Modified HEART score, utilising a single high-sensitive troponin sample, allows early, safe discharge of suspected acute coronary syndrome: a prospective multicentre cohort study of 3016 patients

Background

Combining HSTnT (high sensitive troponin T) values at low levels with composite risk scores may improve early safe, discharge in suspected acute coronary syndromes (ACS). We tested this hypothesis by a prospective study of 3016 consecutive patients with suspected ACS in 2 large hospitals.

Methods

Consecutive chest pain (CP) presentations with HSTnT sampled and ECG undertaken at presentation were prospectively defined in 2 time periods (2011-12, n=1642 [derivation] 2018, n=1376 [validation]).

The HstnT input was modified: dichotomous HSTnT input was lowered to <5 (limit of detection, LOD) or ≥5ng/l (mod TIMI and GRACE), HEART score was re-calibrated (<5 = 0 [LOD], ≥5–14 = 1, >14 = 2 [99th percentile]). All biomarker positive CP index and re-admissions to any regional hospital (catchment population 2.6 million) were independently adjudicated for MI by 2 experienced physicians. Primary outcome was MACE (adjudicated type 1 MI, unplanned coronary revascularisation and all cause death) at 6 weeks.

Results

In the 2 cohorts demographic factors were similar: median age 59 and 56, male 52% and 52%, previous MI 20% and 14% for 2011-12 and 2018 respectively. At 6 weeks 180 (11%) and 75 (5.4%) suffered type 1 MI and 211 (12.9%) and 92 (6.7%) patients suffered MACE in the 2011-12 and 2018 cohorts respectively.

Only Mod HEART ≤3 and undetectable HSTnT, with a nonischaemic ECG, achieved prespecified NPV of >99.5% in both derivation and validation cohorts (table). However Modified HEART ≤3 score could discharge approximately 12% more patients as compared to undetectable HSTnT strategy.

Conclusion

Modified HEART score ≤3, with the use of a single HSTnT, appears the optimum early discharge strategy for suspected ACS

Funding Acknowledgement

Type of funding source: Public Institution(s). Main funding source(s): Liverpool university Hospitals, North-West Educational Cardiac Group

Effect of adhesive ligand on cell deadhesion kinetics on poly(N-isopropylacrylamide)

Thermo-responsive poly(N-isopropylacrylamide) (PIPAAm) with a particular lower critical solution temperature (LCST) have been applied for the non-invasive harvesting of confluent cell layer. Until now, the effect of adhesive ligand on the biophysical responses of cells during cell layer harvesting from PIPAAm has not been elucidated. In this study, the deadhesion kinetics of smooth muscle cells (SMC) on various adhesive ligands immobilized on PIPAAm were investigated. Firstly, the formation of elastin (EL), laminin (LA), hyaluronic acid (HA) and collagen (CL) coating on PIPAAm surfaces were validated with XPS, microBCA assay and AFM. It was shown that EL was most effective in driving cell retraction on PIPAAm surface. Moreover, the highest rate of initial SMC deadhesion on EL-PIPAAm was driven by the formation of stress fibers. Interestingly, HA was most effective in preventing initial SMC detachment from PIPAAm surface in comparison with EL, LA and CL. Also, the adhesion energy of SMC on HA-PIPAAm remained constant, which was two times and six times higher than that on CL-PIPAAm and EL-PIPAAm, respectively from 20 min onward. Overall, the results reported herein pave the way for the engineering of the invasive regeneration/recovery of cells/tissue with adhesive ligand.

One-pot reaction for the large-scale synthesis of hyperbranched polyglycerol-grafted Fe3O4 nanoparticles

Fe3O4 nanoparticles with surface hydroxyl groups (MNP-OH), prepared by the thermal decomposition of ferric oxalate pentahydrate in triethylene glycol, were grafted in situ with polyglycerol through the ring-opening polymerization of glycidol. By this method, hyperbranched polyglycerol-grafted Fe3O4 nanoparticles (HPG-grafted MNPs) can be obtained on an ultra-large scale of 50 g in a single reaction under laboratory conditions, and it is anticipated that the production of the HPG-grafted MNPs could be scaled up with the use of larger reaction vessels. The successful grafting of HPG onto the nanoparticles was confirmed by (1)H NMR and XPS analyses. The as-synthesized nanoparticles can be tuned from 8 to 24 nm in diameter by varying the reaction conditions. The size, morphology, and surface component of the nanoparticles were characterized by TEM, XPS, and XRD. The HPG-grafted MNPs are highly dispersible in aqueous media such as cell culture medium and serum. Since these magnetic nanoparticles possess desirable magnetic properties, controllable size, and can be produced by a facile inexpensive method, they can be potentially applied as a novel contrast agent for enhancing a MRI signal.

In vitro endothelialization of cobalt chromium alloys with micro/nanostructures using adipose-derived stem cells

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 αvβ3 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.

Enhanced endothelial differentiation of adipose-derived stem cells by substrate nanotopography

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.

Combating bacterial colonization on metals via polymer coatings: relevance to marine and medical applications

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.

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.

Surface-functionalized and surface-functionalizable poly(vinylidene fluoride) graft copolymer membranes via click chemistry and atom transfer radical polymerization

Poly(vinylidene fluoride) (PVDF) with azide-functionalized poly(glycidyl methacrylate) (PGMA) side chains (PVDF-g-P[GMA-(N3)(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-(N3)(OH)] copolymer to give rise to the thermoresponsive PVDF-g-P[GMA-click-PNIPAM] copolymer. Both the PVDF-g-P[GMA-(N3)(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-(N3)(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.

Glucose biosensor from covalent immobilization of chitosan-coupled carbon nanotubes on polyaniline-modified gold electrode

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 μA/(mM·cm(2))), good reproducibility, and retention of >80% of the initial response current after 2 months of storage.

Bifunctional Eu(3+)-doped Gd(2)O(3) nanoparticles as a luminescent and T(1) contrast agent for stem cell labeling

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.

Bioactivity of novel carboxymethyl chitosan scaffold incorporating MTA in a tooth model

AIM

To characterise the bioactivity of a novel carboxymethyl chitosan (CMCS) scaffold with and without incorporating mineral trioxide aggregate (MTA) in a tooth model.

METHODOLOGY

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).

RESULTS

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.

CONCLUSIONS

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.

