Key Engineering Materials Vols. 342-343

Abstract: Rod shaped nanocrystalline powders of hydroxyapatite (HAp) were synthesized by a low temperature chemical route involving calcium nitrate tetrahydrate and sodium phosphate. Three types of alkyl ammonium bromide surfactants i.e. tetrapropylammonium bromide, tetraethylammonium bromide and tetramethylammonium bromide were used to regulate the nucleation and crystal growth. The synthesized powders were characterized by XRD, SEM and FTIR. The effect of the various alkyl ammonium bromide surfactants on the phase formation, particle size and morphology of the hydroxyapatite powders has been investigated and reported.

Abstract: Nanosized hydroxyapatite(HAp) was synthesized hydrothermally and influence of processing parameters, such as reaction temperature and time, pH, and Ca/P ratio, on the phase stability of HAp was evaluated after pressureless sintering at 1250°C in air. The highest stability was achieved from the powder obtained at a processing condition for the lowest solubility of Ca2+, which corresponds to temperature close to 200°C, time <4h, pH>9.0, and Ca/P = 1.67. The stability of nanosized HAp in HAp/3Y-TZP composites was slightly inferior to commercial one, but the involvement of hydrothermally synthesized HAp improved sintered density of the composites and stability of t-ZrO2 phase in the composites.

Abstract: Various studies recommend that threaded type implants should be used to maximize initial contact, improve initial stability, enlarge implant surface area, and favor dissipation of interfacial stress. The objective of this study was to compare four types of screw implants placed in posterior region of mandible model and evaluate the influences of implant shape, configuration, length, diameter and abutment connection method on stress distribution using a three-dimensional finite analysis. Four types of two-length implant models — 8.5 and 13 mm — were selected and the wide diameter was also used. Four groups were classified by implant outline and connection manner A load of 100 N was applied vertically on the center of the implant. Oblique and horizontal loads were taken as equal to that of the vertical load. The TMJ area in mandibular model was constrained in all directions. Results show that the stress of two-length implants was similar in all groups and the internal connection implant with appropriate thickness of inner part of the implant had better stress distribution.

Abstract: Plastic substrates were modified with 2-methacryoyloxyethyl phosphorylcholine (MPC) copolymer brushes by surface-initiated atom transfer radical polymerization (ATRP) with a mean chain density of 2.44 chains/nm2 and a chain length around 50nm. Ellipsometry, X-ray photoelectron spectroscopy, gel permeation chromatography, nuclear magnetic resonance and atomic force microscopy were used to characterize the modified surfaces.
MPC was copolymerized with a methacrylate monomer including an active ester unit which can link covalently with antibodies. They latter were immobilized on these well-defined surfaces for characterization and a further use in enzyme-linked immunosorbent assay (ELISA).
All kinds of surfaces displayed a good density of immobilized antibodies mainly forming globular packs of around 500 units. A water-soluble MPC polymer-based stabilizer added to the antibody solution could further their individual immobilization.

Abstract: The 2% NaF and 8% SnF2 have been used in topical fluoridation method in the dental office to increase the resistance of enamel to acid dissolution. Bis-GMA based monomers have been used for the basic materials in the dental pit and fissure sealants. Therefore, the resinous pit and fissure sealant including fluorides may increase the effect of preventing dental caries. In this study, we made a novel dental pit and fissure sealant and evaluated some properties, especially fluoride release. In order to make experimental pit and fissure sealant including fluoride, NaF and SnF2 powder were added into self-made monomer composed of Bis-GMA, TEGDMA, UDMA and photo initiator system by weight percent of 2% and 8% respectively. The just monomer without fluoride powder was used for control. Uncured film thickness and depth of cure were measured according to ISO specification 6874:1988 and the viscosity was measured using rheometer. The five disc specimens were made using light curing unit to evaluate fluoride releasing and each specimen was immersed in the artificial saliva of 10 mL. Fluoride ion concentrations in extracts were measured for 3 days using fluoride electrode at every 12 hrs. There was no significant difference between experimental and control group in the depth of cure, uncured film thickness, and viscosity (p>0.05). The released fluoride ion concentration was continuously retained for 72 hrs.

