Biomedical subjects

Per M Claesson

Publications and source records attributed to Per M Claesson.

18 recordsLinked to original sources

PubMed2006

Immobilization of enamel matrix derivate protein onto polypeptide multilayers. Comparative in situ measurements using ellipsometry, quartz crystal microbalance with dissipation, and dual-polarization interferometry.

The buildup of biodegradable poly(L-glutamic acid) (PGA) and poly(L-lysine) (PLL) multilayers on silica and titanium surfaces and the immobilization of enamel matrix derivate (EMD) protein was followed by utilizing in situ ellipsometry, quartz crystal microbalance with dissipation, and dual-polarization interferometry (DPI). The use of the relatively new DPI technique validated earlier published ellipsometry measurements of the PLL-PGA polypeptide films. The hydrophobic aggregating EMD protein was successfully immobilized both on top of and within the multilayer structures at pH 5.0. DPI measurements further indicated that the immobilization of EMD is influenced by the flow pattern during adsorption. The formed polypeptide-EMD multilayer films are of interest since it is known that EMD is able to trigger cell response and induce biomineralization. The multilayer films thus have potential to be useful as bioactive and biodegradable coatings for future dental implants.

Animals↗

PubMed2006

Globotriose- and oligo(ethylene glycol)-terminated self-assembled monolayers: surface forces, wetting, and surfactant adsorption.

A set of oligo(ethylene glycol)-terminated and globotriose-terminated self-assembled monolayers (SAMs) has been prepared on gold substrates. Such model surfaces are well defined and have good stability due to the strong binding of thiols and disulfides to the gold substrate. They are thus very suitable for addressing questions related to effects of surface composition on wetting properties, surface interactions, and surfactant adsorption. These issues are addressed in this report. Accurate wetting tension measurements have been performed as a function of temperature using the Wilhelmy plate technique. The results show that the nonpolar character of oligo(ethylene glycol)-terminated SAMs increases slightly but significantly with temperature in the range 20-55 degrees C. On the other hand, globotriose-terminated SAMs are fully wetted by water at room temperature. Surface forces measurements have been performed and demonstrated that the interactions between oligo(ethylene glycol)-terminated SAMs are purely repulsive and similar to those determined between adsorbed surfactant layers with the same terminal headgroup. On the other hand, the interactions between globotriose-terminated SAMs include a short-range attractive force component that is strongly affected by the packing density in the layer. In some cases it is found that the attractive force component increases with contact time. Both these observations are rationalized by an orientation- and conformation-dependent interaction between globotriose headgroups, and it is suggested that hydrogen-bond formation, directly or via bridging water molecules, is the molecular origin of these effects.

Adsorption↗

PubMed2006

Short-range interactions between non-ionic surfactant layers.

Short-range interactions between surfactant and lipid layers are of great importance in technical applications in complex fluids such as foams, dispersions and emulsions, as well as in the formulation and performance of dispersants, detergents and flocculants. It is also of utmost importance in biological systems where interactions between biomembranes influence a range of processes. The field of short-range interactions has been thoroughly investigated during the past 30 years, following the emergence of a number of techniques to measure interaction forces. Thus, our understanding has increased considerably and it is timely to summarize relevant knowledge accumulated in this area. In this review we focus on the nature of short-range interactions between non-ionic and zwitterionic surfactant and lipid layers exposing their polar groups to the surrounding medium. We discuss the complex interplay of short-range (van der Waals, hydration, steric and other) forces based on recent theoretical and experimental results.

Emulsions↗

PubMed2006

Chitosan-N-poly(ethylene oxide) brush polymers for reduced nonspecific protein adsorption.

The possibility of using a novel comb polymer consisting of a chitosan backbone with grafted 44 units long poly(ethylene oxide) side chains for reducing nonspecific protein adsorption to gold surfaces functionalized by COOH-terminated thiols has been explored. The comb polymer was attached to the surface in three different ways: by solution adsorption, covalent coupling, and microcontact printing. The protein repellent properties were tested by monitoring the adsorption of bovine serum albumin and fibrinogen employing surface plasmon resonance and imaging null ellipsometry. It was found that a significant reduction in protein adsorption is achieved as the comb polymer layer is sufficiently dense. For solution adsorption this was achieved by adsorption from high pH solutions. On the other hand, the best performance of the microcontact printed surfaces was obtained when the stamp was inked either at low or at high pH. For a given comb polymer layer thickness/poly(ethylene oxide) density, significant differences in protein repellent properties were observed between the different preparation methods, and it is suggested that a reduction in the mobility of the comb polymer layer generated by covalent attachment favors a reduced protein adsorption.

