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

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.

Hydrogel-Based Strategies for Liver Tissue Engineering

The liver's role in metabolism, detoxification, and immune regulation underscores the urgency of addressing liver diseases, which claim millions of lives annually. Due to donor shortages in liver transplantation, liver tissue engineering (LTE) offers a promising alternative. Hydrogels, with their biocompatibility and ability to mimic the liver's extracellular matrix (ECM), support cell survival and function in LTE. This review analyzes recent advances in hydrogel-based strategies for LTE, including decellularized liver tissue hydrogels, natural polymer-based hydrogels, and synthetic polymer-based hydrogels. These materials are ideal for in vitro cell culture and obtaining functional hepatocytes. Hydrogels' tunable properties facilitate creating artificial liver models, such as organoids, 3D bioprinting, and liver-on-a-chip technologies. These developments demonstrate hydrogels' versatility in advancing LTE's applications, including hepatotoxicity testing, liver tissue regeneration, and treating acute liver failure. This review highlights the transformative potential of hydrogels in LTE and their implications for future research and clinical practice.

Antithrombotic Revascularization Strategy of Bioengineered Liver Using a Biomimetic Polymer

A bioengineered liver has the potential to save patients with end-stage liver disease, and a three-dimensional decellularized scaffold is a promising approach for practical use. The main challenge in bioengineered liver transplantation is thrombogenicity during blood perfusion. We aimed to apply a novel antithrombotic polymer to revascularize liver scaffolds and evaluate the thrombogenicity and biosafety of the polymer-treated scaffolds. A biomimetic polymer, 2-metacryloyloxyethyl phosphorylcholine (MPC) was prepared for modification of the extracellular matrix in liver scaffolds. The polymer was injected into the rat liver scaffolds' portal vein and could extensively react to the vessel walls. In an ex vivo blood perfusion experiment, we demonstrated significantly less platelet deposition in the polymer-treated scaffolds than nontreated or re-endothelialized scaffolds with human umbilical vein endothelial cells. In the heterotopic transplantation model, liver volume was better maintained in the polymer-treated groups, and platelet deposition was suppressed in these groups. Additionally, the polymer-treated liver scaffolds maintained the metabolic function of the recellularized rat primary hepatocytes during perfusion culture. The MPC polymer treatment efficiently suppressed thrombus formation during blood perfusion in liver scaffolds and maintained the function of recellularized hepatocytes. Revascularizing liver scaffolds using this polymer is a promising approach for bioengineered liver transplantation.

Bio-Artificial Liver Support System: A Prospective Future Therapy

Whether acute or chronic, liver failure is a state of liver dysfunction that can progress to multiorgan failure. Mortality in liver failure patients is approximately 80–90% and is caused by detoxification failure, which triggers other immediate complications, such as encephalopathy, coagulopathy, jaundice, cholestasis, and acute kidney failure. The ideal treatment for liver failure is liver transplantation, but the long waiting period for the right donor match causes unavoidable deaths in most patients. Therefore, new therapies, such as tissue engineering, hepatocyte transplantation, and stem cells, are now being studied to anticipate the patient’s condition while waiting for liver transplantation. This literature review investigated the effectiveness of some bio-artificial liver support systems using review methods systematically from international publication sites, including PubMed, using keywords, such as bio-artificial liver, acute and chronic liver failure, extracorporeal liver support system (ECLS), MARS, single-pass albumin dialysis (SPAD). Artificial and bioartificial liver systems can show specific detoxification abilities and pathophysiological improvements in liver failure patients but cannot reach the ideal criteria for actual liver function. The liver support system must provide the metabolic and synthetic function as in the actual liver while reducing the pathophysiological changes in liver failure. Aspects of safety, cost efficiency, and practicality are also considered. Identifying the technology to produce high-quality hepatocytes on a big scale is essential as a medium to replace failing liver cells. An increase in detoxification capacity and therapeutic effectiveness must also focus on patient survival and the ability to perform liver transplantation.

