Shaojun Yuan

Lysozyme-coupled poly(poly(ethylene glycol) methacrylate)-stainless steel hybrids and their antifouling and antibacterial surfaces.

An environmentally benign approach to impart stainless steel (SS) surfaces with antifouling and antibacterial functionalities was described. Surface-initiated atom transfer radical polymerization (ATRP) of poly(ethylene glycol) monomethacrylate) (PEGMA) from the SS surface-coupled catecholic L-3,4-dihydroxyphenylalanine (DOPA) with terminal alkyl halide initiator was first carried out, followed by the immobilization of lysozyme at the chain ends of poly(ethylene glycol) branches of the grafted PEGMA polymer brushes. The functionalized SS surfaces were shown to be effective in preventing bovine serum albumin (BSA) adsorption and in reducing bacterial adhesion and biofilm formation. The surfaces also exhibited good bactericidal effects against Escherichia coli and Staphylococcus aureus. The concomitant incorporation of antifouling hydrophilic brushes and antibacterial enzymes or peptides onto metal surfaces via catecholic anchors should be readily adaptable to other metal substrates, and is potentially useful for biomedical and biomaterial applications.

Glucose biosensor from covalent immobilization of chitosan-coupled carbon nanotubes on polyaniline-modified gold electrode.

An amperometric glucose biosensor was prepared using polyaniline (PANI) and chitosan-coupled carbon nanotubes (CS-CNTs) as the signal amplifiers and glucose oxidase (GOD) as the glucose detector on a gold electrode (the Au-g-PANI-c-(CS-CNTs)-GOD biosensor). The PANI layer was prepared via oxidative graft polymerization of aniline from the gold electrode surface premodified by self-assembled monolayer of 4-aminothiophenol. CS-CNTs were covalently coupled to the PANI-modified gold substrate using glutaradehyde as a bifunctional linker. GOD was then covalently bonded to the pendant hydroxyl groups of chitosan using 1,4-carbonyldiimidazole as the bifunctional linker. The surface functionalization processes were ascertained by X-ray photoelectron spectroscopy (XPS) analyses. The field emission scanning electron microscopy (FESEM) images of the Au-g-PANI-c-(CS-CNTs) electrode revealed the formation of a three-dimensional surface network structure. The electrode could thus provide a more spatially biocompatible microenvironment to enhance the amount and biocatalytic activity of the immobilized enzyme and to better mediate the electron transfer. The resulting Au-g-PANI-c-(CS-CNTs)-GOD biosensor exhibited a linear response to glucose in the concentration range of 1-20 mM, good sensitivity (21 μA/(mM·cm(2))), good reproducibility, and retention of >80% of the initial response current after 2 months of storage.

Superhydrophobic CuO nanoneedle-covered copper surfaces for anticorrosion

With unique water-repellency and self-cleaning properties, superhydrophobic surfaces promise a great potential of anticorrosion for engineered metals. The current study reports a facile and controllable anodization approach to fabricate superhydrophobic CuO nanoneedle array (NNA) films for the enhancement of corrosion resistance of copper substrates. The anodic CuO NNA films were grown on copper foils by electrochemical anodization in an aqueous KOH solution for different anodization times. The morphological features and crystalline structures of the anodic CuO NNA were characterized by SEM-EDS and XRD. The superhydrophobicity on the hierarchical CuO NNA films was achieved by chemical modification with fluoroalkyl-silane (FAS-17). The presence of low surface energy fluorosilanized carbon (–CFx) groups on the FAS-modified surfaces was ascertained by EDS, XPS and water contact angle analyses. The wetting behaviour of the FAS-modified surfaces was investigated to elucidate the correlation between the static water contact angles, surface roughness, dynamic water contact angle hysteresis, and anodization time. The FAS-modified copper surfaces demonstrated not only the desirable superhydrophobicity with a water contact angle as high as approximately 169° and contact angle hysteresis as low as about 5°, but also substantially improved corrosion resistance in an aqueous NaCl solution (3.5%) with an inhibition efficiency higher than 90%, as revealed by means of Tafel plots and EIS measurements. The stability and durability of the superhydrophobic FAS-modified surfaces were evaluated by observing the change in surface wettability and geometric microstructures as a function of exposure time in an aqueous NaCl solution.

