PS PI Research Articles

Vps21 Directs the PI3K-PI(3)P-Atg21-Atg16 Module to Phagophores via Vps8 for Autophagy.

Phosphatidylinositol 3-phosphate (PI(3)P) serves important functions in endocytosis, phagocytosis, and autophagy. PI(3)P is generated by Vps34 of the class III phosphatidylinositol 3-kinase (PI3K) complex. The Vps34-PI3K complex can be divided into Vps34-PI3K class II (containing Vps38, endosomal) and Vps34-PI3K class I (containing Atg14, autophagosomal). Most PI(3)Ps are associated with endosomal membranes. In yeast, the endosomal localization of Vps34 and PI(3)P is tightly regulated by Vps21-module proteins. At yeast phagophore assembly site (PAS) or mammalian omegasomes, PI(3)P binds to WD-repeat protein interacting with phosphoinositide (WIPI) proteins to further recruit two conjugation systems, Atg5-Atg12·Atg16 and Atg8-PE (LC3-II), to initiate autophagy. However, the spatiotemporal regulation of PI(3)P during autophagy remains obscure. Therefore, in this study, we determined the effect of Vps21 on localization and interactions of Vps8, Vps34, Atg21, Atg8, and Atg16 upon autophagy induction. The results showed that Vps21 was required for successive colocalizations and interactions of Vps8-Vps34 and Vps34-Atg21 on endosomes, and Atg21-Atg8/Atg16 on the PAS. In addition to disrupted localization of the PI3K complex II subunits Vps34 and Vps38 on endosomes, the localization of the PI3K complex I subunits Vps34 and Atg14, as well as Atg21, was partly disrupted from the PAS in vps21∆ cells. The impaired PI3K-PI(3)P-Atg21-Atg16 axis in vps21∆ cells might delay autophagy, which is consistent with the delay of early autophagy when Atg21 was absent. This study provides the first insight into the upstream sequential regulation of the PI3K-PI(3)P-Atg21-Atg16 module by Vps21 in autophagy.

Persistent Nutritional Deficiency in Pancreatic-Insufficient Children and Adolescents with Cystic Fibrosis Despite Therapeutic Intervention

Abstract Background Cystic fibrosis (CF) is caused by mutations in the gene encoding the CF Transmembrane Conductance Regulator (CFTR) protein, resulting in compromised pulmonary function, malabsorption, and pancreatic insufficiency. The sequelae of CF are heterogeneous, and contributing factors are multifactorial. Nutritional deficiencies, particularly in essential fatty acids (EFA) and vitamins, are known to alter the trajectory of CF unfavorably. The current treatment modalities focus on proactive management of the pulmonary, gastrointestinal, and pancreatic functions; however, information on the monitoring and treatment of nutritional deficiencies in CF patients is scant. The objective of our study was to evaluate the effects of pancreatic function and CFTR modulator therapy on pertinent nutritional deficiencies in children and adolescents diagnosed with CF. Methods The study was approved by our institutional IRB and included 77 non-fasted CF participants, 10.4 + 5.2 years of age (range: 4 months-18 years), and an equal ratio of both sexes. Participants were stratified as pancreatic sufficient (PS, n=6), and pancreatic insufficient with (PI, n=48) or without CFTR modulator treatment (PI-M, n=23). Twenty-two fatty acids were measured in plasma by GC-MS, including omega-6 linoleic acid (LA), and omega-3 α-linoleic acid (ALA). Medical records and 24-hour dietary recalls were reviewed to correlate biochemical and clinical findings. Vitamins A and E and zinc levels of the participants were also obtained. Data analyses were performed by one-way ANOVA and Tukey’s multiple comparisons using Prism software (LaJolla, CA). Results There were no significant differences in BMI and caloric intake among the groups. The concentrations of EFA, LA, and ALA were significantly higher in the PS group (3904±229 nmol/mL and 149±24 nmol/mL) compared to the PI (2387±89 nmol/mL and 53±4 nmol/mL, p<0.01) and PI-M (2335±159 nmol/mL and 58±7 nmol/mL, p<0.01) groups, respectively. Similarly, the biologically active omega-6 arachidonic acid and omega-3 docosahexaenoic acid were lower in the PI and PI-M groups compared to the PS group (p<0.05). Interestingly, EFA deficiency biomarkers, omega-9 mead acid, and the Triene:Tetraene ratio, were significantly higher in the PI group (17±2 nmol/mL and 0.033±0.003) vs PS group (13±3 nmol/mL and 0.019±0.002, p<0.05), respectively. Higher concentrations of vitamins A and E were observed in the PS group vs PI-M groups (p<0.05), and zinc concentrations were not different among the groups. There were no associations between the concentrations of EFA and BMI, age, total caloric intake, and % calories from fat in PS, PI, and PI-M patients. Conclusion While advances in CF therapeutics are remarkable, our data show the persistence of nutritional deficiencies in pancreatic insufficient CF patients regardless of CFTR modulator therapy and support the clinical utility of EFA and vitamins as potential adjuvant biomarkers to assess the severity and assist in the clinical monitoring of CF.

