Lehrstuhl Biomaterialien und Polymerwissenschaften

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Enzyme‐induced ferrification of hydrogels for toughening of functional inorganic compounds
(2022-04-01) Milovanovic, Marko; Rauner, Nicolas; Civelek, Emre; Holtermann, Tim; Jid, Oualid El; Meuris, Monika; Brandt, Volker; Tiller, Jörg C.
Enzyme-induced mineralization (EIM) has been shown to greatly enhance the mechanical properties of hydrogels by precipitation of calcium salts. Another feature of such hydrogels is their high toughness even when containing finely nanostructured mineral content of ≈75 wt%. This might be useful for bendable materials with high content of functional inorganic nanostructures. The present study demonstrates that EIM can form homogeneous nanostructures of water-insoluble iron salts within hydrogels. Crystalline iron(II) carbonate precipitates urease-induced within polyacrylate-based hydrogels and forms platelet structures that have the potential of forming self-organized nacre-like architectures. The platelet structure can be influenced by chemical composition of the hydrogel. Further, amorphous iron(II) phosphate precipitates within hydrogels with alkaline phosphatase, forming a nanostructured porous inorganic phase, homogeneously distributed within the double network hydrogel. The high amount of iron phosphate (more than 80 wt%) affords a stiffness of ≈100 MPa. The composite is still bendable with considerable toughness of 400 J m−2 and strength of 1 MPa. The high water content (>50%) may allow fast diffusion processes within the material. This makes the iron phosphate-based composite an interesting candidate for flexible electrodes and demonstrates that EIM can be used to deliberately soften ceramic materials, rendering them bendable.
Ultrastrong poly(2‐oxazoline)/poly(acrylic acid) double‐network hydrogels with cartilage‐like mechanical properties
(2022-08-11) Benitez-Duif, Paola A.; Breisch, Marina; Kurka, Daniel; Edel, Karlina; Gökcay, Semra; Stangier, Dominic; Tillmann, Wolfgang; Hijazi, Montasser; Tiller, Jörg C.
The exceptional stiffness and toughness of double-network hydrogels (DNHs) offer the possibility to mimic even complex biomaterials, such as cartilage. The latter has a limited regenerative capacity and thus needs to be substituted with an artificial material. DNHs composed of cross-linked poly(2-oxazoline)s (POx) and poly(acrylic acid) (PAA) are synthesized by free radical polymerization in a two-step process. The resulting DNHs are stabilized by hydrogen bridges even at pH 7.4 (physiological PBS buffer) due to the pKa-shifting effect of POx on PAA. DNHs based on poly(2-methyl-2-oxazoline), which have a water content (WC) of around 66 wt% and are not cytotoxic, show biomechanical properties that match those of cartilage in terms of WC, stiffness, toughness, coefficient of friction, compression in body relevant stress conditions and viscoelastic behavior. This material also has high strength in PBS pH 7.4 and in egg white as synovial liquid substitute. In particular, a compression strength of up to 60 MPa makes this material superior.
On the influence of the amorphous phase on the stability of crystals in poly(cis-1,4-isoprene) networks
(2022-09-22) Segiet, Dominik; Weckes, Sebastian; Austermuehl, Juergen; Tiller, Joerg C.; Katzenberg, Frank
Crosslinked natural rubber and synthetic rubber samples are additivated with up to 9 wt% stearic acid (StA) to better understand the influence of StA on the melting temperature Tm of strain-induced crystallized poly(cis-1,4-isoprene) crystals. To this end, lamellae thicknesses are determined from wide-angle x-ray patterns and used to calculate the crystal size dependent melting temperature Tm,calc. Comparing the measured Tm with Tm,calc reveals that Tm deviates downward from Tm,calc and converges Tm,calc with increasing StA concentration until it is identical to Tm,calc, in case of room temperature strain-induced crystallization. In case of strain-induced crystallization at 80°C, it was found that Tm is identical with Tm,calc without added StA and deviates upward from Tm,calc with increasing amount of added StA. We suggest that this is due to internal stress onto the polymer crystals exerted by highly strained macromolecules in the surrounding amorphous phase. Whether this stress has a stabilizing or destabilizing effect on the crystals is assumed to depend on its intensity and direction, which can be efficiently altered by the amount and the location of StA crystals in the amorphous phase.
