Progress and Current Limitations of Materials for Artificial Bile Duct Engineering

Fiber-reinforced gelatin-based hydrogel biocomposite tubular scaffolds with programmable mechanical properties

Tissue-engineered tubular scaffolds (TETS) provide an effective repair solution for human tubular tissue loss and damage caused by congenital defects, disease, or mechanical trauma. However, there are still major challenges to developing TETS with excellent mechanical properties and biocompatibility for human tubular tissue repair. Gelatin-based hydrogels are suitable candidates for tissue-engineered scaffolds because they are hydrolyzed collagen products and have excellent biocompatibility and degradability. However, the mechanical properties of gelatin-based hydrogels are relatively poor and do not align well with the mechanical properties of human tubular tissues. Inspired by the extracellular matrix architecture of human tubular tissues, this study utilizes high-precision 3D printing to fabricate ultrafine fiber network tubular scaffolds (UFNTS) that mimic the arrangement of collagen fibers, which are then embedded in a cell-compatible gelatin-based hydrogel, resulting in the preparation of a fiber/hydrogel biocomposite tubular scaffold (BCTS) with tunable mechanical properties and a J-shaped stress-strain response. Finite element analysis was employed to predict the mechanical behavior of the UFNTS and BCTS. Experimental results indicate that by modifying the structural parameters of the UFNTS, the mechanical properties of the BCTS can be effectively tuned, achieving a programmable range of tensile modulus (0.2-4.35 MPa) and burst pressure (1580-7850 mmHg), which broadly covers the mechanical properties of most human tubular tissues. The design and fabrication of BCTS offer a new approach for the development of TETS while also providing a personalized strategy for such scaffolds in tissue engineering.

3D bioprinting for bile duct tissue engineering: current status and prospects

Bile duct disorders, including cholangiocarcinoma, primary sclerosing cholangitis, and iatrogenic injuries, pose significant clinical challenges due to limited regenerative capacity and the complexity of the biliary tree. In recent years, 3D bioprinting has emerged as a promising approach for bile duct tissue engineering by providing patient-specific geometries and facilitating the spatial organization of cells, scaffolding materials, and bioactive factors. This review presents a comprehensive overview of 3D bioprinting techniques for bile duct tissue engineering, focusing on fundamental principles, biomaterial selection, current achievements, key challenges, and future perspectives. We systematically discuss the latest technological breakthroughs, highlight emerging innovations such as organoid-based strategies and microfluidic-assisted 3D printing, and evaluate the prospects for clinical translation. Finally, we outline the main challenges-such as biocompatibility of materials, vascularization, immunological barriers, standardization of protocols, and regulatory hurdles-and propose directions for future research, emphasizing multidisciplinary collaboration and translational studies.

Local Application of Minimally Manipulated Autologous Stromal Vascular Fraction (SVF) Reduces Inflammation and Improves Bilio-Biliary Anastomosis Integrity

