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Abstract

Water-soluble triblock copolymers of Poly(ethylene oxide) and Poly(propylene oxide) (PEOn–PPOm–PEOn) are nonionic amphiphilic macromolecules, commercially available under the names of Pluronics and Poloxamers. Recently interest has been focused on studying their roles in reducing nonspecific protein adsorption and cell adhesion on biomaterial/biosensor surfaces. Although the ability of the adsorbed PEO–PPO–PEO triblock copolymer to reduce protein adsorption has been observed frequently, its detailed mechanism of functioning is yet to be clarified. In order to delineate this detailed mechanism, one first needs to know the adsorption behavior of Pluronics on various substrates. Although gold is a commonly used substrate for the probes of various biosensors, there is no direct data reporting the adsorption behavior of Pluronics on it. In this study, we use surface plasma resonance (SPR) technique and Ellipsometry to detect the adsorption isotherms of various Pluronics on a gold surface. The adsorption isotherm of Pluronics of P103, P104 and F108 all exhibit two plateaus that corresponding to the desorption of the EO and the micellization in bulk solution. At bulk concentration of 1×10−2mg/ml, the total adsorbed amount of the copolymer increases with the increase of the molar mass of the polymer and with the decrease of the EO/PO ratio that suggests the strong influence of the hydrophobic PPO on the adsorbed amount of the polymer. At the CMC, the plateau value of adsorbed amount of Pluronics on Au is independent of molar mass and EO/PO ratio of copolymer. Protein adsorption on gold surfaces modified with various Pluronics shows good correlation between the amounts of protein adsorbed and the value of the reduced surface coverage, σ* of the Pluronic adlayer. In general, by increasing σ*, the nonspecific adsorption of human serum albumin can be reduced.

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... nm has been observed for normal Pluronic adsorbed on the gold surface. 18 The distribution of copolymer on the surface is randomly, and the surface coverage of copolymer at this regime could be different so that the local concentration of copolymer is therefore considered in this investigation. ...
... Importantly, for PEO blocks to be fully extended into aqueous solution, the adsorbed layer of Pluronic has to pass a transition zone of the flatly adsorbed PEO segments. 18 The film thickness for this transition zone could be up to a few nanometers, 18 while the adsorbed layer of copolymer in this model is only a few Angstroms due to the chosen limited number of copolymer molecules. The flat adsorption of triblock copolymer observed in current work can yield to an assumption that the adsorbed film on each iron surface still stay in the transition zone. ...
... Importantly, for PEO blocks to be fully extended into aqueous solution, the adsorbed layer of Pluronic has to pass a transition zone of the flatly adsorbed PEO segments. 18 The film thickness for this transition zone could be up to a few nanometers, 18 while the adsorbed layer of copolymer in this model is only a few Angstroms due to the chosen limited number of copolymer molecules. The flat adsorption of triblock copolymer observed in current work can yield to an assumption that the adsorbed film on each iron surface still stay in the transition zone. ...
Article
Although a number of experiments have been attempted to investigate the lubrication of aqueous copolymer lubricant, which is applied widely in metalworking operations, a comprehensive theoretical investigation at atomistic level is still lacking. This study addresses the influence of loading pressure and copolymer concentration on the structural properties and tribological performance of aqueous copolymer solution of polypropylene oxide - polyethylene oxide - polypropylene oxide (PPO-PEO-PPO) at mixed lubrication using a molecular dynamic (MD) simulation. An effective interfacial potential, which has been derived from density functional theory (DFT) calculations, was employed for the interactions between the fluid's molecules and iron surface. The simulation results have indicated that the triblock copolymer is physisorption on iron surface. Under confinement by iron surfaces, the copolymer molecules form lamellar structure in aqueous solution and behave differently from its bulk state. The lubrication performance of aqueous copolymer lubricant increases with concentration, but the friction reduction is insignificant at high loading pressure. Additionally, the plastic deformation of asperity is dependent on both copolymer concentration and loading pressure, and the wear behavior shows a linear dependence of friction force on the number of transferred atoms between contacting asperities.
... It is important that the surfactant is adsorbed onto solid surfaces to perform its functions. Research on adsorption have been carried out by employing several experimental approaches including ellipsometry [2][3][4], atomic force microscopy (AFM) [5,6], X-ray reflectometry (XRR) [5], optical waveguide lightmode spectroscopy(OWLS) [1], surface plasmon resonance(SPR) [2,[6][7][8][9] and quartz crystal micro gravimetry (QCM) [7]. ...
... It is important that the surfactant is adsorbed onto solid surfaces to perform its functions. Research on adsorption have been carried out by employing several experimental approaches including ellipsometry [2][3][4], atomic force microscopy (AFM) [5,6], X-ray reflectometry (XRR) [5], optical waveguide lightmode spectroscopy(OWLS) [1], surface plasmon resonance(SPR) [2,[6][7][8][9] and quartz crystal micro gravimetry (QCM) [7]. ...
... Moreover, a more significant adsorption occurred on hydrophobic surfaces than that on hydrophilic surface. The copolymer with a higher hydrophobic content had higher adsorption rates on hydrophobic surface [1,2,8]. As the concentration increased, the adsorbed amount of the copolymer increased and reached the maximum near the critical micelle concentration (CMC) [3,4,6,9]. ...
Article
Full-text available
This paper investigates the adsorption behavior of triblock copolymer Poly (propylene oxide)-poly (ethylene oxide)-poly (propylene oxide), PPO-PEO-PPO on silicon and iron surfaces by using the contact angle goniometer, spectroscopic ellipsometer and atomic force microscopy (AFM). After adsorption, the decrease of water contact angle was observed on each surface; and a larger reduction of water contact angle occurred on the surface covered by the copolymer film with longer and higher weight percent of hydrophilic PEO block. This means that the PEO block may be on the top of the adsorbed copolymer film. The film thickness measurement shows that the copolymer with longer and higher weight percent of PPO block forms a thicker film on the hydrophobic surface, which suggests that the hydrophobic PPO block of the copolymer in the aqueous solution plays the main role during the adsorption of PPO-PEO-PPO onto the hydrophobic surface. It has been found from the AFM results that the roughness of the surface decreased after adsorption and the smoother topography was observed on the surface adsorbed by a thicker adsorbed film.
... Also, more detailed, it has to be taken into the account that protein-resistant characteristics of PEO-PPO-PEO coated surface have been attributed to the low interfacial free energy of the polyethylene-oxide chains with water; their unique solution properties and molecular conformation in aqueous solution; their hydrophilicity and high surface mobility; as well as steric stabilization effects [95]. According to literature data [96][97][98][99] effects of PEO-PPO-PEO on protein adsorption depends also on the macromolecular architecture of the adsorbed molecules. In order to characterize molecular structure of the adsorbed pluronic molecules Baranowski and Whitemore [100] proposed a theoretical model of reduced surface coverage (σ*). ...
... In order to characterize molecular structure of the adsorbed pluronic molecules Baranowski and Whitemore [100] proposed a theoretical model of reduced surface coverage (σ*). The higher the adsorption of PEO-PPO-PEO on the surface of NP is, the larger the value of σ* is [99,100]. According to Owens III and Peppas [85] at low surface coverage, the chains have a larger range of motion and will typically take on what is termed a "mushroom" configuration, where on average they will be located closer to the surface of the particle, while on the other hand at higher surface coverage the chain range of motion will be greatly restricted and they will most often exhibit a semi-linear or "brush" configuration. ...
... Namely, reduced surface coverage σ*≤2 implies lower surface coverage where PEO segments of PEO-PPO-PEO are fully extended and forms mushroom structure on the surface, while if 2≤σ*≤20 the polymers begin to stretch away from the surface and the structure of the adsorbed molecule turn into a "brush form" [100]. In general by increasing the surface coverage the non specific protein adsorption can be reduced [99,102] thus enabling NP prolonged circulation time. Details for calculation of σ* are given elsewhere [99,100]. ...
Thesis
Modified nanoprecipitation method was developed and used for improved incorporation of hydrophilic drug (irinotecan hydrochloride) into the PLGA/PEO-PPO-PEO blended and blended/ adsorbed nanoparticles. OPLS analyses on preliminary experiments and one factor at a time (OFAT) variation experiments pointed to significant variables influencing encapsulation efficiency, drug content and particle size. OFAT experiments were conducted with a rationale of determination of key formulation factors (concentration and volume of drug solution, evaporation rate and PEO-PPO-PEO/PLGA ratio) influencing physico-chemical and biopharmaceutical nanoparticle properties (particle size and size distribution, encapsulation efficiency, drug content, zeta potential, drug dissolution rate, as well as protein binding capacity). The insight of in vivo behavior of prepared nanoparticles and their potential for effective anticancer treatment was gained by performing biodistribution and cell culture studies in the frame of early formulation development stage i.e. as part of OFAT experiments. Prepared nanoparticles were characterized with mean particle size of 112-125 nm, with narrow unimodal distribution (PDI~0.1), encapsulation efficiency of 32-63% and drug content of 0.2-1.51%, as well as controlled release properties related to the influence of tested formulation factors. Structural information for the studied nanoparticles was obtained using DSC and FT-IR spectroscopy. Zeta potential values indicated that presence of PEO-PPO-PEO in the formulations shielded the high surface negative charge of PLGA. PEO-PPO-PEO surface coverage of blended as well as blended/adsorbed nanoparticles depended upon amount of used PEO-PPO-PEO during preparation procedure and was related to the protein resistant characteristics of nanoparticles. Results from in vivo studies evidenced prolonged blood circulation time of the prepared nanoparticles, while cell culture studies indicated higher in vitro bioefficacy compared to free drug. Performed experiments defined possible design space and justified further optimization of formulation using experimental design studies. Well-designed experiments, carefully planned and thought out from the outset of formulation development, produced quality data from an early stage, which minimized lengthy and costly repetition of manufacturing and subsequent studies and analysis during formulation optimization. Central composite design (CCD) was used to follow the influence of PEO-PPO-PEO/ PLGA ratio, initially added/ subsequently adsorbed PEO-PPO-PEO ratio, as well as IR-HCl quantity on particle size, drug content, drug dissolution (burst release and amount of drug released after 24h), PEO-PPO-PEO quantity in PLGA/ PEO-PPO-PEO blended and blended/ adsorbed nanoparticles. CCD was applied with rationale of identification of statistically significant variables, establishment of mathematical correlation and further formulation optimization. Formulation optimization indicated that nanoparticles with desired physico-chemical and biopharmaceutical properties could be produced, thus resulting by formulation with potential for selective drug targeting, controlled drug release at the site of action, enhancement of therapeutic efficacy and lower side effects in the treatment of cancer disease.