Synthesis of amphiphilic antimicrobial polymer-antibiotic conjugates and particle networks
(2023) Romanovska, Alina; Tiller, Jörg C.; Nett, Markus
In previous work by Martin Schmidt^1 in 2018, it was found that amphiphilic polymer systems based on poly(2-oxazolines) (POx) could be successfully conjugated to the antibiotic ciprofloxacin (CIP). These amphiphilic polymer-antibiotic conjugates (PACs) led to the enhanced activity of the antibiotic CIP. In this work, these amphiphilic PAHs were taken up and further investigated for their exact mode of action. Thus, the mode of action of the additional induced membrane activity by the amphiphilic polymer system on the activity of the antibiotic was investigated. A crucial factor is the dependence of the amphiphilic PACs on the hydrophobic/hydrophilic balance (HHG) of the POx tail. Continuation of the mechanistic investigations led to the consideration of replacing the hydrophobic part of the amphiphilic poly(2-oxazoline) block copolymers with a biocompatible naturally occurring substance. In doing so, poly(2-methyl-2oxazoline) (PMOx) should remain as the hydrophobic moiety. The purpose of this consideration is to improve the biocompatibility of amphiphilic PACs and lower blood and cell toxicity. Furthermore, also based on the results of Martin Schmidt^1, the reversible crosslinking of polymer-antibiotic conjugates with amphiphilic ABA triblock copolymers was investigated at the molecular level. It was already known that PACs based on hydrophilic and hydrophobic poly(2-oxazolines) form worm micelles that are very stable and strongly activate the conjugated antibiotic. Further, the exact interaction of the PACs with the ABA triblock copolymers should be investigated and explored to understand the exact background for the controlled and switchable antimicrobial effect of the antibiotic.
Enzyme-induced mineralization of hydrogels with amorphous calcium carbonate for fast synthesis of ultrastiff, strong and tough organic–inorganic double networks
(2021-06-23) Milovanovic, Marko; Mihailowitsch, Lydia; Santhirasegaran, Mathusiha; Brandt, Volker; Tiller, Jörg C.
Hydrogels with good mechanical properties have great importance in biological and medical applications. Double-network (DN) hydrogels were found to be very tough materials. If one of the two network phases is an inorganic material, the DN hydrogels also become very stiff without losing their toughness. So far, the only example of such an organic–inorganic DN hydrogel is based on calcium phosphate, which takes about a week to be formed as an amorphous inorganic phase by enzyme-induced mineralization. An alternative organic–inorganic DN hydrogel, based on amorphous CaCO3, which can be formed as inorganic phase within hours, was designed in this study. The precipitation of CaCO3 within a hydrogel was induced by urease and a urea/CaCl2 calcification medium. The amorphous character of the CaCO3 was retained by using the previously reported crystallization inhibiting effects of N-(phosphonomethyl)glycine (PMGly). The connection between organic and inorganic phases via reversible bonds was realized by the introduction of ionic groups. The best results were obtained by copolymerization of acrylamide (AAm) and sodium acrylate (SA), which led to water-swollen organic–inorganic DN hydrogels with a high Young’s modulus (455 ± 80 MPa), remarkable tensile strength (3.4 ± 0.7 MPa) and fracture toughness (1.1 ± 0.2 kJ m−2).
Insights in the thermal volume transition of poly(2-oxazoline) hydrogels
(2021-06-25) Segiet, Dominik; Stockmann, Annika; Sadowski, Jan; Katzenberg, Frank; Tiller, Jörg C.
Polymers with a lower or an upper critical solution temperature (LCST or UCST) can precipitate in a very narrow temperature range. Cross-linking of such polymers and adding them to suited solvent results in smart gels that are capable of greatly changing their dimensions with changing temperature. This transition occurs very often in a broad temperature range, which limits the applicability of smart materials. To shed some light into the design of thermo-responsive hydrogels with a narrow phase transition, poly(2-ethyl-2-oxazoline) (PEtOx), poly(2-isopropyl-2-oxazoline), and statistical copolymers of 2-butyl-2-oxazoline and 2-ethyl-2-oxazoline, respectively, are synthesized and the concentration-dependent cloud point temperatures (Tcp) of the free polymers in aqueous media are determined in relation to the thermo-responsive swelling behavior of the respective hydrogels. A narrow thermal transition of the hydrogels can only be achieved when the Tcp of the free polymers in water is independent on the concentration. Aqueous salt solutions can render even PEtOx into a concentration independent LCST polymer. However, this salt effect does not work for hydrogels.
