Patent Description:
Current tissue cutting devices often include a symmetric cutting ring for excising a portion of tissue. In theory, a purely symmetric conductive ring will have completely even electrical current flow with the same current density at all ring locations. However, in practice, conductive rings to perform actual tissue cutting are not isolated rings. The application of energy into the ring requires some method of attaching an external energy source to the ring. Likewise, current outflow from the ring will require a connection to an outside element. In addition, cutting rings are often attached to an additional superstructure via additional attachment features so that it can be easily handled and deployed. These attachment features disrupt the geometric symmetry of the ring and may lead to uneven current density and energy propagation at various ring locations, thereby compromising its intended tissue cutting function. This fundamental problem is accentuated if sequential micropulses of energy are delivered via the ring into tissues at fast speeds to achieve adequate tissue disruption while minimizing collateral tissue damage.

A device according to the preamble of claim <NUM> is known from the document <CIT>.

A device is provided according to claim <NUM>.

Examples and Embodiments relate to a microsurgical device for tissue cutting that improves temperature uniformity and current flow around a cutting element of the device. The device includes a series of ring features whose geometries help prevent the formation of cold spots and/or hot spots resulting from structural asymmetries of the cutting element, such as various tabs of the cutting element. In addition, ring features help maintain the mechanical strength of the cutting element and provide a stronger physical attachment to a suction cup of the device due to improved tab configurations. Tabs may include one or more wire tabs, one or more mechanical tabs, and/or one or more anchor tabs. Ring features may include slots, cutouts, and/or bumps. Ring features can also be used to mitigate the formation of hot or cold spots in other situations where electrical current flow in a device is uneven due to any other type of spatial asymmetry in addition to the various types of tab structures discussed herein.

In an example, a device includes a cutting element and one or more electrical leads for providing an electrical discharge to the cutting element. The device further includes one or more wire tabs protruding from the cutting element, each of the one or more wire tabs configured to conductively couple an electrical lead to the cutting element. Each wire tab includes a central conductive path and one or more conductive shunt paths conductively separated by one or more slots. The wire tabs may further include an additional slot disposed within the central conductive path of the wire tab that conductively separates portions of the central conductive path. The device further includes one or more anchor tabs protruding from the cutting element. The anchor tabs are each associated with a slot horizontally disposed along the circumference of the cutting element and positioned to at least partially thermally separate a respective anchor tab from a portion of the cutting element. In some examples, a first width of the cutting element includes a cutout adjacent to each of the one or more anchor tabs, where the first width of the cutting element is less wide than a second width of the cutting element.

The device may further include an anchor thread coupled to the cutting element via the one or more anchor tabs. The anchor thread is configured to compress the cutting element for insertion of the device through an incision. In some examples, the device further includes one or more mechanical tabs protruding from the cutting element. Each mechanical tab is adjacent to a slot horizontally disposed along the circumference of the cutting element and positioned to at least partially separate a respective mechanical tab from a portion of the cutting element. The device may also include a suction cup, where the cutting element is connected to the suction cup along a surface of the suction cup, such as an inner surface. In addition, the device may include a suction tube configured to provide suction to the suction cup. In these examples, the one or more electrical leads may be disposed within the suction tube. In some examples, the device further includes a rigid extender configured to compress the cutting element and/or a controller configured to control one or more electrical discharges to the cutting element. The controller may also be configured to control the amount of suction provided to the suction cup.

The figures depict various example embodiments of the present technology for purposes of illustration only. One skilled in the art will readily recognize from the following description that other alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the technology described herein.

Figures (<FIG> illustrate various views of a microsurgical device <NUM> for tissue cutting. <FIG> illustrates an embodiment of a microsurgical device <NUM>. <FIG> illustrates a cross-sectional view of the microsurgical device <NUM>. <FIG> illustrates a bottom perspective view of the cutting element of the microsurgical device <NUM>.

The device <NUM> shown in <FIG> includes a suction cup <NUM>, a cutting element <NUM> (also referred to as "cutting ring" herein), one or more suction tubes <NUM>, electrical leads 120A, 120B, and a stem <NUM>. The suction cup <NUM> and cutting element <NUM> are located at a distal end of the stem <NUM>, which houses the one or more suction tubes <NUM> and the electrical leads 120A, 120B. The device <NUM> further includes a control console <NUM> (also referred to as "controller" herein) that is configured to provide suction to the suction cup <NUM> and electrical energy to the cutting element <NUM>. The suction cup <NUM> is connected to the control console <NUM> via the one or more suction tubes <NUM> and a suction connector <NUM>. The cutting element <NUM> is connected to the control console <NUM> via the electrical leads 120A, 120B, one or more sets of electrical conductors, such as electrical conductors 140A, 140B, and an electrical connector <NUM>.

