Decellularized liver as a practical scaffold with a vascular network template for liver tissue engineering

Processing and post-processing of fish skin as a novel material in tissue engineering

As a natural material, fish skin contains significant amounts of collagen I and III, and due to its biocompatible nature, it can be used to regenerate various tissues and organs. To use fish skin, it is necessary to perform the decellularization process to avoid the immunological response of the host body. In the process of decellularization, it is crucial to conserve the extracellular matrix (ECM) three-dimensional (3D) structure. However, it is known that decellularization methods may also damage ECM strands arrangement and structure. Moreover, after decellularization, the post-processing of fish skin improves its mechanical and biological properties and preserves its 3D design and strength. Also, sterilization, which is one of the post-processing steps, is mandatory in pre-clinical and clinical settings. In this review paper, the fish skin decellularization methods performed and the various post-processes used to increase the performance of the skin have been studied. Moreover, multiple applications of acellular fish skin (AFS) and its extracted collagen have been reviewed.

Vascular reconstruction of the decellularized biomatrix for whole-organ engineering-a critical perspective and future strategies

Whole-organ re-engineering is the most challenging goal yet to be achieved in tissue engineering and regenerative medicine. One essential factor in any transplantable and functional tissue engineering is fabricating a perfusable vascular network with macro- and micro-sized blood vessels. Whole-organ development has become more practical with the use of the decellularized organ biomatrix (DOB) as it provides a native biochemical and structural framework for a particular organ. However, reconstructing vasculature and re-endothelialization in the DOB is a highly challenging task and has not been achieved for constructing a clinically transplantable vascularized organ with an efficient perfusable capability. Here, we critically and articulately emphasized factors that have been studied for the vascular reconstruction in the DOB. Furthermore, we highlighted the factors used for vasculature development studies in general and their application in whole-organ vascular reconstruction. We also analyzed in detail the strategies explored so far for vascular reconstruction and angiogenesis in the DOB for functional and perfusable vasculature development. Finally, we discussed some of the crucial factors that have been largely ignored in the vascular reconstruction of the DOB and the future directions that should be addressed systematically.

Whole Liver Derived Acellular Extracellular Matrix for Bioengineering of Liver Constructs: An Updated Review

Biomaterial templates play a critical role in establishing and bioinstructing three-dimensional cellular growth, proliferation and spatial morphogenetic processes that culminate in the development of physiologically relevant in vitro liver models. Various natural and synthetic polymeric biomaterials are currently available to construct biomimetic cell culture environments to investigate hepatic cell-matrix interactions, drug response assessment, toxicity, and disease mechanisms. One specific class of natural biomaterials consists of the decellularized liver extracellular matrix (dECM) derived from xenogeneic or allogeneic sources, which is rich in bioconstituents essential for the ultrastructural stability, function, repair, and regeneration of tissues/organs. Considering the significance of the key design blueprints of organ-specific acellular substrates for physiologically active graft reconstruction, herein we showcased the latest updates in the field of liver decellularization-recellularization technologies. Overall, this review highlights the potential of acellular matrix as a promising biomaterial in light of recent advances in the preparation of liver-specific whole organ scaffolds. The review concludes with a discussion of the challenges and future prospects of liver-specific decellularized materials in the direction of translational research.

Advances in Recellularization of Decellularized Liver Grafts with Different Liver (Stem) Cells: Towards Clinical Applications

Liver transplantation is currently the only curative therapy for patients with acute or chronic liver failure. However, a dramatic gap between the number of available liver grafts and the number of patients on the transplantation waiting list emphasizes the need for valid liver substitutes. Whole-organ engineering is an emerging field of tissue engineering and regenerative medicine. It aims to generate transplantable and functional organs to support patients on transplantation waiting lists until a graft becomes available. It comprises two base technologies developed in the last decade; (1) organ decellularization to generate a three-dimensional (3D) extracellular matrix scaffold of an organ, and (2) scaffold recellularization to repopulate both the parenchymal and vascular compartments of a decellularized organ. In this review article, recent advancements in both technologies, in relation to liver whole-organ engineering, are presented. We address the potential sources of hepatocytes and non-parenchymal liver cells for repopulation studies, and the role of stem-cell-derived liver progeny is discussed. In addition, different cell seeding strategies, possible graft modifications, and methods used to evaluate the functionality of recellularized liver grafts are outlined. Based on the knowledge gathered from recent transplantation studies, future directions are summarized.

Angiogenesis and Re-endothelialization in decellularized scaffolds: Recent advances and current challenges in tissue engineering

Decellularization of tissues and organs has recently become a promising approach in tissue engineering and regenerative medicine to circumvent the challenges of organ donation and complications of transplantations. However, one main obstacle to reaching this goal is acellular vasculature angiogenesis and endothelialization. Achieving an intact and functional vascular structure as a vital pathway for supplying oxygen and nutrients remains the decisive challenge in the decellularization/re-endothelialization procedure. In order to better understand and overcome this issue, complete and appropriate knowledge of endothelialization and its determining variables is required. Decellularization methods and their effectiveness, biological and mechanical characteristics of acellular scaffolds, artificial and biological bioreactors, and their possible applications, extracellular matrix surface modification, and different types of utilized cells are factors affecting endothelialization consequences. This review focuses on the characteristics of endothelialization and how to optimize them, as well as discussing recent developments in the process of re-endothelialization.

Perfusion-Based Recellularization of Rat Livers with Islets of Langerhans

Purpose

Artificial organs might serve as alternative solutions for whole organ transplantation. Decellularization of a liver provides a non-immunogenic matrix with the advantage of three afferent systems, the portal vein, the hepatic artery and the bile duct. This study aims to evaluate the recellularization of rat livers with islets of Langerhans via the bile duct and the portal vein for the comparison of different perfusion routes.

Methods

Rat livers were decellularized in a pressure-controlled perfusion manner and repopulated with intact isolated islets of Langerhans via either the portal vein or the bile duct.