RELATIONSHIP BETWEEN THE DURATION OF EQUILIBRATION STEP OF THE VITRIFICATION AND CHANGES ON ABUNDANCE AND COMPOSITION OF OOCYTE MEMBRANE LIPIDS

Volumetric damages and cytotoxicity due to cryoprotectants exposure are time-sensitive in the vitrification process and can trigger the lipid remodeling of the plasma membrane. Here, we investigate the effects of exposure time to equilibration solution (ES) on membrane lipid profile of C57BL/6J mice oocytes using MRM-profiling, a sensitive exploratory method for lipidomics of oocytes and embryos1. We also assessed the effects of supplementing ES with antioxidants and unsaturated fatty acids. Experimental groups included oocytes equilibrated with Irvine Scientific (IRV), a commercial standard vitrification medium; Tvitri-4 (T4) produced in small scale for research by INVITRA®, and Tvitri-4 supplemented with L-carnitine (LC) and oleic and linoleic fatty acids (FA) (T4-LC/FA; Patent n. BR102019013697-9). Experimental study. Oocytes were randomly divided in 7 groups: non-exposed (NE) and exposed to either 10-minute equilibration step (ES10) according to the manufacturer’s procedure or 7-minute equilibration step (ES7), using IRV, T4, or T4-LC/FA media. After equilibration, oocytes were washed in methanol: H2O and lipids extracted with methanol. Diluted lipid extracts were flow injected into the triple quadrupole spectrometer with electrospray ionization (ESI). Relative ion intensities were used for univariate (ANOVA, fold-change, t-test, volcano plot) and multivariate analysis (PCA, PLS-DA, cluster analysis). Most informative lipids were sorted out using statistical significance of p<0.05 or partial least square discriminant analysis (PLS-DA) variables of importance (VIP) scores>1. One-way ANOVA showed PC (38:8) differently represented among NE, ES7 and ES10 groups, upregulated in T4-LC/FA oocytes. In ES7 groups, two by two comparisons between IRV, T4 and T4-LC/FA using volcano plot (p-value≤0.05; fold-change≥2.0) detected 4, 5, and 4 significant lipids between IRV vs. T4, IRV vs. T4-LC/FA, and T4 vs. T4-LC/FA, respectively, with the PEo(36:1) overrepresented in IRV (fold-change=12.5). In ES10 groups, were detected 11, 19 and 4 lipids differentially represented among IRV vs. T4, IRV vs. T4-LC/FA, and T4 vs. T4-LC/FA, respectively. PLS-DAVIP scores identified in IRV oocytes 8 free- fatty acids, phosphatidyletanolamine PEo(36:1), phosphatidylcholines PCo(32:0) and PC(36:3), phosphatidylserines PS(14:1), PS(16:0), PS(30:2), PSo(40:5), and phosphatidylinositols PI(22:4) and PI(40:8) among the top features, whereas unsaturated PC and SM predominated in T4 and T4-LC/FA oocytes. Significant lipids observed between T4 and T4-LC/FA pointed oleic (18:1) and linoleic (18:2) acids upregulated in T4-LC/FA oocytes exposed for 10 min to ES. The duration of the equilibration phase changed the abundance and composition of membrane lipids. Phospholipids were upregulated at 10-minute exposure to ES, except in IRV oocytes. The oleic and linoleic acids used as supplements in T4-LC/FA medium were promptly detected in the oocytes and seem contribute to better preserving membrane phospholipids during cell equilibration.

