Note: Descriptions are shown in the official language in which they were submitted.
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1~0(~370
BAC~GROUND OF T~E INVENTION
Field of Invention
This invention relates to an absorbable composition
useful as a coating and lubricating finish for surgical
sutures. More particularly, this invention reiates to a means
for improving the tie-down properties of synthetic absorb-
able multifilament sutures by coating tne sutures with an
absorbable lubricating composition.
Description of Prior Art
Suture materials are generally classified as either
absorbable or non-absorbable, with each type of suture
material being preferred for certain appiications. Absorb-
~ble suture materials are preferred for internal wound repair
in whic~h tne sewn tissues will hold together after healing
lS without suture reinforcement and in which a non-absorbed
suture may promote tissue irritation or other adverse bodily
reaction over an extended period of time. Suture materials
are considered to be absorbable if they disappear from the
sewn tissue within about a year after surgery, but many
absorbable su-ure materials disappear within shorter periods.
The earliest available absorbable suture materials
were catgut and extruded collagenous materials. More recently,
absorbable sutures derived from synthetic polymers ha~e been
developed which are strong, dimensionally uniform, and storage-
stable in the dry state. Typical of such polymers are lacti~ehomopolymers and copolymers of lactide and glycolide such as
t~lose disclosed in United States Patent No. 3,636,956, and
glycolide homopolymers sucn as those disclosed in Unitea
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1~0~370
States Patent No. 3,565,869.
Monofilament synthetic absorbable suture materials
are generally stiffer than their catgut or collagen counter-
parts, and synthetic absorbable sutures are therefore usually
employed in a multifilament, braided construction in order
to provide the suture with the desired degree of softness
and flexibility. Such multifilament sutures exhibit a cer-
tain degree of undesirable roughness or Ugrabbiness'' in what
has been termed their "tie-down~ performance, i.e., the ease
or difficulty of sliding a knot down the suture into place.
Multifilament non-absorbable sutures such as
braided ~utures of polyethylene terephthalate, for example,
can be improved with respect to tie-down performance by
coating the external surface of the suture with solid par-
ticles of polytetrafluoroethylene and a binder resin as dis-
closed in United States Patent No. 3,527,650. This proce-
dure, however, is undesirable as applied to absorbable
sutures because polytetrafluoroethylene is non-absorbable
and sutures coated therewith would leave a polymer residue
in the sewn tissue, after the suture had absorbed.
Multifilament, non-absorbable sutures can also be
improved with respect to tie-down performance by coating
them with a linear polyester ha~ing a molecular weight be-
tween about 1,000 and about 15,000 and at least two carbon
atoms between the ester linkages in the polymer chain as
disclosed in United States Patent No. 3,942,532. This patent
discloses that the aforementioned polyesters may also be
used to coat absorbable synthetic sutures but does not
consider that such coated sutures would not be totally ab-
sorbable.
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370
The aforementioned U.S. patent number disclose~ that
the synthetic absorbable sutures described therein may be
coated with conventional suture coating materials such as
a qilicone or beeswax in order to modify the handling or
absorption rate of the sutures. These coating materials
are not readily absorbable, however, and will accordingly
leave an undesirable residue in the tissue after the suture
itself is absorbed.
It is accordingly an object of the present inven-
tion to provide an absorbable, lubricating coating for multi-
filament sutures of braided, twisted or covered construction.
It is a further object of this invention to provide an ab-
sorbable coating to improve the tie-down properties of such
multifilament sutures. It is a yet further object of this
invention to provide a wholly absorbable coated synthetic
multifilament suture having good knot tie-down properties.
SUMMARY OF THE INVENTION
In accordance with the instant invention, there is
provided as a coating for sutures, particularly synthetic
absorbable multifilement sutures, an absorbable composition
comprising a film-forming polymer and a substantially water-
insoluble salt of a C6 or higher fatty acid. The coating
is preferably applied to the suture from a solvent solution
to provide a final coating add-on of from about 2 to 10 per
cent by weight of the suture.