... This means that, in vivo, most likely PEO-PPO-PEO adlayer adsorbed onto the NPs would efficiently reduce and block plasma protein adsorption onto the NP surface, decreasing recognition by RES and thus prolonging blood circulation of NPs and favoring their EPR effect (Owens and Peppas, 2006;Santander-Ortega et al., 2007). PEO-PPO-PEO according to literature data (Brandani and Stroeve, 2003;Inami et al., 1999;Lazos et al., 2005;Liou and Tsay, 2011) effects of PEO-PPO-PEO on protein adsorption depends also on the macromolecular architecture of the adsorbed molecules. In order to characterize molecular structure of the adsorbed poloxamer molecules Baranowski and Whitmore (1995) proposed a theoretical model of reduced surface coverage (r à ). ...
... In order to characterize molecular structure of the adsorbed poloxamer molecules Baranowski and Whitmore (1995) proposed a theoretical model of reduced surface coverage (r à ). The higher the adsorption of poloxamer on the surface of NP, the larger the value of r à ( Baranowski and Whitmore, 1995;Liou and Tsay, 2011). ...
... Namely, r à 6 2 implies lower surface coverage where PEO segments of PEO-PPO-PEO are fully extended and form mushroom structure on the surface, while if 2 6 r à 6 20 the polymers begin to stretch away from the surface and the structure of the adsorbed molecule turn into a ''brush form'' (Baranowski and Whitmore, 1995). In general by increasing the surface coverage the nonspecific protein adsorption can be reduced (Liou and Tsay, 2011;Moghimi and Szebeni, 2003) thus enabling NP prolonged circulation time. Details for calculation of r à are given elsewhere (Baranowski and Whitmore, 1995;Liou and Tsay, 2011). ...
Article
Modified nanoprecipitation method was used for improved incorporation of hydrophilic drug (irinotecan hydrochloride) into the PLGA/PEO-PPO-PEO blended and blended/adsorbed nanoparticles. One factor at a time (OFAT) variation experiments were conducted in order to determine key formulation factors (concentration and volume of drug solution, evaporation rate and PLGA/PEO-PPO-PEO ratio) influencing nanoparticle properties (particle size and size distribution, encapsulation efficiency, drug content, zeta potential, drug dissolution rate, as well as protein binding capacity). The insight of in vivo behavior of prepared nanoparticles and their potential for effective anticancer treatment was gained by performing biodistribution and cell culture studies as part of OFAT experiments. The mean particle size, mainly dependent upon PLGA/PEO-PPO-PEO ratio, was in the range of 112-125nm, with narrow unimodal distribution (PDI∼0.1). Encapsulation efficiency (32-63%) was impacted from evaporation rate and PLGA/PEO-PPO-PEO ratio. Drug content (0.2-1.51%) and controlled release properties were related to the influence of all tested formulation factors. Structural information for the studied nanoparticles was obtained using DSC and FT-IR spectroscopy. Zeta potential values indicated that presence of PEO-PPO-PEO in the formulations shielded the high surface negative charge of PLGA. PEO-PPO-PEO surface coverage of PLGA/PEO-PPO-PEO blended as well as blended/adsorbed nanoparticles depended upon amount of used PEO-PPO-PEO during preparation procedure and was related to the protein resistant characteristics of nanoparticles. Results from in vivo studies evidenced prolonged blood circulation time of the prepared nanoparticles, while cell culture studies indicated higher in vitro bioefficacy compared to free drug. Performed experiments defined possible design space and justified further optimization of formulation using experimental design studies.
... This means that, in vivo, most likely PEO-PPO-PEO adlayer adsorbed onto the NPs would efficiently reduce and block plasma protein adsorption onto the NP surface, decreasing recognition by RES and thus prolonging blood circulation of NPs and favoring their EPR effect (Owens and Peppas, 2006;Santander-Ortega et al., 2007). PEO-PPO-PEO according to literature data (Brandani and Stroeve, 2003;Inami et al., 1999;Lazos et al., 2005;Liou and Tsay, 2011) effects of PEO-PPO-PEO on protein adsorption depends also on the macromolecular architecture of the adsorbed molecules. In order to characterize molecular structure of the adsorbed poloxamer molecules Baranowski and Whitmore (1995) proposed a theoretical model of reduced surface coverage (r à ). ...
... In order to characterize molecular structure of the adsorbed poloxamer molecules Baranowski and Whitmore (1995) proposed a theoretical model of reduced surface coverage (r à ). The higher the adsorption of poloxamer on the surface of NP, the larger the value of r à ( Baranowski and Whitmore, 1995;Liou and Tsay, 2011). ...
... Namely, r à 6 2 implies lower surface coverage where PEO segments of PEO-PPO-PEO are fully extended and form mushroom structure on the surface, while if 2 6 r à 6 20 the polymers begin to stretch away from the surface and the structure of the adsorbed molecule turn into a ''brush form'' (Baranowski and Whitmore, 1995). In general by increasing the surface coverage the nonspecific protein adsorption can be reduced (Liou and Tsay, 2011;Moghimi and Szebeni, 2003) thus enabling NP prolonged circulation time. Details for calculation of r à are given elsewhere (Baranowski and Whitmore, 1995;Liou and Tsay, 2011). ...
Article
Abstract Modified nanoprecipitation method was used for improved incorporation of hydrophilic drug (irinotecan hydrochloride) into the PLGA/PEO-PPO-PEO blended and blended/ adsorbed nanoparticles. One factor at a time (OFAT) variation experiments were conducted in order to determine key formulation factors (concentration and volume of drug solution, evaporation rate and PLGA/PEO-PPO-PEO ratio) influencing nanoparticle properties (particle size and size distribution, encapsulation efficiency, drug content, zeta potential, drug dissolution rate, as well as protein binding capacity). The insight of in vivo behavior of prepared nanoparticles and their potential for effective anticancer treatment was gained by performing biodistribution and cell culture studies as part of OFAT experiments. The mean particle size, mainly dependent upon PLGA/PEO-PPO-PEO ratio, was in the range of 112-125 nm, with narrow unimodal distribution (PDI∼0.1). Encapsulation efficiency (32-63%) was impacted from evaporation rate and PLGA/PEO-PPO-PEO ratio. Drug content (0.2-1.51%) and controlled release properties were related to the influence of all tested formulation factors. Structural information for the studied nanoparticles was obtained using DSC and FT-IR spectroscopy. Zeta potential values indicated that presence of PEO-PPO-PEO in the formulations shielded the high surface negative charge of PLGA. PEO-PPO-PEO surface coverage of PLGA/PEO-PPO-PEO blended as well as blended/adsorbed nanoparticles depended upon amount of used PEO-PPO-PEO during preparation procedure and was related to the protein resistant characteristics of nanoparticles. Results from in vivo studies evidenced prolonged blood circulation time of the prepared nanoparticles, while cell culture studies indicated higher in vitro bioefficacy compared to free drug. Performed experiments defined possible design space and justified further optimization of formulation using experimental design studies.
... The micellization process of Pluronics can be also interpreted as a minimization of the surface tension between the hydrophobic PO middle blocks and the surrounding water using only their surfactant properties [232]. Besides their initial use as detergents, emulsi ers, foaming agents and dispersants [54,32,33], Pluronics are used nowadays as coatings for the preparation of highly functionalized surfaces for biological applications [204,233,234,235,236] or as colloidal stabilizers [237,238,239]. ...
... The resulting layer thickness would be close to the hydrodynamic radius of one micelle. Yet, the majority of experimental [235,249,251] and theoretical work [253] strongly suggests that the polypropylene oxide middle block is the driving force for the interaction with hydrophillic surfaces. Using a similar Pluronic variant (P103) and cleaned, polished and heat-treated gold surfaces, L et al. measured very similar layer thicknesses of 100 Å. ...
Thesis
Full-text available
This thesis aims to investigate the form-phase diagram of aqueous solutions of the triblock copolymer Pluronic P123 focusing on its high-temperature phases. P123 is based on polyethylene as well as polypropylene oxide blocks and shows a variety of di erent temperaturedependent micelle morphologies or even lyotropic liquid crystal phases in aqueous solutions. Besides the already well-studied spherical aggregates at intermediate temperatures, the size and internal structure of both worm-like and lamellar micelles, which appear near the cloud point, is determined using light, neutron and X-ray scattering. By combining the results of time-resolved dynamic light as well as small-angle neutron and X-ray scattering experiments, the underlying structural changes and kinetics of the sphere-to-worm transition were studied supporting the random fusion process, which is proposed in literature. For temperatures near the cloud point, it was observed that aqueous P123 solutions below the critical crystallization concentration gelate after several hours, which is linked to the presence and structure of polymeric surface layers on the sample container walls as shown by neutron re ectometry measurements. Using a hierarchical model for the lamellar micelles including their periodicity as well as domain and overall size, it is possible to unify the existing results in literature and propose a direct connection between the near-surface and bulk properties of P123 solutions at temperatures near the cloud point.
... These effects modify the physical and chemical properties of both molecules. However, as reported in the literature, 25 although the ability of triblock copolymers to reduce protein adsorption is known, the detailed procedure involved in this phenomenon has not yet been clarified. Other interesting studies are those concerning polymers blends such as miscible homopolymer−copolymer pair. ...
... It should be noted that electrochemical studies concerning these interactions are scarcer and the most common imply the adsorption of the triblock copolymers or the proteins in an isolated manner. [9][10][11][12][13][14][15][16]24,25 The aim of this work is to study the triblock copolymer−protein−electrode interactions from the fundamental point of view of double-layer capacitance as calculated from EIS measurements and to obtain information about the behavior and apparent size of the interface formed by the adsorbed species on a gold disc electrode at different temperatures. The information obtained from this study is important in sensor and bio-surface design based on the detection of protein liberation or a reduced protein adsorption process in micelles. ...
Article
Full-text available
The interactions of proteins and other molecules and their adsorption onto substrates is a fascinating topic that has been applied to surface technologies, biosensors, corrosion studies, biotechnologies, and other fields. The success of these applications requires a previous characterization using some analytical techniques that, ordinarily, are not electrochemical. This work proposes analyzing the variation of the double-layer capacitance obtained through impedance electrochemical spectroscopy as an alternative strategy to show evidence of the interactions between proteins and triblock copolymers. The proposal is supported through the study of the interaction and adsorption of bovine serum albumin (BSA) and a commercial triblock copolymer (P103) in phosphate buffer on a gold electrode. The double-layer capacitance and the apparent interface thickness vs polarization potential curves as well as the potential of zero charge for pure P103 (0.6 wt %, corresponding to 6 g L–1), pure BSA (3 mg mL–1), and P103-BSA solutions (0.6 wt % and 3 mg mL–1, respectively) are sensitive enough to show not only the interaction and the adsorption of the species but also the polarization potential where these interactions are taking place. A qualitative and quantitative analysis concerning the double-layer capacitance behavior is given. The significance and impact of this work is also presented.