Results

Repopulation via the portal vein showed islet clusters stuck within the vascular system demonstrated by ellipsoid borders of thick reticular tissue around the islet cluster in Azan staining. After recellularization via the bile duct, islets were distributed close to the vessels within the parenchymal space and without a surrounding reticular layer. Large clusters of islets had a diameter of up to 1000 µm without clear shapes.

Conclusion

We demonstrated the bile duct to be superior to the portal vein for repopulation of a decellularized rat liver with islets of Langerhans. This technique may serve as a bioengineering platform to generate an implantable and functional endocrine neo-pancreas and provide scaffolds with the anatomic benefit of three afferent systems to facilitate co-population of cells.

A new strategy for the decellularization of whole organs by hydrostatic pressure

Tissue engineering has been able to develop novel decellularization-recellularization techniques, which facilitates the research for the generation of functional organs. This is based in the initial obtention of the organ's extracellular matrix (ECM). Therefore, any improvement in the decellularization process would have a positive impact in the results of the recellularization process. Nevertheless, commonly the methods and equipment employed for this process are expensive and thus limit the access of this technique to various research groups globally.

AIM

To develop a decellularization technique with the exclusive use of hydrostatic pressure of detergent solutions, to have an easily accessible and low-cost technique that meets the basic requirements of acellularity and functionality of the ECM.

METHODS

This experimental study was performed in 10 male Wistar rats, obtaining the liver to carry out serial washes, with 1, 2 and 3% Triton X-100 solutions and 0.1% SDS. The washes were performed by using a Gravity Perfusion System (GPS), which assured us a continuous hydrostatic pressure of 7.5 mmHg. The obtained ECM was processed using stains and immunostaining to determine the residual cell content and preservation of its components.

RESULTS

The staining showed a removal of cellular and nuclear components of approximately 97% of the acellular ECM, with an adequate three-dimensional pattern of collagen and proteoglycans. Furthermore, the acellular ECM allowed the viability of a primary hepatocyte culture.

CONCLUSIONS

The use of the GPS decellularization technique allowed us to obtain an acellular and functional ECM, drastically reducing experimentation costs. This article is protected by copyright. All rights reserved.

Wnt ligands 3a and 5a regulate proliferation and migration in human fetal liver progenitor cells

Background

Since human fetal liver progenitor cells (hFLPC) can differentiate into multiple liver cell types in vitro and in vivo, hFLPC may be a suitable source for cell therapy and regeneration strategies. Imperative for effective clinical applications of hFLPC is the enhanced knowledge of growth factors that mediate and improve migration and proliferation. The canonical wingless/int-1 (Wnt) signal transduction pathway is known to play a key role in proliferation and migration of stem cells. So, we investigated a role for Wnt3a and Wnt5a ligands in regulating the proliferation and migration of hFLPC.

Methods

We used alamarBlue assay and transwell migration assay and examined proliferation and migration of hFLPC to Wnt3a and Wnt5a. In addition, the target genes of Wnt signal transduction pathway was identified using microarray analysis and validated by quantitative real-time polymerase chain reaction (qPCR).

Results

We found that Wnt3a or Wnt5a independently significantly increased migration and proliferation in a dose-dependent manner which was significantly inhibited by Wnt inhibitors Wnt-C59 or KN-62. Addition of Wnt3a to hFLPC resulted in increased mRNA expression of the known Wnt target genes Axin-2, DKK2, while Wnt5a increased CXCR7, all of which are closely associated with an enhanced proliferation capacity of stem cells.

Conclusions

Thus, we report that Wnt3a and Wnt5a may play an important role in the proliferation and migration of hFLPC by possibly regulating key target genes-involved in these processes. Incorporating recombinant human Wnt3a and Wnt5a in regenerative strategies using liver stem/progenitor cells might improve the process of liver regeneration.

Decellularized Matrix Bioscaffolds: Implementation of Native Microenvironment in Pancreatic Tissue Engineering

ABSTRACT

Type 1 diabetes is an autoimmune disease, and its incidence is usually estimated in the range of 5% to 10%. Currently, the administration of exogenous insulin is the standard of care therapy. However, this therapy is not effective in some patients who may develop some chronic complications. Islet transplantation into the liver is another therapy with promising outcomes; however, the long-term efficacy of this therapeutic option is limited to a small number of patients. Because native extracellular matrix (ECM) components provide a suitable microenvironment for islet functions, engineering a 3-dimensional construct that recapitulates the native pancreatic environment could address these obstacles. Many attempts have been conducted to mimic an in vivo microenvironment to increase the survival of islets or islet-like clusters. With the advent of decellularization technology, it is possible to use a native ECM in organ engineering. Pancreatic decellularized bioscaffold provides proper cell-cell and cell-ECM interactions and retains growth factors that are critical in the determination of cell fate within a native organ. This review summarizes the current knowledge of decellularized matrix technology and addresses its possible limitations before use in the clinic.

Recent advances in optimization of liver decellularization procedures used for liver regeneration

Severe liver diseases have been considered the most common causes of adult deaths worldwide. Until now, liver transplantation is known as the only effective treatment for end stage liver disease. However, it is associated with several problems, most importantly, the side effects of immunosuppressive drugs that should be used after transplantation, and the shortage of tissue donors compared to the increasing number of patients requiring liver transplantation. Currently, tissue/organ decellularization as a new approach in tissue engineering is becoming a valid substitute for managing these kinds of problems. Decellularization of a whole liver is an attractive procedure to create three-dimensional (3D) scaffolds that micro-architecturally and structurally are similar to the native one and could support the repair or replacement of damaged or injured tissue. In this review, the different methods used for decellularization of liver tissue have been reviewed. In addition, the current approaches to overcome the challenges in these techniques are discussed.

