Titanium and titanium alloys are widely used in biomedical devices and components, especially as hard tissue replacements as well as in cardiac and cardiovascular applications, because of their desirable properties, such as relatively low modulus, good fatigue strength, formability, machinability, corrosion resistance, and biocompatibility. However, titanium and its alloys cannot meet all of the clinical requirements. Therefore, in order to improve the biological, chemical, and mechanical properties, surface modification is often performed. This article reviews the various surface modification technologies pertaining to titanium and titanium alloys including mechanical treatment, thermal spraying, sol–gel, chemical and electrochemical treatment, and ion implantation from the perspective of biomedical engineering. Recent work has shown that the wear resistance, corrosion resistance, and biological properties of titanium and titanium alloys can be improved selectively using the appropriate surface treatment techniques while the desirable bulk attributes of the materials are retained. The proper surface treatment expands the use of titanium and titanium alloys in the biomedical fields. Some of the recent applications are also discussed in this paper.

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Surface modification of titanium, titanium alloys, and related materials for biomedical applications

Applications of synthetic polymers in clinical medicine

Teeth and bones: applications of surface science to dental materials and related biomaterials

A wide range of biomedical devices is applied clinically in contact with blood. Tailoring the surface properties of the involved biomaterials is a common approach to enhance performance and to limit adverse reactions. This review summarizes current trends in coating technologies developed for that purpose. Inorganic coatings were shown to substantially improve the durability and inertness of biomaterials while a number of advanced polymer coatings were demonstrated to be very effective by targeting specific biochemical pathways. However, to fully utilize the power of these bioactive coatings safety issues need to be thoroughly addressed in future studies.

Current strategies towards hemocompatible coatings

Ion implantation of titanium based biomaterials

Blood compatibility of titanium-based coatings prepared by metal plasma immersion ion implantation and deposition

Layers of Ti nitride, Ti oxynitrides TiN x O y and Ti oxide were produced by means of metal plasma immersion ion implantation and deposition (MePIIID) from a plasma produced by cathodic arc evaporation of Ti under addition of nitrogen and/or oxygen to the ambient near the substrate. The phase composition and structure of the layers are strongly dependent on the relation of the gases partial pressure. To study the correlation between blood compatibility and physical properties of the coating the thrombocyte adhesion and fibrinogen adsorption on the surface as well as wettability and surface energy were investigated. Thrombocyte adhesion and fibrinogen adsorption are lower for TiN x O y than for TiO 2 . This correlates with a lower hydrophobicity and higher polar component of the surface energy for TiN x O y .

Correlation between blood compatibility and physical surface properties of titanium-based coatings

Coating with titanium oxides is a promising method to improve the blood compatibility of materials to be used for medical implants. Ti oxide layers were deposited on oxidized Si from a plasma produced by cathodic arc evaporation under addition of oxygen to the ambient near the substrate. In dependence on the deposition parameters amorphous and nanocrystalline structures, crystalline layers composed of anatase and brookite as well as layers dominated by the rutile phase have been obtained. The activation of the plasmatic clotting cascade was only minimally influenced by the crystal size and the crystallite structure of the titanium oxide films. As a trend, amorphous, nanocrystalline and fine-grained layers show higher clotting times than well crystallized rutile films. Ion implantation of Cr or P strongly influences the clotting time. Contrasting tendencies in the dependence of clotting time and platelet adhesion on the microstructure of the Ti oxide have been found, however, for P + -doped rutile both, enhanced clotting time and improved platelet adhesion, are observed. Platelet adherence and activation always show similar trends.

Structure and properties of titanium oxide layers prepared by metal plasma immersion ion implantation and deposition

Pretreatment of titanium by implantation of P and Ca is of interest in order to improve the quality of hydroxyapatite coatings used to enhance its biocompatibility. A near surface implantation of high doses of calcium results in an oxidation of the modified layer and the formation of CaO. By post-implantation annealing also Ca4Ti3O10 is formed. For deeper calcium implantations, precipitation of the metastable hexagonal modification of calcium has been observed instead of the cubic equilibrium phase. By high dose implantation of phosphorus, the implanted layer becomes partly amorphized. This hinders the reaction with oxygen during implantation and room temperature aging. The thickness of the surface oxide corresponds to the native oxide layer. For high dose double implantation with both elements, due to the strong swelling effect and the incorporation of oxygen, the second implant is shifted to the surface, if the energies are chosen so that the profiles should be overlapping by implantation into pure titanium. No indication for compound formation besides calcium oxide has been found as a result of the implantation.

Modification of titanium by ion implantation of calcium and/or phosphorus

Ion implantation of Ca and/or P into Ti or Ti alloys is of interest in order to enhance mechanical properties and biocompatibility for medical applications. In this study, the microstructural changes of the implanted surface layer were studied. Surface near implantation of high doses of calcium results in an oxidation of the modified layer and the formation of CaO. For deeper calcium implantations, precipitation of the metastable hexagonal modification of calcium has been observed instead of the cubic equilibrium phase. Besides these new phases, partial amorphization is observed. High dose implantation of phosphorus leads mainly to amorphization of the implanted layer. This hinders the reaction with oxygen during implantation and room temperature aging. High dose double implantation with P followed by Ca also leads to partial amorphization. No indication for new phases containing Ca and P is found.

I. Tsyganov

Papers

Blood compatibility of titanium-based coatings prepared by metal plasma immersion ion implantation and deposition

Correlation between blood compatibility and physical surface properties of titanium-based coatings

Structure and properties of titanium oxide layers prepared by metal plasma immersion ion implantation and deposition

Modification of titanium by ion implantation of calcium and/or phosphorus

Modification of the Ti–6Al–4V alloy by ion implantation of calcium and/or phosphorus