Irem Erel-Goktepe

pH-responsive layer-by-layer films of zwitterionic block copolymer micelles

We report a strategy to incorporate micelles of poly[3-dimethyl (methacryloyloxyethyl) ammonium propane sulfonate]-block-poly[2-(diisopropylamino)ethyl methacrylate] (βPDMA-b-PDPA) into electrostatic layer-by-layer (LbL) films. We obtained micelles with pH-responsive PDPA-cores and zwitterionic βPDMA-coronae at pH 8.5 through pH-induced self-assembly of βPDMA-b-PDPA in aqueous solution. To incorporate βPDMA-b-PDPA micelles into LbL films, we first obtained a net electrical charge on βPDMA-coronae. Negative charges of the zwitterionic units were screened through complexation of βPDMA-b-PDPA micelles and poly(allylamine hydrochloride) (PAH). Positively charged micellar complexes were then self-assembled at the surface using poly(sodium 4-styrenesulfonate) (PSS). The pH-stability of the multilayers was examined by exposing the films to decreasing pH values. Despite the disintegration of micellar complexes below pH 7, no change in film thickness was recorded between pH 8.5 and 3.5. Only ∼20% of the film released at pH < 3.5. Moreover, we demonstrated that when multilayers were exposed to decreasing pH at a temperature below the upper critical solution temperature (UCST) of betainized coronal chains, the film thickness increased by 20% between pH 4.5 and 3. This is probably due to phase separation of the corona block and formation of voids within the film, probably entrapping water molecules within the multilayers. Decreasing temperature also shifted the critical disintegration pH (onset of multilayer dissolution) to a slightly lower pH. By taking advantage of the pH-responsive cores, we showed that multilayers were capable of releasing functional molecules under moderately acidic conditions. Important biological properties of polybetaines, higher loading capacity of zwitterionic block copolymer micelles than linear polybetaines and pH-response of the multilayers at physiologically related pH values make such films promising for biomedical applications.

Bacterial anti-adhesive and pH-induced antibacterial agent releasing ultra-thin films of zwitterionic copolymer micelles☆

UNLABELLED We report on preparation of substrates with dual function coatings, i.e. bacterial anti-adhesive and antibacterial agent releasing polymer films of zwitterionic block copolymer micelles (BCMs). BCMs were obtained by pH-induced self-assembly of poly[3-dimethyl (methacryloyloxyethyl) ammonium propane sulfonate-b-2-(diisopropylamino)ethyl methacrylate] (βPDMA-b-PDPA), resulting in BCMs with zwitterionic βPDMA-coronae and pH-responsive PDPA-core. These zwitterionic BCMs were then used as building blocks to construct mono- and multi-layer films. We found that the number of layers in the film was critical for the anti-adhesive property and 3-layer films were the most anti-adhesive against a model Gram-positive bacterium, Staphylococcus aureus. Antibacterial activity could be introduced to the films by loading Triclosan into βPDMA-b-PDPA micelles. Triclosan containing films were effective against Triclosan-sensitive Staphylococcus aureus specifically at moderately acidic conditions due to pH-induced disintegration of the micellar core blocks and release of Triclosan from the surface. Three-layer films also exhibited anti-adhesive property at physiological pH against a model Gram-negative bacterium, Escherichia coli. At moderately acidic pH, the coatings showed a contact antibacterial effect against an isolate of Escherichia coli with low sensitivity to Triclosan only when micellar cores were loaded with Triclosan. Such dual function films can be promising to combat biofouling at the non-homogeneous and/or defective parts of an anti-adhesive coating. Moreover, considering the moderately acidic conditions around an infection site, these multilayers can be advantageous due to their property of pH-induced antibacterial agent release. STATEMENT OF SIGNIFICANCE This study presents preparation of substrates with dual function ultra-thin coatings of zwitterionic block copolymer micelles which show bacterial anti-adhesive properties against a Gram-positive and a Gram-negative bacterium. Such coatings are also capable of releasing antibacterial compounds in response to pH changes. Films were prepared by self-assembly of polymers at the surface. Our findings showed that zwitterionic micellar coronae introduced bacterial anti-adhesive property to the films, whereas pH-responsive micellar cores enabled release of an antibacterial agent from the surface at acidic pH. Considering the moderately acidic conditions around an infection site, such multilayers can be promising for the coating of implants/medical devices.

Bacterial anti-adhesive properties of a monolayer of zwitterionic block copolymer micelles.

