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

Three-Dimensional Modelling of Ovarian Cancer: From Cell Lines to Organoids for Discovery and Personalized Medicine

Ovarian cancer has the highest mortality of all of the gynecological malignancies. There are several distinct histotypes of this malignancy characterized by specific molecular events and clinical behavior. These histotypes have differing responses to platinum-based drugs that have been the mainstay of therapy for ovarian cancer for decades. For histotypes that initially respond to a chemotherapeutic regime of carboplatin and paclitaxel such as high-grade serous ovarian cancer, the development of chemoresistance is common and underpins incurable disease. Recent discoveries have led to the clinical use of PARP (poly ADP ribose polymerase) inhibitors for ovarian cancers defective in homologous recombination repair, as well as the anti-angiogenic bevacizumab. While predictive molecular testing involving identification of a genomic scar and/or the presence of germline or somatic BRCA1 or BRCA2 mutation are in clinical use to inform the likely success of a PARP inhibitor, no similar tests are available to identify women likely to respond to bevacizumab. Functional tests to predict patient response to any drug are, in fact, essentially absent from clinical care. New drugs are needed to treat ovarian cancer. In this review, we discuss applications to address the currently unmet need of developing physiologically relevant in vitro and ex vivo models of ovarian cancer for fundamental discovery science, and personalized medicine approaches. Traditional two-dimensional (2D) in vitro cell culture of ovarian cancer lacks critical cell-to-cell interactions afforded by culture in three-dimensions. Additionally, modelling interactions with the tumor microenvironment, including the surface of organs in the peritoneal cavity that support metastatic growth of ovarian cancer, will improve the power of these models. Being able to reliably grow primary tumoroid cultures of ovarian cancer will improve the ability to recapitulate tumor heterogeneity. Three-dimensional (3D) modelling systems, from cell lines to organoid or tumoroid cultures, represent enhanced starting points from which improved translational outcomes for women with ovarian cancer will emerge.

Application of Tissue-Specific Extracellular Matrix in Tissue Engineering: Focus on Male Fertility Preservation

In vitro spermatogenesis and xenotransplantation of the immature testicular tissues (ITT) are the experimental approaches that have been developed for creating seminiferous tubules-like functional structures in vitro and keeping the integrity of the ITTs in vivo, respectively. These strategies are rapidly developing in response to the growing prevalence of infertility in adolescent boys undergoing cancer treatment, by the logic that there is no sperm cryopreservation option for them. Recently, with the advances made in the field of tissue engineering and biomaterials, these methods have achieved promising results for fertility preservation. Due to the importance of extracellular matrix for the formation of vascular bed around the grafted ITTs and also the creation of spatial arrangements between Sertoli cells and germ cells, today it is clear that the scaffold plays a very important role in the success of these methods. Decellularized extracellular matrix (dECM) as a biocompatible, functionally graded, and biodegradable scaffold with having tissue-specific components and growth factors can support reorganization and physiologic processes of originated cells. This review discusses the common protocols for the tissue decellularization, sterilization, and hydrogel formation of the decellularized and lyophilized tissues as well as in vitro and in vivo studies on the use of the testis-derived dECM for testicular organoids.

Decellularised extracellular matrix-based biomaterials for repair and regeneration of central nervous system

The central nervous system (CNS), consisting of the brain and spinal cord, regulates the mind and functions of the organs. CNS diseases, leading to changes in neurological functions in corresponding sites and causing long-term disability, represent one of the major public health issues with significant clinical and economic burdens worldwide. In particular, the abnormal changes in the extracellular matrix under various disease conditions have been demonstrated as one of the main factors that can alter normal cell function and reduce the neuroregeneration potential in damaged tissue. Decellularised extracellular matrix (dECM)-based biomaterials have been recently utilised for CNS applications, closely mimicking the native tissue. dECM retains tissue-specific components, including proteoglycan as well as structural and functional proteins. Due to their unique composition, these biomaterials can stimulate sensitive repair mechanisms associated with CNS damages. Herein, we discuss the decellularisation of the brain and spinal cord as well as recellularisation of acellular matrix and the recent progress in the utilisation of brain and spinal cord dECM.

