(A) Structural schematic of the ionic interaction
of PFPE carboxyl
ion end groups, which are released following PFPE-Ester hydrolysis
in aqueous medium, and ionized quaternary groups on exposed chains
of branched 25 kDa PEI, resulting in ammonium salt bridges responsible
for droplet surface stabilization at the PFPE/water interface. (B)
Schematic representation of PFPE ionic surface cross-linked interaction
with PEI in F127 hydrogel matrix. (C) Cross polarized optical microscopy
image of the surface interaction where PFPE droplets are surrounded
by PEI in aqueous medium, 50× magnification. (D–E) PFPE/PEI/F127
hydrogel thermoresponsive behavior. Sol state at 4 °C and gel
state at body temperature (37 °C). (F) Scanning electron microscopy
image of lyophilized cross-linked PFPE/PEI/F127 hydrogel, showing
large and small droplets of PFPE oil dispersed into F127 matrix.