Characterization of Porous TiO2 Surfaces Formed on 316L Stainless Steel by Plasma Electrolytic Oxidation for Stent Applications

Abstract

In this study, a porous oxide layer was formed on the surface of 316L stainless steel (SS) by combining Ti magnetron sputtering and plasma electrolytic oxidation (PEO) with the aim to produce a polymer-free drug carrier for drug eluting stent (DES) applications. The oxidation was performed galvanostatically in Na3PO4 electrolyte. The surface porosity, average pore size and roughness varied with PEO treatment duration, and under optimum conditions, the surface showed a porosity of 7.43%, an average pore size of 0.44 µm and a roughness (Ra) of 0.34 µm. The EDS analyses revealed that the porous layer consisted of Ti, O and P. The cross-sectional morphology evidenced a double-layer structure, with a porous titania surface and an un-oxidized dense Ti film towards the interface with 316L SS. After the PEO treatment, wettability and surface free energy increased significantly. The results of the present study confirm the feasibility of forming a porous TiO2 layer on stainless steel by combining sputtering technology and PEO. Further, the resultant porous oxide layer has the potential to be used as a drug carrier for DES, thus avoiding the complications associated with the polymer based carriers.

Aluminum Oxide Ceramic Coatings on 316l Austenitic Steel Obtained by Plasma Electrolysis Oxidation Using a Pulsed Unipolar Power Supply

“…• the voltage in the direct current PEO mode (320 V in [30,32]) is applied permanently on the sample, while in PEO pulse mode, a time interval of one period is applied, after which it is zero. In our experiment, the pulse voltage applied is over 500 V, much higher than in DC, which allows for higher temperatures in electrical discharge in the microarc and the synthesis of a larger amount of Al 2 O 3 ; • between the two impulses, the oxidation layer material cools and crystallizes the molten portions of the layer, which makes it possible to obtain layers of oxide with much higher thickness than in the continuous PEO mode.…”

“…In the case of non-valve metals (base metals) as steels, it can be used as two methods to develop a porous oxide barrier layer required for initiation of the micro-discharge oxidation processes [30][31][32]:…”

“…• applying a preliminary treatment: the deposition on the steel surface of Al or other valve metal as Ti or Zr layer by a certain method (e.g., a porous oxidation barrier layer necessary to initiate the PEO process can be developed on carbon steel by spraying with an aluminum [28], or by aluminizing using dipping technique [29], and in the case of stainless steel, the specimens can be coated with a Ti film by magnetron sputtering [33], or aluminum/bimetallic stainless steel may be used [34], then it can be obtained the porous oxide film in the anodic oxidation stage of PEO process); the oxidation in autoclave of the stainless steel, which produces a thick layer of magnetite over a substrate [30]; • deposition of the porous oxide (Al 2 O 3 , SiO 2 ) resulted from the micro-arc decomposition of aluminate or silicate electrolyte [35], in the case of carbon steel.…”

Microstructure characterisation of alumina coating on steel by PEO

“…In order to obtain crystal phase, a thermal treatment is usually needed for universal cathodic deposition technique. 17 In addition, PEO treatment of steel reported here can obtain pure Al 2 O 3 simply and directly compared to the indirect PEO treatment of steel reported in literature 12,13 1 Schematic view of PEO system 2 Voltage-time curve during PEO process A1 3z in ethanol solution excited in the form of A1 3z and NO 32 . During the PEO process, NO 32 will be reduced and OH 2 can be obtained.…”

Effects of sintering temperature and particle size on permeability of functionally gradient composite porous materials prepared by hanging slurry process

“…This is especially true fact in the field of filtration and separation where are many applications. It requires that such materials should have higher filtration accuracy and greater transmittance while having smaller pore size, which makes it difficult for traditional homogeneous porous materials to achieve the desired effect, and the emergence of gradient porous composite materials just solves this contradiction [13][14][15][16][17][18]. During the process of practical application, in order to guarantee the various properties of porous materials, asymmetric membrane structure is mostly adopted than before.…”