The suction cup <NUM> is a foldable structure that can provide a water-tight seal between the edges of the suction cup <NUM> and the tissue being excised (e.g., lens capsule, corneal tissue, connective tissue, and the like). Because of the fluidic seal between the suction cup <NUM> and the tissue, vacuum pressure can be applied to the suction cup <NUM> and the tissue so that the resulting pressure presses the cutting element <NUM> against the tissue. Pressing the cutting element <NUM> against the tissue facilitates a more precise, smoother cut. The foldable structure of the suction cup <NUM> is reversibly collapsible such that a cross-section of the suction cup <NUM> can decrease for insertion of the device <NUM> through an incision. As such, the suction cup <NUM> may include a compliant material, such as silicone, polyurethane, and the like.

The cutting element <NUM> is an element designed to cut tissue through application of pressure and/or electrical current via one or more electrical leads 120A, 120B coupled to the cutting element <NUM>. The cutting element <NUM> can be made from various materials. In some embodiments, the metallic components of the cutting element <NUM> may be made by electroforming suitable materials such as nickel, nickel-titanium alloys, gold, steel, copper, platinum, iridium, molybdenum, tantalum, and the like. When the cutting element <NUM> is configured to electrically excise tissue, the material for the cutting element <NUM> is electrically conductive. In addition, the cutting element <NUM> is reversibly collapsible such that a cross-section of the cutting element <NUM> can decrease for insertion of the device <NUM> through an incision. Therefore, the material of the cutting element <NUM> is generally elastic so that it can return to its original shape after insertion of the device <NUM> through the incision. A typical construction example is a superelastic nitinol ring having a wall thickness of <NUM>, height of <NUM>, and tabs as described in this specification. Another strategy is to add to this superelastic body a thin film (e.g., <NUM> to <NUM>) of a more conductive material that does not have to be superelastic because it is very thin. Examples of materials include, but are not limited to, spring steel, stainless steel, titanium nickel alloy, graphite, nitinol, nickel, nickel-chrome alloy, tungsten, molybdenum, tantalum, gold, silver, or any other material that will allow the cutting element <NUM> to return to its prior shape.

The device <NUM> is capable of delivering a wide range of energies (e.g., from <NUM> to <NUM> joules, or more) via the cutting element <NUM>. The energy dissipated by the cutting element <NUM> during use in surgery may be determined empirically through use on a specific tissue of interest. For example, in a capsulotomy of the anterior lens capsule of an adult human, it was found that about <NUM> joules produce a satisfactory result. Some specific example of applications to lens capsulotomies include pediatric, adult, and dog, listed in order of increasing energy need. To accommodate the varying energy needs, the amount of energy dissipated by the cutting element <NUM> may be controlled by controlling parameters such as the number of pulses, duration of each pulse, time between pulses, and/or energy of each pulse applied to the tissue via the cutting element <NUM>. These parameters may be determined empirically for each tissue application and/or via computational modeling. In addition, temperature gradients in the cutting element <NUM> may be designed and/or modified for different tissues.

It is helpful to have a uniform wall thickness over the entire circumference of the cutting element <NUM> to maintain the correct current density and heating everywhere along the cutting element <NUM>. The standard methods of drawing nitinol tubing may result in excessive variation in wall thickness. In areas that are thicker, the temperature will be too low, and a relative cold spot may occur. In areas that are too thin, a relative hot spot may occur. One method of making a uniform wall thickness is to build up the nitinol tubing by sputtering nitinol onto a rotating mandrel in a vacuum chamber.

Another method to make a uniform wall thickness is to take drawn nitinol tubing with a nominal wall thickness greater than the desired final wall thickness of the cutting element <NUM>, cut the tubing into short lengths (e.g., <NUM>). Bring the inner diameter to the correct dimension and roundness by using common machining methods such as honing, ID grinding, lapping, and polishing. Cool it to transform it into low stiffness martensite, and force the piece onto a slightly oversized precision round support shaft to force the inner diameter to be round. Or instead, heat the nitinol to increase its diameter (e.g., heat to <NUM> C) so it can be slid without force over the cold mandrel. Then the outer diameter can be precision ground, lapped, and/or polished to also be round, concentric to the inner diameter and have the desired final wall thickness. The outer surface of the support shaft is a material that can be etched away without affecting nitinol or the body of the shaft. For example, the support shaft may be solid, or tubular <NUM> stainless steel, with a thin layer (e.g., <NUM>) of copper plated or sputtered on it. Other materials that can be etched away without harming the nitinol or mandrel can be used (copper is easy as it can be quickly removed with nitric acid, and nitric acid passivates nitinol). After the nitinol is machined to have uniform wall thickness, the support shaft is mounted onto a femtosecond laser cutting system that supports both ends of the shaft on frictionless air bearings such that it can be precisely rotated and translated by computer-controlled actuators. A side view pattern can then be cut into the tube. The laser beam does not fully penetrate the etchable layer, so the support shaft remains undamaged and can be reused. The cutting element <NUM> slides off the shaft after the etchable layer is etched away. Another option in construction is that after the sacrificial etchable layer is deposited, one or more layers of other materials may be deposited prior to mounting the nitinol on the mandrel. For example, a precision mandrel of <NUM> stainless steel may have a layer of copper deposited (e.g., <NUM>), and on top of the copper, a layer of molybdenum could be deposited (e.g., <NUM>), and then a layer of tantalum (e.g., <NUM>). One way to deposit these layers is by sputtering on the mandrel spinning about its long axis. Another method is by electroplating. The laser cutting beam stops in the Cu layer, so the NiTi, Ta, and Mo layers are all cut through. After etching away the Cu, the Mo/Ta layers are held by compressive force in the nitinol ring (since the NiTi was heated to slide over the mandrel, and then shrunk down when cool). The Mo layer will carry <NUM> times more current than the same thickness of NiTi, so it allows more of the power to be dissipated at the ID of the cutting edge, and the wall thickness of the NiTi can be decreased which enables it to be bent to a smaller radius as needed to enter a smaller incision in tissue.

