Patent Description:
Sterilization methods using plasma have been known in the state of the art for a long time.

<CIT> describes a sterilization method using plasma for articles packaged in a porous package which allows the sterilization of the articles enclosed therein.

Sterilization apparatuses and methods using plasma are further described by <CIT>, <CIT>, <CIT> and <CIT>.

The solutions known in the state of the art have various disadvantages.

One disadvantage of the sterilization methods known in the state of the art is that they are not suitable to be used on an industrial scale since they involve long and laborious procedures.

For example, document <CIT> describes a method in which it is provided to sterilize an object contained in a flexible bag, in which it is provided to create a vacuum, where the plasma is conveyed directly. It is clear that such a solution is laborious and complex from the point of view of the plant and the procedures for its implementation, and therefore is not suitable to be used on an industrial scale.

Another disadvantage of the sterilization methods known in the state of the art is that they provide plasma generation conditions that can generate side effects on the objects to be sterilized.

For example, documents <CIT>, <CIT> describe methods in which it is provided to introduce respectively water vapor and wet gas in the sterilization chamber, and then apply an adequate energy inside the chamber itself.

The humidity present in the sterilization chamber causes the disadvantage that the objects to be sterilized can suffer corrosive phenomena by the acids formed by the discharge in the presence of water vapor, in particular if they comprise metal parts.

Another disadvantage of these methods is due to the fact that the energy used to generate the plasma is applied directly in the sterilization chamber where the objects are placed, which can be subjected to very significant thermal or electromagnetic shocks, which can damage them.

Finally, document <CIT> describes a controlled temperature sterilization method using plasma which requires an expensive and bulky apparatus. Among other things, the apparatus requires means to cool the gases to reduce their temperature, and a particular disposition of pipes able to facilitate the dissipation of the heat from the gases involved in the process.

As known in the state of the art, obtaining the plasma is influenced by many different factors. Among the main ones are the voltage applied to the electrodes, the very geometry of the electrodes, the waveform of the voltage, its value and frequency, its application time, and the composition of the starting gas.

One disadvantage of the sterilization methods using plasma known in the state of the art is that the generation of plasma is a complex and delicate step which requires adjusting the different factors mentioned above optimally, in order to obtain the desired sterilizing effect without creating conditions that can damage the objects that have to be sterilized.

In fact, it is known that the use of certain gases that are suitable to obtain the desired sterilization effect, such as for example ethylene oxide (EtO), presents considerable disadvantages.

A first disadvantage linked to the use of this gas is that it is toxic, having in particular carcinogenic effects. When sterilization is obtained using ethylene oxide, in the presence or absence of discharges, significant traces of this gas have been found on the surfaces of the sterilized objects. Consequently, its use is to be avoided as it is evident that it can be harmful to the health of people who come into contact with the objects.

Another disadvantage linked to the use of this gas is that it is highly flammable. Storing large quantities of this gas is therefore extremely dangerous, and there are considerable risks for the safety of operators working in sterilization plants. Furthermore, the correct management of this material is expensive as it has to comply with the reference standards of personal and environmental safety.

<CIT> discloses a sterilizer including a supply source for a sterilizing agent, a first and a second sterilization chamber each adapted to be filled with the sterilizing agent while placing an object therein, a first pipe line connecting the supply source and each of the first and second sterilization chambers, a second pipe line connecting the first and second sterilization chambers, and a supply mechanism adapted to allow a residual part of the sterilizing agent used for the sterilization treatment in the first sterilization chamber to be introduced into the second sterilization chamber via the second pipe line. Such document does not provide information about the shape and the disposition of a plurality of electrodes in the sterilizer.

<CIT> discloses a sterilizing system having a sterilization chamber and a method for sterilizing an item in the sterilization chamber. The method includes the steps of loading the item into the sterilization chamber, evacuating gas from the sterilization chamber, preparing sterilant gas by use of plasma, and filling the sterilization chamber with the sterilant gas to a preset pressure. Further included are steps of waiting a preset time interval to thereby accomplish an intended sterilization and evacuating the sterilant gas from the sterilization chamber. This document shows a couple of electrodes placed in the same wall of the sterilizer.

