Biomedical Engineering Reference
In-Depth Information
Table 3.2.4-2 Synthetic polymers (
Shalaby, 1996)
Type
Chemical and physical
aspects
Construction/useful forms
Comments/applications
Polyethylene (PE)
High-density PE (HDPE): melting
temperature T
m
¼ 125
C
Low-density PE (LDPE):
T
m
¼ 110
C,
Linear low-density (LLDPE)
Ultrahigh molecular weight PE
(UHMWPE) (T
m
¼ 140-150
C),
exceptional tensile strength and
modulus
Melt spun into continuous yarns
for woven fabric and/or melt
blown onto nonwoven fabric
Converted to very high tenacity yarn
by gel spinning
The HDPE, LDPE and LLDP are used
in a broad range of health care
products
Used experimentally as reinforced
fabrics in lightweight orthopedic
casts, ligament prostheses, and
load-bearing composites
Polypropylene (PP)
Predominantly isotactic, T
m
¼ 165-
175
C; higher fracture toughness
than HDPE
Melt spun to monofilaments and
melt blown to nonwoven fabrics
Hollow fibers
Sutures, hernia repair meshes,
surgical drapes, and gowns
Plasma filtration
High melting (T
m
¼ 325
C) and
high crystallinity polymer (50-
75% for processed material)
Poly(tetrafluoroethylene)
(PTFE)
Melt extruded
Vascular fabrics, heart valve sewing
rings, orthopedic ligaments
T
g
¼ 45
C, T
m
¼ 220
C,
thermoplastic, hydrophilic
Nylon 6
Monofilaments, braids
Sutures
Nylon 66
T
g
¼ 50
C, T
m
¼ 265
C,
thermoplastic, hydrophilic
Monofilaments, braids
Sutures
Poly(ethylene terephthalate)
(PET)
Excellent fiber-forming properties,
T
m
¼ 265
C, T
g
¼ 65-105
C
Multifilament yarn for weaving,
knitting, and braiding
Sutures, hernia repair meshes,
and vascular grafts
final product. In contrast to flat or untexturized yarn,
texturization results in a yarn that imparts bulk to the
fabric for improved ''hand'' or feel, flexibility, ease of
handling and suturing, and more pores for tissue in-
growth. Melt spinning is typically used with thermo-
plastic polymers that are not affected by the elevated
temperatures required in the melt spinning process.
Figure 3.2.4-1
is a schematic representation of a melt
spinning process.
In this process, the molten resin is extruded through
the spinning head containing one (monofilament) or
multiple holes (multifilament). Air is typically used to
cool and solidify the continuous threadline prior to
lubricating, twisting, and winding up on a bobbin.
(
Adanur, 1995
).
Figure 3.2.4-2
presents a schematic of
a typical wet solution spinning process.
Electrospinning
The diameters of fibers spun by melt spinning and wet
solution spinning are controlled by the size of the hole in
the spinneret and the amount of draw or stretch applied
Polymer extruder
Metering pump
Wet spinning
If the polymer system experiences thermal degradation
at elevated temperatures, as is the case with a polymer
containing a drug, a low-temperature wet solution spin-
ning process can be used. In this process the polymer is
dissolved in a solvent and then extruded through a spin-
neret into a nonsolvent in a spin bath. Because the solvent
is soluble in the spin bath, but the polymer is not, the
continuous polymer stream precipitates into a solid fila-
ment, which is then washed to remove all solvents and
nonsolvents,
Spinning head
Filaments
Quench air
Convergence guide
Finish application
Take-up spool
drawn,
and
dried
before
winding
up
Fig. 3.2.4-1 Melt spinning process.
