Materials Science Forum Vol. 987

Abstract: Crosslinker (polyvinylsilicone oil, C gum) and curing agent (2, 5-bis (tert-butyl peroxy)-2, 5-dimethyl hexane, DBPMH) were used to change the crosslink density of the thermal conductivity of silicone rubber filled with Al₂O₃. The results show that the thermal conductivity of silicone rubber changed with its degree of crosslinking. When the Al₂O₃ loading was 5 vol. % and a completely continuous conducting network had not formed, the thermal conductivity of the vulcanizates decreased with increasing crosslink density. The thermal conductivity of the vulcanizate with a suitable amount of C gum increased to 53%, and the tensile strength increased by 0.8 MPa compared to the vulcanizate without C gum. When the Al₂O₃ loading was 30 vol. % and a completely continuous conducting network had formed, the crosslink density of vulcanizates changed as the amount of DBPMH changed. The thermal conductivity of vulcanizates first decreased and then increased with increasing crosslink density. There was a valley value in the thermal conductivity–crosslink density curve.

Abstract: One component room temperature vulcanized (RTV) silicone resin was prepared by combination of a kind of D-T polysiloxane block copolymer with crosslinker and catalyst. Transparent coating with good elastoplasticity without any inorganic filler could be obtained by exposing the RTV silicone to air at room temperature. The structure of D-T block copolymer played an important role in the properties of the cured products. It was synthesized by polycondensation of partially hydrolyzed phenyltrimethoxysilane (phenylsilsesquioxane, T units) with silanol end-capped polydimethylsiloxane (PDMS, D units). The effects of the viscosity of phenylsilsesquioxane and the D/T ratio on the properties of cured product were investigated. When phenylsilsesquioxane (10000cP at 80°C) was used and the D/T ratio was 2.0~2.3, cured products with tensile strength above 2.5MPa and elongation above 70% were prepared. RTV silicone resin composed of such kind of D-T block copolymer had good heat resistance because the existence of phenyl group and the highly cross-linked 3D structure. The T_onset was 387.6°C and the T_max was 518°C.

Abstract: In this study, cathode and lithium-ion conducting solid electrolyte composite pellet with 1:1 wt. % composition of LiFePO₄ and Li_7-3XGa_xLa₃Zr₂O₁₂ (x = 0.1) (LiFePO₄|Ga-LLZO) was prepared via solid-state reaction. The aim of the study is to investigate the phase stability between LiFePO₄ cathode and Ga-LLZO solid electrolyte material when heat treated at 400 to 600 °C. The as-mixed LiFePO₄|Ga-LLZO composite was characterized by TG/DTA and the heat treated sample was then analyzed for its structure using XRD and compared to the just as-mixed composite. XRD patterns of the heat treated composite pellet showed that it retains its as-mixed phases of LiFePO₄ and Ga-LLZO when sintered below 500 °C under Ar gas flow environment. However, upon heat treatment at 600 °C, the sample already reacted and decomposed with the formation of other phases.

Abstract: Biodegradable vascular stent is mainly made of materials that can be naturally decomposed. Magnesium and its alloys have excellent mechanical properties and biocompatibility. The vascular stent made of magnesium and its alloys has the unique advantages of strength of metal scaffolds and bioabsorbability of degradable polymer scaffolds. Due to the special microenvironment inside the blood vessels, the stent should have good resistance against corrosion. After implantation of metal materials for human tissue repair, the surface oxidation film spontaneously formed in the air will react with the human physiological environment. The nature of the interface between materials and tissues will have a certain impact on the corrosion resistance of metals and the degree of metal ion release, thus determining the biocompatibility of materials.

