CA2224083A1 - Process and apparatus for dry sterilization of medical devices and materials - Google Patents

Abstract

Articles which are intended to be sterilized are placed into a confined volume and are subjected to neutral species of an electrical discharge while maintaining the volume glowless and substantially field free by interposing a barrier between the articles and the discharge, the barrier being transparent to neutral species and opaque to charged species emanating from the discharge.

Description

WO 96/40296 PCT~US961'~55 PROCESS AND APPARATUS FOR DRY STERILlZATION OF
MEDICAL DEVICES AND MATERIALS

~ACKGROUND OF l~ rNVl~NlION
Field: This invention relates to plasma .sterili7:-tion, and provides a method for exposing articles to be sterili7~P~ to subst~nti~lly neutral species of a plasma in a field free, glowless volume.
State of the Art: Modern medical and dental practice require the use of 10 aseptic m~teri~l.c and devices, many of them meant for repeat use. In order to achieve this ~tPrili7~ti-ln, processes are nP~PA at the m~nllf~ch-rer, and also at the hospitals or dental offices for tre~tmPnt of reusable materials and devices.
Typical of materials which are reused in the hospital environment and require ,~ealed sterili7~tion are major surgical instrument trays, minor surgical 15 kits, le~ildlol~ sets, fiber optics (endoscopes, proctoscopes, angioscopes, bronchoscopies) and breast pumps. Typical instruments and devices which are reused in a dental environment and require repeated steri1i7~tic)n are hand-pieces, dental mirrors, plastic tips, model i~ lt;s~ions and fabrics.
There are a wide variety of m~P~ic~l devices and m~tPri~lc that are to be 20 supplied from the m~mlf~ctllrer already packaged and sterile. Many of these devices and m~tP.ri~ls are disposable. Typical of this group are barrier packs, head coverups and gowns, gloves, sutures, syringes and ç~
One major ste-rili7~tiQn process in present use is that which employs ethylene oxide (EtO) gas in combin~tion with Freon-12 (CCl2F2) at up to three atmospheres25 of plC;s~ul~ in a special shatter-proof stPrili7~tion chamber. This process, in order to achieve effective asepsis levels, requires exposure of the m~tPri~lc to the gas for at least one to three hours ~ollowed by a ...i~ 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 plo~ei~ eous structure 30 of any microorganism. EtO sterili7zltion requires the attachment of the entire EtO
molecule, a polyatomic structure cu..~ seven atoms to the protein. This is accomp~niP,d by the requirement of hydrogen atom rearrangement on the protein toenable the ~tt~rhm~nt of EtO. Re~ se of kinetic space-hin~ n~e factors governingthe attachment of such a buLky molecule, the process needs to be carried out at high W O 96/40296 PCTAUS~ 55 --2--pressure and be ext~nded 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 m~tPri~l dangerous to hllm~n~ It was recently declared a carcinogen as well as a mutagen. It requires a very thorough aeration process following the exposure of the m~li(-~l m~t~ to the gasin order to flush away toxic EtO residues and other toxic liquid by-products like ethylene glycol and ethylene chlorohydrin. Unrollundlely, it is a characteristic of the gas and the process that EtO and its toxic by-products tend to remain on the10 surface of the materials being treated. Accol~lu~gly, longer and longer flush(aeration) times are required in order to lower the levels of these residues absorbed on the surface of the m~t~.ri~lc to a safe operational value. A typical volume for each batch using this EtO process is 0.00566 cubic meters to 1.416 cubic meters (0.2 to 50 cu. ft.) within the health and dental care environmçnt~
A number of other approaches for performing sterilization have also been employed. One such process is high pl~;S~ulc; steam autoclaving. However, this requires high Le~ alul~ and is not suitable for m~ttori~l~ which are affected byeither moisture or high temperature, e.g., corrodible and shaIp-edged metals, plastic-made devices, etc., employed by the hospital and the dental comml-niti~
Another approach utilizes either x-rays or r~1io~ctive sources. The x-ray approach is difficult and e~lJellsi~e. The use of radioactive sources requires expensive waste disposal procedures, as well as requiring radiation safety uLions. The radiation approach also pl~sel.ls problems because of radiation-inrl-lce l molecular changes of some materials, which, for example, may 25 render flexible m~t~ brittle, e.g., catheters.
It is thcil~lt; a primary object of the present invention to provide a process and a~pal~Lus 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 sterili7ation and surface tre~tmçnt of medic~l and dental devices and m~ten~l~, a process which does not employ toxic feed gases and one which does not yield toxic absorbed surface residues and by-products.

W O 96/40296 PCT/U' ,G1~9~S

SUMMARY OF I~il3 INVl~IION
Broadly speAking, in the present invention, sterili7-Ati-)n or surface trPAtmPntis achieved by exposing the me~i~Al or dental devices and m~t~riAIc to a highly reducing gas plasma like that ge~ ~1 by gas discharging molecular hydrogen, or 5 to a highly oxidi_ing gas plasma, for example, one COIIIA;II;~-~ oxygen. Depending on the specific stPrili7Ation re~uirements, a mildly oxi~li7ing envilvnll,cnt, somewhere b~lweell the environment offered by oxygen and that offered by hydrogen is presented by gas discharging molecular nitrogen, either in pure state, or in multicomponent IllixlwGs with hydrogen or oxygen, suppl~m~nt~A by an inert 10 gas. In such a ma-lllel, plasma discharge chPmi~Al-physical pArAmeters can beadjusted to fit almost any practical application of stPrili7Ation and surface treAtmçnt Such a plasma is generated by creating an electrical discharge in a gaseous atmosphere "IAi.lt-A;~Pd at sub-atmospheric or atmospheric ~JlGS~ulG, within which the mAteri-Al~ to be sterilized are placed.
Generation of gas plasmas is a very well developed discipline, which has been spe-,ifiç-Ally employed in semiconductor pr~ces~ing. See, for example, U.S.Letters Patent Nos. 3,951,709; 4,028,155; 4,353,777; 4,362,632; 4,505,782 and RE 30,505 A~ignP~ to one of the present inventors (Jacob).
In one in~tAnce the gas plasma stPrili7~tion process of this invention involves 20 ev~c~-~tin~ a chamber to a relatively low lJlc;S~ul'~ after the devices or mAtP.riAI~ to be st~rili7P~ or treated have been placed within it.
An oxidi_ing gaseous atmosphere, as an example, is then provided to the chamber at a relatively low pl't~S~ulc;, typically in the range 10 microns Hg to 10 torr, corresponding to a continuous gaseous flow rate range of 20 to 3000 standard 25 cc per minute. An el~ctric~Al discharge is produced within the chAmber by conventional means, such as a microwave cavity or a radio frequency (RF) excitedelectrode. ~ltPrnAtively, RF power in the power density range 0.0125-0.08 W/cm3 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 30 chamber in an electrically symmetrical configuration. In either case the m~t~riAl to be sterili7P~ is placed on one of the electrodes, while the chamber's wall is commonly ...Ah~lAi~Pd at ground potential.

W O 96t40296 PCTAUS961'0~S5 The nonsymmetrical arrangement provides the basis for a low plasma potential mode of operation which is conducive to low sterili~ation L~ n,pel.llul~,s and the suppression of otherwise deleterious ion bombardment and cont~min~tion of the devices and m~teri~1c The reslllt~nt discharge produces a gas plasma inc111~1in~ 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 l.l.Jlei,-aceous components of the 10 microorg~ni~m~ residing on the surfaces of me lic~l or dental devices to be steri1i~d, thereby ~ the proteinaceous molecules and achieving kill rates of microorg~ni~m~ equivalent to a probability of microorganism survival of less than one in a mi11ion The efficiency of this process is due, in part, to the fact that the gaseous 15 plasma entities are very reactive and atomically small (usually monoatomic ordiatomic) and therefore exhibit an enh~nced ability to ch~.mi~lly attach themselves to a pl~Lt;il,aceous structure and/or abstract (remove) hydrogen atoms from it. It was also ascertained that the presence of low levels of water vapor in the plasma feed gas enhances sterilization efficiency dr:lm~ti~ 1y. It is believed that 20 ~centl-~tion of active species con~ntr~ti~ln and/or favorable preconditioning of micro-or~ni~m~' plole;.~ eous structure occurs in the presence of moisture during the discharge process. These processes are responsible for the total kill of themicroorg~nicms. The kinetic space (or steric) r~,strictinn for this type of interaction is at least one thousand times lower than that for EtO alkylation.
Several specific types of int~-r~cti-~n take place. One specific interaction is hydrogen abstraction from amino groups. Another is lul~t~llulg ring structures, particularly those including nitrogen, or carbon-carbon bond cleavages. It is important to note that these processes produce only gaseous effluents, such as water vapor and carbon dioxide, which would not remain absorbed on the surface of 30 medical devices, but would, instead, be carried away from such devices with the main gas stream to the pump.
This sterilization process may be used with pre-packaged m~t~.ri~ls, such as disposable or reusable devices co"t~ ed within gas-permeable bags or pouches.

CA 02224083 l997-l2-08 W O 9"1C296 PCT~US9GJ'~555 --5-With sealed pouches (e.g., polyethylene/Tyvek p~c~ging), the barrier wall of thepackage is pervious to the relatively small active species of the sterili_ing plasma, but impervious to the larger proteinaceous microor~ni~m~. (Tyvek is a bonded polyolefin produced by DuPont.) After evacuation of the chamber, and introduction of the gas or gas ~ Lule, the gas(es) will permeate the package wall with a dynamic free exchange of gas(es) from within and from outside the package.
Upon striking a microwave or an RF discharge to forrn the plasma, and, depending upon ele~tric~l configuration and ~ ,s~u,e, the plasma may actually be10 created within and outside the package or, alternatively, the package may be placedl in a subst~nti~lly electric~lly shielded (field-free) glowless zone, so that it is subject to predo..~ -lly electrically n~llt~l, rather than elect~ically charged, active species which pass through the p~c~ging wall to interact with the surface of the m~t~.ri~l~ it contains.
In yet a dirrel~lll electric~l configuration, the packages co.. ~ devices to be sterili7e~ can be placed on a conveyor belt and swept into an atmospheric s:iure corona discharge gap operated in ambient air. With this confi~uldlion, the discharge electrodes are comprised of a grounded metal-backed conveyor belt forming the bottom electrode, while the top electrode is cc~ lised of a metal block with multiple needle-like nozzles for the dispersion of gas into the discharge gap.
Sterilization with this continuous, in-line, al~al~lus, is brought about by either ozone formation, due to presence of discharged oxygen in air, or due to any other oxi~1i7ing gas Illi;l~lUl't; that can be introduced into the discharge gap via a plurality of no77les, which are an integral part of the top electrode.
This corona discharge will normally operate in the power density range 5-15 W/cm2 and in the frequency range 10-100 KHz and 13-27 MHz, associated with gas flows in the range of several standard liters per second.
For example, in order to enable device sterili7ation by a strongly oxi-li7ing plasma when employing the process with a polyethylene-based p~ck~ging, it is neces~ry to provide that oxygen-bearing active species can permeate through the organic package barrier in the first place, and that a sufficient number of these species traverse that barrier in order to effectively kill all microor~ni~m~ on a medical or dental device enclosed within the pouch.

