Influence of knot complexity on glass-formation in low molecular mass ring polymer melts.

We perform molecular dynamics simulations on a coarse-grained polymer melt to study the dynamics of glass-formation in ring polymer melts of variable knot complexity. After generating melts of non-concatenated polymeric rings having a range of minimum crossing number values, mc, we compute the coherent intermediate scattering function, the segmental α-relaxation time, fragility, and the glass transition temperature as a function of mc. Variation of knot complexity is found to have a pronounced effect on the dynamics of polymer melts since both molecular rigidity and packing are altered, primary physical factors governing glass-formation in polymeric materials.

The interfacial zone in thin polymer films and around nanoparticles in polymer nanocomposites.

We perform coarse-grained simulations of model unentangled polymer materials to quantify the range over which interfaces alter the structure and dynamics in the vicinity of the interface. We study the interfacial zone around nanoparticles (NPs) in model polymer-NP composites with variable NP diameter, as well as the interfacial zone at the solid substrate and free surface of thin supported polymer films. These interfaces alter both the segmental packing and mobility in an interfacial zone. Variable NP size allows us to gain insight into the effect of boundary curvature, where the film is the limit of zero curvature. We find that the scale for perturbations of the density is relatively small and decreases on cooling for all cases. In other words, the interfaces become more sharply defined on cooling, as naively expected. In contrast, the interfacial mobility scale ξ for both NPs and supported films increases on cooling and is on the order of a few nanometers, regardless of the polymer-interfacial interaction strength. Additionally, the dynamical interfacial scale of the film substrate is consistent with a limiting value for polymer-NP composites as the NP size grows. These findings are based on a simple quantitative model to describe the distance dependence of relaxation that should be applicable to many interfacial polymer materials.

Communication: A comparison between the solution properties of knotted ring and star polymers.

We computationally investigate the good solvent solution properties of knotted ring and star polymers by combining molecular dynamics (MD) simulation and path-integral calculations. We consider knotted rings having a minimal crossing number m c in the range, 0 ≤ m c ≤ 9, and star polymers having a range of f star arms, 2 ≤ f ≤ 20, attached to a common core monomer particle. After generating configurational ensembles of these polymers by MD, we use the path-integration program ZENO to calculate basic configurational properties, i.e., radius of gyration, hydrodynamic radius, intrinsic viscosity, as well as fluctuations in these properties. Our simulations indicate that the configurational properties of knotted rings and star polymers in solution show a similar decrease with increasing m c and f. Moreover, fluctuations in these properties also decrease with increasing topological complexity. Our findings should be helpful in polymer characterization and more generally for understanding the role of polymer topology in polymer material properties.

Molecular rigidity and enthalpy-entropy compensation in DNA melting.

Enthalpy-entropy compensation (EEC) is observed in diverse molecular binding processes of importance to living systems and manufacturing applications, but this widely occurring phenomenon is not sufficiently understood from a molecular physics standpoint. To gain insight into this fundamental problem, we focus on the melting of double-stranded DNA (dsDNA) since measurements exhibiting EEC are extensive for nucleic acid complexes and existing coarse-grained models of DNA allow us to explore the influence of changes in molecular parameters on the energetic parameters by using molecular dynamics simulations. Previous experimental and computational studies have indicated a correlation between EEC and changes in molecular rigidity in certain binding-unbinding processes, and, correspondingly, we estimate measures of DNA molecular rigidity under a wide range of conditions, along with resultant changes in the enthalpy and entropy of binding. In particular, we consider variations in dsDNA rigidity that arise from changes of intrinsic molecular rigidity such as varying the associative interaction strength between the DNA bases, the length of the DNA chains, and the bending stiffness of the individual DNA chains. We also consider extrinsic changes of molecular rigidity arising from the addition of polymer additives and geometrical confinement of DNA between parallel plates. All our computations confirm EEC and indicate that this phenomenon is indeed highly correlated with changes in molecular rigidity. However, two distinct patterns relating to how DNA rigidity influences the entropy of association emerge from our analysis. Increasing the intrinsic DNA rigidity increases the entropy of binding, but increases in molecular rigidity from external constraints decreases the entropy of binding. EEC arises in numerous synthetic and biological binding processes and we suggest that changes in molecular rigidity might provide a common origin of this ubiquitous phenomenon in the mutual binding and unbinding of complex molecules.

