A tissue-engineered artificial bile duct grown to resemble the native bile duct

The Past, Present, and Future of Tubular Melt Electrowritten Constructs to Mimic Small Diameter Blood Vessels - A Stable Process?

Melt Electrowriting (MEW) is a continuously growing manufacturing platform. Its advantage is the consistent production of micro- to nanometer fibers, that stack intricately, forming complex geometrical shapes. MEW allows tuning of the mechanical properties of constructs via the geometry of deposited fibers. Due to this, MEW can create complex mechanics only seen in multi-material compounds and serve as guiding structures for cellular alignment. The advantage of MEW is also shown in combination with other biotechnological manufacturing methods to create multilayered constructs that increase mechanical approximation to native tissues, biocompatibility, and cellular response. These features make MEW constructs a perfect candidate for small-diameter vascular graft structures. Recently, studies have presented fascinating results in this regard, but is this truly the direction that tubular MEW will follow or are there also other options on the horizon? This perspective will explore the origins and developments of tubular MEW and present its growing importance in the field of artificial small-diameter vascular grafts with mechanical modulation and improved biomimicry and the impact of it in convergence with other manufacturing methods and how future technologies like AI may influence its progress.

Fabrication of 3D printed PCL/PEG artificial bile ducts as supportive scaffolds to promote regeneration of extrahepatic bile ducts in a canine biliary defect model

In this study, a 3D porous poly(ε-caprolactone)/polyethylene glycol (PCL/PEG) composite artificial tubular bile duct was fabricated for extrahepatic bile duct regeneration. PCL/PEG composite scaffolds were fabricated by 3D printing, and the molecular structure, mechanical properties, thermal properties, morphology, and in vitro biocompatibility were characterized for further application as artificial bile ducts. A bile duct defect model was established in beagle dogs for in vivo implantation. The results demonstrated that the implanted PE1 ABD, serving as a supportive scaffold, effectively stimulated the regeneration of a new bile duct comprising CK19-positive and CK7-positive epithelial cells within 30 days. Remarkably, after 8 months, the newly formed bile duct exhibited an epithelial layer resembling the normal structure. Furthermore, the study revealed collagen deposition, biliary muscular formation, and the involvement of microvessels and fibroblasts in the regenerative process. In contrast, the anastomotic area without ABD implantation displayed only partial restoration of the epithelial layer, accompanied by fibroblast proliferation and subsequent bile duct fibrosis. These findings underscore the limited inherent repair capacity of the bile duct and underscore the beneficial role of the PE1 ABD artificial tubular bile duct in promoting biliary regeneration.

Development of an artificial portal vein using bioabsorbable polymers

PURPOSE

During surgical resection of malignant tumors in the hepatobiliary pancreatic region, portal vein resection and reconstruction may be needed. However, there is no alternative to the portal vein. We therefore developed an artificial portal vein that could be used in the abdominal cavity.

METHODS

In the experiments, hybrid pigs (n = 8) were included. An artificial portal vein was created using a bioabsorbable polymer sheet (BAPS). Subsequently, the portal vein's anterior wall was excised into an elliptical shape. A BAPS in the form of a patch was implanted at the same site. At 2 weeks (n = 3) and 3 months (n = 5) after the implantation, the BAPS implantation site was resected and evaluated macroscopically and histopathologically.

RESULTS

Immediately after the implantation, blood leakage was not detected. Two weeks after implantation, the BAPS remained, and endothelial cells were observed. Thrombus formation was not observed. Three months after implantation, the BAPS had been completely absorbed and was indistinguishable from the surrounding portal vein. Stenosis and aneurysms were not observed.

CONCLUSIONS

BAPS can replace a defective portal vein from the early stage of implantation to BAPS absorption. These results suggest that it can be an alternative material to the portal vein in surgical reconstruction.

Pitfalls and promises of bile duct alternatives: A narrative review

Biliodigestive anastomosis between the extrahepatic bile duct and the intestine for bile duct disease is a gastrointestinal reconstruction that abolishes duodenal papilla function and frequently causes retrograde cholangitis. This chronic inflammation can cause liver dysfunction, liver abscess, and even bile duct cancer. Although research has been conducted for over 100 years to directly repair bile duct defects with alternatives, no bile duct substitute (BDS) has been developed. This narrative review confirms our understanding of why bile duct alternatives have not been developed and explains the clinical applicability of BDSs in the near future. We searched the PubMed electronic database to identify studies conducted to develop BDSs until December 2021 and identified studies in English. Two independent reviewers reviewed studies on large animals with 8 or more cases. Four types of BDSs prevail: Autologous tissue, non-bioabsorbable material, bioabsorbable material, and others (decellularized tissue, 3D-printed structures, etc.). In most studies, BDSs failed due to obstruction of the lumen or stenosis of the anastomosis with the native bile duct. BDS has not been developed primarily because control of bile duct wound healing and regeneration has not been elucidated. A BDS expected to be clinically applied in the near future incorporates a bioabsorbable material that allows for regeneration of the bile duct outside the BDS.