... 5 the ratio of the PEO amount required to completely cover the particle surface to the total amount of PEO present (i.e., 50% of Pluronic P105) at the csmc (R PEOr/PEOa ) vs. the particle surface area concentration. The PEO amount required to cover the particle surface was calculated by taking each block copolymer molecule to occupy about 3 nm 2 surface area [52].Fig. 5 presents three important features: (i) R PEOr/PEOa increases exponentially with increasing surface area concentration; (ii) R PEOr/PEOa can exceed unity; and (iii) R PEOr/PEOa values for different particle sizes (SM, HS, and TM) fall on the same line. ...
... The more likely Pluronic P105 adsorbed layer structure onto silica nanoparticles has been selected by comparing the experimentally observed adsorbed amount with the adsorbed polymer amount estimated considering three models of different organization: (i) single polymer layer, (ii) spherical micelles, or (iii) hemi-micelles. The amount of Pluronic P105 required to form a single layer on particle surfaces is about 3.5 mg/m 2 , assuming each block copolymer molecule to occupy 3.0 nm 2 area [52] (obtained from adsorption isotherm studied by ellipsometry) which is lower than the actual amount of Pluronic P105 on the particle (8 mg/m 2 ). This, together with the adsorbed layer hydrophobic environment, indicates that there is a little possibility of forming a single adsorbed polymer layer onto nanoparticles. ...
Article
Polymers on the surface of nanoparticles are of great scientific and technological importance since they dictate many important properties and functions of dispersed systems. We investigate here the organization of a representative poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) block copolymer on silica nanoparticles dispersed in water. Pluronic P105 (EO36PO56EO36) adsorbs on protonated silica and starts forming hydrophobic domains above a certain bulk polymer concentration, called critical surface micelle concentration (csmc), which is lower than the critical micelle concentration (cmc) of Pluronic P105 in plain water. The csmc decreases with increasing particle concentration and decreasing particle size. Below its csmc, the PEO–PPO–PEO block copolymer adsorption on protonated silica nanoparticles is similar to the adsorption of PEO homopolymers. Above the csmc, the block copolymers form micelle-like aggregates on protonated silica nanoparticles, as suggested by the adsorbed layer thickness, adsorbed polymer amount, and presence of hydrophobic domains.
... Reports in literature discuss the adsorption of PEO-PPO-PEO pluronic block copolymers (PBP) on different surfaces like polypropylene, polyethylene, poly(ethylene terephthalate), polystyrene, clay, nylon, cellulose, and gold [7][8][9][10]. Liu et al. [7] investigated the adsorption of P105 on different surfaces using AFM and concluded that, on hydrophilic surfaces, adsorption of spherical micellar structures occurred, whereas, on the more hydrophobic surfaces, featureless adsorbed layer structures, likely from dangling EO brushes were observed. ...
Article
Full-text available
The diffusion and adsorption behaviors of a few PEO-PPO-PEO type triblock copolymers, namely, Pluronics® L62, L64, F68, F87, and F88 at solid-liquid and liquid-liquid interfaces is investigated using water penetration through packed PTFE powder, dynamic surface tension (DST), interfacial tension (IFT), dynamic light scattering (DLS), and contact angle measurements. The water penetration and DST data reveal that the diffusivity of these block copolymers to the interface decreases with increase in the PEO molecular weight of the polymer and is governed by adsorption of surfactant molecules at the interface through PPO blocks. The DST and IFT results reveal faster diffusion to the interface for low molecular L62 and L64. The adsorption behaviors at isopropyl myristate (IPM)-water and PTFE-water interfaces are in good agreement, where lower molecular weight and lower PEO content favor the faster diffusion kinetics. The size of the formed emulsion droplets in presence of different surfactant molecules is measured using DLS, which shows bigger emulsion droplet size for high molecular weight and PEO containing polymer F88. Thus, it was found that surfactant having lower DST will result in higher wettability, lower contact angle, and lower interfacial tension. Graphical abstractᅟ
... In physisorption, nonfouling materials are typically tethered to a surface via conjugating of the nonfouling polymer chains to an anchoring group. For example, synthetic block copolymers of PEO-PPO-PEO (Fig. 11.5a) have been shown to reduce protein adsorption via the physisorption of the PPO anchoring group to the hydrophobic surfaces [50,51]. Surface modification via physisorption usually has difficulty in reducing the protein adsorption below a certain limit because the adsorbed chain density is limited by the steric issue and the binding strength is not robust enough. ...
Chapter
The development of a nonfouling surface is a major challenge in biomaterials. It is well known that nonspecific protein adsorption could activate thrombosis coagulation, elicit inflammatory responses, cause adverse effects on the healing process for medical implants, and often increase the risk of infection. The development of nonfouling materials thus has a wide range of biomedical applications. Obtaining an antifouling surface requires the use of materials with an intrinsic nonfouling chemical nature and with appropriate physical properties. It is generally accepted that the nonfouling properties of a material are closely related to the hydration behavior of the materials. A nonfouling material should be neutral in charge and contain hydrophilic polar functional groups. There are three types of nonfouling materials, all with superior protein-resistant ability, categorized herein, including nonionic hydrophilic materials, zwitterionic materials, and amphiphilic materials. In addition to chemical factors, the physical factors of surface packing and surface homogeneity of a material also play important roles in determining the antifouling performance of a surface. Finding an appropriate coating method to ensure the optimized physical properties of a surface is also crucial in the development of an antifouling surface.
Article
Triblock Pluronics of polyoxyethylene (PEO) and polyoxypropylene (PPO) are identified as competent suppressors for copper (Cu) electroplating in advanced electronics manufacturing. However, the specific interfacial roles of PEO and PPO blocks in Pluronic suppressors, are not yet fully understood, which is crucial for the rational design of effective suppressors. Herein, the influences of composition and block arrangement of such Pluronics on the inhibition against Cu plating are systematically investigated. The decrease in Cu deposition mass with increasing PPO content suggests that the PPO blocks are the main contributor to the inhibition strength of Pluronics, as demonstrated by the positive correlation between electrodeposited Cu mass and hydrophilic-lipophilic balance (HLB) value. Comparative analysis of normal and reverse Pluronic pairs with similar compositions indicates that an adequately long PEO block is indispensable to maintain the inhibition stability of Pluronics. Moreover, electrochemical attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) offers direct evidence that the PEO block, rather than the PPO block, compactly adsorbs on the chloridion (Cl−) adlayer covered Cu surface. This work highlights the importance of balancing the PPO-dominated inhibition strength and the PEO-dominated inhibition stability in the design of practical copolymer suppressors, for which the HLB may serve a valuable indicator, together with the PEO block length.
Article
Protein therapeutics are exposed to various surfaces during product development, where their adsorption possibly causes unfolding, denaturation, and aggregation. In this paper, we aim to characterize four types of typical surfaces used in the development of biologics: polycarbonate, polyethersulfone, borosilicate glass, and cellulose. Contact angles of these surfaces were measured using three probing liquids: water, formamide, and diidomethane, from which acid/base (AB) and Lifshitz-van der Waals (LW) interaction components were derived. To explore the interactions of surfactants of Pluronics/Poloxamers (PEO-PPO-PEO copolymers) with these surfaces, the adsorption of three Pluronics (F68, F127, and L44) at these surfaces was determined using a quartz crystal microbalance with dissipation technique (QCM-D). For hydrophobic surfaces without AB component (Polycarbonate and polyethersulfone), these copolymers exhibited significant adsorption with a little dissipation at low concentrations. For hydrophilic surfaces with AB component (cellulose and borosilicate), the adsorption at low surfactant concentration is low while dissipation is relatively high. Additionally, the chemical properties of Pluronnics such as the ratio of PPO to PEO, along with the interaction of PPO with surfaces were observed to play a critical role in adsorption. Furthermore, the interfacial structure of the adsorbed layer was affected by both AB interaction and the presence of PEO block.
Article
Purpose The paper aims to assess the adsorption behaviour and the adhesion strength of lubricant films formed by polypropylene oxide-polyethylene oxide-polypropylene oxide (PPO-PEO-PPO) with phosphate ester additive on Ti coated surface, and to identify the influence of molecular architecture and phosphate ester additive. Design/methodology/approach The thickness of the adsorbed PPO-PEO-PPO with phosphate ester lubricant films on Ti surfaces was measured by ellipsometry. The adhesion strength of the copolymer and the copolymer with phosphate ester lubricants was studied by the micro-scratch tests; and the scratch tracks on the surfaces were observed by AFM and SEM Findings The copolymer with a higher weight percentage of PPO not only formed a thicker film but also showed stronger adhesion and better lubrication performance. The added phosphate ester increased the film thickness and improved the tribological behaviour. The finding reveals that the adsorbed film thickness which depends on the PPO chain length and the presence of phosphate ester has a considerable effect on the scratch behaviour. Originality/value This paper fulfils the studies about adsorption behaviour and lubrication mechanism of this new lubricant which has not been adequately investigated on the metal surface.
Article
The adsorption structure of aqueous triblock copolymer polypropylene oxide-polyethylene oxide-polypropylene oxide, PPO-PEO-PPO, on the Si surface was studied using neutron reflectometer. It is found that PEO blocks formed the outer layer of the adsorbed PPO-PEO-PPO film, while PPO blocks formed the inner layer and served as the anchor blocks. The adhesion strength of adsorbed PPO-PEO-PPO copolymer film was evaluated using atomic force microscopy and scratch tests. The results revealed that the molecular structure of triblock copolymer had a considerable effect on the adhesion strength. The triblock copolymer with a longer PPO chain and a higher weight percentage of PPO exhibited stronger adhesion and better lubrication performance.