Relation between micro- and nanostructure features and biological properties of the decellularized rat liver

Organ decellularization is one of the promising technologies of regenerative medicine, which allows obtaining cell-free extracellular matrix (ECM), which provide preservation of the composition, architecture, vascular network and biological activity of the ECM. The method of decellularization opens up wide prospects for its practical application not only in the field of creating full-scale bioengineered structures, but also in the manufacture of vessels, microcarriers, hydrogels, and coatings. The main goal of our work was the investigation of structure and biological properties of lyophilized decellularized Wistar rat liver fragments (LDLFs), as well as we assessed the regenerative potential of the obtained ECM. We obtained decellularized liver of a Wistar rat, the vascular network and the main components of the ECM of tissue were preserved. H&E staining of histological sections confirmed the removal of cells. DNA content of ECM is equal to 0.7% of native tissue DNA content. Utilizing scanning probe nanotomogrphy method, we showed sinuous, rough topography and highly nanoporous structure of ECM, which provide high level of mouse 3T3 fibroblast and Hep-G₂cells biocompatibility. Obtained LDLF had a high regenerative potential, which we studied in an experimental model of a full-thickness rat skin wound healing: we observed the acceleration of wound healing by 2.2 times in comparison with the control.

Liver bioengineering: Recent trends/advances in decellularization and cell sheet technologies towards translation into the clinic

Development of novel technologies provides the best tissue constructs engineering and maximizes their therapeutic effects in regenerative therapy, especially for liver dysfunctions. Among the currently investigated approaches of tissue engineering, scaffold-based and scaffold-free tissues are widely suggested for liver regeneration. Analogs of liver acellular extracellular matrix (ECM) are utilized in native scaffolds to increase the self-repair and healing ability of organs. Native ECM analog could improve liver repairing through providing the supportive framework for cells and signaling molecules, exerting normal biomechanical, biochemical, and physiological signal complexes. Recently, innovative cell sheet technology is introduced as an alternative for conventional tissue engineering with the advantage of fewer scaffold restrictions and cell culture on a Thermo-Responsive Polymer Surface. These sheets release the layered cells through a temperature-controlled procedure without enzymatic digestion, while preserving the cell-ECM contacts and adhesive molecules on cell-cell junctions. In addition, several novelties have been introduced into the cell sheet and decellularization technologies to aid cell growth, instruct differentiation/angiogenesis, and promote cell migration. In this review, recent trends, advancements, and issues linked to translation into clinical practice are dissected and compared regarding the decellularization and cell sheet technologies for liver tissue engineering.

Stem cell therapy and tissue engineering strategies using cell aggregates and decellularized scaffolds for the rescue of liver failure

Liver failure is a lethal condition with hepatocellular dysfunction, and liver transplantation is presently the only effective treatment. However, due to the limited availability of donors and the potential immune rejection, novel therapeutic strategies are actively sought to restore the normal hepatic architectures and functions, especially for livers with inherited metabolic dysfunctions or chronic diseases. Although the conventional cell therapy has shown promising results, the direct infusion of hepatocytes is hampered by limited hepatocyte sources, poor cell viability, and engraftment. Hence, this review mainly highlights the role of stem cells and progenitors as the alternative cell source and summarizes the potential approaches based on tissue engineering to improve the delivery efficiency of cells. Particularly, the underlying mechanisms for cell therapy using stem cells and progenitors are discussed in two main aspects: paracrine effect and cell differentiation. Moreover, tissue-engineering approaches using cell aggregates and decellularized liver scaffolds for bioengineering of functional hepatic constructs are discussed and compared in terms of the potential to replicate liver physiological structures. In the end, a potentially effective strategy combining the premium advantages of stem cell aggregates and decellularized liver scaffolds is proposed as the future direction of liver tissue engineering and regeneration.

A Quick and Reliable Method to Decellularize a Gracilis Flap: A Crucial Step Toward Building a Muscle

INTRODUCTION

Tissue loss as a consequence of congenital anomalies, trauma, malignancy, or gangrene represents a major health care problem in the United States. Because younger individuals are disproportionately affected, the costs are magnified over time and the resultant individual and societal effects are tremendous. The currently available options to restore soft tissue defects are associated with donor site morbidities. Vascularized composite allotransplantation may provide form, function, and esthetics without a donor site; however, it comes with the significant risk associated with toxic immunosuppression (Biomaterials. 2015;61:246-256, Ann Plast Surg. 2015;75(1):112-116, Transplantation. 2009;88(2):203-210). Engineered tissues offer promise in finding viable alternatives to allograft and autologous tissues. In this study, we present our simple and quick method to decellularize a muscle without disrupting the vascular network integrity or the extracellular matrix. Optimizing the decellularization process is a crucial step toward creating an "off-the-shelf" flap that can be used for soft tissue reconstruction.

METHODS

The superficial gracilis muscle of 20 rats were harvested on their circulation and decellularized using perfusion with Krebs-Henseleit buffer and sodium dodecyl sulfate for 6 hours. These flaps were evaluated by gross morphology, histology, DNA quantification, integrity of the vascular network, scanning electron microscopy, and transmission electron microscopy.

RESULTS

All samples were decellularized successfully as determined by DNA content and histological analysis for cellular content. The vascular network was preserved in all samples.

CONCLUSIONS

We present a quick, simple, and affordable method to decellularize a muscle flap through the vascular network. Our proposed method is efficient and can be completed in a significantly shorter time when compared with other methods. It is also safe and does not affect integrity of tissue, and this is essential for a reliable recellularization.

Advanced Biomaterials and Processing Methods for Liver Regeneration: State-of-the-Art and Future Trends

Liver diseases contribute markedly to the global burden of mortality and disease. The limited organ disposal for orthotopic liver transplantation results in a continuing need for alternative strategies. Over the past years, important progress has been made in the field of tissue engineering (TE). Many of the early trials to improve the development of an engineered tissue construct are based on seeding cells onto biomaterial scaffolds. Nowadays, several TE approaches have been developed and are applied to one vital organ: the liver. Essential elements must be considered in liver TE-cells and culturing systems, bioactive agents or growth factors (GF), and biomaterials and processing methods. The potential of hepatocytes, mesenchymal stem cells, and others as cell sources is demonstrated. They need engineered biomaterial-based scaffolds with perfect biocompatibility and bioactivity to support cell proliferation and hepatic differentiation as well as allowing extracellular matrix deposition and vascularization. Moreover, they require a microenvironment provided using conventional or advanced processing technologies in order to supply oxygen, nutrients, and GF. Herein the biomaterials and the conventional and advanced processing technologies, including cell-sheets process, 3D bioprinting, and microfluidic systems, as well as the future trends in these major fields are discussed.

