Patent Description:
Reusable medical instruments are instruments that health care providers can reuse to diagnose and/or treat multiple patients. Examples of reusable medical instruments include medical instruments used in dental care, such as scalpels, syringes, scopes, mirrors, drills, burs, discs, handpieces, excavators, turbines, files, reamers, etc..

When used on patients, reusable instruments become soiled and contaminated with blood, tissue and other biological debris such as microorganisms. To avoid any risk of infection by a contaminated instrument, the reusable instruments can be sterilized. Sterilizing results in a medical instrument that can be safely used more than once in the same patient, or in more than one patient. Adequate sterilizing of reusable medical instruments is vital to protecting patient safety.

Various sterilizing agents can be used for sterilizing medical instruments. Historically, steam or hydrogen peroxide is often used. More recently, plasma devices are being used for ionizing gases or gas mixtures, the ionized gas being used as sterilizing agent. Electrons in the plasma impact on gas molecules causing dissociation and ionization of these molecules, which creates a mix of reactive species. It is known to directly expose the medical instruments to the plasma, or to expose the medical instruments to the (partially) recombined plasma, sometimes referred to as afterglow, see e.g. <NPL>.

Several attempts have been made to improve upon plasma sterilizing. <CIT> discloses a system comprising a chamber and a plasma generator for generating free radicals combined with use of a hydrogen peroxide solution.

<CIT> relates to a system and methods for sterilizing or disinfecting articles, particularly the hollow internal areas of medical instruments. The system includes a plasma generator having an electrode, a shield, and a dielectric gap between the electrode and the shield. A source of electrical power is connected to the plasma generator for applying an electron energy density between the electrode and the shield. A source of gas comprising water vapor, oxygen and nitrogen provides a flow of gas between the electrode and the shield, to form a plasma containing acidic and/or oxidizing species.

<CIT> relates to a device for providing a flow of non-thermal gaseous plasma for treatment of a treatment region comprising a cell for the generation of the non-thermal plasma. The cell has an inlet for gas and an outlet for the non-thermal gaseous plasma. The cell is in a heat conducting relationship with a heat sink through a heat pipe, the heat sink and the heat pipe both forming parts of the device. The cell typically has a dielectric member of high thermal conductivity in heat conducting relationship with the heat pipe. The heat sink is typically a capsule containing the gas to be supplied to the inlet of the cell.

It is also known to use an atmospheric or super atmospheric plasma source.

Plasma sources can have the disadvantage that the composition of the disinfecting and/or sterilizing agent, produced by generating an at least partially ionized gas mixture, can vary significantly with varying temperature and/or pressure of the plasma.

It is an object to provide an improved plasma source for generating a disinfecting and/or sterilizing gas mixture.

Thereto, according to a first aspect, is provided a plasma source for generating a disinfecting and/or sterilizing gas mixture. The plasma source includes an ionization chamber. The ionization chamber includes a dielectric tubular portion. The dielectric tubular portion can form a wall of the ionization chamber. The ionization chamber includes an inflow port for feeding a gas or gas mixture into the chamber. In the ionization chamber the gas or gas mixture is transformed into the disinfecting and/or sterilizing gas mixture. The ionization chamber includes an outflow port for exhausting the disinfecting and/or sterilizing gas mixture out of the chamber. The inflow port can be positioned at a first end of the tubular portion. The outflow port can be positioned at an opposite, second end of the tubular portion. Hence, a gas or gas mixture can be made to flow through the tubular portion. The ionization chamber includes a first electrode positioned inside the dielectric tubular portion, and a second electrode positioned outside the dielectric tubular portion. The first electrode can e.g. extend longitudinally within the tubular portion, such as along the axis of the tubular portion. The second electrode can be formed on an outer surface of the tubular portion. The second electrode can be a separate part, such as a metal sheet. It is also possible that the second electrode is a conductive layer coated onto the outer surface of the tubular portion, such as a metallic layer (plasma) deposited onto the outer surface. The plasma source includes a high voltage source having a high voltage output terminal, wherein an electrical conductor connects the output terminal to the first or second electrode. The high voltage terminal can e.g. be connected to the first electrode. The second electrode can be connected to electrical ground. The electrical conductor is preferably less than <NUM> long. The plasma source includes a forced gas cooling system for cooling the ionization chamber.

