Materials Science Forum Vols. 539-543

Abstract: Plain and notch fatigue properties of a β-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ), which was subjected to various thermomechanical treatments, were investigated in order to judge its potential for biomedical applications. Microstructures of TNTZ aged at 723 K for 259.2 ks after cold rolling and those aged at 723 K for 259.2 ks after solution treatment are composed of a precipitated α phase in the β phase. However, microstructures of TNTZ aged at 598 and 673 K for 259.2 ks after cold rolling and aged at 598 K and 673 K for 259.2 ks after solution treatment are composed of a precipitated ω phase, and precipitated α and ω phases in the β phase, respectively. Futher, plain fatigue strengths of TNTZ aged after solution treatment and those of TNTZ aged after cold rolling increase with the aging temperature. In particular, TNTZ aged at 723 K after cold rolling exhibits the highest fatigue strength in both the low- and high-cycle fatigue life regions. Futher, the run-out, which is about 770 MPa, is nearly equal to that of hot-rolled Ti-6Al-4V ELI conducted with aging, which is one of the representative α+β-type titanium alloys for biomedical applications. The notch fatigue strengths of TNTZ aged at stress concentration factors of 2 and 6 decrease by 30% – 40% and 50% – 60%, respectively, as compared with the plain fatigue strengths in the low-cycle fatigue life region. Futher, the notch run-out range from 450 to 490 MPa and from 220 to 300 MPa, respecitvely; an exception to this is TNTZ aged at 598 K after cold rolling, which has a high volume fraction of the ω phase. Single- and multi- fatigue cracks initiate at the bottom of the notch at stress concentration factors of 2 and 6, respectively.

Abstract: Application of metals will be expanded to new medical devices, scaffold for tissue engineering, artificial organs, etc. with the addition of biofunction. Therefore, immobilization or combination of functional polymers to metals is significant subject for the application of metals to biofunctional materials and sensors. Metal-polymer hybrid materials are promising biomaterials future, especially for artificial organs. To form metal-polymer hybrid for biomedical devices, two techniques are predominant according to the purpose: Immobilization of biofunctional polymers to metals and bonding of biopolymers with metals. In the first case, poly(ethylene glycol: PEG) is a biofuctional molecule on which adsorption of proteins is inhibited. Control of immobilization mode of PEG modified with NH2 to titanium surface by electrodeposition is feasible and the adsorption of proteins is inhibited by the deposited PEG. This technique could be applied to all metallic materials. In the other case, we attempted to form a composite of titanium with segmentated polyurethane (SPU) thorough silane-coupling agent (γ-MPS). This composite material is applied to texture of titanium covered by SPU as artificial organs.

Abstract: The development of tissue engineering provides a novel approach to restore bodily functions by seeding cells onto various scaffolds. Although chitosan is a non-toxic biomaterial, its cytocompatibility still needs to be improved. In this study, gamma-poly(glutamic acid) (γ-PGA) was blended with chitosan to prepare both dense and porous γ-PGA/chitosan composite scaffolds using the freeze-gelation method. This method saves time and energy, and there is less residual solvent. SEM micrographs demonstrated that an interconnected porous structure with a pore size of 30-100 micrometer was present in the scaffolds. The hydrophilicity of the scaffolds was significantly improved by γ-PGA. Further, the tensile strength of the porous γ-PGA-modified chitosan scaffolds was about 50% higher than that of the unmodified chitosan scaffolds. The number of osteosarcoma cells cultured on the γ-PGA-modified scaffolds was about double that on the unmodified chitosan scaffolds on day 7. Thus, the γ-PGA/chitosan composite scaffolds, due to their better hydrophilicity, cytocompatibility, and mechanical strength, are very promising biomaterials for tissue engineering applications. We further demonstrated the use of glutamic acid to enhance the tensile strength of chitosan-based composite porous scaffolds. The tensile strength of the chitosan/collagen composite scaffolds was increased by more than 2 times with the addition of glutamic acids as cross-linking bridges. We found that the hepatocytes attached and proliferated well on these composite scaffolds, demonstrating that the glutamic acid modified-chitosan composite scaffolds are also potential tissue engineering biomaterials.

Abstract: Degradation studies of PP and PVDF monofilaments were carried out using a special chamber for several periods of time. One set of the samples was exposed to a 0.9 % NaCl solution and to ultraviolet radiation at 830 C and the other set involved the exposition in air under the same conditions of irradiation and temperature. Scanning Electron Microscopy (SEM) analysis showed direct evidence of PP degradation. Meanwhile, the PVDF monofilaments showed no apparent evidence of degradation under the same conditions. Differential Thermal Analysis (DTA) curves, FTIR spectra and Oxidation Induction Time experiments confirmed the results of SEM Analysis.