The one or more suction tubes <NUM> are located within the stem <NUM> of the device <NUM>. The one or more suction tubes <NUM> are configured to provide suction to the suction cup <NUM>. The one or more suction tubes <NUM> provide suction to the suction cup <NUM> to compress the suction cup <NUM> against the tissue being excised. The one or more suction tubes <NUM> may also be configured to reverse the suction fluid flow being applied to the suction cup <NUM> to disengage the suction cup <NUM> and cutting element <NUM> from the excised tissue.

The one or more suction tubes <NUM> may be further configured to act as fluid paths. For example, the one or more suction tubes <NUM> may be primed before use with a solution, such as a balanced salt solution. Priming the fluid paths of the one or more suction tubes <NUM> helps ensure that there is little to no compressible air in the device <NUM>. In addition, after excision of the tissue is complete, a hydraulic release of the one or more suction tubes <NUM> may be performed to release the suction cup <NUM> from the tissue. In some embodiments, the hydraulic release consists of forcing <NUM> to <NUM> of a balanced salt solution from the suction tubes <NUM> back into the suction cup <NUM>.

The configuration of the suction tubes <NUM> along the inner surface of the suction cup <NUM> may vary. For example, when there are two or more suction tubes <NUM>, the suction tubes <NUM> may be located at antipodal points of the suction cup <NUM>. This configuration may ensure equal distribution of suction throughout the suction channel of the suction cup <NUM>. In other embodiments, the suction tubes <NUM> may be adjacent, located within a threshold number of degrees of each other, located within a threshold distance of each other, and the like. Further, the suction tubes <NUM> may be located along an outer surface of the suction cup <NUM>, along a bottom surface of the suction cup <NUM>, along a top surface of the suction cup <NUM>, and the like. In embodiments where the device <NUM> includes a single suction tube <NUM>, the suction tube may be located at any point along the inner surface of the suction cup <NUM>. For example, an orifice of the suction tube <NUM> may be located in a roof of the suction cup <NUM>, at a proximal end of the suction cup <NUM>, at a distal end of the suction cup <NUM>, and the like.

The electrical leads 120A, 120B are configured to provide electrical energy to the cutting element <NUM>. The electrical leads 120A, 120B are located within the stem <NUM> of the device <NUM> and coupled to a surface of the cutting element <NUM>. In some embodiments, the electrical leads 120A, 120B are silver wires. In other embodiments, the electrical leads 120A, 120B are made of copper, aluminum, gold, or the like. In addition, the electrical leads 120A, 120B may insulated.

The control console <NUM> is configured to provide suction to the suction cup <NUM> and electrical energy to the cutting element <NUM>. In addition, an operator of the device <NUM> may control the depth of cut via the control console <NUM> by modifying the suction and/or electrical parameters of the device <NUM>.

Suction is provided to the suction cup <NUM> via one or more suction tubes <NUM> connected to the control console <NUM> and a suction connector <NUM>. Using the control console <NUM>, an operator of the device <NUM> may provide suction to the suction cup <NUM>, reverse suction during disengagement of the device <NUM>, and/or flush the fluid paths of the one or more suction tubes <NUM> with a solution. In addition, an operator of the device <NUM> may modify the amount of suction applied to the suction cup <NUM> based on the operation being performed. In some embodiments, an operator of the device <NUM> may manually modify the amount of suction applied to the suction cup <NUM>, for example using a vacuum valve and a vacuum gauge of the control console <NUM>. Alternatively, or additionally, the control console <NUM> may include predetermined suction parameters determined via experimentation, modeling, and/or a combination thereof that are each associated with a procedure. In addition, using the control console <NUM>, different amounts of suction may be provided to different suction tubes. By way of example, suction pressure of <NUM> +/- <NUM> inch of Hg (<NUM> kPa ± <NUM> kPa) vacuum has been used successfully. That is gauge pressure, not absolute pressure, so the same pressure differential is established by the console across the suction cup wall regardless of altitude at which it is used.

