Dynamic Behavior of the Structural Phase Transitionof Hydrogel Formation Induced by Temperature Ramp and Addition ofIbuprofen
2020
Understanding
the dynamic behavior of hydrogel formation induced
by a temperature ramp is essential for the design of gel-based injectable
formulation as drug-delivery vehicles. In this study, the dynamic
behavior of the hydrogel formation of Pluronic F108 aqueous solutions
within different heating rates was explored in both macroscopic and
microscopic views. It was discovered that when the heating rate is
increased, the gelation temperature window (hard gel region) shrinks
and the mechanical strength of the hydrogel decreases. A given system
at different heating rates would lead to different crystalline structural
evolutions. The time-resolved small-angle X-ray scattering (SAXS)
experiments at a heating rate of 10 °C/min disclose that the
crystalline structure of micelle packing in the hydrogel exhibits
a series of transitions: hexagonal close-packed (HCP) to face-centered
cubic (FCC) and body-centered cubic (BCC) structures coexisting and
then to the BCC structure along with the increasing temperature. For
the system at equilibrium, the BCC structure exclusively dominates
the system. Furthermore, the addition of a hydrophobic model drug
(ibuprofen) to the F108 aqueous solution promotes hard gel formation
at even lower temperatures and concentrations of F108. The SAXS results
for the system with ibuprofen at a heating rate of 10 °C/min
demonstrate a mixture of FCC and BCC structures coexisting over the
whole gelation window compared to the BCC structure that exclusively
dominates the system at equilibrium. The addition of ibuprofen would
alter the structural evolution to change the delivery path of the
encapsulated drug, which is significantly related to the performance
of drug release.
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