U.S. patent application number 10/311289 was filed with the patent office on 2003-09-18 for melting and spinning device and melting and spinning method.
Invention is credited to Igaki, Keiji, Yamane, Hideki.
Application Number | 20030173702 10/311289 |
Document ID | / |
Family ID | 18970088 |
Filed Date | 2003-09-18 |
United States Patent
Application |
20030173702 |
Kind Code |
A1 |
Igaki, Keiji ; et
al. |
September 18, 2003 |
Melting and spinning device and melting and spinning method
Abstract
The present invention is relative to a melt spinning apparatus
for melt spinning a biodegradable polymer material. The
biodegradable polymer material is melted by a melt mechanism (4)
including a screw (16) which is mounted in a vertically mounted
cylinder (8) coaxially with the cylinder (8) and which is
rotationally driven by a rotational driving mechanism (7). The
screw includes at least one turn of a helical groove (17) on its
peripheral surface. The biodegradable polymer material being melted
in this way is discharged in the vertical direction from a
discharge opening of a nozzle (10) mounted coaxially on the
cylinder (8).
Inventors: |
Igaki, Keiji; (Kyoto,
JP) ; Yamane, Hideki; (Shiga, JP) |
Correspondence
Address: |
Rader Fishman & Grauer
Suite 501
1233 20th Street NW
Washington
DC
20036
US
|
Family ID: |
18970088 |
Appl. No.: |
10/311289 |
Filed: |
February 19, 2003 |
PCT Filed: |
April 15, 2002 |
PCT NO: |
PCT/JP02/03738 |
Current U.S.
Class: |
264/211.22 ;
425/378.2 |
Current CPC
Class: |
D01D 1/06 20130101; D01D
1/04 20130101; D01D 5/08 20130101 |
Class at
Publication: |
264/211.22 ;
425/378.2 |
International
Class: |
D01D 001/04; D01D
005/08 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 18, 2001 |
JP |
2001-119964 |
Claims
1. A melt spinning apparatus for melt spinning a strand of a
biodegradable polymer material, forming a stent implanted in a
living body, comprising: a vertically mounted cylinder, supplied
with said biodegradable polymer material; a screw mounted in said
cylinder coaxially therewith, said screw being rotationally driven
by a rotational driving unit and having at least one turn of a
helical groove on its peripheral surface; and a nozzle mounted to
the distal end of said cylinder and having a discharge opening
coaxially with said cylinder; said biodegradable polymer material
supplied into said cylinder and melted by rotation of said screw
being emitted vertically from a discharge opening in said nozzle
for spinning the strand.
2. The melt spinning apparatus according to claim 1 wherein a sole
discharge opening is provided in said nozzle for extending in the
vertical direction for spinning a filament.
3. The melt spinning apparatus according to claim 1 further
comprising a plurality of heating units in juxtaposition along the
axial direction of said cylinder, with the heating temperature of
said heating units being controlled independently of one
another.
4. The melt spinning apparatus according to claim 2 further
comprising heating units on the outer periphery of said nozzle for
controlling the nozzle temperature.
5. The melt spinning apparatus according to claim 1 wherein the
helical groove formed on the peripheral surface of said screw is
formed to a pitch smaller than one-half the screw diameter.
6. The melt spinning apparatus according to claim 1 further
comprising a supplying unit for loading a biodegradable polymer
material into said cylinder and temperature controlling mechanism
for controlling the temperature of the biodegradable polymer
material charged into said supplying unit.
7. A method for melt spinning a strand of a biodegradable polymer
material, forming a stent implanted in a living body, comprising:
melting the biodegradable polymer material by a melt mechanism
including a screw which is provided in a vertically mounted
cylinder coaxially therewith and on the peripheral surface of which
at least one turn of the spiral groove is formed, said screw being
rotated by a rotational driving mechanism; the molten biodegradable
polymer material being emitted in the vertical direction through a
discharge opening in a nozzle provided coaxially with said cylinder
for spinning the strand.
8. The melt spinning method according to claim 7 wherein the molten
biodegradable polymer material is emitted in the vertical direction
from a sole discharge opening provided in said nozzle for spinning
into a filament.