In Vitro Digestion of Grape Seed Oil Inhibits Phospholipid-Regulating Effects of Oxidized Lipids.

The intake of dietary lipids is known to affect the composition of phospholipids in gastrointestinal cells, thereby influencing passive lipid absorption. However, dietary lipids rich in polyunsaturated fatty acids, such as vegetable oils, are prone to oxidation. Studies investigating the phospholipid-regulating effect of oxidized lipids are lacking. We aimed at identifying the effects of oxidized lipids from moderately (18.8 ± 0.39 meq O2/kg oil) and highly (28.2 ± 0.39 meq O2/kg oil) oxidized and in vitro digested cold-pressed grape seed oils on phospholipids in human gastric tumor cells (HGT-1). The oils were analyzed for their antioxidant constituents as well as their oxidized triacylglycerol profile by LC-MS/MS before and after a simulated digestion. The HGT-1 cells were treated with polar oil fractions containing epoxidized and hydroperoxidized triacylglycerols for up to six hours. Oxidized triacylglycerols from grape seed oil were shown to decrease during the in vitro digestion up to 40% in moderately and highly oxidized oil. The incubation of HGT-1 cells with oxidized lipids from non-digested oils induced the formation of cellular phospholipids consisting of unsaturated fatty acids, such as phosphocholines PC (18:1/22:6), PC (18:2/0:0), phosphoserine PS (42:8) and phosphoinositol PI (20:4/0:0), by about 40%–60%, whereas the incubation with the in vitro digested oils did not affect the phospholipid metabolism. Hence, the gastric conditions inhibited the phospholipid-regulating effect of oxidized triacylglycerols (oxTAGs), with potential implications in lipid absorption.

Morphology Transitions of Linear A1B1A2B2 Tetrablock Copolymers at Symmetric Overall Volume Fraction

We investigated morphology transitions of linear tetrablock copolymers of polystyrene-block-polyisoprene-block-polystyrene-block-polyisoprene (S1I1S2I2) by varying volume fraction of PI1 block (fPI1), while maintaining the symmetric volume fraction of total PS blocks and PI blocks (fPS1+fPS2:fPI1+fPI2 ≈ 1:1). An interesting sequence of morphology transitions was observed as fPI1 was increased: lamellae (L) → asymmetric lamellae (aL) → hexagonally packed PI-cylinders (CPI) → double gyroid with PI-network domains (GPI) → short-period lamellae (sL). The domain spacing of sL was nearly half that of L, while aL had asymmetric lamellar width of PS and PI microdomains. It is particularly interesting that cylindrical and gyroid morphologies were observed in linear block copolymers with symmetric overall volume fraction at intermediate segregation. The experimentally observed morphologies are in good agreement with the predicted equilibrium phases by self-consistent field theory (SCFT).

MiR-21 is associated with fibrosis and right ventricular failure.

Combined pulmonary insufficiency (PI) and stenosis (PS) is a common long-term sequela after repair of many forms of congenital heart disease, causing progressive right ventricular (RV) dilation and failure. Little is known of the mechanisms underlying this combination of preload and afterload stressors. We developed a murine model of PI and PS (PI+PS) to identify clinically relevant pathways and biomarkers of disease progression. Diastolic dysfunction was induced (restrictive RV filling, elevated RV end-diastolic pressures) at 1 month after generation of PI+PS and progressed to systolic dysfunction (decreased RV shortening) by 3 months. RV fibrosis progressed from 1 month (4.4% ± 0.4%) to 3 months (9.2% ± 1%), along with TGF-β signaling and tissue expression of profibrotic miR-21. Although plasma miR-21 was upregulated with diastolic dysfunction, it was downregulated with the onset of systolic dysfunction), correlating with RV fibrosis. Plasma miR-21 in children with PI+PS followed a similar pattern. A model of combined RV volume and pressure overload recapitulates the evolution of RV failure unique to patients with prior RV outflow tract surgery. This progression was characterized by enhanced TGF-β and miR-21 signaling. miR-21 may serve as a plasma biomarker of RV failure, with decreased expression heralding the need for valve replacement.

