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Class I hybrid poly(N-isopropylacrylamide)/silica hydrogels, PNIPAM/SiO2, were prepared by a new one shot synthesis. In this approach, the free-radical polymerization of vinyl groups of N-isopropylacrylamide (NIPAM) and the hydrolysis-condensation of alkoxy groups of tetramethoxysilane (TMOS) are performed concomitantly using sodium persulfate and 3-(dimethylamino)-propionitrile, a well-known couple to initiate the organic polymerization. The cross-linker is N,N-methylenebisacrylamide. The kinetic study of mechanical properties from the sol-to-gel state for different ratios of TMOS/NIPAM was investigated by rheological ultrasonic measurements. The thermoresponse of hybrid materials was investigated by differential scanning calorimetry and the measurements showed that hybrid gels present a lower critical solution temperature, which is similar with one of single organic hydrogel.

Quantitative ultrasonic characterization yields information that is correlated to the tissue microstructure and increases the diagnostic potential of ultrasound. The measurement of acoustic properties of melanomas in vivo has not yet been reported after proton-beam irradiation. This prospective study was conducted on a cohort of 50 patients diagnosed with primary malignant melanoma to assess in vivo the ability of quantitative echography to detect changes in choroidal malignant melanomas after proton-beam irradiation and to follow the ultrasonographic changes during 24 months posttreatment. Echographic evaluations of these patients were performed at diagnosis and repeated every 6 months after treatment over a 2-y period. The acoustic parameters included in this work are derived from the calibrated tissue backscatter spectra (spectral slope, spectral intercept and apparent integrated backscatter) of a selected tumor volume after correction of the apparatus transfer function and beam diffraction. Clinical parameters resulting from conventional echography were also quantified and included mainly tumor height, tumor vascularity and internal reflectivity. Spectral intercept and apparent integrated backscatter were found to be the most useful to evaluate changes in melanomas after treatment. Significant (p < 0.05) differences of these parameter values were observed between pre- and postproton therapy. In particular, significant changes (compared with baseline) were observed for these parameters, even when the tumor size after treatment was not significantly different from baseline. The results suggest that quantitative spectrum analysis of frequency-dependent backscatter can provide information about the structural modifications of choroidal malignant melanomas as a result of proton-beam irradiation.

The last decades have seen the development of sol-gel (SG) process currently used to develop new materials in a wide range of scientific applications. The SG process leads to an oxide macromolecular network through a sol (liquid phase) to gel transition. To optimize this process, the control of the kinetic of the chemical reaction is required. This kinetic can be deduced from the temporal evolution of the viscoelastic parameters. Upto date no complete investigation during the SG formation can be achieved by a unique non-destructive technique. In this paper, we present an ultrasonic technique to measure the viscoelastic parameters (storage G' and loss G'' shear moduli) of the gel material during its formation. By using a suitable model which takes into account the mass loading on the surface, the viscoelastic parameters of these materials are accurately deduced. In order to study the efficiency of this technique, silica gels transition is monitored at various formation temperatures and for different initial hydrolysis molar ratio (h). In addition, the monitoring is performed at different oscillatory shear measurements in the 6-54 MHz frequency range to determine a new characteristic time t(vs) corresponding to the moment when the material is no more a newtonian liquid. This characteristic time is then compared to the gelation time t(g) determined by rheological or acoustic audible range methods. Thus the new characteristic time is also a good criterion to characterize earlier the SG matrix transition. Our AT-cut quartz technique using our model can also be used as a high frequency rheometer for the sol-gel materials.