Elisabeth Heine

Amphiphilic Branched Polymers as Antimicrobial Agents

Cationic amphiphilic polymers were prepared from PEI and functional ethylene carbonates bearing cationic, hydrophobic or amphiphilic groups. The polymers are designed to exhibit antimicrobial properties. In a one-step addition, different functional ethylene carbonates were added to react with the primary amine groups of PEI. The water soluble polymers were studied regarding their ability to form soluble aggregates. Their hydrodynamic radii, their inhibition potential against proliferation of E. coli and their hemolytic potential were determined. A structure-property relationship was established by analyzing the antimicrobial activity as a function of the ratio of alkyl to cationic groups, length of the alkyl chains, and molecular weight of the PEI.

Synthesis and Characterization of Amphiphilic Monodisperse Compounds and Poly(ethylene imine)s: Influence of Their Microstructures on the Antimicrobial Properties

Amphiphilic monodisperse compounds (series B-I and B-II) and poly(ethylene imine)s (PEI-I, PEI-II, and PEI-III) with different microstructures were prepared from primary amines or poly(ethylene imine) with functional carbonates bearing cationic, hydrophobic, or amphiphilic groups. Their inhibition potential against proliferation of E. coli , S. aureus , and B. subtilis was investigated and their hemolytic activities were determined. The influence of the microstructures, the alkyl chain length and the distribution of cationic and hydrophobic groups, on their antimicrobial efficacy was studied. Amphiphilic compounds with long alkyl chains (C14-C18) directly linked to the cationic groups (series B-I) are more effective against both Gram-positive and Gram-negative bacteria than amphiphilic compounds in which the hydrophobic and cationic groups (series B-II) are connected by a spacer. Poly(ethylene imine)s with amphiphilic grafts (B-I) called PEI-II are more effective than amphiphilic PEIs with the same alkyl chain but with randomly linked cationic and hydrophobic graft called PEI-I or with the amphiphilic grafts (B-II) called PEI-III. The influence of the inoculum size on the MIC value was investigated exemplarily with compounds of series B-I against S. aureus .

Effects of Laccase-Mediator Combinations on Wool

The effects of Myceliophthora thermophila laccase are studied alone and in combina tion with the mediators violuric acid (VA) or l-hydroxybenzotriazole (HBT) on wool fibers, cystine, and tyrosine. Without a mediator, laccase is unable to oxidize wool or the amino acids. In the presence of either VA or HBT, oxygen consumption is observed, indicating oxidation of the secondary substrates of the laccase, i.e., wool, cystine, or tyrosine. The oxidation levels are low. Laccase/HBT reacts more efficiently with wool and tyrosine and laccase/VA with cystine. With the chosen enzyme dosage and mediator concentration, about 2-4% of cystine and about 1 % of tyrosine are oxidized. The slight oxidation of wool fibers is not sufficient to affect the surface chemistry or alkaline solubility of the fibers, although staining of the fibers by the oxidized mediators is significant.

Membrane Affinity and Antibacterial Properties of Cationic Polyelectrolytes With Different Hydrophobicity

The antibacterial behavior of cationic polyelectrolytes is studied using model membrane experiments and in vitro bacterial investigations. The molecular interaction with lipid films is evaluated by the degree of penetration of the polymers into Langmuir monolayers of neutral or negatively charged lipids. The polymer/lipid interaction results in structural changes of the penetrated lipid layer visualized using AFM. The polymers are found to be effective in inhibiting the proliferation of E. coli, B. subtilis and S. aureus. The influence of the chemical structure on the functional behavior is related to the conformational properties. An optimum structure is identified on the basis of antibacterial and hemolytic tests as well as membrane-destroying efficacy of the antimicrobial polymers.

Waterborne physically crosslinked antimicrobial nanogels

Supramolecular nanomaterials are formed by reversible connection of different building blocks; commonly non-covalent interactions lead to the formation of these materials. In this report, we present the preparation of very stable physically crosslinked nanogels (PCNGs) via a simple one pot reaction in water as solvent. Branched poly(ethylene imine) (PEI) is functionalized with C-10 alkyl chains and azetidinium groups yielding an amphiphilic polymer, which due to the hydrophobic interaction of the alkyl chains and the ionic repulsion of the azetidinium groups forms PCNGs with high colloidal stability. As the dynamic hydrophobic interactions are the main driving force in the formation of these nanogels, the PCNG show a temperature responsive behavior with respect to the zeta potential, particle size (hydrodynamic diameter), and polydispersity index. The potential of the PCNGs to form protective coatings is shown by the formation of ultrathin films on mica and highly oriented pyrolytic graphite. Finally the antimicrobial efficacy of the PCNGs was proven against a wide range of bacteria.

