Block Copolymer Surface Research Articles

Zellproliferation und zelluläre Aktivität von Primärzellkulturen der Mundhöhle nach Oberflächenbesiedlung eines abbaubaren, thermoplastischen Blockcopolymers / Cell proliferation and cellular activity of primary cell cultures of the oral cavity after cell seeding on the surface of a degradable, thermoplastic block copolymer

Using standard cell biological and biochemical methods we were able to test the ability of a degradable, thermoplastic block copolymer to support the adhesion, proliferation, and the cellular activity of primary cell cultures of the oral cavity in vitro. The delicate balance between a group of endogenous enzymes, Matrix Metalloproteinases (MMPs), and their inhibitors (Tissue Inhibitor of MMPs, TIMPs) have a decisive function in the remodeling of the extracellular matrix during processes like wound healing or the integration of biomaterials in surrounding tissues after implantation. Recently developed, biodegradable thermoplastic elastomers with shape-memory properties may be the key to develop new therapeutical options in head and neck surgery. Primary cell cultures of the oral cavity of Sprague-Dawley rats were seeded on the surface of a thermoplastic block copolymer and on a polystyrene surface as control. Conditioned media of the primary cells were analyzed for MMPs and TIMPs after different periods of cell growth. The MMP and TIMP expression was analysed by zymography and a radiometric enzyme assay. No statistically significant differences in the appearance and the kinetic of MMP-1, MMP-2, MMP-9 and TIMPs were detected between cells grown on the polymer surface compared to the control. An appropriate understanding of the molecular processes that regulate cellular growth and integration of a biomaterial in surrounding tissue is the requirement for an optimal adaptation of biodegradable, polymeric biomaterials to the physiological, anatomical, and surgical conditions in vivo to develop new therapeutic options in otolaryngology and head and neck surgery.

Facile Creation of a Bionic Super‐Hydrophobic Block Copolymer Surface

Facile Creation of a Bionic Super‐Hydrophobic Block Copolymer Surface

Surface Hydrophobicity of Fluorinated Block Copolymers Enhanced by Supercritical Carbon Dioxide Annealing

Supercritical carbon dioxide (scCO2) annealing enhances the hydrophobicity of the surfaces of asymmetric perfluorinated block copolymers. X-ray photoelectron spectroscopy (XPS) and contact angle measurement reveal that the surface domains of the fluorinated block (PF) of poly[styrene-block-4-(perfluorooctylpropyloxy)styrene] (PS-PF) become thicker than those annealed in a vacuum. Consequently, the contact angles of water on the surfaces of PS-PF block copolymers significantly increase after the scCO2 annealing compared to those annealed in a vacuum. The surface hydrophobicity enhanced by the scCO2 annealing is related to the thickness of the surface PF domain and the conformation of the PF block.

Polyelectrolytes on block copolymer surfaces

AbstractSoft lithography and properties of amphiphilic block copolymers are combined in a new technique for the generation of patterned substrates, which can be used in different ways as templates for further processing. In these processing steps the deposition of polyelectrolytes, metals and grafting from polymerizations are used for the construction of different structures.

Surface characteristics of block-type copolymer composed of semi-fluorinated and phospholipid segments synthesized by living radical polymerization

A series of random and block copolymers composed of hydrophilic and hydrophobic monomer units have been synthesized by the free and living radical polymerization methods, respectively. The hydrophilic monomer unit, 2-methacryloyloxyethyl phosphorylcholine (MPC), was selected because the MPC polymers are well-known for their excellent bio- and blood compatibilities. The semi-fluorinated monomer, 2,2,2-trifluoroethyl methacrylate (TFEMA), was used as the hydrophobic monomer unit. Several analyses of the copolymer surface showed that the TFEMA unit was concentrated at the outermost surface on the random copolymer surface and characteristics of MPC unit was dominant on the block copolymer with a low-MPC-unit composition in the dry state. A reorientation of the MPC unit occurred dynamically in the wet state because of the strong hydrophilicity of the MPC units. In the case of the block copolymer with a low-MPC-unit composition, the surface was covered with the MPC units in the wet state. As a result, the amount of the adsorbed bovine plasma fibrinogen and bovine serum γ-globulin on the block copolymer surface was reduced dramatically.

