Tissue engineered human tracheas for in vivo implantation

Decellularization techniques: unveiling the blueprint for tracheal tissue engineering

Certain congenital or acquired diseases and defects such as tracheo-oesophageal fistula, tracheomalacia, tracheal stenosis, airway ischemia, infections, and tumours can cause damage to the trachea. Treatments available do not offer any permanent solutions. Moreover, long-segment defects in the trachea have no available surgical treatments. Tissue engineering has gained popularity in current regenerative medicine as a promising approach to bridge this gap. Among the various tissue engineering techniques, decellularization is a widely used approach that removes the cellular and nuclear contents from the tissue while preserving the native extracellular matrix components. The decellularized scaffolds exhibit significantly lower immunogenicity and retain the essential biomechanical and proangiogenic properties of native tissue, creating a foundation for trachea regeneration. The present review provides an overview of trachea decellularization advancements, exploring how recellularization approaches can be optimized by using various stem cells and tissue-specific cells to restore the scaffold's structure and function. We examine critical factors such as mechanical properties, revascularization, and immunogenicity involved in the transplantation of tissue-engineered grafts.

Effects of decellularization on glycosaminoglycans and collagen macromolecules in bovine bone extracellular matrix

Bovine bones were decellularized to obtain extracellular matrices with potential use for Tissue Bioengineering. The objective of the present study was to develop a decellularization protocol for bovine trabecular bone while maintaining the integrity of the extracellular matrix (ECM). The protocol proved to be effective in significantly reducing the Amount of genetic material and cellular content, and it was considered innovative, being filed as a patent. The scaffold obtained showed a reduction in the content of glycosaminoglycans (GAGs) and collagen. Even with the loss of these ECM components, the material obtained can be considered an alternative for use in Tissue Engineering and Regenerative Medicine.

Towards Safety and Regulation Criteria for Clinical Applications of Decellularized Organ-Derived Matrices

Whole-organ decellularization generates scaffolds containing native extracellular matrix (ECM) components with preserved tissue microarchitecture, providing a promising advancement in tissue engineering and regenerative medicine. Decellularization retains the ECM integrity which is important for supporting cell attachment, growth, differentiation, and biological function. Although there are consensus guidelines to standardize decellularization processes and ECM characterization, no specific criteria or standards regarding matrix sterility and biosafety have been established so far. This regulatory gap in safety, sterilization, and regulation criteria has hampered the clinical translation of decellularized scaffolds. In this review, we identify essential criteria for the safe clinical use of decellularized products from both human and animal sources. These include the decellularization efficacy, levels of chemical residue, preservation of ECM composition and physical characteristics, and criteria for the aseptic processing of decellularization to assure sterility. Furthermore, we explore key considerations for advancing decellularized scaffolds into clinical practice, focusing on regulatory frameworks and safety requirements. Addressing these challenges is crucial for minimizing risks of adverse reactions or infection transmission, thereby accelerating the adoption of tissue-engineered products. This review aims to provide a foundation for establishing robust guidelines, supporting the safe and effective integration of decellularized scaffolds into regenerative medicine applications.

The Development of Lung Tissue Engineering: From Biomaterials to Multicellular Systems

The challenge of the treatment of end-stage lung disease poses an urgent clinical demand for lung tissue engineering. Over the past few years, various lung tissue-engineered constructs are developed for lung tissue regeneration and respiratory pathology study. In this review, an overview of recent achievements in the field of lung tissue engineering is proposed. The introduction of lung structure and lung injury are stated briefly at first. After that, the lung tissue-engineered constructs are categorized into three types: acellular, monocellular, and multicellular systems. The different bioengineered constructs included in each system that can be applied to the reconstruction of the trachea, airway epithelium, alveoli, and even whole lung are described in detail, followed by the highlight of relevant representative research. Finally, the challenges and future directions of biomaterials, manufacturing technologies, and cells involved in lung tissue engineering are discussed. Overall, this review can provide referable ideas for the realization of functional lung regeneration and permanent lung substitution.

Tissue Engineering and Regenerative Medicine in the Field of Otorhinolaryngology

BACKGROUND

Otorhinolaryngology is a medical specialty that focuses on the clinical study and treatments of diseases within head and neck regions, specifically including the ear, nose, and throat (ENT), but excluding eyes and brain. These anatomical structures play significant roles in a person's daily life, including eating, speaking as well as facial appearance and expression, thus greatly impacting one's overall satisfaction and quality of life. Consequently, injuries to these regions can significantly impact a person's well-being, leading to extensive research in the field of tissue engineering and regenerative medicine over many years.

METHODS

This chapter provides an overview of the anatomical characteristics of otorhinolaryngologic tissues and explores the tissue engineering and regenerative medicine research in otology (ear), rhinology (nose), facial bone, larynx, and trachea.

RESULTS AND CONCLUSION

The integration of tissue engineering and regenerative medicine in otorhinolaryngology holds the promise of broadening the therapeutic choices for a wide range of conditions, ultimately improving quality of a patient's life.

Challenges and Opportunities in Developing Tracheal Substitutes for the Recovery of Long-Segment Defects

Tracheal resection and reconstruction procedures are necessary when stenosis, tracheomalacia, tumors, vascular lesions, or tracheal injury cause a tracheal blockage. Replacement with a tracheal substitute is often recommended when the trauma exceeds 50% of the total length of the trachea in adults and 30% in children. Recently, tissue engineering and other advanced techniques have shown promise in fabricating biocompatible tracheal substitutes with physical, morphological, biomechanical, and biological characteristics similar to native trachea. Different polymers and biometals are explored. Even with limited success with tissue-engineered grafts in clinical settings, complete healing of tracheal defects remains a substantial challenge due to low mechanical strength and durability of the graft materials, inadequate re-epithelialization and vascularization, and restenosis. This review has covered a range of reconstructive and regenerative techniques, design criteria, the use of bioprostheses and synthetic grafts for the recovery of tracheal defects, as well as the traditional and cutting-edge methods of their fabrication, surface modification for increased immuno- or biocompatibility, and associated challenges.

Cardiac Tissue Engineering: A Journey from Scaffold Fabrication to In Vitro Characterization

Cardiac tissue engineering has been rapidly evolving with diverse applications, ranging from the repair of fibrotic tissue caused by "adverse remodeling," to the replacement of specific segments of heart tissue, and ultimately to the creation of a whole heart. The repair or replacement of cardiac tissue often involves the development of tissue scaffolds or constructs and the subsequent assessment of their performance and functionality. For this, the design and/or selection of biomaterials, and cell types, scaffold fabrication, and in vitro characterizations are the first starting points, yet critical, to ensure success in subsequent implantation in vivo. This highlights the importance of scaffold fabrication and in vitro experiments/characterization with protocols for cardiac tissue engineering. Yet, a comprehensive and critical review of these has not been established and documented. As inspired, herein, the latest development and advances in scaffold fabrication and in vitro characterization for cardiac tissue engineering are critically reviewed, with focus on biomaterials, cell types, additive manufacturing techniques for scaffold fabrication, and common in vitro characterization techniques or methods. This article would be of benefit to the ones who are working on cardiac tissue engineering by providing insights into the scaffold fabrication and in vitro investigations.

