ELECTROSURGICAL INSTRUMENT

Abstract: An exceptionally durable coating for electrosurgical instruments (10) is provided. This conductive coating (12) is composed of magnetite, Fe3O4, particles which are spraycoated onto the base metal (18) of a surgical instrument using a thermal spray technique.

Description: ELECTROSURGICAL INSTRUMENT Field of the Invention This invention relates to electrosurgical instruments and in particular to laparoscopic electrosurgical instruments. Background of the Invention The use of high frequency electrical energy for surgical applications dates back almost a century. Electrosurgery is the generation and delivery of radio frequency current between an active electrode and a dispersive electrode to elevate the tissue temperature for cutting, coagulating, fulgurating, and dessicating. Electrosurgical energy is the most commonly used energy source in the discipline of surgery. In open surgery such as laparotomy, the surgeon has a wider vantage point in controlling bleeding and dissection, and has more options to complement his or her surgical technique. In laparoscopy and other closed procedures, precise delivery of electrosurgical energy is a requirement for optimizing surgical outcomes. Historically, there have been difficulties with the use of electrosurgical instruments for cutting and coagulating tissues. For example, the working surfaces of the electrodes of such instruments tend to stick to tissue that comes in contact therewith. Also numerous incidents of inadvertent electrical shocks and burns to the patient and the physician, and even death to the patients have been reported. In a great number of these cases, the cause of the reported injury was specified as resulting from the breakdown of insulation of the electrosurgical instrument . Numerous methods exist for providing an inert electrode working surface for electrosurgical instruments. The most common is the application of a non-stick coating to the base metal which usually is stainless steel, but could be aluminum or other metals. The typical non-stick coating is also an insulation material and thus cannot be applied to the working surface of the electrode portion of the instrument. Illustrative of such non-stick coatings are a fluorocarbon such as a poly (tetrafluoroethylene) , a poly(vinyl chloride) (PVC) , or a heat-shrinkable plastic. While these materials have well-documented electrical insulative characteristics, they are not optimally suited for use in electrosurgial instruments. The major weaknesses of the previously noted non-stick coatings are inadequate abrasion resistance (i.e., the coating rubs off easily leaving bare metal exposed) , decomposition of the coating at the relatively high temperatures used in sterilization and in the electrosurgical process itself, as well as retention of moisture between the coating and the stainless steel instrument . This retention of moisture can ultimately cause corrosion of the instrument and can also result in inadequate sterilization of the instrument. These problems necessitate the continual replacement of the current types of insulation used in electrosurgical instruments today with an attendant escalation of the costs of health care. A suitable insulating ceramic coating is described in commonly owned U.S. Patent No. 5,562,659 to Morris . The present invention provides a substantially non-stick working surface for an electrosurgical electrode by a conductive but inert iron oxide surface. The iron oxide coating is durable, heat resistant, and is easily cleaned. Moreover, the present coating is not susceptible to damage or erosion from thermal stresses derived from sterilization processes or high frequency electrical current when in use . Summary of the Invention A laparoscopic electrosurgical instrument having a conductive magnetite (Fe 3 0 4 ) coating on a metal substrate that serves as a working surface of an electrode is provided. A stainless steel substrate is a preferred electrode surface, but other metals such as aluminum can also be utilized to provide a working surface. The magnetite coating can be up to about 0.01 inch (about 0.25 mm) thick, and can be applied to the metal substrate using a thermal spray process such as is available from a plasma gun, a detonation gun, a high velocity oxygen fuel (HVOF) system, a high energy plasma (HEP) system, or the like. Brief Description of the Drawing In the drawing, FIG. 1 is a fragmentary view, partly in section, of an electrosurgical instrument provided with a coating of magnetite, Fe 3 0 4/ on a working surface of the electrode portion of the instrument . Description of the Preferred Embodiments Through utilization of a thermal spray process implemented by a plasma gun, a detonation gun, a high velocity oxygen fuel