Research of new sustainable and low cost materials, such as cellulose, is of high interest. Modifications of the cellulose can be performed in order to create a “smart” material which responds to external stimuli, such as variations in pH and temperature, by changing its properties. This “smart” behavior is observed in some polymers, however, for certain applications they exhibit poor mechanical properties. These polymers can be bound by physical adsorption to cellulose, both in macro and nano scale, creating an improved “smart” composite material. In this project, thermoresponsive block-copolymers with different lengths of poly (diethylene glycol) methacrylate (PDEGMA) and poly N-(2-dimethylamino ethyl) methacrylate (PDMAEMA) in only one length, PDMAEMA-b-PDEGMA, were synthesized employing atom transfer radical polymerization (ATRP). 1H-NMR, SEC and DLS were used to characterize the block-copolymers. UV-Vis spectroscopy was employed to confirm the thermo-responsive behavior of the charged and uncharged block-copolymers, being lower for the higher molecular weight ones due to the higher polymer-polymer interactions. In a second step, PDMAEMA was charged positively by quaternization of its amine group with ICH3. Polyelectrolyte titration was used to determine the total number of charges in the quaternized block-copolymers. In addition, TEMPO-oxidized nanofibrillated cellulose (NFC) was produced by procedures found in literature. Finally, adsorption of the cationic block-copolymers onto the anionic NFC in tris base at pH 8.3 was performed and purified by consecutive filtrations, creating a novel smart composite material with different PDEGMA lengths in the block-copolymer. FT-IR confirmed that the block-copolymers were successfully adsorbed to the NFC. TGA results showed a higher thermal stability for the composite than for the TEMPO-NFC and quaternized block-copolymers. The block-copolymer modified NFC exhibited thermoresponsive behavior with LCST’s ranging from 30 to 44 °C, from higher to lower molecular weights, respectively.  Adsorption of polyelectrolytes in modified cellulose could be a promising way to create smart improved materials in further research.

In der vorliegenden Arbeit wurde gezeigt, dass enzymresponsive Peptid-Poly(ethylenglycol)-Konjugate (Peptid-PEG-Konjugate) effizient biotransformiert und proteinresistente Beschichtungen ausbilden können. Die oberflächenspezifische Haftung eines linearen Biokonjugates auf Basis einer literaturbekannten Adhäsionsdomäne für Titandioxid-Oberflächen wurde durch Verlängerung mit einer proteolytisch spaltbaren Erkennungssequenz und einer Suppressionsdomäne temporär unterbunden. Aus einer Serie unterschiedlich modifizierter Biokonjugate wurde eine anionische Suppressionsdomäne als besonders leistungsfähige haftungsunterdrückende Einheit identifiziert. Die Prozessierung des nicht-bindenden Vorläufers mit einer spezifischen Cysteinprotease hervorgehend aus dem Tabakätzvirus (TEV Protease) bewirkte die Abtrennung der eingeführten Modifikation. Durch die Biotransformation wurden die Haftungseigenschaften der polymergebundenen Adhäsionsdomäne zurückgebildet. Das aktivierte Biokonjugat ermöglichte die nicht-kovalente PEGylierung der Metalloxid-Oberfläche. Das Konzept wurde auf divalente Peptid-PEG-Konjugate unter Verwendung verzweigter Adhäsionsdomänen und verlängerter Suppressionsdomänen übertragen. Die proteolytisch aktivierte Dimer-Beschichtung zeigte eine erhöhte Stabilität im Vergleich zum linearen Biokonjugat und demonstrierte vielversprechende Antifouling-Eigenschaften gegenüber der unspezifischen Adsorption eines Modellproteins für Serumproteine des menschlichen Blutes auf Titandioxid-Oberflächen. / The present thesis has shown that enzyme-responsive peptide-poly(ethylene glycol) (peptide-PEG) conjugates can be efficiently biotransformed to create protein-resistant coatings. The surface-specific adsorption of a linear bioconjugate is temporarily suppressed by extending a titanium dioxide adhesion domain known from literature with a proteolytically cleavable recognition site and a suitable interfering domain. From a series of differently modified bioconjugates, an anionic interfering domain was identified as particularly effective to suppress adhesive functions. The enzymatic processing of the non-binding precursor with a specific cysteine protease derived from tobacco etch virus (TEV protease) resulted in the separation of the introduced modification. The adhesive properties of the polymer-bound binding sequence were reproduced by the biotransformation process. The activated bioconjugate allowed the non-covalent PEGylation of the metal oxide surface. The concept was applied to divalent peptide-PEG conjugates using branched adhesion domains and extended interfering domains. The proteolytically activated dimer coating showed increased stability against dilution compared to the linear bioconjugate and demonstrated promising antifouling properties against the non-specific adsorption of a model protein for human blood serum proteins to titanium dioxide surfaces.

