Vacuum-assisted decellularization: an accelerated protocol to generate tissue-engineered human tracheal scaffolds

The Prospect of Hepatic Decellularized Extracellular Matrix as a Bioink for Liver 3D Bioprinting

The incidence of liver diseases is high worldwide. Many factors can cause liver fibrosis, which in turn can lead to liver cirrhosis and even liver cancer. Due to the shortage of donor organs, immunosuppression, and other factors, only a few patients are able to undergo liver transplantation. Therefore, how to construct a bioartificial liver that can be transplanted has become a global research hotspot. With the rapid development of three-dimensional (3D) bioprinting in the field of tissue engineering and regenerative medicine, researchers have tried to use various 3D bioprinting technologies to construct bioartificial livers in vitro. In terms of the choice of bioinks, liver decellularized extracellular matrix (dECM) has many advantages over other materials for cell-laden hydrogel in 3D bioprinting. This review mainly summarizes the acquisition of liver dECM and its application in liver 3D bioprinting as a bioink with respect to availability, printability, and biocompatibility in many aspects and puts forward the current challenges and prospects.

Preparation of Decellularized Tissue as Dual Cell Carrier Systems: A Step Towards Facilitating Re-epithelization and Cell Encapsulation for Tracheal Reconstruction

Surgical treatment of tracheal diseases, trauma, and congenital stenosis has shown success through tracheal reconstruction coupled with palliative care. However, challenges in surgical-based tracheal repairs have prompted the exploration of alternative approaches for tracheal replacement. Tissue-based treatments, involving the cultivation of patient cells on a network of extracellular matrix (ECM) from donor tissue, hold promise for restoring tracheal structure and function without eliciting an immune reaction. In this study, we utilized decellularized canine tracheas as tissue models to develop two types of cell carriers: a decellularized scaffold and a hydrogel. Our hypothesis posits that both carriers, containing essential biochemical niches provided by ECM components, facilitate cell attachment without inducing cytotoxicity. Canine tracheas underwent vacuum-assisted decellularization (VAD), and the ECM-rich hydrogel was prepared through peptic digestion of the decellularized trachea. The decellularized canine trachea exhibited a significant reduction in DNA content and major histocompatibility complex class II, while preserving crucial ECM components such as collagen, glycosaminoglycan, laminin, and fibronectin. Scanning electron microscope and fluorescent microscope images revealed a fibrous ECM network on the luminal side of the cell-free trachea, supporting epithelial cell attachment. Moreover, the ECM-rich hydrogel exhibited excellent viability for human mesenchymal stem cells encapsulated for 3 days, indicating the potential of cell-laden hydrogel in promoting the development of cartilage rings of the trachea. This study underscores the versatility of the trachea in producing two distinct cell carriers-decellularized scaffold and hydrogel-both containing the native biochemical niche essential for tracheal tissue engineering applications.

Incompletely Decellularized Tracheal Matrix Scaffold for Tissue Engineering

BACKGROUND

Dense cartilaginous extracellular matrix makes decellularization and repopulation of tracheal cartilage difficult. However, the dense matrix isolates cartilaginous antigens from the recipient's immune system. Therefore, allorejection may be avoided by removing antigens from noncartilaginous tissues. In this study, incompletely decellularized tracheal matrix scaffolds were developed for tracheal tissue engineering.

METHODS

Brown Norway rat tracheae were decellularized with 4% sodium deoxycholate treatment. The cell and antigen removal efficacy, histoarchitecture, surface ultrastructure, glycosaminoglycan, collagen contents, mechanical properties, and chondrocyte viability of the scaffold were evaluated in vitro. Brown Norway rat tracheal matrix scaffolds ( n = 6) were implanted subcutaneously into Lewis rats and observed for 4 weeks. Brown Norway rat tracheae ( n = 6) and Lewis rat scaffolds ( n = 6) were implanted as controls. Histologic analysis of macrophage and lymphocyte infiltration was performed.

RESULTS

One decellularization cycle removed all cells and antigens from noncartilaginous tissue. Incomplete decellularization preserved the structural integrity of the tracheal matrix and chondrocyte viability. Except for 31% glycosaminoglycan loss, the scaffold had comparable collagen content and tensile and compressive mechanical properties to those of the native trachea. The allogeneic scaffold showed remarkably reduced CD68 + , CD8 + , and CD4 + cell infiltration compared with the allografts and demonstrated similar cell infiltration to the syngeneic scaffold. It also maintained the three-dimensional tracheal structure and cartilage viability in vivo.

CONCLUSIONS

Incompletely decellularized trachea did not induce immunorejection and maintained the integrity and viability of cartilage in vivo. Tracheal decellularization and repopulation can be simplified for urgent tracheal replacement.

CLINICAL RELEVANCE STATEMENT

The present study describes the development of an incomplete decellularization protocol that creates a decellularized matrix scaffold for tracheal tissue engineering, aiming to provide preliminary data that this method may generate suitable tracheal scaffolds for use in tracheal replacement.

Psidium guajava L. phenolic compound-reinforced lamellar scaffold for tracheal tissue engineering

The aim of this work was to develop a dense lamellar scaffold, as a biomimetic material with potential applications in the regeneration of tracheal tissue after surgical tumor resection. The scaffolds were produced by plastic compression technique, exploiting the use of total phenolic compounds (TPC) from Psidium guajava Linn as a potential cross-linking agent in a polymeric mixture based on collagen (COL), silk fibroin (SF), and polyethylene glycol 400 (PEG 400). Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) confirmed the chemical interactions between the polymers and the cross-linking of TPC between COL and SF. Morphological analyses showed scaffolds with porosity, interconnectivity, and a porous surface structure with a gyroid-like geometry. The analysis of the anisotropic degree resulted in anisotropic structures (0.1% TFC and 0.3% TFC) and an isotropic structure (0.5% TFC). In the mechanical properties, it was evidenced greater resistance for the 0.3% TFC formulation. The addition of TPC percentages did not result in a significant difference (p > 0.05) in swelling capacity and disintegration rate. The results confirmed that TPC were able to modulate the morphological, morphometric, and mechanical properties of scaffolds. Thus, this study describes a potential new material to improve the regeneration of major tracheal structures after surgical tumor removal.

