HYDROPHILIC SURFACE MODIFICATION OF METALLIC ENDOLUMINAL STENTS

Purpose: Stainless steel endovascular stents are inherently thrombogen ic so that thrombus accumulates on these devices, leading to acute ves sel occlusion. A potential solution to this problem is stent surface m odification with hydrophilic polymers, which might limit platelet adhe sion and reactivity. Methods: N-vinylpyrrolidone (NVP) and potassium s ulfopropyl acrylate (KSPA) hydrophilic monomers were gamma graft polym erized onto 1 cm(2) stainless steel slabs and 4 mm Palmaz stainless st eel stents. Surface characteristics of modified and plain stainless st eel stents were then investigated with contact angle and x-ray photoel ectron spectroscopy measurements, and in vitro and in vivo platelet re activity was assessed as (111)Indium platelet accumulation expressed a s counts/min/cm(2). Results: Surface modification of stainless steel s labs and stents with both NVP and KSPA hydrophilic polymers significan tly reduced in vitro platelet adhesion (plain = 2249 +/- 723 counts/mi n/cm(2), NVP = 428 +/- 156 counts/min/cm(2) KSPA = 958 +/- 223 counts/ min/ cm(2)) and in vivo platelet accumulation after 1 hour of blood fl ow exposure (plain = 1407 +/- 796 counts/min/cm(2), NVP = 426 +/- 175 counts/min/cm(2), KSPA = 399 +/- 124 counts/min/cm(2)). In addition, p latelet accumulation on modified stents indexed to plain stents was lo west in KSPA-modified stents (NVP = 79.3% +/- 31.7% of plain, KSPA = 5 1.2% +/- 36.2% of plain). Surface analysis confirmed surface grafting with both monomers, and SEM documented smoothing of the irregular surf aces of the stainless steel stents after grafting. Conclusion: Hydroph ilic polymer surface modification of stainless steel stents decreases initial stent surface platelet accumulation, which may decrease the ri sk of vessel thrombosis associated with the use of these devices.