Malignant Bowel Obstruction in Relapsed Ovarian Cancer With Peritoneal Carcinomatosis: An Occlusive State.

OBJECTIVE: The aim of this study was to describe the clinical and oncological outcomes of women with malignant bowel obstruction (MBO) for relapsed ovarian cancer and peritoneal carcinomatosis. METHODS: A retrospective cohort study was performed in all consecutive patients admitted at Instituto Valenciano de Oncología, Valencia, Spain, between July 2013 and July 2016 with MBO for relapsed ovarian cancer and peritoneal carcinomatosis. All patients underwent the same protocol of conservative management. Surgical treatment was indicated only in selected cases. RESULTS: There were a total of 22 patients presenting 59 episodes of MBO; 17 (77.2%) of those patients presented more than 1 episode of MBO. All patients had serous epithelial ovarian cancer; 18 (81.8%) were high grade, and 4 (18.2%) low-grade tumors. The median (range) number of episodes per patient was 3 (range, 1-7) with a mean length of hospitalization of 13 (SD, 13.6) days. The median time interval between episodes of MBO (54 episodes in 17 patients) was 17 days (range, 1-727 days). Twenty of 22 patients died with a median overall survival time from the first episode of MBO of 95 days (95% confidence interval, 49-124 days). CONCLUSIONS: Patients with MBO due to relapsed epithelial ovarian cancer in the peritoneal carcinomatosis setting have a short life expectancy, presenting a median of 3 episodes of MBO until death, with a short time interval between episodes. These findings show that bowel obstruction can represent a constant status over time until death.

Universal interrelation between measures of particle and polymer size.

The characterization of many objects involves the determination of a basic set of particle size measures derived mainly from scattering and transport property measurements. For polymers, these basic properties include the radius of gyration Rg, hydrodynamic radius Rh, intrinsic viscosity [η], and sedimentation coefficient S, and for conductive particles, the electric polarizability tensor αE and self-capacity C. It is often found that hydrodynamic measurements of size deviate from each other and from geometric estimates of particle size when the particle or polymer shape is complex, a phenomenon that greatly complicates both nanoparticle and polymer characterizations. The present work explores a general quantitative relation between αE, C, and Rg for nanoparticles and polymers of general shape and the corresponding properties η, Rh, and Rg using a hydrodynamic-electrostatic property interrelation.

Confronting the complexity of CNT materials.

The morphology of commercially available carbon nanotube materials is often much more complex than the term "carbon nanotube" (CNT) would imply. Commercial CNT materials are typically composed of roughly spherical CNT domains having a highly ramified internal structure and a size on the order of microns. Clearly, such structures cannot reasonably be modeled as "rods". To address this problem, we first perform molecular dynamics simulations (MD) to generate structures similar to those measured experimentally, based on the presumptions that CNT domains are composed of worm-like cylinders having observed persistence lengths and that these CNTs are confined to spherical domains having the observed average domain size. This simple model generates structures remarkably similar to those observed experimentally. We then consider numerical path-integral computations to calculate the self-capacitance C and intrinsic conductivity [σ]∞ of these CNT rich domains. This information is then incorporated in a generalized effective medium theory to estimate the conductivity of bulk composite materials composed of these complex-shaped "particles". We term these CNT structures "tumbleweeds", given their evident morphological similarity to this naturally occurring growth form. Based on this model, we find that the conductivity percolation threshold of the tumbleweeds can be quite low, despite their quasi-spherical average shape. We also examine the structure factor S(q) of the CNT-rich domains as function of the number N of CNTs within them, to aid in the structural characterization of CNT nanocomposites. The structure factor S(q) of our model tumbleweed is found to resemble that of hyperbranched, star and dendrimer polymers, and also domain structures observed in polyelectrolytes. Commercial CNT materials at high loading should then have physical features in common with suspension of "soft" colloidal particles by virtue of their deformability and roughly spherical shape.