Processing and post-processing of fish skin as a novel material in tissue engineering

As a natural material, fish skin contains significant amounts of collagen I and III, and due to its biocompatible nature, it can be used to regenerate various tissues and organs. To use fish skin, it is necessary to perform the decellularization process to avoid the immunological response of the host body. In the process of decellularization, it is crucial to conserve the extracellular matrix (ECM) three-dimensional (3D) structure. However, it is known that decellularization methods may also damage ECM strands arrangement and structure. Moreover, after decellularization, the post-processing of fish skin improves its mechanical and biological properties and preserves its 3D design and strength. Also, sterilization, which is one of the post-processing steps, is mandatory in pre-clinical and clinical settings. In this review paper, the fish skin decellularization methods performed and the various post-processes used to increase the performance of the skin have been studied. Moreover, multiple applications of acellular fish skin (AFS) and its extracted collagen have been reviewed.

Recent advances in soluble decellularized extracellular matrix for heart tissue engineering and organ modeling

Despite the advent of tissue engineering (TE) for the remodeling, restoring, and replacing damaged cardiovascular tissues, the progress is hindered by the optimal mechanical and chemical properties required to induce cardiac tissue-specific cellular behaviors including migration, adhesion, proliferation, and differentiation. Cardiac extracellular matrix (ECM) consists of numerous structural and functional molecules and tissue-specific cells, therefore it plays an important role in stimulating cell proliferation and differentiation, guiding cell migration, and activating regulatory signaling pathways. With the improvement and modification of cell removal methods, decellularized ECM (dECM) preserves biochemical complexity, and bio-inductive properties of the native matrix and improves the process of generating functional tissue. In this review, we first provide an overview of the latest advancements in the utilization of dECM in in vitro model systems for disease and tissue modeling, as well as drug screening. Then, we explore the role of dECM-based biomaterials in cardiovascular regenerative medicine (RM), including both invasive and non-invasive methods. In the next step, we elucidate the engineering and material considerations in the preparation of dECM-based biomaterials, namely various decellularization techniques, dECM sources, modulation, characterizations, and fabrication approaches. Finally, we discuss the limitations and future directions in fabrication of dECM-based biomaterials for cardiovascular modeling, RM, and clinical translation.

Nerve regeneration using decellularized tissues: challenges and opportunities

In tissue engineering, the decellularization of organs and tissues as a biological scaffold plays a critical role in the repair of neurodegenerative diseases. Various protocols for cell removal can distinguish the effects of treatment ability, tissue structure, and extracellular matrix (ECM) ability. Despite considerable progress in nerve regeneration and functional recovery, the slow regeneration and recovery potential of the central nervous system (CNS) remains a challenge. The success of neural tissue engineering is primarily influenced by composition, microstructure, and mechanical properties. The primary objective of restorative techniques is to guide existing axons properly toward the distal end of the damaged nerve and the target organs. However, due to the limitations of nerve autografts, researchers are seeking alternative methods with high therapeutic efficiency and without the limitations of autograft transplantation. Decellularization scaffolds, due to their lack of immunogenicity and the preservation of essential factors in the ECM and high angiogenic ability, provide a suitable three-dimensional (3D) substrate for the adhesion and growth of axons being repaired toward the target organs. This study focuses on mentioning the types of scaffolds used in nerve regeneration, and the methods of tissue decellularization, and specifically explores the use of decellularized nerve tissues (DNT) for nerve transplantation.

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.

Development and systematic evaluation of decellularization protocols in different application models for diaphragmatic tissue engineering

BACKGROUND

Tissue engineered bioscaffolds based on decellularized composites have gained increasing interest for treatment of various diaphragmatic impairments, including muscular atrophies and diaphragmatic hernias. Detergent-enzymatic treatment (DET) constitutes a standard strategy for diaphragmatic decellularization. However, there is scarce data on comparing DET protocols with different substances in distinct application models in their ability to maximize cellular removal while minimizing extracellular matrix (ECM) damage.

METHODS

We decellularized diaphragms of male Sprague Dawley rats with 1 % or 0.1 % sodium dodecyl sulfate (SDS) and 4 % sodium deoxycholate (SDC) by orbital shaking (OS) or retrograde perfusion (RP) through the vena cava. We evaluated decellularized diaphragmatic samples by (1) quantitative analysis including DNA quantification and biomechanical testing, (2) qualitative and semiquantitative analysis by proteomics, as well as (3) qualitative assessment with macroscopic and microscopic evaluation by histological staining, immunohistochemistry and scanning electron microscopy.

RESULTS

All protocols produced decellularized matrices with micro- and ultramorphologically intact architecture and adequate biomechanical performance with gradual differences. The proteomic profile of decellularized matrices contained a broad range of primal core and ECM-associated proteins similar to native muscle. While no outstanding preference for one singular protocol was determinable, SDS-treated samples showed slightly beneficial properties in comparison to SDC-processed counterparts. Both application modalities proved suitable for DET.

CONCLUSION

DET with SDS or SDC via orbital shaking or retrograde perfusion constitute suitable methods to produce adequately decellularized matrices with characteristically preserved proteomic composition. Exposing compositional and functional specifics of variously treated grafts may enable establishing an ideal processing strategy to sustain valuable tissue characteristics and optimize consecutive recellularization. This aims to design an optimal bioscaffold for future transplantation in quantitative and qualitative diaphragmatic defects.

Evaluation of Structural Viability of Porcine Tracheal Scaffolds after 3 and 6 Months of Storage under Three Different Protocols

Tracheal replacement with a bioengineered tracheal substitute has been developed for long-segment tracheal diseases. The decellularized tracheal scaffold is an alternative for cell seeding. It is not defined if the storage scaffold produces changes in the scaffold's biomechanical properties. We tested three protocols for porcine tracheal scaffold preservation immersed in PBS and alcohol 70%, in the fridge and under cryopreservation. Ninety-six porcine tracheas (12 in natura, 84 decellularized) were divided into three groups (PBS, alcohol, and cryopreservation). Twelve tracheas were analyzed after three and six months. The assessment included residual DNA, cytotoxicity, collagen contents, and mechanical properties. Decellularization increased the maximum load and stress in the longitudinal axis and decreased the maximum load in the transverse axis. The decellularization of the porcine trachea produced structurally viable scaffolds, with a preserved collagen matrix suitable for further bioengineering. Despite the cyclic washings, the scaffolds remained cytotoxic. The comparison of the storage protocols (PBS at 4 °C, alcohol at 4 °C, and slow cooling cryopreservation with cryoprotectants) showed no significant differences in the amount of collagen and in the biomechanical properties of the scaffolds. Storage in PBS solution at 4 °C for six months did not change the scaffold mechanics.

