Novel airway stent using a thermal shape-memory Ti-Ni alloy

An attempt was made to develop a tracheal or bronchial stent for nonsurgical implantation using a bronchoscope. Titanium-nickel alloy composed of 50% by weight of each metal has unique thermal shape-memory properties, with a transition temperature of 20 degrees C. Each stent consists of one wire with a diameter of 0.9 mm. It is 30 mm long with a cross-sectional profile resembling a horseshoe. The stent is designed to sustain the airway only at the cartilage rings. Tracheal cartilages of dogs were broken to make a tracheomalasia model, and 10 stents were implanted in 10 animals. The stents were made straight by cooling in liquid nitrogen and then inserted into the region of tracheomalasia. Once in place, they were warmed and recovered their initial shape. The animals were killed between 1 week and 6 months after implantation, and then examined. Nine of the ten stents were located in the implanted area. In one dog, the stent had been displaced into the bifurcation. Microscopic observation showed that the wires were gradually covered with epithelium. At 6 months, 58% were covered with epithelium.