Surface functionalization of copper via oxidative graft polymerization of 2,2'-bithiophene and immobilization of silver nanoparticles for combating biocorrosion

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.

Antibacterial inorganic-organic hybrid coatings on stainless steel via consecutive surface-initiated atom transfer radical polymerization for biocorrosion prevention

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.

Grafting of antibacterial polymers on stainless steel via surface-initiated atom transfer radical polymerization for inhibiting biocorrosion by Desulfovibrio desulfuricans

To enhance the biocorrosion resistance of stainless steel (SS) and to impart its surface with bactericidal function for inhibiting bacterial adhesion and biofilm formation, well-defined functional polymer brushes were grafted via surface-initiated atom transfer radical polymerization (ATRP) from SS substrates. The trichlorosilane coupling agent, containing the alkyl halide ATRP initiator, was first immobilized on the hydroxylated SS (SS-OH) substrates for surface-initiated ATRP of (2-dimethylamino)ethyl methacrylate (DMAEMA). The tertiary amino groups of covalently immobilized DMAEMA polymer or P(DMAEMA), brushes on the SS substrates were quaternized with benzyl halide to produce the biocidal functionality. Alternatively, covalent coupling of viologen moieties to the tertiary amino groups of P(DMAEMA) brushes on the SS surface resulted in an increase in surface concentration of quaternary ammonium groups, accompanied by substantially enhanced antibacterial and anticorrosion capabilities against Desulfovibrio desulfuricans in anaerobic seawater, as revealed by antibacterial assay and electrochemical studies. With the inherent advantages of high corrosion resistance of SS, and the good antibacterial and anticorrosion capabilities of the viologen-quaternized P(DMAEMA) brushes, the functionalized SS is potentially useful in harsh seawater environments and for desalination plants.

Concentric hollow nanospheres of mesoporous silica shell-titania core from combined inorganic and polymer syntheses

Nearly monodispersed concentric hollow nanospheres with a mesoporous silica shell and anatase titania inner core were synthesized by the combination of sol-gel reaction and distillation-precipitation polymerization. The well-defined mesoporous concentric hollow nanospheres, comprising two nanostructured functional inorganics, can be used for confined catalytic reactions. The direct synthesis procedures can be readily extended to preparation of the concentric hollow nanospheres with multiple cores, or other functional concentric hollow nanospheres having different core-shell compositions.

Star-shaped cationic polymers by atom transfer radical polymerization from beta-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.

Inorganic-organic hybrid coatings on stainless steel by layer-by-layer deposition and surface-initiated atom-transfer-radical polymerization for combating biocorrosion

To improve the biocorrosion resistance of stainless steel (SS) and to confer the bactericidal function on its surface for inhibiting bacterial adhesion and biofilm formation, well-defined inorganic-organic hybrid coatings, consisting of the inner compact titanium oxide multilayers and outer dense poly(vinyl-N-hexylpyridinium) brushes, were successfully developed. Nanostructured titanium oxide multilayer coatings were first built up on the SS substrates via the layer-by-layer sol-gel deposition process. The trichlorosilane coupling agent, containing the alkyl halide atom-transfer-radical polymerization (ATRP) initiator, was subsequently immobilized on the titanium oxide coatings for surface-initiated ATRP of 4-vinylpyridine (4VP). The pyridium nitrogen moieties of the covalently immobilized 4VP polymer, or P(4VP), brushes were quaternized with hexyl bromide to produce a high concentration of quaternary ammonium salt on the SS surfaces. The excellent antibacterial efficiency of the grafted polycations, poly(vinyl-N-pyridinium bromide), was revealed by viable cell counts and atomic force microscopy images of the surface. The effectiveness of the hybrid coatings in corrosion protection was verified by the Tafel plot and electrochemical impedance spectroscopy measurements.

(Carboxymethyl)chitosan-modified superparamagnetic iron oxide nanoparticles for magnetic resonance imaging of stem cells

Magnetic resonance imaging (MRI) is emerging as a powerful tool for in vivo noninvasive tracking of magnetically labeled stem cells. In this work, we present an efficient cell-labeling approach using (carboxymethyl)chitosan-modified superparamagnetic iron oxide nanoparticles (CMCS-SPIONs) as contrast agent in MRI. The CMCS-SPIONs were prepared by conjugating (carboxymethyl)chitosan to (3-aminopropyl)trimethoxysilane-treated SPIONs. These nanoparticles were internalized into human mesenchymal stem cells (hMSCs) via endocytosis as confirmed by Prussian Blue staining and electron microscopy investigation and quantified by inductively coupled plasma mass spectrometry. A MTT assay of the labeled cells showed that CMCS-SPIONs did not possess significant cytotoxicity. In addition, the osteogenic and adipogenic differentiations of the hMSCs were not influenced by the labeling process. The in vitro detection threshold of cells after incubation with 0.05 mg/mL of CMCS-SPIONs for 24 h was estimated to be about 40 cells. The results from this study indicate that the biocompatible CMCS-SPIONs show promise for use with MRI in visualizing hMSCs.

Structural stability and bioapplicability assessment of hyaluronic acid-chitosan polyelectrolyte multilayers on titanium substrates

Since bacterial infections associated with implants remain a major cause of their failure, this study investigated the use of polyelectrolyte multilayers (PEMs) comprising hyaluronic acid (HA) and chitosan (CH) to confer antibacterial properties on titanium (Ti). HA and CH were deposited on Ti using the layer-by-layer deposition method. The antibacterial efficacy of the functionalized Ti substrates was assessed using Escherichia coli and Staphylococcus aureus. The number of adherent bacteria on Ti functionalized with HA and CH PEMs was up to an order of magnitude lower than that on the pristine Ti. The effects of chemical crosslinking of the PEMs on the structural stability and antibacterial efficacy were investigated. The chemical crosslinking of the PEMs imparts greater structural stability and preserves the antibacterial properties even after the prolonged immersion in phosphate-buffered saline. The cytotoxicity of the PEMs to osteoblasts was evaluated using the MTT assay. The results showed that the biocompatible and long-lasting antibacterial nature of the functionalized Ti substrates offers great potential for reducing implant-associated infections.

