Poly(vinylpyrrolidone-b-styrene) block copolymers tethered surfaces for protein adsorption and cell adhesion regulation

Poly(vinylpyrrolidone-b-styrene) (PVP-b-PS) diblock copolymers tethered to glass surfaces were prepared, and the effects on protein adsorption and cellular behavior to the glass and the modified glass surfaces investigated. The PVP-b-PS grafting process was confirmed by water contact angle and XPS measurements. The results obtained for the water contact angles suggest that there are two phases that coexist on the PVP-b-PS block copolymer tethered surface, under aqueous conditions. Although the PVP-b-PS surface possessed, to some extent, a protein resistant property, following introduction of the PS segment to the end of tethered PVP, both fibrinogen and lysozyme adsorption were increased significantly. The PVP-b-PS modified surface, based on Western-blot analysis, appeared to have the greatest amount of surface bound vitronectin, however the conformation of the adsorbed vitronectin may have subsequently been affected by the surface tethered copolymer as was suggested by cell culture results. From these results, we proposed that protein adsorption and cell adhesion can be regulated by tuning the chemical compositions of diblock copolymers tethered to surfaces.     

Control of pH- and temperature-responsive behavior of mPEG-b-PDMAEMA copolymers through polymer composition

A series of poly(ethylene glycol) monomethyl ether-block-poly(2-(dimethylamino)ethyl methacrylate) (mPEG-b-PDMAEMA) diblock copolymers were synthesized using atom transfer radical polymerization to achieve controlled polymer molecular weight and narrow molecular weight distribution. The thermoresponsive properties of the mPEG-b-PDMAEMA diblock copolymers in aqueous buffered solutions were determined using UV-Visible spectroscopy and dynamic light scattering. The cloud point, a soluble-to-insoluble transition, was observed for all mPEG-b-PDMAEMA diblock copolymer solutions. Increasing either the mPEG or PDMAEMA molecular weight resulted in a decrease in observed cloud points as a function of pH and polymer concentration. Changing the mPEG molecular weight determined whether a second, higher temperature, thermal transition was observed as a function of pH and polymer concentration. Controlling the thermoresponsive properties of mPEG-b-PDMAEMA diblock copolymers through polymer composition, concentration, and pH enables the tailoring of these copolymers for applications ranging from non-viral gene delivery to use as a strengthening agent in paper.     

A kind of modified bovine serum albumin with great potential for applying in gene delivery

Bovine serum albumin(BSA) was modified through a facile synthesis method to increase its isoelectric point(pI) from 4.8 to 6.0.When pH is higher than 6.0,the protein shows a negative surface charge,on the contrary,the protein is positively charged.In this study,the charge-reversal modified BSA(crBSA) was utilized to assemble with the binary complexes of pDNA/poly(vinylpyrrolidone)-graft-poly(2-dimethylaminoethyl methacrylate)(pDNA/PVP-g-PDMAEMA) to shield the excess positive charges of complexes at physiological pH(pH 7.4).When the complex coated with crBSA located in the environment at endosomal pH(pH 5.0),the charge-reversal of crBSA led to the deviation of crBSA from polyplex by electrostatic repulsion,which would benefit the transfection of the target gene.The crBSA shows great potential for improving the transfection efficiency of pDNA/PVP-g-PDMAEMA.     

Single‐step process to produce functionalized multiresponsive polymeric particles

Monodisperse functional multiresponsive particles were prepared by encapsulation of an amphiphilic diblock copolymer during the precipitation polymerization of polystyrene and divinylbenzene in one single step. The amphiphilic diblock copolymer employed throughout this study, polystyrene‐b‐poly (dimethylaminoethyl methacrylate) (PS‐b‐PDMAEMA) has been synthesized by ATRP in two consecutive polymerization steps. After encapsulation of the block copolymer within the microsphere, the surface modification of the particle occurs spontaneously upon exposure to water by surface segregation of the hydrophilic PDMAEMA block, thus without any additional post‐polymerization and/or chemical modification steps. The response of the functionalized particles both to pH and temperature was analyzed by potential zeta and DSC measurements. Upon dispersion of the particles in acidic media, the PDMAEMA block in its charged state is soluble and does not exhibit any change by heating. At higher pH values and temperatures above 35 °C (Low Critical Solubility Temperature of the PDMAEMA block) the hydrophilic segment collapses as detected by differential scanning calorimetry. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3523–3533, 2010     

