Biomedical Engineering Reference
In-Depth Information
•
a variable hydrophobicity/hydrophilicity balance suitable for constructing drug-
sustained/controlled release devices;
•
an erosive mechanism and
in vitro
biodegradation rates ranged from 10
− 3
to
10
− 1
mg/(cm
2
h) that can be regulated by impregnating enzymes;
•
fusibility (
150 °C) and solubility in common organic solvents (ethanol, THF,
chloroform, methylene chloride, etc.) and ease of processing into different
forms and shapes; and
<
•
excellent adhesion to plastic, metallic, and glass surfaces that is important for
their use as coatings.
5.3
Conclusion and Perspectives
The concise review highlights how dimerized and polyfunctional forms of natu-
rally occurring
-AAs are suitable building blocks for constructing new bioanalo-
gous macromolecular systems with non-natural orientation of
α
- AAs ' residues in
the polymeric backbones. This nonconventional architecture of polymer chain is
expected to provide low immunogenicity of
α
- AAs - based polymeric biomaterials
by “confusing nature.” For practical biomedical applications as biodegradable
biomaterials, the most promising are polymers containing hydrolysable ester
bonds in the backbones called as amino acid based biodegradable polymers
(AABBPs). There are various classes of high- molecular - weight AABBPs: PEAs,
PEURs, and PEUs obtained with
α
α
-AAs and other nontoxic building blocks such
as fatty diols, dicarboxylic acids,
-Has, and carbonic acid. The selection of appro-
priate building blocks under optimal polycondensation methods allows the syn-
thesis of AABBPs with tailored material properties. Listed AABBPs contain
H-bond-forming chemical units that enhance their mechanical characteristics,
hydrophilicity, and biocompatibility. The AABBPs exhibit some obvious advan-
tages over existing and commercially successful aliphatic PEs: polyglycolic and
poly(lactic acids), their copolymers, poly(caprolactone), and so forth.
The most extensively studied AABBPs to date are PEAs because of ample avail-
ability, low cost of starting monomers, and desirable material properties that can
be tailored in a wide range. PEAs have been successfully tested, for example, as
medicated wound dressing, also, in animals and humans for cardiovascular appli-
cations.
Ex vivo
cell-based assays have strongly supported recent human trial data
indicating that PEAs are blood and tissue compatible, with advantageous proper-
ties for implantation into tissue. Tremendous value that PEAs have in the health
science and industry is the mechanism by which they degrade, and drug release
profi le. PEAs' biodegradation and mechanism of drug release is believed to
proceed by surface erosion and primarily follows zero-order kinetics. These unique
material properties have shown PEAs' multiuse potential as a new family of bio-
degradable biomaterials as drug delivery platforms or as components of resorbable
surgical implants.
α