9. The melt spinning method according to claim 7 wherein the
biodegradable polymer material is heated in a supplying unit to a
temperature lower than the melting temperature and is loaded into
said melt mechanism for melting.
10. The melt spinning method according to claim 7 wherein said
biodegradable polymer material is one of polylactic acid (PLA),
polyglycolic acid (PGA), polyglactin (a polyglycolic
acid-polylactic acid copolymer), polydioxanone, polyglyconate (a
trimethylene carbonate-glycoid copolymer) and a polylactic
acid-.epsilon.-caprolactone copolymer.
Description
TECHNICAL FIELD
[0001] This invention relates to a method and an apparatus for melt
spinning a medical material implanted in a living body, for
example, a strand of a biodegradable polymer material which forms a
stent implanted in the vascular vessel of a living body.
BACKGROUND ART
[0002] When a stenosed lesion has occurred in the vascular vessel
of a living body, in particular the blood vessel, such as arterial
vessels, the percutaneous transluminal angioplasty (PTA) is
performed by inserting a balloon mounted in the vicinity of the
distal end of a catheter into the stenosed lesion and inflating
this balloon to expand the stenosed lesion to keep the blood
flowing.
[0003] Meanwhile, it is known that, even if PTA is applied, there
is a high probability that re-stenosis is liable to occur at the
once-stenosed portion.
[0004] In order to prevent this re-stenosis from occurring, the
conventional practice is to implant a tubular stent on the site
where the PTA has been performed. This stent is inserted in a
contracted state into the blood vessel, subsequently dilated and
implanted in this state in the blood vessel to support the blood
vessel from its inside to prevent re-stenosis from occurring in the
blood vessel. As this sort of the stent, the metallic stent formed
of such as stainless steel or a Ti--Ni based alloy, is now in
use.
[0005] Meanwhile, the principal objective in implanting a stent in
the blood vessel in PTA is to prevent acute coronary occlusion and
to decrease the frequency of re-stenosis. It has been reported
that, since the acute coronary occlusion and re-stenosis are the
phenomenon which occurs during a predetermined time period, so that
only transient therapy is needed. Consequently, the stent is
required to maintain the function of supporting the blood vessel
from inside for a predetermined time period, while it is more
desirable that the stent is not left in the living body as a
foreign substance.
[0006] If the metallic stent is implanted in the blood vessel, it
is left permanently, so that, when re-stenosis occurs on the stent
site, the stent frequently proves an obstruction to the operation
of re-angioplasty. Moreover, the operation of coronary-artery
bypass graft is difficult to perform on the site of implanted
stent. Thus, implanting the permanently persisting metallic stent
offers various inconveniences to re-treatment.
[0007] In order to overcome the problem inherent in the metallic
stent, such a stent formed of a biodegradable polymer material has
been proposed which i s degraded after a lapse of a predetermined
time, from the time it is implanted in e.g., the blood vessel of
the living body to be then disappear by being absorbed in the
living tissue (JP Patent No. 2842943; JP Laying-Open Patent
Publication H-11-57018).
[0008] The present inventors have proposed a stent comprised of a
knitting obtained on knitting a strand of the biodegradable polymer
material into a tubular form (JP Patent 2842943), and a stent
obtained by bending a strand of a biodegradable polymer in a zigzag
shape and wrapping it in a tubular form under a non-woven
non-knitted condition.
[0009] With the use of the strand formed of a biodegradable
polymer, it is possible to font a stent which exhibits mechanical
characteristics sufficient to support the vessel in the inflated
state for certain time duration and disappears after lapse of the
preset time.
[0010] Since the stent formed of the strand of the biodegradable
polymer can readily be flexed and deformed, it can readily be
delivered through the sinuous blood vessel so as to be implanted on
the target site.
[0011] It should be noted that the biodegradable polymer material,
as a high molecular material, differs in its degradation and
absorption characteristics, and hence in its mechanical properties,
depending on the molecular weight. For example, the molecular
weight of the biodegradable polymer material, such as polylactic
acid (PLA), is lowered by being melted and thermally decomposed.
