Thermoresponsive
amphiphilic Pluronic F127 triblock copolymer solutions
have been widely investigated in smart biomaterial applications due
to the proximity of its critical gel temperature to human body temperature.
Meanwhile, cellulose nanocrystals (CNCs) have quickly become the focus
of many drug delivery and tissue engineering applications due to their
biocompatibility, abundance, ability to conjugate with drug molecules,
and superior rheological properties. Herein, we investigate the phase
behavior and thermo-rheological properties of the composite hydrogels
containing cellulose nanocrystals (up to 5% by weight) and the temperature
responsive Pluronic F127. Our results revealed an unprecedented role
of CNC network formation on micellization and gelation behavior of
the triblock copolymer. Linear and nonlinear rheological analysis
suggest that at low and moderate nanocrystal loadings (1–3%
by weight), the composite gel remarkably becomes softer and deformable
compared to the neat Pluronic F127 gels. The softening effect results
from the disruption of the close packed micelles by the rodlike CNCs.
At high concentrations, however, the nanocrystals form their own network
and the micelles are trapped within the CNC meshes. As a result, the
original (neat F127) hard-gel modulus is recovered at 4 to 5% nanocrystal
loading, yet the composite gel is much more deformable (and tougher)
in the presence of the CNC network. Our temperature sweep experiments
show that the CNC addition up to 3% does not change the rapid thermal
gelation of the F127 solutions; therefore, these composites are suitable
for smart drug delivery systems. On the other hand, at higher CNC
concentrations, abrupt viscosity transition is not observed, rather
the composite gels smoothly thicken with temperature in contrast to
thermal thinning of the aqueous neat CNC. Thus, they can be used as
smartly adaptive biolubricants and bioviscostatic materials.