<CIT> discloses methods and systems for decontaminating food products that include arranging a first electrode and second electrode in an asymmetric relationship on opposite sides of a dielectric layer, providing an insulating covering on the first electrode, and applying a power source to the first and second electrodes. A voltage is applied between the first electrode and the second electrode in ambient atmosphere to create a cold plasma and a food product is decontaminated by the plasma.

There is therefore the need to perfect the sterilization methods using plasma known in the state of the art, so as to overcome at least one of its disadvantages.

It is a purpose of the present invention to perfect a reliable sterilization method using plasma which allows to sterilize the objects effectively with sterilization cycles of reduced duration.

Another purpose of the present invention is to perfect a sterilization method using plasma able to adapt to pre-existing plants and structures, without the need to perform long, complicated and expensive structural adjustment operations.

Another purpose of the present invention is to perfect a safe sterilization method using plasma which does not provide the use of dangerous gases.

It is also a purpose of the present invention to perfect a sterilization method using plasma which is economical, both with regard to the gases used, and also with regard to the structure of an apparatus suitable to implement the method.

Another purpose of the present invention is to perfect a sterilization method using plasma which is suitable to be used in the context of sterilization processes on an industrial scale.

Another purpose of the present invention is to perfect a sterilization method using plasma which is not polluting, since no toxic or polluting gas is released into the atmosphere.

In accordance with the above purposes, a sterilization method using plasma is provided for sterilizing objects, comprising the following steps: introducing the objects to be sterilized in a sterilization chamber defined by a closed environment, bringing the sterilization chamber to pressures lower than atmospheric pressure, activating a plasma generator device disposed on at least one feed pipe leading into the sterilization chamber and configured to generate one or more gaseous compounds comprising a mixture of reactive oxygen species (ROS) and of reactive nitrogen species (RNS), feeding dehumidified air along the feed pipe and putting the latter in communication with the sterilization chamber so that the dehumidified air is the carrier fluid which conveys the gaseous compounds from the sterilization pipe to the sterilization chamber.

According to a characteristic aspect of the present invention, the method comprises a control step, in which it is provided to control, by means of a control unit, the electric power used to produce the plasma during the activation step of the plasma generator device, as a function of the composition and/or the quantity of reactive species present in the sterilization chamber, detected by suitable sensor means.

The feed pipe has a square section. The plasma generator device comprises four electrodes, disposed on walls of the feed pipe, according to a configuration able to optimize the electro-hydrodynamic effect, so as to increase the quantity of reactive species produced in the unit of time, wherein each electrode is disposed on a respective wall of the feed pipe. Each electrode has a circular or polygonal shape defining a configuration of symmetry with respect to central axis of symmetry.

According to embodiments described here, during the activation step of the plasma generator device, in correspondence with each electrode, a jet of the mixture of reactive species is generated which is oriented so as to develop, at least partly, coaxially to the central axis of symmetry, being directed away from the electrode, toward a longitudinal axis of development of the feed pipe, according to a direction substantially perpendicular to the latter.

Advantageously, the electrodes are each disposed on a dielectric material.

In one embodiment, during the activation step, each of the electrodes is subjected to an electric field, suitably regulated during the control step, which is comprised between <NUM><NUM> and <NUM><NUM> volts/meter, preferably between <NUM><NUM> and <NUM><NUM> volts/meter.

According to some embodiments, once the activation step of the plasma generator device is terminated, a deactivation step of the latter is provided, in which it is provided to interrupt the electric power of the electrodes.

In one embodiment, the deactivation step provides to interrupt the flow connection between the feed pipe and the sterilization chamber and, subsequently, to wait for a deposition time during which the mixture of reactive species is deposited on the objects to be sterilized in order to perform their sterilizing function, and once the deposition time has elapsed, to remove the exhausted gases in order to remove the reactive species and the reaction products present.

In one embodiment, the exhausted gases are reintroduced into the feed pipe to be fed back to the sterilization chamber.

