Vascularized subcutaneous human liver tissue from engineered hepatocyte/fibroblast sheets in mice

Construction of highly vascularized hepatic spheroids of primary hepatocytes via pro-angiogenic strategyin vitro

Primary hepatocytes are widely recognized for their ability to accurately represent thein vivohepatocyte phenotype. However, traditional avascular primary hepatocyte culture models are limited by inadequate mass transfer, which leads to a rapid decline in hepatocyte function and survival. To address these challenges, vascularization of hepatic spheroids is crucial for enhancing oxygen and nutrient supply, thereby enabling the construction of larger and more complex hepatic tissuesin vitro. In this study, we achieved vascularization of hepatic spheroids containing freshly isolated primary hepatocytes by incorporating fibroblasts as a source of paracrine factors to induce angiogenesis. Multicellular spheroids composed of primary hepatocytes and fibroblasts were formed in non-adhesive concave wells, and one of the spheroids was subsequently embedded in a fibrin-collagen hydrogel within a microfluidic device. Endothelial cells were then seeded onto adjacent microfluidic channels. They formed microvascular networks that extended toward and penetrated the hepatic spheroid. The vascularized hepatic spheroid closely mimicked hepatic sinusoids, with hepatocytes in close contact with microvessels. Moreover, the vascularized spheroid exhibited significantly enhanced hepatic function, specifically albumin secretion and urea synthesis. Our findings provide insights into the establishment of highly vascularized hepatic spheroidsin vitro, which is crucial for constructing scalable hepatic tissues in the context of biofabrication.

3D printing incorporating gold nanozymes with mesenchymal stem cell-derived hepatic spheroids for acute liver failure treatment

Acute liver failure (ALF) is a highly fatal disease, necessitating the advancement and optimization of alternative therapeutic strategies to benefit patients awaiting liver transplantation. In this study, we innovatively established the antioxidant nanozyme-hepatocyte-like cells (HLCs) microtissue sheets (HS/N-Au@composite) for ALF therapy. We first prepared a 3D-printed hyaluronic acid/gelatin/sodium alginate scaffold with N-acetylcysteine (NAC)-capped gold nanoclusters (NAC-Au NCs), forming the N-Au@hydrogel. For the encapsulation of HLC spheroids, we used a biocompatible hybrid hydrogel composed of decellularized extracellular matrix (dECM), thrombin, and fibrinogen, resulting in the HS@dECM hydrogel. Utilizing 3D printing technology, we integrated the N-Au@hydrogel with the HS@dECM hydrogel to create the HS/N-Au@composite for in situ transplantation to treat ALF. Our results demonstrated that NAC-Au NCs effectively mitigated reactive oxygen species (ROS)-induced liver necrosis in ALF. Additionally, the N-Au@hydrogel provided mechanical support, ensuring the proper landing and effective functioning of the transplanted HLC spheroids. The HS/N-Au@composite synergistically decreased serum transaminase levels, reduced the accumulation of pro-inflammatory cytokines, accelerated liver function recovery, and promoted liver regeneration in ALF treatment. This combination of HLC spheroids and NAC-Au NCs nanozymes via 3D-printed composite scaffolds represents a promising strategy for enhancing hepatocyte transplantation and advancing stem cell regenerative medicine in ALF therapy.

Bioengineering vascularized liver tissue for biomedical research and application

The liver performs a wide range of biological functions that are essential to body homeostasis. Damage to liver tissue can result in reduced organ function, and if chronic in nature can lead to organ scarring and progressive disease. Currently, donor liver transplantation is the only longterm treatment for end-stage liver disease. However, orthotopic organ transplantation suffers from several drawbacks that include organ scarcity and lifelong immunosuppression. Therefore, new therapeutic strategies are required. One promising strategy is the engineering of implantable and vascularized liver tissue. This resource could also be used to build the next generation of liver tissue models to better understand human health, disease and aging in vitro. This article reviews recent progress in the field of liver tissue bioengineering, including microfluidic-based systems, bio-printed vascularized tissue, liver spheroids and organoid models, and the induction of angiogenesis in vivo.

Recent Advances in Alginate-Based Hydrogels for Cell Transplantation Applications

With its exceptional biocompatibility, alginate emerged as a highly promising biomaterial for a large range of applications in regenerative medicine. Whether in the form of microparticles, injectable hydrogels, rigid scaffolds, or bioinks, alginate provides a versatile platform for encapsulating cells and fostering an optimal environment to enhance cell viability. This review aims to highlight recent studies utilizing alginate in diverse formulations for cell transplantation, offering insights into its efficacy in treating various diseases and injuries within the field of regenerative medicine.

bFGF-releasing biodegradable nanoparticles for effectively engrafting transplanted hepatocyte sheet

Hepatic tissue engineering has been applied for the treatment of intractable liver diseases, and hepatocyte sheets are promising for this purpose. However, hepatocyte sheets have poor survival after transplantation because of their high metabolic activity. In this study, we aimed to develop basic fibroblast growth factor (bFGF)-releasing nanoparticles to prolong the survival of hepatocyte sheets after transplantation. The nanoparticles were prepared by electrospraying a bFGF-dispersed poly(D,l-lactide-co-glycolide) emulsion. bFGF-loaded PLGA nanoparticles can be developed by optimizing the applied electrospray voltage and the oil:water ratio of the emulsion. The prepared nanoparticles exhibited prompt release at the initial duration and continuous gradual release at the subsequent duration. Hepatocyte sheet engraftment was evaluated by transplanting hepatocyte sheets containing the prepared nanoparticles into rats. The hepatocyte sheets with the prepared nanoparticles exhibited longer survival than those without the bFGF nanoparticles or solution owing to the local and continuous release of bFGF from the nanoparticles and the subsequent enhanced angiogenesis at the transplantation site. These results indicated that the prepared bFGF-releasing nanoparticles can enhance the efficiency of hepatocyte sheet transplantation. The developed bFGF-releasing nanoparticles would be useful for the transplantation of cellular tissue with post-transplantation survival challenges.

Three Dimensional Bioprinting for Hepatic Tissue Engineering: From In Vitro Models to Clinical Applications

Fabrication of functional organs is the holy grail of tissue engineering and the possibilities of repairing a partial or complete liver to treat chronic liver disorders are discussed in this review. Liver is the largest gland in the human body and plays a responsible role in majority of metabolic function and processes. Chronic liver disease is one of the leading causes of death globally and the current treatment strategy of organ transplantation holds its own demerits. Hence there is a need to develop an in vitro liver model that mimics the native microenvironment. The developed model should be a reliable to understand the pathogenesis, screen drugs and assist to repair and replace the damaged liver. The three-dimensional bioprinting is a promising technology that recreates in vivo alike in vitro model for transplantation, which is the goal of tissue engineers. The technology has great potential due to its precise control and its ability to homogeneously distribute cells on all layers in a complex structure. This review gives an overview of liver tissue engineering with a special focus on 3D bioprinting and bioinks for liver disease modelling and drug screening.

