Controlled processing of a full-sized porcine liver to a decellularized matrix in 24 h

Endotoxin, not DNA, determines the host response and tissue regeneration behavior of acellular biologic scaffolds

Established quantitative standards for assessing decellularization of biologic scaffolds based on residual DNA levels have been well-documented and widely acknowledged. However, post-implantation complications, such as fever and seroma, are commonly observed which negatively impact clinical outcomes. The presence of cellular debris following decellularization or using source tissues that are naturally high in endotoxin may contribute to the host response to a biologic scaffold. In the study, several multi-step decellularization methods were used to decellularize small intestinal submucosa (SIS) to obtain materials with three distinct levels of residual DNA, lipid residues, and endogenous endotoxin. The potential influence of these residual components on macrophage and lymphocyte polarization in vitro, as well as on the host inflammatory response in vivo post intra-abdominal implantation or abdominal wall defect repair in rats, was assessed. Urinary bladder matrix (UBM) meeting established decellularization criteria and naturally devoid of endotoxin was utilized as a control. The presence of endogenous endotoxin in SIS-ECM resulted in notable changes in macrophage phenotype. SIS-ECM samples with endotoxin levels below FDA limits still upregulated pro-inflammatory factors in vitro. Conversely, SIS with minimal endotoxin content and UBM controls prompted a shift towards a pro-remodeling M2 phenotype, fostering constructive tissue remodeling in a rodent model of abdominal wall defects, irrespective of DNA content. These findings suggest that endotoxin may be a crucial factor influencing biologic scaffolds that are not fully accounted by current decellularization standards. STATEMENT OF SIGNIFICANCE: Clinically utilized decellularized biologic scaffolds that meet the established quantitative standards still suffer problems in high incidence of inflammatory complications, including fever and seroma. In this study, we confirmed that endotoxin, rather than residual DNA, is the crucial factor influencing host responses and regenerative outcomes. Tissue sources and decellularization processes are critical for reducing endotoxin levels and attenuating immuno-inflammatory complications. These findings enhance the evaluation of ECM scaffold performance for clinical application, thereby facilitating improved preparation and utilization for tissue defect repairs.

Decellularized Liver Matrices for Expanding the Donor Pool-An Evaluation of Existing Protocols and Future Trends

Liver transplantation is the only curative option for end-stage liver disease and is necessary for an increasing number of patients with advanced primary or secondary liver cancer. Many patient groups can benefit from this treatment, however the shortage of liver grafts remains an unsolved problem. Liver bioengineering offers a promising method for expanding the donor pool through the production of acellular scaffolds that can be seeded with recipient cells. Decellularization protocols involve the removal of cells using various chemical, physical, and enzymatic steps to create a collagenous network that provides support for introduced cells and future vascular and biliary beds. However, the removal of the cells causes varying degrees of matrix damage, that can affect cell seeding and future organ performance. The main objective of this review is to present the existing techniques of producing decellularized livers, with an emphasis on the assessment and definition of acellularity. Decellularization agents are discussed, and the standard process of acellular matrix production is evaluated. We also introduce the concept of the stepwise assessment of the matrix during decellularization through decellularization cycles. This method may lead to shorter detergent exposure times and less scaffold damage. The introduction of apoptosis induction in the field of organ engineering may provide a valuable alternative to existing long perfusion protocols, which lead to significant matrix damage. A thorough understanding of the decellularization process and the action of the various factors influencing the final composition of the scaffold is essential to produce a biocompatible matrix, which can be the basis for further studies regarding recellularization and retransplantation.

Liver tissue engineering using decellularized scaffolds: Current progress, challenges, and opportunities

Liver transplantation represents the only definitive treatment for patients with end-stage liver disease. However, the shortage of liver donors provokes a dramatic gap between available grafts and patients on the waiting list. Whole liver bioengineering, an emerging field of tissue engineering, holds great potential to overcome this gap. This approach involves two main steps; the first is liver decellularization and the second is recellularization. Liver decellularization aims to remove cellular and nuclear materials from the organ, leaving behind extracellular matrices containing different structural proteins and growth factors while retaining both the vascular and biliary networks. Recellularization involves repopulating the decellularized liver with appropriate cells, theoretically from the recipient patient, to reconstruct the parenchyma, vascular tree, and biliary network. The aim of this review is to identify the major advances in decellularization and recellularization strategies and investigate obstacles for the clinical application of bioengineered liver, including immunogenicity of the designed liver extracellular matrices, the need for standardization of scaffold fabrication techniques, selection of suitable cell sources for parenchymal repopulation, vascular, and biliary tree reconstruction. In vivo transplantation models are also summarized for evaluating the functionality of bioengineered livers. Finally, the regulatory measures and future directions for confirming the safety and efficacy of bioengineered liver are also discussed. Addressing these challenges in whole liver bioengineering may offer new solutions to meet the demand for liver transplantation and improve patient outcomes.

