Oxide Block Copolymers Research Articles

In-vitro evaluation of cytotoxic and antioxidant properties of drugs solubilized in EO-PO star block copolymer micelles.

Self-assembly of a biocompatible, nontoxic, commercially available star shaped polyethylene oxide-polypropylene oxide block copolymer, Tetronics®1107 (mol. wt. = 15000, % ethylene oxide = 70, and HLB 18-23) in aqueous solution was examined using surface tension, fluorescence, viscosity, cloud point and dynamic light scattering. The copolymer being very hydrophilic shows poor surface activity and forms thermo-, pH and salt responsive nanosize core-shell micelles above critical micellization temperatures. These micelles showed markedly enhanced solubilization of hydrophobic drugs curcumin and quercetin. In vitro antioxidant activities (by free radical scavenging, reducing capacity and superoxide anion radical scavenging methods) and cytotoxicity (against CHO-K1 cell line) showed desirable properties in micellar drugs as compared to free one and similar cytotoxic effects were observed for free as well as micellar drugs. This suggests T1107 as promising tool for drug delivery.

Enhancement of Resistance to Protein Fouling of Poly(ether imide) Membrane by Surface Grafting with PEG under Organic Solvent-free Condition

Poly(ether imide) (PEI) membrane with enhanced antifouling property was successfully prepared in a mild and simple procedure. The virgin membrane was firstly functionalized with an aqueous solution of diamino-terminated poly(ethylene oxide) block copolymer (PEG-diamine). Glutaraldehyde was used in a second step as a linker to chemically attach additional PEG-diamine to the primary amine groups grafted on PEI membrane surface. Immobilization of PEG segments was confirmed using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and atomic force microscopy. Ultrafiltration experiments revealed that the enhancement of a PEG coverage on the membrane surface provided superior anti-protein-fouling property. Cycles of protein filtration also demonstrated that the antifouling surface was stable over time and excellent ultrafiltration performance could be maintained without the need of harsh cleansing operation.

Fabrication of reusable temperature-controlled-released fertilizer using a palygorskite-based magnetic nanocomposite

Abstract In this work, a temperature-controlled-release and collectable iron fertilizer (TCIF) with a core-shell structure was developed using a nanocomposite consisting of palygorskite (Pal), ferroferric oxide (Fe3O4), ferrous ammonium sulfate hexahydrate (FASH), ethylene oxide/propylene oxide block copolymer (F-127), and amino silicon oil (ASO). Therein, the core was made up of Pal-Fe3O4-FASH mixture, and the shell was composed of ASO-F-127. Pal with a porous micro/nano networks structure could bind a great many of Fe2+ through electrostatic attraction. FASH, as the iron fertilizer and a foaming agent in this system, can produce NH3 at 100 °C to make a plenty of micro/nano pores in the ASO-F-127 shell, which facilitated the release of Fe2+. F-127, a thermally sensitive polymer, can open and close the pores through the liquid-gel transition under different temperature to adjust the release of Fe2+. The hydrophobic ASO endowed TCIF a high stability in aqueous solution for at least 100 days. Fe3O4 made TCIF own a relatively high magnetism so that TCIF could be conveniently collected from water and soil. Significantly, this technology could improve the utilization efficiency of iron fertilizer and promote the absorption of Fe2+ by maize. Besides, TCIF displayed a good reuse performance, which could favor to lower the cost and decrease the residual.

Electrochemically Switchable Ring-Opening Polymerization of Lactide and Cyclohexene Oxide.

An electrochemical method was developed for the redox switchable polymerization of lactide and cyclohexene oxide. Using a lithium reversible sacrificial electrode and a high surface area carbon working electrode, efficient transformation between formally iron(II) and iron(III) oxidation states of a bis(imino)pyridine iron alkoxide complex was possible, which led to the ability to activate the complex for ring opening polymerization reactions. In addition to serving as a redox trigger, an electrochemical toggle switch was developed in which the chemoselectivity for lactide and epoxide polymerization was altered in situ. These findings led to the synthesis of poly(lactic acid- b-cyclohexene oxide) block copolymers in which the sequence of monomers incorporated is controlled by the electrical potential applied.

