| 1. |
- Wannerberger, Kristin, et al.
(author)
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Adsorption from lipase-surfactant solutions onto methylated silica surfaces
- 1996
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In: Colloids and Surfaces B: Biointerfaces. - : Elsevier BV. - 1873-4367 .- 0927-7765. ; 6:1, s. 27-36
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Journal article (peer-reviewed)abstract
- In situ ellipsometry was used to study the adsorption/desorption of highly purified lipase from Humicola lanuginosa in mixtures with surfactants, at the solid/liquid interface. The effect of the surfactant was studied both when it was allowed to adsorb in mixture with lipase and when added after lipase adsorption. Silica surfaces, totally or partially methylated, were used and the surfactants were SDS (anionic), C12E5 and a commercial alcohol ethoxylate (AE) (both nonionic). The experiments were carried out so as to simulate a laundry process and the pH throughout the study was kept at 9 by means of Tris-HCl buffer.From the results it was shown that the lipase did not adsorb until the diluted, that is during the rinsing period. This was found for all the lipase-surfactant mixtures in the study. However, the amount of lipase adsorbed was larger after rinsing in mixture with SDS, compared with C12E5. The results from addition of surfactant after lipase adsorption indicated that the lipase was replaced by surfactant. This was found for SDS and C12E5 at both the hydrophobic surface and the surface with intermediate hydrophobicity.
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| 2. |
- Lestelius, Magnus, et al.
(author)
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Order/disorder gradients of n-alkanethiols on gold
- 1999
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In: Colloids and Surfaces B. - : Elsevier. - 0927-7765 .- 1873-4367. ; 15:1, s. 57-70
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Journal article (peer-reviewed)abstract
- This paper explores the interfacial properties of one-dimensional molecular gradients of alkanethiols (HS-(CH2)(n)- X) on gold. The kinetics and thermodynamics of monolayer formation are important issues for these types of mixed molecular assemblies. The influence of chain length difference on the contact angles with hexadecane (HD), theta(a) and theta(r), and the hysteresis, has been studied by employing alkanethiols HS-(CH2)(n)-CH3, with n = 9, 11, 13, 15 and 17, in the preparation of the self-assembled monolayers (SAM) gradients. The contact angles with hexadecane, at the very extreme ends of the gradients, show characteristic values of a highly ordered CH3-like assembly: theta(a) = 45-50 degrees. In the middle of the gradients theta(a) drops noticeably and exhibits values representative for CH2-like polymethylenes, theta(a) = 20-30 degrees, indicating a substantial disordering of the protruding chains of the longer component in the gradient assembly. As expected, the exposure of CH2-groups to the probing liquid increases with increasing differential chain length of the two n-alkanethiol used, in this case eight methylene units. However, the contact angles always display a non-zero value which means that even at a chain length difference of eight methylene units there is a substantial exposure of methyl (CH3) groups to the probing liquid. With infrared reflection-absorption spectroscopy (IRAS) we have monitored the structural behavior of the polymethylene chains along the gradient. We find complementary evidence for disordered chains in the gradient region, and the IRAS results correlate well with the contact angle measurements. (C) 1999 Elsevier Science B.V. All rights reserved.
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| 3. |
- Eriksson, C, et al.
(author)
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Reactions of two hydrophilic surfaces with detergents, protein and whole human blood
- 1997
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In: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 9, s. 67-79
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Journal article (peer-reviewed)abstract
- The surface chemistry of moscovite mica and hydrophilic glass was characterized by ESCA. The adsorption of detergents and lysozyme was measured by surface force methods, ellipsometry or ESCA. The results show that the peotein has a higher affinity to the mica surface. A biological characterisation of the surfaces was performed by exposure to whole blood, followed by detection of surface-adsorbed plasma proteins and cellular antigens by immunofluorescence. The brighteness of the fluorescence was measured by computer-aided image analysis. The results show that the hydrophilic glass was the most efficient activator of serine protease cascade enzymes. Platelets were activated at both surfaces, but were shown to leave the glass surface with time. The glass surface was more inflammatogenic than the mica surface as determined by the CD 11b - integrin expression of PMN-cells. The results indicate that the nonself recognition of the surfaces is an array of subreactions, the kinetics of which determine the outcome of the blood- material contact.
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| 4. |
- Gerdes, S, et al.