Adsorption↗

PubMed2006

Adsorption properties of polyelectrolyte-surfactant complexes on hydrophobic surfaces studied by QCM-D.

Adsorption and deposition from turbid solutions are common in many industrial processes but notoriously difficult to investigate using standard optical techniques such as ellipsometry and reflectometry. In this report, we have addressed this problem by employing a quartz crystal microbalance with dissipation monitoring ability, QCM-D. The system under investigation consisted of a cationic polyelectrolyte, poly(vinylamine), PVAm, and an anionic surfactant, sodium dodecyl sulfate, SDS, which were mixed together in 10 mM NaCl solution. The polyelectrolyte and the surfactant readily associate in bulk solution, resulting in increased solution turbidity once large aggregates are formed. The solutions were placed in contact with a polystyrene surface, and the adsorption process was monitored by following the changes in the resonance frequency and dissipation factor. The results obtained can in most cases be evaluated using the Sauerbrey relation, but in some cases a more elaborate analysis is necessary. It is found that PVAm adsorbs to polystyrene in the absence of SDS. In the turbid region, deposition is observed, and the sensed mass exceeds the sum of that obtained for each of the components alone. On the other hand, at high SDS concentrations, the surfactant dominates in the adsorbed layer. Adsorption equilibrium is in most cases established within 1-2 h, the exception being found around the solution composition that results in the formation of charge-neutralized aggregates. In this case, a slow deposition of aggregates persists over prolonged times.

Journal Article↗

PubMed2005

Hydration state of nonionic surfactant monolayers at the liquid/vapor interface: structure determination by vibrational sum frequency spectroscopy.

The OH stretching region of water molecules in the vicinity of nonionic surfactant monolayers has been investigated using vibrational sum frequency spectroscopy (VSFS) under the polarization combinations ssp, ppp, and sps. The surface sensitivity of the VSFS technique has allowed targeting the few water molecules present at the surface with a net orientation and, in particular, the hydration shell around alcohol, sugar, and poly(ethylene oxide) headgroups. Dramatic differences in the hydration shell of the uncharged headgroups were observed, both in comparison to each another and in comparison to the pure water surface. The water molecules around the rigid glucoside and maltoside sugar rings were found to form strong hydrogen bonds, similar to those observed in tetrahedrally coordinated water in ice. In the case of the poly(ethylene oxide) surfactant monolayer a significant ordering of both strongly and weakly hydrogen bonded water was observed. Moreover, a band common to all the surfactants studied, clearly detected at relatively high frequencies in the polarization combinations ppp and sps, was assigned to water species located in proximity to the surfactant hydrocarbon tail phase, with both hydrogen atoms free from hydrogen bonds. An orientational analysis provided additional information on the water species responsible for this band.

Alcohols↗

PubMed2005

Interactions between nonpolar surfaces coated with the nonionic surfactant n-dodecyl-beta-D-maltoside.

The forces acting between nonpolar surfaces coated with the nonionic surfactant n-dodecyl-beta-D-maltoside (beta-C(12)G(2)) were investigated at concentrations below and above the critical micelle concentration. The long-range and adhesive forces were measured with a bimorph surface force apparatus (MASIF). It was found that the effect of hydrodynamic interactions had to be taken into account for an accurate determination of the short-range static interactions. The results were compared with disjoining pressure versus thickness curves that were obtained earlier with a thin film pressure balance (TFPB). This comparison led to the conclusion that the charges observed at the air-water interface are not due to charged species present in the surfactant sample. In addition, it was observed that the stability of thin liquid films crucially depends on the surfactant's bulk concentration (c) and thus on the packing density in the adsorbed layer. The force barrier preventing removal of the surfactant layer from between two solid-liquid interfaces increases with increasing c, while for foam films it is the stability of the Newton black film that increases with c. Finally, the results obtained for beta-C(12)G(2) were compared with those obtained for the homologue n-decyl-beta-d-maltoside (beta-C(10)G(2)) as well as with those obtained for nonionic surfactants with polyoxyethylene moieties as polar groups.

Adsorption↗

PubMed2005

Viscoelastic properties of isomeric alkylglucoside surfactants studied by surface light scattering.