W O 9~'1C296 PCTAUS9~ 5S

Relevant strongly re~l--cing, oxifli7ing, mildly oxidi_ing or mildly reducing conditions can be obtained by plasma discharging diatomic gases like hydrogen, oxygen, nitrogen, halogens, or binary mixtures of oxygen and hydrogen, oxygen and nitrogen (e.g., air), oxygen and inert gases, or the gaseous combin~tion of S oxygen, nitrogen and inert gases like helium or argon, depending on the particular substances to be sterilized or treated.
The predomin~n~e of oxygen in the above mixtures is IJlc;rellt;d but not m~n~l~t-)ry. A predomin~n~e of nillugen, for example, will result in mildly oxi-li7ing conditions, but in somewhat higher process tempelaLu~ during 10 sterili7~ti~n for a given reaction pl~,S:~Ult; and power density. The inert gas fraction can be variable in the range 10 to 955~; the higher the fraction, the lower the processing lt;~ Jt;ldlul~ for a given ~ S~ul't~ and power density. However, ~terili7~tion exposure time increases the higher the inert gas fraction in the mix.
Substitution of argon for helium, for example, will result in higher sterilization 15 Lt;lllp~,~dlulCS for a given pressure and power density. In this case, instability of the gas discharge operation may set in, l~Uil.l~g a power density increase at a given pressure, colllpal~,d to that employed with helium, resulting in higher process tempt;;~aLu~cs.
Effective sterilization can also be obtained with a pure reA~ ing hydrogen 20 plasma or with a plasma discharge through pure inert gases like for example, helium, argon, and their mi~lulc~s, due to their very strong hydrogen atom abstraction (removal) capabilities from ~loteihlaceous structures of micro~
The addition of pure helium to an argon sterilizing plasma will enhance the stability of the latter and reduce overall sterilization temperatures. Hydrogen and its 25 llli~lul~;S with either nitrogen or oxygen, or with both, in the ~l~sellce or absence of an inert gas, will show effective st.orili7~tion capabilities over a wide range of concentrations in these Illib~lul~s, thereby enl-~ncillg sterilization process flexibility and versatility.
A first objective of facilit~ting the gaseous permeation through an organic 30 barrier (e.g., plastic or paper) is accomplished by ev~cu~ting the chamber (cont~ining the loaded pouches) to a base ples~ul~; of ~n~illlately 20 microns Hg.
This rids the pouches of previously entrapped atmospheric air, and eqll~li7es the t;S~ulc; inside the pouch to that inside the chamber (across the organic barrier).

W O 96/40296 PCT/U~G~33SS

The subse~uent introduction into the chamber of an oxygen-co............ ~ gas, in a typical situation, will establish an in~ p~us higher prt;S~iul~ inside the chamber (outside the pouch) relative to that inside the pouch. This l~lciS~ulc; gradient across the pouches' barrier will serve as the initial driving force of gas into the pouch. At 5 an equilibrated state, an active and ongoing i,ller~llauge of molecules across the barrier will take place, allelllplillg at all times to ..~ h. the same ~ ,S:~ul~ on both sides of the organic barrier. Upon striking a discharge through this gas, oxygen-bearing active species will be ge~ dled. Typically, these active species will be deactivated in large amounts by the organic barrier or due to inter~cti-)n with 10 neighboring metallic sl-rfaces This will commonly ~ub~ lly reduce the availability of these active species to do the sterilizing job.
In order to accomplish the objective of ~;e~ i..g a s~lfficient number of reactive species traversing the organic barrier of a package to effect efficientsterilization cycles, the plasma discharging of gaseous moisture IlliXlUl~,s proved 15 extremely beneficial. Plasma discharging of various innocuous gases col~ ;.-;..g moisture levels in the range 100 to 10,000 ppm of water vapor enabled the accenhl~tion of active species concentration by more than a factor of two, thereby subst~nti~lly shortening ster7;~tn ~ Josule times. Con~eq~nt~ in a few system configurations which were previously ch~r~cterized by relatively high processing20 tt;lll~eldlulc;s, process temperatures were now kept sufficiently low due to the shortened sterilization cycles. Effective binary moisture mixlult;s were those comprised of oxygen, nitrogen, hydrogen and argon. Ternary moisture lllib~lulcis of nitrogen-oxygen and argon - oxygen were somewhat more effective at similar powercl~n~iti~s than moisture InLXIUl'eS of pure nitrogen or pure argon. Moisture mixtures 25 CO..~ g halogens although very effective, were too corrosive and toxic. The most effective moisture Illi~lUlC; was that of oxygen, reducing ~terili7~tion cycles by more than a factor of two.
In addition, it was found that the organic barrier of a p~ck~ging pouch could be passivated in such a way as to subst~nti~lly reduce its take-up of oxygen-bearing 30 active species needed as a sterilizing agent and one which must render a final non-toxic medical device, without the formation of any toxic by-products.

W 096/40296 PCTAJS~ 3SS

One such passivation method consists of ~imllh~nPously introducing into the ch~mber a gaseous ~ ul~" which in addition to oxygen-co.~ i--g gas(es), also contains selected other gases as set forth below:
1. Organohalogens, based on carbon and/or silicon, ~tt~hP~ to any of the S known halogens. Particularly those organic compounds of carbon and/or silicon that are ~t~l~tf~d or unsdlllldled and contain in their molecular structures one (1) or two (2) carbon or silicon atoms attached to: a predominance of fl~lorinP atoms; a predomin~nre of chlorine atoms; a predomin~nce of bromine or iodine atoms; an equal number of fll-crinP and chlorine atoms .~iml-lt~nP,ously; an equal number of 10 chlorine and bromine atoms ~imlllt~nPously; an equal number of fluorine and bromine atoms ~imlllt~nl-ously; an equal number of fluorine and iodine atoms ~imlllt~n~ously; an equal number of chlorine and iodine atoms ~imlllt~nP~usly. Apredomin~n~ e of fluorine in these compounds includes structures where all otheratoms attached to a carbon or a silicon atom can be all the other halogens, or only 15 one or two other halogens out of the four halogens known, in conjunction with other atoms, as for example hydrogen. The same comment~ apply to a predomin~n~e of chlorine, bromine and iodine. For the latter, however, the cimult~n~ous presence of br~,lnille is unlikely to be pr~ctic~l due to a low volatility of the structure, but the ~imult~nt~ous presence of fluorine or chlorine, or both, is practical. It is worth 20 noting that hydrogen-conf~ining organohalogens will have a tendency to polymerize under plasma conditions, and in some cases, be fl~mm~hle in as-received condition.
Most effective sterilizing Illi~lul~s of oxygen and an organohalogen are those where the organohalogen is a Illi~lur~ of organohalogens in itself, either based on carbon and/or silicon, where the oxygen fraction is over 70% by volume; yet 25 sterilization will be effected for lower oxygen content at the expense of excessive halogenation of the surface of the material to be sterili7Pcl, and at the expense of excessive loss of tn7n~renCy of the Wla~illg pouch.

2. Organohalogens in conjunction with either nitrogen or an inert gas like helium or argon. In these cases, it is considered practical to keep the fraction of 30 the inert gas in predomin~n~e in order to keep the process temperature as low as possible. Inert gas fractions up to 95 % by volume will be effective in killing microorg~ni~m~. The nitrogen fraction is ideally kept below that of the oxygen fraction.

W O 96/40296 PCT/U5jG/~9~55 _9_ 3. Inorganic halogens, defined as compounds not co~ g carbon or silicon, but preferably co..l~ g as the central atom or atoms either hydrogen, ogtin, sulfur, boron, or phosphorus linked to any of the known halogens in a similar manner as described for the organohalogens under item 1 above, or defined 5 as compounds that contain only halogens without a dirr~r~l~L central atom, like for example molec~ r halogens (e.g., F2, Cl2) and the interhalogens which contain two (lissimil:~r halogen atoms (e.g., Cl-F, I-F, Br-Cl based compounds, etc.). Also in this case the in~ ic halogen maybe, in itself, a mi~Lulc of dirl~lG~II inorganichalogens as defined above.
Most effective sterili7ing Illi~lul~,s of oxygen and an ~llOlE~dll~C halogen arethose where the oxygen fraction is over 80% by volume; yet ~t~rili7~tion will beeffected for lower oxygen content at the expense of excessive halogenation of the surface of the material to be sterili7e(l and at the c;~ense of excessive loss of .ency of the wla~ulg pouch.

4. Inorganic halogens in conjunction with either nitrogen or an inert gas as described in item 2 above.

5. Inorganic oxyhalogenated compounds, not co..l~ in~ carbon or silicon, but preferably contain either nitrogen, phosphorus, or sulfur, each of which is cimnltz-nçously ~ ch~oA to oxygen and a halogen (e.g., NOCl, SOCl2, POCl3, etc.).
More specifically, the nitrogen-oxygen, or the sulfur-oxygen, or the phosphorus-oxygen entities in the previous examples are linked to any of the known halogens in a similar m~ulel as described for the organohalogens under item 1 above. The inorganic oxyhalogenated fraction may be, in itself, a mixture of dirre~ inorganic oxyhalogenated compounds as defined above.
Most effective ~terili7ing l~ lulc;s of oxygen and an inorganic oxyhalogenated structure are those where the oxygen fraction is over 70 % by volume; yet effective sterilization will be obtained for lower oxygen content at the expense of excessive halogenation of the surface to be st~rili7~d, and at the expense of excessive loss of tr~n~p~rency of the wld~l~ing pouch.

6. Inorganic oxyhalogenated compounds in conjunction with free nitrogen or an inert gas as described in item 2 above.

7. Multicollll)onelll lllib~lul~s compriced of members in each of the aforementioned groups. The ~imnlt~n~ous presence of free nitrogen and an inert W O 96/40296 PCT~US96/O~SS

gas like helium or argon in any of the above mentioned groups, or in multicomponent Ini~lulGs comprised of members in each of the aforementioned groups, will also be effective in killing microorg~ni~m~. The free nitrogen fraction should be ideally below that of oxygen in order to ...~i..l~i.- a lower reaction S L~;lllp~.alul't;. -More specific and relatively sirnple multicomponent mixtures that are effective sterilants as well as effective organic barrier passivation agents are listed below:

