Biomimetic Model of Contractile Cardiac Tissue with Endothelial Networks Stabilized by Adipose-Derived Stromal/Stem Cells

Versatile human cardiac tissues engineered with perfusable heart extracellular microenvironment for biomedical applications

Engineered human cardiac tissues have been utilized for various biomedical applications, including drug testing, disease modeling, and regenerative medicine. However, the applications of cardiac tissues derived from human pluripotent stem cells are often limited due to their immaturity and lack of functionality. Therefore, in this study, we establish a perfusable culture system based on in vivo-like heart microenvironments to improve human cardiac tissue fabrication. The integrated culture platform of a microfluidic chip and a three-dimensional heart extracellular matrix enhances human cardiac tissue development and their structural and functional maturation. These tissues are comprised of cardiovascular lineage cells, including cardiomyocytes and cardiac fibroblasts derived from human induced pluripotent stem cells, as well as vascular endothelial cells. The resultant macroscale human cardiac tissues exhibit improved efficacy in drug testing (small molecules with various levels of arrhythmia risk), disease modeling (Long QT Syndrome and cardiac fibrosis), and regenerative therapy (myocardial infarction treatment). Therefore, our culture system can serve as a highly effective tissue-engineering platform to provide human cardiac tissues for versatile biomedical applications.

Heart-on-a-chip systems with tissue-specific functionalities for physiological, pathological, and pharmacological studies

Recent advances in heart-on-a-chip systems hold great promise to facilitate cardiac physiological, pathological, and pharmacological studies. This review focuses on the development of heart-on-a-chip systems with tissue-specific functionalities. For one thing, the strategies for developing cardiac microtissues on heart-on-a-chip systems that closely mimic the structures and behaviors of the native heart are analyzed, including the imitation of cardiac structural and functional characteristics. For another, the development of techniques for real-time monitoring of biophysical and biochemical signals from cardiac microtissues on heart-on-a-chip systems is introduced, incorporating cardiac electrophysiological signals, contractile activity, and biomarkers. Furthermore, the applications of heart-on-a-chip systems in intelligent cardiac studies are discussed regarding physiological/pathological research and pharmacological assessment. Finally, the future development of heart-on-a-chip toward a higher level of systematization, integration, and maturation is proposed.

Toward the Next Generation of Neural Iontronic Interfaces

Neural interfaces are evolving at a rapid pace owing to advances in material science and fabrication, reduced cost of scalable complementary metal oxide semiconductor (CMOS) technologies, and highly interdisciplinary teams of researchers and engineers that span a large range from basic to applied and clinical sciences. This study outlines currently established technologies, defined as instruments and biological study systems that are routinely used in neuroscientific research. After identifying the shortcomings of current technologies, such as a lack of biocompatibility, topological optimization, low bandwidth, and lack of transparency, it maps out promising directions along which progress should be made to achieve the next generation of symbiotic and intelligent neural interfaces. Lastly, it proposes novel applications that can be achieved by these developments, ranging from the understanding and reproduction of synaptic learning to live-long multimodal measurements to monitor and treat various neuronal disorders.

Engineered human cardiac tissues for modeling heart diseases

Heart disease is one of the major life-threatening diseases with high mortality and incidence worldwide. Several model systems, such as primary cells and animals, have been used to understand heart diseases and establish appropriate treatments. However, they have limitations in accuracy and reproducibility in recapitulating disease pathophysiology and evaluating drug responses. In recent years, three-dimensional (3D) cardiac tissue models produced using tissue engineering technology and human cells have outperformed conventional models. In particular, the integration of cell reprogramming techniques with bioengineering platforms (e.g., microfluidics, scaffolds, bioprinting, and biophysical stimuli) has facilitated the development of heart-ona- chip, cardiac spheroid/organoid, and engineered heart tissue (EHT) to recapitulate the structural and functional features of the native human heart. These cardiac models have improved heart disease modeling and toxicological evaluation. In this review, we summarize the cell types for the fabrication of cardiac tissue models, introduce diverse 3D human cardiac tissue models, and discuss the strategies to enhance their complexity and maturity. Finally, recent studies in the modeling of various heart diseases are reviewed. [BMB Reports 2023; 56(1): 32-42].

