Capsule shells, changes

The drug dissolution profiles from capsules have been documented to change with time due to changes in the gelatin capsule shell properties, interaction between gelatin and an encapsulated ingredient such as anionic compounds (e.g., substituted benzoic and sulfonic acid dyes), and compounds with keto groups. The... 

Establish the compatibility of the capsule shell and the capsule contents. Determine the hygroscopic nature of the capsule formulation. For example, a hygroscopic formulation (active ingredient and/or excipients) can pull water from the capsule shell, which could affect the Active ingredient—stability issues such as degradation and morphology changes... 

Chang, R-K. Raghavan, K.S. Hussain, M.A A study on gelatin capsule brittleness moisture transfer between the capsule shell and its content. J. Pharm. Sci. 1998, 87, 556-555. 

The empty capsule shells contain 13-15 percent water, a level that is important for optimum performance on capsule filling machines. If the level falls below 13 percent, the capsules become brittle, while if they take up too much water, the gelatin becomes soft and there are problems with capsule separation. The dimensions of the capsule shell will also change with variations in water content, typically increasing by 0.5 percent for every 1 percent increase in moisture content. It is important that capsule shells are both stored and filled in areas where the relative humidity is controlled between 30-50 percent. 

Changes in Capsule Shells with Time and Storage Conditions... 

The porosity of the particles could be shown by encapsulating an aqueous solution of a gadolinium-based magnetic resonance imaging (MRI) contrast agent [Gd-diethylenetriamine penta acetic acid (DTPA)]. As the Gd complex is still accessible by water from the capsule exterior, changing the water s proton relaxation time, it can be concluded, that the shell is porous and allows water to diffuse into the capsules, but restricts the complex to the interior [78]. 

The open state of YFj/PAH capsules for dextran 2000 kDa was observed at pH = 5, but at pH = 10 aU inorganic/organic capsules were closed and the dextran molecules captured inside. Changing the pH again to an acidic medium resulted in an opening of the capsule shell and release of dextran molecules into the surrounding solution (Fig. 3.10). A similar capsule permeability versus pH dependence was pre-... 

To capsulate a substance inside the capsule one needs to switch shells permeability at least twice first, to open capsule shells and second, to close them. The pH change used traditionally for this purpose is not well-suited for biocompatible substances which are usually stable in a pH interval which is not so wide. To avoid pH change of temperature-stimulated capsules... 

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... 

There is a way of encapsulation which doesnt possess the given above features. It is connected with the capsule shell permeability change under the influence of the raised temperature. 

HPMC has no reactive group like lysine in gelatin, HPMC capsules shell dose not react with spiramycin and its disintegration time is not changed. 

One of the first methods for making capsules involved polymer coacervation. In this method, macromolecules are dissolved in either the dispersed or continuous phase of an emulsion and are induced to precipitate as a shell around the dispersed phase. Coacervation can be brought about in several ways, such as changes in temperature or pH, addition of salts or a second macromolecular substance, or solvent evaporation (Bungenberg de Jong 1949). 

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). 

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