The forced gas cooling system is arranged for forcing a cooling gas flow onto the dielectric tubular portion in a direction substantially orthogonal to a longitudinal axis of the tubular portion, e.g. perpendicular to the longitudinal axis of the tubular portion. It has been found that such flow effectively provides high quality of the disinfecting and/or sterilizing gas mixture. The forced gas cooling system comprises an elongate funnel having two sidewalls tapering towards the dielectric tubular portion and extending along the longitudinal axis, wherein the funnel is arranged between at least one fan and the dielectric tubular portion and configured to force the cooling gas flow by the fan into the funnel towards its narrow end where the two sidewalls converge, wherein the narrow end has an elongate exit opening disposed adjacent the dielectric tubular portion and extending along the longitudinal axis, wherein the exit opening is arranged facing the dielectric tubular portion and configured to force the cooling gas flow exiting the opening to flow onto one side of the tubular portion in the direction substantially orthogonal to the longitudinal axis.

The plasma source is arranged for generating a disinfecting and/or sterilizing gas mixture. It will be appreciated that depending on the circumstances it may suffice to generate a disinfecting gas mixture suitable for disinfecting objects, wherein a large proportion of microorganisms is killed, although not all microorganisms are necessarily killed. In other cases it is preferred to generate a sterilizing gas mixture suitable for sterilizing an object, wherein substantially all microorganisms are killed.

It has been found that cooling the ionization chamber, e.g. the tubular portion of the ionization chamber, with forced gas, such as forced air, provides particular good disinfecting and/or sterilizing gas mixture, especially when combined with the relatively short electrical conductor.

It is thought that the forced gas cooling improves quality of the disinfecting and/or sterilizing gas mixture by beneficially influencing temperature stability of the plasma source. In this respect it has been found that gas cooling outperforms liquid cooling such as water cooling. It is thought that liquid cooling has a more corrosive effect on parts of the plasma source than the gas cooling, thus causing larger temperature variations.

Also, the relatively short electrical conductor appears to beneficially influence the quality of the disinfecting and/or sterilizing gas mixture. Although not fully understood, it is believed that the relatively short electrical conductor has a beneficial effect on electromagnetic compatibility (EMC) and/or reduces electrical impedance of the system, which can be beneficial. The reduced variations in temperature can contribute to more stable production of desired disinfecting and/or sterilizing components in the gas mixture.

Optionally, the forced gas cooling system includes a temperature control system for controlling the temperature of the plasma and/or the ionization chamber and/or the tubular portion. The temperature control system can include a temperature sensor and a controller.

Optionally, the forced gas cooling system includes a detector for detecting malfunction of the cooling system and is arranged for shutting down or reducing power of the high voltage source when a malfunction is detected. Hence overheating of the plasma source in case of a malfunction of the cooling system can be avoided.

Optionally, the electrical conductor is less than <NUM> long, preferably less than <NUM> long, more preferably less than <NUM> long.

Optionally, the plasma source includes a first end cap including the inflow port and closing the dielectric tubular portion at a first end. Optionally, the plasma source includes a second end cap including the outflow port and closing the dielectric tubular portion at a second end opposite the first end. The end caps provide an effective and mechanically simple way of providing the inflow port and/or outflow port to the dielectric tubular portion. Preferably, the first and/or second end cap is made of an electrically insulating material.

Optionally, the dielectric tube includes a wall of quartz or a glass, such as a borosilicate glass, such as Pyrex® or Duran®.

Optionally, the plasma source includes a, e.g. metal, housing. Optionally, the ionization chamber, the high voltage source, and at least part of the forced gas cooling system are included in the housing. Hence a plasma source can be provided that can easily be installed and/or replaced. Also, when the housing is a metal housing EMC can easily be obtained.

