Margot Den Hondt

Tracheal Allograft after Withdrawal of Immunosuppressive Therapy

This letter describes findings from an evaluation of a tracheal allotransplant at 2 years, documented with imaging studies and a video. Despite immunologic rejection of the donor mucosal lining, the tracheal cartilage appears to remain intact without immunosuppression.

A comparison of tracheal scaffold strategies for pediatric transplantation in a rabbit model

Despite surgical advances, childhood tracheal stenosis is associated with high morbidity and mortality. Various tracheal scaffold strategies have been developed as the basis for bioengineered substitutes, but there is no consensus on which may be superior in vivo. We hypothesized that there would be no difference in morbidity and mortality between three competing scaffold strategies in rabbits.

Twenty years of experience with the rabbit model, a versatile model for tracheal transplantation research

Pathologies comprising more than half the length of the trachea are a challenge to the reconstructive surgeon. Innovative tracheal transplantation techniques aim to offer the patient a curative solution with a sustained improvement in quality of life. This review summarizes the authors’ experience with the rabbit as a versatile model for research regarding tracheal transplantation. Because of the segmental blood supply of the trachea, it is not feasible to transplant the organ together with a well-defined vascular pedicle. As such, the key element of successful tracheal transplantation is the creation of a new blood supply. This vascularized construct is created by prelaminating the rabbit trachea heterotopically, within the lateral thoracic fascia. After prelamination, the construct and its vascular pedicle are transferred to the orthotopic position in the neck. This model has become gold standard because of the advantages of working with rabbits, the anatomy of the rabbit trachea, and the reliability of the lateral thoracic artery flap. In this paper, the key elements of surgery in the rabbit are discussed, as well as the tracheal anastomosis and the harvest of the lateral thoracic artery flap. Practical tips and tricks are presented. The data described in this review represent the fundaments of ongoing translational research in the center over the past twenty years.

Tracheal tissue-engineering: in-vivo biocompatibility of mechanically-stripped allogenic rabbit trachea with autologous epithelial covering

Abstract Background: Successful trachea transplantation comprises the use of biocompatible constructs with little immune-reactivity, submucosal revascularization and creation of an epithelial covering. Allogenic chondrocytes might be protected from an overt immune-response due to physical isolation. Our aim was to evaluate in-vivo biocompatibility of allotracheae, stripped of their highly-immunogenic inner lining. Secondly, we established whether these constructs might serve as suitable scaffolds for autologous epithelial grafting. Methods: Mucosa and submucosa of 12 rabbit donor tracheae were mechanically peeled off. Cartilage was covered with Integra™ regeneration-template. Constructs were implanted within the recipients lateral thoracic artery flap. Integra of 6 revascularized allotracheae was grafted with autologous buccal mucosa. Macroscopical, histological analysis and immunohistochemistry were performed. Results: Revascularization and buccal grafting was incomplete in the first 2 circular constructs. To enhance blood-vessel outgrowth, the following 10 transplants were opened longitudinally before implantation. Integra revascularized well. Grafted tracheae showed satisfactory mucosa-adherence, albeit with invasion of migrating epithelium within the Integra-scaffold. Conclusions: Mechanically-stripped allotracheae exhibited beneficial biocompatibility up to two months. This approach might open doors in the treatment of long-segment tracheal pathologies of which immunosuppression is contra-indicated. Thickness of this layered construct limited practical feasibility of orthotopic transfer, though with further refinements, a clinically-useful transplant could be created.

Reconstruction of defects of the trachea

The trachea has a complex anatomy to fulfill its tasks. Its unique fibro-cartilaginous structure maintains an open conduit during respiration, and provides vertical elasticity for deglutition, mobility of the neck and speech. Blood vessels pierce the intercartilaginous ligaments to perfuse the ciliated epithelium, which ensures effective mucociliary clearance. Removal of a tracheal segment affected by benign or malignant disease requires airtight restoration of the continuity of the tube. When direct approximation of both tracheal ends is no longer feasible, a reconstruction is needed. This may occur in recurrent short-segment defects in a scarred environment, or in defects comprising more than half the length of the trachea. The resulting gap must be filled with vascularized tissue that restores the mucosal lining and supports the semi-rigid, semi-flexible framework of the trachea. For long-segment or circular defects, restoration of this unique biomechanical profile becomes even more important. Due to the inherent difficulty of creating such a tube, a tracheostomy or palliative stenting are often preferred over permanent reconstruction. To significantly improve and sustain quality of life of these patients, surgeons proposed innovative strategies for complex tracheal repair. In this review, we provide an overview of current clinical applications of tracheal repair using autologous and allogenic tissues. We look at recent advances in the field of tissue engineering, and the areas for improvement of these first human applications. Lastly, we highlight the focus of our research, in an effort to contribute to the development of optimized tracheal reconstructive techniques.

Cell and Gene Transfer Strategies for Vascularization During Skin Wound Healing

Adequate vascularization is pivotal to skin wound healing. Therefore, designing efficient revascularization strategies based on the mechanisms behind electromechanical stimulation of wound vascularization would be beneficial to the growing number of patients in need of improved wound healing. Recent attention has centered on applying gene/protein transfer and cell differentiation/transplantation approaches to stimulate and mimic the molecular events occurring during wound revascularization. Although both gene/protein transfer and cell differentiation/transplantation are faced with important challenges, researchers have made tremendous advances and shown both strategies to be a promising approach. In this chapter, we give an overview of the myriad of molecular players involved in neovascularization. We also discuss the molecular mechanisms of neovascularization during wound healing and provide an in-depth review on neovascular strategies and techniques for wound healing and tissue-engineered skin equivalents.