In Vitro Biocompatibility of Decellularized Cultured Plant Cell-Derived Matrices

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

The Equine Hoof: Laminitis, Progenitor (Stem) Cells, and Therapy Development

The equine hoof capsule, composed of modified epidermis and dermis, is vital for protecting the third phalanx from forces of locomotion. There are descriptions of laminitis, defined as inflammation of sensitive hoof tissues but recognized as pathologic changes with or without inflammatory mediators, in the earliest records of domesticated horses. Laminitis can range from mild to serious, and signs can be acute, chronic, or transition from acute, severe inflammation to permanently abnormal tissue. Damage within the intricate dermal and epidermal connections of the primary and secondary lamellae is often associated with lifelong changes in hoof growth, repair, and conformation. Decades of research contribute to contemporary standards of care that include systemic and local therapies as well as mechanical hoof support. Despite this, consistent mechanisms to restore healthy tissue formation following a laminitic insult are lacking. Endogenous and exogenous progenitor cell contributions to healthy tissue formation is established for most tissues. There is comparably little information about equine hoof progenitor cells. Equine hoof anatomy, laminitis, and progenitor cells are covered in this review. The potential of progenitor cells to advance in vitro equine hoof tissue models and translate to clinical therapies may significantly improve prevention and treatment of a devastating condition that has afflicted equine companions throughout history.

Construction of sinusoid-scale microvessels in perfusion culture of a decellularized liver

There is a great deal of demand for the construction of transplantable liver grafts. Over the last decade, decellularization techniques have been developed to construct whole liver tissue grafts as potential biomaterials. However, the lack of intact vascular networks, especially sinusoids, in recellularized liver scaffolds leads to hemorrhage and thrombosis after transplantation, which is a major obstacle to the development of transplantable liver grafts. In the present study, we hypothesized that both mechanical (e.g., fluid shear stress) and chemical factors (e.g., fibronectin coating) can enhance the formation of hierarchical vascular networks including sinusoid-scale microvessels. We demonstrated that perfusion culture promoted formation of sinusoid-scale microvessels in recellularized liver scaffolds, which was not observed in static culture. In particular, perfusion culture at 4.7 ml/min promoted the formation of sinusoid-scale microvessels compared to perfusion culture at 2.4 and 9.4 ml/min. In addition, well-aligned endothelium was observed in perfusion culture, suggesting that endothelial cells sensed the flow-induced shear stress. Moreover, fibronectin coating of decellularized liver scaffolds enhanced the formation of sinusoid-scale microvessels in perfusion culture at 4.7 ml/min. This study represents a critical step in the development of functional recellularized liver scaffolds, which can be used not only for transplantation but also for drug screening and disease-modeling studies. STATEMENT OF SIGNIFICANCE: Decellularized liver scaffolds are promising biomaterials that allow production of large-scale tissue-engineered liver grafts. However, it is difficult to maintain recellularized liver grafts after transplantation due to hemorrhage and thrombosis. To overcome this obstacle, construction of an intact vascular network including sinusoid-scale microvessels is essential. In the present study, we succeeded in constructing sinusoid-scale microvessels in decellularized liver scaffolds via a combination of perfusion culture and surface coating. We further confirmed that endothelial cells in decellularized liver scaffolds responded to flow-derived mechanical stress by aligning actin filaments. Our strategy to construct sinusoid-scale microvessels is critical for the development of intact vascular networks, and addresses the limitations of recellularized liver scaffolds after transplantation.

Graphene-based 3D scaffolds in tissue engineering: fabrication, applications, and future scope in liver tissue engineering

Tissue engineering embraces the potential of recreating and replacing defective body parts by advancements in the medical field. Being a biocompatible nanomaterial with outstanding physical, chemical, optical, and biological properties, graphene-based materials were successfully employed in creating the perfect scaffold for a range of organs, starting from the skin through to the brain. Investigations on 2D and 3D tissue culture scaffolds incorporated with graphene or its derivatives have revealed the capability of this carbon material in mimicking in vivo environment. The porous morphology, great surface area, selective permeability of gases, excellent mechanical strength, good thermal and electrical conductivity, good optical properties, and biodegradability enable graphene materials to be the best component for scaffold engineering. Along with the apt microenvironment, this material was found to be efficient in differentiating stem cells into specific cell types. Furthermore, the scope of graphene nanomaterials in liver tissue engineering as a promising biomaterial is also discussed. This review critically looks into the unlimited potential of graphene-based nanomaterials in future tissue engineering and regenerative therapy.

A novel evaluation system for whole-organ-engineered liver graft by ex vivo application to a highly reproducible hepatic failure rat model

In recent years, studies on liver graft construction using the decellularized liver as a template for transplantation therapy have attracted much attention. However, the therapeutic effect of constructed liver grafts in hepatic failure has not been evaluated. Therefore, we aimed to develop a novel evaluation system demonstrating the curative effect of a constructed liver graft in animals with hepatic failure. First, we developed a highly reproducible rat model of hepatic failure by combining 80% partial hepatectomy with warm ischemia. In this model, severity could be controlled by the warm ischemic period. We also constructed a liver graft by recellularization of decellularized liver, and confirmed the ammonia metabolic function in the graft in vitro as one of the most important functions for recovery from hepatic failure. The graft was then applied to our developed hepatic failure rat model using a blood extracorporeal circulation system. In this application, the graft metabolized the ammonia in the blood of animals with hepatic failure and was thus suggested to be effective for the treatment of hepatic failure. In summary, a novel evaluation system for whole-organ-engineered liver graft as a preliminary stage of transplantation was developed. This system was expected to provide much information about the curative effect of a constructed liver graft.

