Optimization of Human Myocardium Decellularization Method for the Construction of Implantable Patches

Reconstruction of the human nipple-areolar complex: a tissue engineering approach

Introduction: Nipple-areolar complex (NAC) reconstruction after breast cancer surgery is challenging and does not always provide optimal long-term esthetic results. Therefore, generating a NAC using tissue engineering techniques, such as a decellularization-recellularization process, is an alternative option to recreate a specific 3D NAC morphological unit, which is then covered with an in vitro regenerated epidermis and, thereafter, skin-grafted on the reconstructed breast. Materials and methods: Human NACs were harvested from cadaveric donors and decellularized using sequential detergent baths. Cellular clearance and extracellular matrix (ECM) preservation were analyzed by histology, as well as by DNA, ECM proteins, growth factors, and residual sodium dodecyl sulfate (SDS) quantification. In vivo biocompatibility was evaluated 30 days after the subcutaneous implantation of native and decellularized human NACs in rats. In vitro scaffold cytocompatibility was assessed by static seeding of human fibroblasts on their hypodermal side for 7 days, while human keratinocytes were seeded on the scaffold epidermal side for 10 days by using the reconstructed human epidermis (RHE) technique to investigate the regeneration of a new epidermis. Results: The decellularized NAC showed a preserved 3D morphology and appeared white. After decellularization, a DNA reduction of 98.3% and the absence of nuclear and HLA staining in histological sections confirmed complete cellular clearance. The ECM architecture and main ECM proteins were preserved, associated with the detection and decrease in growth factors, while a very low amount of residual SDS was detected after decellularization. The decellularized scaffolds were in vivo biocompatible, fully revascularized, and did not induce the production of rat anti-human antibodies after 30 days of subcutaneous implantation. Scaffold in vitro cytocompatibility was confirmed by the increasing proliferation of seeded human fibroblasts during 7 days of culture, associated with a high number of living cells and a similar viability compared to the control cells after 7 days of static culture. Moreover, the RHE technique allowed us to recreate a keratinized pluristratified epithelium after 10 days of culture. Conclusion: Tissue engineering allowed us to create an acellular and biocompatible NAC with a preserved morphology, microarchitecture, and matrix proteins while maintaining their cell growth potential and ability to regenerate the skin epidermis. Thus, tissue engineering could provide a novel alternative to personalized and natural NAC reconstruction.

Decellularization of Massive Bone Allografts By Perfusion: A New Protocol for Tissue Engineering

In terms of large bone defect reconstructions, massive bone allografts may sometimes be the only solution. However, they are still burdened with a high postoperative complication rate. Our hypothesis is that the immunogenicity of residual cells in the graft is involved in this issue. Decellularization by perfusion might therefore be the answer to process and create more biologically effective massive bone allografts. Seventy-two porcine bones were used to characterize the efficiency of our sodium hydroxide-based decellularization protocol. A sequence of solvent perfusion through each nutrient artery was set up to ensure the complete decellularization of whole long bones. Qualitative (histology and immunohistochemistry [IHC]) and quantitative (fluoroscopic absorbance and enzyme-linked immunosorbent assay) evaluations were performed to assess the decellularization and the preservation of the extracellular matrix in the bone grafts. Cytotoxicity and compatibility were also tested. Comparatively to nontreated bones, our experiments showed a very high decellularization quality, demonstrating that perfusion is mandatory to achieve an entire decellularization. Moreover, results showed a good preservation of the bone composition and microarchitecture, Haversian systems and vascular network included. This protocol reduces the human leukocyte antigen antigenic load of the graft by >50%. The majority of measured growth factors is still present in the same amount in the decellularized bones compared to the nontreated bones. Histology and IHC show that the bones were cell compatible, noncytotoxic, and capable of inducing osteoblastic differentiation of mesenchymal stem cells. Our decellularization/perfusion protocol allowed to create decellularized long bone graft models, thanks to their inner vascular network, ready for in vivo implantation or to be further used as seeding matrices.

Decellularized Extracellular Matrix for Modeling Cardiac Extracellular Microenvironment

The extracellular matrix (ECM) forms most of the tissue microenvironment and is in a constant and dynamic equilibrium with cells. The decellularization process employs physical or chemical methods, or a combination of them, to remove the cellular components of tissues and organs while preserving the architecture and composition of the ECM. Depending on the methodology used, the decellularized ECM (dECM) is then suitable for research or clinical applications. Here, we describe an optimized protocol for the efficient decellularization of the human myocardium to generate 3D scaffolds of well-preserved cardiac extracellular matrix that can be used for in vitro or in vivo studies.

