Nonleaching antibacterial glass surfaces via "Grafting Onto": the effect of the number of quaternary ammonium groups on biocidal activity

Antimicrobial surfaces were prepared using the "grafting onto" technique. Well-defined block copolymers containing poly(2-(dimethylamino)ethyl methacrylate) and poly(3-(trimethoxysilyl)propyl methacrylate) segments (PDMAEMA/PTMSPMA) and corresponding random copolymers were prepared via atom transfer radical polymerization (ATRP), followed by covalent attachment to a glass surface through reaction of the trimethoxysilyl groups with surface silanol groups. The density of quaternary ammonium (QA) groups available to bind small molecules in solution increased with polymer solution concentration and immobilization time. For the PDMAEMA 97- b-PTMSPMA xdiblock copolymers with a fixed length of PDMAEMA segment (degree of polymerization (DP) = 97) and varied lengths of PTMSPMA segments, maximal available surface charge was observed when the ratio of DP PDMAEMA to DP PTMSPMA was 5:1. The tertiary amino groups in immobilized PDMAEMA segments were reacted with ethyl bromide to form QA groups. Alternatively, block copolymers with prequaternized PDMAEMA segments were attached to surfaces. Biocidal activity of the surfaces with grafted polymers versus Escherichia coli ( E. coli) increased with the density of available QA units on the surface. The number of bacteria killed by the surface increased from 0.06 x 10(5) units/cm2 to 0.6 x 10(5) units/cm2, when the density of surface QA increased from 1.0 x 10(14) unit/cm2 to 6.0 x 10(14) unit/cm2. The killing efficiency of QA on all surfaces was similar with approximately 1 x 10(10) units of QA needed to kill one bacterium. The AFM analysis indicated that grafting onto the surface resulted in small patches of highly concentrated polymer. These patches appear to increase the killing efficiency as compared to surfaces prepared by grafting onto with the same average polymer density but with a uniform distribution.     

Alpha,omega-functionalized poly-N-isopropylacrylamides: controlling the surface activity for vesicle adsorption by temperature

The synthesis of alpha,omega-end-functionalized copolymers of N-isopropylacrylamide and N-(3-dimethylaminopropyl)acrylamide was performed. Monomer ratios of 100:0, 96:4, and 81:19 were investigated. The lower critical solution temperature (LCST) of these polymers was determined by cloud-point measurements and by microcalorimetric measurements. The LCST increased from 32 over 37 to 47 degrees C as the hydrophobicity increased with increasing amount of comonomer N-(3-dimethylaminopropyl)acrylamide. The polymers could successfully be adsorbed onto gold surfaces. Finally, vesicle adsorption onto these self-assembled polymer films on flat gold surfaces was investigated as the vesicle solution temperature was varied. It could be observed that vesicle adsorption was hindered as long as the temperature of the vesicle solution was above the LCST of the polymer. As soon as it dropped below the LCST the vesicle adsorption process was initiated.     

Immobilization and Release Studies of Triazole Derivatives from Grafted Copolymer Based on Gellan-Carrying Betaine Units

New polymer-bioactive compound systems were obtained by immobilization of triazole derivatives onto grafted copolymers and grafted copolymers carrying betaine units based on gellan and N-vinylimidazole. For preparation of bioactive compound, two new types of heterocyclic thio-derivatives with different substituents were combined in a single molecule to increase the selectivity of the biological action. The 5-aryl-amino-1,3,4 thiadiazole and 5-mercapto-1,2,4-triazole derivatives, each containing 2-mercapto-benzoxazole nucleus, were prepared by an intramolecular cyclization of thiosemicarbazides-1,4 disubstituted in acidic and basic medium. The structures of the new bioactive compounds were confirmed by elemental and spectral analysis (FT-IR and ¹H-NMR). The antimicrobial activity of 1,3,4 thiadiazoles and 1,2,4 triazoles was tested on gram-positive and gram-negative bacteria. The triazole compound was chosen to be immobilized onto polymeric particles by adsorption. The Langmuir, Freundlich, and Dubinin–Radushkevich adsorption isotherm were used to describe the adsorption equilibrium. Also, the pseudo-first and pseudo-second models were used to elucidate the adsorption mechanism of triazole onto grafted copolymer based on N-vinylimidazole and gellan (PG copolymer) and grafted copolymers carrying betaine units (PGB1 copolymer). In vitro release studies have shown that the release mechanism of triazole from PG and PGB1 copolymers is characteristic of an anomalous transport mechanism.     