In another embodiment, the exhausted gases are chemically processed so as to reduce, or even eliminate, possible pollutant substances, before re-introducing them into the atmosphere.

According to another aspect of the present invention, an apparatus is provided for sterilizing objects, in particular loose objects or packaged in blisters or pouches or sachets, suitable to actuate the sterilization method using plasma mentioned above, and comprising: a closed chamber to sterilize the objects, a feed pipe to convey air toward the sterilization chamber, a plasma generator device to generate one or more gaseous compounds comprising a mixture of reactive oxygen species and reactive nitrogen species and disposed in the feed pipe, pumping members and valve units configured to control the flow of air and gaseous compounds to and from the sterilization chamber, sensor means configured to detect a quantity of the reactive oxygen species and reactive nitrogen species present inside the sterilization chamber, and a control unit configured to control at least the electric power used to produce the plasma during the activation step of the plasma generator device.

The feed pipe has a square section and the plasma generator device comprises four electrodes placed each on a respective wall of the feed pipe, and each electrode has a circular or polygonal shape defining a configuration of symmetry with respect to a central axis of symmetry.

One advantage of the sterilization method using plasma according to the present invention is that it is reliable and safe, as well as economical.

Another advantage of the sterilization method according to the present invention is that it is environmentally friendly.

These advantages are mainly correlated to the fact that the method according to the present invention provides to use air as a reaction gas which cooperates with the plasma produced by the plasma generator device. Thanks to the latter, the air is substantially "activated", that is, enriched with gaseous compounds including a mixture of reactive substances, in particular of oxygen and of nitrogen.

It is evident that air is a non-polluting and absolutely economical gas, as it is freely available in large quantities.

It should be noted that these advantages also occur in the embodiments provided in accordance with variant embodiments of the present description, in which the air is not atmospheric air, but is instead the so-called "synthetic" air, that is, pre-treated air with a determinate chemical formula free of impurities and atmospheric pollutants. It is clear that in this case the method requires purchasing cylinders containing synthetic air, which is therefore not taken from the atmosphere, but this is in any case more economical than purchasing other particular gases.

Furthermore, the sterilization method according to the present invention is advantageously very safe for the safety and health of both operators and also end users. In fact, the fact that toxic gases are not used, such as for example ethylene oxide (EtO) used in many methods known in the state of the art, guarantees both the safety of the sterilization plants, and therefore of the operators who work there, and also that of the end users who will have to take and handle the sterilized objects (for example, blisters of capsules or tablets). Contrary to what typically happens in the state of the art, thanks to the fact that in the method according to the present invention toxic gases that are persistent over time are not used, there is no risk of residues of such gases, which can harm - even seriously - human health, being deposited on the sterilized objects.

Due to the fact that the sterilization method according to the present invention uses dehumidified air, another advantage is that it does not damage the objects to be sterilized by corrosive phenomena that could be triggered by the humidity present in the atmospheric air.

A further advantage of the sterilization method according to the present invention is that it can be easily implemented on an industrial scale, to sterilize, by means of sterilization cycles with a duration compatible with other working steps of the objects, large quantities of objects, possibly disposed on pallets, or other similar supports.

Another advantage of the method according to the present invention is that it has an advantageous configuration of the plasma generator device which allows to optimize the electro-hydrodynamic aspect of the flow formed by the gaseous compounds (comprising the mixture of reactive oxygen species and of reactive nitrogen species) and by the air. In this way, thanks to the conformation of the electrodes, to their corresponding disposition with respect to the feed pipe, and to the values of the electric field mentioned above to which the electrodes are subjected, it is possible to produce a greater number of reactive oxygen species and of reactive nitrogen species in the unit of time, and their transfer toward the sterilization chamber is faster and more effective.

A further advantage of the present invention is that it allows to implement the sterilization method described above by means of a simple and economical sterilization apparatus.

In fact, the sterilization apparatus according to the present invention can advantageously be easily adapted to existing plant solutions or to existing machines commonly used in the context of industrial or experimental sterilization processes, without requiring complicated and costly operations to adapt their structure.

