The entrapment efficiencies for niosomes prepared using
Tween 60 were superior to those prepared using Tween 80
which in turn were superior to those prepared with Brij 35.
This may be explained by the fact that the vesicles obtained
from stearyl (C18) chain surfactants (Tween 60) produce
higher entrapment efficiencies than surfactants with lauryl
(C12) chain (Brij 35), as the length of alkyl chain is a crucial
factor of permeability. Thus, long chain surfactants produce
high entrapment (33). Additionally, the alkyl chain length
influences the HLB value of the surfactant which in turn
directly influences the drug entrapment efficiency (34). The
lower the HLB of the surfactant the higher will be the drug
entrapment efficiency and stability as in the case of niosomes
prepared using Tween 60 (HLB=14.9), whilst Brij 35 with a
high HLB of 16.9, showed very low entrapment efficiency.
Only Tween 80 has an unsaturated alkyl chain. The
introduction of double bonds made the chains bend, which
led to the formation of a niosomal membrane that is not
sufficiently tight. Thus, the membrane formed was more
permeable, which possibly explains the lower entrapment
efficiency of the Tween 80 formulations compared to Tween
60 formulations (33).