Adsorption of diblock copolymers on stripe-patterned surfaces

We present the results of extensive Monte Carlo simulations of diblock copolymers adsorbed on stripe-patterned surfaces of various widths. We have found that the width of the stripe pattern is an important parameter which dictates favorable recognition on the surface. For certain stripe widths, the adsorption of diblock copolymers to striped surfaces exhibits two transitions. The process involves recognition of the surface pattern by the diblock copolymer which follows a two step process in which the first block getting adsorbed to the appropriate pattern on the surface, without any recognition of the surface pattern, followed by the adsorption of the second block, where a reorganization process happens. For small widths and also for higher widths, the chain behaves just like a homopolymer where the twofold adsorbing process changes to the typical homopolymer adsorption. We have also found that there exists an optimal width of the stripes, independent of the chain length, where the recognition on the surface pattern is most favored. The characteristic temperature of the adsorption of the second block with weaker interactions is found to be independent of the chain length at this optimal width, proving that only local rearrangements take place after the first step. Some of our results describing the thermodynamics compare very well with the recent semianalytical approach of Kriksin et al. [J. Chem. Phys. 122, 114703 (2005)] on multiblock copolymers on heterogeneous surfaces. We also present some interesting conformational properties of the copolymer chain near the stripe-patterned surface.     

Adsorption of multiblock copolymers onto a chemically heterogeneous surface: a model of pattern recognition

We present a statistical mechanical model, which is used to investigate the adsorption behavior of two-letter (AB) copolymers on chemically heterogeneous surfaces. The surfaces with regularly distributed stripes of two types (A and B) and periodic multiblock copolymers (Al)B(l))(x) are studied. It is assumed that A(B)-type segments selectively adsorb onto A(B)-type stripes. It is shown that the adsorption strongly depends on the copolymer sequence distribution and the arrangement of selectively adsorbing regions on the surface. The polymer-surface binding proceeds as a two-step process. At the first step, the copolymer having short blocks adsorbs onto the surface as an effective homopolymer, which does not feel chemical pattern. At the second step, when the polymer-surface attraction is sufficiently strong, the adsorbed chain adjusts its equilibrium conformation to reach the perfect bound state, thereby demonstrating ability for pattern recognition. The key element of this mechanism is the redistribution of strongly adsorbed copolymer diblocks A(l)B(l), which behave as surfactants, between multiple AB interfaces separating A and B stripes on the adsorbing surface. Such redistribution is accompanied by a well-pronounced decrease in the system entropy. We have found that marked pattern recognition is possible for copolymers with relatively short blocks at high polymer/surface affinities, beyond the adsorption threshold.     

A biomimetic alternative to poly(ethylene glycol) as an antifouling coating: resistance to nonspecific protein adsorption of poly(L-lysine)-graft-dextran

Poly( L-lysine)- graft-dextran (PLL- g-dex), graft copolymers with dextran side chains grafted onto a poly( L-lysine) backbone, previously shown to be effective as stabilizers of DNA triple helices and as carriers of functional genes to target cells or tissues, were employed in this work to prevent nonspecific adsorption of proteins, as determined by means of optical waveguide lightmode spectroscopy. PLL- g-dex copolymers readily adsorb from aqueous solution onto negatively charged oxide surfaces and significantly reduce nonspecific protein adsorption onto bare silica-titania surfaces. While effective and equivalent surface adsorption and antifouling properties were observed for PLL- g-dex copolymers in a variety of architectures, nanotribological analysis by atomic force microscopy was able to distinguish between the different brush densities produced.     