Improvement of high voltage direct current material properties upon tailoring the morphology of crosslinked polyethylenes
(2021-09-12) Niedik, Christoph Felix; Jenau, Frank; Maricanov, Michail; Segiet, Dominik; Tiller, Jörg Christian; Katzenberg, Frank
Crosslinked linear low-density polyethylene (XLPE) is the most common polymeric cable insulation material for high-voltage applications with a high number of operating hours in high voltage alternating current (HVAC) systems. High voltage direct current (HVDC) power transmission and polymeric cable systems play a major role in the future and raise, besides numerous systemic benefits, challenges in the design of material properties. The main issue is injection and trapping of space charges in insulation materials under DC-fields. The objective of this work is to increase knowledge of the interplay between microstructure and material performance of XLPE under DC by tailoring its morphology beyond the capabilities of “common crystallization kinetics” upon constrained crystallization at certain elongations. It was found that the tailored oriented morphology influences the energetic depth of traps and a significant reduction of space charge density occurs. Moreover, the optimized oriented morphology leads to a significant reduction of field enhancement for field strengths ELaplace ≥ 20 kV mm−1 compared to unoriented XLPEs with spherulitic morphology. It is shown that this way of morphology tailoring results in a considerable, material dependent reduction of field exposure by a factor of 4, which promises a significant improvement in the electrical life time of polymeric insulation material used.
Intelligente thermo- und lösungsmittelresponsive Polymernetzwerke
(2021) Segiet, Dominik; Tiller, Jörg C.; Weberskirch, Ralf
This work pursued two goals. On the one hand new insights in the thermoresponsive behavior of poly(2-alkyl-2-oxazoline) (POx) were gathered by comparing the thermoresponsiveness of POx-hydrogels with the solubility behavior of linear POx. On the other hand, the shape-memory properties of different POx’ and poly(cis-1,4-isoprene)s were investigated in detail. To this end, as an intermediate goal a suited crosslinking method had to be found that is capable of crosslinking different POx independent of its composition and molecular weight. It was shown for these networks that they exhibit exceptional shape-memory properties. The networks are able to be programmed and triggered using temperature and small amounts of solvents. Other POx also promised very good shape-memory properties and the fixation of a secondary temporary shape, but unfortunately these POx-networks were mechanically very fragile owing to their low molecular weight. In addition, it was found that the solvent affinity of PEtOx-networks decreases depending on the applied strain, which makes PEtOx an adaptive material. With regard to the thermoresponsive properties of POx-hydrogels it was found that the swelling curves of hydrogels with different degree of crosslinking always converge at a distinct temperature. Because of this, it was possible to make important connections between the cloud point curve of a linear polymer and the swelling curve of its hydrogels. By adding salts, it was also found that the thermoresponsive behavior of hydrogels can be retroactively altered and adapted to the requirements of a potential application. For the second goal, the shape-memory properties of different poly(cis-1,4-isoprene)-networks were evaluated. It was shown that through mixing of poly(cis-1,4-isoprene) and small amounts of stearic acid, the trigger temperature can be shifted above room temperature, which lead to a synthetic poly(cis-1,4-isoprene)-network exhibited a shape-memory effect for the first time. On top of that deeper insights in the mechanism behind the shape-memory effect of poly(cis-1,4-isoprene)s were obtained. Also PEtOx was blended and consequently crosslinked with poly(cis-1,4-isoprene) to gain a synergy of the best properties of both polymers. The produced polymer blends showed the expected results. Especially, the polymer blend with 50 wt% PEtOx showed the most promising properties. Apart from a trigger temperature above room temperature, high storable strains, it showed a sensitivity towards hydrophilic and hydrophobic solvents, making it a multisensitive material.
Full thermal switching of enzymes by thermoresponsive poly(2-oxazoline)-based enzyme inhibitors
(2020-07-24) Hijazi, Montasser; Türkmen, Esra; Tiller, Jörg C.
