Developments in mechanical heart valve prosthesis

Artificial heart valves are engineered devices used for replacing diseased or damaged natural valves of the heart. Most commonly used for replacement are mechanical heart valves and biological valves. This paper briefly outlines the evolution, designs employed, materials being used,. and important factors that affect the performance of mechanical heart valves. The clinical performance of mechanical heart valves is also addressed. Efforts made in India in the development of mechanical heart valves are also discussed.     

An Expeditious and Metal‐Free Synthetic Route towards Quinolones,Naphthyridones and Benzonaphthyridones

An efficient, two‐step synthetic strategy has been developed to access the quinolone, naphthyridone and benzonaphthyridone classes of chemotherapeutic agents from Baylis–Hillman adducts. The method involves tandem aza‐Michael addition, S_NAr cyclisation followed by oxidation of the resulting 4‐hydroxy‐1,2,3,4‐tetrahydroquinoline or 4‐hydroxy‐1,2,3,4‐tetrahydro‐1,8‐naphthyridine derivative using IBX, and works well with substrates having a wide variety of substitution pattern.

     

Transmission electron microscopy and X-ray diffraction studies of quantum wells

A series of In _x Ga_1?x As (x=0·47) quantum wells with InP barrier layers have been grown on InP substrates by metalorganic vapour phase epitaxy (MOVPE) at 625°C. The nominal well widths were defined during growth at (i) 25 Å, 39 Å, 78 Å and 150 Å for one sample and (ii) 78 Å for all 4 wells in another sample. The InP barrier widths have been kept constant at 150 Å. These layers have been characterized by X-ray diffraction (XRD) which from simulation gave the nominally 78 Å well width as 84 Å and the nominally 150 Å barrier width as 150·5 Å. Transmission electron microscopy (TEM) and high resolution TEM (HRTEM) have been carried out on etched and ion-milled samples for direct measurement of well and barrier widths. The well widths found from TEM are 25 Å, 40 Å, 75 Å and 150 Å. TEM micrographs revealed that, while the InP barrier layer is of good quality and the growth is confirmed to be epitaxial, dipoles are detected at the interface and the quantum well has some small disordered regions. These thickness measurements are in good agreement with earlier photoluminescence (PL) and secondary ion mass spectrometry (SIMS) studies.     

Laser surface modification of titanium substrate for pulsed laser deposition of highly adherent hydroxyapatite

Biomedical implant devices made out of titanium and its alloys are benefited by a modified surface or a bioactive coating to enhance bone bonding ability and to function effectively in vivo for the intended period of time. In this respect hydroxyapatite coating developed through pulsed laser deposition is a promising approach. Since the success of the bioactive ceramic coated implant depends mainly on the substrate-coating strength; an attempt has been made to produce micro patterned surface structure on titanium substrate for adherent hydroxyapatite coating. A pulsed Nd-YAG laser beam (355 nm) with 10 Hz repetition rate was used for surface treatment of titanium as well as hydroxyapatite deposition. The unfocussed laser beam was used to modify the substrate surface with 500–18,000 laser pulses while keeping the polished substrate in water. Hydroxyapatite deposition was done in a vacuum deposition chamber at 400°C with the focused laser beam under 1 × 10⁻³ mbar oxygen pressure. Deposits were analyzed to understand the physico-chemical, morphological and mechanical characteristics. The obtained substrate and coating surface morphology indicates that laser treatment method can provide controlled micro-topography. Scratch test analysis and microindentation hardness values of coating on laser treated substrate indicate higher mechanical adhesion with respect to coatings on untreated substrates.     

Effect of Strain Rate on Ductile-to-Brittle Transition Temperature of a Free-Standing Pt-Aluminide Bond Coat

The ductile-to-brittle transition temperature (DBTT) of a free-standing Pt-aluminide (PtAl) bondcoat was determined using the microtensile testing method and the effect of strain rate variation, in the range 10⁻⁵ to 10⁻¹ s⁻¹, on the DBTT studied. The DBTT increased appreciably with the increase in strain rate. The activation energy determined for brittle-to-ductile transition, suggested that such transition is most likely associated with vacancy diffusion. Climb of 〈100〉 dislocations observed in analysis of dislocation structure using a transmission electron microscope (TEM) supported the preceding mechanism.     

