Unravelling main- and side-chain motions in polymers with NMR spectroscopy and relaxometry: The case of polyvinyl butyral

Polyvinyl butyral (PVB) is an amorphous polymer employed in many technological applications. In order to highlight the relationships between macroscopic properties and dynamics at a microscopic level, motions of the main-chain and of the propyl side-chains were investigated between Tg − 288◦ C and Tg + 55◦ C, with Tg indicating the glass transition temperature. To this aim, a combination of solid state Nuclear Magnetic Resonance (NMR) methods was applied to two purposely synthesized PVB isotopomers: one fully protonated and the other perdeuterated on the side-chains.1 H time domain NMR and1 H field cycling NMR relaxometry experiments, performed across and above Tg, revealed that the dynamics of the main-chain corresponds to the α-relaxation associated to the glass transition, which was previously characterized by dielectric spectroscopy. A faster secondary relaxation was observed for the first time and ascribed to side-chains. The geometry and rate of motions of the different groups in the side-chains were characterized below Tg by2 H NMR spectroscopy

Thermal, mechanical, and rheological properties of biocomposites made of poly(Lactic acid) and potato pulp powder

The thermal, mechanical, and rheological properties of biocomposites of poly(lactic acid) (PLA) with potato pulp powder were investigated in order to (1) quantify how the addition of this filler modifies the structure of the polymeric material and (2) to obtain information on the possible miscibility and compatibility between PLA and the potato pulp. The potato pulp powder utilized is a residue of the processing for the production and extraction of starch. The study was conducted by analyzing the effect of the potato pulp concentration on the thermal, mechanical, and rheological properties of the biocomposites. The results showed that the potato pulp powder does not act as reinforcement but as filler for the PLA polymeric matrix. A progressive decrease in elastic modulus, tensile strength, and elongation at break was observed with increasing the potato pulp percentage. This moderate loss of mechanical properties, however, still meets the technical requirements indicated for the production of rigid packaging items. The incorporation of potato pulp powder to PLA offers the possibility to reduce the cost of the final products and promotes a circular economy approach for the valorization of agro-food waste biomass

The use of a novel cleaning closed suction system reduces the volume of secretions within the endotracheal tube as assessed by micro-computed tomography: a randomized clinical trial

Background: Early after intubation, a layer of biofilm covers the inner lumen of the endotracheal tube (ETT). Cleaning the ETT might prevent airways colonization by pathogens, reduce resistance to airflow, and decrease sudden ETT obstruction. We investigated the effectiveness of a cleaning closed suction system in maintaining the endotracheal tube free from secretions. Methods: We conducted a single center, randomized controlled trial, in the general intensive care unit of a tertiary-level university hospital. We enrolled 40 adult critically ill patients expected to remain intubated for more than 48\ua0h, within 24\ua0h from intubation. Patients were randomized to receive three ETT cleaning maneuvers/day using a novel device (Airway Medix Closed Suction System\u2122, cleaning group) or to standard care (no ETT cleaning, standard closed suction, control group). After extubation, the amount of secretions in the ETTs was measured by micro-computed tomography. Results: The volume of secretions in the ETTs from the cleaning group was lower than controls (0.081 [0.021\u20130.306] vs. 0.568 [0.162\u20130.756] mL, p\ua0=\ua00.001), corresponding to a cross-sectional area reduction six times lower (1[0\u20133] vs. 6 [2\u201310]\ua0%, p\ua0=\ua00.001). In a subset of 16 patients, the resistance to airflow tended to be lower after 1\ua0day of treatment (p\ua0=\ua00.063) and was lower after 2\ua0days (0.024), while no difference was present at enrollment (p\ua0=\ua00.922). ETT colonization did not differ between the two groups. Conclusions: The use of a novel cleaning closed suction system proved to be effective in reducing secretions present in the ETT after extubation, possibly reducing resistance to airflow during intubation. Trial registration: clinicaltrials.gov NCT0191210

Bedside selection of positive end-expiratory pressure by electrical impedance tomography in hypoxemic patients : a feasibility study

