Key Engineering Materials Vols. 334-335

Abstract: A numerical study of the static behaviours of composite strip with bifurcated type shape memory alloy pins has been conducted. The case of bifurcated type shape memory alloy pins inserted inside the composite strip around the hole to reinforce the laminate, which was subjected to the axial stress was simulated. The models for stress analysis were established by using ANSYS finite element programme. Two types of shape memory alloy pins were proposed to insert along the through thickness direction of the carbon fibre woven fabric composite strip to induce the clamping force. The pre-tensioned load was applied to the shape memory alloy pins in order to reduce occurrence of delamination in the laminate. Three-dimensional elements and contact elements were used to simulate the contact between the composite laminate and shape memory alloy pin to investigate the stress distribution around the hole in the composite strip. The effect of pre-strain of shape memory alloy on the stresses inside composite was studied. The results show that the stress characteristics of the button-shaped and bifurcated shape memory alloy pin models are similar; however, the stresses for the button-shaped pin model are lower. The tensile and compressive stresses, both in button-shaped and bifurcated pin models, are strongly dependent on the percentage of pre-strain of the shape memory alloy. It is therefore concluded that the shape memory alloy pin method was significantly reduced the stress concentration of the composite strip laminate.

Abstract: Polymer composite samples consisting of L-Lactic acid (LA) was reacted by ring-opening polymerization with aluminum triflate as a catalyst, glycerol as an initiator and various particles as fillers. Cellulose particles, kaolin and silica gel with different particle sizes were employed as fillers. Filler content was varied 0 to 100 wt% as ratio of filler weight to PLA weight. L-Lactide (L-LA), aluminum triflate as catalyst, glycerol as an initiator and particles were mixed at room temperature and then were put into plastic tubes. The mixture in tubes was heated and reacted at 100 oC for 6 hours. The samples were removed from tubes after cooling and were cut into the column shape specimen with diameter of 10 mm and ca. 10 mm height. By the above procedure, particles could be mixed to poly(lactic acid) (PLA) matrix easily and homogeneously. The molecular weight and molecular weight distribution of PLA matrix were determined by gel permeation chromatography (GPC). Apparent density of composite samples was calculated by using weight and sizes of column shape specimens. The mechanical properties such as elastic modulus and strength were investigated by compression tests using column shape specimens. Molecular weight and molecular weight distribution were almost constant for all the samples with and without particles. Elastic modulus and compression strength were improved by particles. For the cellulose particles filled samples, the highest values of elastic modulus and compression strength were derived at filler content of around 20 vol%. The influences of sizes and types of particles on the physical properties such as molecular weight, density and mechanical properties were investigated.

Abstract: There has been a concern over many years on the usage of existing metallic and ceramicbased biomaterials for implant design and development due to the necessity of conducting operations for patients to remove and maintain implants after they complete their desired functions. Recently, the development of biodegradable polymers like poly(glycolic acid), poly(lactic acid), and their co-polymers etc. have emerged and provided an entirely new concept to tackle this problem as these polymers can be fully or partly degraded or resorbed by the human body, i.e. an extra operation for removing the implants can be avoided, which can highly alleviate the hard feeling of the patients that come from psychological and physiological pressures. Natural fibres have been well recognized as potential micro-reinforcements for the enhancement of mechanical, thermal and structural properties of biodegradable polymer composites, without generating any harmful by-products and adverse effects during their degrading process to the patients. These natural fibers can be mainly classified depending on their origin into two categories; they are (i) plant-based and (ii) animal-based natural fibers, like spider and silkworm silks. Since the last decade, silkworm silks have been used as reinforcements for fabricating biocomposites. However, no comprehensive study, particularly on the correlation between the mechanical properties of the composites, and fiber orientations and configurations has been done to date. In this paper, an in depth study on the mechanical properties of silk/epoxy composites with different fiber contents and orientations, through experimental approach and fractographic examinations will be conducted. Tensile property tests for all silk/epoxy composite samples will be performed. Failure samples will be examined by using scanning electron microscope (SEM) to investigate the failure mechanism of the composites.

Abstract: Effect of whisker orientation on mechanical properties of hydroxyapatite-SiCw composite bioceramics was studied in this paper. Experiment results show that the mechanical properties of the material are the best when the tensile stress acted on the composite material is parallel with the hot pressing plane or the shearing stress is normal to the hot pressing plane, and they are the worst when the tensile stress acted on the composite material is normal to the hot pressing plane or the shearing stress is parallel with the hot pressing plane. This will offer great guidance for practical applications of the hydroxyapatite-SiCw composite bioceramics.

