Decellularization of fibroblast cell sheets for natural extracellular matrix scaffold preparation

Characterization Methods of Acellularized Tissue and Organs

The extracellular matrix (ECM) of mammalian organs and tissues has been applied as a substitute scaffold to simplify the restoration and reconstruction of several tissues. Such scaffolds are prepared in various arrangements including sheets, powders, and hydrogels. One of the more applicable processes is using natural scaffolds, for this purpose discarded tissues or organs are naturally derived by processes that comprised decellularization of following tissues or organs. Protection of the complex structure and 3D (three dimensional) ultrastructure of the ECM is extremely necessary but it is predictable that all protocols of decellularization end in disruption of the architecture and potential loss of surface organization and configuration. Tissue decellularization with conservation of ECM bioactivity and integrity can be improved by providing well-designed protocols regarding the agents and decellularization techniques operated during processing. An overview of the characterization of decellularized scaffolds and the role of reagnets can validate the applied methods' efficacy.

Recent advancements in decellularized matrix technology for bone tissue engineering

The native extracellular matrix (ECM) provides a matrix to hold tissue/organ, defines the cellular fate and function, and retains growth factors. Such a matrix is considered as a most biomimetic scaffold for tissue engineering due to the biochemical and biological components, 3D hierarchical structure, and physicomechanical properties. Several attempts have been performed to decellularize allo- or xeno-graft tissues and used them for bone repairing and regeneration. Decellularized ECM (dECM) technology has been developed to create an in vivo-like microenvironment to promote cell adhesion, growth, and differentiation for tissue repair and regeneration. Decellularization is mediated through physical, chemical, and enzymatic methods. In this review, we describe the recent progress in bone decellularization and their applications as a scaffold, hydrogel, bioink, or particles in bone tissue engineering. Furthermore, we address the native dECM limitations and the potential of non-bone dECM, cell-based ECM, and engineered ECM (eECM) for in vitro osteogenic differentiation and in vivo bone regeneration.

Decellularized scaffold and its elicited immune response towards the host: the underlying mechanism and means of immunomodulatory modification

The immune response of the host towards a decellularized scaffold is complex. Not only can a number of immune cells influence this process, but also the characteristics, preparation and modification of the decellularized scaffold can significantly impact this reaction. Such factors can, together or alone, trigger immune cells to polarize towards either a pro-healing or pro-inflammatory direction. In this article, we have comprehensively reviewed factors which may influence the immune response of the host towards a decellularized scaffold, including the source of the biomaterial, biophysical properties or modifications of the scaffolds with bioactive peptides, drugs and cytokines. Furthermore, the underlying mechanism has also been recapitulated.

Decellularized Cell Culture ECMs Act as Cell Differentiation Inducers

Decellularized tissues and organs have aroused considerable interest for developing functional bio-scaffolds as natural templates in tissue engineering applications. More recently, the use of natural extracellular matrix (ECM) extracted from the in vitro cell cultures for cellular applications have come into question. It is well known that the microenvironment largely defines cellular properties. Thus, we have anticipated that the ECMs of the cells with different potency levels should likely possess different effects on cell cultures. To test this, we have comparatively evaluated the differentiative effects of ECMs derived from the cultures of human somatic dermal fibroblasts, human multipotent bone marrow mesenchymal stem cells, and human induced pluripotent stem cells on somatic dermal fibroblasts. Although challenges remain, the data suggest that the use of cell culture-based extracellular matrices perhaps may be considered as an alternative approach for the differentiation of even somatic cells into other cell types.

Bioactive Decellularized Extracellular Matrix Derived from 3D Stem Cell Spheroids under Macromolecular Crowding Serves as a Scaffold for Tissue Engineering

Scaffolds for tissue engineering aim to mimic the native extracellular matrix (ECM) that provides physical support and biochemical signals to modulate multiple cell behaviors. However, the majority of currently used biomaterials are oversimplified and therefore fail to provide a niche required for the stimulation of tissue regeneration. In the present study, 3D decellularized ECM (dECM) scaffolds derived from mesenchymal stem cell (MSC) spheroids and with intricate matrix composition are developed. Specifically, application of macromolecular crowding (MMC) to MSC spheroid cultures facilitate ECM assembly in a 3D configuration, resulting in the accumulation of ECM and associated bioactive components. Decellularized 3D dECM constructs produced under MMC are able to adequately preserve the microarchitecture of structural ECM components and are characterized by higher retention of growth factors. This results in a stronger proangiogenic bioactivity as compared to constructs produced under uncrowded conditions. These dECM scaffolds can be homogenously populated by endothelial cells, which direct the macroassembly of the structures into larger cell-carrying constructs. Application of empty scaffolds enhances intrinsic revascularization in vivo, indicating that the 3D dECM scaffolds represent optimal proangiogenic bioactive blocks for the construction of larger engineered tissue constructs.

Accounting for Material Changes in Decellularized Tissue with Underutilized Methodologies

Tissue decellularization has rapidly developed to be a practical approach in tissue engineering research; biological tissue is cleared of cells resulting in a protein-rich husk as a natural scaffold for growing transplanted cells as a donor organ therapy. Minimally processed, acellular extracellular matrix reproduces natural interactions with cells in vitro and for tissue engineering applications in animal models. There are many decellularization techniques that achieve preservation of molecular profile (proteins and sugars), microstructure features such as organization of ECM layers (interstitial matrix and basement membrane) and organ level macrofeatures (vasculature and tissue compartments). While structural and molecular cues receive attention, mechanical and material properties of decellularized tissues are not often discussed. The effects of decellularization on an organ depend on the tissue properties, clearing mechanism, chemical interactions, solubility, temperature, and treatment duration. Physical characterization by a few labs including work from the authors provides evidence that decellularization protocols should be tailored to specific research questions. Physical characterization beyond histology and immunohistochemistry of the decellularized matrix (dECM) extends evaluation of retained functional features of the original tissue. We direct our attention to current technologies that can be employed for structure function analysis of dECM using underutilized tools such as atomic force microscopy (AFM), cryogenic electron microscopy (cryo-EM), dynamic mechanical analysis (DMA), Fourier-transform infrared spectroscopy (FTIR), mass spectrometry, and rheometry. Structural imaging and mechanical functional testing combined with high-throughput molecular analyses opens a new approach for a deeper appreciation of how cellular behavior is influenced by the isolated microenvironment (specifically dECM). Additionally, the impact of these features with different decellularization techniques and generation of synthetic material scaffolds with desired attributes are informed. Ultimately, this mechanical profiling provides a new dimension to our understanding of decellularized matrix and its role in new applications.

