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Size and function of bioartificial tissue models are still limited due to the lack of blood vessels and dynamic perfusion for nutrient supply. In this study, we evaluated the use of cytocompatible methacryl-modified gelatin for the fabrication of a hydrogel-based tube by dip-coating and subsequent photo-initiated cross-linking. The wall thickness of the tubes and the diameter were tuned by the degree of gelatin methacryl-modification and the number of dipping cycles. The dipping temperature of the gelatin solution was adjusted to achieve low viscous fluids of approximately 0.1 Pa s and was different for gelatin derivatives with different modification degrees. A versatile perfusion bioreactor for the supply of surrounding tissue models was developed, which can be adaped to several geometries and sizes of blood-vessel mimicking tubes. The manufactured bendable gelatin tubes were permeable for water and dissolved substances, like Nile Blue and serum albumin. As a proof of concept, human fibroblasts in a three-dimensional collagen tissue model were sucessfully supplied with nutrients via the central gelatin tube under dynamic conditions for 2 days. Moreover, the tubes could be used as scaffolds to build-up a functional and viable endothelial layer. Hence, the presented tools can contribute to solving current challenges in tissue engineering.
The spreading area of cells has been shown to play a central role in the determination of cell fate and tissue morphogenesis; however, a clear understanding of how spread cell area is determined is still lacking. The observation that cell area and force generally increase with substrate rigidity suggests that cell area is dictated mechanically, by means of a force-balance between the cell and the substrate. A simple mechanical model, corroborated by experimental measurements of cell area and force is presented to analyze the temporal force balance between the cell and the substrate during spreading. The cell is modeled as a thin elastic disc that is actively pulled by lamellipodia protrusions at the cell front. The essential molecular mechanisms of the motor activity at the cell front, including, actin polymerization, adhesion kinetics, and the actin retrograde flow, are accounted for and used to predict the dynamics of cell spreading on elastic substrates; simple, closed-form expressions for the evolution of cell size and force are derived. Time-resolved, traction force microscopy, combined with measurements of cell area are performed to investigate the simultaneous variations of cell size and force. We find that cell area and force increase simultaneously during spreading but the force develops with an apparent delay relative to the increase in cell area. We demonstrate that this may reflect the strain-stiffening property of the cytoskeleton. We further demonstrate that the radial cell force is a concave function of spreading speed and that this may reflect the strengthening of cell–substrate adhesions during spreading.
Propofol is an intravenous anesthetic. Currently, it is not possible to routinely measure blood concentration of the drug in real time. However, multi-capillary column ion-mobility spectrometry of exhaled gas can estimate blood propofol concentration.Unfortunately, adhesion of volatile propofol on plastic materials complicates measurements. Therefore, it is necessary to consider the extent to which volatile propofol adheres to various plastics used in sampling tubing. Perfluoralkoxy (PFA), polytetrafluorethylene (PTFE), polyurethane (PUR), silicone, and Tygon tubing were investigated in an experimental setting using a calibration gas generator (HovaCAL). Propofol gas was measured for one hour at 26 °C, 50 °C, and 90 °C tubing temperature. Test tubing segments were then flushed with N2 to quantify desorption. PUR and Tygon sample tubing absorbed all volatile propofol. The silicone tubing reached the maximum propofol concentration after 119 min which was 29 min after propofol gas exposure stopped. The use of PFAor PTFE tubing produced comparable and reasonably accurate propofol measurements. The desaturation time for the PFA was 10 min shorter at 26 °C than for PTFE. PFA tubing thus seems most suitable for measurement of volatile propofol,with PTFE as an alternative.
An apparatus and method for analyzing a flow of material having an inlet region, a measurement range and an outlet region, and having a first diverter and a second diverter, and a deflection area, wherein in a first state of operation, the two diverters form a continuous first material flow space from the inlet region via the first diverter through the measurement range, via the second diverter to the outlet region, and in a second state of operation, form a continuous second material flow space from the inlet region via the first diverter through the deflection area, via the second diverter to the outlet region.
