Materials Science Forum Vols. 638-642

Abstract: A range of benefits of implants containing hydroxyapatites results, among other things, from their phase composition and degree of porosity. Poor mechanical properties of hydroxyapatite (HA) ceramics considerably limit its wider use. One of the methods for improvement of poor HA properties is addition of solid solution of Y2O3 in ZrO2. [1-8]. The investigations focused on compositions of ceramic powders based on hydroxyapatite with addition of zirconium dioxide (ZrO2 + 8%wt. Y2O3 and ZrO2 + 20%wt. Y2O3). The powders were axially compacted and then sintered at the temperature of 13000C for two hours. After the process of sintering the samples were subjected to analysis of microstructure, phase composition and geometrical measurements in order to determine volume density in each sample.

Abstract: Amid increasing numbers of artificial joint implantation surgeries, improving the quality of life (QOL) for patients by accounting for individual variation is a primary concern. Thus, we aim to develop implants designed to optimize the interface between implant and living bone. In particular, for ensuring long-term durability and stability after implantation, we focused on inducement of appropriate alignment for biological apatite (BAp) crystallites and the related collagen (Col) fibers as a bone quality parameter. In this study, we predicted that when stress is applied to bone, the BAp/Col preferential alignment can be formed on the basis of our previous result if osteocytes, which can sense its around stress field, are in an environment that is aligned with the principal stress vector. We tested this idea by introducing grooves with the different angles on the implant surface, considering the principal stress direction. This study finally analyses the effect of stress transmission by a load at the proximal femur on the bone inside and near the grooves by using a mechanical simulation in which groove angles and positions can be changed on the implant surface. Furthermore, we carried out animal experiments using a 2-years-old beagle to examine the effect of grooves in the principal stress direction on the surface in vivo. As a result, bone formation in grooves on the implant surface strongly depends on the grooved angle to the principal stress vector and the grooved position on implants. The new bone preferentially formed inside the grooves parallel to the principal stress direction predicted by three dimensional finite element analysis (FEA) in the proximal area of beagle femur.

Abstract: Microfiber meshes releasing a trace amount of silicon species were prepared by electrospinning silicon-doped vaterite (SiV) and poly(lactic acid) (PLA) hybrids for application to membranes for guided bone regeneration (GBR). A trace amount of silicon-species has been reported to enhance the mineralization and bone-forming abilities of osteogenic cells. The microfiber meshes prepared by electrospinning are regarded to be a useful candidate for the GBR membrane, because they have adequate flexibility and porosity for it. In this study, hydroxyapatite (HA)-forming abilities in simulated body fluid, silicon-releasabilities, compatibility with osteoblast-like cells of the prepared microfiber meshes were examined. The meshes were completely coated with HA after soaking in simulated body fluid for 1 day. The meshes coated with HA released 0.2 -0.7 mg/L of silicon species in a cell culture medium for 7 days. The cells elongated on the microfibers of the meshes and some of them entered the mesh after 1 day-culturing. The meshes are expected to provide an excellent substrate for bone regeneration and enhance bone-forming ability of the cells.

Abstract: Current research focuses on magnesium based alloys in the course of searching a resorbable osteosynthetic material which provides sufficient mechanical properties besides a good biocompatibility. Previous studies reported on a favorable biocompatibility of the alloys LAE442 and MgCa0.8. The present study compared the degradation process of cylindrical LAE442 and MgCa0.8 implants after 12 months implantation duration. Therefore, 10 extruded implants (2.5 x 25 mm, cross sectional area 4.9 mm²) of both alloys were implanted into the medullary cavity of both tibiae of rabbits for 12 months. After euthanization, the right bone-implant-compound was scanned in a µ-computed tomograph (µCT80, ScancoMedical) and nine uniformly distributed cross-sections of each implant were used to determine the residual implants´ cross sectional area (Software AxioVisionRelease 4.5, Zeiss). Left implants were taken out of the bone carefully. After weighing, a three-point bending test was carried out. LAE442 implants degraded obviously slower and more homogeneously than MgCa0.8. The mean residual cross sectional area of LAE442 implants was 4.7 ± 0.07 mm². MgCa0.8 showed an area of only 2.18 ± 1.03 mm². In contrast, the loss in volume of LAE442 pins was more obvious. They lost 64 % of their initial weight. The volume of MgCa0.8 reduced clearly to 54.4 % which corresponds to the cross sectional area results. Three point bending tests revealed that LAE442 showed a loss in strength of 71.2 % while MgCa0.8 lost 85.6 % of its initial strength. All results indicated that LAE442 implants degraded slowly, probably due to the formation of a very obvious degradation layer. Degradation of MgCa0.8 implants was far advanced.

