Biomedical Engineering Reference
In-Depth Information
Various copolymers containing blocks of poly(hydroxyl esters)
and other synthetic polymers have been prepared. For exam-
ple, PCL-b-PEG-b-PCL networks have been synthesized, and they
exhibit a greater compressive modulus and degradation rate than
PCL alone.
111
Networks based on adipic acid, 4-hydroxycinnamic
acid, and PCL diols with elastomeric properties have also been
prepared.
112
,
113
PCLhasalso beencombinedwithtrimethylenecar-
bonate, and the reaction behavior and bulk properties have been
characterized.
114
-
122
Furthermore,star-PCL-b-PLAmacromershave
been synthesized.
113
,
114
These networks show dependence in phys-
ical properties and degradation on the length of the copolymer
block.
123
,
124
Han and Hubbel
105
,
106
and Ju
et al
.
107
prepared lactide-
based PEG networks emanating from glycerol centers. The degrad-
ability of these networks was controlled by the ratio of lactide and
PEG.
105
,
107
8.4 Summary and Outlook
In summary, a wide range of different precursor molecules are
being developed that form networks via photoinitiated polymeriza-
tions for tissue engineering and molecule delivery applications. The
diversity in polymer properties, ranging from highly cross-linked,
hydrophobic networks to loosely cross-linked, swollen hydrophilic
hydrogels, expands the applicability of these biomaterials. As more
knowledge and understanding of biological events such as tis-
sue healing and cell-material interactions becomes available, the
materials used in these applications will become smarter and more
complex. In particular, there is great interest in designing biologi-
cal function into polymers, such as enzymatically degrading cross-
links and adhesion sites, to better control the interactions between
cells and materials. Also, as advances are made in the area of poly-
mersynthesis,itisbecomingeasiertotailorpolymerpropertiesand
structure to match desired properties. Novel materials may open
up avenues for unique material behavior such as externally trig-
gered properties (e.g., temperature induced), shape-memory poly-
mers,andthepatterningofstructuresthree-dimensionally.Thenext
decade is bound to produce previously unimaginable biomaterials
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