Bioengineering liver tissue by repopulation of decellularised scaffolds

Liver transplantation is the only curative therapy for end stage liver disease, but is limited by the organ shortage, and is associated with the adverse consequences of immunosuppression. Repopulation of decellularised whole organ scaffolds with appropriate cells of recipient origin offers a theoretically attractive solution, allowing reliable and timely organ sourcing without the need for immunosuppression. Decellularisation methodologies vary widely but seek to address the conflicting objectives of removing the cellular component of tissues whilst keeping the 3D structure of the extra-cellular matrix intact, as well as retaining the instructive cell fate determining biochemicals contained therein. Liver scaffold recellularisation has progressed from small rodent in vitro studies to large animal in vivo perfusion models, using a wide range of cell types including primary cells, cell lines, foetal stem cells, and induced pluripotent stem cells. Within these models, a limited but measurable degree of physiologically significant hepatocyte function has been reported with demonstrable ammonia metabolism in vivo. Biliary repopulation and function have been restricted by challenges relating to the culture and propagations of cholangiocytes, though advances in organoid culture may help address this. Hepatic vasculature repopulation has enabled sustainable blood perfusion in vivo, but with cell types that would limit clinical applications, and which have not been shown to have the specific functions of liver sinusoidal endothelial cells. Minority cell groups such as Kupffer cells and stellate cells have not been repopulated. Bioengineering by repopulation of decellularised scaffolds has significantly progressed, but there remain significant experimental challenges to be addressed before therapeutic applications may be envisaged.

Decellularized fennel and dill leaves as possible 3D channel network in GelMA for the development of an in vitro adipose tissue model

The development of 3D scaffold-based models would represent a great step forward in cancer research, offering the possibility of predicting the potential in vivo response to targeted anticancer or anti-angiogenic therapies. As regards, 3D in vitro models require proper materials, which faithfully recapitulated extracellular matrix (ECM) properties, adequate cell lines, and an efficient vascular network. The aim of this work is to investigate the possible realization of an in vitro 3D scaffold-based model of adipose tissue, by incorporating decellularized 3D plant structures within the scaffold. In particular, in order to obtain an adipose matrix capable of mimicking the composition of the adipose tissue, methacrylated gelatin (GelMA), UV photo-crosslinkable, was selected. Decellularized fennel, wild fennel and, dill leaves have been incorporated into the GelMA hydrogel before crosslinking, to mimic a 3D channel network. All leaves showed a loss of pigmentation after the decellularization with channel dimensions ranging from 100 to 500 µm up to 3 μm, comparable with those of human microcirculation (5–10 µm). The photo-crosslinking process was not affected by the embedded plant structures in GelMA hydrogels. In fact, the weight variation test, performed on hydrogels with or without decellularized leaves showed a weight loss in the first 96 h, followed by a stability plateau up to 5 weeks. No cytotoxic effects were detected comparing the three prepared GelMA/D-leaf structures; moreover, the ability of the samples to stimulate differentiation of 3T3-L1 preadipocytes in mature adipocytes was investigated, and cells were able to grow and proliferate in the structure, colonizing the entire microenvironment and starting to differentiate. The developed GelMA hydrogels mimicked adipose tissue together with the incorporated plant structures seem to be an adequate solution to ensure an efficient vascular system for a 3D in vitro model. The obtained results showed the potentiality of the innovative proposed approach to mimic the tumoral microenvironment in 3D scaffold-based models.

