Note: Descriptions are shown in the official language in which they were submitted.
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SURGICAL MESH FABRIC
FIELD OF INVENTION
The present invention relates to a surgical mesh fabric and, more
particularly, to a
surgical mesh fabric for use in laparoscopic procedures.
BACKGROUND OF THE INVENTION
Various prosthetic repair materials have been proposed to reinforce the
abdominal wall
and to close abdominal wall defects. Marlex mesh, a single bar warp knit, dual
course Atlas
I o polypropylene monofilament knit, is exemplary of an implant material that
has been successfully
used in hernia repair. Traditionally, prosthetic repair materials are placed
in an open procedure
where a two inch or longer incision is made through the abdominal wall. layers
of healthy tissue
are retracted to expose the void and then the rupture is filled or covered
with the implantable
fabric.
~ 5 Recently, prosthetic surgical fabrics have been implanted laparoscopically
which is a
surgical procedure employing slender tubes (cannulas) that extend through
narrow punctures in
the abdominal wall. Because the abdominal cavity remains closed, the surgeon
employs an
illuminating optical instrument through one of the cannula to visualize the
surgical site on a
television monitor. Surgical instruments are manipulated by the surgeon
through other cannula
2o in the abdominal wall, as the location of the instruments are observed on
the monitor, to place the
prosthetic repair material over or in the defect.
A concern has been raised that light may reflect off of the fabric surface
during
laparoscopy, potentially impairing visualization of the prosthetic repair
material and the
underlying anatomy. Increasing the pore size of a mesh fabric may improve
laparoscopic
25 observability but also may diminish the physical properties that had
suggested the implant for
augmenting or repairing abdominal wall defects. Many large pore mesh fabrics
are known, such
as the various openworks described in Paling, Warp Knitting Technology
(Columbine Press).
Although a dual bar warp knit, hexagonal mesh is described by Paling in Figs.
67f, 74 and 75
and at page 114, there is no indication or suggestion that such a fabric would
be suitable as a
3o prosthetic or that it would obviate the potential laparoscopic
visualization concern.
Accordingly, there is a need for a mesh fabric suitable for hernia repair
which combines
the performance and physical characteristics of conventional prosthetic repair
materials with
good laparoscopic visibility.
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SUMMARY OF THE INVENTION
The present invention is a dual bar warp knit, hexagonal mesh fabric that is
particularly
suitable for use in laparoscopic hernia repair, although it is contemplated
for classical open
procedures as well. The mesh fabric exhibits a favorable combination of
physical and
performance characteristics while still allowing the surgeon to see through
the fabric during
laparoscopy.
In one embodiment of the invention, the prosthetic repair material is formed
of
polypropylene monofilament threads that have been dual bar warp knitted into a
large pore
hexagonal mesh according to a back bar pattern chain of 2/0 2/4 2/0 4/6 4/2
4/6 and a front bar
t 0 pattern chain of 4/6 4/2 4/6 2/0 2/4 2/0.
It is among the general objects of the invention to provide a prosthetic mesh
which
combines good physical and performance properties with acceptable laparoscopic-
visibility.
It is a further object of the invention to provide an
implantable fabric for laparoscopically repairing a tissue or muscle wall
defect such as an
t 5 inguinal hernia.
Other objects and features of the present invention will become apparent from
the
following detailed description when taken in connection with the accompanying
drawings. It is
to be understood that the drawings are designed for the purpose of
illustration only and are not
intended as a definition of the limits of the invention.
DESCRIPTION OF THE DRAWINGS
The foregoing and other objects and advantages of the invention will be
appreciated more
fully from the following drawings in which:
Fig. 1 is a photomicrograph (approximately 1 lx mag.) of a warp knit dual bar,
hexagonal
mesh fabric according to the present invention; and
Fig. 2 is the chain lapping pattern for the mesh fabric shown in Fig. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention is a surgical mesh fabric for reinforcing and closing
soft tissue
defects, and is particularly indicated for chest wall reconstruction and the
repair of inguinal
hernias. The mesh fabric is formed of a biologically compatible, flexible and
strong implantable
material. The dual bar (two partially threaded guide bars) warp knit, diamond
fabric includes
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large openings between adjacent earn columns, ensuring good visibility of the
underlying
anatomy when the fabric is used in laparoscopic procedures without sacrificing
mechanical
properties of the mesh. The porous character of the fabric allows tissue
infiltration to incorporate
the prosthetic. The dual bar construction provides a stable fabric which is
resistant to unraveling;
s or running. The knitted fabric is sufficiently strong to prevent pullout of
anchoring sutures. The
flexible fabric may be collapsed into a slender configuration, such as a roll,
which can be
supported in, and advanced through, a narrow laparoscopic cannula.
