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.