The gas or gas mixture fed to the inflow port can be a humidified gas or gas mixture, such as humidified air. The gas or gas mixture can have a predetermined specific humidity, e.g. of between <NUM> to <NUM> grams of water vapor per kilogram of gas, such as about <NUM> grams of water vapor per kilogram of gas. The gas or gas mixture can be humidified e.g. as described in copending <CIT>, incorporated herein by reference.

According to a second aspect is provided a sterilization apparatus for sterilizing medical instruments, including a plasma source as described hereinabove.

According to a third aspect is provided a method for generating a disinfecting gas mixture. The method includes feeding a gas or gas mixture through a dielectric tubular portion having a first electrode positioned inside the dielectric tubular portion, and a second electrode positioned outside the dielectric tubular portion. The method includes applying a high voltage difference between the first and second electrodes. The method includes
cooling the dielectric tubular portion using a forced gas cooling system, wherein the forced gas cooling system comprises an elongate funnel having two sidewalls tapering towards the dielectric tubular portion and extending along a longitudinal axis of the dielectric tubular portion, wherein at least one fan blows the cooling gas flow into a wide end of the funnel, causing a concentrated and/or accelerated flow of the cooling gas to exit a narrow end of the funnel to impinge one side of the tubular portion in a direction orthogonal to the longitudinal axis, the impinging gas thereafter flowing around the tubular portion to another side of the tubular portion, opposite said one side, thereafter being directed orthogonally away from the tubular portion.

Optionally, the method includes providing the high voltage to the first or second electrode via a relatively short electrical conductor.

It will be appreciated that any of the aspects, features and options described in view of the plasma source apply equally to the sterilization apparatus and the method, and vice versa. It will also be clear that any one or more of the above aspects, features and options can be combined.

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings in which:.

<FIG> shows a schematic representation of a plasma source <NUM> for generating a disinfecting and/or sterilizing gas mixture. The plasma source <NUM> includes an ionization chamber <NUM>. The ionization chamber <NUM> here is bounded by walls. A first wall is formed by a dielectric tubular portion <NUM>. The dielectric tube can e.g. include, or be, a glass tube, e.g. made of quartz or glass, such a borosilicate glass, such as Pyrex® or Duran®.

In this example, a second wall is formed by a first end cap <NUM> closing the dielectric tubular portion <NUM> at a first end. In this example a third wall is formed by a second end cap <NUM> closing the dielectric tubular portion <NUM> at a second end opposite the first end. Here the end caps <NUM>, <NUM> are connected to the tubular portion <NUM> in a gastight manner. Here a seal, such as an O-ring <NUM> is provided between the end cap <NUM>, <NUM> and the tubular portion <NUM>.

The ionization chamber <NUM> includes an inflow port <NUM> for feeding a gas or gas mixture into the chamber <NUM>. Here, the inflow port is positioned at the first end of the tubular portion. In this example, the inflow port <NUM> forms part of the first end cap <NUM>. The ionization chamber <NUM> includes an outflow port <NUM> for exhausting the sterilizing gas out of the chamber <NUM>. Here, the outflow port <NUM> is positioned at the second end of the tubular portion <NUM>. In this example, the outflow port <NUM> forms part of the second end cap <NUM>.

The ionization chamber <NUM> includes a first electrode <NUM>. The first electrode <NUM> is positioned inside the dielectric tubular portion <NUM>. Here, the first electrode extends longitudinally within the tubular portion <NUM>, here along the axis of the tubular portion <NUM>. The first electrode <NUM> in this example is elongate, such as rod shaped. Here the first electrode <NUM> has a thicker rod diameter at the area where plasma is to be generated. In this example, the chamber <NUM> includes an electric feedthrough <NUM> forming an electrical connection from outside the chamber to the first electrode <NUM> inside the chamber <NUM>. Here the feedthrough is positioned in the first end cap <NUM>. In <FIG> a gap is drawn between the feedthrough <NUM> and the first end cap <NUM> for clarity. It will be appreciated that in reality the feedthrough forms a gas tight electrical connection from outside the chamber <NUM> to inside the chamber <NUM>. In this example both the first end cap <NUM> and the second end cap <NUM> include retainers for retaining the first electrode in its position.

