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Electrophoretic deposition (EPD) occurs as a cataphoretic deposition – the coating is deposited on the cathode, and anaphoretic deposition – the coating is deposited on the anode. The primary purpose of EPD is to obtain compact and uniform organic/inorganic coatings of the desired thickness and adhesion on metal surfaces by applying an electric field to the particles of coating precursor. EPD basic principles for coatings deposition concerning fundamental explanations and considerations of practical parameters of the process are presented. Cataphoretic deposition has become popular because it can apply organic coatings to complex structures that are otherwise very difficult to coat. These coatings were found to improve the characteristics of the substrate, such as biocompatibility, appearance and resistance to the corrosion processes. The key EPD parameters are composition, pH value and viscosity of deposition medium, as well as zeta potential of the particles, electric field strength, etc. A special survey is given to the process of anaphoretic deposition, which is relatively new, and its advantages over cataphoretic deposition are discussed. Through the process of joint anaphoresis/substrate anodization process, the surface of the substrate is simultaneously anodized and modified by incorporation of the foreign particles into the anodic layer. The coatings of mixed composition of better adhesion and corrosion resistance with respect to cataphoretically- deposited coatings are obtained as result.

INTRODUCTION: Hydroxyapatite, the main inorganic component of human bone, is a widely used bioceramic for bone implant coatings due to its chemical and structural similarity with bone minerals and approved biocompatibility. Nowadays, the surface properties of implants are also modified by the addition of different biopolymers. Features such as biocompatibility, tuned biodegradability, and non-cytotoxicity make these materials excellent candidates for these applications. Zein is one of the natural polymers that has gained great interest for biomedical applications due to its natural renewable resource, biodegradability, biocompatibility and potential antibacterial activity. EXPERIMENTAL: In this study, zein/titanium dioxide (zein/TiO2), hydroxyapatite/zein/titanium dioxide (HAp/zein/TiO2) and strontium-doped hydroxyapatite/zein/titanium dioxide (Sr-HAp/zein/TiO2) coatings were obtained on a titanium substrate by in situ anodization/anaphoretic deposition method at a constant voltage of 60 V and deposition time of 1 min. For the fabrication of HAp/zein/TiO2 and Sr-HAp/zein/TiO2 composite coatings, HAp and SrHAp nano-sized powders obtained by a modified chemical precipitation method were used. The microstructure and morphology of all coatings were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Adhesion strength was measured according to the ASTM D3359-02 standard. Morphology and cell adhesion were analyzed by SEM. RESULTS AND DISCUSSION: The advantage of this methodological approach compared to cataphoretic deposition is reflected in the simultaneous performance of several processes. The first is the anodization of the substrate surface, whereby a passive oxide layer (TiO2) is formed on the surface, which changes the structure and increases the surface roughnessin a controlled manner. Another parallel process is the deposition of the HAp based coatings on the substrate. This way of coating formation shows better results than cataphoretic deposition in terms of better coating adhesion to the substrate. Adhesion strength was significantly improved compared to coatings obtained by cataphoretic processes, without the need for subsequent treatment. Cytotoxicity tests showed that there was no significant decrease in the survival of healthy human lung fibroblasts (MRC-5) cells exposed to the obtained coatings. CONCLUSIONS: Altogether, zein/TiO2, HAp/zein/TiO2 and Sr-HAp/zein/TiO2 could be promising non-toxic biomaterials for orthopedic and dental applications. [ABSTRACT FROM AUTHOR]