الفهرس 
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Abstract
Significant interest has been increased in the field of coating of the implants by bioactive materials. Widely used implants are orthopedic implants, which are mainly made from metal alloys, such as stainless steel and titanium alloys. Importantly, 316L stainless steel has been used widely in orthopedic field. That is due to its high mechanical strength and low price. Despite of the advantages of such metal alloy it has shortage in implantation field. Where, some toxic ions can be released into the body from the metal surface, additionally, the metal is likely encapsulated by fibrous tissue, which may be resulted in movement and loosening of the metal implant. Nevertheless, coating of metal implant surface with bioactive materials has been applied as an effective solution for these problems. Such bioactive coatings are characterized by their ability to induce osteointegration of metal surface, as well as, they can decrease or even suppress the ions released from the metal.
Therefore, this work was aimed to prepare pure or composite coatings for 316L SS based on borate glass (60B2O3-10CaO-20Na2O-10MgO wt% composition) or silicate-based bioactive glass/chitosan composites using simple and cost effective electrophoretic deposition (EPD) method. The silicate-based glasses were designed by modification of Bioglass® bioactive glass by addition of boron, and Bioglass® was synthesized for comparison. The study was interested to incorporate boron in the glass compositions which is known to enhance a growth of bone tissue, also its anti-inflammatory performance has approved. On the other hand, using of chitosan in the composite coatings acquired the advantage of chitosan, such as antimicrobial activity, enhancement of the coating adhesion on the metal and it could to provide a delivery vehicle for macromolecules, such as proteins, enzymes and drugs. Based on this issue, different coatings were functionalized by incorporation of antibiotic vancomycin to serve as antimicrobial role. Interestingly, EPD technique was used in aqueous electrolyte, as a green and simple method.
Different EPD parameters were investigated to obtain an optimum coating. In case of borate glass suspension, these parameters included pH, applied voltage, glass concentration and time. While, in case of composite coating, pH was replaced by the concentration of chitosan as a parameter for coating process.
The obtained coated substrates were investigated using FT-IR, X-ray diffraction, DTA-TGA and SEM/EDX analyses. As well as, the wettability and roughness were investigated. Moreover, the in vitro bioactivity and the biodegradation tests were performed for the coated metals in two biological fluids; simulated body fluid (SBF) and Dulbecco’s Modified Eagle’s Medium (DMEM) at body temperature (37 oC). Additionally, the electrochemical corrosion behavior of the coated metals was evaluated using potentiodynamic polarization and impedance techniques in SBF and DMEM solutions at 37 oC. The results showed that the optimum conditions applied for borate-based glass coating to obtain smooth, uniform, cracked-free, dense and adhesive layers with even glass particles distribution were achieved at voltage 35 V, pH 7, 4 % w/v glass and 15 min deposition time. The optimum ones for composite coatings were attained at 20 V, deposition time of 5 min, 0.5 g/l polymer concentration and 6 g/L glass concentration.
The thermogravimetric analyses of different samples demonstrated that the total weight losses for 40S, HB5 and H, were 28.5, 25.0 and 31.50%, respectively, and it was only 3% for borate-based glass coating.
XRD patterns of as-prepared glass samples showed that there were no diffraction peaks of all samples, which indicated the amorphous structure of the glasses.
SEM micrographs of different coated substrates represented good adhesive and crack-free coatings. Additionally, the micrographs showed that the composite coatings possessed high roughness, while borate glass coating showed low roughness. On the other hand, EDX analyses of different coating surfaces showed the same elemental components of glass particles.
The hydrophilicity was evaluated by measuring the contact angle of water DROP with the coating surface. The contact angle of the uncoated substrate was 104o and decreased to 60o for the borate glass coated substrate. While, it cannot be measured for the composite coated substrate because the water DROP was completely diffused and adsorbed by the coating surface. This result indicated the high wettability of composite coating layers, which mainly came from the hydrophilicity nature of chitosan polymer and bioactive glass particles.
The roughness values of different coatings for borate glass, 40S, HB5 and H composite coatings were 390 ± 61, 170 ± 18, 234 ± 17 and 201 ± 26 µm, respectively. All coatings showed good roughness which promotes the cell attachment inside the body.
The pH values of different samples immersed in SBF were represented a notable behavior. But, the samples immersed in DMEM showed fluctuated values. Where, a fluctuation of pH values was detected due to the non-buffered nature of such fluid. On the other hand, a measurement of different ion concentrations released from the coated substrates showed a decrease of Ca and P ions with the time, obviously in SBF, due to the formation of hydroxyapatite layer on the coating surfaces, which can be confirmed from SEM/EDX analysis. Consequently, the release of Si and B ions into the solution was also decreased as a result of formation of a bone-like apatite layer. Moreover, the coating layers were affected the release of Fe ions from the metal substrates. They made the release as a steady state release after a short of immersion, and so, such coatings decreased the corrosion of 316L SS substrate.
According to the electrochemical measurements, different coatings proved noticeable improvement for corrosion protection in both SBF and DMEM solutions at 37 oC using potentiodynamic polarization (PDP) techniques, which satisfies the medical requirements of the selected materials.