Surgical blade abstract
A hemostatic surgical blade and methods of manufacturing such blades
are provided, wherein the blade comprises a laminate region having
a hardenable center layer and highly thermally conductive outer
layers, joined to a second region of a low thermal conductivity
material. A heating element is secured to the laminate region and
in thermal communication therewith to thermally reform the collagen
of tissue as it is incised. The heat generated by the heating element
is conducted to the cutting edge of the blade to maintain the cutting
edge temperature within 20.degree. C. to 70.degree. C. of a user-selected
operating temperature. The second region reduces the conduction
of heat to the handle of the instrument. The heating element comprises
a thermally conductive dielectric layer attached to an outer surface
of the laminate region, resistive conductive elements deposited
on the dielectric, a second dielectric layer covering the resistive
conductor elements, and an abherent coating disposed thereon to
reduce coagulum buildup on the blade.
Surgical blade claims
What is claimed is:
1. A blade for use in a surgical instrument for hemostatically
cutting tissue to reduce bleeding, the instrument including a handle
having an electrical terminal, the blade comprising:
a first region of a laminate material having a cutting edge and
two lateral sides, the laminate comprising a core of a high strength
hardenable material and a pair of outer layers of a material having
a high thermal conductivity, each of the pair of outer layers disposed
on opposite sides of the core and in thermal communication therewith;
a second region comprising a low thermal conductivity metallic
material, the second region metallurgically joined to the first
region at a longitudinal joint, the longitudinal joint being mechanically
finished to provide a smooth surface, the second region having a
portion adapted to engage the handle;
a heating element for heating the first region to a temperature
in the range from about 100.degree. C. to about 500.degree. C.,
the heating element secured to first region in thermal communication
therewith and electrically isolated therefrom; and
an electrical lead for connecting the heating element to the electrical
terminal, the electrical lead disposed on the first and second regions
and extending continuously across the longitudinal joint.
2. The apparatus of claim 1 wherein the heating element is secured
to one of the lateral sides of the first region.
3. The apparatus of claim 1 wherein the heating element further
comprises:
a first thin layer of dielectric material having high thermal conductivity
disposed on the first region; and
a resistive conductor material disposed on first dielectric material,
the resistive conductor material having a first resistivity and
a resistance that vary as a function of temperature.
4. The apparatus of claim 3 wherein the electrical lead further
comprises:
a second thin layer of dielectric material disposed on the second
region; and
a conductor material having a second resistivity equal to or less
than the first resistivity, the conductor material disposed on the
second thin layer of dielectric and in electrical contact with the
resistive conductor material.
5. The apparatus of claim 4 wherein the heating element further
comprises a plurality of segments, each of the segments including
a pattern of the resistive conductor material and an electrical
lead of the conductor material, so that each of the segments is
individually temperature controlled.
6. The apparatus of claim 5 further comprising a third dielectric
material disposed on all of the resistive conductor material and
the conductor material except for a portion to be electrically connected
to the electrical terminal.
7. The apparatus of claim 6 further comprising a layer of abherent
material disposed on those portions of the first region, heating
element and electrical lead that contact tissue during use.
8. The apparatus of claim 7 wherein the abherent material retains
non-stick properties at temperatures in the range from about 100.degree.
C. to about 400.degree. C..
9. The apparatus of claim 4 wherein the resistive conductor material
and the conductor material comprise the same material.
10. The apparatus of claim 3 wherein the resistive conductor material
comprises a glass-based material having an expansion coefficient
not less than 12 microinches/inch/.degree.C. and a temperature coefficient
of resistance of at least 0.0005 per .degree.C. in the temperature
range from about 20.degree. C. to about 400.degree. C..
11. The apparatus of claim 10 wherein the glass-based material
is selected from among the group consisting of oxides of silicon,
iron, sodium, potassium, calcium, chromium, aluminum, lithium, lead,
zinc or combinations thereof.
12. The apparatus of claim 3 wherein the resistive conductor material
further comprises a polymer-based material having an expansion coefficient
not less than 12 microinches/inch/.degree.C. and a temperature coefficient
of resistance of at least 0.0005 per .degree.C. at temperatures
in the range from about 20.degree. C. to about 400.degree. C..
13. The apparatus of claim 4 wherein the first and second dielectric
materials further comprise a material selected from among the group
consisting of diamond or diamond-like forms of carbon, and oxides
of silicon, iron, sodium, potassium, calcium, chromium, aluminum,
lithium, lead, zinc or combinations thereof.
14. The apparatus of claim 1 wherein the low thermal conductivity
metallic material is selected from among the group consisting of
the family of austenitic stainless steels.
15. The apparatus of claim 1 wherein the high strength hardenable
material is selected from among the group consisting of the family
of martensitic stainless steels.
16. The apparatus of claim 1 wherein the high thermal conductivity
material comprises aluminum oxide dispersion-strengthened copper
having an aluminum oxide content ranging from about 0.1 to about
0.6 percent of aluminum oxide by weight.
17. The apparatus of claim 1 wherein the low thermal conductivity
material has a thermal conductivity of not greater than 0.2 cal/sec/cm/.degree.C.
18. The apparatus of claim 1 further comprising a thin film of
oxidation resistant material deposited on the cutting edge.
