Triggering protein adsorption on tailored cationic cellulose surfaces.

The equipment of cellulose ultrathin films with BSA (bovine serum albumin) via cationization of the surface by tailor-made cationic celluloses is described. In this way, matrices for controlled protein deposition are created, whereas the extent of protein affinity to these surfaces is controlled by the charge density and solubility of the tailored cationic cellulose derivative. In order to understand the impact of the cationic cellulose derivatives on the protein affinity, their interaction capacity with fluorescently labeled BSA is investigated at different concentrations and pH values. The amount of deposited material is quantified using QCM-D (quartz crystal microbalance with dissipation monitoring, wet mass) and MP-SPR (multi-parameter surface plasmon resonance, dry mass), and the mass of coupled water is evaluated by combination of QCM-D and SPR data. It turns out that adsorption can be tuned over a wide range (0.6-3.9 mg dry mass m(-2)) depending on the used conditions for adsorption and the type of employed cationic cellulose. After evaluation of protein adsorption, patterned cellulose thin films have been prepared and the cationic celluloses were adsorbed in a similar fashion as in the QCM-D and SPR experiments. Onto these cationic surfaces, fluorescently labeled BSA in different concentrations is deposited by an automatized spotting apparatus and a correlation between the amount of the deposited protein and the fluorescence intensity is established.

Interaction and structure in polyelectrolyte/clay multilayers: a QCM-D study.

This study focuses on the investigation of the influence of the ionic strength on the internal structure, film forming behavior, and swelling properties of polyelectrolyte/clay multilayers. Layer-by-layer films were prepared with three different polyelectrolytes [polyethylenimine (PEI), polydiallyldimethylammoniumchloride (pDADMAC), and 2-hydroxy-3-trimethylammonium propyl chloride starch (HPMA starch)] in combination with laponite clay platelets on three different surfaces. All experiments were carried out at two different ionic strengths (30 mM or 500 mM NaCl). The experiments performed with strong polyelectrolytes revealed a higher film thickness and adsorbed masses of clay and polyelectrolyte at 500 mM NaCl. The films containing PEI showed different behavior and were considerably less sensitive to changes in the ionic strength. This was also reflected by the swelling behavior as demonstrated by quartz crystal microbalance with dissipation (QCM-D) measurements. Films comprising PEI showed, in contrast to the other polyelectrolytes, much lower swelling in water leading to more compact and stable films in humid environments which is important for numerous applications of LbL clay coatings.

Generalized indirect Fourier transformation as a valuable tool for the structural characterization of aqueous nanocrystalline cellulose suspensions by small angle X-ray scattering.

Small angle X-ray scattering (SAXS) is employed to characterize the inner structure and shape of aqueous nanocrystalline cellulose suspensions using the generalized indirect Fourier transformation (GIFT). The use of the GIFT approach provides a single fitting procedure for the determination of intra- and interparticle interactions due to a simultaneous treatment of the form factor P(q) and the structure factor S(q). Moreover, GIFT allows for the determination of particle charges and polydispersity indices. As test material, aqueous nanocrystalline cellulose suspensions (aNCS) prepared by the H2SO4 route have been investigated and characterized (SAXS, dynamic light scattering, zeta potential).

A luminescence lifetime-based capillary oxygen sensor utilizing monolithically integrated organic photodiodes.

A novel optical sensor device monolithically integrated on a glass capillary is presented. Therefore, we took advantage of the ability to fabricate organic optoelectronic devices on non-planar substrates. The functionality of the concept is demonstrated by realizing an integrated oxygen sensor based on luminescence decay time measurement.

Increased adipose tissue oxygen tension in obese compared with lean men is accompanied by insulin resistance, impaired adipose tissue capillarization, and inflammation.