Engineering the friction-and-wear behavior of polyelectrolyte multilayer nanoassemblies through block copolymer surface capping, metallic nanoparticles, and multiwall carbon nanotubes

In previous work, it was demonstrated that coating a surface with polyelectrolyte multilayers (PEMs) composed of polyallylamine hydrochloride (PAH) and poly(acrylic acid) (PAA) resulted in increased friction forces at low normal loads. At stress levels sufficient to cause system wear, however, PAH/PAA PEMs provided significant wear protection for the underlying substrate. This report evaluates three strategies for reducing the coefficients of friction associated with PEMs at low normal stress, while retaining their wear-retarding properties at high normal loads. Anchoring polystyrene-block-poly(acrylic acid) to the PAH surface of a multilayer film, less than 10 nm thick, enhanced the hardness, and hence the load-bearing capacity of these structures. The effect of surface capping was most pronounced at high normal stresses, where substantial wear prevention was observed, accompanied by low friction forces. These films are well suited for systems where wear particle generation hinders smooth operation. The second strategy used the in situ synthesis of silver nanoparticles in the PEM matrix for friction reduction. Optimum levels of silver clusters are required at the surface to reduce the friction forces. Finally, multilayer composites were constructed using PAH and multiwall carbon nanotubes. These assemblies exhibited the lowest values of friction among the strategies studied, at all levels of stress; in addition, substrate wear prevention was also achieved. The tribological behavior of the PEM-modification strategies was correlated with the mechanical properties of the films, elicited by nanoindentation. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 439–448, 2004

Block Copolymer Surface Reconstuction: A Reversible Route to Nanoporous Films

AbstractThin films of block copolymers have been used as templates and scaffolds for the fabrication of arrays of nanostructured materials. In general, a chemical modification of the film or the removal of one of the components by photodegradative methods is required to produce a nanoporous film that serves as a template or scaffold. Here, however, the preferential interaction of one of the components with a solvent is shown to produce a reconstruction of the block copolymer film that, upon drying, leads to the generation of a nanoporous template. The area density of the pores is identical to that of the original copolymer thin film. Since no chemical reactions occurr, the process is fully reversible. Upon heating the copolymer film above its glass‐transition temperature, mobility is imparted to the copolymer and the original copolymer film with oriented domains is recovered. The film reconstruction significantly simplifies the generation of nanoporous templates.

Surface Reconstructions of Lamellar ABC Triblock Copolymer Mesostructures

We show that the near surface structure of lamellar ABC triblock copolymer mesostructures can deviate considerably from the “ideal” surface anticipated from the bulk structure of the material. Varying the molecular architecture and the surface energy difference between the respective blocks, we show that such surface reconstructions are caused by a complex balance of enthalpic and entropic contributions to the free energy of the system. The results are compared to the well-known surface behavior of classical crystals and experimental conditions for what may be called “block copolymer surface science” are discussed.

Nanoscale Polypyrrole Patterns Using Block Copolymer Surface Micelles as Templates

Arrays of polypyrrole (Ppy) dots (80−180 nm diameter) have been prepared in a highly parallel fashion. This process is achieved by templating Ppy growth on a 2D surface micelle array, initially formed by the Langmuir−Blodgett (LB) technique. Ppy growth on self-assembled (SA)-based surface micelles produces more complex structures, due to simultaneous reorganization of the SA micelles. These results demonstrate that template growth of conducting polymers can be used to fabricate configurations that are otherwise inaccessible.