A composite scaffold fabricated with an acellular matrix and biodegradable polyurethane for the in vivo regeneration of pig bile duct defects

Bile duct regeneration is urgently needed to restore the normal function of the damaged biliary system. In this study, an artificial bile duct (ABD) was fabricated for extrahepatic bile duct regeneration based on biodegradable polyurethane (BPU) and ureter acellular matrix (UAM) to endow it with favorable biocompatibility and eliminate bile leakage during in vivo bile duct regeneration. The mechanical properties, in vitro simulation of bile flow and cytocompatibility of BPU-UAM ABD were evaluated in vitro, and surgical implantation in the biliary defect site in minipigs was implemented to reveal the in vivo degradation of BPU-UAM and regeneration of the new bile duct. The results indicated that BPU-UAM ABD with a mechanical strength of 11.9 MPa has excellent cytocompatibility to support 3T3 fibroblast survival and proliferation in extraction medium and on the scaffolds. The in vivo implantation of BPU-UAM ABD revealed the change of collagen content throughout the new bile duct regeneration. Biliary epithelial cells were observed at day 70, and continuous biliary epithelial layer formation was observed after 100 days of implantation. Altogether, the BPU-UAM ABD fabricated in this study possesses excellent properties for application study in the regeneration of bile duct. STATEMENT OF SIGNIFICANCE: Extrahepatic bile duct defects carry considerable morbidity and mortality because they are the only pathway for bile to go down into the intestinal tract. At present, no artificial bile duct can promote biliary regeneration. In this study, BPU-UAM ABD was built based on biodegradable polyurethane and ureter acellular matrix to form a continuous compact layer of polyurethane in the internal wall of UAM and avoid bile leakage and experimental failure during in vivo implantation. Our work verified the effectiveness of the synthesized biodegradable polyurethane emulsion-modified urethral acellular matrix in bile regeneration and continuous biliary epithelial layer formation. This study provided a new approach for the curing of bile duct defects and inducing new bile tissue formation.

Bile duct regeneration with an artificial bile duct made of gelatin hydrogel non-woven fabrics

Although choledochojejunostomy is the standard technique for biliary reconstruction, there are various associated problems that need to be solved such as reflux cholangitis. Interposition with an artificial bile duct (ABD) to replace the resected bile duct maintains a physiological conduit for bile and may solve this problem. This study investigated the usefulness of an ABD made of gelatin hydrogel non-woven fabric (GHNF). GHNF was prepared by the solution blow spinning method. The migration and activity of murine fibroblast L929 cells were examined in GHNF sheets. L929 cells migrated into GHNF sheets, where they proliferated and synthesized collagen, suggesting GHNF is a promising scaffold for bile duct regeneration. ABDs made of GHNF were implanted in place of resected bile duct segments in rats. The rats were sacrificed at 2, 6, and 12 weeks post-implantation. The implantation site was histologically evaluated for bile duct regeneration. At postoperative 2 weeks, migrating cells were observed in the ABD pores. The implanted ABD was mostly degraded and replaced by collagen fibers at 6 weeks. Ki67-positive bile duct epithelial cells appeared within the implanted ABD. These were most abundant within the central part of the ABD after 6 weeks. The percentages of Ki67-positive cells were 31.7%±9.1% in the experimental group and 0.8%±0.6% in the sham operation group at 6 weeks (p<0.05), indicating that mature biliary epithelial cells at the stump proliferated to regenerate the biliary epithelium. Biliary epithelial cells had almost completely covered the bile duct lumen at 12 weeks (epithelialization ratios: 10.4%±6.9% at 2 weeks, 93.1%±5.1% at 6 weeks, 99.2%±1.6% at 12 weeks). The regenerated epithelium was positive for the bile duct epithelium marker cytokeratin 19. Bile duct regeneration was accompanied by angiogenesis, as evidenced by the appearance of CD31-positive vascular structures. Capillaries were induced 2 weeks after implantation. The number of capillaries reached a maximum at 6 weeks and decreased to the same level as that of normal bile ducts at 12 weeks. These results showed that an ABD of GHNF contributed to successful bile duct regeneration in rats by facilitating the cell migration required for extracellular matrix synthesis, angiogenesis, and epithelialization.

Transplantation of patient-specific bile duct bioengineered with chemically reprogrammed and microtopographically differentiated cells

Cholangiopathy is a diverse spectrum of chronic progressive bile duct disorders with limited treatment options and dismal outcomes. Scaffold- and stem cell-based tissue engineering technologies hold great promise for reconstructive surgery and tissue repair. Here, we report a combined application of 3D scaffold fabrication and reprogramming of patient-specific human hepatocytes to produce implantable artificial tissues that imitate the mechanical and biological properties of native bile ducts. The human chemically derived hepatic progenitor cells (hCdHs) were generated using two small molecules A83-01 and CHIR99021 and seeded inside the tubular scaffold engineered as a synergistic combination of two layers. The inner electrospun fibrous layer was made of nanoscale-macroscale polycaprolactone fibers acting to promote the hCdHs attachment and differentiation, while the outer microporous foam layer served to increase mechanical stability. The two layers of fiber and foam were fused robustly together thus creating coordinated mechanical flexibility to exclude any possible breaking during surgery. The gene expression profiling and histochemical assessment confirmed that hCdHs acquired the biliary epithelial phenotype and filled the entire surface of the fibrous matrix after 2 weeks of growth in the cholangiocyte differentiation medium in vitro. The fabricated construct replaced the macroscopic part of the common bile duct (CBD) and re-stored the bile flow in a rabbit model of acute CBD injury. Animals that received the acellular scaffolds did not survive after the replacement surgery. Thus, the artificial bile duct constructs populated with patient-specific hepatic progenitor cells could provide a scalable and compatible platform for treating bile duct diseases.

