METHOD AND APPARATUS FOR STERILIZING CONTAMINATED EQUIPMENT

Field of the Invention

The invention relates to the sterilization of equipment such as medical equipment including surgical equipment, gloves and food preparation equipment and utensils.

Background of the Invention

Hospitals and other related medical facilities clearly attract and retain microorganisms and enzymes which must be removed so as to maintain a hygienic environment. Many methods of sterilization are known such as the application of heat and pressure through high pressure steam or merely the application of heat such as baking ovens etc. Whilst the spread of microorganisms is vast, the equipment that can suffer heat pressure and moisture are more limited and, therefore, these traditional methods of sterilization will not work on certain heat and moisture sensitive items without causing damage.

Other methods for the sterilization of apparatus, materials, gases, liquids and waste products include compressed industrial steam for up to 20-30 minutes, administering antibiotics, chlorination, and irradiation with gamma-radiation or ultraviolet light.

Traditional methods such as steam/hot air sterilization whilst well established suffer from the problems of controlling the heat load associated with the steam or hot air. The risk to operators is clear, as is the restriction of such methods to articles that are not susceptible to heat damage or effect.

Further, because sterilization requires elevating the article and microorganisms to the specified temperature, there is also a time lag for the complete sterilization of such an article. For instance, such sterilization methods may take from 10 to 40 minutes.

Irradiation techniques avoid the issues of controlling heat, but are limited to exposure to a particular radiation source. Whereas heat-based methods are effective in infiltrating the entire article, after the time lag for elevating the temperature, radiation methods rely on exposing the article to the radiation. Folds, inclined surfaces and other arrangements that shield a portion of the radiation will result in incomplete sterilization.

Further radiation techniques may have a mutagen effect on pathogenic germs, increasing the threat of hyper-resistant strains of the germ developing.

It is, therefore, an object of the present invention to provide a means of sterilization that is more broadly applicable and also, can be arranged to form part of a sequential process.

Statement of Invention

In a first aspect, the invention provides a system for sterilization of an article comprising: a sterilization zone for receiving the article; apparatus for producing a corona-like discharge within said zone; apparatus for creating an isometric electric field within said zone; a delivery system for delivering the article to the zone and removing the article following sterilization.

In a second aspect, the invention provides a method for sterilizing an article comprising the steps of: delivering the article to a sterilization zone for; producing a corona- like discharge within said zone; creating an isometric electric field within said zone; said corona-like discharge and isometric electric field acting together to consequently sterilize the article.

The invention provides for three advantages, speed of sterilization, compatibility and extended applicability.

The speed of sterilization is important to make a process according to the invention adaptable for batch or continuous processes. The faster a reliable level of sterilization can be achieved, the faster articles or fluids can be processed. As will be discussed, the sterilization time taken for the invention may be in the range 1 second to 10 minutes. Comparing this to thermal methods where the environment and article must be heated, and so take much longer, and the invention clearly provides an advantage for speed.

Compatibility lies in the ability to, according to specific embodiments, use the same or similar equipment to use create the isometric electric field and produce the corona-like discharge. Other types of sterilization systems that may seek to overcome their respective shortcomings by combining with another system cannot rely on being able to use similar equipment.

The extended applicability ensures that certain contamination that is less effectively treated using one system may be more susceptible to the other. Hence, there is a synergistic effect of combining these systems by using such complimentary methods of sterilization. For instance, whilst certain articles may clear have a more uniform type of contamination, many applications may in fact be subject to a wide variety of contamination. Surgical articles may well be a good example, whereby gloves, surgical instruments etc may all come from the same hospital but used in different procedures. With systems of the prior art, different stations may be required to ensure complete sterilization within a reasonable time. More likely, the sterilization time may be extended so that less effective sterilization for some contamination, such as steam for certain microorganisms eventually are sterilized. So, when designing a sterilization system, the operator must balance the cost of additional equipment against the extra time taken for sterilization. With certain embodiments of the present invention, this balance is achieved within the same time period with no additional equipment.

The invention may be arranged to act on a variety materials, and is not limited by thermal affects. Further, sterilization according to the present invention is not limited to exposing the entire article to a single source, with the combine sterilizing effect infiltrating the article completely.

Accordingly, the system according to the present invention provides a broad based arrangement for sterilization that forms part of a processing step for a "production line" application of sterilizing medical equipment. In combination with the use of an isometric electric field, the two means of sterilization reduce the residency time for sterilization and hence may allow the flexibility for the delivery system to act as a one- off, batch or continuous process. In a further embodiment, the system or method may be used as a stand alone device for sterilizing equipment such as dental devices or placed on a pipe flow or stream to treat gases, water or other liquids .

In particular, articles such as surgical gloves may be particularly applicable for the system according to the present invention. Gloves of both synthetic, rubber and latex are both susceptible to heat and so the application of sterilization methods according to the present invention may avoid damage to said gloves and so supporting the recyclability of these gloves.

