Polymers Used for Paclitaxel Stents

Paclitaxel is an impressive anticancer and immunosuppressive drug, which works by inhibiting cellular microtubule polymerization. It can be used to prevent the intimal regrowth and in-stent restenosis often associated with vascular stents. Based on these properties of paclitaxel, over time a number of polymers have been used in different stent systems. Some of the more commonly used polymers, along with the corresponding DBS are detailed below. 

Poly(lactide-co-Z-caprolactone) is a derivative of polycaprolactone, which is a biodegradable polyester used in the synthesis of polyurethane polymers. Drachman et al. placed stents containing the polymer poly(lactide-co-Z-caprolactone) into pig vascular beds to study the effects of the stent on neointimal regrowth. They reported that the paclitaxel releasing stent was able to curtail vascular intimal regrowth and in-stent restenosis at all the time points they tested from 7 to 180 days [2]. However, in studies conducted in other animals it became apparent that arteries did not heal completely following stent-mediated release of paclitaxel [3], 

This product is different from the others described above because not only does it employ a different polymer blend, but it also uses a double polymer approach, where one polymer is used as a primer and the other as a drug reservoir. In this device, PBMA is used to enhance adherence and PVDF-HFP used to enhance drug binding. Additionally, no top coat is applied to the device. The polymer blend and the everoH-mus drug are mixed in the ratio of 83%/17% w/w polymer to drug, and subsequently this mixture is added to the PBMA coated stent. 

This dual use of polymers and a double-layered engineering strategy affects drug release parameters. The Xience V stent has been reported to release 25% of its total everolimus content on the first day after placement in the vascular bed, with the remaining 75% of drug released over 4 months, while most of the drug release remains in the local vascular microenvironment with minimal systemic release of the drug [5]. 

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