Mechanism and in Vitro Release Kinetic Study of Sirolimus from a Biodegradable Polymeric Matrix Coated Cardiovascular Stent

Implantation of Drug Eluting Stents (DES) is the most accepted technique currently available to treat cardiovascular blockages. First generation DES uses polymers for drug delivery which are nondegradable in nature and remains attached to stent surface lifetime. Biodegradable polymers have gained immense attention for controlled drug delivery of therapeutic drugs from cardiovascular stents in recent times as nondegradable polymers are associated with long-term adverse events. Studies showed that permanent contact with this polymer creates local inflammatory reactions and long-term stent thrombosis which raises concerns over the widespread use of DES. Biodegradable polymers are widely accepted biomaterials in human health care area and have proved its biocompatibility as drug delivery vehicle in various medicinal applications. This research work is carried out to study mechanisms affecting drug release kinetics from coated cardiovascular stents composed of biodegradable poly lactide-co-caprolactone and polyvinyl pyrrolidone. A conventional air brush technique was effectively modified so that Co-Cr L605 metallic stents were coated within multiple layers having drug Sirolimus blended together with biodegradable polymeric matrix. Kinetic studies for drug dissolution from a stent are carried out in simulated biological fluid using high performance liquid chromatography (HPLC) with simultaneous monitoring of surface morphology by scanning electron microscopy (SEM). Drug elution data analyzed by mathematical models suggested a combination of surface drug dissolution and diffusion as major drug release mechanisms. Investigation of different top coats revealed that drug release is influenced by the hydrophobicity of the drug free protective layer.