Polymer brush coatings for combating marine biofouling

A variety of functional polymer brushes and coatings have been developed for combating marine biofouling and biocorrosion with much less environmental impact than traditional biocides. This review summarizes recent developments in marine antifouling polymer brushes and coatings that are tethered to material surfaces and do not actively release biocides. Polymer brush coatings have been designed to inhibit molecular fouling, microfouling and macrofouling through incorporation or inclusion of multiple functionalities. Hydrophilic polymers, such as poly(ethylene glycol), hydrogels, zwitterionic polymers and polysaccharides, resist attachment of marine organisms effectively due to extensive hydration. Fouling release polymer coatings, based on fluoropolymers and poly(dimethylsiloxane) elastomers, minimize adhesion between marine organisms and material surfaces, leading to easy removal of biofoulants. Polycationic coatings are effective in reducing marine biofouling partly because of their good bactericidal properties. Recent advances in controlled radical polymerization and click chemistry have also allowed better molecular design and engineering of multifunctional brush coatings for improved antifouling efficacies.     

In vitro endothelialization of cobalt chromium alloys with micro/nanostructures using adipose-derived stem cells

In this study, integrin expression, proliferation, and endothelial differentiation of adipose-derived stem cells (ADSCs) on pristine cobalt chrome (CoCr) surface, microstructured and nanostructured CoCr surfaces (obtained after treatment with piranha solution) were investigated. The results showed that proliferation of ADSCs on the substrates treated with piranha solution is not significantly different from that on the pristine substrates. However, quantitative real-time PCR analysis showed significantly enhanced up-regulation of CD31, vWF and eNOS from gene level by ADSCs on the nanostructured substrates but not on the microstructured substrates. The adsorption of vitronectin from the culture medium on the nanostructured substrates was higher than on the pristine and microstructured substrates. We speculate that this results in increased integrin α_vβ₃ expression in the ADSCs, which may contribute partially to the enhanced endothelial differentiation of ADSCs on the nanostructured substrates. This study shows that ADSCs can be used to endothelialize stents in vitro and the endothelial differentiation of ADSC is enhanced on the nanostructured surfaces.     

Functionalization of reduced graphene oxide nanosheets via stacking interactions with the fluorescent and water-soluble perylene bisimide-containing polymers

Reduced graphene oxide (RGO)-polymer composites were prepared via π-π stacking interactions of RGO with the perylene bisimide-containing poly(glyceryl acrylate) (PBIPGA). PBIPGA was synthesized via atom transfer radical polymerization (ATRP) of solketal acrylate (SA), using bifunctional N,N′-bis{2-[2-[(2-bromo-2-methylpropanoyl)oxy]ethoxy]ethyl}perylene-3,4,9,10-tetracarboxylic acid bisimide (PBI-Br) as the initiator, and subsequent hydrolysis of the acetal-protecting group. PBIPGA was characterized by ¹H NMR spectroscopy, gel permeation chromatography (GPC), UV-visible absorption spectroscopy and fluorescence spectroscopy. The presence of π-π stacking interactions between PBI and the RGO surface was suggested by fluorescence and UV-visible absorption spectroscopy results. The chemical states and π-π stacking interaction, morphology, and composition of RGO-PBIPGA composites were characterized, respectively, by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The low cytotoxicity level of the RGO-PBIPGA composites was revealed by incubation with 3T3 fibroblasts in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assays in vitro.     

Halogen-induced charge transfer polymerization of pyrrole in aqueous media

Simultaneous polymerization and doping of pyrrole have been carried out in the presence of a halogenic electron acceptor, bromine (Br₂) or iodine (I₂), in aqueous dispersion or in a two-phase solvent system. The morphology of the polypyrrole (PPY) so produced is granular and porous. The electrical conductivity of the PPY-I₂ charge transfer (CT) complex is of the order of 10¹ ohm⁻¹ cm⁻¹ while that of the PPY-Br₂ complex is about one order of magnitude less. Both complexes are stable in the atmosphere. The physicochemical properties of the PPY-I₂ and PPY-Br₂ CT complexes prepared under various experimental conditions are examined in detail.     