(author)
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Spreading of oil droplets on silicon oxide surfaces with parallel v-shaped channels
- 1996
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In: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 116, s. 135-144
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Journal article (peer-reviewed)abstract
- The spreading of silicone oil and paraffin oil has been studied on two energetically and chemically different smooth surfaces (gold and polystyrene). It was found that for these surfaces neither the surface tension nor the surface free energy influenced the spreading behaviour of the oils. The data for the two different liquids can be transposed onto a master curve when the product of velocity and viscosity is plotted versus the dynamic contact angle. Spreading of paraffin oil droplets where also studied on a set of silicone oxide surfaces containing parallel v-shaped surface channels at various widths and spacings. It was found that the sharp edges of the channel walls strongly affected spreading and that droplet shape was distorted from the usual circular shape displayed on a smooth surface. Ån elongated droplet was formed with the contact line following a channel edge and with the short sides having a semi-circular shape. Traverse spreading was very slow and decreased as the spacing was decreased. Increased channel size and decreased spacing produced an increase in spreading velocity in the direction of the channels.
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| 5. |
- Landström, K, et al.
(author)
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A fluorescence method for quantitative measurements of specific protein at powder surfaces
- 1999
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In: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 12, s. 429-440
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Journal article (peer-reviewed)abstract
- A new method using fluorescence labeled proteins was developed to determine the quantitative amount of specific protein at the powder surface. The method is based on steady-state fluorescence measurements of pyrene labeled proteins with oxygen gas phase quenching at the powder surface. The surface load of protein was measured for spray-dried dextran powders containing bovine serum albumin (BSA). The results show a patchwise surface load of about 1.3 mg/m2 at a concentration of 0.33 % (dry weight) BSA in the powder. The patchwise surface load stays constant with increased BSA concentration in the powder.
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| 6. |
- Malmsten, M, et al.
(author)
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Competitive protein adsorption at phospholipid surfaces
- 1995
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In: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 4, s. 173-184
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Journal article (peer-reviewed)abstract
- The interfacial exchange processes between human serum albumin (HSA) and fibrinogen at different surfaces was investigated with in situ ellipsometry and TIRF. With ellipsometry, it was found that the total adsorbed amount at silica on addition of fibrinogen after preadsorption of HSA was quite similar to that obtained without HSA preadsorption. From TIRF, it is concluded that the preadsorbed HSA is displaced, although not completely, on addition of fibrinogen. On the other hand, preadsorbed HSA effectively blocked further adsorption of fibrinogen and IgG at hydrophobic surfaces such as methylated silica. Furthermore, the competitive adsorption of HSA and fibrinogen at two phospholipid surfaces, i e, phosphatidylcholine (PC) and phosphatidic acid (PA), was investigated. It was found that at PA, fibrinogen adsorbs extensively even after preadsorption of HSA. This, however, is achieved with essentially no displacement of the preadsorbed HSA. For PC, finally, the fibrinogen adsorption is much lower than that of HSA, and fibrinogen is able neither to coadsorb with HSA nor to displace the preadsorbed protein.
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| 7. |
- Malmsten, M
(author)
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Ellipsometry studies of fibronectin adsorption
- 1995
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In: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 3, s. 371-381
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Journal article (peer-reviewed)abstract
- The adsorption of fibronectin at a series of different surfaces was investigated with in situ ellipsometry. For silica and methylated silica, the adsorbed amount (G), the adsorbed layer thickness (del) and the mean adsorbed layer refractive index (nf) were obtained by a procedure involving studies of the bare substrate at two different ambient refractive indices, as well as four-zone averaging. It was found that the adsorbed amount of fibronectin was the same (1.9±0.1 mg/m2) at silica and methylated silica. However, the adsorbed layers formed at methylated silica were more extended and had a lower average protein concentration than those formed at silica. Furthermore, at both silica and methylated silica, an increasing adsorbed amount is achieved both by a denser packing of the fibronectin molecules and by a growth of the adsorbed layer normal to the surface. Furthermore, the adsorption of fibronectin at lipid surfaces was investigated. It was found that the adsorption of fibronectin to phosphatidic acid was quite significant (2.2±0.2 mg/m2), while that at phosphatidylcholine, phosphatidylinositol and phosphatidylserine was much smaller (all 0.1±0.05 mg/m2). These results are correlated to findings on the adsorption of fibrinogen at these surface, as well as on the opsonization of lipid-stabilized colloidal particles.