Ordered Mesoporous Titania/Carbon Hybrid Monoliths for Lithium-ion Battery Anodes with High Areal and Volumetric Capacity.

Free-standing, binder-free, and conductive additive-free mesoporous titanium dioxide/carbon hybrid electrodes were prepared from co-assembly of a poly(isoprene)-block-poly(styrene)-block-poly(ethylene oxide) block copolymer and a titanium alkoxide. By tailoring an optimized morphology, we prepared macroscopic mechanically stable 300 μm thick monoliths that were directly employed as lithium-ion battery electrodes. High areal mass loading of up to 26.4 mg cm-2 and a high bulk density of 0.88 g cm-3 were obtained. This resulted in a highly increased volumetric capacity of 155 mAh cm-3 , compared to cast thin film electrodes. Further, the areal capacity of 4.5 mAh cm-2 represented a 9-fold increase compared to conventionally cast electrodes. These attractive performance metrics are related to the superior electrolyte transport and shortened diffusion lengths provided by the interconnected mesoporous nature of the monolith material, assuring superior rate handling, even at high cycling rates.

Deformation and Strength Characteristics of Fatty Aromatic Block Copolymers Based on Polycarbonate

Polycarbonate—poly(tetramethylene oxide) block copolymers were synthesized using acceptor—catalytic polycondensation. The phase composition and deformation and strength characteristics of the block copolymers were studied using various methods. It was shown that rigid and elastic blocks were partially aligned in block copolymers containing up to 30 mass% of poly(tetramethylene oxide) blocks. Phase separation of microscopic blocks occurred at higher contents. The deformation and strength properties of the block copolymers were studied. Properties of thermoplastics or thermoplastic elastomers appeared depending on the polymer composition.

Study of microvia filling process based on multi-physical coupling

ABSTRACTThe microvia filling process used in the high-density interconnect printed circuit board manufacturing industry was investigated by multi-physical coupling technology. To achieve a perfect filling, SPS (bis-(sodium-sulphopropyl)-disulphide), EO/PO (ethylene oxide and propylene oxide block co-polymers) and PEOPI (polyethylene oxide-polyimide) were used. Furthermore, electrochemical behaviours of electrodeposition were investigated by cyclic voltammetry, galvanostatic potential transient measurement and dynamic potential polarisation technology. Through numerical simulation, the relationship between coverage of additive, concentration of additive, rotating speed of rotating disc electrode, exchange current density and curve slope was fitted. Based on multi-physical coupling to copper electrodeposition, a mathematical model of microvia filling was built to simulate the filling process by a finite element method, and a systematic analysis of the whole filling process was carried out. The void-free microvia filling and filling process with different shapes were finally achieved in acid copper electroplating solutions consisting of 0.3 M CuSO4·5H2O, 0.2 M H2SO4 and 80 mg L−1 Cl− (virgin make-up solution) plus additives SPS, EO/PO and PEOPI. Subsequently, from images of the microvia filling experiment at different times, shape evolution of the microvia filling and variation of electrodeposition rate at the bottom of the microvia and surface were analysed. The modelling result was compared with the measured data and showed good agreement with the experiment. The results showed that a process model was an excellent tool for quickly and cheaply studying the process behaviour greatly reduced need to execute time-consuming and costly experiments.

Effect of growing glycosylation extents on the self-assembly and active targeting in vitro of branched poly(ethylene oxide)-poly(propylene oxide) block copolymers

