Bone response to machined cast titanium implants

The aim was to evaluate the bone response to machined cast titanium (Ti) implants. Commercially pure (c.p.) machined Ti implants served as controls. Analyses of the surface composition and topography by Auger electron spectroscopy (AES) and scanning electron microscopy (SEM) revealed no differences comparing the two materials. Cast screw-shaped and identical machined Ti implants were inserted in the tibial metaphysis of 6 rabbits. After 3 and 6 months, the amount of bone within threads and the degree of bone-implant contact were histomorphometrically evaluated. The bone area of cast Ti implants was 45% after 3 months and 62% after 6 months. The corresponding values for machined Ti implants were 51% and 58%, respectively. The total bone-implant contact for cast Ti implants was 19% (25% control implants) after 3 months and 45% (37% for control implants) 6 months after implantation. No statistically significant differences were observed between the two materials at any time interval. The present experimental results indicate that machined cast Ti implants integrate equally well in bone as machined c.p. Ti implants do.     

Transient liquid phase bonding of titanium to aluminium nitride

Titanium has been successfully joined to aluminium nitride AlN at a temperature as low as 795 °C, using Ag–Cu Cusil^® commercial braze alloy. While reactive wetting and spreading proceeds at the AlN/braze alloy interface, chemical interactions develop at the titanium side rendering possible isothermal solidification of the joint. The determining factor in the solidification process is the fast formation of TiCu₄ crystals by heterogeneous nucleation and growth in the liquid phase. As a consequence, the braze alloy is depleted in Cu and solid Ag precipitates. After annealing, the re-melting temperature of the resulting joint can be increased up to about 910 °C which is nearly 130 °C higher than the melting point of the starting braze alloy.     

Bone tissue reactions to biomimetic ion-substituted apatite surfaces on titanium implants

The aim of this study was to evaluate the bone tissue response to strontium- and silicon-substituted apatite (Sr-HA and Si-HA) modified titanium (Ti) implants. Sr-HA, Si-HA and HA were grown on thermally oxidized Ti implants by a biomimetic process. Oxidized implants were used as controls. Surface properties, i.e. chemical composition, surface thickness, morphology/pore characteristics, crystal structure and roughness, were characterized with various analytical techniques. The implants were inserted in rat tibiae and block biopsies were prepared for histology, histomorphometry and scanning electron microscopy analysis. Histologically, new bone formed on all implant surfaces. The bone was deposited directly onto the Sr-HA and Si-HA implants without any intervening soft tissue. The statistical analysis showed significant higher amount of bone–implant contact (BIC) for the Si-doped HA modification (P = 0.030), whereas significant higher bone area (BA) for the Sr-doped HA modification (P = 0.034), when compared with the non-doped HA modification. The differences were most pronounced at the early time point. The healing time had a significant impact for both BA and BIC (P < 0.001). The present results show that biomimetically prepared Si-HA and Sr-HA on Ti implants provided bioactivity and promoted early bone formation.     

Mechanical examinations on dental implants with porous titanium coating

Due to its good biocompatibility, porous titanium is an interesting material for biomedical applications. Bone tissue can grow inside the porous structure and maintain a long and stable connection between the implant and the human bone. To investigate its long term stability, the mechanical behavior of porous titanium was tested under static and dynamic conditions and was compared to human bone tissue. A promising application of this material is the coating of dental implants. A manufacturing technique was developed and implants were produced. These implants were fatigue tested according to modified ISO 14801 and the micro structural change was examined. The fatigue test was statically modeled using finite element analysis (FEA). The results show that the implants resist a continuous load which is comparable to the loading conditions in the human jaw. The experiments show that the porous titanium has bone-like mechanical properties. Additionally the porous titanium shows an anisotropic behavior of its mechanical properties depending on the alignment of the pores. Finally, other potential applications of porous titanium are outlined.     

Analysis of coating interlayer between silicon nitride cutting tools and titanium carbide and titanium nitride coatings

Silicon nitride (Si₃N₄) cutting tools exhibit excellent thermal stability and wear resistance in the high-speed machining of cast irons, but show poor chemical wear resistance in the machining of steel. Conventional chemical vapour deposition (CVD) coating of Si₃N₄ tools has not been very successful because of thermal expansion mismatch between coatings and the substrate. This problem was overcome by developing a CVD process to tailor the interface for titanium carbide (TiC) and titanium nitride (TiN) coatings. Computer modelling of the CVD process was done to predict which phases would form at the interface, and the results compared with analyses of the interface. Three Si₃N₄ compositions were considered, including pure Si₃N₄, Si₃N₄ with a glass phase binder, and Si₃N₄ + TiC composite with a glass phase binder. Results of machining tests on coated tools show that the formation of an interlayer provides superior wear resistance and tool life in the machining of steel as compared to uncoated and conventionally coated Si₃N₄ tools.     

