Biomedical Engineering Reference
In-Depth Information
meshes. Commercial sutures are typically monofilament
or braided; they can be constructed of natural materials
such as silk or collagen (catgut), or synthetic materials
such as nylon, PP, and polyester. Sutures can be further
classified into absorbable and nonabsorbable types. For
obvious reasons, when blood vessels are ligated, only
nonabsorbable sutures are used, and these are typically
constructed of either braided polyester or pp mono-
filaments. On the other hand, when ligating soft tissue or
closing wounds subcutaneously, absorbable sutures are
preferred. Absorbable sutures do not create a chronic
inflammatory response and do not require removal.
These are typically made from PGA or poly(glycolide-
co
-lactide) copolymers.
Another common application of biotextiles and fiber
technology in general surgery is the use of absorbable he-
mostatic agents, including those constructed of collagen
and oxidized regenerated cellulose. As mentioned pre-
viously, these can be fabricated as nonwoven mats or
woven and knitted fabrics, or they can be left in fibrillar
form.
Table 3.2.4-7
highlights some commercially available
hemostatic agents and their representative properties. As
canbeseenin
Table 3.2.4-7
, collagen-based hemostatic
devices are available in layered fibril, foam, and powdered
forms. The regenerated cellulose pad is also available as
aknittedfabricandissoldunderthetradenameof
Surgicel. This material is commonly used to control suture
line bleeding. The nonwoven and powdered forms are
generally used to stop diffuse bleeding that results from
trauma to the liver and spleen. Experience has shown that
the loose fibril form is more difficult to use, so most sur-
geons prefer the more structured form of the product.
Various forms of open mesh fabrics are used as sec-
ondary support material in hernia repair. Traditional
constructions are warp knitted from PP monofilaments,
and some forms of the mesh are preshaped for easy
nstallation. More recently three-dimensional Raschel
knits using polyester multifilament yarns have been
found to be more flexible and therefore can be implanted
endoscopically. As with other textile structures, various
properties can be engineered into the mesh to meet
design goals that may include added flexibility, in-
creased strength, reduced thickness, improved hand-
ling, and better suture holding strength. Some designs
include a protein or microporous PTFE layer on one side
only, which reduces the risk of unwanted adhesions
in vivo.
Orthopedics
Attempts have been made to construct replacement lig-
aments and tendons using woven and braided fabrica-
tions. One design, which has had some limited clinical
success, is a prestretched knitted graft, material used
to repair separated shoulder joints. A similar design,
using a high-tenacity polyester woven web inside of
a prestretched knitted graft, was evaluated for ACL
repair in the knee joint with limited success. In general,
biotextiles have had limited success in orthopedic liga-
ment and tendon applications as a result of abrasion wear
problems, inadequate strength, and poor bone attach-
ment (
Guidoin
et al.
, 2000
). An attempt was made to use
a braided PTFE structure for ACL repair, but early fail-
ures occurred as a result of creep problems associated
with the PTFE polymer.
Roolker
et al.
(2000
) recently
reported on using the e-PTFE ligament prosthesis on 52
patients. However, during the follow-up they experi-
enced increasing knee instability over time indicating
prosthesis failure.
Cooper (2000
) and
Lu (2001
) have
reported the development of a three-dimensional
bioabsorbable braid using poly(glycolide-
co
-lactide)
fibers for ligament replacement. They were able to
modify the scaffold porosity, mechanical properties and
matrix design using a three-dimensional braiding tech-
nique. A successful ACL ligament replacement would be
a significant advance for orthopedic surgery, but at
present, no biotextile or other type of prosthesis has
shown clinical promise.
Table 3.2.4-7 Comparison between commercial hemostats (
Ethicon, 1998)
Surgicel fibrillar
hemostat
Oxycel
Collagen
power
Gelfoam
Bacterial activity
Inhibits bacterial growth
No antibacterial activity
No antibacterial activity
No antibacterial activity
Hemostasis time
3.5 to 4.5 minutes
2 to 8 minutes
2 to 4 minutes
Not specified
Bioresorbability
7 to 14 days
3 to 4 weeks
8 to 10 weeks
4 to 6 weeks
Packaging
Foil/Tyvek sterile
Glass vials
Glass jars
Peel envelope
Preparation
Packaged for use
Packaged for use
Packaged for use
Must be cut/soaked