Human-Origin iPSC-Based Recellularization of Decellularized Whole Rat Livers

End-stage liver diseases lead to mortality of millions of patients, as the only treatment available is liver transplantation and donor scarcity means that patients have to wait long periods before receiving a new liver. In order to minimize donor organ scarcity, a promising bioengineering approach is to decellularize livers that do not qualify for transplantation. Through decellularization, these organs can be used as scaffolds for developing new functional organs. In this process, the original cells of the organ are removed and ideally should be replaced by patient-specific cells to eliminate the risk of immune rejection. Induced pluripotent stem cells (iPSCs) are ideal candidates for developing patient-specific organs, yet the maturity and functionality of iPSC-derived cells do not match those of primary cells. In this study, we introduced iPSCs into decellularized rat liver scaffolds prior to the start of differentiation into hepatic lineages to maximize the exposure of iPSCs to native liver matrices. Through exposure to the unique composition and native 3D organization of the liver microenvironment, as well as the more efficient perfusion culture throughout the differentiation process, iPSC differentiation into hepatocyte-like cells was enhanced. The resulting cells showed significantly higher expression of mature hepatocyte markers, including important CYP450 enzymes, along with lower expression of fetal markers, such as AFP. Importantly, the gene expression profile throughout the different stages of differentiation was more similar to native development. Our study shows that the native 3D liver microenvironment has a pivotal role to play in the development of human-origin hepatocyte-like cells with more mature characteristics.

Recent Advances in Liver Engineering With Decellularized Scaffold

Liver transplantation is currently the only effective treatment for patients with end-stage liver disease; however, donor liver scarcity is a notable concern. As a result, extensive endeavors have been made to diversify the source of donor livers. For example, the use of a decellularized scaffold in liver engineering has gained considerable attention in recent years. The decellularized scaffold preserves the original orchestral structure and bioactive chemicals of the liver, and has the potential to create a de novo liver that is fit for transplantation after recellularization. The structure of the liver and hepatic extracellular matrix, decellularization, recellularization, and recent developments are discussed in this review. Additionally, the criteria for assessment and major obstacles in using a decellularized scaffold are covered in detail.

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

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

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.

Cell Therapy and Bioengineering in Experimental Liver Regenerative Medicine: In Vivo Injury Models and Grafting Strategies

Purpose of Review

To describe experimental liver injury models used in regenerative medicine, cell therapy strategies to repopulate damaged livers and the efficacy of liver bioengineering.

Recent Findings

Several animal models have been developed to study different liver conditions. Multiple strategies and modified protocols of cell delivery have been also reported. Furthermore, using bioengineered liver scaffolds has shown promising results that could help in generating a highly functional cell delivery system and/or a whole transplantable liver.

Summary

To optimize the most effective strategies for liver cell therapy, further studies are required to compare among the performed strategies in the literature and/or innovate a novel modifying technique to overcome the potential limitations. Coating of cells with polymers, decellularized scaffolds, or microbeads could be the most appropriate solution to improve cellular efficacy. Besides, overcoming the problems of liver bioengineering may offer a radical treatment for end-stage liver diseases.

Optimizing the Decellularized Porcine Liver Scaffold Protocol

There are few existing methods for shortening the decellularization period for a human-sized whole-liver scaffold. Here, we describe a protocol that enables effective decellularization of the liver obtained from pigs weigh 120 ± 4.2 kg within 72 h. Porcine livers (approx. 1.5 kg) were decellularized for 3 days using a combination of chemical and enzymatic decellularization agents. After trypsin, sodium deoxycholate, and Triton X-100 perfusion, the porcine livers were completely translucent. Our protocol was efficient to promote cell removal, the preservation of extracellular matrix (ECM) components, and vascular tree integrity. In conclusion, our protocol is efficient to promote human-sized whole-liver scaffold decellularization and thus useful to generate bioengineered livers to overcome the shortage of organs.

Plant Tissues as 3D Natural Scaffolds for Adipose, Bone and Tendon Tissue Regeneration

Decellularized tissues are a valid alternative as tissue engineering scaffolds, thanks to the three-dimensional structure that mimics native tissues to be regenerated and the biomimetic microenvironment for cells and tissues growth. Despite decellularized animal tissues have long been used, plant tissue decellularized scaffolds might overcome availability issues, high costs and ethical concerns related to the use of animal sources. The wide range of features covered by different plants offers a unique opportunity for the development of tissue-specific scaffolds, depending on the morphological, physical and mechanical peculiarities of each plant. Herein, three different plant tissues (i.e., apple, carrot, and celery) were decellularized and, according to their peculiar properties (i.e., porosity, mechanical properties), addressed to regeneration of adipose tissue, bone tissue and tendons, respectively. Decellularized apple, carrot and celery maintained their porous structure, with pores ranging from 70 to 420 μm, depending on the plant source, and were stable in PBS at 37°C up to 7 weeks. Different mechanical properties (i.e., Eapple = 4 kPa, Ecarrot = 43 kPa, Ecelery = 590 kPa) were measured and no indirect cytotoxic effects were demonstrated in vitro after plants decellularization. After coating with poly-L-lysine, apples supported 3T3-L1 preadipocytes adhesion, proliferation and adipogenic differentiation; carrots supported MC3T3-E1 pre-osteoblasts adhesion, proliferation and osteogenic differentiation; celery supported L929 cells adhesion, proliferation and guided anisotropic cells orientation. The versatile features of decellularized plant tissues and their potential for the regeneration of different tissues are proved in this work.

