Wen Jing Yang

Biomimetic Anchors for Antifouling and Antibacterial Polymer Brushes on Stainless Steel

Barnacle cement (BC) was beneficially applied on stainless steel (SS) to serve as the initiator anchor for surface-initiated polymerization. The amine and hydroxyl moieties of barnacle cement reacted with 2-bromoisobutyryl bromide to provide the alkyl halide initiator for the surface-initiated atom transfer radical polymerization (ATRP) of 2-hydroxyethyl methacrylate (HEMA). The hydroxyl groups of HEMA polymer (PHEMA) were then converted to carboxyl groups for coupling of chitosan (CS) to impart the SS surface with both antifouling and antibacterial properties. The surface-functionalized SS reduced bovine serum albumin adsorption, bacterial adhesion, and exhibited antibacterial efficacy against Escherichia coli (E. coli). The effectiveness of barnacle cement as an initiator anchor was compared to that of dopamine, a marine mussel inspired biomimetic anchor previously used in surface-initiated polymerization. The results indicate that the barnacle cement is a stable and effective anchor for functional surface coatings and polymer brushes.

Stainless steel surfaces with thiol-terminated hyperbranched polymers for functionalization via thiol-based chemistry

Hyperbranched polyethyleneimine (BPEI) was coupled to a polydopamine-coated stainless steel (SS) substrate. Subsequent mercaptoethylation of BPEI with ethylene sulfide produced thiol functional groups on the SS surface. Functionalization of the surface was achieved by end-capping of the hyperbranches with organic molecules via thiol-based chemistry, including thiol–epoxy coupling, thiol–ene radical photo-addition and thiol–Michael addition. The SS-P(HEMA-b-SBMA) surface was prepared via thiol–ene radical photo-addition of the hyperbranches with an alkene-functionalized poly(2-hydroxyethyl methacrylate) (alkene-PHEMA) from atom transfer radical polymerization (ATRP) and subsequent block copolymerization of the zwitterionic monomer, N-(3-sulfopropyl)-N-(methacryloxyethyl)-N,N-dimethyl ammonium betaine (SBMA). The SS-PPEGMA and SS-PMETA surfaces were prepared, respectively, by thiol-initiated photopolymerization of poly(ethylene glycol)methyl ether methacrylate (PEGMA) and 2-(methacryloyloxy)ethyl trimethylammonium chloride (META). The antifouling SS-P(HEMA-b-SBMA) and SS-PPEGMA surfaces exhibit resistance to bacterial adhesion, while the SS-PMETA surface is bactericidal. Metal surfaces with thiol-terminated hyperbranches thus provide a versatile platform for tailoring surface functionalities.

Functional polymer brushes via surface-initiated atom transfer radical graft polymerization for combating marine biofouling

Dense and uniform polymer brush coatings were developed to combat marine biofouling. Nonionic hydrophilic, nonionic hydrophobic, cationic, anionic and zwitterionic polymer brush coatings were synthesized via surface-initiated atom transfer radical polymerization (SI-ATRP) of 2-hydroxyethyl methacrylate, 2,3,4,5,6-pentafluorostyrene, 2-(methacryloyloxy)ethyl trimethylammonium chloride, 4-styrenesulfonic acid sodium and N,N′-dimethyl-(methylmethacryloyl ethyl) ammonium propanesulfonate, respectively. The functionalized surfaces had different efficacies in preventing adsorption of bovine serum albumin (BSA), adhesion of the Gram-negative bacterium Pseudomonas sp. NCIMB 2021 and the Gram-positive Staphylococcus aureus, and settlement of cyprids of the barnacle Amphibalanus amphitrite (=Balanus amphitrite). The nonionic hydrophilic, anionic and zwitterionic polymer brushes resisted BSA adsorption during a 2 h exposure period. The nonionic hydrophilic, cationic and zwitterionic brushes exhibited resistance to bacterial fouling (24 h exposure) and cyprid settlement (24 and 48 h incubation). The hydrophobic brushes moderately reduced protein adsorption, and bacteria and cyprid settlement. The anionic brushes were least effective in preventing attachment of bacteria and barnacle cyprids. Thus, the best approach to combat biofouling involves a combination of nonionic hydrophilic and zwitterionic polymer brush coatings on material surfaces.

Antifouling and antibacterial hydrogel coatings with self-healing properties based on a dynamic disulfide exchange reaction

Multifunctional self-healing hydrogel coatings based on a dynamic disulfide exchange reaction were developed via surface-initiated thiol–ene photopolymerization. The functional monomers (poly(ethylene glycol)methyl ether methacrylate (PEGMA), N-hydroxyethyl acrylamide (HEAA) and 2-(methacryloyloxy)ethyl trimethylammonium chloride (META)) and a disulfide-containing crosslinker bis(2-methacryloyl)oxyethyl disulfide (BMOD) were employed for the preparation of antifouling, antibacterial and self-healing hydrogel coatings. The hydrogel coatings reduced protein adsorption, as well as bacterial adhesion from Gram-negative Escherichia coli (E. coli). Moreover, the coatings exhibited good self-healing ability at moderate temperatures due to the dynamic disulfide exchange reaction. Introduction of self-healing ability provides a promising means for self-repairing of microcracks of functional polymer coatings and improving their stability and durability in the long-term applications as biomaterials.