The control console <NUM> delivers electrical energy to the cutting element <NUM> via the electrical leads 120A, 120B, one or more sets of electrical conductors 140A, 140B, and an electrical connector <NUM>. A first set of electrical conductors 140A may be configured to provide power to the cutting element <NUM>. A second set of electrical conductors <NUM> may be for resistance measurement and may be connected to a measurement device, such as a Kelvin probe (also known as the <NUM>-wire resistance measurement method). In some embodiments, the first set of electrical conductors 140A and/or the second set of electrical conductors 140B are copper wires, such as (respectively) <NUM> ga copper wires, <NUM> ga copper wires, and the like. In other embodiments, the first set of electrical conductors 140A and/or the second set of electrical conductors 140B are composed of aluminum, gold, silver, or the like. Electrical energy may be provided to the cutting element <NUM> as one or more electrical waveforms. The one or more electrical waveforms are discharged through the cutting element <NUM> to cause the cutting element <NUM> to heat up for a short time, such as <NUM> seconds to <NUM> seconds, depending on the applied voltage and current.

Using the control console <NUM>, the depth of cut may be controlled by controlling the amount of electrical discharge applied to the cutting element <NUM>. For example, the depth of cut may be controlled by modifying one or more of: the energy of each pulse, the number of pulses in the pulse train, the inter-pulse intervals, and the like. As with the suction, these parameters may be manually modified by an operator of the device <NUM> using control elements of the control console <NUM>. Alternatively, or additionally, the control console <NUM> may include predetermined sets of parameters that are each associated with different depths of cut, different patient types, and the like. These sets of parameters may be determined through experimentation, modeling, and/or a combination thereof. The control console <NUM> may be a controller, microprocessor, a programmable hardware logic, etc..

In some embodiments, the control console <NUM> may change the operating parameters of the device <NUM> automatically. For example, the control console <NUM> may change the operating parameters according to a predetermined set of operating steps associated with a procedure. Alternatively, or additionally, the control console <NUM> may change the operating parameters of the device <NUM> based on feedback from the device <NUM> itself. For example, the control console <NUM> may change the operating parameters of the device <NUM> in response to a detection of a pressure, a pressure change, a temperature, a temperature change, a determined depth of cut, or the like, during use.

<FIG> illustrates a cross-sectional view of the microsurgical device <NUM>. As shown, the cutting element <NUM> is coupled to an inner surface of the suction cup <NUM> for excising a portion of the tissue abutting the outer surface of the suction cup <NUM> and/or cutting element <NUM>. In alternative configurations, the cutting element <NUM> may be coupled to an outer surface of the suction cup <NUM>, along a bottom surface of the suction cup <NUM>, along a top surface of the suction cup <NUM>, or the like.

In the embodiment shown, the device <NUM> includes a rigid extender <NUM> and an anchor thread <NUM>. The rigid extender <NUM> is retractable and used to reversibly compress the suction cup <NUM> and cutting element <NUM> for insertion of the device <NUM> through an incision, such as an incision of a lens capsule. To insert the device <NUM> into the eye, the rigid extender <NUM> stretches the suction cup <NUM> and cutting element <NUM> in one direction while the anchor thread <NUM> stretches the suction cup <NUM> and cutting element <NUM> in the opposite direction. This reversibly straightens out and decreases the cross-section of the suction cup <NUM> and cutting element <NUM> so that the suction cup <NUM> and cutting element <NUM> can go through the incision. Examples of incision sizes commonly used in surgery include <NUM>, <NUM>, <NUM>, <NUM>, etc.) As the rigid extender <NUM> is removed from the eye, the suction cup <NUM> and cutting element <NUM> elastically return to their original shape. The rigid extender may also be used to straighten the device after tissue cutting to facilitate device removal from the eye. There may be sufficient slack in the anchor thread <NUM> so that the cutting element <NUM> is not constrained except during extension of the rigid extender <NUM> and removal of the device <NUM> from the eye. The anchor thread <NUM> may be made from Vectran, a fiber that can withstand high temperature. In some embodiments, the device <NUM> includes a pocket <NUM> to house the rigid extender <NUM> once extended. In some embodiments, the device <NUM> does not include a rigid extender <NUM> anchor thread <NUM>, and/or pocket <NUM>.

