Advanced Materials Research Vol. 506

Abstract: We have fabricated a low-cost and flexible NH₃ gas sensor using thermal ink-jet printing. The poly (3,4-ethylene dioxythiophene) doped with polystyrene sulfonated acid (PEDOT/PSS) with thickness of ~ 2 μm was used as a sensing film. The interdigitated electrode using patterned aluminum plate was attached over the sensing film. Atomic force microscopy results show the high homogeneous film and only small roughness is presented on the sensing film. This sensor exhibits high selectivity and sensitivity to NH₃ at room temperature. The sensor response works linearly with gas concentrations between 100-1000 ppm. The modulation of conducting polymer/metal electrode interface plays a role in the sensing mechanism of NH₃. Changes in the position of interdigitated electrodes can change the dominant sensing mechanism of typical polymer gas sensor.

Abstract: We propose the use of molecular networks for drug delivery and diagnosis applications. Three modules of molecular networks such as bus, star,and ring networks are designed and manipulated based on a micro and nanoring resonator system. The transportation of the trapping molecule by light in the networks is described, the theoretical background is reviewed. However, the problems of large microscopic volumes and networks may be caused problems, in which the searching for new guide pipe and medium for instance, nanotube and specific medium and crosstalk effects will be the issue of investigations. Moreover, the qualities of network reliability are measurement in the form of signal transmission, i.e. signal to noise ratio (SNR) and crosstalk effects are discussed in details.

Abstract: In this paper, the use of molecular buffer and network for molecular diagnosis is presented. The trapping molecule is formed and transmitted into the required target via the molecular buffer and bus network. The optical trapping tool in the application of blood circulation manipulation analysis use the PANDA ring resonator system incorporating with bus network. The trapping force is formed by the combination of the gradient field and scattering photons. By using the blood circulation system, the blood pressure control, molecular diagnosis, and in situ surgery can be provided.

Abstract: This paper describes the molecular design of a speciality polyester for use as a fast-absorbable monofilament surgical suture. In the surgical context, fast-absorbable means tensile strength loss within a period of 10-14 days, the minimum period required for secure wound approximation, after which the suture gradually loses its mass integrity leading to complete mass loss within 2-3 months. In order to be fast-absorbable, it is necessary that the main monomer used in synthesizing the polymer is glycolide since the polymer repeating unit, -OCH₂CO-, is the chemical structure which hydrolyses the most rapidly in the human body. However, glycolide alone would give a monofilament suture fibre which would be too stiff and unwieldy for practical purposes and so it needs to be copolymerised with other cyclic ester monomers such as L-lactide and caprolactone to modify its mechanical properties. In this way, a monofilament fibre can be obtained which has an appropriate balance of hydrolysability and flexibility. Thus, this work enters the realm of molecular engineering insofar that it involves the strict control of both the chemical and physical microstructure of the polymer during the synthesis and processing steps respectively. This paper will describe how this controlled molecular architecture can be achieved and some preliminary results will be presented.

Abstract: The biphasic calcium phosphate (BCP) concept was introduced to overcome disadvantages of single phase biomaterials. In this study, we prepared BCP from nanoHA and β-TCP that were synthesized via a solid state reaction. Three different ratios of pure BCP and collagen-based BCP scaffolds (%HA/%β-TCP; 30/70, 40/60 and 50/50) were produced using a polymeric sponge method. Physical and mechanical properties of all materials and scaffolds were investigated. XRD pattern proved the purity of each HA, β-TCP and BCP. SEM showed overall distribution of macropores (80-200 µm) with appropriate interconnected porosities. Total porosity of pure BCP (93% ± 2) was found to be higher than collagen-based BCP (85%± 3). It was observed that dimensional shrinkage of larger scaffold (39% ± 4) is lower than smaller one (42% ± 5) and scaffolds with higher HA (50%) ratio experienced greater shrinkage than those with higher β-TCP (70%) ratio (45% ±3 and 36% ±1 respectively). Mechanical properties of both groups tend to be very low and collagen coating had no influence on mechanical behavior. Further studies may improve the physical properties of these composite BCP.

Abstract: High reliable hydroxyapatite (HAp) coating on commercially pure titanium (cp-Ti) substrate with and without mixed hydroxyapatite/Titanium (HAp/Ti) bond coat was successfully developed by using plasma spraying. The four-point bending with Acoustic Emission attachment (AE) for evaluating failure behavior of the two kinds coated specimens was conducted to investigate the effect of bond coat layer on failure of the coating. The effect of apatite precipitation by immersing in conventional simulated body fluid (c-SBF) on failure behavior of the coated specimens were also investigated. The AE patterns obtained during four-point bending test of the specimens with apatite precipitation after immersion in c-SBF was compared with those of the specimens without apatite precipitation. After a week immersion in c-SBF, the AE patterns obtained from four-point bending test of HAp top coating specimens with and without bond coat clearly showed faster failure of the coating compared to those without c-SBF immersion. In addition, under c-SBF, the bond coating contributed to the retarded failure of the HAp top coating compared to that without bond coat. From XRD analysis, the as-sprayed layer composed of HAp coexisted with CaO. After c-SBF immersion, CaO dissolved into c-SBF and the as-sprayed HAp top coating changed to bone-like apatite which might contribute to the faster failure of the coating.