The ionization chamber <NUM> includes a second electrode <NUM>. The second electrode <NUM> is positioned outside the dielectric tubular portion <NUM>. The second electrode <NUM> can be formed on an outer surface of the tubular portion <NUM>. The second electrode can be a separate part, such as a metal sheet positioned on the outer surface of the tubular portion <NUM>, such as in intimate contact with the outer surface of the tubular portion <NUM>. In this example, the second electrode <NUM> is formed as a conductive layer coated onto the outer surface of the tubular portion <NUM>, such as a metallic layer (plasma) deposited onto the outer surface. In <FIG> a gap is drawn between the second electrode <NUM> and the tubular portion <NUM> for clarity. It will be appreciated that in reality the second electrode <NUM> and the tubular portion are in contact with each other.

The plasma source <NUM> includes a high voltage source <NUM>. The high voltage source <NUM> is arranged for supplying a high voltage difference between two output terminals <NUM>, <NUM>. In this example, the first output terminal <NUM> is a high voltage output terminal, and the second output terminal <NUM> is connected or connectable to electrical ground. The high voltage supplied at the first output terminal <NUM> can be a positive high voltage or a negative high voltage. In this example, a first electrical conductor <NUM> connects the first output terminal <NUM> to the first electrode <NUM>. Here a second electrical conductor <NUM> connects the second output terminal <NUM> to the second electrode <NUM>. It will be appreciated that it is also possible that the second output terminal <NUM> and the second electrode <NUM> are both connected to electrical ground. In such case a dedicated second electrical conductor <NUM> in the form of a lead wire may be omitted.

The plasma source <NUM> includes a forced gas cooling system <NUM>. The forced gas cooling system <NUM> in <FIG> includes a fan <NUM>. The forced gas cooling system <NUM> in <FIG> further includes a guide <NUM> for guiding cooling gas, towards the chamber <NUM>. The guide <NUM> includes a funnel. <FIG> shows an exemplary three-dimensional view of a plasma source <NUM>. <FIG> illustrates a cross-section view of the forced gas cooling system <NUM> acting on the ionization chamber <NUM>. In <FIG> and <FIG> a cross section of the guide <NUM> tapers towards the chamber <NUM>. As shown in <FIG>, the guide is formed by an elongate guide or funnel extending along a length of the tubular portion <NUM>, e.g. between the end caps <NUM> and <NUM>. As shown, a length of the elongate guide or funnel may similar or the same as a length of the tubular portion <NUM>, e.g. within ±<NUM>%. In this way the cooling can take place along substantially the whole length. The forced gas cooling system comprises an elongate funnel <NUM> having two sidewalls 36a,36b tapering towards the dielectric tubular portion <NUM> and extending along the longitudinal axis. As shown, the funnel is arranged between the fan <NUM> and the dielectric tubular portion <NUM>. Also multiple fans (not shown) can be arranged along the wide end of the funnel, e.g. arranged side by side along the longitudinal axis. The cooling system is configured to force the cooling gas flow by the fan into a wide end of the funnel <NUM>, wherein the gas flow exits a narrow end of the funnel to impinge one side of the tubular portion orthogonal to the longitudinal axis. For example, the wide end of the funnel <NUM> is wider than the narrow end by at least a factor <NUM> (<NUM>%), <NUM> (<NUM>%), <NUM> (twice as wide), or more. Accordingly, a relatively high gas flow can be easily established at or near the tubular portion <NUM>. For example, the gas flow can be guided around the tube (e.g. in a split gas flow) from said one side to an opposite side of the tubular portion and carrying heat away from the ionization chamber <NUM>. Additionally to the shown gas flow, also other or further gas flows can be established, e.g. by a fan directing a gas flow away from the ionization chamber <NUM>. For example, one or more fans can be arranged for forcing a gas flow into and/or out of the housing <NUM>.

In the example of <FIG> the plasma source <NUM> includes a housing <NUM>, such as a metallic housing, e.g. shielding electromagnetic radiation. In this example, the ionization chamber <NUM>, the high voltage source <NUM>, and at least part of the forced gas cooling system <NUM> are included in the housing <NUM>. In this particular example, the fan <NUM> forms part of the housing <NUM>. In <FIG> the housing <NUM> is shown as transparent for clarity.

