During the last decade, biodegradable metallic stents have been developed and investigated as alternatives for the currently-used permanent cardiovascular stents. Degradable metallic materials could potentially replace corrosion-resistant metals currently used for stent application as it has been shown that the role of stenting is temporary and limited to a period of 6–12 months after implantation during which arterial remodeling and healing occur. Although corrosion is generally considered as a failure in metallurgy, the corrodibility of certain metals can be an advantage for their application as degradable implants. The candidate materials for such application should have mechanical properties ideally close to those of 316L stainless steel which is the gold standard material for stent application in order to provide mechanical support to diseased arteries. Non-toxicity of the metal itself and its degradation products is another requirement as the material is absorbed by blood and cells. Based on the mentioned requirements, iron-based and magnesium-based alloys have been the investigated candidates for biodegradable stents. This article reviews the recent developments in the design and evaluation of metallic materials for biodegradable stents. It also introduces the new metallurgical processes which could be applied for the production of metallic biodegradable stents and their effect on the properties of the produced metals.

Silicon dioxide films were grown using an atmospheric-pressure plasma jet that was produced by flowing oxygen and helium between two coaxial metal electrodes that were driven by 13.56 MHz radio frequency power. The plasma exiting from between the electrodes was mixed with tetraethoxysilane (TEOS), and directed onto a silicon substrate held at 115-350 • C. Silicon dioxide films were deposited at rates ranging from 20 ± 2 to 300 ± 25 nm min −1. The deposition rate increased with decreasing temperature and increasing TEOS pressure, oxygen pressure and RF power. For the latter two variables, the rate increased as follows: Rd ∝ P 0.3 O 2 (RF) 1.4. Films grown at 115 • C were porous and contained adsorbed hydroxyl groups, whereas films grown at 350 • C were smooth, dense and free of impurities. These results suggest that the mechanism in the atmospheric pressure plasma is the same as that in low-pressure plasmas.

The α and γ modes of an atmospheric pressure, radio-frequency plasma have been investigated. The plasma source consisted of two parallel electrodes that were fed with helium and 0.4 vol% nitrogen. The transition from α to γ was accompanied by a 40% drop in voltage, a 12% decrease in current and a surge in power density from 25 to 2083 W cm −3. Optical emission confirmed that sheath breakdown occurred at the transition point. The maximum light intensity shifted from a position 0.25 mm above the electrodes to right against the metal surfaces. The average density of ground-state nitrogen atoms produced in the atmospheric plasma was determined from the temporal decay of N 2 (B) emission in the afterglow. It was found that 5.2% and 15.2% of the N 2 fed were dissociated into atoms when the plasma was operated in the α and γ modes, respectively. The lower efficiency of the γ discharge may be attributed to the non-uniform distribution of the discharge between the electrodes.

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