Applied Mechanics and Materials Vol. 804

Abstract: Titanium dioxide (TiO₂) is the most widely used photocatalyst because of its high photocatalytic activity and reasonably low cost. Moreover, TiO₂ has strong chemical stability in a large variety of environmental conditions. The combination of TiO₂ with cementatious materials has been widely investigated, and the effects of the TiO₂ contents (10-40% by weight) were studied in this research. The crystalline structures and chemical compositions were analyzed using x-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDS), respectively. Moreover, its microstructure was investigated by scanning electron microscopy (SEM). It was found that the intensity of CS and CH decreased with an increase in the TiO₂ powder content. This was because when adding more TiO₂ powder to the composite system, more water was needed to add to the hydration reaction.

Abstract: Hydroxyapatite (HA) is widely used in biomedical applications as an artificial bone due to its excellent biocompatibility. In this work, the high purity HA powders were synthesized from natural bovine bone by a sequence of thermal processes. Then, the HA-based composites containing titanium nitride (TiN) at various compositions were fabricated by a solid-state reaction mixed oxide method. The green compacts were subsequently pressed and then sintered at 1200-1250°C for 2 hours. Surface morphology, compositions and phases of the as-prepared HA-based composites were analyzed by means of scanning electron microscopy (SEM) utilizing energy dispersive X-ray spectroscopy (EDS) and X-ray diffractometry (XRD), respectively. The results showed that the physical and mechanical properties and also the aesthetic performance of HA-TiN composites were substantially varied through the changes in the microstructure and volume fraction of the reinforcing particulates. The maximum hardness value of 3.5 GPa was obtained for HA-2wt%TiN ceramic sintered at 1250°C.

Abstract: Calcium phosphate is a biomaterial which exhibits excellent biocompatibility, bioactivity and biodegradability for bone replacement and other medical applications. In the present work, multiphasic calcium phosphate compounds consisting of hydroxyapatite (HAp) and tri-calcium phosphates (TCP) were prepared by a solid state reaction method. Effects of calcium carbonate (CaCO₃: ±3-5 wt%) on the properties of the studied powders were investigated where calcium carbonate powder was synthesized from a natural product (cockle shell). The phase formation and morphology of the powders were characterization by many techniques such as XRD, SEM and dynamic light scattering techniques. The results showed that amount of calcium carbonate additive affected on the properties of the studied samples.

Abstract: In this research, the effects of sintering temperatures on structural and bioactivity in BaFe₁₂O₁₉ (BF) /P₂O₅-CaO-Na₂O bioactive glass ceramics were investigated. The BF/P₂O₅-CaO-Na₂O bioactive glass ceramics were fabricated under various sintering temperatures in a range of 550-700 oC. X-ray diffraction (XRD) technique and the scanning electron microscopy (SEM) are used to characterize phase and microstructure. The studied samples were evaluated for mechanical properties by hardness testing. Moreover, the bioactivities of studied samples were studied by using simulated body fluid (SBF) in vitro. It was found that, the sintering temperatures are the most influential parameter on microstructure and mechanical properties of the bioactive glass ceramics. The highest density of studied ceramics was found in the sample sintered at 700 oC. The microstructural properties of the studies samples were investigated and the results were then correlated with the characteristics of sintering temperature as well as the microstructure of the bioactive glass ceramic. Moreover, the covering of bone-like apatite layer on the surface sample after a 7 day immersion in SBF suggested that the BF/P₂O₅-CaO-Na₂O glass ceramics have acceptable bioactivities.

Abstract: This work aims to fabricate and investigate biopolymer electrospun nanofibers of polycaprolactone (PCL) mixed with Centella asiatica (C. asiatica). The nanofibers were manufactured by electrospinning technique. C. asiatica were extracted and loaded into the nanofibers with different contents (0.5, 2.5, 5 and 10 wt%). Fourier transform infrared analysis indicated that both PCL and C. Asiatica presented in the nanofibers without chemical reaction between them. The morphology of the nanofibers was investigated by a scanning electron microscope, exhibiting smooth and bead-free with diameters of 300 to 500 nm. Mechanical properties of the fibers show that the tensile stress notable increased with the C. Asiatica content. Antimicrobial activity test showed that this material had a potential for anti-bactericidal activity.