These and other aspects, characteristics and advantages of the present disclosure will be better understood with reference to the following description, drawings and attached claims. The drawings, which are integrated and form part of the present description, show some embodiments of the present invention, and together with the description, are intended to describe the principles of the disclosure.

The various aspects and characteristics described in the present description can be applied individually where possible. These individual aspects, for example aspects and characteristics described in the description or in the attached dependent claims, can be the object of divisional applications.

It is understood that any aspect or characteristic that is discovered, during the patenting process, to be already known, shall not be claimed and shall be the object of a disclaimer.

The embodiments described here concern a method for processing data, of which some particular embodiments will be described below, by way of a non-limiting example.

The various embodiments described in detail below concern a method and apparatus for sterilizing objects, for example blisters containing a plurality of tablets or capsules or pills.

It is clear that the method and the apparatus according to the present invention can be advantageously also used in any other sector, different from the pharmaceutical sector, without departing from the field of protection of the present invention.

With reference to <FIG>, this shows a block diagram representative of the functioning of a sterilization apparatus according to the present invention, indicated as a whole with reference number <NUM>.

The sterilization apparatus <NUM> comprises a humidity abatement device <NUM>, of a type known in the state of the art.

The sterilization apparatus <NUM> also comprises a plasma generator device <NUM>, which will be described in greater detail below with particular reference to <FIG>, and a sterilization chamber <NUM> configured to receive the objects to be sterilized.

One or more sensors <NUM> are disposed in the sterilization chamber <NUM>, of a type known in the state of the art, configured to detect the presence of reactive species, their quantity and the respective chemical composition. For example, the sensors <NUM> can comprise optical sensors, absorption sensors, etc..

The sensors <NUM> are operatively connected to a control unit <NUM>, configured to command the adjustment of the plasma generator device <NUM>, based on the information received from the sensors <NUM>.

The sterilization apparatus <NUM> comprises a pollutant abatement device <NUM>, associated with the sterilization chamber <NUM> in a suitable position such that it is passed through by the exhausted gaseous components intended to leave the sterilization chamber <NUM> to be released into the atmosphere. In particular, the pollutant abatement device <NUM> is configured to abate.

In one embodiment, the pollutant abatement device <NUM>, of a type known in the state of the art, exerts a mechanical action and comprises one or more filters with apertures of suitable sizes according to the nature of the particles of the polluting substances to be treated.

In another embodiment, the pollutant abatement device <NUM>, of a type known in the state of the art, exerts a chemical action, thanks to which the pollutants interact with suitable reactants able to abate their polluting charge.

The sterilization apparatus <NUM> also comprises a plurality of pumping members and valve elements, of a type known in the state of the art and not shown, which are suitably disposed on the entry pipes of the gaseous components, and on their exit pipes, into/from the sterilization chamber <NUM> so as to suitably allow a sealed insulation which hermetically seals the sterilization chamber itself.

With reference to <FIG>, an example of a sterilization apparatus <NUM> is shown in which the sterilization chamber <NUM> is configured as a large closed compartment. In this embodiment, the sizes of the sterilization chamber <NUM> are comparable to those of a room, or of a space, for example, of up to a few meters for each side.

It is evident that, in other equivalent embodiments, sterilization chambers <NUM> with much larger or smaller sizes can be provided, for example comparable to those of a device resting on a laboratory bench.

In the embodiment of <FIG>, suitable to implement the method according to the present invention on an industrial scale, a plurality of objects <NUM> are disposed inside the sterilization chamber <NUM>, disposed in order on four pallets <NUM>. For example, the objects <NUM> can be disposed in an orderly manner on a plurality of levels, above each pallet <NUM>.

In this embodiment, the sterilization chamber <NUM> comprises access means that can be hermetically sealed, not shown, which are suitably sized so as to allow access to the sterilization chamber <NUM> to loading vehicles suitable to transport the pallets <NUM>.

The sterilization apparatus <NUM> comprises at least one feed pipe <NUM>, configured to introduce gas into the sterilization chamber <NUM>.

