Materials Science Forum Vols. 706-709

Abstract: A novel biomedical titanium alloy with the ability to undergo self-adjustment in its Young’s modulus was developed. In spinal fixation devices, the Young’s modulus of the metallic implant rod should be sufficiently high to suppress springback for the surgeon, but should also be sufficiently low to prevent stress shielding for the patient. Therefore, deformation-induced ω phase transformation was introduced into β-type titanium alloys so that the Young’s modulus of only the deformed part would increase during operation, while that of the non-deformed part would remain low. The increase in the Young’s modulus due to cold rolling was investigated for a binary Ti-12Cr alloy (mass%). Microstructural observation and Young’s modulus measurement reveal that the Ti-12Cr alloy undergoes deformation-induced ω phase transformation and exhibits the increase in the Young’s modulus by deformation.

Abstract: Co-Cr-Mo based alloys have been widely employed as heat resistant materials and as biomaterials for implants because of their high strength and superior wear resistance. In general, the alloys exhibit a very complicated composition-dependent microstructure containing stacking faults and related mechanical properties. Thus, the essential properties must be clarified by using not only polycrystals but also single crystals. To our knowledge, single crystals and related properties have not been reported elsewhere. Thus, Co-Cr-Mo single crystals were grown and used to analyze the microstructure and the related properties. Single crystals with a composition Co-27 mass% Cr-6 mass% Mo alloy defined by ASTM F75 were grown by two single crystal apparatuses: the optical floating zone and the Bridgman methods. The single crystals with the smooth-surface shape were successfully obtained in the Bridgman method under an Ar gas atmosphere at a crystal growth rate of 5.0 or 2.5 mm/h. A portion of the crystals contain Al as Al₂O₃ precipitates from the crucible. Since the Al₂O₃ precipitate induces martensitic phase transformation from fcc (γ) phase to hcp (ε) phase, the single crystals were separated into two parts (a) containing Al₂O₃ precipitate and (b) in the absence of the clear precipitate. The microstructure was significantly altered by the martensitic phase transformation from the γ to ε phase induced by stress field or heating. In addition, variant formation of ε phase has a large influence on the mechanical functions of these Co-Cr-Mo alloys. Novel findings were preliminary obtained in the single crystals.

Abstract: Synthetic materials such as bone substitutes are permanently under development for applications in orthopedic and trauma surgery. Our porous scaffolds were produced from ß-tricalcium phosphate (TCP) using the three dimensional (3D)-printing technology. After sintering the porosity and the pore size of the 3D printed scaffolds reached nearly 50 % and 500 µm, respectively. TCP scaffolds were additionally stabilized by infiltration with polylactic acid (PLA). Because PLA usually impeded cell adhesion we activated the composite surface with plasma polymerized allylamine in a low temperature plasma process. For cell investigations inside the scaffold we used a module system, where two porous discs can be horizontally fixed within a clamping ring. Thereby a 3D cell culture module with four levels and a maximal height of 10 mm was generated. Human MG-63 osteoblasts (ATCC) were seeded apically and placed in serum-containing DMEM. After 14 days of a static cell culture the cell ingrowth and mobility was analyzed by scanning electron microscopy. Osteoblast's initial adhesion and short time occupation of the surface is significantly improved on plasma polymer activated TCP surfaces, which could be a precondition for an enhanced colonization inside a calcium phosphate scaffold. Interestingly, the plasma functionalization of the pure TCP scaffold was possible and successful concerning cell acceptance.

Abstract: Small caliber vascular replacement (<4 mm) still remains a challenge for medical and research teams, as no available vascular substitutes (VS) are suitable for small diameter bypass. Vascular engineering proposes new models of small diameter VS but rare are those that meet the biocompatibility and mechanical criteria. In this study, we developed a new scaffold made by the combination of two natural biomacromolecules: collagen and silk fibroin. The scaffold was further cellularised with porcine smooth muscle cells. First, the behavior of cells in the collagen-fibroin constructs was verified in order to evaluate the biocompatibility of the scaffold with the cells. Then, gel mass loss and cellular attachment, morphology, spreading and viability were analysed. The results showed an excellent interaction and biocompatibility between collagen, silk fibroin fibers and cells. Thus, the collagen-fibroin construct appears to be a very attractive material for vascular tissue engineering.

