Drug-Eluting Stents: Design for Prevention of Angioplastic Restenosis
Chen, Bonnie; Clark, Nisse; Melhem, Molly; Owens, Gwen
Balloon angioplasty and coronary stent deployment are powerful techniques in the treatment of individuals with advanced coronary artery disease. Recent advancements have led to the development of drug-eluting stents designed to release a drug polymer that inhibits restenosis, a bodily defense mechanism characterized by tissue ingrowth and reblockage of the artery. The stent is coated with an anti-cancer or immunosuppressive drug that diffuses through the surrounding tissues over a critical period of time. In this study, diffusion of the drug Rapamycin was modeled using computer-aided design software. Analysis was performed in order to determine the concentration profile of the drug at various time intervals. The stent geometry was reduced to six concentric rings of 1.5 mm width spaced 1.5 mm apart, resulting in a total stent length of 16.5 mm. Diffusion was modeled from only one of these rings and conclusions were drawn considering the global diffusion from multiple rings of this type. A graded mesh was generated in GAMBIT, and simulations were executed in FIDAP to assess the drug concentration as a function of several input parameters. It was concluded that the drug reaches 48 ?g/m3, within a defined therapeutic concentration range of 40-60 ?g/m3, after about nine months at a penetration depth of 0.015 mm. This indicates that after nine months the first tissue layer surrounding the coronary lumen, also known as the intima, is saturated with drug at concentrations necessary for the prevention of restenosis. Sensitivity analysis was performed to test the stability of our solution and to assess factors which may affect the diffusion process. It was found that the concentration of Rapamycin was most sensitive to a change in diffusivity of Rapamycin in the intimal tissue layer, whereas the drug concentration was less sensitive to changes in the stent diffusivity and variance in initial concentration of drug immobilized in the stent.