Preparation of jellyfish-shaped amphiphilic block-graft copolymers consisting of a poly(ε-caprolactone)-block-poly(pentafluorostyrene) ring and poly(ethylene glycol) lateral brushes

A versatile synthetic route to jellyfish-shaped amphiphilic block-graft copolymers with a hydrophobic ring of controllable dimensions, consisting of tailored length and number of poly(e-caprolactone) (PCL) and poly(pentafluorostyrene) (PFS) blocks, and hydrophilic poly(ethylene glycol) (PEG) brushes, has been developed via the combination of ring-opening polymerization (ROP), atom transfer radical polymerization (ATRP), alkyne-azide click reaction and thiol-para-fluorine click reaction. The chemical structures and compositions of all the polymers were characterized by nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography (GPC), thermogravimetric analyses (TGA), and X-ray photoelectron spectroscopy (XPS). The morphology of micelles from self-assembly of the cyclic-[PCL-b-P(FS-g-PEG)] copolymer in an aqueous medium was investigated by field emission scanning electron microscopy (FESEM).

Preparation of stimuli-responsive hydrogel networks with threaded β-cyclodextrin end-capped chains via combination of controlled radical polymerization and click chemistry

Hydrogel networks of poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEG-b-PPG-b-PEG primary network), with threaded sliding β-cyclodextrin-capped poly(2-(methacryloyloxy)ethyl succinate) (βCD-capped-PMES) chains, are described. The hydrogels were prepared by UV-initiated thiol–ene click reaction of the PEG-b-PPG-b-PEG diacrylate polymer with a crosslink agent, pentaerythritol tetrakis(3-mercaptopropionate) (PETMP), in the presence of βCD end-capped chains, βCD-capped-PMES. The latter was prepared a priori by reversible addition–fragmentation chain transfer (RAFT) polymerization. Due to the controlled character of RAFT polymerization and the quantitative yield of thiol–ene click reaction, the as-synthesized PEG-b-PPG-b-PEG-thread-βCD-capped-PMES hydrogels have a well-defined PEG-b-PPG-b-PEG network and tunable PMES chain length. The length of PMES chains can be regulated by varying the molar ratio of 2-(methacryloyloxy)ethyl succinate (MES) monomer to RAFT agent. The molecular structures and thermal properties of the PEG-b-PPG-b-PEG-thread-βCD-capped-PMES hydrogels were studied by 1H NMR, XPS, TGA and DSC measurements. The polymer hydrogels with threaded sliding rings exhibit both pH- and temperature-dependent equilibrium swelling ratios in aqueous media and have potential applications as biomaterials and biomedical materials.

Multi-functionalization of poly(vinylidene fluoride) membranes via combined “grafting from” and “grafting to” approaches

PVDF-g-[PBIEM-co-PPMA] graft copolymers were first synthesized in a “grafting from” process, involving thermally induced graft copolymerization of two inimers, 2-(2-bromoisobutyryloxy)ethyl methacrylate (BIEM) and propargyl methacrylate (PMA), from ozone-preactivated poly(vinylidene fluoride) (PVDF) chains. Microporous membranes were fabricated from the PVDF-g-[PBIEM-co-PPMA] copolymers by phase inversion in an aqueous medium. The tertiary C–Br groups of BIEM repeat units and the propargyl groups of PMA repeat units on the PVDF-g-[PBIEM-co-PPMA] membrane and pore surfaces provided the respective functionalities for the “grafting from” process involving surface-initiated atom transfer radical polymerization (ATRP) of the viologen-containing monomer, N-benzyl-N′-(4-vinylbenzyl)-4,4′-bipyridium dichloride (BVbpy), and the “grafting to” process involving alkyne–azide click reaction with azido-terminated poly(N-isopropylacrylamide) (PNIPAM-N3), prepared a priori via reversible addition–fragmentation chain transfer (RAFT) polymerization. The resulting PVDF-g-[P(BIEM-g-PBVbpy)-co-P(PMA-click-PNIPAM)] membrane exhibited both redox- and temperature-dependent permeability to aqueous solutions. Alternatively, metal ions, such as Ag, Au or Pt ions, can be immobilized and reduced within the viologen-containing PBVbpy brushes on the PVDF-g-[P(BIEM-g-PBVbpy)-co-PPMA] membrane. The functionalized PVDF-g-[P(BIEM-g-PBVbpy)-co-PPMA]-Ag membrane surfaces were shown to be effective in reducing bacterial adhesion and fouling under continuous-flow conditions.