Application of decellularized bone matrix as a bioscaffold in bone tissue engineering

Autologous bone grafts are commonly used as the gold standard to repair and regenerate diseased bones. However, they are strongly associated with postoperative complications, especially at the donor site, and increased surgical costs. In an effort to overcome these limitations, tissue engineering (TE) has been proposed as an alternative to promote bone repair. The successful outcome of tissue engineering depends on the microstructure and composition of the materials used as scaffold. Decellularized bone matrix-based biomaterials have been applied as bioscaffolds in bone tissue engineering. These biomaterials play an important role in providing the mechanical and physical microenvironment needed by cells to proliferate and survive. Decellularized extracellular matrix (dECM) can be used as a powder, hydrogel and electrospun scaffolds. These bioscaffolds mimic the native microenvironment due to their structure similar to the original tissue. The aim of this review is to highlight the bone decellularization techniques. Herein we discuss: (1) bone structure; (2) properties of an ideal scaffold; (3) the potential of decellularized bone as bioscaffolds; (4) terminal sterilization of decellularized bone; (5) cell removing confirmation in decellularized tissues; and (6) post decellularization procedures. Finally, the improvement of bone formation by dECM and the immunogenicity aspect of using the decellularized bone matrix are presented, to illustrate how novel dECM-based materials can be used as bioscaffold in tissue engineering. A comprehensive understanding of tissue engineering may allow for better incorporation of therapeutic approaches in bone defects allowing for bone repair and regeneration.

Development of decellularization protocol for caprine small intestine submucosa as a biomaterial

Decellularized animal tissues have been proven to be promising biomaterials for various tissue engineering (TE) applications. Among various animal tissues, small intestine submucosa (SIS) has gained attention of many researchers due to its easy availability from the abattoir waste, excellent physicochemical and biological characteristics of a good biomaterial. In this study, Caprine SIS was decellularized to get decellularized caprine SIS (DG-SIS). For decellularization, several physical, chemical and enzymatic protocols have been described in the literature. To optimize the decellularization of caprine SIS, several decellularization protocol (DP), including an in-house developed by us, had been attempted, and effect of the different DPs on the obtained DG-SIS were assessed in terms of decellularization, physiochemical and biological properties. All the DPs differ in terms of decellularization, but three DPs where ionic detergent like sodium dodecyl sulphate (SDS) has been used, largely affect the native composition (e.g. glycosaminoglycans (GAGs)), biological properties and other physiochemical properties of the G-SIS as compared to the DP that uses hypertonic solution of potassium iodide (KI) and non-ionic detergent (TritonX-100). The obtained DG-SISs were fibrous, hemocompatible, biocompatible, hydrophilic, biodegradable and exhibited significant antibacterial activity. Therefore, the DG-SIS will be a prospective biomaterial for TE applications.

Characterization of Composite Nano-Bioscaffolds Based on Collagen and Supercritical Fluids-Assisted Decellularized Fibrous Extracellular Matrix

Nano-bioscaffolds obtained from decellularized tissues have been employed in several medical applications. Nano-bioscaffolds could provide structural support for cell attachment and a suitable environment with sufficient porosity for cell growth and proliferation. In this study, a new combined method constitutes a decellularization protocol to remove the tissue and cellular molecules from porcine dermis for preparation of nano-bioscaffolds with fibrous extracellular matrix via pre- and post-treatment of supercritical fluids. The supercritical fluids-assisted nano-bioscaffolds were characterized by peptide identification, infrared spectrum of absorption, morphology, histological observations, DNA quantification, and hemocompatibility. Further, the resulting nano-bioscaffolds could be employed to obtain new cross-linked composite nano-bioscaffold containing collagen and acellular matrix.

Recent Advances in Kidney Bioengineering

Kidney disease is an epidemic that affects more than 600 million people worldwide. The socioeconomic impacts of the disease disproportionately affect Hispanic and non-Hispanic Black Americans, making the disease an issue of social inequality. The urgency of this situation has only become worse during the COVID-19 pandemic, as those who are hospitalized for COVID-19 have an increased risk of kidney failure. For researchers, the kidney is a complex organ that is difficult to accurately model and understand. Traditional cell culture models are not adequate for studying the functional intricacies of the kidney, but recent experiments have offered improvements for understanding these systems. Recent progress includes organoid modeling, 3D bioprinting, decellularization, and microfluidics. Here, we offer a review of the most recent advances in kidney bioengineering.

A tissue-engineered, decellularized, connective tissue membrane for allogeneic arterial patch implantation

BACKGROUND

We have previously applied in vivo tissue-engineered vascular grafts constructed in patients' subcutaneous spaces. However, since the formation of these vascular grafts depends on host health, their application is challenging in patients with suppressed regenerative ability. Therefore, the allogeneic implantation of grafts from healthy donors needs to be evaluated. This study aimed to fabricate allogeneic cardiovascular grafts in animals.

