Materials Science Forum Vols. 783-786

Abstract: Poly (L-lactide-co-D/L-lactide)-based fiber meshes resembling structural features of the native extracellular matrix have been prepared by electrospinning. Subsequent coating of the electrospun fibers with an ultrathin plasma polymerized allylamine (PPAAm) layer changed the hydrophobic nature of the polylactide surface into a hydrophilic polymer network and provided positively charged amino groups on the fiber surface able to interact with negatively charged pericellular matrix components. Cell experiments in vitro using different types of human epithelial cells (gingiva, uroepithel) revealed that the PPAAm-activated surfaces promoted the occupancy of the meshes by cells accompanied by improved initial cell spreading. An in vivo study in a rat intramuscular implantation model demonstrated that the local inflammatory tissue response did not differ between PPAAm-coated and untreated polylactide meshes.

Abstract: The work presents an innovative, interactive device used to support the rehabilitation process in small children with lower limbs dysfunction. The presented equipment combines movement therapy with simultaneous psychological stimulation of the child. EEG sensor measures the activity of the child’s brain waves and at the same time functions as the controller of the rehabilitation process. Application of the discussed equipment in the process of rehabilitation of children supports their optimal development within individual limits.

Abstract: The development of the implant material which works much like bone must be an intrinsic approach to reduce the mechanical mismatch. Bone expresses the anisotropy of the mechanical characteristics based on the microstructual adaptation attributed to the apatite c-axis orientation corresponding to in vivo stress distribution. Therefore, the control of microstructure of implant material was performed by laser beam sintering technique aiming at the modification of mechanical property. The Co-Cr alloy products with three-dimensional geometry were successfully fabricated by laser beam sintering based on the design model. The grain showed an elongated dendritic morphology and aligned along the build direction during laser beam sintering. The crystallographic texture was developed responsible for the macroscopic heat flow along the build direction rather than the macroscopic one through the structures. Thus, the microstructure involving the grain morphology and crystallographic texture formation was anisotropically controlled by laser beam sintering technique. The mechanical properties could be modified anisotropically by the oriented microstructure in the Co-Cr alloy structures with three-dimensional geometry for the biomedical applications.

Abstract: L605 (ASTM F90), a cobalt-chromium-tungsten alloy with excellent mechanical properties and high radiopacity, has been widely accepted as a suitable alloy for stent applications. The presence of carbides in this alloy, primary carbides and secondary carbides, leads to difficulties in controlling mechanical performances and therefore in optimizing stent size and performances. This work is thus to investigate the carbides and their role in advanced mechanical properties of L605 alloy for stent fabrication. Herein, the nature, nucleation, distribution and dissolution of the carbides were investigated in a series of recrystallized L605 tubes from hard-drawn (HD) state. The mechanical properties corresponding to each carbide state were examined by tensile tests and microhardness measurements. The results indicate important relationships among carbide precipitation, grain size and mechanical behaviors, as a function of annealing temperature and duration. The intergranular secondary carbides, induced at the onset of the recrystallization of L605 matrix, were preferentially precipitated at grain boundaries. The nucleation of such particulate phase leads to a pinning effect on grain coarsening, resulting in a strengthening effect of the material. However, the further growth of the secondary carbides brings about considerable reduction of ductility, which is inacceptable for stent application. Therefore, an optimization protocol on carbides controlling was developed to maintain the strengthening effect without losing ductility and small grain size.

Abstract: Titanium alloys typically exhibit a limited ductility (typically 20%) and little strain-hardening. An alloy design with new concept was conducted aiming at improving both ductility and strain hardening while keeping the mechanical resistance at an excellent level. An experimental validation was illustrated with the Ti-12(wt.%)Mo alloy, exhibiting true stress - true strain values at necking, of about 1000MPa and 0.38, respectively, with a large strain hardening rate close to the theoretical limit. In order to clarify the origin of this outstanding combination of mechanical properties, detailed microstructural investigation and phase evolution analysis were conducted by means of in-situ synchrotron XRD, in-situ light microscopy, EBSD mapping and TEM microstructural analysis. In the deformed material, combined Twinning Induced Plasticity (TWIP) and Transformation Induced Plasticity (TRIP) effects are observed. Primary strain/stress induced phase transformations (β->ω and β->α’’) and primary mechanical twinning ({332}<113> and {112}<111>) are simultaneously activated in the β matrix. Secondary martensitic phase transformation and secondary mechanical twinning are then triggered in the twinned β zones. The {332}<113> twinning and the subsequent secondary mechanisms are shown to be dominant at the early stage deformation process. The evolution of the deformation microstructure results in a high strain hardening rate (~2GPa) bringing both a high tensile strength and a large uniform elongation.

Abstract: We have previously established a wet synthesis method of octacalcium phosphate (OCP) in a relatively large scale and found that OCP enhances bone formation more than synthetic hydroxyapatite (HA) if implanted onto bone surface and various bone defects. The present paper reviews, based on our studies, as to how OCP controls in vitro cellular activities of bone-related cells, such as bone marrow stromal cells, and how OCP enhances bone repair in critical sized bone defect experimentally created in animal models. OCP tends to progressively convert to HA in culture media and in rat calvaria defects. OCP is capable of enhancing in vitro osteoblast differentiation and osteoclast formation in the presence of osteoblasts. Recent our studies also indicated that OCP enhances odontoblast differentiation while suppresses chondrogenic differentiation. The physicochemical properties, such as chemical composition and adsorption affinity of serum proteins, vary depending on the advancement of conversion from OCP to HA, which suggests that the change on the surface property during the conversion of OCP may affect the cellular responses in vitro and tissue reaction in vivo. OCP could be used as a scaffold material that can control the activity of bone-related cells.

