WO2012116957A1

WO2012116957A1 - Electrocoagulation device with limited heat damage

Info

Publication number: WO2012116957A1
Application number: PCT/EP2012/053282
Authority: WO
Inventors: Janos VÖRÖS; Robert Neil MACKENZIE; Daniel Eberli; Lukas John HEFERMEHL
Original assignee: Universität Zürich Prorektorat Mnw
Priority date: 2011-03-01
Filing date: 2012-02-27
Publication date: 2012-09-07

Abstract

An electrocoagulation device, such as a bipolar device for use in an electrosurgery procedure, comprises first and second electrode members (1A, 2A) each made of an electrically conductive material and having a contact surface for contacting the electrode member and a tissue portion of an object or subject to be treated with said procedure. At least one of said electrode members comprises a heat sink region (1B and/or 2B) comprising a phase change material (4) or a combination thereof, said phase change material or combination thereof having a phase transition temperature in the range of 25°C to 60°C.

Description

Electrocoagulation Device with Limited Heat Damage

TECHNICAL FIELD The present invention relates to a medical device with limited heat damage, comprising a phase change material.

PRIOR ART As an example of an electrocoagulation device, bipolar devices are electrosurgical instruments having a pair of resilient jaw members that are used for grasping and clamping vascularized tissues. Each jaw member is connected to an an electrically conductive sealing surface. Electrosurgical instruments may be monopolar or bipolar. In monopolar devices, the jaw members are joined to form an active electrode in electrical communication with an electrical generator. Current flows from the active electrode through the patient's tissue to a dispersive electrode in contact with the patient's tissue (which may be at some distance from the forceps) and back to the generator. In bipolar devices, the electrode of each jaw member is in communication with an electrical generator. Current flows from one electrode through the tissue to the electrode of the opposing j aw member. This flow of current is used to cauterize and seal vessels and vascular tissue.

Electrocoagulation devices have significant advantages including reduced hemorrhage time and operating time. However, these instruments are often not used for delicate surgery due to thermal spread, peripheral tissue heating and worry about nerve and tissue damage.

Several approaches to prevent thermal spread have been proposed.

EP 246 350 Al describes coagulation electrodes which are intended for the thermal coagulation of biological tissue by means of high-frequency electrical alternating current. The area adjoining the contact surface of the coagulation electrode is designed as a heat sink with such a great heat capacity value and is cooled to such a low temperature that, during the time span necessary for at least one coagulation procedure, the contact surface has a temperature within a temperature range whose upper temperature limit is below the temperature of the operating room and whose lower limit is above the freezing temperature of water. The heat sink can comprise a cooling facility with an inlet and a discharge line for liquid or gaseous coolant.

In US 6,293,946 Bl, electrosurgical forceps are described which include two electrodes, each having a tip that is composed of pure silver and pure gold, as well as biocompatible alloys of silver and/or gold that are nearly entirely composed of silver and/or gold. The electrodes may include a thermal reservoir of this material spaced apart from a distal end of the electrode, with the thermal reservoir having a greater cross-sectional area than the distal end.

The above mentioned solutions have the following disadvantages:

• According to EP 246 350 Al the inlets for the cooling require additional tubing or piping, which increase the handling complexity of the device for the surgeon. The surgeon must already deal with the existing electrical cable of the device, in addition to other surgical devices in hand, such as clamps, scissors and forceps. The active cooling describes the need for a coolant temperature range low enough to cool the contact surface to within a range of 0<t<room temperature. Thus, the coolant and inlets themselves could be operating temperatures below the freezing point. Such cooling inlets increase the risk of coolant leakage or condensation entering the patient or the operating environment.

