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•Polymer nanofabrication by laser induced periodic surface structures.•Irradiation conditions control both size and shape of the nanostructures.•Irradiation with femtosecond pulses ...allows nanostructuring transparent polymers.•Applications of rippled polymers in cell culture and sensing are proposed.
The generation of nanostructured polymer films has been a challenge during the last decades. Surface nanostructuring based on the imprinting of nanoscale patterns on a homogeneous surface or on the deposition of nanostructures on the surface serves advantageously for nanofabrication of functional polymer materials. Advanced nanolithography typically requires multiple-steps procedures involving clean-room facilities, high vacuum or complex mask fabrication. Alternatively, laser-based methods enable high spatial resolution patterning of soft polymeric matter and afford the sought versatility and reliability without the need of stringent ambient conditions. In particular, the technique of laser induced periodic surface structures (LIPSS) has been successfully applied to nanostructuring of polymer films using a polarized laser source at several laser wavelengths and pulse durations. In this paper the formation of LIPSS on polymer films will be described. In particular, the possibilities of tuning the period and shape of the structures will be discussed since the control of the characteristics of the superficial structures can be crucial in order to match the requirements of a particular application. Additionally, an overview about the main and potential applications of LIPSS in polymer films is provided. In particular, the use of rippled polymer films as substrates for cell culture/alignment, surface enhanced Raman scattering sensors, or applications in photovoltaics will be reviewed.
Natural rubber (NR) and functionalized graphene sheets (FGSs) nanocomposites were prepared by conventional two-roll mill mixing. The morphology and structure of the FGS was characterized confirming ...the successful exfoliation of the FGS. The strong rubber-to-filler interactions accelerate the cross-linking reaction, increase the electrical conductivity and cause an important enhancement on the mechanical behavior of the NR nanocomposites. The nanofiller does not affect the molecular dynamics of NR, while the presence of vulcanizing additives slowdowns the segmental motions and decreases slightly the time scale of the global chain dynamics in NR/FGS nanocomposites. These functional properties make NR/FGS nanocomposites a promising new class of advanced materials.
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•The estimation of temperature upon pulse accumulation shows that a small positive offset is caused by each individual pulse.•Number of pulses needed for LIPSS formation in PS thin ...films depends on polymer thickness.•Thermal conductivity and diffusivity of supporting substrate influence the onset for LIPSS formation and their quality.•Quality of LIPSS is affected by the substrate optical properties.
Here we focus on the influence of both, substrate and film thickness on polymer Laser Induced Periodic Surface Structures (LIPSS) formation in polymer films. For this aim a morphological description of ripples structures generated on spin-coated polystyrene (PS) films by a linearly polarized laser beam with a wavelength of 266nm is presented. The influence of different parameters on the quality and characteristics of the formed laser-induced periodic surface structures (LIPSS) was investigated. We found that well-ordered LIPSS are formed either on PS films thinner than 200nm or thicker than 400nm supported on silicon substrates as well as on thicker free standing films. However less-ordered ripples are formed on silicon supported films with intermediate thicknesses in the range of 200–380nm. The effect of the thermal and optical properties of the substrate on the quality of LIPSS was analyzed. Differences observed in the fluence and number of pulses needed for the onset of surface morphological modifications is explained considering two main effects which are: (1) The temperature increase on polymer surface induced by the action of cumulative laser irradiation and (2) The differences in thermal conductivity between the polymer and the substrate which strongly affect the heat dissipation generated by irradiation.
For years bismuth (Bi) has appealed to a broad community of scientists due to its peculiar electronic, optical, and more recently plasmonic and photocatalytic properties, which enable both the ...understanding of basic science phenomena and the development of a wide range of applications. In spite of this interest, a comprehensive spectral analysis of the dielectric function (ε = ε1 + jε2) of bulk Bi from the far infrared (IR) to the ultraviolet (UV) region is not available. So far, the data have been reported in limited spectral ranges and show a wide dispersion that is especially notorious for the IR region. In this work we report ε for Bi in a wide spectral range from 0.05 to 4.7 eV (24.8 to 0.3 μm, far IR to UV). ε is extracted from spectroscopic ellipsometry measurements of excellent quality (dense and smooth) Bi films by using the transfer matrix formalism and Kramers–Kronig consistent analysis. The higher quality and accuracy of the obtained ε compared with the literature data is demonstrated. The analysis and use of this reference bulk dielectric function provides crucial information for the exploration and understanding of the optical, plasmonic, and photocatalytic properties of Bi nanostructures. From its analysis, it is evidenced that the optical properties of Bi in the mid wave IR-to-UV are driven only by interband transitions, which are responsible for the dominant absorption band peaking at about 0.8 eV. Therefore, the plasmonic behavior and the photocatalytic performance of Bi nanostructures in the visible and UV are likely driven by these interband transitions that make ε1 turn negative in this region without the need of exciting free carriers. Furthermore, classical electrodynamic simulations using the obtained ε show a strong size dependence for the optical extinction of Bi nanospheres in the far IR-to-near IR with Mie-like resonances broadly tunable across this region.
