Biomedical Engineering Reference
In-Depth Information
consist of an adhesive layer that is laminated onto
a woven, knitted, or nonwoven fabric substrate.
configurations. Within each type of construction, various
properties can be incorporated into the product as illus-
trated in Table 3.2.4-5 . Manufacturers recommend that
all woven and knit grafts with water permeability rates
over 50 ml cm 2 min 1 be pre-clotted to prevent blood
loss through the fabric at the time of implantation. To
eliminate the need for this pre-clotting procedure, tex-
tile-based vascular grafts are usually manufactured with
a coating or sealant of collagen or gelatin.
Today a substantial amount of research activity is being
directed toward the development of a small vessel
prosthesis with diameters less than 6 mm for coronary
artery bypass and tibial/popliteal artery replacement.
Currently, no successful commercial products exist to
meet this market need. The question still remains as to
whether a biotextile will work as a small vessel prosthesis
if it is fabricated to have the required compliance and
mechanical properties and its surface is modified with
surface coatings, growth factors, and other bioactive
agents to prevent thrombosis and thrombo-embolic
events. Current development activities are directed
toward tissue-engineered grafts ( Teebken and Haverich,
2002; Huang, 2000 ), coated or surface-modified syn-
thetic and textile grafts ( Chinn et al. , 1998 ), and bio-
logically based grafts ( Weinberg and Abbott, 1995 ).
During the past 10 years, large amounts of financial
and personnel resources have gone into the development
of endovascular stent grafts ( Makaroun et al. , 2002 ).
These grafts have been used for aortic aneurysm repair,
occlusive disease, and vascular trauma. Endovascular
prostheses or stent grafts are tubular grafts with an in-
ternal or external stent or rigid scaffold. The stent grafts
range in size from about 20 mm up to 40 mm ID and are
collapsed and folded into catheters and inserted through
the femoral artery, thus avoiding the need for open sur-
gery. The stents are typically made from nitinol, stainless
steel, and Elgiloy wires and are similar to the coronary
stents, however, much larger in diameter (e.g., 24 mm
versus 4 mm, respectively). There are balloon expand-
able or self-expanding stents, which are manufactured in
straight or bifurcated configurations. The stents are then
covered in either ultrathin ePTFE ( Cartes-Zumelzu
et al. , 2002 ) or woven polyester ( Areydi, 2003 ). Most of
the endovascular graft designs incorporate an ultra-thin
woven polyester tube. Most biotextile tubes are plain
woven structures with water permeabilities ranging from
150 to 300 ml cm 2 min 1 depending on the manufac-
turer. They have been woven from 40 or 50 denier
untexturized polyester yarn so as to minimize the overall
wall thickness of the device.
Topical and percutaneous applications
Textiles have been used for many years as bandages,
wound coverings, and diapers. Gauze, which is basically
an open woven structure made from cotton fiber, is
manufactured in many forms and sold by many com-
panies worldwide. Elastic bandages are basically woven
tapes where an expandable yarn, such as spandex poly-
urethane, is placed in the warp direction to allow for
longitudinal stretch and recovery. Development con-
tinues to improve wound dressing products by the
addition of antibiotics, barrier fabrics, growth factors,
and modification of the basic underlining bandage con-
struction. One example of the latter is the work of
Karamuk et al. (2001) , in which a three-layered lami-
nate was formed from a nonwoven polyester/PP/cotton
outer layer, a monofilament polyester middle layer, and
a three-dimensional embroidered polyester inner layer
with large pores to promote angiogenesis.
Blood access devices are a class of medical devices
where tubes, wires, or other components pass through
the skin. These include percutaneous drug delivery de-
vices, blood access shunts, air or power lines for heart
and left ventricular assist devices, and many types of
leads. All of these devices suffer from the same basic
problem, a high risk of infection at the skin-device in-
terface due to the migration of bacteria along the sur-
face of the percutaneous lead. If a textile cuff is placed
around the tube, at the point of entry through the skin,
aggressive tissue ingrowth into the fabric reduces the
risk of infection at the percutaneous site. These cuffs
are usually made from knits, nonwoven felts, and velour
materials. Once a device is infected, it must be removed
to prevent further spreading of the infection. Surface
additives, such as silver or antibiotics, are sometimes
coated on the fabric to reduce infection rates ( Butany
et al. , 2002; Takai et al. , 2002 ).
In vivo applications
Cardiovascular devices
Biotextiles developed for cardiovascular use include ap-
plications such as heart valve sewing rings, angioplasty
rings,vascular grafts, valved conduits, endovascular stent
grafts, and the components of left ventricular assist de-
vices. One of the most important uses of textile fabrics in
medicine is in the fabrication of large diameter vascular
grafts (10-40 mm in diameter). As previously noted,
polyester [PET] is the principal polymer used to fabri-
cate vascular grafts. These grafts can either be woven or
knitted
General surgery
Three key applications of biotextiles in general surgery
are
and
are
produced
in
straight
or
bifurcated
sutures,
hemostatic
devices,
and
hernia
repair
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