We
found
in
this
study
that
fluidity
of
a
niosome
increased
with
unsaturation
of
the
fatty
acyl
(alcohol)
chain
and
the
size
of
the
headgroup.
Transdermal
drug
delivery
by
a
vesicular
formulation
would
largely
depend
on
the
interaction
of
the
vesicles
and
the
stratum
corneum
(SC)
lipid
layers
but
presently
the
structure
of
the
latter
is
not
known
on
the
molecular
level.
Moreover
experi-
mental
studies
that
compare
the
transdermal
drug
delivery
by
the
liposomes
and
niosomes
of
all
the
surfactants
used
in
this
study
are
not
available.
With
these
limitations
it
is
not
straightforward
to
assess
the
effect
of
fluidity
on
the
transdermal
drug
delivery.
How-
ever,
the
enhanced
transdermal
drug
delivery
by
niosomes
is
often
attributed
to
the
mixing
of
the
niosomal
lipids
with
the
SC
lipids
(Fang
et
al.,
2001b).
A
surfactant
itself
is
a
penetration
enhancer
and
at
the
same
time
increases
the
fluidity
of
the
SC.
In
this
regard
Kato
et
al.
(2008)
reported
that
Span
niosomes,
with
a
higher
fluid-
ity
than
phospholipid
liposomes,
undergo
fusion
that
may
facilitate
drug
delivery:
once
mixed
with
the
SC
lipids,
the
surfactant
origi-
nated
from
niosomes
with
a
higher
fluidity
will
fluidize
the
SC
lipids to
a
greater
extent.
However,
it
is
no
doubt
that
more
extensive
studies
are
needed
to
validate
this
hypothesis.