Automated GMP Production and Preclinical Evaluation of [68Ga]Ga-TEoS-DAZA and [68Ga]Ga-TMoS-DAZA

[⁶⁸Ga]Ga-TEoS-DAZA and [⁶⁸Ga]Ga-TMoS-DAZA are two novel radiotracers suitable for functional PET liver imaging. Due to their specific liver uptake and biliary excretion, the tracers may be applied for segmental liver function quantification, gall tree imaging and the differential diagnosis of liver nodules. The purpose of this study was to investigate problems that occurred initially during the development of the GMP compliant synthesis procedure and to evaluate the tracers in a preclinical model. After low radiolabeling yields were attributed to precursor instability at high temperatures, an optimized radiolabeling procedure was established. Quality controls were in accordance with Ph. Eur. requirements and gave compliant results, although the method for the determination of the ⁶⁸Ga colloid is partially inhibited due to the presence of a radioactive by-product. The determination of logP revealed [⁶⁸Ga]Ga-TEoS-DAZA (ethoxy bearing) to be more lipophilic than [⁶⁸Ga]Ga-TMoS-DAZA (methoxy bearing). Accordingly, biodistribution studies in an in ovo model showed a higher liver uptake for [⁶⁸Ga]Ga-TEoS-DAZA. In dynamic in ovo PET imaging, rapid tracer accumulation in the liver was observed. Similarly, the activity in the intestines rose steadily within the first hour p.i., indicating biliary excretion. As [⁶⁸Ga]Ga-TEoS-DAZA and [⁶⁸Ga]Ga-TMoS-DAZA can be prepared according to GMP guidelines, transition into the early clinical phase is now possible.

Re-Endothelialization of Decellularized Liver Scaffolds: A Step for Bioengineered Liver Transplantation

Bioengineered livers (BELs) are an attractive therapeutic alternative to address the donor organ shortage for liver transplantation. The goal of BELs technology aims at replacement or regeneration of the native human liver. A variety of approaches have been proposed for tissue engineering of transplantable livers; the current review will highlight the decellularization-recellularization approach to BELs. For example, vascular patency and appropriate cell distribution and expansion are critical components in the production of successful BELs. Proper solutions to these components of BELs have challenged its development. Several strategies, such as heparin immobilization, heparin-gelatin, REDV peptide, and anti-CD31 aptamer have been developed to extend the vascular patency of revascularized bioengineered livers (rBELs). Other novel methods have been developed to enhance cell seeding of parenchymal cells and to increase graft functionality during both bench and in vivo perfusion. These enhanced methods have been associated with up to 15 days of survival in large animal (porcine) models of heterotopic transplantation but have not yet permitted extended survival after implantation of BELs in the orthotopic position. This review will highlight both the remaining challenges and the potential for clinical application of functional bioengineered grafts.

Liver scaffolds obtained by decellularization: A transplant perspective in liver bioengineering

Liver transplantation is the only definitive treatment for many diseases that affect this organ, however, its quantity and viability are reduced. The study of liver scaffolds based on an extracellular matrix is a tissue bioengineering strategy with great application in regenerative medicine. Collectively, recent studies suggest that liver scaffold transplantation may assist in reestablishing hepatic function in preclinical diseased animals, which represents a great potential for application as a treatment for patients with liver disease in the future. This review focuses on useful strategies to promote liver scaffold transplantation and the main open questions about this context. We outline the current knowledge about ex vivo bioengineered liver transplantation, including the surgical techniques, recipient survival time, scaffold preparation before transplantation, and liver disease models. We also highlight the current limitations and future directions regarding in vivo bioengineering techniques.

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.

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.

Surgical Models to Explore Acellular Liver Scaffold Transplantation: Step-by-Step

Acellular liver scaffolds (ALS) have arisen as potential candidates for transplantation. Until now, all reports involving ALS transplantation failed in surgical method descriptions and do not offer support to scientists to reproduce the procedures used in experimental microsurgery to make the results comparable to literature. To overcome the lack of detail information, we described surgical steps details to perform heterotopic and partial orthotopic surgical models to promote ALS transplantation. After preservation and vessel cannulation steps, the liver grafts were decellularized. In addition, ex vivo blood perfusion tests were performed to obtain a successful anticoagulation treatment prior in vivo transplantation. Then, methods of partial liver resection, combination of hand-suture and cuff techniques to complete end-to-end anastomosis between the scaffold and the recipient animal were performed. These procedures which take 30-60 min and were efficient to allow acellular liver scaffold viability and recellularization of different types of cell post-surgery. In conclusion, our methods are practical and simple promising approach that provides the opportunity to investigate ways to achieve sufficient liver function post-transplantation in vivo.