Perfusion decellularization of whole organs

Angiosome-Guided Perfusion Decellularization of Fasciocutaneous Flaps

BACKGROUND

 Tissue engineering based on whole-organ perfusion decellularization has successfully generated small-animal organs, including the heart and limbs. Herein, we aimed to use angiosome-guided perfusion decellularization to develop an acellular fasciocutaneous flap matrix with an intact vascular network.

METHODS

 Abdominal flaps of rats were harvested, and the vascular pedicle (iliac artery and vein) was dissected and injected with methylene blue to identify the angiosome region and determine the flap dimension for harvesting. To decellularize flaps, the iliac artery was perfused sequentially with 1% sodium dodecyl sulfate (SDS), deionized water, and 1% Triton-X100. Gross morphology, histology, and DNA quantity of flaps were then obtained. Flaps were also subjected to glycosaminoglycan (GAG) and hydroxyproline content assays and computed tomography angiography.

RESULTS

 Histological assessment indicated that cellular content was completely removed in all flap layers following a 10-hour perfusion in SDS. DNA quantification confirmed 81% DNA removal. Based on biochemical assays, decellularized flaps had hydroxyproline content comparable with that of native flaps, although significantly fewer GAGs (p = 0.0019). Histology and computed tomography angiography illustrated the integrity and perfusability of the vascular system.

CONCLUSION

 The proposed angiosome-guided perfusion decellularization protocol could effectively remove cellular content from rat fasciocutaneous flaps and preserve the integrity of innate vascular networks.

Enhancing organoid culture: harnessing the potential of decellularized extracellular matrix hydrogels for mimicking microenvironments

Over the past decade, organoids have emerged as a prevalent and promising research tool, mirroring the physiological architecture of the human body. However, as the field advances, the traditional use of animal or tumor-derived extracellular matrix (ECM) as scaffolds has become increasingly inadequate. This shift has led to a focus on developing synthetic scaffolds, particularly hydrogels, that more accurately mimic three-dimensional (3D) tissue structures and dynamics in vitro. The ECM-cell interaction is crucial for organoid growth, necessitating hydrogels that meet organoid-specific requirements through modifiable physical and compositional properties. Advanced composite hydrogels have been engineered to more effectively replicate in vivo conditions, offering a more accurate representation of human organs compared to traditional matrices. This review explores the evolution and current uses of decellularized ECM scaffolds, emphasizing the application of decellularized ECM hydrogels in organoid culture. It also explores the fabrication of composite hydrogels and the prospects for their future use in organoid systems.

Assessment of decellularization strategy and biocompatibility testing of full-thickness abdominal wall to produce a tissue-engineered graft

BACKGROUND

Restoration of the abdominal wall defects due to herniation or other complications represents a challenging task of the reconstructive surgery. Synthetic grafts or crosslinked animal-derived grafts, are utilized, followed by significant adverse reactions.

OBJECTIVE

This study aimed to evaluate primarily the production of a decellularized abdominal wall scaffold and secondly its biocompatibility upon transplantation in an animal model.

METHODS

Full-thickness abdominal wall samples were harvested from Wistar Rats and then decellularized utilizing a three-cycle process. To evaluate the decellularization efficacy, histological, biochemical and biomechanical analyses were performed. The biocompatibility assessment involved the implantation of the produced scaffolds to Sprague Dawley rats. The grafts remained for a total period of 4 weeks, followed by immunohistochemistry for the detection of CD11b+, CD4+ and CD8+ cells.

RESULTS

Histological, biochemical and biomechanical results, indicated the production of compatible acellular full-thickness abdominal wall samples. After 4 weeks of implantation, a minor presence of immunity cells was observed.

CONCLUSION

The data of this study indicated the successful production of a full-thickness abdominal wall scaffold. Biologically derived full-thickness abdominal wall scaffolds may have greater potential in restoration of the abdominal wall defects, bringing them one step closer to their clinical utility.

Harnessing cellular therapeutics for type 1 diabetes mellitus: progress, challenges, and the road ahead

Type 1 diabetes mellitus (T1DM) is a growing global health concern that affects approximately 8.5 million individuals worldwide. T1DM is characterized by an autoimmune destruction of pancreatic β cells, leading to a disruption in glucose homeostasis. Therapeutic intervention for T1DM requires a complex regimen of glycaemic monitoring and the administration of exogenous insulin to regulate blood glucose levels. Advances in continuous glucose monitoring and algorithm-driven insulin delivery devices have improved the quality of life of patients. Despite this, mimicking islet function and complex physiological feedback remains challenging. Pancreatic islet transplantation represents a potential functional cure for T1DM but is hindered by donor scarcity, variability in harvested cells, aggressive immunosuppressive regimens and suboptimal clinical outcomes. Current research is directed towards generating alternative cell sources, improving transplantation methods, and enhancing cell survival without chronic immunosuppression. This Review maps the progress in cell replacement therapies for T1DM and outlines the remaining challenges and future directions. We explore the state-of-the-art strategies for generating replenishable β cells, cell delivery technologies and local targeted immune modulation. Finally, we highlight relevant animal models and the regulatory aspects for advancing these technologies towards clinical deployment.

Machine Perfusion and Bioengineering Strategies in Transplantation-Beyond the Emerging Concepts

Solid organ transplantation has progressed rapidly over the decades from the first experimental procedures to its role in the modern era as an established treatment for end-stage organ disease. Solid organ transplantation including liver, kidney, pancreas, heart, and lung transplantation, is the definitive option for many patients, but despite the advances that have been made, there are still significant challenges in meeting the demand for viable donor grafts. Furthermore, post-operatively, the recipient faces several hurdles, including poor early outcomes like primary graft dysfunction and acute and chronic forms of graft rejection. In an effort to address these issues, innovations in organ engineering and treatment have been developed. This review covers efforts made to expand the donor pool including bioengineering techniques and the use of ex vivo graft perfusion. It also covers modifications and treatments that have been trialed, in addition to research efforts in both abdominal organs and thoracic organs. Overall, this article discusses recent innovations in machine perfusion and organ bioengineering with the aim of improving and increasing the quality of donor organs.

Establishment of 3D cell culture systems with decellularized lung-derived extracellular matrix hydrogel scaffold

Decellularized tissue hydrogels, especially that mimic the native tissue, have a high potential for tissue engineering, three-dimensional (3D) cell culture, bioprinting, and therapeutic agent encapsulation due to their excellent biocompatibility and ability to facilitate the growth of cells. It is important to note that the decellularization process significantly affects the structural integrity and properties of the extracellular matrix, which in turn shapes the characteristics of the resulting hydrogels at the macromolecular level. Therefore, our study aims to identify an effective chemical decellularization method for sheep lung tissue, using a mixing/agitation technique with a range of detergents, including commonly [Sodium dodecyl sulfate (SDS), Triton X-100, and 3-((3-cholamidopropyl) dimethylammonio)-1-propanesulfonate] (CHAPS), and rarely used (sodium cholate hydrate, NP-40, and 3-[N,N-Dimethyl(3-myristoylaminopropyl)ammonio]propanesulfonate) (ASB-14). After the effectiveness of the used detergents on decellularization was determined by histological and biochemical methods, lung derived decellularized extracellular matrix was converted into hydrogel. We investigated the interactions between lung cells and decellularized extracellular matrix using proliferation assay, scanning electron microscopy, and immunofluorescence microscopy methods on BEAS-2B cells in air-liquid interface. Notably, this study emphasizes the effectiveness of ASB-14 in the decellularization process, showcasing its crucial role in removing cellular components while preserving vital extracellular matrix biological macromolecules, including glycosaminoglycans, collagen, and elastin. The resulting hydrogels demonstrated favorable mechanical properties and are compatible with both cell-cell and cell-extracellular matrix interactions.