Human bone marrow-derived mesenchymal stem cells and osteoblast differentiation on titanium with surface-grafted chitosan and immobilized bone morphogenetic protein-2

Circulating progenitor cells are known to home to various organs to repair injured tissues or to routinely replace old cells and maintain tissue integrity. Similarly, circulating progenitor bone cells can possibly home to a bone implant, differentiate, and eventually osteointegrate with the prosthesis. Osteointegration of bone cells with the prosthesis can help to reduce the risk of implant failure due to constant movement between bone tissue and implant surface. In this study, we aim to investigate if immobilized bone morphogenetic protein-2 (BMP2) on chitosan-grafted titanium substrate (Ti-CS-BMP2) will enhance bone marrow-derived mesenchymal stem cell (BMMSC) adhesion onto the substrate surface and further induce their differentiation into osteoblasts. The results show that our Ti-CS-BMP2 substrate is able to retain adsorbed BMP2, and is capable of slow release of this growth factor. Despite the lesser number of BMMSCs initially attached onto the Ti-CS-BMP2 substrates and consequently the lower level of cell proliferation, Ti-CS-BMP2 cells had the highest level of ALP activity. RT-PCR results show that Ti-CS-BMP2 cells had a relatively higher level of transcription activity of Runx2, compared with that of bone cell-derived osteoblasts (BC-OB), an indication that the BMMSCs were actively differentiating into osteoblasts. Finally, alizarin red staining reveals the presence of calcium deposits in the differentiated cells. Hence our Ti-CS-BMP2 substrates possess an osteoconductive effect and can possibly be used to fabricate bone implants that can osteointegrate with host bone tissue.

Surface functionalization of Cu-Ni alloys via grafting of a bactericidal polymer for inhibiting biocorrosion by Desulfovibrio desulfuricans in anaerobic seawater

A novel surface modification technique was developed to provide a copper nickel alloy (M) surface with bactericidal and anticorrosion properties for inhibiting biocorrosion. 4-(chloromethyl)-phenyl tricholorosilane (CTS) was first coupled to the hydroxylated alloy surface to form a compact silane layer, as well as to confer the surface with chloromethyl functional groups. The latter allowed the coupling of 4-vinylpyridine (4VP) to generate the M-CTS-4VP surface with biocidal functionality. Subsequent surface graft polymerization of 4VP, in the presence of benzoyl peroxide (BPO) initiator, from the M-CTS-4VP surface produced the poly(4-vinylpyridine) (P(4VP)) grafted surface, or the M-CTS-P(4VP) surface. The pyridine nitrogen moieties on the M-CTS-P(4VP) surface were quaternized with hexylbromide to produce a high concentration of quaternary ammonium groups. Each surface functionalization step was ascertained by X-ray photoelectron spectroscopy (XPS) and static water contact angle measurements. The alloy with surface-quaternized pyridinium cation groups (N+) exhibited good bactericidal efficiency in a Desulfovibrio desulfuricans-inoculated seawater-based modified Barr's medium, as indicated by viable cell counts and fluorescence microscopy (FM) images of the surface. The anticorrosion capability of the organic layers was verified by the polarization curve and electrochemical impedance spectroscopy (EIS) measurements. In comparison, the pristine (surface hydroxylated) Cu-Ni alloy was found to be readily susceptible to biocorrosion under the same environment.

Stimuli-responsive multifunctional membranes of controllable morphology from poly(vinylidene fluoride)-graft-poly[2-(N,N-dimethylamino)ethyl methacrylate] prepared via atom transfer radical polymerization

Poly(vinylidene fluoride) (PVDF) with poly[2-(N,N-dimethylamino) ethyl methacrylate] (PDMAEMA) side chains were synthesized via vinylidene fluoride-initiated atom transfer radical polymerization (ATRP) of 2-(N,N-dimethylamino) ethyl methacrylate (DMAEMA). The graft copolymer can be readily cast into porous pH- and thermo-responsive microfiltration (MF) membranes with enriched "living" PDMAEMA graft chains on the surface (including the pore surfaces) by phase inversion in an aqueous medium. The morphology and surface composition of the membranes were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. The pH and temperature of the aqueous media for phase inversion and the PDMAEMA content in the PVDF-g-PDMAEMA copolymers can be used to adjust the pore size of the membranes. In addition to having pH and temperature-responsive permeability, the PVDF-g-PDMAEMA MF membranes also exhibit both good antifouling and antibacterial properties, making the membrane potentially useful for biorelated applications. Furthermore, the dormant PDMAEMA chain ends on the PVDF-g-PDMAEMA membrane can be reactivated for the consecutive surface-initiated ATRP of other functional monomers, such as 2-naphthyl methacrylate (2NM), to produce fluorescent PDMAEMA-b-P2NM diblock copolymer brushes on the PVDF membrane.

Water-dispersible carbon nanotubes for aqueous surface-initiated atom transfer radical polymerization

A simple one-pot process was developed for the covalent immobilization of atom transfer radical polymerization (ATRP) initiators with quaternized triethylamine moieties on the carboxyl-functionalized multiwalled carbon nanotubes (MWCNTs). The initiator-coupled MWCNTs exhibited good dispersion in water and could be used directly to prepare water-dispersion of polymer-MWCNT hybrids, such as stimuli-responsive poly(N-isopropyl acrylamide)-MWCNT hybrids, via surface-initiated ATRP of N-isopropylacrylamide in an aqueous medium. The present one-pot synthesis of the ATRP initiator-immobilized MWCNTs with good dispersion in water provides an alternative route to the direct preparation of water-soluble polymer-MWCNT hybrids in aqueous media.

pH-Responsive hollow polymeric microspheres and concentric hollow silica microspheres from silica-polymer core-shell microspheres

Nearly monodispersed silica-poly(methacrylic acid) (SiO 2-PMAA) core-shell microspheres were synthesized by distillation-precipitation polymerization from 3-(trimethoxysilyl)propylmethacrylate-silica (SiO 2-MPS) particle templates. SiO 2-PMAA-SiO 2 trilayer hybrid microspheres were subsequently prepared by coating of an outer layer of SiO 2 on the SiO 2-PMAA core-shell microspheres in a sol-gel process. pH-Responsive PMAA hollow microspheres with flexible (deformable) shells were obtained after selective removal of the inorganic SiO 2 core from the SiO 2-PMAA core-shell microspheres by HF etching. The pH-responsive properties of the PMAA hollow microspheres were investigated by dynamic laser scattering (DLS). On the other hand, concentric and rigid hollow silica microspheres were prepared by selective removal of the PMAA interlayer from the SiO 2-PMAA-SiO 2 trilayer hybrid microspheres during calcination. The hybrid composite microspheres, pH-sensitive hollow microspheres, and concentric hollow silica microspheres were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray (EDX) analysis.

