Ulf Jonsson

Adsorption behavior of fibronectin on well-characterized silica surfaces

The adsorption behavior of human plasma fibronectin at physiological pH and ionic strength was investigated by in situ ellipsometry on silica substrates of two different surface energies. The silica substrate was characterized by ellipsometry, galvanic potential, and critical surface tension measurements. Adsorption isotherms in the low concentration range for fibronectin were compared with human fibrinogen and found to be qualitatively similar with increased amounts of protein adsorbed at the plateau on a hydrophobic surface as compared to a hydrophilic one. Reversibility for fibronectin upon dilution was found to be small on a hydrophobic surface while a partial desorption was found on a hydrophilic one. Interaction of antibodies with preadsorbed fibronectin suggests that fibronectin adsorbs in different conformations and/or arrangements on the two types of surfaces. The lectin Concanavalin A and its interaction with preadsorbed fibronectin was also investigated.

Adsorption of immunoglobulin G, protein A, and fibronectin in the submonolayer region evaluated by a combined study of ellipsometry and radiotracer techniques

The adsorption of the proteins: immunoglobulin G, protein A, and fibronectin was quantitated in a study applying both ellipsometry and radiotracer techniques. 14C- and 125I-labeled proteins at different concentrations were adsorbed to silica surfaces with three different solid surface tensions. The interaction of antibodies with a preadsorbed antigen film was also investigated. The surfaces were characterized by ellipsometry, contact angle measurements, and scanning electron microscopy. The proteins were characterized by gel electrophoresis. A linear relationship for the change in the ellipsometric parameter Δ and adsorbed amount was found for immunoglobulin G and protein A. A deviation from linearity was found for fibronectin adsorbed to two types of surfaces. The result was interpreted as similarities in the structure of the adsorbed IgG film on the different types of surfaces, whereas the structure of the adsorbed HFN film showed dependence on the solid surface tension. The results were discussed in view of the ellipsometric theories for adsorbed molecules in the submonolayer region. The amounts of adsorbed proteins obtained from the radiolabeling experiments agreed well with those calculated from ellipsometric data.

Adsorption of proteins on metal surfaces studied by ellipsometric and capacitance measurements

Abstract The adsorption of proteins on metal surfaces has been studied with simultaneous ellipsometric, capacitance and open-cell potential measurements. The effect of the nature of the metal on the amount and the configuration of adsorbed lysozyme and ovalbumin has been investigated. Lysozyme and ovalbumin were adsorbed on well-defined evaporated metal films of platinum, titanium, and zirconium. The metals were characterized in terms of surface free energy, open-cell rest potential, and surface texture. All three metals were found to have a similar surface free energy and to be perfectly smooth at a 600 A level. The open-cell rest potential was +350, -140 and -560 mV (saturated calomel electrode) for platinum, titanium and zirconium, respectively. The adsorbed protein layer was characterized through its surface concentration, optical thickness, refractive index, and relative surface coverage as a function of time. The nature of the metals was shown significantly to determine the configuration of the adsorbed protein molecules. Lysozyme was adsorbed in a two-layer structure, with more extended molecules for the metals, in the order platinum, titanium, and zirconium. Compared with the number of lysozyme molecules on platinum, the number of molecules is slightly smaller than on titanium and considerably larger on zirconium. Ovalbumin was adsorbed in a monolayer structure, with more extended molecules for the metals, in the order platinum, titanium, and zirconium. The number of ovalbumin molecules was markedly smaller on titanium and zirconium than on platinum. The densities of both the adsorbed lysozyme and ovalbumin molecules decrease for the metals in the order platinum, titanium, and zirconium. These results are consistent with electrostatic interactions between protein charges and the characteristic charge of the metal as determining factors for the amount and configuration of the adsorbed molecules. However, the adsorption of lysozyme on platinum also indicates that non-electrical forces might be important. The results are discussed in terms of some possible models for the adsorption of proteins on surfaces.

Chemical vapour deposition of silanes

Abstract Chemical surface modification of oxide-covered surfaces by silanization is a well-known technique in such fields as gas and liquid chromatography, electro-chemistry and immobilization of biomolecules. In the commonly used silanization technique the silane is reacted with the surfaces in a liquid phase. If strict anhydrous conditions do not prevail, however, this technique often results in polymerization, irreproducibility and instability of the silane films. We report here on a gas phase silanization of silicon surfaces at elevated temperatures. The method comprises a washing and surface activation step followed by silanization at about 0.5–1 Nm −2 and 80–190 °C depending on the type of silane. The silanized surfaces were characterized by ellipsometry, contact angle measurements and scanning electron microscopy, which revealed smooth, stable and reproducible silane films of monolayer character. A comparison of surfaces that were silanized in the gas phase with those that were silanized in the liquid phase was also made.

