Water-Soluble Cellulose Derivatives as Coating Agents in Fluidized Bed Processing

Microstructures of encapsulates and their relations with encapsulation efficiency and controlled release of bioactive constituents: A review

Vitamins, peptides, essential oils, and probiotics are examples of health beneficial constituents, which are nevertheless heat-sensitive and possess poor chemical stability. Various encapsulation methods have been applied to protect these constituents against thermal and chemical degradations. Encapsulates prepared by different methods and/or at different conditions exhibit different microstructures, which in turn differently influence the encapsulation efficiency as well as retention of encapsulated core materials. This review provides a summary of various microstructures resulted from the use of selected encapsulation methods or systems, namely, spray coating; co-extrusion; emulsion-, micelle-, and liposome-based; coacervation; and ionic gelation encapsulation, at different conditions. Subsequent effects of the different microstructures on encapsulation efficiency and retention of encapsulated core materials are mentioned and discussed. Encapsulates having compact microstructures resulted from the use of low-surface tension and low-viscosity encapsulants, high-stability encapsulation systems, lower loads of core materials to total solids of encapsulants and appropriate solidification conditions have proved to exhibit higher encapsulation efficiencies and better retention of encapsulated core materials. Encapsulates with hollow, dent, shrunken microstructures or thinner walls resulted from inappropriate solidification conditions and higher loads of core materials, on the other hand, possess lower encapsulation efficiencies and protection capabilities. Encapsulates having crack, blow-hole or porous microstructures resulted from the use of high-viscosity encapsulants and inappropriate solidification conditions exhibit the lowest encapsulation efficiencies and poorest protection capabilities. Compact microstructures and structures formed between ionic biopolymers could be used to regulate the release of encapsulated cores.

Hot tabletting of slow-release tramadol hydrochloride microcapsules with cores obtained via compaction

BACKGROUND

Coating, as a processing technique, applied to active pharmaceutical ingredient (API) crystals or particles (carriers) with an appropriate polymer allows to obtain a modified-release pharmaceutical dosage form. Such carriers can be the basic ingredient of a multi-unit dosage form. Additionally, coated API crystals (microcapsules) can provide an alternative to spherical granulate (pellets) as the main and most commonly used component of multi-unit dosage forms. Coating individual API crystals is a complicated process because of the crystals having insufficient size (below 100 microm), irregular shape, low mechanical durability and the fact that API crystals dissolve upon contact with the coating mixture, and other factors.

METHOD

Compaction process was used to eliminate these inconveniences allowing us to obtain tramadol hydrochloride (TH) microcapsule cores in the size range of 212-500 microm. The coating of the cores was successfully conducted using a fluidized-bed coating technique with four different polymers that allowed us to attain slow release of TH. Then, the microcapsules were subjected to a hot tabletting process conducted by applying a low compression force of about 1 kN at 56 degrees C. Semi-liquid granules containing melted PEG 3000 combined with TH microcapsules were compressed. A tablet matrix of good physical parameters was created when its temperature decreased to room temperature. In the proposed hot tabletting method, PEG 3000 included in the granulate provided the tableted microcapsules sufficient protection against rupture.

RESULTS

The compaction process allowed us to eliminate unwanted physical API properties, which could otherwise have an adverse effect on the fluidized-bed coating process. The microcapsule cores after compaction and coating using a fluidized-bed coating technique showed a TH-release profile similar to that of the compressed microcapsules after applying hot tabletting process.

CONCLUSIONS

Multi-unit dosage forms can be obtained in a relatively simple way by combining three processes: (i) obtaining TH microcapsule cores by compaction, (ii) coating, and (iii) hot tabletting.