Effect of polyisobutylene on ethylcellulose‐walled microcapsules: Wall structure and thickness of salicylamide and theophylline microcapsules

S. Benita, M. Donbrow*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

70 Scopus citations

Abstract

Microcapsules were prepared by the ethylcellulose coacervation process which is based on the differential thermal solubility in cyclohexane. When a protective colloid, polyisobutylene, was present in adequate concentration, individually film‐coated core particles formed. However, they were accompanied by small empty coacervate droplets, detectable by microscopic observation. Below the critical colloid concentration, the product had the form of an aggregate, in contrast to individual film‐coated microcapsules. Increase of colloid concentration yielded microcapsules of higher drug content, because the coating became progressively thinner; there was a corresponding increase in the release rate of drugs from the microcapsules. Since the initial wall polymer/drug ratio and the particle size are constant, the drug content varied with the thicknesses of the wall membrane. This is shown here by removal of empty coacervate droplets by repeated decantations, enabling determination of drug content by chemical analysis. In contrast to results reported in the literature, in the presence of a protective colloid, microcapsule drug content decreased with decreasing particle size of the drug. This was caused by more complete uptake of the wall polymer on the increased surface of core material. The effect of protective colloid concentration on the apparent loss of wall polymer as empty droplets closely paralleled its effect on the size of stabilized coacervate droplets when core material was absent. It is proposed that stabilized droplet formation is a side reaction when core material is present, causing changes in wall thickness. This reaction not only affects the efficiency of the coating process but may be utilized to control wall thickness. First‐order constants for drug release from salicylamide and theophylline microcapsules followed the same pattern as wall thickness and confirmed the validity of the measurements.

Original languageEnglish
Pages (from-to)205-210
Number of pages6
JournalJournal of Pharmaceutical Sciences
Volume71
Issue number2
DOIs
StatePublished - Feb 1982

Keywords

  • Coacervation—ethylcellulose effect on polyisobutylene on microencapsulation process
  • Microencapsulation—effect of polyisobutylene on ethylcellulose‐walled microcapsules, wall structure and thickness of salicylamide and theophylline microcapsules
  • Polyisobutylene—effect on ethylcellulose‐walled microcapsules

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