Development of novel apoptosis-assisted lung tissue decellularization methods

Decellularized tissues hold great potential for both regenerative medicine and disease modeling applications. The acellular extracellular matrix (ECM)-enriched scaffolds can be recellularized with patient-derived cells prior to transplantation, or digested to create thermally-gelling ECM hydrogels for 3D cell culture. Current methods of decellularization clear cellular components using detergents, which can result in loss of ECM proteins and tissue architectural integrity. Recently, an alternative approach utilizing apoptosis to decellularize excised murine sciatic nerves resulted in superior ECM preservation, cell removal, and immune tolerance in vivo. However, this apoptosis-assisted decellularization approach has not been optimized for other tissues with a more complex geometry, such as lungs. To this end, we developed an apoptosis-assisted lung tissue decellularization method using a combination of camptothecin and sulfobetaine-10 (SB-10) to induce apoptosis and facilitate gentle and effective removal of cell debris, respectively. Importantly, combination of the two agents resulted in superior cell removal and ECM preservation compared to either of the treatments alone, presumably because of pulmonary surfactants. In addition, our method was superior in cell removal compared to a previously established detergent-based decellularization protocol. Furthermore, thermally-gelling lung ECM hydrogels supported high viability of rat lung epithelial cells for up to 2 weeks in culture. This work demonstrates that apoptosis-based lung tissue decellularization is a superior technique that warrants further utilization for both regenerative medicine and disease modeling purposes.

Partially Digested Osteoblast Cell Line-Derived Extracellular Matrix Induces Rapid Mineralization and Osteogenesis

An extracellular matrix (ECM) utilized as a biomaterial can be obtained from organs of living organisms. Therefore, it has some limitations in its supply because of insufficient organs. Furthermore, therapeutic efficacy of ECMs varies depending on factors such as donor's health condition and age. For this reason, ECMs obtained from a cell line could be a good alternative because they can be produced under a controlled environment with uniform quality. Thus, the purpose of this study was to investigate the potential of the MC3T3-E1 cell line-derived ECM as bone graft. The optimized decellularization process was developed to separate the ECM from MC3T3-E1, osteoblast cell line, using Trypsin-EDTA and Triton X-100. The decellularized ECM was partially digested using pepsin. Also, human bone marrow-derived mesenchymal stem cells induced faster osteogenesis on the ECM-coated surface than on the collagen-coated surface. Partially digested ECM fragments were embedded on the polyethylene glycol scaffold without additional chemical modification or crosslinking. Micro-computed tomography and histological analysis results showed that the ECM in the scaffold promoted actual bone regeneration after in vivo implantation to a mouse calvarial defect model. This study suggests that the bone-specific ECM derived from the cell line can replace the ECM from organs for application in tissue engineering and regenerative medicine.

Post-decellularization techniques ameliorate cartilage decellularization process for tissue engineering applications

Due to the current lack of innovative and effective therapeutic approaches, tissue engineering (TE) has attracted much attention during the last decades providing new hopes for the treatment of several degenerative disorders. Tissue engineering is a complex procedure, which includes processes of decellularization and recellularization of biological tissues or functionalization of artificial scaffolds by active cells. In this review, we have first discussed those conventional steps, which have led to great advancements during the last several years. Moreover, we have paid special attention to the new methods of post-decellularization that can significantly ameliorate the efficiency of decellularized cartilage extracellular matrix (ECM) for the treatment of osteoarthritis (OA). We propose a series of post-decellularization procedures to overcome the current shortcomings such as low mechanical strength and poor bioactivity to improve decellularized ECM scaffold towards much more efficient and higher integration.

Challenges and Possibilities of Cell-Based Tissue-Engineered Vascular Grafts

There is urgent demand for biologically compatible vascular grafts for both adult and pediatric patients. The utility of conventional nonbiodegradable materials is limited because of their thrombogenicity and inability to grow, while autologous vascular grafts involve considerable disadvantages, including the invasive procedures required to obtain these healthy vessels from patients and insufficient availability in patients with systemic atherosclerosis. All of these issues could be overcome by tissue-engineered vascular grafts (TEVGs). A large body of evidence has recently emerged in support of TEVG technologies, introducing diverse cell sources (e.g., somatic cells and stem cells) and novel fabrication methods (e.g., scaffold-guided and self-assembled approaches). Before TEVG can be applied in a clinical setting, however, several aspects of the technology must be improved, such as the feasibility of obtaining cells, their biocompatibility and mechanical properties, and the time needed for fabrication, while the safety of supplemented materials, the patency and nonthrombogenicity of TEVGs, their growth potential, and the long-term influence of implanted TEVGs in the body must be assessed. Although recent advances in TEVG fabrication have yielded promising results, more research is needed to achieve the most feasible methods for generating optimal TEVGs. This article reviews multiple aspects of TEVG fabrication, including mechanical requirements, extracellular matrix components, cell sources, and tissue engineering approaches. The potential of periodic hydrostatic pressurization in the production of scaffold-free TEVGs with optimal elasticity and stiffness is also discussed. In the future, the integration of multiple technologies is expected to enable improved TEVG performance.

Selection of different endothelialization modes and different seed cells for tissue-engineered vascular graft

Tissue-engineered vascular grafts (TEVGs) have enormous potential for vascular replacement therapy. However, thrombosis and intimal hyperplasia are important problems associated with TEVGs especially small diameter TEVGs (<6 mm) after transplantation. Endothelialization of TEVGs is a key point to prevent thrombosis. Here, we discuss different types of endothelialization and different seed cells of tissue-engineered vascular grafts. Meanwhile, endothelial heterogeneity is also discussed. Based on it, we provide a new perspective for selecting suitable types of endothelialization and suitable seed cells to improve the long-term patency rate of tissue-engineered vascular grafts with different diameters and lengths.

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The material, diameter and length of tissue-engineered vascular graft are all key factors affecting its long-term patency.

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Endothelialization strategies should consider the different diameters and lengths of tissue-engineered vascular grafts.

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Cell heterogeneity and tissue heterogeneity should be considered in the application of seed cells.

Contribution of Physical Methods in Decellularization of Animal Tissues

Biologic scaffolds composed of extracellular matrix (ECM) are frequently used for clinical purposes of tissue regeneration. Different methods have been developed for this purpose. All methods of decellularization including chemical and physical approaches leave some damage on the ECM; however, the effects of these methods are different which make some of these procedures more proper to maintain ECM structure than other methods. This review is aimed to introduce and compare new physical methods for the decellularization of different tissues and organs in tissue engineering. All recent reports and research that have used at least one physical method in the procedure of decellularization, were included and evaluated in this paper. The advantages and drawbacks of each method were examined and compared considering the effectiveness. This review tried to highlight the prospective potentials and benefits of applying physical methods for decellularization protocols in tissue engineering instead of the current chemical methods. These chemical methods are harsh in nature and were shown to be destructive and harmful to essential substances of ECM and scaffold structure. Therefore, using physical methods as a partial or even a whole protocol could save time, costs, and quality of the final acellular tissue in complicated decellularization procedures. Moreover, regarding the control factor that could be achieved easily with physical methods, optimization of different decellularization protocols would be quite satisfactory. Combined methods take advantage of both chemical and physical approaches.