Degassing a Decellularized Scaffold Enhances Wound Healing and Reduces Fibrosis during Tracheal Defect Reconstruction: A Preliminary Animal Study

Few efforts have been made regarding the optimization of porcine small intestinal submucosa (SIS) to improve its biocompatibility. This study aims to evaluate the effect of SIS degassing on the promotion of cell attachment and wound healing. The degassed SIS was evaluated in vitro and in vivo, compared with the nondegassed SIS control. In the cell sheet reattachment model, the reattached cell sheet coverage was significantly higher in the degassed SIS group than in the nondegassed group. Cell sheet viability was also significantly higher in the SIS group than in the control group. In vivo studies showed that the tracheal defect repaired by the degassed SIS patch showed enhanced healing and reductions in fibrosis and luminal stenosis compared to the nondegassed SIS control group, with the thickness of the transplanted grafts in the degassed SIS group significantly lower than those in the control group (346.82 ± 28.02 µm vs. 771.29 ± 20.41 µm, p < 0.05). Degassing the SIS mesh significantly promoted cell sheet attachment and wound healing by reducing luminal fibrosis and stenosis compared to the nondegassed control SIS. The results suggest that the degassing processing might be a simple and effective way to improve the biocompatibility of SIS.

A Multimodal Approach to Quantify Chondrocyte Viability for Airway Tissue Engineering

OBJECTIVES/HYPOTHESIS

Partially decellularized tracheal scaffolds have emerged as a potential solution for long-segment tracheal defects. These grafts have exhibited regenerative capacity and the preservation of native mechanical properties resulting from the elimination of all highly immunogenic cell types while sparing weakly immunogenic cartilage. With partial decellularization, new considerations must be made about the viability of preserved chondrocytes. In this study, we propose a multimodal approach for quantifying chondrocyte viability for airway tissue engineering.

METHODS

Tracheal segments (5 mm) were harvested from C57BL/6 mice, and immediately stored in phosphate-buffered saline at -20°C (PBS-20) or biobanked via cryopreservation. Stored and control (fresh) tracheal grafts were implanted as syngeneic tracheal grafts (STG) for 3 months. STG was scanned with micro-computed tomography (μCT) in vivo. STG subjected to different conditions (fresh, PBS-20, or biobanked) were characterized with live/dead assay, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), and von Kossa staining.

RESULTS

Live/dead assay detected higher chondrocyte viability in biobanked conditions compared to PBS-20. TUNEL staining indicated that storage conditions did not alter the proportion of apoptotic cells. Biobanking exhibited a lower calcification area than PBS-20 in 3-month post-implanted grafts. Higher radiographic density (Hounsfield units) measured by μCT correlated with more calcification within the tracheal cartilage.

CONCLUSIONS

We propose a strategy to assess chondrocyte viability that integrates with vivo imaging and histologic techniques, leveraging their respective strengths and weaknesses. These techniques will support the rational design of partially decellularized tracheal scaffolds.

LEVEL OF EVIDENCE

N/A Laryngoscope, 133:512-520, 2023.

Preparation and Use of Decellularized Extracellular Matrix for Tissue Engineering

The multidisciplinary fields of tissue engineering and regenerative medicine have the potential to revolutionize the practise of medicine through the abilities to repair, regenerate, or replace tissues and organs with functional engineered constructs. To this end, tissue engineering combines scaffolding materials with cells and biologically active molecules into constructs with the appropriate structures and properties for tissue/organ regeneration, where scaffolding materials and biomolecules are the keys to mimic the native extracellular matrix (ECM). For this, one emerging way is to decellularize the native ECM into the materials suitable for, directly or in combination with other materials, creating functional constructs. Over the past decade, decellularized ECM (or dECM) has greatly facilitated the advance of tissue engineering and regenerative medicine, while being challenged in many ways. This article reviews the recent development of dECM for tissue engineering and regenerative medicine, with a focus on the preparation of dECM along with its influence on cell culture, the modification of dECM for use as a scaffolding material, and the novel techniques and emerging trends in processing dECM into functional constructs. We highlight the success of dECM and constructs in the in vitro, in vivo, and clinical applications and further identify the key issues and challenges involved, along with a discussion of future research directions.

Tissue Engineering for Tracheal Replacement: Strategies and Challenges

The critical feature in trachea replacement is to provide a hollow cylindrical framework that is laterally stable and longitudinally flexible, facilitating cartilage and epithelial tissue formation. Despite advanced techniques and sources of materials used, most inherent challenges are related to the complexity of its anatomy. Limited blood supply leads to insufficient regenerative capacity for cartilage and epithelium. Natural and synthetic scaffolds, different types of cells, and growth factors are part of tissue engineering approaches with varying outcomes. Pre-vascularization remains one of the crucial factors to expedite the regenerative process in tracheal reconstruction. This review discusses the challenges and strategies used in tracheal tissue engineering, focusing on scaffold implantation in clinical and preclinical studies conducted in recent decades.

Decellularized extracellular matrix scaffolds: Recent trends and emerging strategies in tissue engineering

The application of scaffolding materials is believed to hold enormous potential for tissue regeneration. Despite the widespread application and rapid advance of several tissue-engineered scaffolds such as natural and synthetic polymer-based scaffolds, they have limited repair capacity due to the difficulties in overcoming the immunogenicity, simulating in-vivo microenvironment, and performing mechanical or biochemical properties similar to native organs/tissues. Fortunately, the emergence of decellularized extracellular matrix (dECM) scaffolds provides an attractive way to overcome these hurdles, which mimic an optimal non-immune environment with native three-dimensional structures and various bioactive components. The consequent cell-seeded construct based on dECM scaffolds, especially stem cell-recellularized construct, is considered an ideal choice for regenerating functional organs/tissues. Herein, we review recent developments in dECM scaffolds and put forward perspectives accordingly, with particular focus on the concept and fabrication of decellularized scaffolds, as well as the application of decellularized scaffolds and their combinations with stem cells (recellularized scaffolds) in tissue engineering, including skin, bone, nerve, heart, along with lung, liver and kidney.