Dimensional reduction of duplex DNA under confinement to nanofluidic slits.

There has been much interest in the dimensional properties of double-stranded DNA (dsDNA) confined to nanoscale environments as a problem of fundamental importance in both biological and technological fields. This has led to a series of measurements by fluorescence microscopy of single dsDNA molecules under confinement to nanofluidic slits. Despite the efforts expended on such experiments and the corresponding theory and simulations of confined polymers, a consistent description of changes of the radius of gyration of dsDNA under strong confinement has not yet emerged. Here, we perform molecular dynamics (MD) simulations to identify relevant factors that might account for this inconsistency. Our simulations indicate a significant amplification of excluded volume interactions under confinement at the nanoscale due to the reduction of the effective dimensionality of the system. Thus, any factor influencing the excluded volume interaction of dsDNA, such as ionic strength, solution chemistry, and even fluorescent labels, can greatly influence the dsDNA size under strong confinement. These factors, which are normally less important in bulk solutions of dsDNA at moderate ionic strengths because of the relative weakness of the excluded volume interaction, must therefore be under tight control to achieve reproducible measurements of dsDNA under conditions of dimensional reduction. By simulating semi-flexible polymers over a range of parameter values relevant to the experimental systems and exploiting past theoretical treatments of the dimensional variation of swelling exponents and prefactors, we have developed a novel predictive relationship for the in-plane radius of gyration of long semi-flexible polymers under slit-like confinement. Importantly, these analytic expressions allow us to estimate the properties of dsDNA for the experimentally and biologically relevant range of contour lengths that is not currently accessible by state-of-the-art MD simulations.

Intrinsic conductivity of carbon nanotubes and graphene sheets having a realistic geometry.

The addition of carbon nanotubes (CNTs) and graphene sheets (GSs) into polymeric materials can greatly enhance the conductivity and alter the electromagnetic response of the resulting nanocomposite material. The extent of these property modifications strongly depends on the structural parameters describing the CNTs and GSs, such as their shape and size, as well as their degree of particle dispersion within the polymeric matrix. To model these property modifications in the dilute particle regime, we determine the leading transport virial coefficients describing the conductivity of CNT and GS composites using a combination of molecular dynamics, path-integral, and finite-element calculations. This approach allows for the treatment of the general situation in which the ratio between the conductivity of the nanoparticles and the polymer matrix is arbitrary so that insulating, semi-conductive, and conductive particles can be treated within a unified framework. We first generate ensembles of CNTs and GSs in the form of self-avoiding worm-like cylinders and perfectly flat and random sheet polymeric structures by using molecular dynamics simulation to model the geometrical shapes of these complex-shaped carbonaceous nanoparticles. We then use path-integral and finite element methods to calculate the electric and magnetic polarizability tensors (αE, αM) of the CNT and GS nanoparticles. These properties determine the conductivity virial coefficient σ in the conductive and insulating particle limits, which are required to estimate σ in the general case in which the conductivity contrast Δ between the nanoparticle and the polymer matrix is arbitrary. Finally, we propose approximate relationships for αE and αM that should be useful in materials design and characterization applications.

High-speed, high-purity separation of gold nanoparticle-DNA origami constructs using centrifugation.

DNA origami is a powerful platform for assembling gold nanoparticle constructs, an important class of nanostructure with numerous applications. Such constructs are assembled by the association of complementary DNA oligomers. These association reactions have yields of <100%, requiring the development of methods to purify the desired product. We study the performance of centrifugation as a separation approach by combining optical and hydrodynamic measurements and computations. We demonstrate that bench-top microcentrifugation is a simple and efficient method of separating the reaction products, readily achieving purities of >90%. The gold nanoparticles play a number of critical roles in our system, functioning not only as integral components of the purified products, but also as hydrodynamic separators and optical indicators of the reaction products during the purification process. We find that separation resolution is ultimately limited by the polydispersity in the mass of the gold nanoparticles and by structural distortions of DNA origami induced by the gold nanoparticles. Our study establishes a methodology for determining the design rules for nanomanufacturing DNA origami-nanoparticle constructs.

