Homopolymer Layers Research Articles

Vapor-based hybrid grafting of heparin-like coating for dialysis membranes with enhanced hemocompatibility

Heparin is commonly used to improve the hemocompatibility of biomaterials, but high doses of heparin may cause significant side effect in clinical applications. Thus, heparin-mimicking surfaces have been urgently explored to reduce the use of heparin. In this work, heparin-like coating was deposited on polylactide (PLA) dialysis membranes using one-step hybrid grafting of a carboxyl-enriched poly(methacrylic acid) (pMAA) coating via initiated chemical vapor deposition (iCVD). The hybrid grafting was conducted by depositing a prime layer of poly(methacrylic acid-co-ethylene glycol dimethacrylate) (p(MAA-co-EGDMA)) copolymer followed by immediate in situ grafting of a pMAA homopolymer layer. The grafting parameters were systematically studied to obtain the maximum grafting density of pMAA. The resulting membrane with maximized surface functionality shows strong hydrophilicity with a water contact angle of 33° without affecting its permeability, excellent suppression of platelet adhesion and deformation, and significantly lengthened clotting time (APTT, TT, and PT prolonged to 308.4 s, 31.0 s, and 31.9 s, respectively). The substantially enhanced hemocompatibility is attributed to the abundant carboxyl groups achieved by hybrid grafting, which effectively disrupts the coagulation cascade. This facile iCVD grafting method can be a promising candidate for improving the hemocompatibility of biomaterials, such as dialysis membranes, catheters, and implants.

Hedgehog, Chamomile, and Multipetal Polymeric Structures on the Nanoparticle Surface: Computer Modelling

A single spherical nanoparticle coated with a densely grafted layer of an amphiphilic homopolymer with identical A-graft-B monomer units was studied by means of coarse-grained molecular dynamics. In solvent, selectively poor for mainchain and good for pendant groups; the grafted macromolecules self-assemble into different structures to form a complex pattern on the nanoparticle surface. We distinguish hedgehog, multipetalar, chamomile, and densely structured shells and outline the area of their stability using visual analysis and calculate aggregation numbers and specially introduced order parameters, including the branching coefficient and relative orientation of monomer units. For the first time, the branching effect of splitting aggregates along with the distance to the grafting surface and preferred orientation of the monomer units with rearrangements of the dense compacted shell was described. The results explain the experimental data, are consistent with the analytical theory, and are the basis for the design of stimulus-sensitive matrix-free composite materials.

Hedgehog, Chamomile and Multipetal Polymeric Structures on the Nanoparticle Surface: Theoretical Insights.

An analytical theory describing the variety of different morphological structures that spontaneously self-assemble in layers of amphiphilic homopolymers tightly grafted to spherical nanoparticle is proposed. For this purpose, the following structures were identified and outlined: hedgehogs, in which macromolecules are combined into cylindrical aggregates; chamomile, when cylindrical aggregates are connected by their ends into loops; multipetal structure with macromolecules self-assembling into thin lamellae; and unstructured, swollen and uniformly compacted shells. The results are presented in the form of state diagrams and serve as a basis for the directional design of the surface pattern by varying system parameters (particle radius, grafting density and degree of polymerization) and solvent properties (quality and selectivity).

Lamellae and parking garage structures in amphiphilic homopolymer brushes with different grafting densities.

This article is devoted to the study of polymer layers of amphiphilic homopolymers tightly grafted to a flat surface at the nodes of a square lattice. It was shown that, due to the amphiphilicity of monomer units containing groups with different affinities, in a selective solvent, such layers form lamellae perpendicular to the grafting surface. The period of the lamellae depends on the grafting density and the quality of the solvent. The results are presented in the form of a state diagram in variables "the energy of attraction of the side groups" (effective solvent quality) and "the distance between the grafting points" (inversely proportional to the square root of the grafting density). The diagram contains the regions of stability of lamellae with significantly different periods, and a transitional area with a parking garage structure. The diagram is constructed by calculating the layer-by-layer structure factor and the angle of inclination of the lamellae in the slice. The calculations were performed for different sizes of the simulation box, and the most commensurate size was determined by a special procedure for each grafting density. The results may be interesting not only to specialists in polymer science but also to all those who investigate the processes of self-organization and rearrangement in dense systems.