19. A blade for a hemostatic surgical instrument comprising:
a first region including a portion defining a cutting edge, the
first region of a laminate comprising a core of a high strength
hardenable material having lateral faces, and first and second outer
layers of a high thermal conductivity material, each one of the
first and second outer layers joined to one of the material faces
of the core;
a second region of a low thermal conductivity material welded to
the first region at a longitudinal joint, the longitudinal joint
mechanically finished to provide a smooth surface, the blade being
heat treated while in blank form by passing it through a reducing
atmosphere at an elevated temperature and then being cooled to obtain
a high hardness level in the core of the first region;
a first layer of a high expansion dielectric material coated on
the first and second regions, the first layer having a thermal expansion
coefficient in the range of the thermal expansion coefficient of
one of the pair of outer layers of the first region and the low
thermal conductivity material of the second region;
a resistive conductor material deposited in a first pattern of
the first layer of dielectric material so that the first pattern
is superimposed over the first region, the resistive conductor material
having a specific sheet resistance in the range of from about 10
to about 50 milliohms per square mm at 20.degree. C.;
a conductor material deposited in a second pattern on the first
dielectric layer superimposed over the second region, the second
pattern overlapping the first pattern of first dielectric material
so that the resistive conductor material and the conductor material
are in electrical contact; and
a second layer of dielectric material deposited over all of the
first pattern and the second pattern except for a portion adapted
for completing an electrical contact between the conductor material
and the hemostatic surgical instrument.
20. The blade as defined in claim 19 further comprising a layer
of material deposited on the blade while still in blank form and
after heat treatment, the layer of material selected from among
the group consisting of chromium, nickel, platinum or gold.
21. The blade as defined in claim 19 wherein the second region
is electron beam welded to the first region.
22. The blade as defined in claim 19 wherein the blade, while in
blank form, is heated during heat treatment to a temperature of
about 1000.degree. C. or greater.
23. The blade as defined in claim 19 wherein the first layer of
a high expansion dielectric material is coated on the first and
second regions by thick-film printing.
24. The blade as defined in claim 19 wherein the first layer of
a high expansion dielectric material is coated on the first and
second regions by vapor deposition of diamond or diamond-like carbon.
25. The blade as defined in claim 19 wherein the resistive conductor
material is deposited by thick-film printing, the resistive conductor
material selected from among the group consisting of a metal-filled
glass containing silver or a high-expansion metal-filled, polymer-based
conducting material.
26. The blade as defined in claim 19 wherein the resistive conductor
material is deposited by vapor or thermal deposition of a metal-filled
glass.
27. The blade as defined in claim 19 wherein the conductor material
is deposited by thick-film printing and comprises a high-expansion
metal-filled, polymer-based conducting material.
28. The blade as defined in claim 19 further comprising:
a layer of an abherent material coating those portions of ht first
and second regions that contact tissue during use of the blade,
the layer of abherent material coated on the blade by dip coating
the blade in the abherent material and air drying the blade at about
120.degree. C. for from about 10 to about 30 minutes, followed by
heating the blade at about 350.degree. C. for from about 10 to about
20 minutes.
29. The blade as defined in claim 19 further comprising:
a thin layer of oxidation resistant material deposited on the cutting
edge.
Surgical blade description
This invention relates to heated surgical instruments, particularly
to improved blade structures for thermally autoregulated hemostatic
instruments, such as scalpers.
BACKGROUND OF THE INVENTION
The control of bleeding during surgery accounts for a major portion
of the time involved in an operation. In particular, bleeding that
occurs when tissue is incised obscures the surgeon's vision, delays
the operation, and reduces the precision of cutting.
One technique for minimizing the bleeding of tissue as it is being
severed is known as hemostatic surgery. This technique uses a heated
instrument to contact bleeding tissue. The heat is transferred from
the instrument to the incised (or torn) tissue to reform thermally
collagen, thereby producing a thin collagenous film that seals over
the severed blood vessels and capillaries, thereby reducing bleeding.
Because heat is applied locally to tissue that contacts the heated
region of the instrument, there is little tissue necrosis or damage
that, if present, would retard healing.
One such hemostatic instrument is known as a hemostatic surgical
scalpel. This scalpel has a sharp cutting edge similar to that of
a conventional steel scalpel blade, and a heating element proximate
to the cutting edge to heat the blade. During cutting, the scalpel
blade is heated and the heat is transferred to the tissue being
cut.
One commercial device using this technique is the Shaw Hemostatic
Scalpel, manufactured and sold by the Hemostatic Surgery Corporation,
San Francisco, Calif., and described in U.S. Pat. Nos. 3768482
30190 4481057 and 4485810. This device uses a multi-segmented
resistive heating element whereby the current flowing through each
segment is individually controlled to maintain each segment, and
hence the blade, within a narrow range of user-selected temperatures.
A drawback of previously known hemostatic heated scalpel blades
has been the inability to deliver an adequate quantity of heat in
close proximity to the cutting edge, to maintain a sharp durable
cutting edge, and to be usable for sustained surgery under a wide
variety of surgical cutting applications. Sufficient thermal delivery
is critical to seal promptly the blood vessels and capillaries being
severed. The quantity of heat that must be delivered increases with
the rate at which the scalpel is being moved through the tissue
and the degree of vascularization of the tissue. These conditions
have limited the cutting rate and depth that the previously known
devices can be used to hemostatically cut tissue.
Good surgical blades are commonly made of hard materials such as
steels and martensitic stain less steels, but these materials generally
have low thermal conductivity. High thermal conductivity materials
are desirable for delivering the necessary heat, but typically do
not maintain a sharp and durable cutting edge. Contact of the high
thermal conductivity blades with the corrosive biological fluids
and operation at elevated temperatures combine to dull the cutting
edges of such blades prematurely. Moreover, they also conduct large
amounts of heat to the handle of the blade, making it uncomfortable
for the surgeon to hold the instrument during surgery.
