Three-dimensional scaffold-free microtissues engineered for cardiac repair

Engineered Gold and Silica Nanoparticle-Incorporated Hydrogel Scaffolds for Human Stem Cell-Derived Cardiac Tissue Engineering

Electrically conductive biomaterials and nanomaterials have demonstrated great potential in the development of functional and mature cardiac tissues. In particular, gold nanomaterials have emerged as promising candidates due to their biocompatibility and ease of fabrication for cardiac tissue engineering utilizing rat- or stem cell-derived cardiomyocytes (CMs). However, despite significant advancements, it is still not clear whether the enhancement in cardiac tissue function is primarily due to the electroconductivity features of gold nanoparticles or the structural changes of the scaffold resulting from the addition of these nanoparticles. To address this question, we developed nanoengineered hydrogel scaffolds comprising gelatin methacrylate (GelMA) embedded with either electrically conductive gold nanorods (GNRs) or nonconductive silica nanoparticles (SNPs). This enabled us to simultaneously assess the roles of electrically conductive and nonconductive nanomaterials in the functionality and fate of human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). Our studies revealed that both GNR- and SNP-incorporated hydrogel scaffolds exhibited excellent biocompatibility and similar cardiac cell attachment. Although the expression of sarcomere alpha-actinin did not significantly differ among the conditions, a more organized sarcomere structure was observed within the GNR-embedded hydrogels compared to the nonconductive nanoengineered scaffolds. Furthermore, electrical coupling was notably improved in GNR-embedded scaffolds, as evidenced by the synchronous calcium flux and enhanced calcium transient intensity. While we did not observe a significant difference in the gene expression profile of human cardiac tissues formed on the conductive GNR- and nonconductive SNP-incorporated hydrogels, we noticed marginal improvements in the expression of some calcium and structural genes in the nanomaterial-embedded hydrogel groups as compared to the control condition. Given that the cardiac tissues formed atop the nonconductive SNP-based scaffolds (used as the control for conductivity) also displayed similar levels of gene expression as compared to the conductive hydrogels, it suggests that the electrical conductivity of nanomaterials (i.e., GNRs) may not be the sole factor influencing the function and fate of hiPSC-derived cardiac tissues when cells are cultured atop the scaffolds. Overall, our findings provide additional insights into the role of electrically conductive gold nanoparticles in regulating the functionalities of hiPSC-CMs.

Improving the development of human engineered cardiac tissue by gold nanorods embedded extracellular matrix for long-term viability

A myocardial infarction (MI), commonly called a heart attack, results in the death of cardiomyocytes (CMs) in the heart. Tissue engineering provides a promising strategy for the treatment of MI, but the maturation of human engineered cardiac tissue (hECT) still requires improvement. Conductive polymers and nanomaterials have been incorporated into the extracellular matrix to enhance the mechanical and electrical coupling between cardiac cells. Here we report a simple approach to incorporate gold nanorods (GNRs) into the fibrin hydrogel to form a GNR-fibrin matrix, which is used as the major component of the extracellular matrix for forming a 3D hECT construct suspended between two flexible posts. The hECTs made with GNR-fibrin hydrogel showed markers of maturation such as higher twitch force, synchronous beating activity, sarcomere maturation and alignment, t-tubule network development, and calcium handling improvement. Most importantly, the GNR-hECTs can survive over 9 months. We envision that the hECT with GNRs holds the potential to restore the functionality of the infarcted heart.

Nanoengineering of gold nanoribbon-embedded isogenic stem cell-derived cardiac organoids