Whole-Heart Tissue Engineering and Cardiac Patches: Challenges and Promises

Despite all the advances in preventing, diagnosing, and treating cardiovascular disorders, they still account for a significant part of mortality and morbidity worldwide. The advent of tissue engineering and regenerative medicine has provided novel therapeutic approaches for the treatment of various diseases. Tissue engineering relies on three pillars: scaffolds, stem cells, and growth factors. Gene and cell therapy methods have been introduced as primary approaches to cardiac tissue engineering. Although the application of gene and cell therapy has resulted in improved regeneration of damaged cardiac tissue, further studies are needed to resolve their limitations, enhance their effectiveness, and translate them into the clinical setting. Scaffolds from synthetic, natural, or decellularized sources have provided desirable characteristics for the repair of cardiac tissue. Decellularized scaffolds are widely studied in heart regeneration, either as cell-free constructs or cell-seeded platforms. The application of human- or animal-derived decellularized heart patches has promoted the regeneration of heart tissue through in vivo and in vitro studies. Due to the complexity of cardiac tissue engineering, there is still a long way to go before cardiac patches or decellularized whole-heart scaffolds can be routinely used in clinical practice. This paper aims to review the decellularized whole-heart scaffolds and cardiac patches utilized in the regeneration of damaged cardiac tissue. Moreover, various decellularization methods related to these scaffolds will be discussed.

Three-dimensional heart extracellular matrix enhances chemically induced direct cardiac reprogramming

Direct cardiac reprogramming has emerged as a promising therapeutic approach for cardiac regeneration. Full chemical reprogramming with small molecules to generate cardiomyocytes may be more amenable than genetic reprogramming for clinical applications as it avoids safety concerns associated with genetic manipulations. However, challenges remain regarding low conversion efficiency and incomplete cardiomyocyte maturation. Furthermore, the therapeutic potential of chemically induced cardiomyocytes (CiCMs) has not been investigated. Here, we report that a three-dimensional microenvironment reconstituted with decellularized heart extracellular matrix can enhance chemical reprogramming and cardiac maturation of fibroblasts to cardiomyocytes. The resultant CiCMs exhibit elevated cardiac marker expression, sarcomeric organization, and improved electrophysiological features and drug responses. We investigated the therapeutic potential of CiCMs reprogrammed in three-dimensional heart extracellular matrix in a rat model of myocardial infarction. Our platform can facilitate the use of CiCMs for regenerative medicine, disease modeling, and drug screening.

Decellularized Extracellular Matrix Scaffolds for Cardiovascular Tissue Engineering: Current Techniques and Challenges

Cardiovascular diseases are the leading cause of global mortality. Over the past two decades, researchers have tried to provide novel solutions for end-stage heart failure to address cardiac transplantation hurdles such as donor organ shortage, chronic rejection, and life-long immunosuppression. Cardiac decellularized extracellular matrix (dECM) has been widely explored as a promising approach in tissue-regenerative medicine because of its remarkable similarity to the original tissue. Optimized decellularization protocols combining physical, chemical, and enzymatic agents have been developed to obtain the perfect balance between cell removal, ECM composition, and function maintenance. However, proper assessment of decellularized tissue composition is still needed before clinical translation. Recellularizing the acellular scaffold with organ-specific cells and evaluating the extent of cardiomyocyte repopulation is also challenging. This review aims to discuss the existing literature on decellularized cardiac scaffolds, especially on the advantages and methods of preparation, pointing out areas for improvement. Finally, an overview of the state of research regarding the application of cardiac dECM and future challenges in bioengineering a human heart suitable for transplantation is provided.

Periosteum and fascia lata: Are they so different?

Introduction: The human fascia lata (HFL) is used widely in reconstructive surgery in indications other than fracture repair. The goal of this study was to compare microscopic, molecular, and mechanical properties of HFL and periosteum (HP) from a bone tissue engineering perspective.

Material and Methods: Cadaveric HP and HFL (N = 4 each) microscopic morphology was characterized using histology and immunohistochemistry (IHC), and the extracellular matrix (ECM) ultrastructure assessed by means of scanning electron microscopy (SEM). DNA, collagen, elastin, glycosaminoglycans, major histocompatibility complex Type 1, and bone morphogenetic protein (BMP) contents were quantified. HP (N = 6) and HFL (N = 11) were submitted to stretch tests.

