Advanced Materials Research Vol. 409

Abstract: Metallic intravascular stents are medical scaffolds commonly used to heal diseased arteries and to restore blood flow in vessels after a balloon angioplasty. Although clinical complications occurs (mainly in-stent-restenosis, representing 30-40% of cases within six months after angioplasty), this clinical procedure reduces the risk of restenosis. In order to improve the long-term clinical performances of stents, different coatings, bioactives or not, are investigated. However, the adhesion of the coating within the substrate is often weak and delamination after stent deployment could be observed. Therefore, our approach was to consider a plasma fluorocarbon film deposit on stainless steel substrates, improving adhesion and providing protection against the stent corrosion, as a carrier for the subsequent grafting of a polysaccharide (dextran). Indeed, a copolymer made of dextran and metacrylate has already demonstrated interesting results toward cell proliferation and appropriate mechanical properties regarding stent deployment. Hence, the aim of this project is to covalently graft the copolymer of dextran-methacrylate to plasma-aminated fluorocarbon film. In this study, dextrans were functionalized in order to conjugate them to amino groups. Two different ways of functionalization were investigated: by carboxylmethylation reaction and by periodate oxidation. Characterizations were performed by FTIR, for organic syntheses and by XPS for the subsequent grafting on the surface. Coatings topography and stability were also investigated. Preliminary results suggest the use of polysaccharides grafted by plasma on fluorocarbon films to provide a stable stent surface.

Abstract: Ti-Nb based alloys are well known to their good mechanical properties, shape memory effect, superelasticity, as well as good biocompatibility. The Ti-24Nb (at%) binary alloy presents a shape memory behavior and low elastic modulus. Our study is focused on the improvement of their mechanical properties by adding a third alloying element (oxygen, nitrogen or silicon). Addition of 0.5 at% of N or O modifies drastically the mechanical behavior of Ti-24Nb alloy that exhibits superelastic behavior instead of shape memory one. On the other hand, addition of 0.5 at% of Si increased yield strength of the Ti-24Nb shape memory alloy.

Abstract: Together with cancer biomarker advance, nanotechnology could lead to a “personalized oncology”, where early tumour detection and diagnosis are more and more specific. A nanosized drug delivery system is mainly composed of three fundamental elements: i) a drug nanocarrier (1-100 nm), ii) an anti-cancer drug; iii) an active targeting molecule, recognizing a tumour associated marker expressed at the cell surface. In our study we used: i) hydroxyapatite nanocrystals (HA-NC), for its properties of large specific surface area, hydrophilicity and biodegradability with very low toxicity and ii) monoclonal antibodies (mAb), directed against CAR-3, a mucin tumour associated surface antigen, and against the Met/HGF-R, both of which are overexpressed on human carcinomas. In our study, nanosized HA-NC, poorly aggregating and biomimetic, were synthetised and characterized. After a preliminary isothermal adsorption of human polyclonal IgG, we functionalized HA-NC, coated or not with protein A (Prot A), with the two mAbs. IgG and Prot A isothermal adsorption curves were obtained; mAb absorption was achieved and prelimary Prot A coating appeared not to improve HA-NC loading capacity. IgG conformation onto HA-NC was investigated by means of Fourier Transformed InfraRed Spectroscopy, revealing a preferential binding with the constant antibody domain, and exposition of the variable domain, involved in antigen binding, on the biomaterial surface. These immunocomplexes are confirmed to be potentially used as targeted drug delivery system.

Abstract: Sterilization is very important for the use of biomaterials in the medical field. This work describes the preparation of chitosan/carboxymethylcellulose thin films with the layer-by-layer deposition technique, and the investigation on the effects that thermal treatments have on them during sterilization. The influence of different heating and sterilization methods on the chemical and physical structure of biopolymer thin films composed of chitosan and carboxymethylcellulose was evaluated. Films were heated in an oven at specified temperatures or autoclaved and their characteristics analyzed with contact angle, profilometry, FTIR, anionic dye uptake and UV-Vis measurements. Results show that, depending on the heating conditions, these thin films may undergo the Maillard reaction that turns the films from being transparent to brownish in color. This reaction may lead to a decrease in the free hydroxyl groups of both carboxymethylcellulose and chitosan and free ammonium groups of chitosan - consequently leading to changes in hydrophilicity and wettability of the film. Temperature effects on the characteristics of the synthetic pre-layer coating composed of poly (diallyldimethylammonium chloride) and poly (sodium 4-styrene-sulfonate) - used to provide a high cationic surface for the deposition of the biopolymer films - were also observed. These findings are of practical interest because biopolymer thin films find a great number of applications where sterilization is a must, such as clinical and medical applications and in the areas of materials science and biotechnology.