Reproducible Preparation of Primary Rat Hepatocyte Sheets Using a Thermoresponsive Culture Dish

Hepatocyte transplantation has been utilized as a therapy for congenital metabolic liver diseases such as hemophilia and for liver function support in acute liver failure. Hepatocyte sheet technology using a thermoresponsive poly(N-isopropylacrylamide) (PIPAAm)-grafted dish is expected to provide an efficient cell transplantation method because the resulting hepatocyte sheet possesses extracellular matrix (ECM) on the basal surface, which enhances attachment to the target sites. However, the cultured hepatocytes consume large amounts of oxygen, leading to the loss of a few hepatocytes within the confluent culture sheet owing to a lack of oxygen. To circumvent this problem, this work demonstrates the shortening of diffusion distance, that is, the medium depth, to accelerate oxygen supply from the gas phase/medium interface to the cultured hepatocytes, allowing them to form a monolayer hepatocyte sheet. Incubation of hepatocytes with medium at a depth of 1.3 mm facilitates confluent culture of hepatocytes for 72 h, whereas viable hepatocytes decreased at 2.6 mm depth. Hepatocyte sheets are formed on a 0.5 μg/cm2 fibronectin-physisorbed PIPAAm-grafted dish during 72 h incubation at 37°C. Detachment of the cultured hepatocyte sheet from the PIPAAm-grafted dish where the surface becomes hydrophilic at 20°C is accomplished by scraping the periphery of the sheet using a cell scraper. Furthermore, the apical side of the hepatocyte sheet can be physically grabbed using a gelatin-coated membrane, and the sheet with ECM on the basal surface can be readily transferred to the target site after melting the coated gelatin at 37°C. Both methods are beneficial for creating tissue models by layering with another type of cell sheets, and for quick transplantation, such as into the subcutaneous space and orthotopic transplantation on the surface of the liver.

The preclinical and clinical progress of cell sheet engineering in regenerative medicine

Cell therapy is an accessible method for curing damaged organs or tissues. Yet, this approach is limited by the delivery efficiency of cell suspension injection. Over recent years, biological scaffolds have emerged as carriers of delivering therapeutic cells to the target sites. Although they can be regarded as revolutionary research output and promote the development of tissue engineering, the defect of biological scaffolds in repairing cell-dense tissues is apparent. Cell sheet engineering (CSE) is a novel technique that supports enzyme-free cell detachment in the shape of a sheet-like structure. Compared with the traditional method of enzymatic digestion, products harvested by this technique retain extracellular matrix (ECM) secreted by cells as well as cell-matrix and intercellular junctions established during in vitro culture. Herein, we discussed the current status and recent progress of CSE in basic research and clinical application by reviewing relevant articles that have been published, hoping to provide a reference for the development of CSE in the field of stem cells and regenerative medicine.

Transfer-Tattoo-Like Cell-Sheet Delivery Induced by Interfacial Cell Migration

A direct transfer of a cell sheet from a culture surface to a target tissue is introduced. Commercially available, flexible parylene is used as the culture surface, and it is proposed that the UV-treated parylene offers adequate and intermediate levels of cell adhesiveness for both the stable cell attachment during culture and for the efficient cell transfer to a target surface. The versatility of this cell-transfer process is demonstrated with various cell types, including MRC-5, HDFn, HULEC-5a, MC3T3-E1, A549, C2C12 cells, and MDCK-II cells. The novel cell-sheet engineering is based on a mechanism of interfacial cell migration between two surfaces with different adhesion preferences. Monitoring of cytoskeletal dynamics and drug treatments during the cell-transfer process reveals that the interfacial cell migration occurs by utilizing the existing transmembrane proteins on the cell surface to bind to the targeted surface. The re-establishment and reversal of cell polarity after the transfer process are also identified. Its unique capabilities of 3D multilayer stacking, freeform design, and curved surface application are demonstrated. Finally, the therapeutic potential of the cell-sheet delivery system is demonstrated by applying it to cutaneous wound healing and skin-tissue regeneration in mice models.

The tendon microenvironment: Engineered in vitro models to study cellular crosstalk

Tendinopathy is a multi-faceted pathology characterized by alterations in tendon microstructure, cellularity and collagen composition. Challenged by the possibility of regenerating pathological or ruptured tendons, the healing mechanisms of this tissue have been widely researched over the past decades. However, so far, most of the cellular players and processes influencing tendon repair remain unknown, which emphasizes the need for developing relevant in vitro models enabling to study the complex multicellular crosstalk occurring in tendon microenvironments. In this review, we critically discuss the insights on the interaction between tenocytes and the other tendon resident cells that have been devised through different types of existing in vitro models. Building on the generated knowledge, we stress the need for advanced models able to mimic the hierarchical architecture, cellularity and physiological signaling of tendon niche under dynamic culture conditions, along with the recreation of the integrated gradients of its tissue interfaces. In a forward-looking vision of the field, we discuss how the convergence of multiple bioengineering technologies can be leveraged as potential platforms to develop the next generation of relevant in vitro models that can contribute for a deeper fundamental knowledge to develop more effective treatments.

Long-term culture of rat hepatocytes using human amniotic membrane as a culture substrate

Amniotic membrane is attracting attention as a new material for regenerative medicine. We herein report that the culture of primary rat hepatocytes on human amniotic membrane maintained their morphology and their production of albumin for at least two months. Human amniotic membrane was collected during planned cesarean section and kept frozen until usage. Primary rat hepatocytes were plated on human amniotic membrane. Hepatocytes accumulated as colonies on amniotic membrane, and their rat albumin level was maintained for two months. Their three-dimensional structure on extracellular matrix, which is abundant in amniotic membranes might influence the maintenance of the hepatocyte-specific function.

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Long-term primary culture of rat hepatocyte on the human amniotic membrane was successful.

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Albumin production from primary isolated hepatocytes was maintained for the long term.

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Amniotic membrane provided the situation of 3D structure for isolated rat hepatocyte.