Results: Histology and IHC highlighted similarities (Type I collagen fibers and two-layer organization) but also differences (fiber thickness and compaction and cell type) between both tissues, as confirmed using SEM. The collagen content was statistically higher in HFL than HP (735 vs. 160.2 μg/mg dry weight, respectively, p < 0.0001). On the contrary, DNA content was lower in HFL than HP (404.75 vs. 1,102.2 μg/mg dry weight, respectively, p = 0.0032), as was the immunogenic potential (p = 0.0033). BMP-2 and BMP-7 contents did not differ between both tissues (p = 0.132 and p = 0.699, respectively). HFL supported a significantly higher tension stress than HP.

Conclusion: HP and HFL display morphological differences, despite their similar molecular ECM components. The stronger stretching resistance of HFL can specifically be explained by its higher collagen content. However, HFL contains many fewer cells and is less immunogenic than HP, as latter is rich in periosteal stem cells. In conclusion, HFL is likely suitable to replace HP architecture to confer a guide for bone consolidation, with an absence of osteogenicity. This study could pave the way to a bio-engineered periosteum built from HFL.

Cardiac-derived extracellular matrix: A decellularization protocol for heart regeneration

Extracellular matrix (ECM) is a fundamental component of the heart, guiding vital cellular processes during organ homeostasis. Most cardiovascular diseases lead to a remarkable remodeling of the ECM, accompanied by the formation of a fibrotic tissue that heavily compromises the heart function. Effective therapies for managing fibrosis and promoting physiological ECM repair are not yet available. The production of a decellularized extracellular matrix (d-ECM) serving as a three-dimensional and bioactive scaffold able to modulate cellular behavior and activities is considered crucial to achieve a successful regeneration. The protocol represents a step-by-step method to obtain a decellularized cardiac matrix through the combination of sodium dodecyl sulphate (SDS) and Triton X-100. Briefly, cardiac samples obtained from left ventricles of explanted, pathological human hearts were dissected and washed to remove residual body fluids. Samples were then snap-frozen and sliced by a cryostat into 350 μm thick sections. The sections obtained were decellularized using a solution containing 1% Triton X-100 and 1% SDS in combination, for 24 hours, until observing the color change from brownish-red to translucent-white. As a result, the protocol shows efficiency in preserving ECM architecture and protein composition during the whole process, suggesting that it is worthwhile, highly reproducible and produces a well- preserved decellularized extracellular matrix from cardiac samples. Notwithstanding, some limitations need to be addressed, such as the risk for microbial contamination and the unpredictable trend of the protocol when applied to decellularize samples other than myocardium, vessels, or skin. These issues require antibiotics mixture supplement during the procedure followed by UV sterilization, and appropriate adjustments for a tissue-specific utilization, respectively. The protocol is intended to produce a cardiac d-ECM for cell settlement, representing the ideal scaffold for tissue engineering purposes.

ECM roles and biomechanics in cardiac tissue decellularization

Natural biomaterials hold enormous potential for tissue regeneration. The rapid advance of several tissue-engineered biomaterials, such as natural and synthetic polymer-based scaffolds, has led to widespread application of these materials in the clinic and in research. However, biomaterials can have limited repair capacity; obstacles result from immunogenicity, difficulties in mimicking native microenvironments, and maintaining the mechanical and biochemical (i.e., biomechanical) properties of native organs/tissues. The emergence of decellularized extracellular matrix (ECM)-derived biomaterials provides an attractive solution to overcome these hurdles since decellularized ECM provides a nonimmune environment with native three-dimensional structures and bioactive components. More importantly, decellularized ECM can be generated from the tissue of interest, such as the heart, and keep its native macro- and microstructure and tissue-specific composition. These decellularized cardiac matrices/scaffolds can then be reseeded using cardiac cells, and the resulting recellularized construct is considered an ideal choice for regenerating functional organs/tissues. Nonetheless, the decellularization process must be optimized and depends on tissue type, age, and functional goal. Although most decellularization protocols significantly reduce immunogenicity and deliver a matrix that maintains the tissue macrostructure, suboptimal decellularization can change ECM composition and microstructure, which affects the biomechanical properties of the tissue and consequently changes cell-matrix interactions and organ function. Herein, we review methods of decellularization, with particular emphasis on cardiac tissue, and how they can affect the biomechanics of the tissue, which in turn determines success of reseeding and in vivo viability. Moreover, we review recent developments in decellularized ECM-derived cardiac biomaterials and discuss future perspectives.