Functionalized conducting polymers for chemical sensors – an in situ ESR/UV‐Vis‐NIR voltammetric study

The redox and optical properties of various well defined polymer and copolymer films containing pyrrole or thiophene units were studied. The in situ ESR/UV‐Vis‐NIR spectroelectrochemistry was applied to investigate polymers and copolymers deposited both electrochemically or by a special chemical procedure using adhesion promoter onto the optically transparent indium‐tin‐oxide (ITO) electrodes. The spectroelectrochemical responses of chemically and electrochemically prepared polythiophenes on ITO were compared and the electronic structures of both polymers found to be similar. In situ ESR/UV‐Vis‐NIR voltammetric studies on electrochemically prepared copolymers containing pyrrole units and various N,N′‐ethylene‐bis(salicylidenimine) (salen) transition metal complexes indicate the presence of both polysalen and polypyrrole redox active centers in the copolymer.     

Amphiphilic graft copolymers - preparation and interfacial properties

Amphiphilic graft copolymers containing poly(ethylene oxide) (PEO) grafts have been prepared by various methods, for example, by coupling of reactive hydrophobic backbone polymers with end-functionalised PEO, by macromonomer copolymerisation, and by anionic graft polymerisation of EO onto polymer backbones carrying functional groups as initiator precursors. The graft copolymers are amphiphilic and were shown to accumulate at surfaces and interfaces in solution and in the solid state. Amphiphilic starch derivatives were prepared by reaction of amylose and starch with aliphatic α-epoxides.     

Dynamic Surface Tension and Adsorption/Desorption Kinetics for Mixtures on Planar Surfaces: I. Under Nonflow Conditions

The adsorption/desorption kinetics for individual polymers and polymer mixtures of the water-soluble associative polymers with molecular weights of 12, 62, and 100 kg/mol onto SiO2 planar substrate have been studied by ellipsometry at room temperature under nonflow conditions. Equations were derived to predict behaviors of the adsorption/desorption kinetics and dynamic surface tension onto planar surfaces for any times. It is shown that the desorption kinetics of the water-soluble associative polymers onto planar SiO2 surface is an irreversible process due to strong interaction between polymer molecules and an interface. Copyright 1999 Academic Press.     

The adsorption of cationic and amphoteric copolymers on glass surfaces: zeta potential measurements,adsorption isotherm determination,and FT Raman characterization

The adsorption of cationic and amphoteric copolymers onto controlled pore glass (CPG) powders has been studied by measurement of the powder particle zeta (zeta) potential, by determination of the adsorption isotherm, and by FT Raman measurements of the polymer-coated powder. The cationic polymers consisted chiefly of homopolymers of dimethyldiallylammonium chloride (DMDAAC) or copolymers of DMDAAC and acrylamide. The amphoteric polymers studied included copolymers of DMDAAC and acrylic acid. The comonomer ratio was varied to explore the dependence of cationic charge density on the extent and effect of adsorption. Both types of polymers adsorb onto the anionic glass surface via an ion-exchange mechanism. Consequently, a correspondingly higher mass of a low-charge-density copolymer adsorbs than of a cationic homopolymer. The presence of the anionic portion in the amphoteric polymers does not significantly alter this picture. The zeta potential, however, reflects the overall nature of the polymer. Cationic polymers effectively neutralize the glass surface, while amphoteric polymers leave the zeta potential net negative. Adsorption isotherms, determined via the depletion technique using colloidal titration, were used to "calibrate" a FT Raman method. The latter was used to determined the amount of adsorbed polymer under solution conditions in which colloidal titration could not be performed.     

