Surgical suture abstract
The invention is a multifilament thermoplastic surgical suture
having a plurality of meltfused filaments where the filaments are
only melt fused for a controlled length from at least one end of
the suture. This melt fused end invention eliminates the end dipping
operation for multifilament sutures. Preferably, the melt fused
or bonded length of suture has at least eighty percent of the tensile
strength of an unfused portion, as a substitute for the end-dipped
suture.
Surgical suture claims
I claim:
1. A multfilament thermoplastic surgical suture having a plurality
of meltfused filaments, the improvement comprising the filaments
being meltfused for a length of less than about forty millimeters
from at least one end of the suture, the tensile strength of the
meltfused length being at least about eighty percent of the tensile
strength of an infused portion of said suture.
2. The suture of claim 1 having a cut end surface at both ends
of said suture, the suture further having an axial centerline, wherein
the cut end surface proximal to the meltfused filaments is perpendicular
to the axial centerline of said suture.
3. The suture of claim 1 having a cut end surface at both ends
of said suture, the suture further having an axial centerline, wherein
the cut end surface proximal to the meltfused filaments is olbique
to the axial centerline of said suture.
4. The suture of claim 3 wherein said end surface is about fifty
to eighty degrees from said centerline.
5. The suture of claim 4 wherein said end surface is about sixty
to seventy degrees from said centerline.
6. The suture of claim 3 having a needle attached to at least a
portion of said length.
7. The suture of claim 6 having a needle attached to both ends
of said suture.
8. The suture of claim 6 having a drilled end needle.
9. The suture of claim 6 having a flanged end needle.
10. The suture of claim 1 or 6 wherein the thermoplastic is selected
from the group consisting of a polyester, a polyamide, and a polyolefin.
11. The suture of claim 10 wherein the polyester is poly(glycolic
acid).
12. The suture of claim 11 wherein the poly(glycolic acid) is a
homopolymer.
13. The suture of claim 11 wherein the poly(glycolic acid) is a
copolymer.
Surgical suture description
BACKGROUND OF THE INVENTION
This invention relates to a multifilament thermoplastic surgical
suture. Less than about fifty percent of the filaments are melt
fused for a suitable controlled length. The controlled length is
from at least one end of the suture. The melt fusion essentially
seals and stiffens at least one end of the suture.
Most braided suture material, for needled and non-needled products,
is skeined onto a frame, `dipped` in a polymer resin solution, oven
dried, cut off from the frame, and sorted for faulty lengths.
This operation is slow and messy, labor intensive and space consuming,
and all that is achieved is the cutting of the sutures to length,
the sealing of the ends to prevent fraying, and stiffening for greater
ease of insertion into a needle. The average product spends 2 days
of in-process time in the end dipping department.
This invention eliminates the end dipping operation for braided
thermoplastic suture materials, and replaces it by an inline system
in the next production operation (viz. needle attaching, or winding
in the case of non-needle sutures) with a reduction of in-process
time and floor space requirements.
For braided thermoplastic suture materials heat is used to achieve
melt fusion of the outer filaments of the braid.
The braid is handled from the reel or spool as a controlled, continuous
strand. Following melt fusion of the desired section of braid, it
is cut to the required suture length and ready for additional processing.
The prevalent method for sealing (prevent brooming) and stiffening
the cut ends of braided suture material involves use of the antiquated
resin solution end-dipping system. FIG. 1 is a process flow chart
describing this method. Examples of this process are given in U.S.
Pat. Nos. 3736646 issued June 5 1973; 3890975 issued June 24
1975; and 3980177 issued Sept. 14 1976. All of these patents
are incorporated herein by reference.
The machine of this invention will fit onto an existing single
operator, attach/wind workstation. The entire system control is
automatic, including temperature control, knot detection and elimination,
suture advancement to length, cutting etc. It has the following
functions and features.
a. Sealing and stiffening of thermoplastic braided sutures by heat
(melt-fusion) with a minimal degradation of tensile strength and
a needle attachment strength equivalent to end-dipped sutures.
b. Measure to length by variable program, automatically controlled
electric motor(s). A new innovation in length measurement is effected
by driving the standard elastomer foam coated, figure eight winding
rollers through discrete steps.
c. A totally new suture cutting concept has been developed, that
of employing a razor blade slice/shear cutting across a hole in
an anvil plate achieving a perfect end (i.e. retaining round cross
section). The ends may be bias cut or straight cut, ready for insertion
into a needle.
d. Automated knot detection and advance to the cutter, thereby
saving an average of about one-half suture length per knot.
e. Automatically feed prepared strand to the operator or collect
as a batch.
f. The new system is compact. The entire drive and cut unit can
be held in the hand.
