Thermoresponsive gelling materials constructed from natural and synthetic polymers can be used to provide triggered action and therefore customised products such as drug delivery and regenerative medicine types as well as for other industries. Some materials give Arrhenius-type viscosity changes based on coil to globule transitions. Others produce more counterintuitive responses to temperature change because of agglomeration induced by enthalpic or entropic drivers. Extensive covalent crosslinking superimposes complexity of response and the upper and lower critical solution temperatures can translate to critical volume temperatures for these swellable but insoluble gels. Their structure and volume response confer advantages for actuation though they lack robustness. Dynamic covalent bonding has created an intermediate category where shape moulding and self-healing variants are useful for several platforms. Developing synthesis methodology-for example, Reversible Addition Fragmentation chain Transfer (RAFT) and Atomic Transfer Radical Polymerisation (ATRP)-provides an almost infinite range of materials that can be used for many of these gelling systems. For those that self-assemble into micelle systems that can gel, the upper and lower critical solution temperatures (UCST and LCST) are analogous to those for simpler dispersible polymers. However, the tuned hydrophobic-hydrophilic balance plus the introduction of additional pH-sensitivity and, for instance, thermochromic response, open the potential for coupled mechanisms to create complex drug targeting effects at the cellular level.

Instrumental techniques such as atomic absorption spectrometry (AAS) and inductively coupled plasma atomic emission spectrometry (ICP-AES) determine only the total vanadium content of a sample, unless the tetravalent and pentavalent forms are first separated. Neutron activation analysis (NAA) is a very sensitive technique, but its use for the determination of trace amounts of vanadium is complicated by the short half-life of 52V (3.75 min) and by the masking of 52V activity by 24Na present in the matrix.* Electron paramagnetic resonance (EPR) spectrometry3 and 51V nuclear magnetic resonance (NMR) spectrometry have been used to determine Vtv and Vv, respectively, but are plagued by non-routine instrumental requirements4Vanadium is ranked tenth in abundance of 29 trace metals in soils, but in surface waters in the USA it was found in only 54 out of a total of 1500 samples.5 The highest concentration of vanadium in surface waters is found in rivers that drain from ore deposits. Air samples from cities that bum large amounts of vanadium-containing fossil fuels contain the highest airborne vanadium levels. Nakano et aZ.6 found that Vtv was the predominant species in samples of natural water, whereas Hirayama et a1.7 found equivalent levels of Vw and Vv in river and sea-water samples. Vanadium(1v) is the major form encountered in mammals.4Paper 3l01292A

The uptake of the three species of the drug model fluorescein (fluorescein sodium salt (FNa), fluorescein free acid (F), and fluorescein diacetate (FDA)) by zeolite NaX and the mesoporous zeotype MCM-41 was investigated as well as their release rates into solutions at pH 7 and pH 4.5. UV/Vis analysis was carried out at a wavelength of 490 nm. Uptakes of the sodium salt of 9 % for zeolite X and 14 % for MCM suggest little penetration of the pores. The use of ethanol as the loading solvent for F resulted in little uptake for both zeolitic materials due to the successful competition of the ethanol for binding sites. Use of acetone (weaker proton acceptor) as loading solvent significantly improved the uptake of F to 17 % and 12 % for zeolite X and MCM, respectively, whilst the uptake of FDA in acetone increased still further to 22 % and 17 % for zeolite X and MCM, respectively. Generally there was a large initial release of the fluorescein analogues from the surface of the zeolites with very little further increase over time. The prescence of an esterase enzyme in the release medium of FDA tripled the release from MCM to 15 % but left the release from zeolite X unaffected at 6 %. The results obtained show that uptake of fluorescein and its analogues is dependent on the loading solvent used, the amount released is influenced by not only the solvent but the pH and the presence of enzymes in the release medium.

Patterns of memory performance were examined for 9 participants with HIV-associated dementia (HAD), 15 HIV-seropositive participants without dementia, and 15 HIV-seronegative controls. Episodic and semantic memory were assessed using the California Verbal Learning Test, the Boston Naming Test, and Verbal Fluency tests. The HAD group showed deficits in episodic memory, with relative sparing of semantic memory. In addition, results suggest a retrieval deficit in HAD rather than a deficit in retention of information. This pattern is consistent with the presence of a subcortical dementing process and supports findings from previous neuropathological, neuroimaging, and neuropsychological studies suggesting that subcortical brain dysfunction is frequently associated with HIV disease (e.g., Navia, Jordan, & Price, 1986).

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A self regulating delivery device, responsive to glucose, has been shown to operate successfully in vitro. This comprises a gel membrane which determines the delivery rate of insulin from a reservoir. The gel consists of a synthetic polysucrose and the lectin, concanavalin A. The mechanism is one of displacement of the branched polysaccharide from the lectin receptors by incoming glucose. The gel loses its high viscosity as a result but reforms on removal of glucose, thus providing the switch controlling the drug diffusion rate. The drug does not require to be chemically modified and thus the device is adaptable to other anti-hyperglycaemic drugs. However, results here indicate that the molecular weight of the solute may be an important parameter. Others include path length, gel formulation and temperature. It had been hypothesised that the reversal might be improved by the use of a non-aqueous reservoir of insulin. However, with the use of insulin, the switching off was found to be superior to that found with other test solutes used in previous studies, irrespective of the reservoir solvent. The advantages in the use of the non-aqueous system include, however, more reproducibility in the magnitude of response and a reduced temperature sensitivity.