Progress and Current Limitations of Materials for Artificial Bile Duct Engineering

Bile duct injury (BDI) and bile tract diseases are regarded as prominent challenges in hepatobiliary surgery due to the risk of severe complications. Hepatobiliary, pancreatic, and gastrointestinal surgery can inadvertently cause iatrogenic BDI. The commonly utilized clinical treatment of BDI is biliary-enteric anastomosis. However, removal of the Oddi sphincter, which serves as a valve control over the unidirectional flow of bile to the intestine, can result in complications such as reflux cholangitis, restenosis of the bile duct, and cholangiocarcinoma. Tissue engineering and biomaterials offer alternative approaches for BDI treatment. Reconstruction of mechanically functional and biomimetic structures to replace bile ducts aims to promote the ingrowth of bile duct cells and realize tissue regeneration of bile ducts. Current research on artificial bile ducts has remained within preclinical animal model experiments. As more research shows artificial bile duct replacements achieving effective mechanical and functional prevention of biliary peritonitis caused by bile leakage or obstructive jaundice after bile duct reconstruction, clinical translation of tissue-engineered bile ducts has become a theoretical possibility. This literature review provides a comprehensive collection of published works in relation to three tissue engineering approaches for biomimetic bile duct construction: mechanical support from scaffold materials, cell seeding methods, and the incorporation of biologically active factors to identify the advancements and current limitations of materials and methods for the development of effective artificial bile ducts that promote tissue regeneration.

Organoids: a promising new in vitro platform in livestock and veterinary research

Organoids are self-organizing, self-renewing three-dimensional cellular structures that resemble organs in structure and function. They can be derived from adult stem cells, embryonic stem cells, or induced pluripotent stem cells. They contain most of the relevant cell types with a topology and cell-to-cell interactions resembling that of the in vivo tissue. The widespread and increasing adoption of organoid-based technologies in human biomedical research is testament to their enormous potential in basic, translational- and applied-research. In a similar fashion there appear to be ample possibilities for research applications of organoids from livestock and companion animals. Furthermore, organoids as in vitro models offer a great possibility to reduce the use of experimental animals. Here, we provide an overview of studies on organoids in livestock and companion animal species, with focus on the methods developed for organoids from a variety of tissues/organs from various animal species and on the applications in veterinary research. Current limitations, and ongoing research to address these limitations, are discussed. Further, we elaborate on a number of fields of research in animal nutrition, host-microbe interactions, animal breeding and genomics, and animal biotechnology, in which organoids may have great potential as an in vitro research tool.

Bile duct reconstruction using scaffold-free tubular constructs created by Bio-3D printer

Introduction

Biliary strictures after bile duct injury or duct-to-duct biliary reconstruction are serious complications that markedly reduce patients’ quality of life because their treatment involves periodic stent replacements. This study aimed to create a scaffold-free tubular construct as an interposition graft to treat biliary complications.

Methods

Scaffold-free tubular constructs of allogeneic pig fibroblasts, that is, fibroblast tubes, were created using a Bio-3D Printer and implanted into pigs as interposition grafts for duct-to-duct biliary reconstruction.

Results

Although the fibroblast tube was weaker than the native bile duct, it was sufficiently strong to enable suturing. The pigs' serum hepatobiliary enzyme levels remained stable during the experimental period. Micro-computed tomography showed no biliary strictures, no biliary leakages, and no intrahepatic bile duct dilations. The tubular structure was retained in all resected specimens, and the fibroblasts persisted at the graft sites. Immunohistochemical analyses revealed angiogenesis in the fibroblast tube and absence of extensions of the biliary epithelium into the fibroblast tube's lumen.

Conclusions

This study's findings demonstrated successful reconstruction of the extrahepatic bile duct with a scaffold-free tubular construct created from pig fibroblasts using a novel Bio-3D Printer. This construct could provide a novel regenerative treatment for patients with hepatobiliary diseases.

Extrahepatic bile duct reconstruction in pigs with heterogenous animal-derived artificial bile ducts: A preliminary experience

BACKGROUND

Extrahepatic biliary duct injury (BDI) remains a complicated issue for surgeons. Although several approaches have been explored to address this problem, the high incidence of complications affects postoperative recovery. As a nonimmunogenic scaffold, an animal-derived artificial bile duct (ada-BD) could replace the defect, providing good physiological conditions for the regeneration of autologous bile duct structures without changing the original anatomical and physiologic conditions.

AIM

To evaluate the long-term feasibility of a novel heterogenous ada-BD for treating extrahepatic BDI in pigs.

METHODS

Eight pigs were randomly divided into two groups in the study. The animal injury model was developed with an approximately 2 cm segmental defect of various parts of the common bile duct (CBD) for all pigs. A 2 cm long novel heterogenous animal-derived bile duct was used to repair this segmental defect (group A, ada-BD-to-duodenum anastomosis to repair the distal CBD defect; group B, ada-BD-to-CBD anastomosis to repair the intermedial CBD defect). The endpoint for observation was 6 mo (group A) and 12 mo (group B) after the operation. Liver function was regularly tested. Animals were euthanized at the above endpoints. Histological analysis was carried out to assess the efficacy of the repair.

RESULTS

The median operative time was 2.45 h (2-3 h), with a median anastomosis time of 60.5 min (55-73 min). All experimental animals survived until the endpoints for observation. The liver function was almost regular. Histologic analysis indicated a marked biliary epithelial layer covering the neo-bile duct and regeneration of the submucosal connective tissue and smooth muscle without significant signs of immune rejection. In comparison, the submucosal connective tissue was more regular and thicker in group B than in group A, and there was superior integrity of the regeneration of the biliary epithelial layer. Despite the advantages of the regeneration of the bile duct smooth muscle observed in group A, the effect on the patency of the ada-BD grafts in group B was not confirmed by macroscopic assessment and cholangiography.

CONCLUSION

This approach appears to be feasible for repairing a CBD defect with an ada-BD. A large sample study is needed to confirm the durability and safety of these preliminary results.

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.

