Key Engineering Materials Vols. 353-358

Abstract: The research of the stress distributions and the structural deformation at the sliding core in artificial intervertebral disc under the dorsiflexion is becoming more significant. This research analyzes the finite element model of sliding core and evaluates the effect of radius of curvature and the friction coefficient at the sliding core on von-Mises stress and the contact pressure. New Models of the artificial intervertebral disc are suggested by the results of the sliding core is evaluated by the comparison of that of SB Charité III. Based on the above facts, the optimized radius of curvature of the sliding core is also suggested.

Abstract: Poly-N-isopropylacrylamide (PNIPA) gel is a typical thermo responsive gel which undergoes a large volume change from the low-temperature swollen phase to the high-temperature shrunken phase. In this study, the mechanical behavior of PNIPA gels was investigated by the experiment and simulation. The cylindrical shaped specimens of PNIPA gel were prepared and tensioned at various temperature. Swelling ratio at equilibrium state was calculated by diameter of swelling gels. Young modulus was obtained from stress-strain curve plotted using tensile load measured by semiconductor gauge. Also swelling and deswelling behavior of thermo sensitive gel were simulated by using finite element method. Polymer-solvent interaction parameter, χ was used as a function of temperature. Calculated swelling ratio at equilibrium was compared with experimental result and theoretical swelling curve. Furthermore, change of volume fraction and stress distribution in swelling process were evaluated.

Abstract: Many kinds of materials are currently used as artificial bone substitutes. Hydroxyapatite (HA), the same as the main inorganic component of bone, is one of commonly used bio-ceramics and has excellent bioactivity and biocompatibility with hard tissues. However, it has problems as the bone filler or bone tissue-engineering scaffold due to low fracture toughness and low degradation rate. Recently, biodegradable materials for bone tissue have been developed to respond the requirement. Collagen, the same as the main organic component of bone, is biocompatible, biodegradable and promotes cell adhesion. A composites associated with HA is expected to have early osteoconduction and bone replacement ability. The present study was to fabricate bone-like composites consist of HA and collagen. Besides the ossiferous ability of the material in vivo is evaluated by using rabbits. Bone-like composites were successfully fabricated in this study, associating the collagen with HA. And the composites presented good osteoconductive and bone replacement potential.

Abstract: Evaluations of elasto-plastic properties and fracture strength were studied utilizing indentation technique. The elasto-plastic properties of nine monolithic metals were estimated using dual indentation method and compared to the properties under tensile loading test. This method could predict stress - strain curve and was found to determine ultimate tensile strength. For brittle coating, fracture strength of diamond -like carbon (DLC) film was estimated by hybrid indentation with acoustic emission (AE), corrosion potential fluctuation (CPF) and finite element method (FEM). AE and CPF data provided information on the timing of film cracking and its mechanism. Fracture strength of the films could be evaluated using Vickers and Rockwell indentation.

Abstract: To analyze the effect of the crystal orientations and the grain size on the Young's modulus of thin polysilicon microelements, two-dimensional finite element models in plain strain condition were developed using a Voronoi structure. The number of grains in a model of a 10 μm square area was changed from 23 to 1200. The grain size and the crystal orientation of the film were analyzed by means of an electron back-scattering diffraction pattern (EBSP) method. The average grain size of the front surface of the thin film was about 0.69 μm, which is almost equal to the grain size of the Voronoi model having 300 grains. From the results of EBSP analysis, the specimen had no oriented structure. Therefore, random crystal orientation was given to each grain of the FEM models. When the number of grains increased, the Young's modulus converged on about 171 GPa and its scatter caused by the different sets of the random orientation was reduced. The Young's modulus obtained by the FEM analysis was larger than the value obtained by the tensile tests.

Abstract: In this study we presented kinematic and kinetic data of foot joints by using passive elastic characteristics of joints during gait. During the calculation process we used approximate equations and partial plantar pressures. The maximum angular displacements of each tarsometatarsal joint ranged from 4o to 7o and the maximum moments were from 200N⋅cm to 1500N⋅cm. It was relatively wide distribution. Foot kinematic data calculated from the approximated equations, which were represented by the correlation between moment and angular displacement, and the data from motion analysis were very similar. We found that the movements of foot joints were mainly decided by the passive characteristics of the joints when ground reaction force acts. The kinematic and kinetic analysis using approximated equations which is presented in this study can be usefully applied to describing the movements of foot joints during gait.

Abstract: Self-oscillating gel is designed by copolymerizing the catalyst for the Belousov-Zhabotinsky (BZ) reaction with thermosensitive polymer. The cylindrical-shaped specimens of NIPAAm-co-(Ru(bpy)3 gel were prepared by copolymerizing (Ru(bpy)3) monomer as catalyst with NIPAAm as thermosensitive polymer. Swelling behavior during self-oscillating of gel by BZ reaction was observed using CCD camera and the force due to this reaction was evaluated using semiconductor gauge. Self-oscillating swelling-deswelling behavior in samples with different swelling ratio was evaluated by this apparatus, and mechanical parameters such as Young’s modulus, stress amplitude and oscillating period were quantitatively estimated.

Abstract: Natural clay minerals are ideal nanofillers for polymer materials and have been attracted tremendous research and development interests in the past decade. The manufacture of clay nanofillers relies largely on the exfoliation of clay particle into individual clay platelets. Thus, understanding the interlayer swelling of clay minerals upon the adsorption of surfactants is important to the fabrication and design of polymer nanocomposites. This paper reports our recent experimental and theoretical studies on a variety of organoclays that show a linear relationship between the increase of d-spacing and the mass ratio between organic and clay.

Abstract: Four kinds of dimers from cyclic peptide [-(1R, 3S)-γ-Acc-D-Phe]3 were investigated using molecular modeling based on the density functional theory (DFT), molecular mechanics (MM) and molecular dynamics (MD). The equilibrium dimer structures reveal that these dimers can be divided into two different types according to stacking formation, in which one type dimer is more stable due to the effect of side chain groups. In each type of dimers, only one can transport CHCl3. When the terminal N-substituent methyl is introduced, the transport character is reversed. Analysis of 500 ps MD trajectory suggests that the inner and terminal sizes of the dimers are the main factor that affects the transport of CHCl3. The modeling results can provide a new way for designing and synthesizing cyclic peptide transport channels.

Abstract: The mechanical properties of bone have been found varying at different structural levels. The different mechanical properties might indicate some important information, such as the ultrastructure of various bone tissue. Descriptions of the structural features of bone are intensive in current studies. However, the mechanical properties of bone, in particular those at the micro-and nanostructural level (material level) remain poorly understood. To probe the mechanical properties at the microstuctural level, the nanoindentation technique is applied. Nanoindentation as a promising technique is widely used in the materials science community for probing the mechanical properties of thin films, small volumes, and small microstructural features. Nanoindentation has been shown to be an effective method to probe the mechanical properties of microstructures at the micron scale.