The Stat family of transcription factors have diverse roles in mammary gland development

The Stat family of transcription factors have diverse roles in mammary gland development. Genetic studies in mice have revealed an essential requirement for Stat5a in development of secretory alveolar cells during pregnancy while Stat6, which is normally associated with differentiation of T helper cells, is important in the commitment of luminal cells to this alveolar lineage. In contrast, Stat3 is specifically activated at the initiation of post-lactational regression when it has an essential function in the regulation of cell death and tissue remodelling. Stat1 and Stat4 have been shown to be regulated during a mammary developmental cycle although whether they have specific, non-redundant roles is not clear. Thus, the adult mammary gland is somewhat unusual in that it is a tissue where different Stats are sequentially activated to orchestrate the processes of functional differentiation, cell death and tissue remodelling.

Bacteria-surface interaction in the presence of proteins and surface attached poly(ethylene glycol) methacrylate chains

This study analyzes the adhesion behavior of the gram positive bacteria, Staphylococcus aureus (S. aureus), and the gram negative bacteria, Escherichia coli (E. coli), on polypyrrole (PPY) surfaces in the presence of poly(ethylene glycol) methacrylate (PEGMA) chains and plasma proteins (bovine serum albumin and bovine plasma fibrinogen) either preadsorbed on the film surface or in the bacterial suspension. Bacterial adhesion experiments performed in a suspension of bacterial cells and protein may give important insights on the behavior of bacterial adhesion in an in vivo environment. Protein adsorption and bacterial adhesion on PEGMA-grafted PPY films were reduced by about a factor of 2-4 compared with those on the pristine PPY films. In addition, the number of bacterial cells adhering on the substrate is dependent not only on the type of protein present, but also the sequence of exposure to the protein relative to the bacteria. Furthermore, bacteria-surface adhesion force was measured using the atomic force microscopy with increasing lateral force to detach the individual cell. The adhesion force of S. aureus is influenced by PEGMA and plasma protein modification and is significantly higher than that of E. coli for all substrates tested. The number of adherent cells on the substrate is shown to be directly correlated to the bacterial adhesion force.

Functionalization of nylon membranes via surface-initiated atom-transfer radical polymerization

The ability to manipulate and control the surface properties of nylons is of crucial importance to their widespread applications. In this work, surface-initiated atom-transfer radical polymerization (ATRP) is employed to tailor the functionality of the nylon membrane and pore surfaces in a well-controlled manner. A simple two-step method, involving the activation of surface amide groups with formaldehyde and the reaction of the resulting N-methylol polyamide with 2-bromoisobutyryl bromide, was first developed for the covalent immobilization of ATRP initiators on the nylon membrane and its pore surfaces. Functional polymer brushes of 2-hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol)monomethacrylate (PEGMA) were prepared via surface-initiated ATRP from the nylon membranes. A kinetics study revealed that the chain growth from the membranes was consistent with a "controlled" process. The dormant chain ends of the grafted HEMA polymer (P(HEMA)) and PEGMA polymer (P(PEGMA)) on the nylon membranes could be reactivated for the consecutive surface-initiated ATRP to produce the corresponding nylon membranes functionalized by P(HEMA)-b-P(PEGMA) and P(PEGMA)-b-P(HEMA) diblock copolymer brushes. In addition, membranes with grafted P(HEMA) and P(PEGMA) brushes exhibited good resistance to protein adsorption and fouling under continuous-flow conditions.

Synthesis and in vitro anti-cancer evaluation of tamoxifen-loaded magnetite/PLLA composite nanoparticles

The present study deals with the synthesis and characterization of tamoxifen-loaded magnetite/poly(l-lactic acid) composite nanoparticles (TMCN), and their in vitro anti-cancer activity against MCF-7 breast cancer cells. The composite nanoparticles with an average size of approximately 200 nm, were synthesized via a solvent evaporation/extraction technique in an oil/water emulsion. The superparamagnetic property (saturation magnetization value of approximately 7 emu/g) of the TMCN is provided by Fe(3)O(4) nanoparticles of approximately 6 nm encapsulated in the poly(l-lactic acid) matrix. The encapsulation efficiency of the Fe(3)O(4) and tamoxifen as a function of the concentration in the organic phase was investigated. The uptake of TMCN and tamoxifen by MCF-7 was estimated from the intracellular iron concentration. After 4h incubation of MCF-7 with TMCN, significant changes in the cell morphology were discernible from phase contrast microscopy. Cytotoxicity assay shows that while the Fe(3)O(4)-loaded poly(l-lactic acid) composite nanoparticles exhibit no significant cytotoxicity against MCF-7, approximately 80% of the these cells were killed after incubation for 4 days with TMCN.

Preparation of conductive polypyrrole-palladium composite nanospheres by inverse microemulsion polymerization

Conductive polypyrrole-palladium (PPy-Pd) composite nanospheres of about 50 nm in diameter, containing dispersed Pd metal nanoparticles of about 2-4 nm in size, were prepared in a 1-step oxidative polymerization of pyrrole by Pd(NO3)2. Pyrrole was oxidized by Pd(NO3)2 in an inverse microemulsion polymerization system, yielding PPy nanospheres and elemental Pd nanoparticles simultaneously. Palladium nanoparticles were uniformly dispersed in the nanospheres of PPy chains. The latter also exhibited an enhanced effective conjugation. The chemical composition of the PPy-Pd composite nanospheres was characterized by X-ray photoelectron spectroscopy and FTIR spectroscopy. The crystalline structure of the Pd nanoparticles was deduced from X-ray diffraction patterns. The morphology of the composites was revealed by scanning and transmission electron microscopy.