Production and Characterization of an Integrated Multi-Layer 3D Printed PLGA/GelMA Scaffold Aimed for Bile Duct Restoration and Detection

We successfully fabricated artificial bile duct via 3D printing technique which was composed of poly (lactic-co-glycolic acid) (PLGA) and gelatin methacrylate (GelMA). The PLGA-inner layer provided sufficient strength to support the bile duct contraction, the GelMA-outer layer possessed good biocompatibility to provide a good living environment for the cells. Moreover, IKVAV laminin peptide (Ile-Lys-Val-Ala-Val) and ultrasmall superparamagnetic iron oxide (USPIO) were used to regulate scaffold cell adhesion and magnetic resonance imaging (MRI) detection, respectively. After BMSCs co-culture with IKVAV at a certain concentration, the survival rate and adhesion of BMSCs was increased obviously. Meanwhile, the fabricated scaffold exhibited the tensile modulus in the range of 17.19 - 29.05 MPa and the compressive modulus in the range of 0.042 - 0.066 MPa, which could meet the needs of human implantation. In an animal experiment in vivo pig bile duct regeneration, PLGA/GelMA/IKVAV/USPIO duct conduits could promote bile duct regeneration and enhance cytokeratin 19 (CK19) expression. In summary, the composite bile duct scaffold with excellent MRI imaging function and biocompatibility could be used to develop bioactive artificial bile ducts.

Evidence for Recipient-Derived Cells in Peribiliary Glands and Biliary Epithelium of the Large Donor Bile Ducts After Liver Transplantation

Introduction

Chimerism after orthotopic liver transplantation (OLT) has largely been investigated in intrahepatic cellular constituents. However, little is known about chimerism in the extrahepatic and large intrahepatic bile ducts. Our aim was to evaluate the presence and extent of chimerism after OLT in the peribiliary glands (PBG) and the luminal epithelium of the large donor bile ducts.

Methods

For this study, we examined six extrahepatic and large intrahepatic bile ducts from livers that were re-transplanted. In all cases there was a sex-mismatch between donor and recipient (female donor organ and male recipient), which allowed to discriminate between donor- and recipient-derived cells. Specimens from female to female transplants were used as negative controls and male to male transplants as positive controls. Fluorescence in situ hybridization (FISH) for Y and X chromosomes was performed and the percentage of XY positive cells was determined among biliary epithelial cells. Immunohistochemistry was used to correlate chimerism with histological features.

Results

Cholangiocellular chimerism in all studied specimens ranged from 14 to 52%. The degree of chimerism was not associated with biliary damage. Marked chimerism was present at 5 days post-OLT. Ki-67-positivity was detected in 1–8% of the epithelial cells at the time of liver re-transplantation, and this correlated inversely with the degree of chimerism.

Conclusion

Recipient-derived cholangiocytes are present in the large bile ducts of the donor liver after OLT. The presence of chimerism in the large bile ducts suggests that recipient-derived cells may play a role in biliary regeneration following ischemia-induced injury during OLT.

A novel 3D printing PCL/GelMA scaffold containing USPIO for MRI-guided bile duct repair

Making artificial bile ducts in vitro for repairing and replacing diseased bile ducts is an important concept in tissue engineering. This study printed a tubular composite scaffold using polycaprolactone (PCL) through the current 3D printing method. It served as a matrix for the organoid cells of the bile duct to proliferation, migration, and differentiation. The PCL scaffold full of bile duct-like organ cells can achieve the effect of bionics, replacing the original bile duct to perform its proper function. In order to enrich the performance of the tubular scaffold, hydrogels were also used in this study. Applying a layer of gelatin methacryloyl (GelMA) hydrogel with an appropriate thickness on the outer layer of the PCL scaffold not only protects and supports the scaffold, but also improves the biocompatibility of the printed bile duct. In addition, ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles dispersed in GelMA served as the contrast agent to monitor the repair of the lesion site and the degradation of the bile duct in real time by magnetic resonance imaging (MRI). In this study, a tubular composite scaffold that could reconstruct bile duct function and possess a real-time MRI imaging property was constructed by 3D printing. After 13 days of the co-culture of bone marrow derived stem cells (BMSCs), the survival rate of the BMSCs was greater than 95%, and the coverage of the BMSCs was as high as 90%. At the same time, the compression modulus of the stent could reach 17.41 kPa and the Young's modulus could reach 5.03 kPa. Thus, the mechanical properties of it can meet the needs of human implantation. USPIO can achieve MRI imaging in situ and nondestructively monitor the degradation of the stent in the body. In summary, PCL/GelMA/USPIO bile duct scaffolds are beneficial to the proliferation of cells on the scaffolds and can be used to construct biologically active artificial bile ducts.

Liver Tissue Engineering: Challenges and Opportunities

Liver tissue engineering aims at the possibility of reproducing a fully functional organ for the treatment of acute and chronic liver disorders. Approaches in this field endeavor to replace organ transplantation (gold standard treatment for liver diseases in a clinical setting) with in vitro developed liver tissue constructs. However, the complexity of the liver microarchitecture and functionality along with the limited supply of cellular components of the liver pose numerous challenges. This review provides a comprehensive outlook onto how the physicochemical, mechanobiological, and spatiotemporal aspects of the substrates could be tuned to address current challenges in the field. We also highlight the strategic advancements made in the field so far for the development of artificial liver tissue. We further showcase the currently available prototypes in research and clinical trials, which shows the hope for the future of liver tissue engineering.

