Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – With means applying electromagnetic wave energy or...
Reexamination Certificate
2000-09-21
2002-01-29
Mayekar, Kishor (Department: 1741)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
With means applying electromagnetic wave energy or...
C422S186290, C422S022000, C204S164000
Reexamination Certificate
active
06342187
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field
This invention relates to plasma sterilization, and provides a method for exposing articles to be sterilized to substantially neutral species of a plasma in a field free, glowless volume.
2. State of the Art
Modern medical and dental practice require the use of aseptic materials and devices, many of them meant for repeat use. In order to achieve this sterilization, processes are needed, at the manufacturer, and also at the hospitals or dental offices for treatment of reusable materials and devices.
Typical of materials which are reused in the hospital environment and require repeated sterilization are major surgical instrument trays, minor surgical kits, respiratory sets, fiber optics (endoscopes, proctoscopes, angioscopes, bronchoscopies) and breast pumps. Typical instruments and devices which are reused in a dental environment and require repeated sterilization are hand-pieces, dental mirrors, plastic tips, model impressions and fabrics.
There are a wide variety of medical devices and materials that are to be supplied from the manufacturer already packaged and sterile. Many of these devices and materials are disposable. Typical of this group are barrier packs, head coverups and gowns, gloves, sutures, syringes and catheters.
One major sterilization process in present use is that which employs ethylene oxide (EtO) gas in combination with Freon-12 (CCl
2
F
2
) at up to three atmospheres of pressure in a special shatter-proof sterilization chamber. This process, in order to achieve effective asepsis levels, requires exposure of the materials to the gas for at least one to three hours followed by a minimum of twelve hours, or longer, aeration period. The initial gas exposure time is relatively long because the sterilization is effected by alkylation of amino groups in the proteinaceous structure of any microorganism. EtO sterilization requires the attachment of the entire EtO molecule, a polyatomic structure containing seven atoms to the protein. This is accompanied by the requirement of hydrogen atom rearrangement on the protein to enable the attachment of EtO. Because of kinetic space-hindrance factors governing the attachment of such a bulky molecule, the process needs to be carried out at high pressure and be extended over a long period of time. It is, therefore, deemed very inefficient by the industry at large.
Perhaps the chief drawback to this system, however, is its dangerous toxicity. Ethylene-oxide (EtO) is a highly toxic material dangerous to humans. It was recently declared a carcinogen as well as a mutagen. It requires a very thorough aeration process following the exposure of the medical materials to the gas in order to flush away toxic EtO residues and other toxic liquid by-products like ethylene glycol and ethylene chlorohydrin. Unfortunately, it is a characteristic of the gas and the process that EtO and its toxic by-products tend to remain on the surface of the materials being treated. Accordingly, longer and longer flush (aeration) times are required in order to lower the levels of these residues absorbed on the surface of the materials to a safe operational value. A typical volume for each batch using this EtO process is 0.2 to 50 cu. ft. within the health and dental care environments.
A number of other approaches for performing sterilization have also been employed. One such process is high pressure steam autoclaving. However, this requires high temperature and is not suitable for materials which are affected by either moisture or high temperature, e.g., corrodible and sharp-edged metals, plastic-made devices, etc., employed by the hospital and the dental communities.
Another approach utilizes either x-rays or radioactive sources. The x-ray approach is difficult and expensive. The use of radioactive sources requires expensive waste disposal procedures, as well as requiring radiation safety precautions. The radiation approach also presents problems because of radiation-induced molecular changes of some materials, which, for example, may render flexible materials brittle, e.g., catheters.
It is therefore a primary object of the present invention to provide a process and apparatus for dry sterilization of medical and dental devices and materials, which can be operated efficiently, both with respect to time and volume and which can be carried out below 70° C.
It is another object of the present invention to provide a safe, nontoxic, process for the sterilization and surface treatment of medical and dental devices and materials, a process which does not employ toxic feed gases and one which does not yield toxic absorbed surface residues and by-products.
SUMMARY OF THE INVENTION
Broadly speaking, in the present invention, sterilization or surface treatment is achieved by exposing the medical or dental devices and materials to a highly reducing gas plasma like that generated by gas discharging molecular hydrogen, or to a highly oxidizing gas plasma, for example, one containing oxygen. Depending on the specific sterilization requirements, a mildly oxidizing environment, somewhere between the environment offered by oxygen and that offered by hydrogen is presented by gas discharging molecular nitrogen, either in pure state, or in multicomponent mixtures with hydrogen or oxygen, supplemented by an inert gas. In such a manner, plasma discharge chemical-physical parameters can be adjusted to fit almost any practical application of sterilization and surface treatment.
Such a plasma is generated by creating an electrical discharge in a gaseous atmosphere maintained at sub-atmospheric or atmospheric pressure, within which the materials to be sterilized are placed.
Generation of gas plasmas is a very well developed discipline, which has been specifically employed in semiconductor processing. See, for example, U.S. Pat. Nos. 3,951,709; 4,028,155; 4,353,777; 4,362,632; 4,505,782 and RE 30,505 assigned to one of the present inventors (Jacob).
In one instance the gas plasma sterilization process of this invention involves evacuating a chamber to a relatively low pressure after the devices or materials to be sterilized or treated have been placed within it.
An oxidizing gaseous atmosphere, as an example, is then provided to the chamber at a relatively low pressure, typically in the range 10 microns Hg to 10 torr, corresponding to a continuous gaseous flow rate range of 20 to 3000 standard cc per minute. An electrical discharge is produced within the chamber by conventional means, such as a microwave cavity or a radio frequency (RF) excited electrode. Alternatively, RF power in the power density range 0.0125-0.08 W/cm
3
may be coupled into the gas via a single electrode disposed within the chamber in a nonsymmetrical electrical configuration, or via two electrodes contained within the chamber in an electrically symmetrical configuration. In either case the material to be sterilized is placed on one of the electrodes, while the chamber's wall is commonly maintained at ground potential.
The nonsymmetrical arrangement provides the basis for a low plasma potential mode of operation which is conducive to low sterilization temperatures and the suppression of otherwise deleterious ion bombardment and contamination of the devices and materials.
The resultant discharge produces a gas plasma including both excited electrically charged gaseous species and excited electrically neutral gaseous species. For example, free radicals of atomic oxygen as well as excited molecular oxygen are formed in a discharge through molecular oxygen. These oxygen-bearing active species interact chemically with the proteinaceous components of the microorganisms residing on the surfaces of medical or dental devices to be sterilized, thereby denaturing the proteinaceous molecules and achieving kill rates of microorganisms equivalent to a probability of microorganism survival of less than one in a million.
The efficiency of this process is due, in part, to the fact that the gaseous plasma entities are very reactive and atomically small (usually monoatomic or diatomic) and
Jacob Adir
Wilder Jonathan Allen
Jacob Adir
Lahive & Cockfield LLP
Mayekar Kishor
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