Adsorption characteristics of zwitterionic diblock copolymers at the silica/aqueous solution interface

The adsorption of a zwitterionic diblock copolymer, poly(2-(diethylamino)ethyl methacrylate)-block-poly(methacrylic acid) (PDEA59-PMAA50), at the silica/aqueous solution interface has been characterised as a function of pH. In acidic solution, this copolymer forms core-shell micelles with the neutral PMAA chains being located in the hydrophobic cores and the protonated PDEA chains forming the cationic micelle coronas. In alkaline solution, the copolymer forms the analogous inverted micelles with anionic PMAA coronas and hydrophobic PDEA cores. The morphology of the adsorbed layer was observed in situ using soft-contact atomic force microscopy (AFM): this technique suggests the formation of a thin adsorbed layer at pH 4 due to the adsorption of individual copolymer chains (unimers) rather than micelle aggregates. This is supported by the remarkably low dissipation values and the relatively low degrees of hydration for the adsorbed layers, as estimated using a combination of quartz crystal microbalance with dissipation monitoring (QCM-D) and optical reflectometry (OR). In alkaline solution, analysis of the adsorption data suggests a conformation for the adsorbed copolymers where one block projects normal to the solid/liquid interface; this layer consists of a hydrophobic PDEA anchor block adsorbed on the silica surface and an anionic PMAA buoy block extending into the solution phase. Tapping mode AFM studies were also carried out on the silica surfaces after removal from the copolymer solutions and subsequent drying. Interestingly, in these cases micelle-like surface aggregates were observed from both acidic and alkaline solutions. The lateral dimension of the aggregates seen is consistent with the corresponding hydrodynamic diameter of the copolymer micelles in bulk solution. The combination of the in situ and ex situ AFM data provides evidence that, for this copolymer, micelle aggregates are only seen in the ex situ dry state as a result of the substrate withdrawal and drying process. It remains unclear whether these aggregates are caused by micelle deposition at the surface during the substrate withdrawal from the solution or as a result of unimer rearrangements at the drying front as the liquid recedes from the surface.     

pH-responsive diblock copolymer micelles at the silica/aqueous solution interface: Adsorption kinetics and equilibrium studies

The adsorption behavior of two examples of a weakly basic diblock copolymer, poly(2-(dimethylamino)ethyl methacrylate)-block-poly(2-(diethylamino)ethyl methacrylate) (PDMA-PDEA), at the silica/aqueous solution interface has been investigated using a quartz crystal microbalance with dissipation monitoring and an optical reflectometer. Dynamic and static light scattering measurements have also been carried out to assess aqueous solution properties of such pH-responsive copolymers. In alkaline solution, core-shell micelles are formed above the critical micelle concentration (cmc) by both copolymers, whereas the chains are molecularly dissolved (as unimers) at all concentrations in acidic solution. As a result, the adsorption behavior of PDMA-PDEA diblock copolymers on silica is strongly dependent on both the copolymer concentration and the solution pH. Below the cmc at pH 9, the cationic PDMA-PDEA copolymers adsorb as unimers and the conformation of the adsorbed polymer is essentially flat. At concentrations just above the cmc, the initial adsorption of copolymer onto the silica is dominated by the unimers due to their faster diffusion compared to the much larger micelles. Rearrangement of the adsorbed unimers and/or their subsequent displacement by micelles from solution is then observed during an equilibration period, and the final adsorbed mass is greater than that observed below the cmc. At concentrations well above the cmc, the much higher proportion of micelles in solution facilitates more effective competition for the surface at all stages of the adsorption process and no replacement of initially adsorbed unimers by micelles is evident. However, the adsorbed layer undergoes gradual rearrangement after initial adsorption. This relaxation is believed to result from a combination of further copolymer adsorption and swelling of the adsorbed layer.     