In this work, we investigated for the first time the effect of the gradual increase of the glycosylation extent on self-assembly of a highly hydrophilic four-arm poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) block copolymer, Tetronic® 1107. After the initial characterization that confirmed the chemical modification, the effect of the glycosylation extent on the critical micellar concentration (CMC) was characterized by dynamic light scattering. Conjugation of a d-gluconic acid (the oxidized form of d-glucose) in each terminal block resulted in a dramatic decrease of the CMC by 8- to 11-fold. In contrast, further glycosylation with lactobionic acid (an oxidized form of lactose) and gluconic acid+lactobionic acid had a detrimental effect due to the increase of the amphiphile hydrophilicity. Then, glycosylated PMs successfully encapsulated the tyrosine kinase inhibitor imatinib, increasing its aqueous solubility by up to 100 times. Glycosylated polymeric micelles showed very good cell compatibility in the Rh30 cell line. These cells are a model of rhabdomyosarcoma, a tumor that overexpresses glucose transporter-1 that is targeted by the sugar residues. Finally, we compared the cytotoxicity of free and nanoencpasulated imatinib to inhibit the proliferation a in which tyrosine kinase signaling promotes growth and glucose transporter-1 (GLUT-1; for which glucose is the main substrate) is overexpressed. Nano-encapsulation reduced the inhibitory concentration 50 (IC50) from 27.80±3.70μM for the free drug to 0.33±0.01μM for the PMs modified with gluconic acid, representing an 84-fold increase in the anti-cancer efficacy in vitro. Overall results highlight the potential of tuned glycosylation to increased the micellization trend of these amphiphiles and, at the same time, increase accumulation in cells that overexpress sugar receptors.

Myoblast Protection by Polyethylene Oxide-Polypropylene Oxide Block Copolymers against Hypo-Osmotic Stress

Amphiphilic poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers, known as poloxamers, have shown the ability to rescue cells from various types of membrane injury. However, the mechanism of cell protection by block copolymers is still unclear. To explore the role of block copolymer architecture on membrane protection, we synthesized diblock copolymers with control over the composition, molecular weight, and endgroup hydrophilicity/hydrophobicity. Membrane protection efficacy was studied in cultured murine myoblasts by the lactate dehydrogenase (LDH) release assay, in which cells are exposed to the stresses of hypo-osmotic shock and isotonic recovery, and membrane integrity is quantitatively evaluated with or without the presence of block copolymers. The cell protection required sufficient hydrophobicity of the block copolymers, controlled by either the hydrophobic PPO block or endgroup modification. At least 9 PPO units were needed for protection at 150 μM. Addition of hydrophobic tert-butyl endgroup enhanced the protection ability at reduced concentration. With fixed hydrophobicity, increasing hydrophilic PEO block length improved protection. In addition to the cellular integrity assay, we synthesized fluorophore-labeled block copolymers and performed confocal microscopy to image subcellular localization to further understand the membrane protection mechanism.

A Comparative Study on Micellar and Solubilizing Behavior of Three EO-PO Based Star Block Copolymers Varying in Hydrophobicity and Their Application for the In Vitro Release of Anticancer Drugs.

The temperature and pH dependent self-assembly of three star shaped ethylene oxide-propylene oxide (EO-PO) block copolymers (Tetronics® 304, 904 and 908) with widely different hydrophobicity was examined in aqueous solutions. Physico-chemical methods viz. viscosity, cloud point, solubilization along with thermal, scattering and spectral techniques shows strongly temperature and salt dependent solution behavior. T304 possessing low molecular weight did not form micelles; moderately hydrophilic T904 remained as micelles at ambient temperature and showed micellar growth while very hydrophilic T908 formed micelles at elevated temperatures. The surface activity/micellization/solubilization power was favored in the presence of salt. The copolymers turn more hydrophilic in acidic pH due to protonation of central ethylene diamine moiety that hinders micelle formation. The solubilization of a model insoluble azo dye 1-(o-Tolylazo)-2-naphthol (Orange OT) and hydrophobic drugs (quercetin and curcumin) for copolymer solutions in aqueous and salt solutions are also reported. Among the three copolymers, T904 showed maximum solubility of dye and drugs, hence the in vitro release of drugs from T904 micelles was estimated and the effect on cytotoxicity of loading the drugs in T904 micelles was compared with the cytotoxicity of free drugs on the CHO-K1 cells. The results from the present work provide a better insight in selection of Tetronics® for their application in different therapeutic applications.