MATERIALS AND METHODS

Silicone rod molds were implanted into subcutaneous pouches in dogs; the implants, along with surrounding connective tissues, were harvested after four weeks. Tubular connective tissues were decellularized and stored before they were cut open, trimmed to elliptical sheets, and implanted into the common carotid arteries of another dog as vascular patches (n = 6); these were resected and histologically evaluated at 1, 2, and 4 weeks after implantation.

RESULTS

No aneurysmal changes were observed by echocardiography. Histologically, we observed neointima formation on the luminal graft surface and graft wall cell infiltration. At 2 and 4 weeks after implantation, α-SMA-positive cells were observed in the neointima and graft wall. At 4 weeks after implantation, the endothelial lining was observed at the grafts' luminal surfaces.

CONCLUSION

Our data suggest that decellularized connective tissue membranes can be prepared and stored for later use as allogeneic cardiovascular grafts.

Construction of extracellular matrix-based 3D hydrogel and its effects on cardiomyocytes

Some discoveries resulted from 2-dimensional (2D) cultured cardiac cells have been disqualified in animal testing and later clinical trials. Extracellular matrix (ECM) plays a vital role in cardiac homeostasis, cardiac ECM (cECM)-based 3D cell cultures can mimics the physiological and pathological conditions in vivo closely, it is hopeful of addressing this challenge. Construction of cECM-based 3-dimensional (3D) hydrogel (cECM3DH) and its effects on cell behaviors were studied here. The results indicated that cellular compartments could be efficiently removed from heart tissue via sodium dodecyl sulfonate (SDS)- and Triton X-100-mediated decellularization, remaining the natural fibrous network structure and major proteins. 3D hydrogel consisted of 1 × 107 cells/mL cells and 75% cECM could promote the proliferation and anti-apoptosis ability of human embryonic kidney (HEK)-293T cells. 0.25% trypsin or 0.20% collagenase was suitable to retrieve these cells from 3D hydrogel for further researches. Compared with 2D culture system, cECM3DH could significantly increase the proportion of GATA 4+ cardiomyocytes (CMs) derived from heart tissue of neonatal mouse or induced differentiation of embryonic stem cells (ESCs) (P < 0.05) The expression levels of mature genes including cTnT, JCN, CaV1.2, MYL2, CASQ2, NCX1, and Cx43 of these CMs in adult pig cECM-based 3D hydrogel (APcECM3DH) were significantly higher than that in 2D culture system and in newborn piglet cECM-based 3D hydrogel (NPcECM3DH), respectively (P < 0.05). Therefore, cECM3DH supports the generation of primary CMs and ESC-derived CMs, APcECM3DH was more conducive to promoting CM maturation, which contributes to building 3D model for pathogenesis exploration, drug screening, and regenerative medicine of heart diseases.

Biomaterials and Their Biomedical Applications: From Replacement to Regeneration

The history of biomaterials dates back to the mists of time: human beings had always used exogenous materials to facilitate wound healing and try to restore damaged tissues and organs. Nowadays, a wide variety of materials are commercially available and many others are under investigation to both maintain and restore bodily functions. Emerging clinical needs forced the development of new biomaterials, and lately discovered biomaterials allowed for the performing of new clinical applications. The definition of biomaterials as materials specifically conceived for biomedical uses was raised when it was acknowledged that they have to possess a fundamental feature: biocompatibility. At first, biocompatibility was mainly associated with biologically inert substances; around the 1970s, bioactivity was first discovered and the definition of biomaterials was consequently extended. At present, it also includes biologically derived materials and biological tissues. The present work aims at walking across the history of biomaterials, looking towards the scientific literature published on this matter. Finally, some current applications of biomaterials are briefly depicted and their future exploitation is hypothesized.

Advances in the proteomic profiling of the matrisome and adhesome

INTRODUCTION

The matrisome and adhesome comprise proteins that are found within or are associated with the extracellular matrix (ECM) and adhesion complexes, respectively. Interactions between cells and their microenvironment are mediated by key matrisome and adhesome proteins, which direct fundamental processes, including growth and development. Due to their underlying complexity, it has historically been challenging to undertake mass spectrometry (MS)-based profiling of these proteins. New developments in sample preparative workflows, informatics databases, and MS techniques have enabled in-depth proteomic characterization of the matrisome and adhesome, resulting in a comprehensive understanding of the interactomes, and cellular signaling that occur at the cell-ECM interface.

AREA COVERED

This review summarizes recent advances in proteomic characterization of the matrisome and adhesome. It focuses on the importance of curated databases and discusses key strengths and limitations of different workflows.

