Classes of materials used in medicine - Biomedical Engineering Desk Reference - page 180

Table 3.2.4-5 Woven graft properties and construction ( King et al., 1991)

Prosthesis Type

of weave

Ends
per inch

Picks
per inch

Bursting
strength
(N)

Water
permeability

Suture
retention
strength (N)

Dilatation
at 120 mm
Hg (%)

Twill woven 1/1 Plain with float 42p22f 48 280 330 25 0

Debakey soft
woven

1/1 Plain 52 32 366 220 35 0.2

Debaky extra
low porosity

1/1 Plain 55 40 439 50 40 d

Vascutek woven 1/1 Plain 56 30 227 80 30 0.5

Meadox woven
double velour

6/4 Satinþ 1/1 plain 36s36p 38 310 310 48 1.2

Meadox cooley
verisoft

1/1 Plain 58 35 211 180 30 0.2

Intervascular
oshner 200

1/1 Plain with leno 42p14L 21 268 250 22 0.5

Intervascular
oshner 500

1/1 Plain with leno 42p14L 21 259 530 26 1.2

applications, some ultralightweight designs have been
known to continuously dilate or expand when implanted
in hypertensive patients. It is not uncommon to have
lighter weight weft knitted grafts increase up to 20% in
diameter shortly after implantation.
As is the case with woven structures, there are sev-
eral variations in knits; the most common are the weft
knit and warp knit constructions (see Fig. 3.2.4-8 ).
Warp knitted structures have less stretch than weft
knits, and therefore are inherently more dimensionally
stable, being associated with less dilation in vivo. Warp
knits do not run and ravel when cut at an angle ( King
et al. , 1991 ). Warp knits can be further modified by the
addition of an extra yarn in the structure, which adds
thickness, bulk, and surface roughness to the fabric.
This structure is commonly known as a velour knit. The
addition of the velour yarn, while making the fabric feel
softer, results in a more intense acute inflammatory re-
action and increases the amount of tissue ingrowth into
the fabric.
Figures 3.2.4-9 A and 3.2.4-9B demonstrate the dif-
ference in the level of inflammatory response as seen
with plain and velour knit designs, respectively.
Figure 3.2.4-9 A is a photomicrograph of a Golaski
Microkit weft knit with high water permeability. This
high porosity weft knit design utilized nontexturized
yarns that resulted in a mild inflammatory response as
seen at 4 weeks. In contrast, the Microvel fabric, which is
a warp knit velour design using texturized yarns, shows
an intense acute response at 3 days ( Fig. 3.2.4-9B ). This
more intense acute reaction was designed intentionally so Fig. 3.2.4-8 Types of knit fabrics ( Spencer, 1983 ).