Specific Multicomponent Mixtures Comprised of Fractions A + B ~percent of fraction is by volume) Fraction A Fraction B
O2(92 - 97 %) CF4(3-8 %) [~2(4~%)-He(60%)] CF4(0.25 - 3%) [O2(8~)- CF4(92%)] He(80%) [O2(17%) - CF4(83 %)] He(80%) [O2(83%) - CF4(17%)] He(80%) [O2(92%) - CF4(8%)] He(80%) Many of the aforementioned gas mixtures are, in themselves, novel ch~mic~l compositions.
The plasma discharge through such a composite mixture will, for exarnple, create both oxygen-bearing and fluorine, or chlorine-bearing active species ~imnlt~n~ously. The latter will predo..-i~u..lly be responsible for passivating the organic barrier, since fluorination or chlorination, rather than oxidation of the organic barrier is favored thermodyn~mi~lly. Thel~,rur~, the take-up of fluorineor chlorine-bearing active species by the organic barrier of the pouch will be preferential. This will leave a relatively larger fraction of oxygen-bearing active species available for sterilization, since the latter cannot easily be taken up by a fluorinated or chlorinated surface.
In ~ ition~ sterili7~tion by oxygen-bearing active species may be aided, for example, by simultaneously discharging an oxygen-co,~ and fluorine or chlorine C(~ g gas residing inside the enclosing pouch. This gas had previously perme~ted thr~ugh the organic barrier prior to the commencement of the -W O 96/40296 PCT~US9G/'~55 discharge. This will create active species that contain both oxygen and flllorine or chlorine within the pouch directly. As previously described, the co...l.c;l;~ion for take-up by the organic barrier (pouch) will be won by the fluorin~ting or chlorin~ting species, leaving a larger net con-ent~tion of active species c~ i..g 5 oxygen to do an effective st~orili7ing job.
However, residual fluorine or chlorine-bearing active species within the pouch and not taken-up by it will also perform effective surface st~rili7~tion, since they are strongly ~hPmic~lly oxidizing agents. But, the fraction of fluorine or chlorine-co.,l;.h~ g gas in the original composite gaseous mixture, is subst~nti~lly 10 smaller than the oxygen-cu..~ g component. Thus, a major portion of microorg~ni~m~ kill will be attributed to the oxygen-bearing species in the plasma.
In either case, however, the end result is a continuous attack on the ~lol~ihlaceous structure of the microorganism res--lting in its ~l~gr~ tinn and frs~gmPnt~tinn into gaseous products. This chemical action by the reactive plasma is to initially modify 15 (de~alulc;) the pn~leillaceous network of the microorganism, dis.u~ g its metabolism at a Illillillll~ but more commonly impeding its reproduction.
In a steri1i7~tion method in which a load is exposed within a sterili7~tion zone to active species of a plasma generated in a reaction zone operably associated with the sterilization zone, improved sterilization efficacy is obtained by cont;~cting 20 the plasma with a textured metal surface prior to contacting the load with those active species. This improvement is ~ ire~l~d by lower load temperatures and better kill ratios. The plasma reaction zone may be operably associated with thesterili7~tion zone in accordance with any of the system configurations proposed within the sft-rili7~tion art for use with either RF or microwave plasma-based 25 systems.
A preconditioning step is often advantageous. Ideally, the plasma is formed from a sterilant precursor, notably hydrogen peroxide or a peracetic acid composition. It has been found advantageous for the sterilization load to be exposed to the sterilant precursor for a period (typically between about lO minutes to about 30 hours, but usually below about 2 hours) prior to energizing that precursor to produce a plasma.
Among other things, this invention provides a method for the sterili7~tion of a load comprising the steps of placing the load within a gas-tight conr,l~illg chamber , W O 96/40296 PCTAJ59GI'~55 formed at least in part from a metal wall; ev~c--~ting the ch~mber to a :"~b~ y low pressure, and introd~ ing a biocidal fluid in vapor or gas state into the chamber. The load is exposed to the biocidal fluid during a preconditioning phase.
A plasma is then inll11ce~1 in the biocidal fluid within the chamber by the application S of e1ectric~1 energy. The plasma is ...~ cl for a controlled period of time. Aportion of the inner surface of the chal.lbel is provided with a textured surface capable of increasing the steady state conce,ntr~tion of active species cont~ting the load.
In a sterilization method in which a load is exposed within a steri1i7~ti~ln 10 zone to active species of a plasma ge..~ fYI in a reaction zone operably associated with the sterili_ation zone, this invention provides an improvement by which biocidal fluid in vapor or gas state is introduced into the st~,ri1i7~tion zone. The load is exposed to the biocidal fluid during a proconditioning phase. A plasma is then induced in the biocidal fluid within the chamber by application of electr 15 energy, ~lerelably RF energy. The plasma is contacted with a textured metal surface prior to the active species of that plasma cont~cting the load.

DESCRIP~ON OF THE DRAWINGS
In the drawing FIG. 1 is a general f1i~g"."",.~tic i1111str~tion of an a~alalus 20 suitable for use in the practice of this invention;
FIG. 2 is a cross sectional view of another a~alaLus suitable for use in the practice of this invention;
FIG. 3 is a generally ~~i~.,...--.. Itic i1h1ctratinn of another a~l,al~lus suitable for use in the practice of this invention;
FIG. 4 is a cross sectional view of another embodiment of a ~teri1i7~tion chamber for use in the practice of the invention;
FIG. 5 is a side view of the ~,~alatus of FIG. 4;
FIGS. 6, 7, 8, 9, l0, ll, 12, 13 and 14 are cross sectional and side views of alternative embo-limeJlt~;
FIG. lS is a fr~ment~ry pictorial view, partially broken away of a sterilization a~pa,~ s of this invention; and FIG. 16 is a s~h~m~tic diagram of a typical st~orili7~tion system of this invention.

W O 96/40296 PcT~u59G/~ss -13-DESCRIPIION OF PREFERR~D EMBODIMENTS
FIG. 1 is a general (liAgr~mmAtic ilhlstrAtif~n of an RF excited dischargechamber of the type used in the process of this invention. The cylin~lricAl chamber 11 is formed, in this in~tAnce, of glass or quartz and encloses within it the material 5 14 to be treated. The chamber is commonly conn~ct~l to a m~hAni~l vacuum pump (not shown) that establishes sub-atmospheric ples~ult; conditions within the chamber. An exciter coil 12 couples RF energy from RF source 13 to the gas enclosed within the gas tight chamber creating a plasma therein.
Alternatively, a microwave discharge cavity operating at 2450 MHz may 10 replace the RF exciter coil to couple power into the gas. With a suitable selection of a rell-cing gas, like hydrogen, or an oxitli7ing gas, such as oxygen, as a typical exAmrle, a discharge may be initiAted and mAinfAinP,cl within the chamber. In the gas plasma formed by such a discharge a number of excited species, both molecular and atomic, are formed. The interaction of these species with a surface of the 15 device or mAt~riAl to be sterilized accomplishes the sterilization in the manner described above. The time duration of the process needed to achieve sAti~f~ctorysterilization will vary with other PAIA~ J~ of the discharge such as gas flow, ~)lGS~iUlG, RF or microwave power density, and load size.
In the embodiment illu~L-dled in ~G. 1 the a~dldlus inch~c~es an inner 20 perforated metallic cylinder 15 mounted generally concentric with the long axis of the chAmher 11, to form within the pe.r~,ldted cylinder a ~ulJ~IA..liAlly glowless, held-free zone. The pGlrold~Gd cylinder 15 is electrically-flo~ting and is cooled by recircl-lAting a suitable coolant (e.g., a 50-~0 mixture of water and ethylene glycol) through cooling coils 9 wrapped around the cylinder's length, to effect low 25 sterilization tçmpçr~tllres (<70~C). Still lower st~rili7Ation lelllpeldlult;s could be effected with two concentric perforated m~.tAllic cylinders 15 and 15a, surrounded by cooling coils 9 and 8, respectively, and enclosed by non-con~ cting chamber 11, as shown in FIG. 2. Energy coupling into this chamber is accomplished in a similar manner as described in FIG. 1. In a few cases, the configurations describedl 30 in FIGS. 1 and 2 may not require cooling coils 8 and 9 if the plasma feed gascontains low levels of water vapor for the enhancement of ster~ Ation efflciencyand the reduction of processing cycle time and temrto,r~tl-re.