Development and Characterization of a Porcine Liver Scaffold

The growing number of patients requiring liver transplantation for chronic liver disease cannot be currently met due to a shortage in donor tissue. As such, alternative tissue engineering approaches combining the use of acellular biological scaffolds and different cell populations (hepatic or progenitor) are being explored to augment the demand for functional organs. Our goal was to produce a clinically relevant sized scaffold from a sustainable source within 24 h, while preserving the extracellular matrix (ECM) to facilitate cell repopulation at a later stage. Whole porcine livers underwent perfusion decellularization via the hepatic artery and hepatic portal vein using a combination of saponin, sodium deoxycholate, and deionized water washes resulting in an acellular scaffold with an intact vasculature and preserved ECM. Molecular and immunohistochemical analysis (collagen I and IV and laminin) showed complete removal of any DNA material, together with excellent retention of glycosaminoglycans and collagen. Fourier-transform infrared spectroscopy (FTIR) analysis showed both absence of nuclear material and removal of any detergent residue, which was successfully achieved after additional ethanol gradient washes. Samples of the decellularized scaffold were assessed for cytotoxicity by seeding with porcine adipose-derived mesenchymal stem cells in vitro, these cells over a 10-day period showed attachment and proliferation. Perfusion of the vascular tree with contrast media followed by computed tomography (CT) imaging showed an intact vascular network. In vivo implantation of whole intact nonseeded livers, into a porcine model (as auxiliary graft) showed uniform perfusion macroscopically and histologically. Using this method, it is possible to create an acellular, clinically sized, liver scaffold with intact vasculature in less than 24 h.

A Survival Model of In Vivo Partial Liver Lobe Decellularization Towards In Vivo Liver Engineering

In vivo liver decellularization has become a promising strategy to study in vivo liver engineering. However, long-term survival after in vivo liver decellularization has not yet been achieved due to anatomical and technical challenges. This study aimed at establishing a survival model of in vivo partial liver lobe perfusion-decellularization in rats. We compared three decellularization protocols (1% Triton X100 followed by 1% sodium dodecyl sulfate [SDS], 1% SDS vs. 1% Triton X100, n = 6/group). Using the optimal one as judged by macroscopy, histology and DNA content, we characterized the structural integrity and matrix proteins by using histology, scanning electron microscopy, computed tomography scanning, and immunohistochemistry (IHC). We prevented contamination of the abdominal cavity with the corrosive detergents by using polyvinylidene chloride (PVDC) film + dry gauze in comparison to PVDC film + dry gauze + aspiration tube (n = 6/group). Physiological reperfusion was assessed by histology. Survival rate was determined after a 7-day observation period. Only perfusion with 1% SDS resulted in an acellular scaffold (fully translucent without histologically detectable tissue remnants, DNA concentration is <2% of that in native lobe) with remarkable structural and ultrastructural integrity as well as preservation of main matrix proteins (IHC positive for collagen IV, laminin, and elastin). Contamination of abdominal organs with the potentially toxic SDS solution was achieved by placing a suction tube in addition to the PVDC film + dry gauze and allowed a 7-day survival of all animals without severe postoperative complications. On reperfusion, the liver turned red within seconds without any leakage from the surface of the liver. About 12 h after reperfusion, not only blood cells but also some clots were visible in the portal vein, sinusoidal matrix network, and central vein, suggesting physiological perfusion. In conclusion, our results of this study show the first available data on generation of a survival model of in vivo parenchymal organ decellularization, creating a critical step toward in vivo organ engineering. Impact Statement Recently, in vivo liver decellularization has been considered a promising approach to study in vivo liver repopulation of a scaffold compared with ex vivo liver repopulation. However, long-term survival of in vivo liver decellularization has not yet been achieved. Here, despite anatomical and technical challenges, we successfully created a survival model of in vivo selected liver lobe decellularization in rats, providing a major step toward in vivo organ engineering.