We report an investigation into the distribution of copper oxidation states in oxide films formed on the surfaces of technical copper. The oxide films were grown by thermal annealing at ambient conditions and studied using Auger depth profiling and UV–Vis spectroscopy. Both Auger and UV–Vis data were evaluated applying multivariate curve resolution (MCR). Both experimental techniques revealed that the growth of Cu2O dominates the initial ca. 40 nm of oxide films grown at 175 °C, while further oxide growth is dominated by CuO formation. The largely coincident results from both experimental approaches demonstrates the huge benefit of the application of UV–Vis spectroscopy in combination with MCR analysis, which provides access to information on chemical state distributions without the need for destructive sample analysis. Both approaches are discussed in detail.
Der ultraschnelle Mechanismus der Alken-Hydrosylilierung lässt sich von den Flüssigsiliconen (LSRs) auf VNB-EPDM-Mischungen übertragen. In der Verarbeitung würde diese für VNB-EPDM die Wettbewerbsfähigkeit hinsichtlich realisierbarer kürzester Zykluszeiten und neue Marktsegmente alternativ zu den LSR-Materialien eröffnen, u.a. in speziellen Dichtungsanwendungen. Peroxidisch vernetzte EPDM-Mischungen können in wässrig-sauren und wässrig-alkalischen Medien eine bessere chemische Beständigkeit als LSR-Materialien bieten. Sie sind duch die radikalische Vernetzung in der Kinetik aber im Vergleich zu additionsvernetzbaren Elastomeren als deutlich träger einzustufen. Ein weiterer Aspekt ist die Permeationsbeständigkeit gegenüber Gasen und Lösemitteldämpfen, die in dieser Arbeit näher untersucht worden ist. In dieser Eigenschaft unterscheiden sich VNB-EPDM und LSR deutlich voneinander. Mit der Bestimmung von zeit- und temperaturabhängigen Permeationsraten von n-Hexan-Lösemitteldämpfen erfolgt ein Vergleich beider Elastomerklassen. Auf die Theorie der Gaspermeation und der sogenannten Pervaporation wird grundlegend eingegangen und zusätzlich der weitere Einfluss von Rezepturbestandteilen beleuchtet. Des Weiteren werden stationäre Permeationskoeffizienten für die Lösemittel-Dampf-Evaporation berechnet, indem die Ausprägung des Quelldrucks im Inneren der Elastomerwerkstoffe durch signifikante Volumenquellungen als eigentliche Triebkraft herangeszogen wird.
Film formation of self synthesized Polymer EPM–g–VTMDS (ethylene–propylene rubber, EPM, grafted with vinyltetramethyldisiloxane, VTMDS) was studied regarding bonding to adhesion promoter vinyltrimethoxysilane (VTMS) on oxidized 18/10 chromium/nickel–steel (V2A) stainless steel surfaces. Polymer films of different mixed solutions including commercial siloxane and silicone, dimethyl, vinyl group terminated crosslinker (HANSA SFA 42100, CAS# 68083-19-2, 0.35 mmol Vinyl/g) and platinum, 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane complex Karstedt's catalyst (ALPA–KAT 1, CAS# 68478-92-2) were spin coated on V2A stainless steel surfaces with adsorbed VTMS thin layers in order to analyze film formation of EPM–g–VTMDS at early stages. Surface topography and chemical bonding of the high performance polymers on different oxidized V2A surfaces were investigated with X–ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM) and surface enhanced Raman spectroscopy (SERS). AFM and SEM as well as XPS results indicated that the formation of the polymer film proceeds via growth of polymer islands. Chemical signatures of the essential polymer contributions, linker and polymer backbones, could be identified using XPS core level peak shape analysis and also SERS. The appearance of signals which are related to Si–O–Si can be seen as a clear indication of lateral crosslinking and silica network formation in the films on the V2A surface.
