Roger Thull

Antimicrobial titanium/silver PVD coatings on titanium

BackgroundBiofilm formation and deep infection of endoprostheses is a recurrent complication in implant surgery. Post-operative infections may be overcome by adjusting antimicrobial properties of the implant surface prior to implantation. In this work we described the development of an antimicrobial titanium/silver hard coating via the physical vapor deposition (PVD) process.MethodsCoatings with a thickness of approximately 2 μm were deposited on titanium surfaces by simultaneous vaporisation of both metals in an inert argon atmosphere with a silver content of approximately 0.7 – 9% as indicated by energy dispersive X-ray analysis. On these surfaces microorganisms and eukaryotic culture cells were grown.ResultsThe coatings released sufficient silver ions (0.5–2.3 ppb) when immersed in PBS and showed significant antimicrobial potency against Staphylococcus epidermis and Klebsiella pneumoniae strains. At the same time, no cytotoxic effects of the coatings on osteoblast and epithelial cells were found.ConclusionDue to similar mechanical performance when compared to pure titanium, the TiAg coatings should be suitable to provide antimicrobial activity on load-bearing implant surfaces.

Binary nitride and oxynitride PVD coatings on titanium for biomedical applications

Abstract The aim of this study was the development and characterization of wear resistant and adhesive (oxy-)nitride refractory metal PVD coatings for biomedical applications. The steered arc technique with a special sector target was used to vaporize two different metal components. The subjects of investigations were layers of (Ti,Zr)N, (Ti, Nb)N and (Ti, Nb)ON with an average thickness of approximately 3–4 μm. By means of the sector target, the zirconium content of the (Ti,Zr)N layers could be varied between 50% and 70%, and the niobium content of the (Ti,Nb)N layers between 30% and 40%. X-Ray diffraction analysis showed for all materials that the cubic TiN lattice structure still dominates while a part of the titanium atoms are successively substituted by the second metal component, Zr and Nb, respectively. An excessive insertion of oxygen at interstitial sites leads to an embrittlement of the resulting coatings. All investigated coatings showed a preferred growth in the (111) direction of the cubic lattice.

Tribochemical structuring and coating of implant metal surfaces with titanium oxide and hydroxyapatite layers

Abstract The sandblasting process with corundum is used for cleaning, roughening and activating of metal surfaces in dentistry and orthopaedics. The high local energy transfer at the impact point originates the displacement of particles in the surface. In principle, this method can be used for coating surfaces by sandblasting. In this work, we present a newly developed technique, which allows the coating of metal surfaces with titanium dioxide (TiO2) and hydroxyapatite (HA) using a sandblasting process. The blasting material is a composite ceramic consisting of an alumina core (carrier material) covered with a porous shell of titanium dioxide or hydroxyapatite. The technique is applied to titanium substrates; the surface roughness, morphology and composition of the samples are analysed. The procedure results in an averaged surface roughness of 10–15 μm. Energy dispersive X-ray analysis (EDX) indicates the formation of a thin layer consisting of coating material on the metal surface. Furthermore, the traces of corundum crystals, which are inevitable by using the common technique, i.e. sandblasting with single-component grains, are clearly decreased. X-ray diffraction analysis (XRD) indicates mainly the existence of crystalline rutile and hydroxyapatite/β-tricalcium phosphate (β-TCP) on the surface. Therefore, the presented method would be suitable for simultaneously roughening, coating and optimizing the biocompatibility of metal implant surfaces in dentistry and endoprosthetics.

Repassivating tantalum/tantalum oxide surface modification on stainless steel implants

Medical implants that require ductility, high mechanical strength and endurance are commonly made of stainless steel (AISI 316L). Depending on environment and function steel surfaces may be attacked by pitting corrosion leading to post-operative complications. However, the electrochemical surface properties of austenitic steel can be modified for higher corrosion resistance. In this work, steel surfaces are coated with a sandwich layer of tantalum and tantalum oxide, using a PVD sputter process. Mechanical stability is tested and crack generation of the modified material is determined by a four-point bending test connected with a corrosion current measurement using physiological saline solution as the electrolyte. The mechanical stability and repassivation properties of the material are guaranteed up to the onset of substrate plastic deformation. While biocompatibility is obtained by tantalum oxide the ductility is achieved by the tantalum interface which at the same time ensures continued film adhesion, even after plastic deformation of the steel substrate.

Hard implant coatings with antimicrobial properties

Infection of orthopaedic implants often leads to inflammation immediately after surgery and increases patient morbidity due to repetitive operations. Silver ions have been shown to combine good biocompatibility with a low risk of inducing bacterial resistance. In this study a physical vapour deposition system using both arc deposition and magnetron sputtering has been utilized to produce silver ion doped TiN coatings on Ti substrates. This biphasic system combines the advantages of silver induced bactericidity with the good mechanical properties of TiN. Crystallographic analysis by X-ray diffraction showed that silver was deposited as well in its elementary form as it was incorporated into the crystal lattice of TiN, which resulted in increasing hardness of the TiN-coatings. Elution experiments revealed a continuous release of Ag ions in phosphate buffered saline. The coatings showed significant inhibitory effects on the growth of Staphylococcus epidermidis and Staphylococcus aureus and practically no cell-toxicity in cytocompatibility tests.

Surface properties of calcium phosphate particles for self setting bone cements.