Inorganic−Organic Hybrid Coatings on Stainless Steel by Layer-by-Layer Deposition and Surface-Initiated Atom-Transfer-Radical Polymerization for Combating Biocorrosion

To improve the biocorrosion resistance of stainless steel (SS) and to confer the bactericidal function on its surface for inhibiting bacterial adhesion and biofilm formation, well-defined inorganic-organic hybrid coatings, consisting of the inner compact titanium oxide multilayers and outer dense poly(vinyl-N-hexylpyridinium) brushes, were successfully developed. Nanostructured titanium oxide multilayer coatings were first built up on the SS substrates via the layer-by-layer sol-gel deposition process. The trichlorosilane coupling agent, containing the alkyl halide atom-transfer-radical polymerization (ATRP) initiator, was subsequently immobilized on the titanium oxide coatings for surface-initiated ATRP of 4-vinylpyridine (4VP). The pyridium nitrogen moieties of the covalently immobilized 4VP polymer, or P(4VP), brushes were quaternized with hexyl bromide to produce a high concentration of quaternary ammonium salt on the SS surfaces. The excellent antibacterial efficiency of the grafted polycations, poly(vinyl-N-pyridinium bromide), was revealed by viable cell counts and atomic force microscopy images of the surface. The effectiveness of the hybrid coatings in corrosion protection was verified by the Tafel plot and electrochemical impedance spectroscopy measurements.

Antibacterial Inorganic−Organic Hybrid Coatings on Stainless Steel via Consecutive Surface-Initiated Atom Transfer Radical Polymerization for Biocorrosion Prevention

To enhance the corrosion resistance of stainless steel (SS) and to impart its surface with antibacterial functionality for inhibiting biofilm formation and biocorrosion, well-defined inorganic-organic hybrid coatings, consisting of a polysilsesquioxane inner layer and quaternized poly(2-(dimethyamino)ethyl methacrylate) (P(DMAEMA)) outer blocks, were prepared via successive surface-initiated atom transfer radical polymerization (ATRP) of 3-(trimethoxysilyl)propyl methacrylate (TMSPMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA). The cross-linked P(TMASPMA), or polysilsesquioxane, inner layer provided a durable and resistant coating to electrolytes. The pendant tertiary amino groups of the P(DMAEMA) outer block were quaternized with alkyl halide to produce a high concentration of quaternary ammonium groups with biocidal functionality. The so-synthesized inorganic-organic hybrid coatings on the SS substrates exhibited good anticorrosion and antibacterial effects and inhibited biocorrosion induced by sulfate-reducing bacteria (SRB) in seawater media, as revealed by antibacterial assay and electrochemical analyses, and they are potentially useful to steel-based equipment under harsh industrial and marine environments.

Poly(methacrylic acid)-grafted chitosan microspheres via surface-initiated ATRP for enhanced removal of Cd(II) ions from aqueous solution.

Cross-linked chitosan (CCS) microspheres tethered with pH-sensitive poly(methacrylic acid) (PMAA) brushes were developed for the efficient removal of Cd(II) ions from aqueous solutions. Functional PMAA brushes containing dense and active carboxyl groups (COOH) were grafted onto the CCS microsphere surface via surface-initiated atom transfer radical polymerization (ATRP). Batch adsorption results showed that solution pH values had a major impact on cadmium adsorption by the PMAA-grafted CCS microspheres with the optimal removal observed above pH 5. The CCS-g-PMAA microsphere was found to achieve the adsorption equilibrium of Cd(II) within 1 h, much faster than about 7 h on the CCS microsphere. At pH 5 and with an initial concentration 0.089-2.49 mmol dm(-3), the maximum adsorption capacity of Cd(II), derived from the Langmuir fitting on the PMAA-grafted microspheres was around 1.3 mmol g(-1). Desorption and adsorption cycle experimental results revealed that the PMAA-grafted CCS microspheres loaded with Cd(II) can be effectively regenerated in a dilute HNO3 solution, and the adsorption capacity remained almost unchanged upon five cycle reuse.

Grafting of antibacterial polymers on stainless steel via surface-initiated atom transfer radical polymerization for inhibiting biocorrosion by Desulfovibrio desulfuricans.

