A fully degradable tracheal stent: in vitro and in vivo characterization of material degradation.

We report on the testing of materials for a fully degradable tracheal stent. Such a stent has several advantages over currently used permanent stents made of metal or silicone polymers. However, the mode of degradation in the trachea is expected to be different from a fully submerged device, because of the uniqueness of the tracheal environment. A physical model was developed to allow an in-depth study of degradation of bioabsorbable polymers exposed to two differing media; namely 70 wt % water (gel) on one side and humidified air on the other, simulating conditions in a tracheal passage. Longitudinal microtome slices were obtained from both polymer surfaces and degradation kinetics data were derived from size exclusion chromatography. On the basis of the data obtained, it is observed that well-studied bulk-degrading polymers might show surface-eroding properties in such an environment. Generally, hydrophobic polymers retard the formation of a water concentration gradient and exhibit bulk-degradation kinetics. However, addition of specific plasticizers can influence the water uptake gradient, and force the polymer towards a pseudo "surface-eroding" behavior. In vivo studies in a rabbit model of degradable stents made from a selected polymer, demonstrate the feasibility of a fully bioabsorbable tracheal stent. This study aims to improve understanding of degradation of polymers under heterogeneous environments.

A novel bioabsorbable drug-eluting tracheal stent.

OBJECTIVES/HYPOTHESIS: Currently available silicone and metallic stents for tracheal stenosis are associated with problems of granulations, mucus trapping, and difficult removals. Our aim was to develop a novel bioabsorbable tracheal stent with mitomycin C (MMC) drug elution to circumvent such problems. STUDY DESIGN: A randomized animal study. METHODS: Twenty-five rabbits were randomly assigned into five test groups: 1) controls (without stent), 2) silicone tubular stents (commercially available currently); 3) bioabsorbable helical stents; 4) bioabsorbable tubular stents; and 5) bioabsorbable tubular stents with MMC. Weekly tracheal endoscopy to document granulation, mucus plugging, and extent of tracheal stenosis was performed for 12 weeks. One rabbit was euthanized every 3 weeks for histological analysis of the trachea. In vitro MMC-release profiles in conditions mimicking tracheal conditions were studied. RESULTS: The bioabsorbable tubular stents with 0.1 mg MMC drug elution performed the best, with the least mucus trapping and airway obstruction due to tracheal stenosis. Tracheal stenosis was most significant for the bioabsorbable helical stents, followed by the control group without stent, the group of bioabsorbable tubular stents, and then the silicone stents. After 12 weeks, tracheal stenosis for the bioabsorbable tubular stents with MMC was only half that of the silicone stents. CONCLUSIONS: This study reports on the development of a novel bioabsorbable tracheal stent with sustained MMC drug elution for preventing tracheal stenosis. Further studies are warranted to optimize stent design and drug dosage.