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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to a suture possessing a solid spiroid braid.
Sutures intended for the repair of body tissues must meet certain
requirements: they must be substantially non-toxic, capable of being
readily sterilized, they must have good tensile strength and have
acceptable knot-tying and knot-holding characteristics and if the sutures
are of the bio-absorbable variety, the bio-absorption of the suture must
be closely controlled.
Sutures have been constructed from a wide variety of materials including
surgical gut, silk, cotton, polyolefins such as polypropylene, polyamides,
polyesters such as polyethylene terephthalate, polyglycolic acid,
glycolide-lactide copolymer, etc. Although the optimum structure of a
suture is that of a monofilament, since certain materials of construction
would provide a stiff monofilament suture lacking acceptable knot-tying
and knot-holding properties, sutures manufactured from such materials have
been provided as braided structures. Thus, for example, sutures
manufactured from silk, polyamide, polyester and bio-absorbable
glycolide-lactide copolymer are usually provided as multifilament braids.
Currently available braided suture products are braided on conventional
braider-carriers which travel around the perimeter of the braider deck to
result in a tubular type braid with the yarns crossing over each other on
the surface of the braid. In the larger sizes, e.g., 5/0 and larger, the
tubular braid, or sheath, is constructed about a core structure which is
fed through the center of the braider. Known tubular braided sutures,
including those possessing cores, are disclosed, e.g., in U.S. Pat. Nos.
3,187,752; 3,565,077; 4,014,973; 4,043,344; and, 4,047,533.
Spiroid braided structures per se are known, e.g., rope, sash cord and the
like, but heretofore have not been known for use as sutures.
As removed from the package, the currently available tubular braided suture
products exhibit one or more deficiencies. Thus, they tend to be stiff and
wiry and retain a "set" or "memory" such that at the time of use, it is
usually necessary for the surgeon or assistant personnel to flex and
stretch the suture to make it more flexible. Furthermore, the surfaces of
these sutures are perceptibly rough. Thus, if one passes one's hand or
fingers along the braid, surface irregularities will be readily detected.
The result of this rough surface is that the suture will exhibit drag or
chatter as it is drawn through tissue, characteristics which militate
against smooth, neat, accurately placed wound approximation so necessary
to excellence in surgical practice.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a braided suture of improved
characteristics, specifically, one exhibiting greater flexibility, better
hand and less chatter and drag, than braided sutures of known
construction.
It is another object of the invention to provide a braided suture
exhibiting improved knot security relative to known tubular braided suture
constructions.
It is a particular object of the invention to improve the storage stability
of a spiroid braided suture fabricated from an absorbable resin which is
susceptible to hydrolysis, e.g., a suture based in whole or in part on a
polyester homopolymer or copolymer such as polyglycolic acid,
polyglycolide-lactide copolymer, etc., by filling the suture with a
storage stabilizing agent or composition.
It is yet another object of the invention to apply one or more
medico-surgically useful compositions to the spiroid braided suture to
enhance or accelerate wound repair and/or tissue growth. A particularly
advantageous composition of this type is one containing at least one Human
Growth Factor (HGF), preferably in combination with a carrier such as
glycerol which protects the HGF from excessive loss of biopotency during
storage.
By way of satisfying the foregoing objects as well as other objects of the
invention, there is provided in accordance with this invention a suture of
spiroid braid construction.
Due to the substantially parallel orientation of the fibers relative to its
axis, the spiroid braided suture of this invention exhibits improved
flexibility and hand and reduced tissue chatter and drag compared with
tubular and/or cored braided sutures where the fibers cross over each
other.
Unlike tubular braided sutures, the spiroid braided suture of this
invention shows little if any tendency to kink or snarl. Bends which might
cause core popping (the penetration of the core through the braided
sheath) in the known types of tubular braided sutures pose no risk of
damage to the preferred spiroid braided suture of this invention.
Knot security in the spiroid braided suture of this invention is also
superior to that obtainable with known tubular braided constructions.