<FIG> illustrates a bottom perspective view of the cutting element <NUM> of the microsurgical device <NUM>. The bottom of the cutting element <NUM> is continuous such that current can flow around the bottom of the cutting element <NUM> in a continuous path and generate the heat necessary for excising tissue. The cutting element <NUM> includes tabs, such as tabs <NUM>, <NUM>, <NUM>, that are configured to couple the electrical leads 120A, 120B to the cutting element <NUM>, couple the suction cup <NUM> to the cutting element <NUM>, and/or couple an anchor thread <NUM> to the cutting element <NUM>. The cutting element <NUM> and/or tabs may include features, such as slots, cutouts, and bumps, to remove hot and/or cold spots and maintain the mechanical strength of the cutting element <NUM>. The design and functionality of the tabs and features are discussed in detail below with reference to <FIG>.

The cutting element <NUM> may be configured so that it lies perpendicular to the surface of the tissue being excised. For example, the cutting element <NUM> shown in <FIG> is cylindrical such that the cutting element <NUM> is substantially perpendicular to the portion of the tissue being excised. In addition, the cutting element <NUM> may be configured such that only an inner corner edge <NUM> of the cutting element <NUM> excises the tissue. Alternatively, the cutting element <NUM> may be configured such that only the outer corner edge <NUM> of the cutting element <NUM> excises the tissue, both the inner corner edge <NUM> and outer corner edge <NUM> of the cutting element <NUM> excise the tissue, or the like. In addition, the cutting element <NUM> may be elliptical, conical, linear, square, rectangular, triangular, or any other suitable shape to match the geometry of the tissue being excised.

The device <NUM> shown includes two electrical leads 120A, 120B. Alternatively, the device <NUM> may include greater or fewer electrical leads, such as one electrical lead, three electrical leads, four electrical leads, etc. The points at which the electrical leads 120A, 120B couple to the cutting element <NUM> may vary. For example, when the electrical leads 120A, 120B are positioned on opposite sides of the cutting element <NUM>, the current can travel in opposite directions to conduct current uniformly around the portion of the tissue being excised. Alternatively, the electrical leads 120A, 120B may be located at positions that are a threshold distance apart, a threshold number of degrees apart, or the like.

The electrical leads 120A, 120B may be located within the one or more suction tubes <NUM>. In other embodiments, the electrical leads 120A, 120B may be located outside of the one or more suction tubes <NUM>. For example, the electrical leads 120A, 120B may be coupled to an outer surface of the one or more suction tubes <NUM>, adjacent to the one or more suction tubes <NUM>, and/or separated by a threshold distance from the one or more suction tubes <NUM>, etc..

<FIG> illustrates the path of electrical current flow (i) within the cutting element <NUM>. Upon entering the cutting element <NUM> through an electrical lead 120A, a portion of the current, such as one half of the current (i<NUM>/<NUM>), travels along one half of the cutting element <NUM>, while another portion of the current, such as the other half of the current (i<NUM>/<NUM>), travels along the other half of the cutting element <NUM>. Current then exits the cutting element <NUM> at the other electrical lead 120B. Due to the electrical resistance of the cutting element <NUM>, the current flow causes a rapid increase in the temperature of the cutting element <NUM>. Because of the rapid increase in temperature, the water molecules near or adjacent to the cutting element <NUM> and the tissue being excised vaporize rapidly and mechanically fracture the tissue along the path dictated by the portion of the cutting element <NUM> abutting the tissue being excised.

As shown in <FIG>, tabs of various tab types protrude from the cutting element <NUM>. Tab types include, but are not limited to wire tabs, such as wire tab <NUM>, mechanical tabs, such as mechanical tab <NUM>, and anchor tabs, such as anchor tab <NUM>. In some embodiments, wire tabs conductively couple the electrical leads 120A, 120B to the cutting element <NUM>, mechanical tabs hold the cutting element <NUM> within the suction cup <NUM>, and anchor tabs couple the cutting element <NUM> to an anchor thread <NUM>. The size, shape, and position of each tab type varies because of their different functions, which introduces structural asymmetries to the cutting element <NUM>.

The problem of uneven current flow and temperature elevation in the cutting element <NUM> due to the required structural asymmetries may be solved by adding an intricate pattern of one or more features to the cutting element <NUM> and/or tabs protruding from the cutting element <NUM>. Features may include a combination of slots, cutouts, and/or bumps. The configuration and geometry of the features also maintain the mechanical strength of the cutting element <NUM>. Mechanical strength is maintained by ensuring that the features do not create mechanically weak regions in the cutting element <NUM> or create hot spots that can become mechanically weak areas after energy pulses have been applied to the cutting element <NUM>.

Slots, such as slot <NUM> in <FIG>, function as empty space devoid of conductive material to provide electrical insulation. For example, slots stop current flow and divert current flow into an alternative path in the cutting element <NUM>. In addition, as regions devoid of conductive material, the slots also provide thermal insulation by eliminating the heat conductive path. Introduction of slots into the cutting element <NUM> and/or tabs protruding from the cutting element <NUM> may be of any size or shape, such as slots <NUM>, <NUM> in <FIG>. The cutting of the slots can be a closed path area, or single pass line. For example, slots may be made by one pass of the laser. In some embodiments, the slot width is around <NUM>. In some embodiments, instead of an empty space devoid of conductive material, slots may be made of a non-conductive material.