Bilio-biliary anastomosis (BBA) is a critical surgical procedure that is performed with the objective of restoring bile duct continuity. This procedure is often required in cases where there has been an injury to the extrahepatic bile ducts or during liver transplantation. Despite advances in surgical techniques, the healing of BBA remains a significant challenge, with complications such as stricture formation and leakage affecting patient outcomes. The stromal vascular fraction (SVF), a heterogeneous cell population derived from adipose tissue, has demonstrated promise in regenerative medicine due to its rich content of stem cells, endothelial progenitor cells, and growth factors. The objective of this study was to evaluate the potential of locally administered autologous SVF to enhance the healing of BBAs. Bilio-biliary anastomosis was performed on a swine model (female Landrace pigs). Six swine were divided into two groups: the treatment group (n = 3) received a local application of autologous SVF around the anastomosis site immediately following BBA formation, while the control group (n = 3) received saline. The primary outcomes were assessed over an eight-week period post-surgery, and included anastomosis healing, stricture formation, and bile leakage. Histological analysis was performed to evaluate fibrosis, angiogenesis, and inflammation. Immunohistochemistry was conducted to assess healing-related markers (CD34, α-SMA) and the immunological microenvironment (CD3, CD10, tryptase). The SVF-treated group exhibited significantly enhanced healing of the BBA. Histological examination revealed increased angiogenesis and reduced fibrosis in the SVF group. Immunohistochemical staining demonstrated higher vascular density in the anastomosed area of the SVF-treated group (390 vs. 210 vessels per 1 mm2, p = 0.0027), as well as a decrease in wall thickness (1.9 vs. 1.0 mm, p = 0.0014). There were no statistically significant differences in mast cell presence (p = 0.40). Immunohistochemical staining confirmed the overexpression of markers associated with tissue repair. Local injections of autologous SVF at the site of BBA have been demonstrated to significantly enhance healing and promote tissue regeneration. These findings suggest that SVF could be a valuable adjunctive therapy in BBA surgery, potentially improving surgical outcomes. However, further investigation is needed to explore the clinical applicability and long-term benefits of this novel approach in clinical practice as a minimally manipulated cell application.

Cerium Oxide Nanoparticles-Reinforced GelMA Hydrogel Loading Bone Marrow Stem Cells with Osteogenic and Inflammatory Regulatory Capacity for Bone Defect Repair

Effective bone defect repair has been a tough clinical challenge due to the complexity of the bone defect microenvironment. Hydrogels loaded with bone marrow mesenchymal stem cells (BMSCs) have been widely applied for bone regeneration. However, the low survival of BMSCs at the site of transplantation and lack of sufficient osteogenic induction capacity greatly limit their applications. In order to solve this puzzle, we fabricated gelatin methacryloyl (GelMA) hydrogels containing BMSCs with cerium oxide (CeO2) nanoparticles via photo-cross-linking to endow the composite hydrogel with osteogenic induction ability and immune induction ability. In vitro results demonstrated that the GelMA-CeO2-BMSC hydrogel presented with good biocompatibility and excellent osteogenic induction ability. In addition, the GelMA-CeO2-BMSC hydrogel could inhibit M1 polarization and promote M2 polarization, providing a good environment for the growth and osteogenic differentiation of BMSCs. Besides, the GelMA-CeO2-BMSC hydrogel was transplanted into critical-sized calvarial defects, and the results further confirmed its excellent bone regeneration capacity. In conclusion, the composite hydrogel provides a perspective for bone repair due to the remarkable potential for application in bone regeneration.

The past, present, and future of endoscopic management for biliary strictures: technological innovations and stent advancements

Biliary stricture can be induced by intrinsic narrowing and extrinsic compression, with the majority of cases being malignant. Clinically, distinguishing between benign and malignant biliary strictures remains a considerable challenge, and the ongoing disagreement over the optimal choice of biliary stents significantly influences treatment strategies and impacts patients' survival and prognosis. The utilization and advancement of endoscopic techniques have heightened the diagnostic sensitivity for biliary strictures. Concurrently, innovative technologies such as endoscopic ultrasound and magnetic compression anastomosis emerge as viable alternatives when endoscopic retrograde cholangiopancreatography (ERCP) is not an option, providing fresh insights for the clinical management of these patients. Traditional plastic and metal stents, characterized by their complex application and limited scope, have been unable to fully satisfy clinical needs. The introduction of novel stent varieties has notably improved this scenario, marking a considerable progression towards precision medicine. However, the clinical validation of the diverse stent materials available is incomplete. Hence, a thorough discussion on the present state and evolving trends of biliary stents is warranted.

