Membrane filter technique permeability

To explore the difficulties in practical implementation of the above concepts, mixed matrix membranes, with 20% molecular sieves (by volume), were prepared by solution deposition on top of a porous ceramic support. The ceramic supports used were Anodise membrane filters which had 200 A pores that open into 2000 A pores and offer negligible resistance to gas flow. Initially the molecular sieve media, zeolites (4A crystals) or carbon molecular sieves, was dispersed in the solvent, dichloromethane, to remove entrapped air. After two hours, Matrimid was added to the mixture, and the solution was stirred for four hours. The solutions used varied in polymer content from 1-5 wt %. The solution was then deposited on top of the ceramic support, and the solvent was evaporated in a controlled manner. The membranes were then dried overnight at 90°C under vacuum. This was followed by a reactive intercalation post treatment technique 15) to eliminate defects. This technique involves imbibing a reactive monomer (e.g. diamine) from an inert solvent (e.g. heptane) into any micro defects. Next, a second reactive monomer (e.g. acid chloride) was introduced to reactively close defects by forming a low permeability polymer. The membranes were dried again to remove the inert solvent. Individual membrane thickness was determined by weight gain and varied from 5 to 25 Jim. 

The successful application of in vitro models of intestinal drug absorption depends on the ability of the in vitro model to mimic the relevant characteristics of the in vivo biological barrier. Most compounds are absorbed by passive transcellular diffusion. To undergo tran-scellular transport a molecule must cross the lipid bilayer of the apical and basolateral cell membranes. In recent years, there has been a widespread acceptance of a technique, artificial membrane permeation assay (PAMPA), to estimate intestinal permeability.117118 The principle of the PAMPA is that, diffusion across a lipid layer, mimics transepithelial permeation. Experiments are conducted by applying a drug solution on top of a lipid layer covering a filter that separates top (donor) and bottom (receiver) chambers. The rate of drug appearance in the bottom wells should reflect the diffusion across the lipid layer, and by extrapolation, across the epithelial cell layer. 

Based on the 96-well format, OCT-PAMPA was proposed and has proved its ability to determine (indirectly) log Poet [87]. PAM PA is a method, first developed for permeability measurements, where a filter supports an artificial membrane (an organic solvent or phospholipids) [88, 89]. With this method, the apparent permeability coefficient (log P ) of the neutral form of tested compounds is derived from the measurement of the diffusion between two aqueous phases separated by 1-octanol layer (immobilized on a filter). A bilinear correlation was found between log Pa and log Poct> therefore log Poet of unknown compounds can be determined from log Pa using a calibration curve. Depending on the detection method used a range oflog P within —2 to +5 (with UV detection) and within —2 to +8 (with LC-MS detection) was successfully explored. This method requires low compound amounts (300 pi of 0.04 mM test compound) and, as for the previous method, samples can be prepared in DM SO stock solutions. For these experiments, an incubation time of 4h was determined as the best compromise in term of discrimination. The limitation of the technique lies in the lower accuracy values... 

The three kinds of reactors already described in this section are all traditional cross-flow reactors with permeable plates or membranes. The electrochemical filter-press cell reactors used, e.g., for electrosynthesis, are equipped with cation-selective membranes to prevent mixing of the anolyte and the catholyte. These cell reactors are therefore good examples of the extended type of cross-flow reactors according to the definition transferred from the filtration field. The application of the electrochemical filter-press cell reactor technique... 

HT-solubility/permeability First, solubility is determined at four pH values by comparing the concentration of a saturated compound solution with its dilute, known as the concentration. The filtered, saturated solution from the solubility assay is then used as input material for the membrane permeability determination. The permeability assay is a parallel artificial membrane technique whereby a membrane is created on a solid support, PAMPA. The two artificial membranes presented here model the GIT and the BBB. Data are presented for control compounds, which are well documented in the literature and exemplify a range of solubility and membrane permeability. The advantages of the combination method are (/) reduction of sample usage and preparation time, ( /) elimination of interference from compound precipitation in membrane permeability determination, Hi) maximization of input concentration to permeability assay for improved reproducibility, and (/v) optimization of sample tracking by streamlining data entry and calculations. BBB permeability ranking of compounds correlates well with literature CNS activity. 

Another assay that has gained popularity and acceptance for the evaluation of permeability is the parallel artificial membrane permeability assay (PAMPA). Earlier versions of this system coated polyvinylidene fluoride (PVDF) filter plates with artificial membrane using dioleoyl-sn-glycerol-3-phosphocholine (Chen et al., 2008). Several companies attempted to develop this technology in the late 1990s with limited success (Kansy et al., 1998). These earlier versions suffered poor correlation to cell models, poor correlation to human absorption, and poor reproducibility. More modem systems have been developed with different lipid formulations and solvation techniques that seem to correlate better with Caco-2 and human data and are more reproducible (Chan et al., 2005). Some companies use the PAMPA as a tier 1 prescreen discovery... 

In recent years, novel techniques called diffusive gradient in thin films technique (DGT) were developed for obtaining speciation data and preconcentration of uranium from aqueous samples (Li et al. 2006). The method employs a bottom layer of a binding phase and an upper layer of a permeable hydrogel covered with a filter membrane. The metal ions diffuse through the membrane and upper layer and are captured by the bottom layer that contains a resin embedded in a gel (usually acrylamide), as shown schematically in Figure 3.14 (Gregusova and Docekal 2011). 

In order to analyse which lipidic compounds are involved in the altered membrane permeability, liposome studies were undertaken Large unilamellar vesicles (80-90 nm LUV) were prepared from purified pollen lipids, employing the technique of repeated extrusion at 500 psi through polycarbonate filters (0 1 /jm pore diameter). The fluorescent dye, 5(6)carboxy-fluorescein (CF), was entrapped during... 

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