Cutouts, such as cutout <NUM> in <FIG>, reduce the cross-section of the cutting element <NUM> at various loci along an edge of the cutting element <NUM> to reduce the amount of material at the various loci. Reducing the amount of material locally increases the current density and provides appropriate heating at specific locations along the cutting element <NUM>. For example, cutouts may be used to offset cold spots caused by anchor tabs and/or mechanical tabs.

Conductive material is added to various portions of the cutting element <NUM> in the form of bumps to accommodate nearby regions of undesired high current density. For example, bumps, such as bump <NUM> in <FIG>, may be used to counteract hot spots that secondarily form through the implementation of slots in other portions of the cutting element <NUM>. Hot spots may potentially translate in mechanically weak regions after use.

The geometry and configuration of features along the cutting element <NUM> may be based on the tab type the feature is associated with, the position of the feature, the proximity of the feature to the electrical leads 120A, 120B, the proximity of the feature to the suction cup <NUM>, and the like. For example, mechanical tabs and/or anchor tabs may have horizontal slots cut in the cutting element <NUM> under the tabs, and wire tabs may have vertical or bent slots disposed within the tab itself. A horizontal slot allows the electrical current to flow horizontally around the cutting element <NUM>, but blocks thermal conduction vertically from the inner corner edge <NUM> of the cutting element <NUM> to the cold tab. A vertical or bent slot may help distribute and/or divert electrical current across various paths of the tab.

The geometry and configuration of each feature may be determined via reiterative empirical testing of their combined effects on current flow and temperature elevation in the cutting element <NUM>. Reiterative empirical testing is particularly relevant for conductive materials, such as shape memory alloys (e.g. nitinol) whose electrical resistance change as a function of temperature since the material's resistance and temperature simultaneously change during use. In addition, because thermal transport out of the cutting element <NUM> changes as adjacent water turns to steam, and because the specific heat capacity and thermal conductivities rapidly change as functions of temperature and pressure, reiterative empirical testing may be used to fine tune feature details, such as size, geometry, and/or curvature, without having to explicitly quantify changes in thermal transport over short timeframes (<NUM> seconds to <NUM> seconds). Therefore, reiterative empirical testing may be used to ensure even current flow and energy delivery via the cutting element <NUM> into tissue during an entire multi-pulse procedure. Alternatively, or additionally, computation modeling may be used to determine the geometry and configuration of each feature.

<FIG> illustrates a wire tab <NUM> of the microsurgical device <NUM> shown in <FIG>. Wire tabs conductively couple the electrical leads 120A, 120B to the cutting element <NUM>. To conductively couple an electrical lead to the cutting element <NUM>, an electrical lead, such as electrical lead 120A or electrical lead 120B, is inserted through a lumen <NUM> of the wire tab <NUM>. Once inserted, the end of the electrical lead protruding from the lumen <NUM> may be formed into a rivet head to secure the electrical lead to the wire tab <NUM>. In some embodiments, the electrical leads 120A, 120B are made of a material that is easily plastically deformed, such as silver. As such, compressive stress on each electrical lead causes the electrical lead to expand within the lumen <NUM>, which ensures sufficient physical contact and electrical connection between the electrical lead and the cutting element <NUM>. In some embodiments, the diameter of the lumen <NUM> is around <NUM>, and the diameter of the wire is around <NUM>.

The wire tab <NUM> includes multiple conductive paths to carry the electrical current from the electrical lead, such as electrical lead 120A or electrical lead 120B, to the cutting element <NUM>. The multiple conductive paths ensure that the proper current density is provided to the inner corner edge <NUM> of the cutting element <NUM> and eliminate a potential cold spot from forming at the portion of the cutting element <NUM> directly underneath the wire tab <NUM>. As shown in <FIG>, the wire tab <NUM> includes central conductive paths <NUM> and a conductive shunt path <NUM> on either side of the central conductive paths <NUM>. Current is carried by the central conductive paths <NUM> to the bottom beams <NUM>. However, the bottom beams <NUM> may be too small to carry the entire current, so the conductive shunt paths <NUM> may carry the rest of the current to cutting element <NUM> including the inner corner edge <NUM>. In some embodiments, the conductive shunt paths <NUM> may carry up to or greater than <NUM>% more current than the central conductive paths <NUM>.