Controlling the activity of enzymes is an important feature for many processes in medicine, bioanalytics, and biotechnology. So far, it has not been possible to fully switch biocatalysts on and off by thermoresponsive enzyme inhibitors. Herein, we present poly(2-oxazoline)s with iminodiacetic acid end groups (POx-IDA) that are lower critical solution temperature (LCST) polymers and thus thermosensitive. They are capable of reversibly inhibiting the activity of horse radish peroxidase and laccase by more than 99 %. Increasing the temperature makes the POx-IDA precipitate, which leads to 100 % recovery of the enzyme activity. This switching cycle is fully reversible. The LCST of the POx-IDA can be tuned by varying the polymer composition to generate a wide range of switching windows.
Small-angle X-Ray scattering measurements on amphiphilic polymer conetworks swollen in orthogonal solvents
(2020-11-23) Benski, Lena; Viran, Ismail; Katzenberg, Frank; Tiller, Jörg C.
Amphiphilic polymer conetworks (APCNs), which combine two different polymer nanophases, have a broad range of applications that involve their unique potential to separately swell one of these nanophases in a selective solvent. Little is known about the structural changes of such APCNs upon swelling in dependence on the topology. Here, conetworks composed of poly(2-ethylhexyl acrylate) crosslinked by poly(2-methyl-2-oxazoline) (PMOx) are investigated with small-angle X-ray scattering in dry and swollen state using the orthogonal solvents water and toluene. The data clearly show that the structural changes induced by swelling are strongly dependent on the topology of the APCNs. While water leads to fusion of PMOx phases resulting in larger structures than found in the dry APCN, toluene is only swelling the hydrophobic phases without structural changes.
Bimetallic systems of silver and platinum nanoparticles: biological effects on human tissue cells and antimicrobial activity
(2019) Breisch, Marina; Tiller, Jörg C.; Nett, Markus
Implant-associated infections still represent major clinical challenges, and the development of novel antimicrobial strategies for preventing implant colonization by microorganisms, such as biomaterials containing silver (Ag), is of great importance. Since ionic Ag (Ag+) is the biologically active form of Ag, the amount of released Ag+ determines its antibacterial activity and can be enhanced by surface enlargement (nanosilver) or by a sacrificial anode effect. Thus, this thesis aimed the crosslinking between nanotechnology and the sacrificial anode principle to achieve an Ag-based system with enhanced Ag+ release resulting in improved antimicrobial properties. Therefore, Ag was combined with the electrochemically more noble platinum (Pt) in the form of (i) bimetallic alloyed silverplatinum nanoparticles (AgPt NP) and (ii) physical mixtures of pure Ag NP and Pt NP. Subsequently, the resulting Ag+ release, the antimicrobial activity as well as cell viability, migration, and differentiation of tissue cells were analyzed. For the bimetallic AgPt NP an overall lower toxicity and decreased dissolution compared to pure Ag NP were demonstrated, which excluded a sacrificial anode effect. These findings were based on electrochemical Ag stabilization in a Pt alloy and not reported previously for AgPt NP. However, during long-term NP exposure, a Pt-related osteopromotive activity was demonstrated for the first time, concomitantly with an inhibited osteoclastogenesis, which correlated with enzyme-mimetic Pt properties. For the physical Ag/Pt NP mixtures, for the first time, biological and analytical examination demonstrated a substantially accelerated and enhanced Ag+ release resulting in improved antimicrobial activity compared to same amounts of pure Ag NP, obviously based on a Ptinduced sacrificial anode effect. In conclusion, considering the Pt-related osteo-promotive activity and the improved antimicrobial activity of physical Ag/Pt NP mixtures, these findings have a high potential in biomedicine for the development of innovative anti-infective and osteo-promotive implant materials and coatings, which may support bone regeneration.
Poly(2‐oxazoline)s with a 2,2′‐iminodiacetate end group inhibit and stabilize laccase
(2020-03-16) Hijazi, Montasser; Türkmen, Esra; Tiller, Jörg C.
