Heterotopic en bloc tracheobronchial transplantation with direct revascularization in pigs

3D Bioprinting of Human Hollow Organs

3D bioprinting is a rapidly evolving technique that has been found to have extensive applications in disease research, tissue engineering, and regenerative medicine. 3D bioprinting might be a solution to global organ shortages and the growing aversion to testing cell patterning for novel tissue fabrication and building superior disease models. It has the unrivaled capability of layer-by-layer deposition using different types of biomaterials, stem cells, and biomolecules with a perfectly regulated spatial distribution. The tissue regeneration of hollow organs has always been a challenge for medical science because of the complexities of their cell structures. In this mini review, we will address the status of the science behind tissue engineering and 3D bioprinting of epithelialized tubular hollow organs. This review will also cover the current challenges and prospects, as well as the application of these complicated 3D-printed organs.

The Bronchial Arterial Circulation in Lung Transplantation: Bedside to Bench to Bedside, and Beyond

Chronic allograft dysfunction (CLAD) remains a major complication, causing the poor survival after lung transplantation (Tx). Although strenuous efforts have been made at preventing CLAD, surgical approaches for lung Tx have not been updated over the last 2 decades. The bronchial artery (BA), which supplies oxygenated blood to the airways and constitutes a functional microvasculature, has occasionally been revascularized during transplants, but this technique did not gain popularity and is not standard in current lung Tx protocols, despite the fact that a small number of studies have shown beneficial effects of BA revascularization on limiting CLAD. Also, recent basic and clinical evidence has demonstrated the relationship between microvasculature damage and CLAD. Thus, the protection of the bronchial circulation and microvasculature in lung grafts may be a key factor to overcome CLAD. This review revisits the history of BA revascularization, discusses the role of the bronchial circulation in lung Tx, and advocates for novel bronchial-arterial-circulation sparing approaches as a future direction for overcoming CLAD. Although there are some already published review articles summarizing the surgical techniques and their possible contribution to outcomes in lung Tx, to the best of our knowledge, this review is the first to elaborate on bronchial circulation that will contribute to prevent CLAD from both scientific and clinical perspectives: from bedside to bench to bedside, and beyond.

Experimental Tracheal Replacement Using 3-dimensional Bioprinted Artificial Trachea with Autologous Epithelial Cells and Chondrocytes

Various treatment methods for tracheal defects have been attempted, such as artificial implants, allografts, autogenous grafts, and tissue engineering; however, no perfect method has been established. We attempted to create an effective artificial trachea via a tissue engineering method using 3D bio-printing. A multi-layered scaffold was fabricated using a 3D printer. Polycaprolactone (PCL) and hydrogel were used with nasal epithelial and auricular cartilage cells in the printing process. An artificial trachea was transplanted into 15 rabbits and a PCL scaffold without the addition of cells was transplanted into 6 rabbits (controls). All animals were followed up with radiography, CT, and endoscopy at 3, 6, and 12 months. In the control group, 3 out of 6 rabbits died from respiratory symptoms. Surviving rabbits in control group had narrowed tracheas due to the formation of granulation tissue and absence of epithelium regeneration. In the experimental group, 13 of 15 animals survived, and the histologic examination confirmed the regeneration of epithelial cells. Neonatal cartilage was also confirmed at 6 and 12 months. Our artificial trachea was effective in the regeneration of respiratory epithelium, but not in cartilage regeneration. Additional studies are needed to promote cartilage regeneration and improve implant stability.

Large animal models for long-segment tracheal reconstruction: a systematic review

BACKGROUND

The reconstruction of extensive tracheal defects is an unresolved problem. Despite decades of research, a reliable and practical substitute remains to be found. While there have been clinical reports of successful long-segment tracheal reconstruction, reproducibility and widespread applicability of these techniques have yet to be achieved. Large animals such as the dog, pig, sheep, and goat have comparable tracheal morphology and physiology to humans making them useful preclinical models to screen potential therapeutic strategies.

MATERIALS AND METHODS

The literature was reviewed to identify large animal models commonly used for tracheal reconstruction. A systematic search of PubMed and EMBASE was performed for large animal studies reporting on the reconstruction of long-segment tracheal and carinal defects. Fifty-seven studies were identified for analysis.

RESULTS

There is no standard large animal model available for tracheal research. In recent years, livestock species have gained favor over dogs as animal models in this field. The minimum requirements for successful tracheal replacement are rigidity, vascularity, and epithelial lining. Early attempts with synthetic prostheses were met with disappointing results. An autologous tracheal substitute is ideal but hindered by limited donor site availability and the lack of a dominant vascular pedicle for microsurgical reconstruction. Although tracheal allotransplantation enables like-for-like replacement, there are unresolved issues relating to graft vascularity, immunosuppression, and graft preservation. Tissue engineering holds great promise; however, the optimal combination of scaffold, cells, and culture conditions is still indeterminate.

