Search

We present a neutron spin echo (NSE) investigation to examine the impact of macromolecular crowding on the dynamics of single-chain nanoparticles (SCNPs), serving as synthetic models for biomacromolecules with flexibility and internal degrees of freedom, such as intrinsically disordered proteins (IDPs). In particular, we studied the dynamics of a medium-size poly(methyl methacrylate) (PMMA)-based SCNP (33 kDa) in solutions with low- (10 kDa) and high- (100 kDa) molecular weight analogous deuterated PMMA linear crowders. The dynamic structure factors of the SCNPs in dilute solution show certain degrees of freedom, yet the analysis in terms of the Zimm model reveals high internal friction that effectively stiffens the chain─a phenomenon also observed for IDPs. Under crowding conditions, the internal dynamics remains essentially unchanged, but the center-of-mass diffusion slows down. The effective viscosity felt by the SCNPs at the timescales probed by NSE is lower than the macroscopic viscosity of the crowder solution, and it does not depend significantly on the molecular weight.

Reconstruction of the right outflow tract with extracardiac conduits has made complete repair of complex cardiac malformations possible. However, reoperation is usually required for a right ventricle-to-pulmonary artery conduit obstruction. We describe a modified peel operation, where the sides and posterior half of the previously placed conduit are preserved, and a prosthetic roof is placed over the conduit remnant. This has been our current technique to manage conduit obstructions. It is a safe operation and to teach residents. This review aims to convey the technical details of each step of this technique.

Congenital heart disease (CHD) survival rate has improved dramatically due to advances in diagnostic and therapeutic techniques. However, concerning the unrepaired CHD population of moderate and severe complexity, the data regarding risk predictors and surgical outcomes are scarce. Our aim was to describe the surgical results and predictors of in-hospital outcomes in adult patients with moderate-to-severe complexity CHD that were not repaired in childhood.

We have combined X-ray diffraction, neutron diffraction with polarization analysis, small-angle neutron scattering (SANS), neutron elastic fixed window scans (EFWS), and differential scanning calorimetry (DSC) to investigate polymeric blends of industrial interest composed by isotopically labeled styrene–butadiene rubber (SBR) and polystyrene (PS) oligomers of size smaller than the Kuhn length. The EFWS are sensitive to the onset of liquid-like motions across the calorimetric glass transition, allowing the selective determination of the “microscopic” effective glass transitions of the components. These are compared with the “macroscopic” counterparts disentangled by the analysis of the DSC results in terms of a model based on the effects of thermally driven concentration fluctuations and self-concentration. At the microscopic level, the mixtures are dynamically heterogeneous for blends with intermediate concentrations or rich in PS, while the sample with highest content of the fast SBR component looks as dynamically homogeneous. Moreover, the combination of SANS and DSC has allowed determining the relevant length scale for the α-relaxation through its loss of equilibrium to be ≈30 Å. This is compared with the different characteristic length scales that can be identified in these complex mixtures from structural, thermodynamical, and dynamical points of view because of the combined approach followed. We also discuss the sources of the non-Gaussian effects observed for the atomic displacements and the applicability of a Lindemann-like criterion in these materials.

Background:Kawasaki disease (KD) is a self-limited vasculitis that mainly affects infants and preschool-age children, characterized by coronary aneurysms and/or stenoses that may lead to the occurrence of ischemia, heart attack, and sudden death. This study aimed to evaluate the clinical and surgical results of pediatric patients with KD and cardiac sequelae who underwent coronary artery bypass grafting. Methods:A retrospective study was carried out. Patients with a diagnosis of KD and cardiac sequelae who underwent coronary artery bypass grafting from January 1, 2004, through March 31, 2021, were included: preoperative characteristics and conditions. Results:Ten patients were included, with a mean age of 6.4 ± 3.7 years; 80% males. Seven (70%) had the compromise of 2 coronary arteries, the most affected being the left anterior descendent artery (36.9%) with aneurysm and the right coronary artery (36.8%) with stenosis. 40% had preoperative moderate-to-severe ventricular dysfunction. The graft most frequently used was the right internal thoracic artery (47.6%), and the most frequent coronary bypass target vessel was the left anterior descending artery (38.1%). There was no early mortality or deaths during follow-up; 90% remained in functional class I. Among the cohort as a group, there was an overall improvement in postoperative ventricular function (P= .03). This persisted, being unchanged at subsequent follow-up (P= .95). Conclusions:Coronary artery bypass grafting is an appropriate treatment option for children with cardiac sequelae of KD, with excellent surgical results. Furthermore, this surgical procedure avoids the deterioration of left ventricular function in pediatric age.

