On the design and development of foamed GO-hydrogel nanocomposite surfaces by ultra-short laser processing.

Graphene oxide (GO) and reduced graphene oxide have outstanding qualities that could be exploited as reinforcement and antibacterial agents in a plethora of biomedical applications. In this contribution, it is reported the deployment of a polyacrylamide GO-hydrogel composite (GO@pAAm) which was photo-converted and structured by ultra-short laser irradiation using a direct laser writing (DLW) approach. The materials were characterized by Fourier Transform Infrared spectroscopy, scanning electron microscopy and confocal microscopy. The laser structure generates a multi-photo-induced effect: surface foaming and patterning, microdomains with enhanced selective water-swelling and effective GO photo-reduction. A first laser scan seems likely to induce the photo-reduction of GO and subsequent laser pulses trigger the structure/foaming. The photo-reduction of GO is evidenced by Raman spectroscopy by the relatively changing intensities of the D to G signals. Macroscopically by an increase in conductivity (decrease in sheet resistance fromRS-GO@pAAm= 304 ± 20 kΩ sq-1toRS-rGO@pAAm-DLW= 27 ± 8 kΩ sq-1) suggesting a reduction of the material measured by 4-Point-Probe.

Mechanochemical Synthesis of Polyanilines and Their Nanocomposites: A Critical Review.

The mechanochemical synthesis of polyanilines (PANIs), made by oxidative polymerization of anilines, is reviewed. First, previous knowledge of the polymerization reaction in solution is discussed to understand the effect of different parameters: oxidant/monomer ratio, added acid, oxidant, temperature and water content on the properties of the conducting polymers (molecular weight, degradation, doping/oxidation level, conductivity, and nanostructure). The work on mechanochemical polymerization (MCP) of anilines is analyzed in view of previous data in solution, and published data are critically reconsidered to clarify the interpretation of experimental results. A key factor is the production of acids during polymerization, which is often overlooked. The production of gaseous HCl during MCP of aniline hydrochloride is experimentally observed. Since some experiments involves the addition of small amounts of water, the kinetics and heat balance of the reaction with concentrated solutions were simulated. A simple experiment shows fast (<2 min) heating of the reaction mixture to the boiling point of water and temperature increments are observed during MCP in a mortar. The form and sizes of PANI nanostructures made by MCP or solution are compared. The extensive work on the production of nanocomposites by MCP of anilines together with different nanomaterials (porous clays, graphene, carbon nanotubes, metal, and oxide nanoparticles) is also described.

Development of micropatterning polyimide films for enhanced antifouling and antibacterial properties.

A commercial biomedical Polyimide (PI) film was topographically and chemically modified by generating micrometric periodic arrays of lines using Direct Laser Interference Patterning (DLIP) in order to improve antifouling and antibacterial properties. DLIP patterning was performed with periods from 1 µm to 10 µm. The physical modification of the surface was characterized by SEM, AFM and contact angle measurements and, the chemical composition of the ablated surfaces was analyzed by ATR-IR and XPS spectroscopies. The antibacterial effects were evaluated through the effect on Pseudomonas aeruginosa colonies growth on the LB (Luria Bertani) broth. The results showed that the laser treatment change the topography and as a consequence the chemistry surface, also that the microstructured surfaces with periods below 2 µm, exhibited a significant bacterial (P. aeruginosa) adhesion decrease compared with non-structured surfaces or with surfaces with periods higher than 2 µm. The results suggest that periodic topography only confer antifouling properties and reduction of the biofilm formation when the microstructure presents periods ranging from 1 µm to 2 µm. On the other hand, the topography that confer strong antifouling superficial properties persists at long incubation times. In that way, polymer applications in the biosciences field can be improved by a surface topography modification using a simple, single-step laser-assisted ablation method.

Improving the retention and reusability of Alpha-amylase by immobilization in nanoporous polyacrylamide-graphene oxide nanocomposites.