CONCLUSIONS

Despite impressive advances in tracheal reconstruction, a durable substitute for extended tracheal defects continues to be elusive.

Tracheal replacement

Tracheal reconstruction is one of the greatest challenges in thoracic surgery when direct end-to-end anastomosis is impossible or after this procedure has failed. The main indications for tracheal reconstruction include malignant tumours (squamous cell carcinoma, adenoid cystic carcinoma), tracheoesophageal fistula, trauma, unsuccessful surgical results for benign diseases and congenital stenosis. Tracheal substitutes can be classified into five types: 1) synthetic prosthesis; 2) allografts; 3) tracheal transplantation; 4) tissue engineering; and 5) autologous tissue composite. The ideal tracheal substitute is still unclear, but some techniques have shown promising clinical results. This article reviews the advantages and limitations of each technique used over the past few decades in clinical practice. The main limitation seems to be the capacity for tracheal tissue regeneration. The physiopathology behind this has yet to be fully understood. Research on stem cells sparked much interest and was thought to be a revolutionary technique; however, the poor long-term results of this approach highlight that there is a long way to go in this research field. Currently, an autologous tissue composite, with or without a tracheal allograft, is the only long-term working solution for every aetiology, despite its technical complexity and setbacks.

Successful tracheal replacement in humans using autologous tissues: an 8-year experience

BACKGROUND

Fifty years of surgical research using synthetic materials and heterologous tissues failed to find a good, durable replacement for the trachea. We investigated autologous tracheal substitution (ATS) without synthetic material or immunosuppression.

METHODS

For ATS, we used a single-stage operation to construct a tube from a forearm free fasciocutaneous flap vascularized by radial vessels that was reanastomosed to internal mammary vessels and reinforced by rib cartilages interposed transversally in the subcutaneous tissue. Tracheal resections 7 to 12 cm long (mean, 11 cm) were done to treat 8 primary tracheal neoplasms, including 5 adenoid cystic carcinomas (ACC) and 3 squamous cell carcinomas (SCC); 3 secondary tracheal neoplasms, including 1 thyroid carcinomas and 2 lymphomas; and 1 postintubation tracheal destruction after a long history of stenting. Transitory tracheotomy was associated to the absence of mucociliary clearance.

RESULTS

ATS has been performed in 12 patients since 2004, with additional resections in 4 patients, comprising 1 carinal resection alone, 1 associated with lobectomy, and 2 pharyngolaryngectomies. All patients were extubated on postoperative day 1. Eight patients are alive at a mean of 36 months (range, 2 to 94 months) postoperatively, with no respiratory distress. The 2 patients with ATS and carinal resections died of pulmonary infection. No airway collapse has been detected by endoscopy, dynamic computed tomography scan, or spirometry. Two patients still have a tracheotomy because the procedure was performed too low at the level of the proximal anastomosis. One patient with a chronic severe respiratory insufficiency recently required a distal, short stent.

CONCLUSIONS

ATS is a good, durable, tracheal substitution that resists respiratory pressure variations because of transverse rigidity, without any immunosuppression.

Autologous tracheal replacement: from research to clinical practice

BACKGROUND

Despite numerous attempts, synthetic materials and heterologous tissues failed to replace durably the trachea. Autologous tracheal substitution (ATS) without synthetic material or immunosuppression was investigated to replace extended tracheal defect. We present our experience regards to this innovative challenge.

METHOD

After a previous research study, we developed a novel reconstruction technique for extended tracheal defects on animals. Through a single stage operation, a tube from a forearm free fascio-cutaneous flap vascularized by radial vessels is re-anastomosed to cervical vessels. This flap is reinforced by rib cartilages interposed transversally in the subcutaneous tissue. It provides also a reliable ATS. Twelve patients benefits from an extended tracheal resections, 7-12 centimeter (mean 11 cm) long. Indications were eight Primary tracheal Neoplasms (including 5 adenoid cystic carcinoma [ACC] and 3 squamous cell carcinoma [SCC]), three secondary tracheal neoplasms (including 1 thyroid carcinoma and 2 lymphoma) and one post-intubation tracheal destruction after long history of stenting. Daily bronchoscopy and transitory tracheotomy was associated due to absence of mucociliary clearance.

RESULTS

The research work leads to present the first described animal model for tracheal resection and replacement with an autologous conduit. It was constructed from costal cartilages and a pediculed cervical skin flap. From 2004 to 2012, 12 patients have had ATS with associated resections in four cases. All patients were extubated on the first postoperative days; eight patients are alive at 2 to 94 months (mean=36) postoperatively, with no respiratory distress. The two patients with ATS after resection extended to the carina died due to pulmonary infection. No airway collapse has been detectable, either by endoscopy, dynamic CT scan or spirometry. Two patients still have a tracheotomy because performed too low at the level of the proximal anastomosis. One patient with a chronic severe respiratory insufficiency required recently a distal and short stent.