Can Heart Valve Decellularization Be Standardized? A Review of the Parameters Used for the Quality Control of Decellularization Processes

When a tissue or an organ is considered, the attention inevitably falls on the complex and delicate mechanisms regulating the correct interaction of billions of cells that populate it. However, the most critical component for the functionality of specific tissue or organ is not the cell, but the cell-secreted three-dimensional structure known as the extracellular matrix (ECM). Without the presence of an adequate ECM, there would be no optimal support and stimuli for the cellular component to replicate, communicate and interact properly, thus compromising cell dynamics and behaviour and contributing to the loss of tissue-specific cellular phenotype and functions. The limitations of the current bioprosthetic implantable medical devices have led researchers to explore tissue engineering constructs, predominantly using animal tissues as a potentially unlimited source of materials. The high homology of the protein sequences that compose the mammalian ECM, can be exploited to convert a soft animal tissue into a human autologous functional and long-lasting prosthesis ensuring the viability of the cells and maintaining the proper biomechanical function. Decellularization has been shown to be a highly promising technique to generate tissue-specific ECM-derived products for multiple applications, although it might comprise very complex processes that involve the simultaneous use of chemical, biochemical, physical and enzymatic protocols. Several different approaches have been reported in the literature for the treatment of bone, cartilage, adipose, dermal, neural and cardiovascular tissues, as well as skeletal muscle, tendons and gastrointestinal tract matrices. However, most of these reports refer to experimental data. This paper reviews the most common and latest decellularization approaches that have been adopted in cardiovascular tissue engineering. The efficacy of cells removal was specifically reviewed and discussed, together with the parameters that could be used as quality control markers for the evaluation of the effectiveness of decellularization and tissue biocompatibility. The purpose was to provide a panel of parameters that can be shared and taken into consideration by the scientific community to achieve more efficient, comparable, and reliable experimental research results and a faster technology transfer to the market.

Cartilaginous Extracellular Matrix Enriched with Human Gingival Mesenchymal Stem Cells Derived "Matrix Bound Extracellular Vesicles" Enabled Functional Reconstruction of Tracheal Defect

Stem cells derived extracellular vesicles (EVs) conceive cues essential for tissue repair. Mammalian cartilaginous extracellular matrix (cECM) may not be optimally inductive for tracheal regeneration because of the granulomatous, instead of regenerative, responses in injured adult mammalian tracheas. Given the high regenerative capacity of gingiva, it is hypothesized human gingival mesenchymal stem cells derived EVs (gEVs) can induce mammalian tracheal epithelia regeneration. Coculturing chondrocytes with GMSCs produce abundant "matrix bound gEVs (gMVs)" in forming cartilaginous ECM, which are further preserved in acellular cECM (cACM) following mild, short-period decellularization. The results show that gMVs-cACM could be well anchored on polyglycerol sebacate microporous patch thus enforce the surgical suturability and mechanical strength. In rabbit tracheal defect, the gMVs-cACM patch induces rapid regeneration of vascularized ciliated columnar epithelium, which supports long-term survival of animals. gMVs-cACM treated groups exhibit proliferation of tracheal progenitors-basal epithelial cells, as well as, activation of JAK2/STAT1 pathway in reparative cells. This study departs from conventional focuses on tissue derived ECM and introduces a new approach for tracheal tissue regeneration.

Decellularization for the retention of tissue niches

Decellularization of natural tissues to produce extracellular matrix is a promising method for three-dimensional scaffolding and for understanding microenvironment of the tissue of interest. Due to the lack of a universal standard protocol for tissue decellularization, recent investigations seek to develop novel methods for whole or partial organ decellularization capable of supporting cell differentiation and implantation towards appropriate tissue regeneration. This review provides a comprehensive and updated perspective on the most recent advances in decellularization strategies for a variety of organs and tissues, highlighting techniques of chemical, physical, biological, enzymatic, or combinative-based methods to remove cellular contents from tissues. In addition, the review presents modernized approaches for improving standard decellularization protocols for numerous organ types.

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.

Optimization of a decellularization protocol of porcine tracheas. Long-term effects of cryopreservation. A histological study

OBJECTIVE

The aim of this study was to optimize a decellularization protocol in the trachea of Sus scrofa domestica (pig) as well as to study the effects of long-term cryopreservation on the extracellular matrix of decellularized tracheas.

METHODS

Porcine tracheas were decellularized using Triton X-100, SDC, and SDS alone or in combination. The effect of these detergents on the extracellular matrix characteristics of decellularized porcine tracheas was evaluated at the histological, biomechanical, and biocompatibility level. Morphometric approaches were used to estimate the effect of detergents on the collagen and elastic fibers content as well as on the removal of chondrocytes from decellularized organs. Moreover, the long-term structural, ultrastructural, and biomechanical effect of cryopreservation of decellularized tracheas were also estimated.

RESULTS

Two percent SDS was the most effective detergent tested concerning cell removal and preservation of the histological and biomechanical properties of the tracheal wall. However, long-term cryopreservation had no an appreciable effect on the structure, ultrastructure, and biomechanics of decellularized tracheal rings.

CONCLUSION

The results presented here reinforce the use of SDS as a valuable decellularizing agent for porcine tracheas. Furthermore, a cryogenic preservation protocol is described, which has minimal impact on the histological and biomechanical properties of decellularized porcine tracheas.

Converging 3D Printing and Electrospinning: Effect of Poly(l-lactide)/Gelatin Based Short Nanofibers Aerogels on Tracheal Regeneration

Recently, various tissue engineering based strategies have been pursued for the regeneration of tracheal tissues. However, previously developed tracheal scaffolds do not accurately mimic the microstructure and mechanical behavior of the native trachea, which restrict their clinical translation. Here, tracheal scaffolds are fabricated by using 3D printing and short nanofibers (SF) dispersion of poly(l-lactide)/gelatin (0.5-1.5 wt%) to afford tracheal constructs. The results display that the scaffolds containing 1.0 wt % of SF exhibit low density, good water absorption capacity, reasonable degradation rate, and stable mechanical properties, which were comparable to the native trachea. Moreover, the designed scaffolds possess good biocompatibility and promote the growth and infiltration of chondrocytes in vitro. The biocompatibility of tracheal scaffolds is further assessed after subcutaneous implantation in mice for up to 4 and 8 weeks. Histological assessment of tracheal constructs explanted at week 4 shows that scaffolds can maintain their structural integrity and support the formation of neo-vessels. Furthermore, cell-scaffold constructs gradually form cartilage-like tissues, which mature with time. Collectively, these engineered tracheal scaffolds not only possess appropriate mechanical properties to afford a stabilized structure but also a biomimetic extracellular matrix-like structure to accomplish tissue regeneration, which may have broad implications for tracheal regeneration.