Surface light scattering (SLS) by capillary waves was used to investigate the adsorption behavior of non-ionic sugar surfactants at the air/liquid interface. SLS by the subphase (water) followed predictions from hydrodynamic theory. The viscoelastic properties (surface elasticity and surface viscosity) of monolayers formed by octyl beta-glucoside, octyl alpha-glucoside, and 2-ethylhexyl alpha-glucoside surfactants were quantified at submicellar concentrations. It is further concluded that a diffusional relaxation model describes the observed trends in high-frequency, nonintrusive laser light scattering experiments. The interfacial diffusion coefficients that resulted from fitting this diffusional relaxation model to surface elasticity values obtained with SLS reflect the molecular dynamics of the subphase near the interface. However, differences from the theoretical predictions indicate the existence of effects not accounted for such as thermal convection, molecular rearrangements, and other relaxation mechanisms within the monolayer. Our results demonstrate important differences in molecular packing at the air-water interface for the studied isomeric surfactants.

Adsorption↗

PubMed2005

Enhanced adsorption of alkyl glucosides on the silica/water interface by addition of amine oxides.

The effect of adding a small amount of dodecyl dimethylamine oxide (DDAO) on adsorption on silica from an aqueous solution of dodecyl maltoside (C12G2) has been investigated. The C12G2 itself does not adsorb significantly on silica at any concentration. DDAO on the other hand readily adsorbs in a bilayer-like structure at concentrations approaching the critical micelle concentration (cmc), but the adsorbed amount at the concentrations it has been applied in these mixtures is small. In contrast, by combination of the two surfactants, significant adsorption is observed at concentrations where the adsorption of the pure DDAO, as well as pure C12G2, is very low. We thus see a strong enhancement of the adsorption from the mixed system. The adsorption is suggested to be a two-step process, where individual DDAO molecules first adsorb to the silica surface through electrostatic interactions, and then C12G2 adsorbs at the hydrophobic sites the DDAO tails constitute through hydrophobic bonding. A minimum concentration of DDAO is required to induce adsorption from a solution with constant C12G2 concentration. This concentration is lower for C12G2 solutions below and equal to cmcC12G2 than above cmcC12G2. In addition, the total adsorbed amount shows a maximum around cmcC12G2 of the mixture for a solution with low DDAO contents. Both these effects are explained by incorporation of DDAO in the mixed micelles above cmc(mix), which leads to a desorption of DDAO from the surface.

Alkylation↗

PubMed2005

Polyelectrolyte-mediated surface interactions.

The current understanding of interactions between surfaces coated with polyelectrolytes is reviewed. Experimental data obtained with various surface force techniques are reported and compared with theoretical predictions. The majority of the studies concerned with interactions between polyelectrolyte-coated surfaces deal with polyelectrolytes adsorbed to oppositely charged surfaces, and this is also the main focus of this review. However, we also consider polyelectrolytes adsorbed to uncharged surfaces and to similarly charged surfaces, areas where theoretical predictions are available, but relevant experimental data are mostly lacking. We also devote sections to interactions between polyelectrolyte brush-layers and to interactions due to non-adsorbing polyelectrolytes. Here, a sufficient amount of both theoretical and experimental studies are reported to allow us to comment on the agreement between theory and experiments. A topic of particular interest is the presence of trapped non-equilibrium states that often is encountered in experiments, but difficult to treat theoretically.

Adsorption↗

PubMed2004

Stability of polypeptide multilayers as studied by in situ ellipsometry: effects of drying and post-buildup changes in temperature and pH.

Polyelectrolyte multilayers (PEM) of poly(L-glutamic acid) (PGA) and poly(L-lysine) (PLL) with an initial layer of polyethyleneimine (PEI) were built on silica and titanium surfaces using the layer-by-layer (LbL) technique. The stability of the film during drying/rewetting, temperature cycles, and pH shifts was studied in situ by means of ellipsometry. The film thickness was found to decrease significantly (approximately 70%) upon drying, but the original film thickness was regained upon rewetting, and the buildup could be continued. The thickness in the dry state was found to be extremely sensitive to ambient humidity, needing several hours to equilibrate. Changes in temperature and pH were also found to influence the multilayer thickness, leading to swelling and deswelling of as much as 8% and 10-20% respectively. The film does not necessarily regain its original thickness as the pH is shifted back, but instead shows clear signs of hysteresis.

Desiccation↗

PubMed2004

Surface interactions during polyelectrolyte multilayer buildup. 1. Interactions and layer structure in dilute electrolyte solutions.