When knitted from polypropylene monofilament yarns, the porous prosthetic
repair fabric
allows a prompt fibroblastic response through the interstices of the mesh,
forming a secure
I o fibrous/prosthetic layer. The polypropylene monofilament fabric is inert
in the presence of
infection, non-wettable and has a low foreign body reaction.
The fabric, illustrated in the lapping pattern and photomicrograph of Figs. 1-
2, is a two
bar warp knit, hexagonal mesh produced by using two partially threaded guide
bars to knit the
same pattern over three needles in a six course repeat. The column portions
are formed by two
15 separate ends of yarn crossing each other on two needles with the crossover
portion traversing
across a third needle. If one end of yarn breaks, a back up yarn will secure
the fabric from at
least two yarns away to prevent unraveling of the mesh. A selvage edge may be
formed using a
double end of yarn and knitting over two empty needle spaces on each side of
the band defining
the band width. The tension on the yarns may be greater when knitting the
selvage as compared
2o to the body of the mesh to encourage the denser selvage to curl over itself
in the direction of
body of the mesh, forming a rigid edge member which can be grasped with
laparoscopic tools
during placement to help position the implant relative to the surgical site.
Although a denser,
knitted selvage is described, other arrangements of one or more edges of the
fabric may be
employed as would be apparent to one of skill in the art.
25 Following knitting, the fabric is washed with water and a cleaning agent,
such as Triton
X-100. to remove processing lubricant. The mesh is dried at low temperature.
The fabric is heat
set under tension, in a crochet hoop or tentering frame, to provide the
desired pore configuration.
Preferably, the pores have an elongated diamond to square shape, although
other shapes
including, without limitation. diamond, square, circular and near-circular,
are contemplated so
30 long as the porous fabric provides good visibility when used in laparoscopy
while retaining the
physical and performance properties necessary for an effective prosthetic
repair of inguinal and
chest wall defects.
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Although the surgical mesh fabric preferably is knit from monofilament
polypropylene,
other monofilament and multifilament yarns that are biologically compatible
may also be
suitable as would be apparent to one of skill in the art. Fabric parameters,
such as quality,
stretch_ and yarn size may vary depending upon the application. In a
representative embodiment,
the fabric is formed of 0.006 inch polypropylene monofilament yarn (160
denier) knitted on a 36
gauge machine. although other gauges are contemplated. The mesh sheets may be
knitted in
twelve inch widths, although other dimensions are contemplated. The surgeon
may cut the mesh
into smaller pieces or shapes, preferably with heated or ultrasonic
instruments, to melt and seal
the edges of the fabric.
~ o EXAMPLES
The following examples are illustrative only and are not intended to limit the
scope of the
present invention.
Physical properties of a representative two bar warp knit, hexagonal mesh
fabric were
evaluated and compared to conventional mesh fabrics. The tested mesh fabric
was formed
~ 5 in a Mayer RM6 knitter under the following parameters:
# of ends in body 210
# of ends in selvage 14
runner length 96"
2o quality 16"
take-up B/A 56/49
pattern chain 2/0 2/4 2/0 4/6 4/2
4/6 FB
4/6 4/2 4/6 2/0 2/4
2/0 BB
gauge 36
25 width 12"
lubricant mineral oil
Physical and performance characteristics were tested including mesh thickness,
pore size,
mesh density, stiffness, tensile strength, suture pullout, burst strength and
tear resistance.
3o Testing methodology and results appear below.
Mesh Thickness: A 6" X 6" sample of mesh was placed on a standard fabric
thickness
gauge with a I .29 inch diameter pressure foot and 10 oz. weight. The
thickness was measured by
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lowering the foot on the middle of the sample and reading the thickness from
the dial gauge. one
reading per sample, to the nearest 0.001 inch.
Pore Size: A sample of mesh was placed on an optical measurement device. The
area of
a shape that closely approximated the shape of a pore was calculated following
acquisition of
several reference points.