Micro and ultrastructural changes monitoring during decellularization for the generation of a biocompatible liver

Decellularization of a whole organ is an attractive process that has been used to create 3D scaffolds structurally and micro-architecturally similar to the native one. Currently used decellularization protocols exhibit disrupted extracellular matrix (ECM) structure and denatured ECM proteins. Therefore, maintaining a balance between ECM preservation and cellular removal is a major challenge. The aim of this study was to optimize a multistep Triton X-100 based protocol (either using Triton X-100/ammonium hydroxide mixture alone or after its modification with DNase, sodium dodecyl sulfate or trypsin) that could achieve maximum decellularization with minimal liver ECM destruction suitable for subsequent organ implantation without immune rejection. Based on our findings, Triton X-100 multistep protocol was insufficient for whole liver decellularization and needed to be modified with other detergents. Among all Triton X-100 modified protocols, a Triton X-100/DNase-based one was considered the most suitable. It maintains a gradual but sufficient removal of cells to generate decellularized biocompatible liver scaffolds without any significant alteration to ECM micro- and ultra-structure.

The analysis of the proliferative activity of cells on microparticles obtained from decellularized liver and kidney tissue

Aim.To develop the protocols for liver and kidney tissue decellularization, and to develop an analysis of the proliferative activity of human Hep-G2hepatocarcinoma cells on various carriers.

Materials and methods.Decellularization of the liver and kidneys was performed by perfusion of detergent solutions with gradually increasing concentrations of Triton X-100 (1, 2 and 3%). A histological analysis of the obtained samples was performed, and the method of optical and scanning electron microscopy was used to study the obtained samples. The proliferative activity of human Hep-G2hepatocarcinoma cells was studied on the obtained samples of decellularized liver and kidney tissue.

Results.Decellularization of the organ does not lead to changes in the specific structure of the tissue matrix. Microparticles with an average size of 200 μm were made from their decellularized matrix of liver and kidney tissues. The level of proliferative activity of human Hep-G2hepatocarcinoma cells cultured on microparticles from a decellularized liver was significantly higher than on microparticles from a decellularized kidney.

Conclusion.The decellularized matrix retains the native three-dimensional structure of the tissue. The level of cell proliferative activity is significantly higher on microparticles from the decellularized liver, which confirms the preservation of the specificity of the extracellular matrix of the tissue after the process of decellularization.

Biocompatibility and hemocompatibility of efficiently decellularized whole porcine kidney for tissue engineering

Whole kidney decellularization is a promising approach in regenerative medicine for engineering a functional organ. The reaction of the potential host depends on the biocompatibility of these decellularized constructs. Despite the proven ability of decellularized kidney scaffolds to guide cell attachment and growth, little is known about biocompatibility and hemocompatibility of these scaffolds. Our aim is to prepare decellularized kidneys of a clinically relevant size and evaluate its biocompatibility and hemocompatibility. Porcine kidneys were cannulated via the renal artery, and then perfused with 0.1% sodium dodecyl sulfate solution. Hematoxylin and eosin as well as DAPI staining confirmed cellular clearance from native kidneys in addition to preservation of the microstructure. SEM confirmed the absence of any cellular content within the scaffold, which is maintained in a well-organized 3D architecture. Decellularized kidneys retained the intact renal vasculature upon examination with contrast radiography. The essential structural extracellular matrix molecules were well-preserved. Scaffolds were susceptible to enzymatic degradation upon collagenase treatment. Scaffolds showed a good hemocompatibility when exposed to porcine blood. Decellularization was efficient to remove 97.7% of DNA from native kidneys in addition to the immunogenic and pathogenic antigens. Scaffolds did not induce the human immune response in vitro. Decellularized kidneys were non-cytotoxic to pig kidney cells (PKs). PKs were able to grow and proliferate within the decellularized renal scaffolds with maintaining a higher function than cells grown as monolayers. Thus, we have developed a rapid decellularization technique for generating biocompatible kidney scaffolds that represents a step toward development of a transplantable organ. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2034-2047, 2018.

[Liver engineering as a new source of donor organs : A systematic review]

BACKGROUND

Organ engineering is a new strategy to cope with the shortage of donor organs. A functional scaffold from explanted organs is prepared by removing all cellular components (decellularization) and the reseeding (repopulation) of the organ scaffold to generate a functional organ in vitro for transplantation. This technique was also applied to the liver (liver engineering).

OBJECTIVES

Outline of the current state of the art and resulting approaches for future research strategies.

MATERIAL AND METHODS

Systematic review according to the PRISMA guidelines: a PubMed-based literature search (search terms liver, decellularization), selection of relevant articles based on predetermined criteria for relevance (e.g. decellularization, repopulation and transplantation), extraction and critical appraisal of data and results concerning the conditions for decellularization, repopulation and transplantation.

RESULTS

Decellularization was successfully performed in small and large animal models. Hepatocytes as well as stem cells and hepatic cell lines were applied for repopulation and 7 publications could show the successful transplantation of acellular and repopulated organ scaffolds. The current scientific need for further studies concerning the source of donor organs, optimization of the decellularization process, the cell type for the reseeding process and the establishment of the optimal conditions for the repopulation of the scaffold is still tremendous. For successful recellularization of the liver three goals need to be achieved: (1) reseeding of the organ scaffold with a sufficient amount of parenchymal cells, (2) endothelialization of the vascular tree to ensure the supply of oxygen and nutrients to parenchymal cells and (3) an appropriate epithelialization of the biliary tree. In order to progress to clinical trials a suitable transplantation model to verify the function of the organ constructs must be established.

CONCLUSION

Liver engineering using biological cell-free organ scaffolds represents a scientific and ethical challenge. The existing results emphasize the potential of this new and promising strategy to create organs for transplantation in the future.

Whole liver engineering: A promising approach to develop functional liver surrogates

Liver donor shortage remains the biggest challenge for patients with end-stage liver failures. While bioartificial liver devices have been developed as temporary supports for patients waiting for transplantation, their applications have been limited clinically. Whole liver engineering is a biological scaffold based regenerative medicine approach that holds promise for developing functional liver surrogates. Significant advancements have been made since the first report in 2010. This review focuses on the recent achievements of whole liver engineering studies.

