Media simulations

One of the interests in confined polymers arises from adsorption behavior— that is, the intake or partitioning of polymers into porous media. Simulation of confined polymers in equilibrium with a bulk fluid requires simulations where the chemical potentials of the bulk and confined polymers are equal. This is a difficult task because simulations of polymers at constant chemical potential require the insertion of molecules into the fluid, which has poor statistics for long chains. Several methods for simulating polymers at constant chemical potential have been proposed. These include biased insertion methods [61,62], novel simulation ensembles [63,64], and simulations where the pore is physically connected to a large bulk reservoir [42]. Although these methods are promising, so far they have not been implemented in an extensive study of the partitioning of polymers into porous media. This is a fruitful avenue for future research. 

Vertzoni M, Dressman J, Reppas C. Dissolution testing in media simulating the gastric composition in the fasted state. Proceedings of the AAPS Annual Meeting, Toronto, Canada, 2002. 

Marques M. Dissolution Media Simulating Fasted and Fed States. Dissolution Technol 2004 11 16. 

Vertzoni M, Fotaki N, Kostewicz E, Stippler E, Leuner C, Nicolaides E, Dressman J, Reppas C (2004) Dissolution media simulating the intralumenal composition of the small intestine Physiological issues and practical aspects. J Pharm Pharmacol 56 453 162... 

Computer experiments on condensed media simulate finite systems and moreover use periodic boundary conditions. The effect of these boundary conditions on the spectrum of different correlation functions is difficult to assess. Before the long-time behavior of covariance functions can be studied on a computer, there are a number of fundamental questions of this kind that must be answered. 

Delmau proposed the combined extraction of cesium and strontium from caustic wastes by adding a crown ether and a carboxylic acid to the CSSX solvent.126 The classical DtBuC18C6 and one carboxylic acid were combined with the components of the CSSX solvent optimized for the extraction of cesium, allowing for the simultaneous extraction of cesium and strontium from alkaline nitrate media simulating alkaline high-level wastes present at the SRS. The promising results of these batch tests showed that the system could reasonably be tested on actual waste. 

Lipophilic drugs, being either weak acids, weak bases or non-ionized compounds, are dissolved in the lipid fraction of the food when the macroscopic structure of the food is broken down into microscopic particles during the formation of chyme. Consequently, lipophilic molecules are predissolved in triglyceride droplets when they enter the small intestine. For these compounds, it is especially relevant to include lipolysis products in the biorelevant media simulating the intestinal fluids. Sunesen et al. (2005) could only obtain fVTVC in the fed state for a non-ionized compound (danazol), when including lipolysis products in the media. 

Weak bases have higher solubility at low pH values, and a combination of media simulating the fasted gastric fluids and media simulating the fasted intestinal fluids will be suitable to simulate their dissolution behaviour in the GI tract. The model used should be able to simulate possible precipitation of a weak base when transferred from an acidic to a neutral medium. In the fed... 

Literature describing simulated media for the fasted stomach and small intestine are available. In the fed state, the simulation of the fed stomach seems to be problematic because the composition is highly dependent on the associated meal. Therefore only a few publications of fed state gastric media are available. With regard to media simulating intestinal fluids in the fed state, several attempts have been made to develop suitable media, both with and without the addition of lipolysis product. 

R. Marques, J. Martel, F. Mesa, and F. Medina, Left-handed media simulation and transmission of EM waves in subwavelength split-ring-resonator-loaded metallic waveguides, Phys. Rev. Lett., vol. 89, paper 183901, 2002. 

Table 7.8 Compositions of selected physiological biomineralisation media ( simulated body fluids ) in millimolar.

Hasmy A, Beurroies I, Bourret D et al (1995) Gas-Transport in Porous-Media - Simulations and Experiments on Partially Densified Aerogels. Europhysics Letters 29 567-572... 

The commercially available Sporanox capsule formulation is a solid dispersion relying on the principle of supersaturation to enhance the intestinal absorption of the antifungal itraconazole (ITR), a weak base (pKa = 4) with an extremely low and pH-dependent aqueous solubility (ca. 1 ng/mL in water, 6 mg/mL in 0.1 M HCl). This formulation comprises a molecular dispersion of ITR in a hydroxypropylmethyl-cellulose (HPMC) matrix, which is coated onto inert sugar spheres. Dissolution of HPMC in media simulating the gastric environment results in supersaturated concentrations which are maintained for at least 4 h. HPMC is believed to prevent ITR from precipitation in the stomach and in the intestine, resulting in significant absorption (maximum fraction absorbed ca. 85 %) and oral bioavailability (ca. 55 % Brewster et al. 2008). 

Fig. 15.5 Two-stage dissolution of tablet formulations made with crystaUine drag substance and amorphous solid dispersion in media simulating normal gastric pH...

Nntrient components are mostly used for selection pressure. Such principle of selection in growth media, simulating the composition of phloem juice of a host plant, is described by Strnadova et al. (1986). Another example is, e.g., acquisition of new strains with modified production qualities through regeneration of protoplasts (Schumaim et al., 1982, 1987). 

Du F, Baune M, Thoming J (2007) insulator-based dielectrophoresis in viscous media - Simulation of particle and droplet velocity. J Electrost 65 452 58... 

J. S. Bader and B. J. Berne,/. Chem. Phys., 104, 1293 (1996). Solvation Energies and Electronic Spectra in Polar, Polarizable Media Simulation Tests of Dielectric Continuum Theory. 

Gianguzza, A., Melia, D., Millero, F.J., and Sammartano, S. (2004) Hydrolysis and chemical speciation of dioxouranium(VI) ion in aqueous media simulating the major ion composition of seawater. Mar. Chem., 85, 103-124. 

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