Effective decellularization of human nerve matrix for regenerative medicine with a novel protocol

Injuries to the peripheral nerves represent a frequent cause of permanent disability in adults. The repair of large nerve lesions involves the use of autografts, but they have several inherent limitations. Overcoming these limitations, the use of decellularized nerve matrix has emerged as a promising treatment in tissue regenerative medicine. Here, we generate longer human decellularized nerve segments with a novel decellularization method, using nonionic, zwitterionic, and enzymatic incubations. Efficiency of decellularization was measured by DNA quantification and cell remnant analysis (myelin, S100, neurofilament). The evaluation of the extracellular matrix (collagen, laminin, and glycosaminoglycans) preservation was carried out by enzyme-linked immunosorbent assay (ELISA) or biochemical methods, along with histological and immunofluorescence analysis. Moreover, biomechanical properties and cytocompatibility were tested. Results showed that the decellularized nerves generated with this protocol have a concentration of DNA below the threshold of 50 ng/mg of dry tissue. Furthermore, myelin, S100, and MHCII proteins were absent, although some neurofilament remnants could be observed. Moreover, extracellular matrix proteins were well maintained, as well as the biomechanical properties, and the decellularized nerve matrix did not generate cytotoxicity. These results show that our method is effective for the generation of decellularized human nerve grafts. The generation of longer decellularized nerve segments would allow the understanding of the regenerative neurobiology after nerve injuries in both clinical assays and bigger animal models. Effective decellularization of human nerve matrix for regenerative medicine with a novel protocol. Combination of zwitterionic, non-ionic detergents, hyperosmotic solution and nuclease enzyme treatment remove cell remnants, maintain collagen, laminin and biomechanics without generating cytotoxic leachables.

Boosting osteogenic potential and bone regeneration by co-cultured cell derived extracellular matrix incorporated porous electrospun scaffold

Implants for bone regeneration to remedy segmental bone defects, osteomyelitis, necrotic bone tissue and non-union fractures have worldwide appeal. Although biomaterials offer most of the advantages by improving tissue growth but developments are more commonly achieved via biologically derived molecules. To aid site specific bone tissue regeneration by synthetic scaffold, cell derived extracellular matrix (ECM) can be a crucial component. In this study, co-cultured bone marrow mesenchymal stem cell and osteoblastic cells derived ECM incorporated electrospun polycaprolactone (PCL) membranes were assessed for bone tissue engineering application. The preliminary experimental details indicated that, co-culture of cells supported enhanced in vitro ECM synthesis followed by successful deposition of osteoblastic ECM into electrospun membranes. The acellular samples revealed retention of ECM related biomacromolecules (collagen, glycosaminoglycan) and partial recovery of pores after decellularization. In vitro biocompatibility tests ensured improvement of proliferation and osteoblastic differentiation of MC3T3-E1 cells in decellularized ECM containing membrane (PCL-ECM) compared to bare membrane (PCL-B) which was further confirmed by osteogenic marker proteins expression analysis. The decellularized PCL-ECM membrane allowed great improvement of bone regeneration over the bare membrane (PCL-B) in 8 mm size critical sized rat skull defects at 2 months of post implantation. In short, the outcome of this study could be impactful in development and application of cell derived ECM based synthetic electrospun templates for bone tissue engineering application.[Formula: see text].

Long-term preservation effects on biological properties of acellular placental sponge patches

Decellularization, preservation protocol and storage time influence the biomechanical and biological properties of allografts and xenografts. Here, we examined the consequences of storage time on the antibacterial, angiogenic and biocompatibility properties of the decellularized placental sponge (DPS) in vitro and in vivo. The DPS samples were preserved for one, three and six months at -20 °C. The decellularized scaffolds showed uniform morphology with interconnected pores compared with not decellularized sponges. Storage time did not interfere with collagen and vascular endothelial growth factor contents, and cytobiocompatibility for Hu02 fibroblast cells. Chorioallantoic membrane assay and subcutaneous implantation indicated a decreased new vessel formation and neovascularization in six months DPS sample compared with other experimental groups. The number of CD4⁺ and CD68⁺ cells infiltrated into the six months DPS on the implanted site showed a significant increase compared with one and three months sponges. The antibacterial activities and angiogenic properties of the DPS decreased over storage time. Three months preservation at -20 °C is suggested as the optimal storage period to retain its antibacterial activity and high stimulation of new vessel formation. This storage protocol could be considered for preservation of similar decellularized placenta-derived products with the aim of retaining their biological properties.

Myocardial infarction affects Cx43 content of extracellular vesicles secreted by cardiomyocytes

Ischemic heart disease has been associated with an impairment on intercellular communication mediated by both gap junctions and extracellular vesicles. We have previously shown that connexin 43 (Cx43), the main ventricular gap junction protein, assembles into channels at the extracellular vesicle surface, mediating the release of vesicle content into target cells. Here, using a comprehensive strategy that included cell-based approaches, animal models and human patients, we demonstrate that myocardial ischemia impairs the secretion of Cx43 into circulating, intracardiac and cardiomyocyte-derived vesicles. In addition, we show that ubiquitin signals Cx43 release in basal conditions but appears to be dispensable during ischemia, suggesting an interplay between ischemia-induced Cx43 degradation and secretion. Overall, this study constitutes a step forward for the characterization of the signals and molecular players underlying vesicle protein sorting, with strong implications on long-range intercellular communication, paving the way towards the development of innovative diagnostic and therapeutic strategies for cardiovascular disorders.

Designing Decellularized Extracellular Matrix-Based Bioinks for 3D Bioprinting

3D bioprinting is an emerging technology to fabricate tissues and organs by precisely positioning cells into 3D structures using printable cell-laden formulations known as bioinks. Various bioinks are utilized in 3D bioprinting applications; however, developing the perfect bioink to fabricate constructs with biomimetic microenvironment and mechanical properties that are similar to native tissues is a challenging task. In recent years, decellularized extracellular matrix (dECM)-based bioinks have received an increasing attention in 3D bioprinting applications, since they are derived from native tissues and possess unique, complex tissue-specific biochemical properties. This review focuses on designing dECM-based bioinks for tissue and organ bioprinting, including commonly used decellularization and decellularized tissue characterization methods, bioink formulation and characterization, applications of dECM-based bioinks, and most recent advancements in dECM-based bioink design.

