Efficient decellularization of whole porcine kidneys improves reseeded cell behavior

Vascular study of decellularized porcine long bones: Characterization of a tissue engineering model

INTRODUCTION

Massive bone allografts enable the reconstruction of critical bone defects in numerous conditions (e.g. tumoral, infection or trauma). Unfortunately, their biological integration remains insufficient and the reconstruction may suffer from several postoperative complications. Perfusion-decellularization emerges as a tissue engineering potential solution to enhance osseointegration. Therefore, an intrinsic vascular study of this novel tissue engineering tool becomes essential to understand its efficacy and applicability.

MATERIAL AND METHODS

32 porcine long bones (humeri and femurs) were used to assess the quality of their vascular network prior and after undergoing a perfusion-decellularization protocol. 12 paired bones were used to assess the vascular matrix prior (N = 6) and after our protocol (N = 6) by immunohistochemistry. Collagen IV, Von Willebrand factor and CD31 were targeted then quantified. The medullary macroscopic vascular network was evaluated with 12 bones: 6 were decellularized and the other 6 were, as control, not treated. All 12 underwent a contrast-agent injection through the nutrient artery prior an angio CT-scan acquisition. The images were processed and the length of medullary vessels filled with contrast agent were measured on angiographic cT images obtained in control and decellularized bones by 4 independent observers to evaluate the vascular network preservation. The microscopic cortical vascular network was evaluated on 8 bones: 4 control and 4 decellularized. After injection of gelatinous fluorochrome mixture (calcein green), non-decalcified fluoroscopic microscopy was performed in order to assess the perfusion quality of cortical vascular lacunae.

RESULTS

The continuity of the microscopic vascular network was assessed with Collagen IV immunohistochemistry (p-value = 0.805) while the decellularization quality was observed through CD31 and Von Willebrand factor immunohistochemistry (p-values <0.001). The macroscopic vascular network was severely impaired after perfusion-decellularization; nutrient arteries were still patent but the amount of medullary vascular channels measured was significantly higher in the control group compared to the decellularized group (p-value <0.001). On average, the observers show good agreement on these results, except in the decellularized group where more inter-observer discrepancies were observed. The microscopic vascular network was observed with green fluoroscopic signal in almost every canals and lacunae of the bone cortices, in three different bone locations (proximal metaphysis, diaphysis and distal metaphysis).

CONCLUSION

Despite the aggressiveness of the decellularization protocol on medullary vessels, total porcine long bones decellularized by perfusion retain an acellular cortical microvascular network. By injection through the intact nutrient arteries, this latter vascular network can still be used as a total bone infusion access for bone tissue engineering in order to enhance massive bone allografts prior implantation.

Optimization of Enzymatic and Chemical Decellularization of Native Porcine Heart Valves for the Generation of Decellularized Xenografts

One of the most important medical interventions for individuals with heart valvular disease is heart valve replacement, which is not without substantial challenges, particularly for pediatric patients. Due to their biological properties and biocompatibility, natural tissue-originated scaffolds derived from human or animal sources are one type of scaffold that is widely used in tissue engineering. However, they are known for their high potential for immunogenicity. Being free of cells and genetic material, decellularized xenografts, consequently, have low immunogenicity and, thus, are expected to be tolerated by the recipient's immune system. The scaffold ultrastructure and ECM composition can be affected by cell removal agents. Therefore, applying an appropriate method that preserves intact the structure of the ECM plays a critical role in the final result. So far, there has not been an effective decellularization technique that preserves the integrity of the heart valve's ultrastructure while securing the least amount of genetic material left. This study demonstrates a new protocol with untraceable cells and residual DNA, thereby maximally reducing any chance of immunogenicity. The mechanical and biochemical properties of the ECM resemble those of native heart valves. Results from this study strongly indicate that different critical factors, such as ionic detergent omission, the substitution of Triton X-100 with Tergitol, and using a lower concentration of trypsin and a higher concentration of DNase and RNase, play a significant role in maintaining intact the ultrastructure and function of the ECM.

