24 research outputs found
Stimuli-responsive behavior of PNiPAm microgels under interfacial confinement
The volume phase transition of microgels is one of the most paradigmatic
examples of stimuli-responsiveness, enabling a collapse from a highly swollen
microgel state into a densely coiled state by an external stimulus. Although
well characterized in bulk, it remains unclear how the phase transition is
affected by the presence of a confining interface. Here, we demonstrate that
the temperature-induced volume phase transition of poly(N-isopropylacrylamide)
microgels, conventionally considered an intrinsic molecular property of the
polymer, is in fact largely suppressed when the microgel is adsorbed to an
air/liquid interface. We further observe a hysteresis in core morphology and
interfacial pressure between heating and cooling cycles. Our results, supported
by molecular dynamics simulations, reveal that the dangling polymer chains of
microgel particles, spread at the interface under the influence of surface
tension, do not undergo any volume phase transition, demonstrating that the
balance in free energy responsible for the volume phase transition is
fundamentally altered by interfacial confinement. These results imply that
important technological properties of such systems, including the
temperature-induced destabilization of emulsions does not occur via a decrease
in interfacial coverage of the microgels
Bacterial urinary tract infection and subclinical bacteriuria in dogs receiving antineoplastic chemotherapy
Background: Immunosuppressive treatment with glucocorticoids and cyclosporine increases the risk for positive urine cultures (PUCs) in dogs.
Objective: To investigate the prevalence and incidence of PUC in dogs diagnosed with cancer and treated with antineoplastic chemotherapy while distinguishing between subclinical bacteriuria (SB) and urinary tract infection (UTI).
Animals: Forty-six client-owned dogs with nonurogenital cancer treated with anti- neoplastic chemotherapy.
Methods: Prospective observational longitudinal clinical study. Dogs in which a urine culture was performed before the start of and at least once during antineoplastic chemotherapy were included. A McNemar's test was used to investigate if the preva- lence of PUC increased during antineoplastic chemotherapy. Positive urine cultures were categorized into SB and UTI and multiple PUCs from the same dog and cate- gory were grouped together as 1 episode of PUC.
Results: Urine culture was positive in 21/185 urine samples in 8/46 dogs. Antineo- plastic chemotherapy did not influence the prevalence of PUC (P = 1.00), which was 11% (5/46 dogs; 95% confidence interval: 5-23%) before the start of and 13% (6/46 dogs; 95% confidence interval: 6-26%) during antineoplastic chemotherapy. Eight dogs had 10 episodes of PUC; 7/10 episodes were classified as SB, and in 3/10 epi- sodes UTI (chronic prostatitis, prostatic abscess, and emphysematous cystitis) was diagnosed. Escherichia coli was the most common pathogen, isolated in 9/10 episodes.
Conclusions and Clinical Importance: We did not find evidence that antineoplastic chemotherapy is a major predisposing factor for the development of PUC. Most dogs with PUC had SB
Soft particles at liquid interfaces: From molecular particle architecture to collective phase behavior
Soft particles such as microgels and core-shell particles can undergo
significant and anisotropic deformations when adsorbed to a liquid interface.
This, in turn, leads to a complex phase behavior upon compression. Here we
develop a multiscale framework to rationally link the molecular particle
architecture to the resulting interfacial morphology and, ultimately, to the
collective interfacial phase behavior, enabling us to identify the key
single-particle properties underlying two-dimensional continuous,
heterostructural, and isostructural solid-solid transitions. Our approach
resolves existing discrepancies between experiments and simulations and thus
provides a unifying framework to describe phase transitions in interfacial
soft-particle systems. We establish proof-of-principle for our rational
approach by synthesizing three different poly(N-isopropylacrylamide)
soft-particle architectures, each of which corresponds to a different targeted
phase behavior. In parallel, we introduce a versatile and highly efficient
coarse-grained simulation method that adequately captures the qualitative key
features of each soft-particle system; the novel ingredient in our simulation
model is the use of auxiliary degrees of freedom to explicitly account for the
swelling and collapse of the particles as a function of surface pressure.
