Effect of Stainless Steel Substrate Preparation on the Adhesion Strength and Morphology of Electrophoretically Deposited Sodium Alginate Coatings

Abstract

In this study, the influence of various mechanical and chemical surface treatments on the adhesion strength and surface properties of sodium alginate coatings electrophoretically deposited (EPD) on 316L stainless steel substrates was investigated. XPS and TEM results revealed the presence of oxide layers containing elements from the substrates, with thicknesses varying from 1 to 45 nm, depending on the treatment used. Most substrates exhibited high roughness and hydrophilic properties (CA with water 62.8–82.6 deg). Sodium alginate coatings with uniform morphology were deposited with the same process parameters, i.e., 5 V and 300 s. The surface topography of the coatings was closely related to that of the substrate on which they were deposited. All coatings exhibited higher hydrophilicity (CA with water 29.5–49.7 deg) compared to the substrates (CA with water 62.8–82.6 deg). The coatings on the etched and anodized substrates demonstrated the highest adhesion strength (class 4B), attributed to the very low oxide layer thickness and the specific substrate surface topography. Mechanical interlocking was identified as the primary adhesion mechanism for these coatings. This work provides insight into optimizing surface treatments for improved adhesion of sodium alginate coatings to stainless steel substrates widely used for temporary bone implants. The results obtained will also be helpful in providing high adhesion of sodium alginate-based composite coatings to steel substrates.