146 research outputs found
A closer physico-chemical look to the Layer-by-Layer electrostatic self-assembly of polyelectrolyte multilayers
The fabrication of polyelectrolyte multilayer films (PEMs) using the
Layer-by-Layer (LbL) method is one of the most versatile approaches for
manufacturing functional surfaces. This is the result of the possibility to
control the assembly process of the LbL films almost at will, by changing the
nature of the assembled materials (building blocks), the assembly conditions
(pH, ionic strength, temperature, etc.) or even by changing some other
operational parameters which may impact in the structure and physico-chemical
properties of the obtained multi-layered films. Therefore, the understanding of
the impact of the above mentioned parameters on the assembly process of LbL
materials plays a critical role in the potential use of the LbL method for the
fabrication of new functional materials with technological interest. This
review tries to provide a broad physico-chemical perspective to the study of
the fabrication process of PEMs by the LbL method, which allows one to take
advantage of the many possibilities offered for this approach on the
fabrication of new functional nanomaterials.Comment: Published Pape
X-Ray Diffraction, Calorimetric and Dielectric Relaxation Study of the Amorphous and Smectic States of a Main Chain Liquid Crystalline Polymer
Los polímeros cristales líquidos (LCP) son sistemas complejos que forman mesofases que presentan orden orientacional y polímeros amorfos. Con frecuencia, el estado amorfo isotrópico no puede ser estudiado debido a la rápida formación de mesofases. En este trabajo se ha sintetizado y estudiado un nuevo LCP: poli(trietilenglicol metil p, p '-bibenzoato), PTEMeB. Este polímero presenta una formación de mesofase bastante lenta haciendo posible estudiar de forma independiente tanto los estados amorfo y de cristal líquidos. La estructura y las transiciones de fase del PTEMeB han sido investigados por calorimetría (DSC), con MAXS / WAXS con temperatura variable que emplean radiación de sincrotrón y con difracción de rayos X. Estos estudios han mostrado la existencia de dos transiciones vítreas, relacionadas con las fases amorfa y cristal líquido. Se ha realizado un estudio de relajación dieléctrica en amplios intervalos de temperatura y presión. Se ha encontrado que la transición vítrea dinámica de la fase amorfa es más lenta que la del cristal líquido. El estudio de la relajación ? nos ha permitido seguir la formación isoterma de la mesofase a presión atmosférica. Además, con el estudio el comportamiento dinámico a alta presión se ha encontrado que se produce la formación rápida de la mesofase inducida por cambios bruscos de presión.
Liquid crystalline polymers (LCPs) are complex systems that include features of both orientationally ordered mesophases and amorphous polymers. Frequently, the isotropic amorphous state cannot be studied due to the rapid mesophase formation. Here, a new main chain LCP, poly(triethyleneglycol methyl p,p'-bibenzoate), PTEMeB, has been synthesized. It shows a rather slow mesophase formation making possible to study independently both the amorphous and the liquid crystalline states. The structure and phase transitions of PTEMeB have been investigated by calorimetry, variable-temperature MAXS/WAXS employing synchrotron radiation, and X-ray diffraction in oriented fibers. These experiments have pointed out the presence of two glass transitions, related to the amorphous or to the liquid crystal phases. Additionally, the mesophase seems to be a coexistence of orthogonal and tilted smectic phases. A dielectric relaxation study of PTEMeB over broad ranges of temperature and pressure has been performed. The dynamic glass transition turns out to be slower for the amorphous state than for the liquid crystal. Monitoring of the α relaxation has allowed us to follow the isothermal mesophase formation at atmospheric pressure. Additionally, the dynamical behavior at high pressures has pointed out the fast formation of the mesophase induced by sudden pressure changes
Influence of the molecular architecture on the adsorption onto solid surfaces: comb-like polymers
The processes of adsorption of grafted copolymers onto negatively charged surfaces were studied
using a dissipative quartz crystal microbalance (D-QCM) and ellipsometry. The control
parameters in the study of the adsorption are the existence or absence on the molecular
architecture of grafted polyethyleneglycol (PEG) chains with different lengths and the chemical
nature of the main chain, poly(allylamine) (PAH) or poly(L-lysine) (PLL). It was found out that
the adsorption kinetics of the polymers showed a complex behavior. The total adsorbed amount
depends on the architecture of the polymer chains (length of the PEG chains), on the polymer
concentration and on the chemical nature of the main chain. The comparison of the thicknesses
of the adsorbed layers obtained from D-QCM and from ellipsometry allowed calculation of the
water content of the layers that is intimately related to the grafting length. The analysis of
D-QCM results also provides information about the shear modulus of the layers, whose values
have been found to be typical of a rubber-like polymer system. It is shown that the adsorption of
polymers with a charged backbone is not driven exclusively by the electrostatic interactions, but