Large-Area Block Copolymer Photonic Gel Films with Solvent-Evaporation-Induced Red- and Blue-Shift Reflective Bands

By choice of large overall molecular weights from 0.5 to 1 M kg/mol, the lamellar microstructures of the high-molecular-weight polystyrene-block-polyisoprene (PS–PI) block copolymers (BCPs) exhibited various long periods and associated different reflected wavelengths. Interestingly, unique solvatochromism-dependent red- and blue-shift reflective bands could be acquired in the PS–PI BCP gel films using a nonselective neutral solvent as an external stimulus. At low polymer concentration, red-shift of the reflectivity was attributed to the increase of BCP long period by the enhancement of the BCP segregation strength, namely, a thermodynamically controlled swelling process. In contrast, at high polymer concentration (ϕp > 0.8), the blue-shifting reflectivity resulted from the decrease of the BCP long period by the collapse of polymer chains, namely, a kinetically controlled deswelling process. Also, well-aligned lamellar microstructures were fabricated using a shear-induced microstructural orientation. This ...

Tunable nanoporous membranes with chemically-tailored pore walls from triblock polymer templates

Membranes derived from self-assembled block polymers have shown promise as highly selective and highly permeable filters, but the complex synthetic routes and limited pore functionalities of existing systems need to be improved if these materials are to serve as a platform for the next generation of nanostructured membranes. Here, the facile synthesis of a polyisoprene-b-polystyrene-b-poly(N,N-dimethylacrylamide) (PI–PS–PDMA) triblock polymer using a controlled reversible addition-fragmentation chain transfer (RAFT) polymerization mechanism is reported. This material is then processed into a membrane using a self-assembly and non-solvent induced phase separation (SNIPS) technique, which creates an asymmetric, porous structure consisting of a selective layer that contains a high density of PDMA-lined pores (9.4×1013poresm−2) with an average diameter of 8.1nm, as determined using solute rejection tests. Solvent flow experiments demonstrate that the PI–PS–PDMA membrane has a pH-independent permeability of 6Lm−2h−1bar−1. The PDMA moiety lining the pore walls is converted, through simple hydrolysis in the solid state, to yield a poly(acrylic acid)-lined (PAA-lined) structure. The permeability of the PI–PS–PAA membrane is pH-dependent, and ranges from 0.6Lm−2h−1bar−1 for solutions with a pH greater than 4 to 16Lm−2h−1bar−1 for a solution at pH 1. Solute rejection tests demonstrated a pore size of 3.4nm for the PI–PS–PAA membrane, which is the smallest pore size reported to date for membranes fabricated from self-assembled block polymers. The facile synthesis of the PI–PS–PDMA material, the scalable SNIPS membrane fabrication protocol, and the simple conversion chemistry of the pore functionality demonstrate that these nanostructured membranes are a strong platform for applications within the range of water purification, pharmaceutical separations, sensors, and drug delivery.

Polystyrene‐block‐Polyisoprene Diblock‐Copolymer Micelles: Coupled Pressure and Temperature Effects

The structural changes of diblock‐copolymer micelles under pressures from 200 to 16 000 psi are investigated using small‐angle neutron scattering (SANS). Asymmetric polystyrene‐block‐polyisoprene (PS–PI) diblock copolymers are dissolved in decane, a selective solvent for PI, to form spherical micelles with a core of PS and a corona of PI. The micellar solutions are put under pressure at temperatures of 25 to 60 °C. At room temperature, elevating the pressure from 200 to 16 000 psi has no effect on the size of the micelles. While the micellar solutions remain stable, instantaneous association of micelles is detected. In contrast to micelles at atmospheric pressure, increasing the temperature at elevated pressures does not lead to dissociation of micelles; instead, the micelles aggregate and evolve into sheet‐like structures, reminiscent of a macroscopic phase separation. Furthermore, higher pressures lead to a smaller temperature range in which shape transitions take place. image

Toward Strong Thermoplastic Elastomers with Asymmetric Miktoarm Block Copolymer Architectures