Artificial lipid bilayers formed on solid surface supports are widespread model systems to study physical, chemical, as well as biological aspects of cell membranes and fundamental interfacial interactions. The approach to use a thin polymer film representing a cushion for lipid bilayers prevents incorporated membrane proteins from pinning to the support and mimics the native environment of a lipid bilayer in certain aspects of the extracellular matrix and intracellular structures. A key component for cell anchorage to extracellular fibronectin is the transmembrane adhesion receptor alpha(5)beta(1) integrin. Its transport dynamics and clustering behavior plays a major role in the assembly of focal adhesions, which mediate mechanical forces and biochemical signals of cells with their surrounding. The system investigated herein is envisioned to use extrinsically controlled stimuli-responsive polymer cushions to tune the frictional drag between polymer cushion and mobile membranes with incorporated integrins to actively regulate lipid membrane characteristics. To attain this goal, a temperature- and pH-responsive polymer based on poly(N-isopropylacrylamide) copolymers containing varying amounts of carboxyl-group-terminated comonomers at different aliphatic spacer lengths (PNIPAAm-co-carboxyAAM) was surface-grafted to a poly(glycidyl methacrylate) anchorage layer. The swelling transitions were characterized using atomic force microscopy, ellipsometry and quartz crystal microbalance with dissipation monitoring (QCM-D) and found to be tunable over a wide range of temperature and pH. In agreement with the behavior of the polymers in solution, longer alkyl spacers decreased the phase transition temperature T(P) and higher contents of carboxylic acid terminated comonomers increased T(P) at alkaline conditions and decreased T(P) at acidic conditions. Remarkably, the point where the degree of carboxyl group deprotonation balances the T(P)-lowering effect of the alkyl spacer was distinctive for each alkyl spacer length. These findings illustrate how the local and global balance of hydrophilic and hydrophobic interactions along the copolymer chain allows to adjust the swelling transition to temperatures below, comparable, or above those observed for PNIPAAm homopolymers. Additionally, it could be shown that surface-grafting leads to a decrease in T(P) for PNIPAAm homopolymers (7°C) and copolymers (5°C - 10°C). The main reason is the increase in local polymer concentration of the swollen film constrained by dense surface anchorage in comparison to the behavior of dilute free chains in solution. In accordance with the Flory-Huggins theory, T(P) decreases with increasing concentration up to the critical concentration. Biological functionalization of the PNIPAAm-co-carboxyAAm thin films was demonstrated for the cell adhesion ligand peptide cRGD via carbodiimide chemistry to mimic extracellular binding sites for the cell adhesion receptors integrin. The outcome of QCM-D measurements of cRGD-functionalized surfaces showed a maintained stimuli-responsiveness with slight reduction in T(P). A drying/rehydration procedure of a 9:1 lipid mixture of the cationic lipid dioleoyl-trimethylammoniumpropane (DOTAP) and the zwitterionic dioleoyl-phosphatidylcholine (DOPC) was utilized to form lipid bilayer membranes on PNIPAAm-co-carboxyAAM cushions. Fluorescence recovery after photobleaching (FRAP) revealed that lipid mobility was distinctively higher (6.3 - 9.6) µm2 s-1 in comparison to solid glass support ((3.0 - 5.9) µm2 s-1). In contradiction to the initial expectations, modulation of temperature and pH led to poor variations in lipid mobility that did not correlate with the PNIPAAm cushion swelling state. The results suggested a weak coupling of the lipid bilayer with PNIPAAm polymer cushions that can be slightly tuned by electrostatic interactions. The transmembrane adhesion receptor alpha(5)beta(1) integrin was reconstituted into liposomes consisting of DOPC/sphingomyelin/cholesterol 2:2:1 for the formation of polymer cushioned bilayers. PNIPAAm- co-carboxyAAM and maleic acid (MA) copolymers were used as cushions, both with the option for cRGD functionalization. On the MA copolymer cushions, fusion of proteoliposomes resulted in supported bilayers with mobile lipids as confirmed by FRAP. However, incorporated integrins were immobile. In an attempt to explain this observation, the medium-sized cytoplasmic integrin domain was accounted to hamper the movement by steric interactions with the underlying polymer chains in conjunction with electrostatic interactions of the cationic cytoplasmic domain with the oppositely charged MA copolymer. On the PNIPAAm-co-carboxyAAM cushion only a drying/rehydration procedure lead to bilayer formation. However, again the integrins were immobile, presumably due to the harsh treatment during preparation. Nevertheless, the results of the investigated set of PNIPAAm copolymer films suggest their application as temperature- and pH-responsive switchable layers to control interfacial phenomena in bio-systems at different physiological conditions. The PNIPAAm-co-carboxyAAm cushioned bilayer system represents a promising step towards extrinsically controlled membrane – substrate interactions.