Abstract: An optical biosensor based on a grating to be utilized for the detection of DNA target molecules was fabricated by photolithographic techniques. The sensor surface implements a grating to create a low effective refractive index platform via the combination of Si₃N₄ and SiO₂ which allows the detection via changes of the reflectivity spectra. The active surface carried a layer of probe biomolecules for specific binding of the target DNA. Immobilization of the probe molecules was carried out via streptavidin using biotin modified ssDNA complementary to the target ssDNA. When molecules attached to the surface of the device, the position of the reflectance spectrum shifted due to the change of the optical path of light that is coupled into the grating structure. The extent of the wavelength shift of the peaks could be used to quantify the amount of materials bound to the sensor surface thereby allowing detection of the surface modifications as well as the quantification of the DNA analyte. The advantages of this device are that it works with a small sample volumes (few microlitres), are integratable in micro array type of setups and can be used at room temperature.

Abstract: In this work, we use photolithography in order to fabricate micro-grating structures on silicon. The first step of device was coated by 3.5 μm thick silicon dioxide (SiO₂) film on top side, whereas the bottom side was coated with 4.5 μm. Next, we deposited silicon nitride (Si₃N₄) film of 2 μm by plasma-enhanced chemical vapor deposition, and used photolithography to prepare the gratings. We compared micro-grating period sizes of 1 μm, 0.8 μm and 0.5 μm, and found the 0.5 μm gave the best sensitivity. These devices can be applied with detection in biosensing in the future.

Abstract: A model was developed to predict the UV absorbance spectra and thus concentration of single stranded DNA (ssDNA) samples. The model was developed from UV absorbance spectra of ssDNA oligodeoxynucleotides determined at different concentrations. The model, which would predict the concentration of ssDNA from the A₂₆₀ value, is shown to predict absorbance spectra of ssDNA as shown when compared to the experimental result.

Abstract: In this study, 2 wt% ZnFe₂O₄/HAp ceramic was prepared to form a promising composite material for future biomedical applications. Firstly, HAp powder was synthesized by precipitation using Ca(NO₃)₂ as the Ca source, (NH₄)₂HPO₄ as the P source and ammonia as a pH adjuster. To prepare 2 wt% of ZnFe₂O₄, ZnO and Fe₂O₃ powders were mixed in ethanol with sequent dehydration and then calcination (using stoichiometric ratio). Finally, 2 wt% of ZnFe₂O₄ powder was milled with 98 wt% of HAp powder for 10 minutes before uniaxial pressing and then sintering at 1200 °C for 3 hours to form 2 wt% ZnFe₂O₄/HAp ceramic. The prepared ceramic was characterized by X- ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and vibrating sample magnetometer (VSM). The XRD results revealed the ZnFe₂O₄/HAp ceramic with only HAp and ZnFe₂O₄ phases obtained, indicating that no impurities phases occurred. The FT-IR results revealed vibration bands of standard HAp and indicated the interaction between ZnFe₂O₄ and HAp. For the VSM results, the magnetization of composite was 0.05 emu/g and its coercivity was 44 Oe. These results could lead us to the development of a method for ZnFe₂O₄/HAp ceramic optimized for specific biomedical applications.

Abstract: The silk sericin/gelatin composite films were successfully prepared for future cosmetic applications. The sericin was extracted from Thai raw cocoons of the Bombyx mori silk worm via boiling and drying. Gelatin was extracted from white perch scales through a chemical treatment. To prepare the silk sericin/gelatin composite film, the silk sericin and gelatin solutions with different volume ratios were blended in distilled water by stirring in a magnetic stirrer for 30 minutes. They were dropped on the plastic mold. The sample was kept at a temperature of 50 °C to let it dry. The prepared composite films were characterized using UV-VIS spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscope (SEM). The silk sericin/gelatin composite films showed elastic behaviour, a homogeneous surface and no porosity which could indicate possible future use for cosmetic applications.