Preparation of fluoroalkyl end-capped vinyltrimethoxysilane oligomeric silica/boric acid/poly(N-methyl benzamide)-b-poly(propylene oxide) block copolymer nanocomposites – no weight loss behavior of the block copolymer in the nanocomposites even after calcination at 800 °C

Fluoroalkyl end-capped vinyltirimethoxysilane oligomeric silica/boric acid nanocomposites [RF-(VM-SiO2) n -RF/B(OH)3] were prepared by the composite reaction of the corresponding fluorinated oligomer [RF-(CH2CHSi(OMe)3) n -RF, n = 2, 3; RF = CF(CF3)OC3F7: RF-(VM) n -RF] with boric acid. The nanocomposites thus obtained were tried to interact with the thermoplastic elastomers such as poly(N-methyl benzamide)-b-poly(propylene oxide) block copolymers [(MAB) m-m -b-PPO32: m = 5, 6, 7, and 8] and poly(ethersulfone)-b-poly(tetrahydrofuran)-b-poly(ethersulfone) triblock copolymer [PES-b-PTHF-b-PES] under alkaline conditions to afford the corresponding RF-(VM-SiO2) n -RF/B(OH)3/thermoplastic elastomers nanocomposites. We also tried to prepare the corresponding RF-(VM-SiO2) n -RF/thermoplastic elastomers nanocomposites under similar conditions, for comparison. In these thermoplastic elastomers, PES-b-PTHF-b-PES triblock copolymers cannot interact with the RF-(VM-SiO2) n -RF/B(OH)3 nanocomposites or the RF-(VM-SiO2) n -RF oligomeric nanoparticles to supply the expected nanocomposite products. However, it was demonstrated that the (MAB) m-m -b-PPO32 block copolymers can react with the RF-(VM-SiO2) n -RF/B(OH)3 nanocomposites under alkaline conditions to afford the RF-(VM-SiO2) n -RF/B(OH)3/(MAB) m-m -b-PPO32 nanocomposites, providing no weight loss characteristic corresponding to the contents of the block copolymers in the composites even after calcination at 800 °C, although these expected nanocomposites were isolated without purification process. The RF-(VM-SiO2) n -RF/(MAB) 5-5 -b-PPO32 nanocomposites, which were isolated under similar process, were also able to supply no weight loss in proportion to the content of the copolymer in the nanocomposites even after calcination at 800 °C.

Mesoporous Cu2O–CeO2 composite nanospheres with enhanced catalytic activity for 4-nitrophenol reduction

In this paper, mesoporous Cu2O–CeO2 nanospheres were fabricated via a facile, low-temperature solution route in the presence of poly(2-vinylpyridine)-b-poly(ethylene Oxide) (P2VP-b-PEO) block copolymers. The prepared mesoporous Cu2O–CeO2 nanospheres were characterized systematically by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption/desorption. The formation mechanism of mesoporous Cu2O–CeO2 nanospheres was discussed. The results show that the molar ratios of Ce3+/Cu2+ and the reaction time have an important influence on the nanostructure of Cu2O–CeO2 composite spheres. The resultant Cu2O–CeO2 nanospheres exhibit superior catalytic activities in the reduction of 4-nitrophenol to 4-aminophenol by NaBH4. The activity factor (K = k/m) for the Cu2O–CeO2 nanospheres prepared with the molar ratio of Ce3+/Cu2+ of 5/1 is 3006.6 s−1 g−1, which is much higher than reported values. This paper demonstrates a highly controllable approach to the production of mesoporous Cu2O–CeO2 nanospheres, which have potential applications in the areas of catalysis, adsorption, sensors and so on.