Recombinant collagen coating 3D printed PEGDA hydrogel tube loading with differentiable BMSCs to repair bile duct injury

Bile duct injury presents a significant clinical challenge following hepatobiliary surgery, necessitating advancements in the repair of damaged bile ducts is a persistent issue in biliary surgery. 3D printed tubular scaffolds have emerged as a promising approach for the repair of ductal tissues, yet the development of scaffolds that balance exceptional mechanical properties with biocompatibility remains an ongoing challenge. This study introduces a novel, bio-fabricated bilayer bile duct scaffold using a 3D printing technique. The scaffold comprises an inner layer of polyethylene glycol diacrylate (PEGDA) to provide high mechanical strength, and an outer layer of biocompatible, methacryloylated recombinant collagen type III (rColMA) loaded with basic fibroblast growth factor (bFGF)-encapsulated liposomes (bFGF@Lip). This design enables the controlled release of bFGF, creating an optimal environment for the growth and differentiation of bone marrow mesenchymal stem cells (BMSCs) into cholangiocyte-like cells. These cells are instrumental in the regeneration of bile duct tissues, evidenced by the pronounced expression of cholangiocyte differentiation markers CK19 and CFTR. The PEGDA//rColMA/bFGF@Lip bilayer bile duct scaffold can well simulate the bile duct structure, and the outer rColMA/bFGF@Lip hydrogel can well promote the growth and differentiation of BMSCs into bile duct epithelial cells. In vivo experiments showed that the scaffold did not cause cholestasis in the body. This new in vitro pre-differentiated active 3D printed scaffold provides new ideas for the study of bile duct tissue replacement.

Exploring the promising potential of induced pluripotent stem cells in cancer research and therapy

The advent of iPSCs has brought about a significant transformation in stem cell research, opening up promising avenues for advancing cancer treatment. The formation of cancer is a multifaceted process influenced by genetic, epigenetic, and environmental factors. iPSCs offer a distinctive platform for investigating the origin of cancer, paving the way for novel approaches to cancer treatment, drug testing, and tailored medical interventions. This review article will provide an overview of the science behind iPSCs, the current limitations and challenges in iPSC-based cancer therapy, the ethical and social implications, and the comparative analysis with other stem cell types for cancer treatment. The article will also discuss the applications of iPSCs in tumorigenesis, the future of iPSCs in tumorigenesis research, and highlight successful case studies utilizing iPSCs in tumorigenesis research. The conclusion will summarize the advancements made in iPSC-based tumorigenesis research and the importance of continued investment in iPSC research to unlock the full potential of these cells.

Pitfalls and promises of bile duct alternatives: There is plenty of room in the regenerative surgery

Current abdominal surgery has several approaches for biliary reconstruction. However, the creation of functional and clinically applicable bile duct substitutes still represents an unmet need. In the paper by Miyazawa and colleagues, approaches to the creation of bile duct alternatives were summarized, and the reasons for the lack of development in this area were explained. The history of bile duct surgery since the nineteenth century was also traced, leading to the conclusion that the use of bioabsorbable materials holds promise for the creation of bile duct substitutes in the future. We suggest three ideas that may stimulate progress in the field of bile duct substitute creation. First, a systematic analysis of the causative factors leading to failure or success in the creation of bile duct substitutes may help to develop more effective approaches. Second, the regeneration of a bile duct is delicately balanced between epithelialization and subsequent submucosal maturation within limited time frames, which may be more apparent when using quantitative models to estimate outcomes. Third, the utilization of the organism's endogenous regeneration abilities may enhance the creation of bile duct substitutes. We are convinced that an interdisciplinary approach, including quantitative methods, machine learning, and deep retrospective analysis of the causes that led to success and failure in studies on the creation of bile duct substitutes, holds great value. Additionally, more attention should be directed towards the balance of epithelialization and submucosal maturation rates, as well as induced angiogenesis. These ideas deserve further investigation to pave the way for bile duct restoration with physiologically relevant outcomes.

