A series of gelatin microspheres (GMs) were prepared through emulsificationcoacervation method in water-in-oil (w/o) emulsions.The influence of preparation parameters on particle size

surface morphology and dispersity of GMs was examined.The studied preparation parameters include concentration of gelatin solutions

concentration of the emulsifier

water/oil ratio

emulsifying time

stirring speed and so on.The surface morphology

dispersity and particle sizes of GMs were determined by the scanning electron microscopy (SEM)

SemAfore 4 Demo software and particle size distribution graphic charts.The experimental results indicated that increasing the concentration of gelatin solution would increase the particle size of GMs.When the solution concentration increasing from 0.050 g/mL to 0.200 g/mL gradually

the particle size increased correspondingly.The relationship between the two quantities was linear.On the contrary

increasing the concentration of the emulsifier would decrease the particle size of GMs.Furthermore

the particle size reduced quickly at initial time and slowed down latterly.With the increase of emulsifier concentration from 0 to 0.020 g/mL

the mean diameters of GMs decreased from 17.32 μm to 5.38 μm.However

the particle size dwindled slowly when emulsifier concentration was higher than 0.020 g/mL.The excellent result was obtained with the condition:0.050 g/mL of emulsifier concentration

0.100 g/mL of gelatin solution concentration

1/5 of water/oil ratio

10 min of emulsifying time and 900 r/min of the stirring speed.The GMs prepared at this condition had the smallest sizes

the narrowest size distribution

the best sphericity and fluidity.The water/oil ratio has the same influence on particle size of GMs as that of gelatin solution concentration.With the increase of water/oil ratio the average particle size increased linearly

and the surface of microspheres became smoother as well.It is supposed that water/oil ratio can be used to change the diameters and surface morphologies of GMs.The emulsifying time had little influence on the mean diameters of GMs

but it affected the dispersity of GMs apparently.When the emulsifying time was shorter than 5 min

the GMs had bad dispersity;after increasing the emulsifying time to 13 min

the dispersity of GMs changed greatly;whereas the dispersity of GMs became bad again when the emulsifying time was longer than 13 min.According to the experimental results

13 min was considered to be the best emulsifying time.The stirring speed had the similar influence on GMs’ morphologies as that of emulsifying time.Slow stirring rate made large size distribution and bad sphericity of GMs;excessive stirring speed resulted in aggregation among GMs likewise.The smaller size distribution and better sphericity of GMs were observed under the stirring rate between 500 r/min to 1500 r/min by SEM.In conclusion

increasing the concentration of gelatin solution or w/o ratio would increase the particle sizes of GMs

increasing the concentration of the emulsifier would decrease the sizes of GMs

proper emulsifying time and stirring speed would resultin in the best sphericity of GMs.