120 V. Bazargan and B. Stoeber
consisting of PEO-PPO block copolymers belong to this group and are commer-
cially available and commonly used to form TRFs.
6.4.2 Properties of Pluronic Solutions
188.8.131.52 Phase Transition of Pluronic Solutions
Pluronics are biocompatible symmetric triblock copolymers of poly(ethylene
These amphiphilic copolymers have hydrophilic EO
and hydrophobic PO
units where x and y can take on speciﬁc values depending on the particular kind
of Pluronic. Aqueous Pluronic solutions undergo reversible gel formation at a
speciﬁc critical solution temperature that depends on the polymer concentration,
its molecular weight and the polymer architecture.
The sol-gel tran-
sition of Pluronic solutions occurs through three dimensional packing of polymer
micelles into a lattice, to achieve a hydrophilic/hydrophobic balance.
Above the critical micelle concentration (CMC) the polymers aggregate into
multi molecular structures with a hydrophobic central core (PO) and a hydrophilic
At higher concentrations, above the
critical gel concentration (CGC) the micelles can take on a cubic lattice structure.
Elevated temperatures lead to dehydration of the hydrophobic core and also
increase the hydrophobicity of the hydrophilic blocks, which eventually leads to
The aggregation and phase behavior of Pluronics have been
extensively studied using several techniques including light scattering, NMR,
SANS, SAXS, DSC, microscopy, and rheology.
Pluronic F127, or Poloxamer 407, has previously been used for several appli-
cations in drug delivery. Its chemical formula is (PEO)
nonionic surfactant, and in aqueous solution it can thermo-reversibly change from
its liquid phase into a gel structure at a gelation temperature T
, which depends
on its concentration. Aqueous solutions of Pluronic F127 are non-Newtonian
ﬂuids with thermo-thickening and shear thinning properties.
properties of Pluronic F127 solutions including the effect of salts on gelation as
well as its biocompatibility will be further discussed.
184.108.40.206 Rheological Characterization of Pluronic Solutions
Pluronic F127 solutions are thermo thickening materials. This means that upon
heating their viscosity increases gradually over a wide range of temperatures
until to their gel point, where the viscosity appears to increase dramatically.
At higher concentration of Pluronic, gel forms at lower temperature. Stoeber
et al. have shown this behavior using rheometry for different concentrations
of Pluronic F127.
Continuous cone and plate vioscometry characterizes this
phase transition under conditions that are relevant for the application to ﬂuids
streaming in microﬂuidic channels. This change in viscosity or phase change is
completely reversible and after one thermal cycle, the shear viscosity returns to its
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