K G Neoh

Publications (233)484.59 Total impact

• Article: An in vitro Assessment of Fibroblast and Osteoblast Response to Alendronate-Modified Titanium and the Potential for Decreasing Fibrous Encapsulation.

  Xuefeng Hu, K G Neoh, Zhilong Shi, E T Kang, Wilson Wang
  [show abstract] [hide abstract]
  ABSTRACT: Fibrous encapsulation can impair implant osseointegration and cause implant failure but currently there are limited strategies to address this problem. Since bisphosphonates (BPs), a class of drugs widely used to treat bone diseases, was recently found to induce fibroblast apoptosis, we hypothesize that by loading BPs on titanium (Ti) implant surface, fibrous encapsulation may be inhibited with simultaneous enhancement of implant osseointegration. This strategy of local administration can also be expected to minimize the adverse side effects of BPs, which are associated with intravenous injections. To verify this hypothesis, alendronate was loaded on Ti surface via a hydroxyapatite (CaP) coating, and the effects of the loaded alendronate on fibroblast proliferation and apoptosis, and osteoblast proliferation, alkaline phosphatase (ALP) activity and apoptosis were investigated in vitro. With a surface density of loaded alendronate of 0.046 mg/cm2 or higher, fibroblast proliferation was suppressed due to increased apoptosis, while osteoblast proliferation and ALP activity increased with minimal apoptosis. In a co-culture of fibroblasts and osteoblasts in a 1:1 ratio, approximately 60% of the cells on these alendronate-loaded substrates were osteoblasts one day after cell seeding. The percentage of osteoblasts increased to about 75% four days after cell seeding. These results suggest that fibroblasts and osteoblasts respond differently towards the alendronate-modified substrates, and this phenomenon can potentially be capitalized to reduce fibrous encapsulation.
  Tissue Engineering Part A 03/2013; · 4.64 Impact Factor
• Article: In vitro endothelialization of cobalt chromium alloys with micro/nanostructures using adipose-derived stem cells.

  Zhilong Shi, K G Neoh, E T Kang
  [show abstract] [hide abstract]
  ABSTRACT: In this study, integrin expression, proliferation, and endothelial differentiation of adipose-derived stem cells (ADSCs) on pristine cobalt chrome (CoCr) surface, microstructured and nanostructured CoCr surfaces (obtained after treatment with piranha solution) were investigated. The results showed that proliferation of ADSCs on the substrates treated with piranha solution is not significantly different from that on the pristine substrates. However, quantitative real-time PCR analysis showed significantly enhanced up-regulation of CD31, vWF and eNOS from gene level by ADSCs on the nanostructured substrates but not on the microstructured substrates. The adsorption of vitronectin from the culture medium on the nanostructured substrates was higher than on the pristine and microstructured substrates. We speculate that this results in increased integrin α(v)β(3) expression in the ADSCs, which may contribute partially to the enhanced endothelial differentiation of ADSCs on the nanostructured substrates. This study shows that ADSCs can be used to endothelialize stents in vitro and the endothelial differentiation of ADSC is enhanced on the nanostructured surfaces.
  Journal of Materials Science Materials in Medicine 01/2013; · 2.32 Impact Factor
• Article: Enhanced endothelial differentiation of adipose-derived stem cells by substrate nanotopography.