Attempts to use other blade materials have been made without any
apparent success, e.g., ceramic blades as described in Shaw U.S.
Pat. No. 3768482 Johnson U.S. Pat. No. 4219025 Lipp U.S. Pat.
No. 4231371 and high thermal conductivity materials treated to
have hardened cutting edges as described in U.S. Pat. No. 4770067.
These devices similarly lack the combination of desirable thermal
transfer properties and a durable sharp cutting edge.
Other types of hemostatic scalpel devices having non-segmented
heating elements for heating the sharp scalpel blades are described
in U.S. Pat. Nos. 4207896 4091813 and 4185632.
Accordingly, there is a continuing need to provide a sharp, durable
scalpel blade capable of delivering sufficient thermal energy to
the tissue to cause hemostasis under a wide variety of operating
conditions.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention
to provide an improved surgical blade for hemostatically cutting
tissue, and methods of making such blades.
It is another object of this invention to provide a sharp, durable,
scalpel blade having improved thermal delivery capabilities over
a broad range of conditions encountered in surgical procedures.
It is another object of this invention to provide a sharp, durable,
scalpel blade using corrosion resistant martensitic steel and methods
of manufacturing the same for use in hemostatic surgical scalpels.
It is another object of this invention to provide a material for
an electrically resistively heated film coating, and methods of
applying the same, for use in heating a surgical instrument.
It is another object of this invention to provide a thermally autoregulated
heated scalpel blade having a cutting region that is maintained
at a nearly uniform temperature over the full range of surgical
cutting conditions.
It is another object of this invention to provide a hemostatic
scalpel blade that permits the sustained operation without restrictions
imposed by the thermal delivery capabilities of the blade components.
It is yet another object of this invention to provide an electrically
heated surgical blade that reduces conduction of heat from the heated
region of the surgical blade to the blade support.
It is another object of the present invention to provide an electrically
heated surgical blade having electrical leads characterized by a
low electrical resistance, to reduce ohmic heating of the blade
support by resistive losses in the electrical leads.
It is another object of this invention to provide a method of manufacturing
a surgical blade to reduce thermal conduction from the heating element
and tissue cutting regions of the blade to the handle supporting
the blade.
This invention provides a surgical blade for contacting and heating
tissue at elevated temperatures to reduce bleeding from incised
tissue, comprising a first region of a material having a high thermal
conductivity joined to a second region of a material having a low
thermal conductivity. The blade includes a heating element for heating
the first region to a temperature in the range of about 100.degree.
C. to about 500.degree. C. This heating element is in thermal contact
with, but electrically isolated from, the first region.
One embodiment of the present invention comprises a surgical blade
for hemostatically cutting tissue, the surgical blade inserted into
a handle having an electrical terminal, the blade comprising:
(a) a first region of a laminate material having a sharp cutting
edge and lateral sides, the laminate comprising a core of high strength
hardenable material and a pair of outer layers of a material having
a high thermal conductivity, each one of the pair of outer layers
being disposed on opposite sides of the core and in thermal communication
therewith;
(b) a second region of a low thermal conductivity material, the
second region being joined to the first region and having a portion
adapted to engage the handle;
(c) a heating element for heating the first region to a temperature
in the range of from about 100.degree. C. to about 500.degree. C.,
the heating element secured to the first region in thermal communication
therewith and electrically isolated therefrom; and
(d) an electrical lead for connecting the heating element to the
electrical terminal of the handle.
The heating element may be located on one or both of the lateral
sides of the first region, on the cutting edge of the first region,
or on any combination of those surfaces.
In one embodiment of the apparatus, the heating element further
comprises a first thin layer of dielectric material having high
thermal conductivity disposed on the first region and a first conductor
material disposed on the first dielectric material, the first conductor
material having a first resistivity and a resistance that vary as
a function of temperature. The electrical lead comprises a second
thin layer of dielectric material disposed on the second region
and a second resistive conductor material having a second resistivity
equal to or less than the first resistivity, the second conductor
material being disposed on the second thin layer of dielectric and
in electrical contact with the first conductor material.
The heating element may comprise a plurality of segments, each
of which is electrically connected to a plurality of electrical
leads, so that the heating element segments are individually temperature
controlled. A third dielectric material is preferably disposed on
the heating elements and electrical leads to cover all but a portion
of the electrical leads that connect to the electrical terminal
of the instrument handle. In addition, a layer of an abherent material
may be disposed on those portions of the blade that are likely to
contact tissue during use. Also, a thin film of oxidation resistant
material may be deposited on the cutting edge.
The surgical blade of the present invention has improved corrosion
resistance, durability, strength, hardness and thermal transfer
properties relative to previously known surgical blades. In the
preferred embodiment, the blade comprises a laminate having a core
comprising a martensitic steel, and outer layers, joined on opposite
sides of the core, composed of a high thermal conductivity metal.
The martensitic steel core provides a hardenable center layer that
can be conventionally heat-treated to provide the composite laminate
with a hardness of 57 Rockwell C or better. The martensitic steel
layer can be configured to provide a sharp cutting edge, while the
high thermal conductivity outer layers conduct heat from the heating
element to the cutting edge.
Another aspect of the present invention is directed to an improved
material for use as a film resistive heating element in a hemostatic
surgical instrument, wherein the heating element is capable of withstanding
elevated temperatures and nonuniform thermal loading. A preferred
embodiment of the material is directed to a high-expansion dielectric
material comprising metal-filled glass having a specific sheet resistance
in the range of from about 10 to about 50 m.OMEGA./mm at 20.degree.