Decellularization of Whole Human Liver Grafts Using Controlled Perfusion for Transplantable Organ Bioscaffolds

Liver transplantation is the only effective treatment for end-stage liver disease, but absolute donor shortage remains a limiting factor. Recent advances in tissue engineering focus on generation of native extracellular matrix (ECM) by decellularized complete livers in animal models. Although proof of concept has been reported for human livers, this study aims to perform whole liver decellularization in a clinically relevant series using controlled machine perfusion. In this study, we describe a mild nondestructive decellularization protocol, effective in 11 discarded human whole liver grafts to generate constructs that reliably maintain hepatic architecture and ECM components using machine perfusion, while completely removing cellular DNA and RNA. The decellularization process preserved the ultrastructural ECM components confirmed by histology, electron microscopy, and proteomic analysis. Anatomical characteristics of the native microvascular network and biliary drainage of the liver were confirmed by contrast computed tomography scanning. Decellularized vascular matrix remained suitable for normal suturing and no major histocompatibility complex molecules were detected, suggesting absence of allo-reactivity when used for transplantation. After extensive washing, decellularized scaffolds were nontoxic for cells after reseeding human mesenchymal stromal or umbilical vein endothelial endothelium cells. Indeed, evidence of effective recellularization of the vascular lining was obtained. In conclusion, we established an effective method to generate clinically applicable liver scaffolds from human discarded whole liver grafts and show proof of concept that reseeding of normal human cells in the scaffold is feasible. This supports new opportunities for bioengineering of transplantable grafts in the future.

Evolution of graft morphology and function after recellularization of decellularized rat livers

Decellularization of livers is a well-established procedure. Data on different reseeding techniques or the functional evolution and reorganization processes of repopulated grafts remains limited. A proprietary, customized bioreactor was established to repopulate decellularized rat livers (n = 21) with primary rat hepatocytes (150 × 10⁶ cells) via the hepatic artery and to subsequently evaluate graft morphology and function during 7 days of ex vivo perfusion. Grafts were analysed at 1 h, 6 h, 12 h, 24 h, 3 days, 5 days and 7 days after recellularization (all n = 3) by immunohistological evaluation, hepatocyte-related enzyme (aspartate transaminase, alanine transaminase and lactate dehydrogenase) and albumin measurement in the perfusate. This appears to be the first available protocol for repopulation of rat livers via the hepatic artery. Within the first 24 h after repopulation, the hepatocytes seemed to migrate out of the vascular network and form clusters in the parenchymal space around the vessels. Graft function increased for the first 24 h after repopulation with a significantly higher function compared to standard two-dimensional culture after 24 h. Thereafter, graft function constantly decreased with significantly lower values after 6 days and 7 days of perfusion, although histologically viable hepatocytes were found even after this period. The data suggests that, owing to a constant loss of function, repopulated grafts should potentially be implanted as soon as cell engraftment and graft re-organization are completed. Copyright © 2016 John Wiley & Sons, Ltd.

Biomaterials and Culture Technologies for Regenerative Therapy of Liver Tissue

Regenerative approach has emerged to substitute the current extracorporeal technologies for the treatment of diseased and damaged liver tissue. This is based on the use of biomaterials that modulate the responses of hepatic cells through the unique matrix properties tuned to recapitulate regenerative functions. Cells in liver preserve their phenotype or differentiate through the interactions with extracellular matrix molecules. Therefore, the intrinsic properties of the engineered biomaterials, such as stiffness and surface topography, need to be tailored to induce appropriate cellular functions. The matrix physical stimuli can be combined with biochemical cues, such as immobilized functional groups or the delivered actions of signaling molecules. Furthermore, the external modulation of cells, through cocultures with nonparenchymal cells (e.g., endothelial cells) that can signal bioactive molecules, is another promising avenue to regenerate liver tissue. This review disseminates the recent approaches of regenerating liver tissue, with a focus on the development of biomaterials and the related culture technologies.

Decellularization of Liver and Organogenesis in Rats

Recently, organ construction has been attempted using decellularized organs. In this study, we used decellularized rat liver to construct liver tissue by recellularization. The right lobe of the rat liver was decellularized with 4% Triton X-100 solution, recellularized with 10⁷ rat hepatocytes, and albumin synthesis in the recellularized right lobe was observed. Therefore, we introduce a method of decellularizing rat liver, which retains its fine vascular structure after removal of all the cells, perform organogenesis using the decellularized liver, and evaluate the structural and functional properties of the products.

Sympathetic neurotransmitters promote the process of recellularization in decellularized liver matrix via activating the IL-6/Stat3 pathway

Recellularized liver, as an approach for hepatic tissue engineering, is an effective alternative to orthotopic liver transplantation for end-stage hepatic failure. When compared with normal liver, recellularized liver has a disparity in hepatocyte viability and function, owing to the difficulty of fully simulating the microenvironment of liver. Although the sympathetic nervous system (SNS) is considered an important constituent of liver function, few studies have examined the effect of the SNS on hepatic tissue engineering. It is imperative to explore the regulation of the SNS on a tissue-like configuration to obtain an intact recellularized liver with better hepatic function. We have observed that various subtypes of adrenergic receptors (ARs) are expressed on the hepatocyte membrane. Salbutamol, an agonist of β2-AR, promoted cell proliferation, albumin secretion and urea synthesis in the recellularized liver. Cytokines were screened in isoprenaline/salbutamol-treated recellularized liver, and the expression of IL-6 was significantly increased. Isoprenaline or salbutamol especially promoted the expression of Stat 3 and phosphorylated Stat 3, contributing to the activation of IL-6/Stat 3 signalling in promoting hepatocyte proliferation and recellularized liver function. This study suggests that activation of β2-AR accelerated hepatocyte proliferation and improved recellularized liver function by mediating the IL-6/Stat 3 signalling pathway, indicating that nervous system regulation may be an essential component contributing to the complexity of recellularized liver in tissue engineering.