Solution pH-regulated interfacial adsorption of diblock phosphorylcholine copolymers

Spectroscopic ellipsometry has been used to examine the pH-responsive interfacial adsorption of a series of biocompatible diblock copolymers incorporating 2-methacryloyloxyethyl phosphorylcholine-based (MPC) residues and 2-(dialkylamino)ethyl methacrylate residues, with a specific focus on 2-(diethylamino)ethyl groups (referred to as MPCm-DEAn, where m and n refer to the mean degrees of polymerization of each block) at the hydrophilic silicon oxide/water interface. For all the copolymers studied the surface excess shows only weak concentration dependence. Increasing the length of the DEA block has little effect on the dynamic or equilibrated adsorption at pH 7, indicating that the DEA block adopts a flat conformation on the silicon oxide surface at this pH. With increasing pH, however, the surface excess shows a dramatic increase, followed by a subsequent decline. The observed maximum in surface excess represents a balance between charge over-compensation of the copolymer with the oppositely charged surface and the subsequently reduced charge density of the copolymer. Variations in the observed maxima for various MPCm-DEAn diblock copolymers indicate different surface conformations at high pH. Salt addition does not affect copolymer adsorption. This behavior is attractive for biomedical applications in which the ionic strength is variable. It was also found that the preadsorbed diblock copolymers immobilized DNA from solution to an extent that is proportional to the relative charge ratio between the anionic DNA and the cationic DEA block of the copolymer.     

pH-responsive non-surface-active/surface-active transition of weakly ionic amphiphilic diblock copolymers

The weakly ionic amphiphilic diblock copolymer polystyrene-b-poly(acrylic acid) was synthesized by nitroxy radical-mediated living radical polymerization with precise control of block length, block ratio, and polydispersity. Systematical surface tension experiments and foam formation observations revealed that this polymer was non-surface active under neutral and alkaline (pH 10) conditions, while it was surface active under an acidic condition (pH 3). This result supports our proposed origin of non-surface activity; the image charge repulsion at the air/water interface is essential in addition to very stable micelle formation in the bulk solution. At a higher pH (pH 12), the polymer showed slight surface activity since the added NaOH played a role as an added salt. The critical micelle concentration (cmc) was estimated by static light scattering. Cmc increased with increasing added salt (NaCl) concentration as was observed for other strongly ionic non-surface-active polymers. Hence, this trend is characteristic for non-surface-active polymers. The pH dependence of cmc was minimum at pH 8–10. Since the acrylic acid block is fully ionized under this condition, the strong image charge repulsion at this condition accelerated micelle formation at a low polymer concentration, which consequently decreased cmc. Micelles in bulk solution were confirmed by dynamic light scattering, and the salt concentration and pH dependencies of the hydrodynamic radius of the micelles were also estimated. The pH-responsive non-surface-active/surface-active transition observed in this study strongly supports the fact that the image charge repulsion is an essential factor for non-surface activity in addition to stable micelle formation in solution.     

Self-assembly and electrochromic property of electroactive tetraaniline-<Emphasis Type="Italic">b</Emphasis>-PEG diblock copolymer

A kind of amphiphilic rod-coil diblock copolymer consisting both of tetraaniline (TAni) and polyethylene glycol (PEG) blocks, TAni-b-PEG, was synthesized. The diblock copolymer shows excellent electrochromic properties, especially, in switching time and coloration efficiency compared with tetraaniline. TAni-b-PEG is able to self-assemble into spherical structure, which is attributed to the formation of conducting channels and increase of ion-exchange capacity of TAni-b-PEG, implying that a block copolymer with electrochromic block and high ionic conductive block simultaneously possesses improving electrochromic properties.     