Dynamic mechanical analysis of ethylene–propylene–diene monomer rubber and styrene–butadiene rubber blends

The effects of blend ratio, crosslinking systems, and fillers on the viscoelastic response of ethylene–propylene–diene monomer (EPDM)/styrene–butadiene rubber (SBR) blends were studied as functions of frequency, temperature, and cure systems. The storage modulus decreased with increasing SBR content. The loss modulus and loss tangent results showed that the EPDM/SBR blend vulcanizate containing 80 wt % EPDM had the highest compatibility. Among the different cure systems studied, the dicumyl peroxide cured blends exhibited the highest storage modulus. The reinforcing fillers were found to reduce the loss tangent peak height. The blend containing 40 wt % EPDM showed partial miscibility. The dispersed EPDM phase suppressed the glass‐transition temperature of the matrix phase. The dynamic mechanical response of rubbery region was dominated by SBR in the EPDM–SBR blend. The morphology of the blend was studied by means of scanning electron microscopy. The blend containing 80 wt % EPDM had small domains of SBR particles dispersed uniformly throughout the EPDM matrix, which helped to toughen the matrix and prevent crack propagation; this led to enhanced blend compatibility. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis,evaluation of kinetic characteristics and investigation of apoptosis of Cu2+-modified ceria nano discs

Ceria nano discs were synthesized by the stepwise thermal decomposition strategy of the oxalate precursor. A series of Ce_1–xCu_xO₂ (x = 0, 0.02, 0.1, 0.2 and 0.3) nano sized oxide systems were prepared through thermal decomposition route. Kinetic characterization of formation of solid solution was made by isoconversional strategy under non-isothermal condition. Introduction of various reactant molar ratios of Cu²⁺:Ce⁴⁺ has a pivotal role in the creation of new oxygen vacancies, decomposition strategy, particle size and shape. Cu²⁺ doping (x = 0.02 and 0.1) damages the disc shaped morphology of ceria. Homogeneous distribution of Cu²⁺ on the oxalate precursor has a significant role in the catalyzing activity for the destruction of oxalate bond to oxide. 2 mol% doped Cu²⁺ promotes breaking of oxalate bonds in nitrogen atmosphere. In vitro cell viability assay illustrates enhanced toxicity to cancer cells with 10 mol% Cu²⁺ doped ceria.     

Residual deposits in green tea shoots and black tea after individual and combined application of propiconazole and copper oxychloride

BACKGROUND: A combination of propiconazole and copper oxychloride is commonly used for controlling blister blight disease caused by the fungus Exobasidium vexans Massee of tea in south India. Field trials were conducted in wet and dry seasons to determine the rate of dissipation of propiconazole and copper oxychloride (COC) in green tea shoots and black tea. High‐performance liquid chromatography was used to quantify propiconazole residues in these matrices. Copper was analysed using atomic absorption spectrometry. RESULTS: The rate of dissipation of propiconazole in both seasons followed first‐order kinetics. Dissipation was faster in the wet than in the dry season. Factors such as rainfall elution and leaf growth dilution lead to faster residual decline in the wet season. However, even in wet season 0.10 mg kg^?1 of propiconazole residues were noted in black tea on the seventh day after fungicide application because of its systemic nature. Thus good control over the disease could be achieved. CONCLUSION: The recommended safe harvest interval and half‐life for the combined application of propiconazole and COC from this study is 5.39 and 2.43 days respectively in green tea shoots during the dry season. Moreover, the residues of propiconazole in green tea shoots on the seventh day is the same as the maximum residue limit (MRL) proposed by the European Union (EU), indicating that combined application of the two chemicals does not leave significant residues on seventh day or thereafter. Hence, upon harvest, which is usually between 8 and 10 days after fungicide application, the green tea shoots are safer from fungicide residues and pose less risk to human consumption. Copyright © 2009 Society of Chemical Industry