In one embodiment, the system may include a gas delivery system for directing a gas to the sterilization zone. The corona-type discharge may tend to produce ozone in quantities sufficient to assist in the sterilization of the article, in combination with the

isometric electric field. To this end, rather than rely on ambient air, the process of ozone production may further be enhanced by delivering a gas to the sterilization zone, such as air, oxygen or oxygen enhanced gas.

A potential application of the system is adapting the sterilization process to a batch or continuous process. To this end, the system according to one embodiment of the present invention may be one station within a larger process. To achieve this, the delivery system may be a conveyor to transport the article to the sterilization zone. In so doing the delivery system may keep the article within the zone for a specific amount of time, say from one second up to 10 minutes, until such time as the article is sterilized. This embodiment may be suitable for a batch type process.

Alternatively, the zone may be large enough to permit the article held within the delivery system to maintain movement, such that the speed of movement of the article is a function of the time take for sterilization and the size of the zone. For instance, for a known sterilization time, and an economically optimized sterilization zone, the speed of the article through the zone may be calculated.

In a further embodiment, the apparatus for producing the corona-like discharge may include at least one pair of electrodes, each of said pair being in close proximity to, and on opposed sides of, the zone.

Brief Description of Drawings

It will be convenient to further describe the present invention with respect to the accompanying drawings that illustrate possible arrangements of the invention. Other arrangements of the invention are possible, and consequently the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention.

Figure 1 is a schematic view of a system according to one embodiment of the present invention;

Figure 2 is a voltage -v- current characteristic for the operation of one embodiment of the present invention.

Description of Preferred Embodiment

The invention refers to a method based on the usage of ultra high voltage which produces an isometric electric field and a Corona-type discharge, for the purpose of sterilization of articles including contaminated apparatus, materials, gases, liquids and waste products with pathogen germs.

Figure 1 shows a schematic view of one embodiment of the present invention. Here electrodes 5 are provided, which may have variable forms and sizes to suit the article(s) to be sterilized. The electrodes are coupled to an ultra high voltage supply which

produces an isometric electric field and a Corona-type discharge, for a residence time in the range 1 second to 10 minutes. The precise time will be a function of, but not limited to, the type of article, the expected form of contamination, the economics of the output voltage and equipment size. In designing the system, the skilled person may consult the literature or conduct basic iterative tests to determine such parameters, which are not, in themselves, a limitation of the invention.

The ultra high voltage equipment may include functional modules, such as:

A power supply module 1, which allows the adaptation of equipment to a conventional energy supply;

A frequency control module 2, which allows the adjusting of work frequency depending on the pathogen germs class to be sterilized, and subject to the contaminated materials;

A control module for ultra high voltage 3, which produces a high voltage (for instance, 6KV-8KV), for the UHV module (see module 4 from Figure 1) and its control;

An ultra high voltage (UHV) module 4, which produces an ultra high voltage in excess of 20KV, bringing at resonation an inductance-capacitor system, which is applied afterwards to the active electrodes;

Active electrodes 5, made from alloy plates, with a matrix or array of recesses or perforations surface, with electromagnetic lens effect for electrostatic charges. Alternatively, the plates may be smooth or profiled without recesses or perforations, need to be reformulated as the plates for some applications are smooth and no holes , other application require different shape holes in a matrix disposure to obtain an intensifying effect. Several applications one or both of the active electrodes be covered with a dielectric, so as to augment the isometric electric field;

A signal view module 6, which registers the status of the functional modules including the existence of an ultra high voltage field at active electrodes level;

One protective module 7, arranged to isolate the low and ultra high voltage equipment, and so stopping the supply voltage in case of malfunction events. Simultaneously, it limits the working electric current of the UHV module 4 for the security of operators, materials and apparatus under sterilization;

One generator 8 to produce modulated types of signal including: sinusoidal, rectangular, triangular, saw tooth, needed to obtain a large field of applicability;

One resonance control module 9, which allows the fine adjusting of inductance- capacitor UHV system, for the optimization of energetic transfer at electrodes level inside the equipment.

The sterilization method according to the present invention may provide the following advantages: i. It may work on any type of surface, gas, liquid and inside the material to be sterilized , subject to the applied voltage; ii. It destroys cellular membranes, iii. It does not require hazardous materials, and so can be used in the presence of human operators . iv. It doesn't require special controlled atmosphere or existence of other neutral gas, though certain embodiments of the invention do not exclude such use; v. It produces in the same time 3 physical phenomena with sterilization effect: electron flux, ionic flux, and ozone generation. In addition the effect caused through plasma creation from the corona discharge will also add to the effectiveness of the system.