Cardiac tissue engineering is an emerging field providing tools to treat and study cardiovascular diseases (CVDs). In the past years, the integration of stem cell technologies with micro- and nanoengineering techniques has enabled the creation of novel engineered cardiac tissues (ECTs) with potential applications in disease modeling, drug screening, and regenerative medicine. However, a major unaddressed limitation of stem cell-derived ECTs is their immature state, resembling a neonatal phenotype and genotype. The modulation of the cellular microenvironment within the ECTs has been proposed as an efficient mechanism to promote cellular maturation and improve features such as cellular coupling and synchronization. The integration of biological and nanoscale cues in the ECTs could serve as a tool for the modification and control of the engineered tissue microenvironment. Here we present a proof-of-concept study for the integration of biofunctionalized gold nanoribbons (AuNRs) with hiPSC-derived isogenic cardiac organoids to enhance tissue function and maturation. We first present extensive characterization of the synthesized AuNRs, their PEGylation and cytotoxicity evaluation. We then evaluated the functional contractility and transcriptomic profile of cardiac organoids fabricated with hiPSC-derived cardiomyocytes (mono-culture) as well as with hiPSC-derived cardiomyocytes and cardiac fibroblasts (co-culture). We demonstrated that PEGylated AuNRs are biocompatible and do not induce cell death in hiPSC-derived cardiac cells and organoids. We also found an improved transcriptomic profile of the co-cultured organoids indicating maturation of the hiPSC-derived cardiomyocytes in the presence of cardiac fibroblasts. Overall, we present for the first time the integration of AuNRs into cardiac organoids, showing promising results for improved tissue function.

Development and Characterization of Isogenic Cardiac Organoids from Human-Induced Pluripotent Stem Cells Under Supplement Starvation Regimen

The prevalence of cardiovascular risk factors is expected to increase the occurrence of cardiovascular diseases (CVDs) worldwide. Cardiac organoids are promising candidates for bridging the gap between in vitro experimentation and translational applications in drug development and cardiac repair due to their attractive features. Here we present the fabrication and characterization of isogenic scaffold-free cardiac organoids derived from human induced pluripotent stem cells (hiPSCs) formed under a supplement-deprivation regimen that allows for metabolic synchronization and maturation of hiPSC-derived cardiac cells. We propose the formation of coculture cardiac organoids that include hiPSC-derived cardiomyocytes and hiPSC-derived cardiac fibroblasts (hiPSC-CMs and hiPSC-CFs, respectively). The cardiac organoids were characterized through extensive morphological assessment, evaluation of cellular ultrastructures, and analysis of transcriptomic and electrophysiological profiles. The morphology and transcriptomic profile of the organoids were improved by coculture of hiPSC-CMs with hiPSC-CFs. Specifically, upregulation of Ca²⁺ handling-related genes, such as RYR2 and SERCA, and structure-related genes, such as TNNT2 and MYH6, was observed. Additionally, the electrophysiological characterization of the organoids under supplement deprivation shows a trend for reduced conduction velocity for coculture organoids. These studies help us gain a better understanding of the role of other isogenic cells such as hiPSC-CFs in the formation of mature cardiac organoids, along with the introduction of exogenous chemical cues, such as supplement starvation.

Passive and Flexible Wireless Electronics Fabricated on Parylene/PDMS Substrate for Stimulation of Human Stem Cell-Derived Cardiomyocytes

In this paper, we report the development of a wireless, passive, biocompatible, and flexible system for stimulation of human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMS). Fabricated on a transparent parylene/PDMS substrate, the proposed stimulator enables real-time excitation and characterization of hiPSC-CMs cultured on-board. The device comprises a rectenna operating at 2.35 GHz which receives radio frequency (RF) energy from an external transmitter and converts it into DC voltage to deliver monophasic stimulation. The operation of the stimulator was primarily verified by delivering monophasic voltage pulses through gold electrodes to hiPSC-CMs cultured on the Matrigel-coated substrates. Stimulated hiPSC-CMs beat in accordance with the monophasic pulses when delivered at 0.5, 1, and 2 Hz pulsing frequency, while no significant cell death was observed. The wireless stimulator could generate monophasic pulses with an amplitude of 8 V at a distance of 15 mm. These results demonstrated the proposed wireless stimulator's efficacy for providing electrical stimulation to engineered cardiac tissues. The proposed stimulator will have a wide application in tissue engineering where a fully wireless stimulation of electroconductive cells is needed. The device also has potential to be employed as a cardiac stimulator by delivering external stimulation and regulating the contractions of cardiac tissue.