Biomaterials and Encapsulation Techniques for Probiotics: Current Status and Future Prospects in Biomedical Applications

Probiotics have garnered significant attention in recent years due to their potential advantages in diverse biomedical applications, such as acting as antimicrobial agents, aiding in tissue repair, and treating diseases. These live bacteria must exist in appropriate quantities and precise locations to exert beneficial effects. However, their viability and activity can be significantly impacted by the surrounding tissue, posing a challenge to maintain their stability in the target location for an extended duration. To counter this, researchers have formulated various strategies that enhance the activity and stability of probiotics by encapsulating them within biomaterials. This approach enables site-specific release, overcoming technical impediments encountered during the processing and application of probiotics. A range of materials can be utilized for encapsulating probiotics, and several methods can be employed for this encapsulation process. This article reviews the recent advancements in probiotics encapsulated within biomaterials, examining the materials, methods, and effects of encapsulation. It also provides an overview of the hurdles faced by currently available biomaterial-based probiotic capsules and suggests potential future research directions in this field. Despite the progress achieved to date, numerous challenges persist, such as the necessity for developing efficient, reproducible encapsulation methods that maintain the viability and activity of probiotics. Furthermore, there is a need to design more robust and targeted delivery vehicles.

Biomechanical Behaviors and Degradation Properties of Multilayered Polymer Scaffolds: The Phase Space Method for Bile Duct Design and Bioengineering

This article reports the electrospinning technique for the manufacturing of multilayered scaffolds for bile duct tissue engineering based on an inner layer of polycaprolactone (PCL) and an outer layer either of a copolymer of D,L-lactide and glycolide (PLGA) or a copolymer of L-lactide and ε-caprolactone (PLCL). A study of the degradation properties of separate polymers showed that flat PCL samples exhibited the highest resistance to hydrolysis in comparison with PLGA and PLCL. Irrespective of the liquid-phase nature, no significant mass loss of PCL samples was found in 140 days of incubation. The PLCL- and PLGA-based flat samples were more prone to hydrolysis within the same period of time, which was confirmed by the increased loss of mass and a significant reduction of weight-average molecular mass. The study of the mechanical properties of developed multi-layered tubular scaffolds revealed that their strength in the longitudinal and transverse directions was comparable with the values measured for a decellularized bile duct. The strength of three-layered scaffolds declined significantly because of the active degradation of the outer layer made of PLGA. The strength of scaffolds with the PLCL outer layer deteriorated much less with time, both in the axial (p-value = 0.0016) and radial (p-value = 0.0022) directions. A novel method for assessment of the physiological relevance of synthetic scaffolds was developed and named the phase space approach for assessment of physiological relevance. Two-dimensional phase space (elongation modulus and tensile strength) was used for the assessment and visualization of the physiological relevance of scaffolds for bile duct bioengineering. In conclusion, the design of scaffolds for the creation of physiologically relevant tissue-engineered bile ducts should be based not only on biodegradation properties but also on the biomechanical time-related behavior of various compositions of polymers and copolymers.

Angiogenic Modification of Microfibrous Polycaprolactone by pCMV-VEGF165 Plasmid Promotes Local Vascular Growth after Implantation in Rats

Insufficient vascular growth in the area of artificial-material implantation contributes to ischemia, fibrosis, the development of bacterial infections, and tissue necrosis around the graft. The purpose of this study was to evaluate angiogenesis after implantation of polycaprolactone microfiber scaffolds modified by a pCMV-VEGF165-plasmid in rats. Influence of vascularization on scaffold degradation was also examined. We investigated flat microfibrous scaffolds obtained by electrospinning polycaprolactone with incorporation of the pCMV-VEGF-165 plasmid into the microfibers at concentrations of 0.005 ng of plasmid per 1 mg of polycaprolactone (0.005 ng/mg) (LCGroup) and 0.05 ng/mg (HCGroup). The samples were subcutaneously implanted in the interscapular area of rats. On days 7, 16, 33, 46, and 64, the scaffolds were removed, and a histological study with a morphometric evaluation of the density and diameter of the vessels and microfiber diameter was performed. The number of vessels was increased in all groups, as well as the resorption of the scaffold. On day 33, the vascular density in the HCGroup was 42% higher compared to the control group (p = 0.0344). The dose-dependent effect of the pCMV-VEGF165-plasmid was confirmed by enhanced angiogenesis in the HCGroup compared to the LCGroup on day 33 (p-value = 0.0259). We did not find a statistically significant correlation between scaffold degradation rate and vessel growth (the Pearson correlation coefficient was ρ = 0.20, p-value = 0.6134). Functionalization of polycaprolactone by incorporation of the pCMV-VEGF165 plasmid provided improved vascularization within 33 days after implantation, however, vessel growth did not seem to correlate with scaffold degradation rate.