To enhance the biocorrosion resistance of stainless steel (SS) and to impart its surface with bactericidal function for inhibiting bacterial adhesion and biofilm formation, well‐defined functional polymer brushes were grafted via surface‐initiated atom transfer radical polymerization (ATRP) from SS substrates. The trichlorosilane coupling agent, containing the alkyl halide ATRP initiator, was first immobilized on the hydroxylated SS (SS‐OH) substrates for surface‐initiated ATRP of (2‐dimethylamino)ethyl methacrylate (DMAEMA). The tertiary amino groups of covalently immobilized DMAEMA polymer or P(DMAEMA), brushes on the SS substrates were quaternized with benzyl halide to produce the biocidal functionality. Alternatively, covalent coupling of viologen moieties to the tertiary amino groups of P(DMAEMA) brushes on the SS surface resulted in an increase in surface concentration of quaternary ammonium groups, accompanied by substantially enhanced antibacterial and anticorrosion capabilities against Desulfovibrio desulfuricans in anaerobic seawater, as revealed by antibacterial assay and electrochemical studies. With the inherent advantages of high corrosion resistance of SS, and the good antibacterial and anticorrosion capabilities of the viologen‐quaternized P(DMAEMA) brushes, the functionalized SS is potentially useful in harsh seawater environments and for desalination plants. Biotechnol. Bioeng. 2009;103: 268–281.

PVDF film tethered with RGD-click-poly(glycidyl methacrylate) brushes by combination of direct surface-initiated ATRP and click chemistry for improved cytocompatibility

To enhance the cytocompatibility of polyvinylidene fluoride (PVDF) films, arginine–glycine–aspartic acid (RGD) peptide-click-poly(glycidyl methacrylate) (PGMA) polymer brushes were grafted onto the PVDF surface by the combination of surface-initiated atom transfer radical polymerization (ATRP) and click reaction. The direct initiation of the secondary fluorine atoms of PVDF backbone allowed for grafting of the PGMA brushes containing reactive epoxy groups. Subsequent introduction of the azide groups onto the side chain of PGMA brushes was achieved by the ring-open reaction of the epoxy groups with sodium azide. The cell adhesive RGD peptide was finally conjugated onto the PGMA brushes via alkyne-azide click reaction. Kinetic studies revealed that the PGMA chain growth from the PVDF surface was consistent with a “controlled” process, and that the amount of immobilized RGD peptide on the PGMA brushes increased with the concentration of the pendant azide groups. The specificity of cellular interactions of adipose tissue-derived stem cells (ASCs) on the functionalized PVDF films was investigated. Results demonstrated that cell adhesion and proliferation of ASCs were significantly improved on the RGD-immobilized PVDF substrates, and this improvement was positively correlated with the surface concentration of covalently-bonded RGD peptide. With the inherent superior chemical and mechanical properties of PVDF films and the biocompatible nature of cell-adhesive peptides, surface functionalized PVDF films are potentially useful for biomedical and tissue engineering applications.

Surface modification of polycaprolactone substrates using collagen-conjugated poly(methacrylic acid) brushes for the regulation of cell proliferation and endothelialisation

The incorporation and presentation of cell recognition ligands on the surfaces of biodegradable blood-vessel implants to promote endothelialisation is considered to be a promising approach to prevent platelet aggregation and hence thrombogenesis. In this study, cell-adhesive collagen was covalently immobilised onto polycaprolactone (PCL) substrates via surface-initiated atom transfer radical polymerization (ATRP) to improve cell–material interactions. Functional polymer brushes of poly(methacrylic acid) (P(MAA)) containing dense and reactive carboxyl groups (–COOH) were formed on the PCL substrates in a controllable manner. The amount of collagen, which was conjugated to the pendant carboxyl groups via carbodiimide chemistry, increased with the concentration of –COOH groups on the grafted P(MAA) brushes. The affinity and growth of endothelial cells (ECs) were found to be significantly improved on the collagen-immobilised PCL substrates, and this improvement is positively correlated with the amount of covalently conjugated collagen. Thus, surface-initiated ATRP provides an alternative methodology for the surface functionalisation of biodegradable polyester scaffolds to enable the formation of a confluent layer of ECs. An optimally endothelialised material surface will play a major role in the minimisation of thrombogenicity and inflammation, and hence can be potentially used for vascular graft applications.

Anti-cAngptl4 Ab-Conjugated N-TiO2/NaYF4:Yb,Tm Nanocomposite for Near Infrared-Triggered Drug Release and Enhanced Targeted Cancer Cell Ablation

Nanomedicine: NIR-active N-TiO(2) /NaYF(4) :Yb,Tm nanocomposites (NCs) were synthesized for the first time and its potential applications in drug release and targeted cancer cell ablation are explored. Upon 980 nm laser irradiation, the anti-cAngptl4 Ab-conjugated N-TiO(2) /NaYF(4) :Yb,Tm NCs shows a significant increase in apoptotic A-5RT3 cells when compared with that of the unconjugated NCs. The mechanisms for NIR-induced photocatalysis, drug release and targeted cancer cell killing are proposed.