Decellularized extracellular matrix biomaterials for regenerative therapies: Advances, challenges and clinical prospects

Tissue engineering and regenerative medicine have shown potential in the repair and regeneration of tissues and organs via the use of engineered biomaterials and scaffolds. However, current constructs face limitations in replicating the intricate native microenvironment and achieving optimal regenerative capacity and functional recovery. To address these challenges, the utilization of decellularized tissues and cell-derived extracellular matrix (ECM) has emerged as a promising approach. These biocompatible and bioactive biomaterials can be engineered into porous scaffolds and grafts that mimic the structural and compositional aspects of the native tissue or organ microenvironment, both in vitro and in vivo. Bioactive dECM materials provide a unique tissue-specific microenvironment that can regulate and guide cellular processes, thereby enhancing regenerative therapies. In this review, we explore the emerging frontiers of decellularized tissue-derived and cell-derived biomaterials and bio-inks in the field of tissue engineering and regenerative medicine. We discuss the need for further improvements in decellularization methods and techniques to retain structural, biological, and physicochemical characteristics of the dECM products in a way to mimic native tissues and organs. This article underscores the potential of dECM biomaterials to stimulate in situ tissue repair through chemotactic effects for the development of growth factor and cell-free tissue engineering strategies. The article also identifies the challenges and opportunities in developing sterilization and preservation methods applicable for decellularized biomaterials and grafts and their translation into clinical products.

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

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

Capturing effects of blood flow on the transplanted decellularized nephron with intravital microscopy

Organ decellularization creates cell-free, collagen-based extracellular matrices that can be used as scaffolds for tissue engineering applications. This technique has recently gained much attention, yet adequate scaffold repopulation and implantation remain a challenge. Specifically, there still needs to be a greater understanding of scaffold responses post-transplantation and ways we can improve scaffold durability to withstand the in vivo environment. Recent studies have outlined vascular events that limit organ decellularization/recellularization scaffold viability for long-term transplantation. However, these insights have relied on in vitro/in vivo approaches that need enhanced spatial and temporal resolutions to investigate such issues at the microvascular level. This study uses intravital microscopy to gain instant feedback on their structure, function, and deformation dynamics. Thus, the objective of this study was to capture the effects of in vivo blood flow on the decellularized glomerulus, peritubular capillaries, and tubules after autologous and allogeneic orthotopic transplantation into rats. Large molecular weight dextran molecules labeled the vasculature. They revealed substantial degrees of translocation from glomerular and peritubular capillary tracks to the decellularized tubular epithelium and lumen as early as 12 h after transplantation, providing real-time evidence of the increases in microvascular permeability. Macromolecular extravasation persisted for a week, during which the decellularized microarchitecture was significantly and comparably compromised and thrombosed in both autologous and allogeneic approaches. These results indicate that in vivo multiphoton microscopy is a powerful approach for studying scaffold viability and identifying ways to promote scaffold longevity and vasculogenesis in bioartificial organs.

Recent Advances in Decellularized Matrix-Derived Materials for Bioink and 3D Bioprinting

As an emerging 3D printing technology, 3D bioprinting has shown great potential in tissue engineering and regenerative medicine. Decellularized extracellular matrices (dECM) have recently made significant research strides and have been used to create unique tissue-specific bioink that can mimic biomimetic microenvironments. Combining dECMs with 3D bioprinting may provide a new strategy to prepare biomimetic hydrogels for bioinks and hold the potential to construct tissue analogs in vitro, similar to native tissues. Currently, the dECM has been proven to be one of the fastest growing bioactive printing materials and plays an essential role in cell-based 3D bioprinting. This review introduces the methods of preparing and identifying dECMs and the characteristic requirements of bioink for use in 3D bioprinting. The most recent advances in dECM-derived bioactive printing materials are then thoroughly reviewed by examining their application in the bioprinting of different tissues, such as bone, cartilage, muscle, the heart, the nervous system, and other tissues. Finally, the potential of bioactive printing materials generated from dECM is discussed.

Decellularization of precision-cut kidney slices-application of physical and chemical methods

The extracellular matrix (ECM) obtained by decellularization provides scaffolds with the natural complex architecture and biochemical composition of the target organ. Whole kidney decellularization by perfusion uses the vasculature to remove cells leaving a scaffold that can be recellularized with patient-specific cells. However, decellularization and recellularization are highly complex processes that require intensive optimization of various parameters. In pursuit of this, a huge number of animals must be sacrificed. Therefore, we used precision-cut kidney slices (PCKS) as a source of natural scaffolds, which were decellularized by immersion in chemical reagents allowing the examination of more parameters with less animals. However, chemical reagents have a damaging effect on the structure and components of the ECM. Therefore, this study aimed at investigating the effects of physical treatment methods on the effectiveness of PCKS decellularization by immersion in chemical reagents (CHEM). PCKS were treated physically before or during immersion in chemicals (CHEM) with high hydrostatic pressure (HHP), freezing-thawing cycles (FTC) or in an ultrasonic bath system (UBS). Biochemical and DNA quantification as well as structural evaluation with conventional histology and scanning electron microscopy (SEM) were performed. Compared to decellularization by CHEM alone, FTC treatment prior to CHEM was the most effective in reducing DNA while also preserving glycosaminoglycan (GAG) content. Moreover, while UBS resulted in a comparable reduction of DNA, it was the least effective in retaining GAGs. In contrast, despite the pretreatment with HHP with pressures up to 200 MPa, it was the least effective in DNA removal. Histological scoring showed that HHP scaffolds received the best score followed by UBS, FTC and CHEM scaffolds. However further analysis with SEM demonstrated a higher deterioration of the ultrastructure in UBS scaffolds. Altogether, pretreatment with FTC prior to CHEM resulted in a better balance between DNA removal and structural preservation.

