An approach to enlarge preformed colloidal Au nanoparticles in solution based on the Au colloidal surface-catalyzed reduction of Au3+ by NH2OH (“seeding”) has been adapted to 12-nm-diameter colloidal ...Au nanoparticles immobilized in monolayers and multilayers. Bulk characterization of the ensuing films was carried out by atomic absorption, UV−vis−near-IR optical spectroscopy, cyclic voltammetry, and dc resistance measurements. Exposure of a 12-nm-diameter Au colloid monolayer on organosilane-modified glass surfaces to NH2OH/Au3+ leads to rapid particle growth and coalescence: after roughly 5−10 min, the optical and electrical properties closely resemble that of conductive Au thin films prepared by evaporation. Evolution of the nanometer-scale architecture was followed using atomic force microscopy (AFM), surface-enhanced Raman scattering (SERS), surface plasmon resonance (SPR), and field emission scanning electron microscopy (FE-SEM), leading to the following key findings: (i) Seeding of surface-confined colloidal Au leads to a very different distribution in particle size/shape than seeding with identical particles in solution. (ii) Au3+/NH2OH-mediated growth of surface-confined colloidal Au is highly dependent on particle coverage, with different particle densities in monolayers leading to distinct film architectures that are easily detected by FE-SEM and SPR.
Lower Cretaceous fossils from central Niger document the succession of sauropod dinosaurs on Africa as it drifted into geographic isolation. A new broad-toothed genus of Neocomian age (∼135 million ...years ago) shows few of the specializations of other Cretaceous sauropods. A new small-bodied sauropod of Aptian-Albian age (∼110 million years ago), in contrast, reveals the highly modified cranial form of rebbachisaurid diplodocoids. Rates of skeletal change in sauropods and other major groups of dinosaurs are estimated quantitatively and shown to be highly variable.
Hollow Thermoresponsive Microgels Nayak, Satish; Gan, Daoji; Serpe, Michael J. ...
Small (Weinheim an der Bergstrasse, Germany),
April 2005, Letnik:
1, Številka:
4
Journal Article
Recenzirano
Thermoresponsive poly(N‐isopropyl acrylamide) (pNIPAm) microgels possessing a hollow structure have been synthesized from core–shell nanoparticles upon oxidation of the particle core, followed by ...removal of the produced polymer segments by centrifugation. N,N′‐(1,2‐dihydroxyethylene)bisacrylamide (DHEA) is used as a cross‐linker for preparing the degradable core, whereas N,N′‐methylenebis(acrylamide) (BIS) is used as a cross‐linker to add a nondegradable pNIPAm shell. Addition of NaIO4 to a suspension of these particles in water leads to controlled degradation of the particle core by cleavage of the 1,2‐glycol bond in DHEA. Fluorescence spectroscopy, UV/Vis spectroscopy, and photon correlation spectroscopy are used to characterize the hollow particles produced.
Hollow nanoparticles have been fabricated by using a core–shell construct (see scheme; NIPAm=N‐isopropyl acrylamide). Core particles with a degradable cross‐linker (DHEA) are synthesized, and a polymer shell of nondegradable cross‐linker (BIS) is then added. Degradation of the core by a degrading reagent (NaIO4) results in hollow particles.
Purpose: Incomplete endovascular graft exclusion of an abdominal aortic aneurysm results in an endoleak. To better understand the pathogenesis, significance, and fate of endoleaks, we analyzed our ...experience with endovascular aneurysm repair.
Methods:Between November 1992 and May 1997, 47 aneurysms were treated. In a phase I study, patients received either an endovascular aortoaortic graft (11) or an aortoiliac, femorofemoral graft (8). In phase II, procedures and grafts were modified to include aortofemoral, femorofemoral grafts (28) that were inserted with juxtarenal proximal stents, sutured endovascular distal anastomoses within the femoral artery, and hypogastric artery coil embolization. Endoleaks were detected by arteriogram, computed tomographic scan, or duplex ultrasound. Classification systems to describe anatomic, chronologic, and physiologic endoleak features were developed, and aortic characteristics were correlated with endoleak incidence.
Results: Endoleaks were discovered in 11 phase I patients (58%) and only six phase II patients (21%;
p < 0.05). Aneurysm neck lengths 2 cm or less increased the incidence of endoleaks (
p < 0.05). Although not significant, aneurysms with patent side branches or severe neck calcification had a higher rate of endoleaks than those without these features (47% vs 29% and 57% vs 33%, respectively), and patients with iliac artery occlusive disease had a lower rate of endoleaks than those without occlusive disease (18% vs 42%). Endoleak classifications revealed that most endoleaks were immediate, without outflow, and persistent (71% each), proximal (59%), and had aortic inflow (88%). One patient with a persistent endoleak had aneurysm rupture and died.
Conclusions: Endoleaks complicate a significant number of endovascular abdominal aortic aneurysm repairs and may permit aneurysm growth and rupture. The type of graft used, the technique of graft insertion, and aortic anatomic features all affect the rate of endoleaks. Anatomic, chronologic, and physiologic classifications can facilitate endoleak reporting and improve understanding of their pathogenesis, significance, and fate. (J Vasc Surg 1998;27:69-80.)