Evaluating Rural Health Disparities in Colombia: Identifying Barriers and Strategies to Advancing Refugee Health.

Health disparities within rural communities, notably those affecting migrant and refugee populations, are well-documented. Refugees often grapple with high disease burdens and mortality rates due to limited access to primary healthcare and their vulnerable socio-economic and political situations. This issue is particularly acute in the rural areas around Medellin, Colombia, where the refugee influx exacerbates the existing public health challenges. Studies highlight a substantial gap between community needs and public health policies, resulting in inadequate healthcare access. Our study, utilizing the Delphi technique, aimed to identify common barriers and strategies to enhance rural healthcare for refugees. Through consensus-building with community leaders, we identified six primary barriers to healthcare access and five barriers to healthcare quality. Community leaders endorsed five strategies to address the access barriers and eight strategies to improve healthcare quality. This research provides valuable insights for optimizing resource allocation and designing effective support programs for these vulnerable populations.

Tack of Entangled Molecular Bottlebrushes.

Polymer softness (i.e., low elastic modulus) is a known requirement for good tack in adhesives. We assess the tack performance of α-olefin molecular bottlebrushes having an elastic modulus from 4 to 30 times lower than a linear polyolefin (polypropylene). Monotonic increases of the tack parameters are observed as the bottlebrush side chain length (Nsc) increases and the modulus decreases. All-atom molecular dynamics simulations reveal that the monomeric bonding energy increases with Nsc due to a strong van der Waals interaction between the side chains and the aluminum sheet, which overcomes the energy penalty imposed by side-chain bending.

Lipoma of the Teres Minor in Rotator Cuff Arthropathy-A Case Report.

Although lipomas are the most common mesenchymal tumors, the intramuscular type is rare. We report the case of a patient with rotator cuff arthropathy with a lipoma in the teres minor. Wide surgical excision and total shoulder arthroplasty with reverse prosthesis was performed and 18 months of follow up showed excellent results with any recurrence. The teres minor is extremely important for the proper function of a reverse prosthesis, and lipoma growth in the muscular belly can compromise the functionality of the prosthesis. To the best of our knowledge, this is the first case report of a rotator cuff arthropathy with a lipoma in the teres minor.

Does compartmental resection really impact retroperitoneal soft tissue sarcomas? A retrospective analysis from a Single Referral Center.

BACKGROUND: The treatment of choice for retroperitoneal soft tissue sarcomas (RPS) is surgical resection; the outcomes with more radical surgeries, notably compartmental resection, remains a subject of debate. Arguments against it, include the complexity of the technique and high morbidity. MATERIALS AND METHODS: A retrospective analysis of cases treated in a single center from January 2010 to December 2019 is presented. Two time periods were evaluated: 2010-2015 and 2016-2019, corresponding to before and after the implementation of routine compartmentectomy. We evaluated the short- and long-term outcomes of compartmental resection compared to limited surgeries through a multivariate analysis of prognostic factors. RESULTS: A total of 176 cases were included, of which 102 met the inclusion criteria. The sex distribution was similar. The average age was 52.9 years, and the average tumor size was 24.5 cm. The most frequent histology was liposarcoma (65.7%), followed by leiomyosarcoma (12.7%), and malignant peripheral nerve sheath tumor (8.8%). The median follow-up period was 40 months. We found a lower local recurrence in the group treated in the recent period (compartmentectomy) 42.3% vs 20% p = 0.007. The median overall survival (OS) was 38.7 months, and there was no difference in distant recurrence between the two time periods. Postoperative morbidity was higher in the recent period (25% vs 10% p 0.041), with no difference in 30-day mortality. CONCLUSIONS: The implementation of extensive surgery, specifically compartmentectomy, for retroperitoneal sarcomas has been linked to reduced local recurrence. We recommend considering this surgical approach for RPS in alignment with current expert consensus guidelines, as highlighted by the updated TARPSWG consensus.