Preparation and Use of Decellularized Extracellular Matrix for Tissue Engineering

The multidisciplinary fields of tissue engineering and regenerative medicine have the potential to revolutionize the practise of medicine through the abilities to repair, regenerate, or replace tissues and organs with functional engineered constructs. To this end, tissue engineering combines scaffolding materials with cells and biologically active molecules into constructs with the appropriate structures and properties for tissue/organ regeneration, where scaffolding materials and biomolecules are the keys to mimic the native extracellular matrix (ECM). For this, one emerging way is to decellularize the native ECM into the materials suitable for, directly or in combination with other materials, creating functional constructs. Over the past decade, decellularized ECM (or dECM) has greatly facilitated the advance of tissue engineering and regenerative medicine, while being challenged in many ways. This article reviews the recent development of dECM for tissue engineering and regenerative medicine, with a focus on the preparation of dECM along with its influence on cell culture, the modification of dECM for use as a scaffolding material, and the novel techniques and emerging trends in processing dECM into functional constructs. We highlight the success of dECM and constructs in the in vitro, in vivo, and clinical applications and further identify the key issues and challenges involved, along with a discussion of future research directions.

Perfusion decellularization for vascularized composite allotransplantation

Vascularized composite allotransplantation is becoming the emerging standard for reconstructive surgery treatment for patients with limb trauma and facial injuries involving soft tissue loss. Due to the complex immunogenicity of composite grafts, patients who undergo vascularized composite allotransplantation are reliant on lifelong immunosuppressive therapy. Decellularization of donor grafts to create an extracellular matrix bio-scaffold provides an immunomodulatory graft that preserves the structural and bioactive function of the extracellular matrix. Retention of extracellular matrix proteins, growth factors, and signaling cascades allow for cell adhesion, migration, proliferation, and tissue regeneration. Perfusion decellularization of detergents through the graft vasculature allows for increased regent access to all tissue layers, and removal of cellular debris through the venous system. Grafts can subsequently be repopulated with appropriate cells through the vasculature to facilitate tissue regeneration. The present work reviews methods of decellularization, process parameters, evaluation of adequate cellular and nuclear removal, successful applications of perfusion decellularization for use in vascularized composite allotransplantation, and current limitations.

Three-Dimensional Bioprinting of Decellularized Extracellular Matrix-Based Bioinks for Tissue Engineering

Three-dimensional (3D) bioprinting is one of the most promising additive manufacturing technologies for fabricating various biomimetic architectures of tissues and organs. In this context, the bioink, a critical element for biofabrication, is a mixture of biomaterials and living cells used in 3D printing to create cell-laden structures. Recently, decellularized extracellular matrix (dECM)-based bioinks derived from natural tissues have garnered enormous attention from researchers due to their unique and complex biochemical properties. This review initially presents the details of the natural ECM and its role in cell growth and metabolism. Further, we briefly emphasize the commonly used decellularization treatment procedures and subsequent evaluations for the quality control of the dECM. In addition, we summarize some of the common bioink preparation strategies, the 3D bioprinting approaches, and the applicability of 3D-printed dECM bioinks to tissue engineering. Finally, we present some of the challenges in this field and the prospects for future development.

Decellularization for the retention of tissue niches

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

Decellularization of porcine kidney with submicellar concentrations of SDS results in the retention of ECM proteins required for the adhesion and maintenance of human adult renal epithelial cells

When decellularizing kidneys, it is important to maintain the integrity of the acellular extracellular matrix (ECM), including associated adhesion proteins and growth factors that allow recellularized cells to adhere and migrate according to ECM specificity. Kidney decellularization requires the ionic detergent sodium dodecyl sulfate (SDS); however, this results in a loss of ECM proteins important for cell adherence, migration, and growth, particularly glycosaminoglycan (GAG)-associated proteins. Here, we demonstrate that using submicellar concentrations of SDS results in a greater retention of structural proteins, GAGs, growth factors, and cytokines. When porcine kidney ECM scaffolds were recellularized using human adult primary renal epithelial cells (RECs), the ECM promoted cell survival and the uniform distribution of cells throughout the ECM. Cells maintained the expression of mature renal epithelial markers but did not organize on the ECM, indicating that mature cells are unable to migrate to specific locations on ECM scaffolds.

