Pharmaceutical Technology: Controlled Drug Release, Volume 2

CH. 9] POLYACRYLATE (EUDRAGIT RETARD) MICROSPHERES 109
Fig. 4—Scanning electron micrograph of nifedipine-loaded microspheres (31% w/w) at various magnifications. For
experimental conditions, see Fig. 1.
Fig. 5—Scanning electron micrograph of a fractured nifedipine-loaded microsphere (31% w/w).
microspheres, probably as a result of molecular interactions between nifedipine and the Eudragit
polymers. Nevertheless, this inflection provided evidence that at least some of the nifedipine
existed in the microsphere in a solid state. This evidence is consistent with the
SEM examinations, which indicated that drug crystals were embedded on the microsphere
surfaces (Fig. 4). It could be noted from Fig. 4 that the microspheres where not quitespherical and
some of them, especially the large microspheres, collapsed and lost their spherical shape owing to
the existence of an internal void volume as evidenced by Fig. 5, exhibiting the internal structure of
a fractured nifedipine microsphere having a payload of 31%. This morphological depression
could be attributed to the method used to prepare the microspheres for SEM evaluation. To
visualize the microsphere, in SEM, a gold coating is imparted. During the gold coating process,