Penetration coefficient

Other fatty acids as absorption enhancers have been reported. Ogiso et al. [112] demonstrated that lauric acid (C12) produced the largest increase in permeation rate, penetration coefficient, and partition coefficient of propranolol. Onuki et al. [113] reported that docosa-hexaenoic acid (DHA) has a strong insulin permeability enhancement effect and little toxicity, compared to oleic acid and eicosapentaenoic acid (EPA) using a water-in-oil-in-water (W/O/W) multiple emulsion with no or little mucosal damage. 

Thus, only one experimental log P value was necessary. The same authors demonstrated that a significant correlation between the penetration coefficient, log BB, and... 

Now consider a poorly penetrating dermally applied compound, or one that is applied for such a short time T that only a small fraction of the applied dose is absorbed. In this case, it is the concentration c of the material in the formulation (as well as other factors that determine the flux across the stratum corneum, such as the dermal penetration coefficient Kp - see below), rather than the total applied amount of material, that determines the amount absorbed both into and through the skin. In simplest terms, the total amount Q absorbed into the systemic circulation is given by the equation ... 

The dermal penetration coefficient Kp in this simplest case depends on both the partitioning of the chemical from its vehicle (usually water) into the stratum corneum, and its diffusion through the stratum corneum. Both of these quantities can be estimated from a chemical s properties or structure. Partitioning from water into the stratum corneum can be estimated from a chemical s octanol-water partition coefficient, Kow Diffusion through the stratum corneum is dependent on the molecular volume of the chemical, which is in turn a function of its molecular weight (MW). Perhaps the most widely used expression of the dependence of stratum corneum permeability on readily available physicochemical properties is the Potts-Guy equation ... 

Table 2 Relevant applied doses for systemic and local effects for rapidly and poorly penetrating materials (Kp is the dermal penetration coefficient)...

A schematic representation of the multicomponent structure of the skin that takes these multiple barri-ers/pathways into account is shown in Figure 2. When penetration through the stratum corneum (including the parallel polar pathways) and through the aqueous layers in series with the stratum corneum are taken into account and combined with clearance into the bloodstream, the overall dermal penetration coefficient fCp(cmh ) for such a (simplified) composite system is given (by analogy with electrical... 

As the lipophilicity of compounds continues to increase (as estimated by their octanol-water partition coefficients), dermal penetration does not increase indefinitely. In fact, it is limited by a number of factors. As we have seen above, penetration into the systemic circulation for lipophilic compounds is limited by their very modest capacities to penetrate the aqueous layers of the skin (dermis and viable epidermis), as well as their relative reluctance to enter the bloodstream. These factors set a natural upper limit to the dermal penetration coefficients for very lipophilic compounds of 10 cmh. In many cases, however, it is not the penetration coefficient itself in which we are interested, but rather the flux of a compound through the skin. This flux is the product of a penetration coefficient and a driving concentration. Since the aqueous layers of the skin are the major impediment for lipophilic compounds, solubility in water plays a major role in determining the maximum flux of such compounds through the skin. Like other parameters we have... 

While the infinite dose technique has been invaluable in the determination of important skin permeability parameters such as dermal penetration coefficients and in the development of transdermal drug delivery concepts, to mimic in vivo conditions, the so-called finite dose technique was developed. This is essentially a modification of the traditional steady-state method. The important difference is that the skin preparation is supported over the receptor so that the epidermal surface is exposed in a manner that mimics the real-life exposure scenario, and the compound of interest is applied to the surface of the skin in a manner also similar to exposure in vivo. Although the results of such studies may give valuable information about the absorption of materials under specific exposure conditions, they are generally not amenable to extrapolation to other exposures since no invariant skin properties such as penetration coefficients can be readily calculated. 

It is usual here to introduce the material dependent thermal penetration coefficient... 

It increases quickly at first and then slower as time t goes on. With large thermal penetration coefficients b the material can swallow large heat flows, so that the surface temperature increases more slowly than in a body with small b. 

The assumption of a time independent contact temperature m was therefore appropriate. Its position depends on the thermal penetration coefficients... 

The time independent contact temperature lies in the vicinity of the initial temperature of the body with the larger thermal penetration coefficient. Equation (2.147) explains why different solids at the same temperature feel as if they were warmed to differing degrees when touched by the hand or foot. 

C8d = specific activity of radionuclide per gram at depth d in core C80 = specific activity of radionuclide at surface p = penetration coefficient... 

The penetration coefficient varies inversely with contact time. As the contact time increases, the value of p decreases. Penetration depth indicated in Table I is that depth in which 99.9% of the activity in the sediment core was concentrated during the indicated contact time. This depth has varied between 2 cm for 65Zn and 13.5 cm for 137Cs. 

Radionuclide Contact Time, Days Penetration Coefficient p, Cm-1 Penetration, Depth... 

They must have a positive penetration coefficient E... 

Sun Jing-lai 2009. Study on the Penetrability coefficient of the coal[D]. China Coal Research Institute. 

The formula (14) shows that grouting quantity is in direct proportion to the penetrating coefficient of the slurry in rock stratum, the sum of grouting and expansion pressure, the grouting time, and the drilling diameter but in inverse proportion to the slurry viscosity. 

Schliinder (1984) gave the formula for the prediction of the contact resistance and bulk penetration resistance for packed beds and stirred beds of materials in contact with the surface of immersed bodies. For the typical engineering applications the time-averaged heat penetration coefficient for a packed bed (or a moving bed with plug flow pattern) can be predicted by... 

If the wave number of the incident particle in the nucleus (before amalgamation to form a compound state) is K then the barrier penetration coefficient T) may be written ... 

Plasticizers may also change properties of a polymer surface from l drophobic to hydrophilic which affects permeability of Itydrophilic penetrants. Decreased hydropho-bidty is recpiired for PVC material to increase its receptivity of water-based coatings. Combinations of plasticizers and metal salts were used to induce hydrophilic properties. ° Rubber print rolls also require to have hydrophilic properties to hold film of water-based ink and this was achieved by use of a special plasticizer. Increase in hpophillicity of plasticizer causes linear increase in water penetration coefficient and water flux across membranes obtained from PVC plasticized with various plasticizers. Compatibility of a polymer and a plasticizer was found to affect staining resistance. Compatible plasticizers were less likely to dissolve stains and help them to penetrate into material. 

Paris, S., Meyer-Lueckel, H., Colfen, H., Kielbassa, A.M. Penetration coefficients of commercially available and experimental composites intended to infiltrate enamel carious lesions. Dent. Mater. 23, 742-748 (2007)... 

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