Regenerative Medicine of the Bile Duct: Beyond the Myth

Cholangiopathies are rare diseases of the bile duct with high mortality rates. The current treatment for cholangiopathies is liver transplantation, but there are significant obstacles including a shortage of donors and a high risk of complications. Currently, there is only one available medicine on the market targeting cholangiopathies, and the results have been inadequate in clinical therapy. To overcome these obstacles, many researchers have used human induced pluripotent stem cells (hPSC) as a source for cholangiocyte-like cell generation and have incorporated advances in bioprinting to create artificial bile ducts for implantation and transplantation. This has allowed the field to move dramatically forward in studies of biliary regenerative medicine. In this review, the authors provide an overview of cholangiocytes, the organogenesis of the bile duct, cholangiopathies, and the current treatment and advances that have been made that are opening new doors to the study of cholangiopathies.

Repopulation of intrahepatic bile ducts in engineered rat liver grafts

Engineered liver grafts for transplantation with sufficient hepatic function have been developed both in small and large animal models using the whole liver engineering approach. However, repopulation of the bile ducts in the whole liver scaffolds has not been addressed yet. In this study, we show the feasibility of repopulating the bile ducts in decellularized rat livers. Biliary epithelial cells were introduced into the bile ducts of the decellularized liver scaffolds with or without hepatocytes in the parenchymal space. The recellularized grafts were cultured under perfusion for up to 2 days and histological analysis revealed that the biliary epithelial cells formed duct-like structures, with the viable hepatocyte mass residing in the parenchymal space, in an arrangement highly comparable to the native tissue. The grafts were viable and functional as confirmed by both albumin and urea assay results and the gene expression analysis of biliary epithelial cells in recellularized liver grafts. This study provides the proof-of-concept results for rat liver grafts co-populated with parenchymal and biliary epithelial cells.

Complex bile duct network formation within liver decellularized extracellular matrix hydrogels

The biliary tree is an essential component of transplantable human liver tissue. Despite recent advances in liver tissue engineering, attempts at re-creating the intrahepatic biliary tree have not progressed significantly. The finer branches of the biliary tree are structurally and functionally complex and heterogeneous and require harnessing innate developmental processes for their regrowth. Here we demonstrate the ability of decellularized liver extracellular matrix (dECM) hydrogels to induce the in vitro formation of complex biliary networks using encapsulated immortalized mouse small biliary epithelial cells (cholangiocytes). This phenomenon is not observed using immortalized mouse large cholangiocytes, or with purified collagen 1 gels or Matrigel. We also show phenotypic stability via immunostaining for specific cholangiocyte markers. Moreover, tight junction formation and maturation was observed to occur between cholangiocytes, exhibiting polarization and transporter activity. To better define the mechanism of duct formation, we utilized three fluorescently labeled, but otherwise identical populations of cholangiocytes. The cells, in a proximity dependent manner, either branch out clonally, radiating from a single nucleation point, or assemble into multi-colored structures arising from separate populations. These findings present liver dECM as a promising biomaterial for intrahepatic bile duct tissue engineering and as a tool to study duct remodeling in vitro.

In Situ Tissue Engineering of the Bile Duct Using Polypropylene Mesh-Collagen Tubes

Multiple attempts have been made to replace biliary defects with a variety of materials. Recently, successful biliary reconstruction using the Gore-Tex vascular graft has been reported experimentally and clinically We designed a new artificial bile duct consisting of collagen sponge and polypropylene mesh. We presently evaluated the feasibility of using this prosthesis as a scaffold for bile duct tissue regeneration in a canine model. Our prosthesis, a sponge made from porcine dermal collagen, is reinforced with a polypropylene mesh cylinder. We used the prosthesis to reconstruct the middle portion of the common bile duct in seven beagle dogs to evaluate its efficacy. While one dog died of biliary stricture 8 months after operation, six survived without problems to scheduled time points for tissue evaluation at 1 to 12 months. All prostheses had become completely incorporated into the host. A confluent epithelial lining was observed within 3 months. In cholangiograms the prosthesis displayed long-term patency in the six dogs and provided satisfactory bile drainage for up to 12 months. Our graft thus shows promise for repair of biliary defects and should lead to development of a new treatment for biliary reconstruction.

Advances in the generation of bioengineered bile ducts

The generation of bioengineered biliary tissue could contribute to the management of some of the most impactful cholangiopathies associated with liver transplantation, such as biliary atresia or ischemic cholangiopathy. Recent advances in tissue engineering and in vitro cholangiocyte culture have made the achievement of this goal possible. Here we provide an overview of these developments and review the progress towards the generation and transplantation of bioengineered bile ducts. This article is part of a Special Issue entitled: Cholangiocytes in Health and Diseaseedited by Jesus Banales, Marco Marzioni and Peter Jansen.

Design and Fabrication of a Thin-Walled Free-Form Scaffold on the Basis of Medical Image Data and a 3D Printed Template: Its Potential Use in Bile Duct Regeneration

Three-dimensional (3D) printing, combined with medical imaging technologies, such as computed tomography and magnetic resonance imaging (MRI), has shown a great potential in patient-specific tissue regeneration. Here, we successfully fabricated an ultrathin tubular free-form structure with a wall thickness of several tens of micrometers that is capable of providing sufficient mechanical flexibility. Such a thin geometry cannot easily be achieved by 3D printing alone; therefore, it was realized through a serial combination of processes, including the 3D printing of a sacrificial template, the dip coating of the biomaterial, and the removal of the inner template. We demonstrated the feasibility of this novel tissue engineering construct by conducting bile duct surgery on rabbits. Moving from a rational design based on MRI data to a successful surgical procedure for reconstruction, we confirmed that the presented method of fabricating scaffolds has the potential for use in customized bile duct regeneration. In addition to the specific application presented here, the developed process and scaffold are expected to have universal applicability in other soft-tissue engineering fields, particularly those involving vascular, airway, and abdominal tubular tissues.

Repair of a common bile duct defect with a decellularized ureteral graft

AIM

To evaluate the feasibility of repairing a common bile duct defect with a decellularized ureteral graft in a porcine model.