Two Decades of Advances and Limitations in Organ Recellularization

The recellularization of tissues after decellularization is a relatively new technology in the field of tissue engineering (TE). Decellularization involves removing cells from a tissue or organ, leaving only the extracellular matrix (ECM). This can then be recellularized with new cells to create functional tissues or organs. The first significant mention of recellularization in decellularized tissues can be traced to research conducted in the early 2000s. One of the landmark studies in this field was published in 2008 by Ott, where researchers demonstrated the recellularization of a decellularized rat heart with cardiac cells, resulting in a functional organ capable of contraction. Since then, other important studies have been published. These studies paved the way for the widespread application of recellularization in TE, demonstrating the potential of decellularized ECM to serve as a scaffold for regenerating functional tissues. Thus, although the concept of recellularization was initially explored in previous decades, these studies from the 2000s marked a major turning point in the development and practical application of the technology for the recellularization of decellularized tissues. The article reviews the historical advances and limitations in organ recellularization in TE over the last two decades.

The Potential of a New Natural Vessel Source: Decellularized Intercostal Arteries as Sufficiently Long Small-Diameter Vascular Grafts

Small-diameter vascular grafts (SDVGs) are severely lacking in clinical settings. Therefore, our study investigates a new source of biological vessels-bovine and porcine decellularized intercostal arteries (DIAs)-as potential SDVGs. We utilized a combination of SDS and Triton X-100 to perfuse the DIAs, establishing two different time protocols. The results show that perfusing with 1% concentrations of each decellularizing agent for 48 h yields DIAs with excellent biocompatibility and mechanical properties. The porcine decellularized intercostal arteries (PDIAs) we obtained had a length of approximately 14 cm and a diameter of about 1.5 mm, while the bovine decellularized intercostal arteries (BDIAs) were about 29 cm long with a diameter of approximately 2.2 mm. Although the lengths and diameters of both the PDIAs and BDIAs are suited for coronary artery bypass grafting (CABG), as the typical diameter of autologous arteries used in CABG is about 2 mm and the grafts required are at least 10 cm long, our research indicates that BDIAs possess more ideal mechanical characteristics for CABG than PDIAs, showing significant potential. Further enhancements may be necessary to address their limited hemocompatibility.

Exosome-loaded decellularized tissue: Opening a new window for regenerative medicine

Mesenchymal stem cell-derived exosomes (MSCs-EXO) have received a lot of interest recently as a potential therapeutic tool in regenerative medicine. Extracellular vesicles (EVs) known as exosomes (EXOs) are crucial for cell-cell communication throughout a variety of activities including stress response, aging, angiogenesis, and cell differentiation. Exploration of the potential use of EXOs as essential therapeutic effectors of MSCs to encourage tissue regeneration was motivated by success in the field of regenerative medicine. EXOs have been administered to target tissues using a variety of methods, including direct, intravenous, intraperitoneal injection, oral delivery, and hydrogel-based encapsulation, in various disease models. Despite the significant advances in EXO therapy, various methods are still being researched to optimize the therapeutic applications of these nanoparticles, and it is not completely clear which approach to EXO administration will have the greatest effects. Here, we will review emerging developments in the applications of EXOs loaded into decellularized tissues as therapeutic agents for use in regenerative medicine in various tissues.

Optimized Decellularization of a Porcine Fasciocutaneaous Flap

Reconstructive techniques to repair severe tissue defects include the use of autologous fasciocutaneous flaps, which may be limited due to donor site availability or lead to complications such as donor site morbidity. A number of synthetic or natural dermal substitutes are in use clinically, but none have the architectural complexity needed to reconstruct deep tissue defects. The perfusion decellularization of fasciocutaneous flaps is an emerging technique that yields a scaffold with the necessary composition and vascular microarchitecture and serves as an alternative to autologous flaps. In this study, we show the perfusion decellularization of porcine fasciocutaneous flaps using sodium dodecyl sulfate (SDS) at three different concentrations, and identify that 0.2% SDS results in a decellularized flap that is efficiently cleared of its cellular material at 86%, has maintained its collagen and glycosaminoglycan content, and preserved its microvasculature architecture. We further demonstrate that the decellularized graft has the porous structure and growth factors that would facilitate repopulation with cells. Finally, we show the biocompatibility of the decellularized flap using human dermal fibroblasts, with cells migrating as deep as 150 µm into the tissue over a 7-day culture period. Overall, our results demonstrate the promise of decellularized porcine flaps as an interesting alternative for reconstructing complex soft tissue defects, circumventing the limitations of autologous skin flaps.

ECM-derived biomaterials for regulating tissue multicellularity and maturation

Recent breakthroughs in developing human-relevant organotypic models led to the building of highly resemblant tissue constructs that hold immense potential for transplantation, drug screening, and disease modeling. Despite the progress in fine-tuning stem cell multilineage differentiation in highly controlled spatiotemporal conditions and hosting microenvironments, 3D models still experience naive and incomplete morphogenesis. In particular, existing systems and induction protocols fail to maintain stem cell long-term potency, induce high tissue-level multicellularity, or drive the maturity of stem cell-derived 3D models to levels seen in their in vivo counterparts. In this review, we highlight the use of extracellular matrix (ECM)-derived biomaterials in providing stem cell niche-mimicking microenvironment capable of preserving stem cell long-term potency and inducing spatial and region-specific differentiation. We also examine the maturation of different 3D models, including organoids, encapsulated in ECM biomaterials and provide looking-forward perspectives on employing ECM biomaterials in building more innovative, transplantable, and functional organs.

Strategies for decellularization, re-cellularIzation and crosslinking in liver bioengineering

Liver transplantation is the only definitive treatment for end-stage liver disease and its availability is restricted by organ donor shortages. The development of liver bioengineering provides the probability to create a functional alternative to reduce the gap in organ demand and supply. Decellularized liver scaffolds have been widely applied in bioengineering because they can mimic the native liver microenvironment and retain extracellular matrix (ECM) components. Multiple approaches including chemical, physical and biological methods have been developed for liver decellularization in current studies, but a full set of unified criteria has not yet been established. Each method has its advantages and drawbacks that influence the microstructure and ligand landscape of decellularized liver scaffolds. Optimizing a decellularization method to eliminate cell material while retaining as much of the ECM intact as possible is therefore important for biological scaffold applications. Furthermore, crosslinking strategies can improve the biological performance of scaffolds, including reinforcing biomechanics, delaying degradation in vivo and reducing immune rejection, which can better promote the integration of re-cellularized scaffolds with host tissue and influence the reconstruction process. In this review, we aim to present the different liver decellularization techniques, the crosslinking methods to improve scaffold characteristics with crosslinking and the preparation of soluble ECM.

The Future of Microsurgery: Vascularized Composite Allotransplantation and Engineering Vascularized Tissue

Background

Microsurgical techniques have revolutionized the field of reconstructive surgery and are the mainstay for complex soft tissue reconstruction. However, their limitations have promoted the development of viable alternatives. This article seeks to explore technologies that have the potential of revolutionizing microsurgical reconstruction as it is currently known, reflect on current and future vascularized composite allotransplantation (VCA) practices, as well as describe the basic science within emerging technologies and their potential translational applications.

Methods

A literature review was performed of the technologies that may represent the future of microsurgery: vascularized tissue engineering (VCA) and flap-specific tissue engineering.

Results

VCA has shown great promise and has already been employed in the clinical setting (especially in face and limb transplantation). Immunosuppression, logistics, cost, and regulatory pathways remain barriers to overcome to make it freely available. Vascularized and flap-specific tissue engineering remain a laboratory reality but have the potential to supersede VCA. The capability of creating an off-the-shelf free flap matching the required tissue, size, and shape is a significant advantage. However, these technologies are still at the early stage and require significant advancement before they can be translated into the clinical setting.

Conclusion

VCA, vascularized tissue engineering, and flap-specific bioengineering represent possible avenues for the evolution of current microsurgical techniques. The next decade will elucidate which of these three strategies will evolve into a tangible translational option and hopefully bring a paradigm shift of reconstructive surgery.