Development of a decellularized hypopharynx with vascular pedicle scaffold for use in reconstructing hypopharynx

BACKGROUND

Hypopharynx reconstruction after hypopharyngectomy is still a great challenge. Perfusion decellularization is for extracellular matrix (ECM) scaffolding and had been used in organ reconstruction. Our study aimed to prepare an acellular, natural, three-dimensional biological hypopharynx with vascular pedicle scaffold as the substitute materials to reconstruct hypopharynx.

RESULT

Scanning electron microscope and histology staining showed that the decellularized hypopharynx with vascular pedicle scaffold retained intact native anatomical ECM structure. Myoblasts were observed on the recellularized scaffolds with bone marrow mesenchymal stem cells induced by 5-azacytidine implanted in the rabbit greater omentum by immunohistochemical analysis.

CONCLUSION

The decellularized hypopharynx with vascular pedicle scaffold prepared by detergent perfusion in our study has a potential to be an alternative material to pharynx reconstruction.

In vitro investigation of the impact of pulsatile blood flow on the vascular architecture of decellularized porcine kidneys

A method was established using a scaffold-bioreactor system to examine the impact pulsatile blood flow has on the decellularized porcine kidney vascular architecture and functionality. These scaffolds were subjected to continuous arterial perfusion of whole blood at normal physiological (650 ml/min and 500 ml/min) and pathophysiological (200 ml/min) rates to examine dynamic changes in venous outflow and micro-/macrovascular structure and patency. Scaffolds subjected to normal arterial perfusion rates observed drops in venous outflow over 24 h. These reductions rose from roughly 40% after 12 h to 60% after 24 h. There were no apparent signs of clotting at the renal artery, renal vein, and ureter. In comparison, venous flow rates decreased by 80% to 100% across the 24 h in acellular scaffolds hypoperfused at a rate of 200 ml/min. These kidneys also appeared intact on the surface after perfusion. However, they presented several arterial, venous, and ureteral clots. Fluoroscopic angiography confirmed substantial alterations to normal arterial branching patterns and patency, as well as parenchymal damage. Scanning electron microscopy revealed that pulsatile blood perfusion significantly disrupted glomerular microarchitecture. This study provides new insight into circumstances that limit scaffold viability and a simplified model to analyze conditions needed to prepare more durable scaffolds for long-term transplantation.

Decellularized kidney extracellular matrix bioinks recapitulate renal 3D microenvironmentin vitro

Decellularized extracellular matrices (ECMs) are able to provide the necessary and specific cues for remodeling and maturation of tissue-specific cells. Nevertheless, their use for typical biofabrication applications requires chemical modification or mixing with other polymers, mainly due to the limited viscoelastic properties. In this study, we hypothesize that a bioink exclusively based on decellularized kidney ECM (dKECM) could be used to bioprint renal progenitor cells. To address these aims, porcine kidneys were decellularized, lyophilized and digested to yield a viscous solution. Then, the bioprinting process was optimized using an agarose microparticle support bath containing transglutaminase for enzymatic crosslinking of the dKECM. This methodology was highly effective to obtain constructs with good printing resolution and high structural integrity. Moreover, the encapsulation of primary renal progenitor cells resulted in high cell viability, with creation of 3D complex structures over time. More importantly, this tissue-specific matrix was also able to influence cellular growth and differentiation over time. Taken together, these results demonstrate that unmodified dKECM bioinks have great potential for bioengineering renal tissue analogs with promising translational applications and/or forin vitromodel systems. Ultimately, this strategy may have greater implications on the biomedical field for the development of bioengineered substitutes using decellularized matrices from other tissues.

The Renal Extracellular Matrix as a Supportive Scaffold for Kidney Tissue Engineering: Progress and Future Considerations

During the past decades, diverse methods have been used toward renal tissue engineering in order to replace renal function. The goals of all these techniques included the recapitulation of renal filtration, re-absorptive, and secretary functions, and replacement of endocrine/metabolic activities. It is also imperative to develop a reliable, up scalable, and timely manufacturing process. Decellularization of the kidney with intact ECM is crucial for in-vivo compatibility and targeted clinical application. Contemporarily there is an increasing interest and research in the field of regenerative medicine including stem cell therapy and tissue bioengineering in search for new and reproducible sources of kidneys. In this chapter, we sought to determine the most effective method of renal decellularization and recellularization with emphasis on biologic composition and support of stem cell growth. Current barriers and limitations of bioengineered strategies will be also discussed, and strategies to overcome these are suggested.