We have disentangled the contributions to the glass transition as observed by differential scanning calorimetry (DSC) on simplified systems of industrial interest consisting of blends of styrene–butadiene rubber (SBR) and polystyrene (PS) oligomer. To do this, we have started from a model previously proposed to describe the effects of blending on the equilibrium dynamics of the α-relaxation as monitored by broadband dielectric spectroscopy (BDS). This model is based on the combination of self-concentration and thermally driven concentration fluctuations (TCFs). Considering the direct insight of small-angle neutron scattering on TCFs, blending effects on the α-relaxation can be fully accounted for by using only three free parameters: the self-concentration of the components φselfSBRand φselfPS) and the relevant length scale of segmental relaxation, 2Rc. Their values were determined from the analysis of the BDS results on these samples, being that obtained for 2Rc≈ 25Å in the range usually reported for this magnitude in glass-forming systems. Using a similar approach, the distinct contributions to the DSC experiments were evaluated by imposing the dynamical information deduced from BDS and connecting the component segmental dynamics in the blend above the glass-transition temperature Tg(at equilibrium) and the way the equilibrium is lost when cooling toward the glassy state. This connection was made through the α-relaxation characteristic time of each component at Tg, τg. The agreement of such constructed curves with the experimental DSC results is excellent just assuming that τgis not affected by blending.

Intrapericardial teratoma is a rare tumor composed of tissue from the three germ cell layers with a rapid growth that may cause severe hemodynamic complications due to compressive effects. We present two clinical cases: the first case had severe fetal heart failure with fatal outcome, and the second underwent surgical treatment during the immediate postnatal period with a favorable evolution. Although teratomas are histologically benign tumors, rapid growth can cause serious hemodynamic complications. The importance of prenatal diagnosis is to allow appropriate monitoring of tumor growth and establish a prompt therapeutic plan. Opportune surgical treatment can prevent death and improve the prognosis of these patients.

We introduce herein a simple model of covalent-bonded single-chain nanoparticles (SCNPs) by considering these intrachain cross-linked nano-objects as elastic unimolecular networks. According to this model, each SCNP is regarded as a network of elastic strands connected by cross-links. The free energy of the SCNP is decomposed in two contributions: (i) an elastic free energy due to the presence of these strands and (ii) an excluded volume contribution arising from the balance of monomer–monomer and monomer–solvent interactions. We provide scaling law expressions for the size (R), diffusion coefficient (D), apparent molar mass (Mapp), and shrinking factor (⟨G⟩) of elastic SCNPs in good, theta, and bad solvents. Also, we derive scaling laws for the height (H) of elastic SCNPs deposited on both low- and high-surface free energy substrates. A comparison of experimental results to model predictions for covalent-bonded polystyrene SCNPs in solution of narrow molecular weight distribution (1.09 ≤ Đ≤ 1.26), different amount of reactive groups (0.025 ≤ x≤ 0.3), and varying precursor molar mass (44 ≤ M≤ 235 kDa) is performed based on literature data. For the same system, a similar comparison of experimental and theoretical Hdata corresponding to the case of SCNPs deposited on low- and high-energy substrates is also carried out. This simple elastic model provides a useful framework for connecting the amount of reactive groups and precursor molar mass with the size upon intrachain cross-linking for a variety of covalent-bonded SCNPs both in solvents of different quality and on substrates of different surface free energy.