Preparation and mechanical behavior of the acellular porcine common bile duct and its immunogenicity in vivo

The current clinical treatments for complications caused by hepatobiliary surgery still have some inevitable weaknesses. This study aimed to prepare the acellular porcine common bile duct (APCBD) for repairing biliary defects and damage. The porcine common bile duct was decellularized by the freeze-thaw method combined with nuclease treatment, and the efficacy of acellularization was confirmed by the DNA quantification and histological structure. The results showed that the residual DNA content was reduced from 854.67 ± 9.71 ng/mg to 5.43 ± 0.85 ng/mg, and the natural structure and shape of the bile duct were well preserved. The biomechanical properties such as the tensile strength, elastic modulus, and elongation-at-break of the APCBD in the transverse and longitudinal direction indicated that the APCBD meets the requirements of the biomechanical strength in replacement. In addition, the results of the immunotoxicity test showed there was no significant difference in the body weights, organ coefficient, hematology, and immune histology between the experimental groups (three subgroups) and the negative control group, which demonstrated the prepared APCBD had no obvious toxicity to the immune system in vivo and might be a suitable biomaterial for the bile duct repairing.

Cellular Homeostasis and Repair in the Biliary Tree

During biliary tree homeostasis, BECs are largely in a quiescent state and their turnover is slow for maintaining normal tissue homeostasis. BTSCs continually replenish new BECs in the luminal surface of EHBDs. In response to various types of biliary injuries, distinct cellular sources, including HPCs, BTSCs, hepatocytes, and BECs, repair or regenerate the injured bile duct. BEC, biliary epithelial cell; BTSC, biliary tree stem/progenitor cell; EHBD, extrahepatic bile ducts; HPC, hepatic progenitor cell.The biliary tree comprises intrahepatic bile ducts and extrahepatic bile ducts lined with epithelial cells known as biliary epithelial cells (BECs). BECs are a common target of various cholangiopathies for which there is an unmet therapeutic need in clinical hepatology. The repair and regeneration of biliary tissue may potentially restore the normal architecture and function of the biliary tree. Hence, the repair and regeneration process in detail, including the replication of existing BECs, expansion and differentiation of the hepatic progenitor cells and biliary tree stem/progenitor cells, and transdifferentiation of the hepatocytes, should be understood. In this paper, we review biliary tree homeostasis, repair, and regeneration and discuss the feasibility of regenerative therapy strategies for cholangiopathy treatment.

Injectable Photo-Crosslinked Bioactive BMSCs-BMP2-GelMA Scaffolds for Bone Defect Repair

Injectable hydrogels offer a new therapy option for irregular bone deformities. Based on gelatin methacryloyl (GelMA), bone marrow mesenchymal stem cells (BMSCs), and bone morphogenetic protein 2 (BMP2), we created a photo-crosslinked composite bioactive scaffold. The composite scaffolds had appropriate mechanical properties for stem cells adhesion and proliferation, as well as good biocompatibility and the ability to stimulate BMSCs osteogenic differentiation in vitro. The synergistic effect of BMSCs and BMP2 enabled the composite bioactive scaffold to exhibit higher osteogenic potential in vivo than scaffolds loaded alone with BMSCs or BMP2, according to imaging and histology studies. In conclusion, by promoting the osteogenic differentiation of BMSCs, the composite bioactive scaffold based on BMSCs-BMP2-GelMA has demonstrated remarkable application potential in bone regeneration and bone defects repair.