Evaluation of magnesium alloys for use as an intraluminal tracheal for pediatric applications in a rat tracheal bypass model.

Tracheal stenting currently using non-degradable stents is commonplace for treatment of trauma, prolonged intubation related adult airway obstructions, and pediatric patients-associated tracheal stenosis conditions. Degradable tracheal stent placement will avoid complications of stent removal and restenosis. Widespread reports exist on degradable magnesium alloys success for orthopedic and cardiovascular applications but none to date for intra tracheal use. This research explores the use of pure Mg, AZ31, and Mg-3Y alloys for degradable tracheal stent assessment. In vitro evaluation of magnesium, prototype stents in a bioreactor simulate the airway environment and corrosion. Micro-CT imaging and biocompatibility evaluation helped assess the 24-week degradation of intraluminal alloy stents following implantation in a rat tracheal in vivo bypass model. Histological analysis indicate tissue response of the harvested stented trachea segments after each time point. Corrosion studies for each alloy indicate significant differences between the simulated and control in vitro conditions. AZ31 exhibited the lowest volume loss of 6.8% in saline, while pure Mg displayed the lowest volume loss of 4.6% in simulated airway fluid (SAF), both at 1-week time points. Significant differences in percentage of total volume lost after 6 months were determined between the alloys over time. MgY alloy displayed the slowest corrosion losing only 15.1% volume after 24 weeks of immersion. Additionally, in vitro magnesium alloy corrosion was not significantly different from the percentage of total volume lost in vivo at 1-week time point. The study demonstrates promise of magnesium alloys for intraluminal tracheal stent application albeit viability of a clinically translatable model warrants further studies. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1844-1853, 2019.

Decellularized tracheal extracellular matrix supports epithelial migration, differentiation, and function.

Tracheal loss is a source of significant morbidity for affected patients with no acceptable solution. Interest in engineering tracheal transplants has created a demand for small animal models of orthotopic tracheal transplantation. Here, we examine the use of a decellularized graft in a murine model of tracheal replacement. Fresh or decellularized tracheas harvested from age-matched female donor C57BL/6 mice were transplanted into syngeneic recipients. Tracheas were decellularized using repeated washes of water, 3% Triton X-100, and 3 M NaCl under cyclic pressure changes, followed by disinfection with 0.1% peracetic acid/4% ethanol, and terminal sterilization by gamma irradiation. Tracheas were explanted for immunolabeling at 1, 4, and 8 weeks following surgery. Video microscopy and computed tomography were performed to assess function and structure. Decellularized grafts supported complete reepithelialization by 8 weeks and motile cilia were observed. Cartilaginous portions of the trachea were maintained in mice receiving fresh transplants, but repopulation of the cartilage was not seen in mice receiving decellularized transplants. We observed superior postsurgical survival, weight gain, and ciliary function in mice receiving fresh transplants compared with those receiving decellularized transplants. The murine orthotopic tracheal transplant provides an appropriate model to assess the repopulation and functional regeneration of decellularized tracheal grafts.

Evaluation of magnesium-yttrium alloy as an extraluminal tracheal stent.

Tracheomalacia is a relatively rare problem, but can be challenging to treat, particularly in pediatric patients. Due to the presence of mechanically deficient cartilage, the trachea is unable to resist collapse under physiologic pressures of respiration, which can lead to acute death if left untreated. However, if treated, the outcome for patients with congenital tracheomalacia is quite good because the cartilage tends to spontaneously mature over a period of 12 to 18 months. The present study investigated the potential for the use of degradable magnesium-3% yttrium alloy (W3) to serve as an extraluminal tracheal stent in a canine model. The host response to the scaffold included the formation of a thin, vascularized capsule consisting of collagenous tissue and primarily mononuclear cells. The adjacent cartilage structure was not adversely affected as observed by bronchoscopic, gross, histologic, and mechanical analysis. The W3 stents showed reproducible spatial and temporal fracture patterns, but otherwise tended to corrode quite slowly, with a mix of Ca and P rich corrosion product formed on the surface and observed focal regions of pitting. The study showed that the approach to use degradable magnesium alloys as an extraluminal tracheal stent is promising, although further development of the alloys is required to improve the resistance to stress corrosion cracking and improve the ductility.