Papers by Author: Xiao Xiang Wang

Abstract: Hydroxyapatite (HAP) coatings have been successfully electrodeposited on the titanium substrate by using Na2EDTA as chelate in electrolytes. The samples obtained were characterized by XRD and SEM. The XRD result indicated that the HAP crystals were preferentially oriented along c-axis. The SEM showed that the HAP crystals were rod like precipitates with a well-defined hexagonal cross section. The size of HAP crystals was well controlled by the addition of Na2EDTA and electrochemical parameters such as deposition times, pH value. It was discussed that the formation of Ca–EDTA complexes effectively restrained the growth of the HAP crystals.

Abstract: In an effort to investigate the growth mechanism of nacre, a conventional vapor diffusion method for CaCO3 crystal precipitation was applied to in vitro growth of calcium carbonate on freshwater H. cumingii Lea shell. In a 10mM/L CaCl2 solution without any additives, aragonite deposit was obtained on the nacre surface, specifically at the edges of nacreous tablets. At the early stage of the deposition (up to 4 hr), the deposit did not take any specific form. After 12hr of deposition, the deposit exhibited faceted morphology characteristic of crystalline. Further increasing the deposition time resulted in the formation of well-faceted crystals of tower-like shape. Both Raman spectra and X-ray diffraction patterns showed that the deposit consists of aragonite polymorph of calcium carbonate.

Abstract: Homogeneous coatings adhered strongly to titanium substrates were attained by electrochemical method in electrolytes containing Ca2+ and PO4 3- ions with Ca/P ratio being 1.67. SEM observation showed that the HAp crystals prepared with higher concentration electrolyte (4x10-2M Ca2+) are ribbon-like with thickness of nanometer size, a morphology seldom reported previously. In an electrolyte of lower concentration (6x10-4M Ca2+), the HAp crystals formed are rod-like with defined hexagonal cross section and diameter of about 70-80nm. The electrolyte of intermediary concentration (5x10-3M Ca2+) produced plate-like HAp crystals. XRD patterns and IR spectra confirmed that the coatings consist of HAp crystals.

Abstract: The corrosion behavior of titanium in hydrogen peroxide solutions was studied by measuring the titanium ions concentration using spectrophotometer. The influence of additives (K+ ， Ca2+ ，Na+ ，Mg2+ ，Cl- ，HPO4 2-, H2PO4 - ) on the corrosion behavior of titanium was examined. The results indicated that Ca2+ exhibited the highest inhibition to the titanium corrosion in hydrogen peroxide solutions, while HPO4 2- behaved as an accelerator to the corrosion. It was suggested that the Ca2+ was absorbed on the titanium surface to form a thin film of CaTiO3 or CaO2, and consequently, inhibited the corrosion of titanium. The acceleration of the titanium corrosion in the present of HPO4 2- was caused probably by the increased defect of surface oxide films after absorption of HPO4 2- ions.

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: Nacre powder suspensions in alcohol added with acetic acid (Suspension I) or calcium chloride (Suspension II) were prepared. Titanium substrates were coated with nacre powder by EPD in the suspensions. The result shows that Suspension II is more stable than Suspension I, and deposition rate in Suspension II is much higher than that in Suspension I. XRD and FTIR results show that the nacre coatings exhibit the same characteristics as the raw nacre powder. SEM morphologies show that uniform coatings are achieved. Scratch test shows that bonding strength of coatings from Suspension I is much higher than that of Suspension II. The higher bonding strength from Suspension I was confirmed to be closely related to the concurrent deposition of organic molecules dissolved in the suspension.

Abstract: Titanium dental implant screws were implanted into the pearl sacs of a fresh water bivalve (hyriopsis cumingii Lea) by replacing the pearls. After 45 days of cultivation, the implant surfaces were deposited with a nacre coating with iridescent luster. The coating was about 200-600 µm in thickness and composed of a laminated nacreous layer and a transitional non-laminated layer that consisted mainly of vaterite and calcite polymorphs of calcium carbonate. The transitional layer was around 2-10 µm thick in the convex and flat region of the implant surface and could form close contact with titanium surface; while the transitional layer was much thicker in the steep concave regions and could not form close contact with the titanium surface. The improvement to the design of the dental implant with respect to this coating method was suggested in the paper. The results suggest that it is possible to fabricate a biologically active and degradable, and mechanically tough and strong nacre coating on titanium dental implant by this novel coating technology.