Mesh Density The weight of a 5" x 5" piece of mesh was determined to the
nearest 0.1
gram. The mesh was then placed in a partially filled graduated cylinder of
water. After removal
of air bubbles, the volume of displaced water was recorded to the nearest 0.1
cc. Density was
calculated as:
to weight (grams) / volume water displaced (cc) - grams/cc
Minimurxi Suture Pullout (Suture Tear Re i anr'g2 ~, monofilament
polypropylene suture
(size 3.0 or larger) was placed 2mm from the edge of the sample. The mesh was
clamped in the
lower jaw and the suture was attached to the upper jaw of an Instron Tensile
Tester. The suture
~ s was then pulled out of the mesh at a rate of 5" per minute with an initial
jaw separation of 2 -
2.5". The peak force required to pull out the suture was recorded. Each mesh
was tested in two
directions with the direction of lowest strength being reported here.
Burst Strength: A 6" x 6" piece of mesh was clamped in the fixture of a
standard Mullen
Burst Tester. Hydraulic pressure was slowly increased causing a rubber
diaphragm to inflate,
?o contact the mesh, and burst the mesh. The peak pressure (psi) required to
burst the mesh was
recorded.
Minimum Tear Resistance: A 3.5" slit was cut parallel to the long dimension of
a 3" x 8"
piece of mesh. The slit was cut at the middle of one 3" side extending 3.5"
into the sample. One
"leg" was placed in the lower jaw and one "leg" in the upper jaw of an Instron
Tensile Tester.
25 The sample was then pulled and a 3" tear completed. The peak force (lbs)
required to tear the
sample was recorded. Each mesh was tested in 4 different directions with the
direction with
lowest strength being reported here.
Minimum Tensile Strength- A 1" x 6" sample of mesh was placed in the jaws of
an
Instron Tensile Tester with the long axis of the sample vertical. The sample
was then pulled to
30 break at a constant rate of traverse of 12 inches/minute with a jaw
pressure of 60 psi and a gauge
length of 2 inches. The force at break (Ibs) was recorded. Each mesh was
tested in both
directions with the direction of lowest strength being reported here.
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Stiffness: A 1 " x 6" sample of mesh was placed in the clamping fixture of a
Tinius Olsen
Stiffness Tester. Once the sample had been mounted and the instrument zeroed,
a force was
applied to the specimen with a metal rod causing the sample to bend. At 10
degree increments of
angular deflection, the percent load scale reading was recorded minus the
initial percent load
scale reading. The load (lbs) at each deflection angle was calculated as
follows:
P = L x M/S where P = Pounds Load (Ibs)
L = Load Scale reading (%)
M = Bending Moment (in lbs)
S = Bending Span (in)
The pounds load at a 40° angle was chosen as the value for comparison
since it is about
mid-way in the range of angular deflection (0-90°).
TABLEI
TEST VISILEX MARLEX PROLENE MERSILENE
n=30 unless otherwiseMean ~ SD Mean ~ SD Mean f SD Mean ~ SD
noted
Thickness (inches) 0.034 ~ 0.0010.027 ~ 0.001 0.025 ~ Not Tested
0.001
Average Large Pore 0.0038 ~ 0.0008 t 0.0001 0.0013 Not Tested
Area 0.0002 t 0.0001
(in2)
Mesh Density (grams/cc)0.8 ~ 0.04 0.93 ~ 0.02 0.93 ~ 0.02 Not Tested
Stiffness at 40 0.018 t 0.0050.013 t 0.002 0.036 ~ Not Tested
Bend (lbs) N=29 0.005
N=6
Minimum Tensile 38.97 t 2.4532.85 ~ 3.19 54.4 ~ 6.5815.64 ~
Strength 0.71
(Ibs.)
Minimum Suture Tear8.32 t 1.32 5.25 t 0.78 7.53 ~ 3.42 Not Tested
Resistance (ibs)
Burst Strength (psi)147 t 6 162 t 10 250 t 9 77 t 3
Minimum Tear Resistancel I .64 ~ 6.63 t 2.38 5.42 f 5.87 Not Tested
(lbs) 1.11
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It should be understood that the foregoing description of the invention is
intended merely
to be illustrative thereof and that other equivalents, embodiments and
modifications of the
invention may apparent to those of~slcilI in the art without departing from
the scope or spirit
thereof.