Propagation and Purification of Human Induced Pluripotent Stem Cells with Selective Homopolymer Release Surfaces

AbstractThe selective detachment of undifferentiated human induced pluripotent stem (iPS) cells from a thermal release coating, fabricated from a tailored poly(di(ethylene glycol) methyl ether methacrylate) (PDEGMA) homopolymer layer on gold, is reported. By exploiting the mild, thermally triggered release of iPS cell colonies in the absence of any releasing reagent, pluripotent iPS cells are shown to be selectively separated from spontaneously differentiated cells. The maintained pluripotency and high cell viability of detached and reseeded iPS cell colonies were confirmed and suggest the feasibility of a generally applicable platform approach for cell separation and purification in the context of iPS cell culture, differentiation of pathologically altered cells and normal cells, as well as isolation of different cell types derived from certain tissues, for example, from biopsies.

Propagation and Purification of Human Induced Pluripotent Stem Cells with Selective Homopolymer Release Surfaces.

The selective detachment of undifferentiated human induced pluripotent stem (iPS) cells from a thermal release coating, fabricated from a tailored poly(di(ethylene glycol) methyl ether methacrylate) (PDEGMA) homopolymer layer on gold, is reported. By exploiting the mild, thermally triggered release of iPS cell colonies in the absence of any releasing reagent, pluripotent iPS cells are shown to be selectively separated from spontaneously differentiated cells. The maintained pluripotency and high cell viability of detached and reseeded iPS cell colonies were confirmed and suggest the feasibility of a generally applicable platform approach for cell separation and purification in the context of iPS cell culture, differentiation of pathologically altered cells and normal cells, as well as isolation of different cell types derived from certain tissues, for example, from biopsies.

Toward Label-Free Selective Cell Separation of Different Eukaryotic Cell Lines Using Thermoresponsive Homopolymer Layers.

Ultrathin thermoresponsive poly(di(ethylene glycol) methyl ether methacrylate) (PDEGMA) homopolymer layers are reported as a novel platform for label-free temperature-stimulated cell separation from a coculture of eukaryotic cell lines. Pancreatic tumor cells (PaTu 8988t) and fibroblasts (NIH 3T3) were shown to attach and proliferate on PDEGMA layers with a dry thickness of 5 ± 1 nm at 37 °C. After the cell medium cooled to below the lower critical solution temperature (LCST), PaTu 8988t cells showed a significantly decreased cell area. By contrast, there was no significant change in cell area for NIH 3T3 cells, while they still exhibited lamellipodia and filopodia. PaTu 8988t cells could be detached at 22 °C after flushing gently with the cell medium, while negligible cell detachment was observed for NIH 3T3 cells under identical conditions. This significant difference between PaTu 8988t and NIH 3T3 was due to the different cell adhesion on the culture-medium-derived protein covering the PDEGMA layer. Thus, cell separation from a coculture was achieved successfully by cooling the cell medium to 22 °C, resulting in the desorption of 95 ± 6% of PaTu 8988t cells, while the NIH 3T3 cells remained adherent. Our findings provide an effective, label-free, rapid, and simple approach, exploiting a thermoresponsive homopolymer layer to separate and enrich or isolate cells from mixed cell populations for basic biological research, medical diagnostics, tissue engineering, and cell therapy.

Parking Garage Bicontinuous Structures of Densely Grafted Layers of Amphiphilic Homopolymers

The features of self-organization of densely grafted layers of macromolecules composed of amphiphilic units in selective solvent have been studied by computer simulation. Depending on solvent quality, strands and lamellas with different period can form in these layers, and the rearrangement of some lamellas into others proceeds by the formation of parking garage bicontinuous structure where lamellas with different periods are separated in height and bound to each other via inclined bridges. A method of quantitative description of parking garage structure has been suggested, the range of its existence has been determined, and the presence of a hysteresis on the plot of the position of the interface of lamellas vs. solvent quality has been revealed. It has been shown that the formation of parking garage structure occurs as a first-order phase transition with heat capacity maximum.

