Jukka Lausmaa

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.

Surface spectroscopic characterization of titanium implant materials

Abstract Titanium is one of the most commonly used biomaterials for dental and orthopedic applications. Its excellent tissue compatibility is mainly due to the properties of the stable oxide layer which is present on the surface. This paper reports a detailed spectroscopic characterization of the surface composition of non-alloyed Ti implant materials, prepared according to procedures commonly used in clinical practice (machining, ultrasonic cleaning and sterilization). The main methods of characterization are XPS and AES, and complementary information is obtained by SIMS, EDX and NMA (nuclear microanalysis). The surface of the implants is found to consist of a thin surface oxide which is covered by a carbon-dominated contamination layer. By comparison with reference spectra from single crystal TiO2 (rutile) the composition of the surface oxide is shown to be mainly TiO2, with minor amounts of suboxides and TiNx. The thickness of the surface oxides is 2–6 nm, depending on the method of sterilization. The surface contamination layer is found to vary considerably from sample to sample and consists of mainly hydrocarbons with trace amounts of Ca, N, S, P, Cl. Some differences in surface composition between directly prepared surfaces, and some possible contamination sources, are identified and discussed shortly.

Bone response to surface modified titanium implants: studies on electropolished implants with different oxide thicknesses and morphology

In a series of experimental studies, bone formation was analysed around systematically modified titanium implants. In the present study, machined, electropolished and anodically oxidized implants were prepared, surface characterized and inserted in the cortical bone of rabbits (7 wks and 12 wks). SEM, scanning Auger electron spectroscopy and atomic force microscopy revealed no differences in surface composition but marked differences in oxide thickness, surface topography and roughness. Light microscopic morphology and morphometry showed that all implants were in contact with bone, and had a large proportion of bone within the threads. The smooth, electropolished implants were surrounded by less bone than the machined implants with similar oxide thickness, (4-5 nm) and the anodically oxidized implants with thicker oxides (21 nm and 180 nm, respectively) after 7 wks. These studies show that a high degree of bone contact and bone formation can be achieved with titanium implants which are modified with respect to oxide thickness and surface topography. However, it appears that a reduction of surface roughness may influence the rate of bone formation in rabbit cortical bone.

Torque and histomorphometric evaluation of c.p. titanium screws blasted with 25‐ and 75‐μm‐sized particles of Al2O3

A comparison was made between screw-shaped c.p. titanium implants blasted with either 25- or 75-microns particles of Al2O3. The implant surfaces were investigated with respect to topography and composition before implantation in rabbit bone. Grit blasting with 25- or 75-microns particles produced two different surface roughnesses, but no significant difference in the surface composition for the two surfaces. After 12 weeks insertion time in the rabbit tibia and femur, a higher removal torque and more bone-to-metal contact was found for the implants blasted with 75-microns particles compared with the 25-microns-blasted ones.

Titanium with different oxides: in vitro studies of protein adsorption and contact activation

Adsorption of albumin (HSA) and fibrinogen (Fib) from human blood plasma onto titanium surfaces with varying oxide properties was studied with an enzyme-linked immunosorbent assay. The intrinsic activation of blood coagulation (contact activation) was studied in vitro using a kallikrein-sensitive substrate. The sample surfaces were characterized with Fourier transform Raman spectroscopy. Auger electron spectroscopy and atomic force microscopy. Low Fib and high HSA adsorption was observed for all titanium samples except for the radio frequency plasma-treated and water-incubated samples, which adsorbed significantly lower amounts of both. Oxide thickness and carbon contamination showed no influence on protein adsorption or contact activation. Smooth samples with a surface roughness (Rrms) < 1 nm showed some correlation between surface wettability and adsorption of Fib and HSA, whereas rough surfaces (Rrms > 5 nm) did not. To varying degrees, all titanium surfaces indicated activation of the intrinsic pathway of coagulation as determined by their kallikrein formation in plasma.

