Increasing the hardening time from 1 to 30 minutes resulted in decrease of the mean values of bead frontal diameter from 1.91 to 1.33 (Fig. 1a).
This could be due to lower drug content since a significant decline of theophylline
content with prolongation of hardening time was observed (data not shown). The
decrease in size as well as improvement of the sphericity of calcium alginate beads
with decreasing theophylline content was also observed by Smrdel et al. [4].
Furthermore, more extensive alginate crosslinking after longer hardening time
contributed to decrease of the bead diameter [20]. These results are in accordance
with findings of other researchers [4, 8, 24]. On the other hand, the mean value of
the lateral diameter and sphericity increased with increasing hardening time. Beads
isolated after 1 and 3 minutes of hardening in calcium chloride solution had a
hollow in the center and were flattened, the estimated sphericity was 0.42 and 0.63,
respectively. Obviously, the alginate crosslinking was not completed in that time
80 P. Smrdel, M. Bogataj, and A. Mrhar:
and consequently the beads flattened and collapsed during drying. Prolongation of
hardening time significantly improved the sphericity; i.e. the sphericity of beads
isolated after 30 minutes of hardening was estimated at 0.88.
Fig.