Riboflavin-mediated photooxidation to improve the characteristics of decellularized human arterial small diameter vascular grafts

Vascular grafts with a diameter of less than 6 mm are made from a variety of materials and techniques to provide alternatives to autologous vascular grafts. Decellularized materials have been proposed as a possible approach to create extracellular matrix (ECM) vascular prostheses as they are naturally derived and inherently support various cell functions. However, these desirable graft characteristics may be limited by alterations of the ECM during the decellularization process leading to decreased biomechanical properties and hemocompatibility. In this study, arteries from the human placenta chorion were decellularized using two distinct detergents (Triton X-100 or SDS), which differently affect ECM ultrastructure. To overcome biomechanical strength loss and collagen fiber exposure after decellularization, riboflavin-mediated UV (RUV) crosslinking was used to uniformly crosslink the collagenous ECM of the grafts. Graft characteristics and biocompatibility with and without RUV crosslinking were studied in vitro and in vivo. RUV-crosslinked ECM grafts showed significantly improved mechanical strength and smoothening of the luminal graft surfaces. Cell seeding using human endothelial cells revealed no cytotoxic effects of the RUV treatment. Short-term aortic implants in rats showed cell migration and differentiation of host cells. Functional graft remodeling was evident in all grafts. Thus, RUV crosslinking is a preferable tool to improve graft characteristics of decellularized matrix conduits.

Optimizing Methods for Bovine Dental Pulp Decellularization

INTRODUCTION

This study aimed to characterize the decellularization effects of different treatment protocols on the bovine dental pulp extracellular matrix (ECM) for tissue regeneration.

METHODS

Seven different decellularization protocols consisting of trypsin/EDTA (for 1 hour, 24 hours, or 48 hours), sodium dodecyl sulfate (SDS, for 24 hours or 48 hours), Triton X-100 (for 1 hour), and deoxyribonuclease treatments were tested on bovine dental pulp tissue. The posttreatment samples were evaluated for remaining DNA and cellular contents, structural durability, immunofluorescence analysis, and in vivo immune responses.

RESULTS

A complete decellularization process in all of the experimental groups was observed. The protocol that included 1 hour of Triton X-100 treatment and 12 hours of trypsin/EDTA treatment with no SDS treatment (P7 [12E-0S-1T]) showed the highest retention of glycosaminoglycan and the absence of nuclei in 4,6-diamidino-2-phenylindole. All groups showed significantly lower DNA content compared with native pulp tissue (P < .05), whereas compared with other protocols, protocols 1 (1 hour of EDTA/trypsin, 24 hours of SDS, and 1 hour of Triton X-100) and 4 (1 hour of EDTA/Trypsin, 48 hours of SDS, and no Triton X-100) resulted in the highest DNA contents (P < .05). Based on these results, P7 was further evaluated by immunofluorescence and in vivo immunogenicity. P7 specimens preserved collagen type I, whereas mononuclear cell infiltration along with neovascularization was observed in vivo.

CONCLUSIONS

All tested treatments displayed the potential ability to decellularize pulp tissue and are viable options for a xenogeneic dental pulp ECM scaffold. The P7 (12E-0S-1T) protocol resulted in decellularized ECM with minimal organic matrix/ultrastructural detriments and an acceptable host immune response.

Fabricating Organized Elastin in Vascular Grafts

Surgically bypassing or replacing a severely damaged artery using a biodegradable synthetic vascular graft is a promising treatment that allows for the remodeling and regeneration of the graft to form a neoartery. Elastin-based structures, such as elastic fibers, elastic lamellae, and laminae, are key functional components in the arterial extracellular matrix. In this review, we identify the lack of elastin in vascular grafts as a key factor that prevents their long-term success. We further summarize advances in vascular tissue engineering that are focused on either de novo production of organized elastin or incorporation of elastin-based biomaterials within vascular grafts to mitigate failure and enhance enduring in vivo performance.

Regulation of decellularized matrix mediated immune response

The substantially growing gap between suitable donors and patients waiting for new organ transplantation has compelled tissue engineers to look for suitable patient-specific alternatives. Lately, a decellularized extracellular matrix (dECM), obtained primarily from either discarded human tissues/organs or other species, has shown great promise in the constrained availability of high-quality donor tissues. In this review, we have addressed critical gaps and often-ignored aspects of understanding the innate and adaptive immune response to the dECM. Firstly, although most of the studies claim preservation of the ECM ultrastructure, almost all methods employed for decellularization would inevitably cause a certain degree of disruption to the ECM ultrastructure and modulation in secondary conformations, which may elicit a distinct immunogenic response. Secondly, it is still a major challenge to find ways to conserve the native biochemical, structural and biomechanical cues by making a judicious decision regarding the choice of decellularization agents/techniques. We have critically analyzed various decellularization protocols and tried to find answers on various aspects such as whether the secondary structural conformation of dECM proteins would be preserved after decellularization. Thirdly, to keep the dECM ultrastructure as close to the native ECM we have raised the question "How good is good enough?" Even residual cellular antigens or nucleic acid fragments may elicit antigenicity leading to a low-grade immune response. A combinative knowledge of macrophage plasticity in the decellularized tissue and limits of decellularization will help achieve the native ultrastructure. Lastly, we have shifted our focus on the scientific basis of the presently accepted criteria for decellularization, and the effect on immune response concerning the interaction between the decellularized extracellular matrix and macrophages with the subsequent influence of T-cell activation. Amalgamating suitable decellularization approaches, sufficient knowledge of macrophage plasticity and elucidation of molecular pathways together will help fabricate functional immune informed decellularized tissues in vitro that will have substantial implications for efficient clinical translation and prediction for in vivo reprogramming and tissue regeneration.

Eclectic characterisation of chemically modified cell-derived matrices obtained by metabolic glycoengineering and re-assessment of commonly used methods

Azide-bearing cell-derived extracellular matrices ("clickECMs") have emerged as a highly exciting new class of biomaterials. They conserve substantial characteristics of the natural extracellular matrix (ECM) and offer simultaneously small abiotic functional groups that enable bioorthogonal bioconjugation reactions. Despite their attractiveness, investigation of their biomolecular composition is very challenging due to the insoluble and highly complex nature of cell-derived matrices (CDMs). Yet, thorough qualitative and quantitative analysis of the overall material composition, organisation, localisation, and distribution of typical ECM-specific biomolecules is essential for consistent advancement of CDMs and the understanding of the prospective functions of the developed biomaterial. In this study, we evaluated frequently used methods for the analysis of complex CDMs. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and (immune)histochemical staining methods in combination with several microscopic techniques were found to be highly eligible. Commercially available colorimetric protein assays turned out to deliver inaccurate information on CDMs. In contrast, we determined the nitrogen content of CDMs by elementary analysis and converted it into total protein content using conversion factors which were calculated from matching amino acid compositions. The amount of insoluble collagens was assessed based on the hydroxyproline content. The Sircol™ assay was identified as a suitable method to quantify soluble collagens while the Blyscan™ assay was found to be well-suited for the quantification of sulphated glycosaminoglycans (sGAGs). Eventually, we propose a series of suitable methods to reliably characterise the biomolecular composition of fibroblast-derived clickECM.