Wetting of heterogeneous surfaces of block copolymers containing fluorinated segments

The wetting of well-characterized heterogeneous surfaces of block copolymers has been studied by low-rate dynamic contact angle measurements using axisymmetric drop-shape analysis. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to investigate the roughness, the heterogeneity and the chemical composition of the surfaces. By changing the block length of polysulfone and semifluorinated polyester segments in the block copolymers, the surface heterogeneity of thin films prepared on silicon wafers could be controlled. Tapping-mode AFM measurements showed that soft, hydrophobic domains of varying size on the submicrometer length scale were obtained on these surfaces (60–250 nm). The mean roughness was of the order of several nanometers. The results of the contact angle measurements showed that neither roughness nor heterogeneity had a significant effect on the advancing contact angle of water, at the scale of the features present; however, the contact angle hysteresis increased with increasing percentage of the soft domains. We assume that liquid retention by the solid upon retraction of the three-phase line is the main cause for the observed increase in contact angle hysteresis. Concerning the molecular composition of these block copolymer surfaces, angle-resolved XPS analysis showed a surface segregation of fluorine within the surface region. A direct correlation was found between the fluorine content of the block copolymer surfaces and the advancing contact angle of water.

Surface morphology of poly(caprolactone)-b-poly(dimethylsiloxane)-b-poly(caprolactone) copolymers: effects on protein adsorption.

Certain triblock copolymer surfaces have beneficial blood contacting properties that remain unexplained from a mechanistic perspective. In this study, poly(caprolactone-block-dimethylsiloxane-block-caprolactone) (PCL-b-PDMS-b-PCL) surfaces are characterized by dynamic contact angle analysis, angle-resolved X-ray photoelectron spectroscopy (XPS), and phase detection imaging atomic force microscopy (AFM). Surface morphology of films cast from 10 wt % MEK solutions are found to be semicrystalline possessing spherulites on the micron scale and alternating semicrystalline PCL-rich and amorphous PDMS-rich lamellae on the nanometer scale. Surface enrichment of the lower surface free energy block, PDMS, is observed using angle-resolved XPS but the surface composition still consists of both copolymer blocks. Films cast from 1 wt % solutions showed similar morphologies but incomplete surface coverage. Different textural features of adsorbed fibrinogen layers on coated and uncoated polypropylene are observed. The hypothesis that patterned block copolymer surfaces can affect protein adsorption and thus influence compatibility is partially supported by the findings of this study.

Microphase separation at the surface of block copolymers, as studied with atomic force microscopy

Atomic force microscopy (AFM) is used to study the phase separation process occurring in block copolymers in the solid state. The simultaneous measurement of the amplitude and the phase of the oscillating cantilever in the tapping mode operation provides the surface topography along with the cartography of the microdomains of different mechanical properties. This technique thus allows to characterize the size and shape of those microdomains and their organization at the surface (e.g. cubic lattice spheres, hexagonal lattice of cylinders, or lamellae). In this study, a series of symmetric triblock copolymers made of a inner elastomeric sequence (poly(butadiene) or poly(alkylacrylate)) and two outer thermoplastic sequences (poly(methylmethacrylate)) is analyzed by AFM in the tapping mode. The microphase separation and their morphology are essential factors for the potential of these materials as a new class of thermoplastic elastomers. Special attention is paid to the control of the surface morphology, as observed by AFM, by the molecular structure of the copolymers (volume ratio of the sequences, molecular weight, length of the alkyl side group) and the experimental conditions used for the sample preparation. The molecular structure of the chains is completely controlled by the synthesis, which relies on the sequential living anionic polymerization of the comonomers. The copolymers are analyzed as solvent-cast films, whose characteristics depend on the solvent used and the annealing conditions. The surface arrangement of the phase-separated elastomeric and thermoplastic microdomains observed on the AFM phase images is discussed on the basis of quantitative information provided by the statistical analysis by Fourier transform and grain size distribution calculations.