Article
The adsorption of aqueous tri-block reverse copolymer polypropylene oxide-polyethylene oxide-polypropylene oxide, PPO-PEO-PPO with phosphate ester on Ti coated surfaces have been studied using a neutron reflectometer (NR). It is found that the adsorbed film consists of two layers. The hydrophobic PPO block forms the inner layer and acts as the anchor of the adsorbed film. Copolymer with higher weight percentage of PPO forms a thicker PPO layer. Phosphate ester affects the adsorbed film structure of PPO-PEO-PPO copolymer by forming a thicker mixed-layer of PPO and phosphate ester on the Ti surface. The tribological performance of the lubricants has also been studied using a ball-on-disc tribometer. The results show that copolymer molecular structure affects lubrication performance. Tri-block copolymer with a higher weight percentage of PPO shows a better performance. The addition of phosphate ester to tri-block copolymer solution not only significantly decreases the coefficient of friction but also increases anti-wear property. The finding indicates that adsorbed film thickness depends on the size of the PPO block and the presence of phosphate ester, and that adsorbed film thickness correlates with friction.
Chapter
Surface properties hold great importance in the response of biomaterials to the host. For better host response, surface modification can be implemented. This chapter describes various methods for the surface modification applied for improving biomaterials surfaces. The surface properties of biomaterials that are important for acceptance in the host include chemical structure, hyrophilicity/hydrophobicity, the presence of ionic group, surface morphology and topography. Controlling the surface properties of biomaterials is a very important factor for their good performance. Surface properties of biomaterials define the stability and their applicability for their implant applications, for instance, in the case of fibroblast cells; the wettability of the surface should be more. The response of biomaterials to the host can be tailored using surface engineering. This chapter presents how surface films can be engineered using self-assembly (SA) or layer-by-layer deposition in order to achieve the required surface activity.
Article
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In this work, poly(ethylene terephthalate) (PET) films were treated by oxygen and helium plasmas and their chemistry and morphology were studied. Samples were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM) and water contact angle (WCA) measurements. The aging of plasma-treated PET films was studied in different media (air and water) by WCA. The anti-fouling properties of the plasma treated surfaces were evaluated by confocal microscopy. Both oxygen and helium plasma-treatments produced hydrophilic and nano-structured surfaces that presented a remarkable reduction of the bioadhesive character. Besides, the grafting of plasma treated surfaces was explored using Pluronic F108 in order to improve the anti-fouling properties of the plasma treated surfaces.
Article
Surface-active substances, which are able to organize themselves spontaneously on surfaces, triggering changes in the nature of the solid-liquid interface, are likely to influence microorganism adhesion and biofilm formation. Therefore, this study aimed to evaluate chemical non-ionic surfactants activity against pathogenic microbial biofilms and to cover biomaterial surfaces in order to obtain an anti-infective surface. After testing 11 different surfactants, Pluronic F127 was selected for further studies due to its non-biocidal properties and capability to inhibit up to 90% of biofilm formation of Gram-positive pathogen and its clinical isolates. The coating technique using direct impregnation on the surface showed important antibiofilm formation characteristics, even after extensive washes. Surface roughness and bacterial surface polarity does not influence the adhesion of Staphylococcus epidermidis, however, the material coated surface became extremely hydrophilic. The phenotype of S. epidermidis does not seem to have been affected by the contact with surfactant, reinforcing the evidence that a physical phenomenon is responsible for the activity. This paper presents a simple method of surface coating employing a synthetic surfactant to prevent S. epidermidis biofilm formation.
Article
A UV energy-controlled exposure process for the fabrication of gradient refractive index lenses was developed. In the proposed method, a V-shaped gel zone was formed in the reaction tube to prevent the formation of bubbles in the polymer matrix after photo-induced polymerization. Gel effects on the fabrication and properties of GRIN polymer rods were clarified, and the effect of concentrations of diphenyl sulfide, poly(methyl methacrylate) and photoinitiator on the optical properties of the rod lenses were investigated. A convenient method for the fabrication of gradient refractive index (GRIN) lenses via a UV energy-controlled process using a sloped UV lamp is described, and theoretically available equipment similar to the sloped UV-controlled polymerization system is also proposed.
Article
This study presents the synthesis of gold–Pluronic core–shell nanoparticles by a two-step method and investigates their biological impact on cancer cells, specifically nanoparticle internalization and cytotoxicity. Uniform, 9–10-nm-sized, hydrophobic gold nanoparticles were synthesized in organic phase by reducing gold salt with oleylamine, after which oleylamineprotected gold nanoparticles were phase-transferred into aqueous medium using Pluronic F127 block copolymer, resulting in gold–Pluronic core–shell nanoparticles with a mean hydrodynamic diameter of ~35 nm. The formation and phase-transfer of gold nanoparticles were analyzed by UV–Vis absorption spectroscopy, transmission electron microscopy, and dynamic light scattering. The obtained gold–Pluronic core–shell nanoparticles proved to be highly stable in salted solution. Cytotoxicity tests showed no modification of cellular viability in the presence of properly purified particles. Furthermore, dark-field cellular imaging demonstrated that gold–Pluronic nanoparticles were able to be efficiently uptaken by cells, being internalized through nonspecific endocytosis. The high stability, proven biocompatibility, and imaging properties of gold–Pluronic core–shell nanoparticles hold promise for relevant intracellular applications, with such a design providing the feasibility to combine all multiple functionalities in one nanoparticle for simultaneous detection and imaging.
Article
Measurements of the advancing contact angle ( ) and adsorption properties were carried out for aqueous solutions of four cationic surfactants, hexadecanol glycidyl ether ammonium chloride (C16PC), guerbet alcohol hexadecyl glycidyl ether ammonium chloride (C16GPC), hexadecanol polyoxyethylene(3) glycidyl ether ammonium chloride(C16(EO)3PC) and guerbet alcohol hexadecyl polyoxyethylene(3) glycidyl ether ammonium chloride (C16G(EO)3PC), on the polytetrafluoroethylene (PTFE) surface using the sessile drop analysis. The obtained results indicate that the contact angle decreases to a minimum with the increasing concentration for all cationic surfactants. Surfactants with branched-chain show lower values. Moreover, an increase of adhensional tension on PTFE-water interface has been observed for the four cationic surfactants, and the branched ones have larger increases of adhensional tension. It is very interesting that the sharp decrease of appears mainly after critical micelle concentration (cmc) for C16GPC, C16(EO)3PC and C16G(EO)3PC, which is quite different from traditional cationic surfactants reported in the literature. Especially for C16G(EO)3PC , there are two saturated adsorption stages on PTFE surface after cmc (which means the saturated adsorption film at air-solution interface has been formed). In the first saturated stage, the C16G(EO)3PC molecules are oriented parallel to the PTFE surface with saturated monolayer formed through hydrophobic interaction and hydrogen bond. In the second saturated stage, the hemimicelle has been formed on the PTFE surface, which can be supported by the QCM-D and SPR measurements.
Article
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Adsorption of four different poly(ethylene oxide)/poly(propylene oxide)/poly(ethylene oxide) triblock copolymers (Pluronics®) onto the hydrophobized surface of the sensor was measured by the optical waveguide lightmode spectroscopy (OWLS). Adsorbed amounts of Pluronic PE10300, PE10500, PE6400, and PE6800 determined in the concentration range of 10−10 gdm were found to follow the order of the hydrophobicity of the Pluronic compounds characterized by their hydrophil–lipophil balance (HLB) values. Wettability of two hydrophobic surfaces, the poly(lactide-co-glycolide), PLGA70/30 copolymer (used as drug carrier in pharmaceutical applications) and silylated glass, in aqueous solutions of the above Pluronics were studied by a dynamic tensiometric method. The significant increase in the wetting tension observed after the adsorption of the surfactants, and hence the decrease of the apparent contact angle as the indication of the wetting effect on both the biopolymer and the hydrophobic glass, was correlated to the poly(ethylene oxide) (PEO) content of the adsorbed layer obtained on the hydrophobized sensor surface by the OWLS method.
Article
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The ultraviolet (UV)/ozone surface cleaning method is reviewed. The UV/ozone cleaning procedure is an effective method of removing a variety of contaminants from surfaces. It is a simple‐to‐use dry process which is inexpensive to set up and operate. It can rapidly produce clean surfaces, in air or in a vacuum system, at ambient temperatures. By placing properly precleaned surfaces within a few millimeters of an ozone producing UV source, the process can produce clean surfaces in less than 1 min. The technique is capable of producing near‐atomically clean surfaces, as evidenced by Auger electron spectroscopy, ESCA, and ISS/SIMS studies. Topics discussed include: the variables of the process,the types of surfaces which have been successfully cleaned, the contaminants which can be removed, the construction of a UV/ozone cleaning facility, the mechanism of the process, UV/ozone cleaning in vacuum systems, rate enhancement techniques, safety considerations, effects of UV/ozone other than cleaning, and applications.
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This review presents piezoelectric quartz crystals as transducers suitable for development of different types of bioanalytical assays. The components of measuring systems for piezosensors are described together with providers of commercial equipment. The piezoelectric biosensors are summarized for determination of viruses, bacterial and other cells, proteins, nucleic acids and small molecules as drugs, hormones and pesticides. In addition to mass changes, some agglutination assays employing viscosity effects are addressed. Finally, the direct label-free and real-time monitoring of affinity interactions using piezosensors is presented. The theoretical background for determination of appropriate kinetic rate and equilibrium constants is shown and the approach is demonstrated on the interaction of antibody with the corresponding antigen (protein secalin). Several examples of affinity studies are provided, including interactions of proteins (antibody and antigens, receptors and ligands), nucleic acids (hybridization, intercalation of metal complexes), lipids and saccharide-based layers.
