Note: Descriptions are shown in the official language in which they were submitted.
The invention relates to surgical sutures made from
ethylene-propylene copolymers~
Background of the Invention
Surgical sutures made from polypropylene have been
successfully used by the medical profession for more than
ten years. The advantages exhibited by polypropylene
sutures include the following:
a) They pass easily through tissue;
b) They resist breakdown and do not promote infection;
c) They provide good knot security;
d) They have minimal reaction with tissue;
e) They have high tensile strength; and
f) They maintain their in viva tensile strength over
extended periods.
The preferred polypropylene suture used in the medical
profession today is described by Listener in US Patent
No. 3,630,20~. The polypropylene sutures described by
Listener have the following properties:
Tensile Strength 3.9 to 8.9 gra~s/denier
(45,000 to 100,000 psi
Knot Strength 3.3 to OWE grams/denier
(3~,000 to 91,000 psi)
wreak Elongation 36 to 62~
Young's Modulus 313,000 to 523,000 psi
. ,
ETCH 592
As good as the current polypropylene sutures are, there is
some room for improvement. In particular it would be
desirable to increase the compliance, limpness, or
flexibility of polypropylene sutures in order to make them
easier to tie and to improve their knot security. The
problem is that previous efforts to accomplish this have
occasioned a concomitant undesirable decrease in strength
properties.
The present invention is based upon the discovery that
surgical sutures can be made from certain ethylene-propy-
tone copolymers, and that such sutures retain to a large
degree the excellent properties of polypropylene sutures,
but, at the same time, are more compliant and are
therefore easier for the surgeon to tie.
Grief Outline of the Invention
The invention provides surgical sutures made from
ethylene-propylene copolymers, such copolymers containing
a small amount, for instance, from about 0.3 to about 7,
and preferably from about 0.5 to about 5, weight per cent,
polymerized ethylene, the remainder being polymerized
- propylene. The sutures are characterized by an excellent
balance of properties
The Prior Art
Usher, US. Patent lo. 3,105,493, discloses sutures made
of high density polyethylene polymers which can contain
small amounts of other olefins, such as propylene,
copoly~erized with the ethylene.
North, in US. Patent No. 39359,983, discloses sutures
made of either polyethylene or polypropylene homopolyrlers.
ETCH 592
-3
Oppenlander, in US. Patent No. 3,S05,164, discloses
conjugate fibers composed of polypropylene and ethylene-
propylene copolymer.
Cash et at., it US. Patent No. 3,432,514, discloses a
compression molded disk made from a copolymer of 94 per
cent propylene and 6 per cent ethylene (see Example II in
Cot. 5).
Listener, in US. Patent Not 3,458,471, discloses
stabilized filaments made from a variety of olefin
polymers, including ethylene-propylene copolymers of
unspecified proportions.
Ziegler et at., in US. Patent No. 3,113,115~ at Cot. 1,
lines 35 et seq., disclose various olefin copolymers,
including ethylene-propylene copolymers. it Cot. 11,
lines 21-23, it is disclosed that the polymers disclosed
in the patent can be spun into threads
Detailed Description of the Invention
The copolymer employed to produce the sutures of the
invention is a random copolymer of ethylene and propylene
containing only a small amount of polymerized ethylene,
erg., from about 0.3 to about 71 and preferably from about
0.5 to about 5, weight per cent, the remainder being
polymerized propylene. The molecular weight of the
copolymer is such as to impart a melt flow of from about
0.5 to about 7 as determined by ASTM D-1238, Condition L.
Ordinarily, a melt flow within this range will be obtained
with weight average molecular weights of the order of
about 200,000 to about 500,000. In many cases where it is
desired to obtain the highest tensile strengths, the melt
flow of the copolymer will be less than about 3
ETA 592
I
--'1--
The copolymer can contain the usual stabilizers against
heat, ultraviolet, and oxidative degradation. Such
stabilizers include hindered phenols, tertiary amine,
and the like, such as SANTONOX R (trademark). The cop-
lamer can also contain dyes, colorants and lubricants.
The sutures of the invention are produced by extruding
monofilaments of the copolymer by known procedures,
drawing the extruded monofilaments to orient the
polymer, and then subjecting the drawn monofilaments to
an annealing/relaxing step. The basic procedure that
can be employed is described by the Listener patent cited
above (No. 3,630,205). Typical conditions that can be
used to produce the sutures of the invention are shown
below in the examples, wherein Listeners procedure is
modified so as to use a three-stage draw.
The sutures of the invention can be produced in the usual
sizes, e.g., from Size 2 down to Size 11/0. They can be
attached to needles by the usual procedures, and can
then be sterilized (as by using ethylene oxide) and
packaged in sterile packs ready -for use.
The following Examples illustrate the invention:
Example 1
A copolymer (A) containing about 1.3 weight per cent
polymerized ethylene and about 98.7 weight per cent
polymerized propylene was employed. The copolymer had
the following properties:
I
--5--
Melt Flow 2.0
Molecular Weight 3 x 105
___________________________________________________
(1) By ASTM D-1238, Condition L
(2) weight average molecular weight
__________________________________________________________
The copolymer was extruded, drawn, and annealed under the
conditions set forth below:
A. extrusion: (screw extrude: 1" dram. 12/1 L/D0
block/die tempt 409/431F.
die dummy holes: 0.050"/1
barrel pressure: 1500 psi
pump pressure 1050 psi
thro~ghputO 376 gph (grams per hour)
quench water tempt 75F.