Surface energy of experimental and commercial nanofiltration membranes: effects of wetting and natural organic matter fouling

Contact angle measurements (captive bubble technique) were used to determine the surface energy of three experimental thin-film composite nanofiltration membranes and a commercial nanofiltration membrane (Hydranautics NTR 7450). The two experimental membranes of practical interest were thin film composites (diblock copolymer on a polysulfone support layer). The two blocks were poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) and poly(1,1-dihydroperfluorooctyl methacrylate) (PFOMA). The concept was to devise a membrane material that takes advantage of the low adhesion of PFOMA to prevent fouling and the hydrophilic nature of PDMAEMA to produce high water permeation rates. Hydranautics NTR 7450 is a sulfonated polysulfone membrane that purportedly lessens fouling because the surface is more hydrophilic. The change in surface energy upon wetting, permeation of water containing natural organic matter (NOM) and chemical cleaning was of interest. Wetting caused reorganization of the experimental block copolymer surface to move more of PDMAEMA block to the membrane–water interface. After permeation of ultrapure water, however, the surface became more hydrophilic. After permeation of NOM containing water, the surface of both experimental and commercial membranes reached about the same surface energy, indicative of adsorption of NOM. The contact angle measurements were used to calculate a negative change in surface free energy for all but the PFOMA membrane; hence, with this exception, the deposition of NOM into a layer adjacent to the membrane surface was spontaneous. Scanning electron micrographs and atomic force micrographs showed that rigorous chemical cleaning failed to remove the NOM. Although the new polymeric materials were not more resistant to NOM fouling than commercial membranes, the surface energy calculations may help in the search for more successful polymers. Systematic study of charge, molecular size and specific functional groups of NOM on membrane fouling warrants further research to understand why similar fouling occurred on very different polymeric materials.

Supramolecular Polymeric Materials with Hierarchical Structure-Within-Structure Morphologies

Hierarchical structure-within-structure morphologies are reported here as being directly imaged for the first time using transmission electron microscopy (TEM). These images reveal that the two structures are oriented perpendicular to the block-copolymer intermaterial dividing surface. The Figure shows a hexagonal array of polystyrene cylinders embedded in a lamellar matrix.

Surface visco-elastic modes in a spread film of a block copolymer

A linear diblock copolymer of polymethyl methacrylate and poly-4-vinyl pyridine quaternised with ethyl bromide has been spread as a thin film at the air/water interface and the properties of the capillary waves obtained using surface quasi-elastic light scattering. The data have been analysed for surface visco-elastic parameters on the basis of the complete absence of any transverse shear viscosity in the spread film. A resonance between capillary and dilatational modes was observed at a block copolymer surface concentration of 0.8 mg m-2. At this surface concentration the frequency dependence of the surface tension, dilatational modulus and dilatational viscosity exhibited behaviour which suggested that spread film could be represented as a Maxwell fluid with a relaxation time of ca. 3 µs. This Maxwell fluid model also described the dependence of an ‘apparent’ relaxation time of the dilatational mode on the surface concentration for a capillary wave of fixed wavenumber. A comparison of the observed dispersion behaviour (damping as a function of capillary wave frequency) with that predicted by theoretical forms of the dispersion equation, showed that there was no need to include a postulated coupling factor. This observation concurred with the modest dimensions of the surface region occupied by the quaternised vinyl pyridine blocks.

Spatially controlled cell engineering on biodegradable polymer surfaces

Controlling receptor-mediated interactions between cells and template surfaces is a central principle in many tissue engineering procedures (1-3). Biomaterial surfaces engineered to present cell adhesion ligands undergo integrin-mediated molecular interactions with cells (1, 4, 5), stimulating cell spreading, and differentiation (6-8). This provides a mechanism for mimicking natural cell-to-matrix interactions. Further sophistication in the control of cell interactions can be achieved by fabricating surfaces on which the spatial distribution of ligands is restricted to micron-scale pattern features (9-14). Patterning technology promises to facilitate spatially controlled tissue engineering with applications in the regeneration of highly organized tissues. These new applications require the formation of ligand patterns on biocompatible and biodegradable templates, which control tissue regeneration processes, before removal by metabolism. We have developed a method of generating micron-scale patterns of any biotinylated ligand on the surface of a biodegradable block copolymer, polylactide-poly(ethylene glycol). The technique achieves control of biomolecule deposition with nanometer precision. Spatial control over cell development has been observed when using these templates to culture bovine aortic endothelial cells and PC12 nerve cells. Furthermore, neurite extension on the biodegradable polymer surface is directed by pattern features composed of peptides containing the IKVAV sequence (15, 16), suggesting that directional control over nerve regeneration on biodegradable biomaterials can be achieved.