WO 96/40296 PCTAUS96/~3~55 The res--lt~n1 glowless and field-free zone within the confines of the electric~lly-floating ~ ruldted cylinders could be ascribed to electrical faraday-cage effects, coupled with catalytic deactivation of active species, which are the precursors of visible emission, on the metallic surface of the perforated cylinder.
S When, as illnstr~tecl in F~G. 3, a microwave energy source 18 at for example, 2540 MHz. is employed in lieu of the RF generator 13, the perforated met~llic cylinder cannot be mounted concentric about the long axis of the chamber.
Tn~te~-l, the microwave cavity 16 is mounted at one end of a metallic or non-metallic chamber 11, and a l~lrolaled met;lllitc shield 17 cooled by 10 coolant-recircnl~ting coils 20 may be placed just beyond it toward the opposite end of the chamber, ~p~nning the entire diameter cross section of the chamber, thus cl~;aL~Ig a field-free and glowless reactive zone imme~ tely below it and away from the microwave cavity. These arrangements permit m~teri~l 14 placed within this zone to be generally isolated from electrir~lly chal~ed species, while allowing the 15 eloctric~lly neutral reactive plasma species, such as, for example, oxygen r~to interact with the surface of the material to be sterili7e~1 In this manner, sterilization is commonly effected at subst~nti~lly lower process temperatures.
.Altern~tively, the perforated metallic shield 17 may be removed, if microwave cavity 16 is remotely located from material 14.
Microwave discharges lend themselves to this mode of operation, since the effectiveness of neutral active species gellGldLGd in such a discharge survive substantial ~ t~nres downstream, and away from, the microwave cavity itself. This is a direct consequence of the higher population of electrons in microwave plasmas, and consequently the higher degree of ionization and dissociation in these 25 discharges. Also, microwave plasma electric probe measurements in~ljc~ted plasma potentials nearly equal to ground ~uu~el-lial, thereby practic~lly eli~ l;..g energic particle bombardment during processing. This mode of operation is thus well suited for low temperature exposure of heat-sensitive devices and material, even for extended periods of sterilization time.
In the most ~ulc~rt;llGd emborliments~ the chamber is formed of a met~llic~
electrically grounded and water-cooled outer shell with either a single internalperforated cylindrical shield, as shown in FIG. 1, or perhaps with two such met~llic shields, as shown in FIG. 2, which may be also purposely cooled, the RF energy , W O 96/40296 PCT~US961'~9S5 being coupled, in this latter configuration, between the two con~1nctin3~ p~,lro,dted cylinders. In either case, conditicn~ for low plasma potentials will prevail, with the discharge glow being confined to the space bel~n the inner wall of the chamber and the surface(s) of the perforated cylinder(s), leaving the work volume defined by 5 the inner pt;~ro~dl~;d cylinder ~U~ Ally field-free, void of the plasma glow, and at a relatively low operating temperature.
One such chamber configuration is illustrated in FIGS. 4 and 5. The cylindrical outer wall 21, typically forrned of ~ ;n.~." or st~inlPss steel, is l~lAilll;~ ~l at ground potential and serves as the chamber enclosure. This enclosure may be water-cooled with the aid of cooling coils 28 wrapped around it. Suitable~lime.n~ions for this chamber are a ~ meter of 91.44 cçnt;mPters (36") and a length of 121.9 centime~ters (48"). A metallic pe~ro~dl~d inner cylinder 23 cooled by cooling coils 19 is mounted on in~ul~tin~ spacers 29 within the chall.bel so that it is positioned generally parallel with the long axis of the outer wall 21 of the charnber and conrentric with it. These spacers may be formed of any suitable non-reactiveand in~ ting type of m~tPri~l such as ceramic. The cylinder perforations are typically 2.5 mm - 4 mm ~ mPter holes spaced in all directions from one another by apl)lv,~ihl,ately 0.5 cm in a triangulated manner. Longih--lin~l support rails 27 are fastened to the inner wall of the ~lrola~ed cylinder 23 to support a wire basket 25 in which the m~teri~lc and devices to be stPrili7~ are placed. A suitable RP
source 22 is coupled between the grounded outer chamber wall 21 and the pelroldted inner cylinder 23. Usually this RF source should be capable of producing an RF output in the range 0.01 W/cm3 to 0.1 W/cm3 at frequenci~Ps in the 10-100 kilohertz or 13-27 megahertz range.
As ilhl~t~tecl in FIG. 5, an evacuation port 31 at the end of cylinder 21 is connectP~l to a pump (not shown) and provides for suitable evacuation of the ch~mher and for continuous gas flow during the stprili7~tion process. The gas supplied for the discharge is generally flowed through the chamber by means of p~,lroldk;d diffusion tubes 35. ~ltern~tPly~ gas may be introduced into the chamber via a gas dispersion device (not shown) mounted behind chamber door 39 from the inside.
Material to be sterili~e~ may be placed within wire basket 25 resting on rail 27 through the entry port behind chamber door 39. Chamber door 39 may be any WO 96/40296 PCTAU59~ 55 suitable closure that can be conveniently opened and closed and left in a sealedposition during evacuation and the gas discharge operation.
FIG. 6 illustrates a second ~lcrelll,d embodiment of the ~l.aldL~ls for pr~cticing the process of the invention. In this configuration, the outer chamber S wall 21 may be water-cooled by cooling coils 28, is again fonned of metal, such as electrically grounded ~ .. or sPin1Pcc steel, and is of similar ~~imtqnciQns to that illustrated in FIG. 4. Mounted within the chamber is an inner conce.ntric cylinder 43 formed of a perforated metal which may be purposely cooled by cooling coils 30, and is supported on inc~ ting support struts 46. The spacing bt;lweel~ the inner wall of the chamber and the perforated interior cylinder may range typically from 10 cm to 17 cm, where the chamber has an I.D. of 91.44 cçntim~ters (36").
A second metallic ~elrol~lled cylinder 41 is concentric~lly mounted interme li~tç
between the inner pelroldted cylinder 43 and the inner wall of the chamber and may also be cooled by cooling coils 19. This second perforated cylinder is supported on in~lllsltin~ struts 47 and is spaced typically 4 cm to 7 cm away from the inner perforated cylinder 43. The in~ tor struts may again be formed of a cer~mic m~t~.ri~l. Mounted on the interior of the inner concentric cylinder 43 are support rails 27 for carrying a wire basket which would contain the m~teri~l~ to be ~tt~rili7eci Both the outer chamber wall 21 and the inner pelrulaled cylinder 43 are electrically conn~t~l to point of potential reference (ground). F1octric~1 connections would most usually be made through ceramic seal feedthroughs 48 and 49. The intermediate cylinder 41 is elP~tric~lly conn~cteA to one side of the RFpower supply 22, the other side of which is connP~tell to the point of potentialreference.
While a variety of conventional RF sources may be used, the most typical value for the RF frequency is 13.56 MHz or, ~lt~rn~tively, 10-100 KHz. As in theembodiment of FIG. S longitl--1in~11y extending gas diffusion tubes 35 may be employed to provide the gas to the interior of the chamber. Typically each tube would have holes of diameter between 0.5 mm and 1.5 mm, spaced ~ vxill,alely 2.54 centimeters (1") apaIt along its length. The hole ~ meters closer to the gas source would be of the smaller tli~m~tt-r. Alternatively, gas inlets may be provided behind chamber door 39. As indicated in the embodiments of PIGS. 4, 5 and 6 the perforated inner cylinders may be open-ended at both ends or, may be closed with WO ~'ID296 PCT/U~,~J'~55 -17-the same perforated stock as is used to form the cylinder(s). The sterili7ation chambers shown in FIGS. 4, 5 and 6 may be connP~t~ to a microwave discharge source, typically operating at 2540MHz, in lieu of an RF energy source. In this case, the con~entric pelroldted met~llic cylinder(s) may be replaced by a single5 perforated shield in accordance with the operAtiQn~l description given for FlG. 3.
FIG. 7 illustrates a third l~lert;ll~d embodiment of the d~dlUS for practicing the process of the invention. In this di~.,--~tic description the outer chamber wall 21 is again formed of metal, such as ~l..... i"~.. , or st~inl~s~ steel, and is of similar ~imensions to that ilhlst~t~l in FIG. 4. Mounted within the chamber 10 are two planar, metallic, electrodes 50 and 51, preferably constructed of Allllllill.l.
which may be coated with in~ ting ~l-.. ~.i,.. oxide. The gap 52 b~lween electrodes 50 and 51, is adjustable by virtue of the movable bottom electrode 50.
Termin~l~ A and B are connected to the electrodes via an in~nl~ting feedthrough 48.
The outer end of these termin~l~ may be connected to an RF source (not shown) in15 such a way that when t.ormin~l B is connected to a ground potential, terminal A
must be connPctecl to the RF source, or vice versa, providing for an electrical symmetric~l configuration. The work load to be ~terili7~1 is placed on lower electrode 50.
It is important to ...~ the ~iist~n~e between the electrodes always smaller than the fii~t~n(~e of the RF-powered electrode's edge to the grounded ch~mber'swall. This enables a well def~ned and intense plasma glow to be confined to space 52 between the electrodes and prevents ~1elet~rinus sparking. The electrode material may also be made of the perforated stock previously mentioned. However, it is desirable to have the RF-powered electrode made of solid stock to enable very efFicient water-cooling of that electrode. The bottom electrode may also be made of solid stock to enable a cooler surface upon which the work load to be sterilized will be placed. This chamber will commonly be evacuated to 10 - 100 microns Hg before gas introduction via the ~ ÇOlal~d gas diffusion tubes 35. Practical device sterilization can be obtained with process parameters for gas flow rates in the range 20 scc/m to 3000 scc/m, corresponding to a total sterilization reaction pl~,S~ul'~; of 10-5000 microns Hg, at a range of RF power fiensiti~.s of 0.0125 W/cm3 to 0.08 W/cm3. Process exposure times will depend on load size and are commonly in the range 2 min. to 120 min.
-CA 02224083 l997-l2-08 W O 96/~C29~ PCTAJS9C~'~3333 FIG. 8 illustrates in ~ gr~mm~ti~ form yet another ~l~r~lled embodiment for practicing the process of the invention. The outer wall of chamber 21 is again formed of metal, such as ;Ill...lil~l.... or st~inlçss steel ...~ ~ at ground potential, and is of similar ~1im~n~inns to that illustrated in FIG. 4. Mounted within the 5 chamber is a single planar, met~llic, electrode 50, preferably constructed of minl-m which may be coated with in~ ting all~ oxide to reduce RF
s~ulle,ulg. I'his electrode is commonly connected to an RF source in the MHz range and carries the work load to be sterilized. This electrode has commonly a total surface area which is at least four times smaller than the total int~rn~l surface 10 area of the grounded chamber, to effect a low plasma polen~ial mode of operation.
This arrangement, coupled with low power tien~iti~s (see below) is conducive to very low sterili7~tinn ~ alules.
This electr~ configuration is usually referred to as asymmetric and is conducive to generating an extremely uniform plasma glow filling the entire volume 15 of the processing chamber. It is also responsible for the development of a characteristic accelerating potential at the surface of electrode 50, associated with a thin "dark space" through which positive plasma ions will accelerate and impinge on the electrode and the work load it normally carries.
This arrangement is recommended for hard-to-sterilize materials almost 20 exclusively, particularly for sterili7~tion of metallic devices replete with a high density of cracks and crevices.
The main advantage of this process chamber configuration is its ability to render efficient sterili7~tion at relatively low power densities in the range of 0.0125 W/cm3 to 0.025 W/cm3. This conhguration is also easily scalable as a function of25 work load size.
This process chamber commonly operates with at least an order of m~gnitllde lower l"~s~,u,c; than the ~ t~iUlC for chambers described in FIGS. 1 through 7, while the gas dispersion tubes 35 are similar in construction to those previously mentioned. To prevent RF sputtering of electrode 50 due to positive ion 30 bombardment, it may either be hard-anodi_ed or alternatively alu~ lulll oxide spray-coated.
One particular sub-configuration to that described in FIG. 8 is illustrated in FIG. 9. In this configuration chamber 21 is water-cooled by cooling coils 28 and W O 96/40296 PCT~U~96J~5955 contains a ~elrol~led metallic enclosure 7i totally s~ oullding and co..~ g electrode 70. This enclosure may be cooled by coolant-recirculating coils 72 andmay be connP~t~A to a separate RF source 22a, of a dil'rert;lll frequency than that of source 22. This pelrc~ldL~d enclosure may be equipped with an open/close hinging5 me~h~ni~m (not shown) to enable access for m~t~ri:ll to be st~rili7P"1 to be placed on electrode 70 contained within enclosure 71. This yields the beneficial effect ofbeing able to s~dlalely control the ab~lnrl~n~ e of sterilizing active species and their impinging energy. RF power applied to electrode 70, which may or may not include a negative DC ~u~e~llial from a sepa,alt; DC supply, (not shown), will 10 control energy of ion impingement, while RF power applied to the auxiliary oldled enclosure 71, will control active species ablm-l~n~ e.
With this confi~-r~tinn, RF power sources optildl,ng at 100 KHz and 13.56 MHz may be used in the various possible pL....~ ons. Illl~l~;,lhlg results are obtained by mixing both freqllen-~-ies while being applied to a single el~ m~nt Commonly, one frequency has to be applied at a higher power fraction, usually around 90 % of the total applied power to the same elPment Such illlt;lC;~ti~l~
process results were obtained when the two dirr. l~ nl freqllenciPs were mixed and applied to electrode 70 in the absence of any auxiliary perforated en-~-losllre. The mixed frequency concept also lends itself to low power density stPrili7~tion in the range 0.0125 W/cm3 to 0.025 W/cm3, with the advantage of .n~ ing the overall temperature relatively low (below 50~C), particularly when electrode 70 is water-cooled by cooling coils 74.
It is worth noting that the auxiliary p~lrJl~led enclosure 71 ought to be of high mesh ~ ~ellcy to allow the plasma glow to extend past it and contact electrode 70. Best operating conditions will be obtained for the .~m~llest surface area of this p~lroldlt;d metallic enclosure. In a few in~t~nnes, this mPt~llic enclosure was connPct~ to ground, yielding effective stprili7~tinn data.
FIG. 10 ilhl~tr~tP,s rli~gr~mm~tie~lly a pl~rell~d embodiment for practicing the process of the invention under atmospheric pressure conditions in ambient air.
In this configuration no vacuum capability is required. Material to be stPrili7ed is placed on grounded and water-cooled conveyor belt 62 which sweeps the load across the discharge gap created between conveyor belt 62 and RF-powered and water-cooled electrode 61. Electrode 61 cooled by cooling coil 76 produces a large W 096/40296 PCT~US9GI~S5 plurality of needle-like discharges which create individual discharge sparks toward the counter grounded electrode 62. The larger the gap between the electrodes, the higher the power needed to initiate the discharge in air.
Sterilization is effected due to ozone formation following the discharge of 5 oxygen in the ambient air. Power density requirements in the range 5 to 15 W/cm2 are not uncommon. M~ i..g a controlled relative hllmi~1ity of 50% to 60% in the discharge gap will facilitate initiation of the discharge and promote atomicoxygen generation. The latter serves as a precursor to ozone formation, the final desired sterilant in this configuration.
Ozone toxicity inhibits wide acceptance of such a corona discharge in air for the purpose of medical or dental device sterili7~tit n. Alternatively, thelGrol~, the RF-powered electrode 61 may assume a configuration comprised of multiple open nozzles 65, capable of dispersing oxi~i7ing gases immedi~tPIy ~ ent to conveyor belt 62. In this configuration the discharge would still be created in arnbient air, however the dispersion through the open-nozzles 65 of a judiciously sel~oct~cl feed gas will increase the local concentration of its active species 63 relative to that of ozone. In this mal),le-, sterilization would be attributable to active species derived from any feed gas introduced into the hollow RF-powered electrode 61 and not to the deleterious ozone gas.
The dispersing nozzles 65 may assume different configurations. For example, separate nozzle tubes may be inserted into a hollow section of electrode block 61, which may or may not be of dirrGlG~l material than electrode block 61.These tubes may also be screwed into the electrode block 61 for easy replacement.
A typical hole size for each individual nozle is in the range 0.038 centimet~r~ to 0.102 centimeters (0.015 - 0.040").
The advantages of this discharge configuration are mainly in terms of system simplicity and in the context of continuous operation, coupled with the ability to easily change the rçsiden~e time of a work load within the discharge gap.
Disadvantages are commonly associated with erosion and degradation of both electrode block 61 and conveyor belt 62. Electrode 61 should be constructed fromoxidation-resistant m~teri~l~ (e.g., tungsten, molybdenum or alloys thereof~. The grounded conveyor belt electrode 62 may be constructed from st~inl~s~ steel or any other suitable nickel-coated metal, and may be cooled by cooling coil 77.

