Motivation
Das stetig ansteigende Interesse an hygienischen Lebensbedingungen führt zu immer größeren Anforderungen für antimikrobielle Materialien in zahlreichen Anwendungen, wie beispielsweise Wasserrohren, Lebensmittelautomaten, Schiffswänden und Einrichtungen von Krankenhäusern. Die meisten biologischen Kontaminationen basieren auf einer primären Kolonisierung durch Mikroorganismen welche dann sogenannte Biofilme bilden, die Infektionen verbreiten können und resistent gegen viele Deinfektionsmittel sind. Aus diesem Grunde können viele biologische Kontaminationen verhindert werden, indem man gefährdete Oberflächen so modifiziert, daß Mikroorganismen nicht darauf wachsen. Es wurde in aktuellen Forschungsarbeiten gefunden, daß die Oberflächenmodifizierung mit bestimmten Polymeren sehr vielversprechend für antimikrobielle Oberflächen ist.
Konzepte*
Kontakt-Zerstörung an Oberflächen basierend auf gepfropften Polymeren
Erkennendes Freisetzungssystem basierend auf Mikroben-sensitiven Netzwerke
Abstoßende Systeme basierend auf gepfropften Polymeren und Polymer-Netzwerken
*(note that the illustrations do not give an exact picture of structure, size relations, and mechanism of the shown principles)
Methoden
Zusätzlich zu den üblichen Polymercharakterisierungsmethoden (NMR, FTIR, GPC, DSC, MALDI-TOF) beinhalten die Projekte die Anwendung von AFM, ESEM, Oberflächentitration, mikrobiellen Studien, Freisetzungskinetiken und Fluoreszenzmikroskopie. Die antimikrobiellen Eigenschaften werden in Lösung und auf Oberflächen getestet.
Combining Lotus-Effect with antimicrobial contact-activity
Protecting surface infection of silicone by fungi and bacteria
Nicolas Rauner, Christoph Mueller, Sabine Ring, Sara Boehle, Arne Strassburg, Jörg C. Tiller
Silicones are an important factor for technical progress and irreplaceable in many applications, so the market for silicone products is still growing with sales totaling 15 billion US$ in 2013. Silicone elastomers exhibit excellent material properties, but they are either susceptible for fungi growth or filled with biocides causing allergies. Non-allergen, contact-active antimicrobials are not used, because they lead to a loss of the water-repelling properties of silicone that counteracts the antimicrobial effect. Here we show the first example for equipping silicon with the contact-active antimicrobial DOW5700 simultaneously improving the hydrophobic surface properties by a Lotus-Effect.
DOW5700 is known from hydrophobic, contact-active antimicrobial glass coatings. The hydrophobicity is caused by its long C18-group shielding the polar ammonium group (Figure 1). Unfortunately, applying DOW5700 onto silicone results in rather hydrophilic surfaces without antimicrobial activity. The reason might be the favored interaction of the hydrophobic C18-group with the silocone resulting in an inversed attachment of DOW5700 compared to glass, pointing the hydrophilic anchor group away from the hydrophobic surface (Figure 1). In order to solve this problem we developed a concept to equip silicone surfaces with DOW5700 by applying modified SiO2-nanoparticles instead of modifying the surface directly. Besides the antimicrobial effect this should also grant ultrahydrophobic properties to the surface caused by the formed microstructure. Having established the synthesis, the modified nanoparticles form a transparent, stable colloidal solution in CHCl3, while unmodified particles sedi-ment directly. Applying the modified particles on a silicone elastomer results in a strong adhesion of the particles to the surface, contrary to glass where the particles are easily removable.
Figure 1: Bonding of DOW5700 and modified SiO2-nanoparticles on glass/silicone with the resulting surface properties.
Placing a drop of water onto such a silicone particle coa-ting, leads to no wetting of the surface and a contact angle of 155° (Figure 2). The drop easily rolls off when tilting the surface by just 5°, confirming a Lotus-Effect. The contact-active, antimicrobial effect was investigated by spraying Staphylococcus aureus on a particle coated silicone surface. After incubation and dyeing no bacteria growth was visible in the coated region unlike to the surrounding area.
Figure 2: DOW5700 modified particles are drop coated on a silicone surface (1.) forming a dense surface layer.
Additionally an image of water drop placed on the coated surface is pictured. In order to measure the antimicrobial properties Staphylococcus aureus is sprayed (2.) onto the surface. (3.) shows the sprayed sample after incubation and dyeing.