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.

Decellularized human-sized pulmonary scaffolds for lung tissue engineering: a comprehensive review

The ultimate goal of lung bioengineering is to produce transplantable lungs for human beings. Therefore, large-scale studies are of high importance. In this paper, we review the investigations on decellularization and recellularization of human-sized lung scaffolds. First, studies that introduce new ways to enhance the decellularization of large-scale lungs are reviewed, followed by the investigations on the xenogeneic sources of lung scaffolds. Then, decellularization and recellularization of diseased lung scaffolds are discussed to assess their usefulness for tissue engineering applications. Next, the use of stem cells in recellularizing acellular lung scaffolds is reviewed, followed by the case studies on the transplantation of bioengineered lungs. Finally, the remaining challenges are discussed, and future directions are highlighted.

Statistical modelling and optimization of print quality and mechanical properties of customized tubular scaffolds fabricated using solvent-based extrusion 3D printing process

Tissue-engineered tubular scaffolds offer huge potential to heal or replace the diseased organ parts like blood vessels, trachea, oesophagus and ureter. However, manufacturing these scaffolds in various scales and shapes is always challenging and requires progressive technology. Developing a flexible and accurate manufacturing method is a major developmental direction in the field of tubular scaffold fabrication. In this context, the present work presents a novel solvent-based extrusion 3D printing which allows extruding over a rotating mandrel to fabricate tubular scaffolds of polycaprolactone (PCL) and polyurethane (PU). Experimental runs were planned as per the central composite design (CCD) to evaluate the effects of input parameters like infill density, layer thickness, print speed and percentage of PU on the output responses like printing quality and mechanical characteristics. The printing quality was quantified by measuring average surface roughness of the printed scaffolds and mechanical properties were evaluated by measuring radial compressive load, and percentage of elongation. The experimental investigations revealed that printing quality was improved at higher infill densities and was deteriorated at higher print speeds and layer thicknesses. Similarly, the radial compressive load was improved with the increase in infill density and was decreased with an increase in layer thickness, print speed and percentage of PU. The percentage of elongation was found to improve at higher infill densities and percentages of PU and was reduced with an increase in layer thickness and print speed. Additionally, a multi-objective optimization using Genetic Algorithm was used to evaluate the optimum conditions to minimize surface roughness and maximizing radial compression load and percentage of elongation. Finally, a case study was performed by comparing the mechanical properties of tubular organs and scaffolds from the existing reports and results of the present work.

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.

Partial Decellularization for Segmental Tracheal Scaffold Tissue Engineering: A Preliminary Study in Rabbits

In this study, we developed a new procedure for the rapid partial decellularization of the harvested trachea. Partial decellularization was performed using a combination of detergent and sonication to completely remove the epithelial layers outside of the cartilage ring. The post-decellularized tracheal segments were assessed with vital staining, which showed that the core cartilage cells remarkably remained intact while the cells outside of the cartilage were no longer viable. The ability of the decellularized tracheal segments to evade immune rejection was evaluated through heterotopic implantation of the segments into the chest muscle of rabbits without any immunosuppressive therapy, which demonstrated no evidence of severe rejection or tissue necrosis under H&E staining, as well as the mechanical stability under stress-pressure testing. Finally, orthotopic transplantation of partially decellularized trachea with no immunosuppression treatment resulted in 2 months of survival in two rabbits and one long-term survival (2 years) in one rabbit. Through evaluations of posttransplantation histology and endoscopy, we confirmed that our partial decellularization method could be a potential method of producing low-immunogenic cartilage scaffolds with viable, functional core cartilage cells that can achieve long-term survival after in vivo transplantation.

A novel detergent-based decellularization combined with carbodiimide crosslinking for improving anti-calcification of bioprosthetic heart valve

Currently, valve replacement surgery is the only therapy for the end-stage valvular diseases because of the inability of regeneration for diseased heart valves. Bioprosthetic heart valves (BHVs), which are mainly derived from glutaraldehyde (GA) crosslinked porcine aortic heart valves or bovine pericardium, have been widely used in the last decades. However, it is inevitable that calcification and deterioration may occur within 10-15 years, which are still the main challenges for the BHVs in clinic. In this study, N-Lauroylsarcosine sodium salt (SLS) combined with N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) were utilized to decellularize and crosslink the heart valves instead of GA treatment. The obtained BHVs exhibited excellent extracellular matrix stability and mechanical properties, which were similar with GA treatment. Moreover, the obtained BHVs exhibited betterin vitrobiocompatibilities than GA treatment. After subcutaneous implantation for 30 d, the obtained BHVs showed mitigated immune response and reduced calcification compare with GA treatment. Therefore, all the above results indicated that the treatment of SLS-based decellularization combined with EDC/NHS crosslink should be a promising method to fabricate BHVs which can be used in clinic in future.

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.

Contribution of Physical Methods in Decellularization of Animal Tissues

Biologic scaffolds composed of extracellular matrix (ECM) are frequently used for clinical purposes of tissue regeneration. Different methods have been developed for this purpose. All methods of decellularization including chemical and physical approaches leave some damage on the ECM; however, the effects of these methods are different which make some of these procedures more proper to maintain ECM structure than other methods. This review is aimed to introduce and compare new physical methods for the decellularization of different tissues and organs in tissue engineering. All recent reports and research that have used at least one physical method in the procedure of decellularization, were included and evaluated in this paper. The advantages and drawbacks of each method were examined and compared considering the effectiveness. This review tried to highlight the prospective potentials and benefits of applying physical methods for decellularization protocols in tissue engineering instead of the current chemical methods. These chemical methods are harsh in nature and were shown to be destructive and harmful to essential substances of ECM and scaffold structure. Therefore, using physical methods as a partial or even a whole protocol could save time, costs, and quality of the final acellular tissue in complicated decellularization procedures. Moreover, regarding the control factor that could be achieved easily with physical methods, optimization of different decellularization protocols would be quite satisfactory. Combined methods take advantage of both chemical and physical approaches.

