Using synthetic bioresorbable polymers for orthopedic tissue regeneration - Durability and Reliability of Medical Polymers - page 131

an innovative strategy to enhance the mechanical properties of
biodegradable polymers is the incorporation of nanomaterials as fillers
within polymer matrices. With the appropriate modifications to facilitate
dispersion into polymers and to enhance interactions with the surrounding
matrix, nanocomposites have demonstrated improved mechanical properties
compared with unfilled polymers or polymers loaded with larger, micrometer-
sized particles. a few studies have also shown enhanced cell function when
bone cells are cultured on nanophase ceramic materials. 102

6.6 Hydrogels
Hydrogels represent another class of polymer scaffolds, which are formed
by polymerization and crosslinking of molecules such as acrylic acid,
and N -isopropylacrylamide. Hydrogels are an attractive option because of
their temperature-dependent physical properties. they can be designed to
be gelatinous at room temperature, but they take on more rigid qualities
at body temperatures. 103 this property could allow for the administration
of tissue-engineering constructs via injection. Hydrogels also allow for
relatively easy chemical manipulation of individual peptides. Incorporation
of arginine-glycine-aspartate (rGD) peptide motifs on these polymers has
been demonstrated to enhance osteoblast adhesion and proliferation. 104
Polymeric hydrogels have the distinct advantage of being injectable,
which allows the delivery of the construct to be less invasive and thereby
reduces surgical risks. employment of these types of polymers also ensures
delivery of an even distribution of a precise number of cells. they can
be configured to provide mechanical support to the cells to maintain their
specific phenotype, without inhibiting migration. Common hydrogel substrates
include the copolymers of poly(ethylene oxide) and poly(propylene oxide),
known as pluronics, and natural polymers, including alginate and agarose.
The delivery of a known concentration of cells is simplified when using a
hydrogel, whereby 100% of the cells are encapsulated within the delivery
system, compared with the fibers, for which cell delivery is dependent on cell
attachment. the hydrogels also allow the suspended cells to be uniformly
distributed throughout the volume of polymer delivered. In contrast, the
distribution of cells in the polymer fiber system is not uniform and is difficult
to predict. 3,84

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6.7 Future trends
their similarity to the biological environment, and reduced likelihood of
toxicity and inflammatory reactions, gives materials of natural origin a
distinct advantage over synthetic ones. Despite this advantage, naturally
derived polymers possess poor mechanical properties. It was concluded that