Synthesis,characterization, and enzymatic degradation of network aliphatic copolyesters

Network copolyesters were prepared from glycerol (Yg) and sebacic acid (10) with 10–90 mol % of either succinic acid (4), 1,12-dodecanedicarboxylic acid (14), 1,18-octadecanedicarboxylic acid (20), or terephthalic acid (T). Prepolymers prepared by melt-polycondensation were cast from dimethylformamide solution and postpolymerized at 230–250°C for various periods of time to form a network. The resultant films were transparent, flexible, and insoluble in organic solvents. The network copolyesters obtained were characterized by infrared absorption spectra, wide angle X-ray diffraction analysis, density measurement, thermomechanical analysis, differential scanning calorimetry, and tensile test. The enzymatic degradation was estimated by weight loss of the network copolyester films in a buffer solution with Rhizopus delemar lipase at 37°C. The weight loss due to the enzymatic degradation was decreased with increasing comonomer content, and the copolyesters with Yg4, Yg20 and YgT more than 50 mol % were not degraded by lipase enzyme at all. On the contrary, Yg-10/14 films were degraded appreciably over whole range of comonomer composition. With increasing comonomer content, the heat distortion temperature increased gradually, while the tensile strength and Young's modulus were not changed much. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2005–2011, 1999     

Large-scale synthesis of nearly monodisperse CdSe/CdS core/shell nanocrystals using air-stable reagents via successive ion layer adsorption and reaction

Successive ion layer adsorption and reaction (SILAR) originally developed for the deposition of thin films on solid substrates from solution baths is introduced as a technique for the growth of high-quality core/shell nanocrystals of compound semiconductors. The growth of the shell was designed to grow one monolayer at a time by alternating injections of air-stable and inexpensive cationic and anionic precursors into the reaction mixture with core nanocrystals. The principles of SILAR were demonstrated by the CdSe/CdS core/shell model system using its shell-thickness-dependent optical spectra as the probes with CdO and elemental S as the precursors. For this reaction system, a relatively high temperature, about 220-240 degrees C, was found to be essential for SILAR to fully occur. The synthesis can be readily performed on a multigram scale. The size distribution of the core/shell nanocrystals was maintained even after five monolayers of CdS shell (equivalent to about 10 times volume increase for a 3.5 nm CdSe nanocrystal) were grown onto the core nanocrystals. The epitaxial growth of the core/shell structures was verified by optical spectroscopy, TEM, XRD, and XPS. The photoluminescence quantum yield (PL QY) of the as-prepared CdSe/CdS core/shell nanocrystals ranged from 20% to 40%, and the PL full-width at half-maximum (fwhm) was maintained between 23 and 26 nm, even for those nanocrystals for which the UV-vis and PL peaks red-shifted by about 50 nm from that of the core nanocrystals. Several types of brightening phenomena were observed, some of which can further boost the PL QY of the core/shell nanocrystals. The CdSe/CdS core/shell nanocrystals were found to be superior in comparison to the highly luminescent CdSe plain core nanocrystals. The SILAR technique reported here can also be used for the growth of complex colloidal semiconductor nanostructures, such as quantum shells and colloidal quantum wells.     

Intra-aneurysmal blood flow based on patient-specific CT angiogram

To discuss the validity of the hemodynamic hypothesis of aneurysm rupture, we used a patient-specific, realistic aneurysm model to reveal the flow structure and wall shear stress distribution in two cases: one with an unruptured aneurysm and the other with a ruptured aneurysm. We used particle imaging velocimetry and laser Doppler velocimetry to measure velocity profiles of intra-aneurysmal flow. Both cases had a circulating flow along the aneurysm wall, although the second case had a recirculating zone only in the minimum phase. Differences in the wall shear stress profile may identify aneurysm rupture.     

Properties of a Thin-Film Optical Waveguide Using Fluorinated Silicon Oxide and Organic Spin-on-Glass Films

A thin-film optical waveguide using a fluorinated silicon oxide (SiOF) as a core layer was investigated. An organic spin-on-glass (SOG) film was used for a cladding layer. The SiOF films were formed at 23°C by a liquid-phase deposition (LPD) technique using a supersaturated hydrofluosilicic acid (H₂SiF₆) aqueous solution. A thin-film optical waveguide structure for single mode was designed and fabricated, based on the dispersion properties of refractive indices for the LPD-SiOF and organic SOG films. The refractive indices at a wavelength of 632.8 nm were 1.430 and around 1.400 for the LPD-SiOF and organic SOG films, respectively. The thickness of LPD-SiOF films deposited was 1.18 μm. Thicknesses of cladding organic SOG films cured at 300 and 400°C were 1.28 and 1.31μm, respectively. The effective refractive indices for single mode were 1.4169 and 1.4158 at a wavelength of 632.8 nm for the cladding organic SOG films cured at 300 and 400°C, respectively, and differences between the measured and calculated incident angles were 0.84° and 1.29° for the cladding organic SOG films cured at these respective temperatures. A streak of guided-light was observed for the LPD-SiOF/SOG structure optical waveguide. The transmission loss was 7.6-7.9 dB/cm.     

