The gelatin used in our experiments is an acidic polymer having an isoelectric
point ( P I )of 4.7. In the PBS of pH 7.4, gelatin molecules are negatively charged
due to the dissociation of carboxylic group on the molecule. The negative charges
of the gelatin molecules result in formation of an electrical double layer on the
surface of the aqueous gelatin droplets which prevents the gelatin droplets from
flocculation and coalescence. After the emulsion was formed, it was cooled down
immediately in a refrigerator. Since the gelatin droplets had been solidified while
the emulsion was converted to a suspension, there was no chance for them to fuse
to larger size. Therefore, even though no emulsifier is used in this nanoencapsulation process, no aggregation and fusion were observed during the process. But
after the suspension was diluted with carbon tetrachloride before filtration, the
suspension showed some aggregation.
Water content of the gelatin nanoparticles
The water content is an important parameter for hydrogel drug delivery
system. It can reflect water uptaking ability and permeability of the hydrogel.
Figure 3 shows that the water content of the gelatin nanoparticles has a linear
dependence on temperature. As shown in figure 3, at 15"C the gelatin nanoparticles can take up 51.6% of water, whereas they can take up 71.4% of water at
42°C. The water content is affected b y the degree of crosslinking of the gelatin
matrix (Wu 199613). At the higher temperature, the gelatin molecules have a higher
mobility and lower degree of crosslinking which increases the swelling degree of
the hydrogel.
D