Block copolymer compatibilization driven frustrated crystallization in electrospun nanofibers of polystyrene/poly(ethylene oxide) blends

The confined crystallization behaviour of poly(ethylene oxide) (PEO) has been studied in electrospun nanofibers of the phase-separated blends of polystyrene (PS) and PEO compatibilized with polystyrene-block-poly(ethylene oxide) (PS-b-PEO) block copolymer. The PS was present as the majority component such that the electrospun nanofibers consisted of PEO domains dispersed in the PS matrix. The phase separation in the blend occurred under the radial constraint of the nanofibers which led to the formation of small-sized fibrillar PEO domains. The use of block copolymer compatibilizer resulted in a noticeable decrease in the PEO domain size in the as-spun nanofibers. Moreover, the decrease in the domain size and domain connectivity was more substantial in the thermally annealed blend nanofibers due to the suppression of the domain coalescence mechanism resulting from the localization of the PS-b-PEO block copolymer at the interface. Consequently, the fraction of PEO domains crystallizing via homogeneous nucleation increased in the compatibilized blend nanofibers due to the presence of higher number of heterogeneity free PEO domains and disruption in their spatial connectivity. Interestingly, in the compatibilized blend nanofibers consisting of low molecular weight PEO, additional crystallization event attributed to surface nucleation was observed. The surface nucleation, plausibly, resulted from the formation of wet-brush structures where the PEO homopolymers homogeneously wet the PEO blocks present at the interface. In such a scenario, the PEO crystallization occurred via surface nucleation at the domain interface. The surface nucleated crystallization was absent in the compatibilized blend nanofibers composed of high molecular weight PEO presumably due to the formation of morphology with dry-brush structures.

Preparation of lactic acid- and glucose-responsive poly(ε-caprolactone)-b-poly(ethylene oxide) block copolymer micelles using phenylboronic ester as a sensitive block linkage.

The present study describes the synthesis, self-assembly and responsiveness to glucose and lactic acid of biocompatible and biodegradable block copolymer micelles using phenylboronic ester as the linkage between hydrophobic poly(ε-caprolactone) (PCL) and hydrophilic poly(ethylene oxide) (PEO). The PCL block with pendant phenylboronic acid (PCLBA) was synthesized by combining ε-caprolactone (ε-CL) ring-opening polymerisation (ROP), using 4-hydroxymethyl(phenylboronic) acid pinacolate as the initiator, and pinacol deprotection. The glucose-terminated PEO (PEOGlc) was prepared by 1,3-dipolar, Cu(i)-catalysed, alkyne-azide cycloaddition of α-methoxy-ω-propargyl poly(ethylene oxide) and 1-azido-1-deoxy-d-glucopyranose. All new compounds were evaluated by 1H NMR spectroscopy and by SEC analysis. PCLBA and PEOGlc blocks were linked in NaOH acetone solution, which was indirectly confirmed by Alizarin Red S fluorescence and directly by 1H NMR spectroscopy. Dialysis against Milli-Q water induced the self-assembly of PCLBA-b-PEOGlc nanoparticles, which were characterised by static (SLS) and dynamic (DLS) light scattering and by cryogenic transmission electron microscopy (cryo-TEM). Furthermore, the microscopic properties of the charged interface between the hydrophobic PCLBA core and the hydrophilic PEOGlc shell were examined by electrophoretic light scattering (zeta potential) and by fluorescence spectroscopy using the fluorescent probe 5-(N-dodecanoyl)aminofluorescein (DAF) as a pH indicator. Subsequently, the nanoparticles were transferred to a phosphate buffer saline (PBS) solution supplemented with different concentrations of glucose to simulate the physiological conditions in blood or lactic acid to simulate acidic cytosolic or endosomal conditions in tumour cells. Adding a surplus of glucose or lactic acid, which competitively binds to PBA, removes the stabilising hydrophilic PEOGlc blocks, thereby triggering marked nanoparticle aggregation. However, the rate of aggregation induced by lactic acid is considerably faster than that induced by glucose, as confirmed by light scattering. Thus, this novel block copolymer may contribute to the field of selective, lactic acid- and/or glucose-responsive drug delivery vehicle design under both pathological and physiological conditions.

Synthesis and Properties of Poly(propylene oxide) Block Copolymer Containing Oligopeptide Segment FormingNetwork Structure via Hydrogen Bond

Synthesis and Properties of Poly(propylene oxide) Block Copolymer Containing Oligopeptide Segment FormingNetwork Structure via Hydrogen Bond

Anticancer activity of Schiff base-Poloxamer P85 combination against kidney cancer.