Alpha-amylase was immobilized inside three different polymeric matrices: polyacrylamide hydrogel (PAAm), polyacrylamide-graphene oxide nanocomposite (PAAm-GO) and alginate in order to study and compare the effect of the matrix on the catalytic performance. The morphology, swelling, mechanical properties, retention efficiency, and the catalytic behavior of these newly supported biocatalysts were studied. Nanocomposite made of PAAm-GO matrix incorporated 98% of the enzyme, likely through a cooperative effect, while alginate gels incorporated only 30%. Moreover, the enzyme retention using PAAm-GO reached a value of 97.5%. Starch hydrolysis catalyzed by the immobilized enzyme in PAAm-GO matrix showed similar kinetics profiles up to 5 cycles suggesting that the enzymatic activity is retained. These results compare very favorably with conventional immobilization in alginate where almost no activity was observed after 3 cycles. All results suggest that the PAAm matrices protect the biocatalyst allowing its reusability. Moreover, the improvements in enzyme catalytic properties via immobilization made this system as an excellent candidate in bio-industrial applications such as bioethanol production. Furthermore, the synthesized catalyst could produce a high yield of bioethanol by using enzymes and yeast immobilized in the same PAAm matrix. In this way, it is possible to produce sequential or simultaneous saccharification and fermentation.

Nanocomposites based on pH-sensitive hydrogels and chitosan decorated carbon nanotubes with antibacterial properties.

The present work aimed to study the properties of a novel nanocomposite with promising biomedical applications. Nanocomposites were prepared by the addition of different concentrations of chitosan decorated carbon nanotubes to acrylamide-co-acrylic acid hydrogels. The nanocomposites chemical structure was characterized by Fourier Transform Infrared Spectroscopy (FT-IR). The FT-IR shows the typical bands due to the hydrogel and additionally the peaks at 1750 cm-1 and 1450 cm-1 that correspond to the carbon nanotubes incorporated into the polymer matrix. Mechanical properties and swelling measurements in different buffer solutions were also performed. The nanocomposites showed improved mechanical properties and a stronger pH-response. In order to evaluate antimicrobial activity, the growth and adhesion of Staphylococcus aureus to nanocomposites were studied. Cytocompatibility was also evaluated by MTT assay on MDCK and 3T3 cell lines. The nanocomposites were found to be cytocompatible and showed a reduced bacterial colonization.

Bioethanol production by reusable Saccharomyces cerevisiae immobilized in a macroporous monolithic hydrogel matrices.

Performance of yeasts on industrial processes can be dramatically improved by immobilization of the biocatalyst. The immobilization of Saccharomyces cerevisiae inside monolithic macroporous hydrogels were produced by in-situ polymerization of acrylamide around a live yeast suspension under cryogelation conditions. Preculture of the yeasts was not necessary and this innovative and simple procedure is amenable to scaling-up to industrial production. The yeasts were efficiently retained in monolithic hydrogels, presenting excellent mechanical properties and high cell viability. Macroporous hydrogels showed a fast mass transport allowing the hydrogel-yeast complexes achieved similar ethanol yield and productivity than free yeasts, which is larger than those reached with yeasts immobilized in compact hydrogels. Moreover, the same yeasts were able to maintain its activity by up to five reaction cycles with a cell single batch during fermentation reactions.

IgY against enterotoxigenic Escherichia coli administered by hydrogel-carbon nanotubes composites to prevent neonatal diarrhoea in experimentally challenged piglets.

In previous studies, the applicability of polymeric hydrogels for the protection of egg yolk immunoglobulin (IgY) against simulated gastric conditions was established. Thereafter, the performance of the hydrogels was improved with the addition of chitosan wrapped carbon nanotubes and the in vitro toxicity for porcine intestinal cells of these nanocomposites was assessed. The objective of the present study was to evaluate in vivo the protective efficacy of the nanocomoposite matrix for IgY when the immunoglobulin is used against enterotoxigenic Escherichia coli (ETEC) in challenged piglets. Groups of piglets orally challenged with 10(11)CFU/mL of ETEC were treated with non-protected and protected IgY. The clinical response of each group was monitored and evaluated in terms of dehydration, rectal temperature, faecal consistency score and body weight gain. Blood parameters and histological aspects were also studied. The results showed that treatment of infected piglets with protected IgY reduced significantly the severity of diarrhea. Non-protected IgY group show a lower recovery rate. Blood parameters and histological aspects were normal in both groups. Collectively, these results support previous in vitro studies showing that the nanocomposites can be an effective method of IgY protection against gastric inactivation.

Cysteine modified polyaniline films improve biocompatibility for two cell lines.

