Biodegradable,implantable sustained release systems based on glutamic acid copolymers

Polymer pellets that contain drugs and may be implanted under the skin offer effective means for providing sustained, controlled drug therapy to humans and animals. Among the most useful drug delivery systems are those based on biodegradable polymers that ultimately are absorbed by the body — eliminating the need for their surgical removal. Copolymers of L-glutamic acid and γ-ethyl L-glutamate biodegrade to L-glutamic acid and ethanol, at rates that are determined by the initial copolymer composition. The materials are permeable to a wide range of drugs, including steroids, narcotic antagonists, peptide hormones, antimalarials, and anticancer agents. When fabricated into matrix rods or capsules, the copolymers have been used to release drugs in animals at constant rates for prolonged periods of time. p]In this study, rods composed of a blend of drug and copolymer were found to be useful for the long-term release (i.e., 6 to 24 months) of drugs having low aqueous solubility, such as progesterone and levonorgestrel. Capsules, composed of a copolymer sheath surrounding the drug, were better suited for shorter durations of release (i.e., up to 6 months) of drugs having higher aqueous solubility, such as luteinizing hormone-releasing hormone and naltrexone. The physical dimensions and copolymer compositions of either dosage form were readily varied to meet specific delivery rate and duration objectives while satisfying equally important degradation requirements.     

Ultrafast nanoporous silica formation driven by femtosecond laser irradiation

A type of glass modifications occurring after femto‐second laser irradiation gives rise to strong (10⁻²) from birefringence. This form birefringence is thought to be related to index nanostructure (called nanogratings). Analyzing induced tracks in fused silica using scanning electron microscopy (SEM) with nm resolution shows that nanostructures are porous nanoplanes with an average index lower than typical silica (Δn ∼ –0.20). Their origin is explained as arising from fast decomposition of the glass under localized, high‐intensity femtosecond laser radiation where strong nonlinear, multiphoton‐induced photoionization leads to plasma generation. Mechanistic details include Coulombic explosions characteristic of strong photoionization and the production of self‐trapped exciton (STE). Rapid relaxation of these STE prevents recombination and dissociated atomic oxygen instead recombines with each other to form molecular oxygen pointed out using Raman microscopy. Some of it is dissolved in the condensed glass whilst the rest is trapped within nanovoids. A chemical recombination can only occur at 1200 °C for many hours. This explains the thermal stability of such a nanostructure. Precise laser translation and control of these birefringent nanoporous structures allo arbitrarily tuning and positioning within the glass, an important tool for controlling optical properties for photonic applications, catalysts, molecular sieves, composites and more.     

Characterizing the structure of preserved information in quantum processes

We introduce a general operational characterization of information-preserving structures-encompassing noiseless subsystems, decoherence-free subspaces, pointer bases, and error-correcting codes-by demonstrating that they are isometric to fixed points of unital quantum processes. Using this, we show that every information-preserving structure is a matrix algebra. We further establish a structure theorem for the fixed states and observables of an arbitrary process, which unifies the Schr?dinger and Heisenberg pictures, places restrictions on physically allowed kinds of information, and provides an efficient algorithm for finding all noiseless and unitarily noiseless subsystems of the process.     

Piezoelectric diaphragm for vibration energy harvesting

This paper presents a technique of electric energy generation using a mechanically excited unimorph piezoelectric membrane transducer. The electrical characteristics of the piezoelectric power generator are investigated under dynamic conditions. The electromechanical model of the generator is presented and used to predict its electrical performances. The experiments was performed with a piezoelectric actuator (shaker) moving a macroscopic 25 mm diameter piezoelectric membrane. A power of 0.65 mW was generated at the resonance frequency (1.71 kHz) across a 5.6 kOmega optimal resistor and for a 80 N force. A special electronic circuit has been conceived in order to increase the power harvested by the piezoelectric transducer. This electrical converter applies the SSHI (synchronized switch harvesting on inductor) technique, and leads to remarkable results: under the same actuation conditions the generated power reaches 1.7 mW, which is sufficient to supply a large range of low consumption sensors.     

Oil coating on hydrophilic surfaces from emulsions and under shear flow

We study the formation of silicone oil coating on negatively charged hydrophilic surfaces via emulsion deposition. Cationic surfactants usually adsorb and form bilayers onto negative surfaces. As a result, direct emulsions stabilized with cationic surfactants are paradoxically poorly efficient at coating negative substrates. We show in this work an alternative and new method, still based on electrostatic attractions, to coat negative substrates. Our method consists of using emulsions stabilized with nonionic surfactants and of adding to the oil cationic additives that are non-water-soluble and of high molecular weight to minimize their solubilization in the micelles formed by the neutral surfactant. The positively charged droplets stick efficiently onto the substrates. They form monolayer and uniform coatings. We study the kinetics and the density of the resulting coating using a flow cell experiment. This technique allows us to finely analyze the influence of several physicochemical parameters.     

Determination of ammonium using a microplate-based fluorometric technique

The determination of ammonium (NH₄⁺) in concentrations ranging from nanomolar to micromolar in fresh and brackish waters often loaded in high suspended particulate matter and dissolved organic acids is presented. The newly described microplate-based fluorometric technique is allowing quick automated readings of different groups of samples with different background fluorescence and matrix effects. The lowest detectable concentration was estimated to 5 nM using the average detected blank ±3S.D. and the practical detection limit (LOD) determined with successive calibration curves was 50 nM with an excellent repeatability. High loading of suspended particular matter, coloured organic acids, and salinity changes were not interfering with the accurate determination of ammonium. To illustrate its robustness and efficiency, this technique has been applied to water samples taken from rivers, saltmarshes and estuaries, spanning a large range of ammonium levels and chemical properties. Measurements of ammonium on reddish turbid waters sampled in south shore of St. Lawrence Estuary showed ammonium concentrations between 0.05 ± 0.01 and 3.89 ± 0.03 μM, indicating a significant source of ammonium from terrestrial and saltmarsh ecosystems.     

Line defect dynamics around a colloidal particle

We study experimentally the dynamics of a topological defect located around a colloidal particle suspended in a thermotropic nematic liquid crystal. The considered defect consists of a disclination loop encircling the particle at the equator. Under specific conditions, it is shown that this disclination continuously shrinks to a hedgehog defect located in the immediate vicinity of the particle. This phenomenon corresponds to a transition between an elastic quadrupolar configuration and an elastic dipolar configuration. We performed a basic numerical calculation to get an estimate of the dissipated energy during the transition; we compare the results with theoretical predictions that describe the elastic energy of particles surrounded by defects. Received 21 December 2001