Bioengineering of a CLiP-derived tubular biliary-duct-like structure for bile transport in vitro

The integration of a bile drainage structure into engineered liver tissues is an important issue in the advancement of liver regenerative medicine. Primary biliary cells, which play a vital role in bile metabolite accumulation, are challenging to obtain in vitro because of their low density in the liver. In contrast, large amounts of purified hepatocytes can be easily acquired from rodents. The in vitro chemically induced liver progenitors (CLiPs) from primary mature hepatocytes offer a platform to produce biliary cells abundantly. Here, we generated a functional CLiP-derived tubular bile duct-like structure using the chemical conversion technology. We obtained an integrated tubule-hepatocyte tissue via the direct coculture of hepatocytes on the established tubular biliary-duct-like structure. This integrated tubule-hepatocyte tissue was able to transport the bile, as quantified by the cholyl-lysyl-fluorescein assay, which was not observed in the un-cocultured structure or in the biliary cell monolayer. Furthermore, this in vitro integrated tubule-hepatocyte tissue exhibited an upregulation of hepatic marker genes. Together, these findings demonstrated the efficiency of the CLiP-derived tubular biliary-duct-like structures regarding the accumulation and transport of bile.

Functional changes of cocultured hepatocyte sheets subjected to continuous liver regeneration stimulation in cDNA-uPA/SCID mouse: Differences in transplantation sites

Aim

The formation of a secondary liver is expected in ectopic transplants in liver therapy. It is reported that the transplantation of hepatocyte sheets constitutes one of the techniques used to form a secondary liver. Accordingly, we established a subcutaneous transplant for hepatocyte/fibroblast sheets in previous studies. In this development study with hepatocyte/fibroblast sheets, we evaluated the differences in transplantation sites to promote the maturation of transplanted tissue in a liver injury model.

Methods

A cocultured hepatocyte sheet of fibroblasts (TIG-118 cells) and human hepatocytes (PXB cells) was prepared on a temperature-responsive culture dish. The prepared cocultured hepatocyte sheet was either transplanted subcutaneously or on the liver surface of a persistent liver injury model (cDNA-uPA/SCID mouse: uPA mouse), and was evaluated by the human albumin concentration in mouse blood. As a control group, hepatocyte cell sheets were used that were transplanted to both areas and compared.

Results

Although the cocultured hepatocyte sheet led to functional improvements in the early stages of culture in subcutaneous transplantation, these did not last in the long-term after transplantation. Although coculture effects were not observed in the liver surface transplantation case, long-term functional expressions in mono- and cocultured sheets in the case of liver surface transplantation were exhibited compared with subcutaneous administration.

Conclusion

These results suggest that sustained stimulation of liver regenerationvaries depending on the transplant site and is largely involved in the maturation of hepatocyte tissue.

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.

Chemical conversion of aged hepatocytes into bipotent liver progenitor cells

AIM

In the aging society, understanding the influence of hepatocyte age on hepatocyte donation may inform efforts to expand alternative cell sources to mitigate liver donor shortage. A combination of the molecules Y27632, A-83-01, and CHIR99021 has been used to reprogram rodent young hepatocytes into chemically induced liver progenitor (CLiP) cells; however, whether it could also reprogram aged hepatocytes has not yet been elucidated.

METHODS

Primary hepatocytes were isolated from aged and young donor rats, respectively. Hepatic histological changes were evaluated. Differences in gene expression in hepatocytes were identified. The in vitro reprogramming plasticity of hepatocytes as evidenced by CLiP conversion and the hepatocyte and cholangiocyte maturation capacity of reprogrammed CLIPs were analyzed. The effect of hepatocyte growth factor (HGF) on cell propagation was also investigated.

RESULTS

The histological findings revealed ongoing liver damage with inflammation, fibrosis, senescence, and ductular reaction in aged livers. Microarray analysis showed altered gene expression profiles in hepatocytes from aged donors, especially with regard to metabolic pathways. Aged hepatocytes could be converted into CLiPs (Aged-CLiPs) expressing progenitor cell markers, but with a relatively low proliferative rate compared with young hepatocytes. Aged-CLiPs possessed both hepatocyte and cholangiocyte maturation capacity. HGF facilitated CLiP conversion in aged hepatocytes, which was partly related to the activation of Erk1 and Akt1 signaling.

CONCLUSIONS

Aged rat hepatocytes have retained reprogramming plasticity as evidenced by CLiP conversion in culture. HGF promoted proliferation and CLiP conversion in aged hepatocytes. Hepatocytes from aged donors may be used as an alternative cell source to mitigate donor shortage.

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.

Fundamental Technologies and Recent Advances of Cell-Sheet-Based Tissue Engineering

Tissue engineering has attracted significant attention since the 1980s, and the applications of tissue engineering have been expanding. To produce a cell-dense tissue, cell sheet technology has been studied as a promising strategy. Fundamental techniques involving tissue engineering are mainly introduced in this review. First, the technologies to fabricate a cell sheet were reviewed. Although temperature-responsive polymer-based technique was a trigger to establish and spread cell sheet technology, other methodologies for cell sheet fabrication have also been reported. Second, the methods to improve the function of the cell sheet were investigated. Adding electrical and mechanical stimulation on muscle-type cells, building 3D structures, and co-culturing with other cell species can be possible strategies for imitating the physiological situation under in vitro conditions, resulting in improved functions. Finally, culture methods to promote vasculogenesis in the layered cell sheets were introduced with in vivo, ex vivo, and in vitro bioreactors. We believe the present review that shows and compares the fundamental technologies and recent advances for cell-sheet-based tissue engineering should promote further development of tissue engineering. The development of cell sheet technology should promote many bioengineering applications.

Regenerative medicine for the hepatobiliary system: A review

Liver transplantation, the only proven treatment for end-stage liver disease and acute liver failure, is hampered by the scarcity of donors. Regenerative medicine provides an alternative therapeutic approach. Tremendous efforts dedicated to liver regenerative medicine include the delivery of transplantable cells, microtissues, and bioengineered whole livers via tissue engineering and the maintenance of partial liver function via extracorporeal support. This brief review summarizes the current status of regenerative medicine for the hepatobiliary system. For liver regenerative medicine, the focus is on strategies for expansion of transplantable hepatocytes, generation of hepatocyte-like cells, and therapeutic potential of engineered tissues in liver disease models. For biliary regenerative medicine, the discussion concentrates on the methods for generation of cholangiocyte-like cells and strategies in the treatment of biliary disease. Significant advances have been made in large-scale and long-term expansion of liver cells. The development of tissue engineering and stem cell induction technology holds great promise for the future treatment of hepatobiliary diseases. The application of regenerative medicine in liver still lacks extensive animal experiments. Therefore, a large number of preclinical studies are necessary to provide sufficient evidence for their therapeutic effectiveness. Much remains to be done for the treatment of hepatobiliary diseases with regenerative medicine.