SURFACE SPECTROSCOPIC CHARACTERIZATION OF TITANIUM IMPLANT MATERIALS

Abstract Titanium is a relatively widely and successfully used biomaterial, especially in the dental and orthopaedic fields. The surface oxide which almost always covers titanium is considered to be an important factor for the favourable tissue response obtained with Ti implants. This paper describes the properties of surface oxides on Ti by discussing some selected examples of surface spectroscopy analyses of Ti surfaces prepared by different methods, including; clinical procedures (machining, solvent cleaning, sterilization), electrochemical methods (electropolishing and anodic oxidation), thermal oxidation in air, and nitrogen-ion implantation. The main analytical techniques are scanning AES and XPS (ESCA). Complementary information is obtained from secondary ion mass spectrometry (SIMS), Rutherford back-scattering (RBS), and nuclear reaction analysis (NRA). Selected spectroscopic results are discussed with reference to microstructural studies published elsewhere. Comparison between pure Ti and Ti6A14V alloy shows many similarities, but also some significant differences between the two materials. The paper also comments briefly on surface contamination and cleaning, and discusses some selected examples of biological studies on different titanium surfaces.

Preparation and surface spectroscopic characterization of oxide films on Ti6Al4V

Abstract Thermal and anodic oxides on Ti6A14V were investigated by XPS, scanning AES, and SIMS, including depth profiling. The oxide layers on the alloy are predominantly TiO2 but have considerable concentrations of the alloying elements included in the oxide. Al, but not V, is observed in the outermost atomic layers of the oxide. Both A1 and V are present at relatively high maximum atomic concentrations (Al/Ti ≈ 0.17 and V/Ti ≈ 0.07) inside anodic oxides. The V concentration varies laterally over the surface, reflecting the variation of the V concentration in the underlying metal due to its two phases. The results are compared with the corresponding results for pure Ti. The implications of these results for the use of Ti6A14V as a biomaterial in surgical implants are discussed shortly.

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.

Structure of the interface between rabbit cortical bone and implants of gold, zirconium and titanium

The role of surface properties (chemical and structural) for the interaction between biomaterials and tissue is not yet understood. In the present study, implants made of titanium, zirconium (transition metals with surface oxides) and gold (metallic surface) were inserted into the rabbit tibia. Light microscopic (LM) morphometry showed that after 1 and 6 mo the gold implants had less amount of bone within the threads and a lower degree of bone-implant contact than the titanium and zirconium implants, which did not differ from each other. These quantitative differences were supported by LM and ultrastructural observations of the interface. The ultrastructural observations in addition demonstrated that the layer of non-collagenous amorphous material located between the implant and the calcified bone was appreciably thicker around zirconium than around titanium implants. The factors potentially responsible for the observed morphological differences in the bone around the different material surfaces are discussed.

Multi-technique surface charaterization of oxide films on electropolished and anodically oxidized titanium

The widespread use of pure Ti in biomedical applications and in basic biomaterials research has led to an increasing interest in the properties of its surface oxides, and how they can be modified. In this work, which was part of a broad surface characterization of oxide films on pure Ti and Ti-6A1-4V, the chemical composition of anodic oxide films formed on pure Ti during electropolishing and anodic oxidation was investigated using multi-technique surface analysis (XPS, AES/SAM, SIMS, RBS and NRA). XPS and AES Ti line shapes show that the oxide formed is mainly TiO2, but the chemical composition can be modified by anion adsorption and/or incorporation when H2SO4 or H3PO4 electrolytes are used. Modification of the anodic oxide film composition also occurs during sterilization; increased Ca and H levels are observed by SIMS and NRA after autoclaving. AES and XPS depth profiles, together with RBS measurements, show that the oxide thickness depends linearly on the anodizing potential in the range 5–80 V, with a growth constant αm≈ 1.1 × 1016 oxygen atoms/V⋯ cm2. The present results are compared with parallel studies of the composition and microstructure of thermal and anodic oxides on pure Ti and Ti-6A1-4V. The demonstrated systematic variation of oxide properties opens up the possibility to study the influence of specific surface properties on the biological response to Ti materials.