B. Drawing: (single-end godet rolls)
sty godet-speed/temp: 27 fpm/170F.
end godet-speed/temp~ 160 fpm/210F.
3rd godet-speed/temp: 180 fpm/ 77F.
heated oven tempt 300F.
Thea godet-speed/temp: 200 fpm/ 77~F.
(The drawing was done in three stages, with the heated
oven being located between the 3rd and Thea godets.)
CO Annealing: (forced air heated oven)
it% relax at 250F. for 5 mix
heat set at 285F. for 30 mix
ETCH 592
The extruded copolymer was drawn a total of 7.4X (before
relaxation). The final product was a size 0 ~onofilament
(diameter about 13.8 miss). After aging for one month,
the tensile properties of the monofilament were the
following:
Tensile strength 62,600 psi
Knot strength 42,200 psi
Young's ladles 232,000 psi
Typical tensile properties for commercial polypropylene
size 0 monofilament suture material are the following:
tensile strength 6~,5~0 psi
Knot Strength 41,300 psi
Young's modulus ~73,000 psi
Fxam~les ? - 8
r1Onofilamerlt suture material was jade from Polymer A (the
ethylene propylene copolymer described in example l),
Polymer I, ethylene-propylene copolymer (about 97.8 weight
per cent propylene, about 2.2 weight per cent ethylene -
royalty Flow = 5), Polymer C (about 95.8 weight per cent
propylene, about 4.2 weight per cent ethylene - Melt Flow
= lo Polymer D (about 95.B weight per cent propylene,
about I weight per cent ethylene - Melt Flow = 3), and
Polymer E (about 94.5 weight per cent propylene, about 5.5
weight per cent ethylene - elite Flow = 3.8). The extra-
soon, drawing, and annealing conditions are displayed instable I. The fiber was cut into suture lengths, packaged,
and ethylene oxide sterilized. Representative physical
properties of the sterilized monofila~ents are displayed
in Table II. In table II, the numbers in parentheses are
values of typical commercial polypropylene sutures of
comparable size. The overall draw ratio (DO) is
TCH 592 determined by the equation:
I
--7--
DO = Dent (1 - S/100
wherein:
speed of IV Godet
Dent =
speed of I Godet
% S = % Shrinkage during annealing
ETCH 592
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The tensile properties (i.e., straight pull, Young's
Modulus, and intrinsic) displayed on Table II were
determined using an INSTRON (trademark) tersely tester
using the procedure of ASTM D-2256-66T. The knot
strength was determined by the test method described in
the US. Pharmacopoeia, Vol. XVII, page 921. The settings
on the Instron Tensile Tester used to determine the
straight tensile, knot -tensile, break elongation, and
Young's modules were the following:
Gauge Chart Crosshead
Length Speed Speed
Tensile Strength Mooney loin
Knot Strength Mooney Mooney
Break Elongation Mooney loin
Young's Modulus Mooney Mooney
The Fatigue Tests were carried out by the procedure of
~STM-D2176-63T. In the memory test, the sutures are
carefully removed from their packages and the average
- distance between package "kinks" is measured. The knot
security test is carried out by the following procedure:
A loop of suture material is formed around a three-inch
mandrel and a knot with varying number of squared
throws -tied by hand The loop is cut on the opposite
side of the mandrel from the knot and the cut ends are
clamped in the jaws of an INSTRON Tensile Tester. The
knot is pulled apart with a crosshead speed of 2 inches/
minute and will either slip or break. The lowest force
at which slipping occurs is measured or, if no slipping
occurs, the force required for breaking. Twenty knots
are pulled apart for the force required for each size
suture and for each number of throws.
-12-
A typical determination is made by tying 20 knots with two
squared throws and pulling them apart. Assuming they all
slip, 20 knots with three squared throws are tied and
pulled apart. This process is continued with increasing
throws until all 20 knots break cleanly without slipping.
The forces are then computed separately for each throw to
determine the average force and standard deviation at
which absolute knot security can be obtained.
As the data in Table II illustrate, the ethylene-propylene
copolymer sutures of the invention can retain to a
substantial degree the desirable strength properties of
comparably sized polypropylene sutures, while having a
lower Young's Modulus (which is an indication, although
not a direct measurement, of compliance). The sutures of
this invention are perceived by Yost surgeons to be more
compliant than are the comparably sized polypropylene
sutures. This subjective feeling by surgeons, which is
difficult to measure with precision by physical testing,
is an important improvement over polypropylene homopolymer
sutures. This improvement in performance is provided by a
small proportion of copolymerized ethylene in the
propylene polymer. It is surprising that the small amount
of ethylene used, an amount too small to have a major
effect on most measurable physical properties, has such a
significant effect on the subjective feeling of compliance
of the sutures made from the copolymer~.
When comparing the sutures of this invention with
polypropylene (homopolymer) sutures, the most appropriate
comparisons are made between sutures ox approximately the
same size that are made from polymers having about the
same molecular weights.
The sutures of this invention will ordinarily have
properties within the ranges set forth in Table III:
ETA 592
TALE III
Tensile strength, psi 40,000 to 100,000
Knot strength, Sue to 90,000
wreak elongation, ~40 to 120
Young's Modulus, psi 100,000 to 350,000
A comparison of the fatigue life of the ethylene-propylene
copolymer sutures with that of polypropylene sutures shows
the former to possess a significantly longer life (as
indicated by the number of cycles to failure).
Consequently, the ethylene-propylene copolymer sutures may
be considered preferable in surgical applications in which
cyclic loading of the suture is expected.
ETCH 592