Engineered human cardiac tissues for modeling heart diseases

Heart disease is one of the major life-threatening diseases with high mortality and incidence worldwide. Several model systems, such as primary cells and animals, have been used to understand heart diseases and establish appropriate treatments. However, they have limitations in accuracy and reproducibility in recapitulating disease pathophysiology and evaluating drug responses. In recent years, three-dimensional (3D) cardiac tissue models produced using tissue engineering technology and human cells have outperformed conventional models. In particular, the integration of cell reprogramming techniques with bioengineering platforms (e.g., microfluidics, scaffolds, bioprinting, and biophysical stimuli) has facilitated the development of heart-ona- chip, cardiac spheroid/organoid, and engineered heart tissue (EHT) to recapitulate the structural and functional features of the native human heart. These cardiac models have improved heart disease modeling and toxicological evaluation. In this review, we summarize the cell types for the fabrication of cardiac tissue models, introduce diverse 3D human cardiac tissue models, and discuss the strategies to enhance their complexity and maturity. Finally, recent studies in the modeling of various heart diseases are reviewed. [BMB Reports 2023; 56(1): 32-42].

The three-dimensionality of the hiPSC-CM spheroid contributes to the variability of the field potential

Background: Field potential (FP) signals from human induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) spheroid which are used for drug safety tests in the preclinical stage are different from action potential (AP) signals and require working knowledge of the multi-electrode array (MEA) system. In this study, we developed in silico three-dimensional (3-D) models of hiPSC-CM spheroids for the simulation of field potential measurement. We compared our model simulation results against in vitro experimental data under the effect of drugs E-4031 and nifedipine. Methods: In silico 3-D models of hiPSC-CM spheroids were constructed in spherical and discoidal shapes. Tetrahedral meshes were generated inside the models, and the propagation of the action potential in the model was obtained by numerically solving the monodomain reaction-diffusion equation. An electrical model of electrode was constructed and FPs were calculated using the extracellular potentials from the AP propagations. The effects of drugs were simulated by matching the simulation results with in vitro experimental data. Results: The simulated FPs from the 3-D models of hiPSC-CM spheroids exhibited highly variable shapes depending on the stimulation and measurement locations. The values of the IC₅₀ of E-4031 and nifedipine calculated by matching the simulated FP durations with in vitro experimental data were in line with the experimentally measured ones reported in the literature. Conclusion: The 3-D in silico models of hiPSC-CM spheroids generated highly variable FPs similar to those observed in in vitro experiments. The in silico model has the potential to complement the interpretation of the FP signals obtained from in vitro experiments.

Recent Advances in Cardiac Patches: Materials, Preparations, and Properties

Cardiac patches are biomaterials that can be used for transplantation and repair of damaged myocardium by combining seed cells with the ability to form cardiomyocytes and suitable scaffold materials. On the one hand, they provide temporary support to the infarcted area, and on the other hand, they repair the damaged myocardium by delivering cells or bioactive factors to integrate with the host, which have gradually become a hot research topic in recent years. This paper summarizes the structural properties of natural myocardium and reviews the recent research progress of cardiac patches, including the seed cells and scaffold materials used in patch preparation, as well as the main methods of scaffold preparation and the structure properties of various scaffolds. In addition, a comprehensive analysis of the problems faced in the clinical implementation of cardiac patches is presented. Finally, we look forward to the development of cardiac patches and point out that precisely tunable anisotropic tissue engineering scaffolds close to natural myocardial tissue will become an important direction for future research.

Adipose mesenchymal stem cell-derived exosomal microRNAs ameliorate polycystic ovary syndrome by protecting against metabolic disturbances

Polycystic ovary syndrome (PCOS) is the most common endocrine and metabolic disorder in women of childbearing age. Adipose mesenchymal stem cells (AMSCs) secrete cytokines involved in the regulation of metabolism and immunity. However, it remains unclear whether exosomes secreted by AMSCs (AMSC-EXOs) can rescue the polycystic phenotype and metabolic dysfunction in PCOS ovaries. Here, we show that AMSC-EXOs can protect against metabolic disturbances, ameliorate ovarian polycystic, and improve fertility in a rat model of PCOS. AMSC-EXOs inhibited the expression of B-cell translocation gene 2 by transferring miR-21-5p to the livers of rats with PCOS, thus activating the IRS1/AKT pathway and increasing hepatic metabolism. The role of AMSC-EXOs in transferring miRNAs to the liver to improve metabolic dysfunction in PCOS and reproduction by rescuing a non-coding RNA pathway was also discovered. This study provides a theoretical basis for the use of rat adipose stem cells and their secreted exosomes to treat PCOS.

