical environment of the myocardium. The mechanical capacity of engineered tissue to biomimetically deform and simultaneously support the damaged native tissue is crucial for its efficacy. To date, however, the biomechanical response of engineered tissue applied directly to live myocardium has not been characterized. In this paper, we utilize optical imaging of a Langendorff ex-vivo cardiac model to characterize the native deformation of the epicardium as well as that of attached engineered scaffolds. We utilize digital image correlation, linear strain, and 2D principal strain analysis to assess the mechanical compliance of acellular ice templated collagen scaffolds. Scaffolds had either aligned or isotropic porous architecture and were adhered directly to the live epicardial surface with either sutures or cyanoacrylate glue. We demonstrate that the biomechanical characteristics of native myocardial deformation on the epicardial surface can be reproduced by an ex-vivo cardiac model. Furthermore, we identified that scaffolds with unidirectionally aligned pores adhered with suture fixation most accurately recapitulated the deformation of the native epicardium. Our study contributes a translational characterization methodology to assess the physio-mechanical performance of engineered cardiac tissue and adds to the growing body of evidence showing that anisotropic scaffold architecture improves the functional biomimetic capacity of engineered cardiac tissue. STATEMENT OF SIGNIFICANCE: Engineered cardiac tissue offers potential for myocardial repair, but engraftment remains a challenge. In-vivo, engineered scaffolds are subject to complex biomechanical stresses and the mechanical capacity of scaffolds to biomimetically deform is critical. To date, the biomechanical response of engineered scaffolds applied to live myocardium has not been characterized. In this paper, we utilize optical imaging of an ex-vivo cardiac model to characterize the deformation of the native epicardium and scaffolds attached directly to the heart. Comparing scaffold architecture and fixation method, we demonstrate that sutured scaffolds with anisotropic pores aligned with the native alignment of the superficial myocardium best recapitulate native deformation. Our study contributes a physio-mechanical characterization methodology for cardiac tissue engineering scaffolds.

MicroBundleCompute: Automated segmentation, tracking, and analysis of subdomain deformation in cardiac microbundles

Advancing human induced pluripotent stem cell derived cardiomyocyte (hiPSC-CM) technology will lead to significant progress ranging from disease modeling, to drug discovery, to regenerative tissue engineering. Yet, alongside these potential opportunities comes a critical challenge: attaining mature hiPSC-CM tissues. At present, there are multiple techniques to promote maturity of hiPSC-CMs including physical platforms and cell culture protocols. However, when it comes to making quantitative comparisons of functional behavior, there are limited options for reliably and reproducibly computing functional metrics that are suitable for direct cross-system comparison. In addition, the current standard functional metrics obtained from time-lapse images of cardiac microbundle contraction reported in the field (i.e., post forces, average tissue stress) do not take full advantage of the available information present in these data (i.e., full-field tissue displacements and strains). Thus, we present "MicroBundleCompute," a computational framework for automatic quantification of morphology-based mechanical metrics from movies of cardiac microbundles. Briefly, this computational framework offers tools for automatic tissue segmentation, tracking, and analysis of brightfield and phase contrast movies of beating cardiac microbundles. It is straightforward to implement, runs without user intervention, requires minimal input parameter setting selection, and is computationally inexpensive. In this paper, we describe the methods underlying this computational framework, show the results of our extensive validation studies, and demonstrate the utility of exploring heterogeneous tissue deformations and strains as functional metrics. With this manuscript, we disseminate "MicroBundleCompute" as an open-source computational tool with the aim of making automated quantitative analysis of beating cardiac microbundles more accessible to the community.

Extracellular macrostructure anisotropy improves cardiac tissue-like construct function and phenotypic cellular maturation

Regenerative cardiac tissue is a promising field of study with translational potential as a therapeutic option for myocardial repair after injury, however, poor electrical and contractile function has limited translational utility. Emerging research suggests scaffolds that recapitulate the structure of the native myocardium improve physiological function. Engineered cardiac constructs with anisotropic extracellular architecture demonstrate improved tissue contractility, signaling synchronicity, and cellular organization when compared to constructs with reduced architectural order. The complexity of scaffold fabrication, however, limits isolated variation of individual structural and mechanical characteristics. Thus, the isolated impact of scaffold macroarchitecture on tissue function is poorly understood. Here, we produce isotropic and aligned collagen scaffolds seeded with embryonic stem cell derived cardiomyocytes (hESC-CM) while conserving all confounding physio-mechanical features to independently assess the effects of macroarchitecture on tissue function. We quantified spatiotemporal tissue function through calcium signaling and contractile strain. We further examined intercellular organization and intracellular development. Aligned tissue constructs facilitated improved signaling synchronicity and directional contractility as well as dictated uniform cellular alignment. Cells on aligned constructs also displayed phenotypic and genetic markers of increased maturity. Our results isolate the influence of scaffold macrostructure on tissue function and inform the design of optimized cardiac tissue for regenerative and model medical systems.

3D-bioprinting of patient-derived cardiac tissue models for studying congenital heart disease

Introduction

Congenital heart disease is the leading cause of death related to birth defects and affects 1 out of every 100 live births. Induced pluripotent stem cell technology has allowed for patient-derived cardiomyocytes to be studied in vitro. An approach to bioengineer these cells into a physiologically accurate cardiac tissue model is needed in order to study the disease and evaluate potential treatment strategies.

Methods

To accomplish this, we have developed a protocol to 3D-bioprint cardiac tissue constructs comprised of patient-derived cardiomyocytes within a hydrogel bioink based on laminin-521.

Results

Cardiomyocytes remained viable and demonstrated appropriate phenotype and function including spontaneous contraction. Contraction remained consistent during 30 days of culture based on displacement measurements. Furthermore, tissue constructs demonstrated progressive maturation based on sarcomere structure and gene expression analysis. Gene expression analysis also revealed enhanced maturation in 3D constructs compared to 2D cell culture.

Discussion

This combination of patient-derived cardiomyocytes and 3D-bioprinting represents a promising platform for studying congenital heart disease and evaluating individualized treatment strategies.