Abstract: Collagen gels have been investigated for a number of applications in tissue engineering because of their excellent biological properties. However, their limited mechanical behavior represents a major bottleneck for clinical use, especially for vascular tissue engineering. The targeting of their mechanical properties may be envisaged by the addition of other biopolymers, such as konjac glucomannan (KGM), a neutral high-molecular weight polysaccharide extracted from the tubers of Amorphophallus konjac, which has already been studied for biomedical applications due to its biocompatibility and biodegradable activity. In the present study, reconstituted collagen gels were prepared at pH 10 and room temperature, by mixing collagen with NaOH, NaCl and 0.05 to 0.2% of KGM. Collagen fibrillogenesis was monitored by spectrophotometric analysis at 310 nm. Gel samples were analyzed by compression tests, FTIR and SEM. Comparing to the control, the addition of KGM reduced the half-time (t_1/2) of gelation from ca. 3 h to 2 h and the mechanical tests showed increases in the compressive strain energy of up to 3 times, and in compressive modulus of almost 4 times. Scanning electron images of collagen gel samples with KGM revealed the presence of micro-domains of KGM in the collagen matrix, revealing a phase separated scaffold for vascular tissue engineering.

Abstract: In this work, porous TiB₂ ceramics were consolidated by pressureless sintering method using metallic Ti and Fe as additives in order to perform sintering at temperatures lower than 1700°C. It was shown that processing parameters including milling time of the starting mixture had a considerable effect on final properties of sintered specimens and their behavior in molten aluminum. Microstructural studies were carried out using optical microscope, SEM and EPMA. It was found that specimens with uniform and crack-free microstructure could be produced using the pre-mixed powders milled for as low as 30 min prior to compaction and sintering. Sessile drop test was performed on the specimens milled for 30 and 240 minutes. Their interaction with molten aluminum was also studied. It was found that 30 min milling time resulted in better electrical conductivity, wettability and stability in liquid aluminum.

Abstract: MgB₂ has the higher critical temperature of superconducting transition (T_C : 39K) among the intermetallic compound superconductive materials, however, MgB₂ is hard for practical use because of its unworkable and lower critical current density (J_C) in a high magnetic field than Nb-based superconductive materials. We have developed the original method of three-dimensional penetration casting (3DPC) to fabricate the MgB₂/Al composite materials. In the composite material we made, MgB₂ particles dispersed to the matrix uniformly. Thus, these composite materials can be processed by machining, extrusion and rolling. The T_C was determined by electrical resistivity and magnetization to be about 37～39K. In this work, we made composite material with ground MgB₂ particle with the purpose of extruding thinner wires of composite material, successfully produced φ1mm wire and changed the matrix from pure Al to Al-In alloy. J_C of composite materials with the matrix of Al-In alloy was calculated from the width of the magnetic hysteresis based on the extended Bean model. The result was better than that of MgB₂/Al composite material without Indium. Microstructures of these samples had been confirmed by SEM observation.

Abstract: Our co-worker, Hishinuma et. al. has established a new route Powder-In-Tube (PIT) process using a high Ga content Cu-Ga compound in order to improve the superconducting property of the V₃Ga compound wire. In this study, we investigated microstructure of this high Ga content Cu-Ga/V composite superconducting wire. The different contrasts of matrix, V-Ga phase and Cu-Ga core were observed by SEM observation in cross section of 19 multifilamentary wire. And V-Ga phase was confirmed by SEM mapping. The area fraction of V-Ga phase increased when Ga content increased from 30% to 50%. Thin film sample with V-Ga phase for TEM was fabricated by FIB and observed by TEM in detail. Selected area diffraction pattern was obtained for V matrix, V-Ga phase and Cu-Ga core. The ratio of V to Ga for V-Ga phase was probably V₃Ga according to the EDS result. There was a linear interface between V matrix and V-Ga phase, while the interface between Cu-Ga core and V-Ga phase was not linear. On the other hand, there were some granular grains observed in V-Ga phase wear Cu-Ga core.

Abstract: One of the most challenging areas in engineering of composite materials is the fabrication of high quality microstructures. This issue is complicated for tungsten composites due to its high melting temperature and this leads to limitations in terms of possible processing techniques. This research investigates the fabrication of W-12%wtCu composites based on powder metallurgy techniques. Due to the very large difference between the melting point of tungsten and copper, there is no common sintering temperature range for them. In this work, 0.5%Wt nickel was added as an activator to decrease the sintering temperature of tungsten using an activated sintering effect. The effects of pressure, sintering time and temperature in solid state and liquid phase conditions were also investigated. While solid state hot pressing did not result in appropriate microstructures, the liquid phase hot pressing provided high quality samples with a relative density of 98.0%.

Abstract: TiC and TiB₂ compounds in the form of interpenetrating network reinforced AZ91D magnesium matrix composites have been successfully synthesized by an in-situ reactive infiltration technique. In this process, the ceramic reinforcement phases, TiC and TiB₂, were synthesized in-situ from elemental powders of Ti and B₄C without any addition of a third metal powder such as Al. The molten Mg alloy infiltrates the preform of Ti_p and B₄C_p by the capillary force. The microstructure and reaction mechanism are investigated using SEM/EDS and XRD analysis. The results show that the processing parameters such as temperature, holding time and the green compact relative density have a significant influence on the reaction mechanism and the fabrication of the composite. In addition, the infiltrated Mg acts as an intermediary that makes the reaction possible at a lower temperature than that required for solid-state reaction between Ti and B₄C. Microstructural characterization reveals a relatively uniform distribution of the reinforcing phases, TiC and TiB₂ in the Mg matrix.