Ionic liquid-based electroactive materials: a novel approach for cardiac tissue engineering strategies

Cardiac tissue regeneration strategies are increasingly taking advantage of electroactive scaffolds to actively recreate the tissue microenvironment. In this context, this work reports on advanced materials based on two different ionic liquids (ILs), 2-hydroxyethyl-trimethylammonium dihydrogen phosphate ([Ch][DHP]) and choline bis(trifluoromethylsulfonyl)imide ([Ch][TFSI]), combined with poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) for the development of ionic electroactive IL/polymer hybrid materials for cardiac tissue engineering (TE). The morphological, physico-chemical, thermal and electrical properties of the hybrid materials, as well as their potential use as scaffolds for cardiac TE applications, were evaluated. Besides inducing changes in surface topography, roughness and wettability of the composites, the incorporation of [Ch][DHP] and [Ch][TFSI] leads to the increase in surface (σ_surface) and volume (σ_volume) electrical conductivities. Furthermore, washing the hybrid samples with phosphate-buffered saline solution strongly decreases the σ_surface, whereas σ_surface and σ_volume of the composites remain almost unaltered after exposure to ultraviolet sterilization treatment. Additionally, it is verified that the incorporation of IL influences the P(VDF-TrFE) microstructure and crystallization process, acting as a defect during its crystallization. Cytotoxicity assays revealed that hybrid films based on [Ch][DHP] alone are not cytotoxic. These films also support H9c2 myoblast cell adhesion and proliferation, demonstrating their suitability for cardiac TE strategies based on electroactive microenvironments.

Bacterial Cellulose and ECM Hydrogels: An Innovative Approach for Cardiovascular Regenerative Medicine

Cardiovascular diseases are considered the leading cause of death in the world, accounting for approximately 85% of sudden death cases. In dogs and cats, sudden cardiac death occurs commonly, despite the scarcity of available pathophysiological and prevalence data. Conventional treatments are not able to treat injured myocardium. Despite advances in cardiac therapy in recent decades, transplantation remains the gold standard treatment for most heart diseases in humans. In veterinary medicine, therapy seeks to control clinical signs, delay the evolution of the disease and provide a better quality of life, although transplantation is the ideal treatment. Both human and veterinary medicine face major challenges regarding the transplantation process, although each area presents different realities. In this context, it is necessary to search for alternative methods that overcome the recovery deficiency of injured myocardial tissue. Application of biomaterials is one of the most innovative treatments for heart regeneration, involving the use of hydrogels from decellularized extracellular matrix, and their association with nanomaterials, such as alginate, chitosan, hyaluronic acid and gelatin. A promising material is bacterial cellulose hydrogel, due to its nanostructure and morphology being similar to collagen. Cellulose provides support and immobilization of cells, which can result in better cell adhesion, growth and proliferation, making it a safe and innovative material for cardiovascular repair.

Cardiac ischemia on-a-chip to investigate cellular and molecular response of myocardial tissue under hypoxia

Tissue engineering has enabled the development of advanced and physiologically relevant models of cardiovascular diseases, with advantages over conventional 2D in vitro assays. We have previously demonstrated development of a heart on-a-chip microfluidic model with mature 3D anisotropic tissue formation that incorporates both stem cell-derived cardiomyocytes and cardiac fibroblasts within a collagen-based hydrogel. Using this platform, we herein present a model of myocardial ischemia on-a-chip, that recapitulates ischemic insult through exposure of mature 3D cardiac tissues to hypoxic environments. We report extensive validation and molecular-level analyses of the model in its ability to recapitulate myocardial ischemia in response to hypoxia, demonstrating the 1) induction of tissue fibrosis through upregulation of contractile fibers, 2) dysregulation in tissue contraction through functional assessment, 3) upregulation of hypoxia-response genes and downregulation of contractile-specific genes through targeted qPCR, and 4) transcriptomic pathway regulation of hypoxic tissues. Further, we investigated the complex response of ischemic myocardial tissues to reperfusion, identifying 5) cell toxicity, 6) sustained contractile irregularities, as well as 7) re-establishment of lactate levels and 8) gene expression, in hypoxic tissues in response to ischemia reperfusion injury.