SUMMARY OF THE INVENTION
The invention is a multifilament thermoplastic surgical suture
comprising less than about fifty percent of the filaments being
melt fused for a suitable controlled length from at least one end
of the suture. In one embodiment, less than about twenty-five percent
of the filaments are fused. In a specific embodiment, less than
about fifteen percent of the filaments are fused. In a more specific
embodiment, about five to ten percent of the filaments are fused.
In another embodiment, the majority of the filaments being fused
are on the surface of the suture. In yet another embodiment, the
tensile strength of the controlled length is at least about eighty
percent of the tensile strength of the remainder of the suture.
Yet another embodiment is wherein the controlled length from an
end of the suture is up to about one hundred millimeters. In a specific
embodiment, the suture has a needle attached to at least a portion
of the length. In a more specific embodiment, a needle is attached
to both ends of the suture.
The invention is also a multifilament thermoplastic surgical suture
comprising about five to ten percent of the filaments being melt
fused for a length of less than about forty millimeters from at
least one end of the suture. The tensile strength of the melt fused
length is at least about eighty percent of the tensile strength
of the remainder of the suture. In one embodiment the cut end surface
proximal to the melt fused filaments is perpendicular to the axial
centerline of the suture.
In another embodiment, the cut end surface proximal to the melt
fused filaments is oblique to the axial centerline to the suture.
In a specific embodiment, the end surface is about fifty to eighty
degrees from said centerline. In a more specific embodiment, the
surface is about sixty to seventy degrees from said centerline.
In yet another embodiment, the suture has a needle attached to
at least a portion of the melt fused length. The needle can be a
drilled end or flanged end needle.
In still another embodiment, the thermoplastic is selected from
the group consisting of a polyester, a polyamide and a polyolefin.
In one embodiment, the polyester is poly(glycolic acid). In a specific
embodiment, the poly(glycolic acid) is a homopolymer. In another
specific embodiment, the poly(glycolic acid) is a copolymer.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing the prior art steps for end dipping
and needling a suture;
FIG. 2 is a graph showing the relationship between suture size
and melt fusion temperature;
FIG. 3 is a schematic view showing the apparatus for melt fusing
and cutting a suture end; and
FIGS. 4 and 5 are broken front and cut away side views, respectively,
of the cutting apparatus of FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
The overall system control as well as the individual process operations
may be attained, in an automated fashion, by several means. In the
preferred embodiment of this invention, the following are the means
of choice:
1. The system is monitored and controlled by means of a microcomputer
or a programmable logic controller (PLC).
2. Thermal `sealing`/stiffening of thermoplastic braid suture mterials
is performed by melt-fusion of the outer filaments using radiant/convective
(i.e. non-contact) heater blocks. When closed, the blocks form a
straight tunnel of circular cross-section to provide the braid with
uniform thermal exposure around its entire periphery. When the braid
is advanced/indexed the blocks open in order to minimize the thermal
exposure of the main suture body which is to be left untreated.
3. Braid advancement and suture length control is achieved by means
of one or more pairs of apposed, elastomer-foam coated, friction
rollers that are driven by a stepper motor. This provides accurate
length control under moderate, controlled tension, for a wide range
of braid diameters, without abrasive damage.
4. Suture presence and knot detection is accomplished using adjustable
intensity/sensitivity, through-beam optical sensor pairs.
5. Straight or bias cutting, without distortion of the braid cross-sectional
shape is performed using an automatically actuated razor blade.
It shear cuts across a hole in an anvil plate through which the
braid protrudes.
Several of these means are described in greater detail below.
SUTURE THERMAL EXPOSURE
The appropriate treatment temperature and time for the braided
suture in the heating tunnel varies according to the suture material
and diameter. FIG. 2 shows the heating temperature versus optical
braid diameter for a silicon coated polyester braided suture at
an exposure time of three (3) seconds.