Regeneration of partially decellularized tracheal scaffolds in a mouse model of orthotopic tracheal replacement

Decellularized tracheal scaffolds offer a potential solution for the repair of long-segment tracheal defects. However, complete decellularization of trachea is complicated by tracheal collapse. We created a partially decellularized tracheal scaffold (DTS) and characterized regeneration in a mouse model of tracheal transplantation. All cell populations except chondrocytes were eliminated from DTS. DTS maintained graft integrity as well as its predominant extracellular matrix (ECM) proteins. We then assessed the performance of DTS in vivo. Grafts formed a functional epithelium by study endpoint (28 days). While initial chondrocyte viability was low, this was found to improve in vivo. We then used atomic force microscopy to quantify micromechanical properties of DTS, demonstrating that orthotopic implantation and graft regeneration lead to the restoration of native tracheal rigidity. We conclude that DTS preserves the cartilage ECM, supports neo-epithelialization, endothelialization and chondrocyte viability, and can serve as a potential solution for long-segment tracheal defects.

Building Scaffolds for Tubular Tissue Engineering

Hollow organs and tissue systems drive various functions in the body. Many of these hollow or tubular systems, such as vasculature, the intestines, and the trachea, are common targets for tissue engineering, given their relevance to numerous diseases and body functions. As the field of tissue engineering has developed, numerous benchtop models have been produced as platforms for basic science and drug testing. Production of tubular scaffolds for different tissue engineering applications possesses many commonalities, such as the necessity for producing an intact tubular opening and for formation of semi-permeable epithelia or endothelia. As such, the field has converged on a series of manufacturing techniques for producing these structures. In this review, we discuss some of the most common tissue engineered applications within the context of tubular tissues and the methods by which these structures can be produced. We provide an overview of the general structure and anatomy for these tissue systems along with a series of general design criteria for tubular tissue engineering. We categorize methods for manufacturing tubular scaffolds as follows: casting, electrospinning, rolling, 3D printing, and decellularization. We discuss state-of-the-art models within the context of vascular, intestinal, and tracheal tissue engineering. Finally, we conclude with a discussion of the future for these fields.

Evaluating the effects of vacuum on the microstructure and biocompatibility of bovine decellularized pericardium

The aim of this study was evaluating the effects of vacuum on microstructure and biocompatibility of bovine decellularized pericardium. So the bovine pericardia were decellularized and then the vacuum was applied for two periods of time; 90 and 180 min. DNA, glucose amino glycan, collagen and elastin content assay, scanning electron microscopy (SEM) examination, hematoxylin and eosin (H&E) and Masson's trichrome stainings performed to evaluate microstructure of tissues. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) test, subcutaneous implantation, and tensile test were used to assay biocompatibility and mechanical properties of decellularized tissues. The results showed that applying vacuum reduced residual DNA significantly. Vacuum after 180 min reduced more residual DNA. There were no significant differences in the content of glucose amino glycan (GAG), collagen, and elastin between the vacuumed and control groups. SEM examination was revealed that vacuum for 180 min increased pore size and porosity more than 90 min and control groups. H&E and Masson's trichrome stainings revealed extracellular matrix preservation after decellularization in all groups. Cell viability was increased in vacuumed samples significantly after 72 h in vaccumed samples. H&E staining and tensile test after implantation of tissues were showed less inflammation in the vacuum applied tissues and increased durability. The vacuum increased DNA removal, pore size, porosity, and biocompatibility in vitro and in vivo and durability of bovine decellularized pericardium in vivo. Considering the important role of time, more studies should be performed to optimize time, intensity, and method of application of vacuum in decellularization of different tissues as well as bovine pericardium.

The current status and outlook of trachea transplantation

PURPOSE OF REVIEW

The trachea is an enigmatic organ due to its complex morphology. Although circumferential tracheal defects are extremely difficult to repair with autologous tissue or with an allotransplant, the trachea has been touted as the first organ that could be regenerated. This review provides a comprehensive evaluation of the published evidence in tracheal tissue replacement surgery.

RECENT FINDINGS

In recent years, reports of successful tracheal regeneration have attracted great interest. Despite descriptions of the trachea as a perhaps uniquely regeneratable tissue since 2008, critical reporting provided insights into the more complex realities of tracheal regeneration attempts and led to the retraction of some articles making tracheal regeneration claims. Allotransplantation of the trachea is hindered by numerous difficult obstacles. The most promising approach developed thus far for difficult-to-repair patch airway defects is tracheal allotransplantation, which allows for tapering and withdrawal of immunosuppressive therapy.

SUMMARY

Restoration of a long-segment circumferential tracheal defect remains an unmet challenge. Future clinical studies require thoroughly documented visual evidence of outcomes to reduce confusion surrounding tracheal replacement and to prevent future scandals like those seen previously in the tracheal regeneration story. VIDEO ABSTRACT: http://links.lww.com/COOT/A6.

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.

Human airway-like multilayered tissue on 3D-TIPS printed thermoresponsive elastomer/collagen hybrid scaffolds

Developing a biologically representative complex tissue of the respiratory airway is challenging, however, beneficial for treatment of respiratory diseases, a common medical condition representing a leading cause of death in the world. This in vitro study reports a successful development of synthetic human tracheobronchial epithelium based on interpenetrated hierarchical networks composed of a reversely 3D printed porous structure of a thermoresponsive stiffness-softening elastomer nanohybrid impregnated with collagen nanofibrous hydrogel. Human bronchial epithelial cells (hBEpiCs) were able to attach and grow into an epithelial monolayer on the hybrid scaffolds co-cultured with either human bronchial fibroblasts (hBFs) or human bone-marrow derived mesenchymal stem cells (hBM-MSCs), with substantial enhancement of mucin expression, ciliation, well-constructed intercellular tight junctions and adherens junctions. The multi-layered co-culture 3D scaffolds consisting of a top monolayer of differentiated epithelium, with either hBFs or hBM-MSCs proliferating within the hyperelastic nanohybrid scaffold underneath, created a tissue analogue of the upper respiratory tract, validating these 3D printed guided scaffolds as a platform to support co-culture and cellular organization. In particular, hBM-MSCs in the co-culture system promoted an overall matured physiological tissue analogue of the respiratory system, a promising synthetic tissue for drug discovery, tracheal repair and reconstruction. STATEMENT OF SIGNIFICANCE: Respiratory diseases are a common medical condition and represent a leading cause of death in the world. However, the epithelium is one of the most challenging tissues to culture in vitro, and suitable tracheobronchial models, physiologically representative of the innate airway, remain largely elusive. This study presents, for the first time, a systematic approach for the development of functional multilayered epithelial synthetic tissue in vitro via co-culture on a 3D-printed thermoresponsive elastomer interpenetrated with a collagen hydrogel network. The viscoelastic nature of the scaffold with stiffness softening at body temperature provide a promising matrix for soft tissue engineering. The results presented here provide new insights about the epithelium at different surfaces and interfaces of co-culture, and pave the way to offer a customizable reproducible technology to generate physiologically relevant 3D biomimetic systems to advance our understanding of airway tissue regeneration.

