Stress Sensitive Gels

Supercritical and Freeze Drying. To eliminate surface tension related drying stresses in fine pore materials such as gels, ware can be heated in an autoclave until the Hquid becomes a supercritical fluid, after which drying can be accompHshed by isothermal depressurization to remove the fluid (45,69,72) (see Supercritical fluid). In materials that are heat sensitive, the ware can be frozen and the frozen Hquid can be removed by sublimation (45,69). 

The rheology of many of the systems displayed gel-like viscoelastic features, especially for the long-range attractive interaction potentials, which manifested a non-zero plateau in the shear stress relaxation function, C/t), the so-called equilibrium modulus, which has been considered to be a useful indicator of the presence of a gel. The infinite frequency shear rigidity modulus, was extremely sensitive to the form of the potential. Despite being the most short-... 

The structure of hard gels is best elucidated using SAXS or SANS because the periods of the ordered structures are on the scale 10-100nm. In addition to tube inversion and rolling ball viscometry, which are sensitive to yield stress, the formation of a hard gel can be identified by other techniques. These include DSC (gelation is an endothermic process), NMR (via transverse relaxation time, T2, measurements), polarized light microscopy and rheometry. 

In addition to Ras, a number of other proteins are known to be substrates for FTase (many of unknown identity or function, determined by 2-D gel shift experiments in the presence and absence of FTI) these may also play a part in determining relative susceptibility to FTase inhibition.46 In particular, RhoB, a farnesylated protein involved with the formation of actin stress fibers and cytoskeletal organization, has been implicated in the growth-inhibitory consequences of FTase inhibition.47,48 Another study using the FTI 19 found that growth inhibition in soft agar of a panel of human tumor cell lines correlated with the mutational status of the H-and N-Ras proteins, but not with K-Ras mutations.49 In this study also, cells with genetic defects in addition to ras were sensitive to FTase inhibition. 

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