the entropic contributions as a result of the trapping of water in the layer structure are of
fundamental importance
Towards understanding the behavior of polyelectrolyte surfactant mixtures at the water vapor interface closer to technologically relevant conditions
Polyelectrolyte surfactant mixtures and their interactions with fluid
interfaces are an important research field due to their use in technological
applications. Most of the existing knowledge on these systems is based on
models in which the polyelectrolyte concentration is around 50 times lower than
that used in commercial formulations. The present work marks a step to close
the gap on the understanding of their behavior under more practically relevant
conditions. The adsorption of concentrated mixtures of
poly(diallyldimethylammonium) chloride and sodium N lauroyl N methyltaurate at
the water-vapor interface with a crude mixing protocol has been studied by
different surface tension techniques, Brewster angle microscopy, neutron
reflectometry, and several bulk characterization techniques. Kinetically
trapped aggregates formed during mixing influence the interfacial morphology of
mixtures produced in the equilibrium one phase region, yet fluctuations in the
surface tension isotherm result depending on the tensiometric technique
applied. At low bulk surfactant concentrations, the free surfactant
concentration is very low, and the interfacial composition matches the trend of
the bulk complexes, which is a behavior that has not been observed in studies
on more dilute mixtures. Nevertheless, a transition to synergistic
co-adsorption of complexes and free surfactant is observed at the higher bulk
surfactant concentrations studied. This transition appears to be a special
feature of these more concentrated mixtures, which deserves attention in future
studies of systems with additional components.Comment: Published pape
Effect of molecular structure of eco-friendly glycolipid biosurfactants on the adsorption of hair-care conditioning polymers
Pseudo-binary mixtures of different glycolipids, four different rhamnolipids
(RL) and an alkyl polyglucoside (APG), with poly(diallyl-dimethylammonium
chloride) (PDADMAC) have been studied in relation to their adsorption onto
negatively charged surfaces to shed light on the impact of the molecular
structure of biodegradable surfactants from natural sources (instead of
synthetic surfactant, such as sodium laureth sulfate) on the adsorption of
hair-care formulations. For this purpose, the self-assembly of such mixtures in
aqueous solution and their adsorption onto negatively charged surfaces
mimicking the negative charge of damaged hair fibres have been studied using
experiments and self-consistent field (SCF) calculations. The results show that
the specific physico-chemical properties of the surfactants (charge, number of
sugar rings present in surfactant structure and length of the hydrocarbon
length) play a main role in the control of the adsorption process, with the
adsorption efficiency and hydration being improved in relation to conventional
sulfate-based systems for mixtures of PDADMAC and glycolipids with the shortest
alkyl chains. SCF calculations and Energy Dispersive X-Ray Spectroscopy (EDS)
analysis on real hair confirmed such observations. The results allow one to
assume that the characteristic of the studied surfactants, especially
rhamnolipids, conditions positively the adsorption potential of
polyelectrolytes in our model systems. This study provides important insights
on the mechanisms underlying the performance of more complex but natural and
eco-friendly washing formulations.Comment: Published articl
Equilibrium and dynamic surface properties of trisiloxane aqueous solutions. Part 2. Theory and comparison with experiment
Oncoplastic Breast Consortium consensus conference on nipple-sparing mastectomy
Purpose Indications for nipple-sparing mastectomy (NSM) have broadened to include the risk reducing setting and locally
advanced tumors, which resulted in a dramatic increase in the use of NSM. The Oncoplastic Breast Consortium consensus
conference on NSM and immediate reconstruction was held to address a variety of questions in clinical practice and research
based on published evidence and expert panel opinion.
Methods The panel consisted of 44 breast surgeons from 14 countries across four continents with a background in gynecology, general or reconstructive surgery and a practice dedicated to breast cancer, as well as a patient advocate. Panelists
presented evidence summaries relating to each topic for debate during the in-person consensus conference. The iterative
process in question development, voting, and wording of the recommendations followed the modified Delphi methodology.
Results Consensus recommendations were reached in 35, majority recommendations in 24, and no recommendations in the
remaining 12 questions. The panel acknowledged the need for standardization of various aspects of NSM and immediate
reconstruction. It endorsed several oncological contraindications to the preservation of the skin and nipple. Furthermore, it
recommended inclusion of patients in prospective registries and routine assessment of patient-reported outcomes. Considerable heterogeneity in breast reconstruction practice became obvious during the conference.
