Biomedical Engineering Reference
In-Depth Information
Figure 9.2
Schematic representation of the structural model of PVA/PEG double-network
hydrogel.
the local stress either by various dissipations or by large deformation of the PEG
chains. The crystalline regions of PVA essentially serve as physical crosslinks to
redistribute external stresses [31] .
9.2.2.2
Formation of Physical Elastic Hydrogels via Hydrophobic Interaction
Polymers with hydrophobic domains can crosslink in aqueous environment via
reverse thermal gelation. Temperature increase promotes hydrophobic interac-
tions resulting in the association of hydrophobic polymer chains. The physical
association of hydrophobic domains holds swollen soft domains together and
makes the polymers stable in water [32]. The common hydrophobic blocks which
can undergo reverse thermal gelation at or near physiological temperature are
PPO, PLGA, poly(
N
- isopropylacrylamide), PCL, and poly(urethane) [33] .
For example, multiblock copolymers of polyethylene oxide and PCL or PLA
were synthesized for the preparation of polymer fi lms by solvent casting method.
The multiblock copolymers formed thermoplastic hydrogels via hydrophobic
interaction. The block copolymer fi lms were rubbery in both dried and swollen
states. The interesting property of these multiblock copolymers was that the swell-
ing increased by increasing temperature and increased further, rather than
decreasing, when the temperature was lowered to the initial temperature [30].
Other types of amphiphilic block copolymers of PCL with PLA and PGA were
also synthesized to prepare elastic PCL/PLA and PCL/PGA physical hydrogels
[4, 27] .