• According to US 6,293,946 Bl the thermal reservoirs, described as majority silver or gold alloys, do not have the necessary heat storage capacity to reduce tissue heating as effectively. Furthermore, the mentioned thermal reservoir excludes other, possibly more effective materials. In addition, the thermal reservoir as described is restricted to the electrode. Other areas of the electrical forceps with the potential of acting as thermal reservoirs are not mentioned. These include, but are not limited to the insulation and packaging of the electrodes or additional inserts/coatings around the electrodes, insulation or packaging at the jaws of the forceps. SUMMARY OF THE INVENTION

It is an object of the present invention to provide electrocoagulation devices with limited heat damage. The electrosurgical instruments may be monopolar or bipolar. This object can be achieved by the use of phase change materials as a thermal reservoir. In contrast to the disclosure of EP 246 350 Al, according to which the contact surface is cooled to a low temperature, the design of the present invention enables heat energy to be actively absorbed away from the electrode/tissue surface and interface. In contrast to the disclosure of US 6,293,946 Bl, according to which the electrodes contain a thermal reservoir of silver or gold alloy, the present invention creates a thermal reservoir of materials that are not themselves part of the electrode or contained therein. This is advantageous because the electrical current flow is not disturbed or disrupted, but the heat resulting from the current is adsorbed away from the tissue.

Phase change materials (henceforth abbreviated as "PCM") exploit the principle that a material requires a relatively significant amount of energy (heat) for a first order phase transition, notably for a change from a solid to a liquid and then back from a liquid to a solid. A PCM can, therefore, absorb large amounts of heat or energy from their environment and return large amounts of heat to their environment. This effective absorption, storage and release of heat can be used to regulate the temperature of an environment, material or surface in thermal contact with the PCM.

The use of PCM materials has been taught, for example, for temperature control by incorporation in clothing, aircraft skin, electronic component packages, foams, roadway surfaces, concrete, asphalt, bridge structures, building materials, potting materials, slurries, building structures such as concrete and gypsum board, solar collecting structures, and alloys used in solar-steam systems. However, none of the prior-art applications provides or suggests the use of such materials for electrocoagulation devices.

Therefore, the objective is achieved by an electrocoagulation device as laid down in claim 1. The device according to the invention comprises first and second electrode members each made of an electrically conductive material and having a contact surface for contacting the electrode member and a tissue portion of an object or subject to be treated with said procedure. At least one of said electrode members comprises a heat sink region comprising a phase change material or a combination thereof, said phase change material or combination thereof having a phase transition temperature in the range of about 25°C to about 60°C.

Preferably, said phase transition temperature corresponds to melting of the phase change material or combination thereof.

In a particularly preferred embodiment the phase transition temperature is i n a physiologically acceptable range of about 35°C to about 45°C, which is the target range for the specific use of the electrocoagulation device, such as a vessel-sealing device in surgery. The upper limit of about 45°C allows the PCM to absorb energy up to the critical temperature for nerve/cell damage. On the other hand, if the phase transition temperature of the PCM is too low (e.g. 25°C), the phase change begins as soon as contact to the tissue is made and before the application of the electrosurgical current. Assuming the tissue during surgery would have a temperature of about 35°C, a PCM designed for a range 35°C to 45°C would only absorb excess or additional energy (i.e. heat from electrosurgical current) rather than thermal energy from tissue at ambient temperature in the patient.

It will be understood that before starting use of the device one has to ensure that the PCM is in its lower temperature phase, which in most cases will be the solid state. In a preferred embodiment of the invention, the device comprises first and second elongated and spaced-apart jaw members with electrodes adapted for conducting electrosurgical current between them during use in an electrosurgery procedure; said first jaw member having a first elongated electrically conductive electrode with said first elongated electrode partially coated with a heat sink material, such that the electrode/tissue interface is not coated; and said second jaw member having a second elongated electrically conductive electrode surface with said second elongated electrode partially coated with a heat sink material, such that the electrode/tissue interface is not coated; said heat sink material comprising a phase change material or a combination thereof.