We report the investigation of surface forces between polyelectrolyte multilayers of poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate sodium salt) (PSS) assembled on mica surfaces during film buildup using a surface force apparatus. Up to four polyelectrolyte layers were prepared on each surface ex situ, and the surface interactions were measured in 10(-4) M KBr solutions. The film thickness under high compressive loads (above 2000 microN/m) increased linearly with the number of deposited layers. In all cases, the interaction between identical surfaces at large separations (>100 A from contact) was dominated by electrostatic double-layer repulsion. By fitting DLVO theory to the experimental force curves, the apparent double-layer potential of the interacting surfaces was calculated. At shorter separations, an additional non-DLVO repulsion was present due to polyelectrolyte chains extending some distance from the surface into solution, thus generating an electrosteric type of repulsion. Forces between dissimilar multilayers (i.e., one of the multilayers terminated with PSS and the other with PAH) were attractive at large separations (30-400 A) owing to a combination of electrostatic attraction and polyelectrolyte bridging.

Journal Article↗

PubMed2004

Interactions between nonpolar surfaces coated with the nonionic surfactant hexaoxyethylene dodecyl ether C12E6 and the origin of surface charges at the air/water interface.

The interactions between nonpolar surfaces coated with the nonionic surfactant hexaoxyethylene dodecyl ether C12E6 were investigated using two techniques and three different types of surfaces. As nonpolar surfaces, the air/water interface, silanated negatively charged glass, and thiolated uncharged gold surfaces were chosen. The interactions between the air/water interfaces were measured with a thin film pressure balance in terms of disjoining pressure as a function of film thickness. The interactions between the solid/liquid interfaces were determined using a bimorph surface force apparatus. The influence of the nature of the surface on the interaction forces was investigated at surfactant concentrations below and above the cmc. The adsorption of the nonionic surfactant on the uncharged thiolated surface does not, as expected, lead to any buildup of a surface charge. On the other hand, adsorption of C12E6 on the charged silanated glass and the charged air/water interface results in a lowering of the surface charge density. The reduction of the surface charge density on the silanated glass surfaces is rationalized by changes in the dielectric permittivity around the charged silanol groups. The reason for the surface charge observed at the air/water interface as well as its decrease with increasing surfactant concentration is discussed and a new mechanism for generation of OH- ions at this particular interface is proposed.

Journal Article↗

PubMed2004

Adsorption of alkyl polyglucosides on the solid/water interface: equilibrium effects of alkyl chain length and head group polymerization.

The equilibrium adsorption behavior of two n-alkyl-beta-D-glucosides (octyl (C8G1) and decyl (C10G1)) and four n-alkyl-beta-D-maltosides (octyl (C8G2), decyl (C10G2), dodecyl (C12G2), and tetradecyl (C14G2)) from aqueous solution on a titania surface, as measured by ellipsometry, has been investigated. The main focus has been on the effect of changes in the alkyl chain length and headgroup polymerization, but a comparison with their adsorption on the silica/water and air/water interfaces is also presented. Some comparison with the corresponding adsorption of ethylene oxide surfactants, in particular C10E6 and C12E6, is given as well. For all alkyl polyglucosides, the maximum adsorbed amount on titania is reached slightly below the critical micelle concentration (cmc), where it levels off to a plateau and the amount adsorbed corresponds roughly to a bilayer. However, there is no evidence that this is the actual conformation of the surfactant assemblies on the surface, but the surfactants could also be arranged in a micellar network. On hydrophilic silica, the adsorbed amount is a magnitude lower than on titania, corresponding roughly to a layer of surfactants lying flat on the surface. A change in the alkyl chain length does not result in any change in the plateau molar adsorbed amount at equilibrium; however, the isotherm slope for the alkyl maltosides increases with increasing chain length. Headgroup polymerization on the other hand affects the adsorbed amount. The alkyl glucosides start adsorbing at lower bulk concentrations than the maltosides and equilibrate at higher adsorbed amounts above the cmc. When compared with the ethylene oxide (EO) surfactants, it is confirmed that the EO surfactants hardly adsorb on titania, since the measured changes in the ellipsometric angles are within the noise level. They do, however, adsorb strongly on silica.

Adsorption↗

PubMed2004

Coadsorption and surface forces for selective surfaces in contact with aqueous mixtures of oppositely charged surfactants and low charge density polyelectrolytes.