Immobilization of functional oxide nanoparticles on silicon surfaces via Si-C bonded polymer brushes

A method for immobilizing and mediating the spatial distribution of functional oxide (such as SiO2 and Fe3O4) nanoparticles (NPs) on (100)-oriented single crystal silicon surface, via Si-C bonded poly(3-(trimethoxysilyl)propyl methacrylate) (P(TMSPM)) brushes from surface-initiated atom transfer radical polymerization (ATRP) of (3-(trimethoxysilyl)propyl methacrylate) (TMSPM), was described. The ATRP initiator was covalently immobilized via UV-induced hydrosilylation of 4-vinylbenzyl chloride (VBC) with the hydrogen-terminated Si(100) surface (Si-H surface). The surface-immobilized Fe3O4 NPs retained their superparamagnetic characteristics and their magnetization intensity could be mediated by adjusting the thickness of the P(TMSPM) brushes.

Au-Pt bimetallic nanoparticles formation via viologen-mediated reduction on polymeric nanospheres

Poly(vinylbenzyl chloride) nanospheres prepared via emulsion polymerization were surface functionalized with viologen moieties. Several methods were investigated to achieve the desired high surface concentration of viologen moieties with minimal aggregation of the nanospheres. The viologen-functionalized nanospheres were used for photoinduced reduction of gold ions and platinum ions, either individually, simultaneously or sequentially, to result in the formation of well-distributed Au-Pt nanoparticles of a few nanometers on the surface of the nanospheres. UV-visible absorption spectroscopy and XPS analyses of these bimetallic nanoparticles were carried out. The reaction time and the sequence of the reduction process play an important role in determining the composition of the bimetallic nanoparticles. High-resolution transmission electron microscopy analysis reveals the highly crystalline nature of the bimetallic nanoparticles.

In vitro antibacterial and cytotoxicity assay of multilayered polyelectrolyte-functionalized stainless steel

Infection of implanted materials by bacteria constitutes one of the most serious complications following prosthetic and implant surgery. In the present study, a new strategy for confering stainless steel with antibacterial property via the alternate deposition of quaternized polyethylenimine (PEI) or quaternized polyethylenimine-silver complex and poly(acrylic acid) (PAA) was investigated. The success of the deposition of the polyelectrolyte multilayers (PEM) and its chemical nature was investigated by static water contact angle and X-ray photoelectron spectroscopy (XPS), respectively. The antibacterial activity was assessed using Escherichia coli (E. coli, a gram-negative bacterium) and Staphylococcus aureus (S. aureus, a gram-positive bacterium). The inhibition of E. coli and S aureus growth on the surface of functionalized films was clearly shown using the LIVE/DEAD Baclight bacterial viability kits and fluorescence microscopy. The cytotoxicity of the PEM to mammalian cells, evaluated by the MTT assay, was shown to be minimal and long-term antibacterial efficacy can be maintained. These results indicate new possibilities for the use of such easily built and functionalized architectures for the functionalization of surfaces of implanted medical devices.

Thermoresponsive comb-shaped copolymer-Si(100) hybrids for accelerated temperature-dependent cell detachment

Well-defined comb-shaped copolymer-Si(100) hybrids were prepared, via successive surface-initiated atom transfer radical polymerizations (ATRPs) of glycidyl methacrylate (GMA) and N-isopropylacrylamide (NIPAAm), for accelerated cell detachment at a lower temperature. The Si-C bonded comb copolymer consisted of a well-defined (nearly monodispersed) poly(glycidyl methacrylate) (P(GMA)) main chain, a well-defined NIPAAm polymer (P(NIPAAm) block, and well-defined P(NIPAAm) side chains. The ring opening reaction of epoxy groups of the P(GMA) main chain with 2-chloropropionic acid resulted in the immobilization of the alpha-chloroester groups (the ATRP initiators for the NIPAAm side chains) and the concomitant formation of hydroxyl groups. P(NIPAAm) acted as the thermoresponsive side chains of the comb copolymer for control of cell adhesion and detachment, while the P(GMA) main chain with hydroxyl groups provided a local hydrophilic microenvironment. The unique microstructure of the comb copolymer brushes facilitated cell recovery at 20 degrees C (below the lower critical solution temperature (LCST) of P(NIPAAm)) without restraining cell attachments and growth at 37 degrees C. The accelerated detachment of cells indicated that the underlying hydrophilic environment of the comb copolymer brushes contributed to speedy hydration of the P(NIPAAm) segments below the LCST. The thermoresponsive comb copolymer-Si(100) hybrids are potentially useful as adhesion modifiers for cells in silicon-based biomedical devices.

Heparin-coupled poly(poly(ethylene glycol) monomethacrylate)-Si(111) hybrids and their blood compatible surfaces

Well-defined (nearly monodispersed) poly(poly(ethylene glycol)monomethacrylate)-Si hybrids were prepared via surface-initiated atom transfer radical polymerization (ATRP) of the poly(ethylene glycol)monomethacrylate (PEGMA) macromonomer on the hydrogen-terminated Si(111) surface (Si-H surface). Both the active chloride groups at the chain ends (from the ATRP process) and the chloride groups converted from some ( approximately 32%) of the -OH groups of the Si-C bonded PEGMA polymer, or P(PEGMA), brushes were used as leaving groups for the covalent coupling of heparin. For the heparinized P(PEGMA)-Si hybrid surfaces, protein adsorption and platelet adhesion were significantly suppressed. The well-defined and dense P(PEGMA) brushes, prepared from surface-initiated ATRP, had allowed the immobilization of a relatively high concentration of heparin (about 14 mug/cm(2)). The resulting silicon surface exhibited significantly improved antithrombogenecity with a plasma recalcification time (PRT) of about 150 min. The persistence of high bioactivity for the immobilized heparin on the hybrid surfaces can be attributed to the biocompatibility of the PEGMA units, as well as their role as spacers in providing the immobilized heparin with a higher degree of conformational freedom in a more hydrophilic environment. Thus, the heparin-coupled P(PEGMA)-Si hybrids with anti-fouling and antithrombogenic surfaces are potentially useful in silicon-based implantable devices and tissue engineering.

