E. T. Kang

Polyaniline: A polymer with many interesting intrinsic redox states

Abstract Due to its environmental stability, high degree of processability and interesting redox properties associated with its chain heteroatom, polyaniline (PANi) has been one of the most extensively studied electroactive (conductive) polymers during the past ten years. A number of fine reviews on the synthesis, physicochemical and electrochemical properties of the polymer have also appeared during this period. The ability of aniline polymers to exist in a large number of intrinsic redox states makes them a unique and interesting class of polymeric materials. The present review attempts for the first time to summarize the explicit and quantitative dealings with the various intrinsic oxidation states of PANi and its derivatives that have been made during the past decade.

Polymer surface with graft chains

Abstract Polymer surface modification has been a significant issue over two decades in many fields of application. Among modification techniques developed to date, surface grafting has emerged as a simple, useful, and versatile approach to improve surface properties of polymers for a wide variety of applications. This review surveys recent literature on polymer surfaces with graft chains, focusing on grafting methods as well as the structure and function of grafted surfaces.

Surface functionalization of titanium with hyaluronic acid/chitosan polyelectrolyte multilayers and RGD for promoting osteoblast functions and inhibiting bacterial adhesion

Titanium (Ti) and its alloys are used extensively in orthopedic implants due to their excellent biocompatibility and mechanical properties. However, titanium-based implant materials have specific complications associated with their applications, such as the loosening of implant-host interface owing to unsatisfactory cell adhesion and the susceptibility of the implants to bacterial infections. Hence, a surface which displays selective biointeractivity, i.e. enhancing beneficial host cell responses but inhibiting pathogenic microbial adhesion, would be highly desirable. This present study aims to improve biocompatibility and confer long-lasting antibacterial properties on Ti via polyelectrolyte multilayers (PEMs) of hyaluronic acid (HA) and chitosan (CH), coupled with surface-immobilized cell-adhesive arginine-glycine-aspartic acid (RGD) peptide. The HA/CH PEM-functionalized Ti is highly effective as an antibacterial surface but the adhesion of bone cells (osteoblasts) is poorer than on pristine Ti. With additional immobilized RGD moieties, the osteoblast adhesion can be significantly improved. The density of the surface-immobilized RGD peptide has a significant effect on osteoblast proliferation and alkaline phosphatase (ALP) activity, and both functions can be increased by 100-200% over that of pristine Ti substrates while retaining high antibacterial efficacy. Such substrates can be expected to have good potential in orthopedic applications.

Conjugated-polymer-functionalized graphene oxide: synthesis and nonvolatile rewritable memory effect.

[*] Prof. Y. Chen, X.-D. Zhuang, P.-P. Li, B. Zhang, J.-H. Zhu, Y.-X. Li Key Laboratory for Advanced Materials Institute of Applied Chemistry East China University of Science and Technology 130 Meilong Road, Shanghai 200237 (P. R. China) E-mail: chentangyu@yahoo.com Prof. E.-T. Kang, Dr. G. Liu, Prof. K.-G. Neoh Department of Chemical & Biomolecular Engineering National University of Singapore 10 Kent Ridge, 119260 (Singapore) E-mail: cheket@nus.edu.sg Prof. Dr. C.-X. Zhu Department of Electrical & Computer Engineering National University of Singapore 10 Kent Ridge, 119260 (Singapore)

Plasma-induced immobilization of poly(ethylene glycol) onto poly(vinylidene fluoride) microporous membrane

Abstract Poly(vinylidene fluoride) (PVDF) microporous membranes with surface-immobilized poly(ethylene glycol) (PEG) were prepared by the argon plasma-induced grafting of PEG. The PEG was pre-coated on the membrane surface, including the pore surfaces, by dipping the membrane in a PEG/CHCl3 solution prior to the argon plasma exposure. The microstructure and composition of the PEG-grafted PVDF (PEG-g-PVDF) membranes were characterized by attenuated total reflectance (ATR) FT-IR, X-ray photoelectron spectroscopy (XPS), and thermogravimetric (TG) analysis. A moderate radio-frequency (RF) plasma power and plasma treatment time led to a high concentration of the grafted PEG polymer. The morphology of the modified membranes was studied by scanning electronic microscope (SEM). The pore size and water flux of the modified membranes were also characterized. The flux decreased with increasing surface concentration of the grafted PEG polymer, while the pore size remained almost unchanged. Protein adsorption experiments revealed that the PEG-g-PVDF membranes with a PEG graft concentration, defined as the [CO]/[CF2] ratio above 3.2 exhibited good anti-fouling property.

