Surface engineering of polymer membranes via mussel-inspired chemistry

Co-deposition towards mussel-inspired antifouling and antibacterial membranes by using zwitterionic polymers and silver nanoparticles

Bacterial attachment and the subsequent colonization on the surfaces of bio-materials usually result in biofilm formation, and thus lead to implant failure, inflammation and so on.

Supramolecular Self-Assembly into Biofunctional Soft Nanotubes: From Bilayers to Monolayers

The inner and outer surfaces of bilayer-based lipid nanotubes can be hardly modified selectively by a favorite functional group. Monolayer-based nanotubes display a definitive difference in their inner and outer functionalities if bipolar wedge-shaped amphiphiles, so-called bolaamphiphiles, as a constituent of the monolayer membrane pack in a parallel fashion with a head-to-tail interface. To exclusively form unsymmetrical monolayer lipid membranes, we focus herein on the rational molecular design of bolaamphiphiles and a variety of self-assembly processes into tubular architectures. We first describe the importance of polymorph and polytype control and then discuss diverse methodologies utilizing a polymer template, multiple hydrogen bonds, binary and ternary coassembly, and two-step self-assembly. Novel biologically important functions of the obtained soft nanotubes, brought about only by completely unsymmetrical inner and outer surfaces, are discussed in terms of protein refolding, drug nanocarriers, lectin detection, a chiral inducer for achiral polymers, the tailored fabrication of polydopamine, and spontaneous nematic alignment.

Bioinspired Multifunctional Membrane for Aquatic Micropollutants Removal

Micropollutants present in water have many detrimental effects on the ecosystem. Membrane technology plays an important role in the removal of micropollutants, but there remain significant challenges such as concentration polarization, membrane fouling, and variable permeate quality. The work reported here uses a multifunctional membrane with rejection, adsorption, and catalysis functions to solve these problems. On the basis of mussel-inspired chemistry and biological membrane properties, a multifunctional membrane was prepared by applying "reverse filtration" of a laccase solution and subsequent "dopamine coating" on a nanofiltration (NF) membrane support, which was tested on bisphenol A (BPA) removal. Three NF membranes were chosen for the preparation of the multifunctional membranes on the basis of the membrane properties and enzyme immobilization efficiency. Compared with the pristine membrane, the multifunctional membrane exhibited significant improvement of BPA removal (78.21 ± 1.95%, 84.27 ± 7.30%, and 97.04 ± 0.33% for NT103, NF270, and NF90, respectively), all of which are clearly superior to the conventional Fenton treatment (55.0%) under similar conditions and comparable to soluble laccase coupled with NF270 membrane filtration (89.0%). The improvement would appear to be due to a combination of separation (reducing the enzymatic burden), adsorption (enriching the substrate concentration as well as prolonging the residence time), and lastly, catalysis (oxidizing the pollutants and breaking the "adsorption saturation limits"). Furthermore, the synergistic effect of the polydopamine (PDA) layer on the enzymatic oxidation of BPA was confirmed, which was due to its enhanced adsorption and electron transfer performance. The multifunctional membrane could be reused for at least seven cycles with an acceptable activity loss, demonstrating good potential for removal of micropollutants.

Copper-Coated Liquid-Crystalline Elastomer via Bioinspired Polydopamine Adhesion and Electroless Deposition

This study explores the functionalization of main-chain nematic elastomers with a conductive metallic surface layer using a polydopamine binder. Using a two-stage thiol-acrylate reaction, a programmed monodomain is achieved for thermoreversible actuation. A copper layer (≈155 nm) is deposited onto polymer samples using electroless deposition while the samples are in their elongated nematic state. Samples undergo 42% contraction when heated above the isotropic transition temperature. During the thermal cycle, buckling of the copper layer is seen in the direction perpendicular to contraction; however, transverse cracking occurs due to the large Poisson effect experienced during actuation. As a result, the electrical conductivity of the layer reduced quickly as a function of thermal cycling. However, samples do not show signs of delamination after 25 thermal cycles. These results demonstrate the ability to explore multifunctional liquid-crystalline composites using relatively facile synthesis, adhesion, and deposition techniques.

In Situ Reduction of Silver by Polydopamine: A Novel Antimicrobial Modification of a Thin-Film Composite Polyamide Membrane

We report a facile method for the antimicrobial modification of a thin-film composite polyamide reverse osmosis (RO) membrane. The membrane surface was first coated with polydopamine (PDA), whose reducing catechol groups subsequently immobilized silver ions in situ to form uniformly dispersed silver nanoparticles (AgNPs) inside the coating layer. Agglomeration of AgNPs was not observed despite a high silver loading of 13.3 ± 0.3 μg/cm(2) (corresponding to a surface coverage of 18.5% by the nanoparticles). Both diffusion inhibition zone tests and colony formation unit tests showed clear antimicrobial effects of the silver loaded membranes on model bacteria Bacillus subtilis and Escherichia coli. Furthermore, the silver immobilized membrane had significantly enhanced salt rejection compared to the control PDA coated membrane, which is attributed to the preferential formation of AgNPs at defect sides within the PDA layer. This self-healing mechanism can be used to prepare antimicrobial RO membranes with improved salt rejection without scarifying the membrane permeability, which provides a new dimension for membrane surface modification.