Impact of Using Processed Urinary Bladder Submucosa and Hydrogel Fabricated from Tendon on Skin Healing Process in Rabbits

This study was intended to evaluate the healing of skin injury by using decellularized urinary bladder submucosa scaffolds and tendon-derived hydrogel. Thirty-six adult local breeds of both sex rabbits, with an average weight of 2.0-2.5 kg, were divided randomly into three groups (12 animals for each group). All groups were subjected to an induced injury (2 cm) in diameter at the right side of the abdominal skin, the rabbits of the 1st group (A) were sutured without the application of any substance as a control group, the rabbits of the 2nd group (B) were sutured and treated with the application of decellularized urinary bladder submucosa scaffolds, and in the 3rd group (C), they were sutured and treated with the application of tendon-derived hydrogel. Postoperative care following had been done for all groups throughout the study period. Specimens from the injured skin were taken for the histopathological study on the postinjury day, 8th, 14th, 21st, and 24th. The study showed a clear effect of materials used in the treatment of wounds through a clear progression in the healing stages with a noticed superiority of the submucosa scaffold group.

Perfusion Window Chambers Enable Interventional Analyses of Tumor Microenvironments

Intravital microscopy (IVM) allows spatial and temporal imaging of different cell types in intact live tissue microenvironments. IVM has played a critical role in understanding cancer biology, invasion, metastases, and drug development. One considerable impediment to the field is the inability to interrogate the tumor microenvironment and its communication cascades during disease progression and therapeutic interventions. Here, a new implantable perfusion window chamber (PWC) is described that allows high-fidelity in vivo microscopy, local administration of stains and drugs, and longitudinal sampling of tumor interstitial fluid. This study shows that the new PWC design allows cyclic multiplexed imaging in vivo, imaging of drug action, and sampling of tumor-shed materials. The PWC will be broadly useful as a novel perturbable in vivo system for deciphering biology in complex microenvironments.

Allo Beta Cell transplantation: specific features, unanswered questions, and immunological challenge

Type 1 diabetes (T1D) presents a persistent medical challenge, demanding innovative strategies for sustained glycemic control and enhanced patient well-being. Beta cells are specialized cells in the pancreas that produce insulin, a hormone that regulates blood sugar levels. When beta cells are damaged or destroyed, insulin production decreases, which leads to T1D. Allo Beta Cell Transplantation has emerged as a promising therapeutic avenue, with the goal of reinstating glucose regulation and insulin production in T1D patients. However, the path to success in this approach is fraught with complex immunological hurdles that demand rigorous exploration and resolution for enduring therapeutic efficacy. This exploration focuses on the distinct immunological characteristics inherent to Allo Beta Cell Transplantation. An understanding of these unique challenges is pivotal for the development of effective therapeutic interventions. The critical role of glucose regulation and insulin in immune activation is emphasized, with an emphasis on the intricate interplay between beta cells and immune cells. The transplantation site, particularly the liver, is examined in depth, highlighting its relevance in the context of complex immunological issues. Scrutiny extends to recipient and donor matching, including the utilization of multiple islet donors, while also considering the potential risk of autoimmune recurrence. Moreover, unanswered questions and persistent gaps in knowledge within the field are identified. These include the absence of robust evidence supporting immunosuppression treatments, the need for reliable methods to assess rejection and treatment protocols, the lack of validated biomarkers for monitoring beta cell loss, and the imperative need for improved beta cell imaging techniques. In addition, attention is drawn to emerging directions and transformative strategies in the field. This encompasses alternative immunosuppressive regimens and calcineurin-free immunoprotocols, as well as a reevaluation of induction therapy and recipient preconditioning methods. Innovative approaches targeting autoimmune recurrence, such as CAR Tregs and TCR Tregs, are explored, along with the potential of stem stealth cells, tissue engineering, and encapsulation to overcome the risk of graft rejection. In summary, this review provides a comprehensive overview of the inherent immunological obstacles associated with Allo Beta Cell Transplantation. It offers valuable insights into emerging strategies and directions that hold great promise for advancing the field and ultimately improving outcomes for individuals living with diabetes.

Conditional blastocyst complementation of a defective Foxa2 lineage efficiently promotes the generation of the whole lung

Millions suffer from incurable lung diseases, and the donor lung shortage hampers organ transplants. Generating the whole organ in conjunction with the thymus is a significant milestone for organ transplantation because the thymus is the central organ to educate immune cells. Using lineage-tracing mice and human pluripotent stem cell (PSC)-derived lung-directed differentiation, we revealed that gastrulating Foxa2 lineage contributed to both lung mesenchyme and epithelium formation. Interestingly, Foxa2 lineage-derived cells in the lung mesenchyme progressively increased and occupied more than half of the mesenchyme niche, including endothelial cells, during lung development. Foxa2 promoter-driven, conditional Fgfr2 gene depletion caused the lung and thymus agenesis phenotype in mice. Wild-type donor mouse PSCs injected into their blastocysts rescued this phenotype by complementing the Fgfr2-defective niche in the lung epithelium and mesenchyme and thymic epithelium. Donor cell is shown to replace the entire lung epithelial and robust mesenchymal niche during lung development, efficiently complementing the nearly entire lung niche. Importantly, those mice survived until adulthood with normal lung function. These results suggest that our Foxa2 lineage-based model is unique for the progressive mobilization of donor cells into both epithelial and mesenchymal lung niches and thymus generation, which can provide critical insights into studying lung transplantation post-transplantation shortly.

Decellularization Techniques for Tissue Engineering: Towards Replicating Native Extracellular Matrix Architecture in Liver Regeneration

The process of tissue regeneration requires the utilization of a scaffold, which serves as a structural framework facilitating cellular adhesion, proliferation, and migration within a physical environment. The primary aim of scaffolds in tissue engineering is to mimic the structural and functional properties of the extracellular matrix (ECM) in the target tissue. The construction of scaffolds that accurately mimic the architecture of the extracellular matrix (ECM) is a challenging task, primarily due to the intricate structural nature and complex composition of the ECM. The technique of decellularization has gained significant attention in the field of tissue regeneration because of its ability to produce natural scaffolds by removing cellular and genetic components from the extracellular matrix (ECM) while preserving its structural integrity. The present study aims to investigate the various decellularization techniques employed for the purpose of isolating the extracellular matrix (ECM) from its native tissue. Additionally, a comprehensive comparison of these methods will be presented, highlighting their respective advantages and disadvantages. The primary objective of this study is to gain a comprehensive understanding of the anatomical and functional features of the native liver, as well as the prevalence and impact of liver diseases. Additionally, this study aims to identify the limitations and difficulties associated with existing therapeutic methods for liver diseases. Furthermore, the study explores the potential of tissue engineering techniques in addressing these challenges and enhancing liver performance. By investigating these aspects, this research field aims to contribute to the advancement of liver disease treatment and management.

Investigation of impacts of decellularized heart extracellular matrix and VEGF on cardiomyogenic differentiation of mesenchymal stem cell through Notch/Hedgehog signaling pathways

OBJECTIVE

Decellularization is the process to obtain natural scaffolds with tissue integrity and extracellular matrix components, and recellularization is used to produce tissue-like constructs with specific cell types. In this study, rat bone marrow-derived mesenchymal stem cells (rBM-MSCs) were cultured on decellularized heart extracellular matrix. These cells were then induced to differentiate into cardiomyogenic cells under the stimulatory effect of vascular endothelial growth factor (VEGF) and other chemicals. This study aimed to investigate the effect of the cardiac extracellular matrix and VEGF on cardiomyogenic differentiation in the context of the Notch and Hedgehog signaling pathways.