C., a thermal expansion coefficient not less than about 12 microinches/inch/.degree.C.,
and a resistance temperature coefficient of at least 0.0005 .OMEGA./.degree.C.
and preferably greater than 0.002 .OMEGA./.degree.C. over the temperature
range of about 20.degree. to about 500.degree. C.. Preferred glass
materials include oxides of silicon, iron, sodium, potassium, calcium,
chromium, aluminum, lithium, lead, zinc or combinations thereof.
Preferred metal materials include finely divided silver, gold, aluminum,
platinum, and tungsten.
The present invention includes methods of manufacturing an electrically
heated surgical blade, comprising the sequence of steps of:
(a) providing a core of a high strength hardenable material having
lateral faces and a pair of outer layers of a high thermal conductivity
material;
(b) joining each one of the pair of outer layers to a lateral face
of the core to form a laminate having a first thickness;
(c) providing a strip of a low thermal conductivity material;
(d) joining the laminate to the strip along a longitudinal joint
to form a sheet;
(e) providing the sheet with a smooth surface at the longitudinal
joint;
(f) plating the sheet with a metallic material selected from among
the group consisting of chromium, nickel, platinum, or silver;
(g) heat treating the sheet by passing it under tension through
a reducing atmosphere at an elevated temperature, and then cooling
the sheet to obtain a high hardness level in the core of the first
region; and
(h) perforating the sheet to define at least one blade blank having
a first region formed of the laminate and a second region formed
of the strip.
The method further comprises forming each blank into a surgical
blade by securing a heating element to the first region and sharpening
the blade blank to provide a sharp cutting edge on the first region.
This sharpening step may be performed either before or after the
heating element is applied. The method therefore comprises the additional
steps of:
(i) coating one side of the plated blank with a first layer of
a high expansion dielectric material having a thermal expansion
coefficient in the range of the thermal expansion coefficient of
the pair of outer layers of the first region and the material of
the second region;
(j) depositing a thin layer of a first resistive conductor material
in a first pattern on the first layer of dielectric material;
(k) depositing a thin layer of a second resistive conductor material
in a second pattern on the first dielectric layer superimposed over
the second region, the second pattern overlapping the first pattern
of first dielectric material so that the first and second resistive
conductors are in electrical contact;
(l) depositing a second layer of dielectric material over the first
and second patterns of resistive conductive material except for
a portion of the second pattern that is left exposed to accommodate
completing an electrical contact between the resistive conductor
materials and the electrical terminal of the handle; and
(m) sharpening the blade to form a sharpened blade having a cutting
edge.
In addition, the methods of the present invention comprise further
steps relating to the heat treatment and deposition of the various
layers, including an abherent coating, on the blade surfaces.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects and advantages of the inventions will
be apparent upon consideration of the following detailed description,
taken in conjunction with the accompanying drawings, in which like
reference characters refer to like parts throughout, and in which:
FIG. 1 is a side view of a surgical blade constructed in accordance
with the present invention;
FIG. 2 is a cross-sectional view taken along line 2--2 of FIG.
1 showing the surgical blade contacting tissue;
FIG. 3 is a cross-sectional view taken along line 3--3 of FIG.
1; and
FIG. 4 is a side view of a sheet of surgical blade material manufactured
in accordance with the methods of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIGS. 1 and 2 surgical blade 10 constructed in accordance
with the present invention is described. Surgical blade 10 is intended
for use with a handle for supporting the blade, and is connected
via a cable to a power source, as is conventional for electrically-powered
resistively heated scalpel blades. The power source may be for example,
one such as that described in copending and commonly assigned U.S.
patent application Ser. No. 07/877699 filed May 1 1992 and includes
panel switches for selecting the desired operating temperature of
the device at, for example, a temperature range in the range from
about 100.degree. C. to about 500.degree. C..
Blade 10 has a cutting region 11 near its distal end comprising
faceted faces 12 that meet at sharp cutting edge 13 for incising
tissue. Proximal portion 14 of blade 10 supports cutting region
11 and reduces the conduction of heat from cutting region 11 to
the handle. Proximal portion 14 is dimensioned to fit securely within
the handle (not shown) of the surgical instrument, for example,
a scalpel handle.
Heating element 16 is disposed on cutting region 11 for heating
that region and cutting edge 13 of blade 10. Heating means 16 comprises
a trace or pathway of an electrically conductive material and is
connected to an electrical lead that extends across proximal portion
14. That electrical lead is connected to an electrical terminal
in the instrument handle, which is in turn connected to the power
source via a cable.
An electrically insulating layer 17 is disposed on cutting region
11 and proximal portion 14 to electrically insulate heating element
16 from blade 10. A layer 18 of electrically insulating material
is applied over heating element 16 to prevent the heating element
from short circuiting through the patient's tissue. A coating 19
of abherent material may optionally be applied over that portion
of blade 10 that contacts tissue, to reduce coagulum buildup on
the blade during use.
In FIG. 2 cutting region 11 of blade 10 is shown in contact with,
and severing, tissue 100 including blood vessels 101 and capillaries
102. To achieve the desired reforming of collagen into a film that
seals blood vessels 101 and capillaries 102 while blade 10 is moving
through tissue 100 blade 10 must be capable of conducting heat
from heating element 16 to cutting edge 13 and faceted faces 12.
In accordance with the present invention, the laminate structure
of cutting region 11 described hereinafter, and electrically insulating
layer 17 have high thermal conductivity to accomplish this task.
Use of abherent coating 19 having high thermal conductivity further
enhances the ability to transfer sufficient heat.