Factors contributing to enhanced knot security include the approximately
perpendicular orientation of the fibers in the knot relative to the axis
of the braid, the reduced density of the knot compared with the knot of a
cored suture of equivalent size and the formation of a narrowed-down
portion which makes the knot more difficult to untie.
The term "suture" as used herein is intended to embrace both the
non-absorbable as well as the bio-absorbable varieties.
The expressions "spiroid braid" and "spiroid braided" as applied to the
suture of this invention refer to a substantially solid arrangement of
discrete units, or bundles, denominated "yarns", made up of individual
filaments or fibers with the yarns arranged substantially parallel to the
longitudinal axis of the suture and internally engaging each other in a
repetitive spiral pattern.
The term "solid" as applied to the suture herein is intended to designate a
suture in which the filamentous material of its construction occupies
substantially the entire cross-sectional area of the suture with at most a
minor percentage, not exceeding about 25% in the larger suture sizes, of
such area constituting void space or interstices between adjacent yarns
and fibers. Such a construction contrasts with that of a standard suture
which, in the absence of a core component, possesses a lumen representing
a significant percentage of the cross-sectional area of the suture.
The term "standard suture" is intended to designate any of the heretofore
known braided sutures, e.g., those described in U.S. Pat. No. 3,565,077,
the contents of which are incorporated by reference herein, and in
particular, braided suture products marketed by Ethicon, Inc. under its
Vicryl brand and those marketed by Davis & Geck, Inc. (American Cyanamid
Company) under its Dexon brand.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1-5 are photomicrographs of linear (FIGS. 1 and 2) and
cross-sectional (FIGS. 3, 4 and 5) views taken by scanning electron
microscopy (SEM) of a spiroid braided suture in accordance with the
present invention;
FIGS. 6 and 7 are photomicrographs of linear (FIG. 6) and cross-sectional
(FIG. 7) views taken by SEM of a commercially available tubular braided
suture possessing a core component; and,
FIG. 8 is a graphical representation of the tissue drag of a spiroid
braided suture compared with that of two types of commercially available
tubular braided sutures.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The spiroid braided suture of this invention can be fabricated from a wide
variety of natural and synthetic fibrous materials such as any of those
heretofore disclosed for the construction of sutures. Such materials
include non-absorbable as well as partially and fully bio-absorbable
(i.e., resorbable) natural and synthetic fiber-forming polymers.
Non-absorbable materials which are suitable for fabricating the spiroid
braided suture of this invention include silk, polyamides, polyesters such
as polyethylene terephthalate, polyacrylonitrile, polyethylene,
polypropylene, silk, cotton, linen, etc. Carbon fibers, steel fibers and
other biologically acceptable inorganic fibrous materials can also be
employed. Bio-absorbable resins from which the spiroid suture can be
fabricated include those derived from glycolic acid, glycolide, lactic
acid, lactide, dioxanone, epsilon-caprolactone, trimethylene carbonate,
etc., and various combinations of these and related monomers. Sutures
prepared from resins of this type are known in the art, e.g., as disclosed
in U.S. Pat. Nos. 2,668,162; 2,703,316; 2,758,987; 3,225,766; 3,297,033;
3,422,181; 3,531,561; 3,565,077, 3,565,869; 3,620,218; 3,626,948;
3,636,956; 3,736,646; 3,772,420; 3,773,919; 3,792,010; 3,797,499;
3,839,297; 3,867,190; 3,787,284; 3,982,543, 4,047,533; 4,060,089;
4,137,921; 4,157,437; 4,234,775; 4,237,920; 4,300,565; and, 4,523,591;
U.K. Patent No. 779,291; D. K. Gilding et al., "Biodegradable polymers for
use in surgery--polyglycolic/poly(lactic acid) homo- and co-polymers: 1,
Polymer, Volume 20, pages 1459-1464 (1979), and D. F. Williams (ed.),
Biocompatibility of Clinical Implant Materials, Vol. II, ch. 9:
"Biodegradable Polymers" (1981).
The defining characteristics of a specific spiroid braided suture in
accordance with this invention, apart from the material of its
construction, are:
(1) suture size (i.e., suture diameter)
(2) overall suture denier;
(3) the pattern of the interlocking yarns;
(4) pick count;
(5) the number of yarns comprising the braid;
(6) the denier of the filaments comprising each yarn; and,
(7) the denier of the core, where present.