METHODS

Heart samples extracted from rats were decellularized by serial application of detergent to remove cells from the tissue, and then recellularized with rBM-MSCs. The recellularized tissue matrices were then analyzed for cardiomyogenesis. Cardiomyogenic differentiation was performed on decellularized heart extracellular matrix (ECM; three-dimensional scaffolds) and culture plates (two-dimensional cell culture system) for 28 days to understand the effects of the heart extracellular matrix. In addition, differentiation was induced with and without the stimulatory effect of VEGF to understand the effect of VEGF on cardiomyogenic differentiation of rBM-MSCs.

RESULTS

Immunofluorescence staining showed that decellularization of the heart was performed effectively and successfully. After decellularization process, the heart extracellular matrix was completely free of cells. It was observed that rBM-MSCs transplanted onto the heart extracellular matrix remained viable and proliferated for 21 days after recellularization. The rBM-MSCs promoted cardiomyogenic differentiation in the conventional differentiation medium but were inversely affected by both VEGF and heart extracellular matrix proteins. Lower expression of connexin43 and cardiac troponin I genes was observed in cells induced by either matrix proteins or VEGF, compared to cells differentiated by chemical agents alone.

CONCLUSION

In this study, we investigated the effect of decellularized heart extracellular matrix and VEGF on cardiomyogenic differentiation of rBM-MSCs. On the decellularized cardiac extracellular matrix, rBM-MSCs maintained their viability by adhering to the matrix and proliferating further. The adhesion of the cells to the matrix also produced a physical stimulus that led to the formation of histological structures resembling myocardial layers. Chemical stimulation of the decellularized heart extracellular matrix and cardiomyogenic differentiation supplements resulted in increased expression of cardiomyogenic biomarkers through modulation of the Notch and Hedgehog signaling pathways.

Automated Decellularization of the Rodent Epigastric Free Flap: A Comparison of Sodium Dodecyl Sulfate-Based Protocols

BACKGROUND

 Free tissue transfer to cover complex wounds with exposed critical structures results in donor-site morbidity. Perfusion decellularization and recellularization of vascularized composite tissues is an active area of research to fabricate complex constructs without a donor site. Sodium dodecyl sulfate (SDS)-based protocols remain the predominant choice for decellularization despite the deleterious effects on tissue ultrastructure and capillary networks. We aimed to develop an automated decellularization process and compare different SDS perfusion times to optimize the protocol.

METHODS

 A three-dimensional-printed closed-system bioreactor capable of continuously perfusing fluid through the vasculature was used for decellularization. The artery and vein of rat epigastric fasciocutaneous free flaps were cannulated and connected to the bioreactor. Protocols had varying durations of 1% SDS solution (3, 5, and 10 days) followed by 1 day of 1% Triton X-100 and 1 day of 1x phosphate-buffered saline. The residual DNA was quantified. Microarchitecture of the constructs was assessed with histology, and the vascular network was visualized for qualitative assessment.

RESULTS

 The structural integrity and the microarchitecture of the extracellular matrix was preserved in the 3- and 5-day SDS perfusion groups; however, the subcutaneous tissue of the 10-day protocol lost its structure. Collagen and elastin structures of the pedicle vessels were not compromised by the decellularization process. Five-day SDS exposure group had the least residual DNA content (p < 0.001). Across all protocols, skin consistently had twice as much residual DNA over the subcutaneous tissues.

CONCLUSION

 A compact and integrated bioreactor can automate decellularization of free flaps to bioengineer regenerative constructs for future use in reconstruction of complex defects. A decellularization protocol with 5 days of 1% SDS exposure was the most successful to keep the residual DNA content at a minimum while preserving the structural integrity of the tissues.

Cell transplantation-based regenerative medicine in liver diseases

This review aims to evaluate the current preclinical state of liver bioengineering, the clinical context for liver cell therapies, the cell sources, the delivery routes, and the results of clinical trials for end-stage liver disease. Different clinical settings, such as inborn errors of metabolism, acute liver failure, chronic liver disease, liver cirrhosis, and acute-on-chronic liver failure, as well as multiple cellular sources were analyzed; namely, hepatocytes, hepatic progenitor cells, biliary tree stem/progenitor cells, mesenchymal stromal cells, and macrophages. The highly heterogeneous clinical scenario of liver disease and the availability of multiple cellular sources endowed with different biological properties make this a multidisciplinary translational research challenge. Data on each individual liver disease and more accurate endpoints are urgently needed, together with a characterization of the regenerative pathways leading to potential therapeutic benefit. Here, we critically review these topics and identify related research needs and perspectives in preclinical and clinical settings.

Efficient Decellularization of the Full-Thickness Rat-Derived Abdominal Wall to Produce Acellular Biologic Scaffolds for Tissue Reconstruction: Promising Evidence Acquired from In Vitro Results

BACKGROUND

Functional restoration of abdominal wall defects represents one of the fundamental challenges of reconstructive surgery. Synthetic grafts or crosslinked animal-derived biological grafts are characterized by significant adverse reactions, which are mostly observed after their implantation. The aim of this study was to evaluate the efficacy of the decellularization protocol to produce a completely acellular full-thickness abdominal wall scaffold.

METHODS

Full-thickness abdominal wall samples were harvested from Wistar rats and submitted to a three-cycle decellularization process. Histological, biochemical, and DNA quantification analyses were applied to evaluate the effect of the decellularization protocol. Mechanical testing and immunogenicity assessment were also performed.

RESULTS

Histological, biochemical, and DNA analysis results showed efficient decellularization of the abdominal wall samples after the third cycle. Decellularized abdominal wall scaffolds were characterized by good biochemical and mechanical properties.

CONCLUSION

The data presented herein confirm the effective production of a rat-derived full-thickness abdominal wall scaffold. Expanding this approach will allow the exploitation of the capacity of the proposed decellularization protocol in producing acellular abdominal wall scaffolds from larger animal models or human cadaveric donors. In this way, the utility of biological scaffolds with preserved in vivo remodeling properties may be one step closer to its application in clinical studies.

Modelling adult stem cells and their niche in health and disease with epithelial organoids

Adult stem cells are responsible for homoeostasis and regeneration of epithelial tissues. Stem cell function is regulated by both cell autonomous mechanisms as well as the niche. Deregulated stem cell function contributes to diseases such as cancer. Epithelial organoid cultures generated from tissue-resident adult stem cells have allowed unprecedented insights into the biology of epithelial tissues. The subsequent adaptation of organoid technology enabled the modelling of the communication of stem cells with their cellular and non-cellular niche as well as diseases. Starting from its first model described in 2009, the murine small intestinal organoid, we discuss here how epithelial organoid cultures have been become a prime in vitro research tool for cell and developmental biology, bioengineering, and biomedicine in the last decade.

Orthotopic Ferret Tracheal Transplantation Using a Recellularized Bioengineered Graft Produces Functional Epithelia

Tracheal grafts may be necessary to bridge long-segment defects after curative resection for airway obstructions. Bioengineered grafts have emerged as an appealing option, given the possibilities of altering the histologic and cellular profile of the conduit. We previously designed a bioreactor capable of luminally decellularizing and recellularizing a ferret trachea with surface airway epithelia (SAE) basal cells (BCs), and we sought to assess the fate of these grafts when transplanted in an orthotopic fashion. As adjuncts to the procedure, we investigated the use of a vascular endothelial growth factor (VEGF)-laden hydrogel and of immunosuppression (IS) in graft revascularization and viability. IS was shown to limit early graft revascularization, but this effect could be counteracted with VEGF supplementation. Submucosal gland (SMG) loss was shown to be inevitable regardless of the revascularization strategy. Lastly, the bioengineered tracheas survived one month after transplant with differentiation of our implanted BCs that then transitioned into a recipient-derived functional epithelium. The work presented in this manuscript has important implications for future cellular and regenerative therapies.

