Chemical penetration

Processes. The most common method for the appHcation of chemicals to the surface of a paper web is by a size press. In the size press, dry paper, which usually is sized to prevent excess water and chemical penetration, is passed through a flooded nip or pond, and a solution or dispersion of the functional chemical contacts both sides of the paper. Excess Hquid is squeezed out in a press and the paper is redried. 

Absorption—The process by which a chemical penetrates the exchange boundaries of an organism after contact, or the process by which radiation imparts some or all of its energy to any material through which it passes. 

Net chemical penetration of the skin is simply the sum of the accumulations by each of the mentioned routes and by other routes, for instance eccrine glands, where these contribute. The latter tiny glands are ubiquitously distributed over the body but are generally discounted in importance due to the limited fractional area they occupy and their unfavorable physiological states, either empty or profusely sweating. 

These two conclusions are the important results from the model because they enable us to say how deep into the soil profile the majority of an organic chemical penetrates due to water inputs. If V centimeters of water are applied to a soil surface, then the water penetrates the soil to a depth of V/9. If V is sufficient to dissolve all the organic chemical present, then depth where the maximum concentration of chemical in the soil will be found is V/pKp. 

Chemical Penetration The movement of material through a suit s closures, such as zippers, buttonholes, seams, flaps, or other design features. Abraded, torn, or ripped suits will also allow penetration. 

Absorption Across the Skin. An aqueous carrier may be used for a variety of dermal products. In fact, carriers can be designed to limit the transportation of the penetration of the active ingredient (such as an insect repellent), if the desired effect is to keep the activity on the surface of the skin. Once again, however, only those materials that are dissolved will be available for penetration across the skin to gain access to the systemic circulation. For almost all chemicals in or about to enter commerce, dermal penetration is a passive process. The relative thickness of the skin makes absorption (into the systemic circulation) slower than the absorption across the GI or pulmonary barriers. This is compounded by the fact that the stratum comeum ftmction is to be impervious to the environment. One of the skin s major functions is protection from infection. Once a chemical penetrates into the dermis, it may partition into the subcutaneous fat. Essentially, absorption across the skin is a two-step process with the first being penetration and deposition into the skin and the second being release from the skin into the systemic circulation. The pattern of blood levels obtained via dermal penetration is generally one with a delayed... 

While there are limitations associated with the use of an in vitro permeability model for assessing the transport of compounds across the buccal mucosa, it can still be useful in assessing and comparing the permeability of compounds under different conditions, such as pH, temperature, and osmolarity, which provide valuable information on the mechanisms involved in drug transport. Additionally, the preliminary effects of potential chemical penetration enhancers or formulation excipients may be assessed, and these may provide a substantial rationale for subsequently assessing the effect of these agents in man. 

The buccal mucosa does serve as an alternative route for administering compounds systematically however, to ensure particular compounds are candidates for delivery across this biological tissue, preclinical screening is essential. While in vivo human permeability studies are ideal, due to their costs and associated issues, it is necessary to perform such screening in vitro. Assessment of compound permeability across porcine buccal mucosa has been widely used and can provide the preclinical biopharmaceutical scientist with much information relating to permeability, routes of transport, and effects of various chemical penetration enhancers. 

CHALLENGES IN DESIGNING MULTICOMPONENT CHEMICAL PENETRATION ENHANCER FORMULATIONS... 

Figure 2 (A) Design of a ternary formulation. (B) Activity phase map of a ternary combination of chemical penetration enhancers. Dark gray indicates highest skin permeabilization and light gray indicates lowest skin permeabilization.

Weichers J. Use of chemical penetration enhancers in transdermal drug delivery—possibilities and difficulties. Acta Pharmeceutica Nordica 1992 4 123-123. 

Kanikkannan N, Kandimalla K, Lamba S, Singh M. Structure-activity relationship of chemical penetration enhancers in transdermal drug delivery. Curr Med Chem 2000 7 593-608. 

To summarize for a sorbing chemical, mass exchange at the sediment-water interface can be treated like the exchange at a wall boundary with phase change. Sorption increases the specific and integrated mass exchange by the factor (l// )l/2 that is, it increases the capacity of the sediment to store the compound. At the same time, it slows down the speed at which the chemical penetrates the sediments (factor Note that the derived equations keep... 

The literature describing such synergy between electrical enhancement techniques with chemical penetration enhancers was reviewed recently [2] and is beyond the scope of this chapter. 

Karande, P., et al. 2005. Design principles of chemical penetration enhancers for transdermal drug delivery. PNAS 102 4688. 

It is therefore desirable to devise strategies both to enhance the penetration of molecules, which can already breach the skin barricade passively to some extent, and also to widen the spectrum of drug molecules that can penetrate the skin at therapeutically beneficial doses. Many tactics have been utilized to help overcome the barrier function. These include chemical means (e.g., chemical penetration enhancers or entrapment of molecules within lipid vesicles) or physical methods (such as ultrasound, microneedles, or electrical methods). Two important electrical methods are iontophoresis and electroporation. 

Chemical Penetration Enhancers of Electroporation-Mediated Delivery.331... 

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