Requirements for Successful Trachea Transplantation: A Study in the Rabbit Model

Tracheal Transplantation

Airway stenosis and malignant tumors are the 2 main reasons to perform a surgical resection of part of the trachea. Tracheal lesions with a length shorter than 5 cm can be resected and primary reconstruction can be safely effected. Excessive anastomotic tension should be avoided because it may lead to restenosis or dehiscence at the anastomosis. Reconstruction of a longer defect may be attempted with a tracheal allotransplant or with autologous tissue.

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.

Reconstruction of tracheal window-shape defect by 3D printed polycaprolatone scaffold coated with Silk Fibroin Methacryloyl

In this study, we aimed to utilize autologous tracheal epithelia and BMSCs as the seeding cells, utilize PCL coated with SilMA as the hybrid scaffold to carry the cells and KGN, which can selectively stimulate chondrogenic differentiation of BMSCs. This hybrid tracheal substitution was carried out to repair the tracheal partial window-shape defect. Firstly, SilMA with the concentration of 10%, 15% and 20% was prepared, and the experiment of swelling and degradation was performed. With the increase of the concentration, the swelling ratio of SilMA decreased, and the degradation progress slowed down. Upon the result of CCK-8 test and HE staining of 3D co-culture, the SilMA with concentration of 20% was selected. Next, SilMA and the cells attached to SilMA were characterized by SEM. Furthermore, in vitro cytotoxicity test shows that 20% SilMA has good cytocompatibility. The hybrid scaffold was then made by PCL coated with 20% SilMA. The mechanical test shows this hybrid scaffold has better biomechanical properties than native trachea. In vivo tracheal defect repair assays were conducted to evaluate the effect of the hybrid substitution. H&E staining, IHC staining and IF staining showed that this hybrid substitution ensured the viability, proliferation and migration of epithelium. However, it is sad that the results of chondrogenesis were not obvious. This study is expected to provide new strategies for the fields of tracheal replacement therapy needing mechanical properties and epithelization.

Development and clinical translation of tubular constructs for tracheal tissue engineering: a review

Effective restoration of extensive tracheal damage arising from cancer, stenosis, infection or congenital abnormalities remains an unmet clinical need in respiratory medicine. The trachea is a 10-11 cm long fibrocartilaginous tube of the lower respiratory tract, with 16-20 tracheal cartilages anterolaterally and a dynamic trachealis muscle posteriorly. Tracheal resection is commonly offered to patients suffering from short-length tracheal defects, but replacement is required when the trauma exceeds 50% of total length of the trachea in adults and 30% in children. Recently, tissue engineering (TE) has shown promise to fabricate biocompatible tissue-engineered tracheal implants for tracheal replacement and regeneration. However, its widespread use is hampered by inadequate re-epithelialisation, poor mechanical properties, insufficient revascularisation and unsatisfactory durability, leading to little success in the clinical use of tissue-engineered tracheal implants to date. Here, we describe in detail the historical attempts and the lessons learned for tracheal TE approaches by contextualising the clinical needs and essential requirements for a functional tracheal graft. TE manufacturing approaches explored to date and the clinical translation of both TE and non-TE strategies for tracheal regeneration are summarised to fully understand the big picture of tracheal TE and its impact on clinical treatment of extensive tracheal defects.

Minimally Invasive Neck Surgery: An Animal Model Study

Background: Minimally invasive surgery (MIS) is replacing conventional surgery as the "gold standard" in different surgical areas. Although cervical MIS is already accepted in the adult population, its use in children is still new and controversial. The natural obstacles to this approach are the absence of a natural cavity, with the inherent complications of creating one artificially, and the limited existing workspace especially in pediatric patients. All endoscopic techniques in the field of neck surgery try to live up to the high cosmetic expectations and the transoral cervical approach as a natural orifice surgery technique excels at it. Aim: Besides the goal of feasibility, we aim to report on the pitfalls of this approach, by using an experimental rabbit model for minimally invasive thyroidectomy. Materials and Methods: Transoral endoscopic thyroidectomies using a vestibular approach were performed in 10 anesthetized rabbits. All surgeries were video recorded. The surgical time, anatomy identified, difficulties, and intraoperative complications were documented. Results: Through one trocar in the vestibular area and two lateral stab incisions, it was possible to create a working space and to reach the peritracheal area. Total thyroidectomies were completed in the 10 animals with a mean operative time of 51 minutes. In all of them we were able to identify the fascial spaces of the neck and the major vessels. During surgery, the lack of space required surgical gestures to be very precise, soft, and gentle. There were 2 cases with a small amount of bleeding and one mild trachea laceration during the procedure, but none of them required suspension or conversion to an open procedure. Animals were euthanized immediately after the surgical procedure. Conclusions: The vestibular approach seems to be a feasible technique to access pediatric neck pathology. Despite the differences in the cervical anatomy, the limited workspace of the rabbit model perfectly matches the requirements of a pediatric training model.