In a preferred embodiment of the invention, the heat sink material comprises a polymeric binder material and a plurality of nano/microcapsules dispersed throughout and submerged within said polymeric binder so as to be surrounded thereby, said nano/microcapsules comprising a phase change material or a combination thereof.

In a preferred embodiment of the invention, the heat sink material comprises a polymeric binder material and a plurality of nano/microcapsules dispersed throughout and submerged within said polymeric binder so as to be surrounded thereby, said nano/microcapsules comprising an encapsulant shell and a heat absorbing material within said shell, the heat absorbing material comprising at least one phase change material.

In particular, it is preferred that the polymeric binder is a biocompatible polymer. In particular, the polymeric binder is selected from the group consisting of polycarbonate (PC), polystyrene (PS), polyimide (PI), polypropylene (PP), cyclic olefin copolymer (COC), polyether ether ketone (PEEK), polydimethyl siloxane (PDMS), polymethyl methacrylate (PMMA), or any combination thereof. In one embodiment, the encapsulant shell is selected from materials such as melamine resin, gelatin, polyamides, polyurethanes, hydrocarbons, fats, fatty acids, surfactants, amino resins and waxes.

In another preferred embodiment, the phase change material is selected from organic, inorganic or eutectic compounds such as thermal salts (e.g. sodium acetate), fatty acids (e.g. lauric acid, palmitic acid), trimethylolethane (TME), and paraffin wax.

In another preferred embodiment, the polymeric binder is PDMS and the phase change material is a mixture of the organic compounds lauric acid and palmitic acid.

BRIEF DESCRIPTION OF THE DRAWINGS The above mentioned and other features and objects of this invention and the manner of achieving them will become more apparent and this invention itself will be better understood by reference to the following description of various embodiments of this invention taken in conjunction with the accompanying drawings, wherein

Fig. 1 shows a device (e.g. a clamp as shown above) coated with a material, in which a phase change material (or a mixture of phase change materials) is encapsulated; Fig. 2 shows a device where an outer sheath portion of the electrode is replaced by a material comprising a PCM;

Fig. 3 shows a removable sheath portion for attachment onto the jaw members of electro surgical forceps, the sheath portion containing a PCM;

Fig. 4 shows the thermal response of various PDMS : PCM mixtures: 100%, 89%

87% and 85% PDMS; the 85% PDMS mixture, thus containing 15% PCM material, was able to absorb and release the most thermal energy; Fig. 5 shows the typical size of a bovine meat sample and an example of the temperature sensor placement when the meat sample is clamped and heated;

Fig. 6 shows repeated measurements of the heating and cooling of a bovine meat sample with a non-coated bipolar vessel-sealing device;

Fig. 7 shows repeated measurements of the heating and cooling of a bovine meat sample with a PDMS/PCM coated bipolar vessel-sealing device;

Fig. 8 shows the temperature of the PDMS/PCM coating before, during and after the heating cycle of the bipolar vessel-sealing device in contact with the bovine meat. DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 shows a medical device according to a first embodiment of the present invention. The device comprises first and second elongated and spaced-apart jaw members with electrodes adapted for conducting electrosurgical current between them during use in an electro surgery procedure. The first jaw member comprises a first elongated electrically conductive electrode (1A) that is partially coated with a heat sink material (IB) in such manner that the electrode/tissue interface is not coated. The second jaw member comprises a second elongated electrically conductive electrode surface (2A) that is partially coated with a heat sink material (2B) in such manner that the electrode/tissue interface is not coated. The heat sink material comprises a polymeric binder material (3) containing a plurality of microcapsules (4) dispersed throughout and submerged within said polymeric binder so as to be surrounded thereby. The microcapsules generally comprise an encapsulant shell and a heat absorbing material within the shell, with the heat absorbing material comprising a phase change material (PCM) or a combination of such materials.