The degree that the molecular weight is lowered changes depending
on the degree of thermal decomposition. Thus, if the melt spinning
heating time of the same biodegradable polymer material is
non-uniform, then the average molecular weight of the spun strand
becomes non-uniform. If the strand is non-uniform in its average
molecular weight, its degradation and absorption characteristics or
mechanical properties undergo localized variations.
[0012] If, with non-uniform average molecular weight, a stent is
formed and implanted in the vascular vessel, such as a blood
vessel, the stent in its entirety cannot be degraded or absorbed
evenly. Moreover, there is a fear that the stent formed using this
sort of the strand cannot support the inner wall of the vascular
vessel, such as blood vessels, with a uniform force, because the
strand itself exhibits strength variations.
DISCLOSURE OF THE INVENTION
[0013] It is therefore an object of the present invention to
provide a method and an apparatus for spinning the strand, whereby
it is possible to spin the strand having uniform mechanical
properties and uniform degradation and absorption characteristics
free from strength variations, that is, it is possible to spin the
strand having a uniform average molecular weight and making it a
suitable construction material for a biodegradable stent.
[0014] The present invention provides a melt spinning apparatus for
melt spinning a strand of a biodegradable polymer material, forming
a stent implanted in a living body. This comprises a vertically
mounted cylinder, supplied with the biodegradable polymer material,
a screw mounted in the cylinder coaxially, rotationally driven by a
rotational driving unit and having at least one turn of a helical
groove on its peripheral surface, and a nozzle mounted to the
distal end of the cylinder and having a discharge opening coaxially
with the cylinder. The biodegradable polymer material supplied into
the cylinder and melted by rotation of the screw is emitted
vertically from a discharge opening in the nozzle for spinning the
strand.
[0015] With the present melt spinning apparatus, the molten
biodegradable polymer material is fed by a screw in the vertical
direction and emitted from a nozzle for spinning a strand, so that
the strand has a uniform molecular weight distribution is spun as
stagnation or non-uniform eddying currents of the biodegradable
polymer material melted in the cylinder or the nozzle may be
prevented from being produced.
[0016] Moreover, with the present melt spinning apparatus, there is
provided a plural number of heating units placed in juxtaposition
along the axial direction of the cylinder, on the outer sides of
the cylinder forming the melt mechanism for melting the
biodegradable polymer material, for controlling the molten state of
the biodegradable polymer material injected into the cylinder. The
heating units are able to perform temperature control independently
of one another.
[0017] The nozzle for discharging the molten biodegradable polymer
material is kept at a constant temperature by the heating units. By
controlling the nozzle temperature, the temperature of the molten
biodegradable polymer material discharged from the nozzle can be
made constant.
[0018] According to the present invention, the biodegradable
polymer material is melted by a melt mechanism including a screw
which is provided in a vertically mounted cylinder coaxially and on
the peripheral surface of which at least one turn of the helical
groove is formed. The screw is rotated by a rotational driving
mechanism. The molten biodegradable polymer material is emitted in
the vertical direction through a discharge opening in a nozzle
provided coaxially with the cylinder for spinning the strand.
[0019] With the melt spinning method of the present invention, a
spun filament having a uniform molecular weight distribution may be
produced.
[0020] Other objects, features and advantages of the present
invention will become more apparent from reading the embodiments of
the present invention as shown in the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a side view showing a melt spinning apparatus
according to the present invention.
[0022] FIG. 2 is a cross-sectional view showing the cylinder and
the screw of a melting mechanism.
[0023] FIG. 3 is a plan view showing a flow resistance plate
mounted to the distal end of the cylinder.
[0024] FIG. 4 is a cross-sectional view showing a discharging unit
at the distal end of the melt mechanism.
[0025] FIG. 5 is a cross-sectional view showing a supply unit for
supplying a polymer material to the melting mechanism.
[0026] FIG. 6 is a side view showing the screw that is placed in
the cylinder forming the melting mechanism.
[0027] FIG. 7 is a side view showing a supply controlling mechanism
which is placed between the melting mechanism and the discharging
unit.
[0028] FIG. 8 is a cross-sectional view showing a set of gears
forming the melt mechanism.