Surface Modification of Fluoropolymers via Molecular Design

Fluoropolymer surfaces with new and specific functionalities, such as metal-free conductivity, biocompatability, and bondability to metals, can be obtained through the intelligent choice of functional monomers for graft copolymerization on pre-activated fluoropolymer surfaces, as highlighted in this review. The Figure shows a gold/fluoropolymer laminate held together by crosslinked glycidyl methacrylate polymer grafted on both surfaces.

Balancing osteoblast functions and bacterial adhesion on functionalized titanium surfaces

The demand for orthopedic and dental implants will continue to grow, and for these applications, titanium and its alloys have been used extensively. While these implants have achieved high success rates, two major complications may be encountered: the lack of bone tissue integration and implant-centered infection. The surface of the implant, through its interactions with proteins, bacteria and tissue cells, plays a determining role in the success or failure of the implant. Ideally, to enhance the success of implants, their surfaces should inhibit bacterial colonization and concomitantly promote osteoblast functions. In this article, we discuss strategies for tailoring implant surfaces by exploiting the differences in the response of bacteria and osteoblasts to proteins and surface structures. Nevertheless, limitations still exist in the quest for an ideal implant surface. Further advances in this field will require concurrent development in surface modification techniques and a better understanding of the complex and highly inter-related events occurring at the implant surface after implantation.

Star-Shaped Cationic Polymers by Atom Transfer Radical Polymerization from β-Cyclodextrin Cores for Nonviral Gene Delivery

Cationic polymers with low cytotoxicity and high transfection efficiency have attracted considerable attention as nonviral carriers for gene delivery. Herein, well-defined and star-shaped CDPD consisting of beta-CD cores and P(DMAEMA) arms, and CDPDPE consisting of CDPD and P(PEGEEMA) end blocks (where CD = cyclodextrin, P(DMAEMA) = poly(2-(dimethylamino)ethyl methacrylate), P(PEGEEMA) = poly(poly(ethylene glycol)ethyl ether methacrylate)) for gene delivery were prepared via atom transfer radical polymerization (ATRP) from the bromoisobutyryl-terminated beta-CD core. The CDPD and CDPDPE exhibit good ability to condense plasmid DNA (pDNA) into 100-200 nm size nanoparticles with positive zeta potentials of 25-40 mV at nitrogen/phosphate (N/P) ratios of 10 or higher. CDPD and CDPDPE exhibit much lower cytotoxicity and higher gene transfection efficiency than high molecular weight P(DMAEMA) homopolymers. A comparison of the transfection efficiencies between CDPD and P(DMAEMA) homopolymer indicates that the unique star-shaped architecture involving the CD core can enhance the gene transfection efficiency. In addition to reducing cytotoxicity, the introduction of a biocompatible P(PEGEEMA) end block to the P(DMAEMA) arms in CDPDPE can further enhance the gene transfection efficiency.

Surface modification of stainless steel by grafting of poly(ethylene glycol) for reduction in protein adsorption.

The surface of stainless steel was first modified by the silane coupling agent (SCA), (3-mercaptopropyl)trimethoxysilane. The silanized stainless-steel surface (SCA-SS surface) was subsequently activated by argon plasma and then subjected to UV-induced graft polymerization of poly(ethylene glycol)methacrylate (PEGMA). The chemical structures and composition of the pristine, silane-treated, plasma-treated and PEGMA graft-polymerized stainless-steel coupon surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy. The graft polymerization of PEGMA onto the plasma-pretreated SCA-SS surface was studied with different argon plasma pretreatment time, macromonomer concentration, and UV graft polymerization time. In general, a brief plasma pretreatment, high PEGMA concentration, and long UV graft polymerization time readily resulted in a high graft concentration. The PEGMA graft-polymerized stainless-steel coupon (PEGMA-g-SCA-SS) with a high graft concentration, and thus a high PEG content, was found to be very effective in preventing bovine serum albumin and gamma-globulin adsorption.

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.