Artificial Trachea

Novel composite trachea grafts using 3-dimensional printing

Objective

Porcine-derived small intestine submucosa (SIS) extracellular matrix (ECM) surgical patches claim to have greater regenerative properties compared with dermal extracellular matrices. We hypothesized that using SIS-ECM in a bioengineered composite tracheal graft would allow better incorporation into the native tissue.

Methods

Two types of size-matched polycaprolactone support scaffolds were designed: rigid and flexible. The SIS-ECM was wrapped around the polycaprolactone supports lining the inside and outside of the graft. The grafts were implanted in 4 Yorkshire pigs, replacing an ∼2 cm segment of native trachea. Airway patency was evaluated with computed tomography scans and explanted grafts were examined grossly and histologically.

Results

All animals survived through the immediate postoperative period. Generally, extraluminal examination showed a smooth transition between native and graft without significant volumetric loss. Animals that received the flexible design survived ∼10 days longer than those that received the rigid design; however, severe perianastomotic intraluminal granulation tissue was observed. The rigid design had less significant intraluminal granulation tissue development at the distal anastomosis, but partial dehiscence had occurred at the proximal anastomosis interrupting graft incorporation.

Conclusions

The generally good extraluminal graft incorporation in our composite tracheal graft highlights some increased regenerative capabilities of SIS-ECM. However, the presence of intraluminal granulation tissue indicates that its use as an off-the-shelf, unaltered substrate in an airway graft is still not ideal. Further research must be conducted to determine whether a modification of the substrate is possible to enhance luminal airway incorporation and to exert control over the mechanisms responsible for granulation tissue development.

A novel technique to increase the length of tracheal resection by adding an autologous pedicled pectoralis major myocutaneous flap transposition

Resection of the trachea is usually limited by the length of involvement. We present a case of long segment tracheal resection performed by adding an autologous pedicled pectoralis major myocutaneous flap transposition. By applying of this technique, a segment of trachea as long as 7.5 cm was safely resected without complications.

Construction of a tube-shaped tracheal substitute using fascial flap-wrapped revascularized allogenic aorta

OBJECTIVES

Animal studies have demonstrated the feasibility of tracheal replacement by silicone-stented allogenic aortas (AAs), showing mature cartilage regeneration into the grafts. In clinical trials, this graft did not prove stiff enough to allow long-term stent withdrawal. This graft insufficiency could be due to ischaemic phase prior to neoangiogenesis. To solve this issue, we investigated both the efficacy of the rabbit lateral thoracic fascial flap as a vehicle for revascularization of the AA and construction of a tube-shaped graft with transferable vascular pedicle, for more efficient replacement of the trachea.

METHODS

Thirty-four New Zealand rabbits were used. After harvesting of donors 'thoracic aortas', the fresh aortic allografts were transplanted within 1 h, and the others were cryopreserved. Fifteen male and four female rabbits were used as recipients for fresh (n = 9) or cryopreserved (n = 10) aortic allografts that were implanted under the skin of the chest wall, after graft wrap using a pedicled lateral thoracic fascial flap. Animal sacrifice was scheduled at regular intervals up to 61 days. Macroscopic and microscopic examinations and fluorescence in situ hybridization (FISH) were used to study the morphology, revascularization process and viability of the construct.

RESULTS

There was no operative death. Animals showed no graft rejection, despite the absence of immunosuppressive therapy. They all had a satisfactory tubular morphology of their construct. Of the 19 rabbits, 15 were found to have a generally preserved histological structure of the aorta and satisfactory neoangiogenesis. In the last four, a severe wound complication was associated with necrosis of the aortic graft. FISH on three aortic grafts with satisfactory neoangiogenesis showed migration of recipient cells into the aortic graft, decreasing from the adventitial to the luminal side, associated with the persistence of cells from the donor.

CONCLUSIONS

Our results showed that the chimeric construct transformed into a well-vascularized tube-shaped organ with transferable pedicle and some degree of stiffness. Persistence of donor's cells of normal morphology into the aortic graft was suggestive of minimal ischaemia during the initial phase of revascularization. This construct might be investigated in the setting of tracheal replacement in the rabbit model.

Tracheal replacement with a bioabsorbable scaffold in sheep

BACKGROUND

A significant native tracheal approximation phenomenon was observed in our previous study [Tsukada H, Ernst A, Gangadharan S, et al. Tracheal replacement with a silicone-stented fresh aortic allograft in sheep. Ann Thorac Surg 2010;89:253-8], in which sheep trachea was replaced with an allogenic aortic graft in order to attempt transplantation. Because an appropriate tracheal replacement graft has yet to be determined, other means to repair or replace tracheal tissue have to be evaluated. The aim of this study was to test a bioabsorbable scaffold for temporary tracheal grafting.