Lamellae—Parking Garage Structure—Lamellae Transition in Densely Grafted Layers of Amphiphilic Homopolymers: Impact of Polymerization Degree

By means of computer modeling, the self-organization of densely grafted macromolecules with amphiphilic monomer units as a function of macromolecular polymerization degree and solvent quality was studied and a diagram of state was constructed. The diagram contains fields of disordered distribution of monomer units and of prolonged aggregates, regions of lamellae with small and big domain spacing, and transition region. Within the transition region, the lamellae with different spacing coexist: the lamellae with big domain spacing are on the top of the grafting layer and the lamellae with small domain spacing are close to the grafting surface. The lamellae are connected with each other and form bicontinuous parking garage structure joining all side groups into a single cluster. The domain spacing of lamellae does not depend on the macromolecular length, but the width of the transition region decreases with the decrease of polymerization degree until total vanishing at relatively short macromolecules. The sharp switch between lamellae and bicontinuous structure opens the perspective for practical applications of densely grafted layers with amphiphilic monomer units.

Homopolymer Nanolithography.

Future progress in nanoscience and nanotechnology necessitates further development of versatile, labor-, and cost-efficient surface patterning strategies. A new approach to nanopatterning is reported, which utilizes surface segregation of a smooth layer of an end-grafted homopolymer in a poor solvent. The variation in polymer grafting density yields a range of surface nanostructures, including randomly organized pinned spherical micelles, worm-like structures, networks, and porous films. The capability to use the polymer patterns for site-specific deposition of small molecules, polymers, or nanoparticles is shown. This versatile strategy enables patterning of curved surfaces with direct access to the substrate and no need in changing polymer composition to realize different surface patterns.

Probing the Utmost Distance of Polymer Dynamics Suppression by a Substrate by Investigating the Diffusion of Fluorinated Tracer-Labeled Polymer Chains

A facile method was developed to measure the utmost distance of polymer dynamics suppressed by a solid substrate by investigating the diffusion of a fluorinated tracer-labeled polymer in the bottom layer of bilayer samples. Here, a labeled layer of fluorinated tracer-labeled at the polymer chain end of variable thickness was supported on a substrate, and the corresponding homopolymer layer of fixed thickness was deposited on top of the bottom layer. From the critical time (t*) required for the fluorinated component to diffuse from the bottom layer to the bilayer film surface as a function of the thickness of the bottom layer, a critical thickness of the bottom layer (hc*), corresponding to the thickness at which t* started to increase, was obtained. This thickness was related to the distance over which polymer dynamics were altered by the substrate. The results showed that hc* was very sensitive to the surface chemistry of the substrate and exhibited both molecular weight and temperature dependencies.

Interfacial stabilization of bilayered nanolaminates by asymmetric block copolymers

Block copolymers are macromolecular surfactants that self-assemble into a variety of nanostructural elements or reduce the interfacial tension between incompatible polymers. Here, we examine the ability of diblock copolymers differing in composition to stabilize bilayered homopolymer nanolaminates on flat solid supports. In this arrangement, self-assembly competes with interfacial modification and, in one case, promotes destabilization of the top film. To discern the corresponding mechanism, we investigate nanolaminates with a thin copolymer layer positioned between the homopolymer layers. Stabilization commences when this middle layer is sufficiently thick so that the block that is miscible with the top layer forms a brush.

Electrochemical Synthesis of Polyaniline/Poly-O-Aminophenol Copolymers in Chloride Medium

The copolymerization ofo-aminophenol (OAP) and aniline (ANI) on Pt and ITO electrodes was studied using cyclic voltammetry in 0.1 M HCl/0.4 M NaCl solution. The films were characterized by SEM, cyclic voltammetry, and UV-Vis spectroscopy. The properties of the copolymer were compared with PANI and POAP films. The results strongly suggest that the growth of PANI-POAP films does not consist of the simple buildup of layers of homopolymers on the electrode surface as a result of OAP or ANI oxidation products in the monomer mixture, but that a new conducting polymer is formed by copolymerization.