Molecular weight distribution formed during free‐radical polymerization in the presence of polyfunctional chain transfer agents

Free‐radical polymerization of styrene was carried out in the presence of chain transfer agents (CTAs) with functionality, f = 1–4. The size exclusion chromatography (SEC) with an ultraviolet absorption detector (UV) was used to measure the molecular weight distribution (MWD). A Monte Carlo simulation method proposed earlier was used to investigate the experimental results. In this simulation method, one can observe the structure of each polymer molecule directly, and very detailed information can be obtained in a straightforward manner, including the elution curve of SEC. It was found that up to the functionality f = 3, the equal reactivity model that assumes the reactivity of all functional groups in a CTA is equal agrees reasonably well with the experimental results. However, with f = 4, the reactivity of the fourth functional group seems to decrease and the substitution effects may need to be accounted for to fine control the formed branched structure. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1267–1275, 1999     

Simple Preparation of Sulfate Anion‐Doped Polyaniline‐Clay Nanocomposites by an Environmentally Friendly Mechanochemical Synthesis Route

Summary: Conducting polyaniline (PANI) and montmorillonite (MMT) nanocomposites were prepared from aniline sulfate and MMT by a mechanochemical synthesis route. X‐Ray diffraction analysis confirmed that, by controlling the aniline sulfate content, mechanochemical synthesis led to two types of different formations. After polymerization, the mechanochemical route synthesized much more PANI between the clay layers compared to a solution method. The electrical conductivities of the synthesized PANI‐MMT nanocomposites in pressed pellets ranged in the order of between 10⁻⁴ and 10⁻³ S · cm⁻¹.

X‐ray powder diffraction patterns of the intercalation products prepared by grinding montmorillonite with various amounts of Ani‐SO₄ in a mortar.     

X-ray microdiffraction and strain gradient crystal plasticity studies of geometrically necessary dislocations near a Ni bicrystal grain boundary

We compare experimental measurements of inhomogeneous plastic deformation in a Ni bicrystal with crystal plasticity simulations. Polychromatic X-ray microdiffraction, orientation imaging microscopy and scanning electron microscopy, were used to characterize the geometrically necessary dislocation distribution of the bicrystal after uniaxial tensile deformation. Changes in the local crystallographic orientations within the sample reflect its plastic response during the tensile test. Elastic strain in both grains increases near the grain boundary. Finite element simulations were used to understand the influence of initial grain orientation and structural inhomogeneities on the geometrically necessary dislocations arrangement and distribution and to understand the underlying materials physics.     

Synthesis of an indole analog of magallanesine via the [1,2]-meisenheimer rearrangement

Ring expansion of azetopyridoindole 11 via the [1,2]-Meisenheimer rearrangement of the corresponding N-oxide 12 gave azocinoindole 14 , which was converted into the N-benzoylenaminone 18 in 5 steps. Intramolecular cyclization of 18 was accomplished by a modified Heck reaction followed by reductive desulfonylation to provide the indole analog 2, 5H -isoindolo[2′,1′;1,2]azocino[5,6-b]indole, of magallanesine 1 .     

Scaffold Design for Tissue Engineering

Tissue engineering has emerged as a promising alternative approach in the treatment of malfunctioning or lost organs. In this approach, a temporary scaffold is needed to serve as an adhesive substrate for the implanted cells and a physical support to guide the formation of the new organs. In addition to facilitating cell adhesion, promoting cell growth, and allowing the retention of differentiated cell functions, the scaffold should be biocompatible, biodegradable, highly porous with a large surface/volume ratio, mechanically strong, and malleable. A number of three‐dimensional porous scaffolds fabricated from various kinds of biodegradable materials have been developed. This paper reviews some of the advances in scaffold design focusing on the hybrid scaffolds recently developed in the authors' laboratory.     

Reactions of cyclic sulfur ylides with some carbonyl compounds

The reaction of a six‐membered sulfonium ylide 5 with aldehydes or ketones afforded the oxirane derivatives 6a–d as a mixture of cis and trans isomers in excellent yields. In addition, the same reactions, using five‐ or six‐membered cyclic oxosulfonium ylides 7 and 11 , gave the corresponding oxirane derivatives in good yields. Moreover, the reaction of 11 with two equimolar amounts of base and 4‐hexen‐3‐one afforded the cyclooctene oxide derivative 16 with high stereoselectivity in 59% yield via a sequential Michael–Michael‐type addition of the ylide and the resulting enolate ion followed by an intramolecular Corey–Chaykovsky reaction. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:216–222, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10022