The film-forming polymer is preferably a copolymer
of lactide and glycolide, while the fatty acid salt is pref-
erably a calcium salt of a C6 to C2~ fatty acid. The ratio
of polymer to fatty acid salt in the coating composition
may be within the range of about 1:4 to 4:1 parts by weight.
The coating is particularly useful for improving the tie-down
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smoothness of braided sutures prepared from homopolymers and
copolymers of lactide and glycolide, and other absorbable
polymers.
In accordance with a broad aspect of the invention,
there is provided a synthetic, absorbable multifilament
suture, having improved tie-down properties. The suture
is coated with from about 2 to 15 per cent by weight of a
composition comprising a mixture of a substantially water-
insoluble, absorbable salt of a C6 or higher fatty acid and
an absorbable, film-forming polymer. The ratio of said fatty
acid salt to the polymer is from about 1:4 to 4:1.
DESC~IPTION OF PREFERRED EMBODIME~T
~ ne coating compositions of the instant invention
may be applied to any suture material where it is desired to
improve fiber lubricity, suture tie-down characteristics, or
the like. The coating is particularly useful with synthetic
absorbable multifilament sutures such as polylactide, poly-
glycolide copolymers of lactide and glycolide, poly(p-diox-
anone), poly(alkylene oxalate), and mixtures of such poly-
mers with each other and with other compatible absorbablecompositions as those described for example in United States
Patent Nos. 3,636,~52 and 2,683,136. Preferred suture com-
positions derived from lactide and glycolide are sometimes
referred to herein as simply homopolymers and copolymers of
lactide and glycolide.
In a preferred embodiment of the present invention,
the coating is applied to the suture surface as a solu-
tion and/or
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dispersion of the polymer and fatty acid salt in a volatile
solvent such as acetone and solidification of the coating on
the suture is accomplished by volatilizing the solvent. Tne
coating may be applied to the suture by any suitable process
such as passing the suture through a solution of the coating
composition, or passed a brush or anplicator wetted with the
solutionJ or passed one or more spray nozzles dispensing the
solution as droplets. The suture wetted with the coating
solution is subsequently passed through or held in a drying
oven for a time and at a temperature sufficient to volatilize
the solvent.
In place of a coating solution, the coating composi-
tion may be applied as a melt of the constituents thereof,
and in this case solidification takes place by cooling. The
melt of the coating composition should, of course, be at a
te~pe~ature below t`he melting temperature of the suture
material, and this embodiment of the invention can be used
only when the coating composition melts at relatively low
temperatures.
The coating composition may also be applied to tne
suture as a solid by passing the suture over or between solid
~locks of the coating composition which is then transferred
to the surface of the suture by a rubbing action, possibly
accompanied by localized melting.
In coating multifilament sutures with the compositions
of this invention, it is not necessary that e~ery filament
within the suture be individually or completely coated.
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In most instances, howe~er, the coating composition will
penetrate into the suture structure, particularly when the
coating composition is applied as a solvent solution.
Suitable film formers useful in the coating
compositions of this invention include homopolymers and co-
polymers of lactide and glycolide, i.e., polylactide, poly-
glycolide, and copolymers of lactide and glycolide with each
other and with other reactive monomers; poly(~-dio~anone),
poly(alkylene oxalate), copolymers of vinyl acetates with
unsaturated carboxylic acids such as crotonic, acrylic,
and methacrylic acids; water soluble or dispersible cellu-
lose derivatives such as methyl cellulose, hydroxymethyl
cellulose and carboxymethyl cellulose; natural gums; ethy-
lene oxide polymers; polyacrylamide; colla~en; gelatin;
polyamino acids; polyvinyl alcohol; polyvinyl pyrrolidone;
absorbable conjugated unsaturated triglycerides such as
dehydrated castor oil, and mixtures of such polymers.
Particularly preferred film-forming polymers are the copoly-
mers of lactide and glycolide which contain from about 15
to ~5 per cent lactide, and have an inherent viscosity of
from about 1.0 to 4.0 measured as a 0.1% solution in hexa-
fl.loroisopropanol at 25C. These polymers are water-
insoluble, rapidly absorbable, and soluble in many common
organic solvents such as acetone, chloroform, toluene, xylene,
and 1,1,2-trichloroethane which facilitates their applica-
tion to the suture as solutions.
