An electrosurgical instrument is provided for cauterization and/or welding of tissue of varying impedances, thicknesses and vascularity especially in the performance of endoscopic procedures. The instrument compresses the tissue in the compression zone between first interfacing surface and second interfacing surfaces. The compression zone is formed by an insulator which forms a compression ridge in one of the interfacing surfaces and separates first and second electrically opposite electrodes. A preferred application of the invention is in a cutting instrument wherein a hemostatic line is formed using RF along a cut line.

FIELD OF THE INVENTION 
This invention relates to an electrosurgical instrument for cauterization, 
coagulation and/or tissue welding in the performance of surgical 
procedures, especially endoscopic procedures. 
BACKGROUND OF THE INVENTION 
Surgical procedures requiring cutting of tissue can cause bleeding at the 
site of the cutting. Various techniques have been adapted to control 
bleeding with varying degrees of success such as, for example, suturing, 
applying clips to blood vessels, and stapling, as well as electrocautery 
and other tissue heating techniques. Advances in tissue joining or 
welding, tissue repair and wound closure also have permitted surgical 
procedures previously not possible or too risky. 
Surgical staplers have been used for tissue joining, and to provide 
hemostasis in conjunction with tissue cutting. Such devices include, for 
example, linear and circular cutting and stapling instruments. Typically, 
a linear cutter has parallel rows of staples with a slot for a cutting 
means to travel between the rows of staples. This type of surgical stapler 
secures tissue for improved cutting, joins layers of tissue, and provides 
hemostasis by applying parallel rows of staples to layers of surrounding 
tissue as the cutting means cuts between the parallel rows. 
Electrocautery devices have been used for effecting improved hemostasis by 
heating tissue and blood vessels to cause coagulation or cauterization. 
Monopolar devices utilize one electrode associated with a cutting or 
cauterizing instrument and a remote return electrode, usually adhered 
externally to the patient. More recently, bipolar instruments have been 
used because the cauterizing current is generally limited to tissue 
between two electrodes of a tissue treating portion of an instrument. 
Bipolar forceps have been used for cutting and/or coagulation in various 
procedures. Generally, bipolar forceps grasp tissue between two poles and 
apply electrical current through the grasped tissue. Bipolar forceps, 
however, have certain drawbacks, some of which include the tendency of the 
current to arc between poles when tissue is thin or the forceps to short 
when the poles of the forceps touch. The use of forceps for coagulation is 
also very technique dependent and the forceps are not adapted to 
simultaneously cauterize a larger area of tissue. Furthermore, forceps 
tend to cause areas of thermal spread, i.e., dissipation of heat outside 
of area defined by grasping or engaging surfaces of the forceps. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a hemostatic 
electrosurgical instrument which can efficiently provide hemostasis in 
multiple tissue types and thicknesses, e.g., in fleshy or vascular tissue 
areas, and high, low or combination impedance tissues. Hemostasis is used 
herein to mean generally the arresting of bleeding including by 
coagulation, cauterization and/or tissue joining or welding. 
It is another object of the invention to provide a hemostatic device which 
is capable of being used to simultaneously cauterize or weld a relatively 
larger area or length of tissue than in previously known devices. 
Another object of the invention is to provide a controlled current delivery 
path by arranging electrodes to provide a desired current path, preferably 
through a zone of high tissue compression. 
It is another object of the invention to provide a electrocautery device 
having elongated or bar electrodes. 
Another object of the invention to is provide a hemostatic means for 
providing a line of coagulation adjacent to a cutting path of a cutting 
means for dividing tissue. 
Another object of the invention is to provide a cutting and stapling device 
with an electrocautery means for tissue welding or cauterization along a 
cutting path. 
These and other objects of the invention are described in an 
electrosurgical device having an end effector with opposing interfacing 
surfaces for engaging tissue therebetween, and two electrically opposite 
electrodes, corresponding to electrically opposite poles, each electrode 
located on one or both of the opposing surfaces. The electrodes are offset 
from each other with respect to interfacing surfaces, i.e., they are 
offset from each other so that they are not diametrically opposed from 
each other on interfacing surfaces. If the electrodes are on the same 
surface, they are separated from each other with an insulating material or 
an insulator (which may include an air gap) which electrically isolates 
the electrodes. 
