Electrophoretic deposition (EPD) of advanced bioactive and antibacterial zein-based coatings on titanium for biomedical applications
Year: 2024
Type: dissertation
Abstract: Metallic biomaterials continue to play a crucial role in medical treatment due to their favorable mechanical properties, including high tensile strength and fracture toughness. Nevertheless, the long-term durability of orthopaedic metallic implants is limited due to their potentially low bone-binding capability and susceptibility to bacterial colonization. In order to address these complications, coatings that are able to facilitate the osseointegration of the medical device and simultaneously supply the implant site with antimicrobial agents in-situ can be applied on the surface of the metallic implant. Electrophoretic deposition (EPD) stands out as a suitable coating technique due to its simple processing equipment, the adaptability to coat complex shapes, the mild processing conditions that allow the deposition of sensitive organic molecules, and the opportunity to modify the properties of the deposit by varying the process parameters. The natural corn protein zein has been widely used as a coating material due to its attractive properties, including biocompatibility, biodegradability, and bioadhesiveness. Thus, the current research project aims to develop bioactive and antibacterial composite coatings based on zein on titanium substrates by EPD. Different coating designs, including i) single-layer composite coatings, ii) coatings containing phytotherapeutics-loaded zein particles and bioactive glasses, and iii) double-layer coatings incorporating bioactive glasses and phytotherapeutic drugs, were prepared. Bioactive glasses with various compositions, e.g., SiO2-CaO-P2O5 (BG), SiO2-CaO-P2O5-CaF2 (BG-F), SiO2-CaO-P2O5-CaF2-CuO (BG-F-Cu) or SiO2-CaO-Na2O-P2O5-CuO (CuBG), phytotherapeutic drugs, berberine chloride (BBR) or tannic acid (TA), and polysaccharides, chondroitin sulfate (CS) or sodium carboxymethylcellulose (CMC), were combined with zein in this work to produce EPD coatings with various architectures and functionalities. The results showed that adding BG, BG-F and BG-F-Cu in single-layer zein coatings significantly improved the scratch resistance and the hardness of the final deposits. Moreover, the composite coatings exhibited enhanced bioactivity in simulated body fluid (SBF) and antibacterial activity against Gram-negative E. coli bacteria. The dual synergistic release of Cu and F ions from zein/BG-F-Cu coatings resulted in increased viability of osteoblast-like MG-63 cells and decreased viability of Gram-positive S. aureus bacteria. Aiming to improve further the biological and mechanical performance of single-layer zein based coatings, a novel in-situ process of combined anti-solvent precipitation and EPD was exploited to synthesize and deposit BBR or TA-loaded zein particles within a coating matrix of CS or CMC together with CuBG. The results showed that the selection of the polymer coating matrix and the drug incorporated in the zein particles could be used to adjust the drug release kinetics, adhesion strength, biocompatibility, and antibacterial properties of the final deposits. Nevertheless, the so-prepared coatings exhibited relatively low adhesion strength to the substrate and insufficient bioactivity in contact with SBF. Thus, as a further attempt to produce bioactive and antibacterial coatings with adjustable therapeutic efficacy, the deposition of double-layer coatings, consisting of a bottom zein layer and phytotherapeutic drugs (BBR or TA), and a top layer made of polysaccharides (CS or CMC) and CuBG, was studied. The outcomes showed that the type of polysaccharide used for the deposition of the second layer, the type of incorporated drug, as well as the application of chemical treatment on the metallic substrate prior to EPD can be utilized to improve further the adhesion strength, wettability, drug release capacity, cellular response and antibacterial activity of the double-layer coatings. In conclusion, the current research demonstrates the versatility of EPD to produce zein containing bioactive and antibacterial coatings based on various coating designs, providing a promising platform for further development of new coating systems for biomedical applications.
Author: Hadzhieva, Zoya
Language: English
Subfield: Biomedical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: gold
OpenAlex ID: W7094941455
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