Tissue engineering applications in otolaryngology-The state of translation

While tissue engineering holds significant potential to address current limitations in reconstructive surgery of the head and neck, few constructs have made their way into routine clinical use. In this review, we aim to appraise the state of head and neck tissue engineering over the past five years, with a specific focus on otologic, nasal, craniofacial bone, and laryngotracheal applications. A comprehensive scoping search of the PubMed database was performed and over 2000 article hits were returned with 290 articles included in the final review. These publications have addressed the hallmark characteristics of tissue engineering (cellular source, scaffold, and growth signaling) for head and neck anatomical sites. While there have been promising reports of effective tissue engineered interventions in small groups of human patients, the majority of research remains constrained to in vitro and in vivo studies aimed at furthering the understanding of the biological processes involved in tissue engineering. Further, differences in functional and cosmetic properties of the ear, nose, airway, and craniofacial bone affect the emphasis of investigation at each site. While otolaryngologists currently play a role in tissue engineering translational research, continued multidisciplinary efforts will likely be required to push the state of translation towards tissue-engineered constructs available for routine clinical use.

LEVEL OF EVIDENCE

NA.

Tissue-Specific Decellularization Methods: Rationale and Strategies to Achieve Regenerative Compounds

The extracellular matrix (ECM) is a complex network with multiple functions, including specific functions during tissue regeneration. Precisely, the properties of the ECM have been thoroughly used in tissue engineering and regenerative medicine research, aiming to restore the function of damaged or dysfunctional tissues. Tissue decellularization is gaining momentum as a technique to obtain potentially implantable decellularized extracellular matrix (dECM) with well-preserved key components. Interestingly, the tissue-specific dECM is becoming a feasible option to carry out regenerative medicine research, with multiple advantages compared to other approaches. This review provides an overview of the most common methods used to obtain the dECM and summarizes the strategies adopted to decellularize specific tissues, aiming to provide a helpful guide for future research development.

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.

Biomedical grafts for tracheal tissue repairing and regeneration "Tracheal tissue engineering: an overview"

Airway system is a vital part of the living being body. Trachea is the upper respiratory portion that connects nostril and lungs and has multiple functions such as breathing and entrapment of dust/pathogen particles. Tracheal reconstruction by artificial prosthesis, stents, and grafts are performed clinically for the repairing of damaged tissue. Although these (above-mentioned) methods repair the damaged parts, they have limited applicability like small area wounds and lack of functional tissue regeneration. Tissue engineering helps to overcome the above-mentioned problems by modifying the traditional used stents and grafts, not only repair but also regenerate the damaged area to functional tissue. Bioengineered tracheal replacements are biocompatible, nontoxic, porous, and having 3D biomimetic ultrastructure with good mechanical strength, which results in faster and better tissue regeneration. Till date, the bioengineered tracheal replacements studies have been going on preclinical and clinical levels. Besides that, still many researchers are working at advance level to make extracellular matrix-based acellular, 3D printed, cell-seeded grafts including living cells to overcome the demand of tissue or organ and making the ready to use tracheal reconstructs for clinical application. Thus, in this review, we summarized the tracheal tissue engineering aspects and their outcomes.

Dexamethasone loaded bilayered 3D tubular scaffold reduces restenosis at the anastomotic site of tracheal replacement: in vitro and in vivo assessments

Despite recent developments in the tracheal tissue engineering field, the creation of a patient specific substitute possessing both appropriate mechanical and biointerfacial properties remains challenging. Most tracheal replacement therapies fail due to restenosis at the anastomosis site. In this study, we designed a robust, biodegradable, 3D tubular scaffold by combining electrospinning (ELSP) and 3D (three-dimensional) printing techniques for use in transplantation therapy. After that, we loaded dexamethasone (DEX) onto the 3D tubular scaffold using mild surface modification reactions by using polydopamine (PDA), polyethyleneimine (PEI), and carboxymethyl-β-cyclodextrin (βCD). As a result, the fabricated 3D tubular scaffold had robust mechanical properties and the chemical modifications were confirmed to have proceeded successfully by physico-chemical analysis. The surface treatments allowed for a larger amount of DEX to be loaded onto the βCD modified scaffold as compared to the bare group. In vitro and in vivo studies demonstrated that the DEX loaded 3D tubular scaffold exhibited significantly enhanced anti-inflammation activity, enhanced tracheal mucosal regeneration, and formation of a patent airway. From our results, we believe that our system may represent an innovative paradigm in tracheal tissue engineering by providing proper mechanical properties and successful formation of tracheal tissue as a means of remodeling and healing tracheal defects for use in transplantation therapy.

Non-Invasive Longitudinal Bioluminescence Imaging of Human Mesoangioblasts in Bioengineered Esophagi

Esophageal engineering aims to create replacement solutions by generating hollow organs using a combination of cells, scaffolds, and regeneration-stimulating factors. Currently, the fate of cells on tissue-engineered grafts is generally determined retrospectively by histological analyses. Unfortunately, quality-controlled cell seeding protocols for application in human patients are not standard practice. As such, the field requires simple, fast, and reliable techniques for non-invasive, highly specific cell tracking. Here, we show that bioluminescence imaging (BLI) is a suitable method to track human mesoangioblast seeding of an esophageal tubular construct at every stage of the preclinical bioengineering pipeline. In particular, validation of BLI as longitudinal quantitative assessment of cell density, proliferation, seeding efficiency, bioreactor culture, and cell survival upon implantation in vivo was performed against standard methods in 2D cultures and in 3D decellularized esophageal scaffolds. The technique is simple, non-invasive, and provides information on mesoangioblast distribution over entire scaffolds. Bioluminescence is an invaluable tool in the development of complex bioartificial organs and can assist in the development of standardized cell seeding protocols, with the ability to track cells from bioreactor through to implantation.