METHODS

Eighteen pigs were randomly divided into three groups. An approximately 1 cm segment of the common bile duct was excised from all the pigs. The defect was repaired using a 2 cm long decellularized ureteral graft over a T-tube (T-tube group, n = 6) or a silicone stent (stent group, n = 6). Six pigs underwent bile duct reconstruction with a graft alone (stentless group). The surviving animals were euthanized at 3 mo. Specimens of the common bile ducts were obtained for histological analysis.

RESULTS

The animals in the T-tube and stent groups survived until sacrifice. The blood test results were normal in both groups. The histology results showed a biliary epithelial layer covering the neo-bile duct. In contrast, all the animals in the stentless group died due to biliary peritonitis and cholangitis within two months post-surgery. Neither biliary epithelial cells nor accessory glands were observed at the graft sites in the stentless group.

CONCLUSION

Repair of a common bile duct defect with a decellularized ureteral graft appears to be feasible. A T-tube or intraluminal stent was necessary to reduce postoperative complications.

Implantation of a Tissue-Engineered Neo-Bile Duct in Domestic Pigs

BACKGROUND

Extrahepatic bile duct injuries remain severe complications during cholecystectomies and often require reconstruction by bilioenteric anastomosis (i.e., hepaticojejunostomy), which comes with further long-term complications (e.g., recurring ascending cholangitis, secondary biliary cirrhosis). In the case of inherent extrahepatic biliary atresia or during liver transplant, artificial or engineered bile ducts could allow novel surgical strategies without the need for hepaticojejunostomy.

METHODS

We present data on the implantation of in vitro-generated neo-bile ducts in 5 domestic pigs. The neo-bile ducts were engineered through decellularization of allogeneic blood vessels and recellularization with autologous cholangiocytes. On postoperative days 0, 1, 7, and 14, blood samples were taken and analyzed (aspartate aminotransferase, alanine aminotransferase, bilirubin, alkaline phosphatase, creatinine, and leukocytes). Magnetic resonance cholangiopancreatography was performed on postoperative day 14 on 1 pig. Fourteen days after implantation, the pigs were sacrificed and the bile ducts were explanted.

RESULTS

All pigs survived the complete study period without severe complications. None of the pigs showed signs of biliary leakage or peritonitis. The neo-bile ducts were infiltrated by neutrophils, and neoangiogenesis was observed around and into the implanted tissue.

CONCLUSION

We present a novel strategy for extrahepatic bile duct replacement by implantation of an autologous neo-bile duct generated ex vivo. Whether the presented technique allows the long-term replacement of native bile ducts must be further evaluated.

An Artificial Bile Duct Made of Bioabsorbable Polymer: A Viable Substitute for Narrowed Portion of the Extrahepatic Bile Duct

The aim of this study was to investigate whether an artificial bile duct made of bioabsorbable polymer could serve as a substitute for narrowed portions of the bile duct. The experiments were performed using hybrid pigs (n = 11). After laparotomy under general anesthesia, the extrahepatic bile duct was identified and ligated around the confluence with the cystic duct. A week later, repeat laparotomy was performed on the animals, and the bile duct on the hepatic side of the ligature was resected. The cut end was connected to the duodenum using a bioabsorbable artificial bile duct fabricated from a copolymer of polycaprolactone and polylactic acid fibers. The grafts were recovered for gross, histologic, and blood chemical studies at 4 months after the surgery. All recipient pigs survived until they were humanely killed for collection of the implants. A week of ligation of the extrahepatic bile duct dilated the duct to approximately 1 cm in diameter and increased total bilirubin. Total bilirubin had returned to the pre-implantation level in all animals at 4 months post implantation. Examinations of the grafts revealed complete freedom of stricture and the regeneration of a neo-bile duct of approximately 1 cm in diameter from the graft site in 10 of 11 animals. Gross observation of the graft from the 1 remaining animal revealed stricture at the anastomosis site and poor bile duct epithelization. We have concluded that this bioabsorbable polymer bile duct can serve as a replacement for narrowed portions of the bile duct.

Extensive regeneration of the stomach using bioabsorbable polymer sheets

BACKGROUND

The growing prevalence of endoscopic surgery in recent years has led to the minimization of postoperative scarring. However, this procedure does not allow for the regeneration of the resected digestive tract, which compromises the postoperative maintenance of digestive function. In this preliminary study, we developed an artificial gastric wall (AGW) using bioabsorbable polymer (BAP), and evaluated the ability of this BAP patch to repair and regenerate a widely defective gastric wall in an animal model.

METHODS

Pigs were laparotomized under general anesthesia. An 8 × 8-cm, round portion of the anterior gastric wall was excised and replaced by an AGW. The AGW was composed of a copolymer comprising 50% lactic acid and 50% caprolactone. The animals were relaparotomized 4, 8, or 12 weeks after implantation, after which they underwent resection of the entire stomach for gross and histologic evaluation of the graft sites.

RESULTS

All recipient pigs survived until killing. By 4-8 weeks, the graft site revealed progressively fewer mucosal defect after each day. Moreover, the grafted area was indistinguishable from the native stomach 12 weeks after AGW implantation. The structures of the regenerated mucous membrane and muscle layers were identical to those of the native stomach. Furthermore, proton pumps were found in the regenerated tissue.

CONCLUSION

The BAP sheets helped to restore extensive gastric defects without causing any deformation. The use of BAP sheets may become a new therapeutic method that prevents alterations of gastric volume after extensive gastrectomy for stomach cancer and other diseases.