An electrical analog permeability model assessing fluid flow in a decellularized organ

BACKGROUND AND OBJECTIVE

In recellularization, cell-seeding efficiency refers to the uniform distribution of cells across the decellularized organ, which should be enhanced to ensure effective functioning. During cell seeding, flow dynamics influence the distribution of cells because the driving force of cell movement is the fluid force. However, after decellularization, because of flow permeability through the vessel wall, the fluid pressure and velocity in the vessels of vascular trees are significantly reduced compared with those in the native organ, which might affect cell seeding efficiency. Therefore, it is necessary to assess the flow characteristics in the vessels of decellularized organs to select appropriate seeding conditions. Although electrical analog models have been widely used to investigate the flow distribution in organs, current models do not reflect the permeable conditions. This study proposes a model to extend the conventional electrical analog model to simulate the flow characteristics in decellularized organs.

METHODS

A resistor reflecting permeable flow was added to the original electrical analog model to describe the permeable conditions in the decellularized organs. Decellularization and pressure drop measurements of the kidney were also conducted for model development, calibration, and validation. The developed model was then applied to a decellularized kidney to reveal changes in flow characteristics.

RESULTS

The resistance calculation of permeable flow was determined for each generation of vascular trees. The coefficient of permeability can be indicated by the measured flow exiting through the outlet or the pressure drop across the decellularized organ. The developed permeability model had a qualitative and quantitative agreement with the experimental data without calibration. The results of the permeability model for the decellularized kidney indicated significant reductions of up to 70% in the flow rate and pressure of the organ compared to the native kidney.

CONCLUSIONS

The developed model can simulate the flow characteristics in each individual vessel of decellularized organs. The results from the model can be used to assess the optimal flow rate condition for the cell seeding process.

Decellularization: Leveraging a Tissue Engineering Technique for Food Production

The edible nature of many plants makes leaves particularly useful as scaffolds for the development of cultured meat, where animal tissue is grown in the laboratory setting. Recently, we demonstrated that decellularized spinach leaves can serve as scaffolds to grow and differentiate cells for cultured meat products. However, conventional decellularization methods use solutions that are not considered safe for use in food, such as organic solvents (hexanes) and detergents (triton X-100 (TX100)). This study modified decellularization protocols to incorporate detergents that are regulated (REG) by the United States Food and Drug Administration (FDA) for use in food, such as Polysorbate 20 (PS20), and eliminates the use of hexanes for cuticle removal. Spinach leaves were decellularized with sodium dodecyl sulfate and then with either TX100 (control) or PS20. The average DNA content for TX100 samples and PS20 samples was similar (1.3 ± 0.07 vs 1.3 ± 0.05 ng/mg; TX100 vs PS20, p = ns). The importance of cuticle removal was tested by removing hexanes from the protocol. Groups that included the cuticle removal step exhibited an average reduction in DNA content of approximately 91.7%, and groups that omitted the cuticle removal step exhibited an average reduction of approximately 90.3% (p = ns), suggesting that the omission of the cuticle removal step did not impede decellularization. Lastly, primary bovine satellite cells (PBSCs) were cultured for 7 days (d) on the surface of spinach leaves decellularized using the REG protocol. After the 7 d incubation period, PBSCs grown on the surface of REG scaffolds had an average viability of approximately 97.4%. These observations suggest that the REG protocol described in this study is an effective decellularization method, more closely adhering to food safety guidelines, that could be implemented in lab grown meat and alternative protein products.

Automation and Optimization of Rat Heart Decellularization Using a Vibrating Fluid Column

This paper presents the validation of a software application to optimize the discoloration process in simulated hearts and to automate and determine the final moment of decellularization in rat hearts using a vibrating fluid column. The implemented algorithm specifically for the automated verification of a simulated heart's discoloration process was optimized in this study. Initially, we used a latex balloon containing enough dye to reach the opacity of a heart. The complete discoloration process corresponds to complete decellularization. The developed software automatically detects the complete discoloration of a simulated heart. Finally, the process stops automatically. Another goal was to optimize the Langendorff-type experimental apparatus, which is pressure-controlled and equipped with a vibrating fluid column that shortens the decellularization time by mechanically acting directly on cell membranes. Control experiments were performed with the designed experimental device and the vibrating liquid column using different decellularization protocols for hearts taken from rats. In this work, we used a commonly utilized solution based on sodium dodecyl sulfate. Ultraviolet spectrophotometry was used to measure the evolution of the dye concentration in the simulated hearts and, similarly, to determine the concentrations of deoxyribonucleic acid (DNA) and proteins in the rat hearts.

Capturing effects of blood flow on the transplanted decellularized nephron with intravital microscopy

Organ decellularization creates cell-free, collagen-based extracellular matrices that can be used as scaffolds for tissue engineering applications. This technique has recently gained much attention, yet adequate scaffold repopulation and implantation remain a challenge. Specifically, there still needs to be a greater understanding of scaffold responses post-transplantation and ways we can improve scaffold durability to withstand the in vivo environment. Recent studies have outlined vascular events that limit organ decellularization/recellularization scaffold viability for long-term transplantation. However, these insights have relied on in vitro/in vivo approaches that need enhanced spatial and temporal resolutions to investigate such issues at the microvascular level. This study uses intravital microscopy to gain instant feedback on their structure, function, and deformation dynamics. Thus, the objective of this study was to capture the effects of in vivo blood flow on the decellularized glomerulus, peritubular capillaries, and tubules after autologous and allogeneic orthotopic transplantation into rats. Large molecular weight dextran molecules labeled the vasculature. They revealed substantial degrees of translocation from glomerular and peritubular capillary tracks to the decellularized tubular epithelium and lumen as early as 12 h after transplantation, providing real-time evidence of the increases in microvascular permeability. Macromolecular extravasation persisted for a week, during which the decellularized microarchitecture was significantly and comparably compromised and thrombosed in both autologous and allogeneic approaches. These results indicate that in vivo multiphoton microscopy is a powerful approach for studying scaffold viability and identifying ways to promote scaffold longevity and vasculogenesis in bioartificial organs.

Decellularization of precision-cut kidney slices-application of physical and chemical methods

The extracellular matrix (ECM) obtained by decellularization provides scaffolds with the natural complex architecture and biochemical composition of the target organ. Whole kidney decellularization by perfusion uses the vasculature to remove cells leaving a scaffold that can be recellularized with patient-specific cells. However, decellularization and recellularization are highly complex processes that require intensive optimization of various parameters. In pursuit of this, a huge number of animals must be sacrificed. Therefore, we used precision-cut kidney slices (PCKS) as a source of natural scaffolds, which were decellularized by immersion in chemical reagents allowing the examination of more parameters with less animals. However, chemical reagents have a damaging effect on the structure and components of the ECM. Therefore, this study aimed at investigating the effects of physical treatment methods on the effectiveness of PCKS decellularization by immersion in chemical reagents (CHEM). PCKS were treated physically before or during immersion in chemicals (CHEM) with high hydrostatic pressure (HHP), freezing-thawing cycles (FTC) or in an ultrasonic bath system (UBS). Biochemical and DNA quantification as well as structural evaluation with conventional histology and scanning electron microscopy (SEM) were performed. Compared to decellularization by CHEM alone, FTC treatment prior to CHEM was the most effective in reducing DNA while also preserving glycosaminoglycan (GAG) content. Moreover, while UBS resulted in a comparable reduction of DNA, it was the least effective in retaining GAGs. In contrast, despite the pretreatment with HHP with pressures up to 200 MPa, it was the least effective in DNA removal. Histological scoring showed that HHP scaffolds received the best score followed by UBS, FTC and CHEM scaffolds. However further analysis with SEM demonstrated a higher deterioration of the ultrastructure in UBS scaffolds. Altogether, pretreatment with FTC prior to CHEM resulted in a better balance between DNA removal and structural preservation.