By way of a non-limiting example, the embodiment shown provides three feed pipes <NUM> with a square section (<FIG>), disposed in parallel.

It is evident that other equivalent embodiments can provide a single feed pipe <NUM>, or a plurality of feed pipes <NUM>, in a number different from three.

According to an alternative embodiment, the feed pipes <NUM> can be disposed according to a parallel configuration, in which a single gas collector is provided, from which the various feed pipes <NUM> depart.

In other equivalent embodiments (not falling under the scope of the appended claims), the feed pipes <NUM> can have a cross-section other than square, for example circular.

According to some embodiments, in proximity to the connection between the feed pipes <NUM> and the sterilization chamber <NUM> suitable valve elements are provided, of a type known in the state of the art and not shown, able to selectively separate the respective feed pipe <NUM> from the sterilization chamber <NUM>.

A respective plasma generator device <NUM> is associated with each feed pipe <NUM> in proximity to the sterilization chamber <NUM>, which have been schematized with dashed rectangles in <FIG>.

According to embodiments provided here, the sterilization apparatus <NUM> comprises an exit pipe <NUM> configured to release the exhausted gases from the sterilization chamber <NUM>, which can be selectively put in flow connection with the latter.

According to embodiments described here, the sterilization apparatus <NUM> comprises a vacuum pump <NUM>, of a type known in the state of the art, suitable to bring the sterilization chamber <NUM> into a condition of depression, or vacuum condition, that is, to a lower pressure than atmospheric pressure, according to modes known in the state of the art.

The plasma generator device <NUM> comprises a plurality of electrodes <NUM>. More precisely, each plasma generator device <NUM> comprises four electrodes <NUM>.

In one embodiment, each electrode <NUM> is disposed on a respective wall 17A, 17B, 17C, 17D of the feed pipe <NUM>.

Each electrode <NUM> is connected to electric supply means, according to modes known in the state of the art, which apply a certain voltage to generate a suitable electric field.

In a preferred embodiment, the electrodes <NUM> are of the type described in the scientific publication by <NPL>), to be considered here incorporated in its entirety as reference.

Two variant embodiments of an electrode <NUM> according to embodiments provided according to the present invention, respectively with reference to <FIG> are described below.

<FIG> shows an electrode <NUM> disposed on a plate <NUM> of dielectric material, for example made of a material selected from the polychlorinated biphenyl (PCB) family, with a thickness for example of about <NUM>. The electrode <NUM> is configured as an annular element made of copper with a thickness of about <NUM> microns, an internal diameter of about <NUM> and an amplitude of about <NUM>.

<FIG> shows an electrode <NUM> disposed on a plate <NUM> of dielectric material, for example made of polyvinyl chloride (PVC) or glass. The electrode <NUM> is configured as an octagonal shaped element made of copper with a thickness of about <NUM> microns, an amplitude of about <NUM>, and an internal length of each side of about <NUM>.

It should be noted that in both these configurations the electrode <NUM> is shaped so as to define a configuration of symmetry with respect to a central axis of symmetry Y (shown in <FIG>).

Applying a differential voltage between the electrode <NUM> and the lower face of the plate <NUM> allows to generate a plasma, according to modes known in the state of the art, which develops, inside the electrode <NUM>, on an area that follows the shape of the electrode, which has been filled with dashes in the drawings and is indicated with reference number <NUM>.

As is known, the plasma <NUM> generates a mixture of reactive species which move away from the electrode <NUM> according to a jet which is schematized with the combination of four curved arrows and is indicated as a whole with reference number <NUM>.

Thanks to the peculiar geometry of the electrodes <NUM> described above, the jet <NUM> is oriented so as to develop, at least partly, coaxially with the central axis of symmetry Y. In particular, the jet <NUM> is directed away from the electrode <NUM> toward an axis of longitudinal development X of the feed pipe <NUM>, in a direction substantially perpendicular to the latter.

The sterilization method using plasma according to the present invention is described below.

Initially, the method provides to introduce the objects <NUM> in the sterilization chamber <NUM>, which, after having been hermetically closed, is put in a vacuum condition.