Article
The aggregation and phase behavior in water of several triblock copolymers of poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene)[(EO)x(PO)y(EO)x] has been studied. The y-values of the compounds ranged from 16 to 70 and the x:y ratios from 0.1 to 2.5. All studied compounds form micelles and lyotropic liquid crystalline phases. For a constant temperature the critical micelle concentrations (cmc) of the compounds decrease exponentially with y. The energy increment for the transfer of a PO group from the aqueous to the micellar state is about (0.25 +/- 0.05) kT. The cmc values for all compounds decrease strongly with increasing temperature. As a consequence the solutions undergo a monomer-micelle transition for constant concentration and increasing temperature. This micellization process is associated with a large endothermic heat which is linearly dependent on the size of the PO block. It is concluded that this heat is due to the dehydration of the PO groups, and it is called the heat of micellization DELTAH(m). For most of the studied compounds DELTAH(m) = 3.0 +/- 0.5 kJ/mol for one PO group. The large change of the cmc values with temperature can quantitatively be explained by the large DELTAH(m) values. The sequence of the lyotropic mesophases is mainly determined by the x:y ratio. Systems with x:y > almost-equal-to 0.5 form spherical micelles for c > cmc. The size of the micelles is independent of the concentration and temperature, if the temperature is about 20-degrees-C above the micellization temperature T(m); in a transition region around Tm the micellar size increases strongly with temperature. Below T(m) or the cmc only monomeric block copolymer molecules are present in the solution. At higher concentrations and temperatures solutions with spherical micelles form in a first-order transition a transparent, optically isotropic, highly viscous, and elastic cubic phase. The formation of this cubic phase can be understood by hard-sphere interaction between the aggregates. With further increasing concentrations transitions to hexagonal and to lamellar phases are observed. Samples with a smaller hydrophilic EO block, i.e., with x:y almost-equal-to 0.25, usually form a hexagonal phase as the first liquid crystalline mesophase, while for systems with ratios xy almost-equal-to 0.15 a lamellar phase is found as the first mesophase; samples with x:y much less than 0.1 are no longer soluble in water. The lyotropic mesophases show also a thermotropic behavior; i.e., reversible transitions cubic --> hexagonal --> lamellar or from isotropic solutions to mesophases occur at constant block copolymer concentration with increasing temperatures. The mesophases usually melt at temperatures below 100-degrees-C to systems consisting of one or more isotropic liquid phase.
Article
The adsorption of BAB-type triblock copolymers (B=poly(ethylene oxide); A=poly(propylene oxide)) from aqueous solution onto hydrophilic silica particles is described with particular reference to the role of the copolymer composition. The adsorbed amount and the layer thickness were determined by the standard depletion method and photon correlation spectroscopy, respectively. Snowtex-YL silica was used as the adsorbent. The results show an increase in the adsorbed amount with increasing molar masses of both PEO and PPO blocks. The adsorbed layer thickness is found to depend strongly on PEO block mass. Both these parameters (adsorbed amount and hydrodynamic layer thickness) show a maximum as a function of the mole fraction of the PPO block present in the copolymer. The conformation of the adsorbed layer is determined by the surface–copolymer interaction; principally by the interaction of the hydrophilic PEO block with the silica surface. A good qualitative agreement of the experimental results with theoretical predictions and self-consistent mean field calculations has been found.
Article
The adsorption of BAB-type triblock copolymers (B=poly(ethylene oxide); A=poly(propylene oxide)) from aqueous solution onto hydrophilic silica particles is described with particular reference to the role of the copolymer composition. The adsorbed amount and the layer thickness were determined by the standard depletion method and photon correlation spectroscopy, respectively. Snowtex-YL silica was used as the adsorbent. The results show an increase in the adsorbed amount with increasing molar masses of both PEO and PPO blocks. The adsorbed layer thickness is found to depend strongly on PEO block mass. Both these parameters (adsorbed amount and hydrodynamic layer thickness) show a maximum as a function of the mole fraction of the PPO block present in the copolymer. The conformation of the adsorbed layer is determined by the surface–copolymer interaction; principally by the interaction of the hydrophilic PEO block with the silica surface. A good qualitative agreement of the experimental results with theoretical predictions and self-consistent mean field calculations has been found.
Article
The influences of copolymer molar mass and PEO/PPO block molar masses, anchor fraction and solution concentration on the adsorption characteristics of PEO/PPO/PEO triblock copolymers adsorbed onto model polystyrene latices have been investigated. The adsorbed amount was determined by the standard depletion method and the hydrodynamic thickness of the adsorbed layer by photon correlation spectroscopy. Model polystyrene latices prepared by the surfactant-free method were used as adsorbents. The adsorbed amount and the hydrodynamic layer thickness were found to be strongly dependent on the copolymer molar mass, PEO/PPO block masses and the copolymer solution concentration. The conformation of the adsorbed copolymer is determined by the surface-copolymer interaction and, principally, by interaction of the hydrophobic PPO block with the latex surface.
Article
We present a numerical, self‐consistent field study of adsorbed diblock copolymers in thermal solvents, with a detailed and quantitative comparison with recent experiments performed on poly(dimethylsiloxane‐block‐styrene) copolymer spread as a monolayer at the free surface of ethyl benzoate [M. S. Kent, L. T. Lee, B. Farnoux, and F. Rondelez, Macromolecules 25, 6240 (1992); M. S. Kent, L. T. Lee, B. J. Factor, F. Rondelez, and G. S. Smith, J. Chem. Phys. 103, 2320 (1995)]. These neutron reflectivity experiments, for the first time, independently varied both the molecular weight and surface density, and probed the size and nature of the depletion layer at the surface. In the calculations, the polymer and solvent are characterized by realistic values of the pure component densities, the Kuhn length and the Flory interaction parameter. We examine the properties of the dangling block, specifically the depletion layer, the thickness of the brush, the maximum polymer concentration and its location, and the dependence of these properties on surface density and molecular weight. We obtain very good agreement with the experiments, especially for the functional dependences, which indicate that these systems are not in the asymptotic brush limit. We also argue that this conclusion applies to many experiments, some of which were previously thought to be in the asymptotic limit. © 1995 American Institute of Physics.
Article
Using pyrene and homologous alkyl derivatives of fluorescein as fluorescent probes, this work examines the partitioning coefficients of hydrophobic solutes in aqueous dispersions of Pluronic block copolymers (poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide)). An incremental approach is developed, allowing measurement of the free energy of transfer of a methylene group from aqueous media into the micelles. Effects of variation of length of the ethylene oxide (EO) and the propylene oxide (PO) blocks in Pluronic molecules on the partitioning characteristics of the solutes are established. A simple reciprocal relationship between partitioning coefficients of the solute and critical micellization concentration is demonstrated.
Article
The adsorption of a series of (ethylene oxide−tetrahydrofuran−ethylene oxide), EOn/2THFmEOn/2, triblock copolymers has been studied at the water/hydrophobic silica interface by time-resolved ellipsometry. The copolymers form monolayers with the middle tetrahydrofuran block anchoring at the surface and the ethylene oxide groups either anchoring at the surface or protruding into the aqueous phase. The degree of anchoring of the EO chains depends critically on the surface coverage. The copolymer isotherms are generally rather well described by the conventional Langmuir expression, and the plateau surface area per polymer molecule increases linearly with the molecular weight. However, the plateau thickness exhibits a more complex behavior. At low coverages, the adsorbed layer thickness is small, and both THF and EO chains form trains at the surface. As the surface coverage increases, however, the EO chains are increasingly forced away from the surface, and the mean thickness of the adsorbed layer exhibits a relatively strong linear dependence on the surface excess. At higher coverages, closer to the adsorption plateau, a weaker dependence is observed. The thickness increase is in this latter region due to the increasing steric repulsion between protruding EO chains. Outside the adsorbed layer, we also found support for the existence of a depletion layer. We show further that there are three regimes in the kinetics of adsorption. In the first (low surface coverage), the process is diffusion controlled and the rate is proportional to the concentration difference between the bulk solution and the subsurface located just outside the adsorbed layer. In the second regime (intermediate coverages and adsorption times), the kinetics are governed by the rate of displacement of anchored EO chains by THF chains of adsorbing copolymers. In the third regime (high surface coverages), the adsorption slows down markedly due to the energy barrier caused by presence of the relatively dense brush of adsorbed EO chains. In this regime, the surface excess varies proportionally with log t, which was also observed to be the case during the desorption process.
Article
We have investigated the adsorption and lubrication properties of a series of poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) (PEO−PPO−PEO) block copolymers (“Pluronic”) to examine the feasibility of using them as aqueous lubricant additives. The adsorption behavior of PEO−PPO−PEO onto poly(dimethylsiloxane) (PDMS) surfaces was studied by optical waveguide lightmode spectroscopy (OWLS). The amount of adsorbed PEO−PPO−PEO copolymer exhibited a systematic variation, mainly according to the formula weight of the PPO block, and was found to increase with increasing PPO block size. The lubricating properties of the copolymers were investigated by means of pin-on-disk tribometry, employing self-mated PDMS as a tribo-pair in an aqueous environment. The lubricating behavior of the PEO−PPO−PEO copolymers was observed to be closely associated with their adsorption properties onto the PDMS surface; effective lubrication under low-velocity conditions was observed for those PEO−PPO−PEO copolymers that exhibited a significant adsorption of the PPO block, yet a significant role of the PEO block was also observed. The lubrication capabilities of PEO−PPO−PEO copolymers in aqueous media were attributed to the reduction of the hydrophobic interaction between PDMS surfaces by coating the surface with the copolymer and facilitating the formation of an aqueous lubricating film at the sliding interface.
Article
The adsorption and desorption behavior of a family of PEO-PPO-PEO triblock copolymers on a gold surface modified by a carboxyl-terminated self-assembled layers of a long-chain mercaptoalkanoic acid, were investigated. A high refractive index LaFSN9 glass slides were used as substrates for surface plasmon resonance (SPR). Self-assembly of MUA monolayer was achieved by injecting a 5mM MUA solution in alcohol into the flow cell containing a freshly prepared gold slide. The Results show that the absorbed amounts go through a maximum near the critical micelle concentration (cmc).
Article
We report on the adsorption from solution of a family of triblock copolymers, copoly(ethylene oxide−propylene oxide−ethylene oxide) (PEO−PPO−PEO), on a gold surface modified by a methyl-terminated, self-assembled monolayer (SAM) of a long-chain alkanethiol (CH3(CH2)10SH). We employed a surface plasmon resonance (SPR) technique to determine polymer-adsorbed amounts. We also performed atomic force microscopy (AFM) in the liquid environment on a selected number of cases to discern the morphology of the copolymer-coated surfaces. This study shows that the adsorbed amounts go through a maximum near the critical micelle concentration (cmc) and that the process is only partially reversible. Trends in the adsorbed amounts with varying relative composition of the copolymer blocks are consistent with scaling law predictions for the adsorption of block copolymers from selective solvents. AFM imaging shows micellar aggregates at the surface for a copolymer with higher relative hydrophobic content. In contrast, for a copolymer with higher hydrophilic content, we observe a uniform, monolayer-like morphology. In both cases, cycling of the force on the AFM tip reveals the presence of a polymer brush.