Antibacterial and mechanical properties of bone cement impregnated with chitosan nanoparticles

Although total joint replacement has become commonplace in recent years, bacterial infection remains a significant complication following this procedure. One approach to reduce the incidence of joint replacement infection is to add antimicrobial agents to the bone cement used to fix the implant. In this in vitro study, we investigated the use of chitosan nanoparticles (CS NP) and quaternary ammonium chitosan derivative nanoparticles (QCS NP) as bactericidal agents in poly(methyl methacrylate) (PMMA) bone cement with and without gentamicin. The antibacterial activity was tested against Staphylococcus aureus (S. aureus) and Staphylococcus epidermidis (S. epidermidis). A 10(3)-fold reduction in the number of viable bacterial cells upon contact with the surface was achievable using QCS NP at a nanoparticle/bone cement weight ratio of 15%. The inhibition of S. aureus and S. epidermidis growth on the surface of the CS NP and QCS NP-loaded bone cements was clearly shown using the LIVE/DEAD Baclight bacterial viability kits and fluorescence microscopy. The CS NP and QCS NP also provided a significant additional bactericidal effect to gentamicin-loaded bone cement. The antibacterial effectiveness remained high even after the modified bone cements had been immersed for 3 weeks in an aqueous medium. No cytotoxic effect of the CS NP- and QCS NP-loaded cements was shown in a mouse fibroblast MTT cytotoxicity assay. Mechanical tests indicated that the addition of the CS and QCS in nanoparticulate form allowed the retention of a significant degree of the bone cement's strength. These results indicate a new promising strategy for combating joint implant infection.

Porous and electrically conductive polypyrrole-poly(vinyl alcohol) composite and its applications as a biomaterial

Bulk modification of polypyrrole (PPY) with poly(vinyl alcohol) (PVA) was carried out by the electropolymerization of pyrrole in the presence of PVA in the reaction solution, with tetraethylammonium perchlorate (TEAP) as the electrolyte. The surface morphology of the as-synthesized PPY-TEAP-PVA film was investigated using scanning electron microscopy, and the film was further characterized using X-ray photoelectron spectroscopy, electrical conductivity, the water contact angle, and BET surface area measurements. The PPY-TEAP-PVA composite is electrically conductive, hydrophilic, and microporous with a high surface area. Its potential as a biomaterial was investigated with respect to its blood compatibility and function as a substrate for biosensor fabrication and cell culture. The presence of PVA in the film attenuates blood protein adsorption, and the porous nature of the PPY-TEAP-PVA film results in a 10-fold increase in the amount of glucose oxidase covalently immobilized on the film over that on a nonporous PPY film. PC12 cell attachment and growth on the PPY-TEAP-PVA film was also shown to be enhanced compared with that on tissue culture polystyrene. The attached cells proliferated and formed a monolayer on the film surface after 48 h of seeding.

Collagen-Coupled Poly(2-hydroxyethyl methacrylate)–Si(111) Hybrid Surfaces for Cell Immobilization

To improve the biocompatibility of silicon-based implantable micro- and nanodevices, and to tailor silicon surfaces for controlled cell immobilization, well-defined functional polymer-Si(111) hybrids, consisting of nearly monodispersed poly(2-hydroxyethyl methacrylate [P(HEMA)] with covalently coupled collagen and tethered (Si-C bonded) on the silicon surfaces, were prepared. HEMA was graft polymerized on the hydrogen-terminated Si(111) surface (Si-H surface) via surface-initiated atom transfer radical polymerization (ATRP) to give rise to the Si-g-P(HEMA) hybrid. The active chloride end groups preserved throughout the ATRP process and the chloride groups converted from some (approximately 20%) of the OH groups of the P(HEMA) brushes were used as the leaving groups for nucleophilic reaction with the -NH2 groups of collagen to give rise to the Si-g-P(HEMA)-collagen surface conjugates. These hybrid surfaces were evaluated by culturing 3T3 fibroblasts. The biocompatible Si-g-P(HEMA) hybrid surface resisted attachment and growth of this cell line. The Si-g-P(HEMA)-collagen hybrid surfaces, on the other hand, exhibited good cell adhesion and growth characteristics, and the extent of cell immobilization could be controlled by adjusting the amount of immobilized collagen. Thus, incorporating the collagen-coupled P(HEMA) onto silicon surfaces via robust Si-C bonds may endow the silicon substrates with new and interesting properties for potential applications in silicon-based implantable devices, such as molecular sensors and biochips.

Brush-type amphiphilic diblock copolymers from "living"/controlled radical polymerizations and their aggregation behavior

Two brush-type amphiphilic diblock copolymers, poly(poly(ethylene glycol)methyl ether methacrylate-block-polystyrene) (P(PEGMA)-b-PS) and poly(glycidyl methacrylate)-block-poly(poly(ethylene glycol)methyl ether methacrylate) (P(GMA)-b-P(PEGMA)) were synthesized, respectively, via consecutive atom-transfer radical polymerizations (ATRPs) and reversible addition-fragmentation chain-transfer (RAFT) polymerizations. The diblock copolymers were characterized by gel permeation chromatography (GPC), (1)H nuclear magnetic resonance (NMR) spectroscopy, and FT-IR spectroscopy. The aggregation behavior of the two amphiphilic diblock copolymers in water was also studied. Scanning electron and transmission electron microscopic images revealed that spherical micelles (40-80 nm in diameter) from self-assembly of the P(PEGMA)-b-PS copolymers and wormlike micelles (60-120 nm in length and 20-30 nm in diameter) from self-assembly of the P(GMA)-b-P(PEGMA) copolymers were prevalent. The spherical P(PEGMA)-b-PS micelles could self-assemble gradually into giant aggregates of several micrometers in diameter.

Surface-initiated atom transfer radical polymerization from halogen-terminated Si(111) (Si-X, X = Cl, Br) surfaces for the preparation of well-defined polymer-Si hybrids

The halogen-terminated Si(111) (Si-X, X = Cl, Br) surfaces contain effective initiators for surface-initiated atom transfer radical polymerization. Well-defined polymer-Si hybrids, consisting of covalently tethered (Si-C bonded) functional polymer brushes, can be prepared directly from the Si-X surfaces.

Three-dimensionally ordered porous membranes prepared via self-assembly and reverse micelle formation from well-defined amphiphilic block copolymers

Block copolymers of poly(pentafluorostyrene) (PFS) and poly(tert-butyl acrylate) (PtBA), or PFS-b-PtBA copolymers, were synthesized via consecutive atom transfer radical polymerizations (ATRPs). Amphiphilic block copolymers of PFS and poly(acrylic acid) (PFS-b-PAAC copolymers) were prepared via hydrolysis of the corresponding PFS-b-PtBA copolymers. The chemical structure and composition of the PFS-b-PtBA and PFS-b-PAAC block copolymers were studied by nuclear magnetic resonance (NMR) spectroscopy, themogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The amphiphilic PFS-b-PAAC copolymers were cast into porous membranes by phase inversion in aqueous media. The surface and cross-sectional morphology of the PFS-b-PAAC membranes were studied by scanning electron microscopy (SEM). Membranes with well-defined pores of sizes in the micrometer range were obtained as a result of inverse micelle formation. The pH of the aqueous media for phase inversion and the PAAC content in the PFS-b-PAAC copolymers could be used to adjust the pore size of the membranes.