BACKGROUND: Adipose tissue (AT) dysfunction in obesity contributes to chronic, low-grade inflammation that predisposes to type 2 diabetes mellitus and cardiovascular disease. Recent in vitro studies suggest that AT hypoxia may induce inflammation. We hypothesized that adipose tissue blood flow (ATBF) regulates AT oxygen partial pressure (AT P(O2)), thereby affecting AT inflammation and insulin sensitivity. METHODS AND RESULTS: We developed an optochemical measurement system for continuous monitoring of AT P(O2) using microdialysis. The effect of alterations in ATBF on AT P(O2) was investigated in lean and obese subjects with both pharmacological and physiological approaches to manipulate ATBF. Local administration of angiotensin II (vasoconstrictor) in abdominal subcutaneous AT decreased ATBF and AT P(O2), whereas infusion of isoprenaline (vasodilator) evoked opposite effects. Ingestion of a glucose drink increased ATBF and AT P(O2) in lean subjects, but these responses were blunted in obese individuals. However, AT P(O2) was higher (hyperoxia) in obese subjects despite lower ATBF, which appears to be explained by lower AT oxygen consumption. This was accompanied by insulin resistance, lower AT capillarization, lower AT expression of genes encoding proteins involved in mitochondrial biogenesis and function, and higher AT gene expression of macrophage infiltration and inflammatory markers. CONCLUSIONS: Our findings establish ATBF as an important regulator of AT P(O2). Nevertheless, obese individuals exhibit AT hyperoxia despite lower ATBF, which seems to be explained by lower AT oxygen consumption. This is accompanied by insulin resistance, impaired AT capillarization, and higher AT gene expression of inflammatory cell markers. CLINICAL TRIAL REGISTRATION- URL: http://www.trialregister.nl. Unique identifier: NTR2451.

Adsorption of carboxymethyl cellulose on polymer surfaces: evidence of a specific interaction with cellulose.

The adsorption of carboxymethyl cellulose (CMC), one of the most important cellulose derivatives, is crucial for many scientific investigations and industrial applications. Especially for surface modifications and functionalization of materials, the polymer is of interest. The adsorption properties of CMC are dependent not only on the solutions state, which can be influenced by the pH, temperature, and electrolyte concentration, but also on the chemical composition of the adsorbents. We therefore performed basic investigation studies on the interaction of CMC with a variety of polymer films. Thin films of cellulose, cellulose acetate, deacetylated cellulose acetate, polyethylene terephthalate, and cyclo olefin polymer were therefore prepared on sensors of a QCM-D (quartz crystal microbalance) and on silicon substrates. The films were characterized with respect to the thickness, wettability, and chemical composition. Subsequently, the interaction and deposition of CMC in a range of pH values without additional electrolyte were measured with the QCM-D method. A comparison of the QCM-D results showed that CMC is favorably deposited on pure cellulose films and deacetylated cellulose acetate at low pH values. Other hydrophilic surfaces such as silicon dioxide or polyvinyl alcohol coated surfaces did not adsorb CMC to a significant extent. Atomic force microcopy confirmed that the morphology of the adsorbed CMC layers differed depending on the substrate. On hydrophobic polymer films, CMC was deposited in the form of larger particles in lower amounts whereas hydrophilic cellulose substrates were to a high extent uniformly covered by adsorbed CMC. The chemical similarity of the CMC backbone seems to favor the irreversible adsorption of CMC when the molecule is almost uncharged at low pH values. A selectivity of the cellulose CMC interaction can therefore be assumed. All CMC treated polymer films exhibited an increased hydrophilicity, which confirmed their modification with the functional molecule.

Nonradiative deactivation of europium(III) luminescence as a detection scheme for moisture.

The nonradiative deactivation of the excited state of europium(III)-based phosphors via OH-vibrations in the presence of water allows the detection of moisture in nitrogen at concentration levels down to at least 25 ppm (0.09% RH).

Adsorption of fucoidan and chitosan sulfate on chitosan modified PET films monitored by QCM-D.

The adsorption behavior of fucoidan as well as chitosan derivatives (chitosan sulfate) on poly(ethylene terephthalate) (PET) model film surface was studied using the quartz crystal microbalance technique. These systems were chosen for this study due to their promising biocompatible properties. Moreover, fucoidan and chitosan sulfate have promising anticoagulant properties and represent an alternative to heparin treatment of vascular grafts. As a first step, PET foils were activated by alkaline hydrolysis to increase their hydrophilicity. From these foils, model PET films were prepared by the spin coating technique on a silica quartz crystal. The selected polysaccharides (chitosan, fucoidan, and chitosan sulfate) were adsorbed from aqueous solutions on the PET surfaces. The adsorption was monitored using a quartz crystal microbalance with a dissipation unit. The surface chemistry and morphology of the chitosan/fucoidan or chitosan/chitosan sulfate coated PET-H films was analyzed using XPS and AFM. It was found that chitosan/fucoidan films were thinner and more compressed, while in the case of chitosan/chitosan sulfate, large amounts of chitosan sulfate were adsorbed, indicating a loose and thick adsorbed film.