Organ Regeneration Through Stem Cells and Tissue Engineering

Loss of organ and tissue due to injuries or diseases led to the development of regenerative therapies to decrease reliance on organ transplantations. It deals with employing the self-renewal ability of stem cells to differentiate into numerous lineages to assist in providing effective treatment for a range of various injuries and diseases. Regenerative engineering of organs or tissues represents an ever-expanding field that is aimed at developing biological replacements for dysfunctional organs or injured tissues. The critical issue, however, with the engineering of organs outside the human body is the insufficient availability of human cells, the absence of a suitable matrix with the same architecture and composition as the target tissue, and the maintenance of organ viability in the absence of the blood supply. The issue regarding the maintenance of the engineered organ viability can be solved using bioreactors consisting of mediums with defined chemical composition, i.e., nutrients, cofactors, and growth factors that can successively sustain the target cell's viability. Engineered extracellular matrices and stem cells to regenerate organs outside the human body are also being used. Clinically, various adult stem cell therapies are readily under practice. This review will focus on the regeneration of organs through various types of stem cells and tissue engineering techniques.

Decellularized Extracellular Matrix Scaffolds for Cardiovascular Tissue Engineering: Current Techniques and Challenges

Cardiovascular diseases are the leading cause of global mortality. Over the past two decades, researchers have tried to provide novel solutions for end-stage heart failure to address cardiac transplantation hurdles such as donor organ shortage, chronic rejection, and life-long immunosuppression. Cardiac decellularized extracellular matrix (dECM) has been widely explored as a promising approach in tissue-regenerative medicine because of its remarkable similarity to the original tissue. Optimized decellularization protocols combining physical, chemical, and enzymatic agents have been developed to obtain the perfect balance between cell removal, ECM composition, and function maintenance. However, proper assessment of decellularized tissue composition is still needed before clinical translation. Recellularizing the acellular scaffold with organ-specific cells and evaluating the extent of cardiomyocyte repopulation is also challenging. This review aims to discuss the existing literature on decellularized cardiac scaffolds, especially on the advantages and methods of preparation, pointing out areas for improvement. Finally, an overview of the state of research regarding the application of cardiac dECM and future challenges in bioengineering a human heart suitable for transplantation is provided.

An efficient strategy to recellularization of a rat aorta scaffold: an optimized decellularization, detergent removal, and Apelin-13 immobilization

Background

Tissue engineering of native vessels is an alternative approach for patients with vascular disease who lack sufficient saphenous vein or other suitable conduits for autologous vascular graft. Moreover, the harvest of vessels prolongs the surgical procedure and it may lead to the morbidity of donor site in elder patients: therefore, it seems that the use of tissue-engineered vessels would be an attractive and less invasive substitute for autologous vascular grafts. Apelin-13 plays a pivotal role in cell proliferation, survival, and attachment; therefore, covalent attachment of apelin-13 to the acellular scaffolds might be a favorable approach for improving recellularization efficacy.

Methods

In the present study, the decellularization process was performed using various detergents. Afterward, the efficacy of decellularization procedure was evaluated using multiple approaches including assessment of DNA, hydroxyproline, and GAG content as well as Masson’s trichrome and orcein staining used for collagen and elastin determination. Subsequently, the scaffold was bioconjugated with apelin-13 using the EDC-NHS linker and acellular scaffolds were recellularized using fibroblasts, endothelial cells, and smooth muscle cells. SEM images and characterization methods were also used to evaluate the effect of apelin-13 attachment to the acellular scaffold on tissue recellularization. We also developed a novel strategy to eliminate the remnant detergents from the scaffold and increase cell viability by incubating acellular scaffolds with Bio-Beads SM-2 resin. Testometric tensile testing machine was also used for the assessment of mechanical properties and uniaxial tensile strength of decellularized and recellularized vessels compared to that of native tissues.

Results

Our results proposed 16-h perfusion of 0.25% sodium dodecyl sulfate (SDS) + 0.5% Triton X-100 combination to the vessel as an optimal decellularization protocol in terms of cell elimination as well as extracellular matrix preservation. Furthermore, the results demonstrated considerable elevation of cell adhesion and proliferation in scaffolds bioconjugated with apelin-13. The immunohistochemical (IHC) staining of CD31, α-SMA, and vimentin markers suggested placement of seeded cells in the suitable sites and considerable elevation of cell attachment within the scaffolds bioconjugated with apelin-13 compared to the non-bioconjugated, and decellularized groups. Moreover, the quantitative analysis of IHC staining of CD31, α-SMA, and vimentin markers suggested considerable elevation in the number of endothelial, smooth muscle, and fibroblast cells in the recellularized scaffolds bioconjugated with apelin-13 group (1.4% ± 0.02, 6.66% ± 0.23, and 9.87% ± 0.13%, respectively) compared to the non-bioconjugated scaffolds (0.03% ± 0.01, 0.28% ± 0.01, and 1.2% ± 0.09%, respectively) and decellularized groups (0.03% ± 0.007, 0.05% ± 0.01, and 0.13% ±0.005%, respectively). Although the maximum strain to the rupture was reduced in tissues decellularized using 0.5% SDS and CHAPS compared to that of native ones (116% ± 6.79, 139.1% ± 3.24, and 164% ± 8.54%, respectively), ultimate stress was decreased in all decellularized and recellularized groups. Besides, our results indicated that cell viability on the 1st, 3rd, and 7th day was 100.79% ± 0.7, 100.34% ± 0.08, and 111.24% ± 1.7% for the decellularized rat aorta conjugated with apelin-13, which was incubated for 48-h with Bio-Beads SM-2, and 73.37% ± 7.99, 47.6% ± 11.69, and 27.3% ± 7.89% for decellularized rat aorta scaffolds conjugated with apelin-13 and washed 48-h by PBS, respectively. These findings reveal that the incubation of the scaffold with Bio-Beads SM-2 is a novel and promising approach for increasing cell viability and growth within the scaffold.

Conclusions

In conclusion, our results provide a platform in which xenograft vessels are decellularized properly in a short time, and the recellularization process is significantly improved after the bioconjugation of the acellular scaffold with apelin-13 in terms of cell adhesion and viability within the scaffold.

Graphical Abstract

Perfusion decellularization for vascularized composite allotransplantation

Vascularized composite allotransplantation is becoming the emerging standard for reconstructive surgery treatment for patients with limb trauma and facial injuries involving soft tissue loss. Due to the complex immunogenicity of composite grafts, patients who undergo vascularized composite allotransplantation are reliant on lifelong immunosuppressive therapy. Decellularization of donor grafts to create an extracellular matrix bio-scaffold provides an immunomodulatory graft that preserves the structural and bioactive function of the extracellular matrix. Retention of extracellular matrix proteins, growth factors, and signaling cascades allow for cell adhesion, migration, proliferation, and tissue regeneration. Perfusion decellularization of detergents through the graft vasculature allows for increased regent access to all tissue layers, and removal of cellular debris through the venous system. Grafts can subsequently be repopulated with appropriate cells through the vasculature to facilitate tissue regeneration. The present work reviews methods of decellularization, process parameters, evaluation of adequate cellular and nuclear removal, successful applications of perfusion decellularization for use in vascularized composite allotransplantation, and current limitations.

Solid fraction determines stiffness and viscosity in decellularized pancreatic tissues

The role of extracellular matrix (ECM) composition and turnover in mechano-signaling and the metamorphic fate of cells seeded into decellularized tissue can be elucidated by recent developments in non-invasive imaging and biotechnological analysis methods. Because these methods allow accurate quantification of the composition and structural integrity of the ECM, they can be critical in establishing standardized decellularization protocols. This study proposes quantification of the solid fraction, the single-component fraction and the viscoelasticity of decellularized pancreatic tissues using compact multifrequency magnetic resonance elastography (MRE) to assess the efficiency and quality of decellularization protocols. MRE of native and decellularized pancreatic tissues showed that viscoelasticity parameters depend according to a power law on the solid fraction of the decellularized matrix. The parameters can thus be used as highly sensitive markers of the mechanical integrity of soft tissues. Compact MRE allows consistent and noninvasive quantification of the viscoelastic properties of decellularized tissue. Such a method is urgently needed for the standardized monitoring of decellularization processes, evaluation of mechanical ECM properties, and quantification of the integrity of solid structural elements remaining in the decellularized tissue matrix.

