Biomedical Engineering Reference
In-Depth Information
biocompatibility and tunable chemical, physical and mechanical properties,
stimuli-responsive hydrogels may be used in a diverse range of biomedical
applications. Examples include smart biomimetic three-dimensional scaf-
folds
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for minimally invasive, e.g., cartilage repair
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and stem cell ther-
apy
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and drug delivery applications.
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They could also be used to engineer
organs or tissues with spatial complexity in composition and organization,
e.g., zonal articular cartilage repair.
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Example composites for a range of
applications, prepared by combining hydrogels with a variety of filler phases
or other polymers, will be described below.
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7.3.2.1 Thermo-responsive Composites
Reversible thermo-responsive composites, produced by incorporating a
thermo-responsive gel layer between two plastic or glass sheets
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or relying
on temperature-dependent match/mismatch of the refractive indices of the
nanofiller and matrix,
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have been used as smart optical switches/lenses for
sensors and eye protection.
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They exhibit an abrupt transparent-opaque
transition when the temperature exceeds a critical value. When the tem-
perature goes down, they become transparent. The thermo-responsive
composites can also be used for targeting drug delivery applications. Con-
trolling the in situ gelling of the hydrogel phase and the way by which this
phase aggregates controls the drug release kinetics and the magnitude of
burst and overall drug release.
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7.3.2.2 Electro-responsive Composites
Smart composites based on electrically conducting polymers, e.g., poly-
pyrrole, can be used for controlled release of a diversity of biologically active
molecules (e.g., proteins or polysaccharides or heparin) or cellular signal
factors (e.g., growth factors). These composites have been shown to support
endothelia cell growth.
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.
7.3.2.3 Thermo- and Mechanico-responsive (Self-healing)
Composites
The integrity of a structural composite can be jeopardized by thermal and
mechanical fatigue induced micro-cracks. Smart composites, with the ability
to repair cracks, have been produced by incorporation of healing agent-
loaded microcapsules within the matrix. Once intruded by a crack, these
microcapsules release the healing agent that polymerizes upon contact with
a catalyst embedded within the polymeric matrix. This self-healing process
yielded
75% recovery in the composite toughness
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(Figure 7.1, panel IV).
Inclusion of microcapsules, however, can reduce the initial mechanical
properties of composites. Use of a thermally mendable matrix, e.g.,men-
domer 401, has been an alternative approach.
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B
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