Human Cardiac Progenitor Cell-Derived Extracellular Vesicles Exhibit Promising Potential for Supporting Cardiac Repair in Vitro

Although human Cardiac Progenitor Cells (hCPCs) are not retained by host myocardium they still improve cardiac function when injected into ischemic heart. Emerging evidence supports the hypothesis that hCPC beneficial effects are induced by paracrine action on resident cells. Extracellular vesicles (EVs) are an intriguing mechanism of cell communication based on the transport and transfer of peptides, lipids, and nucleic acids that have the potential to modulate signaling pathways, cell growth, migration, and proliferation of recipient cells. We hypothesize that EVs are involved in the paracrine effects elicited by hCPCs and held accountable for the response of the infarcted myocardium to hCPC-based cell therapy. To test this theory, we collected EVs released by hCPCs isolated from healthy myocardium and evaluated the effects they elicited when administered to resident hCPC and cardiac fibroblasts (CFs) isolated from patients with post-ischemic end-stage heart failure. Evidence emerging from our study indicated that hCPC-derived EVs impacted upon proliferation and survival of hCPCs residing in the ischemic heart and regulated the synthesis and deposition of extracellular-matrix by CFs. These findings suggest that beneficial effects exerted by hCPC injection are, at least to some extent, ascribable to the delivery of signals conveyed by EVs.

Decellularization for the retention of tissue niches

Decellularization of natural tissues to produce extracellular matrix is a promising method for three-dimensional scaffolding and for understanding microenvironment of the tissue of interest. Due to the lack of a universal standard protocol for tissue decellularization, recent investigations seek to develop novel methods for whole or partial organ decellularization capable of supporting cell differentiation and implantation towards appropriate tissue regeneration. This review provides a comprehensive and updated perspective on the most recent advances in decellularization strategies for a variety of organs and tissues, highlighting techniques of chemical, physical, biological, enzymatic, or combinative-based methods to remove cellular contents from tissues. In addition, the review presents modernized approaches for improving standard decellularization protocols for numerous organ types.

Fully Synthetic 3D Fibrous Scaffolds for Stromal Tissues-Replacement of Animal-Derived Scaffold Materials Demonstrated by Multilayered Skin

The extracellular matrix (ECM) of soft tissues in vivo has remarkable biological and structural properties. Thereby, the ECM provides mechanical stability while it still can be rearranged via cellular remodeling during tissue maturation or healing processes. However, modern synthetic alternatives fail to provide these key features among basic properties. Synthetic matrices are usually completely degraded or are inert regarding cellular remodeling. Based on a refined electrospinning process, a method is developed to generate synthetic scaffolds with highly porous fibrous structures and enhanced fiber-to-fiber distances. Since this approach allows for cell migration, matrix remodeling, and ECM synthesis, the scaffold provides an ideal platform for the generation of soft tissue equivalents. Using this matrix, an electrospun-based multilayered skin equivalent composed of a stratified epidermis, a dermal compartment, and a subcutis is able to be generated without the use of animal matrix components. The extension of classical dense electrospun scaffolds with high porosities and motile fibers generates a fully synthetic and defined alternative to collagen-gel-based tissue models and is a promising system for the construction of tissue equivalents as in vitro models or in vivo implants.

Interindividual heterogeneity affects the outcome of human cardiac tissue decellularization

The extracellular matrix (ECM) of engineered human cardiac tissues corresponds to simplistic biomaterials that allow tissue assembly, or animal derived off-the-shelf non-cardiac specific matrices. Decellularized ECM from human cardiac tissue could provide a means to improve the mimicry of engineered human cardiac tissues. Decellularization of cardiac tissue samples using immersion-based methods can produce acceptable cardiac ECM scaffolds; however, these protocols are mostly described for animal tissue preparations. We have tested four methods to decellularize human cardiac tissue and evaluated their efficiency in terms of cell removal and preservation of key ECM components, such as collagens and sulfated glycosaminoglycans. Extended exposure to decellularization agents, namely sodium dodecyl sulfate and Triton-X-100, was needed to significantly remove DNA content by approximately 93% in all human donors. However, the biochemical composition of decellularized tissue is affected, and the preservation of ECM architecture is donor dependent. Our results indicate that standardization of decellularization protocols for human tissue is likely unfeasible, and a compromise between cell removal and ECM preservation must be established in accordance with the scaffold's intended application. Notwithstanding, decellularized human cardiac ECM supported human induced pluripotent-derived cardiomyocyte (hiPSC-CM) attachment and retention for up to 2 weeks of culture, and promoted cell alignment and contraction, providing evidence it could be a valuable tool for cardiac tissue engineering.