Background: Positive end-expiratory pressure (PEEP) is a key element of mechanical ventilation. It should optimize recruitment, without causing excessive overdistension, but controversy exists on the best method to set it. The purpose of the study was to test the feasibility of setting PEEP with electrical impedance tomography in order to prevent lung de-recruitment following a recruitment maneuver. We enrolled 16 patients undergoing mechanical ventilation with PaO2/FiO2 <300\uc2\ua0mmHg. In all patients, under constant tidal volume (6\ue2\u80\u938\uc2\ua0ml/kg) PEEP was set based on the PEEP/FiO2 table proposed by the ARDS network (PEEPARDSnet). We performed a recruitment maneuver and monitored the end-expiratory lung impedance (EELI) over 10\uc2\ua0min. If the EELI signal decreased during this period, the recruitment maneuver was repeated and PEEP increased by 2\uc2\ua0cmH2O. This procedure was repeated until the EELI maintained a stability over time (PEEPEIT). Results: The procedure was feasible in 87% patients. PEEPEIT was higher than PEEPARDSnet (13\uc2\ua0\uc2\ub1\uc2\ua03 vs. 9\uc2\ua0\uc2\ub1\uc2\ua02\uc2\ua0cmH2O, p\uc2\ua0<\uc2\ua00.001). PaO2/FiO2 improved during PEEPEIT and driving pressure decreased. Recruited volume correlated with the decrease in driving pressure but not with oxygenation improvement. Finally, regional alveolar hyperdistention and collapse was reduced in dependent lung layers and increased in non-dependent lung layers. Conclusions: In hypoxemic patients, a PEEP selection strategy aimed at stabilizing alveolar recruitment guided by EIT at the bedside was feasible and safe. This strategy led, in comparison with the ARDSnet table, to higher PEEP, improved oxygenation and reduced driving pressure, allowing to estimate the relative weight of overdistension and recruitment

Characterization of Supramolecular Polyphenol-Chromium(III) Clusters by Molecular Dynamics Simulations

The binding of Cr(III) with (2R,3S,4R)-(+)-3,3¢,4,4¢,7-flavanpentol in aqueous solution is investigated by atomistic molecular dynamics simulations concentrating the analysis of the sampled data on the polyphenol ability to chelate metal ions and to form large noncovalently bonded molecular and supramolecular architectures

A Computational Study of Conformational and Chiroptical Properties of (2R,3S,4R)- (+)-3,3\u2019,4,4\u2019,7-flavanpentol

Conformational analysis of (2R,3S,4R)-(+)-3,3V,4,4V,7-flavanpentol, a f lavonoid compound displaying both antioxidant and pro-oxidant properties, is performed by molecular mechanics and density functional theory calculations both in the gas phase and in methanol solution by using the Polarizable Continuum Model. Nine different conformations are identified. Absorption (UV) and circular dichroism (CD) spectra and optical rotations are calculated by means of time dependent density functional theory (TDDFT) and compared with experiments. The effects of a complex environment formed by water and proline-rich peptide molecules on the conformational characteristics of (2R,3S,4R)-(+)-3,3V,4,4V,7-flavanpentol and therefore on its UV and CD spectra are investigated by atomistic molecular dynamics simulations

Chemical Methods for Gelatin Crosslinking: A Review

Chemical methods so far experimentally investigated for gelatin crosslinking have been summarized with special emphasis on the reaction mechanisms. Advantages and disadvantages of all reactants have been reported in relation to the significant properties of the final applicative field

Towards the Supramolecular Structure of Collagen: a Molecular Dynamics Approach

The structure, stability, and conformational dynamics of an assembly of two pentameric bundles made of collagen-like triple helical segments are explored using 1.2 ns molecular dynamics simulations in three environments: 8.0% (v/v) formaldehyde/water solution, 1.4% (v/v) gallic acid/water solution, and pure water. Stable supramolecular arrangements, where the two collagen units are very close to each other at interacting distances, are identified via docking and energy minimization procedures. Analysis of the interaction with formaldehyde and gallic acid suggests that they perturb the protein in a similar way depending on hydrogenbonding capability, hydrophobic association properties, and the size and concentration of the compound