EXPERT OPINION

MS-based proteomics has shown promise in characterizing the matrisome and topology of adhesome networks in health and disease. Moving forward, it will be important to incorporate integrative analysis to define the bidirectional signaling between the matrisome and adhesome, and adopt new methods for post-translational modification and in vivo analyses to better dissect the critical roles that these proteins play in human pathophysiology.

Extracellular matrix-derived hydrogels to augment dermal wound healing: a systematic review

BACKGROUND

Chronic, non-healing, dermal wounds form a worldwide medical problem with limited and inadequate treatment options and high societal burden and costs. With the advent of regenerative therapies exploiting extracellular matrix (ECM) components, its efficacy to augment wound healing is to be explored. This systematic review was performed to assess and compare the current therapeutic efficacy of ECM hydrogels on dermal wound healing.

METHODS

The electronic databases of (Embase, Medline Ovid, Cochrane Central) were searched for in vivo and clinical studies on the therapeutic effect of ECM-composed hydrogels on dermal wound healing (13th of April 2021). Two reviewers selected studies independently. Studies were assessed based on ECM content, ECM hydrogel composition, additives and wound healing outcomes such as wound size, angiogenesis and complications.

RESULTS

Of the 2102 publications, nine rodent-based studies were included while clinical studies were not published at the time of the search. Procedures to decellularize tissue or cultured cells and subsequently generate hydrogels were highly variable and in demand of standardization. ECM hydrogels with or without additives reduced wound size and also seem to enhance angiogenesis. Serious complications were not reported.

CONCLUSION

To date, preclinical studies preclude to draw firm conclusions on the efficacy and working mechanism of ECM-derived hydrogels on dermal wound healing. The use of ECM hydrogels can be considered safe. Standardization of decellularization protocols and implementation of quality and cytotoxicity controls will enable obtaining a generic and comparable ECM product.

Uterine Tissue Engineering: Where We Stand and the Challenges Ahead

Tissue engineering is an innovative approach to develop allogeneic tissues and organs. The uterus is a very sensitive and complex organ, which requires refined techniques to properly regenerate and even, to rebuild itself. Many therapies were developed in 20th century to solve reproductive issues related to uterus failure and, more recently, tissue engineering techniques provided a significant evolution in this issue. Herein we aim to provide a broad overview and highlights of the general concepts involved in bioengineering to reconstruct the uterus and its tissues, focusing on strategies for tissue repair, production of uterine scaffolds, biomaterials and reproductive animal models, highlighting the most recent and effective tissue engineering protocols in literature and their application in regenerative medicine. In addition, we provide a discussion about what was achieved in uterine tissue engineering, the main limitations, the challenges to overcome and future perspectives in this research field.

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.

Biofabrication of allogenic bone grafts using cellularized amniotic scaffolds for application in efficient bone healing

INTRODUCTION

The reconstruction/regeneration of human bone injuries/defects represents a crucial challenge due to the lack of suitable bio/immune compatible and implantable biological grafts. The available strategies represent implications of several types of grafting materials in the form of metals, synthetic, and various kinds of biological scaffolds; however, the lack of appropriate biological components required for activating and enhancing repair mechanisms at the lesion-site limits their wider applicability.

METHODS

In this study, a unique approach for generating human osteogenic implantable grafts was developed using biofabrication technology. Using a gradient change of detergents and continuous agitation, developed a unique technique to generate completely cell-free amnion and chorion scaffolds. The absence of cellular components and integrity of biological and mechanical cues within decellularized human amnion (D-HAM) and chorion (D-HCM) were evaluated and compared with fresh membranes. Allogenic bone grafts were prepared through induction of human mesenchymal stem cells (hMSCs) into osteogenic cells on D-HAM and D-HCM and evaluated for their comparative behavior at the cellular, histological and molecular levels.

RESULTS

The common decellularization process resulted in an efficient way to generate D-HAM and D-HCM while retaining their intact gross-anatomical architecture, surface morphology, extracellular matrix components, and mechanical properties. Both these scaffolds supported better growth of human umbilical cord blood derived MSCs as well as osteogenic differentiation. Comparative investigation revealed better growth rate and differentiation on D-HCM compared to D-HAM and control conditions.

CONCLUSION

D-HCM could be used as a better choice for producing suitable allogenic bone grafts for efficient bone healing applications.

