Encapsulation yield

Oral Delivery Amphiphilic P-CD nanocapsules loaded with indomethacin have been evaluated in vivo. The nanocapsules have been applied to the rat model. It was reported that the gastrointestinal mucosa of the rat was significantly protected from the ulcerogenic effects of the active ingredient indomethacin in free form. Drug encapsulation yield in the nanocapsules were >98% and the drug content per CD unit was 7.5% w/w [89],... 

Key words DRV, Protein, Peptide, Hydrophilic drug. Encapsulation yield. Vaccine, DNA, Particulate, Bacteria, Cyclodextrin... 

Weigh the required lipid or lipids and Choi (if included in the liposome composition) quantities for the preparation off mL of liposomes and place them in a 50 mL round-bottomed flask 16.5 pmol of lipid (PC) or 12.5 mg is the amount per each milliliter of aqueous phase that results in the highest encapsulation yield for CF (1). 

The characteristics of the solute solution are important for the final encapsulation yield especially the concentration and ionic strength (see Note 10). Some examples of entrapment yields of some substances in DRVs and the conditions applying in each case are presented in Table 2. 

It is very important and acmally determines the encapsulation yield of the DRVs produced to use the smallest possible volume of d.d. H O for rehydration of the dried liposome-solute mixture. The typical volume added is 1/10 of the solute (solution) volume, in the current case 100 mL (solutions of 1 mL). 

After separation of the DRV s from the nonencapsulated solute molecules and measurement of the entrapment it is found that as sugar/lipid mass ratio increases vesicle size decreases together with the encapsulation yield. Some of the solutes studied and the results obtained (2) are presented in Table 2. 

The solute solution concentration has been demonstrated to influence DRV encapsulation efficiency differently, depending on the solute. As an example, although glucose and CF entrapment values were found to decrease with increasing solute solution concentration, the same was not found true for encapsulation of sodium chloride and potassium chloride (1). For CF, best encapsulation yields in DRVs are demonstrated when a 17 mM solution in a tenfold dilution of an isotonic PBS buffer, is used. The ionic strength of the buffer used to dissolve the solute added at this step, should be at least 10 times less than that of the buffer used for DRV dilution after the hydration step (see below) in order to reduce material losses, due to osmotic activity of liposomes. 

Although we do not have experience of this in our lab, it has been reported that similar encapsulation yields for DRVs may be obtained by drying down the SUV-solute mixture using other procedures, as drying nonfrozen mixtures at 20°C under vacuum, or under a stream of (at 20°C or 37°C). 

This is a very important step, in order to avoid low encapsulation yields that may be caused by the presence of high CD... 

The behavior of immobilized enzymes differs from that of dissolved enzymes because of the effects of the support material, or matrix, as well as conformational changes in the enzyme that result from interactions with the support and covalent modification of amino acid residues. Properties observed to change significantly upon immobilization include specific activity, pH optimum, Km, selectivity, and stability.23 Physical immobilization methods, especially entrapment and encapsulation, yield less dramatic changes in an enzyme s catalytic behavior than chemical immobilization methods or adsorption. The reason is that entrapment and encapsulation result in the enzyme remaining essentially in its native conformation, in a hydrophilic environment, with no covalent modification. 

In particular, the effects of various stabilizers of the primary emulsion on the encapsulation of SCG were studied. Different hydrophilic polymers were employed namely gelatin (250 Bloom grades) or the polyoxyethylene-polyoxypropylene block copolymer, poloxamer 407. To further optimize the encapsulation yield, some experimental contrivances have been performed dispersion by turbine of the drug within the lipidic matrix, rapid emulsion cooling using an ice bath, and rapid separation of LS by filtration. The optimized procedure resulted in a final encapsulation of the drug of 50% (Table 2.10). 

Core/wall ratio cannot only decide the wall thickness of a microcapsule but also the effectiveness of the microencapsulation." The work" on the microencapsulation of xylitol by poly (urethane-urea), which was performed in a water-in-oil system, indicates that the most proper core/wall ratio is 77/23 in terms of high encapsulation yield and xylitol loading content. Another work on the microencapsulation of perfume by polyurea, which was performed in a oil-in-water system, found that with the decrease of the core/wall ratio, the size of the formed microcapsule increased even the original droplet size is roughly the same. An outward diffusion mechanism was proposed to explain... 

Cosco, S. Ambrogi, V. Musto, P Carfagna, C. Urea-formaldehyde microcapsules containing an epoxy resin Influence of reaction parameters on the encapsulation yield. Macromolecular Symposia (2006), 234 (Trends and Perspectives in Polymer Science and Technology), 184-192. 

As shown in Figure 5.12, these authors prepared a model for capsule formation. When SDS is added to the oil/water emulsion, complexation occurs between SDS and the oppositely charged polyelectrolyte (gelatin). This complex deposits at the oil droplet/water interface in the form of a primary layer (Fig. 5.12, B). Addition of the second polyelectrolyte (gum arabic) to the system induces further complexation between the two polyelectrolytes and covering of the primary layer surface. It is observed that the addition of surfactant (SDS) increases the encapsulation yield (Fig. 5.13). 

Figure 5.13 Micro-encapsulation yield (%) as a function of sodium dodecyl sulfate (SDS) concentration [41].

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