Calcium phosphate cements (CPC), consist of multicomponent powder mixtures of calcium orthophosphates with grain sizes in the region of 1-20 microm. Due to the small particle sizes surface properties as the zeta potential and adsorption processes play a significant role during manufacturing and application. In the context of this work zeta potentials of different calcium phosphates, like dicalcium phosphate anhydride (DPCA) tetracalcium phosphate (TTCP) and hydroxyapatite were measured in various organic/aqueous media with different pH values. The results show a strong dependency of the zeta potential on the kind of suspension medium used associated with different milling properties. The addition of sodium phosphate leads to a pH value dependent stabilization of the particles in the liquid phase; the zeta potential of the surface increases from about -15 to -18 mV in water and from -35 to -45 mV in 0.05 mol/l sodium phosphate solution. Besides the interaction of particles with various antibiotics was determined on the basis of the zeta potential of the surface. The substances partly cause a tremendous change of the surface load. This is accompanied by a change of the rheological properties of the cement paste, the morphology of the hardened cement matrix and a significant deterioration of the application-relevant properties as setting time or mechanical strength.

Metallic biomaterial interfaces

I. Interface Influence of Materials and Surface Modifications Passivity-inducing and -retaining Surfaces Topological Surface Modifications Chemical Surface Modifications II. Physical and Physicochemical Surface Characterization Surface Topology Electrochemical Characterization Spectroscopic Interface Characterization Physical Characterization of Protein Adsorption III. Biological Characterization of the Interface and Materials-Related Biosystem Reactions Protein and Cell Adhesion Mechanisms Material-Induced Cellular Interactions Topology-Dependent Cellular Interactions

Influence of spacer length on heparin coupling efficiency and fibrinogen adsorption of modified titanium surfaces

BackgroundChemical bonding of the drug onto surfaces by means of spacer molecules is accompanied with a reduction of the biological activity of the drug due to a constricted mobility since normally only short spacer molecule like aminopropyltrimethoxysilane (APMS) are used for drug coupling. This work aimed to study covalent attachment of heparin to titanium(oxide) surfaces by varying the length of the silane coupling agent, which should affect the biological potency of the drug due to a higher mobility with longer spacer chains.MethodsCovalent attachment of heparin to titanium metal and TiO2 powder was carried out using the coupling agents 3-(Trimethoxysilyl)-propylamine (APMS), N- [3-(Trimethoxysilyl)propyl]ethylenediamine (Diamino-APMS) and N1- [3-(Trimethoxy-silyl)-propyl]diethylenetriamine (Triamino-APMS). The amount of bound coupling agent and heparin was quantified photometrically by the ninhydrin reaction and the tolidine-blue test. The biological potency of heparin was determined photometrically by the chromogenic substrate Chromozym TH and fibrinogen adsorption to the modified surfaces was researched using the QCM-D (Quartz Crystal Microbalance with Dissipation Monitoring) technique.ResultsZeta-potential measurements confirmed the successful coupling reaction; the potential of the unmodified anatase surface (approx. -26 mV) shifted into the positive range (> + 40 mV) after silanisation. Binding of heparin results in a strongly negatively charged surface with zeta-potentials of approx. -39 mV. The retaining biological activity of heparin was highest for the spacer molecule Triamino-APMS. QCM-D measurements showed a lower viscosity for adsorbed fibrinogen films on heparinised surfaces by means of Triamino-APMS.ConclusionThe remaining activity of heparin was found to be highest for the covalent attachment with Triamino-APMS as coupling agent due to the long chain of this spacer molecule and therefore the highest mobility of the drug. Furthermore, the adsorption of fibrinogen on the differently heparinised surfaces in real time demonstrated that with longer spacer chains the ΔD/Δf ratios became higher, which is also associated with better biocompatible properties of the substrates in contact with a biosystem.

Polymerization Behaviour of Organically Modified Titanium Alkoxides in Solution

Modified titanium alkoxides with polymerizable organic ligands allow the synthesis of copolymers consisting of hybrid organic/inorganic networks. In this work titanium based-precursors were characterized in relation to the polymerization behaviour of the organic matrix. Alkoxide sols were prepared by reaction of methacrylic acid, itaconic acid anhydride, isoeugenol, p-vinylbezoic acid, p-vinylphenylacetic acid, and acetoxyacetomethacrylate with titanium tetraisopropoxide and titanium tetraethoxide. Polymerization reactions were carried out in solution using UV-irradiation and a redox-system of dibenzoylperoxide/N, N-dimethyl-p-toluidine as radical initiators. Especially for chemical activation some complexes showed high reactivity similar to silica-based methacrylates. The systems investigated are capable of acting as adhesive promoters between metal and polymer in dental applications.

Oxygen diffusion hardening of cp-titanium for biomedical applications

Common methods to increase the wear resistance of titanium by surface hardening in biomedical applications, such as chemical/physical vapour deposition techniques or thermal/electrochemical oxidation, result in a layer of titanium dioxide or titanium nitride on the metal surface with a sharp interface between the hard and brittle coating and the ductile metallic substrate. A major disadvantage of these methods is that the sharp transition in material properties may cause exfoliation of these coatings. In this work, a two-step heat treatment was used to investigate oxygen diffusion hardening and its capability to produce hard surfaces with a transition zone between the coating and the ductile substrate. During the first step, the native oxide layer was strengthened. In the second step, oxygen diffusion was activated and a transition zone was formed. Different methods of analysis confirmed the success of the thermal treatment, as well as the change of the mechanical properties.