Synthesis and characterization of bioactive molecules grafted on poly(?-caprolactone) by “click” chemistry

A facile and efficient strategy to graft bioactive molecules (nicotinic acid, p-aminobenzoic acid, and phthaloyltryptophan) onto poly(?-caprolactone) (P(?CL)) was achieved by copper-catalyzed Huisgen’s 1,3-dipolar cycloaddition known as click reaction. P(αCl?CL), with 10, 20, and 30% of α-chloro-?-caprolactone (αCl?CL) units were copolymerized by ring opening polymerization using ?CL and αCl?CL as starting materials in the presence of 1,4-butanediol and Sn(Oct)₂. Subsequently, the chloride pendent was converted to azide followed by cycloaddition with terminal alkyne derivatives of the aforementioned bioactive molecules. The complete addition was accomplished at all ratios. The characteristic molecular features of these copolymers were evaluated by FTIR, NMR, and GPC. Thermal analysis data indicated that the grafted compounds led to polymorphic alteration and different pattern of thermal degradation depending on the molecular structure and the size of the grafted compounds. They are the basis for further development of grafted copolymer as drug delivery carriers.     

Electrical,rheological and electromagnetic interference shielding properties of thermoplastic polyurethane/carbon nanotube composites

Electrically conducting rubbery composites based on thermoplastic polyurethane (TPU) and carbon nanotubes (CNTs) were prepared through melt blending using a torque rheometer equipped with a mixing chamber. The electrical conductivity, morphology, rheological properties and electromagnetic interference shielding effectiveness (EMI SE) of the TPU/CNT composites were evaluated and also compared with those of carbon black (CB)‐filled TPU composites prepared under the same processing conditions. For both polymer systems, the insulator–conductor transition was very sharp and the electrical percolation threshold at room temperature was at CNT and CB contents of about 1.0 and 1.7 wt%, respectively. The EMI SE over the X‐band frequency range (8–12 GHz) for TPU/CNT and TPU/CB composites was investigated as a function of filler content. EMI SE and electrical conductivity increased with increasing amount of conductive filler, due to the formation of conductive pathways in the TPU matrix. TPU/CNT composites displayed higher electrical conductivity and EMI SE than TPU/CB composites with similar conductive filler content. EMI SE values found for TPU/CNT and TPU/CB composites containing 10 and 15 wt% conductive fillers, respectively, were in the range ?22 to ?20 dB, indicating that these composites are promising candidates for shielding applications. © 2013 Society of Chemical Industry     

Electrical and rheological percolation in poly(vinylidene fluoride)/multi‐walled carbon nanotube nanocomposites

Nanocomposites of poly(vinylidene fluoride) (PVDF) and multi‐walled carbon nanotubes (MWCNTs) were prepared through melt blending in a batch mixer (torque rheometer equipped with a mixing chamber). The morphology, rheological behavior and electrical conductivity were investigated through transmission electron microscopy, dynamic oscillatory rheometry and the two‐probe method. The nanocomposite with 0.5 wt% MWCNT content presented a uniform dispersion through the PVDF matrix, whereas that with 1 wt% started to present a percolated network. For the nanocomposites with 2 and 5 wt% MWCNTs the formation of this nanotube network was clearly evident. The electrical percolation threshold at room temperature found for this system was about 1.2 wt% MWCNTs. The rheological percolation threshold fitted from viscosity was about 1 wt%, while the threshold fitted from storage modulus was 0.9 wt%. Thus fewer nanotubes are needed to approach the rheological percolation threshold than the electrical percolation threshold. Copyright © 2010 Society of Chemical Industry     

The control mechanisms of the electrokinetic properties of human erythrocytes in emotional stress

A study was made of the influence of psycho-emotional strain, experienced by students when taking examinations, on the erythrocyte electrophoretic mobility (EPM). It has been shown that students under psycho-emotional strain the mean value of EPM remains the same, but changes were observed in the form of EPM distribution, while estimated by asymmetry and excession coefficients. Similar results were obtained when adrenalin was added to the blood.     

Behavioral auditory thresholds for sinusoidal electrical stimuli in the cat

Behavioral thresholds were measured in four cats by training them to respond behaviorally to acoustic auditory stimuli using food as a reward in an operant reinforcement paradigm. Following training, the subjects were implanted unilaterally with either a scaled-UCSF electrode containing four contacts or an electrode array containing eight intracochlear contacts and one extracochlear contact under temporalis muscle. Behavioral thresholds for electrical stimuli were obtained as a function of sinusoidal frequency, duration, and electrode configuration. Threshold functions for both electrode types and all animals had minima between 48 and 125 Hz and, in general, were relatively flat below this minima; functions increased at 3-6 dB/octave from 96 Hz to 1 kHz. Threshold varied predictably as a function of electrode configuration, with thresholds decreasing as much as 20 dB as electrode spacing was widened from a radial bipolar (200-microns separation) to a monopolar configuration (apical stimulating and temporalis return). With long-duration stimuli, increasing the electrode separation systematically increased the slope of the threshold-versus-frequency contours in all animals. Irrespective of electrode type or configuration, charge/phase thresholds for single-cycle sinusoids were relatively flat for stimulus periods up to 1-5 ms, approximating a constant charge/phase determination of threshold. At phase durations greater than 5 ms, charge thresholds increased at a rate slightly above 6 dB/octave (constant peak current), which was suggestive of neural accommodation. Thresholds for the cat share many features with those reported for implanted humans and monkeys.