Subsequently, the sterilization method using plasma provides to activate the plasma generator device <NUM>. The activation of the latter allows to generate one or more gaseous compounds comprising a mixture of reactive oxygen species (ROS), and reactive nitrogen species (RNS). In particular, the reactive oxygen species and the reactive nitrogen species generated by the plasma comprise ozone (O<NUM>), dinitrogen oxide (N<NUM>O), nitrogen pentoxide (N<NUM>O<NUM>) and nitric acid (HNO<NUM>).

According to embodiments provided here, the activation of the plasma generator device <NUM> also allows the generation of free ions, in stable form, which remain stable long enough to reach the sterilization chamber <NUM>. It has been observed, in particular, that the free ions comprise particles with a positive charge, such as for example oxonium (H<NUM>O+). Experimental tests have allowed to verify that the presence of these positively charged particles allows to increase the effectiveness of the sterilizing action of the plasma. In other words, if - in addition to the gaseous compounds comprising the mixture of reactive oxygen species and reactive nitrogen species - the free ions in stable form mentioned above are present, it is possible to sterilize the same quantity of objects <NUM> in a shorter time, with the same effectiveness of the sterilization action.

With reference to <FIG>, the graph shows the trend of the ozone concentration as a function of the discharge time, for four different values of activation time of the plasma generator device <NUM> (respectively at <NUM>%, <NUM>%, <NUM>% and <NUM>%). The curves were respectively obtained by electrically powering the electrode <NUM> for a fraction of time during which the plasma generator device <NUM> is active equal respectively to the percentage value indicated.

Experimental tests show that the <NUM>% curve is the best compromise that allows to obtain an optimal ozone concentration.

It is noted that the experimental tests performed have yielded excellent results. In fact, the ozone concentration values remain approximately equal to, or higher than, <NUM>. 5x10<NUM> cm-<NUM> in the period from <NUM> to <NUM> of the discharge time, for the <NUM>% curve.

These concentration values are advantageously much higher, from three to ten times, than the typical concentrations of other reactive species generated by the plasma generator device <NUM>.

The method then provides to feed air along the feed pipe <NUM>, which is put in communication with the sterilization chamber <NUM>.

According to a preferred embodiment, it is provided to feed dehumidified air along the feed pipe <NUM>.

In one embodiment, the dehumidified air is obtained starting from ambient air that passes through the humidity abatement device <NUM>, disposed upstream of the feed pipe <NUM>.

In one embodiment, the dehumidified air is obtained from pressurized containers (for example cylinders) of synthetic air, directly connected to the feed pipe <NUM>.

The dehumidified air passes through the feed pipe <NUM> in the direction indicated by arrows F in <FIG>, that is, parallel to the longitudinal axis of development X.

The flow of dehumidified air defines the carrier fluid which conveys the gaseous compounds, that is, the reactive species and possibly the free ions mentioned above, toward the sterilization chamber <NUM>. It has been observed that the configuration described above, in which the jets <NUM> are oriented substantially orthogonal with respect to the flow of dehumidified air, is advantageous as it allows to optimize the electro-hydrodynamic effect so as to increase the quantity of reactive species produced in the unit of time.

According to some embodiments, the method provides to maintain flow communication between the feed pipe <NUM> and the sterilization chamber <NUM> for a determinate period of time, such as to allow the gaseous compounds to enter the sterilization chamber <NUM> and to be distributed homogeneously in the latter. In one embodiment, the determinate period of time is, for example, equal to or greater than the time during which the plasma generator device <NUM> remains active. In other words, the determinate period of time has to be sufficient to allow the substantial saturation of the sterilization chamber with the gaseous compounds mentioned above.

According to embodiments of the method according to the present invention, it is provided to control, by means of the control unit <NUM>, the electric power used to produce the plasma as a function of the composition and/or the quantity of reactive species present in the sterilization chamber <NUM>, detected by the sensors <NUM>.

Experimental tests have allowed to identify optimal values of the electric power with which to power the electrodes <NUM> during the activation step of the plasma generator device <NUM> in order to maximize the quantity of reactive species produced in the unit of time.