Multifunctional Poly(Vinyl Amine)s Bearing Azetidinium Groups: One Pot Preparation in Water and Antimicrobial Properties†

A simple, robust one pot procedure for the preparation of waterborne multifunctional poly(vinyl amine)s (PVAms) is presented. By post-polymerization modification of PVAm with a bifunctional coupler and functional couplers cationic, reactive azetidinium groups, and alkyl chains are introduced in the side chains of PVAms. The structure-activity relations (effect of hydrophobic and cationic modifications) of these antimicrobial polymers are studied; the minimum inhibitory concentration (MIC) against both (Gram positive and Gram negative bacteria) of the library of multifunctional poly(vinyl amine)s are determined to identify the candidates with the highest efficacy. Furthermore, the hemolytic activity-the effective concentration at which 50 and 10% of red blood cells are killed (HC50 and HC10 )-of selected polymers is determined. The ability of the polymers prepared to differentiate between microorganisms (Gram positive and Gram negative bacteria) and mammalian cells (red blood cells) is understood by comparing MIC and HC values. Finally, as an example, the best polymer is used to prepare an antimicrobial surface.

Advances in biotechnology for fibre processing

Action 847 on Textile Quality and Biotechnology has investigated the potential of biotechnology in the processing of fibres. Members of the network from 32 countries have coordinated more than 20 European projects focusing on biotechnical and enzymatic technologies in the processing of celluloseand protein-based materials and have recently focused on the functionalization of synthetic polymers. Based on the scientific outcome of these projects, experts have concluded, at the 4th COST 847 Congress in Gran Canaria, Spain, from February 20–23, 2005, that biotechnology plays an important role in the development of environmentally friendly production technologies in textile processing and in strategies to improve the final product quality. Advances in genetic engineering, combined with a better understanding of enzyme structure and function on polymeric materials, have opened up new possibilities for functionalization of fibre materials and/or for improving environmental aspects in processing. Based on the oral contributions of this congress, this Special Issue of Biotechnology Letters provides an overview on recent advances in this area. New hydrolases have been isolated which can partially hydrolyze the surface of polyester-based fibres thereby improving their hydrophilicity and further finishing steps (Alisch et al. 2006–loc. cit.). Transglutaminases have been used for crosslinking of gelatine-based materials used in tissue engineering (Bertoni et al. 2006). Besides such enzymatic methods for the functionalization of polymers, genetic engineering of protein-based polymers can be used to design complex and highly functional macromolecules with applications in the biomedical area (Arias et al. 2006). Despite the high potential of proteases for antishrinking and anti-felting treatment, as well as washing of wool based textiles, partial hydrolytic degradation of the fibres has prevented the use of proteases. Several approaches including chemical modification of enzymes are presented here which can target protease action to the surface of the fibres (Lenting et al. 2006; Zhang et al. 2006; Erlacher et al. 2006; Vasconcelos et al. 2006). Chemical modification of enzymes can also be used to diminish decolorization of fabric-bound Preface by Guest Editors of Special Issue

Spectroscopic methods of studying enzyme action in wool fibre

Enzymes may be used to develop an environmentally friendly alternative to the conventional polluting technologies in textile finishing. The action of the unlabeled and fluorescent labeled proteolytic enzymes subtilisin and trypsin on wool was examined. Scanning electron micrographs and a diffusion study, based on fluorescence microscopy, localized the enzymatic attack on the fiber. A kinetic study was carried out by monitoring the amino acid content of the treatment liquor.Enzymatic action is not confined to the fiber surface. To limit attack to the surface and reduce wool damage new treatment methods such as enzyme immobilization onto a solid carrier must be investigated.

Novel Antibacterial Polyglycidols: Relationship between Structure and Properties

Antimicrobial polymers are an attractive alternative to low molecular weight biocides, because they are non-volatile, chemically stable, and can be used as non-releasing additives. Polymers with pendant quaternary ammonium groups and hydrophobic chains exhibit antimicrobial properties due to the electrostatic interaction between polymer and cell wall, and the membrane disruptive capabilities of the hydrophobic moiety. Herein, the synthesis of cationic–hydrophobic polyglycidols with varying structures by post-polymerization modification is presented. The antimicrobial properties of the prepared polyglycidols against E. coli and S. aureus are examined. Polyglycidol with statistically distributed cationic and hydrophobic groups (cationic–hydrophobic balance of 1:1) is compared to (i) polyglycidol with a hydrophilic modification at the cationic functionality; (ii) polyglycidol with both—cationic and hydrophobic groups—at every repeating unit; and (iii) polyglycidol with a cationic–hydrophobic balance of 1:2. A relationship between structure and properties is presented.

Chlorhexidine Loaded Cyclodextrin Containing PMMA Nanogels as Antimicrobial Coating and Delivery Systems

Antimicrobial nanogels, aggregates, and films are prepared by complexation of the antiseptic and bacteriostatic agent chlorhexidine (CHX) for medical and dental applications. A series of α-, β-, and γ-cyclodextrin methacrylate (CD-MA) containing hydrophobic poly(methyl methacrylate) (PMMA) based nanogels are loaded quantitatively with CHX in aqueous dispersion. The results show that CHX is enhancedly complexed by the use of CD-MA domains in the particles structure. β-CD-MA nanogels present the highest uptake of CHX. Furthermore, it is observed that the uptake of CHX in nanogels is influenced by the hydrophobic PMMA structure. CHX acts as external cross-linker of nanogels by formation of 1:2 (CHX:CD-MA) inclusion complexes of two β-CD-MA units on the surfaces of two different nanogels. The nanogels adsorb easily onto glass surfaces by physical self-bonding and formation of a dense crosslinked nanogel film. Biological tests of the applied CHX nanogels with regard to antimicrobial efficiency are successfully performed against Staphylococcus aureus.