Electroconductive biomaterials for cardiac tissue engineering

Myocardial infarction (MI) is still the leading cause of mortality worldwide. The success of cell-based therapies and tissue engineering strategies for treatment of injured myocardium have been notably hindered due to the limitations associated with the selection of a proper cell source, lack of engraftment of engineered tissues and biomaterials with the host myocardium, limited vascularity, as well as immaturity of the injected cells. The first-generation approaches in cardiac tissue engineering (cTE) have mainly relied on the use of desired cells (e.g., stem cells) along with non-conductive natural or synthetic biomaterials for in vitro construction and maturation of functional cardiac tissues, followed by testing the efficacy of the engineered tissues in vivo. However, to better recapitulate the native characteristics and conductivity of the cardiac muscle, recent approaches have utilized electroconductive biomaterials or nanomaterial components within engineered cardiac tissues. This review article will cover the recent advancements in the use of electrically conductive biomaterials in cTE. The specific emphasis will be placed on the use of different types of nanomaterials such as gold nanoparticles (GNPs), silicon-derived nanomaterials, carbon-based nanomaterials (CBNs), as well as electroconductive polymers (ECPs) for engineering of functional and electrically conductive cardiac tissues. We will also cover the recent progress in the use of engineered electroconductive tissues for in vivo cardiac regeneration applications. We will discuss the opportunities and challenges of each approach and provide our perspectives on potential avenues for enhanced cTE. STATEMENT OF SIGNIFICANCE: Myocardial infarction (MI) is still the primary cause of death worldwide. Over the past decade, electroconductive biomaterials have increasingly been applied in the field of cardiac tissue engineering. This review article provides the readers with the leading advances in the in vitro applications of electroconductive biomaterials for cTE along with an in-depth discussion of injectable/transplantable electroconductive biomaterials and their delivery methods for in vivo MI treatment. The article also discusses the knowledge gaps in the field and offers possible novel avenues for improved cardiac tissue engineering.

Mechanical properties of cell sheets and spheroids: the link between single cells and complex tissues

Cell aggregates, including sheets and spheroids, represent a simple yet powerful model system to study both biochemical and biophysical intercellular interactions. However, it is becoming evident that, although the mechanical properties and behavior of multicellular structures share some similarities with individual cells, yet distinct differences are observed in some principal aspects. The description of mechanical phenomena at the level of multicellular model systems is a necessary step for understanding tissue mechanics and its fundamental principles in health and disease. Both cell sheets and spheroids are used in tissue engineering, and the modulation of mechanical properties of cell constructs is a promising tool for regenerative medicine. Here, we review the data on mechanical characterization of cell sheets and spheroids, focusing both on advances in the measurement techniques and current understanding of the subject. The reviewed material suggest that interplay between the ECM, intercellular junctions, and cellular contractility determines the behavior and mechanical properties of the cell aggregates.

Designing aromatic N-cadherin mimetic short-peptide-based bioactive scaffolds for controlling cellular behaviour

The development of suitable biomaterials is one of the key factors responsible for the success of the tissue-engineering field. Recently, significant effort has been devoted to the design of biomimetic materials that can elicit specific cellular responses and direct new tissue formation mediated by bioactive peptides. The success of the design principle of such biomimetic scaffolds is mainly related to the cell-extracellular matrix (ECM) interactions, whereas cell-cell interactions also play a vital role in cell survival, neurite outgrowth, attachment, migration, differentiation, and proliferation. Hence, an ideal strategy to improve cell-cell interactions would rely on the judicious incorporation of a bioactive motif in the designer scaffold. In this way, we explored for the first time the primary functional pentapeptide sequence of the N-cadherin protein, HAVDI, which is known to be involved in cell-cell interactions. We have formulated the shortest N-cadherin mimetic peptide sequence utilizing a minimalistic approach. Furthermore, we employed a classical molecular self-assembly strategy through rational modification of the basic pentapeptide motif of N-cadherin, i.e. HAVDI, using Fmoc and Nap aromatic moieties to modify the N-terminal end. The designed N-cadherin mimetic peptides, Fmoc-HAVDI and Nap-HAVDI, self-assembled to form a nanofibrous network resulting in a bioactive peptide hydrogel at physiological pH. The nanofibrous network of the pentapeptide hydrogels resembles the topology of the natural ECM. Furthermore, the mechanical strength of the gels also matches that of the native ECM of neural cells. Interestingly, both the N-cadherin mimetic peptide hydrogels supported cell adhesion and proliferation of the neural and non-neural cell lines, highlighting the diversity of these peptidic scaffolds. Further, the cultured neural and non-neural cells on the bioactive scaffolds showed normal expression of β-III tubulin and actin, respectively. The cellular response was compromised in control peptides, which further establishes the significance of the bioactive motifs towards controlling the cellular behaviour. Our study indicated that our designer N-cadherin-based peptidic hydrogels mimic the structural as well as the physical properties of the native ECM, which has been further reflected in the functional attributes offered by these scaffolds, and thus offer a suitable bioactive domain for further use as a next-generation material in tissue-engineering applications.