Solution properties of spherical gold nanoparticles with grafted DNA chains from simulation and theory.

There has been a rapidly growing interest in the use of functionalized Au nanoparticles (NPs) as platforms in multiple applications in medicine and manufacturing. The sensing and targeting characteristics of these NPs, and the realization of precisely organized structures in manufacturing applications using such NPs, depend on the control of their surface functionalization. NP functionalization typically takes the form of polymer grafted layers, and a detailed knowledge of the chemical and structural properties of these layers is required to molecularly engineer the particle characteristics for specific applications. However, the prediction and experimental determination of these properties to enable the rational engineering of these particles is a persistent problem in the development of this class of materials. To address this situation, molecular dynamic simulations were performed based on a previously established coarse-grained single-stranded DNA (ssDNA) model to determine basic solution properties of model ssDNA-grafted NP-layers under a wide range of conditions. In particular, we emphasize the calculation of the hydrodynamic radius for ssDNA-grafted Au NPs as a function of structural parameters such as ssDNA length, NP core size, and surface coverage. We also numerically estimate the radius of gyration and the intrinsic viscosity of these NPs, which in combination with hydrodynamic radius estimates, provide valuable information about the fluctuating structure of the grafted polymer layers. We may then understand the origin of the commonly reported variation in effective NP "size" by different measurement methods, and then exploit this information in connection to material design and characterization in connection with the ever-growing number of applications utilizing polymer-grafted NPs.

Candida albicans Modulates Murine and Human Beta Defensin-1 during Vaginitis.

Vulvovaginal candidiasis (VVC) and recurrent vulvovaginal candidiasis (RVVC) are two forms of a disease caused by Candida spp. ß-defensin (BD) is one of the most important families of antimicrobial peptides in the female genital tract and includes molecules that exert essential local functions as antimicrobial and PMN chemoattractant peptides. However, the information on their role during murine and human VVC and RVVC is limited. Thus, we analyzed the behavior and contribution of BD1 to the local response in a VVC mice model and the local cytokine profile and human BD1 and BD3 expression in cervicovaginal lavage from patients with VVC and RVVC. We demonstrated that, in patients with RVVC BD1, mRNA and protein expression were severely diminished and that the aspartate proteinase and lipase secreted by C. albicans are involved in that decrease. This study provides novel information about the pathogenesis of VVC and describes a highly efficient C. albicans escape strategy for perpetuating the infection; these results may contribute to the development of new or combined treatment approaches.

Fiber Network Formation in Semi-Flexible Polymer Solutions: An Exploratory Computational Study.

The formation of gels through the bundling of semi-flexible polymer chains into fiber networks is ubiquitous in diverse manufactured and natural materials, and, accordingly, we perform exploratory molecular dynamics simulations of a coarse-grained model of semi-flexible polymers in a solution with attractive lateral interchain interactions to understand essential features of this type of gel formation. After showing that our model gives rise to fibrous gels resembling real gels of this kind, we investigate how the extent of fiber bundling influences the "melting" temperature, T m , and the emergent rigidification of model bundled fibers having a fixed number of chains, N, within them. Based on our preliminary observations, we suggest the fiber size is kinetically selected by a reduced thermodynamic driving force and a slowing of the dynamics within the fibers associated with their progressive rigidification with the inclusion of an increasing number of chains in the bundle.

Structure and Dynamics of a Graphene Melt.

