Materials Science Forum Vols. 638-642

Abstract: We report results on Pulsed Laser Deposition (PLD) of ceramic thin films for biomedical applica-tions. The coating of metallic implants with bioceramic thin films (e.g. calcium phosphates, in particular hydroxyapatite) has been proposed as a solution for combining the mechanical properties of the metallic material with the bioactive character of the ceramic layer, leading to a better integration of the entire implant with the newly remodelled bone. Other bioceramics (as e.g. alumina) exhibit a high degree of chemical inertness under physiological conditions, excellent wear resistance, ability to be polished to a high surface finish and excellent hardness as coating. Among the different methods to obtain ceramic coatings that have been widely used so far, PLD was focusing interest due to its versatility and controllability, the aptitude to synthesize and deposit uniform films, with an accurate control of the stoichiometry and crystallinity. We investigated the micro-structural and mechanical characteristics of PLD bioceramic coatings on metal substrate. Various microscopic observations and mechanical characterisations by nanoindentation and scratch tests were used in order to connect the mechanical response to the microstructure of the coatings. Our studies revealed that the pulsed-laser deposition technique appears to be a competitive candidate in biomedical applications as an extremely versatile technology

Abstract: Bipolar plates (BPs) are key components of fuel cells. Functions of materials used for fuel cells include equal distribution of gas fuel and air, conduction of electricity between adjacent cells, heat transfer from the cell as well as prevention of gas leakage and cooldown. Moreover, the material must show particular corrosion resistance in cell’s working conditions. Meeting particular requirements or prevention of the abovementioned situations will enable efficient operation of cells. Due to multifunctional nature of fuel cell plates, choice of materials used for plates is immensely difficult. This paper presents opportunities of application of a new technology of powder sintering for creation of parts for electricity and heat generators. This work also presents analysis of structural and phase-related properties, porosity and strength tests.

Abstract: In this study the influence of edges and spikes of a topographical nanostructure on the adsorption behavior of proteins at a solid-liquid interface is examined by a computer simulation. An algorithm has been developed, which combines a Finite Differences field calculation with Brownian Dynamics. A (16 nm)3 nano-cube with sharp edges as well as flat faces was chosen as model system and the adsorption of Hen Egg White Lysozyme was investigated. An increased adsorption rate along the edges of a the model cube is reached in the initial adsorption phase under consideration of electrostatic and dispersion interactions. At later times also the surfaces of the cube are covered, if the salt concentration is sufficient to screen the repelling protein-protein electrostatic interaction.

Abstract: Bone is a complex natural composite material built of organic and anorganic components and very well adapted to the in vivo loading conditions. The material exhibits an excellent damage resistance under static and fatigue loading conditions. This is partially due to self-healing processes, but to a great extent also to its hierarchical microstructure. The investigation of the deformation behaviour and the damage mechanisms on different length scales gives valuable insight into which level(s) of hierarchy influence the fatigue resistance in which way. In the present work, cyclic deformation tests have been performed on cortical bone specimens. On one hand, stress-strain-hysteresis measurements in different types of tests, such as constant amplitude tests, load increase tests, and combined static and cyclic tests, give information on the active damage mechanisms. For example, changes in the development of the stiffness, non-elastic strain amplitude and non-elastic mean strain as a result of different loading velocities and stress levels allow the discrimination between time and cycle dependent damage mechanisms. These results were correlated with microstructural investigations of the damage development on different hierarchical levels by light and scanning electron microscopy.

Abstract: One the mechanisms of failure in total hip arthroplasty in cemented prosthesis is cement fatigue. The main objective of this work is to use Acoustic Emission (AE) as a non-destructive and non-intrusive monitoring test in a cemented prosthesis. The femoral component was sinusoidally loading in a fatigue machine. Experimental data collected during acoustic emission test was treated and analysed by Wavelet Transform and allowed to locate a crack in cement mantle of femoral component. Other complementary diagnostic tests were used to confirm the existence of a fault (crack). One of them was penetrating liquids in different cut sections of femoral component. The other one was microscopic analysis that allowed observing the existence of a crack which location is pointed out by the results of AE answer. The AE sources locations are situated inside the crack observed in the optical microscope. The Wavelet Transform (WT) AE signals demonstrated the accuracy of damage location in bone cement and thus becoming useful in other orthopedics studies.

Abstract: It has been tried to develop Ti-Ca alloys which demonstrates corrosion resistance in an aqueous fluoride solutions. The Ti-Ca alloys were produced by diffusion-metallizing method. A Ti plate and Ca grains were put in a sealed container of stainless steel. As the container was heated at 1000 oC, Ca was melted and partially vaporized in the inner space. Ca then contacts and permeats into the Ti plate to metallize. In a holding time of 450 h, the alloy surface consisted of two layers, the first was oxide layer and the second was metal layer of about 200 m thick. A Vickers micro hardness of the second layer was quite large, upto about 600 Hv. Evaluation of corrosion resistance for the second layer and the inner part was carried out by electrochemical potentiokinetic method. Test solutions were aqueous fluoride solutions produced with HF and NaF. A concentration of fluoride ion was fixed to 0.024 kmol m-3, and pH of the solution was varied from 3.4 to 4.7. As a result, both Ti and Ti-Ca alloy were passivated under natural immersion condition in the solution of pH 4.7. At pH 3.4, on the other hand, Ti was actively dissolved, but Ti-Ca alloy was still passivated, that means Ti-Ca alloy performs much better corrosion resistance than Ti.

