Tea Stains-Inspired Antifouling Coatings Based on Tannic Acid-Functionalized Agarose

It is well-known that tannic acid (TA) and its analogs bind strongly to various substrates to produce, for example, the familiar and unpleasant “tea stains”. Functionalization of a polymer or macromolecule with TA would confer the resulting biomacromolecules with similar binding or anchoring ability on many surfaces. To verify the hypothesis, the naturally occurring polysaccharide agarose (Agr) was functionalized with alkyl bromo moieties, followed by etherification with tannic acid under basic conditions via Williamson ether synthesis. The TA-functionalized Agr (AgrTA) so obtained can be deposited onto titanium (Ti), stainless steel (SS), and silicon surfaces via direct adsorption and intermolecular oxidative cross-linking. The AgrTA-deposited SS surfaces show good stability in flowing electrolytes of varying pH. The AgrTA-deposited SS surfaces can also effectively reduce the adsorption of bovine serum albumin and the adhesion of <i>Escherichia coli</i> and 3T3 fibroblasts. In perhaps what is an ironic twist, through proper molecular design, the undesirable “tea stains” have inspired the production of sustainable antifouling coatings

Context-Dependent Adsorption Behavior of Cyclic and Linear Peptides on Metal Oxide Surfaces

Peptides with specific binding affinity to inorganic materials bridge biological systems with synthetic inorganic materials. Many inorganic-binding peptides were isolated using combinatorial peptide libraries without a good understanding of the interaction mechanism, which thus hinders the practical application of these peptides. Besides the amino acid composition, peptides’ structure (e.g., cyclic structure constrained by disulfide bond) is believed to play an important role in their binding behavior. A cyclic peptide STB1 (−CHKKPSKSC−) was previously identified to electrostatically bind to TiO2 and SiO2. In the present study, the binding behavior (affinity and conformation) of STB1 and its linear version LSTB1 (−AHKKPSKSA−) on a TiO2 or SiO2 surface was investigated in three different contexts (i.e., free peptides, phage particles displaying peptides, and LacI−peptide fusion protein) using quartz crystal microbalance with energy dissipation measurement (QCM-D). The binding kinetics of STB1 and LSTB1 in the context of fusion protein to either metal oxide was quantitatively analyzed. LSTB1 showed similar binding behavior on both TiO2 and SiO2 surfaces. In the context of phage-displayed and LacI-hosted peptides, STB1 was found to have weaker binding affinity than LSTB1 for either metal oxide, but it was able to distinguish between SiO2 and TiO2. This is probably because LSTB1 has a much more flexible structure than STB1, as shown by the molecular dynamics simulation. The structural flexibility of LSTB1 enables it to explore a wider range of conformations to maximize its interaction with TiO2 and SiO2

Poly(vinylidene fluoride) Membranes with Hyperbranched Antifouling and Antibacterial Polymer Brushes

Graft copolymers of poly­(vinylidene fluoride) (PVDF) with poly­[2-(N,N-dimethylamino)­ethyl methacrylate] (PDMAEMA) side chains (PVDF-g-PDMAEMA copolymers) were synthesized via activators generated by electron transfer for atom transfer radical polymerization (AGET-ATRP) of 2-(N,N-dimethylamino)­ethyl methacrylate (DMAEMA) directly from the secondary fluorine atoms on the PVDF backbone. Microporous membranes were fabricated from the PVDF-g-PDMAEMA amphiphilic copolymers by phase inversion in an aqueous medium. After quaternization by propargyl bromide, the resulting PVDF-g-PQDMAEMA membrane and pore surfaces bearing pendant propargyl moieties could be further functionalized via surface-initiated alkyne–azide click reaction of azido-terminated hyperbranched polyglycerols (HPG-N3) to form the PVDF-g-P­[QDMAEMA-click-HPG] membranes. The PVDF-g-P­[QDMAEMA-click-HPG] membranes exhibit good resistance to protein adsorption and fouling. Alternatively, alkyne–azide click reaction of azido-terminated polyethylenimine (PEI-N3) on the PVDF-g-PQDMAEMA membranes, followed by quaternization with 1-bromohexane, produce the PVDF-g-P­[QDMAEMA-click-QPEI] membrane which is effective in reducing bacterial growth and proliferation under continuous-flow conditions