Regenerative medicine for the upper gastrointestinal tract

The main surgical strategy for gastrointestinal tract malignancy is en bloc resection, which consists of not only resection of the involved organs but also simultaneous resection of the surrounding or adjacent mesenteries that contain lymph vessels and nodes. After resection of the diseased organs, the defect of the gastrointestinal conduit is replaced with organs located downstream, such as the stomach and jejunum. However, esophageal and gastric reconstruction using these natural substitutes is associated with a diminished quality of life due to the loss of the reserve function, damage to the antireflux barrier, and dumping syndrome. Thus, replacement of the deficit after resection with the patient's own regenerated tissue to compensate for the lost function and tissue using regenerative medicine will be an ideal treatment. Many researchers have been trying to construct artificial organs through tissue engineering techniques; however, none have yet succeeded in growing a whole organ because of the complicated functions these organs perform, such as the processing and absorption of nutrients. While exciting results have been reported with regard to tissue engineering techniques concerning the upper gastrointestinal tract, such as the esophagus and stomach, most of these achievements have been observed in animal models, and few successful approaches in the clinical setting have been reported for the replacement of mucosal defects. We review the recent progress in regenerative medicine in relation to the upper gastrointestinal tract, such as the esophagus and stomach. We also focus on the functional capacity of regenerated tissue and its role as a culture system to recapitulate the mechanisms underlying infectious disease. With the emergence of technology such as the fabrication of decellularized constructs, organoids and cell sheet medicine, collaboration between gastrointestinal surgery and regenerative medicine is expected to help establish novel therapeutic modalities in the future.

Engineered Liver Tissue Culture in an In Vitro Tubular Perfusion System

Liver disease and the subsequent loss of liver function is an enormous clinical challenge. A severe shortage of donor liver tissue greatly limits patients' options for a timely transplantation. Tissue engineering approaches offer a promising alternative to organ transplantation by engineering artificial implantable tissues. We have established a platform of cell-laden microbeads as basic building blocks to assemble macroscopic tissues via different mechanisms. This modular fabrication strategy possesses great potential for liver tissue engineering in a bottom-up manner. In this study, we encapsulated human hepatocytes into microbeads presenting a favorable microenvironment consisting of collagen and mesenchymal stem cells, and then we perfused the beads in a three-dimensional printed tubular perfusion bioreactor that promoted oxygen and medium diffusion to the impregnated cells. We noted high cell vitality and retention of parenchymal cell functionality for up to 30 days in this culture system. Our engineering-based approach led to the advancement in tissue size and long-term functionality of an artificial liver tissue in vitro.

Engineering liver microtissues for disease modeling and regenerative medicine

The burden of liver diseases is increasing worldwide, accounting for two million deaths annually. In the past decade, tremendous progress has been made in the basic and translational research of liver tissue engineering. Liver microtissues are small, three-dimensional hepatocyte cultures that recapitulate liver physiology and have been used in biomedical research and regenerative medicine. This review summarizes recent advances, challenges, and future directions in liver microtissue research. Cellular engineering approaches are used to sustain primary hepatocytes or produce hepatocytes derived from pluripotent stem cells and other adult tissues. Three-dimensional microtissues are generated by scaffold-free assembly or scaffold-assisted methods such as macroencapsulation, droplet microfluidics, and bioprinting. Optimization of the hepatic microenvironment entails incorporating the appropriate cell composition for enhanced cell-cell interactions and niche-specific signals, and creating scaffolds with desired chemical, mechanical and physical properties. Perfusion-based culture systems such as bioreactors and microfluidic systems are used to achieve efficient exchange of nutrients and soluble factors. Taken together, systematic optimization of liver microtissues is a multidisciplinary effort focused on creating liver cultures and on-chip models with greater structural complexity and physiological relevance for use in liver disease research, therapeutic development, and regenerative medicine.

3D Culture System for Liver Tissue Mimicking Hepatic Plates for Improvement of Human Hepatocyte (C3A) Function and Polarity

In vitro 3D hepatocyte culture constitutes a core aspect of liver tissue engineering. However, conventional 3D cultures are unable to maintain hepatocyte polarity, functional phenotype, or viability. Here, we employed microfluidic chip technology combined with natural alginate hydrogels to construct 3D liver tissues mimicking hepatic plates. We comprehensively evaluated cultured hepatocyte viability, function, and polarity. Transcriptome sequencing was used to analyze changes in hepatocyte polarity pathways. The data indicate that, as culture duration increases, the viability, function, polarity, mRNA expression, and ultrastructure of the hepatic plate mimetic 3D hepatocytes are enhanced. Furthermore, hepatic plate mimetic 3D cultures can promote changes in the bile secretion pathway via effector mechanisms associated with nuclear receptors, bile uptake, and efflux transporters. This study provides a scientific basis and strong evidence for the physiological structures of bionic livers prepared using 3D cultures. The systems and cultured liver tissues described here may serve as a better in vitro 3D culture platform and basic unit for varied applications, including drug development, hepatocyte polarity research, bioartificial liver bioreactor design, and tissue and organ construction for liver tissue engineering or cholestatic liver injury.

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.

Generation of Transplantable Three-Dimensional Hepatic-Patch to Improve the Functionality of Hepatic Cells In Vitro and In Vivo

Cell therapy and tissue engineering (TE) are considered alternative therapeutic approaches to organ transplantation. Since cell therapy approaches achieved little success for liver failure treatment, liver TE is considered a more promising alternative. In this study, we produced a liver tissue equivalent (called "liver-derived extracellular matrix scaffold [LEMS]-Patch") by co-culture of human bone marrow stromal cells, human umbilical vein endothelial cells, and a hepatoma cell line, Huh7, within an artificial three-dimensional liver-extracellular matrix scaffold. The results showed significant increase in the liver-specific gene expression and hepatic functions, in terms of albumin (ALB) and fibrinogen secretion, urea production, and cytochrome inducibility in the LEMS-Patch compared to controls. In addition, transplanted LEMS-Patch was successfully incorporated into the recipient liver of acute liver failure mice and produced human ALB. Consequently, our data demonstrated that the generated LEMS-Patch could be used as a good platform for functional improvement of hepatic cells in vitro and in vivo.

