A strategy for the synthesis of new cross-linkable bimodal amphiphilic grafts (bAPGs) was developed. These grafts are of hydrophilic PDMAAm backbones carrying low (M n ∼ 17 200 g/mol) and high (M n ∼ 117 000 g/mol) molecular weight hydrophobic PDMS branches, each branch carrying a vinylsilyl end-group. The bAPGs were cross-linked by Karstedt catalyst to bimodal amphiphilic conetworks (bAPCNs) by the use of polyhydrosiloxane-co-PDMS as the cross-linker. Membranes prepared from bAPCNs exhibit mechanical properties surprisingly superior to earlier APCNs prepared with APGs with monomodal low molecular weight branches. Membrane bimodality controls surface morphology and topography by means of elastic wrinkling instability during film formation. Semipermeable bAPCN membranes with precisely controlled nanochannel dimensions were prepared so as to allow rapid insulin diffusion and prevent passage of IgG. bAPCN membranes were designed for immunoprotection of live pancreatic islets and are thus key components for a bioartificial pancreas.

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It is widely accepted that mold temperature has a strong effect on the amount of molecular orientation and morphology developed in a non-isothermal flowing melt.

A novel approach to zero-order constant-rate drug delivery from contact lenses is presented. Quasi-Case II non-Fickian transport is achieved by nonuniform drug and diffusivity distributions within three-layer bimodal amphiphilic conetworks (β-APCNs). The center layer is a highly oxygen permeable β-APCN matrix, which contains the drug and exhibits a high drug diffusivity. The outer β-APCN layers contain no-drug and are loaded with vitamin E, which slows diffusion. In contrast to single-layer neat-polymer and vitamin E-loaded films that display first-order "burst" kinetics, it is demonstrated experimentally and by modeling that the combined effect of nonuniform distribution of drug loading and diffusion constants within the three-layer lens maintains low local drug concentration at the lens-fluid interface and yields zero-order drug delivery. The release rates of topical antibiotics provide constant-rate therapeutic-level delivery with appropriate oxygen permeability for at least 30 h, at which time ≈25% of the drug was released.

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The uniaxial mechano-optical behavior of a series of amorphous l-phenylalanine-based poly­(ester urea) (PEU) films was studied in the rubbery state. A custom, real-time measurement system was used to capture the true stress, true strain, and birefringence during deformation. When the materials were subjected to deformation at temperatures near the glass transition temperature (T g), the photoelastic behavior was manifested by a small increase in birefringence with a significant increase in true stress. At temperatures above T g, PEUs with a shorter diol chain length exhibited a liquid–liquid (T ll) transition (rubbery–viscous transition) at about 1.06T g (K) under the tested strain rate of 0.017 s–1 (stretching speed of 20 mm/min), above which the material transforms from a heterogeneous “liquid of fixed structure” to a “true liquid” state. The initial photoelastic behavior disappears with increasing temperature, as the initial slope of the stress optical curves becomes temperature independent. Fourier transform infrared spectroscopy (FTIR) was used to study the effect of hydrogen bonding on the physical properties of PEUs as a function of temperature. The average strength of hydrogen bonding diminishes with increasing temperature. For PEUs with the longest diol chain length, the area associated with N–H stretching region exhibits a linear temperature dependence. However, a three-stage temperature dependence was observed for PEUs with shorter diol chain length. The presence of hydrogen bonding enhances the “stiff” segmental correlations between adjacent chains in the PEU structure. As a result, the photoelastic constant decreases with increasing hydrogen bonding strength.

Background Point prevalence surveys (PPSs) on antibiotic use are useful for understanding different aspects related to prescription patterns in hospitals. Methods An adaptation of the WHO methodology for a PPS on antibiotic use was applied. Hospital wards were divided into medical (MED), surgical (SUR), ICUs, gynaecology and obstetrics (GO), high-risk (HR) and mixed wards (MIX). A web application (RedCap©) through a mobile device was used for data collection. Results Between December 2018 and August 2019, 5444 patients in 33 hospitals in five countries were included (10 hospitals in Cuba, 7 in Paraguay, 6 in El Salvador, 5 in Mexico and 5 in Peru). Of these patients, 54.6% received at least one antibiotic, with variations between and within hospitals and countries. Antibiotics were more frequently used in ICUs (67.2%), SUR (64.5%) and MED wards (54.2%), with 51.2% of antibiotics prescribed for community-acquired infections (CAIs), 22.9% for healthcare-associated infections (HAIs), 11.1% for surgical prophylaxis and 6.1% for unknown reasons. Adherence to guidelines was observed in 68.6% of cases (72.8% for CAIs, 72.4% for HAIs and 44.3% for prophylaxis). Third-generation cephalosporins were the class of antibiotics most frequently used (26.8%), followed by carbapenems (10.3%) and fluoroquinolones (8%). Targeted treatments were achieved in 17.3% of cases. Conclusions Antibiotic use was generally higher than that published in other studies. There is an urgent need to promote and strengthen the antimicrobial stewardship programmes in Latin America.

Amphiphilic polymer co-networks provide a unique route to integrating contrasting attributes of otherwise immiscible components within a bicontinuous percolating morphology and are anticipated to be valuable for applications such as biocatalysis, sensing of metabolites, and dual dialysis membranes. These co-networks are in essence chemically forced blends and have been shown to selectively phase-separate at surfaces during film formation. Here, we demonstrate that surface demixing at the air-film interface in solidifying polymer co-networks is not a unidirectional process; instead, a combination of kinetic and thermodynamic interactions leads to dynamic molecular rearrangement during solidification. Time-resolved gravimetry, low contact angles, and negative out-of-plane birefringence provided strong experimental evidence of the transitory trapping of thermodynamically unfavorable hydrophilic moieties at the air-film interface due to fast asymmetric solvent depletion. We also find that slow-drying hydrophobic elements progressively substitute hydrophilic domains at the surface as the surface energy is minimized. These findings are broadly applicable to common-solvent bicontinuous systems and open the door for process-controlled performance improvements in diverse applications. Similar observations could potentially be coupled with controlled polymerization rates to maximize the intermingling of bicontinuous phases at surfaces, thus generating true three-dimensional, bicontinuous, and undisturbed percolation pathways throughout the material.