An advantage of the structure of the present invention is the ability
to maintain the temperature of the heater element 16 blade 10
and faceted faces 12 of cutting edge 13 at substantially uniform
levels, preferably within about 20.degree. C. to about 70.degree.
C. of the user-selected operating temperature, and independent of
the heat flux being transferred into tissue 100 during thermal loading.
The user-selected temperature of operation is the steady state temperature
of the device in still air, that is, in the absence of thermal loading.
The heat flux during use depends upon the length of blade 10 in
thermal contact with tissue 100 the rate at which the blade is
moved through the tissue, and the user-selected operating temperature.
A surgical blade constructed in accordance with the present invention
has the ability to transfer large amounts of heat to the tissue,
with little conduction of heat to the instrument handle.
As shown in FIG. 2 in a preferred embodiment, cutting region 11
comprises a laminate having a central core 20 and two outer layers
21. Central core 20 is a material having a high hardness and high
mechanical strength, preferably a martensitic stainless steel, for
example, AISI Type 440 C, or 420 C, or Hitachi Metal's product having
the trade name h, GIN-4. The hardness level and edge sharpness of
such alloys or other materials attained by heat treating central
core 20 must be capable of withstanding subsequent processing conditions
used in the manufacturing operation. For example, the hardness level
must not deteriorate substantially when the core is exposed to high
temperature processing conditions associated with joining outer
layers 21 in depositing dielectric layer 18 on the blade, or when
exposed to corrosive physiological fluids during operation at temperatures
up to 500.degree. C., as described hereinafter.
Outer layers 21 comprise a high thermal conductivity material to
facilitate the transfer of heat generated by heating element 16
to cutting edge 13 of blade 10 more specifically, to the vicinity
of the apex 11 of the cutting edge faceted faces 12. Outer layers
21 may be constructed of, for example, copper or more preferably
an alumina dispersion strengthened copper containing from 0.1 to
about 0.6 percent, by weight, of fine alumina particles. Outer layers
21 may be affixed to the lateral faces of core 20 using conventional
metal fastening techniques, for example, roll-bonding or brazing,
to form a multi-layer laminate. The pair of outer layers 21 are
preferably constructed of the same material.
Outer layers 21 should have a thickness sufficient to maintain
faceted faces 12 of cutting edge 13 in the distal portion of cutting
region 11 at temperatures within from about 20.degree. to about
70.degree. C. of the user-selected operating temperature, for blade
temperatures in the range of 100.degree. C. to over 500.degree.
C. Central core 20 may be selected so that the majority of thermal
energy transferred from heating element 16 to the patient's tissue
is through faceted faces 12 of outer layers 21 rather than through
the apex of cutting edge 13.
Cutting region 11 of blade 10 is sharpened to have a cutting edge
13 and faceted faces 12 along the periphery of the laminate structure
used to contact and sever tissue, similar to conventional surgical
blades. Faceted faces 12 each include a lower portion formed from
central core 20 and an upper portion formed from outer layers 21.
The apex of cutting edge 13 is preferably at or near the mid-thickness
of center core 20 but other configurations could be used, depending
upon the intended application of the surgical blade. The final sharpening,
honing, buffing or stropping of faceted faces 12 results in cutting
edge 13 which has the hardness and durability properties of central
core 20 and heat transfer characteristics dominated by the thermal
conductivity of outer layers 21.
Surgical blade proximal portion 14 comprises a material 22 having
a low thermal conductivity, such as stainless steel AISI Type 304
or 304L. Region 14 supports cutting region 11 and has electrical
leads 23 extending across it. Electrical leads 23 connect heating
element 16 to the power source via connections to electrical terminals
in the instrument handle and a cable. Proximal portion 14 reduces
the thermal conduction of heat from heated region 11 of blade 10
to the handle, so that the handle does not become uncomfortably
hot for the surgeon to manipulate. Materials having a thermal conductivity
of 0.2 cal/sec/cm/.degree.C. or less are suitable for use in proximal
portion 14 and may be, for example, selected from the family of
austenitic stainless steels.
Cutting region 11 and proximal portion 14 are metallurgically joined
as illustrated by bond line 24 in FIGS. 2 and 3. By the use of appropriate
manufacturing techniques, such as welding, brazing or electron beam
welding, a substantially smooth transition can be obtained between
the multi-layer laminate of cutting region 11 and material 22 of
proximal portion 14. This smooth transition is desirable to ensure
that bond line 24 does not interfere with the further processing
required to form a finished surgical blade.
The multi-layer laminate of cutting region 11 is formed by rolling
core 20 and outer layers 21 together under pressure at elevated
temperatures, i.e., hot rolled, to achieve a thickness 25. This
process provides a bond of high mechanical (tensile) strength between
the core and outer layers and provides an interface having high
thermal conductance. Blade proximal portion 14 is then rolled from
a low thermal conductivity metal to a thickness 26 that is close
to or the same as thickness 25. Cutting region 11 and proximal portion
14 are then joined by any of the above-described metal fastening
methods. Alternatively, proximal portion 14 may be thicker than
cutting region 11 or may have a contoured surface that is about
the same thickness at the interface and a different thickness away
from the interface, while providing a smooth surface for dielectric
layer 17 across the interface.
Heating element 16 heats to cutting region 11 to maintain cutting
edge 13 at the selected operating temperature, and particularly,
to compensate for heat loss due to radiation, convection, conduction,
and thermal loads imposed on the blade during use in contacting
and severing tissue. Heating element 16 provides thermal energy
at a rate sufficient to effect reshaping of collagen into a film
which seals over incised blood vessels during the brief time that
cutting edge 13 is in contact with the tissue.