Decellularized human corneal stromal cell sheet as a novel matrix for ocular surface reconstruction

The shortage of donor corneas as well as the limitations of tissue substitutes leads to the necessity to develop alternative materials for ocular surface reconstruction. Corneal surface substitutes must fulfill specific requirements such as high transparency, low immunogenicity, and mechanical stability combined with elasticity. This in vitro study evaluates a decellularized matrix secreted from human corneal fibroblasts (HCF) as an alternative material for ocular surface reconstruction. HCF from human donors were cultivated with the supplementation of vitamin C to form a stable and thick matrix. Furthermore, due to enhanced cultivation time, a three-dimensional like multilayered construct which partly mimics the complex structure of the corneal stroma could be generated. The formed human cell-based matrices (so-called cell sheets [CS]) were subsequently decellularized. The complete cell removal, collagen content, ultrastructure, and cell toxicity of the decellularized CS (DCS) as well as biomechanical properties were analyzed. Surgical feasibility was tested on enucleated porcine eyes. After decellularization and sterilization, a transparent, thick, cell free, and sterile tissue substitute resulted, which allowed expansion of limbal epithelial stem cells with no signs of cytotoxicity, and good surgical feasibility. DCS seem to be a promising new corneal tissue substitute derived from human cells without the limitation of donor material; however, future in vivo studies are necessary to further elucidate its potential for ocular surface reconstruction.

New Insight into Natural Extracellular Matrix: Genipin Cross-Linked Adipose-Derived Stem Cell Extracellular Matrix Gel for Tissue Engineering

The cell-derived extracellular matrix (ECM) is associated with a lower risk of pathogen transfer, and it possesses an ideal niche with growth factors and complex fibrillar proteins for cell attachment and growth. However, the cell-derived ECM is found to have poor biomechanical properties, and processing of cell-derived ECM into gels is scarcely studied. The gel provides platforms for three-dimensional cell culture, as well as injectable biomaterials, which could be delivered via a minimally invasive procedure. Thus, in this study, an adipose-derived stem cell (ADSC)-derived ECM gel was developed and cross-linked by genipin to address the aforementioned issue. The genipin cross-linked ADSC ECM gel was fabricated via several steps, including rabbit ADSC culture, cell sheets, decellularization, freeze-thawing, enzymatic digestion, neutralization of pH, and cross-linking. The physicochemical characteristics and cytocompatibility of the gel were evaluated. The results demonstrated that the genipin cross-linking could significantly enhance the mechanical properties of the ADSC ECM gel. Furthermore, the ADSC ECM was found to contain collagen, fibronectin, biglycan, and transforming growth factor (TGF)-β1, which could substantially maintain ADSC, skin, and ligament fibroblast cell proliferation. This cell-derived natural material could be suitable for future regenerative medicine and tissue engineering application.

Comparative assessment of the efficiency of various decellularization agents for bone tissue engineering

Bone regeneration can be possible through grafts or engineered bone replacement when bone defects are larger than the critical size. Decellularized bone extracellular matrix (ECM) is an alternative that is able to accelerate tissue regeneration, while decellularization protocols influence engineered bone quality. The objective of this study was to compare the quality of decellularized bone produced through different methods. Four decellularization methods were employed using (a) sodium lauryl ether sulfate (SLES), (b) sodium dodecyl sulfate (SDS) 0.5%, (c) SDS 1% and (d) trypsin/EDTA. All samples were then washed in triton X-100. DNA quantification, hematoxylin and eosin, and Hoechst staining showed that although DNA was depleted in all scaffolds, treatment with SLES led to a significantly lower DNA content. Glycosaminoglycan quantification, Raman confocal microscopy, alcian blue and PAS staining exhibited higher carbohydrate retention in the scaffolds treated with SLES and SDS 0.5%. Raman spectra, scanning electron microscopy and trichrom Masson staining showed more collagen content in SLES and SDS-treated scaffolds compared to trypsin/EDTA-treated scaffolds. Therefore, although trypsin/EDTA could efficiently decellularize the scaffolds, it washed out the ECM contents. Also, both MTT and attachment tests showed a significantly higher cell viability in SLES-treated scaffolds. Raman spectra revealed that while the first washing procedure did not remove SLES traces in the scaffolds, excessive washing reduced ECM contents. In conclusion, SLES and, to a lesser degree, SDS 0.5% protocols could efficiently preserve ultrastructure and ECM constituents of decellularized bone tissue and can thus be suggested as nontoxic and safe protocols for bone regeneration.

Decellularized Scaffolds for Skin Repair and Regeneration

The skin is the largest organ in the body, fulfilling a variety of functions and acting as a barrier for internal organs against external insults. As for extensive or irreversible damage, skin autografts are often considered the gold standard, however inherent limitations highlight the need for alternative strategies. Engineering of human-compatible tissues is an interdisciplinary and active field of research, leading to the production of scaffolds and skin substitutes to guide repair and regeneration. However, faithful reproduction of extracellular matrix (ECM) architecture and bioactive content capable of cell-instructive and cell-responsive properties remains challenging. ECM is a heterogeneous, connective network composed of collagens, glycoproteins, proteoglycans, and small molecules. It is highly coordinated to provide the physical scaffolding, mechanical stability, and biochemical cues necessary for tissue morphogenesis and homeostasis. Decellularization processes have made it possible to isolate the ECM in its native and three-dimensional form from a cell-populated tissue for use in skin regeneration. In this review, we present recent knowledge about these decellularized biomaterials with the potential to be used as dermal or skin substitutes in clinical applications. We detail tissue sources and clinical indications with success rates and report the most effective decellularization methods compatible with clinical use.

Cell-derived matrices (CDM)-Methods, challenges and applications

Extracellular matrix (ECM) provides both physical support and bioactive signals such as growth factors and cytokines to cells at their microenvironment or niche. Engineering the matrix niche becomes an important approach to study or manipulate cellular fate. This work presents an overview on the reconstitution of the ECM niche through a wide range of approaches ranging from coating culture dish with ECM molecules to decellularization of native tissues. In particular, we focused on reconstituting the complex ECM niche through cell-derived matrix (CDM) by reviewing the methodological approaches used in our group to derive ECM from mature cells such as chondrocytes and nucleus pulposus cells (NPCs), undifferentiated stem cells such as mesenchymal stem cells (MSCs), as well as MSCs undergoing chondrogenic and osteogenic differentiation, in 2D or 3D models. Specific attention has also been given to key factors that should be considered in various applications and challenges in relation to the CDM. Last but not the least, a few future perspectives and their significance have been proposed.