The wire tab <NUM> shown includes a wire tab slot <NUM> that electrically and thermally insulates the sides of the central conductive path <NUM> from the electrical lead. The wire tab slot <NUM> helps to limit downward current flow to the neck <NUM> of the wire tab <NUM> and causes an appropriate current to flow along the conductive shunt paths <NUM>. The wire tab <NUM> shown also includes a wire tab slot <NUM> that electrically and thermally insulates the sides of the central conductive path <NUM> and the bottom beams <NUM> from the conductive shunt paths <NUM>. The wire tab slot <NUM> also directs current away from the neck <NUM> of the wire tab <NUM>, eliminating a hot spot from forming in the cutting element <NUM> under the wire tab <NUM>. In some embodiments, the wire tab <NUM> and the cutting element <NUM> are continuous and/or made out of the same material.

As a result of the thermal stresses placed on the cutting element <NUM> during use, the mechanical forces applied to the cutting element <NUM> during device <NUM> removal may cause the cutting element <NUM> to break. To minimize stress concentrations in the cutting element <NUM> and maintain its mechanical strength, the end of the wire tab slot <NUM> has a slight upward curve, which removes concentrations of stress in the metal of the cutting element <NUM>. The upward curve of the wire tab slot <NUM> may cause increased current density along the top half of the cutting element <NUM>, particularly at point <NUM>, which is directly above the curved end of the wire tab slot <NUM>. To offset the increased current density, the cutting element <NUM> may include bumps, such as bump <NUM>, on either side of the wire tab <NUM>. A bump increases the amount of material at point <NUM>, and, therefore, reduces the local current density of the cutting element <NUM> at point <NUM>. As shown, a similar bump may be placed on the opposite side of the wire tab <NUM>.

<FIG> illustrates the flow of current through the wire tab <NUM> shown in <FIG>. The total current itotal carried by an electrical lead, such as electrical lead 120A or electrical lead 120B, is distributed through the wire tab <NUM> according to Equation <NUM>.

In Equation <NUM>, ic is the current carried by each central conductive path <NUM> and is is the current carried by each conductive shunt path <NUM>. The electrical current ic carried by each of the central conductive paths <NUM> converges at the neck <NUM> of the wire tab <NUM> and is carried along the bottom beams <NUM> along the path shown. Heat from the neck <NUM> and adjacent bottom beams <NUM> prevents any significant cold spot from occurring underneath the wire tab <NUM>.

The electrical current is carried by each of the conductive shunt paths <NUM> travels to the top half of the cutting element <NUM> along the path shown. The electrical current is carried by a conductive shunt path <NUM> converges with the electrical current ic carried by one of the central conductive paths <NUM>. As a result, a first half of the total current i<NUM>/<NUM> goes clockwise and a second half of the total current i<NUM>/<NUM> goes counterclockwise.

<FIG> illustrates a mechanical tab <NUM> that couples the cutting element <NUM> to the suction cup <NUM>. In other designs, the mass of a mechanical tab can create a cold spot in the cutting element <NUM> underneath the tab because electrical current flowing past below the tab will generate heat in the metal, but the mechanical tab is not heated. Therefore, the tab stays cold and absorbs heat from the cutting element <NUM> by thermal conduction <NUM>. Cold spots can result in the cutting element immediately below a mechanical tab and giving rise to non-uniform tissue cutting and tissue tags. This problem is accentuated if electrical current is delivered as sequential pulses of energy to the cutting element <NUM> because the cold tab acts as a heat sink and takes heat away from the bottom of the cutting element <NUM> via thermal conduction <NUM> in between pulses if slot <NUM> is not there to block thermal conduction.

The design of the mechanical tab <NUM> shown prevents cold spots from forming in the cutting element <NUM> through the implementation of a mechanical tab slot <NUM> disposed horizontally along the cutting element <NUM>. The mechanical tab slot <NUM> allows electrical current ix to flow horizontally around the bottom half of the cutting element <NUM>, but prevents vertical thermal conduction <NUM> from the bottom beam <NUM> to the cold mechanical tab <NUM> and minimizes the amount of electrical current iy flowing through the top half of the cutting element. As a result, the cold mechanical tab <NUM> does not take heat away from the bottom of <NUM>, and a uniform temperature at the inner corner edge <NUM> of the cutting element <NUM> is maintained.

The shape of the mechanical tab <NUM> may vary. The mechanical tab <NUM> shown includes a horizontal beam <NUM> and vertical beam <NUM> that together form a T-shape. The vertical beam <NUM> of the mechanical tab <NUM> is connected to the cutting element <NUM>. In other embodiments, the mechanical tab <NUM> may form a closed circular loop, a closed elliptical loop, a partially open circular loop, a partially open elliptical loop, etc.; the edges of the horizonal beam <NUM> may extend downward, or the like. In some embodiments, the mechanical tab <NUM> and the cutting element <NUM> are continuous and/or made out of the same material.