Renal cell carcinoma (RCC) accounts for approximately 80% of the primary renal cancers, and current treatment strategies are not sufficient to provide a certain solution. Since there are not many treatment options, interest in discovery of alternative drugs has increased. In the current study, anticancer activity of a novel heterodinuclear Cu(II)-Mn(II) complex (Schiff base-SB) in combination with poly(ethylene oxide) and poly(propylene oxide) block copolymer (pluronic) P85 was tested against RCC. Cell viability, apoptosis and gene expression analysis were conducted in vitro by using Renca cells. The results revealed that the SB-P85 combination decreased cell proliferation by increasing the apoptotic gene expressions and apoptosis. Renca-injected BALB/c mice were used to mimic early stage of RCC model. Treatment with SB-P85 combination suppressed tumor formation and growth compared to baseline. Overall, SB-P85 showed promising anticancer activity against RCC in vitro and in vivo.

Micellization Thermodynamics of Pluronic P123 (EO20PO70EO20) Amphiphilic Block Copolymer in Aqueous Ethylammonium Nitrate (EAN) Solutions.

Poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers (commercially available as Pluronics or Poloxamers) can self-assemble into various nanostructures in water and its mixtures with polar organic solvents. Ethylammonium nitrate (EAN) is a well-known protic ionic liquid that is expected to affect amphiphile self-assembly due to its ionic nature and hydrogen bonding ability. By proper design of isothermal titration calorimetry (ITC) experiments, we determined the enthalpy and other thermodynamic parameters of Pluronic P123 (EO20PO70EO20) micellization in aqueous solution at varied EAN concentration. Addition of EAN promoted micellization in a manner similar to increasing temperature, e.g., the addition of 1.75 M EAN lowered the critical micelle concentration (CMC) to the same extent as a temperature increase from 20 to 24 °C. The presence of EAN disrupts the water solvation around the PEO-PPO-PEO molecules through electrostatic interactions and hydrogen bonding, which dehydrate PEO and promote micellization. At EAN concentrations lower than 1 M, the PEO-PPO-PEO micellization enthalpy and entropy increase with EAN concentration, while both decrease above 1 M EAN. Such a change can be attributed to the formation by EAN of semi-ordered nano-domains with water at higher EAN concentrations. Pyrene fluorescence suggests that the polarity of the mixed solvent decreased linearly with EAN addition, whereas the polarity of the micelle core remained unaltered. This work contributes to assessing intermolecular interactions in ionic liquid + polymer solutions, which are relevant to a number of applications, e.g., drug delivery, membrane separations, polymer electrolytes, biomass processing and nanomaterial synthesis.

Modulating effect of different biomolecules and other additives on cloud point and aggregation of amphiphilic linear and starblock copolymer

Non-ionic surfactants based on ethylene oxide-propylene oxide (EO-PO) block copolymers find applications in various industries including pharmaceutics, cosmetics, cleaning and dispersion sciences. This work shows the comparison among the clouding behaviour of two moderately hydrophobic EO-PO block copolymers viz. linear triblock Pluronic® P104 and starblock Tetronic® T1304 (henceforth mentioned as P104 and T1304), showing the effect of several additives viz. inorganic salts (NaCl, NaF, NaBr, NaI, NaCNS, Na2SO4, NaNO3), sugars (dextrose, sucrose, maltose, mannitol, sorbitol), amino acids (glycine, alanine, valine, serine, lysine, leucine, histidine, glutamine), ureas [urea, thiourea, N-methylurea (MMU), N,N′-dimethylurea (DMU), N, N, N′ N′-tetramethylurea (TMU), phenylurea], alcohols [ethanol, 1-butanol, 1-hexanol, 1-octanol, trifluoroethanol (TFE)], diols (ethylene glycol, 1,4-butanediol, 1,6-hexanediol,1,8-octanediol), water soluble polymers [polyvinyl alcohol (PVA 160K, PVA 49K), polyethylene glycol (PEG 300K, PEG 8K), polyvinylpyrrolidone (PVP 55K), and alkyl methylimidazolium ionic liquids [1-butyl-3-methylimidazolium chloride (C4mimCl), 1-butyl-3-methyl imidazolium hexafluorophosphate (C4mimPF6), 1-butyl-3-methyl imidazolium trifluoromethanesulfonate (C4mimCF3SO3), 1-methyl-3-octylimidazolium chloride (C8mimCl), 1-decyl-3-methylimidazolium chloride (C10mimCl)]. The effect of these additives is described in terms of their molecular characteristics and interaction with water or the copolymer. Both, hydrophobicity and structural properties of additives play important roles in the observed cloud point variation. Dynamic light scattering results on apparent micelle size for selected system are also reported. Tuning of phase and aggregation behaviour of ethylene oxide based non-ionic amphiphiles is of industrial and biomedical importance.