W O 96/40296 PCT/U~ 955 Altern~tively, a dielectric conveyor belt may be used. With such an arrangement,the ins~ ting belt is mollntY1 in close proximity to a stationery grounded and fluid cooled metallic block serving as the counter electrode. The conveyor belt ought to be resistant to electrical punch-through and be constructed from fluorinated, S fluorinated/chlorinated or flllorin~ted/chlorinated nitrogen-co,.~ hydrocarbons (e.g., DuPont products). High melting polyimides or Kalrez-like synthetics may serve as ~ltp~rn~tp~ construction materials for the conveyor belt. Kalrez is a polyimide m~mlf~rh1red by DuPont.
Other configurations are ilh-st~tPA in FIGS. 11, 12, 13 and 14. These 10 configurations are ~lc;ft;ll~d emboflim~nts for practicing the process of the invention with narrow bore and elongated hubulation, almost exclusively. They are particularly ~lesign~t~ for the treatment and stPrili7~tion of fiber optics-based hubulations as, for example, endoscopes, proctoscopes, angioscopes or bronchoscopies, having intern~ meters as small as 2 mm and an overall length of 15 about 1000 mm.
The outer wall of elongated chamber 91 is made ~ rerc;lllii~lly of non-meb9llic material (e.g., glass, ce~mic) but, may also be comprised of a metallic/non-metallic structure. The chamber has a minimum internal rli~mPtPr ofone and one half times that of the outside di~meter of elongated tubulation 94. The 20 inner and outer s-lrf~es of narrow bore tubulation 94 need to be treated or stPrili7~A Both ends of narrow and elongated chamber 91 are hermeti-~lly pluggedwith gas permeable but microorganism-impervious membranes 99 (e.g., Tyvek).
This arrangement ensures the dynamic flow of an active plasma through and over tubulation 94, and also secures its aseptic condition after st~-rili7~tion and during 25 prolonged storage.
To effect sterilization or treatment of the inner and outer surfaces of tubulation 94, it is inserted into chamber 91 either bare or sealed within a gaspermeable elongated pouch. The chamber is then plugged at both ends with membranes 99.
The chamber is subsequt-ntly inserted into exciter coil 92 (FIG. 11) whose IGl.nillals are connP~tecl to a suitable RF energy source like the one described with respect to FIG. 1.

CA 02224083 l997-l2-08 WO 9C/4~ PCTrU~9~v3955 In another a,.~u-ge-llent, the chamber may be inserted within the air gap of capacitive plates 93 (FIG. 12) whose termin~l~ are connPct~ to a suitable RF
energy source like the one described with respect to PIG. 1.
~ ltern~tively, chamber 91 may be brought into close pl~xihnily to microwave 5 cavity 16 (FIG. 13) whose terminal is conn~ctecl to a suitable microwave energy source as described with l~felGIlce to FIG. 3.
In cases where the chamber is a met~lli( - non-met~llic structure, the various energy sources described in FIGS. 11, 12 and 13 are coupled to the chamber via the non-metallic portion of the chamber.
In each of the configurations of ~IGS. 11, 12 and 13, one end of elongated chamber 91 is temporarily vacuum-flanged to a gas delivery and moniloli,lg system (not shown), while the other free end of the chamber is tt;lllpol~ily vacuum-flanged to a gas e~h~ll$t ~JUIIIpil~g system (not shown).
At the end of the st~rili7~tion or trP~tm~-nt cycle, the gas flow and the energysource are turned off, chamber 91 is ~ ng;lged from the power source and from both vacuum flanges and stored for future use of narrow bore tubulation 94.
Por practical reasons, a plurality of chambers 91 may be employed in a parallel electric~l arrangement siml~lt~neously, either in an RF or microwave discharge hook-up.
Chamber 91 may have a cooling jacket 95 around it as, for example, shown in PIG. 14. It is not ~ n~ ol~ that exciter coil 92 (PIG. 11) or capacitive plates 93 (E~IG. 12) enclose or extend over the entire length of tubulation 94; the latter may be partially contained or not contained at all within coil 92 or capacitor plates 93.
Set forth below are specific examples of suitable operating p~r?~mP~ters for effective sterili~tinn employing various ~p~dtUS as illustrated in the figures. The particular chamber and corresponding configuration, are referenced in the examples.
However, for each of the examples the general technique involved was one in which the material to be sterilized was placed directly in the reaction chamber, or placed within a Tyvek/polyethylene pouch which itself was sealed and placed in awire basket within the reaction chamber.
The m~teri~l~ used for verification of stt-rili7~tinn effectiveness were "Attest"
vials obtained from 3M Co~ any, or "Spordex" bacterial test strips obtained from -W O 9~ 296 PCTAUS9G~53~S

the AmPrir~n Sterilizer Colllpd~ly, each vial or "Spordex" envelope contained a b~terizll strip having an original spore population of not less than lx106 Bacillus Subtilis var Niger per strip, but more commonly in the range 2.2-4.0 x 10~
spores/strip. The strips contained the permeable plastic vials were not brought into 5 contact with the culture solution contained in any of the vials prior to st~rili7~tinn The vials were placed within the Tyvek/polyethylene bags during the plasma st~rili7~tion, alongside devices or instruments to be stPrili7P,A. The bags werealways sealed during the ~tPrili7~tion process.
For each example the chamber was first ev~cu~tP~ to an initial low plts~uie 10 level after the m~teri~l~ (in the bags or pouches) were placed within it. Thechamber was thel~r~l flled with the a~l~liale gas prior to striking the discharge, and the gas colllillued to flow through the chamber at a controlled rate to establish a steady state stPrili7~tion pleS~ult;. The discharge was initi~tP~ by the application of RF or microwave power as in~iir~tpA. The discharge was 15 for a controlled time period at the end of which the power was turned off, the chamber was first ev~cn3ted7 then b~r~fillP~ with air through a b~f~teri~ retentive filter, and later opened and the samples removed. The lelll~ldlur~ within the chamber during the process was m~int~inPcl at less than 70~ C, and more typically around 25~C to 65~C, as sensed by an iron-con~t~nt~n, type "J", therrnocouple 20 cLI~;uill y and monitored by an analog lell~elalul~ meter.
Subsequent to the tests, the spore strips in the "Attest" vials where brought into contact with the self-cont~ined culture solution and incubated for 72 hr, at the end of which period microorganism growth or no growth would be in(1il-~tP~l by the reslllt~nt color of the culture solution. Alternatively, the spore strips were 25 submitted to an independent testing laboratory which performed a total plate count on the sample strips using a procedure in which 100 millilitPrs of sterile deionized water were added to each strip in a sterile whirl-pak bag. The bag was then placed in a lab blender for 10 minutes. One 10 milliliter aliquot of sample, a duplicate one milliliter sample, and two consecutive 10-' dilutions were plated using Tryptic Soy 30 Agar. The plates were then incl~b~ted at 30~C-35~C for 72 hours. After incubation, the plates were read and recorded, and the results calculated on a Colony Forming Unit (CFU) basis.

_ W O 96/402~6 PCTAUS9~ 55 P,Y~mrle 1 With metal chamber and internal uncooled perforated cylinder, (~IG. 4) s Gas: 02(Pure) Flowrate: 20 scc/min Pressure: 0.30 torr Power Density: 0.050 W/cm3 10 Exposure time: 60 min.
Temrçr~tl-re: 66~C
2~oslllt~nt microbial count: < 10 CFU (below sensitivity limit of counting te~hnique) Percent kill: 99.9999 %
Metal chamber dimensions: 20.3 centimeters D x 20.3 centimeters L (8"D x 8"L) Example 2 With metal cha-l-bel and internal cooled pelrolal~d cylinder, (FIG. 4) Gas: O2(Pure) Flowrate: 20 scc/min Pressure: 0.30 torr Power Density: 0.050 W/cm3 Eixposure time: 60 min.
Temperature: 32~C
Percent kill: Total kill Metal chamber ~limen~ions: 20.3 centimeters D x 20.3 c~ntimeters L (8"D x 8"L) Example 3 With Pyrex chamber and internal cooled pelr~lal~d cylinder, (FIG. 1) Gas: OJCF4 (8 %) Flowrate: 36 scc/min Pressure: 0.35 torr Power Density: 0.050 W/cm3 Exposure time: 60 min.
Temperature: 34~C
l?~s -lt~nt microbial count: < 10 CFU (below the sensitivity limit of counting technique) Percent kill: 99.9999%
Pyrex chamber dimensions: 20.3 centimeters D x 20.3 centimeters L (8"D x 8"L) W O 96/40296 PCTAUS~ S5 Example 4 With metal chamber and two uncooled internal pt;lÇo~dled cylinders, (EiIG. 6) 5 Gas: ~2 Flowrate: 20 scc/min Pressure: 0.30 torr Power Density: 0.050 W/cm3 Exposure time: 60 min.
10 Temperdture: 76~C
Percent kill: Total kill Metal chamber ~limen~ions: 20.3 centimeters D x 20.3 centimeters L (8"D x 8"L) Example 5 With metal chamber and two cooled internal ~.Çoldled cylinders, (FIG. 6) Gas: ~2 Flowrate: 20 scc/min ~SSU1G 0. 30 torr Power Density: 0.050 W/cm3 Exposure time: 60 min.
T~ dlul~;: 36~C
l~toslllt~nt microbial count: < 10 CFU
25 Percent kill: 99.9999%
Metal chamber tlimensionS: 20.3 centimet~rS D x 20.3 centimeters L (8"D x 8"L) Example 6 With Pyrex chamber and cooled internal perforated cylinder, (FIG. 1) Gas: He(S9. 85 %)-02(39.90 %) - C F4(0.25 %) Flowrate: 48 scc/min Pressure: 0.35 torr Power Density: 0.050 W/cm3 Exposure time: 60 min.
Telllpeldlult;: 31~C
~?.oslllt~nt microbial count: < 10 CFU
Percent kill: 99.9999 %
40 Pyrex chamber dimensions: 20.3 centimeters D x 20.3 centimeters L (8"D x 8"L) Example 7 ~ 45 With metal chamber and two cooled internal pelr~ld~ed cylinders, (FIG. 6) Gas: O2(60%)-He(40%) Flowrate: (total) 42 scc/min Pressure: 0.35 torr WO 96/40296 PCTAUS~G~W555 Power Density: 0.050 W/cm3 Exposure time: 60 min.
Temperature: 32 ~C
12eslllt~nt microbial count: < 10 CFU
5 Percent kill: 99.9999 %
Metal chamber ~iimen~ions: 20.3 centimeters D x 20.3 centimeters L (8"D x 8"L) Example 8 With Pyrex chamber and cooled internal perforated cylinder, (E~G. 1) Gas: O2(pure) Flowrate: 25 scc/min 15 Pressure: 0.30 torr Power Density: 0.015 W/cm3 Exposure time: 30 min.
Telllp.,laLult;: 26~C
Percent kill: Total kill 20 Pyrex chamber dimensions: 20.3 centimeters D x 20.3 centimete,rs L (8"D x 8"L) ~xample 9 With Pyrex chamber and uncooled internal pelrolal~d cylinder, (~G. 1) Gas: O2(pure) Flowrate: 25 scc/min Pressure: 0.30 torr Power Density: 0.015 W/cm3 30 Exposure time: 30 min.
Tt;~ dlul~: 83 ~C
Percent kill: Total kill Pyrex chamber r1imen~ ns: 20.3 cenfimeters D x 20.3 centimeters L (8"D x 8"L) For the following examples, the initial spore population was 4X106 spores/strip.