An electrosurgical instrument of a preferred embodiment compresses tissue 
in a compression zone between a first interfacing surface and a second 
interfacing surface and applies electrical energy through the compression 
zone. The first interfacing surface is comprised of: a first electrode 
corresponding to a first pole of a bipolar energy source and located on 
one side lateral to the compression zone; and a second electrode 
corresponding to a second pole of a bipolar energy source and on the side 
laterally opposite of the compression zone as the first electrode. The 
second electrode is located on the same or opposite interfacing surface as 
the first electrode. This arrangement electrically isolates the two poles 
and enables the current path between the first and second electrodes to 
cross through a desired area of compressed tissue. 
In a preferred embodiment, the compression zone is an area defined by a 
compression ridge on one of the interfacing surfaces which compresses the 
tissue against the other interfacing surface. Also, there may be a 
compression ridge on both interfacing surfaces. A coagulation zone is 
defined by the first electrode, the second electrode, and an insulator 
insulating the first electrode from the second electrode. 
It is believed that the tissue compression normalizes tissue impedance by 
reducing structural differences in tissue which can cause impedance 
differences. Compression also stops significant blood flow and squeezes 
out blood and other interstitial fluids which act as a heat sink, 
particularly when flowing through veins, arteries and other vessels. It is 
further believed that high compression causes a higher current density to 
be delivered through compressed tissue in contact with an energy 
delivering electrode. Thus, it is believed that compression optimizes 
delivery of energy to tissue in part by preventing excessive thermal 
dissipation due to blood flow, dissipation through surrounding boundaries, 
and by enabling quick delivery of a higher current density to a controlled 
area of tissue. The arrangement of the electrodes, which make up the 
poles, is important to ensure that the current passing between the two 
poles passes though the compression zone. Also, the electrode arrangement 
permits tissue compression without shorting of the instrument poles or 
electrical arcing common in bipolar instruments. 
Thus, the tissue compression and the arrangement of the electrodes permit 
more efficient cauterization and offer the advantage of achieving 
hemostasis in a wide range of tissue impedance, thickness and vascularity. 
The present invention also provides a device capable of coagulating a line 
or path of tissue along or lateral to a cut line or a cutting path. In one 
embodiment, the first electrode and second electrodes each comprise an 
elongated electrode each on opposite sides and laterally adjacent an 
insulator forming a ridge to compress the tissue to be cauterized. 
In one preferred embodiment, a cutting means for cutting tissue is 
incorporated into the device and the device provides hemostatic lines 
adjacent to the path of the cutting means. Of course, cutting may occur at 
anytime either before, during or after cauterization or welding. In one 
variation of this preferred embodiment, stapling means is provided on one 
or both sides of the cutting path. 
In one embodiment, an indicator means communicates to the user that the 
tissue has been cauterized to a desired or predetermined degree. 
In one embodiment electrosurgical energy is applied in conjunction with 
application of one or more tissue fasteners, such as, for example, 
staples, clips, sutures, absorbable fasteners, etc., with a fastener 
applier, e.g., a staple driver. 
In another embodiment, the coagulation is completed prior to any mechanical 
cutting, i.e., actuation of the cutting means. If an indicator means is 
used, once tissue is cauterized, the cutting means may be actuated to cut 
between the bars while the rows of staples are applied to the tissue. 
In another embodiment, the hemostatic device is incorporated into a linear 
cutter similar to a linear cutting mechanical stapler. In this embodiment 
the hemostatic device comprises two substantially parallel and joined 
elongated electrode bars which form the electrically opposite poles, and a 
slot for a cutting means to travel between the bars. Optionally, one or 
more rows of staples may be provided on each side of the slot and bars to 
provide mechanical tissue security or approximation during the healing 
process. In operation, tissue is clamped between two jaws. Electrical 
energy in the form of radio frequency current is applied to the compressed 
tissue to cauterize tissue along the two bars. 
A variation of the embodiments described herein may provide a tissue 
welding or cauterizing and cutting device similar to an intraluminal 
stapler. 