Biochemical and biomechanical comparisions of decellularized scaffolds derived from porcine subcutaneous and visceral adipose tissue

Decellularized adipose tissue (DAT) is a promising biomaterial for adipose tissue engineering. However, there is a lack of research of DAT prepared from xenogeneic porcine adipose tissue. This study aimed to compare the adipogenic ability of DAT derived from porcine subcutaneous (SDAT) and visceral adipose tissue (VDAT). The retention of key collagen in decellularized matrix was analysed to study the biochemical properties of SDAT and VDAT. For the biomechanical study, both DAT materials were fabricated into three-dimensional (3D) porous scaffolds for rheology and compressive tests. Human adipose-derived stem cells (ADSCs) were cultured on both scaffolds to further investigate the effect of matrix stiffness on cellular morphology and on adipogenic differentiation. ADSCs cultured on soft VDAT exhibited significantly reduced cellular area and upregulated adipogenic markers compared to those cultured on SDAT. In vivo results revealed higher adipose regeneration in the VDAT compared to the SDAT. This study further demonstrated that the relative expression of collagen IV and laminin was significantly higher in VDAT than in SDAT, while the collagen I expression and matrix stiffness of SDAT was significantly higher in comparison to VDAT. This result suggested that porcine adipose tissue could serve as a promising candidate for preparing DAT.

Bioengineering Liver Transplantation

Since the first in-man liver transplantation was performed by Starzl et al [...].

Fast, robust and effective decellularization of whole human livers using mild detergents and pressure controlled perfusion

Human whole-liver perfusion-decellularization is an emerging technique for producing bio-scaffolds for tissue engineering purposes. The native liver extracellular matrix (ECM) provides a superior microenvironment for hepatic cells in terms of adhesion, survival and function. However, current decellularization protocols show a high degree of variation in duration. More robust and effective protocols are required, before human decellularized liver ECM can be considered for tissue engineering applications. The aim of this study is to apply pressure-controlled perfusion and test the efficacy of two different detergents in porcine and human livers. To test this, porcine livers were decellularized using two different protocols; a triton-x-100 (Tx100)-only protocol (N = 3) and a protocol in which Tx100 was combined with SDS (N = 3) while maintaining constant pressure of 120 mm Hg. Human livers (N = 3) with different characteristics (age, weight and fat content) discarded for transplantation were decellularized using an adapted version of the Tx-100-only protocol. Decellularization efficacy was determined by histology and analysis of DNA and RNA content. Furthermore, the preservation of ECM components was assessed. After completing the perfusion cycles with detergents the porcine livers from both protocols were completely white and transparent in color. After additional washing steps with water and DNase, the livers were completely decellularized, as no DNA or cell remnants could be detected. The Tx100-only protocol retained 1.5 times more collagen and 2.5 times more sGAG than the livers decellularized with Tx100 + SDS. The Tx100-only protocol was subsequently adapted for decellularizing whole-organ human livers. The human livers decellularized with pressure-controlled perfusion became off-white in color and semi-transparent within 20 h. Livers decellularized without pressure-controlled perfusion took 64-96 h to completely decellularize, but did not become white or transparent. The addition of pressure-controlled flow did remove all cells and double stranded DNA, but did not damage the ultra-structure of the ECM as was analyzed by histology and scanning electron microscopy. In addition, collagens and sGAG were maintained with the decellularized ECM. In conclusion, we established effective, robust and fast decellularization protocols for both porcine and human livers. With this protocol the duration of decellularization for whole-organ human livers has been shortened considerably. The increased pressure and flow did not damage the ECM, as major ECM components remained intact.

Decellularized liver transplant could be recellularized in rat partial hepatectomy model

In situ recellularization of the liver decellularized scaffold is a potential therapeutic alternative for liver transplantation. We aimed to develop an in situ procedure for recellularization of the rat liver using sodium lauryl ether sulfate (SLES) compared with Triton X-100/SDS. Rat liver specimens were rinsed with PBS, decellularized with either Triton X-100/SDS or SLES, and finally rinsed by distilled water. The efficiency of decellularized liver scaffolds was evaluated by histological, confocal Raman microscopy, histochemical staining, and DNA quantification assessments. Finally, in vivo studies were done to assess the biocompatibility of the liver scaffold by serum biochemical parameters and the recellularization capacity by histological and immunohistochemistry staining. Findings confirmed the preservation of extracellular matrix (ECM) components such as reticular, collagen, glycosaminoglycans, and neutral carbohydrates in both Triton X-100/SDS- and SLES-treated livers. Hoechst, feulgen, Hematoxylin and eosin, and DNA quantification assessments confirmed complete genetic content removal. The serological parameters showed no adverse impact on the liver functions. Transplantation of SLES-treated cell-free decellularized liver showed extensive neovascularization along with migration of the fibrocytes and adipocytes and some immune cells. Also, immunohistochemical staining showed that the oval cells, stellate cells, cholangiocytes and hepatocytes invaded extensively into the graft. It is concluded that SLES can be considered as a promising alternative in the liver decellularization process, and the transplanted decellularized liver can appropriately be revascularized and regenerated.

