Thermoresponsive Brushes Facilitate Effective Reinforcement of Calcium Phosphate Cements

Calcium
phosphate ceramics are frequently applied to stimulate
regeneration of bone in view of their excellent biological compatibility
with bone tissue. Unfortunately, these bioceramics are also highly
brittle. To improve their toughness, fibers can be incorporated as
the reinforcing component for the calcium phosphate cements. Herein,
we functionalize the surface of poly­(vinyl alcohol) fibers with thermoresponsive
poly­(N-isopropylacrylamide) brushes of tunable thickness
to improve simultaneously fiber dispersion and fiber–matrix
affinity. These brushes shift from hydrophilic to hydrophobic behavior
at temperatures above their lower critical solution temperature of
32 °C. This dual thermoresponsive shift favors fiber dispersion
throughout the hydrophilic calcium phosphate cements (at 21 °C)
and toughens these cements when reaching their hydrophobic state (at
37 °C). The reinforcement efficacy of these surface-modified
fibers was almost double at 37 versus 21 °C, which confirms the
strong potential of thermoresponsive fibers for reinforcement of calcium
phosphate cements.