Monte Carlo simulation of a polymer-analogous reaction in a polymer blend

The autocatalytic polymer-analogous reaction A → B in a blend composed of two contacting layers of compatible homopolymers A and B is studied by numerical simulation using the dynamic continuum Monte Carlo method. The evolution of the numerical density of units A and units initially belonged to the chains of homopolymer A is investigated in the course of the reaction and interdiffusion. Local characteristics of the distribution of the homopolymer with respect to its composition and blocks A and B with respect to their length are calculated at different times. The dispersions of the above distributions are appreciably higher than the corresponding dispersion of the Bernoullian copolymer of the same average composition, despite the random character of the reaction. This effect can be provided by changes in the composition of the blend on the scale of the reacting chain as well as by the diffusive mixing of the above chains. For the products of the polymer-analogous reaction, the broadening of the compositional distribution is predicted also by the theoretical model, which describes interdiffusion in the reacting system on scales that are markedly greater than the size of a polymer chain.

Selectively Probing the Glass Transition Temperature in Multilayer Polymer Films: Equivalence of Block Copolymers and Multilayer Films of Different Homopolymers

The temperature dependence of the fluorescence of trace levels of pyrene was employed to measure the glass transition temperatures (Tgs) of polystyrene (PS) domains within ultrathin films of poly(styrene-block-methyl methacrylate) (P(S-b-MMA)) and poly(styrene-block-2-vinylpyridine) (P(S-b-2VP)) diblock copolymers supported on silica after self-assembly into lamellar morphologies. The PS domains within the two block copolymers exhibited dramatically different Tg−nanoconfinement behavior. The Tgs of the PS domains within the P(S-b-MMA) films were observed to decrease with decreasing film thickness in accordance with Tg reductions observed for single-layer PS homopolymer films; in contrast, the Tg of the PS domains within the P(S-b-2VP) films exhibited no change within experimental uncertainty upon confinement. The Tgs of the block copolymer films showed excellent agreement with those of multilayer films constructed from homopolymer layers with an equivalent morphology, indicating that chain connectivity ac...

The influence of grafted polymer architecture and fluid hydrodynamics on protein separation by entropic interaction chromatography

Entropic interaction chromatography (EIC) provides efficient size-based separation of protein mixtures through the entropy change associated with solute partitioning into a layer of hydrophilic homopolymer that has been end-grafted within the pores of a macroporous chromatography support. In this work, surface-initiated atom-transfer radical polymerization (ATRP) is used to prepare a library of EIC stationary phases covering a wide range of grafted-chain densities and molecular weights. Exhaustive chain cleavage and analysis by saponification and GPC-MALLS, respectively, show that the new ATRP synthesis procedure allows for excellent control over graft molecular weight and polydispersity. The method is used to prepare high-density grafts (up to 0.164 +/- 0.005 chains/nm(2)) that extend the range of EIC applications to include efficient buffer-exchange and desalting of protein preparations. Reducing the graft density allows for greater partitioning of high molecular weight solutes, extending the linear range of the selectivity curve. Increasing graft molecular weight also alters selectivity, but more directly affects column capacity by increasing the volume of the grafted layer. Protein partitioning in high-density EIC columns is found to decrease with mobile-phase velocity (u). Although solute mass transfer resistances leading to an increase in plate height can explain this effect, pressure drop data across the column are indicative of weak convective flow through at least a fraction of the grafted architecture. Modeling of the grafted brush properties in the presence of solvent flow by subjecting a self-consistent-field theory representation of the brush to a viscous shear force predicts that the grafted chains will tilt and elongate in the direction of flow. The shear force may therefore act to reduce the number of conformations available to chains, increasing their rigidity without significantly altering the thickness of the grafted layer. A reduction in protein partitioning is then predicted when the dependence on u of the solute entropy loss is stronger than that of the grafted polymer, a condition met at high graft densities.

