3.2.2 Rheological analysis
Rheological analysis was performed for all formulations based on the
different micelle compositions and the presence or absence of
antibodies, and it was possible to determine the elastic (G´) and
viscous (G´´) moduli, viscosity and temperature where the more
pronounced viscosity variation was observed and was considered the
sol-gel temperature (Tsol-gel). Table 2 provides all the information
from the rheological analysis.
For topical delivery, the formulations of the gel should be at skin and
body temperature (32 – 36 ºC) while existing as a solution at room
temperature (Ban et al ., 2017). All formulations meet this
criteria; the highest gelation temperature being 20.04 ºC. The Tsol-gel
(ºC) did not show significant changes independent of the addition of
scFv-Fc antibodies to the PL-based formulations. The results support
reports in the literature, where high PL407 concentrations indicated
Tsol-gel formation between 25 and 33 ºC (Dorraj & Moghimi, 2015;
Freitas Mariano et al ., 2019).
The behavior of the hydrogels was temperature-dependent, as observed for
more gels with the more pronounced viscosity values at 32.5 ºC compared
to those of the gels at 25 ºC. However, the G´ values were lower in the
binary formulation (F2), showing that even a small amount of PL403 could
change the rheological parameters. The differences between G´ and G´´ in
the binary system could be attributed to the physicochemical properties
of PL403 in relation to those of PL407. PL403 had a lower HLB value (8)
compared to that of PL407 (22) (Freitas Mariano et al ., 2019).
The results obtained agree with those of other studies: a hydrogel that
is applied on the skin should be in a solid state. For topical
formulations, the hydrogel should exhibit sufficient viscosity (6000 –
7000 cps) (Freitas Mariano et al ., 2019;,Banet al. , 2017;,Pillai & Panchagnula, 2003). For
all the formulations, the viscosity increased with increasing
temperature, and the elastic modulus was greater than the viscous
modulus.