This is the first broadband dielectric spectroscopy study on the temperature- and frequency-dependent electrical conductivity of polyamide 6 (PA6) composites containing both metal microparticles (Al, ...Fe, or Cu) and carbon nanotubes (CNT). The dually reinforced PA6 hybrids are prepared through compression molding of metal- and CNT-loaded microparticles (MP). These MP are synthesized by activated anionic ring-opening polymerization (AAROP) of ε-caprolactam in suspension, carried out in the presence of the micron-sized metal powders and the nanosized CNT fillers, with a combined load of up to 10 wt%. The good dispersion of the two loads by the AAROP strategy results in a notable increase in the electrical conductivity by up to 11 orders of magnitude. Moreover, the frequency-dependent behavior of the measured conductivity obeys the so-called universal dynamic response. This response involves a direct current (d.c.) electrical conductivity (
σ
dc
) observed beyond a critical frequency,
F
c
, followed by a power-law response characterized by an exponent
s
, which fluctuates between 0.11 and 0.43. The
σ
dc
of the binary composites spans from 1.42
×
10
−5
to 1.63
×
10
−2
S/cm, this increase being attributed to the synergetic effect between CNT and the metal particles that contribute to the carrier mobility within the conductive network.
Graphical Abstract
Background
The aim of this study is to report the experience with conversion surgery from six Gruppo Italiano Ricerca Cancro Gastrico (GIRCG) centers, focusing our analysis on factors affecting ...survival and the risk of recurrence.
Methods
A retrospective, multicenter cohort study was performed in patients who had undergone conversion gastrectomy between 2005 and 2017. Data were extracted from a GIRCG database including all metastatic gastric cancer patients submitted to surgery. Only stage IV unresectable tumors/metastases which became resectable after chemotherapy were included in this analysis.
Results
Forty-five resected M1 patients were included in the analysis. Reasons for being deemed unresectable at diagnosis were peritoneal involvement (PCI > 6) (
n
= 38, 84.4%), distant metastatic nodes (
n
= 3, 6.6%) and extensive liver involvement (
n
= 4, 8.8%). Median follow-up was 25 months (IQR 9-50). Median overall survival from surgery was 15 months and 1-, 3- and 5-year survivals were 57.2, 36.1 and 24%, respectively. Median progression-free survival was 12 months with 1- and 3-year survival of 46.4 and 33.9%, respectively. At cox regression analysis the only independent prognostic factor for OS was the presence of more than one type of metastasis (HR 4.41, 95% CI 1.72–11.3,
p
= 0.002). A positive microscopic resection margin was the only risk factor for recurrence (HR 5.72, 95% CI 1.04–31.4,
p
= 0.045).
Conclusions
Unresectable stage IV GC patients could benefit from radical surgery after chemotherapy and achieve long survivals. The main prognostic factor for these patients was the presence of more than one type of extra-gastric metastatic involvement.
It has been previously demonstrated that T lymphocytes may be involved in the development of hypertension and microvascular remodeling, and that circulating T effector lymphocytes may be increased in ...hypertension. In particular, Th1 and Th 17 lymphocytes may contribute to the progression of hypertension and microvascular damage while T-regulatory (Treg) lymphocytes seem to be protective in this regard. However, no data is available about patients with severe obesity, in which pronounced microvascular alterations were observed.
We have investigated 32 severely obese patients undergoing bariatric surgery, as well as 24 normotensive lean subjects and 12 hypertensive lean subjects undergoing an elective surgical intervention. A peripheral blood sample was obtained before surgery for assessment of CD4+ T lymphocyte subpopulations. Lymphocyte phenotype was evaluated by flow cytometry in order to assess T-effector and Treg lymphocytes.