The Fabrication and Evaluation of a Potential Biomaterial Produced with Stem Cell Sheet Technology for Future Regenerative Medicine

To date, the decellularized scaffold has been widely explored as a source of biological scaffolds for regenerative medicine. However, the acellular matrix derived from natural tissues and organs has a lot of defects, including the limited amount of autogenous tissue and surgical complication such as risk of blood loss, wound infection, pain, shock, and functional damage in the donor part of the body. In this study, we prepared acellular matrix using adipose-derived stem cell (ADSC) sheets and evaluate the cellular compatibility and immunoreactivity. The ADSC sheets were fabricated and subsequently decellularized using repeated freeze-thaw, Triton X-100 and SDS decellularization. Oral mucosal epithelial cells were seeded onto the decellularized ADSC sheets to evaluate the cell replantation ability, and silk fibroin was used as the control. Then, acellular matrix was transplanted onto subcutaneous tissue for 1 week or 3 weeks; H&E staining and immunohistochemical analysis of CD68 expression and quantitative real-time PCR (qPCR) were performed to evaluate the immunogenicity and biocompatibility. The ADSC sheet-derived ECM scaffolds preserved the three-dimensional architecture of ECM and retained the cytokines by Triton X-100 decellularization protocols. Compared with silk fibroin in vitro, the oral mucosal epithelial cells survived better on the decellularized ADSC sheets with an intact and consecutive epidermal cellular layer. Compared with porcine small intestinal submucosa (SIS) in vivo, the homogeneous decellularized ADSC sheets had less monocyte-macrophage infiltrating in vivo implantation. During 3 weeks after transplantation, the mRNA expression of cytokines, such as IL-4/IL-10, was obviously higher in decellularized ADSC sheets than that of porcine SIS. A Triton X-100 method can achieve effective cell removal, retain major ECM components, and preserve the ultrastructure of ADSC sheets. The decellularized ADSC sheets possess good recellularization capacity and excellent biocompatibility. This study demonstrated the potential suitability of utilizing acellular matrix from ADSC sheets for soft tissue regeneration and repair.

In Vitro Biocompatibility of Decellularized Cultured Plant Cell-Derived Matrices

There has been a recent increase in exploring the use of decellularized plant tissue as a novel "green" material for biomedical applications. As part of this effort, we have developed a technique to decellularize cultured plant cells (tobacco BY-2 cells and rice cells) and tissue (tobacco hairy roots) that uses deoxyribonuclease I (DNase I)). As a proof of concept, all cultured plant cells and tissue were transformed to express recombinant enhanced green fluorescent protein (EGFP) to show that the proteins of interest could be retained within the matrices. Decellularization of lyophilized tobacco BY-2 cells with DNase for 30 min depleted the DNA content from 1503 ± 459 to 31 ± 5 ng/sample. The decellularization procedure resulted in approximately 36% total protein retention (154 ± 60 vs 424 ± 70 μg/sample) and 33% EGFP retention. Similar results for DNA removal and protein retention were observed with the rice cells and tobacco hairy root matrices. When exposed to decellularized BY-2 cell-derived matrices, monolayer cultures of human foreskin fibroblasts (hFFs) maintained or increased metabolic activity, which is an indicator of cell viability. Furthermore, hFFs were able to attach, spread, and proliferate when cultured with the decellularized BY-2 cell-derived matrices in an aggregate model. Overall, these studies demonstrate that cultured plant cells and tissue can be effectively decellularized with DNase I with substantial protein retention. The resulting material has a positive impact on hFF metabolic activity and could be employed to create a three-dimensional environment for cell growth. These results thus show the promise of using naturally derived cellulose matrices from cultured plant cells and tissues for biomedical applications.

A prevascularized nerve conduit based on a stem cell sheet effectively promotes the repair of transected spinal cord injury

Spinal cord injury (SCI) can result in severe loss of motor and sensory function caused by ischemia and hypoxia, which are the key limiting factors of SCI rehabilitation. Vascularization is considered an effective way to resolve the issues of ischemia and hypoxia. In this regard, we first fabricated prevascularized nerve conduits (PNC) based on the prevascularized stem cell sheet and evaluated their repair effects by implanting them into transected SCI rats. A better healing effect was presented in the PNC group than in the control group and the nonprevascularized nerve conduit (NPNC) group as shown in H&E staining and the Basso, Beattie, Bresnahan (BBB) Locomotor Rating Scale assessment. In addition, the expression of β-III tubulin (Tuj-1) in the PNC group was higher than that in the control group and the NPNC group because of the introduction of MSCs. Conversely, the expression of the glial fibrillary acidic protein (GFAP) in both experimental groups was lower than that in the control group because of the inhibitory effect of MSCs on glial scar formation. Taken together, the introduction of prevascularization into the neuron conduit was an effective solution for improving the condition of ischemia and hypoxia, inhibiting glial scar formation, and promoting the healing of SCI, which implied that the PNC may be a potential alternative material to biomaterials for SCI rehabilitation. STATEMENT OF SIGNIFICANCE: 1. Prevascularized stem cell sheet was first used to repair spinal cord injury (SCI). 2. Prevascularized stem cell sheet use can effectively resolve the challenges faced during SCI, including ischemia and hypoxia and the limited regenerative ability of the remained neurons. 3. Prevascularized stem cell sheet was found to accelerate the healing of SCI as compared to those in the control group and the pure stem cell sheet group. 4. The introduction of stem cells can effectively inhibit the formation of a glial scar.

Decellularised scaffolds: just a framework? Current knowledge and future directions

The use of decellularised matrices as scaffolds offers the advantage of great similarity with the tissue to be replaced. Moreover, decellularised tissues and organs can be repopulated with the patient's own cells to produce bespoke therapies. Great progress has been made in research and development of decellularised scaffolds, and more recently, these materials are being used in exciting new areas like hydrogels and bioinks. However, much effort is still needed towards preserving the original extracellular matrix composition, especially its minor components, assessing its functionality and scaling up for large tissues and organs. Emphasis should also be placed on developing new decellularisation methods and establishing minimal criteria for assessing the success of the decellularisation process. The aim of this review is to critically review the existing literature on decellularised scaffolds, especially on the preparation of these matrices, and point out areas for improvement, finishing with alternative uses of decellularised scaffolds other than tissue and organ reconstruction. Such uses include three-dimensional ex vivo platforms for idiopathic diseases and cancer modelling.

Decellularized Extracellular Matrix as a Potent Natural Biomaterial for Regenerative Medicine

Decellularization technique is a favorable method used to fabricate natural and tissue-like scaffolds. This technique is important because of its remarkable ability to perfectly mimic the natural extracellular matrix (ECM). ECM-based scaffolds/hydrogels provide structural support for cell differentiation and maturation. Therefore, novel natural-based bioinks, ECM-based hydrogels, and particulate forms of the ECM provide promising strategies for whole organ regeneration. Despite its efficacious characteristics, removal of residual detergent and the presence of various protocols make this technique challenging for scientists and regenerative medicine-related programs. This chapter reviews the most effective physical, chemical, and enzymatic protocols used to remove the cellular components and their challenges. We discuss the applications of decellularized ECM (dECM) in tissue engineering and regenerative medicine with an emphasis on hard tissues.