Stem Cells and Their Cardiac Derivatives for Cardiac Tissue Engineering and Regenerative Medicine

Significance: Heart failure is among the leading causes of morbidity worldwide with a 5-year mortality rate of ∼50%. Therefore, major efforts are invested to reduce heart damage upon injury or maintain and at best restore heart function. Recent Advances: In clinical trials, acellular constructs succeeded in improving cardiac function by stabilizing the infarcted heart. In addition, strategies utilizing stem-cell-derived cardiomyocytes have been developed to improve heart function postmyocardial infarction in small and large animal models. These strategies range from injection of cell-laden hydrogels to unstructured hydrogel-based and complex biofabricated cardiac patches. Importantly, novel methods have been developed to promote differentiation of stem-cell-derived cardiomyocytes to prevascularized cardiac patches. Critical Issues: Despite substantial progress in vascularization strategies for heart-on-the-chip technologies, little advance has been made in generating vascularized cardiac patches with clinically relevant dimensions. In addition, proper electrical coupling between engineered and host tissue to prevent and/or eliminate arrhythmia remains an unresolved issue. Finally, despite advanced approaches to include hierarchical structures in cardiac tissues, engineered tissues do not generate forces in the range of native adult cardiac tissue. Future Directions: It involves utilizing novel materials and advancing biofabrication strategies to generate prevascularized three-dimensional multicellular constructs of clinical relevant size; inclusion of hierarchical structures, electroconductive materials, and biologically active factors to enhance cardiomyocyte differentiation for optimized force generation and vascularization; optimization of bioreactor strategies for tissue maturation. Antioxid. Redox Signal. 35, 143-162.

Enhanced Piezoelectric Fibered Extracellular Matrix to Promote Cardiomyocyte Maturation and Tissue Formation: A 3D Computational Model

Mechanical and electrical stimuli play a key role in tissue formation, guiding cell processes such as cell migration, differentiation, maturation, and apoptosis. Monitoring and controlling these stimuli on in vitro experiments is not straightforward due to the coupling of these different stimuli. In addition, active and reciprocal cell-cell and cell-extracellular matrix interactions are essential to be considered during formation of complex tissue such as myocardial tissue. In this sense, computational models can offer new perspectives and key information on the cell microenvironment. Thus, we present a new computational 3D model, based on the Finite Element Method, where a complex extracellular matrix with piezoelectric properties interacts with cardiac muscle cells during the first steps of tissue formation. This model includes collective behavior and cell processes such as cell migration, maturation, differentiation, proliferation, and apoptosis. The model has employed to study the initial stages of in vitro cardiac aggregate formation, considering cell-cell junctions, under different extracellular matrix configurations. Three different cases have been purposed to evaluate cell behavior in fibered, mechanically stimulated fibered, and mechanically stimulated piezoelectric fibered extra-cellular matrix. In this last case, the cells are guided by the coupling of mechanical and electrical stimuli. Accordingly, the obtained results show the formation of more elongated groups and enhancement in cell proliferation.

Preseeding of Mesenchymal Stem Cells Increases Integration of an iPSC-Derived CM Sheet into a Cardiac Matrix

Cell sheet technology has demonstrated great promise in delivering a large amount of therapeutic cells for tissue repair, including in the myocardium. However, the lack of host integration remains one of the key challenges in using cell sheets for cardiac repair. Paracrine factors secreted by mesenchymal stem cells (MSCs) have been reported to facilitate tissue repair and regeneration in a variety of ways. It has been demonstrated that paracrine factors from MSCs could enhance scaffold recellularization and vascularization. In this study, we used an in vitro cardiac matrix mimic platform to examine the effects of hMSCs preseeding on the interactions between cell sheets and cardiac matrix. The fabricated human induced pluripotent stem cells-derived cardiomyocyte sheets were attached to a decellularized porcine myocardium slice with or without preseeding of hMSCs. The hMSCs preseeding significantly enhanced the interactions between cardiomyocyte sheets and cardiac matrix in terms of cell migration distance, cell distribution, and mature vascular and cardiomyocyte marker expressions in the matrix. Growth factor and matrix metalloproteinases array analysis suggested that hMSCs- induced vascularization and MMPs regulation are the two possible mechanisms that lead to the improved CMs and cardiac matrix interactions. Further examination of these two mechanisms will enable the development of new approaches to facilitate transplanted cells for tissue repair.