Abstract: Plasma sprayed Hydroxyapatite (HAp) coating on commercially pure titanium (cp-Ti) is widely used as implant materials. In this study, fatigue behavior of as-sprayed HAp top coat with HAp/Ti bond coat specimen under ambient environment (A-HTi) as well as under simulated body fluid, SBF, environment (I-HTi) at 36.5°C was investigated by four point bending fatigue test at a stress amplitude of 170 MPa under various frequencies. In order to investigate apatite precipitation during fatigue loading, the test specimen was immersed in SBF at 36.5°C during the fatigue test. For comparison, the test specimen was immersed in SBF at 36.5°C for a day to a week without fatigue loading and then the fatigue test of the immersed specimen was carried out under ambient environment (I-A-HTi). The fatigue loading would not influence the apatite precipitation in the HAp coating layer of the specimen. The fatigue lives of the I-HTi and I-A-HTi specimens were shorter compared to that of A-HTi specimen. The shorter fatigue lives of the I-HTi and I-A-HTi specimens would result from the attack of SBF on titanium substrate. However, the apatite precipitation in the coating layer up to one week immersion did not significantly influence the delamination between HAp top coat and cp-Ti substrate under the bending fatigue.

Abstract: Sulfonic-functionalized carbon material derived from the incomplete carbonization of mungbean vermicelli was reported here as a catalyst for esterification of acetic acid. The catalyst with the highest activity (S_BET = 18.1 m²/g and acid site density of 1.53 mmol H⁺/g_cat) was obtained by carbonization at 573 K and sulfonation at 373 K due to a feasible attachment of more SO₃H groups to flexible carbon sheets compared to the other synthesized solids. Approximate 64% yield of methyl acetate was achieved over (2:1) molar ratio of methanol to acetic acid with 3 wt% of catalyst. From the economic outlook, this environmentally benign C-SO₃H catalyst could be a promising candidate for the esterification of high free fatty acid feedstocks reducing the production cost of biodiesel.

Abstract: Biphasic calcium phosphate (BCP) ceramic is commonly used in the biomedical applications particularly as a bone substitute due to its biocompatibility and directly bond to bones. However, the mechanical strength is quite poor. Therefore, well known biocompatible and strong ceramics such as SiO₂, ZrO₂ and TiO₂ were added to improve the strength of BCP. BCP powder with HA/TCP ratios of 70/30 (HAP7030) was obtained by controlling the calcining temperature of the mixture between a pure HA and TCP. SiO₂, ZrO₂ and TiO₂ powder with 2, 5 and 10 %wt were mixed with the HAP7030 powder by ball milling in ethanol. The mixtures were dried, pressed and sintered at 1100°C for 2 hrs. XRD and SEM were used to determine crystal structures and morphology of the sintered samples, respectively. Physical properties and flexural strength of samples were measured. Results showed that the bending strength of HAP7030 sample was rather improved by adding TiO₂ than the addition of SiO₂ or ZrO₂. With increasing TiO₂, HAP7030 strength was superior and HAP7030 with 10 %wt of TiO₂ obtained the optimum bending strength around 61 MPa. However, the addition of TiO₂ induced the thermal stability of HA/TCP, in which HA completely decomposed to β-TCP in this study.

Abstract: ZnO nanoparticles were successfully synthesized by using zinc dust waste derived from hot-dip galvanizing process as a starting materials via simple hydrothermal method. The zinc dust powder was dissolved in nitric acid, adjusted pH with NaOH and hydrothermally treated at 120-170°C in an oven. The resultant products were characterized for phase, surface area and morphology by X-ray diffraction (XRD), Brunauer-Emmet-Taller (BET) and Scanning electron microscopy (SEM), respectively. Moreover, the photocatalytic activity was investigated by a photodegradation of methylene blue solution under black light irradiation. It was shown that crystallinity of pure ZnO phase, was influenced by solution and hydrothermal treatment temperature. The experimental results exhibited that the crystallinity of ZnO significantly affected its photocatalytic activity. The highest photocatlytic activity was obtained from powders with average crystallite size of 51 nm and surface area of 13.4 m²/g prepared under pH12 and hydrothermally treated at 170°C for 6 h. Moreover, the synthesized ZnO powders performed a good antibacterial activity evaluated using a colony count method with Escherichia coli under the dark condition.