Semantic Segmentation of Intralobular and Extralobular Tissue from Liver Scaffold H&E Images

Decellularized tissue is an important source for biological tissue engineering. Evaluation of the quality of decellularized tissue is performed using scanned images of hematoxylin-eosin stained (H&E) tissue sections and is usually dependent on the observer. The first step in creating a tool for the assessment of the quality of the liver scaffold without observer bias is the automatic segmentation of the whole slide image into three classes: the background, intralobular area, and extralobular area. Such segmentation enables to perform the texture analysis in the intralobular area of the liver scaffold, which is crucial part in the recellularization procedure. Existing semi-automatic methods for general segmentation (i.e., thresholding, watershed, etc.) do not meet the quality requirements. Moreover, there are no methods available to solve this task automatically. Given the low amount of training data, we proposed a two-stage method. The first stage is based on classification of simple hand-crafted descriptors of the pixels and their neighborhoods. This method is trained on partially annotated data. Its outputs are used for training of the second-stage approach, which is based on a convolutional neural network (CNN). Our architecture inspired by U-Net reaches very promising results, despite a very low amount of the training data. We provide qualitative and quantitative data for both stages. With the best training setup, we reach 90.70% recognition accuracy.

The useful agent to have an ideal biological scaffold

Tissue engineering which is applied in regenerative medicine has three basic components: cells, scaffolds and growth factors. This multidisciplinary field can regulate cell behaviors in different conditions using scaffolds and growth factors. Scaffolds perform this regulation with their structural, mechanical, functional and bioinductive properties and growth factors by attaching to and activating their receptors in cells. There are various types of biological extracellular matrix (ECM) and polymeric scaffolds in tissue engineering. Recently, many researchers have turned to using biological ECM rather than polymeric scaffolds because of its safety and growth factors. Therefore, selection the right scaffold with the best properties tailored to clinical use is an ideal way to regulate cell behaviors in order to repair or improve damaged tissue functions in regenerative medicine. In this review we first divided properties of biological scaffold into intrinsic and extrinsic elements and then explain the components of each element. Finally, the types of scaffold storage methods and their advantages and disadvantages are examined.

Decellularization systems and devices: State-of-the-art

Extracellular matrix (ECM) is a natural biomaterial scaffold that provides biochemical and structural support to its surrounding cells, forming tissue and respective organs. These ECM proteins can be extracted from organs and tissues through decellularization, which is the process of removing cellular content and nuclear material from the organs to obtain decellularized ECM (dECM). dECM is a versatile and functional biomaterial that can be used as the base component of bioinks for rebuilding tissue and organs. Intact dECM of whole organs can be used as a scaffold for recellularization with human stem cells to produce a functioning organ. As decellularization is a relatively new lab process, the associated technologies and devices are largely non-standardized and only available in small, lab-specific scales. Additionally, there is a lack of standardized protocols to analyze the quality and consistency of harvested dECM for medical applications. This review discusses the relevant decellularization systems and devices currently available to facilitate further development of this process for larger scales with the intention to commercialize dECM materials. STATEMENT OF SIGNIFICANCE: Extracellular matrix (ECM) is a natural cocktail of biomaterials that provides biochemical and structural support to its surrounding cells. ECM proteins are extracted from organs and tissues through decellularization. Being a versatile and functional biomaterial, decellularized extracellular matrix (dECM) is being used as base component of bioinks/hydrogels for rebuilding of tissue and organ constructs. Decellularization is a relatively new lab process with associated technologies/devices being largely non-standardized and only available in lab-specific scales. We discuss categories of decellularization systems and devices for the first time being used in academic and commercial settings. We highlight inherent challenges with the current systems and suggest possible solutions. We comment on further development of these processes for large-scale and commercial applications of dECM.

Human ucMSCs seeded in a decellularized kidney scaffold attenuate renal fibrosis by reducing epithelial-mesenchymal transition via the TGF-β/Smad signaling pathway

BACKGROUND

Renal fibrosis occurs largely through epithelial-mesenchymal transition (EMT). This study explored the beneficial effects of a human umbilical cord mesenchymal stem cell-loaded decellularized kidney scaffold (ucMSC-DKS) on renal fibrosis in a rodent model of post-transplantation renal failure, and the underlying mechanism.