CONCLUSION

ATS is actually a good, durable tracheal substitute that can resist respiratory pressure variations because of their transverse rigidity without any immunosuppression. The limits of this technique are probably, chronic respiratory insufficiency and cartilage calcifications. Research to develop a method for lining the neo-trachea with ciliated respiratory epithelium is needed.

Tracheal transplant with a prefabricated microsurgical flap

OBJECTIVE

To test the viability of a tracheal autotransplant, with an original technique using a prefabricated flap from a complete tracheal neovascularized segment (CTNVS) of the sternohyoid muscle anastomosed by a microsurgical technique.

STUDY DESIGN

An experimental study using dogs as an animal model.

METHODS

Ten mongrel dogs weighing 23 to 40 kg were divided into two groups: group I (control), five animals submitted to autotransplant of the CTNVS without a microsurgical vascular anastomosis; and group II, five dogs submitted to autotransplant of the CTNVS with a microsurgical vascular anastomosis.

RESULTS

All group I dogs developed respiratory insufficiency and died because of necrosis and stenosis of the autotransplanted CTNVS, whereas all group II dogs completed a minimum period of 90 days of observation without any clinical changes. Macro- and microscopic analysis revealed intact tracheal structures.

CONCLUSIONS

The present clinical and morphological findings demonstrate that the CTNVS autotransplant is viable, when a microsurgical vascular anastomosis is used.

Bone morphogenetic protein-2 stimulation of cartilage regeneration in canine tracheal graft

BACKGROUND

Graft stenosis is among the most serious post-surgical complications that can occur after tracheal transplantation. Typically, stenosis is caused by resorption of tracheal cartilage. Bone morphogenetic protein-2 (BMP-2) is efficient at stimulating bone or cartilage regeneration. In this study, BMP-2 is tested for its effects on stimulation of cartilage regeneration in tracheal transplantation.

METHODS

For tracheal autotransplantation, 24 mongrel dogs were divided equally into four groups and BMP-2 was injected between the cartilage rings at doses of 1, 3, 5 or 7 mg. For tracheal allotransplantation, 12 mongrel dogs were divided equally into two groups. One group received 5 mg of BMP-2 per graft, and the other received collagen only as a control. The grafts were harvested after 4 weeks and subjected to pathologic analysis. The diameter of the graft lumen and areas of new cartilage regeneration were measured.

RESULTS

Regenerated cartilage areas were found in both the injected area and around the perichondrium. The areas of regenerated cartilage, as well as the diameter of the tracheal lumen, increased significantly with increasing concentrations of BMP-2. Five milligrams per milliliter was the most effective dose of BMP-2 in this study.

CONCLUSIONS

BMP-2 can significantly stimulate cartilage regeneration in tracheal grafts and also can be used to prevent stenosis after tracheal transplantation.

Revascularization of trachea in lung and tracheal transplantation

Ischemia is the primary risk factor for airway complications in double lung transplantation using tracheal anastomosis and in tracheal transplantation. Many treatment options as to revascularization for the trachea were herein described and reviewed. They include direct revascularization (using a conduit such as artery or vein), revascularization with tissue wrapping (using omentum, muscle, internal thoracic artery pedicle, pleura, or pericardial fat pad), and with drug administration (using corticosteroid hormone, prostaglandin, or angiogenic factor). As there are few organized reports including new information on revascularization for the trachea these days, this review article would help thoracic surgeons who get engaged transplantation.

Topographic anatomy of bronchial arteries in the pig: a corrosion cast study

The anatomy of porcine bronchial circulation has not been fully described. The purpose of this study was to investigate the extrapulmonary topographic anatomy of bronchial arteries in pig. Ten pigs weighing 15-25 kg were studied. Between one and four bronchial arteries were found in each pig. The bronchoesophageal artery (BEA), tracheobronchial artery (TBA), inferior bronchial artery (IBA) and accessory bronchial artery (ABA) were present in 10/10, 8/10, 6/10 and 2/10 animals, respectively. The trunk of BEA had a diameter of about 3 mm, a length of 1-7 mm, and originated from the anterior and medial aspect of the descending thoracic aorta at the level between the 2nd and 4th thoracic vertebrae (T2-T4) in all animals. The extrapulmonary topographic anatomy of bronchial arteries in pigs exhibits similarities to that of humans. BEA is the main blood supplier of the porcine tracheobronchial tree with a relatively constant location of origin and a sufficient size for anastomosis. These characteristics render BEA the ideal vessel for bronchial revascularization in pigs.