Image-Based Method to Quantify Decellularization of Tissue Sections

Tissue decellularization is typically assessed through absorbance-based DNA quantification after tissue digestion. This method has several disadvantages, namely its destructive nature and inadequacy in experimental situations where tissue is scarce. Here, we present an image processing algorithm for quantitative analysis of DNA content in (de)cellularized tissues as a faster, simpler and more comprehensive alternative. Our method uses local entropy measurements of a phase contrast image to create a mask, which is then applied to corresponding nuclei labelled (UV) images to extract average fluorescence intensities as an estimate of DNA content. The method can be used on native or decellularized tissue to quantify DNA content, thus allowing quantitative assessment of decellularization procedures. We confirm that our new method yields results in line with those obtained using the standard DNA quantification method and that it is successful for both lung and heart tissues. We are also able to accurately obtain a timeline of decreasing DNA content with increased incubation time with a decellularizing agent. Finally, the identified masks can also be applied to additional fluorescence images of immunostained proteins such as collagen or elastin, thus allowing further image-based tissue characterization.

Photocrosslinkable liver extracellular matrix hydrogels for the generation of 3D liver microenvironment models

Liver extracellular matrix (ECM)-based hydrogels have gained considerable interest as biomimetic 3D cell culture environments to investigate the mechanisms of liver pathology, metabolism, and toxicity. The preparation of current liver ECM hydrogels, however, is based on time-consuming thermal gelation and limits the control of mechanical properties. In this study, we used detergent-based protocols to produce decellularized porcine liver ECM, which in turn were solubilized and functionalized with methacrylic anhydride to generate photocrosslinkable methacrylated liver ECM (LivMA) hydrogels. Firstly, we explored the efficacy of two protocols to decellularize porcine liver tissue using varying combinations of commonly used chemical agents such as Triton X-100, Sodium Dodecyl Sulphate (SDS) and Ammonium hydroxide. Then, we demonstrated successful formation of stable, reproducible LivMA hydrogels from both the protocols by photocrosslinking. The LivMA hydrogels obtained from the two decellularization protocols showed distinct mechanical properties. The compressive modulus of the hydrogels was directly dependent on the hydrogel concentration, thereby demonstrating the tuneability of mechanical properties of these hydrogels. Immortalized Human Hepatocytes cells were encapsulated in the LivMA hydrogels and cytocompatibility of the hydrogels was demonstrated after one week of culture. In summary, the LivMA hydrogel system provides a simple, photocrosslinkable platform, which can potentially be used to simulate healthy versus damaged liver for liver disease research, drug studies and cancer metastasis modelling.

Cutting Edge Endogenous Promoting and Exogenous Driven Strategies for Bone Regeneration

Bone damage leading to bone loss can arise from a wide range of causes, including those intrinsic to individuals such as infections or diseases with metabolic (diabetes), genetic (osteogenesis imperfecta), and/or age-related (osteoporosis) etiology, or extrinsic ones coming from external insults such as trauma or surgery. Although bone tissue has an intrinsic capacity of self-repair, large bone defects often require anabolic treatments targeting bone formation process and/or bone grafts, aiming to restore bone loss. The current bone surrogates used for clinical purposes are autologous, allogeneic, or xenogeneic bone grafts, which although effective imply a number of limitations: the need to remove bone from another location in the case of autologous transplants and the possibility of an immune rejection when using allogeneic or xenogeneic grafts. To overcome these limitations, cutting edge therapies for skeletal regeneration of bone defects are currently under extensive research with promising results; such as those boosting endogenous bone regeneration, by the stimulation of host cells, or the ones driven exogenously with scaffolds, biomolecules, and mesenchymal stem cells as key players of bone healing process.

Recent Advancements in Regenerative Approaches for Thymus Rejuvenation

The thymus plays a key role in adaptive immunity by generating a diverse population of T cells that defend the body against pathogens. Various factors from disease and toxic insults contribute to the degeneration of the thymus resulting in a fewer output of T cells. Consequently, the body is prone to a wide host of diseases and infections. In this review, first, the relevance of the thymus is discussed, followed by thymic embryological organogenesis and anatomy as well as the development and functionality of T cells. Attempts to regenerate the thymus include in vitro methods, such as forming thymic organoids aided by biofabrication techniques that are transplantable. Ex vivo methods that have shown promise in enhancing thymic regeneration are also discussed. Current regenerative technologies have not yet matched the complexity and functionality of the thymus. Therefore, emerging techniques that have shown promise and the challenges that lie ahead are explored.

Characterization of perfusion decellularized whole animal body, isolated organs, and multi-organ systems for tissue engineering applications

To expand the application of perfusion decellularization beyond isolated single organs, we used the native vasculature of adult and neonatal rats to systemically decellularize the organs of a whole animal in situ. Acellular scaffolds were generated from kidney, liver, lower limb, heart‐lung system, and a whole animal body, demonstrating that perfusion decellularization technology is applicable to any perfusable tissue, independent of age. Biochemical and histological analyses demonstrated that organs and organ systems (heart‐lung pair and lower limb) were successfully decellularized, retaining their extracellular matrix (ECM) structure and organ‐specific composition, as evidenced by differences in organ‐specific scaffold stiffness. Altogether, we demonstrated that organs, organ systems and whole animal bodies can be perfusion decellularized while retaining ECM components and biomechanics.