Another embodiment provides a means for detecting abnormal impedances or 
other electrical parameters which are out of a predetermined range. For 
example, the means for detecting may be used to indicate when the 
instrument has been applied to tissue exhibiting impedances out of range 
for anticipated good coagulation. It may also be used for detecting other 
instrument abnormalities. It is possible to detect the abnormal condition, 
for example, by using comparisons of normal ranges of initial tissue 
impedances in the interface electronics. This could be sensed in the first 
few milliseconds of the application of RF energy and would not present a 
significant therapeutic dose of energy, i.e., energy required to 
cauterize, coagulate or weld tissue. Alternatively a low voltage signal 
may be applied prior to delivering therapeutic energy to measure tissue 
impedance. A warning mechanism may be used to warn the user when the 
impedance is out of range. Upon repositioning of the instrument, the same 
measurement criteria would apply and if the tissue impedance was again out 
of range, the user would again be warned. This process would continue 
until the normal impedance range was satisfied and good coagulation could 
be anticipated. 
These and other objects of the invention will be better understood from the 
following attached Detailed Description of the Drawings, when taken in 
conjunction with the Detailed Description of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIGS. 1-9, there is illustrated a preferred embodiment of 
the present invention. An endoscopic electrocautery linear cutting and 
stapling instrument 10 is shown having a body 16 coupled to a shaft 30 
with a lumen extending therethrough and an end effector 50 extending from 
the distal end 21 of the shaft 30. The shaft 30 is formed of an insulative 
material and has an electrically conductive sheath 38 extending through 
its lumen. A channel 39 extending through the sheath 38 guides co-axial 
movement of a driver means 44 within the channel 39. In this particular 
embodiment, the driver means 44 includes a firing trigger 14 associated 
with the body 16, coupled to a flexible firing rod 40 coupled to a driving 
rod 41, coupled to a block 43. The block 43 is coupled to a cutting means 
11 and a staple driving wedge 13, which the driving means 44 advances by 
way of the block 43 into the end effector 50. 
The end effector 50 comprises two interfacing jaw members 32, 34. The end 
effector 50 is secured by way of jaw member 34 to the channel 39. The jaw 
member 32 is movably secured to jaw member 34. The body 16 has a clamping 
trigger 12 for closing the jaws 32, 34 which longitudinally advances a 
close rack 45 coupled to the proximal end of the sheath 38. The close rack 
45 advances the sheath 38 co-axially through the shaft 30. The sheath 38 
advances over a camming surface 27 of jaw 32 to close the jaws 32 and 34 
onto tissue situated between the jaws. As described in more detail below, 
the close rack 45 also acts as a switch to close the circuit which 
communicates electrical energy to the end effector 50. 
Referring now to FIGS. 3-9 an enlargement of the end effector 50 of the 
instrument 10 is illustrated. The jaw members 32 and 34 are shown in an 
unclamped position in FIG. 3, in a clamped, unfired position in FIG. 4 and 
in a clamped, fired position in FIG. 5. A knife channel 26 defines a plane 
bisecting the first and second interfacing surfaces 33, 35. Jaw member 32 
comprises an anvil 18. The anvil 18 includes a first electrode 52 
extending longitudinally with respect to the jaw 32, on a first lateral 
side 81 of the anvil 18 with respect to the plane, and a second electrode 
80 extending longitudinally with respect to jaws 32 on the opposite 
lateral side 82 of the anvil 18 with respect to the plane. The first 
electrode 52 and second electrode 80 are electrically isolated from each 
other by an insulator 55 extending through the middle of the anvil 18. 
Jaw member 32 has an inner surface 33 which faces an inner surface 35 of 
jaw 34. The first and second electrodes 52, 80 extend proximally to 
distally along interfacing surface and are separated by insulator 55 
forming a compression ridge 56, proximally to distally, in the interfacing 
surface 33. The ridge 56 extends out relative to anvil portion 33a of the 
inner surface 33 (FIG. 6). The insulator 55 includes a knife channel 42 
extending longitudinally through the insulator 55 to generally form a 
U-shape and permit passage of a cutting element through slot 42. Two 
series of pockets 36, 37 located on anvil 18, for receiving staple ends, 
extend along the inner surface 33, on each side 81, 82 lateral to and 
outside of insulator 55. The electrodes 52, 80 are formed of an 
electrically conductive material such as aluminum and act as first and 
second electrically opposite poles. 