Notably, these combined efforts allow us to establish the first experimental
demonstration of a heterostructural transition to a chain phase in a
single-component system, as well as the first accurate in silico account of the
two-dimensional isostructural transition. Overall, our multiscale framework
provides a bridge between physicochemical soft-particle characteristics at the
molecular- and nanoscale and the collective self-assembly phenomenology at the
macroscale, paving the way towards novel materials with on-demand interfacial
behavior
Interface-induced hysteretic volume phase transition of microgels: simulation and experiment
Thermo-responsive microgel particles can exhibit a drastic volume shrinkage
upon increasing the solvent temperature. Recently we found that the spreading
of poly(N-isopropylacrylamide)(PNiPAm) microgels at a liquid interface under
the influence of surface tension hinders the temperature-induced volume phase
transition. In addition, we observed a hysteresis behavior upon temperature
cycling, i.e. a different evolution in microgel size and shape depending on
whether the microgel was initially adsorbed to the interface in expanded or
collapsed state. Here, we model the volume phase transition of such microgels
at an air/water interface by monomer-resolved Brownian dynamics simulations and
compare the observed behavior with experiments. We reproduce the experimentally
observed hysteresis in the microgel dimensions upon temperature variation. Our
simulations did not observe any hysteresis for microgels dispersed in the bulk
liquid, suggesting that it results from the distinct interfacial morphology of
the microgel adsorbed at the liquid interface. An initially collapsed microgel
brought to the interface and subjected to subsequent swelling and collapsing
(resp. cooling and heating) will end up in a larger size than it had in the
original collapsed state. Further temperature cycling, however, only shows a
much reduced hysteresis, in agreement with our experimental observations. We
attribute the hysteretic behavior to a kinetically trapped initial collapsed
configuration, which relaxes upon expanding in the swollen state. We find a
similar behavior for linear PNiPAm chains adsorbed to an interface. Our
combined experimental - simulation investigation provides new insights into the
volume phase transition of PNiPAm materials adsorbed to liquid interfaces
Versatile strategy for homogeneous drying patterns of dispersed particles
After spilling coffee, a tell-tale stain is left by the drying droplet. This universal phenomenon, known as the coffee ring effect, is observed independent of the dispersed material. However, for many technological processes such as coating techniques and ink-jet printing a uniform particle deposition is required and the coffee ring effect is a major drawback. Here, we present a simple and versatile strategy to achieve homogeneous drying patterns using surface-modified particle dispersions. High-molecular weight surface-active polymers that physisorb onto the particle surfaces provide enhanced steric stabilization and prevent accumulation and pinning at the droplet edge. In addition, in the absence of free polymer in the dispersion, the surface modification strongly enhances the particle adsorption to the air/liquid interface, where they experience a thermal Marangoni backflow towards the apex of the drop, leading to uniform particle deposition after drying. The method is independent of particle shape and applicable to a variety of commercial pigment particles and different dispersion media, demonstrating the practicality of this work for everyday processes
QoS-Enabled B2B Integration
Business-To-Business Integration (B2Bi) is a key mechanism for enterprises to gain competitive advantage. However, developing B2Bi applications is far from trivial. Inter alia, agreement among integration partners about the business documents and the control flow of business document exchanges as well as applying suitable communication technologies for overcoming heterogeneous IT landscapes are major challenges. At the same time, choreography languages such as ebXML BPSS (ebBP), orchestration languages such as WS-BPEL and Web Services are promising to provide the foundations for seamless interactions among business partners. Automatically translating choreography agreements of integration partners into partner-specific orchestrations is an obvious idea for ensuring conformance of orchestration models to choreography models. Moreover, the application of such model-driven development methods facilitates productivity and cost-effectiveness whereas applying a service oriented architecture (SOA) based on WS-BPEL and Web Services leverages standardization and decoupling. By now, the realization of QoS attributes has not yet received the necessary attention that makes such approaches suitable for B2Bi. In this report, we describe a proof-of-concept implementation of the translation of ebBP choreographies into WS-BPEL orchestrations that respects B2Bi-relevant QoS attributes
Impact of CYP2B6 983T>C polymorphism on non-nucleoside reverse transcriptase inhibitor plasma concentrations in HIV-infected patients
Objectives The aim of this study was to investigate the frequency of CYP2B6 polymorphisms (according to ethnicity) and the influence of heterozygosity and homozygosity on plasma concentrations of efavirenz and nevirapine. Methods Following written informed consent, 225 Caucasians and 146 Blacks were recruited from the German Competence Network for HIV/AIDS. Plasma concentrations of efavirenz and nevirapine were assessed by HPLC, and genotyping for 516G>T, 983T>C and 1459T>C polymorphisms in CYP2B6 was conducted by real-time PCR-based allelic discrimination. Results The minor allele frequency for 516G>T, 983T>C and 1459T>C was 0.29, 0 and 0.08 in Caucasians and 0.34, 0.07 and 0.02 in Blacks, respectively. Two Black patients with the 983C allele receiving efavirenz were identified and both were withdrawn from therapy within 1 week of sampling due to toxicity. In multivariate analyses, efavirenz and nevirapine plasma concentrations were significantly associated with 983T>C (P T (P T was not associated with plasma concentrations of either drug (P > 0.05 for both drugs). Conclusions This is the first report that the 983T>C genotype (part of the CYP2B6*18 haplotype) impacts on nevirapine plasma concentrations and the first study to assess the impact of 983C homozygosity on efavirenz concentrations. These data have implications for administration of non-nucleoside reverse transcriptase inhibitors to Black patient
Cytochrome P450 2B6 (CYP2B6) and constitutive androstane receptor (CAR) polymorphisms are associated with early discontinuation of efavirenz-containing regimens
Objectives Cytochrome P450 2B6 (CYP2B6) is responsible for the metabolic clearance of efavirenz and single nucleotide polymorphisms (SNPs) in the CYP2B6 gene are associated with efavirenz pharmacokinetics. Since the constitutive androstane receptor (CAR) and the pregnane X receptor (PXR) correlate with CYP2B6 in liver, and a CAR polymorphism (rs2307424) and smoking correlate with efavirenz plasma concentrations, we investigated their association with early (<3 months) discontinuation of efavirenz therapy. Methods Three hundred and seventy-three patients initiating therapy with an efavirenz-based regimen were included (278 white patients and 95 black patients; 293 male). DNA was extracted from whole blood and genotyping for CYP2B6 (516G → T, rs3745274), CAR (540C → T, rs2307424) and PXR (44477T → C, rs1523130; 63396C → T, rs2472677; and 69789A → G, rs763645) was conducted. Binary logistic regression using the backwards method was employed to assess the influence of SNPs and demographics on early discontinuation. Results Of the 373 patients, 131 withdrew from therapy within the first 3 months. Black ethnicity [odds ratio (OR) = 0.27; P = 0.0001], CYP2B6 516TT (OR = 2.81; P = 0.006), CAR rs2307424 CC (OR = 1.92; P = 0.007) and smoking status (OR = 0.45; P = 0.002) were associated with discontinuation within 3 months. Conclusions These data indicate that genetic variability in CYP2B6 and CAR contributes to early treatment discontinuation for efavirenz-based antiretroviral regimens. Further studies are now required to define the clinical utility of these association