End terminal, poly(ethylene oxide) graft layers: surface forces and protein adsorption.
ABSTRACT Covalently grafted poly(ethylene oxide) coatings have been widely studied for use in biomedical applications, particularly for the reduction of protein and other biomolecule adsorption. However, many of these studies have not characterized the hydrated structure of the coatings. This new study uses a combination of silica colloid probe interaction force measurements using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) in order to determine the grafting density and hydrated layer structure of monomethoxy poly(ethylene oxide) aldehyde layers, covalently grafted onto amine plasma polymer surfaces, and their interactions with silica surfaces. For high grafting densities, purely repulsive interactions were measured as expected for densely grafted polymer brushes. These interactions could be described by theoretical expectations for compression of one polymer brush layer. However, at lower grafting densities, attractive interactions were observed at larger separation distances, originating from bridging interactions due to adsorption of the PEO chains on the surface of the silica colloid probe. This is a new finding indicating that the coupled PEO molecules have sufficient conformational freedom to interact strongly with an adjacent surface or, for example, protein molecules for which there is an affinity. The attractive interactions could be removed by grafting an additional PEO layer onto the silica colloid probe. Protein adsorption measurements confirmed that at high grafting densities, the amount of adsorbed protein on the PEO grafted surfaces was greatly reduced, to the order of the detection limit for the XPS technique.
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ABSTRACT: A common goal across different fields (e.g. separations, biosensors, biomaterials, pharmaceuticals) is to understand how protein behavior at solid-liquid interfaces is affected by environmental conditions. Temperature, pH, ionic strength, and the chemical and physical properties of the solid surface, among many factors, can control microscopic protein dynamics (e.g. adsorption, desorption, diffusion, aggregation) that contribute to macroscopic properties like time-dependent total protein surface coverage and protein structure. These relationships are typically studied through a top-down approach in which macroscopic observations are explained using analytical models that are based upon reasonable, but not universally true, simplifying assumptions about microscopic protein dynamics. Conclusions connecting microscopic dynamics to environmental factors can be heavily biased by potentially incorrect assumptions. In contrast, more complicated models avoid several of the common assumptions but require many parameters that have overlapping effects on predictions of macroscopic, average protein properties. Consequently, these models are poorly suited for the top-down approach. Because the sophistication incorporated into these models may ultimately prove essential to understanding interfacial protein behavior, this article proposes a bottom-up approach in which direct observations of microscopic protein dynamics specify parameters in complicated models, which then generate macroscopic predictions to compare with experiment. In this framework, single-molecule tracking has proven capable of making direct measurements of microscopic protein dynamics, but must be complemented by modeling to combine and extrapolate many independent microscopic observations to the macro-scale. The bottom-up approach is expected to better connect environmental factors to macroscopic protein behavior, thereby guiding rational choices that promote desirable protein behaviors.Advances in Colloid and Interface Science 01/2013; · 8.64 Impact Factor
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ABSTRACT: Plasma polymer films (PPF) find increasing applications in many fields due to the unique combination of properties of this class of materials. Among other notable features arising from the specifics of plasma polymerization synthesis, a high surface reactivity can be advantageously used when exploited carefully. It is related to the presence of free radicals generated during deposition process through manifold molecular bond scissions in the energetic plasma environment. In ambient atmosphere these radicals undergo auto-oxidation reactions resulting in undesired polymer ageing. However, when the reactivity of surface radicals is preserved and they are put in direct contact with a chemical group of interest, a specific surface functionalization or grafting of polymeric chains can be achieved. Therefore, the control of the surface free radical density of a plasma polymer is crucially important for a successful grafting. The present investigation focuses on the influence of the hydrocarbon precursor type, aromatic vs. aliphatic, on the generation and concentration of free radicals on the surface of the PPF. Benzene and cyclohexane were chosen as model precursors. First, in-situ FTIR analysis of the plasma phase supplemented by Density Functional Theory (DFT) calculations allowed the main fragmentation routes of precursor molecules in the discharge to be identified as a function of energy input. Using nitric oxide (NO) chemical labeling in combination with XPS analysis a quantitative evaluation of concentration of surface free radicals as a function of input power has been assessed for both precursors. Different evolutions of the surface free radical density for the benzene- and cyclohexane-based PPF, namely, a continuous increase versus stabilization to a plateau, are attributed to different plasma polymerization mechanisms and resulting structures as illustrated by PPF characterization findings. The control of the surface free radical density can be achieved through the stabilization of radicals due to the proximity of incorporated aromatic rings. Ageing tests highlighted the inevitable random oxidation of plasma polymers upon exposure to air and the necessity of free radical preservation for a controlled surface functionalization.ACS Applied Materials & Interfaces 06/2014; · 5.90 Impact Factor
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ABSTRACT: Serum proteins, especially fibrinogen, inactivate the lung surfactant mixture by adsorbing quickly and irreversibly to the alveolar air/aqueous interface. As a consequence of the inactivation, the surfactant becomes dysfunctional, and respiration cannot be maintained properly. Preventing the adsorption of surface active serum proteins to the air/water interface is important because this phenomenon causes fatal diseases such as acute respiratory distress syndrome (ARDS). Although some treatments exist, improvements in synthetic surfactants that can resist this inactivation are still expected. In this context, a novel ion pair lipid (IPL, CF3(CF2)7SO3(-)(CH2CH3)3N(+)(CH2OCH2)10(CH2)15CH3) has been designed and synthesized. This surfactant reduces the inhibitory effect of fibrinogen by selectively interacting with DPPC (dipalmitoylphosphatidylcholine) and mimicking some of the interfacial properties of the pulmonary surfactant protein B (SP-B). Surface pressure-area isotherms and fluorescence microscopy images demonstrate that IPL can mix and interact synergistically with DPPC due to its unique molecular structure. Hysteresis behaviors of the monolayers, which are composed of mixtures of DPPC and IPL at different molar ratios, indicate that with increasing amounts of IPL, the lipid losses from the interface induced by the presence of fibrinogen significantly decrease. It is also found that IPL is able to adsorb to monolayers formed in the presence of fibrinogen, whereas fibrinogen cannot penetrate the monolayers formed in the presence of IPL. These results indicate that by mimicking some of the interfacial properties of SP-B, this novel hybrid molecule is promising in terms of preventing fibrinogen adsorption and therefore resisting surfactant inactivation.Colloids and surfaces B: Biointerfaces 07/2014; · 4.28 Impact Factor