BEST MODE FOR CARRYING OUT THE INVENTION
[0029] A melt spinning apparatus and method for melt spinning the
biodegradable polymer material using the melt spinning apparatus
are now explained in detail.
[0030] The melt spinning apparatus according to the present
invention is of a vertical type in which a melt spinning unit is
mounted vertically, as shown in FIG. 1.
[0031] The melt spinning apparatus, shown in FIG. 1, includes a
base plate 2, mounted horizontally on a mounting surface, and the
melt spinning unit 1 is supported by member 3a by a support pillar
3 mounted upright on the base plate 2. The melt spinning unit 1
includes: a melt mechanism 4 which is supported by and parallel to
the upstanding support pillar 3, a discharging unit 5 for
discharging the polymer material melted by the melt mechanism 4, a
supplying unit 6 for supplying the polymer material to the melt
mechanism 4, and a rotational driving mechanism 7 for rotationally
driving a screw 16 forming the melt mechanism 4.
[0032] The melt mechanism 4 which is in the melt spinning unit 1,
includes a cylinder 8, as shown in FIG. 2. The screw 16 is provided
within and coaxially of the cylinder 8. The screw 16 pressurizes
the polymer material, injected into the cylinder 8 and extrudes the
pressurized material towards the distal end of the cylinder 8 while
melting it.
[0033] On the outer periphery of the cylinder 8, there is a plural
number of heating units 9 in juxtaposition along the axial
direction of the cylinder 8. These heating units 9 are controlled
independently of one another to enable the multi-stage control of
the temperature axially of the cylinder 8.
[0034] On the distal end of the cylinder 8, there is mounted a
connecting member 21 for connecting the discharging unit 5 to the
cylinder. The discharging unit 5 is adapted for discharging the
melted polymer material. The connecting member 21 is ring-shaped
and has at its center portion a flow resistance plate 22 including
a plural number of through-holes 22a matching the axial direction
of the screw 16, as shown in FIG. 3. The molten polymer material,
supplied from the distal end of the cylinder 8, by rotating the
screw 16, is pressurized by the flow resistance when traversing the
flow resistance plate 22. The pressurized polymer material is
discharged towards the discharging unit 5 from the distal end of
the cylinder 8.
[0035] The diameter or the number of the through-holes 22a provided
on the flow resistance plate 22 is changed depending on the amount
or supply rate of the molten polymer material supplied from the
distal end of cylinder 8, on rotation of screw 16, or on the
viscous resistance of the polymer material.
[0036] The flow resistance plate 22 may be of any shape provided
that it affords the flow resistance to the polymer material
supplied melted from the distal end of the cylinder 8 on rotation
of the screw 16 to pressurize the polymer material.
[0037] The discharging unit 5, mounted by the connecting member 21
at the distal end of the cylinder 8, includes a sprue bush 11,
connected to the distal end of cylinder 8, and a nozzle 10 mounted
to the distal end of the sprue bush 11, as shown in FIG. 4. The
nozzle 10 is secured to the distal end of the sprue bush 11 by a
mounting member 12. Meanwhile, the nozzle 10 and the mounting
member 12 can be the same.
[0038] The sprue bush 11, which is part of the discharging unit 5,
supplies the molten polymer material from cylinder 8, to the nozzle
10 in a stable state at a constant rate of amount per unit time. A
flow passage 11a is in the center co-axially of the cylinder 8, as
shown in FIG. 4. That is, the flow passage 11a and the cylinder 8
are placed vertically with a common axis P1. The flow passage 11a
is tapered moderately from the vertically placed cylinder 8 towards
the nozzle 10 so that the polymer material supplied melted from the
cylinder 8 may be supplied in succession by predetermined amounts
per unit time to the nozzle 10 without producing stagnation or
eddying currents.
[0039] The nozzle 10 includes a discharge opening 10a for
discharging the polymer material supplied melted from the sprue
bush 11, as shown in FIG. 4. The discharge opening 10a operates for
controlling the diameter of the spun strand and is formed by an
optimum diameter depending on the thickness of the spun strand. The
discharge opening 10a is also formed to be coaxial with the flow
passage 11a. That is, the discharge opening 10a and the flow
passage 11a are set upright coaxially as the cylinder 8.