Jaw member 34 comprises a cartridge channel 22 and a cartridge 23. The 
cartridge 23 includes a track 25 for the wedge 13, knife channel 26 
extending longitudinally through the center of the cartridge 23, a series 
of drivers 24 extending into track 25 and staples 100 arranged in two 
single rows. When tissue is engaged between the jaws 32, 34, the driver 
means 44 may be actuated or fired using trigger 14 to advance the cutting 
means 11 and wedge 13 through the engaged tissue to staple and cut the 
tissue. When the firing mechanism 14 is actuated, the wedge 13 is advanced 
through the track 25 causing the drivers 24 to displace towards the 
staples 100, thereby driving the staples 100 through tissue and into anvil 
pockets 36, 37. 
A knob 15 located on the distal end of the body 16 rotates the shaft 30, 
sheath 38, channel 39 and end effector 50 which are directly or indirectly 
coupled to the knob 15 so that the knob 15 may be used for rotational 
placement of the end effector jaws 32,34. 
Bipolar energy is supplied to the end effector 50 from an electrosurgical 
generator 60 through wires 19, 20 extending into the body 16 of the 
instrument. The generator 60 is user controlled by way of a footswitch 65. 
Wire 19 which provides electrical current to the first pole, is coupled 
through a wire or other electrical contact means 61 to electrical contact 
62, associated with the first pole, located on the distal end of close 
rack 45. Wire 20 which carries the current of the opposite pole, is 
coupled through a wire or other electrical contact means 66 to a disc 
contact 67 located at the distal end of the close rack 45 and electrically 
isolated from contact 62. 
A disc contact 63, associated with the first pole, located at the distal 
end of the body 16 is in electrical communication with a wire or other 
contact means 64. Contact means 64 extends through channel 39 to end 
effector jaw 32 where it contacts the first electrode 52. The disc contact 
63 permits the knob 15 to rotate while contact is maintained between the 
disc contact 63 and the contact means 64. The contact means 64 is 
electrically insulated from the sheath 38. 
When the clamping trigger 12 is actuated, the close rack 45 moves distally 
so that the contact 62 comes in electrical communication with the disc 
contact 63, and the disc contact 67, associated with the second electrode 
80, comes in electrical contact with the electrically conductive sheath 
38. The sheath 38 moves over the camming surface 27 of the electrically 
conductive second lateral portion 82 of the anvil 18. The first lateral 
portion 81 of the anvil 18 is coated with an insulative material 83 except 
where the electrode 52 is exposed at interfacing surface 33. Thus, the 
sheath 38 does not come into electrical contact with the first electrode 
52. The electrical circuit is closed when and only when the clamping 
trigger 12 is closed. 
In operation, the end effector 50 of the instrument is located at a tissue 
site where tissue is to be cut. The jaw members 32, 34 are opened by 
pressing a release button 70 which releases a button spring 71 and permits 
the close rack 45 to move proximally. Tissue is then placed between the 
interfacing inner surfaces 33, 35 respectively of the jaw members 32, 34. 
The clamping trigger 12 is squeezed to cause the sheath 38 to move over 
the camming surface 27 and thereby close the jaws 32, 34 and 
simultaneously close the electrical circuit as described above. The 
insulator 55 which forms the ridge 56, compresses the tissue against the 
inner surface 35 of jaw member 34. A user then applies RF energy from the 
generator 60 using the footswitch 65 or other switch. Current flows 
through the compressed tissue and between the first electrode 52 and the 
second electrode 80. 
Preferably the bipolar energy source is a low impedance source providing 
radio frequency energy from about 300 kHz to 3 MHZ. Preferably, the 
current delivered to the tissue is from 0.1 to 1.5 amps and the voltage is 
from 30 to 200 volts RMS. 
An audible, visible, tactile, or other feedback system may be used to 
indicate when sufficient cauterization has occurred at which point the RF 
energy may be turned off. An example of such a feedback system is 
described below. After the RF energy is turned off, the cutting means 11 
is advanced and the staples 100 are fired using the firing trigger 14. 
Firing is accomplished by rotating the firing trigger 14 acting as a lever 
arm about pivot 14a. The driver means 44 advances the cutting means 11 and 
wedge 13. The cutting means 11 cuts the tissue in between the electrodes 
52, 80 where the tissue has been cauterized. Thus, the cut line is lateral 
to the coagulation lines formed by the electrodes 52, 80. The wedge 13 
simultaneously advances the drivers 24 into the staples 100 causing the 
staples 100 to fire through tissue and into the pockets 36, 37 of the 
anvil 18. Staples 100 are applied in a longitudinal single row on each 
side of the cutting means 11 as the cutting means cuts the tissue. 
