Coronary artery disease (CAD) is one of the major causes of death in the world. Percutaneous transluminal coronary angioplasty is one of the mechanical interventions which are used in the treatment of CAD. Restenosis is the recurring of abnormal narrowing of a blood vessel or stenosis after corrective surgery. The recoiling of the vessel during the healing process is the primary cause of restenosis. Stents work as scaffolds and help to prevent recoiling and narrowing of the vessels. As the role of stents is temporary and only till healing, its surgical removal is important as it is foreign to the body. Hence to avoid this procedure the researchers have targeted to develop bioabsorbable stents.
Bioasorbable stents can be classified into two main types: bioabsorbable polymer stents and stents with a bioabsorbable metallic backbone. The polymer based stents have several advantages over permanent metal stents. More targeted drug delivery, limiting smooth muscle proliferation on the abluminal side while simultaneously encouraging endothelialisation on the luminal side are some of the considerations where biodegradable stents win over permanent stents. They also have more drug loading capacity. During diagnosis, as there is no interaction from the polymer stents which would have been due to the metal stents makes bioabsorbable stents a preference.
Bioabsorbable polymer stents
Poly L-Lactic acid (PLLA), polyglycolic acid (PGA), polycaprolactone (PCL) and poly (D, L- lactic/glycolide) copolymer are some of the polymers which are used in fabrication of the polymer stents. However, polymer stents are associated with significant degree of local inflammation. These stents are not as strong as the metal stents and hence may give rise to recoiling. These stents also require proper storage conditions as they have a short shelf life.
Bioabsorbable metallic stents
Metal bioabsorbable stents are trending as they have the potential to overcome the limitations of the polymer stents. Iron and magnesium are the two metals which are accepted and studied for the development of the metal stents. These two metals are well metabolised by the human body and hence their use is justified. Due to its ferromagnetic property, iron may express its interaction in magnetic resonance imaging observation, hence an alloy of iron with manganese is produced which non-ferromagnetic. Cytotoxicity of iron is insignificant. Another proposed design is a hybrid stent which is a combination of polymer stent and the metal backbone to enable strength and prevent recoiling.
The continuing pressure exerted by the stent on the vessel wall leads to neointimal tissue proliferation over the stent which results in luminal narrowing. Even though the stents of biodegradable materials were launched into the market, more advanced research is required to solve the various issues associated with them. The general idea of bioabsorbable stents is to disappear without any residual effects once the disorder is healed. The benefits of bioabsorbable stents are evident and if most of their features come to pass then bioabsorbable stents will definitely replace bare metal and drug eluting stents over time.