Poly(2‐oxazoline)s (POxs) with 2,2′‐iminodiacetate (IDA) end groups were investigated as inhibitors for laccase. The polymers with the IDA end groups are reversible, competitive inhibitors for this enzyme. The IC50 values were found to be in a range of 1–3 mm. Compared with IDA alone, the activity was increased by a factor of more than 30; thus indicating that attaching a polymer chain to an inhibitor can already improve the activity of the former. The enzyme activity drops to practically zero upon increasing the concentration of the most active telechelic inhibitor, IDA‐PEtOx30‐IDA (PEtOx: poly(2‐ethyl‐2‐oxazoline)), from 5 to 8 mm. This unusual behavior was investigated by means of dynamic light scattering, which showed specific aggregation above 5 mm. Furthermore, the laccase could be stabilized in the presence of POx‐IDA, upon addition at a concentration of 20 mm and higher. Whereas laccase becomes completely inactive at room temperature after one week, the stabilized laccase is fully active for at least a month in aqueous solution.
Investigation of the swelling behavior of hydrogels derived from high molecular weight Poly(2-Ethyl-2-Oxazoline)
(2020-02-13) Segiet, Dominik; Jerusalem, Robert; Katzenberg, Frank; Tiller, Jörg C.
Thermoresponsive hydrogels are of great importance as smart materials. They are usually composed of cross‐linked polymers with a lower critical solution temperature (LCST). Although much is known about networks of poly(N‐isopropylacrylamide), all other polymers are somewhat neglected. In this work, the temperature‐dependent swelling behavior of differently cross‐linked thermoresponsive poly(2‐ethyl‐2‐oxazoline) (PEtOx) hydrogels were investigated with regard to varying parameters of the network composition. It was found that the degrees of swelling of the hydrogels converge for a certain polymer/solvent system at a distinct temperature independent of its degree of cross‐linking. Furthermore, this temperature correlates with the LCST of the respective starting PEtOx. Its net chain molecular weight Mc only affects the maximum degree of swelling and thus, the swelling–deswelling rate of the hydrogel. The fundamental structure/property relations found in this study could be useful to predict the behavior of other thermoresponsive hydrogels.
Artifizielle Metalloenzyme in organischen Medien
(2019) Leurs, Melanie; Tiller, Jörg C.; Vogt, Dieter
The aim of this work was the generation of artificial metalloenzymes (AMEs) for use in organic solvent systems and the optimization of such reactions. The asymmetric dihydroxylation of styrene with Osmate-laccase-PMOx as AME was studied in detail to find more suitable reaction conditions for this reaction. By optimizing different reac-tion parameters, it was possible to increase the turnover frequency up to 48-fold compared to the previously used reaction system and to achieve high enantiomeric excesses of up to 99.4% ee (R) of the reaction product. The reaction can also be catalyzed under the usage of other metal species, especially KMnO4 and iron chloride. In addition, other styrene derivatives could be converted with different AMEs. Thereby turnover and selectivity of the reaction strongly depends on both the AME and the solvent system used. Furthermore a tandem catalytic dihydroxylation with subsequent esterification could be suc-cessfully performed by immobilized Osmat-modified lipase from Candida antarctica as well as by Os-lipase-PMOx. Further investigations suggest that this reaction is an auto-tandem cataly-sis. The proportion of in situ formed intermediate 1-phenyl-1,2-ethanediol in the product mix-ture is less than 5% in all cases. In addition, proteins and enzymes have been converted into highly selective and active AMEs for asymmetric dihydroxylation and epoxidation of styrene and its derivatives by targeted ac-ylation of the primary amino groups of these biomolecules and thus blocking of these potential metal-binding sites. Thereby it could be shown on the example of the asymmetric epoxidation that lysozyme from egg white as well as bovine serum albumin possess different enantioselec-tive directing binding sites for catalytically active metal species. This demonstrates that pro-teins are very rich in different chiral domains suitable for complexation with various catalytical-ly active metal species and underlines the great potential of such systems in the development of novel asymmetric catalysts.