Operation of linear staplers are known in the art and are discussed, for 
example, in U.S. Pat. Nos. 4,608,981, 4,633,874, and U.S. application Ser. 
No. 07/917,636 incorporated herein by reference. 
The above described preferred embodiment may be incorporated into a 
circular stapler. Operation of circular staplers is known in the art and 
is described, for example in U.S. Pat. No. 5,104,025 incorporated herein 
by reference. A variation of the embodiments described herein may provide 
a tissue welding and cauterizing cutting device similar to an intraluminal 
stapler. In this embodiment, a device similar to that described in Parent 
application Ser. No. 08/095,797 filed on Jul. 22, 1993 is provided. The 
electrodes are formed in two concentric circle electrodes separated by an 
insulator. The electrodes are located radially inward or radially outward 
of the insulator which forms the compression ridge and on either of the 
interfacing surfaces. The electrodes of the stapling embodiment of the 
circular cutting device may be located on either the stapler cartridge or 
the anvil. 
In a embodiment, the cartridge provides multifire stapling capabilities by 
having single rows of staples, as opposed to the convention double row of 
staples of the cartridges in the laparoscopic stapling and cutting devices 
presently in use. In order to provide better hemostasis, this type of 
stapler was designed to provide a double row of staples for each parallel 
row. Because of the size of the space necessary to contain the double row 
of staples, a refireable cartridge with stacked staples has not been 
preferred because of the additional space required for stacking staples. 
In the multifire stapling embodiment a single row of staples is used. 
Using a single row of staples permits stacking of staples in the space 
previously occupied by the second row of staples, providing multifire 
capabilities. The device of the present may however, if desired, include 
double, triple, etc., staple rows. Also, in a further embodiment, no 
staples are required and the electrical coagulation lines provide the 
necessary hemostasis or tissue welding effect. 
A preferred embodiment of the present invention includes a feedback system 
designed to indicate when a desired or predetermined degree of coagulation 
has occurred. This is particularly useful where the coagulation zone is 
not visible to the user. In a particular embodiment, the feedback system 
measures electrical parameters of the system which include coagulation 
level. 
The feedback system may also determine tissue characteristics at or near a 
coagulation zone which indicate degree of coagulation. The electrical 
impedance of the tissue to which the electrical energy is applied may also 
be used to indicate coagulation. Generally, as energy is applied to the 
tissue, the impedance will initially decrease and then rise as coagulation 
occurs. An example of the relationship between electrical tissue impedance 
over time and coagulation is described in Vaellfors, Bertil and Bergdahl, 
Bjoern "Automatically controlled Bipolar Electrocoagulation," Neurosurg. 
Rev. p. 187-190 (1984) incorporated herein by reference. Also as 
desiccation occurs, impedance increases. Tissue carbonization and or 
sticking to instrument as a result of over application of high voltage may 
be prevented using a feedback system based on tissue impedance 
characteristics. Other examples of tissue characteristics which may 
indicate coagulation include temperature and light reflectance. 
Referring to FIG. 10, a flow chart illustrates a feedback system which is 
implemented in a preferred embodiment of the present invention. First, 
energy is applied to the tissue. Then the system current and voltage 
applied to the tissue is determined. The impedance value is calculated and 
stored. Based on a function of the impedance, for example, which may 
include the impedance, the change in impedance, and/or the rate of change 
in impedance, it is determined whether desired coagulation has occurred. 
If coagulation has occurred to a predetermined or desired degree, an 
indication means indicates that the energy should be turned off. Such an 
indication means may include a visible light, an audible sound or a 
tactile indicator. The feedback means may also control the generator and 
turn the energy off at a certain impedance level. An alternative 
embodiment provides a continuous audible sound in which the tone varies 
depending on the impedance level. An additional feature provides an error 
indication means for indicating an error or instrument malfunction when 
the impedance is below a normal minimum and/or above a maximum range. 