The plasma source <NUM> as described thus far can be used as follows in a method <NUM> for generating a disinfecting and/or sterilizing gas mixture, also see <FIG>. A gas or gas mixture, such as air, e.g. air having a predetermined specific humidity, is fed <NUM> into the ionization chamber <NUM> via the inflow port <NUM>. In the ionization chamber <NUM> a plasma is generated <NUM> by applying a high voltage difference between the first electrode <NUM> and the second electrode <NUM>. As a result the gas or gas mixture flowing through the ionization chamber <NUM> is at least partially ionized to form the disinfecting and/or sterilizing gas mixture. The disinfecting and/or sterilizing gas mixture flows <NUM> out of the ionization chamber via the outflow port <NUM>.

During ionization, i.e. during generation of the plasma, the ionization chamber is cooled <NUM> using the forced gas cooling system <NUM>. In this example, the fan <NUM> generates a stream of air blowing towards the ionization chamber <NUM>. Here, the stream of air is directed towards the ionization chamber, e.g. towards the tubular portion <NUM>, by the guides <NUM>. Here, the stream of air is directed in a direction substantially orthogonal to a longitudinal axis of the tubular portion <NUM>, here perpendicular to the longitudinal axis of the tubular portion <NUM>. In principle, the forced gas cooling system can also be arranged for forcing a cooling gas flow onto the dielectric tubular portion in a direction substantially parallel to a longitudinal axis of the tubular portion. However, by blowing the gas orthogonal to the tubular portion, heat can be more quickly dissipated and/or more homogenous. For example, the orthogonally flowing heated gas can immediately leave the vicinity of the tubular portion compared to heated gas flowing along a length of the tube. For example, the orthogonally flowing gas can have a substantially uniform temperature along the length of the tube compared to a gas flowing heating up as it flows along the length of the tube. By using the forced gas cooling, the temperature of the ionization chamber, and the gas or gas mixture therein, can be maintained substantially constant. It has been found that this has a beneficial effect on the quality of the disinfecting and/or sterilizing gas mixture.

It has also been found that providing the first electrical conductor <NUM>, providing the high voltage, having a relatively short length appears to beneficially influence the quality of the disinfecting and/or sterilizing gas mixture. Although not fully understood, it is believed that the relatively short electrical conductor reduces variations in supply voltage which reduces the variations in temperature. The reduced variations in temperature can contribute to more stable production of desired disinfecting and/or sterilizing components in the gas mixture. Here the relatively short length is a length of <NUM> or less, preferably <NUM> or less, more preferably <NUM> or less. It will be appreciated that it is possible that the first output terminal <NUM> is directly connected to the first electrode <NUM>. Then the length of the first electrical conductor <NUM> is zero. The second output terminal <NUM> can also be directly connected to the second electrode <NUM>. Then the length of the second electrical conductor <NUM> is zero.

The forced gas cooling system <NUM> cooling the chamber <NUM>, such as cooling the outside of the tubular portion <NUM>, while the plasma is being generated, can cause a gradient in temperature in the ionization chamber <NUM>.

The forced gas cooling system <NUM> can include a temperature control system <NUM> for controlling the temperature of the plasma and/or the ionization chamber <NUM> and/or the tubular portion <NUM>. The temperature control system <NUM> can include a temperature sensor <NUM>. The sensor <NUM> can e.g. be mounted inside the ionization chamber <NUM>, to an inner surface or outer surface of the tubular portion, or in the proximity of the tubular portion <NUM> outside the chamber <NUM>. Alternatively, or additionally, a temperature sensor <NUM> can be placed in the gas stream output from the ionization chamber <NUM>. Controlling the temperature of the plasma, e.g. by controlling the temperature of the ionization chamber <NUM> or the tubular portion <NUM>, can provide two advantages. The controlled temperature of the plasma aids in beneficially influencing temperature stability of the plasma source. Also, by adjusting the setpoint of the controlled temperature of the plasma a quality of the disinfecting and/or sterilizing gas mixture, e.g. a composition of the disinfecting and/or sterilizing gas mixture, can be selected.