Approaches to kidney replacement therapies—opportunities and challenges

One out of seven people develop chronic kidney disease (CKD). When kidney function continues to decline, CKD patients may develop end-stage renal disease (ESRD, or kidney failure). More than 2 out of 1,000 adults develop ESRD and these patients must live on dialysis or get a kidney transplant to survive. Each year, more than $51 billion is spent to treat patients with ESRD in the United States. In addition, ESRD greatly reduces longevity and quality of life for patients. Compared to dialysis, kidney transplant offers the best chance of survival, but few donor organs are available. Thus, there is an urgent need for innovative solutions that address the shortage of kidneys available for transplantation. Here we summarize the status of current approaches that are being developed to solve the shortage of donor kidneys. These include the bioartificial kidney approach which aims to make a portable dialysis device, the recellularization approach which utilizes native kidney scaffold to make an engineered kidney, the stem cell-based approach which aims to generate a kidney de novo by recapitulating normal kidney organogenesis, the xenotransplantation approach which has the goal to make immunocompatible pig kidneys for transplantation, and the interspecies chimera approach which has potential to generate a human kidney in a host animal. We also discuss the interconnections among the different approaches, and the remaining challenges of translating these approaches into novel therapies.

Human Endothelial Cell Seeding in Partially Decellularized Kidneys

The excessive demand for organ transplants has promoted the development of strategies that increase the supply of immune compatible organs, such as xenotransplantation of genetically modified pig organs and the generation of bioartificial organs. We describe a method for the partial replacement of rat endothelial cells for human endothelial cells in a rat's kidney, obtaining as a final result a rat-human bioartificial kidney. First, in order to maintain parenchymal epithelial cells and selectively eliminate rat endothelial cells, three methods were evaluated in which different solutions were perfused through the renal artery: 0.1% sodium dodecyl sulfate (SDS), 0.01% SDS, and hyperosmolar solutions of sucrose. Then, partially decellularized kidneys were recellularized with human endothelial cells and finally transplanted in an anesthetized rat. The solution of 0.1% SDS achieved the highest vascular decellularization but with high degree of damage in the parenchyma side. On the contrary, 0.01% SDS and hyperosmolar solutions achieved a partial degree of endothelial decellularization. TUNEL assays reveal that hyperosmolar solutions maintained a better epithelial cell viability contrasting with 0.01% SDS. Partially decellularized kidneys were then recellularized with human endothelial cells. Histological analysis showed endothelial cells attached in almost all the vascular bed. Recellularized kidney was transplanted in an anesthetized rat. After surgery, recellularized kidney achieved complete perfusion, and urine was produced for at least 90 min posttransplant. Histological analysis showed endothelial cells attached in almost all the vascular bed. Therefore, endothelial decellularization of grafts and recellularization with human endothelial cells derived from transplant recipients can be a feasible method with the aim to reduce the damage of the grafts.

A Bioink Derived From Human Placenta Supporting Angiogenesis

Bioprinting is an emerging approach for constructing sophisticated tissue analogues with detailed architectures such as vascular networks, which requires bioink fulfill the highly printable property and provide a cell-friendly microenvironment mimicking native extracellular matrix (ECM). Here, we developed a human placental ECM-derived bioink (hp-bioink) meeting the requirements of 3D printing for printability and bioactivity. We first decellularized the human placenta, followed by enzymatic digestion, dialysis, lyophilization, and re-solubilization to convert the extracts into hp-bioink. Then, we demonstrated that 3%-5% of hp-bioink can be printed with self-standing and 1%-2% of hp-bioink can be embedded with suspended hydrogels. Moreover, hp-bioink supports HUVEC assembly in vitro and angiogenesis in mice in vivo. Our research enriched the bank of human-derived bioink, and provided a new opportunity to further accelerate bioprinting research and application.

Bladder Acellular Matrix Prepared by a Self-Designed Perfusion System and Adipose-Derived Stem Cells to Promote Bladder Tissue Regeneration

The bladder patch constructed with the bladder acellular matrix (BAM) and adipose-derived stem cells (ASCs) was incubated with the omentum for bladder reconstruction in a rat model of bladder augmentation cystoplasty. A self-designed perfusion system and five different decellularization protocols were used to prepare the BAM. Finally, an optimal protocol (group C) was screened out by comparing the cell nucleus residue, collagen structure preservation and biologically active components retention of the prepared BAM. ASCs-seeded (BAM-ASCs group) and unseeded BAM (BAM group) were incubated with the omentum for 7 days to promote neovascularization and then perform bladder reconstruction. Hematoxylin and eosin and Masson’s trichrome staining indicated that the bladder patches in the BAM-ASCs group could better regenerate the bladder wall structure compared to the BAM group. Moreover, immunofluorescence analyses demonstrated that the ASCs could promote the regeneration of smooth muscle, neurons and blood vessels, and the physiological function (maximal bladder capacity, max pressure prior to voiding and bladder compliance) restoration in the BAM-ASCs group. The results demonstrated that the self-designed perfusion system could quickly and efficiently prepare the whole bladder scaffold and confirmed that the prepared BAM could be used as the scaffold material for functional bladder tissue engineering applications.

A Novel Bioreactor for Reconstitution of the Epithelium and Submucosal Glands in Decellularized Ferret Tracheas

Tracheal grafts introduce the possibility to treat airway pathologies that require resection. While there has been success with engraftment of the surface airway epithelium (SAE) onto decellularized tracheas, there has been minimal advancement in regenerating the submucosal glands (SMGs). We designed a cost-effective open-system perfusion bioreactor to investigate the engraftment potential of ferret SAEs and murine myoepithelial cells (MECs) on a partly decellularized ferret trachea with the goal of creating a fully functional tracheal replacement. An air-liquid interface was also arranged by perfusing humidified air through the lumen of a recellularized conduit to induce differentiation. Our versatile bioreactor design was shown to support the successful partial decellularization and recellularization of ferret tracheas. The decellularized grafts maintained biomechanical integrity and chondrocyte viability, consistent with other publications. The scaffolds supported SAE basal cell engraftment, and early differentiation was observed once an air-liquid interface had been established. Lastly, MEC engraftment was sustained, with evidence of diffuse SMG reconstitution. This model will help shed light on SMG regeneration and basal cell differentiation in vitro for the development of fully functional tracheal grafts before transplantation.

Perfusion-Based Recellularization of Rat Livers with Islets of Langerhans

Purpose

Artificial organs might serve as alternative solutions for whole organ transplantation. Decellularization of a liver provides a non-immunogenic matrix with the advantage of three afferent systems, the portal vein, the hepatic artery and the bile duct. This study aims to evaluate the recellularization of rat livers with islets of Langerhans via the bile duct and the portal vein for the comparison of different perfusion routes.

Methods

Rat livers were decellularized in a pressure-controlled perfusion manner and repopulated with intact isolated islets of Langerhans via either the portal vein or the bile duct.

Results

Repopulation via the portal vein showed islet clusters stuck within the vascular system demonstrated by ellipsoid borders of thick reticular tissue around the islet cluster in Azan staining. After recellularization via the bile duct, islets were distributed close to the vessels within the parenchymal space and without a surrounding reticular layer. Large clusters of islets had a diameter of up to 1000 µm without clear shapes.

Conclusion

We demonstrated the bile duct to be superior to the portal vein for repopulation of a decellularized rat liver with islets of Langerhans. This technique may serve as a bioengineering platform to generate an implantable and functional endocrine neo-pancreas and provide scaffolds with the anatomic benefit of three afferent systems to facilitate co-population of cells.