(1) Suture Size (i.e.. Suture Diameter)
The suture size can be expressed in terms of standard sizes, corresponding
to certain ranges of diameter (in millimeters), as set forth in the United
States Pharmacopoeia (USP). Standard sizes of the spiroid braided suture
herein are set forth in Table I as follows:
TABLE I
______________________________________
SUTURE SIZE
USP
Suture Size Diameter (mm)
______________________________________
2 0.50-0.599
1 0.40-0.499
.sup. 0 (1/0)
0.35-0.399
2/0 0.30-0.399
3/0 0.20-0.249
4/0 0.15-0.199
5/0 0.10-0.149
6/0 0.070-0.099
7/0 0.050-0.069
8/0 0.040-0.049
______________________________________
(2) Overall Denier of the Suture
The overall denier of the braided suture can vary from about 20 to about
4000. Within this range, the ranges of overall denier for particular
sutures are: from about 50 to about 125 denier; from above about 200 to
about 300 denier; from above about 300 to about 500 denier; from above
about 500 to about 800 denier; from above about 800 to about denier; from
above about 1500 to about 2000 denier; and, from above about 2000 to about
3600 denier.
(3) Pattern of the Interlocking Yarns
Unlike a tubular braided structure where the yarns form a crisscross
pattern which may be thought of as confined to the surface of a hollow
cylinder, the spiroid braided suture of this invention consists of a
pattern of interlocking yarns which may be considered as extending from
the surface of cylinder to its center thus providing a substantially solid
structure as defined above.
The characteristic pattern of a spiroid braided suture is clearly different
from that of a tubular braided suture. In the former, the yarns are
essentially parallel to the longitudinal axis of the suture whereas in the
latter, the yarns cross over each other at some angle to the longitudinal
axis of the suture. The structural differences between a spiroid braided
suture of this invention and a tubular braided suture are clearly evident
from a comparison of the linear and cross-sectional views of a spiroid
braided suture (FIGS. 2 and 3) and a tubular braided suture (FIGS. 6 and
7).
(4) Pick Count
Pick count is the number of stitches per inch lying in a single line
parallel to the longitudinal axis of the suture as viewed from the surface
of the suture. Suitable pick counts can vary from about 10 to about 80
stitches/inch and preferably from about 20 to about 60 stitches/inch.
(5) The Number of Yarns
The number of yarns employed in the construction of the suture bears some
relation to overall suture denier, the number of yarns generally
increasing with the weight of the suture. Thus, across the range of suture
weight (denier) indicated above, the spiroid braided suture of this
invention can be fabricated with from about 6 up to as many as about 30
individual yarns constructed from individual filaments having the deniers
discussed below.
Table II below sets forth broad and preferred ranges for the numbers of
yarns which are suitable for the construction of spiroid braided sutures
of various ranges of overall denier. The deniers of individual filaments
in a yarn can vary from about 0.2 to about 6.0 for the broad range of
number of yarns and the deniers of individual filaments can vary from
about 0.8 to about 3.0, and advantageously from about 1.2 to about 2.5,
for the preferred range of number of yarns.
TABLE II
______________________________________
NUMBER OF YARNS RELATED TO SUTURE DENIER
Number
Overall Suture
Suture of Yarns Number of Yarns
Denier Size (Broad Range)
(Preferred Range)
______________________________________
50 to about 125
7/0, 8/0 3-12 3-6
greater than about
6/0 6-15 6-12
125 to about 200
greater than about
5/0 6-15 6-12
200 to about 300
greater than about
4/0 6-15 9-12
300 to about 500
greater than about
3/0 9-20 12-15
500 to about 800
greater than about
2/0 12-25 15-20
800 to about 1200
greater than about
0 12-25 15-20
1200 to about 2000
greater than about
1, 2 15-25 20-25
2000 to about 4000
______________________________________
While the yarns need not be twisted, it is generally preferred that they be
provided with a slight twist so as to minimize snagging during braid
construction.