Synthese von antimikrobiellen Polymer-Antibiotika-Konjugaten und Konjugat-Netzwerken
(2018) Schmidt, Martin; Tiller, Jörg C.; Weberskirch, Ralf
In Zeiten sich schnell ausbreitender Infektionskrankheiten und resistenter Bakterien existiert ein wachsender Bedarf an neuen Antibiotika. Die Formulierung und Derivatisierung von bekannten Antibiotika ist eine viel versprechende Alternative zur Entwicklung neuer antimikrobieller Verbindungen. Dabei rückt vor allem die Kombination mit Makromolekülen in den Fokus der Wissenschaft. Daher war das Ziel dieser Arbeit die kovalente Verknüpfung von Ciprofloxacin und Penicillin mit dem Polymer Poly(2-oxazolin). Zusätzlich sollten die Konjugate für die Herstellung von antimikrobiellen Materialien verwendet werden. Die Konjugation von Ciprofloxacin mit Poly(2-oxazolinen) führt zu antimikrobiell aktiven Polymer-Antibiotika-Konjugaten. Dabei zeigt die Aktivität dieser Konjugate eine starke Abhängigkeit von der Polymer-Antibiotikum-Bindung. So besitzen die Ciprofloxacin-Konjugate verschiedene Aktivitätsprofile abhängig vom „Spacer“ der zwischen Polymerrückgrat und Antibiotikum liegt. Weiterhin zeigen sowohl das Polymerrückgrat als auch das Molekulargewicht einen Einfluss auf die Aktivität der Konjugate. Die Konjugate besitzen eine hohe Hämo- und Biokompatibilität. Außerdem konnte für eines der Konjugate ein geringes Potential zur Resistenzbildung bei S. aureus im Vergleich zu reinem Ciprofloxacin festgestellt werden. Die Konjugation von Penicillin G und Penicillin V mit Poly(2-oxazolin) wurde mittels einer Direktterminierung des lebenden Polymerkettenendes mit den Antibiotika durchgeführt. Die resultierenden Penicillin-Konjugate zeigen eine niedrigere Aktivität im Vergleich zu den entsprechenden Penicillinen. Jedoch verlieren die unmodifizierten Penicilline in Anwesenheit des Enzyms Penicillinase ihre Aktivität im Gegensatz zu den Penicillin-Konjugaten, welche noch aktiv sind. Der Einbau einer quartären Ammoniumgruppe führt zu einer Erhöhung der Konjugataktivität in Anwesenheit und Abwesenheit von Penicillinase. Des Weiteren konnten mit Hilfe der Antibiotika-Konjugate und amphiphile ABA-Triblockcopolymere antimikrobielle Materialien hergestellt werden. Diese Materialien sind hinsichtlich ihrer antimikrobiellen Aktivität schaltbar.
Synthese und Charakterisierung neuartiger antimikrobieller Polymere
(2017) Straßburg, Arne; Tiller, Jörg C.; Nett, Markus
Ziel dieser Arbeit war die Synthese und Charakterisierung definierter Ionene und die Untersuchung ihrer Struktur-Eigenschafts-Beziehungen in Bezug auf ihre antimikrobielle Aktivität und Hämokompatibilität. Des Weiteren sollten auf Basis von Ionenen antimikrobielle Polymernetzwerke hergestellt und charakterisiert werden. Durch einen sequentiellen Aufbau mit trans-1,4-Dibrom-2-buten und N,N,N´,N´-Tetramethyl-1,3-propandiamin, konnten 3,4en-Ionene (PBI) mit definierten Molekulargewichten und Endgruppen unter kontrollierten Synthesebedingungen generiert werden. Die antimikrobiellen Untersuchungen zeigen eine Abhängigkeit der antimikrobiellen Aktivität vom Molekulargewicht und der Art der Endgruppen. Viele der Makromoleküle weisen eine exzellente Hämokompatibilität (Lyse ~1%), bei einer Konzentration von 40 000 μg/mL, auf. Die identifizierten Einflüsse ermöglichen die Herstellung verschiedener, hämokompatibler Biozide mit einer breiten oder einer spezifischen antimikrobiellen Aktivität. Zudem kann PBI zur Entgiftung von antimikrobiell wirksamen Monomeren, wie Dodecyltrimethylammoniumchlorid, genutzt werden, ohne dass diese an antimikrobieller Aktivität verlieren. Insgesamt unterscheidet sich das Verhalten der PBI, als typische Vertreter der hydrophilen, kationischen Polymere, aufgrund der hohen Selektivität gegenüber Säugetierzellen, maßgeblich von dem amphiphiler, antimikrobieller Polymere. Dies macht diese Verbindungen zu einer neuen Klasse von antimikrobiellen Polymeren. Im zweiten Teil dieser Arbeit wurden beidseitig Brom-terminierte PBIn über ihre Endgruppen mit Tris(2-aminoethyl)amin zu schnell quellbaren, antimikrobiellen Superabsorbern (PBIN) vernetzt. Diese Superabsorber nehmen innerhalb einer Minute das Vielfache ihres Eigengewichts an Wasser auf. PBIN wurde in 2-Hydroxyethylacrylat und Glyceroldimethacrylat gequollen und zu transparenten, stabilen interpenetrierenden Hydrogelen (IPH) photovernetzt. Der PBI-Gehalt im IPH variiert im Bereich von 1.4 - 7.8 wt%. Antimikrobielle Untersuchungen zeigen, dass die Zellen der klinisch relevanten Keime Staphylococcus aureus, Escherichia coli und Pseudomonas aeruginosa bei der geringsten PBI-Konzentration auf den IPH, selbst nach 4 Wochen waschen in Wasser, abgetötet werden. Mittels eines neuen quantitativen Nachweises für PBI in Lösung, konnte jedoch selbst weit unterhalb der minimal inhibierenden Konzentration eine Freisetzung für die IPH nachgewiesen werden. Die IPH stellen ein vielversprechendes Material für Wundauflagen, beispielsweise für Brandwunden und infizierte Wunden, dar.