In keeping with the present embodiment, the following provides an example used for the sterilization of, say, re-usable surgical gloves, which are subject to a wide range of contamination sources.

The electrodes may be made from chromed copper of size of 2 mm x 150 mm x 280 mm. They may be placed at a distance of 35 mm one from the other, with the sterilization zone located within this space.

The electrodes may be in communication with ultra high voltage supply which produces an isometric electric field and a Corona-type discharge, for instance with preset parameters of: ~ 50 KV, ~ 900Hz, ~ 8mA, for a residence time of 3 seconds.

Figure 2 shows a Voltage -v- Current characteristic for an arrangement according to a further embodiment of the present invention. In this embodiment, the apparatus is arranged to produce the sterilizing effect at various stages along the characteristic, depending upon the intended application. For instance:

• In the region defined between points C to F, the characteristic is shown to be effective for soft materials and liquids;

• In the region defined between points D to G the characteristic is shown to be effective for gases;

• In the region defined between points H to J the characteristic is shown to be effective for surfaces and liquids especially on water.

It should be noted that, by itself, it is not optimum to rely on this characteristic alone in order to effect full sterilization for some if not all of the above cases. Nevertheless, more optimum conditions may be created by adjusting the frequency range of the apparatus, with different applications requiring different frequencies for maximizing the sterilization.

Another important parameter may include the resonance. The maximum use of energy is obtained at resonance of the targeted germs.

The following further defines the regions of the characteristic of Figure 2.

Dark Discharge 10

The regime between A and E on the voltage-current characteristic is termed a dark discharge 10 because, except for corona discharges 15, 20 and the breakdown 40 itself, the discharge 10 remains invisible to the eye.

A - B During the background ionization 28 stage of the process the electric field applied along the axis of the discharge tube sweeps out the ions and electrons created by ionization from background radiation. Background radiation from cosmic rays, radioactive minerals, or other sources, produces a constant and measurable degree of ionization in air at atmospheric pressure.

The ions and electrons migrate to the electrodes in the applied electric field producing a weak electric current. Increasing voltage sweeps out an increasing fraction of these ions and electrons.

B - C If the voltage between the electrodes is increased far enough, eventually all the available electrons and ions are swept away, and the current saturates. In the saturation region 30, the current remain constant while the voltage is increased. This current depends linearly on the radiation source strength, a regime useful in some radiation counters.

C - E If the voltage across the low pressure discharge tube is increased beyond point C, the current will rise exponentially. The electric field is now high enough so the electrons initially present in the gas can acquire enough energy before reaching the anode to ionize a neutral atom. As the electric field becomes even stronger, the secondary electron may also ionize another neutral atom leading to an avalanche of electron and ion production. The region of exponentially increasing current is called the Townsend discharge 25.

D - E Corona 35 discharges occur in Townsend dark discharges in regions of high electric field near sharp points, edges, or wires in gases prior to electrical breakdown. If the coronal currents are high enough, corona discharges can be technically "glow discharges" 15, visible to the eye. For low currents, the entire corona is dark, as appropriate for the dark discharges. Related phenomena include the silent electrical discharge, an inaudible form of filamentary discharge, and the brush discharge, a luminous discharge in a non-uniform electric field where many corona discharges are active at the same time and form streamers through the gas.

E Electrical breakdown 40 occurs in Townsend regime 25 with the addition of secondary electrons emitted from the cathode due to ion or photon impact. At the breakdown, or sparking potential, the current might increase by a factor of 104 to 108, and is usually limited only by the internal resistance of the power supply connected between the plates. If the internal resistance of the power supply is very high, the discharge tube cannot draw enough current to break down the gas, and the tube will remain in the corona regime with small corona points or brush discharges being evident on the electrodes. If the internal resistance of the power supply is relatively low, then the gas will break down at the voltage, and move into the normal glow discharge regime.

The breakdown voltage 40 for a particular gas and electrode material depends on the product of the pressure and the distance between the electrodes, Pd, as expressed in Paschen's law (1889).

Glow Discharge 15

The glow discharge 15 regime owes its name to the fact that the plasma is luminous. The gas glows because the electron energy and number density are high enough to generate visible light by excitation collisions. The applications of glow discharge include fluorescent lights, DC parallel plate plasma reactors, "magnetron" discharges used for depositing thin films, and electro-bombardment plasma sources.

F - G After a discontinuous transition from E to F, the gas enters the normal glow region, in which the voltage is almost independent of the current over several orders of magnitude in the discharge current. The electrode current density is independent of the total current in this regime. This means that the plasma is in contact with only a small part of the cathode surface at low currents. As the current is increased from F to G, the fraction of the cathode occupied by the plasma increases, until plasma covers the entire cathode surface at point G.