In Vitro Expansion of Keratinocytes on Human Dermal Fibroblast-Derived Matrix Retains Their Stem-Like Characteristics

The long-term expansion of keratinocytes under conditions that avoid xenogeneic components (i.e. animal serum- and feeder cell-free) generally causes diminished proliferation and increased terminal differentiation. Here we present a culture system free of xenogeneic components that retains the self-renewal capacity of primary human keratinocytes. In vivo the extracellular matrix (ECM) of the tissue microenvironment has a major influence on a cell's fate. We used ECM from human dermal fibroblasts, cultured under macromolecular crowding conditions to facilitate matrix deposition and organisation, in a xenogeneic-free keratinocyte expansion protocol. Phospholipase A2 decellularisation produced ECM whose components resembled the core matrix composition of natural dermis by proteome analyses. Keratinocytes proliferated rapidly on these matrices, retained their small size, expressed p63, lacked keratin 10 and rarely expressed keratin 16. The colony forming efficiency of these keratinocytes was enhanced over that of keratinocytes grown on collagen I, indicating that dermal fibroblast-derived matrices maintain the in vitro expansion of keratinocytes in a stem-like state. Keratinocyte sheets formed on such matrices were multi-layered with superior strength and stability compared to the single-layered sheets formed on collagen I. Thus, keratinocytes expanded using our xenogeneic-free protocol retained a stem-like state, but when triggered by confluence and calcium concentration, they stratified to produce epidermal sheets with a potential clinical use.

Extracellular matrix from decellularized mesenchymal stem cells improves cardiac gene expressions and oxidative resistance in cardiac C-kit cells

OBJECTIVE

Myocardial infarction remains the number one killer disease worldwide. Cellular therapy using cardiac c-kit cells (CCs) are capable of regenerating injured heart. Previous studies showed mesenchymal stem cell-derived (MSC) extracellular matrices can provide structural support and are capable of regulating stem cell functions and differentiation. This study aimed to evaluate the effects of human MSC-derived matrices for CC growth and differentiation.

METHODS

Human Wharton's Jelly-derived MSCs were cultured in ascorbic acid supplemented medium for 14 days prior to decellularisation using two methods. 1% SDS/Triton X-100 (ST) or 20 mM ammonia/Triton X-100 (AT). CCs isolated from 4-week-old C57/BL6N mice were cultured on the decellularised MSC matrices, and induced to differentiate into cardiomyocytes in cardiogenic medium for 21 days. Cardiac differentiation was assessed by immunocytochemistry and qPCR. All data were analysed using ANOVA.

RESULTS

In vitro decellularisation using ST method caused matrix delamination from the wells. In contrast, decellularisation using AT improved the matrix retention up to 30% (p < 0.05). This effect was further enhanced when MSCs were cultured in cardiogenic medium, with a matrix retention rate up to 90%. CCs cultured on cardiogenic MSC matrix (ECMcardio), however, did not significantly improve its proliferation after 3 days (p < 0.05), but the viability of CCs was augmented to 67.2 ± 0.7% after 24-h exposure to H2O2 stress as compared to 42.9 ± 0.5% in control CCs (p < 0.05). Furthermore, CCs cultured on cardiogenic MSC matrices showed 1.7-fold up-regulation in cardiac troponin I (cTnI) gene expression after 21 days (p < 0.05).

CONCLUSION

Highest matrix retention can be obtained by decellularization using Ammonia/Triton-100 in 2-D culture. ECMcardio could rescue CCs from exogenous hydrogen peroxide and further upregulated the cardiac gene expressions, offering an alternate in vitro priming strategy to precondition CCs which could potentially enhance its survival and function after in vivo transplantation.

Biomimetic polyetheretherketone microcarriers with specific surface topography and self-secreted extracellular matrix for large-scale cell expansion

Reusable microcarriers with appropriate surface topography, mechanical properties, as well as biological modification through decellularization facilitating repeated cell culture are crucial for tissue engineering applications. Herein, we report the preparation of topological polyetheretherketone (PEEK) microcarriers via gas-driven and solvent exchange method followed by hydrothermal treatment at high temperature and pressure. After hydrothermal treated for 8 h, the resulting topological PEEK microcarriers exhibit walnut-like surface topography and good sphericity as well as uniform size distribution of 350.24 ± 19.44 µm. And the average width between ravine-patterned surface of PEEK microcarriers is 780 ± 290 nm. After repeated steam sterilization by autoclaving for three times, topological PEEK microcarriers show nearly identical results compared with previous ones indicating strong tolerance to high temperature and pressure. This is a unique advantage for large-scale cell expansion and clinical applications. Moreover, PEEK microcarriers with special topography possess higher protein adsorption efficiency. In addition, the reutilization and biofunctionalization with repeated decellularization of topological PEEK microcarriers show highly beneficial for cell adhesion and proliferation. Therefore, our study is of great importance for new generation microcarriers with micro-and nano-scale surface feature for a broad application prospect in tissue engineering.

Recent Trends in Decellularized Extracellular Matrix Bioinks for 3D Printing: An Updated Review

The promise of regenerative medicine and tissue engineering is founded on the ability to regenerate diseased or damaged tissues and organs into functional tissues and organs or the creation of new tissues and organs altogether. In theory, damaged and diseased tissues and organs can be regenerated or created using different configurations and combinations of extracellular matrix (ECM), cells, and inductive biomolecules. Regenerative medicine and tissue engineering can allow the improvement of patients' quality of life through availing novel treatment options. The coupling of regenerative medicine and tissue engineering with 3D printing, big data, and computational algorithms is revolutionizing the treatment of patients in a huge way. 3D bioprinting allows the proper placement of cells and ECMs, allowing the recapitulation of native microenvironments of tissues and organs. 3D bioprinting utilizes different bioinks made up of different formulations of ECM/biomaterials, biomolecules, and even cells. The choice of the bioink used during 3D bioprinting is very important as properties such as printability, compatibility, and physical strength influence the final construct printed. The extracellular matrix (ECM) provides both physical and mechanical microenvironment needed by cells to survive and proliferate. Decellularized ECM bioink contains biochemical cues from the original native ECM and also the right proportions of ECM proteins. Different techniques and characterization methods are used to derive bioinks from several tissues and organs and to evaluate their quality. This review discusses the uses of decellularized ECM bioinks and argues that they represent the most biomimetic bioinks available. In addition, we briefly discuss some polymer-based bioinks utilized in 3D bioprinting.

