Chemical and Structural Disorder in Eumelanins: A Possible Explanation for Broadband Absorbance

Processing and properties of extruded starch/polymer foams

The location of octenyl succinate groups within octenyl succinic anhydride (OSA)-modified waxy maize (WM) starch granules was studied in order to better understand the relationship between the structure and physical properties of OSA starches. OSA starches of D.S. 0.03—0.11 were prepared by reaction between starch, OSA and NaOH in aqueous suspension; the native granular structure of starch was retained after reaction. Backscattered electron imaging of osmium-stained, sectioned OSA starch granules showed a uniform distribution of OSA groups over the cross-section of the granules. Anion-exchange chromatography of OSA starches solubilized in water showed that most of the amylopectin molecules contain some negative charge, suggesting that most of the starch granule is accessible to and reacts with OSA. However, after partial debranching with pullulanase, more of the resulting chains were neutral than would be expected on statistical grounds, suggesting heterogeneity in OSA substitution at the branch level. X-ray photoelectron spectroscopy suggested that the concentration of OSAgroups on the immediate surface of the OSA starch granules was about 3—4 times that of the bulk.

Distribution of octenyl succinate groups in octenyl succinic anhydride modified waxy maize starch

Poly(3,4-ethylene dioxythiophene) (PEDOT) is a chemically stable, conjugated polymer that is of considerable interest for a variety of applications including coatings for interfacing electronic biomedical devices with living tissue. Here, we describe recent work from our laboratory and elsewhere to investigate the morphology of PEDOT in the solid state. We discuss the importance of oxidative chemical and electrochemical polymerization, as well as the critical role of the counterion used during synthesis and film deposition. We have obtained information about the morphology of PEDOT from a number of different complimentary techniques including X-ray diffraction, optical microscopy, scanning electron microscopy, transmission high-resolution electron microscopy, and low-voltage electron microscopy. We also discuss results from ultraviolet-visible light spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). PEDOT is a relatively rigid polymer that pa...

The Morphology of Poly(3,4-Ethylenedioxythiophene)

Electrospinning has attracted tremendous interest in the research community as a simple and versatile technique to produce synthetic polymeric ultrafine fibres with diameters ranging from a few micrometres to tens of nanometres. Recently, some natural origin polymers have also been successfully electrospun. Owing to their very small diameter, polymeric nanofibres exhibit unusual properties such as high specific surface area, flexibility in surface functionalities and superior mechanical properties. In addition, electrospun non-woven meshes could physically mimic the extracellular matrix structure of native tissues. These remarkable properties render electrospun nanofibres useful for many applications, particularly those related to the field of biomedical engineering. The first part of this review is intended to provide a fundamental survey of the electrospinning process (apparatus, governing parameters) and of recent improvements of the technique, including associated structural modifications of polymeric nanofibre meshes. The prospective tissue engineering/biomedical applications of electrospun polymeric nanofibres are then reviewed, namely, wound dressings, medical prostheses, drug delivery systems, DNA release and tissue engineering scaffolds. The essential properties of scaffolds in terms of the structural features of electrospun nanofibre meshes are discussed. Finally, the future perspectives for applications of electrospun nanofibres, particularly in the field of tissue engineering, are considered.

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John F. Watts

Papers

Surface analysis of polymers by XPS and static SIMS