E~cample 10 With microwave discharge and internal perforated met~llic shield disc, (E;IG. 3) Gas: ~eli~lm/Argon (50%/50%, v/v) Flowrate (total): 80 scc/min Pressure: 0.40 torr CA 02224083 l997-l2-08 W O 96/40296 PCT/US~ 355 Power Density: 0.015 W/cm3 Exposure Time: 90 min Temperature: 29~C
s-llt~nt Microbial Count: 1.7 X 102 CFUs S Percent Kill 99.9993 Pyrex chamber dimensions: 15.24 c~ontimp~rs D x 25.4 c~ e., L (6"D
x 10"L) Example 11 With microwave discharge and internal ~ ruldl~d me~t~ c shield disc, (FIG 3) Gas: Oxygen (Pure) Power Density: 0.015 W/cm3 12~s~lt~nt 20 FlowRate P~C.~U1C Exposure MicrobialPercent (scc/min) (torr! (min) Count (CFUs)Kill(%) 0.20 20 5.8x10577.6923 30* 0.22 45 < 10 99.9999 Te.,.p~Lulc: 24~-30~C
*Sample enclosed in barrier cloth, 2-ply, ~m~ric~n Textiles, Inc.
Pyrex chamber ~limçncions: 15.24 centimPters D x 25.4 centimeters L (6"D x 30 10"L) Example 12 With Pyrex chamber and two uncooled internal peRorated cylinders, (FIG. 1) Gas: ~2 Flowrate 70 scc/min Pressure: 0.275 torr Power Density: 0.016 W/cc Exposure Time: 45 min Tc--~ dLu-t;: 92~C

W O 96/40296 PCT~U~9~'05~55 Percent Kill: Total Kill Pyrex chamber dimensions: 22.86 centim~ters D x 33.02 centimeters L (9"D x 13"L) S
Sample was the standard st~rili7~tion test pack provided by g~ lin~s of the Association for the Advancement of MeAi(~l Instrumentation (AAMI) Px~mRle 13 With Pyrex chamber and two cooled internal perforated cylinders, (FIG. 1) Same experimental co~ ition~ as in ~ mrle 12 T~ dlul~: 54~C
Percent Kill: Total Kill St~.rili7~tion test pack employed was according to AAMI g--itlelines.

E~cample 14 With Pyrex chamber and uncooled intPrn~ roldled cylinder.
Gas: ~2 Flowrate 70 scc/min Pressure: 0.275 torr Power Density: 0.014 W/cc Exposure Time: 30 min T~ el~lul'~: 85~C
Percent Kill: Total Kill Pyrex chamber dimensions: 22.86 centimeters D x 33.02 centimP~terS
L (9"D x 13"L) Example 15 With Pyrex chamber and cooled internal perforated cylinder, (FIG. 1) Same experimental contlition~ as in Example 14 T~ ~dlul~: 47~C
Percent Kill: Total Kill WO 96/40296 PCTAU~ S5 Pyrex chamber ~lim~n~ ns: 22.~6 ce.ntimeters D x 33.02 centimeters L (9"D x 13"L) ~ 5 P.x~mEle 16 With Pyrex chamber and cooled internal p~lr~,.dled cylinder, (FIG. 1) Same e~ nt~l conditions as in Example 14 Exposure time: 2 lt4 hr.
T~ la~ule: ~il ~C
Percent Kill: Tot~l Kill Pyrex chamber tlimçn~ionS 22.86 centimeters D x 33.02 centimeters 15 L (9"D x 13"L) Example 17 With Pyrex chamber and uncooled internal p~,lrolaled cylinder.
Gas: O2(co~ n~ 500ppm of H20) Flowrate: 70 scc/min Pressure: 0.275 torr Power Density: 0.015 W/cc ~ixposure Time: 20 min.
Temperature: 61 ~C
Percent Kill: Total Kill Pyrex Chamber Dimensions: 22.86 centimeters D x 33.02 centimeters L (9"D x 13"L) Example 18 With Pyrex chamber (9"D x 13"L) and cooled intern~l pelroldled metallic cylinder, (FIG. 1) Gas: Dry and moist Oxygen, Nitrogen and Argon OEI2~ level: 300 ppm) Flowrate: 100 scc/min Pressure: 0.280 - 0.300 torr RF Power Density: 0.020 W/cc Temperature: 38~C - 57~C
Sample Size per Exl~t;lil~lent: Ten (10) 3M
"Attest" vials with 4 x 106 spores/strip in each vial, placed in a sealed Tyvek/polyethylene pouch.

W 096/40296 PCTAUS9G~9~5 Exposure Dry O2 Moist ~2 Time fmin) 4 vials - total kill 9 vials - total kill 6 vials - total kill 10 vials - total kill 8 vials - total kill 10 vials - total kill Dry N2 Moist N2 0 vials - total kill 0 vials - total kill 0 vials - total kill O vials - total kill 1 vial - total kill 2 vials - total kill 2 vials - total kill 3 vials - total kill Dry Ar Moist Ar 0 vials - total kill 0 vials - total kill 0 vials - total kill 1 vial - total kill 1 vial - total kill 2 vials - total kill 2 vials - total kill 3 vials - total lcill Example 19 With Pyrex chamber 22.86 centimeters D x 33.02 centimeters L (9"D
x 13"L) and cooled internal metallic perforated cylinder, (FIG. 1) Gas: ~2 Flowrate: 100 scc/min Pressure: 0.280 torr RF Power Density: 0.020 W/cc Exposure time: 70-105 min Temperature: 50~C
Samples:

_ W 096/40296 PCT/U~K~ 9~5 a. 61 centim~ter (24-inch) long PVC tubing with intt~,rnz~ m~t~r of 11 mm and wall thi~ of 2 mm.
b. 61 centimtoter (24-inch) long silicone rubber tubing with int~,rn~ m~,ter of 0.48 centimt~ter (3/16") and wall thickness of 0.16 c~ e~el (1/16").

Spore strip was placed in middle of tubing at apl)lo,~il,.alely 45.7 centim~,ters (18-inch) from either free end of tubing. The latter was bent into a U-shape andplaced within a Tyvelc/polyethylene pouch and sealed prior to plasma sterili7~tion.
Percent Kill: Total Kill E~nple 2Q
With Pyrex chamber 22.86 c~ntim~ters D x 33.02 centimPter~ L (9"D
x 13"L) and cooled internal ~rolal~d metallic ~;ylinder, (FIG. 1) Gas: Dry and Moist Nitrogen-Oxygen and Argon-Oxygen Mixtures (O2:5-15%);
(H2O level: 300 ppm) Flowrate: 100 scc/min Pressure: 0.275 - 0.300 torr RF Power Density: 0.020 W/cc T~ dlul~ 34~C - 53~C
Sarnple Size per Experiment: Ten (10) 3M
"Attest" vials with 4 x 106 spores/strip in each vial, placed in a sealed Tyvek/polyethylene pouch Exposure Dry N2-O2 Moist N2-O2 Time (min) 1 vial - total lcill 1 vial - total kill ~ 40 45 1 vial - total kill 1 vial - total kill 2 vials - total kill 3 vials - total kill 3 vials - total kill 4 vials - total kill W096/40296 PCT~US9~'~5~5S

Dry Ar-O2 Moist Ar-O2 1 vial - total kill 1 vial - total kill 1 vial - total kill 2 vials - total kill 3 vials - total kill 4 vials - total kill 4 vials - total kill 5 vials - total kilI

Certain embodiments of this invention rely upon neutral actives species produced by subjecting a vapor of a peracid m~tPri~l to an electrical 10 discharge at reduced pleS~iult;. The a~ ,dl~ls and methods described in this disclosure may be operated generally in harmony with the previous examples, using either RF or microwave energy to create a plasma from either hydrogen peroxide or peracetic acid vapors.
A precon~itioning step may be practiced prior to plasma ge~ ion.
15 The articles to be stprili7p~l are thereby first exposed to vapors of peracetic acid or an equivalent peracetic precursor m~teri~l. Thel~drler~ peracetic vapors may be used as a precursor for generation of a plasma. An electrical shield, such as a perforated metal cage or plate, is positioned b~Lween the plasma and the articles to e~clude charged species from direct contact with the articles.
Peracetic acid (PAA) solutions may be prepared either with high residual acetic acid, or with high residual hydrogen peroxide. In either case, peracetic acid is vapori7ed at a non-decomposing temperature, typically about 60~ C. Flow linesshould be kept at slightly higher It;lllpc;ldlult, typically below about 65~ C. By comparison, hydrogen peroxide may be vapori7ed at 74~ C with the flow lines 25 Z~ ;.ie(l at 77~ C. The flow line should ideally be kept about 3~ C higher than the sel~ctP~ peracetic acid vapori7ation len-l~el~.lulc;.
FIG. 15 i~ st~tPS an RF sterili7p~r~ generally 110 of this invention constructed within a cylindrical outer shell 111 having an approximately rectangular cross section. An inner shell 112 is concentric with the outer shell, 30 and is connP~te~l to the grounded side of an RF generator 113. It thus serves as a grounded electrode for the system. The inner surface of the shell 112 is rough.on~, as by sand blasting. The chamber and its co--L~--L~ may be preheated by flowing a heat-exchange medium through the coils 114 or the intPrn~l volume W 096/~0296 PCT~US~G/0~555 115 between the liners 111, 112. Space is provided between a rear flange 116 anda fr(mt flange 118 to accommodate in~ tion (not shown). Plasma is gene~dted in the annular space 120 between the grounded shell 110 and an inner electrode 122 connP~P~d to the ungrounded side of the power supply 113. Ceramic spacers 124 5 are positioned as shown within the space 120 between the inner shell 112 and the inner electrode 122. The inner electrode 122 is pelruldled with openings selected to pass neutral gaseous species or vapor but to excl~lde charged plasma species. It may thus be viewed as a Faraday cage.
The stçrili7~r 110 iS shown within a system by ~G. 16. A prog-,.,-,.nAhle 10 logic controller (PLC), generally 124, or other suitable ci~;uilly, iS connecte(l through cables 125 to the power supply 113 and other components of the system as shown. Fluid flow between system components is accommodated by ayp~ lidle conduits 126. Precursor vapors are supplied from a source 127 to the annular space 120, and thus the interior 126 of the pe~roldled inner electrode 122. These 15 vapors are distributed through diffusion tubes 128 positioned around the perimeter of the inner electrode 122. Vapor flow is through a control valve 128 opened andclosed by the controller 124. Liquid sterilant ~l~ul~or is ~d~ ~ed by a heater 129 associated with the source 127 and cycled ~lu~lialely by the controller 124.A pump 130, also rt;~ollsi~le to the controller 124, circulates coolant through coils 114 mounted to the inner electrode 122. P~t;s~ul~ within the ch~mber 120, 126 isadjusted by operation of a vacuum pump 135 and associated control valve 137, both of which are tumed on and off by the controller 124. Pressure and elalulc~ sensors (not shown) are positioned strategically within the sterilizer 110 to provide input signals to the controller 124.
A dwell preconditioning phase may decrease the volume of sterilant precursor required per cycle. A preconditioning step is also considered beneficial to the sterili7ing efficacy of the system. Referring to FIGS. 15 and 16, a preconditioning phase may consist of the following steps:
1. The chamber shells 111,112 and electrode 122 are heated to a 30 presPIP~,t~P~ lelllpe,alulc; (around 40~ C).
2. The vacuum pump 135 is operated to establish a base ~lt;;S;!iUlt; (typically 500 microns).

W O 96/40296 PCTAUS9G~'u~SS

3. A pr~s~ul~ controller 140 associated with the PLC 124 is adjusted to a first (lower) sc~ u-L (typically 2 torr), and vapor (typically hydrogen peroxide or peracetic acid) is introduced through the diffusion tubes 128 to allow this setpoint to be achieved.
4. After the ~ Ule within the chamber 120, 126 has equilibrated at the first selecte~ St;LyO~Il level, the yl~S~iUlt; controller 140 is ~ignP~ a second (higher) setpoint (typically 6.5 torr), and the controller 124 operates to adjust the control valve 137 to achieve this second setpoint.
5. After the ~ ul~ equilibrates at the second setpoint, and subsP~!-P-nt to 10 any se.lPctPA timed dwell period, the pltSSulc; controller 140 is ~SignP~i a third setpoint (typically ~lvx~ at~ly the same as the first, or lower, setpoint, e.g., 2 torr), and the valve 137 to the vacuum pump 135 is again adjusted by the controller 124 to achieve this third setpoint.
6. Steps 4 and 5 may be repeated for a pre~letPrmined time period.
7. After the plGdciltillllilled time period has expired, the IJleS~ulc; controller 140 establishes an o~ .ling S~tLJo~ (typically 600 microns) for plasma processing.
8. When the ~lJelalillg selyoilll is reached, the plasma is ignited within the space 120 by operation of the power supply, and ~ellllilled to run for the 20 predetP.rminPci cycle time.