A newly designed anal fistula plug: clinicopathological study in an experimental iatrogenic fistula model

We report on a clinicopathologic study in an animal model of treatment with a new bioabsorbable polymer plug (BAPP). Over a 2-week period, 6 porcine models, which each had 4 anal fistulae, were created using Blake drains. The pigs were divided into 2 groups: the BAPP-treatment group (n = 12 fistulae) and the control group (n = 12 fistulae). Two weeks later, the pigs were humanely killed, and the perianal sites were excised and examined with gross and pathologic studies. Each fistula in the BAPP group was completely cured. In the pathologic study, the treatment sites had little disarray, few defects in the muscular layer, and small numbers of inflammatory cells. The control group had a significantly greater number of inflammatory cells and microabscesses than the BAPP group. The newly developed BAPP reduced the infection and induced good healing in anal fistulae. The BAPP may be a useful new device for the clinical treatment of anal fistulae.

Cell and tissue engineering for liver disease

Despite the tremendous hurdles presented by the complexity of the liver's structure and function, advances in liver physiology, stem cell biology and reprogramming, and the engineering of tissues and devices are accelerating the development of cell-based therapies for treating liver disease and liver failure. This State of the Art Review discusses both the near- and long-term prospects for such cell-based therapies and the unique challenges for clinical translation.

Are synthetic scaffolds suitable for the development of clinical tissue-engineered tubular organs?

Transplantation of tissues and organs is currently the only available treatment for patients with end-stage diseases. However, its feasibility is limited by the chronic shortage of suitable donors, the need for life-long immunosuppression, and by socioeconomical and religious concerns. Recently, tissue engineering has garnered interest as a means to generate cell-seeded three-dimensional scaffolds that could replace diseased organs without requiring immunosuppression. Using a regenerative approach, scaffolds made by synthetic, nonimmunogenic, and biocompatible materials have been developed and successfully clinically implanted. This strategy, based on a viable and ready-to-use bioengineered scaffold, able to promote novel tissue formation, favoring cell adhesion and proliferation, could become a reliable alternative to allotransplatation in the next future. In this article, tissue-engineered synthetic substitutes for tubular organs (such as trachea, esophagus, bile ducts, and bowel) are reviewed, including a discussion on their morphological and functional properties.

Tamoxifen decreases the myofibroblast count in the healing bile duct tissue of pigs

OBJECTIVE

The aim of this study was to evaluate the effect of oral tamoxifen treatment on the number of myofibroblasts present during the healing process after experimental bile duct injury.

METHODS

The sample consisted of 16 pigs that were divided into two groups (the control and study groups). Incisions and suturing of the bile ducts were performed in the two groups. Tamoxifen (20 mg/day) was administered only to the study group. The animals were sacrificed after 30 days. Quantification of myofibroblasts in the biliary ducts was made through immunohistochemistry analysis using anti-alpha smooth muscle actin of the smooth muscle antibody. Immunohistochemical quantification was performed using a digital image system.

RESULTS

In the animals treated with tamoxifen (20 mg/day), there was a significant reduction in immunostaining for alpha smooth muscle actin compared with the control group (0.1155 vs. 0.2021, p = 0.046).

CONCLUSION

Tamoxifen reduced the expression of alpha smooth muscle actin in the healing tissue after bile duct injury, suggesting a decrease in myofibroblasts in the scarred area of the pig biliary tract. These data suggest that tamoxifen could be used in the prevention of biliary tract stenosis after bile duct surgeries.

Repair of bile duct defect with degradable stent and autologous tissue in a porcine model

AIM: To introduce and evaluate a new method to repair bile duct defect with a degradable stent and autologous tissues.

METHODS: Eight Ba-Ma mini-pigs were used in this study. Experimental models with common bile duct (CBD) defect (0.5-1.0 cm segment of CBD resected) were established and then CBD was reconstructed by duct to duct anastomosis with a novel degradable stent made of poly [sebacic acid-co-(1,3-propanediol)-co-(1,2-propanediol)]. In addition, a vascularized greater omentum was placed around the stent and both ends of CBD. Cholangiography via gall bladder was performed for each pig at postoperative months 1 and 3 to rule out stent translocation and bile duct stricture. Complete blood count was examined pre- and post-operatively to estimate the inflammatory reaction. Liver enzymes and serum bilirubin were examined pre- and post-operatively to evaluate the liver function. Five pigs were sacrificed at month 3 to evaluate the healing of anastomosis. The other three pigs were raised for one year for long-term observation.

RESULTS: All the animals underwent surgery successfully. There was no intraoperative mortality and no bile leakage during the observation period. The white blood cell counts were only slightly increased on day 14 and month 3 postoperatively compared with that before operation, the difference was not statistically significant (P = 0.652). The plasma level of alanine aminotransferase on day 14 and month 3 postoperatively was also not significantly elevated compared with that before operation (P = 0.810). Nevertheless, the plasma level of γ-glutamyl transferase was increased after operation in both groups (P = 0.004), especially 2 wk after operation. The level of serum total bilirubin after operation was not significantly elevated compared with that before operation (P = 0.227), so did the serum direct bilirubin (P = 0.759). By cholangiography via gall bladder, we found that the stent maintained its integrity of shape and was still in situ at month 1, and it disappeared completely at month 3. No severe CBD dilation and stricture were observed at both months 1 and 3. No pig died during the 3-mo postoperative observation period. No sign of necrosis, bile duct stricture, bile leakage or abdominal abscess was found at reoperation at month 3 postoperatively. Pigs had neither fragments of stent nor stones formed in the CBD. Collagen deposit was observed in the anastomosis by hematoxylin and eosin (HE) and Masson’s trichrome stains. No severe cholestasis was observed in liver parenchyma by HE staining. Intestinal obstruction was found in a pig 4 mo after operation, and no bile leakage, bile duct stricture or biliary obstruction were observed in laparotomy. No sign of bile duct stricture or bile leakage was observed in the other two pigs.

