Fabrication of scaffolds with suitable chemical, mechanical, and electrical properties is critical for the success of nerve tissue engineering. Electrical stimulation was directly applied to electrospun conductive nanofibrous scaffolds to enhance the nerve regeneration process. In the present study, electrospun conductive nanofibers were prepared by mixing 10 and 15 wt% doped polyaniline (PANI) with poly (epsilon-caprolactone)/gelatin (PG) (70:30) solution (PANI/PG) by electrospinning. The fiber diameter, pore size, hydrophilicity, tensile properties, conductivity, Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy spectra of nanofibers were determined, and the in vitro biodegradability of the different nanofibrous scaffolds was also evaluated. Nanofibrous scaffolds containing 15% PANI was found to exhibit the most balanced properties to meet all the required specifications for electrical stimulation for its enhanced conductivity and is used for in vitro culture and electrical stimulation of nerve stem cells. 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay and scanning electron microscopy results showed that conductive nanofibrous scaffolds are suitable substrates for the attachment and proliferation of nerve stem cells. Electrical stimulation through conductive nanofibrous PANI/PG scaffolds showed enhanced cell proliferation and neurite outgrowth compared to the PANI/PG scaffolds that were not subjected to electrical stimulation.

Electrical Stimulation of Nerve Cells Using Conductive Nanofibrous Scaffolds for Nerve Tissue Engineering

We propose a new type of ammonia sensor with polyaniline (electroconducting polymer) as the sensitive element. Such sensors are characterized by high sensitivity, wide range of measured concentrations (1–2000 ppm) and high stability of electrical parameters. The use of polyaniline ensures high chemical stability of the sensors in oxidizing ambients. A sensor design based on a silicon chip custom-packed into a linear plastic case is presented. The chip is provided with a system of heaters and thermometers to check the temperature regime of sensor operation. We have studied I – V curves, temperature, concentration and kinetic characteristics of the sensors, as well as their ageing. The possibility for thermoregeneration of the sensor parameters after long-term functioning in an ammonia ambient is emphasized.

Ammonia sensors based on sensitive polyaniline films

Hydrogen causes a reversible decrease in the resistance of a thin film of camphorsulfonic acid doped polyaniline nanofibers. For a 1% mixture of hydrogen in nitrogen, a 3% decrease in resistance is observed (DeltaR/R = -3%). The hydrogen response is completely suppressed in the presence of humidity. In contrast, oxygen does not inhibit the hydrogen response. A deuterium isotope effect on the sensor response is observed in which hydrogen gives a larger response than deuterium: (DeltaR/R)H/(DeltaR/R)D = 4.1 +/- 0.4. Mass sensors using nanofiber films on a quartz crystal microbalance also showed a comparable deuterium isotope effect: DeltamH/DeltamD = 2.3 +/- 0.2 or DeltanH/DeltanD = 4.6 +/- 0.4 on a molar basis. The resistance change of polyaniline nanofibers is about an order of magnitude greater than conventional polyaniline, consistent with a porous, high-surface-area nanofibrillar film structure that allows for better gas diffusion into the film. A plausible mechanism involves hydrogen bonding to the amine nitrogens along the polyaniline backbone and subsequent dissociation. The inhibitory effect of humidity is consistent with a stronger interaction of water with the polyaniline active sites that bind to hydrogen. These data clearly demonstrate a significant interaction of hydrogen with doped polyaniline and may be relevant to recent claims of hydrogen storage by polyaniline.

Hydrogen Sensors Based on Conductivity Changes in Polyaniline Nanofibers

A new material, polyethynylfluorenol (PEFl), has been prepared and characterized, either undoped or homogeneously doped with SnCl 2 . We have chosen as basic device for the sensor a simple humistor (humidity sensor resistor) since we have observed that the PEFl conductivity varies with the environmental relative humidity (r.h.). This behaviour is completely reversible without any noticeable 'memory effect'. PEFl can be considered a promising material for the fabrication of humidity sensors.

B.Z. Lubentsov

Papers

Conducting polymer interaction with gaseous substances II. PANI-H2O, PANI-NH3

The study of conducting polymer interaction with gaseous substances IV. The water content influence on polyaniline crystal structure and conductivity

Conducting polymer interaction with gaseous substances I. Water

Conductivity control as basis for chemical storage batteries and molecular electronics device production