Decellularization Following Fixation of Explanted Aortic Valves as a Strategy for Preserving Native Mechanical Properties and Function

Mechanical or biological aortic valves are incorporated in physical cardiac simulators for surgical training, educational purposes, and device testing. They suffer from limitations including either a lack of anatomical and biomechanical accuracy or a short lifespan, hence limiting the authentic hands-on learning experience. Medical schools utilize hearts from human cadavers for teaching and research, but these formaldehyde-fixed aortic valves contort and stiffen relative to native valves. Here, we compare a panel of different chemical treatment methods on explanted porcine aortic valves and evaluate the microscopic and macroscopic features of each treatment with a primary focus on mechanical function. A surfactant-based decellularization method after formaldehyde fixation is shown to have mechanical properties close to those of the native aortic valve. Valves treated in this method were integrated into a custom-built left heart cardiac simulator to test their hemodynamic performance. This decellularization, post-fixation technique produced aortic valves which have ultimate stress and elastic modulus in the range of the native leaflets. Decellularization of fixed valves reduced the valvular regurgitation by 60% compared to formaldehyde-fixed valves. This fixation method has implications for scenarios where the dynamic function of preserved valves is required, such as in surgical trainers or device test rigs.

Engineering pro-angiogenic biomaterials via chemoselective extracellular vesicle immobilization

Nanoscale extracellular vesicles (EVs) represent a unique cellular derivative that reflect the therapeutic potential of mesenchymal stem cells (MSCs) toward tissue engineering and injury repair without the logistical and safety concerns of utilizing living cells. However, upon systemic administration in vivo,EVs undergo rapid clearance and typically lack controlled targeted delivery, thus reducing their effectiveness in therapeutic regenerative therapies. Here, we describe a strategy that enables long-term in vivo spatial EV retention by chemoselective immobilization of metabolically incoporated azido ligand-bearing EVs (azido-EVs) within a dibenzocyclooctyne-modified collagen hydrogel. MSC-derived azido-EVs exhibit comparable morphological and functional properties as their non-labeled EV counterparts and, when immobilized within collagen hydrogel implants via click chemistry, they elicited more robust host cell infiltration, angiogenic and immunoregulatory responses including vascular ingrowth and macrophage recruitment compared to ten times the higher dose required by non-immobilized EVs. We envision this technology will enable a wide range of applications to spatially promote vascularization and host integration relevant to tissue engineering and regenerative medicine applications.

Towards organoid culture without Matrigel

Organoids-cellular aggregates derived from stem or progenitor cells that recapitulate organ function in miniature-are of growing interest in developmental biology and medicine. Organoids have been developed for organs and tissues such as the liver, gut, brain, and pancreas; they are used as organ surrogates to study a wide range of questions in basic and developmental biology, genetic disorders, and therapies. However, many organoids reported to date have been cultured in Matrigel, which is prepared from the secretion of Engelbreth-Holm-Swarm mouse sarcoma cells; Matrigel is complex and poorly defined. This complexity makes it difficult to elucidate Matrigel-specific factors governing organoid development. In this review, we discuss promising Matrigel-free methods for the generation and maintenance of organoids that use decellularized extracellular matrix (ECM), synthetic hydrogels, or gel-forming recombinant proteins.

Renal bioengineering with scaffolds prepared from discarded human kidneys by human mesenchymal stem cells

AIMS

Regeneration of discarded human kidneys has been considered as an ideal approach to overcome organ shortage for the end-stage renal diseases (ESRDs). The aim of this study was to develop an effective method for preparation of kidney scaffolds that retain the matrix structure required for proliferation and importantly, differentiation of human adipose-derived mesenchymal stem cells (hAd-MSCs) into renal cells.

MAIN METHODS

we first compared two different methods using triton X-100 and sodium dodecyl sulfate (SDS) for human kidney decellularization; and characterized developed human renal extracellular matrix (ECM) scaffolds. Then, hAd-MSCs were seeded on human decellularized kidney scaffolds and cultured for up to 3 weeks. Next, viability, proliferation, and migration of seeded hAd-MSCs within the scaffolds, underwent histological and scanning electron microscopy (SEM) assessments. Moreover, differentiation of hAd-MSCs into kidney-specific cell types was examined using immunohistochemistry (IHC) staining and qRT-PCR.

KEY FINDINGS

Our results indicated that triton X-100 was a more effective detergent for decellularization of human kidneys compared with SDS. Moreover, attachment and proliferation of hAd-MSCs within the recellularized human kidney scaffolds, were confirmed. Seeded cells expressed epithelial and endothelial differentiation markers, and qRT-PCR results indicated increased expression of platelet and endothelial cell adhesion Molecule 1 (PECAM-1), paired box 2 (PAX2), and e-cadherine (E-CDH) as factors required for differentiation of hAd-MSCs into epithelial and endothelial cells.

SIGNIFICANCE

These observations indicate effectiveness of decellularization by triton X-100 to generate suitable human ECM renal scaffolds, which supported adhesion and proliferation of hAd-MSCs and could induce their differentiation towards a renal lineage.

Towards Biomanufacturing of Cell-Derived Matrices

Cell-derived matrices (CDM) are the decellularised extracellular matrices (ECM) of tissues obtained by the laboratory culture process. CDM is developed to mimic, to a certain extent, the properties of the needed natural tissue and thus to obviate the use of animals. The composition of CDM can be tailored for intended applications by carefully optimising the cell sources, culturing conditions and decellularising methods. This unique advantage has inspired the increasing use of CDM for biomedical research, ranging from stem cell niches to disease modelling and regenerative medicine. However, while much effort is spent on extracting different types of CDM and exploring their utilisation, little is spent on the scale-up aspect of CDM production. The ability to scale up CDM production is essential, as the materials are due for clinical trials and regulatory approval, and in fact, this ability to scale up should be an important factor from the early stages. In this review, we first introduce the current CDM production and characterisation methods. We then describe the existing scale-up technologies for cell culture and highlight the key considerations in scaling-up CDM manufacturing. Finally, we discuss the considerations and challenges faced while converting a laboratory protocol into a full industrial process. Scaling-up CDM manufacturing is a challenging task since it may be hindered by technologies that are not yet available. The early identification of these gaps will not only quicken CDM based product development but also help drive the advancement in scale-up cell culture and ECM extraction.

Bioengineering Approaches for the Advanced Organoid Research

Recent advances in 3D cell culture technology have enabled scientists to generate stem cell derived organoids that recapitulate the structural and functional characteristics of native organs. Current organoid technologies have been striding toward identifying the essential factors for controlling the processes involved in organoid development, including physical cues and biochemical signaling. There is a growing demand for engineering dynamic niches characterized by conditions that resemble in vivo organogenesis to generate reproducible and reliable organoids for various applications. Innovative biomaterial-based and advanced engineering-based approaches have been incorporated into conventional organoid culture methods to facilitate the development of organoid research. The recent advances in organoid engineering, including extracellular matrices and genetic modulation, are comprehensively summarized to pinpoint the parameters critical for organ-specific patterning. Moreover, perspective trends in developing tunable organoids in response to exogenous and endogenous cues are discussed for next-generation developmental studies, disease modeling, and therapeutics.

Advanced human-relevant in vitro pulmonary platforms for respiratory therapeutics

Over the past years, advanced in vitro pulmonary platforms have witnessed exciting developments that are pushing beyond traditional preclinical cell culture methods. Here, we discuss ongoing efforts in bridging the gap between in vivo and in vitro interfaces and identify some of the bioengineering challenges that lie ahead in delivering new generations of human-relevant in vitro pulmonary platforms. Notably, in vitro strategies using foremost lung-on-chips and biocompatible "soft" membranes have focused on platforms that emphasize phenotypical endpoints recapitulating key physiological and cellular functions. We review some of the most recent in vitro studies underlining seminal therapeutic screens and translational applications and open our discussion to promising avenues of pulmonary therapeutic exploration focusing on liposomes. Undeniably, there still remains a recognized trade-off between the physiological and biological complexity of these in vitro lung models and their ability to deliver assays with throughput capabilities. The upcoming years are thus anticipated to see further developments in broadening the applicability of such in vitro systems and accelerating therapeutic exploration for drug discovery and translational medicine in treating respiratory disorders.