A marked reduction of several Treg subpopulations was observed in obese patients compared with controls, together with an increased in CD4+ effector memory T-effector cells.
In severely obese patients, Treg lymphocytes are clearly reduced and CD4+ effector memory cells are increased. It may be hypothesized that they might contribute to the development of marked microvascular alterations previously observed in these patients.
Nanomechanical properties of alginate/chitosan (Alg/Chi) multilayer films, obtained through spray assisted layer-by-layer assembly, were studied by means of PeakForce quantitative nanomechanical ...mapping atomic force microscopy (PF-QNM AFM). Prepared at two different alginate concentrations (1.0 and 2.5 mg/mL) and a fixed chitosan concentration (1.0 mg/mL), Alg/Chi films have an exponential growth in thickness with a transition to a linear growth toward a plateau by increasing the number of deposited bilayers. Height, elastic modulus, deformation, and adhesion maps were simultaneously recorded depending on the number of deposited bilayers. The elastic modulus of Alg/Chi films was found to be related to the mechanism of growth in contrast to the adhesion and deformation. A comparison of the nanomechanical properties obtained for non-cross-linked and thermally cross-linked Alg/Chi films revealed an increase of the elastic modulus after cross-linking regardless alginate concentration. The incorporation of iron oxide nanoparticles (NPs), during the spray preparation of the films, gave rise to nanocomposite Alg/Chi films with increased elastic moduli with the number of incorporated NPs layers. Deformation maps of the films strongly suggested the presence of empty spaces associated with the method of preparation. Finally, adhesion measurements point out to a significant role of NPs on the increase of the adhesion values found for nanocomposite films.
We have investigated the crystallization of the thermoplastic polymer Poly(vinylidene Fluoride) (PVDF) during “operando” 3D printing Fused Filament Fabrication (FFF). The performance of the 3D ...printing set-up and the corresponding methodology for performing simultaneous SAXS/WAXS with synchrotron radiation have been discussed. Simultaneous SAXS and WAXS experiments were performed across the printed line with a resolution of 50 μm. The experiments indicate that crystallization is faster at the polymer-air interface than in other points within the printed line. The final crystallinity varies with position being lower at both the interfaces, i.e. polymer-air (13%) and welding zone (11%), while being higher (18%) in the middle part of the printed line. Orientation of the crystalline lamellae is higher at both interfaces, suggesting higher shear rate than in the bulk of the printed line where elongational flow is dominant. The final crystallinity levels in the different locations of the printed line are relatively low, as compared with reported values in melt pressed samples (≈30%), due to the extremely fast crystallization kinetics involved in the solidification of PVDF 3D printed lines. Therefore, it is expected that 3D printed PVDF pieces will exhibit significant structural modifications due to the potential crystallization that eventually will proceed during storage because the glass transition of PVDF is well below room temperature.
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•The crystallization of Poly(vinylidene Fluoride) (PVDF) has been characterized during “operando” 3D printing.•A methodology for performing simultaneous SAXS/WAXS with synchrotron radiation during 3D printing have been discussed.•The results provide useful information about structural heterogeneity across the printed lines.•“Operando” structural characterization can be useful to understand post printing effects of 3D printed polymer pieces.
We reported on the interaction between poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and high-boiling-point additives in PEDOT:PSS aqueous dispersions and in the final polymer ...films with the aim of stablishing correlations between the structure of both inks and solid thin films. By Small-Angle X-ray Scattering (SAXS) using synchrotron radiation, it was found that the structural changes of dispersions of PEDOT:PSS with high-boiling-point additives can be explained as a two-step mechanism depending on the additive concentration. A compaction of PEDOT:PSS grains was observed at low concentrations while a swelling of the grains together with a phase segregation between PEDOT and PSS segments was evidenced at larger concentrations. Thin films' morphology and structure were investigated by atomic force microscopy (AFM) and synchrotron Grazing Incidence Wide-Angle X-ray Scattering (GIWAXS) respectively. Our two-step model provides an explanation for the small and sharp domains of PEDOT:PSS thin films observed for low-additive concentrations (first step) and larger domains and roughness found for higher-additive concentrations (second step). A reduction of the ratio of PSS in PEDOT:PSS thin films upon the presence of additives was also observed. This can be related to a thinning of the PSS shells of PEDOT:PSS grains in the dispersion. The results discussed in this work provide the basis for a controlled tuning of PEDOT:PSS thin films structure and the subsequent electrical properties.
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