Sustainable Antibiofouling Properties of Thin Film Composite Forward Osmosis Membrane with Rechargeable Silver Nanoparticles Loading

Microbial attachment and biofilm formation on filtration membrane can greatly compromise its flux and separation efficiency. Here, a simple and facile approach has been developed to in situ generate silver nanoparticles (Ag NPs) on the thin film composite forward osmosis (TFC FO) membrane for sustainable antibiofouling performances. Mussel-inspired dopamine chemistry was applied to grow polydopamine coating on both surfaces of FO membranes, followed by the generation of Ag NPs upon a simple dip coating in silver nitrate aqueous solution. Furthermore, the Ag NPs deposited membranes had a long-term silver release profile with rechargability for multiple times upon their depletion, and exhibited strong sustainable bactericidal efficacy against Gram-negative bacteria and Gram-positive bacteria. The Ag NPs had a controllable effect on the membrane performances including the water flux and reverse salt flux in the FO test mode. Our practicable antibacterial strategy may apply to other types of filtration membranes with diverse material surfaces and may pave a new way to achieve the sustainable membrane antibiofouling performance on a large scale.

Interfacial Design of Mixed Matrix Membranes for Improved Gas Separation Performance

High-performance metal-organic framework (MOF)/polyimide (PI) mixed matrix membranes (MMMs) are fabricated by a facile strategy by designing the MOF/PI matrix interface via poly dopamine coating. The overall separation performance of the designed MMMs surpasses the state-of-the-art 2008 Robeson upper bound for the H2 /CH4 and H2 /N2 gas pairs and approaches the 2008 upper bound for the O2 /N2 gas pair.

Ultrasmooth Polydopamine Modified Surfaces for Block Copolymer Nanopatterning on Flexible Substrates

Nature has engineered universal, catechol-containing adhesives which can be synthetically mimicked in the form of polydopamine (PDA). In this study, PDA was exploited to enable the formation of block copolymer (BCP) nanopatterns on a variety of soft material surfaces. While conventional PDA coating times (1 h) produce a layer too rough for most applications of BCP nanopatterning, we found that these substrates could be polished by bath sonication in a weakly basic solution to form a conformal, smooth (root-mean-square roughness ∼0.4 nm), and thin (3 nm) layer free of large prominent granules. This chemically functionalized, biomimetic layer served as a reactive platform for subsequently grafting a surface neutral layer of poly(styrene-random-methyl methacrylate-random-glycidyl methacrylate) to perpendicularly orient lamellae-forming poly(styrene-block-methyl methacrylate) BCP. Moreover, scanning electron microscopy observations confirmed that a BCP nanopattern on a poly(ethylene terephthalate) substrate was not affected by bending with a radius of ∼0.5 cm. This procedure enables nondestructive, plasma-free surface modification of chemically inert, low-surface energy soft materials, thus overcoming many current chemical and physical limitations that may impede high-throughput, roll-to-roll nanomanufacturing.

CuSO4/H2O2-Induced Rapid Deposition of Polydopamine Coatings with High Uniformity and Enhanced Stability

Mussel-inspired polydopamine (PDA) deposition offers a promising route to fabricate multifunctional coatings for various materials. However, PDA deposition is generally a time-consuming process, and PDA coatings are unstable in acidic and alkaline media, as well as in polar organic solvents. We report a strategy to realize the rapid deposition of PDA by using CuSO4/H2O2 as a trigger. Compared to the conventional processes, our strategy shows the fastest deposition rate reported to date, and the PDA coatings exhibit high uniformity and enhanced stability. Furthermore, the PDA-coated porous membranes have excellent hydrophilicity, anti-oxidant properties, and antibacterial performance. This work demonstrates a useful method for the environmentally friendly, cost-effective, and time-saving fabrication of PDA coatings.

APTES assisted surface heparinization of polylactide porous membranes for improved hemocompatibility

The Hep-APTES/PLA was synthesized through the amidation reaction and results showed that surface heparinization significantly improved the hemocompatibility of PLA porous membrane.

Hydrophilic modification of PVDF porous membrane via a simple dip-coating method in plant tannin solution

A plant tannin coating is constructed on the PVDF surface via a simple dip-coating method that significantly improve its hydrophilicity.

Manipulating the multifunctionalities of polydopamine to prepare high-flux anti-biofouling composite nanofiltration membranes

An anti-biofouling composite NF membrane was prepared through the rational manipulation of the adhesion, reaction and separation functionalities of PDA.

Surface-independent one-pot chelation of copper ions onto filtration membranes to provide antibacterial properties

Surface-independent one-pot chelation of copper ions onto filtration membranes to provide antibacterial properties.

A critical review on recent polymeric and nano-enhanced membranes for reverse osmosis

Current and recent advances in polymeric and nano-enhanced membrane developments for reverse osmosis are reported in terms of membrane performance and fouling.

Stepwise membrane fouling model for shear-enhanced filtration of alfalfa juice: experimental and modeling studies

Stepwise membrane fouling model.