The Microenvironment of Decellularized Extracellular Matrix from Heart Failure Myocardium Alters the Balance between Angiogenic and Fibrotic Signals from Stromal Primitive Cells

Cardiac adverse remodeling is characterized by biological changes that affect the composition and architecture of the extracellular matrix (ECM). The consequently disrupted signaling can interfere with the balance between cardiogenic and pro-fibrotic phenotype of resident cardiac stromal primitive cells (CPCs). The latter are important players in cardiac homeostasis and can be exploited as therapeutic cells in regenerative medicine. Our aim was to compare the effects of human decellularized native ECM from normal (dECM-NH) or failing hearts (dECM-PH) on human CPCs. CPCs were cultured on dECM sections and characterized for gene expression, immunofluorescence, and paracrine profiles. When cultured on dECM-NH, CPCs significantly upregulated cardiac commitment markers (CX43, NKX2.5), cardioprotective cytokines (bFGF, HGF), and the angiogenesis mediator, NO. When seeded on dECM-PH, instead, CPCs upregulated pro-remodeling cytokines (IGF-2, PDGF-AA, TGF-β) and the oxidative stress molecule H₂O₂. Interestingly, culture on dECM-PH was associated with impaired paracrine support to angiogenesis, and increased expression of the vascular endothelial growth factor (VEGF)-sequestering decoy isoform of the KDR/VEGFR2 receptor. Our results suggest that resident CPCs exposed to the pathological microenvironment of remodeling ECM partially lose their paracrine angiogenic properties and release more pro-fibrotic cytokines. These observations shed novel insights on the crosstalk between ECM and stromal CPCs, suggesting also a cautious use of non-healthy decellularized myocardium for cardiac tissue engineering approaches.

Tissue-Specific Decellularization Methods: Rationale and Strategies to Achieve Regenerative Compounds

The extracellular matrix (ECM) is a complex network with multiple functions, including specific functions during tissue regeneration. Precisely, the properties of the ECM have been thoroughly used in tissue engineering and regenerative medicine research, aiming to restore the function of damaged or dysfunctional tissues. Tissue decellularization is gaining momentum as a technique to obtain potentially implantable decellularized extracellular matrix (dECM) with well-preserved key components. Interestingly, the tissue-specific dECM is becoming a feasible option to carry out regenerative medicine research, with multiple advantages compared to other approaches. This review provides an overview of the most common methods used to obtain the dECM and summarizes the strategies adopted to decellularize specific tissues, aiming to provide a helpful guide for future research development.

Young at Heart: Combining Strategies to Rejuvenate Endogenous Mechanisms of Cardiac Repair

True cardiac regeneration of the injured heart has been broadly described in lower vertebrates by active replacement of lost cardiomyocytes to functionally and structurally restore the myocardial tissue. On the contrary, following severe injury (i.e., myocardial infarction) the adult mammalian heart is endowed with an impaired reparative response by means of meager wound healing program and detrimental remodeling, which can lead over time to cardiomyopathy and heart failure. Lately, a growing body of basic, translational and clinical studies have supported the therapeutic use of stem cells to provide myocardial regeneration, with the working hypothesis that stem cells delivered to the cardiac tissue could result into new cardiovascular cells to replenish the lost ones. Nevertheless, multiple independent evidences have demonstrated that injected stem cells are more likely to modulate the cardiac tissue via beneficial paracrine effects, which can enhance cardiac repair and reinstate the embryonic program and cell cycle activity of endogenous cardiac stromal cells and resident cardiomyocytes. Therefore, increasing interest has been addressed to the therapeutic profiling of the stem cell-derived secretome (namely the total of cell-secreted soluble factors), with specific attention to cell-released extracellular vesicles, including exosomes, carrying cardioprotective and regenerative RNA molecules. In addition, the use of cardiac decellularized extracellular matrix has been recently suggested as promising biomaterial to develop novel therapeutic strategies for myocardial repair, as either source of molecular cues for regeneration, biological scaffold for cardiac tissue engineering or biomaterial platform for the functional release of factors. In this review, we will specifically address the translational relevance of these two approaches with ad hoc interest in their feasibility to rejuvenate endogenous mechanisms of cardiac repair up to functional regeneration.

Decellularized Human Dermal Matrix as a Biological Scaffold for Cardiac Repair and Regeneration

The complex and highly organized environment in which cells reside consists primarily of the extracellular matrix (ECM) that delivers biological signals and physical stimuli to resident cells. In the native myocardium, the ECM contributes to both heart compliance and cardiomyocyte maturation and function. Thus, myocardium regeneration cannot be accomplished if cardiac ECM is not restored. We hypothesize that decellularized human skin might make an easily accessible and viable alternate biological scaffold for cardiac tissue engineering (CTE). To test our hypothesis, we decellularized specimens of both human skin and human myocardium and analyzed and compared their composition by histological methods and quantitative assays. Decellularized dermal matrix was then cut into 600-μm-thick sections and either tested by uniaxial tensile stretching to characterize its mechanical behavior or used as three-dimensional scaffold to assess its capability to support regeneration by resident cardiac progenitor cells (hCPCs) in vitro. Histological and quantitative analyses of the dermal matrix provided evidence of both effective decellularization with preserved tissue architecture and retention of ECM proteins and growth factors typical of cardiac matrix. Further, the elastic modulus of the dermal matrix resulted comparable with that reported in literature for the human myocardium and, when tested in vitro, dermal matrix resulted a comfortable and protective substrate promoting and supporting hCPC engraftment, survival and cardiomyogenic potential. Our study provides compelling evidence that dermal matrix holds promise as a fully autologous and cost-effective biological scaffold for CTE.