Thermoplastic elastomers (TPEs) are designed by embedding discrete glassy or semicrystalline domains in an elastomeric matrix. Typical styrenic-based amorphous TPEs are made of linear ABA-type triblock copolymers, where the volume fraction f of the glassy domains A is typically less than 0.3. This limitation ultimately restricts the range of mechanical strength attainable with these materials. We had previously predicted using self-consistent field theory (SCFT) that A(BA′)n miktoarm block copolymers with an approximately 8:1 ratio of the A to A′ block molecular weights and n ≥ 3 should exhibit discrete A domains at considerably larger f and offer potential for the combination of high modulus, high recoverable elasticity, and high strength and toughness. Using transmission electron microscopy and small-angle X-ray scattering on model polystyrene-b-polyisoprene (PS–PI) miktoarm copolymers, we show that such polymers indeed possess discrete PS domains for f values considerably higher than 0.3. The hexagonal morphology with PS cylinders was achieved for f = 0.5 and n = 3. Mechanical testing indicates that these miktoarm materials are strong, tough, and elastic and thus may be potential candidates for a new generation of thermoplastic elastomers.

Membrane binding properties of IRSp53-missing in metastasis domain (IMD) protein

The 53-kDa insulin receptor substrate protein (IRSp53) organizes the actin cytoskeleton in response to stimulation of small GTPases, promoting the formation of cell protrusions such as filopodia and lamellipodia. IMD is the N-terminal 250 amino acid domain (IRSp53/MIM Homology Domain) of IRSp53 (also called I-BAR), which can bind to negatively charged lipid molecules. Overexpression of IMD induces filopodia formation in cells and purified IMD assembles finger-like protrusions in reconstituted lipid membranes. IMD was shown by several groups to bundle actin filaments, but other groups showed that it also binds to membranes. IMD binds to negatively charged lipid molecules with preference to clusters of PI(4,5)P2. Here, we performed a range of different in vitro fluorescence experiments to determine the binding properties of the IMD to phospholipids. We used different constructs of large unilamellar vesicles (LUVETs), containing neutral or negatively charged phospholipids. We found that IMD has a stronger binding interaction with negatively charged PI(4,5)P2 or PS lipids than PS/PC or neutral PC lipids. The equilibrium dissociation constant for the IMD–lipid interaction falls into the 78–170μM range for all the lipids tested. The solvent accessibility of the fluorescence labels on the IMD during its binding to lipids is also reduced as the lipids become more negatively charged. Actin affects the IMD–lipid interaction, depending on its polymerization state. Monomeric actin partially disrupts the binding, while filamentous actin can further stabilize the IMD–lipid interaction.

ABAC Tetrablock Terpolymers for Tough Nanoporous Filtration Membranes

Nanoporous poly(styrene)-b-poly(isoprene)-b-poly(styrene) (PS–PI–PS) was prepared from PS–PI–PS–PLA (PLA = poly(d,l-lactide)) tetrablock terpolymer precursors. Hydroxy end-functionalized PS–PI–PS was synthesized by sequential anionic polymerizations and used to initiate the ring-opening polymerization of d,l-lactide. A combination of small-angle X-ray scattering, transmission electron microscopy and scanning electron microscopy data supports a core–shell cylinder morphology with PLA as the core component. The inherently robust mechanical properties associated with PS–PI–PS block copolymers provide the materials with enhanced flexibility and toughness compared to analogous nanoporous polystyrene samples prepared by etching of PS–PLA diblocks. Composite membranes containing nanoporous PS–PI–PS on top of microporous poly(ether sulfone) (PES) were prepared by direct spin-coating and also by a salt-plate coating/film-transfer strategy. Nanopores (dpore ≈ 15 nm) were created by a combination of reactive ion etc...

PTEN binding properties for different model membrane morphologies

PTEN acts as an agonist to PI 3‐kinase signaling by removing the phosphate group in the 3 position of PI(3,4,5)P3. PTEN membrane association and activation requires the interaction with PI(4,5)P2 and PS. In biological membranes, these lipids may form upon interaction with other molecular entities domains that exhibit distinct compositional and physicochemical characteristics. It is the objective of this study to elucidate the relationship between lipid bilayer morphologies and the extent of PTEN binding and PTEN membrane association dynamics.MethodsTo characterize lipid morphologies in the absence and presence of PTEN, we used fluorescence microscopy measurements of mixed lipid giant unilamellar vesicles (GUVs). PTEN binding extent is evaluated using SPR and Trp fluorescence measurements. The binding kinetics of PTEN bilayer interaction is elucidated using stopped‐flow experiments.ResultsThe interaction of PTEN with mixed PC/PI(4,5)P2 model membranes results in the formation of PI(4,5)P2 enriched domains. Domain formation in the absence of PTEN is also observed when cholesterol is added when making mixed PC/PI(4,5)P2 vesicles. We find an increased PTEN binding in the presence of PI(4,5)P2 domains, which is probably due to increased local PI(4,5)P2 concentration. This work was supported by NIH R01 NS021716 and NSF CHEM 0922848 and 1058719.