METHODS

Rat-derived DKSs were examined after preparation, and then recellularized with human ucMSCs to prepare cell-loaded patches. A rat model of renal failure was established after subtotal nephrectomy (STN). The cell patches were transplanted to remnant kidneys. Changes in renal function, histology, EMT, and proteins related to the transforming growth factor-β (TGF-β)/Smad signaling pathway in the remnant kidneys were examined 8 weeks after surgery, compared with non-cell patch controls.

RESULTS

The DKSs were acellular and porous, with rich cytokine and major extracellular matrix components. The ucMSCs were distributed uniformly in the DKSs. Renal function was improved, renal fibrosis and EMT were reduced, and the TGF-β/Smad signaling pathway was inhibited compared with controls at 8 weeks after ucMSC-DKS patch transplantation.

CONCLUSIONS

The ucMSC-DKS restores renal function and reduces fibrosis by reducing EMT via the TGF-β/Smad signaling pathway in rats that have undergone STN. It provides an alternative for renal fibrosis treatment.

Fast Automated Approach for the Derivation of Acellular Extracellular Matrix Scaffolds from Porcine Soft Tissues

Decellularized extracellular matrix (ECM) scaffolds derived from tissues and organs are complex biomaterials used in clinical and research applications. A number of decellularization protocols have been described for ECM biomaterials derivation, each adapted to a particular tissue and use, restricting comparisons among materials. One of the major sources of variability in ECM products comes from the tissue source and animal age. Although this variability could be minimized using established tissue sources, other sources arise from the decellularization process itself. Overall, current protocols require manual work and are poorly standardized with regard to the choice of reagents, the order by which they are added, and exposure times. The combination of these factors adds variability affecting the uniformity of the final product between batches. Furthermore, each protocol needs to be optimized for each tissue and tissue source making tissue-to-tissue comparisons difficult. Automation and standardization of ECM scaffold development constitute a significant improvement to current biomanufacturing techniques but remains poorly explored. This study aimed to develop a biofabrication method for fast and automated derivation of raw material for ECM hydrogel production while preserving ECM composition and controlling lot-to-lot variability. The main result was a closed semibatch bioreactor system with automated dosing of decellularization reagents capable of deriving ECM material from pretreated soft tissues. The ECM was further processed into hydrogels to demonstrate gelation and cytocompatibility. This work presents a versatile, scalable, and automated platform for the rapid production of ECM scaffolds.

Effect of Decellularization Parameters on the Efficient Production of Kidney Bioscaffolds

The most preferred decellularization technique in creating bioscaffolds for complex organs such as kidneys is through detergent perfusion. Detergents such as sodium dodecyl sulfate (SDS) flow to the kidneys to remove cells but using this technique alone requires long treatment times. Coupling this technique with sonication treatment decreases decellularization time but may cause damages in the microarchitecture of the kidney. This study evaluated the effects of decellularization parameters specifically SDS concentration (0.25%, 0.625%, and 1.0%wt/vol), flowrate (15, 30, and 45 mL/min), and sonicator power (0, 60, and 120 W) on the length of time needed to produce acellular and intact bioscaffolds. Decellularization was carried out by perfusing SDS to the renal artery of the cadaveric porcine kidney while exposed to sonication treatment. Results showed that a significant decrease in decellularization time was observed in producing acellular scaffold when perfusion decellularization was coupled with sonication. In addition, SDS concentration, SDS flowrate, and sonicator power had significant effects on the decellularization time while only sonicator power had a significant effect on the microarchitecture integrity of the scaffold. Lastly, H&E results showed that the produced bioscaffold showed complete cell removal with only minimal to moderate disruptions on the microarchitecture of the kidney.

Whole organ sheep kidney tissue engineering and in vivo transplantation: Effects of perfusion-based decellularization on vascular integrity

INTRODUCTION

During the past decade, increased efforts have been made to develop alternative management options instead of dialysis and homograft renal transplantation for end-stage renal disease. State-of-the-art methods employ tissue engineering to produce natural acellular scaffolds that could resolve the concern of allograft rejection and obviate the need for immunosuppressive therapy. Complete decellularization of kidney with intact extracellular matrix is crucial for in vivo compatibility and success of transplantation. Herein, we evaluate the efficacy of two different whole organ decellularization protocols, vasculature integrity, and in vivo transplantation of sheep kidneys.

MATERIALS AND METHODS

Eight sheep kidneys were decellularized by perfusion-based method utilizing two different protocols (Protocol 1: 1% Triton X-100 and 0.5% SDS vs. Protocol 2: 1% SDS). The samples were evaluated by histopathology in terms of decellularization and extracellular matrix preservation. Computerized tomography angiography was performed to evaluate vasculature. Subsequently, both methods were transplanted in four sheep and monitored for vascular integrity and extravasations in short-term.

