Mg2+/Na+-doped rutile TiO2 nanofiber mats for high-speed and anti-fogged humidity sensors.

Mg(2+) and Na(+) doped rutile TiO2 nanofibers have been prepared through in situ electrospinning technique and calcination with poly(vinyl pyrrolidone) (PVP) nanofibers as sacrificed template. The as-prepared composite nanofibers are spin-coated onto a ceramic substrate with three pairs of carbon interdigital electrodes to measure its humidity sensing behaviors. The product exhibits high-speed response (2s) and recovery (1s) for detecting moisture. Additionally, under UV irradiation, a water contact angle (theta) of nearly 0 degrees has been observed based on the product, providing our humidity sensor with the anti-fogged properties.

Synthesis of nanoparticles and nanofibers of polyaniline by potentiodynamic electrochemical polymerization.

Potentiodynamic electrochemical synthesis was used to controllably synthesize nanofibers (mean diameter 48 nm) and/or nanoparticles (mean diameter 88 nm) of polyaniline (PANI) on gold electrodes. The films were characterized by cyclic voltammetry (CV), field emission gun scanning electron microscopy (FEG-SEM) and atomic force microscopy (AFM). The type and dimensions of the nanostructures depend on deposition conditions such as monomer concentration and scan rate. This study shows that the nucleation and growth steps play a key role on the film development and its nano-morphology.

Flexible thin films of single-walled carbon nanotubes deposited on plastic substrates.

In the present study, an experimental procedure used to produce thin films of single-walled carbon nanotubes is described. The method was used to prepare solid-state thin films of single walled carbon nanotubes (SWNTs) for various types of studies, such as scanning electron microscopy (SEM) and electrical resistance characterization. In particular, a series of experiments were carried out and, for the first time, a simple and reliable method for removing surfactant (Triton X-100) was described. The scanning electron microscopy studies showed that the SWNTs were shortened after the sonication process used to prepare the SWNT aqueous dispersion in the presence of Triton X-100.

Highly sensitive and stable humidity nanosensors based on LiCl doped TiO2 electrospun nanofibers.

A new type of humidity nanosensor based on LiCl-doped TiO2 nanofibers with poly(vinyl pyrrolidone) (PVP) nanofibers as sacrificial template has been fabricated through electrospinning and calcination. The sensor exhibited excellent sensing characteristics, such as ultrafast response and recovery times, good reproducibility, linearity, and environmental stability, which are of importance for applications in humidity monitoring and control.

Electroactive oligoaniline-containing self-assembled monolayers for tissue engineering applications.

A novel electroactive silsesquioxane precursor, N-(4-aminophenyl)-N'-(4'-(3-triethoxysilyl-propyl-ureido) phenyl-1,4-quinonenediimine) (ATQD), was successfully synthesized from the emeraldine form of amino-capped aniline trimers via a one-step coupling reaction and subsequent purification by column chromatography. The physicochemical properties of ATQD were characterized using mass spectrometry as well as by nuclear magnetic resonance and UV-vis spectroscopy. Analysis by cyclic voltammetry confirmed that the intrinsic electroactivity of ATQD was maintained upon protonic acid doping, exhibiting two distinct reversible oxidative states, similar to polyaniline. The aromatic amine terminals of self-assembled monolayers (SAMs) of ATQD on glass substrates were covalently modified with an adhesive oligopeptide, cyclic Arg-Gly-Asp (RGD) (ATQD-RGD). The mean height of the monolayer coating on the surfaces was approximately 3 nm, as measured by atomic force microscopy. The biocompatibility of the novel electroactive substrates was evaluated using PC12 pheochromocytoma cells, an established cell line of neural origin. The bioactive, derivatized electroactive scaffold material, ATQD-RGD, supported PC12 cell adhesion and proliferation, similar to control tissue-culture-treated polystyrene surfaces. Importantly, electroactive surfaces stimulated spontaneous neuritogenesis in PC12 cells, in the absence of neurotrophic growth factors, such as nerve growth factor (NGF). As expected, NGF significantly enhanced neurite extension on both control and electroactive surfaces. Taken together, our results suggest that the newly electroactive SAMs grafted with bioactive peptides, such as RGD, could be promising biomaterials for tissue engineering.

Synthesis and characterization of electroactive and biodegradable ABA block copolymer of polylactide and aniline pentamer.