Bioengineered Livers: A New Tool for Drug Testing and a Promising Solution to Meet the Growing Demand for Donor Organs

BACKGROUND

Organ engineering is a new innovative strategy to cope with two problems: the need for physiological models for pharmacological research and donor organs for transplantation. A functional scaffold is generated from explanted organs by removing all cells (decellularization) by perfusing the organ with ionic or nonionic detergents via the vascular system. Subsequently the acellular scaffold is reseeded with organ-specific cells (repopulation) to generate a functional organ.

SUMMARY

This review gives an overview of the state of the art describing the decellularization process, the subsequent quality assessment, the repopulation techniques and the functional assessment. It emphasizes the use of scaffolds as matrix for culturing human liver cells for drug testing. Further, it highlights the techniques for transplanting these engineered scaffolds in allogeneic or xenogeneic animals in order to test their biocompatibility and use as organ grafts. Key Messages: The first issue is the so-called decellularization, which is best explored and resulted in a multitude of different protocols. The most promising approach seems to be the combination of pulsatile perfusion of the liver with Triton X-100 and SDS via hepatic artery and portal vein. Widely accepted parameters of quality control include the quantitative assessment of the DNA content and the visualization of eventually remaining nuclei confirmed by HE staining. Investigations regarding the composition of the extracellular matrix focused on histological determination of laminin, collagen, fibronectin and elastin and remained qualitatively. Repopulation is the second issue which is addressed. Selection of the most suitable cell type is a highly controversial topic. Currently, the highest potential is seen for progenitor and stem cells. Cells are infused into the scaffold and cultured under static conditions or in a bioreactor allowing dynamic perfusion of the scaffold. The quality of repopulation is mainly assessed by routine histology and basic functional assays. These promising results prompted to consider the use of a liver scaffold repopulated with human cells for pharmacological research. Transplantation of the (repopulated) scaffold is the third topic which is not yet widely addressed. Few studies report the heterotopic transplantation of repopulated liver tissue without vascular anastomosis. Even fewer studies deal with the heterotopic transplantation of a scaffold or a repopulated liver lobe. However, observation time was still limited to hours, and long-term graft survival has not been reported yet. These exciting results emphasize the potential of this new and promising strategy to create physiological models for pharmacological research and to generate liver grafts for the transplant community to treat organ failure. However, the scientific need for further development in the field of liver engineering is still tremendous.

Optimization of Liver Decellularization Maintains Extracellular Matrix Micro-Architecture and Composition Predisposing to Effective Cell Seeding

Hepatic tissue engineering using decellularized scaffolds is a potential therapeutic alternative to conventional transplantation. However, scaffolds are usually obtained using decellularization protocols that destroy the extracellular matrix (ECM) and hamper clinical translation. We aim to develop a decellularization technique that reliably maintains hepatic microarchitecture and ECM components. Isolated rat livers were decellularized by detergent-enzymatic technique with (EDTA-DET) or without EDTA (DET). Histology, DNA quantification and proteomics confirmed decellularization with further DNA reduction with the addition of EDTA. Quantification, histology, immunostaining, and proteomics demonstrated preservation of extracellular matrix components in both scaffolds with a higher amount of collagen and glycosaminoglycans in the EDTA-DET scaffold. Scanning electron microscopy and X-ray phase contrast imaging showed microarchitecture preservation, with EDTA-DET scaffolds more tightly packed. DET scaffold seeding with a hepatocellular cell line demonstrated complete repopulation in 14 days, with cells proliferating at that time. Decellularization using DET preserves microarchitecture and extracellular matrix components whilst allowing for cell growth for up to 14 days. Addition of EDTA creates a denser, more compact matrix. Transplantation of the scaffolds and scaling up of the methodology are the next steps for successful hepatic tissue engineering.

Decellularized spleen matrix for reengineering functional hepatic-like tissue based on bone marrow mesenchymal stem cells

BACKGROUND AND AIMS

Decellularized liver matrix (DLM) hold great potential for reconstructing functional hepatic-like tissue (HLT) based on reseeding of hepatocytes or stem cells, but the shortage of liver donors is still an obstacle for potential application. Therefore, an appropriate alternative scaffold is needed to expand the donor pool. In this study, we explored the effectiveness of decellularized spleen matrix (DSM) for culturing of bone marrow mesenchymal stem cells (BMSCs), and promoting differentiation into hepatic-like cells.

METHODS

Rats' spleen were harvested for DSM preparation by freezing/thawing and perfusion procedure. Then the mesenchymal stem cells derived from rat bone marrow were reseeded into DSM for dynamic culture and hepatic differentiation by a defined induction protocol.

RESULTS

The research found that DSM preserved a 3-dimensional porous architecture, with native extracellular matrix and vascular network which was similar to DLM. The reseeded BMSCs in DSM differentiated into functional hepatocyte-like cells, evidenced by cytomorphology change, expression of hepatic-associated genes and protein markers, glycogen storage, and indocyanine green uptake. The albumin production (2.74±0.42 vs. 2.07±0.28 pg/cell/day) and urea concentration (75.92±15.64 vs. 52.07±11.46 pg/cell/day) in DSM group were remarkably higher than tissue culture flasks (TCF) group over the same differentiation period, P< 0.05.

CONCLUSION

This present study demonstrated that DSM might have considerable potential in fabricating hepatic-like tissue, particularly because it can facilitate hepatic differentiation of BMSCs which exhibited higher level and more stable functions.

Procedure for Decellularization of Rat Livers in an Oscillating-pressure Perfusion Device

Decellularization and recellularization of parenchymal organs may enable the generation of functional organs in vitro, and several protocols for rodent liver decellularization have already been published. We aimed to improve the decellularization process by construction of a proprietary perfusion device enabling selective perfusion via the portal vein and/or the hepatic artery. Furthermore, we sought to perform perfusion under oscillating surrounding pressure conditions to improve the homogeneity of decellularization. The homogeneity of perfusion decellularization has been an underestimated factor to date. During decellularization, areas within the organ that are poorly perfused may still contain cells, whereas the extracellular matrix (ECM) in well-perfused areas may already be affected by alkaline detergents. Oscillating pressure changes can mimic the intraabdominal pressure changes that occur during respiration to optimize microperfusion inside the liver. In the study presented here, decellularized rat liver matrices were analyzed by histological staining, DNA content analysis and corrosion casting. Perfusion via the hepatic artery showed more homogenous results than portal venous perfusion did. The application of oscillating pressure conditions improved the effectiveness of perfusion decellularization. Livers perfused via the hepatic artery and under oscillating pressure conditions showed the best results. The presented techniques for liver harvesting, cannulation and perfusion using our proprietary device enable sophisticated perfusion set-ups to improve decellularization and recellularization experiments in rat livers.