Novel acrylonitrile-based copolymers containing phospholipid moieties: synthesis and characterization

Novel acrylonitrile-based copolymers containing phospholipid moieties were synthesized by a three-step process, which included the copolymerization of acrylonitrile and 2-hydroxyethyl methacrylate (HEMA) in water and the reaction of the resulting poly[acrylonitrile-co-(2-hydroxyethyl methacrylate)]s (PANCHEMA) with 2-chloro-2-oxo-1,3,2-dioxaphospholane (COP) followed by the ring-opening reaction of COP with trimethylamine. The chemical structure of PANCHEMA and the phospholipid-containing acrylonitrile-based copolymers (PLCANCP) was analyzed with FT-IR spectroscopy, (1)H and (31)P NMR, and XPS. Surface properties of the studied copolymers were evaluated by the pure water contact angle, protein adsorption and platelets adhesion measurements. The water contact angle measured by sessile drop method decreased for the polymers in the following sequence: PAN, PANCHEMA, and PLCANCP. The adsorption amount of bovine serum albumin and the adhesive number of platelet followed the same decline sequence. These results demonstrate that the biocompatibility of the acrylonitrile-based copolymer membranes could be improved efficiently by the introduction of phospholipid moieties.     

Controlling the assembly of nanoparticle mixtures with two orthogonal polymer complexation reactions

Self-assembly from mixed dispersions of three sizes of monodisperse polystyrene nanoparticles, large (L), medium (M), and small (S), was controlled by coating each particle type with either a monofunctional or bifunctional polymer capable of participating in specific complexation reactions. The complexation reactions were (1) complexation between phenolic polymers and polyethylene glycol (PEG) containing polymers and (2) condensation of phenylboronic acid containing polymers with polyols. These complexation reactions function independently and can be "turned off" independently; phenylboronic acid complexation was reversed by lowering the pH, whereas the interactions of phenolic copolymers with PEG copolymers could be reversed by adding excess PEG homopolymer. The specificity and reversibility of the interactions was demonstrated by the formation of simple binary aggregates from mixtures. The bifunctional copolymers were poly(vinyl phenol-co-diallyldimethyl ammonium chloride), Ph-DADMAC, and poly(3-acrylamide phenylboronic acid-co-PEG methacrylate), PBA-PEG. The monofunctional polymer was polyvinylalcohol, PVA. Ph-DADMAC forms complexes with PBA-PEG (H-bonding) and with anionic surfaces or polymers (electrostatic/polyelectrolyte complexation). PBA-PEG complexes with Ph-DADMAC (H-bonding) and with PVA (boronate ester formation). PVA does not interact with Ph-DADMAC; therefore, PVA coated particles do not deposit onto Ph-DADMAC coated particles.     

Highly protein-resistant coatings from well-defined diblock copolymers containing sulfobetaines

Three well-defined diblock copolymers of poly(sulfobetaine methacrylate) [poly(SBMA)] and poly(propylene oxide) (PPO) were synthesized by the sequential addition of SBMA monomer to fixed amounts of PPO using an atom transfer radical polymerization method and varying poly(SBMA) lengths. These copolymers were characterized by 1H NMR and aqueous gel permeation chromatography. These copolymers were physically adsorbed onto a surface plasmon resonance (SPR) sensor surface covered by methyl-terminated self-assembled monolayers, followed by the in situ evaluation of protein adsorption on the adsorbed copolymers. It is found that the behavior of the protein adsorption depends on the molecular weight of the copolymers. Results show that the diblock copolymers containing poly(SBMA) can be highly protein resistant when surface SBMA densities are well controlled. Thus, copolymers containing zwitterionic groups are ideal for resisting protein adsorption when the surface density of zwitterionic groups is controlled.     