Article
We study the adsorption of A-B diblock copolymers on a solid plane in a highly selective solvent. The A part is in a poor solvent and forms a molten layer on the solid wall where the solvent does not penetrate. The B part, in a good solvent, forms a brush grafted on this molten layer. The structure of the adsorbed copolymer film is governed by the chemical potential in the solution in contact with the wall. Copolymer chains have a tendency to self-aggregate in this solution forming several different mesophases. We present first a scaling theory of micelle and lamella formation and then study the geometry of the adsorbed film in equilibrium with these two phases. An important issue of this work is the role of the van der Waals interaction between the wall and the adsorbed A layer. If the copolymer asymmetry is large enough, Le., if the B part has a higher molecular mass than the A part, in a wide range of concentration, and this quite independent of the phase behavior of the solution, the thickness of the molten A layer results from a balance between the van der Waals energy and the stretching energy of the brush. The B chains are almost fully extended in the
Article
The critical micellization temperature (cmt) and critical micellization concentration (cmc) values of 12 Pluronic poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers, covering a wide range of molecular weights (2,900--14,600) and PPO/PEO ratios (0.19--1.79), were determined employing a dye solubilization method. A closed association model was found to describe adequately the copolymer micellization process for the majority of the Pluronics and used to obtain the standard free energies ([Delta]G[degree]), enthalpies ([Delta]H[degree]), and entropies ([Delta]S[degree]) of micellization. It was determined that the micellization process is entropy-driven and has an endothermic micellization enthalpy. The hydrophobic part of the Pluronics, PPO, was responsible for the micellization, apparently due to diminishing hydrogen bonding between water and PPO with increasing temperature. The cmc dependence on temperature and size of headgroup (PEO) of Pluronics follows a similar trend with lower molecular weight C[sub i]E[sub j] nonionic surfactants, the effect of temperature being more pronounced with the Pluronics. The PEO-PPO-PEO block copolymers were compared to PPO-PEO-PPO block and PEO-PPO random copolymers, in an attempt to probe the effect of molecular architecture in the formation of micelles. No micelles were observed in aqueous PPO-PEO-PPO block copolymer solutions with increasing temperature, up to the cloud point.
Article
The adsorption at silica of block copolymers of the type PEO-PPO-PEO [PEO and PPO being poly(ethylene oxide) and poly(propylene oxide), respectively], as well as that of PEO, has been studied. For a number of polymers of a total molecular weight of about 15 000, it was found that the adsorbed amount is rather low (0.35-0.40 mg/m2), independent of the PO content in the range 0-30% PO. For a copolymer of a total molecular weight of 4000 and a PO content of 50% the adsorbed amount was about 0.20 Mg/M2. All polymers investigated formed thin adsorbed layers, with hydrodynamic thicknesses of about 2-5 nm. The pH dependence of the adsorbed amount and the hydrodynamic thickness is similar to that displayed by PEO homopolymers. Ellipsometry experiments on silica surfaces showed good agreement with the experiment on silica dispersions. Furthermore, ellipsometry experiments provided information on both adsorption and desorption kinetics. Both adsorption and desorption are fast processes in these systems, occurring over minutes. Finally,ellipsometry experiments showed that, just prior to solution micellization, an abrupt increase in the adsorbed amount occurred. At temperatures above the critical micellization temperature, the adsorbed amount remained independent of temperature in the temperature range studied. At all temperatures the hydrodynamic thickness was much smaller than the hydrodynamic diameter of the solution micelles. On hydrophobic surfaces, no abrupt increase in the adsorbed amount was observed. The experimental findings were interpreted with a modified mean-field theory.
Article
A simple but quantitative mathematical formalism for interpretation of surface plasmon resonance (SPR) signals from adsorbed films of a wide variety of structures is presented. It can be used to estimate adsorbed film thicknesses, surface coverages, or surface concentrations from the SPR response over the entire range of film thicknesses without relying on calibration curves of response versus known thicknesses or surface concentrations. This formalism is compared to more complex optical simulations. It is further tested by (1) calibrating the response of two SPR spectrometers to changes in bulk index of refraction, (2) using these calibrations with this formalism to predict responses to several well-characterized adlayer structures (alkanethiolates and serum albumin on gold, propylamine on COOH-functionalized gold), and then (3) comparing these predictions to measured SPR responses. Methods for estimating the refractive index of the adlayer material are also discussed. Detection limits in both bulk and adsorption-based analyses are discussed. The planar system used here has a detection limit of 0.003 nm in average film thickness for adsorbates whose refractive index differs from that of the solvent by only 0.1. The temperature sensitivities of these two SPR spectrometers are characterized and discussed in terms of detection limits.
Article
Poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) (PEO−PPO−PEO) triblock copolymers are used in a wide range of industrial applications from detergents to pharmaceutical materials. We have employed surface plasmon resonance (SPR) to monitor the adsorption of these materials, from aqueous solutions to a model hydrophobic surface. The effect of varying the PPO or PEO block size of the copolymer on adsorption has been investigated, and a linear increase in SPR angle shift with increasing PPO or PEO chain length is observed. The SPR angle shifts show a greater increase in SPR angle with increasing PPO block size compared to an equivalent increase in PEO block size. This has been explained by considering the effect each block has on the dielectric properties of the adsorbed polymer at the interface. The presence of micelles in solution and their influence on Pluronic adsorption has also been considered, and adsorption from micellar solutions has been determined to be dependent on the PPO content of the copolymer.
Article
Interactions between two air−water interfaces stabilized by poly(ethylene oxide)−poly(butylene oxide) block copolymers were investigated by employing the microinterferometric thin-film balance technique. A series of three block copolymers, two linear diblock copolymers, B8E41 and E106B16, and one linear triblock copolymer, E21B8E21, were investigated. In particular the range of the steric forces operating across the thin foam films was quantified. As expected, higher concentrations were required of the triblock copolymer than for the diblocks for the formation of a stable foam film. Despite the low polydispersity of the sample (Mw/Mn = 1.03), effects due to polydispersity on the concentration dependence of the disjoining pressure isotherm were noted. Furthermore, the adsorption at the air−water interface was determined by surface tension measurements. It was noted that long equilibrium times are required to obtain (quasi) equilibrium surface tension data. Time-resolved ellipsometry was used to follow the adsorption rates and determine the amounts adsorbed in situ at hydrophobic solid surfaces. The adsorbed amount at the solid−liquid interface determined by ellipsometry was similar to that at the air−water interface estimated from the surface tension isotherm provided polydispersity effects on the surface tension isotherm were taken into account. Moreover, interactions in foam films formed from mixtures of the diblock copolymer, B8E41, and a cationic surfactant, hexadecyltrimethylammonium bromide, were studied. Both electrostatic double-layer forces and, at shorter range, steric forces were present, demonstrating the formation of a mixed layer at the interface.
Article
Dynamic surface tension (DST) experiments have been combined with time-resolved ellipsometry (TRE) to study the adsorption kinetics of symmetric triblock copolymers at the air-water interface. The equilibrium behavior of these adsorbed monolayers has been studied in the preceding paper in this issue (part 1), pointing out evidence for brush formation at sufficiently high surface concentrations. The dynamic results are consistent with a diffusive mechanism delayed by adsorption barriers in the full adsorption regime at lower concentrations. The first-order phase transition scenario evidenced from the equilibrium results is now also perceptible from the dynamic results: a competition between the bulk diffusion and molecular reorientation mechanisms is found in the brush regime. This two-step adsorption kinetics is characterized by an intermediate plateau, dγ(t)/dt) 0, which gives evidence for phase coexistence while final steady-state equilibrium is attained.
Article
Critical micelle concentrations (cmc) were determined for aqueous solutions of 15 EO-PO-EO (EO) ethylene oxide, PO) propylene oxide) block copolymers by using three different techniques: spectral changes of an iodine/iodide mixture, methyl yellow solubilization, and surface tension measurements. Two polymers showed no sign of micelle formation up to phase separation: one reverse (PO-EO-PO) and the other with low EO/PO ratio. The obtained cmc's were consistent for the different techniques employed and allowed the determination of the ∆G values associated with the micellization. These values were analyzed in terms of the EO and PO contributions, confirming the leading role of the hydrophobic PO units and revealing a small, but favorable, contribution of the hydrophilic EO chains, in contrast to the usual behavior of small nonionic surfactants. The polarity of the micelle solubilization sites was determined using the solvatochromic dye ET30, revealing environments similar to those observed for micelles of hydrocarbon surfactants. These findings, allied to the thermodynamic similarity between the micellization and the phase separation processes for the copolymers and PPO, support the view that the micellization is accompanied by a large dehydration of the PO units.
Article
In this review article we discuss a large number of the studies of interactions between protein-coated surfaces that has been presented in the literature. We also demonstrate how to relate surface force data to results from other techniques in order to provide a more full picture of protein behaviour at interfaces. One aim of the article is to discuss the experimental procedure and the difficulties with surface force measurements in protein systems. It is particularly important to point out how the sensitivity of this technique differs from that of other techniques, e.g. in determining structural changes in adsorbed proteins and in detecting proteins adsorbed on top of an inner firmly bound layer. It is also important to realize which surface force data cannot easily be compared with findings from other techniques (one example is the kinetics of adsorption and desorption). We have tried to group proteins into different classes depending on their size and structure, and to try to find results that are common within these classes. It was found that some observations for unordered proteins with amphiphilic character, and for the small compact proteins, appear consistently within the respective class. Hence, for these types of protein common features/principles of the interfacial behaviour are identified. The very large and flexible glycoproteins behave in a similar way to synthetic polymers, but we found it hard to draw any firm conclusions based on the surface force studies presented so far. Perhaps, the most complicated surface behaviour is observed for soft globular proteins that undergo large-scale conformational changes upon adsorption and when the layers are held under a high compressive force.
Article
The X-ray diffraction profiles on nanocrystalline gold prepared by the gas deposition method were studied by Warren-Averbach and integral breadth analysis for the evaluation of grain sizes and internal strains. The grain size of as-prepared specimens, estimated by Warren-Averbach analysis, was in the range of 7 to 20nm. The thermal stability of these specimens was found to be quite high; when annealed for 1h, the grain size remained unchanged up to 770K and grew about twice at 1070K. The root mean square strain, estimated by integral breadth analysis, was in the range of 0.8–2.3 × 10−3 and reduced to ~3 × 10−4 after annealing at 870K and higher.
Article
Surface plasmon resonance (SPR) is an optical technique that is widely gaining recognition as a valuable tool to investigate biological interactions. SPR offers real time in situ analysis of dynamic surface events and, thus, is capable of defining rates of adsorption and desorption for a range of surface interactions. In this review we highlight the diversity of SPR analysis. Examples of a wide range of applications of SPR are presented, concentrating on work relevant to the analysis of biomaterials. Particular emphasis is given to the use of SPR as a complimentary tool, showing the broad range of techniques that are routinely used alongside SPR analysis.
