Sustained drug release using cobalt oxide nanowires for the preparation of polymer-free drug-eluting stents

Abstract

Polymer-based drug-eluting stents (DESs) represented attractive application for the treatment of cardiovascular diseases; however, polymer coating has caused serious adverse responses to tissues such as chronic inflammation due to acidic by-products. Therefore, polymer-free DESs have recently emerged as promising candidates for the treatment; however, burst release of drug(s) from the surface limited its applications. In this study, we focused on delivery of therapeutic drug from polymer-free (or -less) DESs through surface modification using cobalt oxide nanowires (Co₃O₄ NWs) to improve and control the drug release. The results demonstrated that Co₃O₄ NWs could be simply fabricated on cobalt–chromium substrate by ammonia-evaporation-induced method. The Co₃O₄ NWs were uniformly arrayed with diameters of 50–100 nm and lengths of 10 µm. It was found that Co₃O₄ NWs were comparatively stable without any delamination or change of the morphology under in vitro long-term stability using circulating system. Sirolimus was used as a model drug for studying in vitro release behavior under physiological conditions. The sirolimus release behavior from flat cobalt–chromium showed an initial burst (over 90%) after one day. On the other hand, Co₃O₄ NWs presented a sustained sirolimus release rate for up to seven days. Similarly, the polymer-less specimens on Co₃O₄ NWs substrates sustained sirolimus release for a longer-period of time when compared to flat Co–Cr substrates. In summary, the current approach of using Co₃O₄ NWs-based substrates might have a great potential to sustain drug release for drug-eluting implants and medical devices including stents.