system, a high energy plasma system, or the like for the deposition of a magnetite coating, a high quality non-stick working surface for electrosurgical instruments can be realized. Such a coating is readily cleanable and also provides exceptional wear and abrasion characteristics, including being resistant to scratching, nicking or cutting. In addition, such coating is chemically inert, non-toxic, non-irritating and otherwise suitable for use in the human body. Deposition of the magnetite coating using the aforementioned thermal spray techniques promotes good adhesion of the coating to the base metal of the instrument, thereby minimizing a likelihood of corrosion and permitting steam and chemical sterilization without difficulty. The magnetite coating is easily applied to various shapes and sizes of instruments by thermal spraying and is cost effective. The preferred material for the working surfaces of an electrosurgical instrument is a coating of magnetite, Fe 3 0 4 , with a thickness in the range of about 0.001 to about 0.01 inches (about 0.025 mm to about 0.25 mm) . A more preferred coating thickness is in the range of about 0.001 to about 0.004 inches (about 0.025 mm to about 0.1 mm) . Relatively thinner or thicker magnetite coatings can also be applied if indicated by a specific use. Referring to FIGURE 1, a portion of a typical electrosurgical electrode 10 suitable for laparoscopic use is depicted. Electrode 10 is shown with a hook tip; however, other tip configurations such as a knife tip, cone tip, button tip, spatula tip, sling tip, scissor tip, forcep tip, and the like, are also available. The tip configuration of the electrosurgical instrument forms no part of the present invention. Magnetite coating 12 is provided on the conductive tip portion 14 of electrode 10. The insulating layer 16, typically a ceramic material such as an alumina composite, or the like, surrounds electrode 10 except for the conductive tip portion 14 and necessary connections to a radio frequency (RF) current source. Shaft 18 of electrode 10 is typically made of surgical grade stainless steel . Hook portion 14 is unitary with shaft 18, defines the working surface of electrode 10, and is also made of stainless steel which provides the substrate for magnetite coating 12. The present invention is further illustrated by the following examples which demonstrate the magnetite coating for electrosurgical instruments. EXAMPLE 1 : Conductive Magnetite Coating for Electrosurgical Instruments The following table, Table I, lists the chemical analysis of a typical lot of magnetite, Fe 3 0 4 , coating. The particle size of the black oxide is -32/+10 micron. This coating was applied to a steel substrate with a plasma gun to a thickness of about 0.003 inches (0.08 mm) and was found to be a conductive coating. TABLE I CHEMICAL ANALYSIS OF MAGNETITE POWDER ELEMENT/COMPOUND PERCENT BY WEIGHT Iron (Fe 3 0 4 ) 70.5 Silica (Si0 2 ) 0.740 Titanium (Ti0 2 ) 0.112 Aluminum (Al 2 0 3 ) 0.105 Calcium (CaO) 0.150 Magnesium (MgO) 0.044 Sodium (Na 2 0) 0.214 Potassium (K 2 0) 0.033 EXAMPLE 2: Comparative Performance of Coated Electrodes Spatula-tip electrosurgical electrodes having a stainless steel working surface were provided with surface coatings of various compositions. These electrodes were then evaluated at 500 KHZ, and various power settings for ease of use and for cleanability. Contact time prior to the onset of electrode sticking to tissue was also noted. The observed results are presented in Table II, below. TABLE II NON-STICK TRIAL MATRIX 1 Abbreviations in Table II: ss-stainless steel WC & Co-tungsten carbide & cobalt slt-slight hvy-heavy mod-moderate scr-only by scraping esy-easy imp-impossible imd-immediate n/a-not applicable s- seconds The foregoing specification is intended to illustrate the present invention but is not to be taken as limiting. Still other variations within the spirit and scope of the present invention are possible and will readily present themselves to those skilled in the art .

Claims: WE CLAIM : 1. An electrosurgical instrument comprising: (a) a metal electrode having an exposed working surface; and (b) a conductive magnetite coating on the working surface of the metal electrode. 2. The instrument of claim 1 wherein the thickness of the coating is in the range of about 0.001 to about 0.01 inches. 3. The instrument of claim 1 wherein the thickness of the coating is in the range of about 0.001 to about 0.004 inches. 4. The instrument of claim 1 wherein the metal electrode is stainless steel.

Inventors: HENDERSON MICHAEL, JONES RICHARD F, SORENSEN NELS, HENDERSON, MICHAEL, JONES, RICHARD, F., SORENSEN, NELS
Applicants: MEDICOR CORP, MEDICOR CORPORATION
Application year: 1998
Main classification: A61B17
IPC codes: A61B18