Example 21 The efficacies of hydrogen peroxide and peracetic acid solutions in the ,sterili7~tirm process of this invention were studied as part of a series of $t~ti~ti~
25 flesi~npA e~t;lilllents.
AAMI EO Test Packs: Modified AA~ Standard EO packs were yrepalc;d in which the BI strip was removed from its gl~inç wrap before processing.
Three strips were placed in each syringe, and the syringe was closed at its large end with the standard rubber stopper. A second syringe was prepared conl;.ining 30 one MDT Biosign CLBI (results reported as fractional negative). The syringes were placed adjacent to one another and were wrapped in a huckabuck towel per the AAMI EO Test Pack standard. The entire assembly was placed in a Baxter W O ~4029~ PCTAU~9.~3~55 -35-'Tower Dual-Peel' 19 centimeters x 33 centimeters (7.5" x 13") paper-plastic peel pouch, which was subseqllently heat sealed.
St~tiSti~l DesiPn of Experiment~- This example is based upon both Taguchi and Greco-Latin Square experim-~.nt~l designs in accordance with standard S .st~ti~ti(~ design of e~ nent techniques [CSS:St~ticti~ a, StatSoft, Tulsa, OKI.
These ~iA~e.il,lental designs p-,llllill~d variation of four p~r~m~ters over four discrete levels (Greco-Latin Square) or five p~r~meters over four discrete levels (Taguchi L'16 design). The res-llt~nt data, reported as log reduction, is analyzed to provide mean values for each of the palalll~,t~ at each p?lr~meter level. Also 10 provided are ANOVA and correlation results (for reduction vs. exposure time), which evaluate the st~ti~ti~l validity of the data.
Experimental: For all of the experim~nt~, the packs were placed in a rectangular sterili7~tion chamber (FIG. 15) in an o~ ld~ing configuration (paperto paper and plastic to plastic. The packs were allowed to overlap only to the 15 extent required by the size of pouches and the basket in which they were placed.
This al,dngelllent provided a maAillwlll overlap of about 2/3 of the pack width.The packs were placed a~l~Aullately in the middle of the chamber and filled the area of the basket from front to back.
In cases where no RF was applied, after the cycle was complete, the strips 20 were placed in a sterile residual nPut~li7ing solution for ten ...i...-(es, followed by immersion in sterile water for another ten Illulu~s. For hydrogen peroxide, the neut~li7ing solution was c~t~ e in phosphate buffer and for peracetic acid, ~ 5 uM sodium thiosulfate was used.
The process variables explored in these studies have been: RF on/off, base 25 pressure (--~i-~;-------- pl~S~Ul~ experienced by the load in initial pumpdown), process ~lt;s~u,e (~s~ur~; at which the plasma is actually run), exposure time (plasma phase only-precondition was held fixed at 30 minutes with default pulsing parameters), steril~nt precursor (hydrogen peroxide and peracetic acid), and biological in-lic~t-)r organism and lot. The plasma excitation frequency was 40 30 l~Iz throughout at a power level of S kW.

W096/40296 PCT~US36~ 35 Results:
The results are reported selJdld~ely as mean values for each parameter in a given experimental design. Based on these results, it is possible to choose an optimal value for each process p~ cle~.
Base I'~ur~
The base ~ ul~ is the initial ~ ulc to which the system is pumped down before a co.. ~ ~~.. ent of the preconditioning phase. Data was taken on efficacy at base ~lGSsult;s of 100, 200, 250, 300, 400, S00 microns and 1 and 1.5 torr.
In the Greco-Latin Square experiment, the base pressure took the values of 100, 200, 300 and 400 microns. The mean log reductions for these base plt;S~ulc~S for Bstm were 2.45, 1.99, 3.08 and 3.26, c;*~e~ ely. These data suggest that a base ~l~,SsulG of 400 microns yielded the most ef~lcacy. However, .ct~ti~ti.~l analysis for Bstm was less positive, with the F-value being 1.41 and p-value being 0.26. For Bg, however, the results were st~ti~ti~ ~lly more palatable, with F for base pressure being 15.2 and p being 0.000002. The Bg results confirmP~ 400 microns as the base ~llG~:!iUl~; providing the most efficacy in the tested set.
(100 microns, 3.28 mean log reduction; 200 microns, 4.64 mean log reduction; 300 microns, 3.30 mean log reduction; 400 microns, 5.64 log reduction).
In the Taguchi set, the best results are seen at 500 microns and 1.5 torr, with a dropoff in efficacy at 1 torr. The actual mean results were 1.83 log reduction at 250 microns, 2.67 log reduction at 500 microns, 1.7 log reduction at 1 torr and 2.59 log reduction at l.S torr. A possible explanation for this drop in efficacy is that there are two co~ elil.g effects that can improve or hinder stf~rili~tion efficacy; air removal and desiccation of the bioburden (in this case, spores). A deeper vacuum will improve air removal while simultaneously increasing the desiccation of the spores. If there are multiple stages of vacuum-indllced d~sicc~tion possible for the sores, their resi~t~n~ e to the process will increase in a stepwise manner, until increased air removal permits increased pelle~ldlion and efficacy. Although the results are essentially the same at S00 microns and W O 9''~29~ PCT~USg~'O~S5 1.5 torr, the lower base pressure value of 500 microns is preferred, because a lower plt;S5ul~ will facilitate air removal before a possible dwell preconditioning step.
Precursor: Both peracetic acid (5% and 15%) and hydrogen peroxide 5 (50% and 70%) were tested. The lower concentrations of each precursor has beendetermined to be less efficacious than the higher concentrations. The mean results for 15% peracetic acid and 70% hydrogen peroxide were 2.8 log reduction and 3.1 log reduction, respectively. However, in this series, the peracetic acid wasrun at the same vaporization lell~peldlu~t; (74~ C) as was the hydrogen peroxide.
10 Peracetic acid decomposes fairly rapidly at this temperature. Accoldillgly, a direct comparison was made with the peracetic acid vaporization temperature set at 60~
C. (See Example 22.) Plasma pressure: The Taguchi L'16 designed experiment incl~lded variation of base pressure as one of its parameters. The values used were 500, 15 600, 700, and 800 microns. Analysis of this t;~ye~ullental set shows 600 microns plasma yl~s~ure to be the most efficacious for the process. It showed a mean logreduction of 3.55 log, with 500 microns having a mean reduction of 1.58, 700 microns having a mean reduction of 0.9, and 800 microns having a mean reduction of 2.76. ANOVA analysis of this data shows it to be st~ti~tic~lly valid 20 with F = 18.55 and a p-value of 0 to 6 decimal places. Based on these data, 600 microns is ~;ull~,lllly ylc;rell~d as the wrapped cycle process plessul~
RF: This series of e~ ullents conf;rmed the improved rate of kill due to the presence of a plasma vs. that observed when only the sterilant precursor wasused in the process. The Taguchi L'16 ~e.;,..ent~l data set yields a mean log reduction with RF off of 0.2 log, while with RF on, the mean reduction was 4.35 log. This result is also confirmed by the Greco-Latin Square experimçnt~l set, in which the mean log reduction for Bstm with RF off was 1.13, while the mean log reduction with RF on was 4.26. For Bg, the results were 3.10 for RF off and 5.33 with RF on.
Exposure Time: In the Taguchi L'16 ~ e~ lental set, testing was done at exposure times of 40, 50, 60, and 70 minutes. Within a reasonable a~l.~xihllalion, the log reduction values fall on an essentially straight line (correlation coefficient 0.9559). This trend was also observed for Bg kill in the WO 96/40296 PCT~US96/09955 Greco-Latin Square ~;~e~ ental set (c;o~l~la~ion coefficient of 0.965). For Bstmin that set, near log-linear kinetics were observed (correlation coefficient of 0.9643). The D-values that result from these analyses, although not done at optimal con~iti~nC, range between 10.53 and 10.87 mimlte.s for Bstm and 7.87 Example 22 A direct co,-lpalison of 15% peracetic acid and 70% hydrogen peroxide sterilant precursors was made by exposing AAMI standard EO test packs for 45 minutes to plasma in-1~lced by 40 kHz excitation frequency with 5 kW RF power.
10 The procedure consisted of proces,sing four AAMI standard EO test packs usingeither ~teril~nt precursor at a plasma ~res~u.c; of 600 microns, using a 30 minute preconditioning phase with lower and upper setpoints of 2 torr and 6.5 torr, respectively, a base ~lc;~Ul~ of 100 microns and an exposure time of 45 minlltes.
No gl~lsimp~ was used on the BI strips (Bstm, 106 spore population, ~IDT lot 601).
15 The peracetic acid was vapor,7ed at 60~ C vs. a 74~ C hydrogen peroxide vapori~ation Ic;lllpt;lalulc;. in this measurement set, 70% hydrogen peroxide and 15% peracetic acid were seen to be essenti~lly iden~iç~l in efflcacy (5.43 mean log reduction vs. 5.57, respectively).
In sterilizers in which a plasma is generated within a volume in which a 20 sterilization load is also present, the load is exposed to infrared, visible and (ultraviolet) light, as well as the active plasma species desired for ste.rili7~tion.
Plasma sterilization processes are run at very low pressures. Radiant heat from both the plasma and any surfaces heated by the plasma may heat the load above a temperature suitable for the load. It has been discovered that positioning a 25 textured surface adjacent the situs at which plasma is generated (for example, a portion of the interior surfaces defining a plasmas reaction zone) is generally effective in lowering both load heating and the steady state t~ t;lalul~; achievable within the sterilizer.
The positive inflllen-~e of a rollghPnPcl reactor surface on the steady-state concentration of active species available for dry sterilization procedures has also been observed. This effect has been observed in processes employing various gaseous and vaporous sterilization precursors. Increased roughnP.s~, within the range tested, generally increases the steady state concentration of active species in CA 02224083 l997-l2-08 W O 96/40296 PCT~US~G~ 3SS

a plasma generation zone, and the steady-state concentration of neutral active species pene~ the perforated shield to reach the glowless, sub~t~nti~lly field free sterilization zone favored by this disclosure.
Processes conducted in accordance with any of the examples of this 5 disclosure would be expected to benefit from structural mo-lifiç~tions which provide rollghened surfaces in contact with the plasma, preferably while it is being generated.

