Interaction between biopolyelectrolytes and sparingly soluble mineral particles.

We investigate the complex physicochemical behavior of dispersions containing calcium carbonate (CaCO(3)) particles, a sparingly soluble mineral salt; and carrageenans, negatively charged biopolyelectrolytes containing sulfate groups. We reveal that the carrageenans suspend and stabilize CaCO(3) particles in neutral systems by absorbing on the particle surface which provides electrosteric stabilization. In addition, carrageenans provide a weak apparent yield stress which keeps the particles suspended for several months. The absorption measurements of carrageenan on the CaCO(3) particle indicate that more carrageenan is removed from the solution than expected from the case of a simple monolayer adsorption. Confocal laser scanning microscopy observations confirm that polyelectrolyte-containing precipitate is formed in both CaCO(3)-carrageenan and CaCl(2)-carrageenan mixtures. On the basis of these results, we confirm that in the presence of carrageenan some CaCO(3) dissolves and the Ca(2+) ions interact with the sulfate groups leading to aggregation and formation of particle-like structures. These new insights are important for fundamental understanding of other mineral-polyelectrolyte systems and have important implications for various industrial applications where calcium carbonate is used.

Colloidal particles for the delivery of steroid glycosides.

Water insoluble bioactive molecules with very high melting temperature and low solubility in water are difficult to formulate in food products. We demonstrate the synthesis of nanoscale particles from steroid glycosides using a facile liquid antisolvent precipitation method in the presence of various food grade stabilizers. Colloidal particles with sizes well below 200 nm are prepared from steroid glycosides containing extracts, as well as mixtures with phytosterol. In the mixtures, the formation of the typical for the phytosterol rod-like particles is suppressed. Particle size and structure are investigated by electron microscopy and dynamic light scattering. Due to the presence of surface charge and steric stabilization, colloidal particles do not display aggregation and are stable for a period of longer than one year. The results of this study are important for the formulation and delivery of steroid glycoside and phytosterol bioactive molecules in the fields of food, nutraceuticals, and medical applications.

Microscopic origin of light scattering in tissue.

A newly designed instrument, the static light-scattering (SLS) microscope, which combines light microscopy with SLS, enables us to characterize local light-scattering patterns of thin tissue sections. Each measurement is performed with an illumination beam of 70-microm diameter. On these length scales, tissue is not homogeneous. Both structural ordering and small heterogeneities contribute to the scattering signal. Raw SLS data consist of a two-dimensional intensity distribution map I(theta, phi), showing the dependence of the scattered intensity I on the scattering angle theta and the azimuthal angle phi. In contrast to the majority of experiments and to simulations that consider only the scattering angle, we additionally perform an analysis of the azimuthal dependence I(phi). We estimate different contributions to the azimuthal scattering variation and show that a significant fraction of the azimuthal amplitude is the result of tissue structure. As a demonstration of the importance of the structure-dependent part of the azimuthal signal, we show that this function of the scattered light alone can be used to classify tissue types with surprisingly high specificity and sensitivity.

Synthesis of voltage-sensitive fluorescence signals from three-dimensional myocardial activation patterns.

Voltage-sensitive fluorescent dyes are commonly used to measure cardiac electrical activity. Recent studies indicate, however, that optical action potentials (OAPs) recorded from the myocardial surface originate from a widely distributed volume beneath the surface and may contain useful information regarding intramural activation. The first step toward obtaining this information is to predict OAPs from known patterns of three-dimensional (3-D) electrical activity. To achieve this goal, we developed a two-stage model in which the output of a 3-D ionic model of electrical excitation serves as the input to an optical model of light scattering and absorption inside heart tissue. The two-stage model permits unique optical signatures to be obtained for given 3-D patterns of electrical activity for direct comparison with experimental data, thus yielding information about intramural electrical activity. To illustrate applications of the model, we simulated surface fluorescence signals produced by 3-D electrical activity during epicardial and endocardial pacing. We discovered that OAP upstroke morphology was highly sensitive to the transmural component of wave front velocity and could be used to predict wave front orientation with respect to the surface. These findings demonstrate the potential of the model for obtaining useful 3-D information about intramural propagation.