Enhanced viability of corneal epithelial cells for efficient transport/storage using a structurally modified calcium alginate hydrogel.

AIMS: Therapeutic limbal epithelial stem cells could be managed more efficiently if clinically validated batches were transported for 'on-demand' use. MATERIALS & METHODS: In this study, corneal epithelial cell viability in calcium alginate hydrogels was examined under cell culture, ambient and chilled conditions for up to 7 days. RESULTS: Cell viability improved as gel internal pore size increased, and was further enhanced with modification of the gel from a mass to a thin disc. Ambient storage conditions were optimal for supporting cell viability in gel discs. Cell viability in gel discs was significantly enhanced with increases in pore size mediated by hydroxyethyl cellulose. CONCLUSION: Our novel methodology of controlling alginate gel shape and pore size together provides a more practical and economical alternative to established corneal tissue/cell storage methods.

A flow system for the on-line quantitative measurement of the retention of dosage forms on biological surfaces using spectroscopy and image analysis.

Measuring the retention, or residence time, of dosage forms to biological tissue is commonly a qualitative measurement, where no real values to describe the retention can be recorded. The result of this is an assessment that is dependent upon a user's interpretation of visual observation. This research paper outlines the development of a methodology to quantitatively measure, both by image analysis and by spectrophotometric techniques, the retention of material to biological tissues, using the retention of polymer solutions to ocular tissue as an example. Both methods have been shown to be repeatable, with the spectrophotometric measurement generating data reliably and quickly for further analysis.

Nature of alpha and beta particles in glycogen using molecular size distributions.

Glycogen is a randomly hyperbranched glucose polymer. Complex branched polymers have two structural levels: individual branches and the way these branches are linked. Liver glycogen has a third level: supramolecular clusters of beta particles which form larger clusters of alpha particles. Size distributions of native glycogen were characterized using size exclusion chromatography (SEC) to find the number and weight distributions and the size dependences of the number- and weight-average masses. These were fitted to two distinct randomly joined reference structures, constructed by random attachment of individual branches and as random aggregates of beta particles. The z-average size of the alpha particles in dimethylsulfoxide does not change significantly with high concentrations of LiBr, a solvent system that would disrupt hydrogen bonding. These data reveal that the beta particles are covalently bonded to form alpha particles through a hitherto unsuspected enzyme process, operative in the liver on particles above a certain size range.

Extracting physically useful information from multiple-detection size-separation data for starch.

A method for interpreting multiple-detection size separation data of complex branched homopolymers [Konkolewicz, D.; Gilbert, R. G.; Gray-Weale, A. Phys. Rev. Lett. 2007, 98, 238301] is applied to starch. The method, whose application is described in detail, uses the sample's weight and number distributions over polymer sizes, along with the molecular weight distribution of the individual branches (or their average degree of polymerization). The branch-length and number size distributions are used to generate the weight distribution of a hypothetical molecule with the same branch-length and number distributions but where the branches are randomly joined; this reference weight distribution is then compared to the actual one. The method is applied to size-exclusion chromatography (SEC) data for starch from a particular rice variety, the first time such data have been reported for a native starch. Comparison with the randomly branched reference function shows that the amylopectin component is consistent with random branching on the distance scale of this measurement, 10(2)-10(3) nm. This implies that on the size scale commensurate with that of a whole amylopectin chain, branching is pseudorandom, even though there is nonrandom branching on the much smaller scale of individual branches and clusters.

Characterization of starch by size-exclusion chromatography: the limitations imposed by shear scission.

Shear degradation is examined in size-exclusion chromatography (SEC, or GPC) of native starch in an eluent system (dimethylsulfoxide and LiBr) in which the starch is completely dissolved. Changes in apparent size distribution with flow rate suggested extensive shear scission of the amylopectin region. For smaller sizes, largely amylose, there was no significant scission for lower flow rates. Quantification by analogy to shear breakup of dispersed droplets gives a scaling law for conditions for shear scission of highly branched polymers. This shows both that it is impossible to obtain reliable size distributions for the amylopectin component of starch using current SEC technology and also that the amylose region is not significantly polluted by degraded amylopectin for lower flow rates. Hence, the complete size distribution of starch can only be obtained with SEC for smaller sizes (largely amylose), plus a size-separation technique with very low shear, such as field-flow fractionation, for the amylopectin region.