  Zhilong Shi, K G Neoh, E T Kang, Chye Khoon Poh, Wilson Wang
  [show abstract] [hide abstract]
  ABSTRACT: Adipose-derived stem cells (ADSCs) have great potential as a cell source for tissue engineering and regenerative medicine because they are easier to obtain, have lower donor-site morbidity and are available in larger numbers than stem cells harvested using bone marrow aspiration. Until now, little has been known about how nanotopography affects the proliferation and endothelial differentiation of ADSCs. In the present study, two nanograting substrates with a period (ridge and groove) of about 250 and 500 nm, respectively, were fabricated on quartz and their effect on ADSC fate was investigated. The results showed that proliferation of ADSCs on nanograting substrates decreased while cell attachment was not significantly affected compared to a flat substrate. Endothelial differentiation of ADSCs on both flat and nanograting substrates can be induced with vascular endothelial growth factor, as shown by immunofluorescent staining. Quantitative real-time PCR analysis showed significantly enhanced upregulation of vWF, PECAM-1 and VE-cadherin at the gene level by ADSCs on the nanograting substrates. In vitro angiogenesis assay on Matrigel showed that nanograting substrates enhanced capillary tube formation. This study highlights the beneficial influence of nanotopography on the differentiation of ADSC into endothelial cells which play an important role in vascularization. Copyright © 2012 John Wiley & Sons, Ltd.
  Journal of Tissue Engineering and Regenerative Medicine 05/2012; · 3.28 Impact Factor
• Article: Antibacterial poly(D,L-lactide) (PDLLA) fibrous membranes modified with quaternary ammonium moieties

  Chen Yao, Xin-song Li, K. G. Neoh, Zhi-long Shi, E. T. Kang
  [show abstract] [hide abstract]
  ABSTRACT: Antibacterial poly(D,L-lactide) (PDLLA) fibrous membranes were developed via electrospinning, followed by surface modification which involved plasma pretreatment, UV-induced graft copolymerization of 4-vinylpyridine (4VP) and quaternization of the grafted pyridine groups with hexylbromide. The success of modification with quaternized pyridinium groups on the PDLLA fibrous membranes was ascertained by X-ray photoelectron spectroscopy (XPS). The antibacterial activities of these membranes were assessed against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli). The PDLLA fibrous membranes modified with quaternized pyridinium groups showed antibacterial efficiency against both bacteria as high as 99.999%. The results demonstrated that the antibacterial activity was based on the interaction of the positive charge of pyridinium group and negatively charged cell membrane of bacteria, resulting in loss of membrane permeability and cell leakage. KeywordsPoly(D,L-lactide)-Antibacterial-Electrospinning-Surface modification
  Chinese Journal of Polymer Science 04/2012; 28(4):581-588. · 0.92 Impact Factor
• Article: Antimicrobial surfaces of viologen-quaternized poly((2-dimethyl amino)ethyl methacrylate)-Si(100) hybrids from surface-initiated atom transfer radical polymerization

  F. J. Xu, S. J. Yuan, S. O. Pehkonen, E. T. Kang, K. G. Neoh
  [show abstract] [hide abstract]
  ABSTRACT: To improve the antimicrobial ability of silicon-based bioelectronics and to tailor the silicon surfaces for inhibiting biofilm formation, well-defined functional polymer-Si(100) hybrids, consisting of nearly monodispersed poly((2-dimethylamino)ethyl methacrylate) (P(DMAEMA)) covalently tethered on the silicon surface and functionalized by viologen moieties, were prepared. P(DMAEMA)-Si hybrids were prepared via surface-initiated atom transfer radical polymerization (ATRP) of (2-dimethylamino)ethyl methacrylate (DMAEMA) on the hydrogen-terminated Si(100) surfaces (Si−H surfaces). The tertiary amino groups of the covalently immobilized (Si−C bonded) P(DMAEMA) brushes on the silicon substrates were quaternized by an alkyl halide to produce a high concentration of quaternary ammonium groups with biocidal functionality. Alternatively, covalent coupling of viologen moieties to the tertiary amino groups of P(DMAEMA) brushes produced the quaternized P(DMAEMA)-Si(100) hybrids with substantially enhanced antimicrobial capability, as well as capability to effectively inhibit biofilm formation. Thus, the viologen-quaternized P(DMAEMA)-Si(100) hybrids possess good antibacterial surface properties and are potentially useful to the silicon-based bioelectronics to ensure their efficiency, durability and reliability.
  Nanobiotechnology 04/2012; 2(3):123-134.
• Article: Combating bacterial colonization on metals via polymer coatings: relevance to marine and medical applications.