Preparation and properties of some water-soluble,comb-shaped,amphiphilic polymers

Water-soluble comb-shaped polymers were prepared through grafting of poly(ethylene glycol) monomethyl ethers (MPEG) onto acrylic and methacrylic ester copolymers by transesterification reactions. The grafting was alkali-catalyzed, and performed in refluxing toluene solution or in melt at 155°C. The grafting efficiency was found to be on the order of 1 graft/10 monomer units. Epoxy groups in glycidyl methacrylate copolymers were also utilized for grafting. The crude graft copolymers were purified through chromatography and characterized by NMR and IR spectroscopy. Polymers prepared from MPEG 2000 were crystalline with melting points 10–15°C lower than the MPEG used. All polymers were shown to be surface active with CMC on the order of 1.5 g/L, and surface tensions of 38–45 dyn/cm. When used as emulsifiers the graft copolymers containing bulky lipophilic ester groups (2-ethylhexyl t-butyl) gave oil-in-water (o/w) and water-in-oil (w/o) emulsions from xylene/water with higher stability than those containing straight chain ester groups (methyl nbutyl n-docecyl). The most stable emulsions were obtained by dissolving the polymers in the organic phase.     

Thermally Regenerable Ion-Exchange Resins by Photografting

Crosslinked polymer beads containing regions of acidic and basic groups are the preferred structures for the efficient operation of a thermally regenerable ion-exchange process. Such systems can be prepared by various methods. Here the approach of using polymers and copolymers containing photo-labile groups as grafting sites is described. The polymers studied were polytriallylamine hydrochloride (polyTAA) and copolymers of propyldiallylamine hydrochloride (PDAA) and allyl benzoin methyl ether (ABME), of ABME and acrylic acid (AA), and of ABME and methyl acrylate (MA). The maximum amount of photografting of MA onto polyTAA was 12%. Very little photografting of MA onto PDAA:ABME copolymers was obtained. Photografting of TAA to AA:ABME and to MA:ABME copolymers occurred readily by using radiation of 360 nm wavelength, with the best yields of photografted polymer being about 60% when a MA:ABME copolymer was irradiated in a suspension. The effect of suspending medium, stirring rate, irradiation time, irradiation intensity, solvent, solids concentration, percentage of ABME in the MA:ABME copolymer, additional crosslinkers, surfactants, and the acid:base ratio in the hy-drolyzed resin prepared by photografting TAA onto MA:ABME copolymers on the yield, physical strength, shape, and ion-exchange properties of the resins is reported.     

Adsorption of comb copolymers on weakly attractive solid surfaces

In this work continuum and lattice Monte Carlo simulation methods are used to study the adsorption of linear and comb polymers on flat surfaces. Selected polymer segments, located at the tips of the side chains in comb polymers or equally spaced along the linear polymers, are attracted to each other and to the surface via square-well potentials. The rest of the polymer segments are modeled as tangent hard spheres in the continuum model and as self-avoiding random walks in the lattice model. Results are presented in terms of segment-density profiles, distribution functions, and radii of gyration of the adsorbed polymers. At infinite dilution the presence of short side chains promotes the adsorption of polymers favoring both a decrease in the depletion-layer thickness and a spreading of the polymer molecule on the surface. The presence of long side chains favors the adsorption of polymers on the surface, but does not permit the spreading of the polymers. At finite concentration linear polymers and comb polymers with long side chains readily adsorb on the solid surface, while comb polymers with short side chains are unlikely to adsorb. The simple models of comb copolymers with short side chains used here show properties similar to those of associating polymers and of globular proteins in aqueous solutions, and can be used as a first approximation to investigate the mechanism of adsorption of proteins onto hydrophobic surfaces.     