Conclusions In case of conflicting or missing evidence to guide treatment, the consensus conference revealed substantial
disagreement in expert panel opinion, which, among others, supports the need for a randomized trial to evaluate the safest
and most efficacious reconstruction techniques
Oncoplastic breast consortium recommendations for mastectomy and whole breast reconstruction in the setting of post-mastectomy radiation therapy
Aim: Demand for nipple-and skin-sparing mastectomy (NSM/SSM) with immediate breast reconstruction (BR) has increased at the same time as indications for post-mastectomy radiation therapy (PMRT) have broadened. The aim of the Oncoplastic Breast Consortium initiative was to address relevant questions arising with this clinically challenging scenario. Methods: A large global panel of oncologic, oncoplastic and reconstructive breast surgeons, patient advocates and radiation oncologists developed recommendations for clinical practice in an iterative process based on the principles of Delphi methodology. Results: The panel agreed that surgical technique for NSM/SSM should not be formally modified when PMRT is planned with preference for autologous over implant-based BR due to lower risk of long-term complications and support for immediate and delayed-immediate reconstructive approaches. Nevertheless, it was strongly believed that PMRT is not an absolute contraindication for implant-based or other types of BR, but no specific recom-mendations regarding implant positioning, use of mesh or timing were made due to absence of high-quality evidence. The panel endorsed use of patient-reported outcomes in clinical practice. It was acknowledged that the shape and size of reconstructed breasts can hinder radiotherapy planning and attention to details of PMRT techniques is important in determining aesthetic outcomes after immediate BR. Conclusions: The panel endorsed the need for prospective, ideally randomised phase III studies and for surgical and radiation oncology teams to work together for determination of optimal sequencing and techniques for PMRT for each patient in the context of BRPeer reviewe
Complement component C4 structural variation and quantitative traits contribute to sex-biased vulnerability in systemic sclerosis
Altres ajuts: Fondo Europeo de Desarrollo Regional (FEDER), "A way of making Europe".Copy number (CN) polymorphisms of complement C4 play distinct roles in many conditions, including immune-mediated diseases. We investigated the association of C4 CN with systemic sclerosis (SSc) risk. Imputed total C4, C4A, C4B, and HERV-K CN were analyzed in 26,633 individuals and validated in an independent cohort. Our results showed that higher C4 CN confers protection to SSc, and deviations from CN parity of C4A and C4B augmented risk. The protection contributed per copy of C4A and C4B differed by sex. Stronger protection was afforded by C4A in men and by C4B in women. C4 CN correlated well with its gene expression and serum protein levels, and less C4 was detected for both in SSc patients. Conditioned analysis suggests that C4 genetics strongly contributes to the SSc association within the major histocompatibility complex locus and highlights classical alleles and amino acid variants of HLA-DRB1 and HLA-DPB1 as C4-independent signals
Global patient outcomes after elective surgery: prospective cohort study in 27 low-, middle- and high-income countries.
BACKGROUND: As global initiatives increase patient access to surgical treatments, there remains a need to understand the adverse effects of surgery and define appropriate levels of perioperative care. METHODS: We designed a prospective international 7-day cohort study of outcomes following elective adult inpatient surgery in 27 countries. The primary outcome was in-hospital complications. Secondary outcomes were death following a complication (failure to rescue) and death in hospital. Process measures were admission to critical care immediately after surgery or to treat a complication and duration of hospital stay. A single definition of critical care was used for all countries. RESULTS: A total of 474 hospitals in 19 high-, 7 middle- and 1 low-income country were included in the primary analysis. Data included 44 814 patients with a median hospital stay of 4 (range 2-7) days. A total of 7508 patients (16.8%) developed one or more postoperative complication and 207 died (0.5%). The overall mortality among patients who developed complications was 2.8%. Mortality following complications ranged from 2.4% for pulmonary embolism to 43.9% for cardiac arrest. A total of 4360 (9.7%) patients were admitted to a critical care unit as routine immediately after surgery, of whom 2198 (50.4%) developed a complication, with 105 (2.4%) deaths. A total of 1233 patients (16.4%) were admitted to a critical care unit to treat complications, with 119 (9.7%) deaths. Despite lower baseline risk, outcomes were similar in low- and middle-income compared with high-income countries. CONCLUSIONS: Poor patient outcomes are common after inpatient surgery. Global initiatives to increase access to surgical treatments should also address the need for safe perioperative care. STUDY REGISTRATION: ISRCTN5181700
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