Cardiac tissue-derived extracellular matrix scaffolds for myocardial repair: advantages and challenges

Decellularized extracellular matrix (dECM) derived from myocardium has been widely explored as a nature scaffold for cardiac tissue engineering applications. Cardiac dECM offers many unique advantages such as preservation of organ-specific ECM microstructure and composition, demonstration of tissue-mimetic mechanical properties and retention of biochemical cues in favor of subsequent recellularization. However, current processes of dECM decellularization and recellularization still face many challenges including the need for balance between cell removal and extracellular matrix preservation, efficient recellularization of dECM for obtaining homogenous cell distribution, tailoring material properties of dECM for enhancing bioactivity and prevascularization of thick dECM. This review summarizes the recent progresses of using dECM scaffold for cardiac repair and discusses its major advantages and challenges for producing biomimetic cardiac patch.

Diversity of dermal fibroblasts as major determinant of variability in cell reprogramming

Induced pluripotent stem cells (iPSCs) are adult somatic cells genetically reprogrammed to an embryonic stem cell-like state. Notwithstanding their autologous origin and their potential to differentiate towards cells of all three germ layers, iPSC reprogramming is still affected by low efficiency. As dermal fibroblast is the most used human cell for reprogramming, we hypothesize that the variability in reprogramming is, at least partially, because of the skin fibroblasts used. Human dermal fibroblasts harvested from five different anatomical sites (neck, breast, arm, abdomen and thigh) were cultured and their morphology, proliferation, apoptotic rate, ability to migrate, expression of mesenchymal or epithelial markers, differentiation potential and production of growth factors were evaluated in vitro. Additionally, gene expression analysis was performed by real-time PCR including genes typically expressed by mesenchymal cells. Finally, fibroblasts isolated from different anatomic sites were reprogrammed to iPSCs by integration-free method. Intriguingly, while the morphology of fibroblasts derived from different anatomic sites differed only slightly, other features, known to affect cell reprogramming, varied greatly and in accordance with anatomic site of origin. Accordingly, difference also emerged in fibroblasts readiness to respond to reprogramming and ability to form colonies. Therefore, as fibroblasts derived from different anatomic sites preserve positional memory, it is of great importance to accurately evaluate and select dermal fibroblast population prior to induce reprogramming.

Tissue-Engineered Grafts from Human Decellularized Extracellular Matrices: A Systematic Review and Future Perspectives

Tissue engineering and regenerative medicine involve many different artificial and biologic materials, frequently integrated in composite scaffolds, which can be repopulated with various cell types. One of the most promising scaffolds is decellularized allogeneic extracellular matrix (ECM) then recellularized by autologous or stem cells, in order to develop fully personalized clinical approaches. Decellularization protocols have to efficiently remove immunogenic cellular materials, maintaining the nonimmunogenic ECM, which is endowed with specific inductive/differentiating actions due to its architecture and bioactive factors. In the present paper, we review the available literature about the development of grafts from decellularized human tissues/organs. Human tissues may be obtained not only from surgery but also from cadavers, suggesting possible development of Human Tissue BioBanks from body donation programs. Many human tissues/organs have been decellularized for tissue engineering purposes, such as cartilage, bone, skeletal muscle, tendons, adipose tissue, heart, vessels, lung, dental pulp, intestine, liver, pancreas, kidney, gonads, uterus, childbirth products, cornea, and peripheral nerves. In vitro recellularizations have been reported with various cell types and procedures (seeding, injection, and perfusion). Conversely, studies about in vivo behaviour are poorly represented. Actually, the future challenge will be the development of human grafts to be implanted fully restored in all their structural/functional aspects.