Dielectric Behavior of Guestcis-Polyisoprene Confined in Spherical Microdomain of Triblock Copolymer.

Dielectric behavior was examined for ternary blends of guestcis-polyisoprene (PI) chains, coguest PS chains, and host PS–PI–PS triblock copolymers. The guest PI chains had the molecular weight Mg-PI well below Mb-PI of the PI blocks and were mixed in the spherical PI domains formed in the copolymers. PI has the type-A dipoles parallel along the chain backbone and its end-to-end vector fluctuation activates dielectric relaxation. The dielectric test was conducted at temperatures well below the glass transition temperature of the PS blocks, so that the PI blocks had their ends fixed on the glassy PS matrix and exhibited no end-to-end vector fluctuation. Thus, the slow dielectric response of the systems exclusively detected the global motion of the guest PI chains confined in the spherical PI domain. The dielectric mode distribution of the guest PI chains thus observed was broader than that of the same chains in bulk systems, reflecting the osmotic and spatial constraints on the chain dynamics in the spherical domains. The guest PI chains of different Mg-PI exhibited nearly the same extent of mode broadening, despite their average coil size approached the domain size with increasing Mg-PI. This result suggested that the osmotic constraint was the primary factor affecting (broadening and retarding) the guest chain dynamics. The osmotic constraint appeared to be stronger in the spherical domain than in the lamellar domain, the latter being examined in literature.

InSitu Imaging and Height Reconstruction of Phase Separation Processes in Polymer Blends during Spin Coating

Spin coating polymer blend thin films provides a method to produce multiphase functional layers of high uniformity covering large surface areas. Applications for such layers include photovoltaics and light-emitting diodes where performance relies upon the nanoscale phase separation morphology of the spun film. Furthermore, at micrometer scales, phase separation provides a route to produce self-organized structures for templating applications. Understanding the factors that determine the final phase-separated morphology in these systems is consequently an important goal. However, it has to date proved problematic to fully test theoretical models for phase separation during spin coating, due to the high spin speeds, which has limited the spatial resolution of experimental data obtained during the coating process. Without this fundamental understanding, production of optimized micro- and nanoscale structures is hampered. Here, we have employed synchronized stroboscopic illumination together with the high light gathering sensitivity of an electron-multiplying charge-coupled device camera to optically observe structure evolution in such blends during spin coating. Furthermore the use of monochromatic illumination has allowed interference reconstruction of three-dimensional topographies of the spin-coated film as it dries and phase separates with nanometer precision. We have used this new method to directly observe the phase separation process during spinning for a polymer blend (PS-PI) for the first time, providing new insights into the spin-coating process and opening up a route to understand and control phase separation structures.

Structure and kinetic characterization of human sperm-specific glyceraldehyde-3-phosphate dehydrogenase, GAPDS

hGAPDS (human sperm-specific glyceraldehyde-3-phosphate dehydrogenase) is a glycolytic enzyme essential for the survival of spermatozoa, and constitutes a potential target for non-hormonal contraception. However, enzyme characterization of GAPDS has been hampered by the difficulty in producing soluble recombinant protein. In the present study, we have overexpressed in Escherichia coli a highly soluble form of hGAPDS truncated at the N-terminus (hGAPDSΔN), and crystallized the homotetrameric enzyme in two ligand complexes. The hGAPDSΔN-NAD+-phosphate structure maps the two anion-recognition sites within the catalytic pocket that correspond to the conserved Ps site and the newly recognized Pi site identified in other organisms. The hGAPDSΔN-NAD+-glycerol structure shows serendipitous binding of glycerol at the Ps and new Pi sites, demonstrating the propensity of these anion-recognition sites to bind non-physiologically relevant ligands. A comparison of kinetic profiles between hGAPDSΔN and its somatic equivalent reveals a 3-fold increase in catalytic efficiency for hGAPDSΔN. This may be attributable to subtle amino acid substitutions peripheral to the active centre that influence the charge properties and protonation states of catalytic residues. Our data therefore elucidate structural and kinetic features of hGAPDS that might provide insightful information towards inhibitor development.