The coadsorption of a positively charged polyelectrolyte (with 10% of the segments carrying a permanent positive charge, AM-MAPTAC-10) and an anionic surfactant (sodium dodecyl sulfate, SDS) on silica and glass surfaces has been investigated using optical reflectometry and a noninterferometric surface force technique. This is a selective coadsorption system in the sense that the polyelectrolyte does adsorb to the surface in the absence of surfactant, whereas the surfactant does not adsorb in the absence ofpolyelectrolyte. It is found that the total adsorbed amount goes through a maximum when the SDS concentration is increased. Maximum adsorption is found when the polyelectrolyte/surfactant complexes formed in bulk solution are close to the charge neutralization point. Some adsorption does occur also when SDS is present in significant excess. The force measured between AM-MAPTAC-10-coated surfaces on approach in the absence of SDS is dominated at long range by an electrostatic double-layer force. Yet, layers formed by coadsorption from solutions containing both polyelectrolyte and surfactant generate long-range forces of an electrosteric nature. On separation, adhesive interactions are found only when the adsorbed amount is low, i.e., in the absence of SDS and in a large excess of SDS. The final state of the adsorbed layer is found to be nonhysteretic, i.e., independent of the history of the system. The conditions for formation of long-lived trapped adsorption states from mixed polymer-surfactant solutions are discussed.

Journal Article↗

PubMed2003

Polyelectrolytes as adhesion modifiers.

Adsorbed layers of polyelectrolytes have been studied with atomic force microscopy (AFM) and the interferometric surface force apparatus (SFA). Particular emphasis was put on determining the effect of the polyelectrolyte charge density on surface topography, and the effect of the polyelectrolyte coating on the adhesive properties. The AFM was employed to image individual polymer chains at low adsorption densities and to characterize the layer topography and coverage at higher adsorption densities. The adhesive properties between two polyelectrolyte-coated surfaces in air were determined as a function of the number of contacts made at any given spot. The data provide evidence for formation of electrostatic bridges, particularly when highly charged polyelectrolytes are used. Further, material transport between the surfaces is observed when the polyelectrolyte is either highly charged or have a very low charge density. For intermediate charge densities we could not observe any indication of material transfer. The adhesion between one polyelectrolyte-coated surface and one bare surface was initially higher than that between two polyelectrolyte-coated surfaces. However, due to material transfer between the two surfaces the adhesion decreased significantly with the number of times that the surfaces were driven into contact. For the polyelectrolytes of the lowest charge density the results suggest that entanglement effects contribute to the adhesive interaction. The modification of the adhesion by polyelectrolytes in practical systems such as in the case of dry-strength additives to improve paper resistance is also considered.

Adsorption↗

PubMed2002

Interfacial Behavior of n-decyl-beta-D-maltopyranoside on hydrophobic interfaces and the effect of small amounts of surface-active impurities.

The effect of small amounts of surface-active impurities on the interfacial properties of n-decyl-beta-D-maltopyranoside was investigated using various methods. The n-Decyl-beta-D-maltopyranoside was used both as received from Sigma (<98% by GC) and after being purified with the surfactant-purifying apparatus developed by Lunkenheimer, which removes impurities that are more surface active than the major component. Surface tension measurements demonstrate that the surface elasticity of the surfactant-loaded liquid-vapor interface increased after purification. Measurements of interactions across single foam films revealed that the purified solution formed considerably less charged and less stable films compared with the as-received sample. These results are consistent with the lower foam stability for the purified sample as determined by simple shaking experiments. The lower film stability for the purified solution was attributed to the lower double-layer force. The forces acting between spherical silanated glass surfaces across surfactant solutions were determined with the MASIF (measurement and analysis of surface interaction forces) technique. On approach, the same interactions were experienced in solutions of the as-received and purified surfactant. On the other hand, the adhesion force was lower after purification. Both for the as-received and the purified sample it was observed that the adhesion increased with increasing contact time up to a certain limit. This was explained in terms of partial pressure-induced desorption of surfactants from the disordered silane layers. Wetting experiments also indicated that the surfactants were difficult to remove completely from this surface.

Hydrophobic and Hydrophilic Interactions↗

PubMed2002

Structural forces reflecting polyelectrolyte organization from bulk solutions and within surface complexes.

The interactions between two macroscopic surfaces approaching one another underlies many of the phenomena observed in Colloid and Interface science. In Russia this gave rise to the branch of colloid science now referred to as Surface Forces. Important discoveries, such as the molecular organization of solvent molecules at an interface, have been unveiled by surface force measurements. More recently, forces and structures at macromolecular length scales have been uncovered. In particular, oscillatory force profiles have been detected from aqueous solutions containing polyelectrolytes. The force-structure relationship can reflect organization in the bulk solution or the internal structure of the adsorbed layer. Using a range of surface force techniques, combined with X-ray and neutron scattering results, we review the main features of these fascinating systems and provide an overview of how they relate to other systems such as micellar solutions, polymer-surfactant complexes and simple solvents.

Journal Article↗