Article
The association properties of poly(ethylene oxide)-block-poly(propyleneoxide)-block-poly(ethylene oxide) (PEOPPOPEO) copolymers (commercially available as Poloxamers and Pluronics) in aqueous solutions, and the adsorption of these copolymers at interfaces are reviewed. At low temperatures and/or concentrations the PEOPPOPEO copolymers exist in solution as individual coils (unimers). Thermodynamically stable micelles are formed with increasing copolymer concentration and/or solution temperature, as revealed by surface tension, light scattering, and dye solubilization experiments. The unimer-to-micelle transition is not sharp, but spans a concentration decade or 10 K. The critical micellization concentration (CMC) and temperature (CMT) decrease with an increase in the copolymer PPO content or molecular weight. The dependence of CMC on temperature, together with differential scanning calorimetry experiments, indicates that the micellization process of PEOPPOPEO copolymers in water is endothermic and driven by a decrease in the polarity of ethylene oxide (EO) and propylene oxide (PO) segments as the temperature increases, and by the entropy gain in water when unimers aggregate to form micelles (hydrophobic effect). The free energy and enthalpy of micellization can be correlated to the total number of EO and PO segments in the copolymer and its molecular weight. The micelles have hydrodynamic radii of approximately 10 nm and aggregation numbers in the order of 50. The aggregation number is thought to be independent of the copolymer concentration and to increase with temperature. Phenomenological and mean-field lattice models for the formation of micelles can describe qualitatively the trends observed experimentally. In addition, the lattice models can provide information on the distribution of the EO and PO segments in the micelle. The PEOPPOPEO copolymers adsorb on both airwater and solidwater interfaces; the PPO block is located at the interface while the PEO block extends into the solution, when copolymers are adsorbed at hydrophobic interfaces. Gels are formed by certain PEOPPOPEO block copolymers at high concentrations, with the micelles remaining apparently intact in the form of a “crystal”. The gelation onset temperature and the thermal stability range of the gel increase with increasing PEO block length. A comparison of PEOPPO copolymers with PEOPBO and PEO PS block copolymers and CiEj surfactants is made, and selected applications of PEOPPOPEO block copolymer solutions (such as solubilization of organics, protection of microorganisms, and biomedical uses of micelles and gels) are presented.
Article
A methodology to correlate the absolute surface concentration of protein to the surface plasmon resonance (SPR) response is described. The thickness and the optical constants for each layer on the sensor chip used were determined with different optical techniques. In a flow injection system, the steady-state SPR response was correlated to the absolute amount of radiolabeled protein adsorbed by using a surface scintillation counter. The proteins used, 14C-labeled human transferrin and chymotrypsinogen A, as well as in vivo35S-labeled monoclonal antibodies, were adsorbed via electrostatic interaction to a carboxymethylated dextran hydrogel on the sensor chip. For these proteins, surface concentrations from 2 to 50 ng mm−2 correspond linearly to the SPR response, with specific response in the range 0.10 ± 0.01° (ng mm−2)−1, independent of protein size. The minimum detectable surface concentration of protein is estimated to be 50 pg mm−2 with this SPR instrument. Optical models have been developed to describe how the SPR response depends on the distribution of the adsorbed protein within the hydrogel volume at the surface. With a thin-film optical program, the theoretical SPR responses for the different models were calculated. Comparison with experimental data shows that the protein is distributed within an approximately 100-nm-thick dextran hydrogel layer.
Article
Adsorbed layers of three PEO-PPO-PEO triblock copolymers on a hydrophilic SiO2 and a hydrophobic polystyrene surface were studied by atomic force microscopy, X-ray reflectometry, ellipsometry, and contact angle measurements. Adsorption from aqueous solutions at the hydrophilic surface is found to depend in a delicate way on N-EO and N-PO, the total numbers of hydrophilic EO and hydrophobic PO groups of the polymers, as quantified by the asymmetry parameter beta = N-EO(3/5)/N-PO(1/2). Only for the polymer of medial beta value, F127 (beta = 2.76), an adsorbed layer is retained after extensive rinsing with pure water. At the hydrophobic surface all polymers, L64 (beta = 1.2), F127 (beta = 2.76), and F68 (beta = 3.47), form stable ad-layers and their thickness scales with the number of EO units of the hydrophilic blocks. From this result and the observed decrease of the contact angle of water droplets caused by the ad-layer, it is conjectured that the polymers adsorb with their PPO block to the hydrophobic substrate and the PEO blocks directed outwards. At the hydrophilic surface the ad-layer of F127 is oriented in the opposite way, i.e., with the PPO blocks oriented outwards. In all cases, the ad-layers form uniform coatings on a micrometer scale, with a thickness in the range 1.0-2.3 nm, again suggesting monolayer coverage of the surface.
Article
In this article the influence of preadsorbed block copolymers on lipase adsorption is studied. The Pluronic triblock copolymers used in this study (P75 and F108, respectively) both have one hydrophobic (poly-(propylene oxide)) block in the middle and two hydrophilic (poly(ethylene oxide)) blocks at the ends of the molecules. It was concluded that block copolymers adsorb onto a hydrophobic surface with the middle block; the buoy groups are extended into the water, thus forming a brush. The hydrodynamic layer thickness of F108 is 10 nm. At a hydrophilic surface the buoy groups adsorb and a flat pancake configuration is formed. The hydrodynamic layer thickness is 1 nm. Protein (lipase and bovine serum albumin) adsorption is prevented by F108, provided this is adsorbed in a brush configuration; a pancake configuration is not effective. Prevention of protein adsorption is not solely caused by the presence of F108 at the surface; above that the configuration of the adsorbed molecule is essential. The steric repulsion caused by a brush is stronger than that caused by a pancake. The effect of brush density on protein adsorption has been systematically studied for the F108/lipase system. Both the protein adsorption rate and the final adsorption level were measured as a function of the amount of preadsorbed F108. It is found that small amounts of adsorbed F108 (10% saturation of the surface) reduce the initial adsorption rate of lipase severely (approximately 20-fold). The maximum value of the adsorbed amount at such a surface is 3 times lower as compared to a "bare" surface. It can therefore also be concluded that protein binding to the surface is already hindered by low levels of preadsorbed block copolymer. In the case of a saturated F108 layer no protein adsorption takes place.
Article
A primary advantage of label-free detection methods over fluorescent measurements is its quantitative detection capability, since an absolute measure of adsorbed material facilitates kinetic characterization of biomolecular interactions. Interferometric techniques relate the optical phase to biomolecular layer density on the surface, but the conversion factor has not previously been accurately determined. We present a calibration method for phase shift measurements and apply it to surface-bound bovine serum albumin, immunoglobulin G, and single-stranded DNA. Biomolecules with known concentrations dissolved in salt-free water were spotted with precise volumes on the array surface and upon evaporation of the water, left a readily calculated mass. Using our label-free technique, the calculated mass of the biolayer was compared with the measured thickness, and we observed a linear dependence over 4 orders of magnitude. We determined that the widely accepted conversion of 1 nm of thickness corresponds to approximately 1 ng/mm(2) surface density held reasonably well for these substances and through our experiments can now be further specified for different types of biomolecules. Through accurate calibration of the dependence of thickness on surface density, we have established a relation allowing precise determination of the absolute number of molecules for single-stranded DNA and two different proteins.
Article
A well-controlled biocompatible nonfouling surface is significant for biomedical requirements, especially for the improvement of biocompatibility. We demonstrate the low or nonbiofouling surfaces by coating hydrophobic-hydrophilic triblock copolymers of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) on the CH(3)-terminated self-assembled monolayer (SAM). Two types of copolymers are used to modify the surface, one with different PEO/PPO ratios ( approximately 20/80, 40/60, and 80/20, w/w) but the same PPO molecular weight ( approximately 2 k), the other with different copolymer MWs ( approximately 9, 11, and 15 k) but the same PEO/PPO ratio (80/20, w/w). In situ surface plasmon resonance (SPR) sensor is used to evaluate polymer adsorption on the SAMs and subsequent protein adsorption on the copolymer-treated surface. The effects of PEO-PPO-PEO molecular weight, PPO-to-PEO ratio, and ionic strength on protein adsorption from single protein solutions of fibrinogen, BSA, and complex mixed proteins are systematically investigated. A Pluronic F108 treated surface is highly resistant to nonspecific protein adsorption under the optimized conditions (MW of 15 k and PEO/PPO ratio of 80/20). This work demonstrates that the PEO-PPO-PEO polymer is able to achieve ultra low fouling surface via surface modification by controlling surface packing density of polymers (molecular weight, hydrophobic/hydrophilic ratio, and hydrophilic group coverage).
Article
Fibrinogen adsorption and platelet adhesion on to dimethyldichlorosilane-treated glass and low-density polyethylene were examined. The surfaces were treated with poly(ethylene glycol) and poly(ethylene oxide)/poly(propylene oxide)/poly(ethylene oxide) triblock copolymers (Pluronics). Poly(ethylene glycol) could not prevent platelet adhesion and activation, even when the bulk concentration for adsorption was increased to 10 mg/ml. Pluronics containing 30 propylene oxide residues could not prevent platelet adhesion and activation, although the number of ethylene oxide residues varied up to 76. However, Pluronics containing 56 propylene oxide residues inhibited platelet adhesion and activation, even though the number of ethylene oxide residues was as small as 19. Fibrinogen adsorption on the Pluronic-coated surfaces was reduced by more than 95% compared to the adsorption on control surfaces. The ability of Pluronics to prevent platelet adhesion and activation was mainly dependent on the number of propylene oxide residues, rather than the number of ethylene oxide residues. The large number of propylene oxide residues was expected to result in tight interaction with hydrophobic dimethyldichlorosilane-treated glass and low-density polyethylene surfaces and thus the tight anchoring of Pluronics to the surfaces. The presence of 19 ethylene oxide residues in the hydrophilic poly(ethylene oxide) chains was sufficient to repel fibrinogen and platelets by the mechanism of steric repulsion.
Article
The adsorption of a range of plasma proteins to metal and polymer surfaces has been examined using surface plasmon resonance (SPR). The adsorption of proteins was initially studied on the SPR silver sensor surface, and then on a model polystyrene film spun coated directly onto this substrate. In both cases, reproducible adsorption profiles for albumin were attained which compared well with corresponding atomic force microscopy (AFM) and ellipsometry data on protein monolayer packing and thickness respectively. The SPR data revealed the influence of concentration on both protein adsorption kinetics and the time for formation of a monolayer coating. SPR data also highlighted different adsorption kinetics and final monolayer SPR angle shift values for three plasma proteins which have been interpreted in terms of their molecular dimensions and orientation at the polymer interface. AFM data confirmed the presence of a closely packed protein layer for all three protein systems. These studies are discussed in terms of employing SPR in the study of protein interactions at surfaces which are important in the design and evaluation of novel biomedical polymeric materials.