Liver Tissue Engineering as an Emerging Alternative for Liver Disease Treatment

Chronic liver diseases affect thousands of lives throughout the world every year. The shortage of liver donors for transplantation has been the main driving force to employ alternative methods such as liver tissue engineering (LTE) in fabricating a three-dimensional transplantable liver tissue or enhancing cell delivery techniques alleviating the need for liver donors. LTE consists of three components, cells, ECM (extracellular matrix), and signaling molecules, which we discuss the first and second. The three most common cell sources used in LTE are human and animal primary hepatocytes, and stem cells for different applications. Two major categories of ECM are used to mimic the microenvironment of these cells, named scaffolds and microbeads. Scaffolds have been made by numerous methods with a wide range of synthetic and natural biomaterials. Cell encapsulation has also been utilized by many polymeric biomaterials. To investigate their functions, many properties have been discussed in the literature, such as biochemical, geometrical, and mechanical properties, in both of these categories. Overall, LTE shows excellent potential in assisting hepatic disorders. However, some challenges exist that prevent the practical use of it clinically, making LTE an ongoing research subject in the scientific society.

Hepatitis C Virus Improves Human Tregs Suppressive Function and Promotes Their Recruitment to the Liver

Background: The role of regulatory T cells (Tregs) is now well established in the progression of hepatocellular carcinoma (HCC) linked to Hepatitis C virus (HCV) infection. However, nothing is known about the potential interplay between Tregs and HCV. In this pilot study, we have investigated the ability of Tregs to hang HCV on and the subsequent effect on their suppressive function and phenotype. Moreover, we have evaluated how HCV could promote the recruitment of Tregs by infected primary human hepatocytes. Methods: Tregs of healthy donors were incubated with JFH-1/HCVcc. Viral inoculation was assessed using adapted assays (RT-qPCR, Flow Citometry (FACS) and Western Blot (WB). Expression of Tregs phenotypic (CD4, CD25, CD127 and Foxp3) and functional (IL-10, GZMB, TGF-β1 and IL-2) markers was monitored by RT-qPCR, FACS and ELISA. Suppressive activity was validated by suppressive assays. Tregs recruitment by infected primary hepatic cells was evaluated using Boyden Chamber. Results: Tregs express the classical HCV receptors (CD81, CLDN1 and LDLR) and some co-receptors (CD5). HCV inoculation significantly increases the suppressive phenotype and activity of Tregs, and raises their anergy by inducing an unexpected IL-2 production. Moreover, HCV infection induces the expression of chemokines (CCL17, CXCL16, and CCL20) by primary hepatic human hepatocytes and chemokine receptors (CCR4, CXCR6 and CCR6) by Tregs. Finally, infected hepatocytes have a significantly higher potential to recruit Tregs in a seemingly CCL20-dependent manner. Conclusions: Direct interaction between HCV and Tregs represents a newly defined mechanism that could potentiate HCV immune evasion and favor intratumoral recruitment contributing to HCC progression.

In Vitro Production of Human Ballooned Hepatocytes in a Cell Sheet-based Three-dimensional Model

Ballooned hepatocytes (BH) are enlarged, abnormal hepatocytes, which are usually involved in liver diseases, in particular, nonalcoholic steatohepatitis (NASH). However, formation of BHs in vitro has been seldom reported. This study reported an in vitro strategy to produce human BHs in a cell sheet-based three-dimensional (3D) model where primary human hepatocytes were cocultured with normal human dermal fibroblasts. Enlargement of hepatocytes (2.3 times larger than normal, p < 0.01), loss of cytoplasmic keratin, appearance of Mallory-Denk bodies (MDBs), and abundant fat droplets accumulation were observed after only a few days culture. Additionally, ultrastructural characteristic findings of BHs in human NASH, including enlarged mitochondria with crystalline inclusions, dilated endoplasmic reticulum, and MDBs formation were also observed in the 3D model. Furthermore, pathophysiological features of human NASH, such as increased secretion of sonic hedgehog ligands and myofibroblast activation were found. This study reports in vitro production of human BHs by using a cell sheet-based 3D model. Similar histological, ultrastructural, and pathophysiological features to human NASH are discovered in this model. This model may facilitate study of BHs and increase our knowledge of the pathogenesis of human liver diseases. Impact Statement Human ballooned hepatocytes (BH), which are present in nonalcoholic steatohepatitis (NASH) are mainly studied based on human liver biopsies and animal models. In this study, human BHs can be successfully reproduced in a cell sheet-based in vitro model, which, as far as we know, is the first in vitro model that recapitulates so many histological and ultrastructural hallmarks of BHs found in human NASH. Additionally, this study also demonstrated presence of some NASH pathophysiological features. This model may facilitate the study of hepatocellular ballooning and prove beneficial in translational preclinical drug discovery in NASH.

Fabrication of Functional Cell Sheets with Human Thyrocytes from Non-Tumorous Thyroid Tissue

Background

Engineered cell sheet transplantation has been considered an alternative physiological therapy for endocrine disorders. In this study, we attempted to fabricate functional human thyroid cell sheets using the engineering technology by culturing primary thyrocytes in free-feeder monolayers and assessed their proliferation and function in two different media.

Methods

The non-tumorous tissues (approximately 2 g) were dissected during surgery. Primary human thyroid cells were isolated by mechanical dispersion and treatment with isolation solution. The cells were cultured on tissue culture dishes or temperature-responsive culture dishes to induce the formation of detached cell sheets.

Results

Primary thyroid cells isolated from nine patients were positive for thyroid transcription factor 1, thyroglobulin (TG) and cytokeratin 7. Cell sheets with follicles were fabricated by cells incubated in both Dulbecco's Modified Eagle Medium (DMEM) and hepatocyte-defined medium (HDM) culture medium. The diameter and thickness of sheets fabricated in HDM were larger and thicker than those fabricated from DMEM. Furthermore, the cells incubated in HDM secreted higher levels of fT3 and fT4 than those incubated in DMEM. The thyroid peroxidase and TG mRNA of cells maintained in HDM were higher than those in cells maintained in DMEM.

Conclusion

HDM appears suitable as a culture medium for maintaining primary thyrocytes and fabricating functional cell sheets. These in vitro findings may contribute to the development of appropriate culture conditions for human thyrocytes as well as engineered functional cell sheets.

