Surgical suture abstract
A surgical suture and a process for producing the same are disclosed,
which surgical suture comprising a porous body of polytetrafluoroethylene
having an outer circumference that is substantially free of pores,
with only the interior being made porous.
Surgical suture claims
What is claimed is:
1. A surgical suture comprising a porous body of sintered polytetrafluoroethylene
having an outer circumference that is substantially free of pores,
with only the interior being made porous.
2. A surgical suture comprising a porous body of sintered polytetrafluoroethylene
having an outer circumference that is substantially free of pores,
with only the interior being made porous, being prepared by the
steps of:
extruding a polytetrafluoroethylene paste to make an unsintered
shape;
stretching said unsintered shape at a temperature not higher than
the melting point of the polytetrafluoroethylene to form a stretched
shape;
sintering said stretched shape; and
drawing the resultant sintered stretched shape into a filament
through dies.
3. A surgical suture comprising a porous body of sintered polytetrafluoroethylene
having an outer circumference that is substantially free of pores,
with only the interior being made porous, being prepared by the
steps of:
extruding a polytetrafluoroethylene paste to make an unsintered
shape;
stretching said unsintered shape at a temperature not higher than
the melting point of the polytetrafluoroethylene;
drawing the shape into a filament through dies at a temperature
not higher than the melting point of the polytetrafluoroethylene;
and
sintering said filament.
Surgical suture description
FIELD OF THE INVENTION
The present invention relates to a surgical suture and a process
for producing the same.
BACKGROUND OF THE INVENTION
Currently used surgical sutures are available in various types
made from both natural and artificial materials. In terms of shape,
surgical sutures are classified as monofilaments (FIG. 4), braided
multifilaments (FIG. 5) and twisted multifilaments (FIG. 6).
Surgical sutures made of synthetic polytetrafluoroethylene (PTFE)
have recently been developed with a view to taking advantage of
the low tissue interaction of PTFE and an example of such sutures
is described in JP-B-61-34346. (The term "JP-B" as used
herein means an examined Japanese patent publication.) Disclosed
in JP-B-61-34346 is a surgical suture made of twisted or braided
PTFE tapes or filaments that have a microstructure in which a number
of fibrils oriented in a longitudinal direction are bound with small
nodes at selected sites.
Commercially available porous PTFE sutures, on the other hand,
have low tensile strength values that are smaller than those specified
by the standards for plastic sutures in Notification No. 444 of
the Ministry of Public Welfare of Japan (Extra Circular of Dec.
28 1970). Examples of the diameters and tensile strength values
of the commercial products and an extract of the Notification No.
444 are shown in Table 1 below. Further, these commercial sutures
have fine asperities on the surface as shown in FIG. 7.
TABLE 1 ______________________________________ Standards in Commercial
product Notification No. 444 Tensile Tensile Diameter strength Diameter
strength (mm) (kg) (mm) (kg) ______________________________________
0.221 1.10 0.203-0.245 .gtoreq.1.13 0.163 0.62 0.152-0.203 .gtoreq.0.68
0.132 0.43 0.102-0.152 .gtoreq.0.45 ______________________________________
The suture shown in JP-B-61-34346 is composed of twisted tapes
or filaments, and thus it has the following two major problems because
of twisting: (1) it has low porosity and elasticity, and (2) the
surface asperities reduce the slipping property of the suture and
increase the chance of adversely affecting the tissues of wounds
or surgical incisions.
The commercial porous PTFE sutures have a problem in that they
do not have a sufficient tensile strength to satisfy the standards
specified by the Ministry of Public Welfare of Japan in Notification
No. 444.
SUMMARY OF THE INVENTION
The present invention has been achieved under these circumstances.
An object of present invention is to provide a surgical suture
having predetermined tensile strength and elasticity and exhibiting
good slipping property.
Another object of the present invention is to provide a process
for producing a surgical suture having predetermined tensile strength
and elasticity and exhibiting good slipping property.
Other objects and effects of the present invention will be apparent
from the following description.
The present invention relates to a surgical suture comprising a
porous body of polytetrafluoroethylene having an outer circumference
that is substantially free of pores, with only the interior being
made porous.