We report on bacterial anti-adhesive properties of a monolayer of block copolymer micelles (BCMs) with zwitterionic coronae and pH-responsive cores. BCMs were obtained by pH-induced self-assembly of selectively betainized poly[3-dimethyl (methacryloyloxyethyl) ammonium propane sulfonate-b-2-(diisopropylamino)ethyl methacrylate] (βPDMA-b-PDPA) in aqueous solution above neutral pH. Monolayer films were self-assembled at pH 7.5 when βPDMA-b-PDPA was in the micellar form. Bacterial anti-adhesive properties of the zwitterionic micellar coatings were examined against S. aureus through: i) a macroscopic test based on viable cell counting; ii) direct microscopic visualization of adherent bacteria by live/dead staining and iii) crystal violet staining to evaluate surface adherent biomass. 95% reduction in cell adhesion was observed by microscopy indicating the anti-adhesive properties of βPDMA-b-PDPA micellar monolayer. Results obtained from the viable cell count assay and crystal violet staining showed similar trends and were in good agreement with the microscopy results. Such coatings are promising to impart both anti-adhesive and antimicrobial properties to a surface due to bacterial anti-adhesive properties of zwitterionic coronae and the potential of pH-responsive cores to release antimicrobial agents.

Hydrogen-Bonded Multilayers With Controllable pH-Induced Disintegration Kinetics for Controlled Release Applications From Surfaces

We report on incorporation of coordination complexes into hydrogen-bonded multilayers which was found to be an effective method to control pH-induced disintegration kinetics of hydrogen-bonded multilayers. By taking advantage of the strong metal chelating and hydrogen donating properties of Tannic Acid (TA), coordination complexes of Zr4+ and TA (Zr(IV)-TA complexes) were prepared and then self-assembled at the surface using hydrogen accepting polymers such as poly (N-vinyl caprolactam) (PVCL) or poly(N-isopropyl acrylamide) (PNIPAM). Incorporation of Zr(IV)-TA complexes into hydrogen-bonded multilayers allowed controlling kinetics of pH-induced disintegration of the films. We found that the onset of pH-triggered disintegration of the multilayers could be delayed for ∼10 h at a physiologically related pH, which may be an important feature for controlled delivery applications from surfaces. In contrast to neutral polymer/TA multilayers which dissolve rapidly above their critical pH, multilayers of Zr(IV)-TA complexes dissolved in a linear fashion in a longer period of time than that of multilayers composed solely from hydrogen bonding polymers. Multilayers of Zr(IV)-TA complexes could uptake methylene blue at a moderately acidic pH and release the dye molecules at strongly acidic conditions. This study contributes to fundamental understanding of structure-property relationship in hydrogen-bonded LbL films. Considering the interesting biological properties of TA, multilayers of Zr(IV)-TA complexes may be promising for future biomedical applications.

Biologically Functional Ultra-thin Films Made of Zwitterionic Block Copolymer Micelles

We report the preparation of ultrathin coatings of zwitterionic block copolymer micelles and a comparison of their protein adsorption, adhesiveness, and antibacterial properties. Zwitterionic block copolymer micelles were obtained through pH-induced self-assembly of poly[3-dimethyl(methacryloyloxyethyl)ammonium propanesulfonate- b-2-(diisopropylamino)ethyl methacrylate] (βPDMA- b-PDPA) at pH 7.5. βPDMA- b-PDPA micelles with zwitterionic βPDMA-corona and pH-responsive PDPA-core were then used as building blocks to prepare layer-by-layer (LbL) assembled multilayer films together with hyaluronic acid (HA), tannic acid (TA), or poly(sodium 4-styrenesulfonate) (PSS). Protein adsorption tests showed that 3-layer βPDMA- b-PDPA micelles/HA films were the most effective to reduce the adhesion of BSA, lysozyme, ferritin, and casein. In contrast, βPDMA- b-PDPA micelles/TA films were the most attractive surfaces for protein adsorption. Bacterial antiadhesive tests against a model Gram-negative bacterium, Escherichia coli, and a model Gram-positive bacterium, Staphylococcus aureus, were in good agreement with the protein adsorption properties of the films. The differences in the antiadhesive properties between these three different film systems are discussed within the context of chemical nature and the functional chemical groups of the polyanions, layer number, and surface morphology of the films. Multilayers were found to lose their antiadhesiveness in the long term. However, by taking advantage of the pH-responsive hydrophobic micellar cores, we show that an antibacterial agent could be loaded into the micelles and multilayers could exhibit antibacterial activity in the long term especially at moderately acidic conditions. In contrast to antiadhesive properties, no significant differences were recorded in the antibacterial properties between the different film types.