Thiol Reactive Maleimido-Containing Tannic Acid for the Bioinspired Surface Anchoring and Post-Functionalization of Antifouling Coatings

Inspired by tea stains, a new surface anchor, maleimido-containing tannic acid (TAMA), was developed to introduce the maleimido functionality onto stainless steel (SS) surfaces. The feasibility of maleimido groups to serve as anchoring sites for surface functionalization via Michael addition was explored in a model experiment using thiol-containing 1<i>H</i>,1<i>H</i>,2<i>H</i>,2<i>H</i>-perfluorodecanethiol. The surface conjugation efficiency of TAMA with the thiol-containing compounds via Michael addition was also compared to that of the surface with tannic acid (TA) only. Water-soluble thiolated carboxymethyl chitosan (CMCSSH) was then grafted on the SS surface preanchored with TAMA via solution immersion and spin coating. The deposition of CMCSSH was characterized by contact angle measurement, surface zeta potential, and X-ray photoelectron spectroscopy (XPS). The antifouling efficacy of the CMCSSH coatings was evaluated by protein adsorption and bacterial adhesion. The cytotoxic effect of the CMCSSH coatings on mammalian cells was evaluated using the standard 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay with 3T3 fibroblasts

Dopamine-Induced Reduction and Functionalization of Graphene Oxide Nanosheets

Dopamine-Induced Reduction and Functionalization of Graphene Oxide Nanosheet

Nonvolatile Electrical Switching and Write-Once Read-Many-Times Memory Effects in Functional Polyimides Containing Triphenylamine and 1,3,4-Oxadiazole Moieties

This work reports the synthesis and characterization of a series of functional aromatic polyimides (OXTA-PI)s containing triphenylamine and 1,3,4-oxadiazole moieties. All the polyimides exhibit high glass transition temperatures of 309−319 °C. A resistive switching device with the sandwich structure of indium−tin oxide/polymer/Al was fabricated using the soluble polyimide from 4,4′-hexafluoroisopropylidenediphthalic anhydride (OXTA-PIa). The device exhibits two conductivity states and can be switched from the initial low-conductivity (OFF) state to the high-conductivity (ON) state at the threshold voltages of 1.8 V under both positive and negative electrical sweeps, with an ON/OFF state current ratio in the order of 105. The ON state of the device is nonvolatile and can withstand a constant voltage stress of −1 V for 6 h and 108 pulse read cycles at −1 V under ambient conditions. Upon reversing the bias, the ON state cannot be reset to the initial OFF states. The nonvolatile and inerasable nature of the ON state, as well as the ability to write, read, and sustain the electrical states, fulfills the requirements of a write-once read-many-times (WORM) memory

Layer-by-Layer Click Deposition of Functional Polymer Coatings for Combating Marine Biofouling

“Click” chemistry-enabled layer-by-layer (LBL) deposition of multilayer functional polymer coatings provides an alternative approach to combating biofouling. Fouling-resistant <i>azido</i>-functionalized poly­(ethylene glycol) methyl ether methacrylate-based polymer chains (<i>azido</i>-poly­(PEGMA)) and antimicrobial <i>alkynyl</i>-functionalized 2-(methacryloyloxy)­ethyl trimethyl ammonium chloride-based polymer chains (<i>alkynyl</i>-poly­(META)) were click-assembled layer-by-layer via alkyne–azide 1,3-dipolar cycloaddition. The polymer multilayer coatings are resistant to bacterial adhesion and are bactericidal to marine Gram-negative Pseudomonas sp. NCIMB 2021 bacteria. Settlement of barnacle (Amphibalanus (=Balanus) amphitrite<i></i>) cyprids is greatly reduced on the multilayer polymer-functionalized substrates. As the number of the polymer layers increases, efficacy against bacterial fouling and settlement of barnacle cyprids increases. The LBL-functionalized surfaces exhibit low toxicity toward the barnacle cyprids and are stable upon prolonged exposure to seawater. LBL click deposition is thus an effective and potentially environmentally benign way to prepare antifouling coatings