Harnessing Human Decellularized Blood Vessel Matrices and Cellular Construct Implants to Promote Bone Healing in an Ex Vivo Organotypic Bone Defect Model

Decellularized matrices offer a beneficial substitute for biomimetic scaffolds in tissue engineering. The current study examines the potential of decellularized placental vessel sleeves (PVS) as a periosteal protective sleeve to enhance bone regeneration in embryonic day 18 chick femurs contained within the PVS and cultured organotypically over a 10 day period. The femurs are inserted into decellularized biocompatibility-tested PVS and maintained in an organotypic culture for a period of 10 days. In femurs containing decellularized PVS, a significant increase in bone volume (p < 0.001) is evident, demonstrated by microcomputed tomography (µCT) compared to femurs without PVS. Histological and immunohistological analyses reveal extensive integration of decellularized PVS with the bone periosteum, and enhanced conservation of bone architecture within the PVS. In addition, the expressions of hypoxia inducible factor-1 alpha (HIF-1α), type II collagen (COL-II), and proteoglycans are observed, indicating a possible repair mechanism via a cartilaginous stage of the bone tissue within the sleeve. The use of decellularized matrices like PVS offers a promising therapeutic strategy in surgical tissue replacement, promoting biocompatibility and architecture of the tissue as well as a factor-rich niche environment with negligible immunogenicity.

A novel bioscaffold with naturally-occurring extracellular matrix promotes hepatocyte survival and vessel patency in mouse models of heterologous transplantation

BACKGROUND

Naïve decellularized liver scaffold (nDLS)-based tissue engineering has been impaired by the lack of a suitable extracellular matrix (ECM) to provide "active micro-environmental" support.

AIM

The present study aimed to examine whether a novel, regenerative DLS (rDLS) with an active ECM improves primary hepatocyte survival and prevents thrombosis.

METHODS

rDLS was obtained from a 30-55% partial hepatectomy that was maintained in vivo for 3-5 days and then perfused with detergent in vitro. Compared to nDLS generated from normal livers, rDLS possesses bioactive molecules due to the regenerative period in vivo. Primary mouse hepatocyte survival was evaluated by staining for Ki-67 and Trypan blue exclusion. Thrombosis was assessed by immunohistochemistry and ex vivo diluted whole-blood perfusion. Hemocompatibility was determined by near-infrared laser-Doppler flowmetry and heterotopic transplantation.

RESULTS

After recellularization, rDLS contained more Ki-67-positive primary hepatocytes than nDLS. rDLS had a higher oxygen saturation and blood flow velocity and a lower expression of integrin αIIb and α4 than nDLS. Tumor necrosis factor-α, hepatocyte growth factor, interleukin-10, interleukin-6 and interleukin-1β were highly expressed throughout the rDLS, whereas expression of collagen-I, collagen-IV and thrombopoietin were lower in rDLS than in nDLS. Improved blood vessel patency was observed in rDLS both in vitro and in vivo. The results in mice were confirmed in large animals (pigs).

CONCLUSION

rDLS is an effective DLS with an "active microenvironment" that supports primary hepatocyte survival and promotes blood vessel patency. This is the first study to demonstrate a rDLS with a blood microvessel network that promotes hepatocyte survival and resists thrombosis.

Technology features of decellularization of human liver fragments as tissue-specific fine-grained matrix for cell-engineering liver construction

One of the problems when you create a bioengineered liver, as an alternative to transplantation of the donor liver in the treatment of end-stage liver failure, is the matrix, able to temporarily perform the functions of the natural extracellular matrix (ECM) and provide the necessary conditions to maintain the viability of the liver cells. The main disadvantage of resorbable biopolymer matrices is the absence of tissue specifi c properties and the impossibility of reproducing the unique structure of the ECM of the liver.

Aim:to develop technology for decellularization of liver tissue fragments, saving the structural properties of native ECM of the liver.

Materials and methods.The decellularization of mechanically grinded human liver fragments was carried out in three changes of buffer solution (pH = 7.4) containing 0.1% sodium dodecyl sulfate and increasing the concentration of Triton X100 (1%, 2% and 3%, respectively). During technology development were investigated the effects of duration, conditions (static, dynamic, rotary system, magnetic stirrer) washing and methods of liver tissue grinding on the completeness of removal of cellular elements and detritus preserving the the liver ECM structure. Slices of decellularized liver tissue samples were stained by hematoxylin and eosin, and Masson method for the detection of connective-tissue elements.