(6) Individual Filament Denier
The individual filaments comprising each yarn can vary from about 0.2 to
about 6.0 denier, preferably from about 1.2 to about 2.5 denier and more
preferably from about 0.8 to about 1.4 denier. The number of such
filaments present in a particular yarn will depend on the overall denier
of the suture as well as the number of yarns utilized in the construction
of the suture. Table III sets forth some typical numbers of filaments per
yarn for both the broad and preferred ranges of filament weight:
TABLE III
______________________________________
NUMBER OF FILAMENTS PER YARN
approximate approximate
Filament
minimum maximum Denier
______________________________________
45 1500 0.2
15 500 0.5
5 200 1.5
3 150 1.8
1 50 6.0
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(7) Core (Optional)
For all but the smallest sizes of spiroid braided suture, the suture,
although substantially solid in the sense defined above, can optionally
contain some small amount of void space, generally not exceeding 25% or so
in the larger suture sizes, which, if desired, can be partially or
substantially completely filled with a core component. A core may be
advantageous where it is desired to increase the density of the suture
and/or preserve its roundness. The core, where present, can be
monofilamentous or multifilamentous. In the case of the latter, the core
itself can be braided or can be provided with some other configuration
such as a twist, ply, cable, etc. The filament(s) comprising the core can
be fabricated from a material which is the same as, or is different from,
that of the braid. The core filament(s) can also possess a denier which is
the same as, or is different from, that of the braid filaments.
Table IV below provides some typical core deniers for sutures of various
deniers:
TABLE IV
______________________________________
CORE DENIER RELATED TO SUTURE DENIER
Maximum Maximum
Denier of Denier of
Overall Suture
Suture Optional Core
Optional Core
Denier Size (Broad Range)
(Preferred Range)
______________________________________
from about 50 to
8/0, 7/0 none none
about 125
greater than about
6/0 25-40 10-20
125 to about 200
greater than about
5/0 40-60 20-30
200 to about 300
greater than about
4/0 60-100 30-50
300 to about 500
greater than about
3/0 125-200 75-120
500 to about 800
greater than about
2/0 200-300 120-180
800 to about 1200
greater than about
0 300-500 180-300
1200 to about 2000
greater than about
1, 2 500-1000 300-600
2000 to about 4000
______________________________________
It is to be understood that Table IV merely sets forth suitable maximum
core deniers where a core is present. The actual core denier for a given
suture can be substantially less than the indicated maximum.
When the spiroid braided suture of this invention is fabricated from a
material which is susceptible to hydrolysis, e.g., any of the absorbable
resins previously mentioned, care must be taken to rigorously exclude
moisture from contacting the suture during storage or to otherwise
preserve the suture from excessive hydrolytic attack which would
compromise its in vivo strength to the point where the suture would no
longer be serviceable.
According to U.S. Pat. Nos. 3,728,839 and 4,135,622, the in vivo strength
of polyglycolic acid surgical elements such as sutures undergoes
significant deterioration on long term standing in the package even on
exposure of the contents to very small amounts of water for very short
periods of time, e.g., 20 minutes or less, just prior to packaging due to
the tendency of a moisture impervious package to seal the moisture in with
the suture. To prevent or minimize the extent of hydrolytic degradation of
an absorbable suture during storage expressed, for example, as a reduction
in out-of-package tensile strength, U.S. Pat. Nos. 3,728,839 and 4,135,622
disclose removing moisture from the suture before sealing the package so
that no more than about 0.5 percent of water by weight of suture remains
in the package once the package is sealed. This approach to improving the
suture's storage stability, while effective, is in practice difficult and
expensive to carry out. Prior to sealing the suture within its moisture
impervious package, it is essential that the suture be "bone dry", a
condition achieved by heating the suture for a sufficient period to remove
the water therefrom, e.g., 180.degree.-188.degree. C. for 1 hour under a
26 inch vacuum. However, once the water is removed, the suture cannot be
allowed to contact a moisture-containing environment even for a limited
duration since as previously noted, even brief exposure to moisture can
cause severe deterioration of suture in vivo strength. It therefore become
necessary following the water removal step to temporarily store the suture
in a dry area, i.e., an environment which is essentially free of moisture,
where the possibility of contact with moisture is largely eliminated.