[0040] Meanwhile, plural different nozzles with different diameters
R.sub.1 at the discharge opening 10a may be provided and exchanged
from time to time to spin the strand with different
thicknesses.
[0041] On the outer periphery of the discharging unit 5, there is a
heating unit 13 for controlling the temperature of the discharging
unit 5. This heating unit 13 controls the temperature of the
discharging unit 5 to control the temperature of the polymer
material discharged from the nozzle 10.
[0042] The supplying unit 6 for supplying the molten polymer
material to the melt mechanism 4 includes a hopper 14 for loading
the polymer material into the cylinder 8 and a mounting unit 6a for
mounting the unit 6 to the cylinder 8, as shown in FIG. 5. On the
outer periphery of the mounting unit 6a, there is provided a
temperature controller 15 for controlling the temperature of the
supplying unit 6. This temperature controller 15 keeps the polymer
material, loaded into the hopper 14, at a constant temperature, and
is comprised of a heating/cooling means.
[0043] The melt mechanism 4 is explained more specifically.
Referring to FIG. 6, the melt mechanism 4 includes the screw 16,
having a helically extending groove 17 on its peripheral surface,
is mounted coaxially within the cylinder 8. The screw 16 is
rotationally driven by the rotational driving mechanism 7 at the
proximal end where the screw is connected. When the screw 16 is
driven rotationally, the polymer material, loaded into the cylinder
8 and melted by the heating units 9, is fed to the distal end of
the cylinder 8.
[0044] Meanwhile, the helical groove of the screw used in the
routine melt spinning apparatus, is formed to a pitch subsequently
equivalent to the screw diameter. The helical groove 17 of the
screw 16 used in the melt spinning apparatus according to the
present invention has a pitch Tp equal to one-half the diameter Sr
of the screw 16. By forming the helical groove 17 in this manner,
the dwelling time of the injected polymer material in the cylinder
8 can be protracted, such that melting can be achieved reliably by
sufficient heating in the heating unit 9 even though the screw 16
is of a reduced length. By employing the screw 16, the screw length
may be reduced, as a result of which the melt mechanism 4 including
the cylinder 8 can be reduced in size.
[0045] It should be noted that the melt spinning apparatus of the
present invention may be provided with a supply controlling
mechanism 18, between the melt mechanism 4 and the discharging unit
5, for controlling the supply quantity of the polymer material in
molten state, which is supplied to the discharging unit 5. This
supply controlling mechanism 18 may be configured as shown for
example in FIG. 7. The supply controlling mechanism 18, shown in
FIG. 7, includes a pressure detection means 19 for measuring the
pressure of the polymer material extruded from the melt mechanism 4
and circulated in the molten state through a flow passage 18a, and
a set of gears 20 for feeding the melted polymer material to the
discharging unit 5. This supply controlling mechanism 18 detects
the pressure of the polymer material flowing through the flow
passage 18a by the pressure detection means 19. The rotation of the
set of gears 20 is controlled by this detection output to keep the
pressure of the polymer material flowing through the flow passage
18a constant. By controlling the pressure of the polymer material
flowing through the flow passage 18a at a constant magnitude, a
preset constant quantity of the polymer material can be supplied to
the discharging unit 5.
[0046] A heating unit 23 is on the outer periphery of the portion
of the supply controlling mechanism 18, which controls the
temperature of the polymer material flowing through the flow
passage 18a at a preset temperature.
[0047] The melt spinning method employed by the melt spinning
apparatus of the present invention is now explained.
[0048] The present invention melt-spins the strand, formed of a
biodegradable polymer material used for forming a stent implanted
in the living body. The melt spun polymer material, used herein, is
the biodegradable polymer material. The biodegradable polymer
material may be enumerated by polylactic acid (PLA), polyglycolic
acid (PGA), polyglactin (polyglycolic acid-polylactic acid
copolymer), polydioxanone, polyglyconate (trimethylene
carbonate-glycoid copolymer) and a polylactic
acid-.epsilon.-caprolactone copolymer.