Quantifying Binding of Ethylene Oxide-Propylene Oxide Block Copolymers with Lipid Bilayers.

Block copolymers composed of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) have been widely used in cell membrane stabilization and permeabilization. To explore the mechanism of interaction between PPO-PEO block copolymers and lipid membranes, we have investigated how polymer structure influences the polymer-lipid bilayer association by varying the overall molecular weight, the hydrophobic and hydrophilic block lengths, and the end-group structure systematically, using 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) unilamellar liposomes as model membranes. Pulsed-field-gradient NMR (PFG-NMR) was employed to probe polymer diffusion in the absence and presence of liposomes. The echo decay curves of free polymers in the absence of liposomes are single exponentials, indicative of simple translational diffusion, while in the presence of liposomes, the decays are biexponential, with the slower decay corresponding to polymers bound to liposomes. The binding percentage of polymer to the liposome was quantified by fitting the echo decay curves to a biexponential model. The NMR experiments show that increasing the total molecular weight and hydrophobicity of the polymer can significantly enhance the polymer-lipid bilayer association, as the binding percentage and liposome surface coverage both increase. We hypothesize that the hydrophobic PPO block inserts into the lipid bilayer due to the fact that little molecular exchange between bound and free polymers occurs on the time scale of the diffusion experiments. Additionally, as polymer concentration increases, the liposome surface coverage increases and approaches a limit. These results demonstrate that PFG-NMR is a simple yet powerful method to quantify interactions between polymers and lipid bilayers.

Asymmetric Polymersomes from an Oil-in-Oil Emulsion: A Computer Simulation Study.

Asymmetric vesicles are valuable for understanding and mimicking cell and practical biomedicine applications. Recently, a very straightforward methodology for fabricating asymmetric polymersome was developed by Lodge's group through the coassembly of polystyrene-b-poly(ethylene oxide) (PS-b-PEO) and polybutadiene-b-poly(ethylene oxide) (PB-b-PEO) block copolymers at the interface of a polystyrene/polybutadiene/chloroform (PS/PB/CHCl3) emulsion. However, the in-depth microscopic mechanism for the formation of asymmetric polymersomes remains unclear. To address this issue, in this article, the coassembly process for the formation of the asymmetric polymersomes in Asano's experimental system was systematically investigated by employing a dissipative particle dynamics (DPD) simulation. Our results definitely demonstrate the formation of the asymmetric polymersomes such as that in the experiments and that the bilayer formed through the folding and crossing of the PEO blocks. Besides, from the microscopic view, three stages can be discerned in the formation process: (1) the formation of micelles, (2) the micelle diffusion to the interface, and (3) the micelle rearrangement at the interface to form an asymmetric polymersome. Meanwhile, the incompatibility among PS, PB, and PEO is proven to be the main driving force for asymmetric polymersome formation. Moreover, the effects of the order of addition of copolymers and the volume fraction of PEO blocks on the structure of the asymmetric polymersomes are also investigated. We find that the formation process is affected severely by the order of addition, and adding PS-b-PEO first can make the asymmetric bilayer more perfect. Not only that, but perfect asymmetric polymersomes can be formed only when the volume fraction of PEO (fPEO) is greater than 0.55. We believe the present work can extend the knowledge of the self-assembly of asymmetric polymersomes, especially with respect to the self-assembly mechanism.