Quantitative bone tissue response to commercially pure titanium implants

Commercially pure titanium implants were inserted in rabbit tibia for 3, 6 and 12 weeks. Each rabbit had two implants inserted, one for removal torque measurements and the other for histomorphometrical analysis. Light microscopic observations revealed that there was a continuing bone remodelling, with new bone formation in the periosteal region after 3 and 6 weeks, which diminished with time, i.e. up to 12 weeks of follow-up. A higher removal torque was observed with increasing time of implant insertion. The removal torque values for the 12 week samples were converted to three different shear forces depending on three different theoretically calculated implant to bone attachment levels. The mean shear forces related to the entire length of the implant surface was 0.6 N mm^-2. If considering the length of the implant inside the cortical bone only, the mean shear force was 1.9 N mm^-2, and if the bone-metal contact length as related to an estimate of the bone-implant contact a mean shear force of 14.8 N mm^-2 was calculated. Histomorphometrical measurements revealed more bone-metal contact as well as a larger bone area in the threads with increasing time of insertion. Statistically significant differences were observed between all measurements of the 3 and 6 week samples and between the 3 and 12 week samples. For the 6 and 12 week sections a statistically eignificant difference could be demonstrated only when comparing bone areas in the three best consecutive threads located in the cortical region.     

Characterization of delamination in titanium nitride coating on steel using acoustic microscopy

The melting behavior of the 2212 phase in the Bi(Pb)SrCaCuO system has been investigated using DTA, XRD and EPMA. The effect of Pb and Ca on the melting of 2212 have also been discussed. The results indicate that the melting point of 2212 decreases monotonicaly with increasing Pb, however it reaches a peak value with the increase of Ca. 2212 melts incongruently into a liquid and (Sr,Ca)CuO₂, and the crystals formed when the liquid is quenched in air vary with the starting concentrations of Pb and Ca.     

One role of titanium compound particles in aluminium nitride sintered body

Microstructure of titanium compound particle in polycrystalline aluminium nitride (AlN) has been investigated using micro-auger electron spectroscopy (μ-AES). AlN-0.5 wt% TiO2-1.5 wt% Y2O3-0.4 wt% CaO system was sintered at 1850°C in nitrogen atmosphere using a graphite furnace. The AES studies show that the composition of the titanium compound particle is titanium, aluminium, carbon, oxygen, nitrogen and calcium. On the other hand, no calcium is observed by AES in the AlN grains and grain boundary. It is found that one role of the titanium compound particle is to trap calcium included in polycrystalline AlN. This revised version was published online in November 2006 with corrections to the Cover Date.     

Chitosan reinforced apatite–wollastonite coating by electrophoretic deposition on titanium implants

A novel bioactive porous apatite–wollastonite/chitosan composite coating was prepared by electrophoretic deposition. The influence of synthesis parameters like pH of suspension and current density was studied and optimized. X-ray diffraction confirmed crystalline phase of apatite–wollastonite in powder as well as composite coating with coat crystallinity of 65%. Scanning electron microscope showed that the porosity had interconnections with good homogeneity between the phases. The addition of chitosan increased the adhesive strength of the composite coating. Young’s modulus of the coating was found to be 9.23 GPa. One of our key findings was sheet-like apatite growth unlike ball-like growth found in bioceramics. Role of chitosan was studied in apatite growth mechanism in simulated body fluid. In presence of chitosan, dense negatively charged surface with homogenous nucleation was the primary factor for sheet-like evolution of apatite layer. The results suggest that incorporation of chitosan with apatite–wollastonite in composite coating could provide excellent in vitro bioactivity with enhanced mechanical properties.     

Novel fluorapatite/niobium composite coating for metallic human body implants

This study's aim was to design and prepare a novel composite coating in order to improve the biocompatibility of the metallic implants. AISI 316L stainless steel (SS) was used as a substrate and a filler-matrix fluorapatite/niobium (FA/Nb) composite coating was performed on the substrate by using plasma-spray technique. XRD and SEM analyses were utilized to characterize the coatings. Electrochemical polarization tests were carried out in two types of physiological solutions in order to evaluate the corrosion behavior of the coated specimens as an indication of biocompatibility. The results indicated that the corrosion current density of the FA/Nb coated samples was much lower than the obtained values for the FA coated SS substrates. Obviously, the novel FA/Nb composite coating could improve the corrosion resistance and the biocompatibility of the SS implants.     

