8 research outputs found

    Characterization of Polymer Membranes by MALDI Mass-Spectrometric Imaging Techniques

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    For physical and chemical characterization of polymers, a wide range of analytical methods is available. Techniques like NMR and X-ray are often combined for a detailed characterization of polymers used in medical applications. Over the past few years, MALDI mass-spectrometry has been developed as a powerful tool for space-resolved analysis, not least because of its mass accuracy and high sensitivity. MALDI imaging techniques combine the potential of mass-spectrometric analysis with imaging as additional spatial information. MALDI imaging enables the visualization of localization and distribution of biomolecules, chemical compounds, and other molecules on different surfaces. In this study, surfaces of polymeric dialyzer membranes, consisting of polysulfone (PS) and polyvinylpyrrolidone (PVP), were investigated, regarding chemical structure and the compound’s distribution. Flat membranes as well as hollow fiber membranes were analyzed by MALDI imaging. First, analysis parameters like laser intensity and laser raster step size (spatial resolution in resulting image) were established in accordance with polymer’s characteristics. According to the manufacturing process, luminal and abluminal membrane surfaces are characterized by differences in chemical composition and physical characteristics. The MALDI imaging demonstrated that the abluminal membrane surface consists more of polysulfone than polyvinylpyrrolidone, and the luminal membrane surface displayed more PVP than PS. The addition of PVP as hydrophilic modifier to polysulfone-based membranes increases the biocompatibility of the dialysis membranes. The analysis of polymer distribution is a relevant feature for characterization of dialysis membranes. In conclusion, MALDI imaging is a powerful technique for polymer membrane analysis, regarding not only detection and identification of polymers but also localization and distribution in membrane surfaces

    Macroporous StarPEG-Heparin Cryogels

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    Macroporous scaffolds with adaptable mechanical and biomolecular properties can be instrumental in enabling cell-based therapies. To meet these requirements, a cryostructuration method was adapted to prepare spongy hydrogels based on chemically cross-linked star-shaped poly­(ethylene glycol) (starPEG) and heparin. Subzero temperature treatment of the gel forming reaction mixtures and subsequent lyophilization of the incompletely frozen gels resulted in macroporous biohybrid cryogels showing rapid swelling, porosity of up to 92% with interconnected large pores (30–180 μm), low bulk stiffness, and high mechanical stability upon compression. The applicability of the cryogel scaffolds was investigated using human umbilical vein endothelial cells. Cell attachment and three-dimensional spreading resulted in evenly distributed viable cells within the macroporous starPEG-heparin materials, demonstrating the significant translational potential of the developed three-dimensional cell carriers

    Remaining open cross-sectional area as a function of the number of cells.

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    <p>The ratio between the space to be filled (i.e. remaining open cross-sectional area) and the initial cross-sectional area of the pores was plotted as a function of the number of cells within that pore for the different categories. Experimental data is shown as circles for the different categories. Simulation data is displayed as lines with different shadings from black to light grey for different variation ranges for the covered area (R = 1: new cells positioned at locations of largest covered area per cell; R = 0: random position of new cells on the remaining inner pore surface). Simulation was based on a 2D model. Experimental data points were extracted from z-stack maximum projection for 2D analysis. Lines represent the average of ten simulations. Simulation stopped when the remaining inner diameter of the pore was smaller than the cell size. Within each graph the cell organization for a remaining area between 0.5 and 0.6 of the initial pore area according to the simulation is given. Dashed lines represent pore closure extracted from experimental data. Due to the porosity of the fibronectin network the remaining open area did not reach a zero value.</p

    Maximal spreading length of fibroblasts and pore wall to wall distance within StarPEG-heparin cryogel.

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    <p>Maximal spreading length <i>d</i><sub>cell,spread</sub> of the different human dermal fibroblasts are represented by white bars and wall to wall distance <i>d</i><sub>pore,min</sub> of the pore analyzed in the scaffold by dark grey bars. The overlapping area is displayed in light grey. Gaussian fit was performed for maximum cell spreading (continuous line) and pore diameter (dashed line) distribution. The data was obtained by combining all the imaging performed on the starPEG-heparin cryogel (N<sub>pores</sub> >100) and cells contained in pores (N<sub>cells</sub> >200).”</p

    Filling of scaffold pores by fibroblasts for three pore size categories and three time points.

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    <p>Confocal microscopy for visualization of actin cytoskeleton (green) and cell nuclei (blue) to illustrate the filling of scaffold pores by human fibroblasts at day 1, 3, and 7 for the three pore size categories (scale bar equals 100 µm). Data shown corresponds to the maximum projection images of the 3D image stacks recorded inside scaffolds. During the imaging, scaffold pores could be identified due to background staining of the scaffold material and are highlighted by dashed lines.</p

    Fibronectin organization for three pore size categories and three time points.

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    <p>Confocal microscopy for visualization of fibronectin network (red) to illustrate the filling of scaffold pores until day 1, 3, and 7 and the three pore size categories (scale bar equals 100 µm). Data shown corresponds to the maximum projection images of the 3D image stacks recorded inside scaffolds. During the imaging, scaffold pores were observed due to some background staining and where delimited here by dashed lines.</p

    Schematic representation of pore filling as a function of time.

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    <p>Cells are represented by tensioned chords in green and fibronectin is in red. Initially cells are spreading on the pore wall and fibronectin is being produced but not visible as a connected network yet by the cells (top). The pore is subsequently filled by cells with time according to the model and produce fibronectin fibers being unfolded due to cell forces (middle). Finally the pore closes completely and at the same time fibronectin is further compacted towards the center (bottom).</p

    Biohybrid Networks of Selectively Desulfated Glycosaminoglycans for Tunable Growth Factor Delivery

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    Sulfation patterns of glycosaminoglycans (GAG) govern the electrostatic complexation of biomolecules and thus allow for modulating the release profiles of growth factors from GAG-based hydrogels. To explore options related to this, selectively desulfated heparin derivatives were prepared, thoroughly characterized, and covalently converted with star-shaped poly­(ethylene glycol) into binary polymer networks. The impact of the GAG sulfation pattern on the network characteristics of the obtained hydrogels was theoretically evaluated by mean field methods and experimentally analyzed by rheometry and swelling measurements. Sulfation-dependent differences of reactivity and miscibility of the heparin derivatives were shown to determine network formation. A theory-based design concept for customizing growth factor affinity and physical characteristics was introduced and validated by quantifying the release of fibroblast growth factor 2 from a set of biohybrid gels. The resulting new class of cell-instructive polymer matrices with tunable GAG sulfation will be instrumental for multiple applications in biotechnology and medicine
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