CONCLUSION: The novel method for repairing bile duct defect yielded a good short-term effect without postoperative bile duct stricture. However, the long-term effect should be further studied.

Extrahepatic bile duct regeneration in pigs using collagen scaffolds loaded with human collagen-binding bFGF

Extrahepatic bile duct defects and their complications are benign lesions but with malignant outcomes. Extrahepatic bile duct regeneration at the injury site could be important for the repair. In our previous work, a human basic fibroblast growth factor (bFGF) fused with a collagen-binding domain (CBD) was produced to activate the collagen membrane to obtain targeted tissue regeneration. This collagen/growth factor functional biomaterial could promote the regeneration of skin, bladder and full-thickness abdominal wall by accelerating vascularization and cellularization of autologous tissues. We speculate that the functional biomaterial could also provide the repairing effect on extrahepatic bile duct injuries. Using a pig extrahepatic bile duct injury model, we found that the collagen/CBD-bFGF composite biomaterial could significantly promote the extrahepatic bile duct regeneration at the injury site without causing structure deformation or hepatic dysfunction during both short- and long-time observations.

An extrahepatic bile duct grafting using a bioabsorbable polymer tube

BACKGROUND

Thus far, no ideal substitutions have been developed for completely replacing the extrahepatic bile duct (EHBD).

METHODS

We used a bioabsorbable polymer tube (BAPT) for the complete reconstruction of an EHBD in pigs. A 2-cm-long EHBD was resected from the duodenal side, and a 4-cm-long BAPT graft was implanted at that site. The animals were re-laparotomized at 1 or 4 months after the grafting; subsequently, gross, histological, and blood chemical studies were performed.

RESULTS

At 1 month after grafting, tubular structure was observed in all resected specimens, and the lumen of the graft site had remnants of degraded BAPT. Gross examination at 4 months after grafting revealed that the BAPT had been completely absorbed, and the graft site was indistinguishable from the native extrahepatic bile duct. The lengths of the graft region at 4 months were 70% of the replaced BAPT. Simultaneously performed histological examination revealed the growth of a neo-bile duct at the graft site, with an epithelium identical to that of the native bile duct.

CONCLUSION

The BAPT graft implanted in this study completely replaced the EHBD defect. Hence, BAPT has the potential for application as a novel treatment modality for hepatobiliary diseases.

Novel reconstruction of the extrahepatic biliary tree with a biosynthetic absorbable graft

OBJECTIVES

The reference standard technique for the reconstruction of the extrahepatic biliary tree is Roux-en-Y hepaticojejunostomy. This procedure is not without complications and may not be feasible in some patients. This project sought to evaluate a novel approach for repairing common bile duct injuries with a biosynthetic graft. This allows for the reconstruction of the anatomy without necessitating an intestinal bypass.

METHODS

Study subjects were 11 mongrel hounds. Utilizing an open approach, the common bile duct was transected in each animal. A 1-cm graft of a synthetic bioabsorbable prosthesis was interposed over a 5-Fr pancreatic stent and sewn in place as an interposition tube graft with absorbable sutures. Intraoperative cholangiograms and monthly liver function tests were completed. Animals were killed at 6, 7, 8, 10 and 12 months.

RESULTS

The first five animals were killed early in the process of protocol development. One animal developed obstructive symptoms and was killed on postoperative day 14. The next five animals were longterm survivors without evidence of clinically significant graft stenosis. Mean alkaline phosphatase and total bilirubin were normal, at 140 U/l and 0.2 mg/dl, respectively. Histology showed the complete replacement of the graft with native tissue at 6 months.

CONCLUSIONS

  Biliary reconstruction using a synthetic bioabsorbable prosthetic as an interposition tube graft is feasible based on initial results.

Recent trends and challenges in complex organ manufacturing

Presently, there is a recognized and imperative need for bioartificial organs. The technological advances in transgenosis, tissue engineering, and rapid prototyping have led to the development of spatially complex tissues. An ideal artificial organ should provide nutrient transport system, mechanical stable architecture, and synergetic multicellular organization in one construct. The multinozzle rapid prototyping technique simultaneously assembles vascular systems including hierarchical multicellular structures in an automated and reproducible manner and offers an effective way for treating organ failures. In this article, a brief overview of the recent trends and outstanding challenges in organ manufacturing is provided. From the viewpoint of disciplinary crossing, integration, and development, future directions in the coming years were pointed out.

Morphological changes during creation of a neo-bile duct using a vein and a biodegradable endoluminal stent

Major bile duct lesions are usually treated by a hepaticojejunostomy which is often complicated by cholangitis and liver fibrosis. The aim of this study was to investigate the morphologic features of a neo-bile duct created from a vein and a biodegradable endoluminal stent. The neo-bile duct was created using a segment of the external jugular vein which was endoluminally stented by a biodegradable poly-lactate-acid stent. In 18 pigs, the common bile duct was resected and replaced by the vein with (n = 12) or without endoluminal stent (n = 6). Six animals served as controls. Survival, liver function and morphological changes of the neo-bile duct and the liver were observed for six months. After six months, the neo-bile duct morphologically resembled the native bile duct showing Ck7-positive columnar epithelium and newly formed capillaries in the bile duct wall. The biodegradable stent disappeared after four months. All animals survived and showed normal liver function and no cholestasis. In contrast, after sole vein reconstruction of the bile duct, four animals died due to biliary peritonitis and cholangitis. Creation of a neo-bile duct which morphologically resembles the native bile duct is feasible by using a body's own vein and a biodegradable endoluminal stent.