Construction of dental pulp decellularized matrix by cyclic lavation combined with mechanical stirring and its proteomic analysis

The decellularized matrix has a great potential for tissue remodeling and regeneration; however, decellularization could induce host immune rejection due to incomplete cell removal or detergent residues, thereby posing significant challenges for its clinical application. Therefore, the selection of an appropriate detergent concentration, further optimization of tissue decellularization technique, increased of biosafety in decellularized tissues, and reduction of tissue damage during the decellularization procedures are pivotal issues that need to be investigated. In this study, we tested several conditions and determined that 0.1% Sodium dodecyl sulfate and three decellularization cycles were the optimal conditions for decellularization of pulp tissue. Decellularization efficiency was calculated and the preparation protocol for dental pulp decellularization matrix (DPDM) was further optimized. To characterize the optimized DPDM, the microstructure, odontogenesis-related protein and fiber content were evaluated. Our results showed that the properties of optimized DPDM were superior to those of the non-optimized matrix. We also performed the 4D-Label-free quantitative proteomic analysis of DPDM and demonstrated the preservation of proteins from the natural pulp. This study provides a optimized protocol for the potential application of DPDM in pulp regeneration.

Global Bibliometric and Visualized Analysis of Tracheal Tissue Engineering Research

The development of tracheal tissue engineering (TTE) has seen a rapid growth in recent years. The purpose of this study was to investigate the global status, trends, and hotspots of TTE research based on bibliometrics and visualization analysis. Publications related to TTE were retrieved and included in the Web of Science Core Collection. VOSviewer and CiteSpace were used to generate knowledge maps. Six hundred fifty-five publications were identified, and the quantity of the annual publications worldwide was on the increase. International collaboration is a widespread reality. The United States led the world in the field of trachea tissue engineering, whereas University College London was the institution with the greatest contribution. In addition, Biomaterials had a great influence in this field, attracting the largest number of papers. Moreover, the topics of TTE research largely concentrated on the biomechanical scaffold preparation, the vascularization and epithelialization of scaffold, the tracheal cartilage regeneration, and the tissue-engineered tracheal transplantation. And the research on the application of decellularization and 3D printing for the construction of a tissue-engineered trachea was likely to receive more widespread attention in the future. Impact statement In recent years, tracheal tissue engineering (TTE) has experienced rapid growth. In this study, we investigated the worldwide status and trends of TTE research, and revealed the countries, institutions, journals, and authors that had made significant contributions to the field of TTE. Moreover, the possible research hotspots in the future were predicted. According to our research, researchers can gain a better understanding of the trends in this field, and stay informed of the most current research by tracking key journals, institutions, and authors.

Synergistic Effects of SDS and H2O2 Combinations on Tracheal Scaffold Development: An In Vitro Study Using Goat Trachea

Currently, a tissue-engineered trachea has been popularly used as a biological graft for tracheal replacement in severe respiratory diseases. In the development of tissue-engineered tracheal scaffolds, in vitro studies play a crucial role in allowing researchers to evaluate the efficacy and safety of scaffold designs and fabrication techniques before progressing to in vivo or clinical trials. This research involved the decellularization of goat trachea using SDS, H2O2, and their combinations. Various quantitative and qualitative assessments were performed, including histological analysis, immunohistochemistry, and biomechanical testing. Hematoxylin and eosin staining evaluated the cellular content, while safranin O-fast green and Masson's trichrome staining assessed glycosaminoglycan content and collagen distribution, respectively. The immunohistochemical analysis focused on detecting MHC-1 antigen presence. Tensile strength measurements were conducted to evaluate the biomechanical properties of the decellularized scaffolds. The results demonstrated that the combination of SDS and H2O2 for goat tracheal decellularization yielded scaffolds with minimal cellular remnants, low toxicity, preserved ECM, and high tensile strength and elasticity. This method holds promise for developing functional tracheal scaffolds to address severe respiratory diseases effectively.

Whole Model Path Planning-Guided Multi-Axis and Multi-Material Printing of High-Performance Intestinal Implantable Stent

The problems of step effects, supporting material waste, and conflict between flexibility and toughness for 3D printed intestinal fistula stents are not yet resolved. Herein, the fabrication of a support-free segmental stent with two types of thermoplastic polyurethane (TPU) using a homemade multi-axis and multi-material conformal printer guided with advanced whole model path planning is demonstrated. One type of TPU segment is soft to increase elasticity, and the other is used to achieve toughness. Owing to advancements in stent design and printing, the obtained stents present three unprecedented properties compared to previous three-axis printed stents: i) Overcoming step effects; ii) Presenting comparable axial flexibility to a stent made of a single soft TPU 87A material, thus increasing the feasibility of implantation; and iii) Showing equivalent radial toughness to a stent made of a single hard TPU 95A material. Hence, the stent can resist the intestinal contractive force and maintain intestinal continuity and patency. Through implanting such stents to the rabbit intestinal fistula models, therapeutic mechanisms of reducing fistula output and improving nutritional states and intestinal flora abundance are revealed. Overall, this study develops a creative and versatile method to improve the poor quality and mechanical properties of medical stents.

Numerical analysis of the mechanical response of novel swelling bone implants in polyurethane foams

In this study, a numerical framework was developed in order to analyze the swelling properties, mechanical response and fixation strength of swelling bone anchors. Using this framework, fully porous and solid implants, along with a novel hybrid design (consisting of a solid core and a porous sleeve), were modeled and studied. Free swelling experiments were conducted to investigate their swelling characteristics. The finite element model of swelling was validated using the conducted free swelling. Compared with the experimental data, results obtained from the finite element analysis proved the reliability of this frame-work. Afterwards, the swelling bone anchors were studied embedded in artificial bones with different densities with two different interface properties: considering frictional interface between the bone anchors and artificial bones (simulating the stages prior to osteointegration, when the bone and implant are not fully bonded and the surface of the implant can slide along the interface), and perfectly bonded (simulating the stages subsequent to osteointegration, when the bone and implant are fully bonded). It was observed that the swelling considerably decreases while the average radial stress on the lateral surface of the swelling bone anchor surges in the denser artificial bones. Ultimately, the pull-out experiments and simulations of the swelling bone anchors from the artificial bones were conducted to look into the fixation strength of the swelling bone anchors. It was found that the hybrid swelling bone anchor exhibits mechanical and swelling properties close to those of solid bone anchors, while also bone in-growth is expected to happen, which is an integral factor to these bone anchors.

Decellularization compromises mechanical and structural properties of the native trachea

Tracheal replacement using tissue engineering technologies offers great potential to improve previously intractable clinical interventions, and interest in this area has increased in recent years. Many engineered airway constructs currently rely on decellularized native tracheas to serve as the scaffold for tissue repair. Yet, mechanical failure leading to airway narrowing and collapse remains a major cause of morbidity and mortality following clinical implantation of decellularized tracheal grafts. To understand better the factors contributing to mechanical failure in vivo, we characterized the histo-mechanical properties of tracheas following two different decellularization protocols, including one that has been used clinically. All decellularized tracheas deviated from native mechanical behavior, which may provide insights into observed in vivo graft failures. We further analyzed protein content by western blot and analyzed microstructure by histological staining and found that the specific method of decellularization resulted in significant differences in the depletion of proteoglycans and degradation of collagens I, II, III, and elastin. Taken together, this work demonstrates that the heterogeneous architecture and mechanical behavior of the trachea is severely compromised by decellularization. Such structural deterioration may contribute to graft failure clinically and limit the potential of decellularized native tracheas as viable long-term orthotopic airway replacements.