Early tissue response to titanium implants inserted in rabbit cortical bone

The tissue response to screw-shaped implants of commercially pure titanium was studied by light microscopy 3–180 days after insertion in the rabbit tibia. The implant site in the tibial metaphysis consisted mainly of cortical bone. Three days after implantation, osteoblasts, producing osteoid, were observed at the endosteal surface and elongated mesenchymal cells were present in the injury area. Some macrophages but rather few other inflammatory cells were identified. Multinuclear giant cells were in direct contact with the implant and formed an almost continuous layer along the surface from the 7th day. The number of giant cells decreased with time and with increased bone-titanium contact. Bone formation was never seen direct on the implant surface but was first observed at day 7 as a woven trabecular bone formed at the endosteal surface and extending towards the implant and as a solitary formation of woven bone close to the implant. The solitary bone matrix served as a base for surface osteoblasts which produced osteoid in a lamellar arrangement. With time the two types of newly formed bone fused and more bone filled the threads and became remodelled by bone remodelling units. Light microscopic morphometry in ground sections demonstrated that the bone/titanium contact and bone area in the threads increased with time up to 6 months after implantation     

Early tissue response to titanium implants inserted in rabbit cortical bone

The tissue response to screw-shaped implants of commercially pure titanium was studied 3–180 days after insertion in the rabbit tibia by means of transmission electron microscopy. Red blood cells and scattered macrophages predominated at the implant surface after 3 days. At day 7 and later intervals, multinuclear giant cells were the cell type found at the implant surface protruding into the bone marrow and in areas with no bone-titanium contact. Osteoblasts or mesenchymal cells were rarely seen at the implant surface at any time period. Two modes of mineralization could be distinguished in the interface. Firstly, the typical mineralization of osteoid seams produced by osteoblasts. Secondly, an accumulation of scattered hydroxyapatite crystals in the unmineralized collagen matrix in the interface. Mineralized tissue was observed close to the implants surface from day 14. However, the innermost 2–20 m were poorly mineralized although scattered hydroxyapatite crystals were present. The collagen fibrils did not reach the implant surface but were separated from it by an amorphous layer, being 0.3–0.5 m thick which did not decrease in width with time. An electron-dense lamina limitans-like line containing mineral was observed between the amorphous layer and the bone tissue.     

The effect of titanium current on structure and hardness of aluminium titanium nitride deposited by reactive unbalanced magnetron co-sputtering

Nanocrystalline aluminium titanium nitride (AlTi₃N) thin films were deposited on Si (100) wafer and grid substrates without external heating and biasing at room temperature by reactive unbalanced magnetron co-sputtering technique using pure individual titanium and aluminium targets. The effects of titanium current (I_Ti) on the structure and hardness of these films have been studied. The films were sputtered with Ar and N₂ gases flow rate of 8 and 4 sccm, respectively. The sputtering current of the aluminium current (I_Al) was kept at 600 mA and the sputtering current of titanium (I_Ti) was varied from 600 to 800 mA. The films were deposited for different deposition times ranging from 15 to 60 min. The deposited films were then characterized and analyzed by X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and nanoindentation measurement. The results indicated that the modification of the crystal structure, surface morphology and microstructure were dependent on the deposition parameters. The XRD patterns show polycrystalline structure with preferred orientations in (112), (004) and (153) planes which agree with the standard structure of aluminium titanium nitride (AlTi₃N) films. In addition, the structure of AlTi₃N was also confirmed by TEM. These results show that the films are composed of high Al content. The root mean square surface roughness and the average thicknesses were strongly influenced by I_ti and deposition times. Cross section analysis by SEM showed dense and compact columnar morphology. The typical hardness of the films was approximately 26.24-30.37 GPa.     

Superior high-temperature resistance of aluminium nitride particle-reinforced aluminium compared to silicon carbide or alumina particle-reinforced aluminium

Aluminium-matrix composites containing AlN, SiC or Al₂O₃ particles were fabricated by vacuum infiltration of liquid aluminium into a porous particulate preform under an argon pressure of up to 41 MPa. Al/AlN had similar tensile strengths and higher ductility compared to Al/SiC of similar reinforcement volume fractions at room temperature, but exhibited higher tensile strength arid higher ductility at 300–400 °C and at room temperature after heating at 600 °C for 10–20 days. The ductility of Al/AIN increased with increasing temperature from 22–400 °C, while that of Al/SiC did not change with temperature. At 400 °C, Al/AlN exhibited mainly ductile fracture, whereas Al/SiC exhibited brittle fracture due to particle decohesion. Moreover, Al/AlN exhibited greater resistance to compressive deformation at 525 °C than Al/SiC. The superior high-temperature resistance of Al/AlN is attributed to the lack of a reaction between aluminium and AlN, in contrast to the reaction between aluminium and SiC in Al/SiC. By using Al-20Si-5Mg rather than aluminium as the matrix, the reaction between aluminium and SiC was arrested, resulting in no change in the tensile properties after heating at 500 °C for 20 days. However, the use of Al-20Si-5Mg instead of aluminium as the matrix caused the strength and ductility to decrease by 30% and 70%, respectively, due to the brittleness of Al-20Si-5Mg. Therefore, the use of AIN instead of SiC as the reinforcement is a better way to avoid the filler-matrix reaction. Al/Al₂O₃ had lower room-temperature tensile strength and ductility compared to both Al/AlN and Al/SiC of similar reinforcement volume fractions, both before and after heating at 600 °C for 10–20 days. Al/Al₂O₃ exhibited brittle fracture even at room temperature, due to incomplete infiltration resulting from Al₂O₃ particle clustering.