US RE39657 E1
A sterilization apparatus wherein one or more electron beam tubes are used to direct electron beams into an ambient gaseous environment to create an electron plasma cloud into which non-sterile target objects may be moved. The electron plasma cloud is formed by interaction of the electron beam with the ambient atmosphere. Helium or other like gaseous may be used to expand the effective volume of the electron plasma cloud. Manipulators are used to move target objects in the electron plasma cloud, exposing non-sterile surfaces to the cloud and then joining the surfaces together where appropriate. The beam tube used to generate the electron beam has a thin low energy absorbing window which allows relatively low energy beams to be used, minimizing damage to materials within the surface of the target objects.
1. A sterilization apparatus comprising,
an electron beam tube having a window permitting emergence of an electron beam from said tube into an ambient gaseous environment while preserving a vacuum environment in the tube, the electron beam having a trajectory within a plasma cloud defining a reactive volume stimulated by interaction of the electron beam with the ambient environment, with a beam energy less than 100 kVkeV at the target, and
a moveable member manipulating objects in a plurality of directions within the reactive volume wherein the manipulated objects are sterilized.
2. The apparatus of
3. The apparatus of
4. The apparatus of
5. The apparatus of
6. The apparatus of
7. The apparatus of
8. The apparatus of
9. The apparatus of
10. The apparatus of
11. A sterilization apparatus comprising,
a chamber with ports allowing insertion of objects to be sterilized and having a gaseous environment therein,
a plurality of vacuum tubes fixed relative to the chamber, each emitting an electron beam along a path into the chamber through a window separating the gaseous environment of the chamber from the vacuum of the tube, the beam paths from the tubes within a common plasma cloud stimulated by the electron beams interacting with the gaseous environment within the chamber, defining a volume associated with the plasma cloud wherein the objects to be sterilized are exposed to the plasma cloud, and
at least one moveable member manipulating objects in a plurality of directions in the reactive volume wherein manipulated objects are sterilized.
12. The apparatus of
13. The apparatus of
14. The apparatus of
15. The apparatus of
16. The apparatus of
17. The apparatus of
18. A sterilization apparatus comprising,
a single electron beam tube having a window permitting emergence of an electron beam from said tube into an ambient gaseous environment while preserving a vacuum environment in the tube, the electron beam having a trajectory within a plasma cloud defining a reactive volume stimulated by interaction of the electron beam with the ambient environment, with a beam of energy less than 100 kVkeV at the target, and
a glove box hand and a robotic member having a robotic hand and a robotic arm, said glove box hand and robotic member manipulating objects, the glove box hand manipulating objects including objects that differ in variety, size and shape from the objects manipulated by said robotic hand, in a plurality of directions within the reactive volume wherein the manipulated objects are sterilized by said single electron beam tube.
The invention relates to beam sterilization of surfaces of objects and, more particularly, to sterilization which relies mainly on electron beam interaction with surfaces of objects.
In the fields of medicine, pharmaceutical production, and food processing there is a critical need for sterilization to protect against the danger of harmful microorganisms. Most of the sterilization methods currently in use require the sterilizing agent to systemically permeate the article being sterilized. These methods include heat sterilization, where the object to be sterilized is subjected to heat and pressure, such as in an autoclave. The heat and pressure penetrates though the object being sterilized and after a sufficient time will kill the harmful microorganisms. Gases such as hydrogen peroxide or ethylene oxide have also been used to sterilize objects. For the complete sterilization of an object, the gas must permeate the entire object. An alternate sterilization method uses ionizing radiation, such as gamma-rays, x-rays, or energetic electrons for sterilization.
There are a number of target objects where exposure of the object to ionizing radiation would cause some deleterious effect on the target object. Examples include objects which would melt or degrade under heat sterilization, products that would degrade or react with chemical sterilizing agents, and materials that would be harmfully altered by exposure to high energy radiation, particularly ionizing radiation. It has previously been recognized that by confining ionizing radiation to the surface of a target object, the deleterious effect will not occur. On the other hand, most ionizing radiation is created by powerful beam generators, such as accelerators, and so a beam of ionizing radiation is inherently penetrating.
In U.S. Pat. No. 4,801,427 A. Jacob teaches a process for dry sterilization of medical devices subjected to an electrical discharge in a gaseous atmosphere to produce an active plasma. In one embodiment, Jacob teaches placement of articles on a conveyor belt which carries articles into an atmospheric pressure corona discharge gap operated in ambient air. The plasma is formed by a discharge between the grounded conveyor belt, acting as a cathode, and multiple needle-like nozzles, acting as anodes, which disperse a gas to be ionized, which may be an oxidizing gas such as oxygen or a reducing gas such as hydrogen. U.S. Pat. No. 5,200,158, also to A. Jacob teaches sterilization by exposure of an object to a gas plasma created by an electrical discharge in a sub-atmospheric gaseous atmosphere. Hydrogen, oxygen, nitrogen, and inert gasses are all taught as possible gasses to use in forming the plasma.
In contradistinction to the high energy approach of Jacob, U.S. Pat. No. 3,780,308 to S. Nablo teaches surface sterilization of objects using low energy electrons, even though a relatively high energy starting point is present. One of the advantages of low energy electrons is that bulk properties essential to the mechanics of the material sterilized are not affected. Nablo expanded upon his idea in U.S. Pat. No. 4,652,763 which teaches use of an electron beam producing electrons with energies that penetrate an outer layer but with insufficient energy to pierce an inner layer of target material.