Immunoglobulin G and secretory fibronectin adsorption to silica: The influence of conformational changes on the surface

Abstract The adsorption isotherms for immunoglobulin G (IgG) and secretory fibronectin (HFN) on silica with two different surface free energies were compared by in situ ellipsometry. The isotherms were obtained by either direct- or successive-addition of the proteins. The influence of the initial concentration, the incubation time, and the ionic strength were investigated. The adsorption isotherms for IgG were also compared with isotherms obtained for IgG interacting with a surface immobilized film of Protein A. A significant difference between the direct- and successive-addition isotherms was found for both proteins on hydrophobic silica, whereas the isotherms essentially coincide for the proteins on hydrophilic silica. The same qualitative behavior was found for both proteins on both types of surfaces for the two different ionic strengths tested. The results were interpreted as time-dependent conformational changes in the adsorbed protein film, where the degree of changes was dependent on the solid surface free energy. These changes were most pronounced on hydrophobic silica.

Goretex prosthetic ligament vs. Kennedy ligament augmentation device in anterior cruciate ligament reconstruction. A prospective randomized 3-year follow-up of 41 cases.

In a prospective randomized study on patients with functional instability due to old anterior cruciate ligament tears, 18 were randomized to a Goretex reconstruction and 23 to augmentation with the Kennedy Ligament Augmentation Device (LAD). All operations were performed with use of a modified over-the-top technique. At follow-up (median 36 months), improvements in Lysholm scores, activity scores, and arthrometry values were recorded in both groups as compared with preoperative levels. The LAD group had better Lysholm scores than the Goretex group. Among Goretex-reconstructed knees, effusion and pain occurred, and major effusions in two knees caused by the Goretex artificial ligament were indications for graft explant after 4 years. Our short-term results with the Goretex prosthetic ligament are not acceptable because of effusions and of pain. Our short-term results of the LAD polypropylene braid as an augmentation to an autologous graft seem promising.

Flow-injection ellipsometry — an in situ method for the study of biomolecular adsorption and interaction at solid surfaces

Abstract An ellipsometric technique for the study of biomolecular interactions at the solid—liquid interface is described. The technique consists of a flow-injection system and a micro flow cell with low dead volume together with a dynamic ellipsometric set-up. The kinetics of biomolecular adsorption and interactions, as well as the effect of flow rate and rinsing, may be studied in an easy and reproducible way. The system was exemplified by the reversible adsorption of lysozyme on silica surfaces and by the reversible interaction of Immunoglobulin G with an immobilized film of Protein A.

Bone and muscle mass after hip arthroplasty A quantitative computed tomography study in 20 arthrosis cases

We performed a prospective, quantitative computed tomography (QCT) study of bone mineral density (BMD), cortical bone volume, bone mass and muscle volume in 20 patients who were operated on with cemented total hip arthroplasty because of unilateral arthrosis. Both extremities were measured preoperatively, 3 and 6 months after the operation by a single-energy computer tomograph equipped for bone mineral densitometry. Preoperatively, we found a 25 percent decrease in muscle volume of the thigh on the arthrosis side compared to the contralateral side, but only a 6 percent decrease in bone mass, mainly of the cortical bone volume in the middle femur. In the cancellous bone of distal femur and proximal tibia there was a reduction in BMD of 11 and 14 percent, respectively, compared to the contralateral side. After 6 months, we found no changes in cortical bone mass, either on the operated femur or on the contralateral, control femur. The BMD of cancellous bone in distal femur and proximal tibia had not changed. However, the thigh muscle on the operated side showed a strong recovery; 6 months after the operation there was a 19 percent gain on the operated side.

[34] Surface immobilization techniques in combination with ellipsometry

Publisher Summary The rapid development of bioanalytical methods and biosensors involving immobilized enzymes or antibodies focuses interest on the interaction of biomolecules at inorganic surfaces. It is also of importance to use efficient, gentle, and durable immobilization techniques and that the techniques are suited for large-scale production of sensor devices. The function of several surface-sensitive sensors based on electrochemical, optical, and gravimetric methods requires a proper immobilization of biomolecules to inorganic surfaces. Most such surfaces do not carry suitable chemically reactive groups. Such groups may, however, be introduced by chemical surface modification such as silanization. This process is commonly performed by deposition of the silane from a liquid phase. Several problems, such as nonuniformity of the deposited silane film thickness, codeposition of polymeric silane particles, and hydrolytic removal of the deposited film, occur using this method and are not acceptable for optimum performance of the surface-sensitive measuring devices. Vapor phase silanization can overcome some of these problems. The chemical vapor deposition technique is used for alkoxysilanes. The technique is exemplified by the covalent binding of protein A to silanized silica surfaces and the interaction of the immobilized protein A with immunoglobulins. The result is evaluated by in situ ellipsometry, an optical technique based on reflection of polarized light from a surface.

Applicability of 8OCB for temperature calibration of temperature modulated calorimeters

Abstract Calibration of temperature modulated calorimeters (TMC) is essential because it is often not possible to calculate heat capacity and sample temperature directly from the quantities measured. The question arises whether temperature calibration used in conventional calorimetry is also valid for TMC’s. To prove this, a well defined transition is needed which does not disturb the temperature profile within the sample during modulation. The response of the whole system (calorimeter, sample, transition) must be linear. Some low energy liquid crystal transitions behave in this way, under certain conditions, and can be used for temperature calibration in TMC’s. The procedure is demonstrated for the nematic to smectic-A transition in a cyanobiphenyl liquid crystal (8OCB). The applicability of 8OCB for temperature calibration is shown for temperature modulated DSC, AC calorimeter, 3 ω method and photo-acoustic method.