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| 8. |
- Malmsten, M
(author)
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Ellipsometry studies of the effect of surface hydrophobicity on protein adsorption
- 1995
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In: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 3, s. 297-308
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Journal article (peer-reviewed)abstract
- The adsorption of some model proteins, human serum albumin (HSA), IgG, fibrinogen and lysozyme at silica surfaces was investigated with in situ ellipsometry and compared to previous results obtained for methylated silica surfaces. The adsorbed amount (G), the adsorbed layer thickness (del) and the mean adsorbed layer refractive index (nf) were obtained by a procedure involving studies of the bare substrate at two different ambient refractive indices, as well as four-zone averaging. The surface hydrophobicity strongly influenced the adsorption properties of all the proteins studied. For HSA, IgG and fibrinogen, the adsorbed amount was significantly lower at the hydrophilic surface than at the hydrophobic one, whereas the reverse was found for lysozyme. For fibrinogen, the adsorbed layer thickness at silica was smaller than that at methylated silica, whereas the adsorbed layer was more concentrated. For IgG, on the other hand, end-on adsorption was observed at both silica and methylated silica. For lysozyme, side-on adsorption in a dense monolayer was observed at silica, whereas at methylated silica, the adsorption occurs in 2-3 rather dilute molecular layers. Furthermore, the build-up of the adsorbed layers was studied. For fibrinogen, qualitatively the same behaviour was observed for silica and methylated silica, i e, as the adsorbed amount increases, both del and nf increase initially, while closer to adsorption saturation, nf levels off. However, at a given G, del was lower and nf higher at silica than at methylated silica. A similar finding was obtained for lysozyme. These findings are discussed in terms of the adsorbed layer structure and formation.
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| 9. |
- Malmsten, M, et al.
(author)
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Protein adsorption at n-butane plasma polymer surfaces
- 1996
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In: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 6, s. 191-199
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Journal article (peer-reviewed)abstract
- The adsorption of human serum albumin (HSA) and fibrinogen at n-butane plasma polymer surfaces prepared by low temperature plasma polymerization at different energy inputs have been investigated with in situ ellipsometry. Within experimental uncertainty, the adsorption of both fibrinogen and HSA is constant over the power range used for the preparation of the n-butane surfaces and corresponds to that found for other hydrophobic surfaces at similar conditions. Furthermore, novel copolymer surfaces of n-butane and nitrogen at different ratios were prepared and investigated. Increasing the nitrogen content in the gas mixture during deposition resulted in an increased density of interfacial amine groups, as evidenced by an increased wettability, an increased interfacial nitrogen content, and an increased surface positive charge. This, in turn, was found to result in an increased fibrinogen adsorption, but in a weak decrease in the HSA adsorption.
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| 10. |
- Nylander, T, et al.
(author)
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Wetting of β-casein layers adsorbed at the solid-aqueous interface
- 1999
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In: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 15, s. 253-261
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Journal article (peer-reviewed)abstract
- The wetting by water of adsorbed layer of β-casein on hydrobised silica and pure (hydrophilic) silica surface was investigated by dynamic contact angle measurements based on the Wilhelmy plate principle. The results are discussed in relation to adsorption studies on similar surfaces using in situ ellipsometry. The results show that adsorbing β-casein to a hydrophobic surface lead to a significant decrease of the contact angle in particular in terms of the receding contact angle, for which a decrease of about 70 degrees was observed. This indicates a strong shielding of the hydrophobic surface by hydrophilic β-casein groups. Adding a specific enzyme, endoproteinase Asp-N, which previously have been proposed to remove a large fraction of these segments, results in a significantly decreased wettability of the solid surface. The layer is now more hydrophobic and the hysterises is much smaller. The receding contact angle after the proteolysis is roughly 70°. The results are consistent with the hypothesis that β-casein adsorb at hydrophobic surface to form a monolayer with the hydrophobic part of the protein anchored at the surface, leaving the hydrophilic segments dangling into the solution. On the hydrophilic surface, less dramatic effects are observed in terms of changes of the wettability. The surface is still quite hydrophilic both after adsorbing β-casein and exposing the layer to endoporteinase Asp-N. These results confirm previously discussed differences in the structure of β-casein layers on the hydrophobic and hydrophilic surface.
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