Tissues with Patterned Vessels or Protein Release Induce Vascular Chemotaxis in an In Vitro Platform

Engineered tissues designed for translational applications in regenerative medicine require vascular networks to deliver oxygen and nutrients rapidly to the implanted cells. A limiting factor of in vivo translation is the rapid and successful inosculation, or connection, of host and implanted vascular networks and subsequent perfusion of the implant. An approach gaining favor in vascular tissue engineering is to provide instructive cues from the engineered tissue to enhance host vascular penetration and connection with the implant. Here, we use a novel in vitro platform based on the aortic ring assay to evaluate the impact of patterned, endothelialized vessels or growth factor release from engineered constructs on preinosculative vascular cell outgrowth from surrogate host tissue in a controlled, defined environment, and introduce robust tools for evaluating vascular morphogenesis and chemotaxis. We demonstrate the creation of engineered vessels at the arteriole scale, which develop basement membrane, exhibit tight junctions, and actively sprout into the surrounding bulk hydrogel. Vessel-containing constructs are co-cultured adjacent to rodent aortic rings, and the resulting heterocellular outgrowth is quantified. Cells originating from the aortic ring migrate preferentially toward constructs containing engineered vessels with 1.5-fold faster outgrowth kinetics, 2.5-fold increased cellular density, and 1.6-fold greater network formation versus control (no endothelial cells and growth factor-reduced culture medium). Growth factor release from constructs with nonendothelialized channels and in reduced factor medium equivalently stimulates sustained vascular outgrowth distance, cellular density, and network formation, akin to engineered vessels in endothelial growth medium 2 (EGM-2) medium. In conclusion, we show that three-dimensional endothelialized patterned vessels or growth factor release stimulate a robust, host-derived vascular cell chemotactic response at early time points critical for instructive angiogenic cues. Further, we developed robust, unbiased tools to quantify metrics of vascular morphogenesis and preinosculative heterocellular outgrowth from rat aortic rings and demonstrated the utility of our complex, controlled environment, heterocellular in vitro platform. Impact statement Using a novel in vitro platform, we show that engineered constructs with patterned vessels or angiogenic growth factor release, two methods of instructing host revascularization responses, equivalently improve early host-derived vascular outgrowth. Our platform leverages the aortic ring assay in a tissue engineering context to study preinosculative vascular cell chemotaxis from surrogate host vascular cells in response to paracrine cues from co-cultured engineered tissues using robust, open-source quantification tools. Our accessible and flexible platform enables translationally focused studies in revascularization using implantable therapeutics containing prepatterned vessels with greater environmental control than in vivo studies to advance vascular tissue engineering.

Passive myocardial mechanical properties: meaning, measurement, models

Passive mechanical tissue properties are major determinants of myocardial contraction and relaxation and, thus, shape cardiac function. Tightly regulated, dynamically adapting throughout life, and affecting a host of cellular functions, passive tissue mechanics also contribute to cardiac dysfunction. Development of treatments and early identification of diseases requires better spatio-temporal characterisation of tissue mechanical properties and their underlying mechanisms. With this understanding, key regulators may be identified, providing pathways with potential to control and limit pathological development. Methodologies and models used to assess and mimic tissue mechanical properties are diverse, and available data are in part mutually contradictory. In this review, we define important concepts useful for characterising passive mechanical tissue properties, and compare a variety of in vitro and in vivo techniques that allow one to assess tissue mechanics. We give definitions of key terms, and summarise insight into determinants of myocardial stiffness in situ. We then provide an overview of common experimental models utilised to assess the role of environmental stiffness and composition, and its effects on cardiac cell and tissue function. Finally, promising future directions are outlined.