An efficient protocol for decellularization of the human endometrial fragments for clinical usage

The present study was aimed to compare different decellularization protocols for human endometrial fragments. The freeze-thaw cycles in combination with treatment by Triton X-100 and four concentrations of sodium dodecyl sulfate (SDS; 0.1, 0.5, 1, and 1.5%) with two exposure times (24 and 72 h) were applied for tissues decellularization. After analysis the morphology and DNA content of tissues the group with better morphology and lower DNA content was selected for further assessments. The nucleus by Acridine orange and extracellular matrix (ECM) using Masson's trichrome, Alcian blue, and periodic acid-Schiff staining were studied. The amount of tissues collagen types I and IV, fibronectin, glycosaminoglycans (GAGs), and elastin was analyzed by Raman spectroscopy. The ultrastructure and porosity of decellularized scaffold were studied by scanning electron microscopy (SEM). The MTT assay was applied for assessments of cytotoxicity of scaffold. The treated group with 1% SDS for 72 h showed the morphology similar to native control in having the minimum level of DNA and well preserved ECM. Raman spectroscopy results demonstrated, the amount of collagen types I and IV, GAG, and fibronectin was not significantly different in decellularized scaffold compared with native group but the elastin protein level was significantly decreased (P < 0.001). SEM micrographs also showed a porous and fiber rich ECM in decellularized sample similar to the native control. This combined protocol for decellularization of human endometrial tissue is effective and it could be suitable for recellularization and clinical applications in the future.

Cardiac Organoids to Model and Heal Heart Failure and Cardiomyopathies

Cardiac tissue engineering aims at creating contractile structures that can optimally reproduce the features of human cardiac tissue. These constructs are becoming valuable tools to model some of the cardiac functions, to set preclinical platforms for drug testing, or to alternatively be used as therapies for cardiac repair approaches. Most of the recent developments in cardiac tissue engineering have been made possible by important advances regarding the efficient generation of cardiac cells from pluripotent stem cells and the use of novel biomaterials and microfabrication methods. Different combinations of cells, biomaterials, scaffolds, and geometries are however possible, which results in different types of structures with gradual complexities and abilities to mimic the native cardiac tissue. Here, we intend to cover key aspects of tissue engineering applied to cardiology and the consequent development of cardiac organoids. This review presents various facets of the construction of human cardiac 3D constructs, from the choice of the components to their patterning, the final geometry of generated tissues, and the subsequent readouts and applications to model and treat cardiac diseases.

Effects of Human and Porcine Adipose Extracellular Matrices Decellularized by Enzymatic or Chemical Methods on Macrophage Polarization and Immunocompetence

The decellularized extracellular matrix (ECM) obtained from human and porcine adipose tissue (AT) is currently used to prepare regenerative medicine bio-scaffolds. However, the influence of these natural biomaterials on host immune response is not yet deeply understood. Since macrophages play a key role in the inflammation/healing processes due to their high functional plasticity between M1 and M2 phenotypes, the evaluation of their response to decellularized ECM is mandatory. It is also necessary to analyze the immunocompetence of macrophages after contact with decellularized ECM materials to assess their functional role in a possible infection scenario. In this work, we studied the effect of four decellularized adipose matrices (DAMs) obtained from human and porcine AT by enzymatic or chemical methods on macrophage phenotypes and fungal phagocytosis. First, a thorough biochemical characterization of these biomaterials by quantification of remnant DNA, lipids, and proteins was performed, thus indicating the efficiency and reliability of both methods. The proteomic analysis evidenced that some proteins are differentially preserved depending on both the AT origin and the decellularization method employed. After exposure to the four DAMs, specific markers of M1 proinflammatory and M2 anti-inflammatory macrophages were analyzed. Porcine DAMs favor the M2 phenotype, independently of the decellularization method employed. Finally, a sensitive fungal phagocytosis assay allowed us to relate the macrophage phagocytosis capability with specific proteins differentially preserved in certain DAMs. The results obtained in this study highlight the close relationship between the ECM biochemical composition and the macrophage’s functional role.

Comparison of porcine corneal decellularization methods and importance of preserving corneal limbus through decellularization

Background

The aim of this study is to compare the three previously applied, conventional porcine corneal decellularization methods and to demonstrate the importance of preserving the corneal limbus through decellularization.

