Biomedical Engineering Reference
In-Depth Information
behavior of cells from soft tissue is strongly influenced by the
mechanical properties of the material used as substrate for cell
adhesion and proliferation. Indeed, cells have greater proliferation,
differentiation, as well as an encouraged cell-cell communication
when the substrate possesses an elasticity that matches that of the
native tissue. Moreover, when mechanical stimulation can be applied,
cell behavior and the properties of the engineering tissue may be
controlled. Thus, the design of biomedical elastomers has become
very important since they may create a biomimetic environment
favorable to cell growth and tissue development [YOU 11].
Elastomers may be cross-linked physically (thermoplastic) or
chemically (thermoset). High-molecular-weight polyurethanes (PU)
have been widely used as thermoplastic elastomeric biomaterials.
They are synthesized from macrodiols, chain extenders and
diisocyanates to develop heterogeneous multiblock structures that
contain an amorphous zone providing the flexibility, while the
physical cross-linking occurs through crystalline or glassy zones
resulting from contributions of chain extender and diisocyanate
components [YOU 11]. PU elastomers possess a wide range of
chemical structures based on the chosen macrodiols which can be
ether-, ester-, carbonate-based polymers, such as poly(ethylene oxide),
poly(
-caprolactone) and poly(trimethylene carbonate) [BOR 98]. PU
elastomers have found applications as pacemaker wire coatings,
components of artificial heart, as well as the design of scaffolds for
the regeneration of cardiovascular tissue, anterior cruciate ligament
and cartilage. Copoly(ether-esters), such as poly(ethylene
oxide)/poly(butylene terephthalate) (PEO/PBT), are also thermoplastic
elastomers. The amorphous soft segments are constituted of
polyethers and the hard crystalline segments are constituted of
polyesters. PEO/PBT elastomers have tensile strength ranging from 8
to 23 MPa and elongation at break from 500 to 1,300%. Recently,
they found applications in dermal tissue regeneration and for cartilage
engineering [YOU 11].
ε
Thermoset elastomers are stronger materials than thermoplastic
elastomers due to the covalent cross-linking. They possess