Polymer vitrimers are a new class of materials that combine the advantages of thermoplastics and thermosets. This is due to the dynamic nature of the chemical bonds linking different chains. However, how this property affects the polymer dynamics at different length scales is still an open question. Here, we investigate the dynamics of model vitrimers based on well-defined polyisoprene (PI) chains using broadband dielectric spectroscopy. In this way, we study the polymer dynamics from the segmental to the whole chain scale, taking advantage of the fact that PI belongs to the class of molecules that exhibit a net dipole moment associated with the end-to-end vector. Three distinct relaxation phenomena are identified. The fastest relaxation is attributed to the segmental PI dynamics with a small influence of the cross-linking. An intermediate relaxation attributed to the dipolar character of the cross-linker is also observed. The slower identified relaxation component, corresponding to limited fluctuations of the end-to-end PI chains, is found to be determined by the dynamics of the clusters formed by the cross-linkers with an average time scale orders of magnitude faster than that of the terminal relaxation as inferred from the viscous flow.

Severe acute respiratory syndrome coronavirus 2, the etiologic agent of coronavirus disease 2019, has caused more than 160 million infections globally. The experience of our department showed that the execution of a strict surgery protocol, universal severe acute respiratory syndrome coronavirus 2 screening, surgical prioritization, and an orderly reactivation of the cardiac surgery program is a feasible way to keep congenital heart diseases surgery program.

We present a small-angle neutron scattering (SANS) and neutron spin echo investigation on the structure and dynamics of irreversible single-chain nanoparticles (SCNPs) in dilute solution. SCNPs are ultra-small soft nano-objects obtained by intramolecular folding/collapse of individual linear polymer chains (precursors). SANS has demonstrated the compaction of macromolecules upon creation of internal cross-links, although their conformation is far from a globular topology. To describe the dynamic structure factor of the SCNPs in solution, we have taken into account their dual polymer/nanoparticle character and applied theoretical approximations based on the Zimm model. The study reveals relaxation of internal degrees of freedom but clearly slowed down with respect to the precursor counterparts. This effect is attributed to the internal friction associated to the compartmentation in domains within the macromolecule. We discuss the structural and dynamical similarities of SCNPs with disordered proteins, in particular with intrinsically disordered proteins. The high internal friction in both cases seems to be associated to the existence of internal domains.

Applying small-angle neutron scattering (SANS) on isotopically labeled samples, we have characterized the thermally driven concentration fluctuations (TCFs), one of the main factors in the phenomenology of blend dynamics, in mixtures of styrene–butadiene rubber (SBR) and oligomers of polystyrene (PS) with different compositions. This system displays a large dynamic asymmetry and is thus a good model to explore the tunability of properties of interest in the rubber industry. The SANS experiments, complemented with neutron diffraction with polarization analysis, have allowed one to determine the UCST behavior of the blend and establish its phase diagram. We find a close vicinity of the spinodal and vitrification lines for intermediate concentrations and samples rich in PS. This induces the freezing of the correlation length for TCF when decreasing the temperature and also has an impact on the reported dielectric response of these mixtures. Furthermore, we have deduced the relevant length scale for segmental relaxation from the comparison of SANS and dielectric results. The values found (≈1.5–2 nm) are close to the Kuhn lengths of the components. The relevance of nanometric length scales in this system could also be tentatively attributed to an underlying nanodomain structure associated with the segregation of phenyl rings and main chains, supported by complementary X-ray diffraction experiments.

We address the dynamics of isofrictional bimodal polyisoprene (PI) blends and emphasize the effect of concentration and topology of the short component on the dynamics of the long-chain component. The experiments were performed on blends of long well-entangled linear chains with shorter linear and star-branched chains varying systematically the concentration of the short component (additive). Small-angle neutron scattering showed that the conformation of the long chains does not change either with concentration or with the additive topology. Applying different spectroscopic techniques, we studied the terminal times of both the long chain and the additives. Thereby, the dielectric and viscoelastic terminal times for the long-chain dynamics, as well as the diffusion times deduced from pulsed-field-gradient (PFG)-NMR measurements, follow the same scaling behavior as a function of the volume fraction of the long chains (ϕL). For the case of the linear additive, the scaling τL∼ ϕLis observed in the full concentration range covered (0.1 ≤ ϕL≤ 1). In the case of the star additives, deviations from this scaling law are evident at ϕL≲ 0.4. The zero-shear viscosity scales as η0∼ ϕL3for ϕL≳ 0.4. Deviations are observed at lower values of ϕLfor both additive topologies. On the other hand, the terminal relaxation time of the short chain or the arm retraction time for the stars obtained from dielectric spectroscopy (DS) is only weakly affected by blending and stays nearly constant over the full concentration range. However, the diffusion times of both types of additives depend significantly on ϕL. Finally, measuring the dynamic structure factor by neutron spin echo (NSE), we directly observe the process of constraint removal at the molecular scale. These results are discussed in terms of the different theoretical approaches available. Thereby, the nearly quantitative agreement of the rheological results with the Read extension of the Viovy theory for long-chain volume fractions ϕL≥ 0.5 is emphasized. On the other hand, the low ϕLresults cannot be accounted for. Also, predictions of the tension equilibration mechanism leading to an enhanced ϕL-dependence are not supported by our data.

