Surgical suture abstract
A surgical suture fabricated from a copolymer containing dioxanone,
trimethylene carbonate and glycolide is treated with gamma radiation
to enhance bioabsorbability without adversely effecting handling
Surgical suture claims
What is claimed is:
1. A method for treating a surgical suture to enhance the bioabsorbability
thereof, comprising the steps of:
a) providing a bioabsorbable surgical suture fabricated from a
terpolymer having repeating units derived from p-dioxanone, trimethylene
carbonate and glycolide;
b) exposing the surgical suture at ambient temperature to gamma
radiation at a first dosage ranging from about 2 Mrad to about 12
2. The method of claim 1 wherein said bioabsorbable surgical suture
is a monofilament suture.
3. The method of claim 1 wherein the suture is a multifilament
4. The method of claim 1 wherein step (a) comprises providing a
suture made from a block copolymer.
5. The method of claim 4 wherein step (a) comprises providing a
suture made from a triblock copolymer having a center block with
randomly combined p-dioxanone and trimethylene carbonate and end
blocks with a predominant amount of glycolide.
6. The method of claim 5 wherein the end blocks comprise randomly
combined repeating units derived from glycolide and p-diohanone.
7. The method of claim 1 further comprising the step of exposing
the suture to gamma radiation a second time at a second dosage,
wherein the second dosage is equal to the first dosage.
8. A suture comprising a fiber of gamma irradiated block copolymer
having repeating units derived from p-dioxanone, trimethylene carbonate
9. The suture of claim 8 wherein the surgical suture loses at
least about 2/3 of its initial strength after being implanted for
three weeks in body tissue.
10. The suture of claim 8 wherein the block copolymer is a triblock
11. The suture of claim 10 wherein the triblock copolymer has a
center block containing a random combination of units derived from
p-diohanone and trimethylene carbonate.
12. The suture of claim 10 wherein the end blocks comprise randomly
combined repeating units derived from glycolide and p-dioxanone.
13. The suture of claim 8 wherein the fiber is gamma irradiated
at a dose ranging from about 2 Mrad to about 5 Mrad.
14. The suture of claim 8 wherein the fiber is gamma irradiated
15. A monofilament suture in accordance with claim 8.
16. A monofilament suture in accordance with claim 11.
17. The suture of claim 8 wherein the block copolymer contains
a first block that is a copolymer of p-dioxanone and trimethylene
carbonate and the second block that is a copolymer of glycolide
Surgical suture description
1. Technical Field
The disclosure herein relates to a surgical suture, and in particular
to a surgical suture which has been subjected to radiation treatment.
2. Background of Related Art
Implantable surgical devices such as surgical fasteners, clips,
staples, and sutures are typically employed in surgical procedures
to hold body tissue together to promote the healing and joining
of the tissue. Such surgical devices are often made from synthetic
bioabsorbable polymers. The advantage of bioabsorbable devices is
that, once implanted, they do not need to be removed by a separate
surgical operation since they are degraded and absorbed by the body.
Ideally, the surgical device maintains its strength for as long
as it takes the body tissues to heal. Thereafter, the device should
rapidly degrade and disappear.
In various applications the body tissue heals much faster than
the suture implanted therein is absorbed. In such cases, the suture
remains in the body tissue longer than is necessary. Accordingly,
it would be advantageous to treat the suture so that it degrades
faster, without adversely affecting the mechanical properties of
U.S. Pat. No. 4496446 discloses modifying the absorption rate
of anastomosis rings by the inclusion of certain filler materials
in the ring, pre-treatment of the ring with hot water or steam,
and subjecting the ring to gamma radiation. U.S. Pat. No. 4435590
discloses that exposure of sutures to radiation leads to distinct
degradation in mechanical properties and to clinically unacceptable
in vivo strength retention. Thus, those skilled in the art would
not expect a treatment that includes radiating the suture to provide
an acceptable product.
It would be desirable to provide a suture treatment that enhances
absorption rate while not adversely affecting the desired physical
qualities of the suture.
A method is provided herein for treating a surgical suture to enhance
its bioabsorbability. The surgical suture is preferably fabricated
from a terpolymer of glycolide, dioxanone and trimethylene carbonate.
In particularly useful embodiments, the suture is made from a block
copolymer containing glycolide, dioxanone and trimethylene carbonate
such as, for example, a block copolymer wherein the center block
is a p-dioxanone/trimethylene carbonate copolymer and the two end
blocks are p-dioxanone/glycolide copolymer. The surgical suture
is exposed to gamma radiation in an amount ranging from about 2
Mrad to about 12 Mrad. Various sizes of monofilament or multifilament
sutures can be treated in this manner to enhance the rate at which
the suture is absorbed, but, quite surprisingly, without any significant
adverse effect on the physical properties of the suture.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The method described herein relates to the irradiation of a suture
fabricated from synthetic bioabsorbable polymer to increase the
rate of absorption of the suture in the body.
Suture sizes referred to below are USP synthetic suture sizes as
listed in the United States Pharmacopeia (USP XXII, page 1307).