In a preferred embodiment, heating element 16 comprises a resistive
conductive trace or pathway disposed on cutting region 11 in a serpentine
path adjacent to cutting edge faceted faces 12. Electrical leads
23 extend from heating element 16 to proximal portion 14 of blade
10. Heating element 16 may be located on one or both of the lateral
surfaces of blade 10 adjacent to cutting edge 13 depending upon
the intended application of the surgical blade.
To electrically insulate heating element 16 from outer layer 21
a thin layer of high thermal conductance, dielectric material 17
is first deposited on the lateral surface of blade 10 adjacent to
the cutting edge facets before the heating element is attached.
To facilitate good adhesion between layer 17 and outer layer 21
of cutting region 11 and the material of proximal portion 14 the
blade surfaces may first be coated with an oxidation resistant material,
e.g., chromium. To provide for efficient heat transfer from heating
element 16 to outer layer 21 layer 17 may comprise a thick-film
printed, high-expansion glass, having a thermal expansion coefficient
approximately matching the expansion coefficient of outer layer
21. Dielectric material 17 may be, for example, a glass material
such as oxides of silicon, iron, sodium, potassium, calcium, chromium,
aluminum, lithium, lead, zinc or combinations thereof, or diamond
or a diamond-like form of carbon.
As shown in FIG. 1 heating element 16 preferably comprises two
segments 27 and 28. Segment 27 heats the tip of the cutting region,
while segment 28 heats the heel portion of the cutting region. Segments
27 and 28 are arranged in a pattern designed to create a uniform
temperature in cutting region 11 despite the non-uniform construction
of that region. Heating element 16 also includes a plurality of
electrical leads 23 deposited in a second pattern that connects
each of segments 27 and 28 to electrical terminals provided in the
instrument handle. Electrical leads 23 permit the heating element
segments to be separately controlled to maintain a uniform temperature
in the blade, even for different thermal loading in the tip and
heel regions. More or fewer heating element segments can be used
as appropriate for the size and surgical application of the device.
The geometry of heating element 16 and electrical leads 23 that
is, the cross sectional area and current path that define the resistance
of the conductive elements, are selected to reduce joulean heating
in proximal portions of electrical leads 23 so that energy is efficiently
delivered to segments 27 and 28. Accordingly, heating element 16
and electrical leads 23 may be constructed of the same material,
but applied in different dimensions. The heat generated by the controlled
current flow in segments 27 and 28 is conducted to those regions
of cutting edge 13 in good thermal communication with tissue, as
illustrated by the heat flux lines 29 shown in FIG. 2.
Heating element 16 and electrical leads 23 may comprise, for example,
a metal-filled glass-based conducting material having an expansion
coefficient of not less than 12 microinches/inch/.degree.C. and
a temperature coefficient of resistance of at least 0.0005 per .degree.C.
in the temperature range from about 20.degree. to about 400.degree.
C.. For example, fine silver particles less than about 0.001 inches
in diameter dispersed in a glass material such as oxides of silicon,
iron, sodium, potassium, calcium, chromium, aluminum, lithium, lead,
zinc or combinations thereof, and similar materials, are suitable.
Alternatively, heating element 16 and electrical leads 23 may comprise
a polymer-based conducting material having a temperature coefficient
of resistance of at least 0.0005 per .degree.C. at temperatures
in the range from about 20.degree. C. to about 500.degree. C., for
example, silver-filled polymide thick film pastes available from
Electro-Science Laboratories, Inc., King of Prussia, Pa.
The end portions of electrical leads 23 are exposed on proximal
portion 14 of blade 10 and are adapted to contact corresponding
spring contact electrical terminals, as described heretofore, mounted
in the instrument handle. Blade 10 is preferably configured to extend
length 30 into the handle, for example, about 0.2 to about 1.0 inch
(5 mm to about 25 mm). The length of proximal portion 14 that extends
beyond the instrument handle may be, for example, about 0.5 inch
(12.7 mm) or greater, and serves to thermally isolate the heated
(distal) end of blade 10 from the handle to prevent the handle from
becoming uncomfortably hot during use. The blade and handle interconnection
is designed so that blades 10 may be easily replaced when worn,
and so that different blade configurations may be used with the
handle during the same or different surgical procedures.
Heating element 16 also may comprise a material having either a
positive or negative temperature coefficient of resistance, so that
the resistance of the heating element varies as a function of temperature.
If the heating element has a temperature coefficient of resistance
of at least 500.times.10.sup.-6 per .degree.C., and preferably greater
than 2000.times.10.sup.-6 per .degree.C., the power source may
be configured to sense a change in the heating element temperature
by detecting a change in the heating element resistance. The power
source can therefore adjust to the heat dissipation rates from the
surgical blade during use, while maintaining the blade at a substantially
constant temperature.
In an alternative embodiment (not shown), heating element 16 may
be directly disposed on faceted faces 12 of cutting edge 13 for
example, as described in Cage et al. U.S. Pat. No. 4198957.
A second layer of dielectric material 18 is disposed over heating
element 16 and electrical leads 23 to electrically isolate those
components from the patient's tissue. This second layer 18 comprises
the same material as that described heretofore with respect to layer
17.
Abherent coating 19 may be disposed on all portions of blade 10
that contact tissue during surgery. Abherent materials have "non-sticking"
properties that reduce the sticking or adherence of tissue, blood,
coagulated blood and other biological fluids or residues to the
blade during use, so called coagulum buildup. Advantageously, the
use of an abherent coating reduces the added thermal impedance associated
with coagulum buildup, which can reduce the hemostatic effect of
the instrument. Abherent materials such as fluorinated polymers,
fluorine containing inorganic compounds or silicone are suitable
for use.