Though bioprinting is a forward-looking approach in bone tissue engineering, the development of bioinks which are on the one hand processable with the chosen printing technique, and on the other hand possess the relevant mechanical as well as osteoconductive features remains a challenge. In the present study, polymer solutions based on methacrylated gelatin and methacrylated hyaluronic acid modified with hydroxyapatite (HAp) particles (5 wt%) were prepared. Encapsulation of primary human adipose derived stem cells in the HAp-containing gels and culture for 28 d resulted in a storage moduli significantly increased to 126% ± 9.6% compared to the value on day 1 by the sole influence of the HAp. Additional use of osteogenic media components resulted in an increase of storage module up to 199% ± 27.8%. Similarly, the loss moduli was increased to 370% ± 122.1% under the influence of osteogenic media components and HAp. Those changes in rheological material characteristics indicate a distinct change in elastic and viscous hydrogel properties, and are attributed to extensive matrix production in the hydrogels by the encapsulated cells, what could also be proven by staining of bone matrix components like collagen I, fibronectin, alkaline phosphatase and osteopontin. When using the cell-laden polymer solutions as bioinks to build up relevant geometries, the ink showed excellent printability and the printed grid structure's integrity remained intact over a culture time of 28 d. Again, an intense matrix formation as well as upregulation of osteogenic markers by the encapsulated cells could be shown. In conclusion, we demonstrated that our HAp-containing bioinks and hydrogels on basis of methacrylated gelatin and hyaluronic acid are on the one hand highly suitable for the build up of relevant three-dimensional geometries with microextrusion bioprinting, and on the other hand exhibit a significant positive effect on bone matrix development and remodeling in the hydrogels, as indicated by rheological measurements and staining of bone components. This makes the developed composite hydrogels an excellent material for bone bioprinting approaches.
Background aims: In vitro engineered adipose tissue is in great demand to treat lost or damaged soft tissue or to screen for new drugs, among other applications.However, today most attempts depend on the use of animal-derived sera. To pave the way for the application of adipose tissue-engineered
products in clinical trials or as reliable and robust in vitro test systems, sera should be completely excluded from the production process. In this study, we aimed to develop an in vitro adipose tissue model in the absence of sera and maintain its function long-term.
Methods: Human adipose tissue-derived stem cells were expanded and characterized in a xeno- and serum-free environment. Adipogenic differentiation was induced using a completely defined medium. Developed adipocytes were maintained in a completely defined maturation medium for additional 28 days. In addition to cell-viability and adherence, adipocyte-specific markers such as perilipin A expression of leptin release were evaluated.
Results: The defined differentiation medium enhanced cell adherence and lipid
accumulation at a significant level compared with the corresponding negative control. The defined maturation medium also significantly supported cell adherence and functional adipocyte maturation during the long-term culture period.
Conclusions: The process described here enables functional adipocyte generation and maintenance without the addition fo unknown or unimal-derived constituents, achieving an important milestone in the introduction of adipose tissue engineered products into clinical trials or in vitro screening.
Continuum physics modeling of tumor growth is a rich topic with room for rather sophisticated models of reaction-transport and mechanics. It also has the attraction of being able to pose and examine solutions to certain questions on tumor growth that are difficult to access using experimental methods alone. However, the imperative of experimental biophysical investigations cannot by understated.