Article
We report on the adsorption of a series of poly(ethylene oxide)-polytetrahydrofuran-poly(ethylene oxide) copolymers, EOn/2THFmEOn/2, at hydrophilic silica surfaces and relate our findings to the corresponding behavior at hydrophobic surfaces. The adsorption of these copolymers is similar to that of poly(ethylene oxide) homopolymers at low bulk concentrations. However, the copolymer adsorption increases strongly above a certain threshold concentration. This increase, which begins more than 1 order of magnitude below the critical micellar concentration (cmc), is related to the concomitant formation of micellar-like structures at the hydrophilic surfaces. We show in this work that a commercial (ethylene oxide-propylene oxide-ethylene oxide) triblock copolymer, Pluronic F127, exhibits a similar behavior at silica. Due to surface aggregation, much thicker layers are measured on silica than at the hydrophobic surface, where the adsorption results in the formation of a monolayer structure. The adsorbed amount and layer thickness measured on bare silica tend to decrease when the bulk concentration is raised above the cmc. We infer that this is due to changes of the molecular weight distribution and relative block sizes of the copolymers in the surface aggregates, i.e., a polydispersity effect. This study also covers some aspects of the adsorption and desorption kinetics exhibited by the copolymers at silica. As is common for adsorbing polymers, the concentration dependent adsorption process is generally observed to be much faster than the desorption process. The adsorption process is in parts diffusion controlled but overall to a complex to be fully analyzed. During adsorption from solutions with bulk concentrations exceeding the cmc, a clear overshoot of the surface excess is observed after intermediate adsorption times. Again, this is interpreted as being due to polydispersity. Finally, after an initial rapid desorption regime, the surface excess exhibits a logarithmic decay with time during desorption.
Article
Pluronic surfactants, PEO-PPO-PEO triblock copolymers, have been investigated widely due to their protein-resistant properties in applications as coatings for implants and in controlled drug release systems. We have studied a wide range of these copolymers, varying in both PEO and PPO block size, by adsorbing them to a polystyrene surface and investigating their subsequent resistance to human serum albumin adsorption. This investigation has been carried out in real time, using surface plasmon resonance, with the surfaces subsequently visualized by atomic force microscopy. This approach has allowed determination of the effect of the lengths of the PEO and PPO polymer chains on protein resistivity. For low-molecular-weight Pluronics a significant, yet not complete, reduction in albumin adsorption has been observed whereas higher molecular weight Pluronics appear to completely inhibit adsorption within the time frame of this experiment. An increase in the PPO block size of the copolymer also appears to increase its protein resistance. This work further confirms that the binding strength of the anchoring block to the hydrophobic surface, rather than the length of the protruding hydrophilic PEO chains, determines a copolymer's protein resistance capability.
Article
PEO/PPO/PEO triblock copolymers have previously been shown to reduce the binding of proteins to a variety of surfaces. In this study, mixtures of long- and short-chain copolymers have been shown to adhere to gold substrate surface plasmon resonance slides. The mixtures have been shown to significantly reduce the binding of BSA to gold surfaces, compared to the more commonly used long chain PEO copolymers. These mixtures have been shown to be more effective, than either short, or long-chain copolymers used individually, complementing a published theoretical treatise of PEO surfactant behaviour towards protein interaction with surfaces.
Article
The solution behavior of the polymeric surfactant Pluronic F127 (PEO(99)PPO(65)PEO(99)) and its adsorption behavior on aqueous-silica and aqueous-air interfaces, as well as the disjoining pressure isotherms of asymmetric films (silica/aqueous film/air) containing F127, are studied. The interfacial properties of adsorbed F127 layers (the adsorbed amount Gamma and the thickness h) as well as the aqueous wetting film properties [film thickness (h) and refractive indexes] were studied via ellipsometry. The solution properties of F127 were investigated using surface tensiometry and light scattering. The interactions between the air-water and silica-water interfaces were measured with a thin film pressure balance technique (TFB) and interpreted in terms of disjoining pressure as a function of the film thickness. The relations between the behaviors of the asymmetric films, adsorption at aqueous air, and aqueous silica interfaces and the solution behavior of the polymeric surfactant are discussed. Special attention is paid to the influence of the concentrations of F127 and NaCl. Addition of electrolyte lowers the critical micelle concentration, diminishes adsorption on silica, and increases the thickness of the asymmetric film.
Article
Solid surfaces are modified by grafting poly(ethylene oxide), PEO, to influence their interaction with indwelling particles, in particular molecules of bovine serum albumin and human plasma proteins. As a rule, the grafted PEO layers suppress protein adsorption. The suppression is most effective when the PEO layer is in a molecular brush conformation having a reciprocal grafting density (area per grafted PEO chain) less than the dimensions of the protein molecules. Nevertheless, the protein molecules may penetrate the PEO brush to some extent. For a given grafting density, the penetration is facilitated by increasing thickness of the brush. Tenuous brushes of reciprocal grafting densities exceeding the protein molecular dimensions enhance protein adsorption. The results point to a weak attractive interaction between PEO and protein. The protein repellency of a densely PEO-brushed surface is ascribed to a high activation energy for the protein molecules to enter the brush. Varying the temperature between 22 and 38 degrees C does not significantly affect the range of grafting density over which the brush changes from protein-attractive to protein-repellent.
Article
The dilatational rheological properties of monolayers of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)-type block copolymers at the air-water interface have been investigated by employing an oscillating ring trough method. The properties of adsorbed monolayers were compared to spread layers over a range of surface concentrations. The studied polymers were PEO26-PPO39-PEO26 (P85), PEO103-PPO40-PEO103 (F88), and PEO99-PPO65-PEO99 (F127). Thus, two of the polymers have similar PPO block size and two of them have similar PEO block size, which allows us to draw conclusions about the relationship between molecular structure and surface dilatational rheology. The dilatational properties of adsorbed monolayers were investigated as a function of time and bulk solution concentration. The time dependence was found to be rather complex, reflecting structural changes in the layer. When the dilatational modulus measured at different concentrations was replotted as a function of surface pressure, one unique master curve was obtained for each polymer. It was found that the dilatational behavior of spread (Langmuir) and adsorbed (Gibbs) monolayers of the same polymer is close to identical up to surface concentrations of approximately 0.7 mg/m2. At higher coverage, the properties are qualitatively alike with respect to dilatational modulus, although some differences are noticeable. Relaxation processes take place mainly within the interfacial layers by a redistribution of polymer segments. Several conformational transitions were shown to occur as the area per molecule decreased. PEO desorbs significantly from the interface at segmental areas below 20 A(2), while at higher surface coverage, we propose that segments of PPO are forced to leave the interface to form a mixed sublayer in the aqueous region.
Article
We report about the surface modification of polystyrene (PSt) with photoreactive alpha-4-azidobenzoyl-omega-methoxy poly(ethylene glycol)s (ABMPEG) of three different molecular weights (MWs of approximately 2, approximately 5, and approximately 10 kg/mol) and with two poly(ethylene glycol)/poly(propylene glycol) triblock copolymers (PEG-PPG-PEG) of about identical PEG/PPG ratio (80/20, w/w) and MW(PEG) of approximately 3 and approximately 6 kg/mol, all via adsorption from aqueous solutions. For ABMPEGs, an additional UV irradiation was used for photografting to the PSt. Contact angle (CA) and atomic force microscopy data revealed pronounced differences of the hydrophilicity/hydrophobicity and topography of the surfaces as a function of PEG type and concentration used for the modification. In all cases, an incomplete coverage of the PSt was observed even after modification at the highest solution concentrations (10 g/L). However, clear differences were seen between PEG-PPG-PEGs and ABMPEGs; only for the latter was a nanoscale-ordered interphase structure with an influence of MW(PEG) on the PEG density observed; after modification at the same solution concentrations, the density was significantly higher for lower MW(PEG). The adsorption of three proteins, myoglobin (Mgb), bovine serum albumin (BSA), and fibrinogen to the various surfaces was analyzed by surface plasmon resonance. Pronounced differences between the two PEG types with respect to the reduction of protein adsorption were found. At high, but still incomplete, surface coverage and similar CA, the shielding of ABMPEG layers toward the adsorption of Mgb and BSA was much more efficient; e.g., the adsorbed Mgb mass relative to that of unmodified PSt was reduced to 10% for ABMPEG 2 kg/mol while for both PEG-PPG-PEGs the Mgb mass was still around 100%. In addition, for the ABMPEG layers an effect of MW(PEG) on adsorbed protein mass-decrease with decreasing MW-could be confirmed; and the highest Mgb/BSA selectivities were also observed. A "two-dimensional molecular sieving", based on PEG molecules having a nanoscale order at the hydrophobic substrate polymer surface has been proposed, and the main prerequisites were the use of PEG conjugates which are suitable for an "end-on" grafting (e.g., ABMPEGs), the use of suitable (not too high) concentrations for the surface modification via adsorption/self-assembly, optionally the photografting on the substrate (possible only for ABMPEG), and presumably, a washing step to remove the excess of unbound PEGs. The results of this study also strongly support the hypothesis that the biocompatibility of hydrophobic materials can be very much improved by PEG modifications at surface coverages that are incomplete but have an ordered layer structure controlled by the size and steric interactions of surface-bound PEGs.
Article
We investigated the thinning of wetting films formed from aqueous solution of non-ionic triblock copolymer Pluronic F127 on the surface of silica using a home-made thin film balance and time-resolved ellipsometry. Imaging ellipsometry was used to visualize the film structures at subsequent stages of their development. The results unambiguously show that the time required for the formation of steady films strongly depends on the electrolyte concentration. When increasing the latter from 10(-4) to 0.1 M, this time typically increases with several orders of magnitude, from a few minutes to several hours. Moreover, for sufficiently large amounts of salt, two characteristic relaxation regimes can be clearly identified. After initial quick thinning, further thinning slows down enormously. These typical kinetic regimes are thought to result from the coupled dependencies of the bulk and interfacial properties of F127 on salt concentration. Possible explanations of the phenomenon are discussed.
Adsorption and Desorption of PEO–PPO–PEO Triblock
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A Surface Plasmon Resonance Study of Albumin Adsorption to PEO–PPO–PEO Triblock Copolymers
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