ISSN:
0021-8995
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
A systematic study of the mild alginate/polycation microencapsulation process, as applied to encapsulation of bioactive macromolecules such as proteins, was conducted. When protein drugs were suspended in sodium alginate solution and sprayed into 1.3% buffered calcium chloride to form cross-linked microcapsules, large (up to 90%) losses of encapsulation species were encountered, and moderate to strong protein-alginate interactions caused poor formation of capsules. As a result, a diffusion-filling technique was adopted in which blank alginate beads, coated twice with small amounts of polycation, were formed prior to drug loading. Protein was then loaded into these capsules by stepwise diffusion from solutions of increasing drug concentration. The drug-loaded capsules were coated with a final layer of polycation. In all, three polycation coatings were used, two prior to filling and one after filling. The first coating strongly influenced the size, integrity, and loading capacity of the capsules. Low concentrations of polycation resulted in poorly formed capsules with very low retention of the drug in the final capsule, while very high concentrations prevented the drug from entering the capsule at the filling stage. This first coat also affected the duration of drug release from the capsule and the size of the burst effect. The second coat had less effect on the capsule integrity, but it did influence the drug payload and relase profile. The final, sealing-coat had little effect on drug payload and only limited effect on the release profile up to a critical concentration, above which the release profile was not affected. For all coats, increasing polycation concentration decreased the burst effect, and caused the release profile to be more sustained. Encapsulation of a series of dextrans with increasing molecular weight revealed that the release profile was directly related to the molecular weight of the diffusing species, which was more sustained as molecular weight increased. We have shown that the choice of coating parameters in the diffusion-filled, alginate/polycation system is critical for successful drug delivery from these capsules. By carefully choosing the coating parameters, both the drug payload and the release profile can be fine-tuned to meet the desired profile.
Additional Material:
9 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/app.1991.070431120
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