Adsorption of chitosan on PET films monitored by quartz crystal microbalance.

The adsorption behavior of chitosan on poly(ethylene terephthalate) (PET) model film surface was studied using the quartz crystal microbalance (QCM) technique. QCM with a dissipation unit (QCM-D) represents a very sensitive technique for adsorption studies at the solid/liquid interface in situ, with capability of detecting a submonolayer of adsorbate on the quartz crystal surface. Chitosan as well as PET were chosen for this study due to their promising biocompatible properties and numerous possibilities to be used in biomedical applications. As a first step, PET foils were activated by alkaline hydrolysis in order to increase their hydrophilicity. Model thin films were prepared from PET foils by the spin coating technique. The chemical composition of the obtained model PET films was analyzed using X-ray photoelectron spectroscopy (XPS) and their morphology was characterized by atomic force microscopy (AFM). Furthermore, the adsorption behavior of chitosan on these activated PET films and the influence of adsorption parameters (pH, ionic strength and chitosan solution concentration) were investigated in detail. Additionally, the surface chemistry and morphology of the PET films and the chitosan coated PET films were analyzed with XPS and AFM.

Advanced Photonic Sensors Based on Interband Cascade Lasers for Real-Time Mouse Breath Analysis.

A multiparameter gas sensor based on distributed feedback interband cascade lasers emitting at 4.35 µm and ultrafast electro-spun luminescence oxygen sensors has been developed for the quantification and continuous monitoring of 13CO2/12CO2 isotopic ratio changes and oxygen in exhaled mouse breath samples. Mid-infrared absorption spectra for quantitatively monitoring the enrichment of 13CO2 levels were recorded in a miniaturized dual-channel substrate-integrated hollow waveguide using balanced ratiometric detection, whereas luminescence quenching was used for synchronously detecting exhaled oxygen levels. Allan variance analysis verified a CO2 measurement precision of 1.6‰ during a 480 s integration time. Routine online monitoring of exhaled mouse breath was performed in 14 mechanically ventilated and instrumented mice and demonstrated the feasibility of online isotope-selective exhaled breath analysis within microliters of probed gas samples using the reported combined sensor platform.

Development and Characterization of a Parallelizable Perfusion Bioreactor for 3D Cell Culture.

The three dimensional (3D) cultivation of stem cells in dynamic bioreactor systems is essential in the context of regenerative medicine. Still, there is a lack of bioreactor systems that allow the cultivation of multiple independent samples under different conditions while ensuring comprehensive control over the mechanical environment. Therefore, we developed a miniaturized, parallelizable perfusion bioreactor system with two different bioreactor chambers. Pressure sensors were also implemented to determine the permeability of biomaterials which allows us to approximate the shear stress conditions. To characterize the flow velocity and shear stress profile of a porous scaffold in both bioreactor chambers, a computational fluid dynamics analysis was performed. Furthermore, the mixing behavior was characterized by acquisition of the residence time distributions. Finally, the effects of the different flow and shear stress profiles of the bioreactor chambers on osteogenic differentiation of human mesenchymal stem cells were evaluated in a proof of concept study. In conclusion, the data from computational fluid dynamics and shear stress calculations were found to be predictable for relative comparison of the bioreactor geometries, but not for final determination of the optimal flow rate. However, we suggest that the system is beneficial for parallel dynamic cultivation of multiple samples for 3D cell culture processes.

Measurements of transient membrane potential after current switch-off as a tool to study the electrochemical properties of supported thin nanoporous layers.

