Papers by Author: Sam Zhang

Abstract: Soft magnetic material FeCoV is sensitive to magnetic field and its cost is lower than giant magnetostriction materials (Terfenol-D et al.). In the present investigation Pb (Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) with different thickness and FeCoV laminate with 0.8mm thickness were assembled into layer structure to study the effect of the PMN-PT volume fraction on the magnetoelectric coefficient of PMN-PT/FeCoV laminate composites. The ME coefficients and voltages have been characterized in the longitudinally magnetized and transversely polarized mode. The measurement was conducted under a static magnetic field superimposed with an alternating magnetic field. The influences of the static and the alternating field strength were discussed. The peak ME coefficient was obtained at 430 Oe. With the volume fraction of PMN-PT increased, the ME coefficient decreased within the experiment fraction. It can be explained by the module of M.I.Bichurin. A linear relationship was observed between the magnetoelectric voltage and the alternating field strength under a static field of 400 Oe. The ME voltage decreased when the PMN-PT volume fraction increased in the experiment fraction.

Abstract: A series of the magnesium apatite coatings according to (Ca_10-xMg_x)(PO₄)₆(OH)₂, where x = 0 to 2, was synthesized through a sol-gel dip-coating method. The roughness of the magnesium coatings increased as more magnesium incorporated into the coatings. The mechanical properties of the coatings were analyzed with Nanoindentor. The incorporation of magnesium decreased the hardness and the Young’s modulus of the coating. The X-ray Photoelectron Spectroscopy (XPS) analysis revealed that only part of magnesium was incorporated into the apatite structure while the rest existed in the form of MgO in the coating.

Abstract: For dental/orthopedic implants to achieve better bone apposition and bone-implant bonding, various approaches to improve titanium surfaces have been developed. Recently, a fluoridated hydroxyapatite (FHA) coating on titanium (Ti) implants was made by sol–gel method and shown to be a possible applicative bone implant. The purpose of the current study was to evaluate biological responses and biomechanical bonding strength of FHA coated Ti implants as compared with that of the conventional Ti alloys and hydroxyapatite (HA) coated Ti implants. In vitro assays were made using human osteoblast-like cell (MG63) culture on different implants with cell attachment, morphology and differentiation evaluations. The implant plates were also implanted into the proximal metaphysis of New Zealand White rabbit tibiae. After 8 and 16 weeks implantation, mechanical and histological assessments were performed to evaluate biomechanical and biological behavior in vivo. The results showed that the cell adhesion and cell growth rate on the FHA and HA surface was higher than that on cp Ti surface (p<0.01), and insignificant difference was observed between two coated groups. Mechanical test demonstrated that the FHA implants had a higher interface shear strength than the both controls at 8 and 16 wks, with no significant difference with HA-Ti. Histologically, the coated implants revealed a significantly greater percentage of bone-implant contact when compared with the uncoated implants. Results demonstrated that the new FHA surface improved cell adhesion and proliferation. The coating exhibited a bioactive mechanical and histological behavior at bone-implant interface, suggesting that a useful approach by combined coating processes could optimize implant surfaces for bone deposition and early implant fixation.

Abstract: The objective of this study was to evaluate the interface shear strength and the responses of osteoblast-like cells to titanium implants with a sandblasted and acid-etched surface modified by alkali and heat treatments (SLA-AH). The implants with machined and SLA surface served as controls. Each type of implant was characterized by scanning electron microscopy (SEM) and energy-dispersive x-ray (EDX) analysis. In vitro assays were made using human osteoblast-like cell culture on different surfaces. The rectangle plates were also transcortically implanted into the proximal metaphysis of New Zealand White rabbit tibiae. After 4, 8 and 12 weeks implantation, mechanical and histological assessments were performed to evaluate biomechanical and biological behavior in vivo. By SEM examination, SLA surface combined with AH treatments revealed a macro-rough surface with finely microporous structure. The in vitro assays showed that the SLA-AH surfaces exhibited more extensive cell deposition and improved cell proliferation as compared with controls. Pull-out test demonstrated that the SLA-AH treated implants had a higher mechanical strength than the controls at all interval time after implantation. Histologically, the test implants revealed a significantly greater percentage of bone-implant contact when compared with controls. The results of this study suggest that a useful approach by combined processes could optimize implant surfaces for bone deposition and produce distinct biological surface features.

Abstract: Nanocrystalline TiN (or nc-TiN) has been imbedded in amorphous silicon nitride (a-SiNx)matrix to form a nanocomposite thin film (nc-TiN/a-SiNx) via magnetron sputtering deposition on silicon wafer. Two important effects of the Si3N4 sputtering target power on the formation of nc-TiN/a-SiNx have been studied: (1) Aside from forming a-SiNx in the matrix, Si atoms also imbed into TiN to form (Ti,Si)N solid solution crystallites. At low target power, the solid solution is substitutional. With increase of power, the amount of silicon “dissolved” in the TiN crystallite increases, and in the meantime, the interstitial components increase which is manifested in the increase in the TiN lattice parameter. (2) The crystallites have a preferred orientation varying with the deposition target power. As conveniently described by the coefficient of texture, the degree of preferred orientation along [111] direction decreases and finally tails off with increase of power. At the same time, the crystallites orient along [200] and [220] direction and eventually [220] direction dominants.