Abstract: The hybrid Silver(Ag) nanoparticles were synthesized by gamma-irradiation, and characterized by field-emission transmittance electron microscopy (FE-TEM), field-emission scanning electron microscopy (FE-SEM), and energy dispersive X-ray spectroscopy (EDXS). The electron microscopy images show that well-dispersed Ag nanoparticles of about 3-7 nm were loaded to the outer and inner side of SiO2 nanoparticles of about 5-30 nm. Antifungal efficiency of the hybrid nanoparticles was tested against Aspergillus flavus ATCC 64025, Aspergillus fumigatus ATCC 16424, Aspergillus terreus ATCC 46941, Candida albicans ATCC 10231, Candida albicans A207(clinical isolate), Candida glabrata ATCC 48435, Candida krusei ATCC 6258, Candida lusitaniae ATCC 42720, Candida parapsilosis ATCC 34136, Candida tropicalis ATCC 13803, Cryptococcus neoformans ATCC 36556, and Mucor ramosissmus ATCC 90286. At the presence of hybrid Ag nanoparticles at 1 ppm, they did not grow fully even after 58 hrs except for Cryptococcus neoformans ATCC 36556. The hybrid Ag nanoparticle can be used for antifungal agents.

Abstract: In order to evaluate the mechanical properties of the human skeletal muscles, the elasticity and viscosity of the human calf muscles were measured with Magnetic Resonance Elastography (MRE). MRE is a novel method to measure the mechanical properties of living soft tissues in vivo quantitatively by observing the strain waves propagated in the object. In this study, the shear modulus and viscosity coefficient were measured with MRE. The shear modulus was 3.7 kPa in relaxed state, and increased with increasing the muscle forces. Interestingly, the viscosity was changed with the vibration frequency applied to the muscles, that was 4.5 Pa·s at 100Hz vibration and 2.4 Pa·s at 200Hz vibration. This shows clearly the visco-elastic property.

Abstract: Tissue-engineering must be either manufactured aseptically or sterilized after processing. To extend protection of medical devices against microbial contamination, various sterilization methods have been suggested. Hydrogen peroxide gas plasma sterilization has been applied in hospitals worldwide for almost a decade. In this study, we investigated the sterilization efficacy of hydrogen peroxide gas plasma sterilizer with porous polyurethane sample. The result is suggested that hydrogen peroxide gas plasma can be applicable to the sterilization of polymer scaffold for tissue engineering materials.

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 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 implant-bone interface. SGP generation is known to require intraosseous fluid flow related with generations of pore pressure gradient in bone. Therefore, SGP would interact with properties determining interstitial fluid flow characteristics such as viscosity, velocity, flow path directions, and interstitial fluid flow boundary conditions. Since interstitial fluid flow characteristics in bone are governed by pore pressure gradient, it could be possible to predict SGP indirectly through the prediction of pore pressure generation in bone. The aim of this study is to predict the distribution of pore pressure in OI bone-implant composite representing a completely osseointegrated rabbit tibia-titanium implant composite. The theoretical background of this prediction is based on the poroelasticity of 2-phase material that grounds on fluid flow and behavior of cortical bone material. In this study, we constructed a finite element (FE) model of the composite from images of micro-CT scanning. In the next step, we examined analysis of the FE model about pore pressure by using ABAQUS. In this analysis, the constitutive behavior was externally computed by utilizing a user subroutine. The results showed the different spatial distributions of pore pressure in the composite. The magnitudes of pore pressure were found to be significantly increased when the position was approached for the interface of implant-bone. Further analytical study is required to fully understand relationships between SGP and pore pressure distributions in OI bone-implant composite materials.