<FIG> illustrates an example embodiment of an anchor tab <NUM> of the microsurgical device <NUM> shown in <FIG>. In use, an anchor thread <NUM> may be looped around the anchor tab <NUM> to hold the cutting element <NUM> back while the other end of the cutting element <NUM> is stretched forward by a rigid extender <NUM>. The stretched cutting element <NUM> may then be inserted through an incision. In some embodiments, the anchor tab <NUM> and the cutting element <NUM> are continuous and/or made out of the same material.

The anchor tab <NUM> includes a bent portion <NUM> that forms a space <NUM> around which the anchor thread <NUM> may be looped. In the embodiment shown, the cutting element <NUM> includes an anchor tab slot <NUM> under the anchor tab <NUM>. As with the mechanical tab <NUM>, the mass of the anchor tab <NUM> may cause a cold spot in the cutting element <NUM> underneath the anchor tab <NUM>. The anchor tab slot <NUM> allows the electrical current to flow horizontally around the cutting element <NUM>, but prevents vertical thermal conduction from the bottom beam <NUM> to the cold anchor tab <NUM>. The anchor tab slot <NUM> also prevents thermal propagation in between pulses into the anchor tab <NUM>. As a result, a uniform temperature at the inner corner edge <NUM> of the cutting element <NUM> is maintained during tissue cutting.

The size and geometry of the anchor tab slot <NUM> may vary. In some embodiments, the anchor tab slot <NUM> is longer than the slots under the other tabs. For example, the anchor tab slot <NUM> may be a predetermined length longer than the mechanical tab slot <NUM>. Additionally, in some embodiments, there is a reduction in current carrying cross-section to provide one or more hot spots <NUM> next to the anchor tab <NUM>. For example, in the anchor tab <NUM> shown, the cross-section of the cutting element <NUM> adjacent to the anchor tab <NUM> is reduced to create local hot spots <NUM> on either side of the anchor tab <NUM>. Hot spots <NUM> may offset the cooling effects of the anchor tab <NUM> on the cutting element <NUM>.

In some embodiments, the edges <NUM> of the anchor tabs that contact the anchor thread <NUM> are smoothed to reduce the risk of cutting the anchor thread <NUM> during use. For example, the edges <NUM> may be smoothed by lapping the edges <NUM> with a thread and <NUM>-micron diamond lapping paste. In some embodiments, the device <NUM> includes an additional anchor tab adjacent to anchor tab <NUM>. In these embodiments, the anchor thread <NUM> is looped around both the anchor tab <NUM> and the additional anchor tab. The additional anchor tab may be a mirror image of the anchor tab <NUM>. Alternatively, the specifications of the additional anchor tab may differ from the anchor tab <NUM>.

<FIG> illustrates a variation of anchor tabs 605A, 605B of a microsurgical device. The anchor tabs 605A, 605B protrude from a microsurgical device with the same or similar functionality to the device <NUM> described with reference to <FIG>. An anchor thread <NUM> may be looped around the anchor tabs 605A, 605B to hold the cutting element <NUM> back while the other end of the cutting element <NUM> is stretched forward by a rigid extender <NUM>.

The specifications, such as the width, height, curvature, etc., of each of the anchor tabs 605A, 605B may be modified. For example, the width of the anchor tabs 605A, 605B may be reduced to reduce the mass of the anchor tabs 605A, 605B. The anchor tabs 605A, 605B shown are mirror images of each other. In other embodiments, the specifications of each anchor tab may differ from each other based on the procedure, tissue shape, and the like. Alternatively, or additionally, a device may include greater or fewer anchor tabs, such as one anchor tab, three anchor tabs, or the like.

A slot, e.g., slots 610A, 610B, is disposed along the cutting element <NUM> under each of the anchor tabs. The slots 610A, 610B include the same or similar functionality to the anchor tab slot <NUM> described with reference to <FIG>. The length of the slots 610A, 610B may be longer, shorter, or of the same length as other slots disposed along the cutting element <NUM>. The base of the anchor tabs may be filleted to reduce mechanical stress. In addition, the cross-section of the cutting element <NUM> adjacent to either slot 610A, 610B may be reduced to locally increase the current density of the cutting element <NUM>.

The foregoing description of the embodiments of the disclosure has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed.

Claim 1:
A device (<NUM>) for capsulotomy, the device (<NUM>) comprising:
a stem (<NUM>);
a cutting element (<NUM>) coupled to a distal end of the stem (<NUM>);
one or more electrical leads (120A, 120B) for providing an electrical discharge to the cutting element (<NUM>); and
one or more wire tabs (<NUM>) protruding from the cutting element (<NUM>), each of the one or more wire tabs (<NUM>) configured to conductively couple an electrical lead (120A, 120B) of the one or more electrical leads (120A, 120B) to the cutting element (<NUM>), characterised in that each of the one or more wire tabs (<NUM>) includes one or more conductive paths (<NUM>) and one or more conductive shunt paths (<NUM>) conductively separated by one or more slots (<NUM>).