Abstract: One of the merging methods to produce tissue-engineered vascular substitutes is to process scaffolds to direct the regeneration of vascular tissues. Collagen, as one of the main protein in the vascular extracellular matrix, is one of biopolymers that exhibits a major potential for scaffold technology. However, gels made from reconstituted collagen generally exhibit poor mechanical properties and limited manipulability. Therefore, adding a reinforcement to the scaffold to make the structure resist to the physiological constraints applied during the regeneration represents a valid alternative. Silk fibroin is an interesting reinforcing candidate being a mechanically strong natural fibre, susceptible to proteolytic degradation in vivo and showing acceptable biological performances. Therefore, the aim of this study was to develop a model of a composite scaffold obtained by controlling the filament geometry winding of silk fibroin in the collagen gel. A finite element model taking into account the orthotropic elasticity of arteries has been combined with classic laminate theory applied to the filament winding of a tubular vessel. The design of the small structure susceptible to scaffold the vascular tissue regeneration was optimised by mean of an evolutive algorithm with the imperative to mimic the experimentally measured mechanical properties (compliance) of a native artery.

Abstract: Osseointegration (OI) could be described as the modality for stable fixation of titanium implant to bone structure. The OI has become a realized phenomenon of importance in the dental and rehabilitation sciences since recently developed dentures and artificial limbs are directly attached to human skeleton by using osseointegrated (OI) implants. Previously, a study showed that bone strain generated potential (SGP) that is an electrical potential and considered to be generated by fluid flow in bone could be used as a parameter to examine the amount of OI on bone-implant interface. Since no study was performed to understand effects of loading rate changes on behavior of SGP for the bone-implant composite, rate dependent behavior of SGP was investigated in this study. Four different displacement rates, 100, 200, 500, and 1000 mm per minute were applied to the bone-implant composites. During the compression tests, SGPs were also measured. Magnitude of SGP was found to be significantly increased as the rate increased for OI bone-implant composite. In contrast, the time duration of SGP was decreased as the rate increased. These results could imply that the temporal SGP behavior of bone-implant composite is significantly affected by the loading rate.

Abstract: We successfully synthesized near infrared (NIR) sensitive Au(shell)-Au2S(core) nanoparticles, where Au2S dielectric core was encapsulated by a thin gold shell. The cytotoxicity in vitro and biodistribution in vivo of Au-Au2S nanoparticles was studied by using NIH3T3 cells and KM mice, respectively. The quantitative analysis of Au in each tissue of mice was done by using the Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Au-Au2S nanoparticles (< 300 μg/ml) showed good biocompatibility. Au-Au2S nanoparticles were preferentially taken up by the liver and spleen, and ultimately eliminated mostly in the feces.

Abstract: In contrast to the classical composites, microfibrillar reinforced composites are not prepared via melt blending of the matrix and the reinforcing material. In fact, the reinforcing elements of this composite, the microfibrils, are created during processing. This advantage allows the manufacturing of a full biodegradable composite material with improved mechanical properties. Basing on a blend of two common biodegradable polymers, polylactide and polyglycolide, this new composite shows promising values under ambient conditions.

Abstract: The magnetite (Fe3O4) nanoparticles were prepared by coprecipitation of Fe3+ and Fe2+ with aqueous NaOH solution. The Fe3O4/polyaniline (PANI) magnetic composite nanoparticles with core-shell structure with diameter of 30-50 nm were prepared via an in-situ polymerization of aniline in aqueous solution containing Fe3O4 magnetic fluid. The inductive heat property of Fe3O4/polyaniline composite nanoparticles in an alternating current (AC) magnetic field was investigated. The potential of Fe3O4/polyaniline nanoparticles was evaluated for localized hyperthermia treatment of cancers. The saturation magnetization Ms and coercivity Hc of Fe3O4 nanoparticles are 50.05 emu/g and 137 Oe respectively, the Fe3O4/polyaniline composite nanoparticles, 26.34 emu/g and 0 Oe. Exposed in the alternating current (AC) magnetic field for 29 min, the temperatures of physiological saline suspension containing Fe3O4 nanoparticles or Fe3O4/polyaniline composite nanoparticles are 63.6 °C and 52.4 °C respectively. The Fe3O4/polyaniline composite nanoparticles would be useful as good thermoseeds for localized hyperthermia treatment of cancers.