The present invention also relates to a process for producing a
surgical suture which comprises the steps of: extruding a polytetrafluoroethylene
paste to make an unsintered shape; stretching the unsintered shape
at a temperature not higher than the melting point of the polytetrafluoroethylene
to form a stretched shape; sintering the stretched shape; and drawing
it into a filament through dies.
The present invention further relates to a process for producing
a surgical suture which comprises the steps of: extruding a polytetrafluoroethylene
paste to make an unsintered shape; stretching the unsintered shape
at a temperature not higher than the melting point of the polytetrafluoroethylene;
drawing the shape into a filament through dies at a temperature
not higher than the melting point of the polytetrafluoroethylene;
and sintering the filament.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a scanning micrograph (magnification: 50) showing the
outer surface of one of the sutures prepared in the example of the
present invention;
FIG. 2 is a scanning electron micrograph (magnification: 1000)
showing the outer surface of the same suture;
FIG. 3 is a scanning electron micrograph (magnification: 1000)
of the surface of the interior of the same suture;
FIGS. 4A and 4B are a front view and a cross-sectional view, respectively,
of a conventional monofilament suture;
FIGS. 5A and 5B are a front view and a cross-sectional view, respectively,
of another conventional suture that is in the form of braided filaments;
FIGS. 6A and 6B are a front view and a cross-sectional view, respectively,
of still another conventional suture that is in the form of twisted
filaments; and
FIG. 7 is a scanning electron micrograph (magnification: 50) showing
the outer surface of commercial porous PTFE sutures.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows the outer surface (circumference) of the suture of
the present invention at a magnification of 50; FIG. 2 shows the
outer surface (circumference) of the same suture at a higher magnification
of 1000; and FIG. 3 shows the inner surface of the same suture
at a magnification of 1000.
The surgical suture according to the present invention comprises
a porous body of PTFE having an outer circumference that is substantially
free of pores, with only the interior being made porous.
The thickness of the outer circumference substantially free of
pores is not limited but is preferably such a thickness that does
not deteriorate the properties of the porous body of PTFE such as
elasticity.
The diameter of the suture of the present invention is not limited
and any diameters used in this field of art can be applied.
The PTFE used in the present invention is generally a homopolymer
composed of substantially only tetrafluoroethylene, and generally
has a number average molecular weight of 500000 or more, more preferably
5000000 or more. The PTFE is generally used in the form of fine
powder as a starting material for the extrusion step.
In the process according to the present invention, methods for
the extrusion, stretching and sintering steps, and the conditions
therefor are not particularly limited, and may be those used in
this field of art as described, e.g., JP-B-61-34346.
In the drawing step of the process according to the present invention,
the drawdown ratio in the drawing operation through dies is preferably
in the range of from 30 to 90%, and is more preferably in the range
of from 60 to 90%, in total. The "drawdown ratio" as used
herein is defined by the following formula: ##EQU1##
The drawing operation through dies is preferably conducted repeatedly,
i.e., the drawing operation of a drawdown ratio of 80% or more,
more preferably 90% or more, is preferably conducted repeatedly
to obtain a predetermined total drawdown ratio. The drawing operation
is preferably conducted at a temperature not higher than the melting
point of the PTFE at a drawing speed of from 1 to 100 m/min.
The surgical suture of the present invention is porous and has
a diameter slightly greater than the diameter of a needle so that
its elasticity will prevent the leakage of blood through the eye
of the needle.
In order to solve the problems associated with the prior art suture
as described, e.g., in JP-B-61-34346 the suture of the present
invention has the following characteristics: (i) it is made of a
monofilament, and (ii) it has no pores in the outer surface (circumference),
with only the interior being made porous. At the same time, in order
to solve the problems with commercial porous PTFE sutures, the suture
of the present invention is provided with increased tensile strength
by reshaping through dies, while care should be taken to minimize
the deterioration of the elastic characteristic of the suture that
is necessary to prevent the leakage of blood through the eye of
a needle.
The present invention is illustrated in more detail referring to
the following example, but is not construed as being limited thereto. |