Advanced Materials Research Vols. 47-50

Abstract: Mussel adhesive proteins (MAPs) have received increased attention as potential environmentally friendly adhesives under aqueous conditions and in medicine. However, attempts to produce functional recombinant MAPs (mainly foot protein type 1, fp-1) by several expression systems have failed. Even though we previously reported a functional expression of recombinant foot protein type 5 (fp-5) with significant adhesive ability in Escherichia coli, its practical use was limited by several problems such as low production yield, low purification yield, and high levels of post-purification insolubility. Here, to overcome these limitations, we designed and constructed the novel type of hybrid mussel bioadhesive fp-151, a fusion protein comprising six fp-1 decapeptide repeats at each fp-5 terminus. Using micro- and bulk-scale characterization and mammalian celladhesion analyses, we demonstrate that fp-151 has the potential to be a practical bioadhesive with strong adhesive ability, a simple purification process (~1 g-purified protein per 1 liter-pilot-scale fed-batch bioreactor culture), proper manipulation properties (~330 g/l solubility), and high biocompatibility.

Abstract: Mussel foot protein is widely known for candidate of strong adhesive materials. Six times fp-1 decapeptide repeats and fp-5 are chosen among the various type of foot protein and fused into (MAP) fp-151. Through various cell-adhesion analyses, we previously demonstrated that fp- 151 has the potential to be used as a cell or tissue bioadhesive. In the present study, to improve the cell-adhesion properties of fp-151, it was designed a new cell-adhesive protein, fp-151-RGD, which is a fusion with the GRGDSP residues, a RGD peptide sequence that has previously been identified at the cell-attachment site of fibronectin, at the C-terminus of fp-151. Also, recombinant fp-151- RGD maintained the advantages associated with fp-151, such as a high production yield in Escherichia coli and simple purification, it showed superior spreading ability, which is important for cell proliferation under serum-free conditions, as well as better cell-adhesion ability compared with other commercially produced cell-adhesion materials such as poly-L-lysine (PLL) and the naturally extracted MAP mixture Cell-Tak. The excellent adhesion and spreading abilities of fp- 151-RGD might be due to the fact that it utilizes three types of cell-binding mechanisms: DOPA adhesion of Cell-Tak, cationic binding force of PLL, and RGD sequence-mediated adhesion of fibronectin. Therefore, the new recombinant fp-151-RGD is suitable for use as a cell-adhesion material in cell culture or tissue engineering, and in any other area where efficient cell adhesion is required.

Abstract: In the present study, Al-Si samples with a graded structure were produced via horizontal centrifugal casting. The distribution of primary and eutectic silicon particles within the produced specimens was investigated by optical microscopy. The microstructure of one end of the sample (closed to rotating axis) consisted of primary Si particles distributed within a eutectic matrix. The volume fraction of these particles decreased towards the other end of the sample and exhibited mostly primary Al-α and eutectic structure. Microhardness and macrohardness measurements conducted along the sample length showed a gradual decreasing value from one end (near the rotation axis) towards the other end of sample demonstrating functionally graded properties. These results were rationalized in terms of the lower density of Si compared to Al alloy which provided the movement of Si particles under the action of centrifugal forces during rotation.

Abstract: Continuum level modeling of damage is a complex problem because of existence of several failure mechanisms at various length-scales, e.g., matrix crack, interfacial crack and delamination. Several macroscopic models have been proposed in the literature for the characterization of the influence of these damage modes. However, very few models account for the micro-level mechanisms. Further, most micromechanical models are two-dimensional (2D) in nature. Hence, the effect of finite size and orientation of the damage is not captured. The present work focuses on developing a generalized macro level damage model for unidirectional composites based on the micromechanical analysis in the presence of finite sized damages. The effect of microdamage mechanisms is modeled through effective stiffness reduction at a macro point. A series of numerical experiments, based on the mathematical theory of homogenization, have been conducted at the level of the constituents to obtain the effective stiffness properties for the Representative Volume Element (RVE) with existing damage. The effect of various damage mechanisms, size and mode of damage on effective macro properties is studied and definitive conclusions are drawn. The dependency of these effects on the volume fraction is also studied. Based on the conclusions, a generalized macro level damage model is proposed.

Abstract: AgNi and AgFe are known as contact materials with high workability and low contact resistance for medium to weak current contacts. However, AgNi and AgFe contact materials are difficult to manufacture using conventional melting and casting procedure because they exhibit no range of solid solubility of Ni and Fe in Ag for all temperature range. The purpose of this research is to develop a process for low-cost AgNi and AgFe contact materials based on solidification process control. AgNi and AgFe contact materials were produced by rotation cylinder method (RCM). The hardness value of AgNi and AgFe contact materials by RCM were higher than that of AgNi and AgFe contact materials produced by conventional powder metallurgy and co-precipitation processes. The higher hardness values of contact materials produced by RCM may be attributed to the uniform distribution and small size of Ni and Fe particles in Ag matrix.

Abstract: Experiments have shown that the localization of transformation in NiTi shape memory alloys (SMAs) is an important factor in determining their mechanical response during cyclic loading. A one-dimensional constitutive model for the cyclic behavior of SMAs is presented that takes into account the localization of transformation and transformation-induced plasticity. An internal variable is introduced that characterizes the amount of temperature-dependent cyclic change. The results of simulations at two different temperatures are also presented.

Abstract: In this paper, a reasonable three dimensional finite element beam model was developed to predict the mechanical behaviors of carbon fiber reinforced polymer (CFRP) strengthened RC box beam under combined bending, shear and torque. The comparison of calculated results with the experiment results of torque-twist relationship, the strain developments in steels and CFRP strips and the force of non-linear string element indicates that the finite element method presented in this study can simulate the behavior of beams well.

Abstract: Cyclic loading and unloading tensile tests were carried out for Cu-11.30wt. %Al-0.32wt. % Be Shape Memory Alloys (SMA) wires to investigate the effect of temperature and cyclic condition on the pseudoelastic behavior. It is shown that σc increases with the isothermal external temperature in single cycle tests and loading stress in constant stress increment tests while tends to a stable level after the 1st cycle in constant maximum strain tests. Both modes of loading and unloading improve the pseudoelasticity obviously.

Abstract: Molecularly imprinted composite materials (PM) selective to S-naproxen were prepared in the surface of mesoporous silica sphere (SBA-15) by surface imprinting technique. FT-IR, SEM and surface area analysis were used to study the structural morphology of PM and MIPs particles and probe the incorporation of polymer into the SBA-15 framework. The results revealed that PM showed better binding affinity and selectivity to the template molecule than MIPs and the maximum saturated binding capacity of PM to S-naproxen and R-naproxen was about 10.3332 and 6.0063µmol·g-1. Meanwhile, we achieve a reference strategy for the development of molecularly imprinting polymer for drugs and to handle forms in certain applications such as chromatographic stationary phases for chiral separations.

Abstract: The microstructure and thermal cyclic oxidation resistance of the wide-gap region brazed with different filler metal powder (BNi-3 and DF 4B) comparing with that of Ni-based IN738 alloy were investigated. The microstructure characterization showed that Cr borides with a blocky morphology were existed in the brazed region in both filler metal powder. The normalized weight gain with cyclic oxidation showed that weight loss of the specimen brazed with BNi-3 filler metal occurred after 600 cycles. However, the specimen brazed with DF 4B filler metal had no obvious weight loss until 700 cycles. It was observed that the oxidation kinetics of the all oxidized specimens followed the quasi-parabolic law, and the oxide layer was mainly composed of NiO, Al2O3 and NiCr2O4.