Isabelle Royaud

Electrodeposition of a biopolymeric hydrogel: potential for one-step protein electroaddressing.

The electrodeposition of hydrogels provides a programmable means to assemble soft matter for various technological applications. We report an anodic method to deposit hydrogel films of the aminopolysaccharide chitosan. Evidence suggests the deposition mechanism involves the electrolysis of chloride to generate reactive chlorine species (e.g., HOCl) that partially oxidize chitosan to generate aldehydes that can couple covalently with amines (presumably through Schiff base linkages). Chitosans anodic deposition is controllable spatially and temporally. Consistent with a covalent cross-linking mechanism, the deposited chitosan undergoes repeated swelling/deswelling in response to pH changes. Consistent with a covalent conjugation mechanism, proteins could be codeposited and retained within the chitosan film even after detergent washing. As a proof-of-concept, we electroaddressed glucose oxidase to a side-wall electrode of a microfabricated fluidic channel and demonstrated this enzyme could perform electrochemical biosensing functions. Thus, anodic chitosan deposition provides a reagentless, single-step method to electroaddress a stimuli-responsive and biofunctionalized hydrogel film.

Tuning the Hydrophilic/Hydrophobic Balance to Control the Structure of Chitosan Films and Their Protein Release Behavior

The control over the crystallinity of chitosan and chitosan/ovalbumin films can be achieved via an appropriate balance of the hydrophilic/hydrophobic interactions during the film formation process, which then controls the release kinetics of ovalbumin. Chitosan films were prepared by solvent casting. The presence of the anhydrous allomorph can be viewed as a probe of the hydrophobic conditions at the neutralization step. The semicrystalline structure, the swelling behavior of the films, the protein/chitosan interactions, and the release behavior of the films were impacted by the DA and the film processing parameters. At low DAs, the chitosan films neutralized in the solid state corresponded to the most hydrophobic environment, inducing the crystallization of the anhydrous allomorph with and without protein. The most hydrophilic conditions, leading to the hydrated allomorph, corresponded to non-neutralized films for the highest DAs. For the non-neutralized chitosan acetate (amorphous) films, the swelling increased when the DA decreased, whereas for the neutralized chitosan films, the swelling decreased. The in vitro release of ovalbumin (model protein) from chitosan films was controlled by their swelling behavior. For fast swelling films (DA = 45%), a burst effect was observed. On the contrary, a lag time was evidenced for DA = 2.5% with a limited release of the protein. Furthermore, by blending chitosans (DA = 2.5% and 45%), the release behavior was improved by reducing the burst effect and the lag time. The secondary structure of ovalbumin was partially maintained in the solid state, and the ovalbumin was released under its native form.

Dielectric and physicochemical behavior of aged PVC insulated cables

Radial field, medium voltage cables operated at 6.6 kV are the object of this study. Dielectric properties of those aged PVC insulated cables have been measured as a function of temperature and voltage in a frequency range of 1 mHz to 1 kHz. The range of temperature tested was between 30°C to 110°. The dielectric material shows a resistive behavior at low frequency. Deduced conductivities are in good agreement with DC conductivities measured at the considered temperatures. The conductivity follows an Arrhenius law over the range studied with an activation energy of 0.96 eV. The conductivity of some sample is high enough to induce an increase of the losses at industrial frequency. The increase of the low frequency capacity is revealing an interfacial polarization. This increase of capacity is due to local accumulation of electric charges in the insulation, particularly at the electrodes. Physicochemical characterizations have been done to understand this decrease of resistivity. A migration of plasticizers did not occur as evidenced by IR micro-spectroscopy. Therefore, the decrease of resistance cannot be attributed to such mechanism. Physical aging is evidenced by DSC, which leads to the working temperature of the cables. TMA has shown modifications of thermo-mechanical properties along aging. These evolutions are attributed to the formation of double bonds resulting from dehydrochlorination.