  K G Neoh, E T Kang
  [show abstract] [hide abstract]
  ABSTRACT: Metals are widely used in engineering as well as medical applications. However, their surfaces are easily colonized by bacteria that form biofilms. Among the numerous concerns with biofilm formation, biocorrosion is of particular importance in industry, because structural integrity may be compromised, leading to technical failures. In the food industry and medical field, biofilms also pose health risks. To inhibit bacterial colonization, the surfaces of metals can be coated with a polymeric layer which is antiadhesive and/or bactericidal. This article describes polymers that have these desired properties and the methodologies for immobilizing them on metal surfaces of relevance to the marine and medical fields. The focus is on polymer coatings that have a high degree of stability in aqueous medium and do not leach out. The efficacies of the different polymer coatings against bacteria commonly encountered in marine (Desulfovibrio desulfuricans) and medical applications (Staphylococcus aureus, Staphylococcus epidermidis and Escherichia coli) are demonstrated.
  ACS Applied Materials & Interfaces 07/2011; 3(8):2808-19. · 4.53 Impact Factor
• Article: Poly(vinylidene fluoride) Graft Copolymer Membranes with “Clickable” Surfaces and Their Functionalization

  Tao Cai, K. G. Neoh, E. T. Kang
  [show abstract] [hide abstract]
  ABSTRACT: PVDF-g-PPMA copolymers bearing pendant propargyl functionalities were prepared by thermally induced graft copolymerization of propargyl methacrylate (PMA) from the ozone-preactivated poly(vinylidene fluoride) (PVDF) backbones. Microporous membranes were fabricated from the PVDF-g-PPMA comb copolymers by phase inversion in aqueous media. The PVDF-g-PPMA membrane and pore surfaces with pendant propargyl moieties from the PPMA side chains could be further functionalized via the one-step surface-initiated thiol−yne click reaction or alkyne−azide click reaction. The electrolyte-responsive PVDF-g-P[PMA-click-MPS] membranes were prepared via thiol−yne click reaction with 3-mercapto-1-propanesulfonic acid sodium salt (MPS) on the microporous PVDF-g-PPMA membranes. The permeability of aqueous solutions through the PVDF-g-P[PMA-click-MPS] membranes exhibited a dependence on the electrolyte concentration. The PVDF-g-P[PMA-click-β-CD] membranes were synthesized via the alkyne−azide click reaction of mono(6-azido-6-desoxy)-β-cyclodextrin (azido-β-CD) on the PVDF-g-PPMA membranes. The PVDF-g-P[PMA-click-β-CD-guest-PEO] membranes, from surface inclusion complexation of diadamantyl-poly(ethylene oxide) (AD-PEO) guest polymer with the β-cyclodextrin (β-CD) host molecules, exhibited good resistance to protein adsorption and fouling under continuous-flow conditions.
  05/2011;
• Article: ESCA studies of charge transfer interactions in electroactive polymers

  E. T. Kang, K. G. Neoh, K. L. Tan
  [show abstract] [hide abstract]
  ABSTRACT: X-ray photoelectron spectroscopy (XPS) data suggest that proton modifications of nitrogens in polypyrrole (PPY) give rise to a number of intrinsic redox states analogous to those observed in polyaniline (PAN). The behavior of the corresponding oxidation states in both polymers towards oxidation/reduction, deprotonation/reprotonation or charge transfer (CT) interactions are grossly similar. For the thiophene polymers, such as the poly(2,2′-bithiophene) (PBT) complexes and poly(3-methylthiophene) (P3MT) complexes, XPS results reveals the simultaneous presence of neutral and polarized (or partially charged) species in both carbon and sulfur. The relative amounts of the neutral and polarized species vary in accordance with the oxidation level of the polymer. These results suggest that each dopant anion is associated with a thiophenium ion in the polymer chain. Substantially lower extent of CT is observed in the complexes involving photoconductive substituted polyacetylenes, such as polyphenylacetylene (PPA) and poly[[o-(trimethylsilyl)phenyl] acetylene] or poly(o-Me3SiPA).
  Macromolecular Symposia 03/2011; 53(1):275 - 287.
• Article: Surface-Functionalized and Surface-Functionalizable Poly(vinylidene fluoride) Graft Copolymer Membranes via Click Chemistry and Atom Transfer Radical Polymerization.