A number of patents teach use of a gas plasma to effect surface sterilization. Fraser et al., in U.S. Pat. No. 3,948,601 teaches use of a continuous flow gas plasma supplied at very low pressure in a chamber with a target object to be sterilized. Cool plasma from a gas such as argon is continuously produced by exposure to a radio-frequency field.
One of the problems encountered in prior art sterilization devices involves three dimensional structures, such as vials, cuvettes and hoses. Sometimes such structures have contours which create shadows for a beam of ionizing radiation nor even a diffuse discharge such that reactive electrons or ions do not reach the contours and so there is little sterilization in such regions. One solution would be to rotate or otherwise turn the object being sterilized.
An object of the invention was to devise a sterilization apparatus for medical equipment and the like, having three dimensional structure, with full sterilization of contoured regions, using ionizing radiation, but not deleteriously effecting the target substance. Another object of the invention was to devise a sterilization apparatus which is more efficient than sterilization apparatus of the prior art.
The above object has been achieved with a sterilization chamber featuring one or more electron beam tubes generating low energy electron beams, preferably under 100 kVkeV, in air or a surrounding gas at atmospheric pressure close to target objects to be sterilized. The low energy beams interact with air or surrounding gas to cause some ionization but a substantial fraction of the beam energy is delivered to the surface of a target object causing the object to be sterilized. A multiplicity of beam tubes may be used to eliminate shadows in cases where the target object has complex surface contours. Each tube has a stripe shaped beam which forms a plasma cloud in the beam path a short distance from a window in the beam tube by interaction of the electron beam with the ambient environment. Unlike metal foil windows of the prior art which cause high beam energy losses, the window of the beam tube used herein is preferably a thin semiconductor window which reduces losses in a high energy electron beam.
A manipulator, such as a robot arm or a glove box arm, moves target objects into a reactive volume of charged particles. It has been found that a sheath of helium gas, around the reactive volume, will enlarge the reactive volume by making a larger plasma cloud, consequently expanding the effective range of the beam. The sheath of helium gas is introduced by one or more nozzles near the window of the beam tube. Helium and surrounding oxygen atoms become excited by encounters with electrons, with some helium atoms becoming ionized and the oxygen converted to ozone. The positive ions of helium and the ozone contribute to the sterilization effectiveness of energetic electrons in breaking down proteinaceous material found in biological substances thereby sterilizing the substances. The zone of interacting electrons, helium and ozone atoms is termed a “plasma cloud” which is a volumetric zone where electrons and activated helium are mixing. Without introduction of helium an electron beam “plasma cloud” can still exist, but its effective range is limited to a space quite close to the window of the electron beam tube. As helium is introduced, the volume of the active species, electrons and helium ions, increases, thereby increasing the volume of the plasma cloud. Helium can be introduced by a nozzle directed at the electron beam emerging from the electron beam tube or by an annular nozzle coaxial with the beam tube.
A plurality of electron beam tubes can be arranged in a spatial pattern to create a composite plasma cloud which will eliminate any hidden surfaces or “shadows” of three dimensional objects that have complex surfaces. Also, a plurality of electron beam tubes can be arranged in patterns which would cover a large two dimensional area. For example, a triangular pattern of electron beam tubes would cover a large circular or triangular pattern on a flat surface, compared to the coverage of a single beam tube.
With reference to
Beam 15 is seen to be directed out of the window toward tubing 29 and 31 for an operation which involves filling bag 27 from a reservoir bag 25. Such a fill operation requires that the tubing from each bag be cut, connected for the filling operation, disconnected and the tubes resealed. In order to perform this operation, the size of window 13 is sufficiently large to create a plasma cloud consisting of the electrons in beam 15 and ionized gas from the ambient environment. Additionally, a nozzle 23 from a light inert gas supply, such as a helium tank, directs gas toward the beam and has the effect of expanding the effective volume of the plasma cloud as some helium atoms become ionized. The helium nozzle 23 can be used to shape the direction of the beam as well as to confine the beam to a desired location depending upon the nozzle design and configuration. Window 13 is seen to have a stripe shape, i.e. oblong, with a long dimension aligned so that the emerging electron beam has a corresponding stripe shape aligned with the linear dimension of the tubing to be connected. A typical width for window 13 is in the range of 1 to 3 centimeters.
A bag filling operation may be seen with reference to
An empty vial 40 is seen to be placed in chamber 41 through the open door 42. This vial is filled with a sterile liquid, but the cap is unsterilized and so there is some risk that a syringe module might contaminate the sterile liquid either through the syringe itself or through the unsterilized cap. By bringing both the syringe module and the unsterilized cap into the electron plasma cloud, both members to be joined become sterilized, with the joint between the vial and the syringe being sterilized.
The environment within chamber 35 is an ambient air environment at atmospheric pressure and ambient temperature. For a beam current of one milliamp, emerging from window 13 at 50 kVkeV, a helium flow velocity from nozzle 23 of a few liters per minute is appropriate.
With reference to
Although helium gas has been mentioned as the preferred gas for expanding a plasma cloud, other light gasses, with atomic numbers less than oxygen, would also work. In particular, it has been found that if argon is used, argon becomes excited and persists as in a metastable state for a brief period of time which allows sterilization to occur by a different mechanism than ionized atoms.