In recent decades, self-confinement effects arising from the folding of individual synthetic polymer chains to single-chain nanoparticles (SCNPs) have been exploited for the construction of efficient enzyme-mimetic catalysts, improved drug delivery nanosystems and innovative sensing nanomaterials, among other uses. Remarkably, the imperfect folding of a unimolecular synthetic chain to a functional soft nano-object resembles – to some extent – the folding of a protein to its native, functional state. However, the huge possibilities that can be deployed by determining how external confinement modulates the structure, dynamics and properties of SCNPs have not been totally appreciated yet. In this article, after considering the opportunites that internal confinement in SCNPs offers for catalysis; encapsulation, transport and delivery of therapeutic cargos; and sensing, targeting and bioimaging applications, as well as other diverse advanced applications, we try to provide a unifying vision of what is the expected effect of external confinement – as imposed under different geometrical constraints as well as in solution, in the melt state, on surfaces and in membranes – on the size, shape and, hence, potential functionality/foreseen applications of SCNPs. We anticipate a plethora of opportunities that open up arising from external confinement of SCNPs: from innovative purification techniques and improved all-polymer nanocomposites, to smart responsive surfaces and new topological nanostructures.

Through a combination of neutron scattering, dielectric spectroscopy, and rheological measurements we study the impact of purely intramolecular cross-linking on a melt fully made of polymeric single-chain nanoparticles (SCNPs)—a novel class of ultrasoft nano-objects. While the α-relaxation is unaffected with respect to the reference melt of linear chains, the emerging polymer/colloid duality of SCNPs leads to the almost complete smearing out of the rubbery plateau. This is the opposite effect to the creation of a permanent 3D network by intermolecular bonds. In addition, neutron scattering shows that a new relaxation mechanism slower than the α-relaxation appears at intermediate length scales. These are beyond the interchain distance but yet far from the hydrodynamic regime. This new slow relaxation—also detected by dielectric spectroscopy—contributes to the hierarchy of processes needed for the full relaxation of the SCNP melt and is tentatively related to the heterogeneities provoked by the internal multiloop topology of the SCNPs and the segregation of their internal domains.

The conformation of single-chain nanoparticles (SCNPs) in the presence of linear polystyrene crowding molecules has been studied by small-angle neutron scattering under contrast-matching of the crowders. A model describing the scattering of aggregating polydisperse SCNPs has been developed, resulting in the determination of the potentially squeezed size of the individual SCNPs within aggregates, their local chain statistics, and the average aggregation number, as a function of crowding. Two different crowders, of low and high molecular weights, are shown to have a different effect: while long chains tend to impede their aggregation above their overlap concentration, short ones are found to mediate depletion interactions leading to aggregation. Self-imposed crowding within the aggregates has a similar impact on chain conformation independently of the crowding of the surrounding medium. Our results are compared to recent simulations and shall contribute to the microscopic understanding of the phase behavior of soft intrinsically disordered nano-objects and in particular the effect of crowding on biomacromolecules.

Una de las principales herramientas para optimizar el uso de los antibióticos es la formación de los prescriptores. El objetivo de este trabajo es conocer la opinión de los estudiantes de Medicina españoles sobre la formación en enfermedades infecciosas.