Neue Strategien zur Vernetzung von Hochpolymeren
(2017) Raidt, Thomas; Tiller, Jörg C.; Thommes, Markus
Das Ziel der vorliegenden Dissertation war die Entwicklung neuartiger Strategien zur nachträglichen Vernetzung von thermoplastischen Polymeren. Diesem Ziel folgend wurden neue Strategien zur Vernetzung sowie neu angepasste Vernetzungssysteme für isotaktisches Polypropylen (iPP), syndiotaktisches Polypropylen (sPP), Polybuten-1 (PB-1), Polyethylenterephthalat (PET), Polybutylenterephthalat (PBT), Polyamid 6 (PA6), Polyamid 11 (PA11), Polyether-Block-Amid (PEBA), Polyethyloxazolin (PEtOx), Chloropren-Kautschuk (CR) sowie Polymethylmethacrylat (PMMA) entwickelt. Bei der Untersuchung der Polymernetzwerke konnten hervorragende Form-gedächtniseigenschaften wie hohe rückstellbare Dehnungen (iPP, sPP, PA11, CR), hohe Triggertemperaturen (PET, PBT, PA6), Kaltprogrammierbarkeit (sPP, PET, PBT, PEBA, CR), ein Zwei-Wege-Formgedächtniseffekt (PB-1) und ein Triple-Shape-Memory Effekt (sPP, PET, PEBA) entdeckt werden. Zudem wird gezeigt, dass vernetzten Thermoplasten eine permanente, über den Querschnitt homogene Orientierung im Schmelzzustand aufgeprägt werden kann. Im Falle von PET war es dadurch möglich durch Kristallisation aus der orientierten Schmelze beeindruckende mechanische Eigenschaften zu erzeugen, die sonst nur PET-Fasern aus klassischen Schmelzspinnverfahren vorbehalten sind. Weiterhin wird am Beispiel von leicht vernetztem sPP gezeigt, dass sich Formgedächtnispolymere unter bestimmten Bedingungen hervorragend zur Absorption und Dämpfung mechanischer Energie, bzw. schlagartiger Belastungen eignen. Zuletzt wird anhand des Triple-Shape-Memory Effekts von Netzwerken auf Basis von sPP und PET ein Konzept für ein neuartiges heizratensensitives Smart Material vorgestellt, welches beispielsweise dazu verwendet werden kann eine potenziell drohende Überhitzung bei Aufheizprozessen zu verhindern.
Funktionale anorganisch/organische Hybridmaterialien für ultrasteife Hydrogele und antimikrobielle Lotusoberflächen
(2017) Rauner, Jan Nicolas; Tiller, Jörg C.; Kreßler, Jörg
Organolösliche Polymer-Enzym Konjugate auf Basis von Poly-2-Alkyloxazolinen
(2014) Konieczny, Stefan; Tiller, Jörg C.; Schmid, Andreas
Neuartige Materialien für magnetisch bzw. thermisch getriggerte Freisetzungssysteme
(2014) Thiel, Matthias; Tiller, Jörg; Behr, Arno

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