METHODS

Eight male sheep underwent cervical tracheal replacement (5 cm) using a copolymer of L-lactide and ε-caprolactone sponge tube reinforced by polyglycolic acid. A silicone stent (7 cm) was placed perioperatively to prevent graft collapse. Routine bronchoscopy and computed tomographic scans were scheduled for up to 9 months and necropsies with histologic examinations were scheduled at 9 months (n = 3), 6 months (n = 2), 4 months (n = 1), 3 months (n = 1), and 2 months (n = 1) after surgery.

RESULTS

No procedural deaths and postoperative complications occurred. Planned follow-up points were reached in all animals. Computed tomographic imaging of the grafted area showed tracheal approximation up to 75% at 9 months after surgery. Silicone stents were removed at 9 months in three animals. Symptomatic airway collapse was observed at 6 hours, 1 week, and 2 weeks after stent removal. Epithelialization of the entire grafted area was confirmed in all sheep that were followed beyond 4 months.

CONCLUSIONS

Tracheal axial approximation occurs consistently after tracheal resection and replacement. Our data suggest that bioabsorbable materials can be used as a reliable, temporary, tracheal replacement conduit.

Surgical technique and results of tracheal and carinal replacement with aortic allografts for salivary gland-type carcinoma

OBJECTIVE

We describe the surgical technique and peroperative management of tracheal and carinal replacement with aortic allografts for large salivary gland-type carcinoma and report the results with a mean 34 months' follow-up.

METHODS

We performed tracheal and carinal replacements with aortic allografts in 6 patients with extensive mucoepidermoid (n = 1) or adenoid cystic (n = 5) carcinomas. Tracheal tumor resection was followed by carinal restitution (n = 3) and interposition of the graft, splinted by a silicone stent. The allograft consisted of an aortic segment, either fresh (in the first 2 patients) or cryopreserved (in the last 4). All grafts were wrapped with bulky and well-vascularized flaps (pectoral muscle flap all patients, with an additional "thymopericardial fat flap" in the last 2) to promote revascularization and to prevent erosion of adjacent large vessels or fistulas. No immunosuppressive therapy was administered.

RESULTS

Complete resection (R0) was achieved in 5 (83%) of 6 patients. Three of the first 4 patients experienced major morbidity, mainly fistulas between the esophagus and graft. The last 2 patients had an uneventful outcome. All grafts transformed into well-vascularized conduits focally lined with respiratory epithelium. So far, the last 4 patients are disease-free and 3 of them have returned to full-time employment. Stent removal has not been attempted in any patient.

CONCLUSION

Tracheal replacement with aortic allografts enables resection of extensive tumors with a curative intent. Efficient protective wrap around the graft is mandatory. Further follow-up is required to determine whether cartilage rings are generated within the graft, as in animal models.

Tracheal replacement with a silicone-stented, fresh aortic allograft in sheep

BACKGROUND

Tracheal tissue regeneration after allogeneic aortic transplants in sheep has been reported. We sought to confirm these findings and elucidate the mechanism of this transformation.

METHODS

Ten male sheep underwent cervical tracheal replacement with fresh, descending thoracic aortic allografts, 8 cm long, from female sheep, without postoperative immunosuppressive therapy. A 10-cm silicone stent was placed to prevent airway collapse. Graft evaluations with flexible bronchoscopy and computed tomography were conducted between 2 weeks and 1 year after surgery.

RESULTS

There were no procedural deaths, but 6 animals died or required euthanasia between 12 days and 3 months postoperatively owing to severe tracheitis, cervical lymphadenitis, pneumonia, graft necrosis, stent migration, or airway obstruction after stent removal. The 4 remaining sheep were euthanized as planned at 6 to 12 months after surgery. Harvested tracheas revealed no evidence of graft incorporation into the surrounding tissue, and there was no histologic evidence of any neocartilage within or around the graft at any point. Bronchoscopy revealed marked graft necrosis in the 4 animals surviving to planned euthanasia. In all sheep, computed tomography imaging revealed that the graft was replaced by connective tissue without any signs of cartilage regeneration. Image analysis also indicated profound shortening of the grafted area up to 87.5% at 1 year after implantation, secondary to axial shift of the native trachea.

CONCLUSIONS

Fresh aortic allografts appear to be unsuitable for primary tracheal replacement. However, the observed graft shortening may allow for two-staged, end-to-end reconstruction of large tracheal defects with temporary grafting techniques.