Thickness of polymer coating.
The amount of coating affects how much compaction can modify it. Applying a thick polymeric coating to the surface of pellets
imparts good elasticity and crushing strength to them (22). Damage to the coated pellets thus can be minimized during compression
by applying a thick, rather than thin, coating of polymer solution (21–22). Bodmeier observed increased elastic and plastic
deformation upon application of thick coating (5). The thickness of applied coatings provides good resistance to frictional
forces, thus showing a direct dependence of cracks and elasticity on the film. To prevent the coatings from rupturing during
compaction, the coating should have good elasticity and flexibility and be able to undergo structural changes and adapt to
the deformation process (16, 22, 40, 41).
Plasticizer.
Plasticizers are added to polymeric dispersions, especially to water-dispersions, to lower their glass-transition temperature
and expedite the coalescence of the distinct polymer particles in the dispersion. Thus, coalescence of polymer particles directly
relies on the time and temperature of coating and postcoating processes. Onions proposed a two-stage theory for the process
of coalescence of aqueous polymeric dispersions.
The first stage includes the evaporation of the aqueous layer and the formation of a dry, transparent, apparently continuous
film on the surface of the coated material. The coalescence of distinct polymer particles is completed gradually in the second
stage. The water in the interstitial spaces starts evaporating slowly, bringing the separate particles close to each other
and finally fusing the particles to form a strong and continuous film on the surface of the coated material (42–43). Further
studies revealed that the amount of plasticizer did not influence drug release from compacted reservoir pellets (44). The
flexibility of the aqueous-based coatings was improved by adding plasticizers, but Aulton observed that plasticizers led to
a reduction in tensile strength (45). Felton proposed that increasing plasticizer content would increase the tensile strength
of film-coated beads. The increased degree of plasticization of the polymer made the film more elastic and allowed it to withstand
the deformation process during compression (46).
Conclusion
With its promising controlled-release mechanism for oral delivery, MUPS will be a focus of future research and development.
The selection of excipients plays a key role in the success of MUPS. A thorough understanding of the factors that affect the
performance of MUPS helps the formulator tailor the drug-release profiles. MUPS may soon become one of the most popular oral
controlled-release systems.
Mitesh D. Phale* is a scientist and Abhijit V. Gothoskar is a global technical manager, both at Divakar Chemicals, 203–204, Sant Bhavan, Sharma Industrial Estate, Walbhat Rd., Goregaon–East,
Mumbai 400 063, Maharashtra, India, phalemitesh@gmail.com
.
*To whom all correspondence should be addressed.
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