We have studied the potential of chronopotentiometry after current switch-off as a tool for electrochemical characterization of thin supported nanoporous layers. Within the scope of this technique, a thin supported electrochemically active layer is polarized by direct electric current until a steady state is reached. After that, the current is switched-off in a stepwise manner, and the reading of transient membrane potential begins. A linear non-steady-state theory of the method has been developed in terms of a model-independent approach of network thermodynamics. The measurements of transient membrane potential after current switch-off have been carried out in KCl solutions of various concentrations for a commercially available nanofiltration membrane (Desal5 DK). Such membranes consist of micron-thick active (or barrier) nanoporous layers and much thicker (100-200 microm) and coarse-porous supports (the pore size usually is 0.1-5 microm). The reproducibility of the method has been found to be quite reasonable especially in not too dilute electrolyte solutions and at not too short times (> or = 10 ms). The relaxation measurements have been complemented by the measurements of the steady-state membrane potential and by sample measurements of salt rejection in the pressure-driven mode, which enabled us to carry out a self-consistent interpretation of the experimental data. This has revealed, in particular, that the ion rejection mechanism related to the fixed electric charges is not the dominant one in the case of the Desal5 DK nanofiltration membrane. Proceeding from a quantitative interpretation of relaxation patterns, we could also determine some properties of membrane support, namely, the porosity and the salt diffusivity. They have been found to have reasonable values remarkably independent of salt concentration, which confirms the self-consistency of our interpretations.

Surface thermodynamic properties of polyelectrolyte multilayers.

Multilayer architectures of polyelectrolytes fabricated by the layer-by-layer technique (LbL) on pretreated polymeric and inorganic substrates were studied by contact angle measurements. Poly(diallyldimethylammonium chloride), PDADMAC, and poly(sodium 4-styrenesulfonate), PSS, were used as polyelectrolytes. Contact angle data were used to calculate the van der Waals and Lewis acid-base components of the surface tension of the investigated surfaces. Knowledge of these quantities provides valuable information on surface composition, coating density, and possible interactions of the surface with other substances. Unusual wetting behavior of PDADMAC layers upon prewetting of the multilayer surfaces was found and described in terms of surface tension changes. A model of polymer chain rearrangement upon wetting was proposed to explain this behavior.

Antifouling coating of cellulose acetate thin films with polysaccharide multilayers.

In this investigation, partially deacetylated cellulose acetate (DCA) thin films were prepared and modified with hydrophilic polysaccharides with the layer-by-layer (LbL) technique. As polysaccharides, chitosan (CHI) and carboxymethyl cellulose (CMC) were used. DCA thin films were manufactured by exposing spin coated cellulose acetate to potassium hydroxide solutions for various times. The deacetylation process was monitored by attenuated total reflectance-infrared spectroscopy, film thickness and static water contact angle measurements. A maximum of three bilayers was created from the alternating deposition of CHI and CMC on the DCA films under two different conditions namely constant ionic strengths and varying pH values of the CMC solutions. Precoatings of CMC at pH 2 were used as a base layer. The sequential deposition of CMC and CHI was investigated with a quartz crystal microbalance with dissipation, film thickness, static water contact angle and atomic force microscopy (AFM) measurements. The versatility and applicability of the developed functional coatings was shown by removing the multilayers by rinsing with mixtures containing HCl/NaCl. The developed LbL coatings are used for studying the fouling behavior of bovine serum albumin (BSA).

Gold nanoparticles in the engineering of antibacterial and anticoagulant surfaces.

Simultaneous antibacterial and anticoagulant surfaces have been prepared by immobilization of engineered gold nanoparticles onto different kinds of surfaces. The gold nanoparticle core is surrounded by a hemocompatible, anticoagulant polysaccharide, 6-O chitosan sulfate, which serves as reduction and stabilizing agent for the generation of gold nanoparticles in a microwave mediated reaction. The particle suspension shows anticoagulant activity, which is investigated by aPTT and PT testing on citrated blood samples of three patients suffering from congenital or acquired bleeding disorders. The amount of nanoparticles deposited on the surfaces is quantified by a quartz crystal microbalance with dissipation unit. All gold containing surfaces exhibit excellent antimicrobial properties against the chosen model organism, Escherichia coli MG 1655 [R1-16]. Moreover, blood plasma coagulation times of the surfaces are increased after deposition of the engineered nanoparticles as demonstrated by QCM-D.

Increased shear stress- and ristocetin-induced binding of von Willebrand factor to platelets in cord compared with adult plasma.