Abstract: Material science is playing an increasing role in bioengineering and biomedical sciences, aiming to develop new systems and materials capable of overcoming the highly demanding environment of a living organism. One of those materials, Hydroxyapatite (HAp), is the principal calcium phosphate present in the mineral phase of bone. Hydroxyapatite-based materials have been used for dental and biomedical applications, and the control of morphology and structure at micro and nanoscale levels in the synthesis processes, is crucial for several of those applications. Hydroxyapatite crystalline particles were obtained by the so-called sol-gel technique, in which silica gels induce the formation of apatite particles in a simulated body fluid at nearly 37°C, different chemical additives were used to control morphology and particle size, as previously reported by our group. Recently, the synthesis of HAp particles with similar morphologies obtained by different methods, have been reported by other groups. Differences and similarities in morphologies, as well as in the synthesis processes, are established in the present work, along with a discussion of possible crystal growth and assembly mechanisms, which lead to a better understanding of the particle growth processes, is included. This knowledge could be the basis for further synthesis methods aimed to obtain HAp nanostructures with a crystal preferential orientation.

Abstract: Composite systems composed of nanocrystalline apatites and oligolactide-based polymer networks were prepared resulting in malleable and even injectable formulations which can be cured to compact materials at body temperature. Porous devices with inter-connective porosity were obtained after addition of suitable foaming agents to the composite mixtures. Setting time, porosity and mechanical properties of the composites can be properly adjusted by varying the educt composition. The determined compressive strengths and Young’s moduli of the porous composites perfectly match the mechanical characteristics of cancellous bone material. Preliminary in vitro cell culture experiments with compact composite materials demonstrated their good cytocompatibility. Based on these findings, the synthesized nano-structured composites represent promising candidates for the development of new biomaterials usable in hard tissue regeneration.

Abstract: Composite systems composed of nanocrystalline apatites and oligolactide-based polymer networks were prepared resulting in malleable and even injectable formulations which can be cured to compact materials at body temperature. Porous devices with inter-connective porosity were obtained after addition of suitable foaming agents to the composite mixtures. Setting time, porosity and mechanical properties of the composites can be properly adjusted by varying the educt composition. The determined compressive strengths and Young’s moduli of the porous composites perfectly match the mechanical characteristics of cancellous bone material. Preliminary in vitro cell culture experiments with compact composite materials demonstrated their good cytocompatibility. Based on these findings, the synthesized nano-structured composites represent promising candidates for the development of new biomaterials usable in hard tissue regeneration.

Abstract: A crucial factor for in-growth of metallic implants in the bone stock is the rapid cellular acceptance whilst prevention of bacterial adhesion on the surface. Such contradictorily adhesion events could be triggered by surface properties. There already exists fundamental knowledge about the influence of physicochemical surface properties like roughness, titanium dioxide modifications, cleanness, and (mainly ceramic) coatings on cell and microbial behavior in vitro and in vivo. The titanium surface can be equipped with antimicrobial properties by plasma-based copper implantation, which allows the release and generation of small concentrations of copper ions during contact with water-based biological liquids. Additionally, the titanium surface was equipped with amino groups by the deposition of an ultrathin plasma polymer. This coating on the one hand does not significantly reduce the generation of copper ions, and on the other hand improves the adhesion and spreading of osteoblast cells. The process development was accompanied by physicochemical surface analyses like XPS, FTIR, contact angle, SEM, and AFM. Very thin modified layers were created, which are resistant to hydrolysis and delamination. These titanium surface functionalizations were found to have either an antimicrobial activity or cell-adhesive properties. Intramuscular implantation of titanium samples coated with the cell-adhesive plasma polymer in rats revealed a reduced inflammation reaction compared to uncoated titanium.

Abstract: Residual stress has large effect to the service life of biomedical ceramic coatings. It is therefore important to characterize it precisely. Since in-service damage of the prostheses is generally characterized by cracking of the substrate layers located close to the metal / ceramic interface, our study was focused on these particular zones of the parts. High energy synchrotron radiation diffraction techniques were therefore developed to evaluate the residual stress profiles of the metal / ceramic interfaces. The method requires, however, defining precisely the true position of the X-ray probe inside the materials. A complete modeling of the instrument, using a ray tracing Monte Carlo simulation method, was developed for that purpose. Fourier analysis of the diffraction peaks was also implemented to evaluate the micro stresses of second and third kind. These diffraction techniques were tested on a glassy ceramic coating used for the manufacturing of dental prostheses.

Abstract: In the Ti-6Al-4V-ELI alloy, the alpha phase is gradually transformed into the beta phase until beta-transus temperature ( 980°C) is reached, and the transformation is completed. It is important to identify the transformation kinetics to accomplish the solution heat treatments in which a phase alpha percentage remains unchanged. Kinetics and other transformation characteristics are evaluated, as well as their influence on subsequent cooling transformations, by differential and dilatometric thermal analysis, electric conductivity measurements, hardness measurements and metallographic observation, after performing controlled thermal treatments. Starting from the mill annealed condition, samples were heated at temperatures between 650-1000 °C for 1 hour, then water quenched and subsequently heated for aging, air cooled. Finally, the mechanical properties of samples heat treated were obtained.