Abstract: Chitosan was used in this study to form polyelectrolyte complex (PEC) with water-soluble acidic polysaccharides, including gum arabic and pectin. Porous membranes made of gum arabic or pectin only were quiet fragile. After incorporating with chitosan, the usability of the membranes was greatly improved. The results showed that the gum arabic/chitosan composite membranes had detectable tensile stress and elongation capability. Moreover, the pectin/chitosan composite membranes had significantly improved tensile stress and elongation capability. Both of the two composite membranes had greater water uptake capability than the membranes composed of chitosan only. We have demonstrated that chitosan can function as a material stabilizer to maintain the solid status of the acidic polysaccharides and thus improve the performance of these acidic polysaccharides.

Abstract: A microbeam X-ray diffractometer is a powerful tool to analyze oriented biological apatite (BAp) crystallites in bones since BAp orientation is one of the dominant controlling factors for bone mechanical function. The formation of BAp orientation seems to be partly affected by the bone formation process, including membranous or intracartilaginous ossification, the direction and the rate of bone growth, the mineral apposition rate, etc. However, the detailed process and the mechanisms of the organization of BAp orientation during the bone formation process are still not understood. In this study, we focused on a calvarial bone as a flat bone to establish a procedure to analyze BAp orientation in calvarial bone and examined the variation in BAp orientation with age and position in growing rats. Microbeam X-ray diffraction analysis was performed on the extracted calvaria of 5- to 10-week-old Wister rats. The transmission optical system was selected to analyze the orientation of the BAp c-axis along the bone surface. An incident molybdenum (Mo)-K X-ray, which was collimated into a 300-m diameter, was vertically radiated on the calvaria surface, and the diffraction pattern was registered on an imaging plate. Diffraction peak intensities from the (002) and (310) planes of the hexagonal BAp were detected, and then an intensity ratio of (002)/(310) was calculated to evaluate the degree of BAp orientation. BAp orientation in a calvarial bone was successfully analyzed, and the two-dimensional distribution of the BAp c-axis along the calvarial bone surface was identified. A parietal bone, which is a part of the calvarial bone, showed a unique two-dimensional distribution of the BAp c-axis. The distribution remarkably changed depending on the position on a parietal bone and age. The anisotropy in the preferred BAp orientation was very significant at a region that showed high growth rate. Even though the bone formation process seems to affect BAp orientation in the parietal bone, further investigation is needed to understand the mechanism for the development of BAp texture, which is closely related to bone mechanical function.

Abstract: Isothermal phase transformation in Ti-15Nb-10Zr (at%) alloys has been examined by mainly means of transmission electron microscopy. Specimens solution-treated at 1000°C in  phase field were directly held at temperatures between 350 and 450°C for 1.8-86.4ks, which are called "DH (direct holding)-specimen". On the other hand, some specimens solution-treated at 1000°C were quenched into iced brine and then aged at temperatures between 350 and 450°C, which are called "QA(quench and aging)-specimen". In the DH-specimen held at 400°C α phase formed in β matrix. Microstructure evolution of QA-specimen aged at 400°C, on the other hand, is as follows.  phase formed in β matrix after aging for 1.8ks and further aging led to growth of  phase. After prolonged aging, α phase started to form in β matrix. These experimental results indicate that process of the quenching and reheating promotes the formation of  phase. Specimen quenched into iced brine after solution treatment exhibited α'' phase formation. The α'' phase in the quenched specimen would transform into β phase during reheating to the aging temperature. Reversion process of α''  β phase could promote the formation of  phase in β. Microstructure formation in the DH- and QA-specimens at 350 and 450°C will also be explained.

Abstract: The diagnosis of hard tissues is generally carried out by bone mineral density (BMD) measurement as a bone quantity parameter. BMD, however, does not necessarily explain bone fracture risks in some clinical cases. Recently, various parameters relating to bone strength have been investigated. These additional parameters, so-called bone quality, reflect intrinsic bone conditions. We have been studying the preferential alignment of the biological apatite (BAp) c-axis among various bone quality parameters. BAp, a dominant component of hard tissue, is an ionic crystal that crystallizes in a hexagonal lattice accompanied with the anisotropic property. In this article, we investigated the osteoclast role in the recovery process of BAp orientation during bone regeneration using osteopetrotic (op/op) mice in which the number of osteoclasts decreases. A surgically drilled, 500-μm diameter hole on each tibia of both control and op/op 8-week-old mice was introduced from the medial surface into the medullary cavity located at a 30% length from the proximal tibia end. After surgery, tibiae injuries were regularly observed by in situ micro-CT, and then the mice were sacrificed four to eight weeks after surgery. BAp orientation was analyzed in and near the regenerated portion by the microbeam X-ray diffraction system. As a result, we found the insufficient recovery of BAp orientation in spite of the apparent repair of bone appearance and quantity from CT images, even eight weeks after surgery in both cases of control and op/op mice. We conclude that this defective animal model can be used to evaluate bone quantity and quality at the cortical portion during bone regeneration in gene-defect mice in which the expression of bone cells is controlled, for example.