Polymeric Biomaterials for the Treatment of Cardiac Post-Infarction Injuries

Cardiac regeneration aims to reconstruct the heart contractile mass, preventing the organ from a progressive functional deterioration, by delivering pro-regenerative cells, drugs, or growth factors to the site of injury. In recent years, scientific research focused the attention on tissue engineering for the regeneration of cardiac infarct tissue, and biomaterials able to anatomically and physiologically adapt to the heart muscle have been proposed as valuable tools for this purpose, providing the cells with the stimuli necessary to initiate a complete regenerative process. An ideal biomaterial for cardiac tissue regeneration should have a positive influence on the biomechanical, biochemical, and biological properties of tissues and cells; perfectly reflect the morphology and functionality of the native myocardium; and be mechanically stable, with a suitable thickness. Among others, engineered hydrogels, three-dimensional polymeric systems made from synthetic and natural biomaterials, have attracted much interest for cardiac post-infarction therapy. In addition, biocompatible nanosystems, and polymeric nanoparticles in particular, have been explored in preclinical studies as drug delivery and tissue engineering platforms for the treatment of cardiovascular diseases. This review focused on the most employed natural and synthetic biomaterials in cardiac regeneration, paying particular attention to the contribution of Italian research groups in this field, the fabrication techniques, and the current status of the clinical trials.

Bioengineering approaches to mature induced pluripotent stem cell-derived atrial cardiomyocytes to model atrial fibrillation

Induced pluripotent stem cells (iPSCs) serve as a robust platform to model several human arrhythmia syndromes including atrial fibrillation (AF). However, the structural, molecular, functional, and electrophysiological parameters of patient-specific iPSC-derived atrial cardiomyocytes (iPSC-aCMs) do not fully recapitulate the mature phenotype of their human adult counterparts. The use of physiologically inspired microenvironmental cues, such as postnatal factors, metabolic conditioning, extracellular matrix (ECM) modulation, electrical and mechanical stimulation, co-culture with non-parenchymal cells, and 3D culture techniques can help mimic natural atrial development and induce a more mature adult phenotype in iPSC-aCMs. Such advances will not only elucidate the underlying pathophysiological mechanisms of AF, but also identify and assess novel mechanism-based therapies towards supporting a more 'personalized' (i.e. patient-specific) approach to pharmacologic therapy of AF.

Mechanical stimulation enhances development of scaffold-free, 3D-printed, engineered heart tissue grafts

Current efforts to engineer a clinically relevant tissue graft from human-induced pluripotent stem cells (hiPSCs) have relied on the addition or utilization of external scaffolding material. However, any imbalance in the interactions between embedded cells and their surroundings may hinder the success of the resulting tissue graft. Therefore, the goal of our study was to create scaffold-free, 3D-printed cardiac tissue grafts from hiPSC-derived cardiomyocytes (CMs), and to evaluate whether or not mechanical stimulation would result in improved graft maturation. To explore this, we used a 3D bioprinter to produce scaffold-free cardiac tissue grafts from hiPSC-derived CM cell spheroids. Static mechanical stretching of these grafts significantly increased sarcomere length compared to unstimulated free-floating tissues, as determined by immunofluorescent image analysis. Stretched tissue was found to have decreased elastic modulus, increased maximal contractile force, and increased alignment of formed extracellular matrix, as expected in a functionally maturing tissue graft. Additionally, stretched tissues had upregulated expression of cardiac-specific gene transcripts, consistent with increased cardiac-like cellular identity. Finally, analysis of extracellular matrix organization in stretched grafts suggests improved remodeling by embedded cardiac fibroblasts. Taken together, our results suggest that mechanical stretching stimulates hiPSC-derived CMs in a 3D-printed, scaffold-free tissue graft to develop mature cardiac material structuring and cellular fates. Our work highlights the critical role of mechanical conditioning as an important engineering strategy toward developing clinically applicable, scaffold-free human cardiac tissue grafts.