Active platelet movements on hydrophobic/hydrophilic microdomain-structured surfaces.

The early motion and interaction of platelets on a microdomain-structured block copolymer surface composed of 2-hydroxyethyl methacrylate (HEMA)-styrene were analyzed and compared with those on a compositionally identical random copolymer, homopolymer poly (HEMA) (hydrophilic) and polystyrene (hydrophobic) surfaces. Contacting platelets were quantitatively more active, with motions including rolling, detachment, oscillatory vibration, and change of direction only on the HEMA-St block copolymer surface. Active platelet movements were observed for long time periods (>20 min) on HEMA-St block copolymer surfaces and were distinct from those for inert PSt latex particles on these same surfaces, demonstrating that platelet movements were not due to physical forces such as convection, hydrophobic interactions, or microbrownian movement. To study the cause and mechanism underlying the platelet movements, platelets treated with an adenosine triphosphate (ATP) synthesis inhibition, NaN3, or a membrane skeleton-disrupting chemical agent, dibucaine, were also studied on these surfaces. Both treatments reduced platelet movement and demonstrated that platelets in contact with the HEMA-St block copolymer surface require metabolic processes consuming ATP and involve dynamics of their membrane skeleton. These energy-consuming active movements might explain the previously observed lower platelet activation and low thrombogenicity of the HEMA-St block copolymers. Enhanced platelet movements on the HEMA-St block copolymer surface show that the microdomain surface interacts uniquely with platelets to hinder activation and preserve passive platelet function despite surface contact.

Active platelet movements on hydrophobic/hydrophilic microdomain‐structured surfaces

The early motion and interaction of platelets on a microdomain-structured block copolymer surface composed of 2-hydroxyethyl methacrylate (HEMA)-styrene were analyzed and compared with those on a compositionally identical random copolymer, homopolymer poly (HEMA) (hydrophilic) and polystyrene (hydrophobic) surfaces. Contacting platelets were quantitatively more active, with motions including rolling, detachment, oscillatory vibration, and change of direction only on the HEMA-St block copolymer surface. Active platelet movements were observed for long time periods (>20 min) on HEMA-St block copolymer surfaces and were distinct from those for inert PSt latex particles on these same surfaces, demonstrating that platelet movements were not due to physical forces such as convection, hydrophobic interactions, or microbrownian movement. To study the cause and mechanism underlying the platelet movements, platelets treated with an adenosine triphosphate (ATP) synthesis inhibition, NaN3, or a membrane skeleton-disrupting chemical agent, dibucaine, were also studied on these surfaces. Both treatments reduced platelet movement and demonstrated that platelets in contact with the HEMA-St block copolymer surface require metabolic processes consuming ATP and involve dynamics of their membrane skeleton. These energy-consuming active movements might explain the previously observed lower platelet activation and low thrombogenicity of the HEMA-St block copolymers. Enhanced platelet movements on the HEMA-St block copolymer surface show that the microdomain surface interacts uniquely with platelets to hinder activation and preserve passive platelet function despite surface contact. © 1998 John Wiley & Sons, Inc. J. Biomed Mater Res, 42, 148–155, 1998.

Chemical Contrast on a Microphase-Separated Block Copolymer Surface Observed by Scanning Force Microscopy

Chemical Contrast on a Microphase-Separated Block Copolymer Surface Observed by Scanning Force Microscopy

Surfaces of Semi-Fluorinated Block Copolymers Studied Using Nexafs

ABSTRACTThe molecular orientation within a surface liquid crystalline layer made up of semifluorinated side-groups [-CO-(CH2)x−x-(CF2)yF] (SF groups) attached to the isoprene block of a styrene-isoprene diblock copolymer was determined by analyzing the partial electron yield Cedge NEXAFS signal. The results show that in contrast to the bulk, where the SF groups lie parallel to the diblock copolymer lamellae and thus parallel to the surface, the surface SF groups make an average angle with the surface normal of between 29 and 46° depending on x and y.