Mouse placental scaffolds: a three-dimensional environment model for recellularization

The rich extracellular matrix (ECM) and availability make placenta eligible as alternative biomaterial source. Herein we produced placental mouse scaffolds by decellularization, and structure, composition, and cytocompatibility were evaluated to be considered as a biomaterial. We obtained a cell-free scaffold containing 9.42 ± 5.2 ng dsDNA per mg of ECM, presenting well-preserved structure and composition. Proteoglycans were widespread throughout ECM without cell nuclei and cell remnants. Collagen I, weak in native placenta, clearly appears in the scaffold after recellularization, opposite distribution was observed for collagen III. Fibronectin was well-observed in placental scaffolds whereas laminin and collagen IV were strong expressed. Placental scaffolds recellularization potential was confirmed after mouse embryonic fibroblasts 3D dynamic culture, resulting in massive scaffold repopulation with cell–cell interactions, cell-matrix adhesion, and maintenance of natural morphology. Our small size scaffolds provide a useful tool for tissue engineering to produce grafts and organ fragments, as well as for cellular biology purposes for tridimensional culture substrate.

Fabrication and characterization of extracellular matrix scaffolds obtained from adipose-derived stem cells

Chronic non-healing wounds are detrimental for the quality of life of the affected individuals and represent a major burden for the health care systems. Adipose-derived stem cells (ASCs) are being investigated for the development of novel treatments of chronic wounds, as they have shown several positive effects on wound healing. While these effects appear to be mediated by the release of soluble factors, it is has also become apparent that the extracellular matrix (ECM) deposited by ASCs is essential in several phases of the wound healing process. In this work, we describe an approach to produce ECM scaffolds derived from ASCs in culture. Upon growth of ASCs into an overconfluent cell layer, a detergent-based cell extraction approach is applied to remove the cellular components. The extraction is followed by an enzymatic treatment to remove the residual DNA. The resultant cell-derived scaffolds are depleted of cellular components, display low DNA remnant, and retain the native fibrillar organization of the ECM. Analysis of the molecular composition of the ECM scaffolds revealed that they are composed of collagens type I and III, and fibronectin. The decellularized scaffolds represent a substrate that supports adhesion and proliferation of primary human fibroblasts and dermal microvascular endothelial cells, indicating their potential as platforms for wound healing studies.

Immune tolerance of tissue-engineered skin produced with allogeneic or xenogeneic fibroblasts and syngeneic keratinocytes grafted on mice

Organs are needed for the long-term replacement of diseased or wounded tissues. Various technologies based on cells seeded in synthetic or biomaterial scaffolds, or scaffold-free methods have been developed in order to produce substitutes that mimic native organs and tissues. For cell-based approaches, the use of living allogeneic fibroblasts could potentially lead to the production of "off-the-shelf" bioengineered organs/tissues. However, questions remain regarding the outcome of allogeneic grafts in terms of persistence of allogeneic cells, tolerance and the host immune reaction against the tissue after implantation. To evaluate graft tolerance of engineered-tissues containing non-autologous fibroblasts, tissue-engineered skin substitutes (TESs) produced with syngeneic, allogeneic or xenogeneic fibroblasts associated with syngeneic, allogeneic or xenogeneic epithelial cells were grafted in mice as primary and secondary grafts. The immune response was evaluated by histological analysis and immunodetection of M2 macrophages, CD4- and CD8-positive T cells, 15, 19, 35 and 56 days after grafting. Tissue-engineered skin composed of non-autologous epithelial cells were rejected. In contrast, TESs composed of non-autologous fibroblasts underlying syngeneic epithelial cells were still present 56 days after grafting. This work shows that TES composed of non-autologous fibroblasts and autologous epithelial cells are not rejected after grafting. STATEMENT OF SIGNIFICANCE: We found that tissue-engineered skin substitutes produced by a scaffold-free cell-based approach from allogeneic fibroblasts and autologous epithelial cells are not rejected after grafting and allow for the permanent coverage of a full-thickness skin wounds. In the field of tissue engineering, these findings open the possibility of selecting a human fibroblastic or stromal cell population based on its biological properties and adequate biosafety, banking it, in order to produce "ready-to-use" bioengineered organs/tissues that could be grafted to any patient without eliciting immune reaction after grafting. Our results can be generalized to any organs produced from fibroblasts. Thus, it is a great step with multiple applications in tissue engineering and transplantation.

Cell-Free Demineralized Bone Matrix for Mesenchymal Stem Cells Survival and Colonization

Decellularized bone matrix is receiving much attention as biological scaffolds and implantable biomaterials for bone tissue regeneration. Here, we evaluated the efficacy of a cell-free demineralized bone matrix on mesenchymal stem cells (MSCs) survival and differentiation in vitro. The seeding of human umbilical cord-derived MSCs (hUC-SCs) on decellularized bone matrices up to 14 days was exploited, assessing their capability of scaffold colonization and evaluating gene expression of bone markers. Light and Scanning Electron Microscopies were used. The obtained cell-free decalcified structures showed elastic moduli attributable to both topology and biochemical composition. Morphological observation evidenced an almost complete colonization of the scaffolds after 14 days of culture. Moreover, in hUC-SCs cultured on decalcified scaffolds, without the addition of any osteoinductive media, there was an upregulation of Collagen Type I (COL1) and osteonectin (ON) gene expression, especially on day 14. Modifications in the expression of genes engaged in stemness were also detected. In conclusion, the proposed decellularized bone matrix can induce the in vitro hUC-SCs differentiation and has the potential to be tested for in in vivo tissue regeneration.

Engineering stem cell cardiac patch with microvascular features representative of native myocardium

The natural myocardium is a highly aligned tissue with an oriented vasculature. Its characteristic cellular as well as nanoscale extracellular matrix (ECM) organization along with an oriented vascular network ensures appropriate blood supply and functional performance. Although significant efforts have been made to develop anisotropic cardiac structure, currently neither an ideal biomaterial nor an effective vascularization strategy to engineer oriented and high-density capillary-like microvessels has been achieved for clinical cardiovascular therapies. A naturally derived oriented ECM nanofibrous scaffold mimics the physiological structure and components of tissue ECM and guides neovascular network formation. The objective of this study was to create an oriented and dense microvessel network with physiological myocardial microvascular features.

METHODS

Highly aligned decellularized human dermal fibroblast sheets were used as ECM scaffold to regulate physiological alignment of microvascular networks by co-culturing human mesenchymal stem cells (hMSCs) and endothelial cells (ECs). The influence of topographical features on hMSC and EC interaction was investigated to understand underlying mechanisms of neovasculature formation.

RESULTS

Results demonstrate that the ECM topography can be translated to ECs via CD166 tracks and significantly improved hMSC-EC crosstalk and vascular network formation. The aligned ECM nanofibers enhanced structure, length, and density of microvascular networks compared to randomly organized nanofibrous ECM. Moreover, hMSC-EC co-culture promoted secretion of pro-angiogenic growth factors and matrix remodeling via metalloprotease-2 (MMP-2) activation, which resulted in highly dense vascular network formation with intercapillary distance (20 μm) similar to the native myocardium.

CONCLUSION

HMSC-EC co-culture on the highly aligned ECM generates physiologically oriented and dense microvascular network, which holds great potential for cardiac tissue engineering.