Fabrication of 2D and 3D constructs from reconstituted decellularized tissue extracellular matrices

We demonstrated a novel process to reconstitute a decellularized extracellular matrix (Recon-ECM) of heart and liver tissue using a combination of mechanical homogenization and enzymatic digestion. Such Recon-ECM was used as a biomaterial to produce flat or micro-patterned 2D films after crosslinking using replica molding. The mechanical properties of the resulting films were tuned by changing the type of crosslinking reagents. We also demonstrated the fabrication of mechanically robust 3D scaffolds by freeze-drying of the Recon-ECM solution. The porosity of the 3D scaffold was controlled by changing the concentration of the Recon-ECM. HepG2 cells were used to investigate the potential substrate of these engineered 2D patterned and 3D porous structures. The cell attachment, proliferation, and urea synthesis were evaluated, and the results indicate that the scaffold generated from Recon-ECM provides a biologically friendly environment for cells to grow. This method provides a new way to use decellularized ECM as a source of biomaterial to produce novel scaffolds with better controlled micro- and nano-scale structures, tunable physicochemical properties with desired biological functions.

Three-dimensional culture of mouse pancreatic islet on a liver-derived perfusion-decellularized bioscaffold for potential clinical application

The cutting-edge technology of three-dimensional liver decellularized bioscaffold has a potential to provide a microenvironment that is suitable for the resident cells and even develop a new functional organ. Liver decellularized bioscaffold preserved the native extracellular matrix and three-dimensional architecture in support of the cell culture. The goal of this study was to discover if three-dimensional extracellular matrix derived from mouse liver could facilitate the growth and maintenance of physiological functions of mouse isolated islets. We generated a whole organ liver decellularized bioscaffold which could successfully preserve extracellular matrix proteins and the native vascular channels using 1% Triton X-100/0.1% ammonium protocol. To evaluate the potential of decellularized liver as a scaffold for islets transplantation, the liver decellularized bioscaffold was infused with mouse primary pancreatic islets which were obtained through Collagenase P digestion protocol. Its yield, morphology, and quality were estimated by microscopic analysis, dithizone staining, insulin immunofluorescence and glucose stimulation experiments. Comparing the three-dimensional culture in liver decellularized bioscaffold with the orthodoxy two-dimensional plate culture, hematoxylin-eosin staining, immunohistochemistry, and insulin gene expression were tested. Our results demonstrated that the liver decellularized bioscaffold could support cellular culture and maintenance of cell functions. In contrast with the conventional two-dimensional culture, three-dimensional culture system could give rise to an up-regulated insulin gene expression. These findings demonstrated that the liver bioscaffold by a perfusion-decellularized technique could serve as a platform to support the survival and function of the pancreatic islets in vitro. Meanwhile three-dimensional culture system had a superior role in contrast with the two-dimensional culture. This study advanced the field of regenerative medicine towards the development of a liver decellularized bioscaffold capable of forming a neo-organ and could be used as potential clinical application.

Recent advances in re-engineered liver: de-cellularization and re-cellularization techniques

Allogeneic transplantation is the definitive treatment for patients with end-stage liver disease but is limited by donor shortage and very high cost. Through de-cellularization and re-cellularization methods, re-engineered liver may provide a promising alternative for treating patients with end-stage liver disease. To achieve this, the prevention of the native extracellular matrix ultrastructure plays a central role in de-cellularization protocol; the re-seeding cell types, as well as re-seeding strategies, need more explorations in re-cellularization protocol. Some success of this approach has been published in a rat model; however, the re-engineered liver remains functional in vivo for only several hours, which suggests that the recent protocol may be far from the ideal target. This Review highlights the challenges still to be overcome and presents an overview and summary of methods of de-cellularization and re-cellularization strategies, together with a view on future directions that may lead to the regeneration of a functional liver.

A review of cellularization strategies for tissue engineering of whole organs

With the advent of whole organ decellularization, extracellular matrix scaffolds suitable for organ engineering were generated from numerous tissues, including the heart, lung, liver, kidney, and pancreas, for use as alternatives to traditional organ transplantation. Biomedical researchers now face the challenge of adequately and efficiently recellularizing these organ scaffolds. Herein, an overview of whole organ decellularization and a thorough review of the current literature for whole organ recellularization are presented. The cell types, delivery methods, and bioreactors employed for recellularization are discussed along with commercial and clinical considerations, such as immunogenicity, biocompatibility, and Food and Drug Administartion regulation.

Stem cells with decellularized liver scaffolds in liver regeneration and their potential clinical applications

End-stage hepatic failure is a potentially life-threatening condition for which orthotopic liver transplantation (OLT) is the only effective treatment. However, a shortage of available donor organs for transplantation each year results in the death of many patients waiting for liver transplantation. Cell-based therapies and hepatic tissue engineering have been considered as alternatives to liver transplantation. However, primary hepatocyte transplantation has rarely produced therapeutic effects because mature hepatocytes cannot be effectively expanded in vitro, and the availability of hepatocytes is often limited by shortages of donor organs. Decellularization is an attractive technique for scaffold preparation in stem cell-based liver engineering, as the resulting material can potentially retain the liver architecture, native vessel network and specific extracellular matrix (ECM). Thus, the reconstruction of functional and practical liver tissue using decellularized scaffolds becomes possible. This review focuses on the current understanding of liver tissue engineering, whole-organ liver decellularization techniques, cell sources for recellularization and potential clinical applications and challenges.