Assessment of the effects of four crosslinking agents on gelatin hydrogel for myocardial tissue engineering applications

Cardiomyocyte (CM) transplantation is a promising option for regenerating infarcted myocardium. However, poor cell survival and residence rates reduce the efficacy of cell transplantation. Gelatin (GA) hydrogel as a frequently-used cell carrier is a possible approach to increase the survival rate of CMs. In this study, microbial transglutaminase (mTG) and chemical crosslinkers glutaraldehyde, genipin, and 1-ethyl-3-(3-dimethyl aminopropyl)-carbodiimide were employed to prepare GA hydrogels. The mechanical properties and degradation characteristics of these hydrogels were then evaluated. Neonatal rat CMs (NRCMs) were isolated and inoculated on the surface of these hydrogels or encapsulated in mTG-hydrogels. Cellular growth morphology and beating behavior were observed. Cellular viability and immunofluorescence were analyzed. Intracellular Ca²⁺transient and membrane potential propagation were detected using fluorescence dyes (Fluo-3 and di-4-ANEPPS, respectively). Results showed that the chemical crosslinkers exhibited high cytotoxicity and resulted in high rates of cell death. By contrast, mTG-hydrogels showed excellent cell compatibility. The CMs cultured in mTG-hydrogels for a week expressed CM maturation markers. The NRCMs begun independently beating on the third day of culture, and their beating synchronized after a week of culture. Furthermore, intracellular Ca²⁺transient events with periodicity were observed. In conclusion, the novel mTG-crosslinked GA hydrogel synthesized herein has good biocompatibility, and it supports CM adhesion, growth, and maturation.

Protocol for the Use of a Novel Bioreactor System for Hydrated Mechanical Testing, Strained Sterile Culture, and Force of Contraction Measurement of Tissue Engineered Muscle Constructs

Bioreactor systems are built as controlled environments for biological processes and utilized in the field of tissue engineering to apply mechanical, spatial, and chemical cues to developing tissue grafts. Often the systems are applied to instruct differentiation and maturation of the cells grown inside. Perhaps the most obvious targets for strain and compression-based bioreactors are mechanically active tissues, as it is hypothesized that biomimetic mechanical environments instruct immature cells to form differentiated tissues. One such tissue, skeletal muscle, has been identified as a key candidate for strain application due to the close structure-function relationship of myofibers. Here we detail the multiple uses of a custom-built bioreactor system in combination with electrospun fibrin microfibers for muscle tissue engineering. Outlined below are the methods used in the system to test the mechanical properties of hydrogel-based scaffolds in an aqueous environment, including Young’s modulus and poroelasticity. Additionally, we demonstrate the application of tensile strain to sterile cell cultures grown on electrospun scaffolds and perform end-point testing of tissue contractility with the addition of an electrode.

Biomimetic microsystems for cardiovascular studies

Traditional tissue culture platforms have been around for several decades and have enabled key findings in the cardiovascular field. However, these platforms failed to recreate the mechanical and dynamic features found within the body. Organs-on-chips (OOCs) are cellularized microfluidic-based devices that can mimic the basic structure, function, and responses of organs. These systems have been successfully utilized in disease, development, and drug studies. OOCs are designed to recapitulate the mechanical, electrical, chemical, and structural features of the in vivo microenvironment. Here, we review cardiovascular-themed OOC studies, design considerations, and techniques used to generate these cellularized devices. Furthermore, we will highlight the advantages of OOC models over traditional cell culture vessels, discuss implementation challenges, and provide perspectives on the state of the field.

Whole Heart Engineering: Advances and Challenges

Bioengineering a solid organ for organ replacement is a growing endeavor in regenerative medicine. Our approach - recellularization of a decellularized cadaveric organ scaffold with human cells - is currently the most promising approach to building a complex solid vascularized organ to be utilized in vivo, which remains the major unmet need and a key challenge. The 2008 publication of perfusion-based decellularization and partial recellularization of a rat heart revolutionized the tissue engineering field by showing that it was feasible to rebuild an organ using a decellularized extracellular matrix scaffold. Toward the goal of clinical translation of bioengineered tissues and organs, there is increasing recognition of the underlying need to better integrate basic science domains and industry. From the perspective of a research group focusing on whole heart engineering, we discuss the current approaches and advances in whole organ engineering research as they relate to this multidisciplinary field's 3 major pillars: organ scaffolds, large numbers of cells, and biomimetic bioreactor systems. The success of whole organ engineering will require optimization of protocols to produce biologically-active scaffolds for multiple organ systems, and further technological innovation both to produce the massive quantities of high-quality cells needed for recellularization and to engineer a bioreactor with physiologic stimuli to recapitulate organ function. Also discussed are the challenges to building an implantable vascularized solid organ.