  Tao Cai, K G Neoh, E T Kang, S L M Teo
  [show abstract] [hide abstract]
  ABSTRACT: Poly(vinylidene fluoride) (PVDF) with azide-functionalized poly(glycidyl methacrylate) (PGMA) side chains (PVDF-g-P[GMA-(N(3))(OH)]) were synthesized via free radical-initiated graft copolymerization of glycidyl methacrylate (GMA) from ozone-pretreated PVDF backbone (PVDF-g-PGMA), followed by reaction of the oxirane rings in the GMA side chains with sodium azide. Alkyne-functionalized poly(N-isopropylacrylamide) (alkynyl-PNIPAM), prepared a priori by atom transfer radical polymerization (ATRP), was used for the click reaction with the azido-containing PGMA side chains of the PVDF-g-P[GMA-(N(3))(OH)] copolymer to give rise to the thermoresponsive PVDF-g-P[GMA-click-PNIPAM] copolymer. Both the PVDF-g-P[GMA-(N(3))(OH)] and PVDF-g-P[GMA-click-PNIPAM] copolymers can be readily cast into microporous membranes by phase inversion in an aqueous medium. The PVDF-g-P[GMA-(N(3))(OH)] microporous membranes with azido-containing surfaces could be further functionalized via surface click reaction with alkyne-terminated PNIPAM of controlled chain lengths to obtain the PVDF-g-P[GMA-click-PNIPAM](surface) microporous membranes. The surface composition and morphology of the PVDF-g-P[GMA-click-PNIPAM] membranes can be adjusted by the temperature of casting medium, while the flux through both types of membranes exhibits thermoresponsive behavior.
  Langmuir 02/2011; · 4.19 Impact Factor
• Article: Lysozyme-Coupled Poly(poly(ethylene glycol) methacrylate)-Stainless Steel Hybrids and Their Antifouling and Antibacterial Surfaces.

  Shaojun Yuan, Dong Wan, Bin Liang, S O Pehkonen, Y P Ting, K G Neoh, E T Kang
  [show abstract] [hide abstract]
  ABSTRACT: 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.
  Langmuir 02/2011; · 4.19 Impact Factor
• Article: Bioactivity of novel carboxymethyl chitosan scaffold incorporating MTA in a tooth model.

  R Budiraharjo, K G Neoh, E T Kang, A Kishen
  [show abstract] [hide abstract]
  ABSTRACT: To characterise the bioactivity of a novel carboxymethyl chitosan (CMCS) scaffold with and without incorporating mineral trioxide aggregate (MTA) in a tooth model. Cross-linked CMCS scaffold (CaC) and MTA-coated CaC (CaMT) scaffold were prepared by freeze-drying. The bioactivity of the scaffolds was tested in vitro in four different mineralisation solutions (bulk system) and ex vivo in simulated body fluid (SBF) in the tooth model. After mineralisation, the mineral deposits on the scaffolds were analysed using scanning electron microscopy, energy dispersive X-ray, and inductively coupled plasma mass spectroscopy. All data were statistically analysed using the two-sample t-test (P < 0.05). Hydroxyapatite (HAP) deposition was observed on CaC and CaMT scaffolds after 1 week of mineralisation in the tooth model and in the bulk system. The deposition was significantly higher (P < 0.05) on CaMT scaffold than that on CaC scaffold. The amount of HAP formed in the tooth model was significantly lower (P < 0.05) than that in the bulk solution. The CMCS scaffolds are bioactive and capable of biomineralisation by forming HAP within a tooth model ex vivo. The bioactivity of the CMCS scaffold can be enhanced by incorporating MTA.
  International Endodontic Journal 10/2010; 43(10):930-9. · 2.18 Impact Factor
• Article: Glucose Biosensor from Covalent Immobilization of Chitosan-Coupled Carbon Nanotubes on Polyaniline-Modified Gold Electrode