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The fatty acid salts useful in the coating composi-
tions of the present invention include the calcium, magnesium,
barium, aluminum, and zinc salts of C6 and higher fatty
acids, particularly those having from about 12 to 22 carbon
atoms and mixtures thereof. The calcium salts of stearic,
palmitic and oleic acids are particularly preferred for use
in the present invention.
The ratio of the film-forming polymer and the fatty
acid salt in the coating com~osition ma,~ vary depending upon
t'le specific co~ponents selected and the particular suture
being coated. In general, the preferred ratio of polymer
to salt is within the range of 2:1 to 1:2 by weight,
although useful compositions are obtained over a wider range
of from about 1:4 to 4:1 parts by weight.
~ith sutures composed of homopolymers or copolymers
of lactide and glycolide, the film former in the coating
composition is preferably polylactide or a copolymer of lac-
tide and glycolide containing at least about 15 per cent
lactide, and preferably having different solubility charac-
teristics than the suture. For example, a suture made of a
lactide-glycolide copolymer containing about 10 per cent of
dilactyl moieties mav be coated with a composition contain-
ing, as a film former, a lactide-glycolide copolymer containing
about ~5 per cent o~ dilactyl moieties, which copolymer is
more readily soluble in com~on organic solvents than the
suture material.
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The film former in the coating composition may,
if desired, be the same composition as the suture provided
that precautions are ta~en to avoid dissolving the suture
when the coating composition is applied. This can be done
by utilizing a coating composition in which the film former
is a finely divided suspension in a non-solvent liquid, or
by utilizing a coating co~position in which the film former
is in solution at substantially saturation levels and the
contact time of the suture with the coating composition is
short before the solvent is driven off.
~ here the compositions of the suture and the film
former are identical, and in other instances where the suture
material may be subject to some surface dissolution and/or
surface swelling or softening by reason of the action of
the film former solvent thereon, there may be a gradual
transition between the substrate composition and the coating
composition rather than a sharp interface between them. There
may also be some wea~ening of the suture accompanying the
application of such coating compositions.
The coating composition may, if desired, also contain
components other than those discussed above for other useful
purposes including dyes, antibiotics, antiseptics, anesthetics
and anti-inflammatory agents.
The amount of coating composition applied to the fiber,
or the coating add-on, will vary depending upon the con-
struction of the fiber, e.g., the nu~ber of filaments and
tightness of braid or twist, and the nature of the coating
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1 370
material, e.g., melt, solution or solid. In general, the
coating composition applied to a braid will constitute
from about 5 to about 10 per cent by weight of the coated
fiber, but coating composition add-on may range from as little
as about two per cent by weight to as much as ~bout 15 per
cent or higher in some ~ases. As a practical matter, and
for reasons of econo~y and general performance, it is
generally preferred to apply the minimum amount of coating
composition consistent with good tie-down perfor~ance, and
this level of add-on is readily determined exPerimentally for
any ~articular fiber-coating system.
The improve~ent in tie-down properties ~mparted to
synthetic absorbable sutures may be determined semi-
quantitatively by comparing the feel of coated and uncoated
sutures during the act of tying down a single throw knot.
Such comparisons are preferably made on both wet and dry
sutures since many suture materials have different tie-down
properties when tested wet or dry. Suture tie-down
roughness is graded from 0 to 10 with 0 being comparable to
an uncoated suture and 10 indicating no detectable roughness.
Suture tie-down properties are evaluated dry after
the sutures have been conditioned ~or at least 2 days in a
vacuum dryin~ oven at room temperature and 100 microns absolute
pressure, and wet after being ~mmersed in water at 25C for 1
minute. Roughness values above 4 are considered acceptable,
while values of 7 or hi~her are comparable to conventional
silicon coated silk and are considered fully satisfactory.
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The following examples are provided to further
illustrate and demonstrate the method and product of the
present invention. Unless otherwise stated, all parts
and percentages are by weight.