Antifouling, Antimicrobial, and Antibiocorrosion Multilayer Coatings Assembled by Layer-by-layer Deposition Involving Host–Guest Interaction

Layer-by-layer (LBL) deposition of polyethylenimine-β-cyclodextrin (PEI-β-CD) and ferrocene-modified chitosan (Fc-CHT) via host–guest interaction chemistry was developed for the fabrication of low-fouling, antimicrobial, and biocorrosion inhibition multilayer coatings on stainless steel. An electrochemical method is proposed to monitor and determine the LBL deposition process. The resulting multilayer coatings exhibit good resistance to bacterial adhesion, including Pseudomonas sp. and Staphylococcus aureus, and microalgal attachment of Amphora coffeaeformis. Settlement of barnacle cyprids is also significantly reduced on the bilayer-coated substrates. As the number of assembled host–guest bilayers increases, the antifouling efficacy, antimicrobial efficiency, and antibiocorrosion performance also improve progressively. The stability and durability of the multilayer coatings were ascertained after a 30-day immersion treatment in seawater. Thus, the multilayer coatings deposited via LBL method are potentially useful as environmentally friendly coatings for combatting biofouling and biocorrosion in marine and aquatic environments

One-Pot Preparation of Ferrocene-Functionalized Polymer Brushes on Gold Substrates by Combined Surface-Initiated Atom Transfer Radical Polymerization and “Click Chemistry”

A gold substrate with surface-grafted ferrocene functional polymer brushes, or Au-g-PFTMA surface [PFTMA = poly(5-ferrocene-triazolyl methacrylate)], was prepared by a combination of surface-initiated atom transfer radical polymerization (SI-ATRP) and “click chemistry” in one pot, in the presence of 2-azidoethyl methacrylate (AzEMA), ethynyl ferrocene, CuBr catalyst, CuBr2 deactivator, and pentamethyldiethylenetriamine ligand. Thus, SI-ATRP of AzEMA from the Au substrate (the “grafting from” process) and click chemistry of the ethynyl ferrocene to the azide functional group of AzEMA (the “grafting to” process) proceeded simultaneously to produce the functional PFTMA brushes on the Au surface. Kinetic studies suggest that the reaction involving simultaneous SI-ATRP and click chemistry is still consistent with a controlled/“living” process. The composition and physical properties of the modified gold surface were analyzed by X-ray photoelectron spectroscopy, water contact angle measurement, and cyclic voltammetry. The redox-responsive properties of the ferrocene-functionalized polymer brushes on the Au-g-PFTMA surface were demonstrated in the reversible loading−unloading step of the β-cyclodextrin polymer via host−guest interaction

Tea Stains-Inspired Initiator Primer for Surface Grafting of Antifouling and Antimicrobial Polymer Brush Coatings

Inspired by tea stains, plant polyphenolic tannic acid (TA) was beneficially employed as the primer anchor for functional polymer brushes. The brominated TA (TABr) initiator primer was synthesized by partial modification of TA with alkyl bromide functionalities. TABr with trihydroxyphenyl moieties can readily anchor on a wide range of substrates, including metal, metal oxide, polymer, glass, and silicon. Concomitantly, the alkyl bromide terminals serve as initiation sites for atom transfer radical polymerization (ATRP). Cationic [2-(methacryloyloxy)­ethyl]­trimethylammonium chloride (META) and zwitterionic 2-methacryloyloxyethyl phosphorylcholine (MPC) and <i>N</i>-(3-sulfopropyl)-<i>N</i>-(methacryloxyethyl)-<i>N</i>,<i>N</i>-dimethylammonium betaine (SBMA) were graft-polymerized from the TABr-anchored stainless steel (SS) surface. The cationic polymer brushes on the modified surfaces are bactericidal, while the zwitterionic coatings exhibit resistance against bacterial adhesion. In addition, microalgal attachment (microfouling) and barnacle cyprid settlement (macrofouling) on the functional polymer-grafted surfaces were significantly reduced, in comparison to the pristine SS surface. Thus, the bifunctional TABr initiator primer provides a unique surface anchor for the preparation of functional polymer brushes for inhibiting both microfouling and macrofouling