New liquid-crystalline homo-and copolymers with phenyl benzoate side groups and a chiral center in a flexible spacer

The phase behavior and structure of liquid-crystalline homo-and copolymers based on structurally isomeric units belonging to the family of phenyl benzoates that differ in orientation of an ester link situated between benzene rings have been studied with X-ray diffraction, scanning calorimetry, and polarization optical microscopy. The orientation of this link in the monomer unit affects the temperature of phase transition, the type of the smectic phase, and the packing mode of side mesogenic groups in smectic layers of homopolymers. When monomer units commensurable with the monomer units of the basic component in terms of geometry but not identical to them in terms of smectogenity are randomly incorporated into macromolecules of the LC polymer, the resulting copolymer is characterized by layered packing not typical of either of the components.

Diblock Copolymer Surfactant Transport across the Interface between Two Homopolymers

Dynamics of adsorption and desorption of a diblock copolymer to an interface between two homopolymers was measured using dynamic secondary-ion mass spectrometry (SIMS). Thin films were constructed consisting of a layer of saturated polybutadiene with 90% 1,2-addition (sPB90), followed by a layer of saturated polybutadiene with 63% 1,2-addition (sPB63), and finally by another layer of the sPB90 homopolymer. A sPB90-sPB63 diblock copolymer was initially included only in the top sPB90 layer of the film at a volume fraction of 0.05. The thin films were annealed at ambient temperature for times ranging between 0.2 and 108 h, and the concentration profiles of the diblock copolymer through the films were measured using SIMS. The dynamics of adsorption and desorption of the diblock copolymer at the two sPB90-sPB63 interfaces was gauged by comparing the different transient concentration profiles. The sorption process was modeled as diffusion in an external field, generated from self-consistent field theory (SCFT). All parameters for the model were determined independently. Although the model neglects the dynamics of conformational change, experimental results matched theory very well.

Suppression of the Keto‐Emission in Polyfluorene Light‐Emitting Diodes: Experiments and Models

AbstractThe spectral characteristics of polyfluorene (PF)‐based light‐emitting diodes (LEDs) containing a defined low concentration of either keto‐defects or of the polymer poly(9,9‐octylfluorene‐co‐benzothiadiazole) (F8BT) are presented. Both types of blend layers were tested in different device configurations with respect to the relative and absolute intensities of green and blue emission components. It is shown that blending hole‐transporting molecules into the emission layer at low concentration or incorporation of a suitable hole‐transporting layer reduces the green emission contribution in the electroluminescence (EL) spectrum of the PF:F8BT blend, which is similar to what is observed for the keto‐containing PF layer. We conclude that the keto‐defects in PF homopolymer layers mainly constitute weakly emissive electron traps, in agreement with the results of quantum‐mechanical calculations.

Polymer Melt Intercalation in Clay Modified by Diblock Copolymers

AbstractSummary: The thermodynamic equilibrium in a melt of homopolymer C mixed with clay modified by a diblock copolymer AB is considered in theory. It is assumed that mixing is carried out in two stages. At first, the diblock copolymer penetrates into the interlayers formed by long clay sheets. Then, the clay with adsorbed diblock copolymer chains is added to the homopolymer melt. It is shown that the first process is thermodynamically favorable only if the interlayer width exceeds some threshold value that depends mostly on the difference in the adsorption energy of units A and B. A spontaneous mixing at the second stage is possible only if the enthalpic interactions between homopolymer and copolymer units are not very unfavorable. If so, the formation of an intercalated state is expected for a homopolymer of length comparable to the copolymer length, while for a long homopolymer the anticipated equilibrium state is exfoliation. The spatial distribution of A, B, and C units across the interlayer has been studied for different parameters of the system. The most readily adsorbing units A occupy almost all clay surface. However, the layer of block A is considerably swelled by both B and C units. The mutual distribution of units B and C may vary from almost homogeneous to having rather sharp boundary depending on the value of the Flory‐Huggins parameter χBC. The formation of a pure homopolymer layer at the center of the interlayer indicates about a tendency to exfoliate.Interlayer profiles of the fractions of units A, B, and C, respectively.imageInterlayer profiles of the fractions of units A, B, and C, respectively.