Artificial lipid bilayers formed on solid surface supports are widespread model systems to study physical, chemical, as well as biological aspects of cell membranes and fundamental interfacial interactions. The approach to use a thin polymer film representing a cushion for lipid bilayers prevents incorporated membrane proteins from pinning to the support and mimics the native environment of a lipid bilayer in certain aspects of the extracellular matrix and intracellular structures. A key component for cell anchorage to extracellular fibronectin is the transmembrane adhesion receptor alpha(5)beta(1) integrin. Its transport dynamics and clustering behavior plays a major role in the assembly of focal adhesions, which mediate mechanical forces and biochemical signals of cells with their surrounding. The system investigated herein is envisioned to use extrinsically controlled stimuli-responsive polymer cushions to tune the frictional drag between polymer cushion and mobile membranes with incorporated integrins to actively regulate lipid membrane characteristics. To attain this goal, a temperature- and pH-responsive polymer based on poly(N-isopropylacrylamide) copolymers containing varying amounts of carboxyl-group-terminated comonomers at different aliphatic spacer lengths (PNIPAAm-co-carboxyAAM) was surface-grafted to a poly(glycidyl methacrylate) anchorage layer. The swelling transitions were characterized using atomic force microscopy, ellipsometry and quartz crystal microbalance with dissipation monitoring (QCM-D) and found to be tunable over a wide range of temperature and pH. In agreement with the behavior of the polymers in solution, longer alkyl spacers decreased the phase transition temperature T(P) and higher contents of carboxylic acid terminated comonomers increased T(P) at alkaline conditions and decreased T(P) at acidic conditions. Remarkably, the point where the degree of carboxyl group deprotonation balances the T(P)-lowering effect of the alkyl spacer was distinctive for each alkyl spacer length. These findings illustrate how the local and global balance of hydrophilic and hydrophobic interactions along the copolymer chain allows to adjust the swelling transition to temperatures below, comparable, or above those observed for PNIPAAm homopolymers. Additionally, it could be shown that surface-grafting leads to a decrease in T(P) for PNIPAAm homopolymers (7°C) and copolymers (5°C - 10°C). The main reason is the increase in local polymer concentration of the swollen film constrained by dense surface anchorage in comparison to the behavior of dilute free chains in solution. In accordance with the Flory-Huggins theory, T(P) decreases with increasing concentration up to the critical concentration. Biological functionalization of the PNIPAAm-co-carboxyAAm thin films was demonstrated for the cell adhesion ligand peptide cRGD via carbodiimide chemistry to mimic extracellular binding sites for the cell adhesion receptors integrin. The outcome of QCM-D measurements of cRGD-functionalized surfaces showed a maintained stimuli-responsiveness with slight reduction in T(P). A drying/rehydration procedure of a 9:1 lipid mixture of the cationic lipid dioleoyl-trimethylammoniumpropane (DOTAP) and the zwitterionic dioleoyl-phosphatidylcholine (DOPC) was utilized to form lipid bilayer membranes on PNIPAAm-co-carboxyAAM cushions. Fluorescence recovery after photobleaching (FRAP) revealed that lipid mobility was distinctively higher (6.3 - 9.6) µm2 s-1 in comparison to solid glass support ((3.0 - 5.9) µm2 s-1). In contradiction to the initial expectations, modulation of temperature and pH led to poor variations in lipid mobility that did not correlate with the PNIPAAm cushion swelling state. The results suggested a weak coupling of the lipid bilayer with PNIPAAm polymer cushions that can be slightly tuned by electrostatic interactions. The transmembrane adhesion receptor alpha(5)beta(1) integrin was reconstituted into liposomes consisting of DOPC/sphingomyelin/cholesterol 2:2:1 for the formation of polymer cushioned bilayers. PNIPAAm- co-carboxyAAM and maleic acid (MA) copolymers were used as cushions, both with the option for cRGD functionalization. On the MA copolymer cushions, fusion of proteoliposomes resulted in supported bilayers with mobile lipids as confirmed by FRAP. However, incorporated integrins were immobile. In an attempt to explain this observation, the medium-sized cytoplasmic integrin domain was accounted to hamper the movement by steric interactions with the underlying polymer chains in conjunction with electrostatic interactions of the cationic cytoplasmic domain with the oppositely charged MA copolymer. On the PNIPAAm-co-carboxyAAM cushion only a drying/rehydration procedure lead to bilayer formation. However, again the integrins were immobile, presumably due to the harsh treatment during preparation. Nevertheless, the results of the investigated set of PNIPAAm copolymer films suggest their application as temperature- and pH-responsive switchable layers to control interfacial phenomena in bio-systems at different physiological conditions. The PNIPAAm-co-carboxyAAm cushioned bilayer system represents a promising step towards extrinsically controlled membrane – substrate interactions.