We explore the structural and dynamic properties of bulk materials composed of graphene nanosheets using coarse-grained molecular dynamics simulations. Remarkably, our results show clear evidence that bulk graphene materials exhibit a fluid-like behavior similar to linear polymer melts at elevated temperatures and that these materials transform into a glassy-like "foam" state at temperatures below the glass-transition temperature ( Tg) of these materials. Distinct from an isolated graphene sheet, which exhibits a relatively flat shape with fluctuations, we find that graphene sheets in a melt state structurally adopt more "crumpled" configurations and correspondingly smaller sizes, as normally found for ordinary polymers in the melt. Upon approaching the glass transition, these two-dimensional polymeric materials exhibit a dramatic slowing down of their dynamics that is likewise similar to ordinary linear polymer glass-forming liquids. Bulk graphene materials in their glassy foam state have an exceptionally large free-volume and high thermal stability due to their high Tg (≈ 1600 K) as compared to conventional polymer materials. Our findings show that graphene melts have interesting lubricating and "plastic" flow properties at elevated temperatures, and suggest that graphene foams are highly promising as high surface filtration materials and fire suppression additives for improving the thermal conductivities and mechanical reinforcement of polymer materials.

Knot Energy, Complexity, and Mobility of Knotted Polymers.

The Coulomb energy E C is defined by the energy required to charge a conductive object and scales inversely to the self-capacity C, a basic measure of object size and shape. It is known that C is minimized for a sphere for all objects having the same volume, and that C increases as the symmetry of an object is reduced at fixed volume. Mathematically similar energy functionals have been related to the average knot crossing number 〈m〉, a natural measure of knot complexity and, correspondingly, we find E C to be directly related to 〈m〉 of knotted DNA. To establish this relation, we employ molecular dynamics simulations to generate knotted polymeric configurations having different length and stiffness, and minimum knot crossing number values m for a wide class of knot types relevant to the real DNA. We then compute E C for all these knotted polymers using the program ZENO and find that the average Coulomb energy 〈E C〉 is directly proportional to 〈m〉. Finally, we calculate estimates of the ratio of the hydrodynamic radius, radius of gyration, and the intrinsic viscosity of semi-flexible knotted polymers in comparison to the linear polymeric chains since these ratios should be useful in characterizing knotted polymers experimentally.

Axial view of the shoulder. Description of a technique / Proyección axial de hombro. Descripción de una técnica

Shoulder fracture is one of the most frequently treated injuries in trauma centers, with an overall incidence that appears to have increased in recent years, ranging from 219 to 419 cases per 100 000 person-years. In clinical terms, shoulder girdle injury is difficult to diagnose due to the close relationship between the shoulder and the chest, and imaging identification of the different types of injuries can be challenging. In this context, X-rays are the most appropriate method and the cornerstone of the initial approach to shoulder trauma, and at least 3 views are recommended: true anteroposterior view (AP), axial or axillary projection or modified axial projection (Velpeau view), and lateral scapula shoulder or Y view. However, patient positioning is often problematic due to the additional pain associated with limb mobilization in order to achieve the proper position for radiographic projection. The following is the description of a technique for performing an axial shoulder projection that is free of these complications, easy to standardize, and applicable to any traumatic or degenerative disease of the proximal humerus or glenohumeral joint, which, to the best of the authors' knowledge, has not been previously published.

El trauma de hombro es una de las patologías más frecuentemente vista en los centros de trauma con una incidencia global que aparentemente ha aumentado en los últimos años y que se ha reportado entre 219 a 419 casos por 100000 personas-año. El diagnóstico del trauma de la cintura escapular no es fácil clínicamente por la íntima relación entre el hombro y el tórax, y la identificación imagenológica de las distintas lesiones puede ser desafiante. Las radiografías son el método más apropiado y piedra angular del estudio inicial en el trauma de hombro, el set de trauma tiene al menos 3 planos: la vista Anteroposterior (AP) verdadera, una proyección axial o axilar o su modificación descrita por Velpeau. Y una proyección Y de escápula. Sin embargo, el posicionamiento del paciente muchas veces no es fácil por el dolor adicional que puede generar la movilización de la extremidad para lograr la posición adecuada para la proyección radiográfica. Describimos una técnica para realizar una proyección axial de hombro sin estas dificultades, fácilmente estandarizable para cualquier patología traumática o degenerativa del húmero proximal o de la articulación gleno-humeral y que creemos no ha sido publicada previamente.