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.

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

Currently, 3D-bioprinting technique has emerged as a promising strategy to offer native-like tracheal substitutes for segmental trachea reconstruction. However, there has been very limited breakthrough in tracheal repair using 3D-bioprinted biomimetic trachea owing to the lack of ideal bioinks, the requirement for precise structural biomimicking, and the complexity of multi-step surgical procedures by mean of intramuscular pre-implantation. Herein, we propose a one-step surgical technique, namely direct end-to-end anastomosis using C-shape 3D-bioprinted biomimetic trachea, for segmental trachea defect repair. First, two types of tissue-specific matrix hydrogels were exploited to provide mechanical and biological microenvironment conducive to the specific growth ways of cartilage and fibrous tissue respectively. In contrast to our previous O-shape tracheal design, the tubular structure of alternating C-shape cartilage rings and connecting vascularized-fibrous-tissue rings was meticulously designed for rapid 3D-bioprinting of tracheal constructs with optimal printing paths and models. Furthermore, in vivo trachea regeneration in nude mice showed satisfactory mechanical adaptability and efficient physiological regeneration. Finally, in situ segmental trachea reconstruction by direct end-to-end anastomosis in rabbits was successfully achieved using 3D-bioprinted C-shape biomimetic trachea. This study demonstrates the potential of advanced 3D-bioprinting for instant and efficient repair of segmental trachea defects. 

Instant trachea reconstruction using 3D-bioprinted C-shape biomimetic trachea based on tissue-specific matrix hydrogels

Abstract Formation of functional and perfusable vascular network is critical to ensure the long‐term survival and functionality of the engineered tissue tracheae after transplantation. However, the greatest challenge in tracheal‐replacement therapy is the promotion of tissue regeneration by rapid graft vascularization. Traditional prevascularization methods for tracheal grafts typically utilize omentum or muscle flap wrapping, which requires a second operation; vascularized segment tracheal orthotopic transplantation in one step remains difficult. This study proposes a method to construct a tissue‐engineered tracheal graft, which directly forms the microvascular network after orthotopic transplantation in vivo. The focus of this study was the preparation of a hybrid tracheal graft that is non‐immunogenic, has good biomechanical properties, supports cell proliferation, and quickly vascularizes. The results showed that vacuum‐assisted decellularized trachea‐polycaprolactone hybrid scaffold could match most of the above requirements as closely as possible. Furthermore, endothelial progenitor cells (EPCs) were extracted and used as vascularized seed cells and seeded on the surfaces of hybrid grafts before and during the tracheal orthotopic transplantation. The results showed that the microvascularized tracheal grafts formed maintained the survival of the recipient, showing a satisfactory therapeutic outcome. This is the first study to utilize EPCs for microvascular construction of long‐segment trachea in one‐step; the approach represents a promising method for microvascular tracheal reconstruction.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/btm2.10534

Biomimetic in situ tracheal microvascularization for segmental tracheal reconstruction in one‐step

Long segment trachea defects are repaired by tracheal substitution, while decellularized technology has been effectively employed to prepare tissue engineering trachea (TET). However, its clinical application is restricted by the long preparation cycle, while poor vascularization is associated with the transplantation failure. In the present study, we used sodium lauryl ether sulfate (SLES) to develop a novel rapid decellularized tracheal preparation method, then constructed a TET with revascularization functions. Summarily, we decellularized rabbit trachea using various SLES concentrations. Results from histological analysis, immunohistochemical and DAPI staining, as well as DNA quantitative assay, revealed that 1-0.1% (v/v) SLES treatment not only entirely removed cellular components to reduce its immunogenicity, but also retained the tracheal matrix's gross structure. SEM images, safranine O-fast green staining, total collagen content assay and collagen II immunofluorescence revealed that low SLES concentrations preserved the bioactive components of the decellularized tracheal matrix. Next, we performed cytobiocompatible and cytotoxin assays to verify biocompatibility of the decellularized tracheal matrix, and is confirmed by the omentum transplantation of rats. Results from omentum transplantation revealed that the decellularized tracheal matrix had low immunogenicity and excellent biocompatibility. Its revascularization capacity was confirmed by histologic appearance and CD31 immunofluorescence. Based on these findings, we selected 0.1% (v/v) as the optimal SLES concentration for preparing a decellularized tracheal matrix. Next, we seeded allogeneic bone marrow stem cells (BMSC) onto the matrix to construct TET patches. In vivo tracheal defect reconstruction confirmed the biocompatibility and revascularization capacity of this novel TET, and the formation of a vascular network around the patch promoted submucosa and mucosa regeneration without significant stenosis, 4 weeks post-surgery. In conclusion, we used SLES to successfully develop a novel decellularized approach for the preparation of TET, which has low immunogenic and inflammatory responses, as well as excellent biocompatibility, and revascularization ability in vivo without additional exogenous cytokines.

A novel decellularized trachea preparation method for the rapid construction of a functional tissue engineered trachea to repair tracheal defects.

Tracheal reconstruction represents a challenge when primary anastomosis is not feasible. Within this scenario, the study aim was to develop a new pig-derived decellularized trachea (DecellT) to be compared with the cryopreserved counterpart (CryoT) for a close predictive analysis. Tracheal segments underwent decellularization by a physical + enzymatic + chemical method (12 cycles); in parallel, cryopreserved samples were also prepared. Once decellularized (histology/DNA quantification), the two groups were characterized for Alpha-Gal epitopes/structural proteins (immunohistochemistry/histology/biochemical assays/second harmonic generation microscopy)/ultrastructure (Scanning Electron Microscopy (SEM))/mechanical behaviour. Cytotoxicity absence was assessed in vitro (extract-test assay/direct seeding, HM1SV40 cell line) while biocompatibility was verified in BALB/c mice, followed by histological/immunohistochemical analyses and SEM (14 days). Decellularization effectively removed Alpha-Gal epitopes; cartilage histoarchitecture was retained in both groups, showing chondrocytes only in the CryoT. Cryopreservation maintained few respiratory epithelium sparse cilia, not detectable in DecellT. Focusing on ECM, preserved structural/ultrastructural organization and collagen content were observed in the cartilage of both; conversely, the GAGs were significantly reduced in DecellT, as confirmed by mechanical study results. No cytotoxicity was highlighted by CryoT/DecellT in vitro, as they were also corroborated by a biocompatibility assay. Despite some limitations (cells presence/GAGs reduction), CryoT/DecellT are both appealing options, which warrant further investigation in comparative in vivo studies.

/pdf/development-and-in-vitro-in-vivo-comparative-2c30gu1q.pdf

Development and In Vitro/In Vivo Comparative Characterization of Cryopreserved and Decellularized Tracheal Grafts

Directly construct microvascularization of tissue engineering trachea in orthotopic transplantation.

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Directly construct microvascularization of tissue engineering trachea in orthotopic transplantation.