Exam~le 1
Forty-fi~e parts of a low molecular weignt (~inh
1.5 in I~FIP) lactide/glycolide co~olymer [65 mol % L(-)
- lactide and 35 mol % glycolide] and fortY-five parts of
calcium stearate~ were placed in a porcelain pebble mill
with ~10 parts of 1,1,2-trichloroethane. Dissolving of the
lactide/glycolide copolymer and dispersion of the calcium
stearate were accomplished simultaneously by milling the
mixture for two days. The solution/dispersion (Brookfield
viscosity of 218 CPS at 35C.) was then transferred to a
suture c'oating bath. A size 3-0 braided suture of 90/10
(weight percent) glycolide/lactide copol~ymer was coated with
the composition by passing the suture through the mixture while
using a folded felt pad to wipe excess material from the
suture as .t exited the coating bath. The suture was coated
at a speed of ~ feet per minute which provided an immersion
time of about 5 seconds in the coating bath. After passing
through the coating bath and the felt wiping pads, the suture
*Calcium stearate, a commercial food grade product con-
sisting of about l/3 C16 ar.d 2/3 Clg fatty acid, with small
amounts of C14 and C22 fatty acids.
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immediately entered a drying tower where enough solvent was
removed to render the suture t~ck free by the time the first
guide was contacted. Drying was completed by winding the
coated braid on a spool and keepin~ it in vacuum at 100 `~
microns for two days. The coating solids pick-up was
determined to be 5.3% of the uncoated braid. The suture was
finished by winding the coated braid on an annealing rack
under mild tension and heating 10 minutes at 110C.
Using afore described semi-quantitative smoothness-
of-tie-down test, the coated braid in a single throw knot
tie-down rated 8-9 dry, and 8 wet. The tensile strength of
the coated braid was 9.9 lbs. under straight tension and
5.4 lbs. knotted, while in the uncoated control, tensiles
were 9.9 lbs. and 5.8 lbs., respectively. Braided synthetic
absorbable sutures coated in a similar manner were sterilized
with ethylene oxide and i~planted in animals. After 21
days, the strength of the coated braid was the same as in the
uncoated control, and absorption was almost complete at 90
days, indicating that the coating composition or method of
application had no significant effect on suture tensile
strength or absorbabiiity.
Example 2
~ Using a coating solution/dispersion identical in
composition to that in Example 1 e~.cept that ;otal solids
were 6% rather than 10~, the glycolide/lactide braided
suture was coated by the same method. After vacuum arying,
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the coating solids pick-up was found to be 2.9% based on
the uncoated braid.
As in Example 1, the suture was finished by heating
the dry coated braid on an annealing rack at 110C. for
10 minutes. After ethylene oxide sterilization, s~oothness-
of-tie-down was 7 dry and 6 wet. Tensile strengths were
10 lbs. and 5.4 lbs. strai~ht ar.d knot, respectively.
Implantation in animals showed the same strength retained at
21 days as for the uncoated control. At 90 days post
implantation, absorption was com~lete and tissue reaction
was minimal throughout the test period.
Example 3
The procedure of Example 2 was repeated by coating a
size 4-0 braided sut~re comprised of poly(~-dioxanone)
polymer with the 6~/, solids coating solution/dispersion
composition. The coating solids pick-up of about 4% based
on the weight of the uncoated suture. After drying, suture
tie-down was tested and rated as excellent, being comparable
to standard waxed silk suture material.
Example 4
Twenty-five parts of a low molecular weight ( ~inh
1.5 in HFIP) lactide/glycolide copolymer [65 mol 7O L(-)
lactide and 35 mol ~ glycolide3 and twenty-fi~e parts of
magnesium s~earate were placed in a flask with 360 parts
of 1,1,2-trichloroethane and 90 parts by weight of chloroform.
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Solution of the polymer and dispersion of the stearate were
obtained by stirring the mixture for about one week, resulting
in a mixture having Brookfield viscosity of 299 CPS.
Using the methods described in Example 1, the
glycolide/lactide braided suture was coated, and drie~,
and coating pick-up was determined to be 3.1% based on the
uncoated suture. Using the smoothness-of-tie-down test
described in Exam~le 1, the dry and wet both rated 4-5.