We apply the methodology and concepts developed over the past years for the study of segmental dynamics on miscible polymer blends to the investigation of a blend made of styrene–butadiene rubber (SBR) and an oligomer of polystyrene (PS) as an example of a simplified industrial system. In this way we obtain detailed information about the segmental dynamics of both components within the blend. To this end, a judicious combination of broad-band dielectric spectroscopy (BDS) and quasi-elastic neutron scattering (QENS) results on deuterium-labeled blends was required. Difficulties on the comparison between isotopically different samples arose due to changes in polymer microstructure associated with the obtention of deuterated polymers. Nevertheless, the strategy for data analysis developed in this work made it possible to readily resolve the components’ segmental dynamics of the investigated mixtures. It was found that Gaussian distributions of the components’ effective glass-transition temperatures provide a very good description of all the experimental data collected in the SBR/PS (50/50 wt %) mixtures over the whole accessible temperature range, not only by BDS and QENS but also those obtained by differential scanning calorimetry and by neutron elastic fixed window scan experiments.

Background: The indications for pediatric coronary revascularization are diverse. There are a large proportion of patients with sequelae of severe inflammatory diseases such as Kawasaki disease, and other less common causes.Methods: Retrospective review of ten pediatric patients undergoing coronary artery bypass surgery from January 2004 to December 2016.Results: Ten children and adolescents ranging in age from 2 to 17 (median, 6) years at operation were followed up for as long as 13 years with a median follow-up of 2 years. The surgical indications include ischemia symptoms and/or coronary stenosis angiographically documented. Diagnoses include Kawasaki disease, anomalous origin of the left coronary artery from the pulmonary artery, and iatrogenic lesion of the right coronary artery. All the surgical procedures were performed with cardiopulmonary bypass with crystalloid cardioplegic arrest. The number of distal anastomoses was 1.6 per patient, and the left internal thoracic artery was used in one patient, the right internal thoracic artery in four patients, bilateral internal thoracic artery in four patients, and bilateral internal thoracic artery plus left radial artery in one patient, most frequently for right coronary artery revascularization. The patients underwent noninvasive diagnostic study during follow-up to evaluate their coronary status. The ten patients had no symptoms, and there was no mortality.Conclusions: Although survival was excellent after pediatric coronary bypass in our center, we need to continue the follow-up. Coronary revascularization by means of arterial grafting is a safe and reliable surgical modality for coronary disease in children.

Background: Surgical repair of common arterial trunk (CAT) by means of a homograft conduit has become a standard practice. We report our experience in the correction of this heart disease with a handmade bovine pericardial-valved woven Dacron conduit as an alternative procedure to homografts, with a focus on early, mid-term, and long-term results.Methods: We designed a retrospective study that included 15 patients with a mean age of 1.5 years (range: three months to eight years), who underwent primary repair of simple CAT. Right ventricular outflow tract was reconstructed in all the cases with this handmade graft that was explanted at the time of its biological stenotic degeneration. A peeling procedure was performed at this time, in order to reconstruct the right ventricle-to-pulmonary artery continuity.Results: Overall mortality was 13.3% (one death at the early postoperative primary repair and the other at the mid-term postoperative peeling reoperation). Actuarial survival rate was 93.3%, 86.7%, and 86.7% at 5, 10, and 15 years, respectively. All of the 14 survivors developed stenosis of the handmade conduit at the mid-term period (8 ± 3 years), but after the peeling procedure, 13 survivors remain asymptomatic to date.Conclusions: Primary repair of common arterial trunk using a handmade conduit can be performed with very low perioperative mortality and satisfactory mid-term and long-term results, which can be favorably compared with those reported with the use of homografts. When graft obstruction develops, peeling procedure is a good option because it does not affect the overall survival, although long-term outcomes warrant further follow-up.

The conformation of poly(methyl methacrylate) (PMMA)-based single-chain nanoparticles (SCNPs) and their corresponding linear precursors in the presence of deuterated linear PMMA in deuterated dimethylformamide (DMF) solutions has been studied by small-angle neutron scattering (SANS). The SANS profiles were analyzed in terms of a three-component random phase approximation (RPA) model. The RPA approach described well the scattering profiles in dilute and crowded solutions. Considering all the contributions of the RPA leads to an accurate estimation of the single chain form factor parameters and the Flory–Huggins interaction parameter between PMMA and DMF. The value of the latter in the dilute regime indicates that the precursors and the SCNPs are in good solvent conditions, while in crowding conditions, the polymer becomes less soluble.