The forced gas cooling system <NUM> can include a detection system <NUM> for detecting malfunction of the cooling system. The detection system <NUM> can be arranged for shutting down or reducing power of the high voltage source <NUM> when a malfunction of the cooling system <NUM> is detected. Hence overheating of the plasma source in case of a malfunction of the cooling system <NUM> can be avoided. The detection system can include a detector <NUM> for detecting malfunction of the cooling system <NUM>. The detector <NUM> can include a gas flow sensor for monitoring flowing of the cooling gas. The detector <NUM> can include a current sensor for sensing a motor current of the fan <NUM>. The detector <NUM> can include a temperature sensor, e.g. the sensor <NUM>, for sensing a temperature of the plasma source <NUM>, e.g. a temperature of the chamber <NUM>, the tubular portion <NUM> and/or the housing <NUM>. The detector <NUM> can e.g. be a thermal switch.

<FIG> shows an example of a sterilization apparatus <NUM> for sterilizing medical instruments <NUM>, such as dental instruments. The sterilization apparatus <NUM> includes a plasma source <NUM> as described in view of <FIG> and <FIG>. The sterilization apparatus <NUM> includes a sterilization chamber <NUM>. The disinfecting and/or sterilizing gas mixture is fed from the plasma source <NUM> into the sterilization chamber <NUM>, towards the instruments <NUM> included in the chamber <NUM>.

Herein, the invention is described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made.

In the example of <FIG> the first electrode is connected to high voltage and the second electrode is connected to electrical ground. It will be appreciated that it is also possible that the first electrode is connected to electrical ground and the second electrode is connected to high voltage. It is also possible that both the first and second electrodes are connected to high voltage, for example one to positive high voltage and the other to negative high voltage. Preferably the electrical conductor(s) providing the high voltage to the first or second electrode has the relatively short length of <NUM> or less, preferably <NUM> or less, more preferably <NUM> or less.

Claim 1:
A plasma source (<NUM>) for generating a disinfecting and/or sterilizing gas mixture, including:
- an ionization chamber (<NUM>) having:
- a dielectric tubular portion (<NUM>),
- an inflow port (<NUM>) for feeding a gas or gas mixture into the chamber,
- an outflow port (<NUM>) for exhausting the disinfecting and/or sterilizing gas mixture out of the chamber,
- a first electrode (<NUM>) positioned inside the dielectric tubular portion (<NUM>), and
- a second electrode (<NUM>) positioned outside the dielectric tubular portion (<NUM>);
- a high voltage source (<NUM>) having a high voltage output terminal (<NUM>, <NUM>), wherein an electrical conductor (<NUM>, <NUM>) connects the output terminal (<NUM>, <NUM>) to the first or second electrode (<NUM>, <NUM>); and
- a forced gas cooling system (<NUM>) for cooling the ionization chamber (<NUM>), characterized in that,
the forced gas cooling system is arranged for forcing a cooling gas flow onto the dielectric tubular portion (<NUM>) in a direction substantially orthogonal to a longitudinal axis of the tubular portion,
wherein the forced gas cooling system comprises an elongate funnel (<NUM>) having two sidewalls (36a, 36b) tapering towards the dielectric tubular portion (<NUM>) and extending along the longitudinal axis, said forced gas cooling system (<NUM>) further comprising at least one fan (<NUM>), wherein the funnel (<NUM>) is arranged between at least one fan (<NUM>) and the dielectric tubular portion (<NUM>) and configured to force the cooling gas flow by the fan into the funnel (<NUM>) towards its narrow end where the two sidewalls converge, wherein said narrow end has an elongate exit opening disposed adjacent the dielectric tubular portion and extending along the longitudinal axis, wherein the exit opening is arranged facing the dielectric tubular portion and configured to force the cooling gas flow exiting the opening to flow onto one side of the tubular portion in the direction substantially orthogonal to the longitudinal axis.