Biomedical Engineering Reference
In-Depth Information
systems, and as such, they represent an important ex-
tension of polymeric biomaterials beyond their well-
known uses in implants and medical devices. Several
review articles are available on these interesting smart
hybrid
Biocompatible polymer
backbone
(may also be biodegradable or
stimuli-responsive to pH, T, E)
biomaterials
( Hoffman,
1987,
1995,
1997;
Biofunctional molecule
(linked by biodegradable
spacer arm)
B
Hoffman et al. , 1999 , 2000; Okano et al. , 2000 ).
Ligand (for cell receptor,
mucin, E.C.M. component,
plasma protien,
Smart polymers in solution
)
There are many polymers that exhibit thermally induced
precipitation ( Table 3.2.6-2 ), and the polymer that has
been studied most extensively is PNIPAAm. This poly-
mer is soluble in water below 32 C, and it precipitates
sharply as temperature is raised above 32 C( Heskins
and Guillet, 1968 ). The precipitation temperature is
called the LCST. If the solution contains buffer and salts
the LCST will be reduced several degrees. If NIPAAm
X
Signal group (for imaging)
Liphophilic group (for
insertion in cell membrane,
liposome, micelle,
nanoparticle)
Plasmid vector (for
insertion into cell nucleus)
Table 3.2.6-2 Some polymers and surfactants that exhibit
thermally-induced phase separation in aqueous solutions
Non-fouling group
(to repel IgGs)
Polymers/Surfactants with Ether Groups
Poly(ethylene oxide) (PEO)
Fig. 3.2.6-2 Schematic illustration showing the variety of natural
or synthetic biomolecules which may be conjugated to a smart
polymer. In some cases, only one molecule may be conjugated,
such as a recognition protein, which may be linked to the protein
at a reactive terminal group of the polymer, or it may be linked at
a reactive pendant group along the polymer backbone. In other
cases more than one molecule may be conjugated along the
polymer backbone, such as a targeting ligand along with many
drug molecules. (Hoffman et al., Journal of Biomedical Materials
Research 2000).
Poly(ethylene oxide/propylene oxide) random copolymers
[poly(EO/PO)]
PEO-PPO-PEO triblock surfactants (Polyoxamers or Pluronics)
PLGA-PEO-PLGA triblock polymers
Alkyl-PEO block surfactants (Brij)
Poly(vinyl methyl ether)
Polymers with Alcohol Groups
conjugated to the smart polymer backbone to provide it
with ''stealth'' properties ( Fig. 3.2.6-2 ).
Combining a smart polymer and a biomolecule pro-
duces a new, smart ''biohybrid'' system that can syner-
gistically combine the individual properties of the two
components to yield new and unusual properties. One
could say that these biohybrids are ''doubly smart.''
Among the most important of these systems are the
smart polymer-biomolecule conjugates, especially the
polymer-drug and polymer-protein conjugates. Such
smart bioconjugates, and even a physical mixture of the
individual smart polymers and biomolecules, may be
physically adsorbed or chemically immobilized on solid
surfaces. The biomolecule may also be physically or
chemically entrapped in smart hydrogels. All of these
hybrid systems have been extensively studied and
this section reviews these studies. There have been
a number of successful applications in both medicine and
biotechnology
Poly(hydropropyl acrylate)
Hydroxypropyl cellulose
Methylcellulose
Hydroxypropyl methylcellulose
Poly(vinyl alcohol) derivatives
Polymers with Substituted Amide Groups
Poly(N-substituted acrylamides)
Poly(N-acryloyl pyrrolidine)
Poly(N-acryloyl piperidine)
Poly(acryl- L -amino acid amides)
Others
Poly(methacrylic acid)
for
such
smart
polymer-biomolecule
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