Effect of temperature on surface characteristics of nitrogen ion implanted biocompatible titanium

It has been established that nitrogen implantation can modify metals surface properties such as corrosion, wear, friction, etc. Recent studies have shown that nitrogen implantation into titanium and its alloys leads to the formation of titanium nitride, which has interesting biological, chemical, and mechanical properties. In the present investigation, commercially pure biocompatible titanium implanted by nitrogen. Implantation of ions performed at 80 keV and a dose of 2.1 × 10¹⁸ ions/cm² at four different temperatures of 300, 473, 673 and 873 k. Phase and chemical compositions of modified surfaces after implantation obtained using grazing incidence X-ray diffraction technique (GIXRD) and Fourier transform infrared spectrum (FTIR), respectively. The roughness variations before and after ion implantation were observed by atomic force microscopy (AFM). Electrochemical behavior of the samples was investigated in Ringer solution by using electrochemical impedance spectroscopy and polarization tests. Scanning electron microscopy micrographs was used to evaluate the surface morphology of the samples. Variation of the Young's modulus and hardness of samples were examined using nano-indentation technique before and after ion implantation. Compared to nano-hardness of unimplanted sample, the maximum nano-hardness value of implanted samples is as high as 14.2 GPa, which is at least eight times larger than hardness of the unimplanted sample. The elastic modulus of unimplanted sample was obtained 106 GPa and the maximum elastic modulus value of implanted samples is as high as 178 GPa. Corrosion test results showed that implantation could increase the corrosion resistance of samples, but by increasing the implantation temperature, the corrosion resistance will decrease.

Bone response to surface-modified titanium implants: studies on the early tissue response to implants with different surface characteristics

In a series of experimental studies, the bone formation around systematically modified titanium implants is analyzed. In the present study, three different surface modifications were prepared and evaluated. Glow-discharge cleaning and oxidizing resulted in a highly stoichiometric TiO₂ surface, while a glow-discharge treatment in nitrogen gas resulted in implants with essentially a surface of titanium nitride, covered with a very thin titanium oxide. Finally, hydrogen peroxide treatment of implants resulted in an almost stoichiometric TiO₂, rich in hydroxyl groups on the surface. Machined commercially pure titanium implants served as controls. Scanning Auger Electron Spectroscopy, Scanning Electron Microscopy, and Atomic Force Microscopy revealed no significant differences in oxide thickness or surface roughness parameters, but differences in the surface chemical composition and apparent topography were observed. After surface preparation, the implants were inserted in cortical bone of rabbits and evaluated after 1, 3, and 6 weeks. Light microscopic evaluation of the tissue response showed that all implants were in contact with bone and had a large proportion of newly formed bone within the threads after 6 weeks. There were no morphological differences between the four groups. Our study shows that a high degree of bone contact and bone formation can be achieved with titanium implants of different surface composition and topography.

Comparison of wear of ultra-high molecular weight polyethylene acetabular cups against surface-engineered femoral heads

Alumina ceramic heads have been previously shown to reduce polyethylene wear in comparison to cobalt chrome (CoCr) heads in artificial hip joints. However, there are concerns about the brittle nature of ceramics. It is therefore of interest to investigate ceramic-like coatings on metallic heads. The aim of this study was to compare the friction and wear of ultra-high molecular weight polyethylene (UHMWPE) against alumina ceramic, CoCr, and surface-engineered ceramic-like coatings in a friction simulator and a hip joint simulator. All femoral heads tested were 28 mm diameter and included: Biolox Forte alumina, CoCr, arc evaporative physical vapour deposition (AEPVD) chromium nitride (CrN) coated CoCr, plasma-assisted chemical vapour deposition (PACVD) amorphous diamond-like carbon (aDLC) coated CoCr, sputter CrN coated CoCr, reactive gas controlled arc (RGCA) AEPVD titanium nitride (TiN) coated CoCr, and Graphit-iC coated CoCr. These were articulated against UHMWPE acetabular cups in a friction simulator and a hip joint simulator. Alumina and CoCr gave the lowest wear volumes whereas the sputter coated CrN gave the highest. Alumina also had the lowest friction factor. There was an association between surface parameters and wear. This study indicates that surface topography of surface-engineered femoral heads is more important than friction and wettability in controlling UHMWPE wear.