[0049] For spinning the polymer material, a pellet-like polymer
material Pp is charged into a hopper 14 of the supplying unit 6.
The polymer material, loaded into the hopper 14, is supplied to the
cylinder 8 of the melt mechanism 4.
[0050] In order for the polymer material, loaded into the hopper
14, to be quickly supplied into the helical groove 17 formed in the
screw 16 rotating in the cylinder 8, the polymer material needs to
be in solid state. That is, the polymer material, supplied into the
cylinder 8, needs to be controlled to a temperature not higher than
its melting point (Tm) or softening point. For shortening the melt
time in the melt mechanism 4, the polymer material, supplied to the
cylinder 8, needs to be melted immediately. Thus, the temperature
controller 15, provided in the supplying unit 6, sets the
temperature of the polymer material, charged into the hopper 14, to
a temperature at which the polymer material can be melted
immediately as it maintains its solid state.
[0051] The polymer material, supplied into the cylinder 8 through
the hopper 14, is introduced into the helical groove 17 of the
screw 16, rotated by the rotational driving mechanism 7, so as to
be extruded towards the distal end of the cylinder 8, as it is
heated by the heating units 9 provided on the outer periphery of
the cylinder 8. As the polymer material is extruded, the
temperature of the polymer material is controlled to be lower than
its thermal decomposition temperature so as not to cause
transmutation of the polymer material. The polymer material, thus
controlled to a temperature not higher than its thermal
decomposition temperature, is positively extruded from the distal
end of the cylinder 8 as it is kept in molten state without
undergoing transmutation.
[0052] The polymer material, extruded at the distal end of the
cylinder 8 while in its molten state, is afforded with flow
resistance by the flow resistance plate 22, in such a manner that
it is evenly pressurized by the through-holes 22a. The polymer
materia, thus pressurized, is supplied to the discharging unit
5.
[0053] Since the through-holes 22a formed in the flow resistance
plate 22 are oriented vertically in order not to produce stagnation
or eddying currents in the polymer material, the polymer material
can be supplied to the discharging unit 5 as the molecular weight
distribution is maintained to be constant.
[0054] If the melt spinning apparatus has the supply controlling
mechanism 18 between the melt mechanism 4 and the discharging unit
5, the molten polymer material, extruded from the cylinder 8 of the
melt mechanism 4, is maintained at a constant pressure by the
supply controlling mechanism 18, so that it is controlled in flow
rate at the discharging unit 5 and is reliably supplied to the
discharging unit 5 at a constant flow rate.
[0055] The polymer material supplied to the supply controlling
mechanism 18 is heated by the heating unit 23 provided on the outer
periphery of the supply controlling mechanism 18 and hence is
delivered to the discharging unit 5, reliably in its molten state.
The heating unit 23 maintains the heating temperature at less than
the thermal decomposition temperature so as not to cause
transmutation of the polymer material.
[0056] The molten polymer material, delivered from the melt
mechanism 4 or the supply controlling mechanism 18 to the
discharging unit 5, is heated in the sprue bush 11 by the heating
unit 23 to a temperature less than the thermal decomposition
temperature. Since the flow path of the discharging unit 5 from the
sprue bush 11 to the nozzle 10 is oriented vertically, the polymer
material flowing therein is not subjected to stagnation or eddying
currents. Since the polymer material, maintained in its molten
state, may thus be supplied to the nozzle 10 through the vertical
flow path, it can be discharged at the nozzle 10 as it maintained
in the state of uniform molecular weight distribution, and hence
the strand of the polymer material can be spun with uniform
molecular weight distribution.
[0057] It should be noted that a monofilament strand may be spun
because the sole discharge opening 10a is formed through the nozzle
10 for extending in the vertical direction.
[0058] Industrial Applicability
[0059] With the melt spinning method and apparatus of the present
invention, it is possible to prevent stagnation or nonuniform
eddying currents of the biodegradable polymer material in order to
spin the strand into a uniform average molecular weight. That is,
the strand of the biodegradable polymer material may be spun which
is uniform mechanical properties and degradation and absorption
characteristics. This spun strand can be used to the utmost
advantage for forming a stent inserted into the vascular vessel of
the living body.
* * * * *