Mesoscopic study of cylindrical phases of poly(styrene)-poly(isoprene) copolymer: Order–order phase transitions by temperature control

Abstract Phase transitions of cylindrical structures of poly(styrene)–poly(isoprene) copolymer (PS–PI) toward spherical and gyroid structures were explored using DPD simulations and a coarse-grained model. Cylindrical phases were first obtained within a composition interval (“predominance region”) 0.2 f PS

Effect of the Soluble Block Size on Spherical Diblock Copolymer Micelles

While the effect of the insoluble block length on micelle properties is well understood, the effect of the soluble block is still controversial. We, therefore, have investigated the effect of the molecular weight of the soluble block on the critical micelle concentration (CMC), aggregation number, and hydrodynamic radius of spherical polymer micelles. Spherical micelles were formed from polystyrene-b-polyisoprene (PS-b-PI) in heptane, which was a good solvent for PI and a poor solvent for PS. Measurements were performed on two series of PS-b-PI with a constant PS block (19 and 39 kDa, respectively) and PI blocks varying from 10 to 100 kDa. For samples with large PI blocks, the experimental data were found to be in agreement with the commonly used star-like model. However, the experimental data for samples with short PI blocks deviated from the crew-cut micelle model. To correctly capture the crossover between the crew-cut and star-like regimes, it was found necessary to use recently developed scaling theo...

Mesoscopic simulation of metastable microphases in the order–order transition from gyroid-to-lamellar states of PS–PI diblock copolymer

The formation of metastable microphases during the order–order transition (OOT) from gyroid-to-lamellar states of a poly(styrene)–poly(isoprene) (PS–PI) copolymer has been investigated on a mesoscopic level using dissipative particle dynamics simulations. The formation of the gyroid microphase was obtained via an order–disorder transition process (ODT). The microphase was then subjected to thermal heating cycles. A thermodynamic instability of poly(styrene) microdomains due to temperature effects induces anisotropic composition fluctuations in the gyroid structure and a microphase transformation from gyroid-to-lamellar takes place via an OOT. Two metastable microphases (hexagonal perforated layers and cylinders) were detected during the thermal process. Results are consistent with experimental and theoretical studies.

Mesoscopic simulation of asymmetric-copolymer/homopolymer blends: Microphase morphological modification by homopolymer chains solubilization

In this work we present the results of a mesoscopic dynamic simulation study of ordered microphases modification in asymmetric-copolymer/homopolymer binary blends, where we explore the influence of the composition, packing density and solubilization of homopolymer chains into the compatible microdomains of the asymmetric copolymer. The poly(styrene)–poly(isoprene) (PS–PI) and homopoly(styrene) (HPS) molecules were built and represented by Gaussian chain models. The pure asymmetric copolymer generates spherical microdomains of poly(styrene) (PS) in the matrix of majority component, poly(isoprene) (PI), and is taken as the base for the binary blends. The mesoscopic dynamic evolution of asymmetric-PS–PI/HPS blends display a coarse-grained system sufficiently large to determine the separation of the microphase and the formation of ordered structures. The HPS chains tend to be selectively solubilized in the PS microdomains of the asymmetric copolymer, the repulsive interaction forces between homopoly(styrene) and poly(isoprene) chains assure that essentially all the HPS homopolymer exists in the PS microdomains. As the asymmetric-PS–PI/HPS composition is varied the mesoscale simulations predict ordered structures with defined morphologies of body-centred-cubic (BCC), hexagonal packed cylinders (HPC), hexagonal perforated layers (HPL) and lamellar phases (LAM). Ordered microphases appear in reverse order when the homopoly(styrene) composition is increased in the binary blend. The agreement between our mesoscopic simulation results and available experimental outcome open a new strategy to modify the microphase morphology of asymmetric copolymers.