  D. Wan, S. J. Yuan, G. L. Li, K. G. Neoh, E. T. Kang
  [show abstract] [hide abstract]
  ABSTRACT: 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 mu A/(mM.cm(2))), good reproducibility, and retention of >80% of the initial response current after 2 months of storage.
  ACS Applied Materials & Interfaces 10/2010; 2(11):3083-3091. · 4.53 Impact Factor
• Article: Surface functionalization of copper via oxidative graft polymerization of 2,2'-bithiophene and immobilization of silver nanoparticles for combating biocorrosion.

  Dong Wan, Shaojun Yuan, K G Neoh, E T Kang
  [show abstract] [hide abstract]
  ABSTRACT: An environmentally benign approach to surface modification was developed to impart copper surface with enhanced resistance to corrosion, bacterial adhesion and biocorrosion. Oxidative graft polymerization of 2,2'-bithiophene from the copper surface with self-assembled 2,2'-bithiophene monolayer, and subsequent reduction of silver ions to silver nanoparticles (Ag NPs) on the surface, give rise to a homogeneous bithiophene polymer (PBT) film with densely coupled Ag NPs on the copper surface (Cu-g-PBT-Ag NP surface). The immobilized Ag NPs were found to significantly inhibit bacterial adhesion and enhance the antibacterial properties of the PBT modified copper surface. The corrosion inhibition performance of the functionalized copper substrates was evaluated by Tafel polarization curves and electrochemical impedance spectroscopy. Arising from the chemical affinity of thiols for the noble and coinage metals, the copper surface functionalized with both PBT brushes and Ag NPs also exhibits long-term stability, and is thus potentially useful for combating the combined problems of corrosion and biocorrosion in harsh marine and aquatic environments.
  ACS Applied Materials & Interfaces 06/2010; 2(6):1653-62. · 4.53 Impact Factor
• Article: Bifunctional Eu(3+)-doped Gd(2)O(3) nanoparticles as a luminescent and T(1) contrast agent for stem cell labeling.

  Zhilong Shi, K G Neoh, E T Kang, Borys Shuter, Shih-Chang Wang
  [show abstract] [hide abstract]
  ABSTRACT: Magnetic resonance tracking of stem cells has recently become an emerging application for investigating cell-tissue interactions and guiding the development of effective stem cell therapies for regeneration of damaged tissues and organs. In this work, anionic Eu(3+)-doped Gd(2)O(3) hybrid nanoparticles were applied as a contrast agent both for fluorescence microscopy and T(1)-weighted MRI. The nanoparticles were synthesized through the polyol method and further modified with citric acid to obtain anionic nanoparticles. These nanoparticles were internalized into human mesenchymal stem cells (hMSCs) as confirmed by confocal laser scanning microscopy and quantified by inductively coupled plasma-mass spectrometry. MTT assay of the labeled cells showed that the nanoparticles did not possess significant cytotoxicity. In addition, the osteogenic, adipogenic and chondrogenic differentiation of the hMSCs was not influenced by the labeling process. With MRI, the in vitro detection threshold of cells after incubation with nanoparticles at a Gd concentration of 0.5 mM for 2 h was estimated to be about 10 000 cells. The results from this study indicate that the biocompatible anionic Gd(2)O(3) nanoparticles doped with Eu(3+) show promise both as a luminescent and T(1) contrast agent for use in visualizing hMSCs.
  Contrast Media & Molecular Imaging 03/2010; 5(2):105-11. · 3.33 Impact Factor
• Article: Antibacterial inorganic-organic hybrid coatings on stainless steel via consecutive surface-initiated atom transfer radical polymerization for biocorrosion prevention.