Methods

Fresh, wild-type (with or without) limbus porcine corneas were decellularized using three different methods, including (i) sodium dodecyl sulfate (SDS), (ii) hypertonic saline (HS), and (iii) N₂ gas (NG). Post-treatment evaluation was carried out using histological, residual nuclear material, and ultrastructural analyses. Glycerol was used to help reduce the adverse effects of decellularization. The corneas were preserved for two weeks in cornea storage medium.

Results

All three decellularization methods reduced the number of keratocytes at different rates in the stromal tissue. However, all methods, except SDS, resulted in the retention of large numbers of cells and cell fragments. The SDS method (0.1% SDS, 48h) resulted in almost 100% decellularization in corneas without limbus. Low decellularization capacity of the NG method (<50%) could make it unfavorable. Although HS method had a more balanced damage-decellularization ratio, its decellularization capacity was lower than SDS method. Preservation of the corneoscleral limbus could partially prevent structural damage and edema, but it would reduce the decellularization capacity.

Conclusion

Our results suggest that SDS is a very powerful decellularization method, but it damages the cornea irreversibly. Preserving the corneoscleral limbus reduces the efficiency of decellularization, but also reduces the damage.

Comparison of Decellularization Protocols to Generate Peripheral Nerve Grafts: A Study on Rat Sciatic Nerves

In critical nerve gap repair, decellularized nerve allografts are considered a promising tissue engineering strategy that can provide superior regeneration results compared to nerve conduits. Decellularized nerves offer a well-conserved extracellular matrix component that has proven to play an important role in supporting axonal guiding and peripheral nerve regeneration. Up to now, the known decellularized techniques are time and effort consuming. The present study, performed on rat sciatic nerves, aims at investigating a novel nerve decellularization protocol able to combine an effective decellularization in short time with a good preservation of the extracellular matrix component. To do this, a decellularization protocol proven to be efficient for tendons (DN-P1) was compared with a decellularization protocol specifically developed for nerves (DN-P2). The outcomes of both the decellularization protocols were assessed by a series of in vitro evaluations, including qualitative and quantitative histological and immunohistochemical analyses, DNA quantification, SEM and TEM ultrastructural analyses, mechanical testing, and viability assay. The overall results showed that DN-P1 could provide promising results if tested in vivo, as the in vitro characterization demonstrated that DN-P1 conserved a better ultrastructure and ECM components compared to DN-P2. Most importantly, DN-P1 was shown to be highly biocompatible, supporting a greater number of viable metabolically active cells.

Nanofibrous nerve guidance conduits decorated with decellularized matrix hydrogel facilitate peripheral nerve injury repair

Rationale: Peripheral nerve injury (PNI) is a great challenge for regenerative medicine. Nerve autograft is the gold standard for clinical PNI repair. Due to its significant drawbacks, artificial nerve guidance conduits (NGCs) have drawn much attention as replacement therapies. We developed a combinatorial NGC consisting of longitudinally aligned electrospun nanofibers and porcine decellularized nerve matrix hydrogel (pDNM gel). The in vivo capacity for facilitating nerve tissue regeneration and functional recovery was evaluated in a rat sciatic nerve defect model.

Methods: Poly (L-lactic acid) (PLLA) was electrospun into randomly oriented (PLLA-random) and longitudinally aligned (PLLA-aligned) nanofibers. PLLA-aligned were further coated with pDNM gel at concentrations of 0.25% (PLLA-aligned/0.25% pDNM gel) and 1% (PLLA-aligned/1% pDNM gel). Axonal extension and Schwann cells migration were evaluated by immunofluorescence staining of dorsal root ganglia cultured on the scaffolds. To fabricate implantable NGCs, the nanofibrous scaffolds were rolled and covered with an electrospun protection tube. The fabricated NGCs were then implanted into a 5 mm sciatic nerve defect model in adult male Sprague-Dawley rats. Nerves treated with NGCs were compared to contralateral uninjured nerves (control group), injured but untreated nerves (unstitched group), and autografted nerves. Nerve regeneration was monitored by an established set of assays, including T2 values and diffusion tensor imaging (DTI) derived from multiparametric magnetic resonance imaging (MRI), histological assessments, and immunostaining. Nerve functional recovery was evaluated by walking track analysis.