In vitro and in vivo fabrication of stable human hepatocyte tissue in combination with normal fibroblasts derived from donors of various ages

In order to establish a minimally invasive and safe liver regenerative technology, a technique for fabricating liver tissue possessing a vascular network was developed by subcutaneously transplanting a cell sheet composed of primary human hepatocytes and normal fibroblasts. However, differences in fibroblast characteristics owing to donor age may threaten the stability of liver tissue regenerated via this technology. Herein we describe the influence of fibroblasts from multiple donors on the fabrication of engineered human hepatocyte tissues invitro and in vivo. Primary human hepatocytes were cultured with seven strains of fibroblasts derived from the skins of donors of various ages, ranging from a fetus (12 weeks) to the elderly (69 years). Engineered hepatocyte sheets were successfully harvested for all strains. At 2 weeks after the subcutaneous transplantation of the hepatocyte sheets into mice, the highest human albumin (hALB) serum concentration was noted in the mouse containing fibroblasts from a 12 year old (TIG-118). Since the platelet-derived growth factor subunit B (PDGFB) gene expression of TIG-118 cells was significantly higher than that in the other cells, PDGFB may be considered to play an important role in the initial subcutaneous engraftment of primary human hepatocytes. Even though hALB concentration exhibited a parabolic tendency with age, there was no statistically significant difference noted within 6-8 weeks after transplantation. The present study demonstrates that this technology can produce consistent and stable hepatocyte sheets that exhibit long-term survival and liver-specific functionality in vivo regardless of the fibroblast donor age.

The influence of the ratio of liver cells and bone marrow in the implantable cell-engineering structures of the liver on the recovery efficiency of functional and morphological parameters in chronic liver failure

Aim:to determinate the most effective liver cells and multipotent mesenchymal stromal cells of bone marrow (MMSC BM) ratio into implantable cell engineering constructions (CECs) used for chronic liver failure (CLF) correcting.

Materials and methods.For creating liver CECs it was used a biopolymer implant – a composition of a heterogeneous collagen-containing gel (BMCG) (Sphero®GEL trademark) containing viable liver cells and MMSC BM in the following ratios – 1 : 1; 5 : 1 and 10 : 1 respectively. CECs with different ratios of liver cells and MMSC BM were implanted into liver of rats in which chronic liver failure (CLF), was modeled by using CCl4. The effectiveness of the regulatory effects of CECs (with different cell ratios) on regenerative processes in livers were assessed by using biochemical, morphological and morphometric methods at different periods after their implantation.

Results.Corrective effect of CECs with different cell composition on biochemical and morphological parameters of livers at chronic liver failure was established. During studying the liver CECs with various cell ratios of liver cells and MMSC BM (1 : 1; 5 : 1 and 10 : 1 respectively), it was found that the most optimal ratio of cells into the CECs is 5 : 1, because at this ratio of cells, there were a more distinct normalization of the morphological and functional liver parameters within 365 days after modeling CLF and maintenance of the structural homeostasis into the CECs. Themselves, which allows predicting their long-term regulatory effect on the liver tissue in CLF and maintaining its normal structural and functional state.

Conclusion.The effective correction of chronic liver failure can be carried out by using the implanted liver CECs, in which donor liver cells and MMSC BM where presented in ratios – 1 : 1; 5 : 1 and 10 : 1. But analysis of prolonged correction of liver morphological and functional parameters at CECs using it was allow to recommend the preferences using of CECs with ratio 5 : 1, because prolonged preservation of structural homeostasis into these CECs makes possible to prognosticate their prolonged regulatory action on the liver tissue at CLF, especially for recipients on a waiting list for liver transplantation.

Regenerative medicine using stem cells from human exfoliated deciduous teeth (SHED): a promising new treatment in pediatric surgery

Stem cells from human exfoliated deciduous teeth (SHEDs), being a type of mesenchymal stem cell, are an ideal cell source for regenerative medicine. They have minimal risk of oncogenesis, high proliferative capacity, high multipotency, and immunosuppressive ability. Stem cell transplantation using SHED has been found to have an anti-fibrotic effect on liver fibrosis in mice. SHED transplantation and the bio 3D printer, which can create scaffold-free 3-D images of the liver and diaphragm, provide a new innovative treatment modality for intractable pediatric surgical diseases such as biliary atresia and diaphragmatic hernia.

Construction of Pedicled Smooth Muscle Tissues by Combining the Capsule Tissue and Cell Sheet Engineering

The survival of engineered tissue requires the formation of its own capillary network, which can anastomose with the host vasculature after transplantation. Currently, while many strategies, such as modifying the scaffold material, adding endothelial cells, or angiogenic factors, have been researched, engineered tissue implanted in vivo cannot timely access to sufficient blood supply, leading to ischemic apoptosis or shrinkage. Constructing vascularized engineered tissue with its own axial vessels and subsequent pedicled transfer is promising to solve the problem of vascularization in tissue engineering. In this study, we used the tissue expander capsule as a novel platform for vascularizing autologous smooth muscle cell (SMC) sheets and fabricating vascularized engineered tissue with its own vascular pedicle. First, we verified which time point was the most effective for constructing an axial capsule vascular bed. Second, we compared the outcome of SMC sheet transplantation onto the expander capsule and classical dorsal subcutaneous tissue, which was widely used in other studies for vascularization. Finally, we transplanted multilayered SMC sheets onto the capsule bed twice to verify the feasibility of fabricating thick pedicled engineered smooth muscle tissues. The results indicated that the axial capsule tissue could be successfully induced, and the capsule tissue 1 week after full expansion was the most vascularized. Quantitative comparisons of thickness, vessel density, and apoptosis of cell sheet grafts onto two vascular beds proved that the axial capsule vascular bed was more favorable to the growth and vascularization of transplants than classical subcutaneous tissue. Furthermore, thick vascularized smooth muscle tissues with the vascular pedicle could be constructed by multi-transplanting cell sheets onto the capsule bed. The combination of axial capsule vascular bed and cell sheet engineering may provide an efficient strategy to overcome the problem of slow or insufficient vascularization in tissue engineering.

Generation of Hepatic Organoids with Biliary Structures

Incorporation of bile drainage system into engineered liver tissue is an important issue to advance liver regenerative medicine. Our group reported that three-dimensional (3D) coculture of fetal liver cells (FLCs) and adult rat biliary epithelial cells (BECs) allows reconstruction of hepatic spheroids that possess bile ductular structures. In this chapter, we describe the detailed protocol to isolate FLCs and BECs and to generate the spheroids with bile drainage system using these two types of primary cells.

