Biomedical Engineering Reference
In-Depth Information
a rapid collapse. These materials had the ability to
collapse from a fully swollen conformation in less than
20 minutes, whereas comparable gels that did not contain
graft chains required up to a month to fully collapse. Such
systems show major promise for rapid and abrupt or
oscillatory release of drugs, peptides, or proteins.
used poly(
N
-2-hydroxypropyl methacrylamide) carriers
for the treatment of ovarian cancer.
Self-assembled structures
In the past few years there have been new, creative
methods of preparation of novel hydrophilic polymers
and hydrogels that may represent the future in drug
delivery applications. The focus in these studies has
been the development of polymeric structures with
precise molecular architectures. Stupp
et al.
(1997)
synthesized self-assembled triblock copolymer nano-
structures that may have very promising biomedical
applications.
Complexation hydrogels
Another promising class of hydrogels that exhibit re-
sponsive behavior is complexing hydrogels.
Bell and
Peppas (1995)
have discussed a class of graft copolymer
gels of PMAA grafted with PEG, poly(MAA-
g
-EG).
These gels exhibited pH-dependent swelling behavior
due to the presence of acidic pendant groups and the
formation of interpolymer complexes between the ether
groups on the graft chains and protonated pendant
groups. In these covalently cross-linked, complexing
poly(MAA-
g
-EG) hydrogels, complexation resulted in
the formation of temporary physical cross-links due to
hydrogen bonding between the PEG grafts and the
PMAA pendant groups. The physical cross-links were
reversible in nature and dependent on the pH and ionic
strength of the environment. As a result, these
complexing hydrogels exhibit drastic changes in their
mesh size in response to small changes of pH.
Promising new methods for the delivery of chemo-
therapeutic agents using hydrogels have been recently
reported. Novel biorecognizable sugar-containing co-
polymers have been investigated for the use in targeted
delivery of anti-cancer drugs.
Peterson
et al.
(1996)
have
Star polymers
Dendrimers and star polymers (
Dvornik and Tomalia,
1996
) are exciting new materials because of the large
number of functional groups available in a very small
volume. Such systems could have tremendous promise
in drug targeting applications.
Merrill (1993)
has of-
fered an exceptional review of PEO star polymers and
applications of such systems in the biomedical and
pharmaceutical fields.
Griffith and Lopina (1995)
have
prepared gels of controlled structure and large bi-
ological functionality by irradiation of PEO star poly-
mers. Such new structures could have particularly
promising drug delivery applications when combined
with
emerging
new
technologies
such
as
molecular
imprinting.
Bibliography
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