Biomedical Engineering Reference
In-Depth Information
Table 3.2.4-3 Absorbable synthetic polymers
Type
Chemical and physical
aspects
Construction/useful forms
Comments/applications
Poly(glycolide) (PGA)
Thermoplastic crystalline
polymer (T
m
¼ 225
C,
T
g
¼ 40-45
C)
Multifilament yarns, for weaving,
knitting and braiding, sterilized
by ethylene oxide
Absorbable sutures and
meshes (for defect repairs
and periodontal inserts)
10/90 Poly(
L
-lactide-co-glycolide)
(Polyglactin 910)
Thermoplastic crystalline
co-polymer (T
m
¼ 205
C,
T
g
¼ 43
C)
Multifilament yarns, for weaving,
knitting and braiding, sterilized
by ethylene oxide
Absorbable sutures and
meshes
Poly(p-dioxanone) (PDS)
Thermoplastic crystalline
co-polymer (T
m
¼ 110-115
C,
T
g
¼ 10
C)
Melt spun to monofilament yarn
Sutures, intramedullary pins
and ligating clips
Poly(alkylene oxalates)
A family of absorbable polymers
with T
m
between 64 and 104
C
Can be spun to monofilament
and multifilament yarns
Experimental sutures
Isomorphic
poly(hexamethylene-co-trans-1,
4-cyclohexane dimethylene
oxalates)
A family of crystalline
polymers with T
m
between
64 and 225
C
Can be spun to monofilament
and multifilament yarns
Experimental sutures
Modified natural fibers
Silk and collagen are two natural fibers that have been
widely used in medicine for multiple applications. Silk
from the silkworm,
Bombyx mori,
has been used for
decades as a suture. Because of the fineness of individual
silk fibers, it is necessary to braid the individual fibers or
brins together into thicker yarn bundles. Collagen has
been used either in a reconstituted form or in its natural
state. Reconstituted collagen is obtained from enzymatic
chemical treatment of either bovine skin or tendon
followed by reconstitution into fibrils. These fibrils can
then be spun into fibers and fabricated into textile
structures or can be left in their native fibrillar form for
use in hemostatic mats and tissue-engineered substrates.
''Catgut,'' a natural collagen-based suture material
obtained from ovine intestine, which is cross-linked and
In addition to synthetic polymers, a class of fibers exists
that is composed of natural biopolymer based materials.
In contrast to synthetic fibers that have been adapted
for medical use, natural fibers have evolved naturally and
so can be particularly suited for medical applications.
Cellulose, which is obtained from processed cotton or
wood pulp, is one of the most common fiber-forming
biopolymers. Because of the highly absorbent nature of
cellulose fibers, they are commonly used in feminine
hygiene products, diapers, and other absorbable appli-
cations, but typically are not used
in vivo
because of the
highly inflammatory reactions associated with these
materials. In certain cases, these properties can be used
to advantage such as in the aforementioned hemostat
Surgicel. In this application, the thrombogenicity and
hydration characteristics of the regenerated cellulose are
used in stopping internal bleeding from blood vessels
and the surface of internal organs. Also of growing in-
terest are fibers created from modified polysaccha-rides
including alginates, xanthan gum, chitosan, dextran, and
reticulated cellulose (
Shalaby and Shah, 1991; Keys,
1996
). These materials are obtained from algae, crusta-
cean shells, and through bacterial fermentation. A list of
several forms of alginates and their proposed uses is
presented in
Table 3.2.4-4
(
Keys, 1996
). Another natural
material, chitosan, has been used to fabricate surgical
sutures and meshes, and it is currently under in-
vestigation for use as a substrate or scaffold for tissue-
engineered materials (
Skjak-Braek and Sanford, 1989
).
Chitosan and alginate fibers are formed when the poly-
mer is coagulated in a wet solution spinning process.
Table 3.2.4-4 Potential uses of alginates (
Keys, 1996)
Type
Current use
Ca alginate (non-woven)
Absorbent wound dressings
Pledgets
Scaffold for cell culture
Surgical hemostats
Ca alginate (particulate)
Acid-labile conjugates of alginate and
doxirubicin
Sequestration of 90Sr from ingested
contaminated food and water
Na alginate (ultra pure)
Microencapsulation
Bioreactors
Ca/Na alginate (hydrogel)
Wound management