Antibacterial activity of polymeric substrate with surface grafted viologen moieties

An asymmetric viologen, N-hexyl-N'-(4-vinylbenzyl)-4,4'-bipyridinium bromide chloride (HVV), was synthesized and graft copolymerized with commercial PET films. The surface graft concentration of HVV on the PET film is easily controlled by varying the monomer concentration used in the UV-induced graft copolymerization process. The HVV surface functionalized PET film functions as a smart window whose transmittance is reduced upon exposure to light. Concomitantly, the film possesses antibacterial activity, as shown by its bactericidal effect on Escherichia coli (E. coli). The antibacterial activity depends on the concentration of pyridinium groups on the surface and a surface concentration of 25 nmol/cm2 on PET has been shown to be highly effective in killing the bacteria.

Covalent Immobilization of Glucose Oxidase on Well-Defined Poly(glycidyl methacrylate)−Si(111) Hybrids from Surface-Initiated Atom-Transfer Radical Polymerization

A simple one-step procedure was employed for the covalent immobilization of an atom-transfer radical polymerization (ATRP) initiator, via the robust Si-C bond, on the hydrogen-terminated Si(111) surface (Si-H surface). Well-defined poly(glycidyl methacrylate) [P(GMA)] brushes, tethered directly on the (111)-oriented single-crystal silicon surface, were prepared via surface-initiated ATRP. Kinetics study on the surface-initiated ATRP of glycidyl methacrylate revealed that the chain growth from the silicon surface was consistent with a "controlled" process. A relatively high concentration of glucose oxidase (GOD; above 0.2 mg/cm2) could be coupled directly to the well-defined P(GMA) brushes via the ring-opening reaction of the epoxide groups with the amine moieties of the enzyme. The resultant GOD-functionalized P(GMA) brushes, with the accompanying hydroxyl groups from the ring-opening reaction of the epoxide groups, serves as an effective spacer to provide the GOD with a higher degree of conformational freedom and a more hydrophilic environment. An equivalent enzyme activity above 1.6 units/cm2 [micromoles of beta-D-(+)-glucose oxidized to d-gluconolactone per minute per square centimeter] and a corresponding relative activity of about 60% could be readily achieved. The immobilized GOD also exhibited an improved stability during storage over that of the free enzyme. The GOD-functionalized silicon substrates are potentially useful to the development of silicon-based glucose biosensors.

Controlled grafting of comb copolymer brushes on poly(tetrafluoroethylene) films by surface-initiated living radical polymerizations

Surface modification of poly(tetrafluoroethylene) (PTFE) films by well-defined comb copolymer brushes was carried out. Peroxide initiators were generated directly on the PTFE film surface via radio frequency Ar plasma pretreatment, followed by air exposure. Poly(glycidyl methacrylate) (PGMA) brushes were first prepared by surface-initiated reversible addition-fragmentation chain transfer polymerization from the peroxide initiators on the PTFE surface in the presence of a chain transfer agent. Kinetics study revealed a linear increase in the graft concentration of PGMA with the reaction time, indicating that the chain growth from the surface was consistent with a "controlled" or "living" process. alpha-Bromoester moieties were attached to the grafted PGMA by reaction of the epoxide groups with 2-bromo-2-methylpropionic acid. The comb copolymer brushes were subsequently prepared via surface-initiated atom transfer radical polymerization of two hydrophilic vinyl monomers, including poly(ethylene glycol) methyl ether methacrylate and sodium salt of 4-styrenesulfonic acid. The chemical composition of the modified PTFE surfaces was characterized by X-ray photoelectron spectroscopy.

Controlled release of heparin from polypyrrole-poly(vinyl alcohol) assembly by electrical stimulation

A surface modification technique was developed for the covalent immobilization of poly(vinyl alcohol) (PVA)-heparin hydrogel onto electrically conductive polypyrrole (PPY) film with the objective of achieving controlled release of heparin. First, aldehyde groups were introduced onto PPY film through poly(ethylene glycol) monomethacrylate graft copolymerization and subsequent oxidation in acetic anhydride and dimethyl sulfoxide mixture. Then, the prepared PVA-heparin hydrogel was cast onto the PPY film and covalently immobilized to the film through the reaction between the aldehyde groups on the PPY film and the hydroxyl groups of PVA. X-ray photoelectron spectroscopy was used to characterize the surface-modified film after each stage. The strong attachment of the PVA-heparin layer on the PPY film was confirmed by peel test and scanning electron microscopy. The release behavior of heparin from the substrate with and without electrical stimulation was studied and the experimental results showed that the heparin release rate from the prepared substrate using an electric current of 3.5 mA is twofold higher than that without current.

Antibacterial and antifungal efficacy of surface functionalized polymeric beads in repeated applications

A simple method was developed to prepare polymeric microbeads with antibacterial and antifungal properties. The microbeads of approximately spherical shape and narrow size distribution were prepared from a mixture of poly (4-vinyl pyridine) (P4VP) and poly (vinylidene fluoride) (PVDF) by a phase inversion technique and subsequently derivatized with alkyl bromides having 4-10 carbon atoms. The quaternization of the pyridine groups into pyridinium groups confers the surface with highly effective and long-lasting antibacterial and antifungal properties, as shown by the effect on Escherichia coli and Aspergillus niger. Upon contact with the N-alkylated beads, the bacteria and fungal spores are lysed and intracellular constituents leach out into the medium. The efficacy of the alkyl chains in disrupting the cell membrane was investigated. The stability of the functional group and microbiocidal effectiveness of the microbeads in repeated applications was also assessed.