These operations for improving the storage stability of an absorbable
suture are time consuming, expensive and constitute a relatively complex
solution to the storage stability problem.
In an entirely different approach to improving the storage stability of an
absorbable suture, one that avoids the foregoing drawbacks associated with
the method of U.S. Pat. Nos. 3,728,839 and 4,135,622, the storage
stability of an absorbable spiroid braided suture which is susceptible to
hydrolysis is improved by applying to the suture a storage stabilizing
amount of at least one water soluble liquid polyhydroxy compound and/or
ester thereof. In addition to imparting an enhanced degree of storage
stability to the suture, practice of this embodiment of the present
invention confers other benefits as well. So, for example, a spiroid
braided suture which has been filled with a storage stabilizing amount of,
e.g., glycerol, exhibits better flexibility and "hand" characteristics
than the untreated suture. Moreover, since the polyhydroxy compounds are
generally capable of dissolving a variety of medico-surgically useful
substances, they can be used as vehicles to deliver such substances to a
wound or surgical site at the time the suture is introduced into the body.
The useful storage stabilizing agents are generally selected from the water
soluble, liquid polyhydroxy compounds and/or esters of such compounds,
preferably those having no appreciable toxicity for the body at the levels
present. The expression "liquid polyhydroxy compound" contemplates those
polyhydroxy compounds which in the essentially pure state are liquids, as
opposed to solids, at or about ambient temperature, e.g., at from about
15.degree. C. to about 40.degree. C. The preferred polyhydroxy compounds
possess up to about 12 carbon atoms and where the esters are concerned,
are preferably the monoesters and diesters. Among the specific storage
stabilizing agents which can be used with generally good results are
glycerol and its mono- and diesters derived from low molecular weight
carboxylic acids, e.g., monoacetin and diacetin (respectively, glyceryl
monoacetate and glyceryl diacetate), ethylene glycol, diethylene glycol,
triethylene glycol, 1,3-propanediol, trimethylolethane,
trimethylolpropane, pentaerythritol, sorbitol, and the like. Glycerol is
especially preferred. Mixtures of storage stabilizing agents, e.g.,
sorbitol dissolve din glycerol, glycerol combined with monoacetin and/or
diacetin, etc., are also useful.
To prevent or minimize run-off or separation of the storage stabilizing
agent from the suture, a tendency to which relatively low viscosity
compounds such as glycerol are especially prone, it can be advantageous to
combine the agent with a non-aqueous thickener. Many kinds of
pharmaceutically acceptable non-aqueous thickeners can be utilized
including water-soluble polysaccharides, e.g., hydroxypropyl
methylcellulose (HPMC), and the other materials of this type which are
disclosed in European Patent Application 0 267 015 referred to above,
polysaccharide gums such as guar, xanthan, and the like, gelatin,
collagen, etc. An especially preferred class of thickeners are the
saturated aliphatic hydroxycarboxylic acids of up to 6 carbon atoms and
the alkali metal and alkaline earth metal salts and hydrates thereof.
Within this preferred class of compounds are those corresponding to the
general formula
##STR1##
wherein R is hydrogen or methyl, R' is a metal selected from the group
consisting of alkali metal and alkaline earth metal and n is 0 or 1 and
hydrates thereof. Specific examples of such compounds include salts of
lactic acid such as calcium lactate and potassium lactate, sodium lactate,
salts of glycolic acid such as calcium glycolate, potassium glycolate and
sodium glycolate, salts of 3-hydroxy propanoic acid such as the calcium,
potassium and sodium salts thereof, salts of 3-hydroxybutanoic acid such
as the calcium, potassium and sodium salts thereof, and the like. As
stated hereinbefore, hydrates of these compounds can also be used. Calcium
lactate, especially calcium lactate pentahydrate, is a particularly
preferred thickener.
Where a thickener is utilized, it will be incorporated in the filling
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