Natural myocardial ECM patch drives cardiac progenitor based restoration even after scarring

Processing of Human Cardiac Tissue Toward Extracellular Matrix Self-assembling Hydrogel for In Vitro and In Vivo Applications

Acellular extracellular matrix preparations are useful for studying cell-matrix interactions and facilitate regenerative cell therapy applications. Several commercial extracellular matrix products are available as hydrogels or membranes, but these do not possess tissue-specific biological activity. Because perfusion decellularization is usually not possible with human heart tissue, we developed a 3-step immersion decellularization process. Human myocardial slices procured during surgery are first treated with detergent-free hyperosmolar lysis buffer, followed by incubation with the ionic detergent, sodium dodecyl sulfate, and the process is completed by exploiting the intrinsic DNase activity of fetal bovine serum. This technique results in cell-free sheets of cardiac extracellular matrix with largely preserved fibrous tissue architecture and biopolymer composition, which were shown to provide specific environmental cues to cardiac cell populations and pluripotent stem cells. Cardiac extracellular matrix sheets can then be further processed into a microparticle powder without further chemical modification, or, via short-term pepsin digestion, into a self-assembling cardiac extracellular matrix hydrogel with preserved bioactivity.

Strategies to develop endogenous stem cell-recruiting bioactive materials for tissue repair and regeneration

A leading strategy in tissue engineering is the design of biomimetic scaffolds that stimulate the body's repair mechanisms through the recruitment of endogenous stem cells to sites of injury. Approaches that employ the use of chemoattractant gradients to guide tissue regeneration without external cell sources are favored over traditional cell-based therapies that have limited potential for clinical translation. Following this concept, bioactive scaffolds can be engineered to provide a temporally and spatially controlled release of biological cues, with the possibility to mimic the complex signaling patterns of endogenous tissue regeneration. Another effective way to regulate stem cell activity is to leverage the inherent chemotactic properties of extracellular matrix (ECM)-based materials to build versatile cell-instructive platforms. This review introduces the concept of endogenous stem cell recruitment, and provides a comprehensive overview of the strategies available to achieve effective cardiovascular and bone tissue regeneration.

Site-specific gene expression analysis of implant-near cells in a soft tissue infection model - Application of laser microdissection to study biomaterial-associated infection

Analysis of the implant-tissue interface is important for an understanding of the cellular response to biomaterials with different surface characteristics. However, inaccessibility to the site has restricted the detailed evaluation of the tissue surrounding the implant. Laser microdissection enables the isolation of specific cells and tissues for subsequent DNA, RNA, or protein analysis. The present experimental study employed laser microdissection to analyze tissue-specific differences in gene expression in cells around infected or control titanium implants 72 h after subcutaneous implantation in a rat model. Three different tissue zones located 0-800 μm away from the implant-tissue interface were analyzed. Implant sites challenged with a dose of 10⁶  CFU Staphylococcus epidermidis demonstrated higher gene expression of selected markers for inflammation (TNF-α, IL-6), cell recruitment (MCP-1, IL-8, IL-8 R), infection (TLR2), and tissue remodeling (MMP-9) compared with control implants. Furthermore, the gene expression analysis of the three extracted tissue zones revealed marked spatial differences, depending on the distance to the implant. Control implants continuously induced higher cell gene expression in the implant-tissue interface compared with cells 200-800 μm away from the implant, whereas the sites inoculated with S. epidermidis resulted in high gene expression further away from the implant as well. In conclusion, this study demonstrates that laser microdissection is an interesting tool, revealing both gene- and site-specific gene expression patterns in the implant-tissue interface. The technique provides an opportunity for detailed molecular dissection of the biological events related to the implant but occurring at different distances from the implant. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2210-2217, 2017.

Naturally Engineered Maturation of Cardiomyocytes

Ischemic heart disease remains one of the most prominent causes of mortalities worldwide with heart transplantation being the gold-standard treatment option. However, due to the major limitations associated with heart transplants, such as an inadequate supply and heart rejection, there remains a significant clinical need for a viable cardiac regenerative therapy to restore native myocardial function. Over the course of the previous several decades, researchers have made prominent advances in the field of cardiac regeneration with the creation of in vitro human pluripotent stem cell-derived cardiomyocyte tissue engineered constructs. However, these engineered constructs exhibit a functionally immature, disorganized, fetal-like phenotype that is not equivalent physiologically to native adult cardiac tissue. Due to this major limitation, many recent studies have investigated approaches to improve pluripotent stem cell-derived cardiomyocyte maturation to close this large functionality gap between engineered and native cardiac tissue. This review integrates the natural developmental mechanisms of cardiomyocyte structural and functional maturation. The variety of ways researchers have attempted to improve cardiomyocyte maturation in vitro by mimicking natural development, known as natural engineering, is readily discussed. The main focus of this review involves the synergistic role of electrical and mechanical stimulation, extracellular matrix interactions, and non-cardiomyocyte interactions in facilitating cardiomyocyte maturation. Overall, even with these current natural engineering approaches, pluripotent stem cell-derived cardiomyocytes within three-dimensional engineered heart tissue still remain mostly within the early to late fetal stages of cardiomyocyte maturity. Therefore, although the end goal is to achieve adult phenotypic maturity, more emphasis must be placed on elucidating how the in vivo fetal microenvironment drives cardiomyocyte maturation. This information can then be utilized to develop natural engineering approaches that can emulate this fetal microenvironment and thus make prominent progress in pluripotent stem cell-derived maturity toward a more clinically relevant model for cardiac regeneration.