Epithelial grafting of a decellularized whole-tracheal segment: an in vivo experimental model

OBJECTIVES Prerequisites for successful trachea transplantation include the use of a biocompatible construct, submucosal vascularization and an epithelial covering. Implantation of non-epithelialized tracheal scaffolds may lead to stenosis. However, epithelial grafting or seeding can only be attempted onto a well-vascularized submucosal bed. Our aim was to investigate a method to prevent stenosis during prelamination of non-epithelialized, gently decellularized rabbit tracheae and to evaluate whether grafting of revascularized constructs with buccal mucosa is feasible. METHODS Allotracheae underwent two 48-h cycles of detergent-enzymatic decellularization using sodium deoxycholate and DNAse. In the first series, 12 circular scaffolds were implanted bilaterally in lateral thoracic artery flaps (n = 6 rabbits). Right-sided transplants were covered internally with Integra™. In the second series, 10 decellularized tracheae covered with Integra were prelaminated in flaps (n = 10 rabbits). Twenty-one days after implantation, revascularized tracheae were grafted with buccal mucosa. A macroscopic, histological analysis and immunohistochemistry were performed on explants. RESULTS In the first series, tracheae without Integra covering developed significantly greater intraluminal (P = 0.032) and subepithelial narrowing (P = 0.0345) compared with tracheae with Integra covering. All tracheae exhibited insufficient submucosal revascularization. In the second series, submucosal revascularization was incomplete in the first 2 constructs, which were implanted circularly. These tracheae only showed marginal buccal graft ingrowth. To accelerate revascularization, the subsequent 8 transplants were opened longitudinally before implantation. Compared to circularly implanted tracheae, submucosal revascularization of these transplants was superior (P = 0.0008). Graft adherence was complete in 6 opened constructs. Mild lymphocytic infiltration within the buccal graft was detected in 5 specimens. CONCLUSIONS We observed satisfactory host integration of opened tracheae that were temporarily covered with Integra during revascularization and subsequently grafted with buccal mucosa. Integra successfully prevented stenosis during revascularization. This model may provide an example of an immunosuppressive-free approach in the treatment of long-segment tracheal lesions. With the aid of further refinements such as a respiratory epithelial lining, an orthotopically transplantable construct could be created.

Abstract 28: Tracheal Tissue-Engineering

RESULTS: 3 men and 20 women were included in the study with an average age of 63 (±6 years). The average BMI was 26.0 (±4.6 kg/m). 26 feet were injected in Group 1, and 17 were injected in Group 2. There was no variance in BMI or age across groups. In Group 1, fat pad thickness was increased until 12 months postoperatively (p<0.05). In Group 2, fat pad thickness was increased until 6 months postoperatively (p<0.05). In Group 1, dermal thickness was greater in the 5 metatarsal at 12 months postoperatively (p<0.05). However, this difference was clinically negligible. In Group 2, there was no significant difference between dermal thickness preoperatively and at 12 months postoperatively. With regard to clinical outcomes, Group 1 had significant improvement in pain through 24 months (p<0.001) and foot function through 18 months post-injection (p<0.05). Group 2 had significant improvement in pain and increased work and leisure activities through 6 months post-injection (p< 0.05).

Abstract: 11.30 Tracheal Tissue-Engineering

Materials and Methods: A retrospective review of all patients admitted during 2011–2014, who developed Ulcer of the leg and were treated by lipofilling in the National centre for burns and plastic surgery, University Hospital, Ibn-Rochd Casablanca, Morocco. Patients with large ulcers and those with exposure of bone exposure were omitted from the study. Patient demographic data and digital photographs were taken on the day of surgery and every other day thereafter. Each patient received 3 sessions of 20 cc of autologous Adipose stem cells injection in subcutaneous tissue surrounding the ulcer. Time to wound closure was defined as the time at which the wound bed was completely reepithelialized and filled with new tissue.

Tissue engineering and surgery: from translational studies to human trials

Abstract Tissue engineering was introduced as an innovative and promising field in the mid-1980s. The capacity of cells to migrate and proliferate in growth-inducing medium induced great expectancies on generating custom-shaped bioconstructs for tissue regeneration. Tissue engineering represents a unique multidisciplinary translational forum where the principles of biomaterial engineering, the molecular biology of cells and genes, and the clinical sciences of reconstruction would interact intensively through the combined efforts of scientists, engineers, and clinicians. The anticipated possibilities of cell engineering, matrix development, and growth factor therapies are extensive and would largely expand our clinical reconstructive armamentarium. Application of proangiogenic proteins may stimulate wound repair, restore avascular wound beds, or reverse hypoxia in flaps. Autologous cells procured from biopsies may generate an ‘autologous’ dermal and epidermal laminated cover on extensive burn wounds. Three-dimensional printing may generate ‘custom-made’ preshaped scaffolds – shaped as a nose, an ear, or a mandible – in which these cells can be seeded. The paucity of optimal donor tissues may be solved with off-the-shelf tissues using tissue engineering strategies. However, despite the expectations, the speed of translation of in vitro tissue engineering sciences into clinical reality is very slow due to the intrinsic complexity of human tissues. This review focuses on the transition from translational protocols towards current clinical applications of tissue engineering strategies in surgery.