Vacuum sterilization process and devices

Abstract

Vacuum sterilization process with the application of vapour of a mixture of peracetic acid with hydrogen peroxide and residual gas plasma from atmospheric air, excited by pulsed electrical discharge; operational devices and methods used in the sterilization process, preferably a process of sterilization in vacuum, dry, and at low temperature (room temperature).

1 . A vacuum sterilization process with the application of steam of a mixture of peracetic acid with hydrogen peroxide and residual gas plasma from atmospheric air, excited by pulsed electrical discharge for sterilization of articles, such that the start of the sterilization process makes provision for the articles to be sterilized to be arranged and subjected to vacuum in a stainless steel chamber ( 1 ), optionally with one or two doors; characterised in that the process uses, connected to the chamber, a vacuum system comprising at least one mechanical vacuum pump and at least one liquid ring pump, connected in parallel and linked to said chamber by a first and second valve; the process makes provision for a device with an injector system for sterilizing gas, in which the evaporation and separation take place of the water from the solution of the mixture of peracetic acid or peroxide solution, and a system for the admission of atmospheric air, consisting of a filter and dehumidifier, connected to the chamber by a third and fourth valve and to the dehumidifier by a fifth valve; in its interior the chamber is provided with a stand, composed of flat surfaces, which, as well as serving to give support to the articles which are to be sterilized, also comprise electrodes at which the plasma is formed for the sterilization process; said process is automatic, being controlled by a programmable logic controller, being responsible for: 
 Reduction of the pressure on the articles which are to be sterilized by means of a liquid ring pump following the mechanical vacuum pump in order to attain the required pressure of the plasma;    Elimination of the residual vapour from the solution of the liquid mixture of peracetic acid with hydrogen peroxide by way of dilution with filtered atmospheric air using the liquid ring pump;    Application of the vapour from the solution of the liquid mixture of peracetic acid and hydrogen peroxide evaporated in vacuum with heating and separation of the water from the solution;    Dilution of the vapour from the peracetic acid or hydrogen peroxide by the injection of filtered air into the chamber;    Provision of stands, acting as a source electrode for generating a pulsed DC discharge, and the discharge of plasma close to the articles (M) arranged on the stands;    Generation of plasma from the residual atmospheric air with the excitation of pulsed DC in order to obtain an adequate temperature for sterilization;    Generation of pulsed DC discharge plasma from atmospheric air in order to complement the sterilization and elimination of the residues;    The application of vacuum takes place within the pressure range from 5×10 −2  mbar to 1×10 2  mbar.    
     
     
         2 . The process according to  claim 1 , characterised in that an operational method comprises the following steps: 
 a) the articles, eventually packed with non-woven surgical grade material, are placed on the stands;    b) the vacuum is induced in the chamber by means of the liquid ring pump and the first valve, reducing the pressure to approximately 100 mbar;    c) the pressure is reduced by the mechanical high-vacuum pump, and energy is supplied simultaneously in order for plasma to be generated, which continues to be applied until the obtaining of the sterilization conditions, and the pressure reaches approximately 2×10 −1  mbar;    d) the water from the solution is separated and the sterilizing vapour is injected into the chamber;    e) after the pumping to vacuum has been interrupted and the chamber isolated by the second valve, the stabilized mixture of the solution of peracetic acid and hydrogen peroxide is vaporised in vacuum with heating;    f) a period of time is allowed to elapse in order for the vapour to diffuse in the articles and to act on the micro-organisms;    g) the process of the elimination of the remaining vapour and of the residues of the materials is started;    h) the filtered atmospheric air is admitted into the chamber via the HEPA® filter, raising the pressure to atmospheric pressure; and    i) the pressure is again reduced by the liquid ring pump; items (h) and (i) are eventually repeated one or more times;    j) the pressure is reduced by the mechanical vacuum pump to a pressure in the range from 5×10 −2  mbar to 5×10 −1  mbar;    k) pulsed DC discharge plasma is generated from atmospheric air in order to complement the sterilization process and eliminate the residues; and    l) filtered air is admitted by the HEPA® filter in order for the chamber to be opened.    
     
     
         3 . The process according to  claim 1 , characterised by the fact that pulsed DC voltage is applied up to 10 KV and at a frequency of up to 250 KHz for the generation of plasma from atmospheric air at a pressure from 8×10 −2  to 1×10 0  mbar in order to begin and conclude the sterilization under vacuum and elimination of the residues.  
     
     
         4 . The process according to  claim 3 , characterised in that: 
 the water from the solution (ML) provided in the ampoule is evaporated in vacuum with heating of the guide element;    the resultant evaporation is conducted to the chamber via the needle;    the evaporation present in the chamber is conducted to the liquid ring pump via the fourth valve;    the fourth valve closes;    the remnant of the solution present in the ampoule is evaporated under vacuum with heating;    the sterilizing vapour is conducted to the chamber via the needle;    the sterilizing vapour present in the chamber is conducted to the chamber via the third valve, where it is expanded and diffused on the articles which are to be sterilized.    
     
     
         5 . The process according to  claim 2 , characterised in that, for the plasma generation, stands comprise an electric connection circuit between the electrodes and the pulsed DC source, said electrical connection between the DC source and the electrodes of the stand being connected in series with a resistor.  
     
     
         6 . The process according to  claim 1 , characterised by the fact that the value of the resistor may vary between 100 and 5 KΩ.  
     
     
         7 . The process according to  claim 1  for the sanitization/sterilization of articles without the need for plasma, characterised in that it comprises the following steps: 
 a) articles are packed in non-woven material and arranged in the interior of the vacuum chamber;    b) they are subjected to vacuum;    c) the water from the solution is separated and the sterilizing vapour is injected into the chamber;    d) after pumping to vacuum is interrupted and the chamber is isolated by the second valve, the remaining mixture of the stabilized solution of peracetic acid and hydrogen peroxide is vaporised in vacuum with heating;    e) the exposure must be carried out during a certain period of time, depending on the material which is to be treated, allowing for the diffusion of the vapour over the article and so eliminating the micro-organisms;    f) the vapour is eliminated from the chamber by means of successive dilutions with atmospheric air and suction with the liquid ring pump;    g) the articles are again submitted to a vacuum from 1×10 −1  mbar to 100 mbar for the elimination of the residues; and    h) filtered air is admitted through the HEPA® filter in order for the chamber to be opened.    
     
     
         8 . A device for vacuum sterilizating according to the process of  claim 7 , characterised by the fact that the device comprises means of applying vapour from the solution of the liquid mixture of peracetic acid and hydrogen peroxide evacuated in vacuum with heating, and by the provision of means to separate the water from the solution.  
     
     
         9 . The device according to  claim 8 , characterised by the fact that said means for applying vapour consists of a needle fixed in a base which contains in its interior an expansion chamber to which said needle is connected, said expansion chamber being provided with means of communication with the third and fourth valve.  
     
     
         10 . The device according to  claim 8 , characterised by the fact that the configuration of each electrode which makes up the stand allows for the homogenous distribution of the plasma in the interior of the chamber.  
     
     
         11 . The device according to  claim 8 , characterised by the fact that the configuration of each electrode of the stands allows for the plasma to be kept close to the articles which are to be sterilized.  
     
     
         12 . The device according to  claim 8 , characterised by the fact that the configuration of each electrode of the stands comprises two parallel shafts connected by segments which can be configured as squares, spirals, or any other suitable shape.  
     
     
         13 . The device according to  claim 8 , characterised by the fact that the configuration of each electrode of the stands is electrically connected to a power source which generates a pulsed DC signal responsible for the supply of the energy for the excitation of the plasma.