The modified nanoparticles are easyly applicable and besides silicone also suited to coat other hydrophobic polymers, like polyethylene e.g. for an antimicrobial design of air filters.
N. Rauner, C. Müller, J. C. Tiller; TU Dortmund. Derivatized Silicone Dioxide Nanoparticles. European patent WO 02015189405; patent registered 12.06.2014, publicized 17.12.2015
Double Action Polyoxazolines for Dental Applications
Antimicrobial and collagenase-inhibiting polymer for caries prevention in dental materials
Christoph Fik, Stefan Konieczny, Joerg C. Tiller
Mechanical removal of caries infected tooth material is already inducing secondary caries, because the caries-causing cells are forced into the tubuli below the treated dentin. Eventually, the surviving bacteria will form caries below the dental filling. Even if the microbial cells are killed in the process, there is still the problem of the bacteria-related enzyme collagenase, which is still active causing degradation of the collagen fibers below the filling, which results in decreased adhesion of the filling. Thus, the optimal additive for a dental filling will be a compound that kills microbial cells, inhibits collagenase, and is bound to the surface of the dental filling for prolonged activity. The here developed telechelic polyoxazoline is a promising candidate for meeting these requirements.
Modern dental repair materials face the problem that the dentin below the composite fillings is actively decomposed by secondary caries and extracellular proteases such as MMP.
Figure 1. Chemical structure of DDA-X-PMOX-AMA
To address this problem, poly(2-methyloxazoline) (PMOx) with a biocidal and a polymerizable terminal was synthesized by cationic ring-opening polymerization of 2-methyloxazoline using a tailored antimicrobial initiator and a double bond-containing termination agent (structure see Fig. 1).
Figure 2. Photographs of eppendorf tubes containing cow tooth slices after 1 day of incubation in growth medium. The slices were infected with caries and treated with AdheSE® One F containing different concentrations of DDA-X-PMOx-AMA.
This polymer was explored as additive for a commercial dental adhesive. The additive rendered the adhesive contact-active antimicrobial against the caries related bacterium Streptococcus mutans at a concentration of 2.5 wt% and even constant washing with water for 101 days did not diminish this effect. Five wt.% of the additive in the adhesive allowed killing S. mutans cells in the tubuli of bovine dentin (see Fig. 2). No clouding, i.e. no bacterial growth, could be observed indicating successful killing.
Further, the additive fully inhibited bacterial collagenase at 0.5 wt% and signifi cantly reduced activity of human recombinant collagenase MMP-9. Human MMPs naturally bound to dentin were inhibited by more than 96% in a medium containing 5 wt% of the additive One wt% of the polymer fully prevents degradation of cow tooth collagen for at least 48h (see Fig. 3b).
Figure 3. Photographs of decalcified cow dentine disks impregnated in citrate buffer with 1 mg collagenase. a) Non-treated disks. b) disks incubated with a 1.0 wt% DDA-X-PMOx-AMA/citrate solution for 1 h at room temperature and air dried.
In order to explore if the dental adhesive is still effective with the additive, its infl uence on the enamel and dentine bond strength of AdheSE® One F was measured. The macromer DDA-X-PMOx-AMA was added to AdheSE® One F (2.5 wt.%) and the respective shear bond strengths were determined for both formulations. In comparison to the reference, no significant decrease in both bond strengths was detected; the measured values were in a common range for corresponding dental adhesive compositions.
C. P. Fik, S. Konieczny, D. H. Pashley, C. J. Waschinski, R. S. La-disch, U. Salz, T. Bock, J.C. Tiller
Telechelic Poly(2-oxazoline)s with a Biocidal and a Polymerizable Terminal as Collagenase Inhibiting Additive for Long-Term Active Antimicrobial Dental Materials
Macromolecular Bioscience 14 (11), 1569-1579 (2014)
Semipermanent antimicrobial coatings
Solubility Switching of Star-like Poly(styrene)-block-Poly(4-vinyl-N-methylpyridinium)
Felix Siedenbiedel, Thorsten Moll,Joerg C. Tiller
Rendering surfaces antimicrobial for prevention of biofouling and spreading diseases is an important topic in material science and medicine. Although permanent contact-active bacteria-killing coatings are advantages, they sometimes render other surface properties in undesirable ways. In order to address this, we have developed a contact-active antimicrobial coating that can be applied from an aqueous solution and forms a coating that resists typical environmental conditions, but can be removed and reapplied deliberately.
Goal of the present work was to develop an antimicrobial coating that can be applied from an aqueous solution and resists short washing cycles and bacterial colonization, but can be rinsed off by thorough washing (Figure 1).