Limitations of recellularized biological scaffolds for human transplantation

A shortage of donor organs for transplantation and the dependence of the recipients on immunosuppressive therapy have motivated researchers to consider alternative regenerative approaches. The answer may reside in acellular scaffolds generated from cadaveric human and animal tissues. Acellular scaffolds are expected to preserve the architectural and mechanical properties of the original organ, permitting cell attachment, growth, and differentiation. Although theoretically, the use of acellular scaffolds for transplantation should pose no threat to the recipient's immune system, experimental data have revealed significant immune responses to allogeneic and xenogeneic transplanted scaffolds. Herein, we review the various factors of the scaffold that could trigger an inflammatory and/or immune response, thereby compromising its use for human transplant therapy. In addition, we provide an overview of the major cell types that have been considered for recellularization of the scaffold and their potential contribution to triggering an immune response.

Long-segmental tracheal reconstruction in rabbits with pedicled Tissue-engineered trachea based on a 3D-printed scaffold

Long-segmental tracheal defects constitute an intractable clinical problem, due to the lack of satisfactory tracheal substitutes for surgical reconstruction. Tissue engineered artificial substitutes could represent a promising approach to tackle this challenge. In our current study, tissue-engineered trachea, based on a 3D-printed poly (l-lactic acid) (PLLA) scaffold with similar morphology to the native trachea of rabbits, was used for segmental tracheal reconstruction. The 3D-printed scaffolds were seeded with chondrocytes obtained from autologous auricula, dynamically pre-cultured in vitro for 2 weeks, and pre-vascularized in vivo for another 2 weeks to generate an integrated segmental trachea organoid unit. Then, segmental tracheal defects in rabbits were restored by transplanting the engineered tracheal substitute with pedicled muscular flaps. We found that the combination of in vitro pre-culture and in vivo pre-vascularization successfully generated a segmental tracheal substitute with bionic structure and mechanical properties similar to the native trachea of rabbits. Moreover, the stable blood supply provided by the pedicled muscular flaps facilitated the survival of chondrocytes and accelerated epithelialization, thereby improving the survival rate. The segmental trachea substitute engineered by a 3D-printed scaffold, in vitro pre-culture, and in vivo pre-vascularization enhanced survival in an early stage post-operation, presenting a promising approach for surgical reconstruction of long segmental tracheal defects. STATEMENT OF SIGNIFICANCE: We found that the combination of in vitro pre-culture and in vivo pre-vascularization successfully generated a segmental tracheal substitute with bionic structure and mechanical properties similar to the native trachea of rabbits. Moreover, the stable blood supply provided by the pedicled muscular flaps facilitated the survival of chondrocytes and accelerated epithelialization, thereby improving the survival rate of the rabbits. The segmental trachea substitute engineered by a 3D-printed scaffold, in vitro pre-culture, and in vivo pre-vascularization enhanced survival in an early stage post-operation, presenting a promising approach for surgical reconstruction of long segmental tracheal defects.

Evaluation methods as quality control in the generation of decellularized peripheral nerve allografts

Nowadays, the high incidence of peripheral nerve injuries and the low success ratio of surgical treatments are driving research to the generation of novel alternatives to repair critical nerve defects. In this sense, tissue engineering has emerged as a possible alternative with special attention to decellularization techniques. Tissue decellularization offers the possibility to obtain a cell-free, natural extracellular matrix (ECM), characterized by an adequate 3D organization and proper molecular composition to repair different tissues or organs, including peripheral nerves. One major problem, however, is that there are no standard quality control methods to evaluate decellularized tissues. Therefore, in this review, a brief description of current strategies for peripheral nerve repair is given, followed by an overview of different decellularization methods used for peripheral nerves. Furthermore, we extensively discuss the available and currently used methods to demonstrate the success of tissue decellularization in terms of the cell removal, preservation of essential ECM molecules and maintenance or modification of biomechanical properties. Finally, orientative guidelines for the evaluation of decellularized peripheral nerve allografts are proposed.

Characterization and in vivo study of decellularized aortic scaffolds using closed sonication system

Extracellular matrix (ECM) based bioscaffolds prepared by decellularization has increasingly emerged in tissue engineering application because it has structural, biochemical, and biomechanical cues that have dramatic effects upon cell behaviors. Therefore, we developed a closed sonication decellularization system to prepare ideal bioscaffolds with minimal adverse effects on the ECM. The decellularization was achieved at 170 kHz of ultrasound frequency in 0.1% and 2% Sodium Dodecyl Sulphate (SDS) solution for 10 hours. The immersion treatment as control was performed to compare the decellularization efficiency with our system. Cell removal and ECM structure were determined by histological staining and biochemical assay. Biomechanical properties were investigated by the indentation testing to test the stiffness, a residual force and compression of bioscaffolds. Additionally, in vivo implantation was performed in rat to investigate host tissue response. Compared to native tissues, histological staining and biochemical assay confirm the absence of cellularity with preservation of ECM structure. Moreover, sonication treatment has not affected the stiffness [N/mm] and a residual force [N] of the aortic scaffolds except for compression [%] which 2% SDS significantly decreased compared to native tissues showing higher SDS has a detrimental effect on ECM structure. Finally, minimal inflammatory response was observed after 1 and 5 weeks of implantation. This study reported that the novelty of our developed closed sonication system to prepare ideal bioscaffolds for tissue engineering applications.

De-epithelialization of porcine tracheal allografts as an approach for tracheal tissue engineering

Replacement of large tracheal defects remains an unmet clinical need. While recellularization of acellular tracheal grafts appeared to be a viable pathway, evidence from the clinic suggests otherwise. In hindsight, complete removal of chondrocytes and repopulation of the tracheal chondroid matrix to achieve functional tracheal cartilage may have been unrealistic. In contrast, the concept of a hybrid graft whereby the epithelium is removed and the immune-privileged cartilage is preserved is a radically different path with initial reports indicating potential clinical success. Here, we present a novel approach using a double-chamber bioreactor to de-epithelialize tracheal grafts and subsequently repopulate the grafts with exogenous cells. A 3 h treatment with sodium dodecyl sulfate perfused through the inner chamber efficiently removes the majority of the tracheal epithelium while the outer chamber, perfused with growth media, keeps most (68.6 ± 7.3%) of the chondrocyte population viable. De-epithelialized grafts support human bronchial epithelial cell (BEAS-2B) attachment, viability and growth over 7 days. While not without limitations, our approach suggests value in the ultimate use of a chimeric allograft with intact donor cartilage re-epithelialized with recipient-derived epithelium. By adopting a brief and partial decellularization approach, specifically removing the epithelium, we avoid the need for cartilage regeneration.