الفهرس 
AbstractOnly 14 pages are availabe for public view
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Abstract
Metallic materials have been traditionally used by humans to replace body parts and treat fractures for more than a century. Metallic biomaterials are engineered systems designed to provide internal support to biological tissues and they are being used largely in joint replacements, dental implants, orthopaedic fixations and stents. Higher biomaterial usage is associated with an increased incidence of implant-related complications due to poor implant integration, inflammation, mechanical instability, necrosis and infections, and associated prolonged patient care, pain and loss of function. Chitosan/calcium phosphate nanocomposites are widely used as a biocompatible coating for titanium bio-implants in the fields of dentistry and orthopedics to enhance the integration between the implants and the hard bone. However, the poor adhesion strength between the coating and the metal substrate was found to be one of the major problems in the clinical application of these implants. In this study, titanium (Ti) metallic biomaterials as an implant with modified the surface of the substrate by coating it with chitosan/calcium phosphate has been investigated. It was found that the adhesion strength and the formation of calcium phosphate coating on titanium substrate using electrodeposition method affected by different parameters such as, applied voltage, pH, deposition time and the change of chitosan’s solvent from a commonly used acetic acid to acrylic acid in the electrolyte. The results showed that, the structural analysis including X-ray diffraction (XRD), Raman spectroscopy, and attenuated total reflectance (ATR) confirmed the formation of three phases of Ca-Ps; octacalcium phosphate (OCP), dicalcium phosphate dihydrate (DCPD) brushite, and hydroxyapatite (HA). These phases completely changed into HA after hydrothermal treatment (HT) process with high concentrations of the two acids. Moreover, X-ray photoelectron spectroscopy (XPS) support the formation of the HA phase with a high concentration of acrylic acid. The bond strength was performed by the tape test (ASTM D3359-09) which showed that nearly 65% of the coatings were removed in the case of using 2, 4, and 6% (v/v) acetic acid as chitosan solvent, while only 5% of the coatings were removed when high concentrations (4 and 6%) of acrylic acid is used in addition to increasing of the surface wettability. Furthermore, the morphology and thickness of the calcium phosphate layer coated on the surface of Ti metal were inspected by scanning electron microscopy (SEM) and transmission electron microscope (TEM). Accordingly, it was proved that a well distribution of particles on the surface and the shape of hydroxyapatite changed from a needle-like structure in acetic acids to a plate and hexagonal shape in acrylic acids, similar to those in the inorganic mineral of the bone. Furthermore, the corrosion resistance, and in vivo study of the coated implants are evaluated to assess their suitability for biomedical applications. The corrosion behaviour was investigated by electrochemical impedance spectroscopy (EIS). Results showed high corrosion resistance with phase angles close to 80◦ and high impedance values 80.5 kΩ cm2 with high concentrations of acrylic acid. These results indicated the formation of a highly stable film on these implants in the test solution. Finally, an in vivo application was conducted on the optimized coating by surgically placing the coated and control discs into rats’ clavicular bones for 2-weeks healing period. Then biomechanical evaluation was performed to verify the effect of treatment on the interface resistance to shear force, and histological analysis was performed to evaluate the bone tissue reactions to coated discs. The results showed that using acrylic acid compared with acetic acid to dissolve chitosan before in-situ electrodeposition might be an innovative approach to enhance the adhesion strength between chitosan/calcium phosphate-based coatings and titanium metal to be used in orthopedic and dental implant technology.