This work focuses on one of the most exciting application areas of conjugated conducting polymers, which is cell culture and tissue engineering. To improve the biocompatibility of conducting polymers we present an easy method that involves the modification of the polymer backbone using l-cysteine. In this publication, we show the synthesis of polyaniline (PANI) films supported onto Polyethylene terephthalate (PET) films, and modified using cysteine (PANI-Cys) in order to generate a biocompatible substrate for cell culture. The PANI-Cys films are characterized by Fourier Transform infrared and UV-visible spectroscopy. The changes in the hydrophilicity of the polymer films after and before the modification were tested using contact angle measurements. After modification the contact angle changes from 86°±1 to 90°±1, suggesting a more hydrophylic surface. The adhesion properties of LM2 and HaCaT cell lines on the surface of PANI-Cys films in comparison with tissue culture plastic (TCP) are studied. The PANI-Cys film shows better biocompatibility than PANI film for both cell lines. The cell morphologies on the TCP and PANI-Cys film were examined by florescence and Atomic Force Microscopy (AFM). Microscopic observations show normal cellular behavior when PANI-Cys is used as a substrate of both cell lines (HaCaT and LM2) as when they are cultured on TCP. The ability of these PANI-Cys films to support cell attachment and growth indicates their potential use as biocompatible surfaces and in tissue engineering.

A direct and quantitative three-dimensional reconstruction of the internal structure of disordered mesoporous carbon with tailored pore size.

A new technique that allows direct three-dimensional (3D) investigations of mesopores in carbon materials and quantitative characterization of their physical properties is reported. Focused ion beam nanotomography (FIB-nt) is performed by a serial sectioning procedure with a dual beam FIB-scanning electron microscopy instrument. Mesoporous carbons (MPCs) with tailored mesopore size are produced by carbonization of resorcinol-formaldehyde gels in the presence of a cationic surfactant as a pore stabilizer. A visual 3D morphology representation of disordered porous carbon is shown. Pore size distribution of MPCs is determined by the FIB-nt technique and nitrogen sorption isotherm methods to compare both results. The obtained MPCs exhibit pore sizes of 4.7, 7.2, and 18.3 nm, and a specific surface area of ca. 560 m(2)/g.

Electroanalysis using modified hierarchical nanoporous carbon materials.

The role of the electrode nanoporosity in electroanalytical processes is discussed and specific phenomena (slow double layer charging, local pH effects) which can be present in porous electrode are described. Hierarchical porous carbon (HPC) materials are synthesized using a hard template method. The three dimensional carbon porosity is examined using scanning electron microscopy on flat surfaces cut using a focused ion beam (FIB-SEM). The electrochemical properties of the HPC are measured using cyclic voltammetry, AC impedance, chronoamperometry and Probe Beam Deflection (PBD) techniques. Chronoamperometry measurements of HPC seems to fit a transmission line model. PBD data show evidence of local pH changes inside the pores, during double layer charging. The HPC are modified by in situ (chemical or electrochemical) formation of metal (Pt/Ru) or metal oxide (CoOx, Fe3O4) nanoparticles. Additionally, HPC loaded with Pt decorated magnetite (Fe3O4) nanoparticles is produced by galvanic displacement. The modified HPC materials are used for the electroanalysis of different substances (CO, O2, AsO3(-3)). The role of the nanoporous carbon substrate in the electroanalytical data is evaluated.

Easy way to fabricate nanostructures on a reactive polymer surface.

The fabrication of advanced architectures in poly(glycidylmethacrylate-co-styrene) (PGMA-S) copolymers using direct laser interference patterning (DLIP) and its selective functionalization is reported. The structure features depend mainly on the laser energy used and on the styrene content in the copolymer. The topography, measured by electronic scanning microscopy, show regular and ordered arrays for the polystyrene (PS) and for the copolymers PGMA-S. The surface PS homopolymer is ablated at the position of maximum light fluence (constructive interference), while in the copolymers the surfaces swell up at the regions with maximal fluence. The styrene units are shown to absorb the laser energy giving photothermally ablated regions or promoting the chemical decomposition of acrylate units or polymer segments. In that way, DLIP provides a unique way to produce regularly ordered structures protruding or depressing from the polymer surface without altering to a large extent the chemical nature of the material. In addition, it is shown, using fluorescence microscopy, that amine-polyethylenglycol-CdSe quantum dots (NH(2)-PEG-QDs) could be spatially localized by reaction with patterned surfaces of PGMA-S. In that way, it is proven that a patterned and chemically reactive surface can be created using DLIP of PGMA-S.