Abstract: The electron-atom ratio (e/a) dependence of the appearance of the lattice modulation and physical properties in β-phase Ti-xNb alloys (x = 28, 30, 34 and 40) were investigated by using some physical properties measurements, compressive test and transmission electron microscope observations (TEM observations), focusing on the β-phase stability. The microstructure, physical properties, deformation mode depend on the e/a ratio which is closely related to the β-phase stability in Ti-Nb alloys. The e/a ratio is defined by the average electrons per atom in free atom configuration. Athermal ω-phase is suppressed in Ti-30Nb alloy single crystal with low e/a ratio. The Ti-30Nb alloy single crystal also exhibits a lattice modulation and low Debye temperature. These results imply that the β-phase stability in β-phase Ti alloys decreases with decreasing the e/a ratio and are related to the softening of elastic stiffness, c′. Consequently, a decrease in the e/a ratio leads to the softening of c′ and a significant reduction in modulus along the [100] direction in β-phase Ti alloys single crystal. In fact, the Young’s modulus along [100] of the Ti-15Mo-5Zr-3Al alloy (wt.%) single crystal with low e/a ratio exhibits as low as 45 GPa, which is comparable to that the human cortical bone. That is, controlling the e/a ratio is an ultimate strategy to develop the future superior biocompatible implant materials with extremely low Young’s modulus and good deformability.

Abstract: Titanium (Ti) is one of the most widely used for biomaterials, because of its excellent anti-corrosion and high mechanical properties. In addion to these properies, the bioactivity of Ti is required. Recently, coating of the titanium dioxide (TiO₂) film on Ti plate surface is useful methods to obtain biocompatibility of Ti plate. If periodic nanostructures were formed on the film surface, direction of cell spreading might be controlled due to grooves direction. Then, femtosecond laser is one of the useful tools of periodic nanostructures formation. Peiriod of periodic nanostructures might be varied by changing the laser wavelength. In the experiments, the film was formed on Ti plate with an aerosol beam which was composed of submicron size TiO₂ particles and helium gas. The film was irradiated with the femtosecond laser. Laser wavelengths of the laser was at 1044, 775 and 388 nm, respectively. Periodic nanostructures, lying perpendicular to the laser electric field polarization vector, were formed on the film by femtosecond laser irradiation at 1044, 775 and 388 nm, respectively. The period of the periodic nanostructures on the film produced by femtosecond laser irradiation at 1044, 775 and 388 nm was about 350, 230 and 130 nm, respectively. In the cell test, cell spreading along the grooves of the periodic nanostructures was observed although it was not done for the film without the periodic nanostructures. These results suggested that direction of cell spreading could be controlled by the periodic nanostructures formation

Abstract: Titanium and its alloys have been employed in bone plates/screws, which must be removed after recovery. Conduction of bone occurs on the surface of Ti alloys that reside in the body for a long period. This can lead to re-fracture of cured bone in removal operations. On the other hand, bone has been reported not to be formed on the surface of Zr alloys. The purpose of this study was to synthesize Zr-containing TiO₂ film on commercial purity titanium (CP-Ti) by chemical-hydrothermal treatment. In addition, apatite formation on the films in Hanks’ solution and bone conduction in the tibiae of rats were also investigated. CP-Ti substrates were chemically treated with H₂O₂/HNO₃ aqueous solutions at 353 K for 20 min. The substrates were hydrothermally treated with ZrOCl₂/NH₃/hydroxy acid aqueous solutions in a Teflon-lined autoclave at 453 K for 12 h. The hydroxy acid was selected to be C₃H₆O₃ (lactic acid), C₄H₆O₆ (tartaric acid) or C₆H₈O₇ (citric acid). In the hydrothermal treatment without hydroxy acid, the surface product was anatase-type TiO₂. In contrast, when hydroxy acid was added the surface of Ti was covered homogeneously with a Zr-containing TiO₂ film. Some of the Zr (OH)₄ sol in the solution is thought to have dissolved into the solution by coordinate bonding with hydroxy acid carboxyl groups, leading to incorporation of Zr as ZrO₂ into the TiO₂. The product films suppressed the apatite precipitation in the Hanks’ solution soaking. In animal test, the small amount of ZrO₂ effectively suppressed the bone conduction.

Abstract: Bacterial contamination of biomedical devices is an ongoing problem. One method to alleviate such contamination is the introduction of surface compounds onto devices which can kill bacteria on contact. Polymers containing quaternary ammonium groups are known for their antimicrobial properties. Here we report a substrate-independent two-step method for the immobilisation of quaternary ammonium groups onto any type of surface. To achieve this glycidlytrimethylammonium chloride was covalently bound to plasma polymerised allylmine interlayer. Changes in the membrane permeability of Escherichia coli were observed by BacLight LIVE\DEAD staining. 30% of E. coli grown on the treated surfaces showed high levels of membrane permeability within 4 hours. Importantly, there was no observable cytotoxic effect on human dermal fibroblasts.