The exposure temperature and/or time must be increased with an
increase in diameter of any given material. The required exposure
temperature set point also varies directly with the heater tunnel
diameter but is inversely related to the exposure time. Keeping
all other parameters constant, there is a temperature range below
which there is insufficient heat (radiation) in order to achieve
any melting at all of the outer filaments, or above which there
is almost total melt/fusion of the entire cross section of the suture
material. For example, for a 4 mm diameter heating tunnel the temperature
range would be about b 260.degree. C. to 300.degree. C. for such
as a size 2/0 silicone coated polyester suture on a 3.0 second cycle.
MELT FUSION OF OUTER FILAMENTS
1. Initial Melting Action
The loose outer filaments that protrude from the basic outer diameter
of the braid are initially melted back to the true outer diameter
by the radiant heat. While this is not the same as the open flame
singeing process commonly used for silk sutures, it does achieve
the same result. The initial melting of loose filaments reduces
or eliminates the resistance to an easy insertion into the needle's
drilled hole.
2. Surface Filament Melt Fusion
After the initial melting of the protruding filaments, the material
temperature rises enough to commence the melt fusion of the outer
surface of the outer filaments. Note that only a small percentage
(estimated to be 5-10%) of the outer filaments actually undergo
surface melting and fuse with adjacent filaments at the respective
contact points. FIG. 2 is a graph showing the relationship between
USP (United States Pharmacopoeia Convention, Inc., MD U.S.A.) suture
sizes and melt fusion temperatures.
Hence the suture stiffens on cooling but with only a comparatively
small loss in strength. This melt fusion of the outer filaments
has the effect of both:
a. Holding the filaments together when the stiffened section is
cut, avoiding the brooming that would otherwise occur.
b. Stiffening the suture for ease of control and insertion into
the drilled hole of a needle.
SUTURE END STIFFNESS
The stiffness of the heat treatable sutures can be increased by
either:
a. increasing the temperature of the heating tunnel, or
b. by reducing the diameter of the heating tunnel, or
c. by increasing the dwell time in the tunnel. Table I shows the
flexural stiffness measurements for USP size 3/0 silicone coated
polyester braided sutures that have been heat stiffened at 260.degree.
C. (setpoint) for 3 seconds. The measurements were made using a
Karl Frank Bending Stiffness Tester (Model No. 58963 Karl Frank
GmbH, Weinheim-Birkenau, W. Germany). The higher measured stiffness
of the heat stiffened sutures, as contrasted to the end-dipped ones,
of Table 2 provides for ease of suture insertion into drilled end
needles. This degree of stiffening is obtained with less than approximately
10% reduction in suture tensile strength. Higher or lower stiffness
may, of course, be obtained as described above.
SUTURE DIAMETER REGULATION
In the current embodiment of this invention, the diameter of the
stiffened suture section is regulated by controlling the braid tension
during heating. Normally it is desired to maintain approximately
the untreated suture diameter. While the stiffened end must be easily
insertable into the standard drilled end needle, its diameter must
not be reduced to the point of decreasing the needle attachment
strength obtainable after swaging. The tension (during heat stiffening)
required to achieve this varies with suture size, construction,
material and previous thermal/drawing history. As indicated in Table
1 the appropriate heating tension for this particular example is
approximately 40 to 80 g. Higher tensions during heating, generally
cause a stretching of the braid with a concurrent reduction in diameter.
Lower tensions, or free feed operation allows the braid to shrink
axially and increase in diameter.
Table 2 shows the contrasting stiffness values for a prior art
end-dipped suture.
TABLE 1 ______________________________________ STIFFNESS (Units
= mN at 1 mm Suture Length) Material = Silicone Coated Dacron Suture
Size = USP 3/0 PROCESS PARAMETERS: TEMPERATURE SETPOINT = 260.degree.
C. EXPOSURE TIME = 3 Sec. BRAID TENSION = 40-80 g. HEATER TUNNEL
DIAMETER = 4 mm Sample No. HEAT STIFFENED ______________________________________
1 200 2 219 3 203 4 250 5 221 6 195 7 220 8 233 9 217 10 253 11
219 12 218 13 204 14 235 15 186 Avg. = 218 S.D. = 18 ______________________________________
TABLE 2 ______________________________________ STIFFNESS (Units
= mN at 1 mm Suture Length) Material = Silicone Coated Dacron Suture
Size = USP 3/0 END-DIPPED IN Sample No. POLYMER RESIN SOLUTION*
______________________________________ 1 46 2 33 3 37 4 39 5 34
6 35 7 38 8 27 9 33 10 39 11 38 12 45 13 34 14 31 15 28 Avg. = 36
S.D. = 5 ______________________________________ *TICRON .TM. Suture
(American Cyanamid Company, Wayne, NJ 07470 U.S.A.)