Results: PLLA-aligned/0.25% pDNM gel scaffold exhibited the best performance in facilitating directed axonal extension and Schwann cells migration in vitro due to the combined effects of the topological cues provided by the aligned nanofibers and the biochemical cues retained in the pDNM gel. Consistent results were obtained in animal experiments with the fabricated NGCs. Both the T2 and fractional anisotropy values of the PLLA-aligned/0.25% pDNM gel group were the closest to those of the autografted group, and returned to normal much faster than those of the other NGCs groups. Histological assessment indicated that the implanted PLLA-aligned/0.25% pDNM gel NGC resulted in the largest number of axons and the most extensive myelination among all fabricated NGCs. Further, the PLLA-aligned/0.25% pDNM gel group exhibited the highest sciatic nerve function index, which was comparable to that of the autografted group, at 8 weeks post-surgery.

Conclusions: NGCs composed of aligned PLLA nanofibers decorated with 0.25% pDNM gel provided both topological and biochemical guidance for directing and promoting axonal extension, nerve fiber myelination, and functional recovery. Moreover, T2-mapping and DTI metrics were found to be useful non-invasive monitoring techniques for PNI treatment.

Extracellular matrix grafts: From preparation to application (Review)

Recently, the increasing emergency of traffic accidents and the unsatisfactory outcome of surgical intervention are driving research to seek a novel technology to repair traumatic soft tissue injury. From this perspective, decellularized matrix grafts (ECM-G) including natural ECM materials, and their prepared hydrogels and bioscaffolds, have emerged as possible alternatives for tissue engineering and regenerative medicine. Over the past decades, several physical and chemical decellularization methods have been used extensively to deal with different tissues/organs in an attempt to carefully remove cellular antigens while maintaining the non-immunogenic ECM components. It is anticipated that when the decellularized biomaterials are seeded with cells in vitro or incorporated into irregularly shaped defects in vivo, they can provide the appropriate biomechanical and biochemical conditions for directing cell behavior and tissue remodeling. The aim of this review is to first summarize the characteristics of ECM-G and describe their major decellularization methods from different sources, followed by analysis of how the bioactive factors and undesired residual cellular compositions influence the biologic function and host tissue response following implantation. Lastly, we also provide an overview of the in vivoapplication of ECM-G in facilitating tissue repair and remodeling.

Potential of Soluble Decellularized Extracellular Matrix for Musculoskeletal Tissue Engineering - Comparison of Various Mesenchymal Tissues

Background

It is well studied that preparations of decellularized extracellular matrix (ECM) obtained from mesenchymal tissues can function as biological scaffolds to regenerate injured musculoskeletal tissues. Previously, we reported that soluble decellularized ECMs derived from meniscal tissue demonstrated excellent biocompatibility and produced meniscal regenerate with native meniscal anatomy and biochemical characteristics. We therefore hypothesized that decellularized mesenchymal tissue ECMs from various mesenchymal tissues should exhibit tissue-specific bioactivity. The purpose of this study was to test this hypothesis using porcine tissues, for potential applications in musculoskeletal tissue engineering.

Methods

Nine types of porcine tissue, including cartilage, meniscus, ligament, tendon, muscle, synovium, fat pad, fat, and bone, were decellularized using established methods and solubilized. Although the current trend is to develop tissue specific decellularization protocols, we selected a simple standard protocol across all tissues using Triton X-100 and DNase/RNase after mincing to compare the outcome. The content of sulfated glycosaminoglycan (sGAG) and hydroxyproline were quantified to determine the biochemical composition of each tissue. Along with the concentration of several growth factors, known to be involved in tissue repair and/or maturation, including bFGF, IGF-1, VEGF, and TGF-β1. The effect of soluble ECMs on cell differentiation was explored by combining them with 3D collagen scaffold culturing human synovium derived mesenchymal stem cells (hSMSCs).

Results

The decellularization of each tissue was performed and confirmed both histologically [hematoxylin and eosin (H&E) and 4’,6-diamidino-2-phenylindole (DAPI) staining] and on the basis of dsDNA quantification. The content of hydroxyproline of each tissue was relatively unchanged during the decellularization process when comparing the native and decellularized tissue. Cartilage and meniscus exhibited a significant decrease in sGAG content. The content of hydroxyproline in meniscus-derived ECM was the highest when compared with other tissues, while sGAG content in cartilage was the highest. Interestingly, a tissue-specific composition of most of the growth factors was measured in each soluble decellularized ECM and specific differentiation potential was particularly evident in cartilage, ligament and bone derived ECMs.

Conclusion

In this study, soluble decellularized ECMs exhibited differences based on their tissue of origin and the present results are important going forward in the field of musculoskeletal regeneration therapy.

Applications of decellularized materials in tissue engineering: advantages, drawbacks and current improvements, and future perspectives

Decellularized materials (DMs) are attracting more and more attention in tissue engineering because of their many unique advantages, and they could be further improved in some aspects through various means.