In one embodiment, the optimum values provide to subject each electrode <NUM> to an electric field which is comprised between <NUM><NUM> and <NUM><NUM> volts/meter, preferably comprised between <NUM><NUM> and <NUM><NUM> volts/meter.

According to some embodiments, the electric field values can be obtained by applying to the electrodes <NUM> voltage values comprised between <NUM> V and <NUM> kV and frequencies comprised between <NUM> and <NUM>.

Once the activation step of the plasma generator device <NUM> has ended, it is provided to interrupt the electric power supply of the electrodes <NUM>, thus deactivating the plasma generator device <NUM>.

The deactivation step of the plasma generator device <NUM> provides to interrupt the flow connection between the feed pipe <NUM> and the sterilization chamber <NUM> by driving suitable valve elements and subsequently waiting for a deposition time during which the mixture of reactive species, and possibly the free ions, is/are deposited on the objects <NUM> to be sterilized to perform their sterilizing function. Once the deposition time has elapsed, the method provides a step of removing the exhausted gases in order to remove the reactive species and the possible free ions still present in the sterilization chamber <NUM>, again returned to a vacuum condition by means of the vacuum pump <NUM>.

In one embodiment, the step of removing the exhausted gases provides to reintroduce the gases into the feed pipe <NUM>, upstream of the plasma generator device <NUM> (<FIG>).

In another embodiment, alternative to or actuated together with the previous one, the step of removing the exhausted gases provides to release the gases into the atmosphere by means of the exit pipe <NUM>, after performing suitable treatments to reduce, or even eliminate, possible polluting substances in order to respect the legal limits provided (<FIG>).

Finally, before the operator removes the sterilized objects <NUM>, the method provides to bring the sterilization chamber <NUM> back to atmospheric pressure.

It is clear that modifications and/or additions of steps or parts may be made to the sterilization method and apparatus as described heretofore, without departing from the field and scope of the present invention.

Claim 1:
Sterilization method using plasma for sterilizing objects (<NUM>), comprising the steps of:
- introducing the objects (<NUM>) to be sterilized into a sterilization chamber (<NUM>) defined by an environment hermetically separated from the outside,
- bringing said sterilization chamber (<NUM>) to pressures lower than atmospheric pressure by means of a vacuum pump (<NUM>),
- activating a plasma generator device (<NUM>) disposed on at least one feed pipe (<NUM>) leading to said sterilization chamber (<NUM>) so that one or more gaseous compounds comprising a mixture of reactive oxygen species (ROS) and of reactive nitrogen species (RNS), and optionally free ions with positive charge, are generated by the plasma generator device (<NUM>) and conveyed to said sterilization chamber (<NUM>),
- feeding air along said at least one feed pipe (<NUM>) and putting the latter in communication with said sterilization chamber (<NUM>) for a determinate period of time to allow said gaseous compounds to enter said sterilization chamber (<NUM>) and spread in a substantially homogeneous way therein, said period of time being, for example, equal to or more than the activation time of said plasma generator device (<NUM>), said air being the carrier fluid which conveys the gaseous compounds into said sterilization chamber (<NUM>),
- controlling, by means of a control unit (<NUM>), the electric power used to produce the plasma during said activation step of the plasma generator device (<NUM>) as a function of the composition and/or the quantity of reactive species present in said sterilization chamber (<NUM>), detected by suitable sensor means (<NUM>);
characterized in that said feed pipe (<NUM>) has a square section, in that said plasma generator device (<NUM>) comprises four electrodes (<NUM>) on the walls (17A, 17B, 17C, 17D) of said feed pipe (<NUM>), according to a configuration able to optimize the electro-hydrodynamic effect so as to increase the quantity of reactive species produced in the unit of time, wherein each electrode (<NUM>) is disposed on a respective wall (17A, 17B, 17C, 17D) of said feed pipe (<NUM>);
and in that each of said electrodes (<NUM>) has a circular or polygonal shape defining a configuration of symmetry with respect to a central axis of symmetry (Y).