A triblock copolymer PLA-b-AP-b-PLA (PAP) of polylactide (PLA) and aniline pentamer (AP) with the unique properties of being both electroactive and biodegradable is synthesized by coupling an electroactive carboxyl-capped AP with two biodegradable bi-hydroxyl-capped PLAs via a condensation reaction. Three different molecule weight PAP copolymers are prepared. The PAP copolymers exhibit excellent electroactivity similar to the AP and polyaniline, which may stimulate cell proliferation and differentiation. The electrical conductivity of the PAP2 copolymer film ( approximately 5x10(-6)S/cm) is in the semiconducting region. Transmission electron microscopic results suggest that there is microphase separation of the two block segments in the copolymer, which might contribute to the observed conductivity. The biodegradation and biocompatibility experiments in vitro prove the copolymer is biodegradable and biocompatible. Moreover, these new block copolymer shows good solubility in common organic solvents, leading to the system with excellent processibility. These biodegradable PAP copolymers with electroactive function thus possess the properties that would be potentially used as scaffold materials for neuronal or cardiovascular tissue engineering.

Fuel-powered artificial muscles.

Artificial muscles and electric motors found in autonomous robots and prosthetic limbs are typically battery-powered, which severely restricts the duration of their performance and can necessitate long inactivity during battery recharge. To help solve these problems, we demonstrated two types of artificial muscles that convert the chemical energy of high-energy-density fuels to mechanical energy. The first type stores electrical charge and uses changes in stored charge for mechanical actuation. In contrast with electrically powered electrochemical muscles, only half of the actuator cycle is electrochemical. The second type of fuel-powered muscle provides a demonstrated actuator stroke and power density comparable to those of natural skeletal muscle and generated stresses that are over a hundred times higher.

Polyaniline, an electroactive polymer, supports adhesion and proliferation of cardiac myoblasts.

Conductive polymers, such as polypyrrole, have recently been studied as potential surfaces/matrices for cell- and tissue-culture applications. We have investigated the adhesion and proliferation properties of H9c2 cardiac myoblasts on a conductive polyaniline substrate. Both the non-conductive emeraldine base (PANi) and its conductive salt (E-PANi) forms of polyaniline were found to be biocompatible, viz., allowing for cell attachment and proliferation and, in the case of E-PANi, maintaining electrical conductivity. By comparison to tissue-culture-treated polystyrene (TCP), the initial adhesion of H9c2 cells to both PANi and E-PANi was slightly reduced by 7% (P < 0.05, n = 18). By contrast, the overall rate of cell proliferation on the conductive surfaces, although initially decreased, was similar to control TCP surfaces. After 6 days in culture on the different surfaces, the cells formed confluent monolayers which were morphologically indistinguishable. Furthermore, we observed that E-PANi, when maintained in an aqueous physiologic environment, retained a significant level of electrical conductivity for at least 100 h, even though this conductivity gradually decreased by about 3 orders of magnitude over time. These results demonstrate the potential for using polyaniline as an electroactive polymer in the culture of excitable cells and open the possibility of using this material as an electroactive scaffold for cardiac and/or neuronal tissue engineering applications that require biocompatibility of conductive polymers.

Electrospinning polyaniline-contained gelatin nanofibers for tissue engineering applications.

Polyaniline (PANi), a conductive polymer, was blended with a natural protein, gelatin, and co-electrospun into nanofibers to investigate the potential application of such a blend as conductive scaffold for tissue engineering purposes. Electrospun PANi-contained gelatin fibers were characterized using scanning electron microscopy (SEM), electrical conductivity measurement, mechanical tensile testing, and differential scanning calorimetry (DSC). SEM analysis of the blend fibers containing less than 3% PANi in total weight, revealed uniform fibers with no evidence for phase segregation, as also confirmed by DSC. Our data indicate that with increasing the amount of PANi (from 0 to approximately 5%w/w), the average fiber size was reduced from 803+/-121 nm to 61+/-13 nm (p<0.01) and the tensile modulus increased from 499+/-207 MPa to 1384+/-105 MPa (p<0.05). The results of the DSC study further strengthen our notion that the doping of gelatin with a few % PANi leads to an alteration of the physicochemical properties of gelatin. To test the usefulness of PANi-gelatin blends as a fibrous matrix for supporting cell growth, H9c2 rat cardiac myoblast cells were cultured on fiber-coated glass cover slips. Cell cultures were evaluated in terms of cell proliferation and morphology. Our results indicate that all PANi-gelatin blend fibers supported H9c2 cell attachment and proliferation to a similar degree as the control tissue culture-treated plastic (TCP) and smooth glass substrates. Depending on the concentrations of PANi, the cells initially displayed different morphologies on the fibrous substrates, but after 1 week all cultures reached confluence of similar densities and morphology. Taken together these results suggest that PANi-gelatin blend nanofibers might provide a novel conductive material well suited as biocompatible scaffolds for tissue engineering.