Large area fabrication of tuned polystyrene/poly(methylmethacrylate) periodic structures using laser interference patterning.

The fabrication of advanced architectures in poly(methylmethacrylate-co-styrene) (PMMA-S) copolymers (ranging from 12 to 66% mol content of methylmethacrylate) using direct laser interference patterning is reported. For all copolymer compositions, two different regimes were observed. At low laser intensities, the irradiated surfaces swell up due to the formation of microbubbles that result from the degradation of the methylmetacrylate (MMA) component. While laser ablation produces concave holes, the swelling process permits fabrication of convex hemispherical dots. At higher intensities the bubbles release from the surface forming a periodic micropored structure. In addition, the laser fluence necessary to swell the polymeric surface (swelling threshold) does not depend on polymer composition, while the ablation threshold, which determines the transition to the periodic micropored structure, strongly depends on the MMA content. This observation can be explained by the mechanical and chemical properties of the copolymer. The method provides a unique way to produce periodical structures protruding from the polymer surface.

Fabrication of highly ordered arrays of platinum nanoparticles using direct laser interference patterning.

Highly ordered electrode arrays composed of lines of platinum nanoparticles deposited onto gold substrates have been made by direct laser interference patterning of polyaniline thin films, followed by electrochemical deposition of platinum nanoparticles. Nanostructured arrays of electrocatalytic platinum particles are built in that way.

Influence of conducting polymers based on carboxylated polyaniline on in vitro CaCO3 crystallization.

Conducting polymers are interesting materials of technological applications, while the use of polymers as additives controlling crystal nucleation and growth is a fast growing research field. In the present article, we make a first step in combining both topics and report the effect of conducting polymer derivatives, which are based on carboxylated polyanilines (c-PANIs), on in vitro CaCO3 crystallization by the Kitano and gas diffusion method. This is the first example of the mineralization control of CaCO3 by a rigid carboxylated polymer. Both the concentration of c-PANI and the presence of carboxylate groups have a strong influence on the CaCO3 crystallization behavior and crystal morphology. X-ray diffraction (XRD) analysis shows crystalline calcite particles confirmed by FTIR spectra. pH and Ca2+ measurements during CaCO3 crystallization utilizing the Kitano and a constant-pH approach show a defined nucleation period of CaCO3 particles. The measurements allow for the calculation of the supersaturation time development, and the kinetic data can be combined with time-dependent light microscopy. The presence of c-PANIs delays the time of nucleation indicative of calcite nucleation inhibition. Microscopy illustrates the morphologies of CaCO3 crystals at all crystallization stages, from homogeneous spherical amorphous CaCO3 (ACC) particles corresponding to the first steps of crystallization to transition stage calcite crystals also involving a dissolution-recrystallization process in a late stage of crystallization. The data show that it is not possible to conclude the crystallization mechanism even for a very simple additive controlled crystallization process without time-resolved microscopic data supplemented by the analysis of the species present in the solution. Finally, fluorescence analysis indicates that conducting polymer derivatives can be incorporated into precipitated calcite particles. This gives rise to CaCO3 particles with novel and interesting optical properties.

Functionalised conjugated materials as building blocks of electronic nanostructures.

Two different approaches towards conjugated material (carbon nanotubes, conjugated polymers) functionalisation are presented: covalent bonding of functional groups and covalent interaction with soluble polymers. Covalent functionalisation of carbon nanotubes is made by reaction of the aromatic ring with aryl radicals, produced by reduction of diazonium ions. In the case of conducting polymers, covalent functionalisation is brought about by reaction of polyanilines with diazotized aromatic amines (including amino terminated azo dyes). The non covalent functionalisation of carbon nanotubes is made by wrapping the nanotubes with soluble conducting polyanilines. The functionalised materials are characterised by FTIR spectroscopy, X-ray diffraction, dynamic light scattering, ultraviolet-visible absorption and emission spectroscopy, transmission electron microscopy, cyclic voltammetry, differential electrochemical mass spectroscopy and conductivity measurements. The materials are to build ionic self assembled multilayers using a layer-by-layer deposition process. The charge transport and electrocatalytic behaviour of the assemblies, relevant to the application of the assemblies in nanostructured electrochemical biosensors, are evaluated using different redox molecules and/or its intrinsic electroactivity as probes.