Abherent layer 19 should be deposited in a layer that is sufficiently
thin, for example, less than 10 microns, to ensure good heat transfer
from cutting region 11 of blade 10 to the tissue, whether from outer
layers 21 faceted faces 12 or both, to achieve the desired sealing
and cessation of blood flow. In addition, the abherent material
should retain its non-stick properties at temperatures in the range
from about 100.degree. C. to about 350.degree. C..
To provide for good adhesion between abherent layer 19 and its
underlying substrate, portions of the blade may be coated with an
optional metallic or non-metallic coating 31 using conventional
plating, thin film deposition, or vapor deposition techniques. In
particular, coating 31 may improve adhesion between abherent coating
19 and exposed metallic surfaces of outer layers 21 not covered
by electrically insulating layer 18 which surface might otherwise
oxidize and permit coating 19 to slough off. Coating 31 of a thickness
of about 3000 to 5000 Angstroms have been determined to provide
satisfactory performance.
The methods and apparatus of the present invention are further
described in connection with the following illustrative examples,
with reference to FIG. 4.
EXAMPLE I
A surgical blade 10 for example a scalpel blade, may be constructed
in accordance with a preferred embodiment of the present invention
as follows. Multi-layer laminate strip 40 is formed by roll bonding
two outer layers 21 of low-oxygen, alumina dispersion strengthened
copper, SCM Corporation product designation AL-15 to AL-60 (preferably
low-oxygen grade AL-25) to both lateral surfaces of central core
20 comprising stainless steel AISI Type 440 C or equivalent. The
finished rolled thicknesses of copper outer layers 21 are equal
on both sides of the stainless steel core 20 and range between 0.0007
and 0.030 inches (0.018 to 0.762 Mm); core 20 has a thickness of
from 0.003 to about 0.015 inches (0.076 to 0.38 mm). The laminate
has a width from the cutting edge to the top of the scalpel, ranging
from 0.70 to about 1.40 inches, depending upon the blade size being
manufactured.
A solid layer 22 of low thermal conductivity stainless steel (AISI
Type 304 or 304L) is rolled to form a strip having about the same
thickness as the multi-layer laminate. This strip has a width ranging
from about 1.0 to about 3.0 inches.
The laminate and solid sections are then electron-beam welded together
in vacuum to obtain a composite sheet 40 having a longitudinal joint
or bond line 24. The composite sheet is then rerolled and/or ground
using a grinding wheel to achieve a surface in the region of the
weld zone that is sufficiently smooth to allow the deposition of
dielectric layer 17.
Sheet 40 is then plated with a chromium or nickel layer about 100
to about 200 microinches thick. Alternatively, this plating step
may be conducted subsequent to the heat treatment process.
Composite sheet 40 is then heat treated by mechanically passing
the sheet through a conventional furnace. A reducing atmosphere,
such as nitrogen, is provided within the furnace to prevent oxidation
of the sheet surfaces. The heat treatment time and temperature are
specified by the vendor of the material used for core 20 and differ
depending upon the exact material. The duration of exposure and
the temperature profile obtained in the sheet are selected to achieve
a high hardness level in the stainless steel AISI Type 440 C at
the core of the laminate portion of the sheet. Preferably, a hardness
level of 57 to about 63 (Rockwell C scale) is achieved.
The heating step is immediately followed by passing the sheet between
cooling platens, which quench the material to the final hardness
and prevent warping of the sheet. The combined effects of the heat
treatment provide the desired flatness of the sheet, which is important
for application of the dielectric and heating elements and electrical
leads by thick-film printing techniques, as well as for blade sharpening.
The plated heated-treated composite sheet is then perforated by
an electro-discharge machining (EDM) or blanking operation to define
blanks corresponding to the desired finished blade shape. The EDM
or blade blanking operation is performed so that cutting region
11 of the blade is formed from the laminate of core 20 and outer
layers 21 while proximal portion 14 is formed from the low thermal
conductivity material 22.
When it desired to perforate the heat-treated composite sheet with
an EDM process, it may be desirable to first cut the composite sheet
40 into lengths suitable for processing with the EDM equipment prior
to performing the heat treatment step, for example 18-24 inches
long. In this case, the strips may be heat treated using a vacuum
furnace, and then quenched in a nitrogen atmosphere. Alternatively,
if it is desired to perform the blade blanking step prior to the
heat treatment step, the blade blanks may be retained in position
in the blanked sheet via ligaments extending along the upper and
lower region of the sheet.
The resulting plated blanks are then coated on one side with high-expansion
glass dielectric that matches the thermal expansion coefficient
of one or both outer layers 21 and proximal portion 14. To provide
efficient heat transfer, it is desirable that layer 17 comprise
a thick-film printed high expansion glass having a thermal expansion
coefficient of approximately 12 to 18 microinches/inch/.degree.C.
The thick film printing step is followed by firing the coated blades
in air to about 460.degree. C. for about five minutes.
Next, heating element material 16 is thick film printed in a first
pattern on dielectric 17 in region 11 of the blade blank. The heater
material is preferably a metal filled glass containing silver to
achieve a relatively high specific sheet resistance, e.g., 10 to
50 m.OMEGA. per square mm at 20.degree. C., such as is available
from Electro-Science Laboratories, Inc.