Antifouling PVDF membrane grafted with zwitterionic poly(lysine methacrylamide) brushes

Antifouling PVDF membranes were fabricated through the covalent binding of lysine methacrylamide (LysAA) brushes on the membrane surface via mussel-inspired surface-initiated atom transfer radical polymerization (SI-ATRP).

High-performance multilayer composite membranes with mussel-inspired polydopamine as a versatile molecular bridge for CO2 separation

It is desirable to develop high-performance composite membranes for efficient CO2 separation in CO2 capture process. Introduction of a highly permeable polydimethylsiloxane (PDMS) intermediate layer between a selective layer and a porous support has been considered as a simple but efficient way to enhance gas permeance while maintaining high gas selectivity, because the introduced intermediate layer could benefit the formation of an ultrathin defect-free selective layer owing to the circumvention of pore penetration phenomenon. However, the selection of selective layer materials is unfavorably restricted because of the low surface energy of PDMS. Various highly hydrophilic membrane materials such as amino group-rich polyvinylamine (PVAm), a representative facilitated transport membrane material for CO2 separation, could not be facilely coated over the surface of the hydrophobic PDMS intermediate layer uniformly. Inspired by the hydrophilic nature and strong adhesive ability of polydopamine (PDA), PDA was therefore selected as a versatile molecular bridge between hydrophobic PDMS and hydrophilic PVAm. The PDA coating endows a highly compatible interface between both components with a large surface energy difference via multiple-site cooperative interactions. The resulting multilayer composite membrane with a thin facilitated transport PVAm selective layer exhibits a notably enhanced CO2 permeance (1887 GPU) combined with a slightly improved CO2/N2 selectivity (83), as well as superior structural stability. Similarly, the multilayer composite membrane with a hydrophilic CO2-philic Pebax 1657 selective layer was also developed for enhanced CO2 separation performance.

Polydopamine-Coated Porous Substrates as a Platform for Mineralized β-FeOOH Nanorods with Photocatalysis under Sunlight

Immobilization of photo-Fenton catalysts on porous materials is crucial to the efficiency and stability for water purification. Here we report polydopamine (PDA)-coated porous substrates as a platform for in situ mineralizing β-FeOOH nanorods with enhanced photocatalytic performance under sunlight. The PDA coating plays multiple roles as an adhesive interface, a medium inducing mineral generation, and an electron transfer layer. The mineralized β-FeOOH nanorods perfectly wrap various porous substrates and are stable on the substrates that have a PDA coating. The immobilized β-FeOOH nanorods have been shown to be efficient for degrading dyes in water via a photo-Fenton reaction. The degradation efficiency reaches approximately 100% in 60 min when the reaction was carried out with H2O2 under visible light, and it remains higher than 90% after five cycles. We demonstrate that the PDA coating promotes electron transfer to reduce the electron-hole recombination rate. As a result, the β-FeOOH nanorods wrapped on the PDA-coated substrates show enhanced photocatalytic performance under direct sunlight in the presence of H2O2. Moreover, this versatile platform using porous materials as the substrate is useful in fabricating β-FeOOH nanorods-based membrane reactor for wastewater treatment.

Mussel-Inspired Hybrid Coatings that Transform Membrane Hydrophobicity into High Hydrophilicity and Underwater Superoleophobicity for Oil-in-Water Emulsion Separation

We first report here mussel-inspired, hybrid coatings formed in a facile manner via simultaneous polymerization of mussel-inspired dopamine and hydrolysis of commercial tetraethoxysilane in a single-step process. The hybrid coatings can firmly adhered on hydrophobic polyvinylidene fluoride (PVDF) substrate, and the hydrophilicity of the coating can be tuned by adjusting silane concentration. The reason for the changed hydrophilicity of the coating is disclosed by a series of characterization, and was applied to rationally design optimized hybrid coatings that transform commercial PVDF microfiltration (MF) membrane hydrophobicity into high hydrophilicity with excellent water permeability and underwater superoleophobicity for oil-in-water emulsion separation. The PVDF MF membrane decorated with optimized coatings has ultrahigh water flux (8606 L m(-2) h(-1) only under 0.9 bar, which is 34 times higher than that of pristine membrane), highly efficient oil-in-water emulsion separation ability at atmospheric pressure (filtrate flux of 140 L m(-2) h(-1)) and excellent antifouling performance. More importantly, these membranes are extremely stable as underwater superoleophobicity are maintained, even after rigorous washings or cryogenic bending, disclosing outstanding stability. The simplicity and versatility of this novel mussel-inspired one-step strategy may bridge the material-induced technology gap between academia and industry, which makes it promising for eco-friendly applications.

Carbon nanotube based polymer nanocomposites: biomimic preparation and organic dye adsorption applications

Poly(sodium-p-styrene sulfonate) modified multi-walled carbon nanotubes (CNTs) have been prepared via a combination of mussel inspired chemistry and SET-LRP, and utilized for methylene blue removal with high efficiency.

Highly selective thin film composite hollow fiber membranes for mixed vapor/gas separation

In the present study, thin film composite membranes have been prepared using an interfacial polymerization method.