G - H In the abnormal glow 50 regime above point G, the voltage increases significantly with the increasing total current in order to force the cathode current density above its natural value and provide the desired current. Starting at point G and moving to the left, a form of hysteresis is observed in the voltage-current characteristic. The discharge maintains itself at considerably lower currents and current densities than at point F and only then makes a transition back to Townsend regime 25.Arc Discharges 20.

H - K At point H, the electrodes become sufficiently hot that the cathode emits electrons thermo-ionically. If the DC power supply has a sufficiently low internal resistance, the discharge will undergo a glow-to-arc transition, H-I. The arc regime, from I through K is one where the discharge voltage decreases as the current increases, until large currents are achieved at point J, and after that the voltage increases slowly as the current increases.

Experimental Results

The following experiments were conducted using a device according to one embodiment of the present invention. In particular, the device operated with parameters of:

The parameters of the signal at the electrodes to create the sterilizing effect on the glove are:

Signal is compound from 2 waves:

1 Carrier: impulses: 62.4 Hz

1 Modulated: Sinus Attenuated: 2.78 kHz.

Voltage: 20 - 50KV (deducted)

Intensity in the field: 1 - 3.5mA (deducted)

Distance between Electrodes: 4.5 cm Humidity 10%- 30%

Temperature 19 - 22 degree Celsius

Experiment #1 - Sterilization Apparatus Protocol 1-15.11.2007

Goal: Test usage of the sterilization apparatus efficiency against dilutions. Required Materials:

1. Eltyser 0243 Sterilisation Apparatus 2. Referential microbiological cultures: a -Escherichia CoIi ATCC

3. sterile Petri dishes

4. Thermostat to ensure a temperature of 37° C

5. sterile water

6. nutrient broth (BioRad) 7. Sterile Gloves

8. test tubes & sterile bottles

9. Means to inseminate with biocultures different materials

10. Surgical scissors

11. dropper with scale marks 1, 5 and 10 ml

After 48 hours Escheria CoIi in BioRad at 37° C is at maximum density of E.Coli/mm3

From this medium we do progressive dilutions as:

Dilution 10 ^"1 10 ^"z 1(T 10 ^" 10 ^"

Sample Volume 0,1 0,01 0.001 0,0001 0,00001

In every E.coli and nutrient sample we introduce lcm glove squares

Every square is removed from the nutrient and exposed immediately to the sterilization apparatus for 30 seconds. The sterilization apparatus is set at medium intensity (no discharges). After exposure, the sample is introduced in recipients with 0.1% peptone water. Every recipient is numbered according with the dilution. After the sample is harvested a dish is made for every sample. The dishes are read at the microscope.

Results: Sample no. 1

The read show a drastically reduction but we still observe between 15 and 20 germs / microscopic field.

Sample no.2

At 10 ^"2 , 4-5 germs/ microscopic field

The samples 3, 4, 5 showed nothing at microscopic reading.

Conclusions: The experiment was repeated 6 times and the results are:

Dilution lO ^"1 10 ^"z 10 ^"J 1(T 10"

Sample Volume 0,1 0,01 0.001 0,0001 0,00001

Microscopic 15-20 3-5 reading germs/ m. field (pes)

The protocol shows that the efficiency of the sterilization apparatus is related to the germ dilution. In order to obtain quantifiable results we used medium intensity of the device and wet samples.

In an older protocol we observe that the sterilization efficiency of the sterilization apparatus is affected by the humidity of the sample.

Example #2 - Sterilization Apparatus Protocol 17.09.2007

Goal: Test usage of the sterilization apparatus in most similar conditions of real usage for Glove Sterilization.

Required Materials:

1. Referential microbiological cultures: a -Escherichia CoIi ATCC b -Pseudomonas Aeruginosa ATCC

2. sterile Petri dishes

3. Thermostat to ensure a temperature of 37° C

4. sterile water 5. nutrient broth (BioRad)

6. Sterile Gloves

7. test tubes & sterile bottles

8. Means to inseminate with biocultures different materials

9. Surgical scissors 10. dropper with scale marks 1, 5 and 10 ml

Method:

In this method 4 fingers from the glove were used according to one for every microbiological culture, i.e. 1 for l.a , 1 for l.b and 2 for Ia mixed with l.b. The cultures used had uncountable number of germs /ml.

It takes about 10 minutes for the outside and inside of the glove fingers to dry in sterile laminar flow at ambient temperature (around 20 degree Celsius).

Each finger is put one by one between electrodes of the sterilization apparatus for about one minute, except one with mixture as a control. After this all the fingers were put in a fresh nutrient broth and incubated at 37 degree Celsius for 24 hours. After this period the probes were visually checked. The nutrient broth for the first 3 fingers was clear. The 4th finger nutrient broth was opaque. Then slides were prepared with samples from every finger . No germs was observed at microscope at the first 3 samples. The forth have presented a countless number of germs (see the following picture).

A difference between a culture made from the forth finger and the third finger was observed.