Perpendicular implantation of porcine trachea extracellular matrix for enhanced xenogeneic scaffold surface epithelialization in a canine model

Objective

The availability of clinically applied medical materials in thoracic surgery remains insufficient, especially materials for treating tracheal defects. Herein, the potential of porcine extracellular matrix (P-ECM) as a new airway reconstruction material was explored by xenotransplanting it into a canine trachea.

Methods

P-ECM was first transplanted into the buttocks of Narc Beagle dogs (n = 3) and its overall immuno-induced effects were evaluated. Subsequently, nine dogs underwent surgery to create a tracheal defect that was 1 × 2 cm. In group A, the P-ECM was implanted parallel to the tracheal axis (n = 3), whereas in group B the P-ECM was implanted perpendicular to the tracheal axis (n = 6). The grafts were periodically observed by bronchoscopy and evaluated postoperatively at 1 and 3 months through macroscopic and microscopic examinations. Immunosuppressants were not administered. Statistical evaluation was performed for Bronchoscopic stenosis rate, graft epithelialization rate, shrinkage rate and ECM live-implantation rate.

Results

No sign of P-ECM rejection was observed after its implantation in the buttocks. Bronchoscopic findings showed no improvement concerning stenosis in group A until 3 months after surgery; epithelialization of the graft site was not evident, and the ECM site appeared scarred and faded. In contrast, stenosis gradually improved in group B, with continuous epithelium within the host tissues and P-ECM. Histologically, the graft site contracted longitudinally and no epithelialization was observed in group A, whereas full epithelialization was observed on the P-ECM in group B. No sign of cartilage regeneration was confirmed in both groups. No statistically significant differences were found in bronchoscopic stenosis rate, shrinkage rate and ECM live-implantation rate, but graft epithelialization rate showed a statistically significant difference (G-A; sporadic (25%) 3, vs. G-B; full covered (100%) 3; p = 0.047).

Conclusions

P-ECM can support full re-epithelialization without chondrocyte regeneration, with perpendicular implantation facilitating epithelialization of the ECM. Our results showed that our decellularized tracheal matrix holds clinical potential as a biological xenogeneic material for airway defect repair.

Preclinical and clinical orthotopic transplantation of decellularized/engineered tracheal scaffolds: A systematic literature review

Severe tracheal injuries that cannot be managed by mobilization and end-to-end anastomosis represent an unmet clinical need and an urgent challenge to face in surgical practice; within this scenario, decellularized scaffolds (eventually bioengineered) are currently a tempting option among tissue engineered substitutes. The success of a decellularized trachea is expression of a balanced approach in cells removal while preserving the extracellular matrix (ECM) architecture/mechanical properties. Revising the literature, many Authors report about different methods for acellular tracheal ECMs development; however, only few of them verified the devices effectiveness by an orthotopic implant in animal models of disease. To support translational medicine in this field, here we provide a systematic review on studies recurring to decellularized/bioengineered tracheas implantation. After describing the specific methodological aspects, orthotopic implant results are verified. Furtherly, the only three clinical cases of compassionate use of tissue engineered tracheas are reported with a focus on outcomes.

Highlights on Advancing Frontiers in Tissue Engineering

The field of tissue engineering continues to advance, sometimes in exponential leaps forward, but also sometimes at a rate that does not fulfill the promise that the field imagined a few decades ago. This review is in part a catalog of success in an effort to inform the process of innovation. Tissue engineering has recruited new technologies and developed new methods for engineering tissue constructs that can be used to mitigate or model disease states for study. Key to this antecedent statement is that the scientific effort must be anchored in the needs of a disease state and be working toward a functional product in regenerative medicine. It is this focus on the wildly important ideas coupled with partnered research efforts within both academia and industry that have shown most translational potential. The field continues to thrive and among the most important recent developments are the use of three-dimensional bioprinting, organ-on-a-chip, and induced pluripotent stem cell technologies that warrant special attention. Developments in the aforementioned areas as well as future directions are highlighted in this article. Although several early efforts have not come to fruition, there are good examples of commercial profitability that merit continued investment in tissue engineering. Impact statement Tissue engineering led to the development of new methods for regenerative medicine and disease models. Among the most important recent developments in tissue engineering are the use of three-dimensional bioprinting, organ-on-a-chip, and induced pluripotent stem cell technologies. These technologies and an understanding of them will have impact on the success of tissue engineering and its translation to regenerative medicine. Continued investment in tissue engineering will yield products and therapeutics, with both commercial importance and simultaneous disease mitigation.

Contributions of supercritical fluid technology for advancing decellularization and postprocessing of viable biological materials

The demand for tissue and organ transplantation worldwide has led to an increased interest in the development of new therapies to restore normal tissue function through transplantation of injured tissue with biomedically engineered matrices. Among these developments is decellularization, a process that focuses on the removal of immunogenic cellular material from a tissue or organ. However, decellularization is a complex and often harsh process that frequently employs techniques that can negatively impact the properties of the materials subjected to it. The need for a more benign alternative has driven research on supercritical carbon dioxide (scCO₂) assisted decellularization. scCO₂ can achieve its critical point at relatively low temperature and pressure conditions, and for its high transfer rate and permeability. These properties make scCO₂ an appealing methodology that can replace or diminish the exposure of harsh chemicals to sensitive materials, which in turn could lead to better preservation of their biochemical and mechanical properties. The presented review covers relevant literature over the last years where scCO₂-assisted decellularization is employed, as well as discussing major topics such as the mechanism of action behind scCO₂-assisted decellularization, CO₂ and cosolvents' solvent properties, effect of the operational parameters on decellularization efficacy and on the material's properties.

A Novel Decellularized Trachea Preparation Method for Rapid Construction of a Functional Tissue Engineered Trachea to Repair Tracheal Defects

Long segment trachea defects are repaired by tracheal substitution, while the decellularized technology has been effectively employed to prepare tissue engineering trachea (TET). However, its clinical application is restrictied by...

Decellularized tracheal scaffolds in tracheal reconstruction: An evaluation of different techniques

In humans, the trachea is a conduit for ventilation connecting the throat and lungs. However, certain congenital or acquired diseases may cause long-term tracheal defects that require replacement. Tissue engineering is considered a promising method to reconstruct long-segment tracheal lesions and restore the structure and function of the trachea. Decellularization technology retains the natural structure of the trachea, has good biocompatibility and mechanical properties, and is currently a hotspot in tissue engineering studies. This article lists various recent representative protocols for the generation of decellularized tracheal scaffolds (DTSs), as well as their validity and limitations. Based on the advancements in decellularization methods, we discussed the impact and importance of mechanical properties, revascularization, recellularization, and biocompatibility in the production and implantation of DTS. This review provides a basis for future research on DTS and its application in clinical therapy.