Thermoresponsive poly(N-isopropylacrylamide) (pNIPAm) microgel particles cross-linked with various concentrations of PEG diacrylates of 3 different PEG chain lengths were synthesized via free-radical ...precipitation polymerization in order to investigate the phase transition and protein adsorption behavior as the hydrophilicity of the network is increased. Photon correlation spectroscopy (PCS) reveals that, as the concentration of PEG cross-linker incorporated into the particles is increased, an increase in the temperature and breadth of the phase transition occurs. Qualitative differences in particle density using isopycnic centrifugation confirm that higher PEG concentrations result in denser networks. The efficient incorporation of PEG cross-linker was confirmed with 1H NMR, and variable temperature NMR studies suggest that, in the deswollen state, the longer PEG cross-links protrude from the dense globular network. This behavior apparently manifests itself as a decrease in nonspecific protein adsorption with increasing PEG length and content. Furthermore, when electrostatically attached to a glass surface, the particles containing the longer chain lengths exhibited enhanced nonfouling behavior and were resistant to cell adhesion in serum-containing media. The excellent performance of these particulate films and the simplicity with which they are assembled suggests that they may be applicable in a wide range of applications where nonfouling coatings are required.
We report investigations on the thermally regulated uptake and release of the chemotherapeutic drug doxorubicin from microgel thin films. A spin coating, layer-by-layer (scLbL) assembly approach was ...used to prepare thin films composed of thermoresponsive poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAm-AAc) microgels by alternatively exposing a 3-aminopropyltrimethoxysilane (APTMS) functionalized glass substrate to polyanionic pNIPAm-AAc microgels and polycationic poly(allylamine hydrochloride) (PAH). Using this method, 10, 20, and 30 microgel layer films were constructed with uniform layer buildup, as confirmed by quartz crystal microgravimetry (QCM). The films were subsequently loaded with doxorubicin by cycling the temperature of the film in an aqueous doxorubicin solution between 25 and 50 °C. Release characteristics were then examined using UV−vis spectroscopy, which revealed temperature-dependent release properties.
We report the synthesis and characterization of temperature and pH responsive hydrogel particles (microgels) with core−shell morphologies. Core particles composed of cross-linked ...poly(N-isopropylacrylamide) (p-NIPAm) or poly(NIPAm-co-acrylic acid) (p-NIPAm-AAc) were synthesized via precipitation polymerization and then used as nuclei for subsequent polymerization of p-NIPAm-AAc and p-NIPAm, respectively. The presence of a core−shell morphology was confirmed by transmission electron microscopy (TEM). Thermally initiated volume phase transitions were interrogated via temperature-programmed photon correlation spectroscopy (TP-PCS) as a function of solution pH. The p-NIPAm-AAc core hydrogel displays both a strong temperature and pH dependence on swelling. However, both p-NIPAm-AAc (core)/p-NIPAm (shell) and p-NIPAm (core)/p-NIPAm-AAc (shell) particles display a more complex pH dependence than the homogeneous particles. Specifically, a multistep volume phase transition appears when the AAc component becomes highly charged at a high pH. It is apparent from the measured deswelling curves that a portion of the particle swelling behavior is dominated by p-NIPAm, regardless of its location in the particle. However, deswelling behavior that is due to a mixture of p-NIPAm-AAc and p-NIPAm is evident, as well as a regime that is largely attributed to p-NIPAm-AAc alone. Small differences in the effect of pH on the two core−shell particles indicate that the influence of p-NIPAm is somewhat greater when it is localized in the shell.
Photoresponsive microgels have been prepared by precipitation polymerization of the thermoresponsive polymer poly(N-isopropylacrylamide) followed by covalent conjugation of the temperature-jump dye ...malachite green. The photoresponsivity of these dye-labeled microgels was characterized by a pump−probe optical setup. A HeNe laser is used for exciting the dye molecules and a near-IR-diode laser is used to simultaneously measure the turbidity of the colloidal dispersion. Irradiation of malachite green increases the temperature of the sample through rapid nonradiative decay, thereby causing the polymer chains to aggregate. On deswelling, a decrease in the intensity of transmitted light is observed due to scattering. It is also observed that the photoresponsive behavior of the microgels is dependent on the concentration of the dye, intensity of the laser, and bath temperature.
The Sudbury Neutrino Observatory Boger, J; Hahn, R.L; Rowley, J.K ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2000, Letnik:
449, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The Sudbury Neutrino Observatory is a second-generation water Cherenkov detector designed to determine whether the currently observed solar neutrino deficit is a result of neutrino oscillations. The ...detector is unique in its use of D
2O as a detection medium, permitting it to make a solar model-independent test of the neutrino oscillation hypothesis by comparison of the charged- and neutral-current interaction rates. In this paper the physical properties, construction, and preliminary operation of the Sudbury Neutrino Observatory are described. Data and predicted operating parameters are provided whenever possible.
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