Morphological behavior of osteoblast-like cells on surface-modified titanium in vitro

In recent papers, we reported the results of a study on the graded porous titanium coatings on titanium by plasma spraying and amino-group ion implantation. The paper is to preliminarily evaluate the biocompatibility of surface-modified titanium through 2, 5 and 7 days cell culture in vitro. Cell morphology was observed by a scanning electron microscope. Cell proliferation and type I collagen synthesis were measured by 3(4.5-dimethyl-thiazole-2-yl)2,5-diphenyl tetrazolium bromide (MTT) and enzyme-linked immunosorbent assay (ELISA), respectively. Our experimental results showed that osteoblast-like cells attached and spread well on surface-modified titanium. Cells were observed to grow into the pores and form extracellular matrix. MTT and ELISA results showed no detrimental effect on the development of cell. These studies support the biocompatibility of surface-modified titanium.

Glow discharge plasma treatment for surface cleaning and modification of metallic biomaterials

Glow discharge plasma treatment is a frequently used method for cleaning, preparation, and modification of biomaterial and implant surfaces. The merits of such treatments are, however, strongly dependent on the process parameters. In the present work the possibilities, limitations, and risks of plasma treatment for surface preparation of metallic materials are investigated experimentally using titanium as a model system, and also discussed in more general terms. Samples were treated by different low-pressure direct current plasmas and analyzed using Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), atomic force microscopy, scanning electron microscopy, and light microscopy. The plasma system is a home-built, ultra-high vacuum-compatible system that allows sample introduction via a load-lock, and precise control of pressure, gas composition and flow rate, etc. This system allows uniform treatment of cylindrical and screw-shaped samples. With appropriate plasma parameters, argon plasma remove all chemical traces from former treatments (adsorbed contaminants and other impurities, and native oxide layers), in effect producing cleaner and more well-controlled surfaces than with conventional preparation methods. Removal (sputtering) rates up to 30 nm/min are possible. However, when inappropriate plasma parameters are used, the result may be increased contamination and formation of unintentional or undesired surface layers (e.g., carbides and nitrides). Plasma-cleaned surfaces provide a clean and reproducible starting condition for further plasma treatments to form well-controlled surface layers. Oxidation in pure O2 (thermally or in oxygen plasmas) results in uniform and stoichiometric TiO2 surface oxide layers of reproducible composition and thicknesses in the range 0.5-150 nm, as revealed by AES and XPS analyses. Titanium nitride layers were prepared by using N2 plasmas. While mild plasma treatments leave the surface microstructure unaffected, heavy plasma treatment can give rise to dramatic morphologic changes. Comparison of these results with corresponding analyses of commercial implants and electropolished and/or anodically oxidized samples shows that the plasma treatment offers superior control of the surface status. However, it is also shown that improper control of the plasma process can produce unwanted and irreproducible results.

Bone response to surface-modified titanium implants: studies on the early tissue response to machined and electropolished implants with different oxide thicknesses

The bone formation around titanium implants with varied surface properties is investigated. Machined and electropolished samples with and without thick, anodically formed surface oxides were prepared, surface characterized and inserted in the cortical bone of rabbits (1, 3 and 6 weeks). Scanning electron microscopy, scanning Auger electron spectroscopy and atomic force microscopy revealed marked differences in oxide thickness, surface topography and roughness, but no significant differences in surface chemical composition, between the different groups of implants. Light microscopic morphology and morphometry showed that all implants were in contact with bone and had a large proportion of bone within the threads at 6 weeks. The smooth, electropolished implants, irrespective of anodic oxidation, were surrounded by less bone than the machined implants after 1 week. After 6 weeks the bone volume as well as the bone-implant contact were lower for the merely electropolished implants than for the other three groups. Our study shows that a high degree of bone contact and bone formation are achieved with titanium implants which are modified with respect to oxide thickness and surface topography. However, the result with the smooth (electropolished) implants indicates that a reduction of surface roughness, in the initial phase, decreases the rate of bone formation in rabbit cortical bone.