Novel pH‐responsive mixed‐charge copolymer brushes based on carboxylic acid and quaternary amine monomers

In this study, we report on the fabrication of tunable mixed‐charged copolymer brushes consisting of negatively charged carboxylic acid monomer (4‐vinylbenzoic acid, VBA) and positively charged quaternary amine monomer ((ar‐vinylbenzyl)trimethylammonium chloride) via reversible addition–fragmentation chain transfer‐mediated polymerization. The copolymer brushes have negative charge under neutral and basic conditions, and are positively charged under acidic conditions owing to the protonation of the carboxylate groups. The copolymer brushes revealed a unique reversible wetting behavior with pH. The reversible properties of the copolymer brushes can be employed to regulate the adsorption of charged biomacromolecules such as DNA and proteins. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

The effect of PVP-<Emphasis Type="Italic">b</Emphasis>-PMAA block copolymer on morphologies control of calcium carbonate

A novel double-hydrophilic block copolymer (DHBC) poly(vinyl pyrrolidone)–block–poly(methacrylic acid) (PVP-b-PMAA) was synthesized via reversible addition–fragmentation chain transfer polymerization. The structure of the resulting copolymer was characterized by ¹H nuclear magnetic resonance, and the molecular weight of the block copolymer was determined by gel permeation chromatography. The study of morphological control of calcium carbonate (CaCO₃) has been performed in the presence of the PVP-b-PMAA block copolymer. Various morphologies of CaCO₃ particles such as rhombohedral, multilayered, and aggregated with cavities can be produced by varying the copolymer concentrations. The all-obtained CaCO₃ particles were calcite, which was confirmed by either X-ray diffraction or Fourier transform infrared spectra. Such calcium carbonate/polymer hybrids with complex morphologies may find valuable applications in biomimic mineralization.     

The adsorption of polyampholytes on negatively and positively charged polystyrene latex

The adsorption of two polyampholytes (a random copolymer of -glutamic acid and -lysine, and a well-defined tetramer of -lysyl- -glutamyl-glycine) onto positively and negatively charged latex was studied as a function of the pH and the ionic strength. The adsorbed amount proved to be almost independent of the salt concentration. The pH dependence was found to follow the same trends on negatively charged and positively charged latex. At low pH, where the polyampholytes are positively charged, a high adsorbed amount was found irrespective of the sign of the surface charge. At high pH, where the macromolecules are negatively charged, no adsorption was measured, not even with the positive latex. This is probably due to the very good solubility of the polyampholytes at this pH. Electrophoretic mobility measurements revealed that already at very low concentrations of polyampholyte charge reversal of the particles occurred.     

Analogy in adsorption behavior of homopolyelectrolyte mixtures as compared to analogous diblock polyampholytes

The adsorption behavior of aqueous mixtures of the homopolyelectrolytes poly(methacrylic acid) (PMAA) and poly[(dimethylamino)ethyl methacrylate] (PDMAEMA) was investigated in comparison with the adsorption of the ampholytic diblock copolymer PMAA‐b‐PDMAEMA on silicon substrates. Ellipsometry was used to determine the amount of adsorbed homopolyelectrolyte and diblock polyampholyte. Furthermore, the topography of the adsorbed polymers was investigated with atomic force microscopy (AFM) and compared with the structures observed in aqueous solutions by dynamic light scattering (DLS). For all types of investigated polyelectrolytic mixtures or the single polyampholyte, the adsorption was strongly influenced by the pH of the polymer solution. Although single homopolyelectrolytes showed only one maximum in adsorption according to their charge, the mixtures made from these homopolyelectrolytes showed two or three maxima. The third maximum near the isoelectric point of the mixture was assigned to a new species formed by aggregation of the two homopolyelectrolytes. Altogether, the adsorption behavior of the polyelectrolytic mixtures was in between the behavior of the pure homopolyelectrolytes and the analogous polyampholytes and therefore understandable from both of these polymer species. © 2002 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 338–345, 2002; DOI 10.1002/polb.10091     

