POLYMERIC SURFACE MODIFICATIONS OF TANTALUM STENTS

Purpose: To compare two kinds of polymer-coated tantalum stents with b are tantalum stents (control) to determine if the coatings can improve thromboresistance. Methods: Twenty-seven Fontaine-Dake stents were ba lloon expanded in three 8-mm x 80-cm polytetrafluoroethylene (PTFE) gr afts; 9 stents were bare tantalum (T); 9 were coated with polyetherure thane (PL); and 9 were coated with parylene (PA). There were 9 stents placed in each graft as follows: 3 tantalum, 3 polyetherurethane, and 3 parylene. In swine whose platelets had been radiolabeled with indium 111, the ends of each stented graft were connected to 14F femoral and venous sheaths to create an ex vivo fistula. Each graft was exposed t o blood for 30, 60, and 120 minutes. At the end of each test period, t he stented grafts were disconnected from the sheaths, flushed with sal ine until clear, and then flushed with formalin. The stents were remov ed from the grafts, and a radionuclide well counter recorded radionucl ide counts from each stent type at each period of blood contact. These values were converted to platelet density per 1000 mu m(2). Stents we re then photographed and scanned with electron microscopy (EM) for qua litative analysis. Possible significant differences in platelet adhesi on with the three types of stents (both between stent groups and withi n stent groups) were examined using a two-tailed Student's t-test. Res ults: There were significantly fewer platelets adsorbed on PA versus T at all time periods (p < 0.005); on PL versus T at 60 and 120 minutes (p < 0.005); and on PA versus PL at 30 and 120 minutes (p < 0.0005). There was no significant difference in platelet density within each st ent group (p = 0.1). Mean platelet density (number of platelets per 10 00 mu m(2) +/- SD) was as follows: at 30 minutes: T = 1891 +/- 965; PL = 373 +/- 193; and PA = 27 +/- 3; at 60 minutes: T = 6226 +/- 1621; P L = 1573 +/- 793; and PA = 1185 +/- 710; at 120 minutes: T = 5307 +/- 591; PL = 3164 +/- 318; and PA = 180 +/- 100. Gross inspection of the 120-minute groups demonstrated focal areas of thrombus on T, less on F L, and none on PA. Scanning EM demonstrated extensive platelet accumul ation covering T at all time periods, less on PL, and even less on PA.