Isolation of multipotent progenitor cells from pleura and pericardium for tracheal tissue engineering purposes

Tissue engineering (TE) of long tracheal segments is conceptually appealing for patients with inoperable tracheal pathology. In tracheal TE, stem cells isolated from bone marrow or adipose tissue have been employed, but the ideal cell source has yet to be determined. When considering the origin of stem cells, cells isolated from a source embryonically related to the trachea may be more similar. In this study, we investigated the feasibility of isolating progenitor cells from pleura and pericard as an alternative cells source for tracheal tissue engineering. Porcine progenitor cells were isolated from pleura, pericard, trachea and adipose tissue and expanded in culture. Isolated cells were characterized by PCR, RNA sequencing, differentiation assays and cell survival assays and were compared to trachea and adipose‐derived progenitor cells. Progenitor‐like cells were successfully isolated and expanded from pericard and pleura as indicated by gene expression and functional analyses. Gene expression analysis and RNA sequencing showed a stem cell signature indicating multipotency, albeit that subtle differences between different cell sources were visible. Functional analysis revealed that these cells were able to differentiate towards chondrogenic, osteogenic and adipogenic lineages. Isolation of progenitor cells from pericard and pleura with stem cell features is feasible. Although functional differences with adipose‐derived stem cells were limited, based on their gene expression, pericard‐ and pleura‐derived stem cells may represent a superior autologous cell source for cell seeding in tracheal tissue engineering.

Fabrication and evaluation of an optimized xenogenic decellularized costal cartilage graft: preclinical studies of a novel biocompatible prosthesis for rhinoplasty

On account of the poor biocompatibility of synthetic prosthesis, millions of rhinoplasty recipients have been forced to choose autologous costal cartilage as grafts, which suffer from limited availability, morbidity at the donor site and prolonged operation time. Here, as a promising alternative to autologous costal cartilage, we developed a novel xenogeneic costal cartilage and explored its feasibility as a rhinoplasty graft for the first time. Adopting an improved decellularization protocol, in which the ionic detergent was substituted by trypsin, the resulting decellularized graft was confirmed to preserve more structural components and better mechanics, and eliminate cellular components effectively. The in vitro and in vivo compatibility experiments demonstrated that the decellularized graft showed excellent biocompatibility and biosecurity. Additionally, the functionality assessment of rhinoplasty was performed in a rabbit model, and the condition of grafts after implantation was comprehensively evaluated. The optimized graft exhibited better capacity to reduce the degradation rate and maintain the morphology, in comparison to the decellularized costal cartilage prepared by conventional protocol. These findings indicate that this optimized graft derived from decellularized xenogeneic costal cartilage provides a new prospective for future investigations of rhinoplasty prosthesis and has great potential for clinical application.

Directly construct microvascularization of tissue engineering trachea in orthotopic transplantation

Tissue engineering technology provides effective alternative treatments for tracheal reconstruction. The formation of a functional microvascular network is essential to support cell metabolism and ensure the long-term survival of grafts. However, given the lack of an identifiable vascular pedicle of the trachea that could be anastomosed to the blood vessels directly in the recipient's neck, successful tracheal transplantation faces significant challenges in rebuilding the adequate blood supply of the graft. Herein, we describe a one-step method to construct microvascularization of tissue-engineered trachea in orthotopic transplantation. Forty rabbit tracheae were decellularized using a vacuum-assisted decellularization (VAD) method. Histological appearance and immunohistochemical (IHC) analysis demonstrated efficient removal of cellular components and nuclear material from natural tissue, which was also confirmed by 4'-6-diamidino-2-phenylindole(DAPI) staining and DNA quantitative analysis, thus significantly reducing the antigenicity. Scanning electron microscopy (SEM), immunofluorescence (IF) analysis, GAG and collagen quantitative analysis showed that the hierarchical structures, composition and integrity of the extracellular matrix (ECM) were protected. IF analysis also demonstrated that basic fibroblast growth factor (b-FGF) was preserved during the decellularization process, and also exerted biocompatibility and proangiogenic properties by the chick chorioallantoic membrane(CAM) assay. Xenotransplantation assays indicated that the VAD tracheal matrix would no longer induced inflammatory reactions implanted in the body for 4 weeks after treated by VAD more than 16 h. Furthermore, we seeded the matrix with bone marrow-derived endothelial cells (BMECs) in vitro and performed in vivo tracheal patch repair assays to prove the biocompatibility and neovascularization of VAD-treated tracheal matrix, and the formation of a vascular network around the patch promoted the crawling of surrounding ciliated epithelial cells to the surface of the graft. We conclude that this natural VAD tracheal matrix is non-immunogenic and no inflammatory reactions in vivo transplantation. Seeding with BMECs on the grafts and then performing orthotopic transplantation can effectively promote the microvascularization and accelerate the native epithelium cells crawling to the lumen of the tracheal graft.

Vascularization strategies for tissue engineering for tracheal reconstruction

Tissue engineering technology provides effective alternative treatments for tracheal reconstruction. The formation of a functional microvascular network is essential to support cell metabolism and ensure the long-term survival of grafts. Although several tracheal replacement therapy strategies have been developed in the past, the critical significance of the formation of microvascular networks in 3D scaffolds has not attracted sufficient attention. Here, we review key technologies and related factors of microvascular network construction in tissue-engineered trachea and explore optimized preparation processes of vascularized functional tissues for clinical applications.

A digital light processing 3D printed magnetic bioreactor system using silk magnetic bioink

Among various bioreactors used in the field of tissue engineering and regenerative medicine, a magnetic bioreactor is more capable of providing steady force to the cells while avoiding direct manipulation of the materials. However, most of them are complex and difficult to fabricate, with drawbacks in terms of consistency and biocompatibility. In this study, a magnetic bioreactor system and a magnetic hydrogel were manufactured by single-stage three-dimensional (3D) printing with digital light processing (DLP) technique for differentiation of myoblast cells. The hydrogel was composed of a magnetic part containing iron oxide and glycidyl-methacrylated silk fibroin, and a cellular part printed by adding mouse myoblast cell (C2C12) to gelatin glycidyl methacrylate, that was placed in the magnetic bioreactor system to stimulate the cells in the hydrogel. The composite hydrogel was steadily printed by a one-stage layering technique using a DLP printer. The magnetic bioreactor offered mechanical stretching of the cells in the hydrogel in 3D ways, so that the cellular differentiation could be executed in three dimensions just like the human environment. Cell viability, as well as gene expression using quantitative reverse transcription-polymerase chain reaction, were assessed after magneto-mechanical stimulation of the myoblast cell-embedded hydrogel in the magnetic bioreactor system. Comparison with the control group revealed that the magnetic bioreactor system accelerated differentiation of mouse myoblast cells in the hydrogel and increased myotube diameter and lengthin vitro. The DLP-printed magnetic bioreactor and the hydrogel were simply manufactured and easy-to-use, providing an efficient environment for applying noninvasive mechanical force via FDA-approved silk fibroin and iron oxide biocomposite hydrogel, to stimulate cells without any evidence of cytotoxicity, demonstrating the potential for application in muscle tissue engineering.