[Research progresses on electroactive and electrically conductive polymers for tissue engineering scaffolds].

Electroactive and/or electrically conductive polymers have shown potential applications in the culture of excitable cells and as the electroactive scaffolds for neuronal or cardiac tissue engineering. The biocompatibility of the conductive polymer can be improved by covalently grafting or blending with oligo- or polypeptides. The new progresses in this area on two types of conductive polymers, polypyrrole and polyaniline (PANi) are reviewed in this paper. The studies of oligopeptide-modified PANi and electrospun PANi/gelatin nanofibers are highlighted.

Absolute molecular weight of polyaniline.

The absolute molecular weight of polyaniline in the pernigraniline, emeraldine, and leucoemeraldine oxidation states has been measured by light scattering and the exact number of aniline repeat units determined for the first time. Using potential-time profiling to monitor the chemical oxidative polymerization of aniline using ammonium peroxydisulfate oxidant, all three oxidation states of polyaniline can be synthesized in one step and the evolution of polymer molecular weight monitored. The pernigraniline intermediate formed during the chemical oxidative polymerization of aniline increases by 17-20% when it is converted to emeraldine, which is consistent with a two-step polymerization mechanism. These findings establish a solid experimental framework to chemically synthesize block copolymers of polyaniline by using different monomers to intercept the reaction at the pernigraniline oxidation state.

Chemical synthesis of PEDOT nanofibers.

A one-step, room-temperature method is described to chemically synthesize bulk quantities of microns long, 100-180 nm diameter nanofibers of electrically conducting poly(3,4-ethylenedioxythiophene)(PEDOT) in the form of powders, or as optically transparent, substrate-supported films using a V2O5 seeding approach.

"Synthetic Metals": A Novel Role for Organic Polymers (Nobel Lecture) Copyright((c)) The Nobel Foundation 2001. We thank the Nobel Foundation, Stockholm, for permission to print this lecture.

Since the initial discovery in 1977, that polyacetylene (CH)(x), now commonly known as the prototype conducting polymer, could be p- or n-doped either chemically or electrochemically to the metallic state, the development of the field of conducting polymers has continued to accelerate at an unexpectedly rapid rate and a variety of other conducting polymers and their derivatives have been discovered. Other types of doping are also possible, such as "photo-doping" and "charge-injection doping" in which no counter dopant ion is involved. One exciting challenge is the development of low-cost disposable plastic/paper electronic devices. Conventional inorganic conductors, such as metals, and semiconductors, such as silicon, commonly require multiple etching and lithographic steps in fabricating them for use in electronic devices. The number of processing and etching steps involved limits the minimum price. On the other hand, conducting polymers combine many advantages of plastics, for example, flexibility and processing from solution, with the additional advantage of conductivity in the metallic or semiconducting regimes; however, the lack of simple methods to obtain inexpensive conductive polymer shapes/patterns limit many applications. Herein is described a novel, simple, and cheap method to prepare patterns of conducting polymers by a process which we term, "Line Patterning".

"Synthetic Metals": A Novel Role for Organic Polymers (Nobel Lecture).

Since the initial discovery in 1977, that polyacetylene (CH)x , now commonly known as the prototype conducting polymer, could be p- or n-doped either chemically or electrochemically to the metallic state, the development of the field of conducting polymers has continued to accelerate at an unexpectedly rapid rate and a variety of other conducting polymers and their derivatives have been discovered. Other types of doping are also possible, such as "photo-doping" and "charge-injection doping" in which no counter dopant ion is involved. One exciting challenge is the development of low-cost disposable plastic/paper electronic devices. Conventional inorganic conductors, such as metals, and semiconductors, such as silicon, commonly require multiple etching and lithographic steps in fabricating them for use in electronic devices. The number of processing and etching steps involved limits the minimum price. On the other hand, conducting polymers combine many advantages of plastics, for example, flexibility and processing from solution, with the additional advantage of conductivity in the metallic or semiconducting regimes; however, the lack of simple methods to obtain inexpensive conductive polymer shapes/patterns limit many applications. Herein is described a novel, simple, and cheap method to prepare patterns of conducting polymers by a process which we term, "Line Patterning".