Biomedical Engineering Reference
In-Depth Information
[18]. h ese polymers are an increasingly important class of smart materials
because they can transform electrical energy into mechanical energy and
have promising applications in energy transduction, biomechanics, chemi-
cal separations, artii cial muscle actuation and controlled drug delivery,
[19, 20]. Electrically responsive delivery systems are prepared from poly-
electrolytes (polymers that contain a relatively high concentration of ioniz-
able groups along the backbone chain) and are thus pH-responsive as well.
Typically, electric-sensitive polymers have been investigated in the form
of polyelectrolyte hydrogels [21-24]. Polyelectrolyte gels deform under an
electric i eld due to anisotropic swelling or deswelling as charged ions are
directed toward the anode or cathode side of the gel [18].
2.3.4 Magneto-responsivePolymers
Generally, magneto-responsive polymers consist of inorganic magnetic
nanoparticles which are physically entrapped within or covalently immo-
bilized to a three-dimensional crosslinked network, leading to materials
with shape and size distortion that occurs reversibly and instantaneously
in the presence of a non-uniform magnetic i eld [25, 26]. As a result of
the magnetic susceptibility of the particles, these materials have received
signii cant attention for use as sot biomimetic actuators, sensors, cancer
therapy agents, artii cial muscles, switches, separation media, membranes,
and drug delivery systems [27, 28]. Most examples of magneto-responsive
polymer systems involve non-covalent interactions between polymer
chains and magnetic particles [28]. However, recent advances in polymer
synthesis have facilitated the covalent immobilization of polymer chains
directly to the surface of magnetic particles [29].
2.3.5 Photo-responsivePolymers
Photo-responsive polymers are macromolecules that change their properties
when irradiated with light of the appropriate wavelength [30]. Typically these
changes are the result of light-induced structural transformations of specii c
functional groups along the polymer backbone or side chains [31]. Among,
these functional groups (chromophores), we can i nd, azobenzenes [32], spi-
ropyran groups [33, 34], or nitrobenzyl groups [35, 36]. Because light can be
applied instantaneously and under specii c conditions with high accuracy, it
renders photo-responsive polymers highly advantageous for possible appli-
cation which include reversible optical storage, polymer viscosity control,
photomechanical transduction and actuation, bioactivity switching of pro-
teins, tissue engineering, and drug delivery [37-40]. An important aspect