Hollow nanoparticles prepared from pH‐responsive template polymer micelles

Water‐soluble crosslinked hollow nanoparticles were prepared using pH‐responsive anionic polymer micelles as templates. The template micelles were formed from pH‐responsive diblock copolymers (PAMPS‐PAaH) composed of the poly(sodium 2‐(acrylamido)‐2‐methylpropanesulfonate) and poly(6‐(acrylamido)hexanoic acid) blocks in an aqueous acidic solution. The PAMPS and PAaH blocks form a hydrophilic anionic shell and hydrophobic core of the core‐shell polymer micelle, respectively. A cationic diblock copolymer (PEG‐P(APTAC/CEA)) with the poly(ethylene glycol) block and random copolymer block composed of poly((3‐acrylamidopropyl)trimethylammonium chloride) containing a small amount of the 2‐(cinnamoyl)ethylacrylate photo‐crosslinkable unit can be adsorbed to the anionic shell of the template micelle due to electrostatic interaction, which form a core‐shell‐corona three‐layered micelle. The shell of the core‐shell‐corona micelle is formed from a polyion complex with anionic PAMPS and cationic P(APTAC/CEA) chains. The P(APTAC/CEA) chains in the shell of the core‐shell‐corona micelle can be photo‐crosslinked with UV irradiation. The template micelle can be dissociated using NaOH, because the PAaH blocks are ionized. Furthermore, electrostatic interactions between PAMPS and PAPTAC in the shell are screened by adding excess NaCl in water. The template micelles can be completely removed by dialysis against water containing NaOH and NaCl to prepare the crosslinked hollow nanoparticles. Transmission electron microscopy observations confirmed the hollow structure. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Adsorption of polyelectrolyte versus surface charge: in situ single-molecule atomic force microscopy experiments on similarly, oppositely, and heterogeneously charged surfaces

We have studied the effect of the pH and surface charge of mica on the adsorption of the positively charged weak polyelectrolyte (PE) poly(2-vinylpyridine) (P2VP) using atomic force microscopy (AFM) single-molecule experiments. These AFM experiments were performed in situ directly under aqueous media. If the mica's surface and the PE are oppositely charged (pH > 3), the PE forms a flat adsorbed layer of two-dimensionally (2D) equilibrated self-avoiding random walk coils. The adsorbed layer's structure remains almost unchanged if the pH is decreased to pH 3 (the mica's surface is weakly charged). At pH 2 (the mica surface is decorated by spots of different electrical charges), the polyelectrolyte chains take the form of a 2D compressed coil. In this pH range, at an increased P2VP concentration in solution, the PE segments preferentially adsorb onto the top of previously adsorbed segments, rather than onto an unoccupied surface. We explain this behavior as being caused by the heterogeneous character of the charged surface and the competitive adsorption of hydronium ions. The further increase of polymer concentration results in a complete coverage of the mica substrate and the charge overcompensation by P2VP chains adsorbed on the similarly charged substrate, due to van der Waals forces.     

Solid-supported block copolymer membranes through interfacial adsorption of charged block copolymer vesicles

The properties of amphiphilic block copolymer membranes can be tailored within a wide range of physical parameters. This makes them promising candidates for the development of new (bio)sensors based on solid-supported biomimetic membranes. Here we investigated the interfacial adsorption of polyelectrolyte vesicles on three different model substrates to find the optimum conditions for formation of planar membranes. The polymer vesicles were made from amphiphilic ABA triblock copolymers with short, positively charged poly(2,2-dimethylaminoethyl methacrylate) (PDMAEMA) end blocks and a hydrophobic poly( n-butyl methacrylate) (PBMA) middle block. We observed reorganization of the amphiphilic copolymer chains from vesicular structures into a 1.5+/-0.04 nm thick layer on the hydrophobic HOPG surface. However, this film starts disrupting and dewetting upon drying. In contrast, adsorption of the vesicles on the negatively charged SiO2 and mica substrates induced vesicle fusion and formation of planar, supported block copolymer films. This process seems to be controlled by the surface charge density of the substrate and concentration of the block copolymers in solution. The thickness of the copolymer membrane on mica was comparable to the thickness of phospholipid bilayers.     