Electrostatic self-assembly of PEG copolymers onto porous silica nanoparticles

A critical requirement toward the clinical use of nanocarriers in drug delivery applications is the development of optimal biointerfacial engineering procedures designed to resist biologically nonspecific adsorption events. Minimization of opsonization increases blood residence time and improves the ability to target solid tumors. We report the electrostatic self-assembly of polyethyleneimine-polyethylene glycol (PEI-PEG) copolymers onto porous silica nanoparticles. PEI-PEG copolymers were synthesized and their adsorption by self-assembly onto silica surfaces were investigated to achieve a better understanding of structure-activity relationships. Quartz-crystal microbalance (QCM) study confirmed the rapid and stable adsorption of the copolymers onto silica-coated QCM sensors driven by strong electrostatic interactions. XPS and FT-IR spectroscopy were used to analyze the coated surfaces, which indicated the presence of dense PEG layers on the silica nanoparticles. Dynamic light scattering was used to optimize the coating procedure. Monodisperse dispersions of the PEGylated nanoparticles were obtained in high yields and the thin PEG layers provided excellent colloidal stability. In vitro protein adsorption tests using 5% serum demonstrated the ability of the self-assembled copolymer layers to resist biologically nonspecific fouling and to prevent aggregation of the nanoparticles in physiological environments. These results demonstrate that the electrostatic self-assembly of PEG copolymers onto silica nanoparticles used as drug nanocarriers is a robust and efficient procedure, providing excellent control of their biointerfacial properties.     

Surface modification of polyethylene terephthalate using PEO-polybutadiene-PEO triblock copolymers

The initial step of thrombus formation on blood-contacting biomaterials is known to be adsorption of blood proteins followed by platelet adhesion. It is generally accepted that surface modification of the biomaterials with poly(ethylene oxide) (PEO) substantially reduces protein adsorption and cell adhesion. Dacron® (polyethylene terephthalate) fabric, which is one of the biomaterials commonly used in blood-contacting devices, was grafted with PEO. A simple two-step procedure for covalent grafting of PEO onto the surface of Dacron® fabric was used. The surface was first treated with PEO-polybutadiene-PEO (PEO-PB-PEO) triblock copolymer, to introduce a layer of double bonds onto the surface. The Dacron® surface was then exposed to a solution of Pluronic® F108 (PF108), a commercially available PEO-poly(propylene oxide)-PEO (PEO-PPO-PEO) triblock copolymer. The surface with two adsorbed layers of PEO-PB-PEO and PF108 was γ-irradiated in the presence of PF108 in the bulk solution for a total radiation dose of 0.8 Mrad. The bulk concentrations of PEO-PB-PEO and PF108 were varied to maximize the efficiency of PEO grafting. Fibrinogen adsorption on PEO-grafted surfaces was reduced more than 90%, compared with that on control surfaces, irrespective of the bulk concentrations of polymers used for grafting. Platelet adhesion was also reduced substantially by PEO grafting. Only a few round platelets were able to adhere to the PEO-grafted surface, while the control surface was fully covered with aggregates of activated platelets. PEO grafting on polyethylene terephthalate using PEO-PB-PEO and PEO-PPO-PEO block copolymers is a simple approach that can be used for various other biomaterials.     

Adsorptionsuntersuchungen an Organokieselsäurepolymeren

Adsorption Studies on Organosilic Acid Polymers We present four organosilic acid polymers containing double-4-ring silicate units cross-linked at different degree by different organosilicon bridges. BET surfaces were determined and adsorption isotherms of n-hexane, benzene, nitrogen and water were measured. All polymers are hydrophobic, one of them behaves microporously, the other are unporous. With organic adsorptives, swelling and adsorption occur simultaneously. Possible relations of microporosity and structure are discussed.     

Preparation of thin surface layers by grafting of PEO

We have developed a two‐stage process to graft poly(ethylene oxide) (PEO) onto a silica surface. In the first stage the adsorption of an anchor reactive polymer to the surface is carried out, and in the second stage the grafting of compatibilizing macromolecular tails is performed via the reactions of functional groups of the polymer anchored. Random copolymers of styrene and maleic anhydride (SM) were chosen as reactive anchoring polymers. The kinetics of adsorption of SM from dilute solutions onto the silica surface as well as the grafting of PEO to SM macromolecules adsorbed was experimentally investigated by null ellipsometry. A model of the structure at the surface is proposed.