What are the different types of airway stents?

There are several main types of airway stents used to treat obstruction in the trachea (windpipe) or bronchi (branches of the trachea that go to the lungs):

- Metal stents: These are made from metals like nitinol or stainless steel. They have a mesh design and can be self-expanding. Metal stents provide good radial force to keep the airway open.

- Silicone stents: Silicone is softer and more flexible than metal. Silicone stents conform well to the airway anatomy. They are also less likely to migrate. However, they provide less outward radial force than metal stents.

- Hybrid stents: These combine metal and silicone. The metal provides outward radial force while the silicone prevents migration and minimizes tissue reaction. 

- Bioabsorbable stents: These stents dissolve over time and are made of materials like polydioxanone. This avoids the need to remove the stent later.

- Covered vs. uncovered: Both metal and silicone stents come in covered and uncovered varieties. Covered stents have a membrane over the mesh which aims to prevent tumor ingrowth.

The choice depends on factors like location/extent of obstruction, expected longevity of stent, and physician preference. In general, silicone and bioabsorbable stents are used for benign obstructions while metal stents are preferred for malignant obstructions in patients with limited life expectancy.