Permeability, of capsule

The use of pH to induce reversible changes in the permeability of capsules has been well documented however, the film structure can also respond to other stimuli. 

The polyelectrolyte shells containing at least one weak polyelectrolyte are stable in the limited pH interval. The H values close to extreme ones lead to the disbalance of charges inside a polyelectrolyte shell followed by its swelling and increase in permeability. However, the shell permeability can be reverted to the original state returning pH to the normal values. Thus it is possible to realize an reversible "switch" of capsule shells permeability between "open" and "closed" states via pH change. The influence of pH value on permeability of capsules (PAH/PSS)4 was investigated in Ref. It was shown that pH below... 

FS Horn, SA Veresh, WR Ebert. Soft gelatin capsules II. Oxygen permeability study of capsule shells. J Pharm Sci 64 851-857, 1975. 

Many challenges remain to be addressed in this field. The use of immobilized catalysts can often reduce the activity of a catalyst Reduced reaction rates due to diffusion limitations through a permeable membrane capsule and the ease or practicality of the synthesis of these catalyst scaffolds are issues that may pose problems. In some cases, these issues have been resolved, but this is often at the expense of other properties of the capsule. For example, the use of thin walls to reduce mass transfer limitations can be at the expense of nanocapsule strength and stability. 

Capsules were equilibrated with a tracer solution overnight. A capsule pellet (0.2-0.5 ml) was then placed in 5 ml test buffer (PBS or RPMI-1640 medium, Gib-co/BRL, New York, NY) on a shaker and a 0.2-ml aliquot was immediately sampled by a screen-protected pipette with further samples being taken over the next 700 s. The tracer quantity was assayed using the methods described below. A final sample was taken after the capsules has been in contact with the buffer for several hours (equilibrated tracer quantity) and the increment to the tracer concentration at each time was calculated. From the progress of tracer to equilibrium on a semilog plot a slope denoted as the zero -order rate flux constant was obtained and has been used as a measure of capsule permeability. [3H] -Glucose (580 daltons),insulin (6.2 kDa), and ovalbumin (45 kDa) have been used as tracers. Radioactivity was measured by means of a Packard 2000CA Liquid Scintillation Counter (Packard Instruments,... 

In addition to the efflux method, several experiments have been performed by means of an inverse GPC method to assess the capsule permeability. Such measurements are considered to be more accurate and representative for high molecular weight species since they are not sensitive to protein adsorption on the capsule surface. This method, however, cannot be used for a massive screening of capsule permeability due to its time requirements. 

In Table 3, the membranes of capsules 2,7,8, and 10 are quite dense and have low permeability. In Table 4, capsule entries 2 and 4 are again relatively impermeable and are probably unsuitable for xenogeneic cell encapsulation. By comparison the alginate/cellulose sulfate//polydimethylene-co-guanidine/calcium chloride capsules seem to offer the most suitable MWCO (approximately 100 kD). This type of capsule is photographed in Fig. 2, with... 

Dissolution characteristics of solid dosage forms, which depend on formulation in addition to the properties of the chemical itself (e.g., vehicle may decrease permeability of suspension or capsule to water and retard dissolution and diffusion). 

Hwang JR, Sefton MV. Effect of capsule diameter on the permeability to horseradish peroxidase of individual HEMA-MMA microcapsules. J Controlled Release 1997 49 217-227. 

Kono et al. [92] made use of this polyelectrolyte complexation between PAA and PEI in the formation of pH sensitive capsules that could release the contents contained in their aqueous centers as a function of pH. In this work, PAA-PEI complex capsule membranes were produced which contained 43.7 % PAA and 56.3% PEI (confirmed by elementary analysis). These capsules showed a minimum degree of swelling between a pH of 3.5 and 7.0 due to complex formation. Consequently, the permeability of phenylethylene glycol through the capsule membrane was lowest between pH 3.5 and 7.0 and increased above 7.0 and below 3.5. These investigators also used turbidimetric and potentiometric techniques to confirm the presence of these polyelectrolyte complexes. 

A related system is that of the lipid-bilayer corked capsule membranes which are formed from ultrathin (about 1 pm thick), spongy, 2.0- to 2.5-mm-diameter, more-or-less spherical nylon bags in which multiple bilayers are immobilized (Fig. 43) [343-345]. They were considered to combine the advantages of mechanical and chemical stabilities of polymeric membranes with the controllable permeabilities of surfactant vesicles. Polymerization of the bilayers, in situ,... 

Peniche et al. (2004) successfully encapsulated up to 65 % of shark liver oil (rich in polyunsaturated fatty acids) in chitosan/alginate capsules in order to mask the oil s unpleasant taste. Here again it was found that the chitosan coating allowed a greater degree of control of capsule permeability. The capsules could be degraded by enzymes such as lipase or pancreatin. They were initially resistant to the acid environment of the stomach, although after 4 hours under intestinal conditions (pH = 7.4) the capsule walls were finally disrupted. 

Horn F. S., S. A. Veresh, and W R. Ebert. 1975. Softgelatin capsules. 2. Oxygen permeability study of capsule shells.Journal of Pharmaceutical Sciences, 64 851-857. 

The capsules with a defined shell (so-called hollow multilayered polyelectrolyte capsules) are free-standing LbL films with a peculiar advantage - the ability to uptake the material inside the capsule, in other words to encapsulate it and to control its release by changing the LbL film permeability properties. Macromolecules like proteins have been successfully loaded into polyelectrolyte LbL capsules through pH-controlled and water/ethanol mixture-controlled methods [118, 119], Alternative stimuli could be applied, e.g., a magnetic field [120], This approach consists of destabilization of the LbL membrane, which then becomes more permeable. The capsule is loaded with molecules of interest under destabilized conditions and then the conditions are changed back to the initial ones (under which the LbL shell is stable). 

Conjunctiva and Tenon s capsule 1) Diffusion across these tissues 2) Clearance via conjunctival blood and lymphatic flow 1) In vitro permeability of rabbit conjunctiva and Tenon s capsule 2) Limited data on blood and lymphatic flow and on capillary permeabiUty... 

With the pupil dilated, the area of posterior iris surface in contact with the anterior lens capsule decreases. Moreover, the cycloplegia produced by atropine is of additional value in reducing both the thickness and convexity of the lens. If posterior synechiae should develop even when the pupil is dilated, there is less chance of iris bombe. Atropine may also help decrease the excessive permeability of the inflamed vessels and thereby reduce cells and protein in the anterior chamber (aqueous flare). 

Kono, K. Tabata, F. Takagishi, T. pH responsive permeability of poly(acrylic acid)-poly(ethylenimine) complex capsule membrane. J. Membrance Sci. 1993, 76 (2-3), 233-243. 

Murthy, K.S. Enders, N.A. Mahjour, M. Fawzi, M.B. A comparative evaluation of aqueous enteric polymers in capsule coatings. Pharm. Tech. 1986, 10 (Oct), 36 6. Thoma, K. Oschmann, R. Investigations of the permeability of enteric coatings, part 5 pharmaceutical-technological and analytical studies of enteric-coated preparations. Pharmazie 1991, 46, 278-282. 

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