RESULTS

Scaffolds obtained from both protocols were entirely decellularized. However; the extracellular matrix was better preserved in protocol 1 compared to protocol 2. In addition, the vascular integrity was intact in decellularized scaffolds treated with Triton X-100 plus SDS (protocol 1). After transplantation, the samples treated with protocol 2 showed extravasation of fluid in the interstitial space while the samples treated with protocol 1 showed intact extracellular matrix and vasculature.

CONCLUSIONS

This study demonstrated the efficacy of well-preserved acellular scaffold and vasculature network in post renal transplant outcome in a sheep model. These results have potential to pave the road for further investigations in acellular whole organ transplantation.

Bioengineering Organs for Blood Detoxification

For patients with severe kidney or liver failure the best solution is currently organ transplantation. However, not all patients are eligible for transplantation and due to limited organ availability, most patients are currently treated with therapies using artificial kidney and artificial liver devices. These therapies, despite their relative success in preserving the patients' life, have important limitations since they can only replace part of the natural kidney or liver functions. As blood detoxification (and other functions) in these highly perfused organs is achieved by specialized cells, it seems relevant to review the approaches leading to bioengineered organs fulfilling most of the native organ functions. There, the culture of cells of specific phenotypes on adapted scaffolds that can be perfused takes place. In this review paper, first the functions of kidney and liver organs are briefly described. Then artificial kidney/liver devices, bioartificial kidney devices, and bioartificial liver devices are focused on, as well as biohybrid constructs obtained by decellularization and recellularization of animal organs. For all organs, a thorough overview of the literature is given and the perspectives for their application in the clinic are discussed.

Renal Tubular- and Vascular Basement Membranes and their Mimicry in Engineering Vascularized Kidney Tubules

The high prevalence of chronic kidney disease leads to an increased need for renal replacement therapies. While there are simply not enough donor organs available for transplantation, there is a need to seek other therapeutic avenues as current dialysis modalities are insufficient. The field of regenerative medicine and whole organ engineering is emerging, and researchers are looking for innovative ways to create (part of) a functional new organ. To biofabricate a kidney or its functional units, it is necessary to understand and learn from physiology to be able to mimic the specific tissue properties. Herein is provided an overview of the knowledge on tubular and vascular basement membranes' biochemical components and biophysical properties, and the major differences between the two basement membranes are highlighted. Furthermore, an overview of current trends in membrane technology for developing renal replacement therapies and to stimulate kidney regeneration is provided.

Impact of different intratracheal flows during lung decellularization on extracellular matrix composition and mechanics

Aim: To evaluate different intratracheal flow rates on extracellular matrix content and lung mechanics in an established lung decellularization protocol. Materials & methods: Healthy mice were used: 15 for decellularization and five to serve as controls. Fluids were instilled at 5, 10 and 20 ml/min flow rates through tracheal cannula and right ventricular cavity (0.5 ml/min) in all groups. Results: The 20 ml/min rate better preserved collagen content in decellularized lungs. Elastic fiber content decreased at 5 and 10 ml/min, but not at 20 ml/min, compared with controls. Chondroitin, heparan and dermatan content was reduced after decellularization. Conclusion: An intratracheal flow rate of 20 ml/min was associated with lower resistance and greater preservation of collagen to that observed in ex vivo control lungs.

Decellularized kidney matrix as functional material for whole organ tissue engineering

Renal transplantation is currently the most effective treatment for end-stage renal disease, which represents one of the major current public health problems. However, the number of available donor kidneys is drastically insufficient to meet the demand, causing prolonged waiting lists. For this reason, tissue engineering offers great potential to increase the pool of donated organs for kidney transplantation, by way of seeding cells on supporting scaffolding material. Biological scaffolds are prepared by removing cellular components from the donor organs using a decellularization process with detergents, enzymes or other cell lysing solutions. Extracellular matrix which makes up the scaffold is critical to directing the cell attachment and to creating a suitable environment for cell survival, proliferation and differentiation. Researchers are now studying whole intact scaffolds produced from the kidneys of animals or humans without adversely affecting extracellular matrix, biological activity and mechanical integrity. The process of recellularization includes cell seeding strategies and the choice of the cell source to repopulate the scaffold. This is the most difficult phase, due to the complexity of the kidney. Indeed, no studies have provided sufficient results of complete renal scaffold repopulation and differentiation. This review summarizes the research that has been conducted to obtain decellularized kidney scaffolds and to repopulate the scaffolds, evaluating the best cell sources, the cell seeding methods and the cell differentiation in kidney scaffolds.