  S J Yuan, S O Pehkonen, Y P Ting, K G Neoh, E T Kang
  [show abstract] [hide abstract]
  ABSTRACT: 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.
  Langmuir 12/2009; 26(9):6728-36. · 4.19 Impact Factor
• Article: Enzyme-mediated amperometric biosensors prepared via successive surface-initiated atom-transfer radical polymerization.

  Z B Zhang, S J Yuan, X L Zhu, K G Neoh, E T Kang
  [show abstract] [hide abstract]
  ABSTRACT: The development of enzyme-mediated amperometric biosensors on the indium-tin oxide (ITO) glass electrode via surface-initiated atom-transfer radical polymerization (ATRP) was investigated. A trichlorosilane coupling agent, containing the sulfonyl halide ATRP initiator, was immobilized initially on the ITO electrode surface for consecutive surface-initiated ATRP of ferrocenylmethyl methacrylate (FMMA) and glycidyl methacrylate (GMA). Glucose oxidase (GOD) was subsequently immobilized on the modified ITO electrode surface via coupling reactions between the epoxide groups of GMA and the amine groups of GOD. The surface composition after each functionalization step was ascertained by X-ray photoelectron spectroscopy (XPS). With the introduction of redox-P(FMMA) block as the electron-transfer mediator, the enzyme-mediated ITO electrode exhibits high sensitivity, as revealed by cyclic voltammetry measurement. The sensitivities of the ITO-g-P(GMA-GOD)-b-P(FMMA) and ITO-g-P(FMMA)-b-P(GMA-GOD) electrodes are about 3.6 microA/(mM cm(2)) (in the linear concentration range 0-5 mM of glucose) and 10.9 microA/(mM cm(2)) (in the linear concentration range of 0-17 mM of glucose), respectively. For both biosensors, the steady-state response time and the detection limits are estimated to be less than 20 s and 0.4+/-0.1 mM of glucose concentration, respectively. Furthermore, the spatial effect of the redox mediator on the electrode surface is revealed by the fact that the block copolymer brush-functionalized ITO electrode with P(FMMA) as the inner (first) block is more sensitive to glucose than that with P(GMA) as the inner block.
  Biosensors & bioelectronics 10/2009; 25(5):1102-8. · 5.43 Impact Factor
• Article: Antioxidant and antibacterial activities of eugenol and carvacrol‐grafted chitosan nanoparticles

  Fei Chen, Zhilong Shi, K.G. Neoh, E.T. Kang
  [show abstract] [hide abstract]
  ABSTRACT: Essential oils are known to possess antimicrobial and antioxidant activity while chitosan is a biocompatible polymer with antibacterial activity against a broad spectrum of bacteria. In this work, nanoparticles with both antioxidant and antibacterial properties were prepared by grafting eugenol and carvacrol (two components of essential oils) on chitosan nanoparticles. Aldehyde groups were first introduced in eugenol and carvacrol, and the grafting of these oils to chitosan nanoparticles was carried out via the Schiff base reaction. The surface concentration of the grafted essential oil components was determined by X-ray photoelectron spectroscopy (XPS). The antioxidant activities of the carvacrol-grafted chitosan nanoparticles (CHCA NPs) and the eugenol-grafted chitosan nanoparticles (CHEU NPs) were assayed with diphenylpicrylhydrazyl (DPPH). Antibacterial assays were carried out with a representative gram-negative bacterium, Escherichia coli (E. coli) and a gram-positive bacterium, Staphylococcus aureus (S. aureus). The grafted eugenol and carvacrol conferred antioxidant activity to the chitosan nanoparticles, and the essential oil component-grafted chitosan nanoparticles achieved an antibacterial activity equivalent to or better than that of the unmodified chitosan nanoparticles. Cytotoxicity assays using 3T3 mouse fibroblast showed that the cytotoxicity of CHEU NPs and CHCA NPs were significant lower than those of the pure essential oils. Biotechnol. Bioeng. 2009; 104: 30–39 © 2009 Wiley Periodicals, Inc.
  Biotechnology and Bioengineering 08/2009; 104(1):30 - 39. · 3.95 Impact Factor
• Article: Comb-shaped copolymers composed of hydroxypropyl cellulose backbones and cationic poly((2-dimethyl amino)ethyl methacrylate) side chains for gene delivery.