Example 23 A number of stPri~ ti~-n cycles were run under the conditions specified in ~xample 21 in a system such as that illustrated by FIG. 16. A stPrili7Pr of the type ilhl~t~tef~ by FIG. 15 was used. The inner shell was constructed of 316 SSTwith a 220-300 grit polish followerl by sand blasting with # 46 ~ mim~m oxide at551,600 Newtons per square meter gauge to 689,500 Newtons per square meter 15 gauge (80-100 psig.) to produce a roughPnP~ surface.
These tests demon~t~tPcl improved sterilization efficacies with the inner surface of the shell 112 roughPnPCl in this fashion as compared to similar control cycles in which this surface had a polished finish. They also demon~ P,d lower load temperature after equivalent exposure durations under similar conditions with 20 the inner surface of the shell 112 roughPnP~ in this fashion as compared to similar control cycles in which this surface had a polished finish.
Specifically, with process conditions of 0.600 torr pressure, 15 % peracetic acid feed vapor, RF power density of 0.031 W/cm3, 40 kHz RF frequency and exposure times of 90 .ui...-~es, load tempe~,lur~s fell from 70~ C with a polished 25 chamber to 57~ C in the roughened chamber. The roughPnP{I chambers thus appear to absorb radiant energy from a plasma glow. It is thus available to select plasma chemistries that produce active biocidal species under conditions in which they do not transfer to the load as readily as they undergo nonradiative decay.
Several other cycles were run in reaction chambers structured as ilhlstr~tP~
30 by FIGS. 4 and 5, but with roughened cylindrical metal chamber inserts composed either of SST 304 (st~inless steel alloy) or 60601T6 (~h....i.-....~ alloy). The inserts were positionP~ effectively to replace the outer chamber ~IPsi~n~tP~i 21 in the figures. These cycles demonstrated that both surface roughnP~ and chamber W O 96/40296 PCTrUS~ S5 m~t~ri~l have an impact on process efficacy. The following table reports resultsobtained using an oxygen plasma with feed gas entering the chamber at a flow rate of 250 sccm, a reaction ~ 3:jUl~; of 0.650 torr, RF power density of 0.097 W/cm3and the load being AAMI standard EO test packs. The Spore strips used were B.
s subtilis v. niger, with an initial population of 4 X 106. Exposure time was 105 minntes, and the final processing temperature was 60~ C.

Table Chamber Material R~n~hn~cc Results (G~t S~e) (Fl ~ -i S~r~

15Al 6061T6 180 8/9 Al 6061T6 600 9/9 The SST-lined chambers had significantly greater efficacy in these cycles 20 than did the ;llu~ lined chambers. The effect of grit size is also apparent, with the best results achieved with a 180 grit size. Both coarser and finer gritsizes produced less efficacious results.
A pr~rell~d d~JalaL~ls of this invention includes a gas-cu..ri..i.-g chamber constructed and arranged for co"~ an electrical discharge. The portion of the25 chamber in contact with the plasma has a textured surface. For purposes of this disclosure, the term "textured" is by comparison to a polished or unaltered millfinish, such as is conventionally produced by cold rolling. An article-co"~ g (sterilization) zone is positioned to receive sub~t~nti~lly neutral active species from the electrical discharge, and a barrier structure transparent to subst~nti~lly neutral 30 active species and opaque to charged species is positioned between the sterilization zone and the discharge. The barrier structure, typically a perforated inner electrode as shown by FIG. 15, comprises a first electrode, and the chamber W O 96140296 PCT/U~,Gl'a3~55 comprises a second electrode, the first and second electrodes con~ means for i,lil;AI;Ilg the electrical discharge.
A portion of the second electrode is provided with a textured surface which is rough colllpalcd to an unaltered mill surface f~ish of the mAtt-riAl from which S that portion is constructed. The gas-col~~ g chamber may be or include a plasma-reaction zone def~ed in part by an inner surface of the chamber. That inner surface, which sometimÇs includes the entire inner surface of the gas-confining chamber, is preferably constructed of a metal selected from the group con.~i.cting essentially of stAinl~ steel and Alnminllm alloys. Other metals are10 operable, but are often impractical or uneconomical to use. The textured portion is roughPn~A by means equivalent to sand blasting with ~ . oxide grit, the precise lc~ulihlg method employing being a matter of choice. Various chtomi~Al and physical etching techni~lues are within contemplation. A st~inl~s~ steel metal surface textured equivalent to a surface sand blasted with Al.. i.. " oxide grit 15 having a grit size of between about 120 and about 300 is presently ~lcrcLrcd.Sandblasting at about 100 psig for a period of between about one half hour to about 2 hours is generally snfflçiPnt to produce an effective t~ g for purposes of this invention.

Example 24 A reactor such as that illustrated by FIGS. 4 and 5 was provided with grounded metal electrode inserts. Inserts were constructed of various st;~inl~s.~
steel and Ahlminllm alloys. Cycles were run to compare the ~.rolulallce of the reactor when provided with inserts of different surface textures. Selected inserts were subjected to conventional sand blasting with Alnminllm oxide grit sizes of 120, 180,250, 300, 450 and 600. The inserts with textured surfaces uniformly produced improved sterilization efficacy c~)lllpA~ed to similar inserts having polished surfaces.

Claims (37)

What is claimed is:

1. Apparatus for sterilizing articles, comprising:
a gas-confining chamber constructed and arranged for containing an electrical discharge which includes substantially electrically neutral active species;
an article-containing zone positioned to receive substantially neutral active species from said electrical discharge; and barrier means between said zone and said discharge, said barrier means being transparent to said substantially neutral active species and opaque to charged species;
a portion of said chamber having a textured surface which is rough compared to an unaltered mill surface finish of the material from which said portion is constructed.

2. The apparatus of claim 1, wherein said barrier means comprises:
a first electrode and said chamber comprising a second electrode, said first andsecond electrodes constituting means for initiating an electrical discharge within said chamber; and a portion of said second electrode has a textured surface which is rough compared to an unaltered mill surface finish of the material from which said portion is constructed.

3. Apparatus according to claims 1 or 2, wherein said gas-confining chamber includes a plasma-reaction zone defined in part by an inner surface of said chamber, said inner surface being constructed of a metal selected from the group consisting essentially of stainless steel and aluminum alloys.

4. Apparatus according to claims 1 or 2, wherein said portion is roughened by means equivalent to sand blasting with aluminum oxide grit.

5. Apparatus according to claim 4, wherein said portion is a stainless steel metal surface textured equivalent to being sand blasted with aluminum oxide grit having a grit size of between about 120 and about 300.

6. A method for sterilization of a load, comprising the steps of:
placing said load within a gas-tight confining chamber wherein said chamber is formed at least in part from a metal wall;
evacuating said chamber to a substantially low pressure, and introducing into said chamber a biocidal fluid in vapor or gas state;
exposing said load to said biocidal fluid during a preconditioning phase;
inducing a plasma in said biocidal fluid within said chamber by application of electrical energy; and maintaining said gas plasma for a controlled period of time;
a portion of the inner surface of said chamber being provided with a textured surface capable of increasing the steady state concentration of active species contacting said load.

7. A method according to claim 6, wherein said plasma is initiated adjacent an inner surface of said chamber, and said inner surface has a texture which is rough compared to an unaltered mill surface finish of the material fromwhich said surface is constructed.

8. A method according to claim 7, wherein said inner surface is constructed of a metal selected from the group consisting essentially of stainless steel and aluminum alloys.

9. A method according to claim 7, wherein said inner surface is roughened by means equivalent to sand blasting with aluminum oxide grit.

10. A method according to claim 9, wherein said inner surface is a stainless steel metal surface textured equivalent to being sand blasted with aluminum oxide grit having a grit size of between about 120 and about 300.

11. In a sterilization method wherein a load is exposed within a sterilization zone to active species of a plasma generated in a reaction zone operably associated with said sterilization zone; the improvement which comprises:
introducing a biocidal fluid in vapor or gas state into said sterilization zone;

exposing said load to said biocidal fluid during a preconditioning phase;
inducing a plasma in said biocidal fluid within said chamber by application of electrical energy; and contacting said plasma with a textured metal surface prior to contacting said load with said active species.

12. An improvement according to claim 11, wherein said plasma is generated within a gas-confining chamber containing said sterilization zone, said plasma being induced by the application of RF energy.

13. An improvement according to claim 12, wherein said chamber is defined by a surface of aluminum or stainless steel and said sterilization zone is defined by a perforated metallic shield constructed to be transparent to neutralplasma species and opaque to charged plasma species.

14. An improvement according to claim 11, wherein said plasma is generated within a reaction zone separated from said sterilization zone by a barrier constructed to be transparent to neutral plasma species and opaque to charged plasma species.

15. An improvement according to claim 14, wherein said reaction zone comprises an annular volume surrounding said sterilization zone.

16. An improvement according to claim 15, wherein said plasma is induced by the application of RF energy.

17. An improvement according to claim 14, wherein said plasma is induced by the application of microwave energy.

18. An improvement according to claim 17, wherein said barrier is in the form of a perforated metal plate interposed between said reaction zone and said sterilization zone.

19. An improvement according to claim 14, wherein said load is exposed to a sterilant precursor within said sterilization zone during a preconditioning period, and thereafter energy is applied to said precursor to produce said plasma.

20. An improvement according to claim 19, wherein said precursor is se1ected from the group consisting essentially of hydrogen peroxide solutions and peracetic acid solutions.

21. An improvement according to claim 20, wherein said sterilization load is exposed to said sterilant precursor for a period of between about 10 minutes and about 8 hours prior to energizing that precursor to form a plasma.

22. A method for sterilization of medical devices and materials comprising the steps of:
placing said devices and materials within a gas-tight confining chamber wherein said chamber is formed at least in part from a metal wall and includes an internal perforated metallic element positioned within said chamber;
evacuating said chamber to a substantially low pressure, and introducing a gas into said chamber;
initiating an electrical discharge in said gas within said chamber by application of RF energy between said metal chamber wall and said internal perforated metallic element, creating a gas plasma; and maintaining said gas plasma for a controlled period of time, said perforated metallic element creating a field free and glowless volume within said chamber, said devices and materials being placed within said field free and glowless volume;
a portion of the inner surface of said chamber being provided with a textured surface.

23. A method according to claim 22, wherein said plasma is initiated adjacent an inner surface of said chamber, and said inner surface has a texture which is rough compared to an unaltered mill surface finish of the material fromwhich said surface is constructed.

24. A method according to claim 23, wherein said inner surface is constructed of a metal selected from the group consisting essentially of stainless steel and aluminum alloys.

25. A method according to claim 23, wherein said inner surface is roughened by means equivalent to sand blasting with aluminum oxide grit.

26. A method according to claim 25, wherein said inner surface is a stainless steel metal surface textured equivalent to being sand blasted with aluminum oxide grit having a grit size of between about 120 and about 300.

27. In a sterilization method wherein a load is exposed within a sterilization zone to active species of a plasma generated in a reaction zone operably associated with said sterilization zone; the improvement which comprises contacting said plasma with a textured metal surface prior to contacting said load with said active species.

28. An improvement according to claim 27, wherein said plasma is generated within a gas-confining chamber containing said sterilization zone, said plasma being induced by the application of RF energy.

29. An improvement according to claim 28, wherein said chamber is defined by a surface of aluminum or stainless steel and said sterilization zone is defined by a perforated metallic shield constructed to be transparent to neutralplasma species and opaque to charged plasma species.

30. An improvement according to claim 27, wherein said plasma is generated within a reaction zone separated from said sterilization zone by a barrier constructed to be transparent to neutral plasma species and opaque to charged plasma species.

31. An improvement according to claim 30, wherein said reaction zone comprises an annular volume surrounding said sterilization zone.

32. An improvement according to claim 31, wherein said plasma is induced by the application of RF energy.

33. An improvement according to claim 30, wherein said plasma is induced by the application of microwave energy.

34. An improvement according to claim 33, wherein said barrier is in the form of a perforated metal plate interposed between said reaction zone and said sterilization zone.

35. An improvement according to claim 30, wherein said load is exposed to a sterilant precursor within said sterilization zone during a preconditioning period, and thereafter energy is applied to said precursor to produce said plasma.

36. An improvement according to claim 35, wherein said precursor is selected from the group consisting essentially of hydrogen peroxide solutions and peracetic acid solutions.

37. An improvement according to claim 36, wherein said sterilization load is exposed to said sterilant precursor for a period of between about 10 minutes and about 8 hours prior to energizing that precursor to form a plasma.