Referring now to FIG. 11, there is illustrated an alternative embodiment of 
an end effector 150 of the present invention. A jaw member 132 is 
illustrated having an anvil 118 including a first interfacing surface 133 
comprised of a first electrode 152 of a first electrical potential and a 
second electrode 180 of an opposite electrical potential. The first and 
second electrodes 152, 180 extend proximally to distally along interfacing 
surface 133 and are separated by insulator 155. A second opposing 
interfacing surface 135 includes a compression ridge 156 formed therein 
and extending proximally to distally along the interfacing surface 135. 
The compression ridge 156 is arranged to compress tissue against the 
insulated portion of the first interfacing surface and is electrically 
isolated from the first and second electrodes. First and second electrodes 
152, 180 are adapted to be in electrical contact with an energy source in 
the same manner as first and second electrodes 52, 80 respectively of FIG. 
6. Insulation 183 prevents electrical contact of electrode 152 with sheath 
38. 
Referring now to FIG. 12, there is illustrated another alternative 
embodiment of the present invention. End effector 250 includes jaw member 
232 having an anvil 218 including a first interfacing surface 233. The 
anvil 218 is comprised of a first electrode 252 of a first electrically 
potential on a first lateral side 281 of the end effector 250. The first 
electrode 252 extends proximally to distally along interfacing surface 
233. An insulator 255a forms a ridge 256a extending proximally to distally 
along interfacing surface 233 and separates the first electrode 252 from 
the opposite or second lateral side 282 of the end effector 250. The end 
effector 250 includes a second interfacing surface 235 opposite the first 
interfacing surface 233. Second interfacing surface 235 includes a second 
electrode 280 located on second lateral side 282 of end effector 250. A 
second insulator 255b forms a ridge 256b in interfacing surface 235 
extending proximally to distally with respect to the end effector 250. 
Ridge 256a and 256b oppose each other. In this embodiment electrical 
energy is supplied to the first and second electrodes in a manner similar 
to the embodiment in FIG. 6 except that the first electrode 252 is in 
electrical contact with a sheath 38 and electrode 280 is in contact with 
contact means 64. Insulation 283 prevent electrical contact of the second 
lateral side 282 of first jaw 232 with sheath 38 and thereby prevents 
shorting or arcing with electrode 280. 
Referring now to FIG. 13, there is illustrated another embodiment of the 
present invention. End effector 350 includes jaw member 332 having an 
anvil 318 formed of an electrically insulative material such as a ceramic 
insulator. The anvil 318 includes a first electrode 352 of a first 
electrical potential on a first lateral side 381 of the end effector 350. 
The first electrode 352 is disposed on anvil 318 and extends proximally to 
distally along interfacing surface 333. A second electrode 380 is disposed 
on the anvil 318 on a second lateral side 382 on the opposite lateral side 
from the first lateral side 381. The second electrode 380 extends 
proximally to distally along interfacing surface 382. Insulator 355 forms 
a ridge on interfacing surface 333 located between the first electrode 352 
on the first side 381 and the second electrode 380 on the lateral side 382 
of the end effector. 
Alternative electrical connections may be used to provide or deliver 
electrical current from an electrosurgical generator and through the 
handle 16 of the device to the electrodes at the end effector 50, 150, 250 
or 350. For example, wireforms, contact blocks, and low impedance snap fit 
contacts may be used. The device may also provide a lockout which prevents 
firing of RF energy until the clamping trigger 12 has been closed, and 
which prevents cutting element actuation and stapling until the clamping 
trigger 12 is closed and RF energy has been applied. An example of these 
features are described in co-pending U.S. application entitled "Impedance 
Feedback Monitor with Query Electrode for Electrosurgical Instrument" to 
David Yates et al., filed on Dec. 22, 1994, incorporated herein by 
reference. 
Alternative variations of the described invention may include, for example, 
compression ridges formed in either one or both interfacing surfaces, 
electrodes located on the first, second or both interfacing surface; 
electrodes or multiple electrodes associated with each pole located on one 
or both of the interfacing surfaces. Also the device may have no 
compression ridges. 
Several variations of this invention have been described in connection with 
specific embodiments involving endoscopic cutting and stapling. Naturally, 
the invention may be used in numerous applications where hemostasis in 
desired including instruments without cutting or stapling. Accordingly, 
will be understood by those skilled in the art that various changes and 
modifications may be made in the invention without departing from its 
scope, which is defined by the following claims and their equivalents.