Within the scope of the present cumulative doctoral thesis six scientific papers were published which illustrates that modern reaction model-free (=isoconversional) kinetic analysis (ICKA) methods represents a universal and effective tool for the controlled processing of thermosetting materials. In order to demonstrate the universal applicability of ICKA methods, the thermal cure of different thermosetting materials having a very broad range of chemical composition (melamine-formaldehyde resins, epoxy resins, polyester-epoxy resins, and acrylate/epoxy resins) were analyzed and mathematically modelled. Some of the materials were based on renewable resources (an epoxy resin was made from hempseed oil; linseed oil was modified into an acrylate/epoxy resin). With the aid of ICKA methods not only single-step but also complex multi-step reactions were modelled precisely. The analyzed thermosetting materials were combined with wood, wood-based products, paper, and plant fibers which are processed to various final products. Some of the thermosetting materials were applied as coating (in form of impregnated décor papers or powder and wet coatings respectively) on wood substrates and the epoxy resin from hempseed oil was mixed with plant fibers and processed into bio-based composites for lightweight applications. From the final products mechanical, thermal, and surface properties were determined. The activation energy as function of cure conversion derived from ICKA methods was utilized to predict accurately the thermal curing over the course of time for arbitrary cure conditions. Furthermore the cure models were used to establish correlations between the cross-linking during processing into products and the properties of the final products. Therewith it was possible to derive the process time and temperature that guarantee optimal cross-linking as well as optimal product properties
The establishment of adipose tissue test systems is still a major challenge in the investigation of cellular and molecular interactions responsible for the pathogenesis of inflammatory diseases involving adipose tissue. Mature adipocytes are mainly involved in these pathologies, but rarely used in vitro, due to the lack of an appropriate culture medium which inhibits dedifferentiation and maintains adipocyte functionality. In our study, we showed that Dulbecco's Modified Eagle's Medium/Ham's F-12 with 10% fetal calf serum (FCS) reported for the culture of mature adipocytes favors dedifferentiation, which was accompanied by a high glycerol release, a decreasing release of leptin, and a low expression of the adipocyte marker perilipin A, but high expression of CD73 after 21 days. Optimized media containing FCS, biotin, pantothenate, insulin, and dexamethasone decelerated the dedifferentiation process. These cells showed a lower lipolysis rate, a high level of leptin release, as well as a high expression of perilipin A. CD73-positive dedifferentiated fat cells were only found in low quantity. In this work, we showed that mature adipocytes when cultured under optimized conditions could be highly valuable for adipose tissue engineering in vitro.
Long-term stability of membranes in membrane distillation operation is a problem nowadays which prevents the industrial breakthrough of this separation process. Fouling or slow pore wetting are the basic reasons for this.
Membrane distillation membranes were made by NIPS process rendering the membrane asymmetrically to achieve low permeation resistance and pores which can be over coated with polyelectrolyte polymers thus leading to thermopervaporation membranes. Those membranes prohibit pore wetting and may strongly reduce resorption of organic substances on for membrane distillation typically used hydrophobic surfaces thus leading to longterm operation stability in dewatering including stable membrane cleaning.
Asymmetric PVDF membranes have been coated with cation exchange polyelectrolyte leading to a very thin, defect-free layer which has a high permeation rate for water due to the domain structure of phase-separated hydrophilic and hydrophobic three-dimensional structures.
Die Landessprache in der Lehre - welche Bedeutung kommt ihr bei der Internationalisierung zu?
(2019)
Seit der Jahrhundertwende wird erfolgreich die Intensivierung des Austauschs zwischen wissenschaftlichen Einrichtungen betrieben, auch national, aber vor allem international. Anfänglich schien klar, dass gute Indikatoren für die "Internationalisierung" genannte Entwicklung die Anteile ausländischer Wissenschaftler und Studierender sind. Konsens über sinnvolle Zielgrößen für die Indikatoren gibt es jedoch bisher nicht. Nach einiger Zeit flachte sich der anfängliche Anstieg dieser Quoten etwas ab. Mit der Folge einer weiteren Steigerung dieses Indikators ist neuerdings international der Trend zur Anglophonisierung der Lehre zu beobachten.
The self-healing effect of melamine-based surfaces, triggered by temperature, was investigated. The temperature triggered reversible healing chemistry, on which the self-healing effect is based, was the Diels-Alder (DA) reaction between furan and malemeide groups. Melamine-furan containing building blocks were connected by multi-functional maleimide crosslinker via a Diels-Alder (DA) reaction to giva a DA adduct. The DA adduct was then reacted with formaldehyde to form a network by conventional condensation reaction of melamine amino groups with formaldehyde. The obtained resin was characterised and used for the impregnation of paper. Impregnated papers and neat resin werde used to perform scratch-healing tests and mechanical analysis of the novel coating system.
