Penetration experiments, apparatus

Given the overwhelming influence of the physical properties of skin in determining bioavailabilities via the dermal route, assessment of dermal penetration is one area in metabolism and toxicology where in vitro methods can be effectively used to predict in vivo results and to screen chemicals. Apparatus and equipment exist that one can use to maintain sections of skin (obtained from euthanized animals or from human cadavers or surgical discard) for such experiments (Holland et al., 1984). These apparatus are set up to maintain the metabolic integrity of the skin sample between two reservoirs the one on the stratum comeum side, called the application reservoir and the one on the subcutaneous side, called the receptor reservoir. One simply places radiolabeled test material in the application reservoir and collects samples from the receptor fluid at various time points. 

Example 11.4. McGuiggan et al. [492] measured the friction on mica surfaces coated with thin films of either perfluoropolyether (PFPE) or polydimethylsiloxane (PDMS) using three different methods The surface forces apparatus (radius of curvature of the contacting bodies R 1 cm) friction force microscopy with a sharp AFM tip (R 20 nm) and friction force microscopy with a colloidal probe (R 15 nm). In the surface force apparatus, friction coefficients of the two materials differed by a factor of 100 whereas for the AFM silicon nitride tip, the friction coefficient for both materials was the same. When the colloidal probe technique was used, the friction coefficients differed by a factor of 4. This can be explained by the fact that, in friction force experiments, the contact pressures are much higher. This leads to a complete penetration of the AFM tip through the lubrication layer, rendering the lubricants ineffective. In the case of the colloidal probe the contact pressure is reduced and the lubrication layer cannot be displaced completely. 

For the low-temperature experiment the rate of extension apparatus, as described by Hajek (25) and Haas (26), was used to determine the stiffness of test specimen of SA binder based concrete mixes at — 10° and — 25°C. The asphalt cements chosen were 40-50, 85-100, and 300-400 penetration grade to cover the entire range as well as to ensure that if a difference in properties did exist, it would be noticeable. The other test variables included temperature susceptibility (obtained by using asphalts based on crude oils from various sources), SA ratio, and binder content. 

There are two established methods for measuring the distribution of pore volumes. The mercury-penetration method depends on the fact that mercury has a significant surface tension and does not wet most catalytic surfaces. This means that the pressure required to force mercury into the pores depends on the pore radius. The pressure varies inversely with a 100 psi (approximately) is required to fill pores for which a = 10,000 A, and 10,000 psi is needed for a — 100 A. Simple techniques and equipment are satisfactory for evaluating the porervolume distribution down to 100 to 200 A, but special high-pressure apparatus is necessary to go below a = 100 A, where much of the surface resides. In the second method, the nitrogen-adsorption experiment (described in Sec. 8-5 for surface area measurement) is continued until the nitrogen pressure approaches the... 

The required properties to be looked for in an ideal medium include the following (1) zero shear strength, (2) chemically inert, (3) zero penetration into the sample and the construction of high-pressure apparatus, (4) zero compressibility, (5) easy to handle (including nontoxic and nonflammable), (6) easy to seal within the high-pressure enclosure, and (7) inexpensive and readily available. In addition, for spectroscopic experiments, only optically neutral materials without intrinsic absorption and emissions are acceptable. 

In his 11 lecture (March 27, 1858) Virchow started with malaria pigmentation. Citing Tigri s milza nera ,. Virchow declared that his cellular pathology had been established on the basis of experience, but with the help of speculative thinking and to establish a speculative notion (Altmann 1992, p.LXIII). Indeed, he had not any material in pneumoconiosis, neither human nor experimental. When Traube (1860) demonstrated square and hooked black particles in the spit and later in the pulmonary tissue of a 54-year-old charcoal trimmer who had inhaled this type of dust for 12 years, there was no longer any doubt about the penetration of fine carbon particles into the respiratory apparatus. There was not any trace of newly formed connective tissue. Lewin (1862) made rabbits inhale powdered charcoal and found the dust particles in their alveoli. Powdered charcoal admixed to the food was resorbed and transferred to the mesenteric lymph nodes. 

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