Reconstruction of structure and function in tissue engineering of solid organs: Toward simulation of natural development based on decellularization

Failure of solid organs, such as the heart, liver, and kidney, remains a major cause of the world's mortality due to critical shortage of donor organs. Tissue engineering, which uses elements including cells, scaffolds, and growth factors to fabricate functional organs in vitro, is a promising strategy to mitigate the scarcity of transplantable organs. Within recent years, different construction strategies that guide the combination of tissue engineering elements have been applied in solid organ tissue engineering and have achieved much progress. Most attractively, construction strategy based on whole-organ decellularization has become a popular and promising approach, because the overall structure of extracellular matrix can be well preserved. However, despite the preservation of whole structure, the current constructs derived from decellularization-based strategy still perform partial functions of solid organs, due to several challenges, including preservation of functional extracellular matrix structure, implementation of functional recellularization, formation of functional vascular network, and realization of long-term functional integration. This review overviews the status quo of solid organ tissue engineering, including both advances and challenges. We have also put forward a few techniques with potential to solve the challenges, mainly focusing on decellularization-based construction strategy. We propose that the primary concept for constructing tissue-engineered solid organs is fabricating functional organs based on intact structure via simulating the natural development and regeneration processes.

Liver cell therapy: is this the end of the beginning?

The prevalence of liver diseases is increasing globally. Orthotopic liver transplantation is widely used to treat liver disease upon organ failure. The complexity of this procedure and finite numbers of healthy organ donors have prompted research into alternative therapeutic options to treat liver disease. This includes the transplantation of liver cells to promote regeneration. While successful, the routine supply of good quality human liver cells is limited. Therefore, renewable and scalable sources of these cells are sought. Liver progenitor and pluripotent stem cells offer potential cell sources that could be used clinically. This review discusses recent approaches in liver cell transplantation and requirements to improve the process, with the ultimate goal being efficient organ regeneration. We also discuss the potential off-target effects of cell-based therapies, and the advantages and drawbacks of current pre-clinical animal models used to study organ senescence, repopulation and regeneration.

Exosome-Mimetic Nanovesicles from Hepatocytes promote hepatocyte proliferation in vitro and liver regeneration in vivo

The liver has great regenerative capacity after functional mass loss caused by injury or disease. Many studies have shown that primary hepatocyte-derived exosomes, which can deliver biological information between cells, promote the regenerative process of the liver. However, the yield of exosomes is very limited. Recent studies have demonstrated that exosome-mimetic nanovesicles (NVs) can be prepared from cells with almost 100 times the production yield compared with exosomes. Thus, this study investigated the therapeutic capacity of exosome-mimetic NVs from primary hepatocytes in liver regeneration. Exosome-mimetic NVs were prepared by serial extrusions of cells through polycarbonate membranes, and the yield of these NVs was more than 100 times that of exosomes. The data indicated that the NVs could promote hepatocyte proliferation and liver regeneration by significantly enhancing the content of sphingosine kinase 2 in recipient cells. To the best of our knowledge, this is the first time that exosome-mimetic NVs from primary hepatocytes have been prepared, and these NVs have components similar to exosomes from primary hepatocytes and, in some respects, biofunctions similar to exosomes. Strategies inspired by this study may lead to substitution of exosomes with exosome-mimetic NVs for biofunctional purposes, including utilization in tissue repair and regeneration.

Engineering a microcirculation for perfusion control of ex vivo-assembled organ systems: Challenges and opportunities

Donor organ shortage remains a clear problem for many end-stage organ patients around the world. The number of available donor organs pales in comparison with the number of patients in need of these organs. The field of tissue engineering proposes a plausible solution. Using stem cells, a patient's autologous cells, or allografted cells to seed-engineered scaffolds, tissue-engineered constructs can effectively supplement the donor pool and bypass other problems that arise when using donor organs, such as who receives the organ first and whether donor organ rejection may occur. However, current research methods and technologies have been unable to successfully engineer and vascularize large volume tissue constructs. This review examines the current perfusion methods for ex vivo organ systems, defines the different types of vascularization in organs, explores various strategies to vascularize ex vivo organ systems, and discusses challenges and opportunities for the field of tissue engineering.

A decade of progress in liver regenerative medicine

Liver diseases can be caused by viral infection, metabolic disorder, alcohol consumption, carcinoma or injury, chronically progressing to end-stage liver disease or rapidly resulting in acute liver failure. In either situation, liver transplantation is most often sought for life saving, which is, however, significantly limited by severe shortage of organ donors. Until now, tremendous multi-disciplinary efforts have been dedicated to liver regenerative medicine, aiming at providing transplantable cells, microtissues, or bioengineered whole liver via tissue engineering, or maintaining partial liver functions via extracorporeal support. In both directions, new compatible biomaterials, stem cell sources, and bioengineering approaches have fast-forwarded liver regenerative medicine towards potential clinical applications. Another important progress in this field is the development of liver-on-a-chip technologies, which enable tissue engineering, disease modeling, and drug testing under biomimetic extracellular conditions. In this review, we aim to highlight the last decade's progress in liver regenerative medicine from liver tissue engineering, bioartificial liver devices (BAL), to liver-on-a-chip platforms, and then to present challenges ahead for further advancement.

The Self-Assembling Process and Applications in Tissue Engineering

Tissue engineering strives to create neotissues capable of restoring function. Scaffold-free technologies have emerged that can recapitulate native tissue function without the use of an exogenous scaffold. This review will survey, in particular, the self-assembling and self-organization processes as scaffold-free techniques. Characteristics and benefits of each process are described, and key examples of tissues created using these scaffold-free processes are examined to provide guidance for future tissue-engineering developments. We aim to explore the potential of self-assembly and self-organization scaffold-free approaches, detailing the recent progress in the in vitro tissue engineering of biomimetic tissues with these methods toward generating functional tissue replacements.

Hepatocyte Transplantation: Cell Sheet Technology for Liver Cell Transplantation

Purpose of Review

We will review the recent developments of cell sheet technology as a feasible tissue engineering approach. Specifically, we will focus on the technological advancement for engineering functional liver tissue using cell sheet technology, and the associated therapeutic effect of cell sheets for liver diseases, highlighting hemophilia.

Recent Findings

Cell-based therapies using hepatocytes have recently been explored as a new therapeutic modality for patients with many forms of liver disease. We have developed a cell sheet technology, which allows cells to be harvested in a monolithic layer format. We have succeeded in fabricating functional liver tissues in mice by stacking the cell sheets composed of primary hepatocytes. As a curative measure for hemophilia, we have also succeeded in treating hemophilia mice by transplanting of cells sheets composed of genetically modified autologous cells.