Advances in the Knowledge about Kidney Decellularization and Repopulation

End-stage renal disease (ESRD) is characterized by the progressive deterioration of renal function that may compromise different tissues and organs. The major treatment indicated for patients with ESRD is kidney transplantation. However, the shortage of available organs, as well as the high rate of organ rejection, supports the need for new therapies. Thus, the implementation of tissue bioengineering to organ regeneration has emerged as an alternative to traditional organ transplantation. Decellularization of organs with chemical, physical, and/or biological agents generates natural scaffolds, which can serve as basis for tissue reconstruction. The recellularization of these scaffolds with different cell sources, such as stem cells or adult differentiated cells, can provide an organ with functionality and no immune response after in vivo transplantation on the host. Several studies have focused on improving these techniques, but until now, there is no optimal decellularization method for the kidney available yet. Herein, an overview of the current literature for kidney decellularization and whole-organ recellularization is presented, addressing the pros and cons of the actual techniques already developed, the methods adopted to evaluate the efficacy of the procedures, and the challenges to be overcome in order to achieve an optimal protocol.

Essential design considerations for the resazurin reduction assay to noninvasively quantify cell expansion within perfused extracellular matrix scaffolds

Precise measurement of cellularity within bioartificial tissues and extracellular matrix (ECM) scaffolds is necessary to augment rigorous characterization of cellular behavior, as accurate benchmarking of tissue function to cell number allows for comparison of data across experiments and between laboratories. Resazurin, a soluble dye that is reduced to highly fluorescent resorufin in proportion to the metabolic activity of a cell population, is a valuable, noninvasive tool to measure cell number. We investigated experimental conditions in which resazurin reduction is a reliable indicator of cellularity within three-dimensional (3D) ECM scaffolds. Using three renal cell populations, we demonstrate that correlation of viable cell numbers with the rate of resorufin generation may deviate from linearity at higher cell densities, lower resazurin working volumes, or longer incubation times that all contribute to depleting the pool of resazurin. In conclusion, while the resazurin reduction assay provides a powerful, noninvasive readout of metrics enumerating cellularity and growth within ECM scaffolds, assay conditions may strongly influence its applicability for accurate quantification of cell number. The approach and methodological recommendations presented herein may be used as a guide for application-specific optimization of this assay to obtain rigorous and accurate measurement of cellular content in bioengineered tissues.

Re-epithelialization of whole porcine kidneys with renal epithelial cells

Decellularized porcine kidneys were recellularized with renal epithelial cells by three methods: perfusion through the vasculature under high pressure, perfusion through the ureter under high pressure, or perfusion through the ureter under moderate vacuum. Histology, scanning electron microscopy, confocal microscopy, and magnetic resonance imaging were used to assess vasculature preservation and the distribution of cells throughout the kidneys. Cells were detected in the magnetic resonance imaging by labeling them with iron oxide. Perfusion of cells through the ureter under moderate vacuum (40 mmHg) produced the most uniform distribution of cells throughout the kidneys.

The impact of decellularization agents on renal tissue extracellular matrix

The combination of patient-specific cells with scaffolds obtained from natural sources may result in improved regeneration of human tissues. Decellularization of the native tissue is the first step in this technology. Effective decellularization uses agents that lyse cells and remove all cellular materials, leaving intact collagenous extracellular matrices (ECMs). Removing cellular remnants prevents an immune response while preserving the underlying structure. In this study, the impact of five decellularization agents (0.1 N NaOH, 1% peracetic acid, 3% Triton X-100, 1% sodium dodecyl sulfate (SDS), and 0.05% trypsin/EDTA) on renal tissue was examined using slices of porcine kidneys. The NaOH solution induced the most efficient cell removal, and resulted in the highest amount of cell viability and proliferation after recellularization, although it also produced the most significant damage to collagenous fiber networks, glycosaminoglycans (GAGs) and fibroblast growth factor (FGF). The SDS solution led to less severe damage to the ECM structure but it resulted in lower metabolic activity and less proliferation. Peracetic acid and Triton X-100 resulted in minimum disruption of ECMs and the most preserved GAGs and FGF. However, these last two agents were not as efficient in removing cellular materials as NaOH and SDS, especially peracetic acid, which left more than 80% of cellular material within the ECM. As a proof of principle, after completing the comparison studies using slices of renal ECM, the NaOH process was used to decellularize a whole kidney, with good results. The overall results demonstrate the significant effect of cell lysing agents and the importance of developing an optimized protocol to avoid extensive damage to the ECM while retaining the ability to support cell growth.