Rapid Preparation Method for Preparing Tracheal Decellularized Scaffolds: Vacuum Assistance and Optimization of DNase I

Decellularized scaffolds are an effective way for tracheal tissue engineering to perform alternative treatments. However, clinically used decellularized tracheal scaffolds have a long preparation cycle. The purpose of this study is to improve the efficiency of decellularization by vacuum assistance and optimizing the concentration of DNase I in the decellularization process and to quickly obtain tracheal decellularized scaffolds. The trachea of New Zealand white rabbits was decellularized with 2, 4, 6, and 8 KU/mL DNase I under vacuum. The performance of the decellularized tracheal scaffold was evaluated through histological analysis, immunohistochemical staining, DNA residue, extracellular matrix composition, scanning electron microscopy, mechanical properties, cell compatibility, and in vivo experiments. Histological analysis and immunohistochemical staining showed that compared with the native trachea, the hierarchical structure of the decellularized trachea remained unchanged after decellularization, nonchondrocytes were effectively removed, and the antigenicity of the scaffold was significantly weakened. Deoxyribonucleic acid (DNA) quantitative analysis showed that the amount of residual DNA in the 6-KU group was significantly decreased. Scanning electron microscopy and mechanical tests showed that small gaps appeared in the basement membrane of the 6-KU group, and the mechanical properties decreased. The CCK-8 test results and in vivo experiments showed that the 6-KU group's acellular scaffold had good cell compatibility and new blood vessels were visible on the surface. Taken together, the 6-KU group could quickly prepare rabbit tracheal scaffolds with good decellularization effects in only 2 days, which significantly shortened the preparation cycle reducing the required cost.

Photooxidation crosslinking to recover residual stress in decellularized blood vessel

Decellularization method based on trypsin-digestion is widely used to construct small diameter vascular grafts. However, this method will reduce the opening angle of the blood vessel and result in the reduction of residual stress. Residual stress reduced has an adverse effect on the compliance and permeability of small diameter vascular grafts. To improve the situation, acellular blood vessels were treated with glutaraldehyde and photooxidation crosslinking respectively, and the changes of opening angle, circumferential residual strain of native blood vessels, decellularized arteries and crosslinked blood vessels were measured by means of histological examination, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) in this study. The opening angle of decellularized arteries significantly restored after photooxidation crosslinking (P = 0.0216), while that of glutaraldehyde crosslinking blood vessels reduced. The elastic fibers inside the blood vessels became densely rearranged after photooxidation crosslinking. The results of finite element simulation showed that the residual stress increased with the increase of opening angle. In this study, we found at the first time that photooxidation crosslinking method could significantly increase the residual stress of decellularized vessels, which provides biomechanical support for the development of new biomaterials of vascular grafts.

Post-decellularization techniques ameliorate cartilage decellularization process for tissue engineering applications

Due to the current lack of innovative and effective therapeutic approaches, tissue engineering (TE) has attracted much attention during the last decades providing new hopes for the treatment of several degenerative disorders. Tissue engineering is a complex procedure, which includes processes of decellularization and recellularization of biological tissues or functionalization of artificial scaffolds by active cells. In this review, we have first discussed those conventional steps, which have led to great advancements during the last several years. Moreover, we have paid special attention to the new methods of post-decellularization that can significantly ameliorate the efficiency of decellularized cartilage extracellular matrix (ECM) for the treatment of osteoarthritis (OA). We propose a series of post-decellularization procedures to overcome the current shortcomings such as low mechanical strength and poor bioactivity to improve decellularized ECM scaffold towards much more efficient and higher integration.

Applications of decellularized materials in tissue engineering: advantages, drawbacks and current improvements, and future perspectives

Decellularized materials (DMs) are attracting more and more attention because of their native structures, comparatively high bioactivity, low immunogenicity and good biodegradability, which are difficult to be imitated by synthetic materials. Recently, DMs have been demonstrated to possess great potential to overcome the disadvantages of autografts and have become a kind of promising material for tissue engineering. In this systematic review, we aimed to not only provide a quick access for understanding DMs, but also bring new ideas to utilize them more appropriately in tissue engineering. Firstly, the preparation of DMs was introduced. Then, the updated applications of DMs derived from different tissues and organs in tissue engineering were comprehensively summarized. In particular, their advantages, drawbacks and current improvements were emphasized. Moreover, we analyzed and proposed future perspectives.

Photocrosslinked natural hydrogel composed of hyaluronic acid and gelatin enhances cartilage regeneration of decellularized trachea matrix

Repair of long segmental trachea defects is always a great challenge in the clinic. The key to solving this problem is to develop an ideal trachea substitute with biological function. Using of a decellularized trachea matrix based on laser micropore technique (LDTM) demonstrated the possibility of preparing ideal trachea substitutes with tubular shape and satisfactory cartilage regeneration for tissue-engineered trachea regeneration. However, as a result of the very low cell adhesion of LDTM, an overly high concentration of seeding cell is required, which greatly restricts its clinical translation. To address this issue, the current study proposed a novel strategy using a photocrosslinked natural hydrogel (PNH) carrier to enhance cell retention efficiency and improve tracheal cartilage regeneration. Our results demonstrated that PNH underwent a rapid liquid-solid phase conversion under ultraviolet light. Moreover, the photo-generated aldehyde groups in PNH could rapidly react with inherent amino groups on LDTM surfaces to form imine bonds, which efficiently immobilized the cell-PNH composite to the surfaces of LDTM and/or maintained the composite in the LDTM micropores. Therefore, PNH significantly enhanced cell-seeding efficiency and achieved both stable cell retention and homogenous cell distribution throughout the LDTM. Moreover, PNH exhibited excellent biocompatibility and low cytotoxicity, and provided a natural three-dimensional biomimetic microenvironment to efficiently promote chondrocyte survival and proliferation, extracellular matrix production, and cartilage regeneration. Most importantly, at a relatively low cell-seeding concentration, homogeneous tubular cartilage was successfully regenerated with an accurate tracheal shape, sufficient mechanical strength, good elasticity, typical lacuna structure, and cartilage-specific extracellular matrix deposition. Our findings establish a versatile and efficient cell-seeding strategy for regeneration of various tissue and provide a satisfactory trachea substitute for repair and functional reconstruction of long segmental tracheal defects.

Porcine Tracheal Mucosa-Derived Decellularized Patch to Prevent Septal Perforation in a Rabbit Model

BACKGROUND

Nasal septal perforation is caused by bilateral septal mucosal injuries resulting from nasal trauma and septal surgeries. Previous studies have reported that biocompatible materials may be effective for repairing nasal septal perforations. However, they were primarily used for treatment; no study has investigated their use for prevention of nasal septal perforation.

OBJECTIVE

To determine whether porcine tracheal mucosa-derived decellularized patch can prevent the progression of nasal mucosa injuries to septal perforations.