Injectable decellularized nucleus pulposus-based cell delivery system for differentiation of adipose-derived stem cells and nucleus pulposus regeneration

Stem cell-based tissue engineering is a promising treatment for intervertebral disc (IVD) degeneration. A bio-scaffold that can maintain the function of transplanted cells and possesses favorable mechanical properties is needed in tissue engineering. Decellularized nucleus pulposus (dNP) has the potential to be a suitable bio-scaffold because it mimics the native nucleus pulposus (NP) composition. However, matrix loss during decellularization and difficulty in transplantation limit the clinical application of dNP scaffolds. In this study, we fabricated an injectable dNP-based cell delivery system (NPCS) and evaluated its properties by assessing the microstructure, biochemical composition, water content, biosafety, biostability, and mechanical properties. We also investigated the stimulatory effects of the bio-scaffold on the NP-like differentiation of adipose-derived stem cells (ADSCs) in vitro and the regenerative effects of the NPCS on degenerated NP in an in vivo animal model. The results showed that approximately 68% and 43% of the collagen and sGAG, respectively, remained in the NPCS after 30 days. The NPCS also showed mechanical properties similar to those of fresh NP. In addition, the NPCS was biocompatible and able to induce NP-like differentiation and extracellular matrix (ECM) synthesis in ADSCs. The disc height index (almost 81%) and the MRI index (349.05 ± 38.48) of the NPCS-treated NP were significantly higher than those of the degenerated NP after 16 weeks. The NPCS also partly restored the ECM content and the structure of degenerated NP in vivo. Our NPCS has good biological and mechanical properties and has the ability to promote the regeneration of degenerated NP. STATEMENT OF SIGNIFICANCE: Nucleus pulposus (NP) degeneration is usually the origin of intervertebral disc degeneration. Stem cell-based tissue engineering is a promising treatment for NP regeneration. Bio-scaffolds which have favorable biological and mechanical properties are needed in tissue engineering. Decellularized NP (dNP) scaffold is a potential choice for tissue engineering, but the difficulty in balancing complete decellularization and retaining ECM limits its usage. Instead of choosing different decellularization protocols, we complementing the sGAG lost during decellularization by cross-linking via genipin and fabricating an injectable dNP-based cell delivery system (NPCS) which has similar components as the native NP. We also investigated the biological and mechanical properties of the NPCS in vitro and verified its regenerative effects on degenerated IVDs in an animal model.

Current Trends in Biomaterial Utilization for Cardiopulmonary System Regeneration

The cardiopulmonary system is made up of the heart and the lungs, with the core function of one complementing the other. The unimpeded and optimal cycling of blood between these two systems is pivotal to the overall function of the entire human body. Although the function of the cardiopulmonary system appears uncomplicated, the tissues that make up this system are undoubtedly complex. Hence, damage to this system is undesirable as its capacity to self-regenerate is quite limited. The surge in the incidence and prevalence of cardiopulmonary diseases has reached a critical state for a top-notch response as it currently tops the mortality table. Several therapies currently being utilized can only sustain chronically ailing patients for a short period while they are awaiting a possible transplant, which is also not devoid of complications. Regenerative therapeutic techniques now appear to be a potential approach to solve this conundrum posed by these poorly self-regenerating tissues. Stem cell therapy alone appears not to be sufficient to provide the desired tissue regeneration and hence the drive for biomaterials that can support its transplantation and translation, providing not only physical support to seeded cells but also chemical and physiological cues to the cells to facilitate tissue regeneration. The cardiac and pulmonary systems, although literarily seen as just being functionally and spatially cooperative, as shown by their diverse and dissimilar adult cellular and tissue composition has been proven to share some common embryological codevelopment. However, necessitating their consideration for separate review is the immense adult architectural difference in these systems. This review also looks at details on new biological and synthetic biomaterials, tissue engineering, nanotechnology, and organ decellularization for cardiopulmonary regenerative therapies.

Cardiac Progenitor Cells: The Matrix Has You

Components of the cardiac extracellular matrix (ECM) are synthesized by residing cells and are continuously remodeled by them. Conversely, residing cells (including primitive cells) receive constant biochemical and mechanical signals from the ECM that modulate their biology. The pathological progression of heart failure affects all residing cells, inevitably causing profound changes in ECM composition and architecture that, in turn, impact on cell phenotypes. Any regenerative medicine approach must aim at sustaining microenvironment conditions that favor cardiogenic commitment of therapeutic cells and minimize pro‐fibrotic signals, while conversely boosting the capacity of therapeutic cells to counteract adverse remodeling of the ECM. In this Perspective article, we discuss multiple issues about the features of an optimal scaffold for supporting cardiac tissue engineering strategies with cardiac progenitor cells, and, conversely, about the possible antifibrotic mechanisms induced by cell therapy. Stem Cells Translational Medicine2018;7:506–510