Results.Histological analysis methods showed that the best from the point of view of effi ciency of decellularization and the safety of the structure of own human liver ECM, is a mode of washing of liver fragments for three days at room temperature in static conditions, accompanied by stirring by a magnetic stirrer for 2–3 times a day for one hour. Longer time or a large multiplicity of mixing mode is accompanied by increased risk of liver tissue damage. On the basis of the experimental results obtained the algorithm of preliminary study of donor human liver designed to optimize the process of obtaining decellularization fragments of liver tissue was elaborated.

Conclusion.It was elaborated the algorithm and technology of obtaining of decellularized liver tissue fragments from the human donor liver which saved the structural properties of native ECM of the liver and complete removal of cellular elements and detritus. 

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.

Bio-scaffolds in organ-regeneration: Clinical potential and current challenges

Cadaveric organ transplantation represents the definitive treatment option for end-stage disease but is restricted by the shortage of clinically-viable donor organs. This limitation has, in part, driven current research efforts for in vitro generation of transplantable tissue surrogates. Recent advances in organ reconstruction have been facilitated by the re-purposing of decellularized whole organs to serve as three-dimensional bio-scaffolds. Notably, studies in rodents indicate that such scaffolds retain native extracellular matrix components that provide appropriate biochemical, mechanical and physical stimuli for successful tissue/organ reconstruction. As such, they support the migration, adhesion and differentiation of reseeded primary and/or pluripotent cell populations, which mature and achieve functionality through short-term conditioning within specialized tissue bioreactors. Whilst these findings are encouraging, significant challenges remain to up-scale the present technology to accommodate human-sized organs and thereby further the translation of this approach towards clinical use. Of note, the diverse structural and cellular composition of large mammalian organ systems mean that a "one-size fits all" approach cannot be adopted either to the methods used for their decellularization or the cells required for subsequent re-population, to create fully functional entities. The present review seeks to highlight the clinical potential of decellularized organ bio-scaffolds as a route to further advance the field of tissue- and organ-regeneration, and to discuss the challenges which are yet to be addressed if such a technology is ever to become a credible rival to conventional organ allo-transplantation.

Research progress in liver tissue engineering

Liver transplantation is the definitive treatment for patients with end-stage liver diseases (ESLD). However, it is hampered by shortage of liver donor. Liver tissue engineering, aiming at fabricating new livers in vitro, provides a potential resolution for donor shortage. Three elements need to be considered in liver tissue engineering: seeding cell resources, scaffolds and bioreactors. Studies have shown potential cell sources as hepatocytes, hepatic cell line, mesenchymal stem cells and others. They need scaffolds with perfect biocompatiblity, suitable micro-structure and appropriate degradation rate, which are essential charateristics for cell attachment, proliferation and secretion in forming extracellular matrix. The most promising scaffolds in research include decellularized whole liver, collagens and biocompatible plastic. The development and function of cells in scaffold need a microenvironment which can provide them with oxygen, nutrition, growth factors, et al. Bioreactor is expected to fulfill these requirements by mimicking the living condition in vivo. Although there is great progress in these three domains, a large gap stays still between their researches and applications. Herein, we summarized the recent development in these three major fields which are indispensable in liver tissue engineering.

Supercritical carbon dioxide extracted extracellular matrix material from adipose tissue

Adipose tissue is a rich source of extracellular matrix (ECM) material that can be isolated by delipidating and decellularizing the tissue. However, the current delipidation and decellularization methods either involve tedious and lengthy processes or require toxic chemicals, which may result in the elimination of vital proteins and growth factors found in the ECM. Hence, an alternative delipidation and decellularization method for adipose tissue was developed using supercritical carbon dioxide (SC-CO₂) that eliminates the need of any harsh chemicals and also reduces the amount of processing time required. The resultant SC-CO₂-treated ECM material showed an absence of nuclear content but the preservation of key proteins such as collagen Type I, collagen Type III, collagen Type IV, elastin, fibronectin and laminin. In addition, other biological factors such as glycosaminoglycans (GAGs) and growth factors such as basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) were also retained. Subsequently, the resulting SC-CO₂-treated ECM material was used as a bioactive coating on tissue culture plastic (TCP). Four different cell types including adipose tissue-derived mesenchymal stem cells (ASCs), human umbilical vein endothelial cells (HUVECs), immortalized human keratinocyte (HaCaT) cells and human monocytic leukemia cells (THP-1) were used in this study to show that the SC-CO₂-treated ECM coating can be potentially used for various biomedical applications. The SC-CO₂-treated ECM material showed improved cell-material interactions for all cell types tested. In addition, in vitro scratch wound assay using HaCaT cells showed that the presence of SC-CO₂-treated ECM material enhanced keratinocyte migration whilst the in vitro cellular studies using THP-1-derived macrophages showed that the SC-CO₂-treated ECM material did not evoke pro-inflammatory responses from the THP-1-derived macrophages. Overall, this study shows the efficacy of SC-CO₂ method for delipidation and decellularization of adipose tissue whilst retaining its ECM and its subsequent utilization as a bioactive surface coating material for soft tissue engineering, angiogenesis and wound healing applications.

