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Author: search.filters.author.Tovar, Günter E. M.Subject: search.filters.subject.660

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    ItemOpen Access
    Acid catalyzed cross‐linking of polyvinyl alcohol for humidifier membranes
    (2021) Michele, Andre; Paschkowski, Patrick; Hänel, Christopher; Tovar, Günter E. M.; Schiestel, Thomas; Southan, Alexander
    Polyvinyl alcohol (PVA) is a hydrophilic polymer well known for good film forming properties, high water vapor permeance JW, and low nitrogen permeance. However, depending on molar mass and temperature, PVA swells strongly in water until complete dissolution. This behavior affects the usability of PVA in aqueous environments and makes cross‐linking necessary if higher structural integrity is envisaged. In this work, PVA networks are formed by thermal cross‐linking in the presence of p‐toluenesulfonic acid (TSA) and investigated in a design of experiments approach. Experimental parameters are the cross‐linking period tc, temperature ϑ and the TSA mass fraction wTSA. Cross‐linking is found to proceed via ether bond formation at all reaction conditions. Degradation is promoted especially by a combination of high wTSA, tc and ϑ. Thermal stability of the networks after preparation is strongly improved by neutralizing residual TSA. Humidification membranes with a JW of 6423 ± 63.0 gas permeation units (GPU) are fabricated by coating PVA on polyvinyliden fluoride hollow fibers and cross‐linking with TSA. Summarizing, the present study contributes to a clearer insight into the cross‐linking of PVA in presence of TSA, the thermal stability of the resulting networks and the applicability as selective membrane layers for water vapor transfer.
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    ItemOpen Access
    Unravelling parameter interactions in calcium alginate/polyacrylamide double network hydrogels using a design of experiments approach for the optimization of mechanical properties
    (2024) Gorke, Oliver; Stuhlmüller, Marc; Tovar, Günter E. M.; Southan, Alexander
    Calcium alginate/polyacrylamide double network hydrogels were reported to be exceptionally tough. However, literature reports so far varied the sample compositions mainly by one parameter at a time approaches, thus only drawing an incomplete picture of achievable material properties. In this contribution, sample compositions are varied according to a face-centered central composite experimental design taking into account the four parameters of alginate concentration cAlg, high/low molar mass alginate mixing ratio RP, acrylamide concentration cAAm, and N,N′-methylenebisacrylamide concentration cMBA. Each sample composition is investigated in triplicate. Thus, 75 samples were investigated by tensile testing, and a detailed analysis of the significant parameters and parameter interactions influencing the mechanical properties is conducted. The data shows that two parameter interactions, involving all four tested parameters, have a large effect on the Young's modulus, the strength, the toughness and the strain at material failure. As a consequence, it becomes evident that the experimental procedure from previous studies did not always result in optimum sample compositions. The results allow optimization of the mechanical properties within the studied parameter space, and a new maximum value of the strength of 710 kPa is reported. The data also give rise to the assumption that other parameters and parameter interactions ignored also in this study may allow further tailoring of mechanical properties.
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    ItemOpen Access
    Beta-glucan production of Phaeodactylum tricornutum, Monodopsis subterranea and Cylindrotheca fusiformis during nitrogen depletion
    (2023) Frick, Konstantin; Ebbing, Tobias; Yeh, Yen-Cheng; Schmid-Staiger, Ulrike; Tovar, Günter E. M.
    AbstractBeta-glucans are polysaccharides that can be used for different applications, for example as an immunomodulator in food or feed or for managing high cholesterol levels. Certain microalgae species use beta-glucans as energy storage, accumulating them during nutrient depletion. In this study, we examined and compared beta-glucan production during nitrogen depletion in three different algae species, Phaeodactylum tricornutum, Monodopsis subterranea and Cylindrotheca fusiformis, grown in artificially illuminated flat panel airlift reactors, in order to determine the most promising microalgae species for beta-glucan production. Co-products such as fatty acids (especially eicosapentaenoic acid) and the carotenoid fucoxanthin (not produced by M. subterranea) were also considered. Biomass analysis showed that P. tricornutum cultures reached a maximal beta-glucan content of 317 ± 9 mg gDW-1, M. subterranea cultures reached 188 ± 6 mg gDW-1 and C. fusiformis cultures reached 129 ± 13 mg gDW-1. Furthermore, beta-glucan production was faster in P. tricornutum cultures. However, the maximum volumetric beta-glucan concentration reached was higher in M. subterranea cultures compared to P. tricornutum cultures as M. subterranea cultures produced more biomass during nitrogen depletion. In terms of possible co-products, P. tricornutum produced fucoxanthin and EPA, whereas M. subterranea did not produce fucoxanthin. However, M. subterranea exhibited a higher EPA content, which remained above 45 mg g-1 even after several days of nitrogen depletion. Overall, our results suggest that P. tricornutum and M. subterranea are both suitable species for beta-glucan production in flat panel airlift reactors.
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    ItemOpen Access
    Soft sub‐structured multi‐material biosensor hydrogels with enzymes retained by plant viral scaffolds
    (2023) Grübel, Jana; Wendlandt, Tim; Urban, Daniela; Jauch, Corinna O.; Wege, Christina; Tovar, Günter E. M.; Southan, Alexander
    An all‐soft multi‐material combination consisting of a hydrogel based on poly(ethylene glycol) (PEG) coated with spatially defined spots of gelatin methacryloyl (GM) containing selectively addressable viral nanorods is presented, and its basic application as a qualitative biosensor with reporter enzymes displayed on the tobacco mosaic virus (TMV) bioscaffolds within the GM is demonstrated. Biologically inert PEG supports are equipped with GM spots serving as biological matrix for enzymes clustered on TMV particles preventing diffusion out of the gel. For this multi‐material combination, i) the PEG‐based hydrogel surface is modified to achieve a clear boundary between coated and non‐coated regions by introducing either isothiouronium or thiol groups. ii) Cross‐linking of the GM spots is studied to achieve anchoring to the hydrogel surface. iii) The enzymes horseradish peroxidase or penicillinase (Pen) are conjugated to TMV and integrated into the GM matrix. In contrast to free enzymes, enzyme‐decorated TMVs persist in GM spots and show sustained enzyme activity as evidenced by specific color reaction after 7 days of washing, and for Pen after 22 months after dry storage. Therefore, the integration of enzyme‐coupled TMV into hydrogel matrices is a promising and versatile approach to obtaining reusable and analyte‐specific sensor components.