The means used for controlling the braid tension is illustrated
schematically in FIG. 3. Upon entering the system a frictional `drag`
force is applied to the braid by a spring loaded pair of tension
disks. Increasing the compression of the spring with the retainer
nut, results in greater disk compression and a higher drag force
on the braid. This may alternatively be achieved by any variable
electromagnetic disks, mechanical or magnetic clutch or other tensioning
device commonly used especially in the textile industry. Maintenance
of the braid tension at the other end of the system (i.e. beyond
the heater) is achieved by the pair of apposed, elastomer foamcoated
friction rollers, one of which is driven by the stepper motor. These
rollers are compressed against each other, by a spring or other
means to exert a frictional `drag` force on the suture which is
advanced between them. This `drag` force is at least equal to that
of the tension disks, and usually greater, so that the suture advance
may be controlled without slippage of the braid between the rollers.
As an alternative to the diameter regulation means described above
in which braid tension is the controlled parameter, it is also possible
to firmly clamp the braid at both ends of the heating tunnel and
regulate the diameter by controlling the relative motion of the
two clamps toward or away from each other. Although this clamp relative
motion control is not yet quantified, the following principles are
generally observed.
If the clamps are moved inwards, the portion of suture in the heating
tunnell increases in diameter. If the clamps are held still when
heating, the diameter reduces slightly. In order to maintain a constant
diameter during heating, the clamps must move inwards a very small
amount.
The amount of movement inwards and outwards in order to, for example,
reduce the diameter by 10%, has not yet been established. This is
currently being achieved by the controlled tension system described
above.
None of the automated systems developed thus far contain a diameter
measuring device. An optical sensor or other means may be incorporated
in future machines with a feed back control loop.
Any of the diameter regulation means described here may be used
in conjunction with the heat stiffening process to provide a number
of suture product variants.
One such product is a controlled release suture/needle combination
as defined in The United States Pharmacopeia Twenty-first Rev. (hereafter
abbreviated as USP), United States Pharmacopeial Convention, Inc.,
Rockville MD, U.S.A., 1984 Section 871. The lower needle holding
strength may be obtained by a greater degree of thermal exposure
(i.e. more suture strength degradation) or by reducing, the diameter
of the stiffened section during heating by increasing the tension
or by moving the clamps apart to stretch the braid.
Another product variant is a suture with a 1:1 needle-to-suture
diameter ratio. The stiffened section of the braid is reduced in
diameter during heating by using one of the techniques described
above. Then, once cut, the reduced diameter end(s) may be inserted
into a drilled end needle having essentially the same outside diameter
as the main body of the suture. In surgery, the suture will then
fill the hole left in the tissue by the needle.
SUTURE CUTTING
The primary objective in cutting the braid after heat stiffening
is to obtain non-broomed ends that retain the approximately round
cross-sectional shape of the braid. While this may be accomplished
by various assemblies that differ in the design details, the concept
embodied in this invention will be described here.
The location of the cutting assembly in this system is shown schematically
in FIG. 3. One design that has been built and run successfully is
shown in somewhat greater detail in FIG. 4.
The new suture cutting technique of this invention achieves the
objective described above by means of the shearing action of a razor
blade across an anvil plate. The suture is advanced through a tear-drop
shaped hole in the anvil plate. The cutting edge of the razor blade
is then driven (i.e. sheared) across the hole, in a straight or
arcing motion, in such a manner that an acute angle (i.e. generally
less than approx. 15.degree.) exists between the edge and its direction
of motion. As a result, the edge pushes the braid sideways into
the end of the tear-drop shaped hole that has the smallest radius
of curvature. With the contour of the braid supported by the hole
in this way, further motion of the blade cuts the braid with minimal
distortion of its shape. If the anvil plate, and therefore the blade's
cutting plane, are perpendicular to the axial centerline of the
braid a straight cut is obtained. Alternatively, a `bias` cut may
be obtained by inclining the anvil plate to the suture's axial centerline.
It has been found empirically, that a bias cut made at an angle
of about 60.degree. to 70.degree. to the suture's axial centerline,
facilitates insertion into the needle without significant reducing
the needle attachment strength. An angle significantly greater than
about 70.degree. does little to facilitate insertion into the needle
drill hole. An angle significantly lower than about 60.degree. would
reduce the length of the suture end that is engaged by the swaged
end of the needle, thereby lowering the needle attachment strength.