Multiple indications do exist that the extensive neonatal platelet adhesion and aggregation, and the shorter closure time of neonatal compared with adult whole blood in the platelet function analyzer 100 are attributable to the physiological high plasma concentrations and high concentrations of unusually large von Willebrand factor (vWf) multimers in neonates. However, to date the direct experimental evidence is lacking. Therefore, we compared in the present study the ability of neonatal vWf to bind to platelets to that of adult vWf. Platelet-poor plasma of neonatal or adult origin, containing antibody-stained vWf, was incubated with neonatal or adult platelet suspension. Subsequently, vWf-platelet interaction was induced by exposing the mixture to shear stress by means of a cone/plate measuring system or by incubating the mixture with ristocetin. Finally, samples were analyzed in a FACScan flow cytometer. Detected fluorescence intensities directly correlate with the amount of vWf attached to the platelet surface. We found that significantly higher amounts of neonatal vWf were attached to platelets in the presence of shear stress or ristocetin. This efficient neonatal vWf-platelet interaction is an effect intrinsic to the neonatal vWf, and not to the neonatal platelet: the amount of neonatal vWf attached to neonatal platelets was not different from the amount of neonatal vWf attached to adult platelets. Furthermore, decreasing the vWf content in cord plasma to adult level resulted in significantly suppressed vWf-platelet attachment in the presence of ristocetin, indicating that the high neonatal vWf level contributes to the efficient vWf-platelet binding in neonates.

Application of mid-infrared spectroscopy: measuring hydrogen peroxide concentrations in bleaching baths.

The presented work applies mid-infrared attenuated total reflection (ATR) spectroscopy to the measurment of hydrogen peroxide in aqueous matrices. The performance of different ATR crystals mounted in flow cells was investigated in the presence of aqueous hydrogen peroxide solutions. Quantitative determination has been achieved by evaluation of specific OH stretching and deformation vibrations with linear correlation between peak areas or peak heights and hydrogen peroxide concentration in the range of 1-10% (weight in water). Important aspects such as chemical stability of the waveguide material and influences of pH and ionic strength on the performance are discussed. Feasibility for the investigation of real world samples is demonstrated by measuring industrial bleaching solutions with known concentrations of hydrogen peroxide fitting well with calibration graphs established with neat hydrogen peroxide solutions. The presented sensor system is capable of determining hydrogen peroxide within complex matrices and clearly corroborates the potential of providing an in situ measurement concept for on-line hydrogen peroxide detection.

Interaction and enrichment of protein on cationic polysaccharide surfaces.

In this study, the interaction of fluorescein isothiocyanate functionalized bovine serum albumin (FITC-BSA) with cellulose surfaces decorated with trimethyl chitosan (TMC) is investigated. Two types of TMC, one exhibiting a lower and one with a higher degree of cationization are used for protein adsorption. The adsorption is carried out at different pH values and concentrations of the protein solution. The amount, morphology and wettability of FITC-BSA coating on TMC/cellulose films are determined using quartz crystal microbalance with dissipation (QCM-D), atomic force microscopy, fluorescence microscopy and contact angle measurements. A lower pH and higher concentration of protein solution resulted in a greater amount of irreversibly adsorbed material owing to the reduced solubility and minimized electrostatic repulsion. A maximum adsorption of protein is observed on cellulose surfaces functionalized with TMC carrying a higher degree of cationization compared to TMC with a lower degree of cationization and pure cellulose surfaces at all applied concentrations and pH values. BSA is a commonly used model protein and is applied in this study to better understand its interaction with cationically rendered cellulose surfaces. Such knowledge is essential for creation of multifunctional polysaccharide-based biomaterials.

Design of anticoagulant surfaces based on cellulose nanocrystals.

The anticoagulant activity of surfaces decorated with cellulose nanocrystals (CNCs) prepared via sulfuric acid hydrolysis, is explored. Such surfaces bear a high amount of negatively charged sulfate groups, which mimic the naturally occurring anticoagulant heparin in terms of charge density. It is demonstrated that CNC decorated surfaces significantly enhance the coagulation times of blood plasma and whole blood as proven by QCM-D and simple clotting tests.

Viscoelastic properties of fibrinogen adsorbed onto poly(ethylene terephthalate) surfaces by QCM-D.

In presented study a new approach using QCM-D for biocompatibility determination was introduced. The adsorption of fibrinogen on PET and modified PET surfaces was monitored in situ using QCM-D. Protein layer thicknesses were estimated on the basis of a Voight based viscoelastic model. The hydrophilicities and morphologies of the surfaces were investigated using a goniometer and AFM. The results showed that PET surfaces coated with sulphated polysaccharides are more hydrophilic and more fibrinogen-repulsive than non-modified PET surfaces. QCM-D equipped with QTools modelling software is well-applicable to the characterisation of surface properties and can be optimised for biocompatibility determination.