Example 5
Twenty-five parts of a low molecular weight ( ~inh
1.5 in HFIP) lactide/glycolide copolymer [65 mol % L(-)
lactide and 35 mol % glycolide] and twenty-fivc parts of
zinc stearate were placed in a flask with 360 parts of
1,1,2-trichloroethane and 90 parts by weight of chloroform.
Solution and dispersion were obtained as in Example 3 to
yield a coating composition having a viscosity of 139 CPS.
Using the metllods described in Exa~ple 1, the
glycolide/lactide braided suture was coated wi,h 6.1% of
coating solids based on the uncoated suture. TJsing the
smoothness-of-tie-down test, the dry suture rated 5 while
the wet suture rated 4.
Example 6
Seven and one-half ~arts of the same lactide/
glycolide copolymer described in the above examples and seven
and one-halr parts of calci-~m ~almltate were placed in a
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11(~(~370
flask containing 108 parts of 1,1,2-trichloroethane and 27
parts of chloroform. The polymer and palmitate salt were
dissolved and dispersed by stirring vigorously several days.
Using methods of application and finishing described
in Example 1, the glcyolide/lactide braided suture was
coated with the solution/dispersion, and after drving, was
found to have picked u~ 5.4% coating solids.
Using the smoothness-of-tie-down test, the dry and
wet sutures rated 8 and 7, respectively.
Example 7
Seven and one-half parts of the same lactide/glycolide
copolymer described in the above examples and seven and one-
half parts of calcium oleate were placed in a flask containing
108 parts of I,1,2-tric-nloroethane and 27 parts-of chloroform.
The polymer and oleate salt were dissolved and dispersed by
stirring vigorously several days.
Using methods of application and finishing described
in Example 1, the glycolide/lactide braided suture was
coated with the solution/dispersion, and after drying, was
found to have picked up 9.8% coating solids.
Using the smoothness-of-tie-down test, the dry
and wet sutures rated 5-1/2 and 4-1/2, respectively.
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110(1370
Exam~le
Calcium salts of C6 (caDroic), C~ (caprvlic), Clo
(ca~ric), Cll (undecylenic) and Cl2 (lauric) fatty acids
were ~repared and applied to the glycolide1lactide braided
suture of Claim l. After drying, suture tie-do~n properties
were found to be significantly improved over the uncoated
suture material. Metal salts of C6 and higher saturated
and unsaturated fatty acids are tl~us shown to be efficacious
in the nractice of the present invention.
l~n~ile the foregoing s~ecification and exam~les nave
be~n directed to coating absorbable ~ultifilament braided
sutures, it will be readily appreciated that the coating may
likewise be used with good results on absorbable monofila-
ment sutures as well as on non-absorbable monofila~ent and
multifilament sutures.
Non-absorbable sutures such as cotton, linen, silk,
nvlon, polyeti~ylene terephthalate and ~olyolefins are normally
coated with non-absorbable compositions. Polyolefins are
usually of ~onofilament construction wnile cotton, linen,
silk and polyester are usually of braided, t~isted or covered
multifilament construction. ~hile there is usually no
re~uirement that the coating on such sutures be absorbable,
the composition of the instant invention may, nPvertheless,
be used as a lubricating finisn for non-absorbable sutures if
desired.
In the abo~Je examples, tl;e coating soiution was
ap~lied to the final suture structure in order to-provide a
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substantiall~ continuous coating on at least the outward-
facing surfaces of the outer-most filaments of the braid.
It is understood, however, that the coating solution may be
applied, if desired, to the individual filaments before
they are formed into strands or to the individual strands
before they are formed into strands or to t~e individual
strands before they are formed into the final suture struc-
ture. Also, while all the above examples were conducted
with size 3-0 braided suture prepared fro~ a 90/lO weig~lt
per cent glycolide/lactide copolymer, this was for the sake
of convenience only, and invention is not limited as to
suture size or composition but may be practiced for example
with sutures from size 9-0 to size 2 and larger, and with
other suture materials. The foregoing examples are intended
to be merely illustrative, and many modifications and varia-
tions thereof will be apparent to those skilled in the art.