Assessment of in Vitro Bioactivity of Hyaluronic Acid and Sulfated Hyaluronic Acid Functionalized Electroactive Polymer†

Electrically conductive polypyrrole (PPY) was surface functionalized with hyaluronic acid (HA) and sulfated hyaluronic acid (SHA) to improve its surface biocompatibility. The immobilization of HA on the PPY film was facilitated by the use of a cross-linker having the appropriate functional groups. The biological activity of the HA functionalized PPY film was assessed by means of an in vitro PC12 cell culture. The cell attachment on different substrates was studied and determined by bicinchoninic acid protein analysis. Cell attachment on the HA functionalized PPY film surface was significantly enhanced in the presence of nerve growth factor. The SHA functionalized PPY film was obtained by the sulfonation of the immobilized HA using pyridinesulfonate. The retention of the biological activity of the immobilized HA after sulfonation was evaluated by the in vitro assessment of the plasma recalcification time (PRT) and platelet adhesion on the substrate. The PRT observed from the SHA functionalized PPY film was significantly prolonged compared with the HA functionalized PPY. Some reduction of platelet adhesion was observed for the SHA functionalized PPY film, compared with that of the HA functionalized PPY film.

Functionalization of hydrogen-terminated silicon via surface-initiated atom-transfer radical polymerization and derivatization of the polymer brushes

Surface-initiated atom-transfer radical polymerization (ATRP) of poly(ethylene glycol) monomethacrylate (PEGMA) was carried out on the hydrogen-terminated Si(100) substrates with surface-tethered alpha-bromoester initiator. Kinetic studies confirmed an approximately linear increase in polymer film thickness with reaction time, indicating that chain growth from the surface was a controlled "living" process. The "living" character of the surface-grafted PEGMA chains was further ascertained by the subsequent extension of these graft chains, and thus the graft layer. Well-defined polymer brushes of near 100 nm in thickness were grafted on the Si(100) surface in 8 h under ambient temperature in an aqueous medium. The hydroxyl end groups of the poly(ethylene glycol) (PEG) side chains of the grafted PEGMA polymer were derivatized into various functional groups, including chloride, amine, aldehyde, and carboxylic acid groups. The surface-functionalized silicon substrates were characterized by reflectance FT-IR spectroscopy and X-ray photoelectron spectroscopy (XPS). Covalent attachment and derivatization of the well-defined PEGMA polymer brushes can broaden considerably the functionality of single-crystal silicon surfaces.

Metal ion reduction and resultant deposition on viologen-functionalized LDPE films and viologen-containing microporous membranes

Photo-induced reduction of gold and platinum metal salt solutions was carried out using viologen graft copolymerized on low-density polyethylene (LDPE) films and viologen-containing poly(vinylidene fluoride) (PVDF-PVBV) microporous membranes. The effects of the UV irradiation time and concentration of the metal salt solutions on the metal ion reduction process and the resultant metal deposition on the polymeric substrates were investigated. The metal-polymer composites were characterized using X-ray photoelectron spectroscopy (XPS), scanning and transmission electron microscopy (SEM and TEM), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and UV-visible absorption spectroscopy. The amount of metal uptake, the state of the metal, and the size of the metal particles were found to be strongly dependent on the UV irradiation time and the type and concentration of the metal salt solution. The microporous structure and the high viologen content of the PVDF-PVBV membrane constitute an effective matrix for metal ion reduction and preparation of metal nanoparticles.

Surface-Active and Stimuli-Responsive Polymer−Si(100) Hybrids from Surface-Initiated Atom Transfer Radical Polymerization for Control of Cell Adhesion

A simple two-step method was developed for the covalent immobilization of atom-transfer radical polymerization (ATRP) initiators on the hydrogen-terminated Si(100) (Si-H) surface. Well-defined functional polymer-Si hybrids, consisting of covalently tethered brushes of poly(ethylene glycol) monomethacrylate (PEGMA) polymer, N-isopropylacrylamide (NIPAAm) polymer, and NIPAAm-PEGMA copolymers and block copolymers on Si-H surfaces, were prepared via surface-initiated ATRP. Kinetics study revealed that the chain growth from the silicon surface was consistent with a "controlled" process. Surface cultures of the cell line 3T3-Swiss albino on the hybrids were evaluated. The PEGMA graft-polymerized silicon [Si-g-P(PEGMA)] surface is very effective in preventing cell attachment and growth. At 37 degrees C [above the lower critical solution temperature (LCST, approximately 32 degrees C) of NIPAAm], the seeded cells adhered, spread, and proliferated on the NIPAAm graft polymerized silicon [Si-g-P(NIPAAm)] surface. Below the LCST, the cells detached from the Si-g-P(NIPAAm) surface spontaneously. Incorporation of PEGMA units into the NIPAAm chains of the Si-g-P(NIPAAm) surface via copolymerization resulted in more rapid cell detachment during the temperature transition. The "active" chain ends on the Si-g-P(PEGMA) and Si-g-P(NIPAAm) hybrids were also used as the macroinitiators for the synthesis of diblock copolymer brushes. Thus, not only are the hybrids potentially useful as stimuli-responsive adhesion modifiers for cells in silicon-based biomedical microdevices but also the active chain ends on the hybrid surfaces offer opportunities for further surface functionalization and molecular design.

Controlled grafting of well-defined epoxide polymers on hydrogen-terminated silicon substrates by surface-initiated ATRP at ambient temperature

Controlled grafting of well-defined epoxide polymer brushes on the hydrogen-terminated Si(100) substrates (Si-H substrates) was carried out via the surface-initiated atom-transfer radical polymerization (ATRP) at room temperature. Thus, glycidyl methacrylate (GMA) polymer brushes were prepared by ATRP from the alpha-bromoester functionalized Si-H surface. Kinetic studies revealed a linear increase in GMA polymer (PGMA) film thickness with reaction time, indicating that chain growth from the surface was a controlled "living" process. The graft polymerization proceeded more rapidly in the dimethylformamide/water (DMF/H(2)O) mixed solvent medium than in DMF, leading to much thicker PGMA growth on the silicon surface in the former medium. The chemical composition of the GMA graft-polymerized silicon (Si-g-PGMA) surfaces were characterized by X-ray photoelectron spectroscopy (XPS). The fact that the epoxide functional groups of the grafted PGMA were preserved quantitatively was revealed in the reaction with ethylenediamine. The "living" character of the PGMA chain end was further ascertained by the subsequent growth of a poly(pentafluorostyrene) (PFS) block from the Si-g-PGMA surface, using the PGMA brushes as the macroinitiators.