When GLS/A droplets were collected at low CaCl2 concentration
media (e.g. 0.01 M), instantaneous crosslinking was not accomplished,
most likely due to insufficient Ca2+ ions. The GLS/A droplets crosslinked
slowly, and coagulated to lumps. The coagulation phenomenon indicates
that the Ca2+ ions were insufficient. As the CaCl2 concentration increased,
the higher amount of Ca2+ ions accelerated the crosslinking
process and the time required for the formation of beads was reduced.
The drug release profile of encapsulated alginate beads is related
with their size and degree of crosslinking, which is highly related to
the CaCl2 concentration. CaCl2 concentration of 0.5 M was found to produce
the most uniform GLS encapsulated alginate beads in the current
study. Although highly symmetrical alginate gel beads were formed at
the calcium concentration of 0.05 M, further increasing of CaCl2 concentration
is necessary to obtain GLS/A beads with sufficient strength to
maintain their structural integrity on handling, similar to iron loaded alginate
beads [26].
Alginate beads prepared at higher CaCl2 presented slower release
rate [27]. This was attributed to the high crosslinking density of the
beads, the penetration of water, and thus the diffusion of drugs was
slowed down. Therefore, CaCl2 concentration of 0.5 M was used in the
following experiments in order to produce GLS/A beads with controllable
and sustainable release rate.
3.1.2. Needle to collector distance
To determine the effect of dropping distance on the formation of
beads, the distance between nozzle exit was varied from 50 mm to
350 mm (under a controlled infuse rate of 30 μL/min). There is a general
trend of positive relationship between the size of GLS/A beads and the
dropping distance to the collector, as shown in Fig. 2a. When needle
to collector distance was fixed at 50 mm, the average beads size was
2.4 ± 0.2 mm. The size was unchanged (2.4 ± 0.1 mm) when the distance
increased to 150 mm. As the dropping distance further increased
to 250 mm, the average size of beads increased slightly (2.6 ± 0.4 mm,
p b 0.05), but almost unchanged when the distance increased to
350 mm (2.7 ± 0.4 mm, p N 0.05).
When comparing the morphology of GLS/A beads, it was found that
the beads formed at longer dropping distance (250 mm and 350 mm)
were not spherical than those produced at the shorter dropping distance
(50 mm and 150 mm). The shape of a bead is dictated by the
shape of the droplet before crosslinking. At the dropping distance of
50 or 150 mm, the GLS/A droplets were relatively spherical when entering
the CaCl2 solution, so spherical beads (with an aspect ratio of 1.1 ±
0.04) were formed by maintaining the shape after further crosslinking.
In comparison, as the dropping distance increases, the GLS/A droplets
stretched and became relatively elongated due to the gravity. The resultant
GLS/A beads were elongated with the dropping distance, the aspect
When GLS/A droplets were collected at low CaCl2 concentrationmedia (e.g. 0.01 M), instantaneous crosslinking was not accomplished,most likely due to insufficient Ca2+ ions. The GLS/A droplets crosslinkedslowly, and coagulated to lumps. The coagulation phenomenon indicatesthat the Ca2+ ions were insufficient. As the CaCl2 concentration increased,the higher amount of Ca2+ ions accelerated the crosslinkingprocess and the time required for the formation of beads was reduced.The drug release profile of encapsulated alginate beads is relatedwith their size and degree of crosslinking, which is highly related tothe CaCl2 concentration. CaCl2 concentration of 0.5 M was found to producethe most uniform GLS encapsulated alginate beads in the currentstudy. Although highly symmetrical alginate gel beads were formed atthe calcium concentration of 0.05 M, further increasing of CaCl2 concentrationis necessary to obtain GLS/A beads with sufficient strength tomaintain their structural integrity on handling, similar to iron loaded alginatebeads [26].Alginate beads prepared at higher CaCl2 presented slower releaserate [27]. This was attributed to the high crosslinking density of thebeads, the penetration of water, and thus the diffusion of drugs wasslowed down. Therefore, CaCl2 concentration of 0.5 M was used in thefollowing experiments in order to produce GLS/A beads with controllableand sustainable release rate.3.1.2. Needle to collector distanceTo determine the effect of dropping distance on the formation ofbeads, the distance between nozzle exit was varied from 50 mm to350 mm (under a controlled infuse rate of 30 μL/min). There is a generaltrend of positive relationship between the size of GLS/A beads and thedropping distance to the collector, as shown in Fig. 2a. When needleto collector distance was fixed at 50 mm, the average beads size was2.4 ± 0.2 mm. The size was unchanged (2.4 ± 0.1 mm) when the distanceincreased to 150 mm. As the dropping distance further increasedto 250 mm, the average size of beads increased slightly (2.6 ± 0.4 mm,p b 0.05), but almost unchanged when the distance increased to350 mm (2.7 ± 0.4 mm, p N 0.05).When comparing the morphology of GLS/A beads, it was found thatthe beads formed at longer dropping distance (250 mm and 350 mm)were not spherical than those produced at the shorter dropping distance(50 mm and 150 mm). The shape of a bead is dictated by theshape of the droplet before crosslinking. At the dropping distance of50 or 150 mm, the GLS/A droplets were relatively spherical when enteringthe CaCl2 solution, so spherical beads (with an aspect ratio of 1.1 ±0.04) were formed by maintaining the shape after further crosslinking.In comparison, as the dropping distance increases, the GLS/A dropletsstretched and became relatively elongated due to the gravity. The resultantGLS/A beads were elongated with the dropping distance, the aspect
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