The suture can be a monofilament or multifilament suture and is
preferably fabricated from a terpolymer of glycolide, p-dioxanone,
and trimethylene carbonate. Particularly useful herein are substances
made from block copolymers of glycolide, dioxanone and trimethylene
Suitable block copolymers have two specific types of blocks, a
"A" block having a proportion of glycolic acid ester units
as the predominant component thereof and a "B" block comprising
13 dioxane-2-one randomly copolymerized with 14 dioxane-2-one.
Such copolymers can advantageously be formed into fibers and irradiated
to provide relatively fast absorbing sutures with good physical
The preferred block copolymer compositions for use in making sutures
to be irradiated include an A block formed from a copolymer which
has glycolide as the predominant component thereof. That is glycolide
comprises at least 50 mole percent of the first block. Preferably,
glycolide comprises at least about 60 mole percent of the first
block and most preferably at least about 95 mole percent glycolide.
The glycolide may be copolymerized with any monomer which provides
an absorbable copolymer to form the A block. Such monomers include
but are not limited to lactide, trimethylene carbonate, p-diohanone,
and epsilon-caprolactone. The copolymers of glycolide which form
the first block can be random or block copolymers and can be synthesized
by known methods. See, for example, U.S. Pat. Nos. 4653497; 4838267;
4429080; 4665730; and 4788979 the disclosures of which are
incorporated herein by reference.
The B block of the preferred copolymers has 14-dioxane-2-one and
13-dioxane-2-one linkages. Preferably 14-dioxane-2-one comprises
from about 20 mole percent to about 80 mole percent, and more preferably
from about 35 mole percent to about 65 mole percent of the B block.
Most preferably, 14-dioxane-2-one comprises at least about 35 mole
percent of the B block, the remainder of the block comprising 13-dioxane-2-one.
Copolymers of 13-dioxane-2-one and 14-dioxane-2-one having an
inherent Viscosity of from about 0.5 to about 2 dl/g measured at
30.degree. C. and a concentration of 0.25 g/dI in chloroform or
hexafluoroisopropanol (HFIP) may generally be used as the second
The block copolymers can be prepared by preparing the individual
polymers which make up the blocks and then copolymerizing these
polymers to form a block or graft copolymer. Alternatively, a pre-polymer
having 14-dioxane-2-one and 13-dioxane-2-one linkages may be prepared
in a reactor and then the monomers needed to form the other block
or blocks are added directly to the reactor to thereby form the
block copolymer. In one embodiment the polymerization reaction used
in the formation of the above mentioned pre-polymer is stopped short
of completion, leaving residual 14-dioxane-2-one. Then monomers
needed to form the block or blocks are added directly to the reactor
vessel to react the residual 14-dioxane-2-one and the pre-polymer
to form block copolymers having 14-dioxane-2-one linkages in each
In forming the preferred block copolymers from which the sutures
are made, the A (predominately glycolide) block may be present in
an amount from about 50 to about 80 percent by weight based on the
weight of the final block copolymer. The B (random copolymer) block
may be present in an amount from about 20 to about 50 weight percent
based on the weight of the final block copolymer. Preferably, the
R block comprises between about 60 and about 70 weight percent of
the block copolymer. In a particularly useful embodiment, the A
block comprises about 65 weight percent and the B block comprises
about 35 weight percent of the final block copolymer. The copolymers
of the present invention have a molecular weight such that their
inherent viscosity is from about 0.5 to about 2.0 dl/g, and preferably
from about 1 to about 1.40 dl/g measured at 30.degree. C. at a concentration
of 0.25 g/dl in chloroform or HFIP.
Each A and B block may comprise a single type of recurring monomeric
unit. Alternatively, each block may comprise more than one type
of recurring monomeric unit randomly distributed throughout each
block. The block copolymers used to form the sutures may have repeating
block units such as AB, ABA, ABAB, ABABA, BABA, etc.; with ABA being
A particularly useful suture for use herein is BIOSYN.TM. sutures
available from United States Surgical Corporation, Norwalk, Conn.
If the suture is multifilament it can be manufactured by any of
the known methods for combining multiple strands, such as braiding,
twisting, and the like. Prior or subsequent to the irradiation treatment
the suture can be coated or filled with various coating and/or filling
agents to improve handling characteristics and storage stability.
Such agents are disclosed, for example, in U.S. Pat. Nos. 5306289
5269808 and 5226912 all of which are incorporated by reference.
The irradiation treatment is performed by subjecting the suture
to gamma-radiation from, for example, a cobalt-60 source. The total
dose rate can range about 2 to about 12 preferably from about 5
to 8 Mrad. The suture is preferably exposed to the radiation while
under vacuum or in an atmosphere from which oxygen is excluded.
The suture is preferably kept at about temperature while being irradiated.
The irradiation treatment results in a suture with enhanced bioabsorbability
as illustrated by the examples given below.
Advantageously, irradiation of sutures of the preferred block copolymer
compositions exhibit strength retention and mass loss profiles similar
to the profiles of gut sutures. However, because they are synthetic
absorbable sutures, the irradiated sutures do not exhibit any of
the perceived disadvantages (e.g., fraying, inconsistent strength,
etc.) typically associated with gut sutures.