Environmental stability of electrically conductive viologen–polyaniline systems

Viologen–polyaniline (PANI) systems were prepared by PANI being coated onto viologen‐grafted low‐density polyethylene films. PANI in this system could undergo photoinduced doping with ultraviolet irradiation. The electrical stability of the electrically conductive viologen–PANI systems was found to be stable in air, but the conductivity decreased rapidly when the sample was treated in aqueous media of pH > 5 because of the migration of the anions out of PANI into water. However, the conductivity increased by a factor of 2 after treatment in a 1M HCl solution because of the further protonation of PANI by acid. The structural changes of these systems were monitored with ultraviolet–visible absorption spectroscopy, Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and resistance measurements. The electrical stability of the viologen–PANI system in water could be enhanced via spin coating with poly(methyl methacrylate) (PMMA) because this layer inhibited the migration of the anions out of the system. The photoinduced doping of PANI could be carried out either before or after the spin coating of PMMA. The advantages and limitations of each method were demonstrated. A PMMA coating with a thickness of approximately 10 μm allowed a significant doping level to be achieved within a short period of irradiation and, at the same time, effectively shielded the film from the effects of the aqueous medium. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2099–2107, 2002     

Electroactive polymer patterns with metal incorporation on a polymeric substrate

Electroactive polymer patterns on a polymeric substrate were fabricated using either a UV lithographic approach or plasma polymerization method. For the lithographic patterning technique, photosensitive thin films comprising polyaniline (PANI) coatings on viologen‐grafted low‐density polyethylene (LDPE) substrates were first prepared. The composite film was subsequently exposed to UV irradiation through a mask. Under UV irradiation, reactions between PANI and viologen occurred, resulting in the conversion of the PANI to a doped state. The PANI micropatterns were developed by using N‐methylpyrrolidinone (NMP) to dissolve the soluble‐unexposed (and hence undoped) parts. The use of Ar plasma treatment of the composite film instead of UV irradiation was not successful in inducing the doping reaction between PANI and viologen. On the other hand, plasma polymerization was shown to be another convenient way for the selective surface deposition of aniline polymer on the surface of the LDPE substrate through a mask. The further incorporation of metal/metal ions in both the PANI‐viologen and plasma polymerized aniline system was successfully carried out on the micropatterns. Polym. Eng. Sci. 44:2061–2069, 2004. © 2004 Society of Plastics Engineers.     

Electroless plating of copper on polyimide films modified by surface grafting of tertiary and quaternary amines polymers

Argon plasma-pretreated polyimide (PI, Kapton^® HN) films were subjected to UV-induced surface graft copolymerization with N,N′-(dimethylamino)ethyl methacrylate (DMAEMA) and 2-(trimethylammonium)ethyl methacrylate chloride (TMMAC). The DMAEMA graft-copolymerized PI (DMAEMA-g-PI) surfaces were also quaternized and amino-functionalized with 3-bromopropylamine hydrobromide (the Q-DMAEMA-g-PI surfaces). The surface composition and the degree of quaternization of the graft-modified PI films were determined by X-ray photoelectron spectroscopy. The DMAEMA-g-PI, Q-DMAEMA-g-PI and TMMAC graft-copolymerized PI (TMMAC-g-PI) surfaces can be activated directly by PdCl₂, in the absence of prior sensitization by SnCl₂ (the ‘Sn-free’ activation process), for the subsequent electroless plating of copper. A shorter induction time for the electroless deposition of copper was found for the palladium-activated Q-DMAEMA-g-PI and TMMAC-g-PI surfaces than for the palladium-activated DMAEMA-g-PI surface. The T-peel adhesion strength of the electrolessly deposited copper with the Q-DMAEMA-g-PI surface was enhanced to above 6 N/cm, in comparison to only about 4 N/cm for the DMAEMA-g-PI surface, about 2.5 N/cm for the TMMAC-g-PI surface, or about 0.5 N/cm for the PI surface with argon plasma treatment alone.