Membranes silastic

Katoh and Yoshida evaluated the oxygen permeability (membrane resistance) of various membranes in the presence of water using this equipment. Table 2 lists the results obtained [277]. The membranes used are mainly hydrophobic. A silicone membrane that is supported by a mesh or a composite of a porous polypropylene membrane and homogeneous membrane are the subject of the permeation measurement. For example, the permeation coefficient of a silicone membrane (Silastic 500-1) with a thickness of 125 pm has a permeation coefficient of 1.04cm/min (the membrane resistance is 0.96min/cm). One of the advantages of this method is that not only can the membrane resistance be measured, but... 

In an effort to optimize the solvent-containing passive sampler design, Zabik (1988) and Huckins (1988) evaluated the organic contaminant permeability and solvent compatibility of several candidate nonporous polymeric membranes (Huckins et al., 2002a). The membranes included LDPE, polypropylene (PP), polyvinyl chloride, polyacetate, and silicone, specifically medical grade silicone (silastic). Solvents used were hexane, ethyl acetate, dichloromethane, isooctane, etc. With the exception of silastic, membranes were <120- um thick. Because silicone has the greatest free volume of all the nonporous polymers, thicker membranes were used. Although there are a number of definitions of polymer free volume based on various mathematical treatments of the diffusion process, free volume can be viewed as the free space within the polymer matrix available for solute diffusion. 

Megrab, N.A., A.C. Williams, and B.W. Barry. 1995. Oestradiol permeation across human skin, silastic and snakeskin membranes The effects of ethanol/water co-solvent systems. Int J Pharm 116 101. 

Megrab NA, Williams AC, and Barry BW. Oestradiol Permeation Across Human Skin, Silastic and Snake Skin Membranes the Effects of Ethanol/Water cosolvent Systems. IntJPharm 1995 116 101—112. 

Permeation-skin-gas chromatography (GC)/MS A silastic membrane was coated onto a fiber to be used as a permeation membrane. The MCF was immersed in the donor phase to partition the compounds into the membrane. At a given partition time, the MCF was transferred into a GC injector to evaporate the partitioned compounds for quantitative and qualitative analyses. This technique was developed and demonstrated to study the percutaneous permeation of a complex mixture consisting of 30 compounds. Each compound permeated into the membrane was identified and quantified with GC/MS. The standard deviation was less than 10% in 12 repeated permeation experiments. The partition coefficients and permeation rates in static and stirred donor solutions were obtained for each compound. The partition coefficients measured by this technique were well correlated (Pf — 0.93) with the reported octanol/water partition coefficients. This technique can be used to study the percutaneous permeation of chemical mixtures. No expensive radiolabeled chemicals were required. Each compound permeated into the membrane can be identified and quantified. The initial permeation rate and equilibrium time can be obtained for each compound, which could serve as characteristic parameters regarding the skin permeability of the compound. 

The stratum comeum is composed of flat comeocytes embedded in a continuous intercellular lipid matrix. The intercellular lipid matrix is the main route for percutaneous absorption of many exogenous chemicals. However, it is difficult to use stratum comeum to conduct absorption experiments because of the hair follicles. Synthetic membranes, including lipid and silastic membranes, have been used to simulate the absorption properties of this lipidal layer. 

Assuming that significant levels of permethrin were transferred from the military imiform to the skin, this insecticide did not appear to influence DEET absorption in the porcine skin flaps but appeared to blimt DEET absorption in porcine skin sections and silastic membranes. This blimting effect apparently occurred on the skin smface or stratum comeiun as it was also observed in silastic membranes. It is quite conceivable that this physicochemical interaction on the skin surface had to have been overcome by the diffusion of DEP or PB from the cutaneous capillaries for these agents to enhance DEET penetration from the surface. 

Van der Merwe, D. and Riviere, J.E., Comparative studies on the effect of water, ethanol and water/ethanol mixtures on chemical partitioning into porcine stratum comeum and silastic membrane, Toxicol. In Vitro, 19, 69—11, 2005b. 

The R S flux ratios of the enantiomers of propranolol through a silastic membrane of the three cellulose derivatives were equivalent, and the flux rate of the R enantiomer was about twice that of the S enantiomer when pure enantiomers were used. The data for two carbamate derivatives (R2 or 3,5-Cl and R3 or 3,5-CH3) are shown in Fig. 5. Differences in flux values of... 

Stereoselective retardants have been used by some researchers in the donor vehicles as a means of blocking one enantiomer and thereby facilitating the permeation of the other enantiomer [19,40]. Stereoselective retardants such as cellulose tris (3,5-dimethyl phenyl carbamate), which are known for their ability to resolve enantiomers when used as chromatographic stationary phases, were examined. When pure propranolol enantiomers were used, the steady-state flux ratio of R/S was 1.70 across silastic membrane. No such differences in the permeation were observed in the absence of retardants. 

The results show that the reduction in the melting temperature of testosterone by 114°C, accompanied by an elevation in its solubility, brought about an increase in the transdermal flux of the drug through skin and silastic membrane. In permeation experiments of testosterone from... 

Silastic membrane for delivery of Levonorestrel NORPLANT Wyeth-Ayerst Contraceptive agent... 

Desorp. temp. 200°C Desorp. time 60 s Membrane material Silastic medical grade tubing i.d. 0.025 in. o.d. 0.047 in. 

Various membrane materials can be used including rubber, silastic. Teflon, and polyethylene. Membrane thickness determines electrode response time, with thin membranes (0.001 in.) being the most responsive. Response time is similar to that of pOj electrodes (1-2 min) which is to be expected as the same sorts of processes are involved. 

Results for the performance of a halothane membrane electrode are given in Figure 10. The membrane has to be permeable to halothane and ve have used silicone rubber or silastic membranes. The half wave potential for the reduction of halothane is close to that of oxygen and therefore it is difficult to separate the waves on the silver electrode. However by constructing two working electrodes -one of silver on which halothane reacts and one of platinum on which it does not - and by placing both electrodes behind the same membrane one can determine both O2 and halothane. 

Megrab, N. A Williams, A. C., and Barry, B. W. 1995. Oestradiol permeation across human skin and silastic membranes Effects of propylene glycol and supersaturation. Journal of Controlled Release, 36, 277-294. 

Most studies of the controlled release of drugs from subdermally implanted polymer devices have centered on the use of silicone rubber (Silastic). In 1964 Folkman and Long (3) demonstrated the potential of this polymer for the controlled release of certain cardioactive steroids. The good permeability of silicone rubber to a variety of drugs and its favorable biocompatibility encouraged other workers in its use as membrane material for diffusion controlled delivery devices (4). 

Figure 4.28 Rates of dialysis of chlorpromazine, a micelle forming drug with a CMC 0.7 % in water, through cellophane membranes in aqueous solutions above and below its critical micelle concentration. This may be compared with the rate of permeation of the drug through Silastic membranes (both in arbitrary units). From Florence [3].

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