State of the art of clinical applications of Tissue Engineering in 2021

Tissue engineering (TE) was introduced almost 30 years ago as a potential technique for regenerating human tissues. However, despite promising laboratory findings, the complexity of the human body, scientific hurdles, and lack of persistent long-term funding still hamper its translation towards clinical applications. In this report, we compile an inventory of clinically applied TE medical products relevant to surgery. A review of the literature, including articles published within the period from 1991 to 2020, was performed according to the PRISMA protocol, using databanks PubMed, Cochrane Library, Web of Science, and Clinicaltrials.gov. We identified 1039 full-length articles as eligible; due to the scarcity of clinical, randomised, controlled trials and case studies, we extended our search towards a broad surgical spectrum. Forty papers involved clinical TE studies. Amongst these, 7 were related to TE protocols for cartilage applied in the reconstruction of nose, ear, and trachea. Nine papers reported TE protocols for articular cartilage, 9 for urological purposes, 7 described TE strategies for cardiovascular aims, and 8 for dermal applications. However, only two clinical studies reported on three-dimensional (3D) and functional long-lasting TE constructs. The concept of generating 3D TE constructs and organs based on autologous molecules and cells is intriguing and promising. The first translational tissue-engineered products and techniques have been clinically implemented. However, despite the 30 years of research and development in this field, TE is still in its clinical infancy. Multiple experimental, ethical, budgetary, and regulatory difficulties hinder its rapid translation. Nevertheless, the first clinical applications show great promise and indicate that the translation towards clinical medical implementation has finally started.

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.

Bioengineered airway epithelial grafts with mucociliary function based on collagen IV- and laminin-containing extracellular matrix scaffolds

Current methods to replace damaged upper airway epithelium with exogenous cells are limited. Existing strategies use grafts that lack mucociliary function, leading to infection and the retention of secretions and keratin debris. Strategies that regenerate airway epithelium with mucociliary function are clearly desirable and would enable new treatments for complex airway disease.Here, we investigated the influence of the extracellular matrix (ECM) on airway epithelial cell adherence, proliferation and mucociliary function in the context of bioengineered mucosal grafts. In vitro, primary human bronchial epithelial cells (HBECs) adhered most readily to collagen IV. Biological, biomimetic and synthetic scaffolds were compared in terms of their ECM protein content and airway epithelial cell adherence.Collagen IV and laminin were preserved on the surface of decellularised dermis and epithelial cell attachment to decellularised dermis was greater than to the biomimetic or synthetic alternatives tested. Blocking epithelial integrin α2 led to decreased adherence to collagen IV and to decellularised dermis scaffolds. At air-liquid interface (ALI), bronchial epithelial cells cultured on decellularised dermis scaffolds formed a differentiated respiratory epithelium with mucociliary function. Using in vivo chick chorioallantoic membrane (CAM), rabbit airway and immunocompromised mouse models, we showed short-term preservation of the cell layer following transplantation.Our results demonstrate the feasibility of generating HBEC grafts on clinically applicable decellularised dermis scaffolds and identify matrix proteins and integrins important for this process. The long-term survivability of pre-differentiated epithelia and the relative merits of this approach against transplanting basal cells should be assessed further in pre-clinical airway transplantation models.

Factors Influencing Poor Outcomes in Synthetic Tissue-Engineered Tracheal Replacement

OBJECTIVES

Humans receiving tissue-engineered tracheal grafts have experienced poor outcomes ultimately resulting in death or the need for graft explantation. We assessed the performance of the synthetic scaffolds used in humans with an ovine model of orthotopic tracheal replacement, applying standard postsurgical surveillance and interventions to define the factors that contributed to the complications seen at the bedside.

STUDY DESIGN

Large animal model.

SETTING

Pediatric academic research institute.

SUBJECTS AND METHODS

Human scaffolds were manufactured with an electrospun blend of polyethylene terephthalate and polyurethane reinforced with polycarbonate rings. They were seeded with autologous bone marrow-derived mononuclear cells and implanted in sheep. Animals were evaluated with routine bronchoscopy and fluoroscopy. Endoscopic dilation and stenting were performed to manage graft stenosis for up to a 4-month time point. Grafts and adjacent native airway were sectioned and evaluated with histology and immunohistochemistry.

RESULTS

All animals had signs of graft stenosis. Three of 5 animals (60%) designated for long-term surveillance survived until the 4-month time point. Graft dilation and stent placement resolved respiratory symptoms and prolonged survival. Necropsy demonstrated evidence of infection and graft encapsulation. Granulation tissue with signs of neovascularization was seen at the anastomoses, but epithelialization was never observed. Acute and chronic inflammation of the native airway epithelium was observed at all time points. Architectural changes of the scaffold included posterior wall infolding and scaffold delamination.

CONCLUSIONS

In our ovine model, clinically applied synthetic tissue-engineered tracheas demonstrated infectious, inflammatory, and mechanical failures with a lack of epithelialization and neovascularization.