Thermostructural Numerical Analysis of the Thrust Chamber of a Liquid Propellant Rocket Engine.

The numerical simulation of rocket engine thrust chambers is very challenging as several damaging phenomena, such as plasticity, low-cycle-fatigue (LCF) and creep occur during its service life. The possibility of simulating the thermostructural behavior of the engine, by means of non-linear finite element analyses, allows the engineers to guarantee the structural safety of the structure. This document reports the numerical simulations developed with the aim of predicting the thermostructural behaviour and the service life of the thrust chamber of a liquid-propellant rocket engine.

Stress Relaxation Behavior of Additively Manufactured Polylactic Acid (PLA).

In this work, the stress relaxation behavior of 3D printed PLA was experimentally investigated and analytically modeled. First, a quasi-static tensile characterization of additively manufactured samples was conducted by considering the effect of printing parameters like the material infill orientation and the outer wall presence. The effect of two thermal conditioning treatments on the material tensile properties was also investigated.

Model-based evaluation of the microhemodynamic effects of PEGylated HBOC molecules in the rat brain cortex: a laser speckle imaging study.

Hemoglobin-based oxygen carriers (HBOCs) were developed with the aim of substituting transfusions in emergency events. However, they exhibit adverse events, such as nitric oxide (NO) scavenging, vasoactivity, enhanced platelet aggregation, presently hampering their clinical application. The impact of two prototypical PEGylated HBOCs, Euro-PEG-Hb and PEG-HbO, endowed by different oxygen affinities and hydrodynamic volumes, was assessed on the cerebrocortical parenchymal microhemodynamics, and extravasation through the blood-brain-barrier (BBB) by laser speckle contrast imaging (LSCI) method and near-infrared (NIR) imaging, respectively.

PEGylation promotes hemoglobin tetramer dissociation.

Hemoglobin conjugated with poly(ethylene glycol) (PEG) acts as an oxygen carrier free in plasma, substituting red blood cells in supplementing oxygen in hypo-oxygenation pathologies. Given the complexity of oxygen delivery controls, subtle structural and functional differences in PEGylated hemoglobins might be associated with distinct physiological responses and, potentially, adverse effects. We have compared hemoglobin PEGylated under anaerobic conditions, called PEG-Hb(deoxy), with hemoglobin PEGylated under aerobic conditions, called PEG-Hb(oxy), a product that mimics Hemospan, produced by Sangart, Inc.

Modulation of the NO/cGMP pathway reduces the vasoconstriction induced by acellular and PEGylated haemoglobin.

Activation of the NO/cGMP pathway modulates smooth muscle cells relaxation and hence vasoconstriction, a major hindrance for the use of cell-free haemoglobin (Hb) as blood substitute, despite conjugation with 5-kDa maleimide poly(ethylene)-glycol (PEG) reduces vasoconstriction in vivo. We aimed at assessing how a recently developed PEGylated-Hb (Deoxy-PEGHb) and manipulation of the NO/cGMP pathway enable modulation of vasoconstriction in isolated rat hearts. Hearts were Langendorff-perfused with oxygenated Krebs-Henseleit (15 ml/min) while monitoring the coronary pressure (CPP) after injection (1 min) of 50 nM norepinephrine followed by a 1 microM Hb or Deoxy-PEGHb bolus, without altering the flow.

Identification of the sites of deoxyhaemoglobin PEGylation.

The 2-iminothiolane reaction with protein amino groups adds a spacer arm ending with a thiol group, which can be further treated with molecules carrying a maleimido ring. This approach is currently used for the preparation of a candidate 'blood substitute' in which human Hb (haemoglobin) is conjugated with long chains of PEG [poly(ethylene glycol)]. To identify the thiolation sites by MS, we have carried out the reaction using deoxyHb bound to inositol hexaphosphate to protect some of the residues crucial for function and NEM (N-ethylmaleimide) to block and stabilize the thiol groups prior to enzymatic digestion by trypsin and pepsin.

The hemoglobin cyanomet ligation analogue and carbon monoxide induce similar allosteric mechanisms.

Current thermodynamic models of protein cooperativity predicting sigmoidal ligand equilibrium curves differ in the assumptions regarding the structural/functional properties of the intermediate ligation states. Quantitative information on the intermediates cannot be extracted from the equilibrium curves, but must be obtained from direct studies of the intermediates. Since the intermediates are intrinsically unstable species, ligation analogues with reduced mobility are indispensable tools for cooperativity studies provided that the tertiary/quaternary changes triggered by the ligation analogue are similar to those observed using the physiological ligands.

Allosteric proteins: lessons to be learned from the hemoglobin intermediates.

Allosteric proteins, such as hemoglobin, are assemblies of functional units, which undergo quaternary structural transitions in response to concentration changes of a specific ligand. Functional properties of hemoglobin ligation intermediates indicate that the tertiary structural changes induced by the ligand do not promote an equilibrium of quaternary structures.