Summary

Tissue engineering using cell sheet technology provides the opportunity to create new therapeutic options for patients with various types of liver diseases.

In vivo construction of liver tissue by implantation of a hepatic non-parenchymal/adipose-derived stem cell sheet

Subcutaneous hepatocyte sheet implantation is an attractive therapeutic option for various liver diseases. However, this technique is limited by the availability of hepatocytes. Thus, the use of hepatic non-parenchymal cells (NPCs) containing small hepatocytes, which have the ability to proliferate more rapidly than mature hepatocytes, for transplantation has been suggested. The aim of our study was to construct liver tissue subcutaneously in rats by implanting NPC sheets co-cultivated with adipose-derived stem cells (ADSCs), which produce certain angiogenic factors. We crafted NPC-ADSC sheets on temperature-responsive culture dishes. NPCs formed functioning bile canaliculi and stored glycogen. In addition, their ability to produce albumin was not inferior to that of hepatocytes. Albumin production increased over time when co-cultivated with ADSCs. We then implanted the co-cultivated cell sheets subcutaneously. The co-cultivated sheets retained glycogen, formed bile canaliculi, showed signs of vascularization and survived subcutaneously without pre-vascularization. These results suggest that NPCs can be a viable option in cell therapy for liver diseases. This technique using co-cultivated cell sheets may be useful in the field of regenerative medicine. Copyright © 2017 John Wiley & Sons, Ltd.

Construction of three-dimensional vascularized functional human liver tissue using a layer-by-layer cell coating technique

The creation of artificial liver tissue is an active area of research due to the shortage of donors for liver transplantation. Here we investigated whether a simple and efficient cell coating technique developed in our laboratory could be used to generate functional vascularized liver tissue. This technique creates three-dimensional tissue by loading cells sterically onto other cells that have been coated with layer-by-layer (LbL) nanofilms of fibronectin and gelatin, two extracellular matrix proteins. We used this technique to construct homogenous, dense, well-vascularized liver tissue from cryopreserved human primary hepatocytes, human umbilical vein endothelial cells, and normal human dermal fibroblasts. Using LbL cell coating technique resulted in higher cellular function in terms of human albumin production (P < 0.01) and cytochrome P450 activity (P < 0.01) in vitro. Furthermore, after being transplanted subcutaneously into NOD/SCID mice, the vascularized liver tissue showed greater albumin production in the early stage than non-vascularized tissue or a hepatocyte suspension (P < 0.01). Histological examination demonstrated that compare to non-vascularized tissue, there were many less-morphologically changed and intact hepatocytes in the vascularized tissue. This cell coating technique would be applicable to the generation of vascularized functional liver tissue for regenerative medicine in the future.

Effects of Differentiation and Antisenescence from BMSCs to Hepatocy-Like Cells of the PAAm-IGF-1/TNF-α Biomaterial

Aiming at the cells' differentiation phenomenon and senescence problem in liver tissue engineering, this work is designed to synthesize three different chargeable polymers (polypropylene acid (PAAc), polyethylene glycol (PEG), and polypropylene amine (PAAm)) coimmobilized by the insulin-like growth factor 1 (IGF-1) and tumor necrosis factor-α (TNF-α). We explore the hepatocyte differentiation effect and the antisenecence effect of PSt-PAAm-IGF-1/TNF-α biomaterial which was selected from the three different chargeable polymers in bone marrow mesenchymal stem cells (BMSCs). Our work will establish a model for studying the biochemical molecular regulation mechanism and signal transduction pathway of cell senescence in liver tissue engineering, which provide a molecular basis for developing biomaterials for liver tissue engineering.

Vascularization of three-dimensional engineered tissues for regenerative medicine applications

Engineering of three-dimensional (3D) tissues is a promising approach for restoring diseased or dysfunctional myocardium with a functional replacement. However, a major bottleneck in this field is the lack of efficient vascularization strategies, because tissue constructs produced in vitro require a constant flow of oxygen and nutrients to maintain viability and functionality. Compared to angiogenic cell therapy and growth factor treatment, bioengineering approaches such as spatial micropatterning, integration of sacrificial materials, tissue decellularization, and 3D bioprinting enable the generation of more precisely controllable neovessel formation. In this review, we summarize the state-of-the-art approaches to develop 3D tissue engineered constructs with vasculature, and demonstrate how some of these techniques have been applied towards regenerative medicine for treatment of heart failure.

STATEMENT OF SIGNIFICANCE

Tissue engineering is a promising approach to replace or restore dysfunctional tissues/organs, but a major bottleneck in realizing its potential is the challenge of creating scalable 3D tissues. Since most 3D engineered tissues require a constant supply of nutrients, it is necessary to integrate functional vasculature within the tissues in order to facilitate the transport of nutrients. To address these needs, researchers are employing biomaterial engineering and design strategies to foster vessel formation within 3D tissues. This review highlights the state-of-the-art bioengineering tools and technologies to create vascularized 3D tissues for clinical applications in regenerative medicine, highlighting the application of these technologies to engineer vascularized cardiac patches for treatment of heart failure.

Human mesenchymal stem cell-engineered hepatic cell sheets accelerate liver regeneration in mice

Mesenchymal stem cells (MSCs) are an attractive cell source for cell therapy. Based on our hypothesis that suppression of Wnt/β-catenin signal enhances hepatic differentiation of human MSCs, we developed human mesenchymal stem cell-engineered hepatic cell sheets by a small molecule compound. Screening of 10 small molecule compounds was performed by WST assay, TCF reporter assay, and albumin mRNA expression. Consequently, hexachlorophene suppressed TCF reporter activity in time- and concentration-dependent manner. Hexachlorophene rapidly induced hepatic differentiation of human MSCs judging from expression of liver-specific genes and proteins, PAS staining, and urea production. The effect of orthotopic transplantation of human mesenchymal stem cell-engineered hepatic cell sheets against acute liver injury was examined in one-layered to three-layered cell sheets system. Transplantation of human mesenchymal stem cell-engineered hepatic cell sheets enhanced liver regeneration and suppressed liver injury. The survival rates of the mice were significantly improved. High expression of complement C3 and its downstream signals including C5a, NF-κB, and IL-6/STAT-3 pathway was observed in hepatic cell sheets-grafted tissues. Expression of phosphorylated EGFR and thioredoxin is enhanced, resulting in reduction of oxidative stress. These findings suggest that orthotopic transplantation of hepatic cell sheets manufactured from MSCs accelerates liver regeneration through complement C3, EGFR and thioredoxin.