METHODS

Bilateral nasal septal mucosal defects were surgically induced in 36 rabbits. Silastic sheets were applied bilaterally in all rabbits, and decellularized mucosal patch was applied unilaterally (n = 12) or bilaterally (n = 12) at the defect site in the respective experimental groups. Between 1 and 8 weeks postoperatively, the animals were sacrificed, and their nasal septa were completely removed. The excised septa were examined macroscopically and microscopically (histopathological examinations). Moreover, glycosaminoglycan (GAG) estimations of the septa were performed to evaluate mucosal regeneration and mechanical properties.

RESULTS

Septal perforations occurred in 5 animals in the control group (5/12; 42%), 1 in the unilateral group (1/12; 9%), and in none in the bilateral group. Compared with the control group, the experimental groups showed significantly different mucosal and cartilage regeneration.

CONCLUSION

Decellularized porcine tracheal mucosa can prevent mucosal defects from progressing to septal perforation, promote the repair of mucosal defects, and protect the nasal cartilage.

The use of the chick embryo CAM assay in the study of angiogenic activiy of biomaterials

The chick embryo chorioallantoic membrane (CAM) is a highly vascularized extraembryonic membrane, which carries out several functions during embryonic development, including exchange of respiratory gases, calcium transport from the eggshell, acid-base homeostasis in the embryo, and ion and water reabsorption from the allantoic fluid. Due to its easy accessibility, affordability and given that it constitutes an immunodeficient environment, CAM has been used as an experimental model for >50 years and in particular it has been broadly used to study angiogenesis and anti-angiogenesis. This review article describes the use of the CAM assay as a valuable assay to test angiogenic activity of biomaterials in vivo before they are further investigated in animal models. In this context, the use of CAM has become an integral part of the biocompatibility testing process for developing potential biomaterials.

Rapid preparation of decellularized trachea as a 3D scaffold for organ engineering

OBJECTIVE

To shorten the preparation time of rabbit decellularized tracheal matrix through a modified detergent-enzymatic method with higher concentration of DNase (50 kU/mL), providing an experimental and theoretical basis for clinical decellularization technology.

METHODS

The control group was a natural trachea, and the experimental group was a tracheal matrix subjected to two and four decellularization cycles. The performance of each group of samples was evaluated by histology and immunohistochemical staining, scanning electron microscopy, biomechanical property testing, inoculation and cytotoxicity tests, and allograft experiments.

RESULTS

The results showed that the nuclei of the nonchondral areas of the tracheal stroma were essentially completely removed and MHC-I and MHC-II antigens were removed after two decellularization cycles. Histological staining and scanning electron microscopy showed that the extracellular matrix was retained and the basement membrane was intact. Cell inoculation and proliferation tests confirmed that the acellular tracheal matrix had good biocompatibility, and the proliferation capacity of bone mesenchymal stem cells on the matrix was increased in the experimental group compared with the control group (p < 0.05). Histological staining and CD68 molecular marker analysis after the allograft experiment showed that the inflammatory response of the acellular tracheal matrix was weak and the infiltration of surrounding macrophages was reduced.

CONCLUSION

A modified detergent-enzymatic method with an increased DNase (50 kU/mL) concentration requires only two cycles (4 days) to obtain a decellularized rabbit tracheal matrix with a short preparation time, good biocompatibility, suitable mechanical properties, and reduced preparation cost.

Development of Acellular Respiratory Mucosal Matrix Using Porcine Tracheal Mucosa

BACKGROUND

Respiratory mucosa defects result in airway obstruction and infection, requiring subsequent functional recovery of the respiratory epithelium. Because site-specific extracellular matrix (ECM) facilitates restoration of organ function by promoting cellular migration and engraftment, previous studies considered decellularized trachea an ideal ECM; however, incomplete cell removal from cartilage and mucosal-architecture destruction are frequently reported. Here, we developed a decellularization protocol and applied it to the respiratory mucosa of separated porcine tracheas.

METHODS

The trachea was divided into groups according to decellularization protocol: native mucosa, freezing-thawing (FT), FT followed by the use of Perasafe-based chemical agents before mucosal separation (wFTP), after mucosal separation (mFTP), and followed by DNase decellularization (mFTD). Decellularization efficacy was evaluated by DNA quantification and hematoxylin and eosin staining, and ECM content of the scaffold was evaluated by histologic analysis and glycosaminoglycan and collagen assays. Biocompatibility was assessed by cell-viability assay and in vivo transplantation.

RESULTS

The mFTP mucosa showed low antigenicity and maintained the ECM to form a proper microstructure. Additionally, tonsil-derived stem cells remained viable when cultured with or seeded onto mFTP mucosa, and the in vivo host response showed a constructive pattern following implantation of the mFTP scaffolds.

CONCLUSION

These results demonstrated that xenogenic acellular respiratory mucosa matrix displayed suitable biocompatibility as a scaffold material for respiratory mucosa engineering.

Construction of a NT-3 sustained-release system cross-linked with an acellular spinal cord scaffold and its effects on differentiation of cultured bone marrow mesenchymal stem cells

OBJECTIVE

This study sought to promote the adhesion, proliferation and differentiation of rat bone marrow mesenchymal stem cells by constructing a neurotrophin-3 (NT-3) sustained-release system cross-linked with an acellular spinal cord scaffold.

METHODS

1-Ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride (EDC) chemistry combined with chemical extraction was used to construct an acellular spinal cord scaffold. The decellularization completion was validated. An EDC cross-linking method was used to construct the NT-3 cross-linked acellular spinal scaffold. ELISA was used to verify sustained release of NT-3; the dorsal root ganglion method was used to verify the biological activity of the sustained-release NT-3. DAPI staining was used to confirm the adhesion of the cultured rat bone marrow mesenchymal stem cells (P3) to the NT-3 scaffold, and cell counting kit-8 (CCK-8) analysis was used to verify the cellular proliferation after 24 h and 48 h of culture. Immunohistochemistry was used to confirm the differentiation of the bone marrow cells into neuron-like cells.

RESULTS

An NT-3 sustained-release system cross-linked to an acellular spinal cord scaffold was successfully constructed. Sustained-release NT-3 could persist for 35 days and had biological activity for at least 21 days. It could promote the adhesion, proliferation and differentiation of rat bone marrow mesenchymal stem cells.

CONCLUSION

As a composite scaffold, an NT-3 sustained-release system cross-linked with an acellular spinal cord scaffold has potential applications for tissue engineering.

Preparation of an acellular spinal cord scaffold to improve its biological properties

In recent years, acellular spinal cord scaffolds have been extensively studied in tissue engineering. Notably, acellular spinal cord scaffolds may be used to treat spinal cord injury; however, the method of preparation can result in low efficiency and may affect the biological properties of cells. This study aimed to use EDC crosslinking, combined with chemical extraction for tissue decellularization, in order to improve the efficiency of acellular scaffolds. To make the improved stent available for the clinical treatment of spinal cord injury, it is necessary to study its immunogenicity. Therefore, this study also focused on the adherence of rat bone marrow mesenchymal stem cells to scaffolds, and their differentiation into neuron-like cells in the presence of suitable trophic factors. The results revealed that EDC crosslinking combined with chemical extraction methods may significantly improve the efficiency of acellular scaffolds, and may also confer better biological characteristics, including improved immunogenicity. Notably, it was able to promote adhesion of rat bone marrow mesenchymal stem cells and their differentiation into neuron-like cells. These results suggested that the improved preparation method may be promising for the construction of multifunctional acellular scaffolds for the treatment of spinal cord injury.

