Substantial separation of single-wall carbon nanotubes (SWNTs) according to type (metallic versus semiconducting) has been achieved for HiPco and laser-ablated SWNTs. We presently argue that stable dispersions of SWNTs with octadecylamine (ODA) in tetrahydrofuran (THF) originate from the physisorption and organization of ODA along the SWNT sidewalls in addition to the originally proposed zwitterion model. Furthermore, the reported affinity of amine groups for semiconducting SWNTs, as opposed to their metallic counterparts, contributes additional stability to the physisorbed ODA. This provides a venue for the selective precipitation of metallic SWNTs upon increasing dispersion concentration, as indicated by Raman investigations.

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The development of zero-order release systems capable of delivering drug(s) over extended periods of time is deemed necessary for a variety of biomedical applications. We hereby describe a simple, yet versatile, delivery platform based on physically cross-linked poly(vinyl alcohol) (PVA) microgels (cross-linked via repetitive freeze/thaw cycling) containing entrapped dexamethasone-loaded poly(lactic-co-glycolic acid) (PLGA) microspheres for controlled delivery over a 1-month period. The incorporation of polyacids, such as humic acids, Nafion, and poly(acrylic acid), was found to be crucial for attaining approximately zero-order release kinetics, releasing 60% to 75% of dexamethasone within 1 month. Microspheres alone entrapped in the PVA hydrogel resulted in negligible drug release during the 1-month period of investigation. On the basis of a comprehensive evaluation of the structure-property relationships of these hydrogel/microsphere composites, in conjunction with their in vitro release performance, it was concluded that these polyacids segregate on the PLGA microsphere surfaces and thereby result in localized acidity. These surface-associated polyacids appear to cause acid-assisted hydrolysis to occur from the surface inwards. Such systems show potential for a variety of localized controlled drug delivery applications such as coatings for implantable devices.

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An electrostatic layer-by-layer deposition technique was employed for the formation of thin films consisting of alternating layers of perfluorinated ionomer (Nafion) and ferric ions. UV-vis spectroscopic and ellipsometric data indicate a stepwise growth that in certain cases is as high as 47 nm per dip cycle. The growth characteristics of these assemblies can be correlated with Nafion's hydrodynamic radius, iron content, as well as the ionic strength and pH of Nafion and the wash solution. When these assemblies were compared to cast Nafion films, they exhibit the following advantages: (i) increased hydrolytic stability, attained without thermal treatment required for pristine Nafion films, and (ii) resistance to calcification, by more than an order of magnitude. These results, along with the ability to control glucose permeability by varying the number of Nafion/Fe3+ layers, could prove vital in prolonging the lifetime of implantable biosensors.