Electrical leads 23 are then formed of a silver filled glass material
having a relatively low specific sheet resistance, e.g., 5 m.OMEGA.
per square Mm at 20.degree. C., such as those available from Electro-Science
Laboratories, Inc. Electrical leads 23 are thick-film printed in
a second pattern on dielectric 17 in proximal portion 14 and overlap
the heating element film in cutting region 11 for a length of about
0.010 to about 0.020 inches to provide an electrical interconnection
therebetween.
Optionally, overcoat dielectric material 18 may be printed over
the entire printed heater element conductor film and most of the
printed electrical lead film to electrically insulate the heater
from the patient's body fluids and tissues. The proximal ends of
the electrical lead film traces are left exposed to accommodate
connection with the electrical terminals within the instrument handle.
Alternatively, abherent coating 19 may serve to electrically insulate
the blade from the tissue.
The resultant blank is sharpened conventionally using a multiple
stage sharpening process that ends with a final honing or stropping
operation. Thereafter, thin-film coating 31 of oxidation resistant
metallic or non-metallic material, e.g., platinum, may be deposited
on cutting edge faceted faces 12 exposed during sharpening, to a
thickness of about 1000 Angstroms. This is followed by application
of a non-stick, abherent coating, e.g., Vydex 1000 which can be
applied by dip coating followed by air drying at 120.degree. C.
for ten to thirty minutes and oven curing at 350.degree. C. for
ten to twenty minutes. Vydex 1000 is the tradename of a fluorotelemer
material manufactured by Du Pont. Following the application of the
non-stick coating, each finished blade is placed in an appropriate
container and sterilized for use.
EXAMPLE II
An alternative process for manufacturing blades in accordance with
the present invention follows the same sequence of steps for manufacturing
blades as described in Example I, through forming the individual
blade blanks. In this alternative process, the plated blade blank
is then sharpened and coating 31 of oxidation resistant metallic
or non-metallic material is applied to cutting edge faceted faces
12 exposed by the sharpening step. The remaining steps of the process
are then performed in the same sequence as for the process described
in Example I.
Laboratory tests have shown that blades constructed in accordance
with above methods preferred embodiment, and having the same shape
and size as a conventional No. 20 scalpel blade, dissipate in excess
of 210 watts while operating at 300.degree. C., when the side of
the blade opposite the heating element is in contact with a moist
sponge. In surgical studies involving animals, surgical blades constructed
according to the present invention have been used to incise and
simultaneously cause hemostasis of blood vessels as large as about
1.5 mm while operating at set point temperatures in excess of 200.degree.
C..
Scalpel blades manufactured in accordance with Examples I and II
were tested and found to provide sufficient heat transfer and durability
in retaining edge sharpness, kinesthetics similar to steel scalpels,
and improved thermal isolation of the heated portion from the handle
for sustained use at elevated temperatures. In particular, during
use under widely varying thermal loading, faceted faces 12 were
maintained within from about 20.degree. C. to 70.degree. C. of the
user-selected operating temperature.
The present invention includes methods of manufacturing an electrically
heated surgical blade, comprising the sequence of steps of:
(a) providing a core of a high strength hardenable material having
lateral faces and a pair of outer layers of a high thermal conductivity
material;
(b) joining each one of the pair of outer layers to a lateral face
of the core to form a laminate having a first thickness;
(c) providing a strip of a low thermal conductivity material;
(d) joining the laminate to the strip along a longitudinal joint
to form a sheet;
(e) providing the sheet with a smooth surface at the longitudinal
joint;
(f) plating the sheet with a metallic material selected from among
the group consisting of chromium, nickel, platinum, or silver;
(g) heat treating the sheet by passing it under tension through
a reducing atmosphere at an elevated temperature, and then cooling
the sheet to obtain a high hardness level in the core of the first
region; and
(h) perforating the sheet to define at least one blade blank having
a first region formed of the laminate and a second region formed
of the strip.
The step of forming the blade blanks from the heat treated sheet
may be performed using either an EDM process, a conventional blade
blanking process, or other metal cutting process. Alternatively,
the blade blanking or EDM process may be performed on the composite
sheet prior to heat treatment to harden the core material.
The method further comprises forming each blank into a surgical
blade by securing a heating element to the first region and sharpening
the blade blank to provide a sharp cutting edge on the first region.
This sharpening step may be performed either before or after the
heating element is applied. The method therefore comprises the additional
steps of:
(i) coating one side of the plated blank with a first layer of
a high expansion dielectric material having a thermal expansion
coefficient in the range of the thermal expansion coefficient of
the pair of outer layers of the first region and the material of
the second region;
(j) depositing a thin layer of a first resistive conductor material
in a first pattern on the first layer of dielectric material;
(k) depositing a thin layer of a second resistive conductor material
in a second pattern on the first dielectric layer superimposed over
the second region, the second pattern overlapping the first pattern
of first dielectric material so that the first and second resistive
conductors are in electrical contact;
(l) depositing a second layer of dielectric material over the first
and second patterns of resistive conductive material except for
a portion of the second pattern that is left exposed to accommodate
completing an electrical contact between the resistive conductor
materials and the electrical terminal of the handle; and
(m) sharpening the blade to form a sharpened blade having a cutting
edge.
The method of the present invention further includes those process
steps described above with respect to Examples I and II, for example,
coating the blade with coating 19 of abherent material.
It is to be understood that the various aspects of the present
invention also are applicable to medical devices other than hemostatic
surgical blades, and that the various dimensions of the heating
element components and the support member may be adjusted for the
specific application. One skilled in the art will appreciate that
the present invention can be practiced by other than the described
embodiments, which are presented for purposes of illustration and
not of limitation and that the present invention is limited only
by the claims that follow. |