Advanced Materials Research Vols. 15-17

Abstract: Influence of SO2 concentration on initial corrosion of aluminum was studied in simulated marine atmosphere. Variation of initial corrosion morphology, relation between weight gain and time in the course of initial corrosion, corrosion speed (token with maximum pitting depth and weight gain) were analyzed and discussed. Primary results is list below: In marine atmosphere, SO2 sedimentation above 0.1 mg/100cm2 can accelerate Al pitting with low Cl- sedimentation. Both corrosion weight gain and pitting depth increase obviously. For pitting surface of LY12 with SO2 and Cl- sedimentation, corrosion potential change little, Nyquist Graph was single arc of capacitance resist with retractile real part, Rr can’t reflect corrosion degree.

Abstract: In this work effect of cooling rate on the size of the grains, SDAS, β phases and thermal characteristic results of Al-Si cast alloys have been described. The solidification process was studied using the cooling and crystallization curve at cooling rate ranging from 0,1 °Cs-1 up to 1 °Cs-1. The main observation made from this work was that when cooling rate is increased the aluminum dendrites nucleation temperature and solid fraction at the dendrite coherency point increases, which implies that mass feeding is extended. In addition to that, it was observed that solidus temperature and size of the β phases decreases when cooling rate increases. Investigations were showed, that the thermal modification could be quantitatively assessed by analysis of the crystallization curve.

Abstract: The aim of this report was to investigate the behavior of human mesenchymal stem cells (hMSCs) when cultured on different porous 3D scaffolds, having natural or synthetic origination. Natural scaffolds were obtained by hand made processing of human bone tissue (allograft), because its well known osteoconductive features, using different procedures to eliminate the donor cellular phase. Cancellous bone was frozen, heated or demineralized before being loaded with hMSCs. Among the variety of synthetic materials, biodegradable polymeric spongy matrices were chosen and comparatively tested as scaffolds for hMSCs growth.

Abstract: Various types of titanium alloys with high strength and low elastic modulus and, at the same time, vanadium and aluminium free have been developed as surgical biomaterials in recent years. Moreover, porous metals are promising hard tissue implants in orthopaedic and dentistry, where they mimic the porous structure and the low elastic modulus of natural bone. In the present study, new biocompatible Ti-based alloy foams with approximate relative densities of 0.4, in which Sn and Nb were added as alloying metals, were synthesised through powder metallurgy method. The new alloys were prepared by mechanical alloying and subsequently sintered at high temperature using a vacuum furnace. The characteristics and the processability of the ball milled powders and the new porous titanium-based alloys were characterised by X-ray diffraction, optical microscopy and scanning electron microscopy .The mechanical properties of the new titanium alloys were examined by Vickers microhardness measurements and compression testing.

Abstract: A new technique for micropatterning surfaces for cell growth support is described and characterized. This technique allows covering of large three-dimensional surfaces at low cost with controllable micropatterns. This method takes advantage of the random properties of aerosols and the principles of liquid atomization. Parameters of interest were the pressure of atomization air, the flow rate and volume of the atomised liquid, and the distance between the spray nozzle and the surface of the sample. The experimental setup permitted to obtain mean diameters of spots between 10 and 20 microns with a maximum surface coverage of 20%. In an initial step, polytetrafluoroethylene (PTFE) films were treated with ammonia plasma to insert amino groups on the surface. The ammonia plasma treated films were immersed in a solution containing sulfosuccinimidyl 4-(N-maleidomethyl)cyclohexane-1-carboxy-late (SSMCC) to permit the introduction of maleimido groups on the PTFE surface to subsequently conjugate peptides through a sulfhydryl containing N-terminal cystein residue. Plasma/S-SMCC pretreated surfaces were then sprayed with peptide sequences CGRGDS and CWQPPRARI. Our data showed that spots of CGRGDS peptides over a background of CWQPPRARI peptides were the most effective combination to enhance endothelialization.

Abstract: Collagen is the most used naturally occurring scaffold material. It’s a structural protein ubiquitous among mammalian. The ability of collagen type I to host different cell phenotype in vitro and its low antigenecity in vivo are well known. However, the principal drawback of collagenbased materials consists in their low mechanical properties. For vascular tissue engineering this represents a major limit, as the aim is to mimic the structure of a native vessel, which is known to be resistant and viscoelastic. Moreover, vascular cells are known to be susceptible in vivo to reorganize the matrix in which they proliferate. Therefore, the aim of this project is to study the micro structural organization of collagen-based scaffolds, and to assess the interactions between collagen and smooth muscle cells during regeneration. This knowledge will then allow the development of appropriate strategies to tailor the microstructure of the scaffold and its properties. Smooth muscle cells (SMCs) were selected to study the interactions between cells and matrix during the proliferation. Atomic Force Microscopy (AFM) in dry state in tapping mode and Confocal Laser Scanning Microscopy (CLSM) in reflection mode were used to investigate the microstructure of the scaffold. For the former technique cells were seeded on top of the collagen gel after jellification, while for the latter, cells were embedded into the collagen gel and stained with Rhodamine. The contact points between matrix and cells were investigated, as well as the capacity of vascular cells to induce a structural reorganization of collagen fibrils in the scaffold.

Abstract: Titanium and some of its alloys are widely used as load-bearing implant materials. In particular, titanium-zirconium (Ti-Zr) alloys have a high potential for biomedical applications due to the excellent biocompatibility of both Ti and Zr. Nevertheless, the surfaces of the Ti-Zr alloys need to be modified to provide the implant material’s bioactivity. In the present study, an alkali-heat (AH) treatment process followed by the soaking in simulated body fluid (SBF) was attempted for the preparation of calcium phosphate (CaP) coatings on the surface of the TiZr alloy. Phase transformation, surface morphology, and interfacial microstructure were investigated using scanning electron microscope (SEM) with an energy-dispersive electron probe X-ray analyser (EDS). The results indicate that the AH treatment produced a nano-porous bioactive sodium titanate / zirconate hydrogel surface layer which induced the deposition of a Ca-P layer during soaking in the SBF. This Ca-P layer on the TiZr alloy surface can be expected to bond to the surrounding bones directly after implantation.

Abstract: Three-dimensional gelatin-chondroitin 6 sulphate-hyanuronic acid biomatrix was used as the scaffold to investigate the phenotypic and molecular expression in human keratinocytes (K) and dermal fibroblasts (FB) in three different culture conditions in vitro. The cells were cultured in either monolayer (K or FB only) or coculture (K&FB) model. The deposition of basement membrane proteins secreted by these two kinds of cells was quantitatively characterized by real-time PCR. In the results, dermal fibroblasts were shown to synthesize and deposit laminin 5, type IV and type VII collagen, whereas keratinocytes produced integrin alpha 6 and beta 4 as well as laminin 5 and collagen type IV, VII. Interestingly, the integrin beta 4 subunit was not expressed either in keratinocytes or dermal fibroblasts monoculture but was seen in organotypic coculture model in the early culture period. Furthermore, we found that the expression of those marker compounds was reciprocally regulated when keratinocytes and dermal fibroblasts were cultured together. These results indicated that keratinocyes and dermal fibroblasts worked together to reconstruct dermal-epidermal basement membrane (BM) zone. In brief, our data provide the first time in directly quantifying the expression of BM proteins by using real-time PCR, and also demonstrate that BM proteins were regulated by cell-cell interaction.