Biohybrid cardiac ECM-based hydrogels improve long term cardiac function post myocardial infarction

Injectable scaffolds for cardiac tissue regeneration are a promising therapeutic approach for progressive heart failure following myocardial infarction (MI). Their major advantage lies in their delivery modality that is considered minimally invasive due to their direct injection into the myocardium. Biomaterials comprising such scaffolds should mimic the cardiac tissue in terms of composition, structure, mechanical support, and most importantly, bioactivity. Nonetheless, natural biomaterial-based gels may suffer from limited mechanical strength, which often fail to provide the long-term support required by the heart for contraction and relaxation. Here we present newly-developed injectable scaffolds, which are based on solubilized decellularized porcine cardiac extracellular matrix (pcECM) cross-linked with genipin alone or engineered with different amounts of chitosan to better control the gel's mechanical properties while still leveraging the ECM biological activity. We demonstrate that these new biohybrid materials are naturally remodeled by mesenchymal stem cells, while supporting high viabilities and affecting cell morphology and organization. They exhibit neither in vitro nor in vivo immunogenicity. Most importantly, their application in treating acute and long term chronic MI in rat models clearly demonstrates the significant therapeutic potential of these gels in the long-term (12weeks post MI). The pcECM-based gels enable not only preservation, but also improvement in cardiac function eight weeks post treatment, as measured using echocardiography as well as hemodynamics. Infiltration of progenitor cells into the gels highlights the possible biological remodeling properties of the ECM-based platform.

STATEMENT OF SIGNIFICANCE

This work describes the development of new injectable scaffolds for cardiac tissue regeneration that are based on solubilized porcine cardiac extracellular matrix (ECM), combined with natural biomaterials: genipin, and chitosan. The design of such scaffolds aims at leveraging the natural bioactivity and unique structure of cardiac ECM, while overcoming its limited mechanical strength, which may fail to provide the long-term support required for heart contraction and relaxation. Here, we present a biocompatible gel-platform with custom-tailored mechanical properties that significantly improve cardiac function when injected into rat hearts following acute and chronic myocardial infarction. We clearly demonstrate the substantial therapeutic potential of these scaffolds, which not only preserved heart functions but also alleviated MI damage, even after the formation of a mature scar tissue.

Optimizing the host substrate environment for cardiac angiogenesis, arteriogenesis, and myogenesis

INTRODUCTION

The diseased host milieu, such as endothelial dysfunction (ED), decreased NO bioavailability, and ischemic/inflammatory post-MI environment, hamper the clinical success of existing cardiac regenerative therapies. Area covered: In this article, current strategies including pharmacological and nonpharmacological approaches for improving the diseased host milieu are reviewed. Specifically, the authors provide focus on: i) the mechanism of ED in patients with cardiovascular diseases, ii) the current results of ED improving strategies in pre-clinical and clinical studies, and iii) the use of biomaterials as a novel modulator in damaged post-MI environment. Expert opinion: Adjunct therapies which improve host endothelial function have demonstrated promising outcomes, potentially overcoming disappointing results of cell therapy in human studies. In the future, elucidation of the interactions between the host tissue and therapeutic agents, as well as downstream signaling pathways, will be the next challenges in enhancing regenerative therapy. More careful investigations are also required to establish these agents' safety and efficacy for wide usage in humans.

Prevascularization of Decellularized Porcine Myocardial Slice for Cardiac Tissue Engineering

Prevacularization strategies have been implemented in tissue engineering to generate microvasculature networks within a scaffold prior to implantation. Prevascularizing scaffolds will shorten the time of functional vascular perfusion with host upon implantation. In this study, we explored key variables affecting the interaction between decellularized porcine myocardium slices (dPMSs) and reseeded stem cells toward the fabrication of prevascularized cardiac tissue. Our results demonstrated that dPMS supports attachment of human mesenchymal stem cells (hMSCs) and rat adipose derived stem cells (rASCs) with high viability. We found that cell seeding efficiency and proliferation are dPMS thickness dependent. Compared to lateral cell seeding, bilateral cell seeding strategy significantly enhanced seeding efficiency, infiltration, and growth in 600 μm dPMS. dPMS induced endothelial differentiation and maturation of hMSCs and rASCs after 1 and 5 days culture, respectively. These results indicate the potential of dPMS as a powerful platform to develop prevascularized scaffolds and fabricate functional cardiac patches.