Figure 1. Concept of semipermanent antimicrobial coatings.
To this end a series of star-shaped polystyrene (PS)-block-poly(4-vinyl-N-methylpyridinium iodide) (P4VMP) polymers were synthesized by anionic polymerization using a core-first approach.
The polymer structure in terms of arm-number, -length, and -composition was optimized regarding solubility in water after heating, water-insolubility of a coating formed from this solution and antimicrobial activity. We found that star-polymers with 3-4 arms and P4VMP/PS ratios of 3-7 were best suited regarding the targeted properties. These polymers are insoluble in water, but become soluble after heating to 100°C for 5min (see Figure 2, left).
Figure 2. Left: 5 wt% suspension of polymer in water at room temperature and Middle: after heating to 100°C for 5 min Right: AFM image of a cross-section of a coating formed from this solution.
The coatings formed from these aqueous solutions resisted more than 20 flush-like washing cycles. Investigations of these coatings with atomic force microscopy (Figure 2, right) revealed that the change in water-solubility might be due to a transition from unimicellar structures of the star-polymers in solution to network-like structures in the coating.
All coatings were tested regarding their antimicrobial activity against the Gram-positive Staphylococcus aureus and the Gram-negative Escherichia coli. The coatings did kill both bacterial strains with great efficiency.
All coating could be removed by intensive washing with water water, proofing the concept valid.
F. Siedenbiedel, A. Fuchs, T. Moll, M. Weide, R. Breves, J.C. Tiller
Star-shaped Poly(styrene)-block-Poly(4-vinyl-N-methylpyridiniumiodide) for semipermanent antimicrobial coatings
Macromolecular Bioscience 13 (10), 1447-1455 (2013)
Antimicrobial Coatings and The Phospholipid-Sponge Effect
Cellulose-based antimicrobial coatings with different working mechanisms
Arno Bieser,Joerg C. Tiller
Antifouling paints are the most advanced method to keep surfaces free of biological contaminations.They work by being degraded in water releasing a biocide and constantly refreshing their surface. However, the constant release of these self- polishing coatings is a big environmental issue. We have developed a series of cellulose derivatives that can be applied as antimicrobial coatings, which are degraded by bacterial enzymes and thus release biocides and polish themselves only in the presence of a microbial contamination. Further, the derivatives gave mechanistic insights that led us to propose a new working mechanism of contact-active antimicrobial surfaces.
The novel class of antimicrobial coatings was realized by grafting the antimicrobial quarternary ammonium group N,N-Dimethyldodecyl-ammonium(DDA)to acellulose backbone via a polymeric polyoxazoline spacer.
Figure1: Structural concept of antimicrobial coatings based on antimicrobial DDA-groups grafted via cellulose to sylate initiated cationic ring-opening polymerization of
2-ethyl-1,3-oxazoline and termination with DDA.
The antimicrobial activity of these coatings, their biode- gradability and their self-polishing potential was investigated. It was found that all coatings were antimicrobially active against Staphylococcus aureus. Further, the coatings with higher DS (degreeof substitution) values and long polymeric spacers proved to degrade in water with time, while coatings with low DS values and short spacers where not hydrolyzed even in the presence of cellulase. Only one coating was found to be selectively degradable by cellulase. This coating was found to recover most of its antimicrobial activity after overloading and subsequent treatment with cellulase, i.e. showed a biologically induced self-polishing effect.
Interestingly, it was found that the cellulose derivatives containing no polymeric spacer or a biocidal DDA group, but only hydrophobic tosylates and a quarternary N,N-di- methylbutylammonium group (DBA) did also kill S.aureus cells on contact.
Figure2: Scheme of the proposed phospholipid-sponge-effect.
Considering the hydrophobic/cationic balance in the active derivatives, we propose a new mechanism that involves the selective adhesion of an ionic phospholipids from the bacterial cell membrane. This so-called phospholipid-sponge-effect of the surface is supported by the fact that all coatings could be deactivated by treating them with the negatively charged surfactant SDS, negatively charged phospholipids ,but not with neutral phospholipids. In contrast to those, the DDA- polyethyloxazoline grafted cellulose derivatives with chain length of 90 repeating units and more could not be deactivated by SDS, indicating that such derivatives act differently, probably according to the polymeric spacer effect proposed for antimicrobial surfaces earlier.
A.M. Bieser, J.C. Tiller
Mechanistic Considerations on Contact-Active Antimicrobial Surfaces with Controlled Functional Group DensitiesMacromolecular Bioscience 11 (4), 526-534 (2011)