Abstract: During the last few decades, titanium alloys are more and more popular and developed as biomedical devices because of their excellent biocompatibility, very good combination of mechanical properties and prominent corrosion resistance [1-3]. Recently, a new generation of beta titanium alloys dedicated to biomedical applications has been developed. Based on biocompatible alloying elements such as Ta, Nb, Zr and Mo, these alloys were designed as low modulus alloys [4] or nickel-free superelastic materials [5, 6] mainly for orthopedic or dental applications as osseointegrated implants. Beta type titanium alloys take great advantages from their capacity to display several deformation mechanisms as a function of beta phase stability. Therefore, from low to high beta stability, stress assisted martensitic phase transformation (β-α’’), mechanical twinning or simple dislocation slip can alternatively be observed [7]. As a consequence, a very large range of mechanical properties can be reached, including low apparent modulus, large reversible elastic deformation or high yield stress. Although titanium alloys display now a long history of successful applications in orthopedic and dental devices, none of them have been commercially exploited in the area of coronary stents, despite their superior long term haemocopatibility compared to the 316L stainless steel. However, according to previous researches on the biocompatibility of various metals, the corrosion behavior of stainless steel is dominated by its nickel and chromium components, which may induce redox reaction, hydrolysis and complex metal ion–organic molecule binding reactions, whereas none are observed with titanium [8, 9].

Abstract: Electrospinning technique is an efficient processing method to manufacture micro-and nanosized fibrous structures by electrostatic force for different applications. In biomaterial field, electrospinning technique has been successfully utilized to prepare new drug delivery materials and tissue engineering scaffolds. Fiber mats of biodegradable polymers having a diameter in the nanoto submicro-scale can be considered to mimic the nanofibrous structure of native extracellular matrix (ECM). Native extracellular matrix, constituted of proteins and polysaccharides improving cells growth in its nanofibrous porous structure, controls not only the cell phenotype, but the whole structure of the biological tissues. In the present study we investigated the effect of electrospun reconstituted collagen fibers onto metals for oral implants devices manufacturing as far as the osteoblastic differentiation potential of stem cells and cytofunctionality of osteoblasts in-vitro. The cells cultured onto titanium samples coated with ECM constituents showed faster osteoblastic differentiation and more efficient deposition of mineralized matrix in comparison with those onto uncoated substrates.

Abstract: Material science is taking an increasing important role in bioengineering and biomedical sciences, aiming to develop new systems and materials capable of adapting to the highly demanding environment of a living organism. One of those materials, Hydroxyapatite (HAp), is the principal calcium orthophosphate present in the mineral phase of bone.

Abstract: Collagen-based materials were prepared and their properties were studied. The shape of collagen materials was as follows: thin films, hydrogels, and sponges. Microstructure and mechanical properties of films and sponges were studied. The effect of cross-linking agents and the effect of synthetic polymer on the properties of collagen materials were studied and analyzed. Collagen-based materials can be considered as potential biomaterials in tissue engineering.

Abstract: The paper present the analysis of metal prosthesis head stress state of hip joint endoprosthesis which is a result of variable loads during human motor activity and its influence on the erosion of materials. The analysis of stress state was made with use of FEM – ADINA numerical tool. The analysis of surface erosion process was made with use of the scanning electron microscope. To the researches was taken for heads from CoCrMo bearing shell and polyethylene UHMWPE.

Abstract: The developed Mg-based metallic glass shows great potential as implants in biomedical applications instead of crystalline Mg alloys, which may possesses acceptable corrosion properties. In this study, corrosion behaviors of melt-spun amorphous Mg₆₇Zn₂₈Ca₅ ribbons were investigated in physiological saline solution. Electrochemical testing and hydrogen evolution rate indicated that the glassy ribbons obtained at lower wheel speed were more noble with smaller corrosion current, and possessed a comparatively lower corrosion rate in physiological saline solution. Surface morphology analysis revealed that glassy Mg₆₇Zn₂₈Ca₅ ribbons exhibited a strong susceptibility to localized pitting corrosion. A Zn-rich passive layer was formed on the surfaces of the glassy ribbons, indicating that Zn was an effective alloying element to enhance the corrosion resistance of amorphous Mg₆₇Zn₂₈Ca₅ alloys.