Concise Review: Liver Regenerative Medicine: From Hepatocyte Transplantation to Bioartificial Livers and Bioengineered Grafts

Donor organ shortage is the main limitation to liver transplantation as a treatment for end-stage liver disease and acute liver failure. Liver regenerative medicine may in the future offer an alternative form of therapy for these diseases, be it through cell transplantation, bioartificial liver (BAL) devices, or bioengineered whole organ liver transplantation. All three strategies have shown promising results in the past decade. However, before they are incorporated into widespread clinical practice, the ideal cell type for each treatment modality must be found, and an adequate amount of metabolically active, functional cells must be able to be produced. Research is ongoing in hepatocyte expansion techniques, use of xenogeneic cells, and differentiation of stem cell-derived hepatocyte-like cells (HLCs). HLCs are a few steps away from clinical application, but may be very useful in individualized drug development and toxicity testing, as well as disease modeling. Finally, safety concerns including tumorigenicity and xenozoonosis must also be addressed before cell transplantation, BAL devices, and bioengineered livers occupy their clinical niche. This review aims to highlight the most recent advances and provide an updated view of the current state of affairs in the field of liver regenerative medicine. Stem Cells 2017;35:42-50.

Ambiguity in the Presentation of Decellularized Tissue Composition: The Need for Standardized Approaches

Decellularization offers great potential to the field of tissue engineering, as this method gives rise to scaffold material with the native organ architecture by removing all cellular material and leaving much of the extracellular matrix (ECM) intact. However, many parameters may affect decellularization efficacy and ECM retention and, therefore, decellularization protocols need to be optimized for specific needs. This requires robust methods for comparison of decellularized tissue composition. Various representation methods are used in literature to express tissue composition (DNA, glycosaminoglycans, collagen, other ECM proteins, and growth factors). Here, we present and compare the various methods used and demonstrate that normalization to either dry or wet decellularized weight might be misleading and may overestimate true component retention. Moreover, the magnitude of the confounding effect is likely to be decellularization treatment dependent. As a result, we propose alternative comparison strategies: normalization to whole organ or to a unit of whole initial organ weight. We believe proper assessment of decellularized tissue composition is paramount for the successful comparison of different decellularization protocols and clinical translation.

Nondestructive Methods for Monitoring Cell Removal During Rat Liver Decellularization

Whole liver engineering holds the promise to create transplantable liver grafts that may serve as substitutes for donor organs, addressing the donor shortage in liver transplantation. While decellularization and recellularization of livers in animal models have been successfully achieved, scale up to human livers has been slow. There are a number of donor human livers that are discarded because they are not found suitable for transplantation, but are available for engineering liver grafts. These livers are rejected due to a variety of reasons, which in turn may affect the decellularization outcome. Hence, a one-size-fit-for all decellularization protocol may not result in scaffolds with consistent matrix quality, subsequently influencing downstream recellularization and transplantation outcomes. There is a need for a noninvasive monitoring method to evaluate the extent of cell removal, while ensuring preservation of matrix components during decellularization. In this study, we decellularized rat livers using a protocol previously established by our group, and we monitored decellularization through traditional destructive techniques, including evaluation of DNA, collagen, and glycosaminoglycan (GAG) content in decellularized scaffolds, as well as histology. In addition, we used computed tomography and perfusate analysis as alternative nondestructive decellularization monitoring methods. We found that DNA removal correlates well with the Hounsfield unit of the liver, and perfusate analysis revealed that significant amount of GAG is removed during perfusion with 0.1% sodium dodecyl sulfate. This allowed for optimization of our decellularization protocol leading to scaffolds that have significantly higher GAG content, while maintaining appropriate removal of cellular contents. The significance of this is the creation of a nondestructive monitoring strategy that can be used for optimization of decellularization protocols for individual human livers available for liver engineering.

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.