Figure 2 shows a medical device according to a further embodiment of the present invention. The device comprises first and second elongated and spaced-apart electrode arms adapted for conducting electrosurgical current between them during use in an electro surgery procedure. As indicated by the arrow, an outer sheath portion that surrounds each electrode arm in substantially U-shaped manner has been replaced by a corresponding cover portion (2) made of a material comprising at least one PCM. Figure 3 illustrates a further embodiment of the invention according to which a removable sheath element is provided for temporary attachment onto an electrosurgical forceps. The removable sheath is made of a material comprising at least one PCM.

Feasibility study in vitro

To test the feasibility of a PCM to absorb heat and thereby influence the peripheral heating of tissue, a thin PCM coating was developed and applied to a bipolar vessel-sealing device. The substrate material of the coating was PDMS. The PCM material was formed through a combination of lauric acid (LA) and palmitic acid (PA) in a 69:31 ratio to obtain a melting temperature of 35.2 °C as described in Tuncbilek, K.; Sari, A.; Tarhan, S.; Ergiines, G.; Kaygusuz, K., "Lauric and palmitic acids eutectic mixture as latent heat storage material for low temperature heating applications". Energy 2005, 30, 677-692. From literature it is reported that this ratio of LA:PA has a latent heat of fusion of 166.3 J/g. The PCM material was then encapsulated in the PDMS substrate, applied to the device surface, and cured to form stable polymer. This concept is shown in Figure 1. The ability of this PDMS/PCM coating to absorb and to release heat was measured with a Differential Scanning Calorimeter (DSC, Model 823e from Mettler-Toledo) compared to the base PDMS substrate and other mixture ratios PDMS:PCM. Such a measurement is shown in Figure 4, in which the thermal response is normalized by the sample weight.

The peripheral heating from a bipolar vessel- sealing device was tested in vitro by cauterizing bovine meat, measuring and recording the temperature change of the meat with a Voltcraft K202 Thermometer. Strips of bovine meat, 8 mm thick, were clamped into the bipolar vessel-sealing device. Temperature sensors were place in the proximity of the clamp electrodes and at increasing distances from the electrodes (Figure 5). The bipolar vessel-sealing device was activated and allowed to heat for an automated cycle. The temperature change of the bovine meat was measured without a coating (Figure 6) and with a PDMS/PCM coating (Figure 7). The measurements with the coating repeatedly prevented temperature spikes above 80°C and noticeably altered the temperature profile (i.e. cooling) of the bovine meat after the heating cycle of the bipolar vessel-sealing device. In addition, the temperature of the coating itself in the neighborhood of, but not at the tissue surface, was measured (see Figure 8). It is shown that the coating also absorbed thermal energy from the tissue.

Claims

1. An electrocoagulation device for use in an electrosurgery procedure, the device comprising first and second electrode members (1A, 2 A) each made of an electrically conductive material and having a contact surface for contacting the electrode member and a tissue portion of an object or subject to be treated with said procedure, characterized in that at least one of said electrode members comprises a heat sink region (IB and/or 2B) comprising a phase change material (4) or a combination thereof, said phase change material or combination thereof having a phase transition temperature in the range of 25°C to 60°C.

2. The electrocoagulation device as defined in claim 1, wherein said phase change material or combination thereof has a phase transition temperature in the range of 35°C to 45°C

3. The electrocoagulation device as defined in claim 1 or 2, wherein at least one of said heat sink regions is configured as a sheath portion (2) substantially surrounding the respective electrode member except for said contact surface.

4. The electrocoagulation device as defined in claim 3, wherein said sheath portion is removably mounted to the respective electrode member.

5. The electrocoagulation device as defined in any one of claims 1 to 4, wherein said heat sink region comprises a polymeric binder material and a plurality of nano/microcapsules dispersed throughout and submerged within said polymeric binder so as to be surrounded thereby, said nano/microcapsules comprising said phase change material or combination thereof.

6. The electrocoagulation device as defined in claim 5, wherein said polymeric binder is PDMS and wherein said phase change material is a mixture of lauric acid and palmitic acid.