Palladium-doped silica materials with SiCH3 groups were fabricated by sol-gel method under various calcination atmospheres and membranes were made thereof by coating process. The results showed that air atmosphere can lead to the partial oxidation of metallic Pd0 to PdO while N2 and H2 atmospheres can effectively prevent metallic Pd0 from being oxidized. H2 atmosphere is proved to be a more prominent way to slow down the decomposition of organic SiCH3 group than N2 and air atmospheres. The surface area, micropore volume and porosity of palladium-doped silica membrane material calcined in H2 atmosphere are much higher than those calcined in N2 atmosphere. Compared with N2 atmosphere, the palladium-doped silica membranes calcined in H2 atmosphere showed higher H2 permeability and H2/CO2 selectivity before and after the steam exposure. The apparent activation energy of H2 permeation through the palladium-doped silica membrane calcined under H2 atmosphere (2.51 ± 0.05 kJ/mol) was slightly lower than that calcined under N2 atmosphere (2.84 ± 0.04 kJ/mol). Calcination atmosphere plays some role in membrane performance, which has greater influence on the permeance than on the gas permselectivity. Calcination under H2 atmosphere is well conducive to improve the gas permeance and H2 permselectivity of palladium-doped silica membrane.
Here, we report the continuous peroxide-initiated grafting of vinyltrimethoxysilane (VTMS) onto a standard polyolefin by means of reactive extrusion to produce a functionalized liquid ethylene propylene copolymer (EPM). The effects of the process parameters governing the grafting reaction and their synergistic interactions are identified, quantified and used in a mathematical model of the extrusion process. As process variables the VTMS and peroxide concentrations and the extruder temperature setting were systematically studied for their influence on the grafting and the relative grafting degree using a face-centered central composite design (FCD). The grafting degree was quantified by 1H NMR spectroscopy. Response surface methodology (RSM) was used to calculate the most efficient grafting process in terms of chemical usage and graft yield. With the defined processing window, it was possible to make precise predictions about the grafting degree with at the same time highest possible relative degree of grafting.
Hypothesis
The origin of negative surface charge at water/air interface is still not clear. The most probable origin is specific adsorption of OH− ions. From diffuse layer potential, we can evaluate the surface density of ions in the Stern layer which can be a measure for the specific adsorption of ions and determines whether the surface charge is solely due to the specific adsorption of OH− ions.
Experiments
Equilibrium thickness of foam films of pure water and aqueous solutions of NaCl, HCl, and NaOH was measured as a function of disjoining pressure for water and as a function of concentration for the aqueous solutions at 298.15 K. Quartz-glass cells thoroughly cleaned and immersed in pure water before use were used for the measurement.
Findings
Application of a modified Poisson-Boltzmann equation to the equilibrium film thickness gave the diffuse layer potential and the surface density of ions in the Stern layer. From the concentration dependence of the surface density, it was concluded that not only OH− ions but also Cl− ions and HCO3− and/or CO32− ions adsorb specifically at the water/air interface.
Functionalised particles are highly requested in materials research, as they can be used as vital components in many advanced applications such as smart materials, functional coatings, drug carrier systems or adsorption materials. In this study, furan-functionalised melamine-formaldehyde (MF) particles were successfully prepared for the first time using an organic sol-gel process. Commercially available 2-Aminomethylfuran (AMF) and 2-Aminomethyl-5-methylfuran (AMMF) were used as modifying agents. In the isolated polymer particles, a melamine (M) to modifying agent ratio of M:AMF mol/mol 2.04:1 and M:AMMF ratio of mol/mol 1.25:1 was used. The obtained particles were isolated in various centrifugation and re-dispersion cycles and analysed using ATR-FT-IR, Raman and solid state 13C NMR spectroscopy, TGA, SEM and DSC measurements. Upon functionalisation the size of the MF particles increased (MF 1.59 µm, 27% CV (coefficient of variation); MF-AMF 2.56 µm, 25% CV; MF-AMMF 2.20 µm, 35% CV). DSC measurements showed that another type of exothermic residual reactivity besides condensation-based curing takes place with the furan-modified particles that is not related to the liberation of volatile compounds. The newly obtained particles are able to undergo Diels-Alder reactions with maleimide groups. The characteristic IR and Raman absorbance bands of the reaction products after the particles were reacted with 4,4′-Diphenylmethanebismaleimide reagent confirm the formation of a Diels-Alder adduct.