Abstract. We report for the first time the deposition of fluorocarbon thin films on outer and inner surfaces of millimetric sized diameter stainless steel mini-tubes by radiofrequency pulsed plasma polymerization for coronary stent applications. The deposition was performed under a glow discharge with a mixture of hexafluorethylene (C₂F₆) and hydrogen in a post-discharge configuration with substrates kept at floating potential or continuously biased with a negative voltage of up to 1000 V. Film composition, structure, uniformity and covering efficiency on outer and inner surfaces along the mini-tubes were characterized by scanning electron microscopy, Fourier-transformed infrared spectroscopy, x-ray photoelectron spectroscopy and atomic force microscopy. At floating potential, a coating of fluorocarbon (CF_x) was deposited varying in chemical composition and thickness along the mini-tube axis. The application of a −400 V bias voltage led to outer surfaces with a fluorocarbon coating uniform in thickness and homogeneous in composition, along the full length of the mini-tube (10 mm). Despite the application of a negative bias, the covering efficiency for the inner surface was lower compared with the outer surface, with fluorocarbon films homogeneous in both composition and thickness until half length of the mini-tube (5 mm) but thickness decreasing afterwards. Strategies for amelioration of the latter limitation are proposed.

Print publication: Issue 22 (21 November 2009)
Received 23 April 2009, in final form 28 September 2009
Published 30 October 2009