Trachea Engineering Using a Centrifugation Method and Mouse-Induced Pluripotent Stem Cells

The outcomes of tracheal transplantation for the treatment of airway stenosis are unsatisfactory. We investigated the feasibility of regeneration of the trachea using a rat decellularized tracheal scaffold and mouse-induced pluripotent stem (iPS) cells for in vivo transplantation. The rat trachea was first decellularized using a detergent/enzymatic treatment method. We successfully established a centrifugation method that can transplant cells onto the luminal surface of the decellularized rat tracheal scaffold circumferentially. Two types of mouse iPS cells were differentiated into definitive endoderm cells and transplanted onto the luminal surface of the decellularized tracheal matrix scaffold using this centrifugation method. For in vivo study, normal rat tracheas, no-cell rat tracheal scaffolds, or rat tracheal scaffolds recellularized with rat tracheal epithelial cells (EGV-4T) were orthotopically transplanted on F344 rats, and rat tracheal scaffolds recellularized with mouse iPS cells were transplanted on F344/NJc1-rnu/rnu rats. Rats transplanted with no-cell scaffolds or scaffolds recellularized with EGV-4T survived for 1 month, although airway stenosis was observed. One of the F344/NJc1-rnu/rnu rats transplanted with rat trachea regenerated using mouse iPS cells survived over 5 weeks. Histological analysis indicated the cause of death was airway stenosis due to colonic cellular proliferation of undifferentiated iPS cells. Re-epithelialization with numerous ciliated epithelial cells was observed in one of the rats transplanted with trachea bioengineered using iPS cells. In this study, we present a simple and efficient tracheal tissue engineering model using a centrifugation method in a small-animal model. Tissue-engineered trachea using decellularized tracheal scaffolds and iPS cells is potentially applicable for tracheal transplantation.

Spectroscopic Analysis of Human Tracheal Tissue during Decellularization

OBJECTIVE

To use mid-infrared (IR) spectroscopy to assess changes in the cartilaginous framework of human trachea during decellularization.

STUDY DESIGN

Laboratory-based study.

SETTING

Research laboratory.

METHODS

Six cadaveric human tracheas were decellularized using a detergent enzymatic method (DEM). Tissue samples were obtained from each specimen after 0, 1, 10, and 25 DEM cycles for histologic and spectroscopic analysis. Decellularization was confirmed using hematoxylin and eosin (H&E) and 2-(4-amidinophenyl)-1H-indole-6-carboxamidine (DAPI) staining. Changes in cartilaginous framework were examined using Fourier transform infrared imaging spectroscopy (FT-IRIS) and an attenuated total reflectance (ATR) probe in the mid-IR frequencies. Results were statistically analyzed using 1-way analysis of variance (ANOVA) and principal component analysis (PCA).

RESULTS

Six decellularized tracheal scaffolds were successfully created using a DEM protocol. Histologic examination showed near-complete nuclear loss following 25 DEM cycles. As observed with FT-IRIS analysis, the collagen absorbance signal (1336 cm-1) was predominantly in the perichondria and remained stable after 25 DEM cycles ( P = .132), while the absorbance from sugar rings in proteoglycans and nucleic acids in hyaline cartilage (1080 cm-1) showed a significant decrease after 1 DEM cycle ( P = .0007). Examination of the luminal surface of the trachea with an ATR probe showed raw mid-IR spectra consistent with cartilage. PCA showed significant separation of spectra corresponding to treatment cycle along the principal components 1 and 2.

CONCLUSION

Mid-IR spectroscopy is a viable method of monitoring changes in extracellular matrix components during the decellularization of human trachea.

Evaluation of changes in cartilage viability in detergent-treated tracheal grafts for immunosuppressant-free allotransplantation in dogs

OBJECTIVES

The first tissue-engineered clinical tracheal transplant prepared using the detergent-enzymatic method resulted in graft stenosis, possibly from detergent-enzymatic method-induced graft non-viability. We reported on the transplantation of de-epithelialized tracheal allografts while maintaining cartilage viability in dogs. No lethal stenosis occurred in allografts. Herein, on the basis of previous experimentation, we assessed cartilage viability in detergent-treated cartilages.

METHODS

Six canine tracheal grafts were treated with detergent [1% t-octylphenoxypolyethoxyethanol (Triton X-100)] before transplantation. The histoarchitecture was evaluated, and the viable chondrocytes ratio was calculated. Glycosaminoglycan was detected using safranin-O staining. Collagen II was tested using immunohistochemistry.

RESULTS

The epithelium was completely removed in 5 grafts. Compared with fresh tracheas, the viable chondrocyte ratio was significantly reduced in the de-epithelialized grafts (100 vs 54.70 ± 8.56%; P < 0.001). Image analysis revealed that the mean optical density of glycosaminoglycan (0.363 ± 0.027 vs 0.307 ± 0.012; P = 0.007) and collagen II (0.115 ± 0.013 vs 0.092 ± 0.011; P = 0.028) was decreased. The observation period ranged from 91 to 792 days. No stenosis occurred in 5 allografts; moderate stenosis developed in 1 allograft during the 4th week after surgery. The chondrocyte nuclei almost completely disappeared. Both glycosaminoglycan (0.307 ± 0.012 vs 0.164 ± 0.104; P = 0.044) and collagen II (0.092 ± 0.011 vs 0.068 ± 0.022; P = 0.022) were significantly degraded.

CONCLUSIONS

This study demonstrated successful tracheal transplantation; about 50% of the viable chondrocytes were retained in the cartilage that could prevent development of a lethal stenosis in tracheal grafts.

Tissue-Engineered Grafts from Human Decellularized Extracellular Matrices: A Systematic Review and Future Perspectives

Tissue engineering and regenerative medicine involve many different artificial and biologic materials, frequently integrated in composite scaffolds, which can be repopulated with various cell types. One of the most promising scaffolds is decellularized allogeneic extracellular matrix (ECM) then recellularized by autologous or stem cells, in order to develop fully personalized clinical approaches. Decellularization protocols have to efficiently remove immunogenic cellular materials, maintaining the nonimmunogenic ECM, which is endowed with specific inductive/differentiating actions due to its architecture and bioactive factors. In the present paper, we review the available literature about the development of grafts from decellularized human tissues/organs. Human tissues may be obtained not only from surgery but also from cadavers, suggesting possible development of Human Tissue BioBanks from body donation programs. Many human tissues/organs have been decellularized for tissue engineering purposes, such as cartilage, bone, skeletal muscle, tendons, adipose tissue, heart, vessels, lung, dental pulp, intestine, liver, pancreas, kidney, gonads, uterus, childbirth products, cornea, and peripheral nerves. In vitro recellularizations have been reported with various cell types and procedures (seeding, injection, and perfusion). Conversely, studies about in vivo behaviour are poorly represented. Actually, the future challenge will be the development of human grafts to be implanted fully restored in all their structural/functional aspects.