Mixed micelles of oppositely charged poly(N‐isopropylacrylamide) diblock copolymers

Mixed micelle formation between two oppositely charged diblock copolymers that have a common thermosensitive nonionic block of poly(N‐isopropylacrylamide) (PNIPAAM) has been studied. The block copolymer mixed solutions were investigated under equimolar charge conditions as a function of both temperature and total polymer concentrations by turbidimetry, differential scanning calorimetry, two‐dimensional proton nuclear magnetic nuclear Overhauser effect spectroscopy (2D ¹H NMR NOESY), dynamic light scattering, and small angle X‐ray scattering measurements. Well‐defined and electroneutral cylindrical micelles were formed with a radius and a length of about 3 nm and 35 nm, respectively. In the micelles, the charged blocks built up a core, which was surrounded by a corona of PNIPAAM chains. The 2D ¹H NMR NOESY experiments showed that a minor block mixing occurred between the core blocks and the PNIPAAM blocks. By approaching the lower critical solution temperature of PNIPAAM, the PNIPAAM chains collapsed, which induced aggregation of the micelles. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1457–1469     

pH responsive surfaces with nanoscale topography

We report the preparation of nanostructured adaptive polymer surfaces by diffusion of an amphihilic block copolymer toward the interface. The surface segregation of a diblock copolymer, polystyrene‐block‐poly(acrylic acid) (PS‐b‐PAA), occurred when blended with high molecular weight polystyrene employed as a matrix. On annealing, the polymer surfaces changed both the chemical composition and the hydrophilicity depending on the environment and pH, respectively. By exposure to either water vapor or air, the surface wettability varied between hydrophilic and hydrophobic. In addition, surface enrichment on diblock copolymer by water vapor annealing led to self‐assembly occurring at the interface. Hence, nanostructured domains can be observed by AFM in liquid media. Moreover, the PAA segments placed at the interface respond to pH and can switch from an extended hydrophilic state at basic pH values to a collapsed hydrophobic state in acidic media. Accordingly, the surface morphology changed from swelled micelles to nanometer size holes. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2982–2990, 2010     

Diblock polyampholytes at the silicon–water interface: Adsorption as a function of block ratio and molecular weight

Polyampholytes are highly charged macromolecules carrying oppositely charged functional groups. This article reports on the adsorption of a weak diblock polyampholyte, poly(methacrylic acid)‐block‐poly[(dimethylamino)ethyl methacrylate], as a function of the copolymer composition and molecular weight. The adsorption experiments were performed on silicon substrates from aqueous polymer solutions at different pHs. The amount of adsorbed polyampholyte chains to the surface was determined by ellipsometry, whereas lateral structures were investigated by scanning force microscopy. A strong influence of pH on the adsorbed amount and the lateral structure formation at the surface was observed. Especially at the isoelectric point, drastic changes in adsorption behavior were detected. At low molecular weights, an increased adsorbed amount was detected, a behavior in contrast to common theoretical predictions. This phenomenon is explained by the high stability of absorbed micelles, which cover the silicon surface as a dense layer. We conclude that micelle formation is an important process for polyampholyte adsorption, which needs to be taken into account more explicitly. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 709–718, 2001     

Novel Amphiphilic Poly(N-vinylpyrrolidone) Block Copolymer: Aggregative Behavior and Interaction with DNA

Summary: Novel block copolymers poly(N-vinylpyrrolidone)-block-poly[(tert-butoxy) carbonyl] tryptophanamido-N′-methacryl thiourea (PVP-b-PTAM-I, II and III) were synthesized by atom transfer radical polymerization (ATRP) in DMF using PVP-Cl as macroinitiator. The structures of the copolymers were characterized by UV-vis and GPC-MALLS. The results revealed that the copolymers with controlled molecular weight and relatively low polydispersity (PDI < 1.34) were obtained through ATRP. By means of dynamic light scattering (DLS) and transmission electron microscopy (TEM), we demonstrated that copolymer PVP-b-PTAM self-aggregated to form spherical micelles in aqueous solution and the size of the micelles increased with increasing hydrophobic contents. The interaction of PVP-b-PTAM with DNA was explored using ethidium bromide (EB) quenching experiments. The interaction between PVP-b-PTAM and DNA markedly depended on both the copolymer concentration and composition. The PVP-b-PTAM-II and III with higher hydrophobic contents exhibited highly complexed DNA ability at low copolymer concentration, such as 0.017 mg/mL, relative to PVP-b-PTAM-I. As the copolymer concentration further increased for PVP-b-PTAM-II and III, they first exhibited a sharply decreased affinity for DNA and then kept steady. The interaction mechanism between the amphiphilic copolymers and the EB-DNA complex was discussed in detail.