NEEDLE ATTACHMENT STRENGTH
The needle attachment strength data shown in Tables 3 and 4 indicate
an essentially equivalent quality of attachment for the heat stiffened
sutures in value for sutures heat stiffened by this invention and
by means of end-dipping in a polymer resin solution. Both sets of
results are well above the required average minimum of 0.68 kg (as
per The United States Pharmacopeia Twenty-first Rev. (hereinafter
abbreviated as USP), United States Pharmacopeial Convention, Inc.,
Rockville MO, U.S.A., 1984 Section 871) for this size (i.e. 3/0)
suture. The sample Nos. in Tables 1 and 2 are identical. The sample
Nos. in Tables 3 and 4 are identical.
OVERALL SYSTEM OPERATION
An apparatus of this invention is shown schematically in FIGS.
3 to 5. A pair of feed rollers 1 driven by a stepper motor 2 advance
a suture braid 3 until a predetermined length is reached. Braid
tension is maintained between these feed rollers 1 and the tension
disk assembly 4 by the frictional drag force exerted on the braid
at these two locations.
The second pair of friction (take-up) rollers 5 is driven by an
electric DC motor or a stepper motor 6. These rollers take up the
slack braid beyond the cutting assembly 7.
After the braid 3 is advanced to a predetermined suture length
it is stopped. The heater blocks 8 close so that the section of
braid to be heat-stiffened is enclosed, without physical contact,
in the heater tunnel. Once the required exposure time is reached,
the heater blocks 8 reopen and the feed rollers 1 advance the heat-stiffened
section to the cutting assembly 7. Generally, the distance from
the center of the heater blocks 8 to the cutting line 9 is adjusted
to be equal to the desired suture length. This allows the next section
of suture braid 3 to be heat-stiffened while the previous one is
being cut. With the cut at the midpoint of each treated section
of braid, a suture with both ends stiffened is manufactured, suitable
for a double-armed product, i.e. having two needles.
Once the braid is cut, the take up rollers complete the advancement
of the suture so that an operator may proceed with the next process
step, such as needle attachment. Alternatively, the sutures may
be collected as a batch for future additional processing.
FIGS. 4 and 5 specifically describe the cutting assembly 7. The
cutting blade 13 can be adjusted by screws 14 to provide the desired
shearing angle. Also, a spring clip 15 can optionally be placed
in the cutting blade bracket 16 to assist in keeping the blade 13
against the anvil plate 12.
Referring further to FIGS. 4 and 5 a pusher 20 acts against a
pin 21. The pusher 20 is moveably mounted on a threaded shaft 22
and is activated by an electric motor 25. A block 23 moves against
a track 24 thus separating the pin 21 from the shaft 22. The point
of contact between the block 23 and the track 24 can be adjusted
by a set screw 26.
The pusher 20 acts against the pin 21 until the block 23 contacts
the ramp 27. The block 23 then moves against the ramp 27 in approximately
a diagonal motion (relative to the horizontal motion of the pusher
20) until the pin 21 clears the top of the pusher 20.
After the pin 21 clears the pusher 20 the blade 13 is forced across
the opening 11 by the spring 29. The blade 13 is then arrested by
a stationary block 30.
The pusher 20 is then moved down the threaded shaft 22 by the motor
25 and slides under the pin 21. The cycle can then be repeated for
the next suture strand 3. As shown in FIG. 3 the cutting assembly
7 is oblique to the axial centerline of the suture braid 3. However,
it is to be understood that the base 30 shown in FIGS. 3 to 5 is
movable, and therefore the angular relationship of the cutting assembly
7 to the axial centerline of the suture braid can be varied. It
is further to be understood that an actual showing of the various
angular relationships is not necessary for an understanding of this
invention.
Referring again to FIG. 3 if during braid advancement, a knot
is detected by a through-beam optical sensor 10 the control system
automatically causes the last "good" suture to be completed.
It then advances the knot to a position just beyond the heater blocks
8. A new section is then heat-stiffened and the knot is subsequently
advanced to just beyond the cut line 9. The take-up rollers 5 serve
to aid in pulling the knot through the hole 11 (shown in FIG. 4)
in the anvil plate 12 of the cutter assembly 7. The flawed section
is then cut and the take up rollers 5 discharge it from the machine
to be discarded. The normal process cycle is then repeated for the
next "good" suture. |