Decellularization of Trachea With Combined Techniques for Tissue-Engineered Trachea Transplantation

Objectives

The purpose of this study is to shorten the decellularization time of trachea by using combination of physical, chemical, and enzymatic techniques.

Methods

Approximately 3.5-cm-long tracheal segments from 42 New Zealand rabbits (3.5±0.5 kg) were separated into seven groups according to decellularization protocols. After decellularization, cellular regions, matrix and strength and endurance of the scaffold were followed up.

Results

DNA content in all groups was measured under 50 ng/mg and there was no significant difference for the glycosaminoglycan content between group 3 (lyophilization+deoxycholic acid+de-oxyribonuclease method) and control group (P=0.46). None of the decellularized groups was different than the normal trachea in tensile stress values (P>0.05). Glucose consumption and lactic acid levels measured from supernatants of all decellularized groups were close to group with cells only (76 mg/dL and 53 mg/L).

Conclusion

Using combination methods may reduce exposure to chemicals, prevent the excessive influence of the matrix, and shorten the decellularization time.

A rational tissue engineering strategy based on three-dimensional (3D) printing for extensive circumferential tracheal reconstruction

Extensive circumferential tracheal defects remain a major challenging problem in the field of tracheal reconstruction. In this study, a tissue-engineered tracheal graft based on three-dimensional (3D) printing was developed for extensive circumferential tracheal reconstruction. A native trachea-mimetic bellows scaffold, a framework for a tissue-engineered tracheal graft, was indirectly 3D printed and reinforced with ring-shaped bands made from medical grade silicone rubber. A tissue-engineered tracheal graft was then created by stratifying tracheal mucosa decellularized extracellular matrix (tmdECM) hydrogel on the luminal surface of the scaffold and transferring human inferior turbinate mesenchymal stromal cell (hTMSC) sheets onto the tmdECM hydrogel layer. The tissue-engineered tracheal graft with critical length was anastomosed end-to-end to the native trachea and complete re-epithelialization was achieved on the entire luminal surface within 2 months in a rabbit model with no post-operative complications. With this successful result, the present study reports the preliminary potential of the tissue-engineered tracheal graft as a rational tissue engineering strategy for extensive circumferential tracheal reconstruction.

A Modular Strategy to Engineer Complex Tissues and Organs

Currently, there are no synthetic or biologic materials suitable for long-term treatment of large tracheal defects. A successful tracheal replacement must (1) have radial rigidity to prevent airway collapse during respiration, (2) contain an immunoprotective respiratory epithelium, and (3) integrate with the host vasculature to support epithelium viability. Herein, biopolymer microspheres are used to deliver chondrogenic growth factors to human mesenchymal stem cells (hMSCs) seeded in a custom mold that self-assemble into cartilage rings, which can be fused into tubes. These rings and tubes can be fabricated with tunable wall thicknesses and lumen diameters with promising mechanical properties for airway collapse prevention. Epithelialized cartilage is developed by establishing a spatially defined composite tissue composed of human epithelial cells on the surface of an hMSC-derived cartilage sheet. Prevascular rings comprised of human umbilical vein endothelial cells and hMSCs are fused with cartilage rings to form prevascular-cartilage composite tubes, which are then coated with human epithelial cells, forming a tri-tissue construct. When prevascular- cartilage tubes are implanted subcutaneously in mice, the prevascular structures anastomose with host vasculature, demonstrated by their ability to be perfused. This microparticle-cell self-assembly strategy is promising for engineering complex tissues such as a multi-tissue composite trachea.

Compositional Assessment of Human Tracheal Cartilage by Infrared Spectroscopy

Objectives To assess the potential of infrared fiber-optic spectroscopy to evaluate the compositional properties of human tracheal cartilage. Study Design Laboratory-based study. Methods Twenty human cadaveric distal tracheas were harvested (age range 20-78 years; 6 females, 14 males) for compositional analysis. Histologic staining, Fourier transform infrared imaging spectroscopy data on collagen and proteoglycan (PG) content, and near-infrared (NIR) fiber-optic probe spectroscopic data that reflect protein and water content were evaluated. NIR fiber-optic probe data were also obtained from the proximal trachea in 4 human cadavers (age range 51-65 years; 2 females, 2 males) in situ for comparison to distal trachea spectral data. Results In the distal trachea cohort, the spectroscopic-determined ratio of PG/amide I, indicative of the relative amount of PG, was significantly higher in the tissues from the younger group compared to the older group (0.37 ± 0.08 vs 0.32 ± 0.05, P = .05). A principal component analysis of the NIR spectral data enabled separation of spectra based on tracheal location, likely due to differences in both protein and water content. The NIR-determined water content based on the 5200-cm-1 peak was significantly higher in the distal trachea compared to the proximal trachea ( P < .001). Conclusions Establishment of normative compositional values and further elucidating differences between the segments of trachea will enable more directed research toward appropriate compositional end points in regenerative medicine for tracheal repair.

Optimising the decellularization of human elastic cartilage with trypsin for future use in ear reconstruction

Decellularized scaffolds can induce chondrogenic differentiation of stem cells. This study compares different methods to optimise the decellularization of auricular cartilage. The process consisted of an initial 12 hour dry freeze thaw which froze the cartilage specimens in an empty tube at -20 °C. Samples were allowed to thaw at room temperature followed by submersion in phosphate buffer solution in which they were frozen at -20 °C for a 12 hour period. They were then allowed to thaw at room temperature as before. Protocol A subsequently involved subjecting specimens to both deoxyribonuclease and sodium deoxycholate. Protocol B and C were adaptations of this using 0.25% trypsin (7 cycles) and a 0.5 molar solution of ethylenediaminetetraacetic acid (3 hours for each cycle) respectively as additional steps. Trypsin accelerated the decellularization process with a reduction in DNA content from 55.4 ng/μL (native) to 17.3 ng/μL (P-value < 0.05) after 14 days. Protocol B showed a faster reduction in DNA content when compared with protocol A. In comparison to protocol C after 14 days, trypsin also showed greater decellularization with a mean difference of 11.7 ng/μL (P-value < 0.05). Histological analysis with H&E and DAPI confirmed depletion of cells at 14 days with trypsin.

Engineered Tissue-Stent Biocomposites as Tracheal Replacements

Here we report the creation of a novel tracheal construct in the form of an engineered, acellular tissue-stent biocomposite trachea (TSBT). Allogeneic or xenogeneic smooth muscle cells are cultured on polyglycolic acid polymer-metal stent scaffold leading to the formation of a tissue comprising cells, their deposited collagenous matrix, and the stent material. Thorough decellularization then produces a final acellular tubular construct. Engineered TSBTs were tested as end-to-end tracheal replacements in 11 rats and 3 nonhuman primates. Over a period of 8 weeks, no instances of airway perforation, infection, stent migration, or erosion were observed. Histological analyses reveal that the patent implants remodel adaptively with native host cells, including formation of connective tissue in the tracheal wall and formation of a confluent, columnar epithelium in the graft lumen, although some instances of airway stenosis were observed. Overall, TSBTs resisted collapse and compression that often limit the function of other decellularized tracheal replacements, and additionally do not require any cells from the intended recipient. Such engineered TSBTs represent a model for future efforts in tracheal regeneration.