  F J Xu, Y Ping, J Ma, G P Tang, W T Yang, J Li, E T Kang, K G Neoh
  [show abstract] [hide abstract]
  ABSTRACT: Cationic polymers have been of interest and importance as nonviral gene delivery carriers. Herein, well-defined comb-shaped cationic copolymers (HPDs) composed of long biocompatible hydroxypropyl cellulose (or HPC) backbones and short poly((2-dimethyl amino)ethyl methacrylate) (or P(DMAEMA)) side chains were prepared as gene vectors via atom transfer radical polymerization (ATRP) from the bromoisobutyryl-terminated HPC biopolymers. The P(DMAEMA) side chains of HPDs can be further partially quaternized to produce the quaternary ammonium HPDs (QHPDs). HPDs and QHPDs were assessed in vitro for nonviral gene delivery. HPDs exhibit much lower cytotoxicity and better gene transfection yield than high-molecular-weight P(DMAEMA) homopolymers. QHPDs exhibit a stronger ability to complex pDNA, due to increased surface cationic charges. Thus, the approach to well-defined comb-shaped cationic copolymers provides a versatile means for tailoring the functional structure of nonviral gene vectors to meet the requirements of strong DNA-condensing ability and high transfection capability.
  Bioconjugate Chemistry 08/2009; 20(8):1449-58. · 4.93 Impact Factor
• Article: Superparamagnetic Hyperbranched Polyglycerol‐Grafted Fe3O4 Nanoparticles as a Novel Magnetic Resonance Imaging Contrast Agent: An In Vitro Assessment

  Liang Wang, K. G. Neoh, E. T. Kang, Borys Shuter, Shih-Chang Wang
  Advanced Functional Materials 07/2009; 19(16):2615 - 2622. · 10.18 Impact Factor
• Article: Surface functionalization of titanium with carboxymethyl chitosan and immobilized bone morphogenetic protein-2 for enhanced osseointegration.

  Zhilong Shi, K G Neoh, E T Kang, Chye Khoon Poh, Wilson Wang
  [show abstract] [hide abstract]
  ABSTRACT: Orthopedic implant failure has been attributed mainly to loosening of the implant from host bone, which may be due to poor bonding of the implant material to bone tissue, as well as to bacterial infection. One promising strategy to enhance tissue integration is to develop a selective biointeractive surface that simultaneously enhances bone cell function while decreasing bacterial adhesion. In this in vitro study, the surfaces of titanium alloy substrates were functionalized by first covalently grafting carboxymethyl chitosan (CMCS), followed by the conjugation of bone morphogenetic protein-2 (BMP-2) to the CMCS-grafted surface. Bacterial adhesion on the substrates was assayed with Staphylococcus aureus and Staphylococcus epidermidis . Cell functions were investigated using osteoblasts and human bone marrow-derived mesenchymal stem cells. The results showed that bacterial adhesion on both the CMCS and CMCS-BMP-2 functionalized surfaces was significantly reduced compared to that on the pristine substrates. In addition, the CMCS-BMP-2 modified substrates significantly promoted attachment, alkaline phosphatase activity, and calcium mineral deposition of both osteoblast and human bone marrow-derived mesenchymal stem cells. The achievement of the dual functions of bacterial adhesion reduction and cell function promotion by the CMCS-BMP-2 modified titanium substrates illustrates the good potential of such surfaces for enhancement of tissue integration and implant longevity.
  Biomacromolecules 05/2009; 10(6):1603-11. · 5.48 Impact Factor