Abstract: The main objective of the present investigation was to develop buccal tablets of ramipril, to bypass the first pass metabolism and to improve its oral bioavailability. Ramipril, an ACE inhibitor used in the treatment of hypertension undergoes extensive first pass metabolism and about 25% of the drug reaches the systemic circulation. A unidirectional, bilayered mucoadhesive tablet of ramipril was prepared using HPMC as polymer by direct compression technique. Initially, a backing layer was made by using ethyl cellulose, onto which the drug containing layer as placed and recompressed to get a bilayered tablet. The buccal tablets were evaluated for various parameters such as weight variation test, thickness, hardness, friability, in vitro swelling studies, in vitro mucoadhesion study and in vitro dissolution study. Among the different formulation, the formulation (F1) prepared using 5% HPMC as polymer exhibited satisfactory performance over the other batches and considered as an ideal batch. The release of the drug from the tablets exhibited zero order kinetics and the mechanism of release was governed by diffusion process.

Abstract: The main aim of the present investigation was to formulate and evaluate gastroretentive floating tablets of theophylline. Theophylline, a brochodialator, used in the treatment of asthma, has good absorption at the gastric pH. Therefore, a floating drug delivery system in a gastric pH could deliver the drug in a slow and sustained manner which could be a useful for broncho dilation in the treatment of asthma. The formulated gastroretentive tablets of theophylline were evaluated for various parameters such as weight variation, hardnesss, friability, drug content, swelling index, buoyancy time and drug release studies. Among the different formulations, formulation F7 prepared using HPMC:Carbopol (1:1 ratio) exhibited better release profile (93.36%) for 8 hours and this batch was selected as an ideal batch. The release of theophylline from the ideal batch was found to follow diffusion mechanism.

Abstract: Biodegradable vascular stent is mainly made of materials that can be naturally decomposed. After implantation into human blood vessels, the vascular stent can be continuously degraded over time and eventually disappear completely after the treated blood vessels are healed and support from the vascular stent is not needed. The vascular stent materials used in clinic should have good biocompatibility, which mainly involves blood compatibility and cell compatibility. In terms of cell compatibility, the influence of materials on cell growth should be observed. The various biological materials should have good anticoagulant character, so as to reduce the tendency of thrombosis and avoid the occurrence of various risk events in clinical treatment.

Abstract: Monodisperse mesoporous SiO₂ microsphere is a potential fine candidate carrier of dry powder inhalation, but large numbers of active surface hydrophilic hydroxyls enhance surface energy, hydrogen bonding and electrostatic force, environmental water adsorption and particle agglomeration. Conventional hydrophobic modification of surface hydroxyls, which is conducive to solve the above-mentioned disadvantages, will limit the loading of water-soluble drugs and the drug dissolution in water simultaneously. In this study, monodisperse mesoporous SiO₂ microspheres were prepared as carrier and modified innovatively by amphiphilic modifier octaphenylpolyoxyethyiene and 3-aminopropyltriethoxysilane, particle diameter about 60 nm, mean pore size 21.4 nm, specific pore volume 0.95 cm³/g, and specific surface area 130 m²/g. Model drug pentoxyverine citrate was loaded by pressure infiltration and spray drying process, drug loading 8.24%, repose angle 34°, mass median aerodynamic diameter 1.03 μm, and more than 90% of drug could dissolve within 30 min both in water and organic solvents.

Abstract: The effect of plasticizers and content on rheological behaviour of Caesalpinia pulcherrima gum aqueous solutions and on mechanical properties on gum films was investigated. Three plasticizers as glycerol and sorbitol and propylene glycol at different ratios were used. The results presented that plasticizer adding reduced the apparent viscosity of mixture solution, caused by polymer interaction weakening. However, they exhibited shear-thinning behaviour and typical shape for macromolecular solutions in viscoelastic property.

Abstract: The gum edible films were prepared from Caesalpinia pulcherrima seeds. The effects of plasticizer types and contents on physical and mechanical properties of gum edible film were investigated. Three plasticizers as glycerol and sorbitol and propylene glycol at different adding concentrations (0.5%, 1.0%, and 1.5%) were used. Glycerol provided flexible and sticky films with the highest water vapour permeability and elongation at break but the lowest tensile strength. In contrast, propylene glycol provided brittle films with the highest tensile strength but the lowest elongation at break and water vapour permeability. In addition, increasing in plasticizer content resulted in decreased tensile strength concomitant with an increased in elongation at break and water vapor permeability.