Abstract: The paper presents the first part of the work focused on preparation of biodegradable chitosan microcapsules with tailored properties for potential applications in medical field as drug temporary carriers. In this paper, we aimed to prepare chitosan and chondroitin sulphate microcapsules using TPP as the second cross-linker and investigate the formation of the capsule membrane and its permeability in dependence on conditions of polyionic complexation. As a model, TPP was used to assess an influence of concentration and reaction time on the microcapsule formation. The method of inverse SEC was used for pores size and permeability limit of capsules assessment. For chitosan/CHS/TPP capsules, the distribution of pores size in the membrane is rather broad, which can be suitable for applications in tissue engineering and drug delivery systems.

Abstract: Hydroxyapatite-based materials have been used for dental and biomedical applications. Newly developed synthesis techniques give cause to a broad field in the study of these materials and industry demands products with better properties day by day. The purpose of the present work was to evaluate the mechanical properties of hydroxyapatite-based (HAp-based), organic-inorganic composites. HAp-based, organic-inorganic composites were obtained by modified gel casting process and organic molecules in a gelatin solution. HAp samples of different sizes and shapes were obtained with controlled micro and macro porosity and then were immersed into several gelatin solutions with different concentrations. X-ray powder Diffraction (XRD), Infra Red (IR) Spectroscopy and Scanning Electron Microscopy (SEM) techniques were used to analyze samples before and after gel casting process in order to assure that chemical and physical properties remains the same after this process. IR Spectroscopy and SEM techniques were used to characterize samples after the introduction of organic phase in order to analyze the final morphology of samples. Mechanical characterization was made in compression mode to samples without and with different concentrations of organic phase in order to establish the optimum conditions in which the highest compressive strength and Young’s modulus is reached.

Abstract: In order to decrease its degradation rate, pure magnesium was subjected to the following treatments: (1) heat treatment at 345oC for 15 min and (2) heat treatment at 380°C for 30 min followed by hot rolling at 350°C. The treated samples and non-treated controls were immersed in simulated body fluid (SBF) at 37oC for different periods of time. In all cases, the magnesium released into the SBF, the weight loss of the specimens and the pH of SBF increased with time of immersion. The hot-rolled samples showed a lower degradation rate and lower pH values. A lower increase of magnesium concentration in the SBF corresponding to the hot-rolled samples was also observed. The main and unexpected positive finding of this work was that in all cases, a layer of Ca, P-rich was formed on the substrates after only 3 days of immersion in SBF. This indicates that metallic magnesium is a potential bioactive material. In the aim to promote the formation of a thicker bioactive layer than the one observed on the samples immersed in single SBF, hot-rolled magnesium was biomimetically-treated using wollastonite ceramics, SBF and a more concentrated solution (1.5 SBF). A homogeneous and dense bone-like apatite layer was observed on the biomimetically-treated samples.

Abstract: Interest in microcantilever based biosensors in the biomedical field has largely increased during the last years. Potentially, this kind of sensor can provide a considerable contribution to complex disease diagnosis, which requires the detection of biological molecules. Microcantilever biosensors allow the detection of complementary DNA fragment hybridization or specific antibody-antigen binding; it is known that adsorption of specific biological molecules upon the microcantilever surface induces cantilever deflection due to the interaction of the molecules with the surface. To date, the phenomena which determine the deflection mechanism are not completely known. The present work investigates the electrostatic field within the molecules and the forces consequently acting on the molecules and on the cantilever in order to provide a description of the deflection mechanism. The electrostatic potential of arrays of double strand DNA molecules immersed in an ionic solution was modelled by means of cylinders negatively charged at the surface and a FE (Finite Element) continuum electrostatics analysis was implemented in order to numerically solve the second order non-linear Poisson-Boltzmann equation. Then, a FE structural analysis of the cantilever was performed coupled with the continuum electrostatics analysis. In this way, the effects of the molecules’ electrostatic interactions on the cantilever deflection were taken into account. The model was run to describe the microcantilever deflection due to the electrostatic field under different design and operating conditions, and it was also set to compare hexagonal and square disposition of double strand DNA molecules.

Abstract: The use of specific remineralizing agents in toothpastes may help to prevent caries and treat dentinal sensitivity. In this study, applied nanotechnologies were used to develop a filler for toothpastes with remineralizing properties. Carbonate hydroxyapatite nanocrystals, with size, morphology, chemical composition and crystallinity comparable with that of dentine, were synthesized in mild condition. The remineralizing effect was studied with a scanning electron microscopy putting materials onto the slices of dentine previously demineralized with ortophosphoric acid. The application of the materials showed the progressive closure of the tubular openings of the dentine with plugs within 10 minutes and a regeneration of a surface mineral layer within 6 hours. This rates of remineralization seems to be compatible with the development of toothpastes with remineralizing effect.