CA2132615A1

CA2132615A1 - Improvement in methods and apparatus for sterilizing objects

Info

Publication number: CA2132615A1
Application number: CA002132615A
Authority: CA
Inventors: Barry S. Kutner; Daniel A. Latowicki
Original assignee: Individual
Current assignee: Flexiclave Inc
Priority date: 1992-03-25
Filing date: 1993-03-25
Publication date: 1993-09-30
Also published as: AU3935193A; EP0637969A4; EP0637969A1; JPH07505301A; WO1993018798A1; US5871702A

Abstract

An arrangement (10) for sterilizing objects (22) in which a quantity of liquid (20) and one or more objects to be sterilized are introduced into a pouch (16) formed of flexible sheet material at least partially transparent to microwave radiation whereupon the pouch is sealed to form a gas-tight assembly (14). The gas-tight assembly is situated in an inner rigid cavity (26a) of an enclosure which is at least partially formed of material that is substantially transparent to microwave radiation. The enclosure is irradiated with microwave radiation which passes into the cavity and then into the gas-tight pouch assembly situated therein to vaporize the liquid to produce an atmosphere of hot vapor under pressure in the pouch. The pouch expands under pressure until the sheet material of which it is formed presses against the rigid inner surfaces of the enclosure cavity. At least a part of the gas-tight pouch assembly may be surrounded with microwave radiation shielding (24) which divides the interior of the pouch into shielded (38a) and unshielded (38b) interior portions, the object to be sterilized being situated in the shielded pouch portion while the liquid to be vaporized is situated in the second unshielded pouch portion.

Description

W~93~1~98 ' PCT/U593/027g3 ~ i ~ % 6 1 ~ !

IMPROVEMENT IN METHODS AND APPARATUS
FOR STERILIZING OBJECTS

BACKGROUND OF TH~_INy~ Q~
This is a continuation~in-part of application Serial No. 07/692,736 filed April 29, 19~1, which is a continuation of Serial No- 07/274,768 filed No~ember 22, ~988, now U.S. Patent 5,039,495, which is a continuation-in-part of application Serial No.
07/184,246, filed April 21, 1988, now U.S~ Patent 5,019,344.
This invention relates g~inerally to methods ~nd apparatus for disinfecting or sterilizing objects, and more particularly, to methods and apparatus for disinfecting or sterilizing objects, such as dental and medical instruments. As used hereinbelow, ~he terms ~Isterilizing~ "sterilization", and the like will be used in their broadest sensi and should be understood to mean the killing of bacteria and spores, as well as the killing of bacteria to the extent necessary for a particular purpose, and may include the process of "disinfection."
The need for effective sterilization of dental instruments, such as dental handpieces, is more ~;lJBSTlTUTE SHEEI

W~g3tl87g8 PCT/VS93/0~93 2 ~ 1 ~

important today than ever before due to the realiza-tion of the significant potential for infection via dental procedures and the increase in the rate of transmission of serious diseases by blood and saliva.
However, from a practical viewpoint, not only must the sterilization procedure be effective, it must also be rapid, i.e., have a short turn-around or cycIe time. Thus, it will be understood that the quantity of any one instrument that a practitioner or institution must purchase and have available for use will depend on the frequency of treatments requiring that instrument and on the turn-around time required to sterilize the instrument. In the case of dental handpieces, which generally are required for most treatments performed in the dental operatory, an extended sterilization cycle means that a larger inventory of available handpieces must be maintained.
The high cost of dental handpieces, on the other hand, often limits the number of available hand-pieces, which in turn may result in hasty and there-fore ineffective attempts at, or even dispensing with, lengthy sterilization procedures. This of course is unacceptable.
Heat sterilization methods, such as steam heat (autoclave), dry ~heat, and chemical vapor, are generally preferred over cold immersion methods, SUBSmUTE SHEET
: ::

WO93/1~9B PCT/US93/02793 6 1 ~

which are generally not effective unless glutaralde-hyde is used and the instrument is immersed for 7 -10 hours. Chemical vapor sterilization has the advantages of minimal corrosion of burr~ and other sharp instruments (steam sterilization or immersion in most liquid sterilents produces dullness and rusting) and a cycle time which is relatively short compared to cold sterilization techniques.
One type of chemical vapor sterilizing arrange-ment which is in commercial use (available from MDT
Corporation of Gardena, California under th~ desig-nation Harvey Chemiclave) comprises apparatus which uses moderate heat (about 270F)g pressure (about 20 psi) and a special solution composed primarily of 3A
alcohol (a~out 80%) and water (about 9%) with small amounts of acetone, ketone and formaldehyde. The cycle time is about 20 minutes after proper pressure is reached. The length of time reguired to reach pressure depends on the size of the load. On the other hand, the purchase price of this arrangement is higher than steam and dry heat processors. Additional drawbacks are that relatively large quantities of sterilizing solution are required, and odor and minor irritation of eyes, nose and throat from chemical vapors often accompanies use, the process chamber must be cleaned on a frequent basis, the instruments SUBSllTUTE SHEET

wO93/t~g8 ` PCT/US93/027g3 -2Gl~

should be wrapped to prevent recontamination, and the simultaneous sterilization of a plurality of instru-ments results in the possibility of cross contamina-tion. Moreover, the sterilization cycle time, al-though less than the time required for the sterili-zation by solution immersion, is still relatively long, essentially because of the relatively laxge chamber volume.
U.S. Patent No. 4,400,357 issued August 23, 1983 to Hohmann, discloses an arrangement for chemical vàpor sterilization of articles, such as dental hand-~-~ pieaes, which would appear to overcome some of the above-mentioned probIems. The patent discloses an arrangement in which the article to be sterilized is situated in an enlarged portion of a rigid vessel.
A liquid reaction agent is charged into a narrow por-tion of the ve~sel which is in communication with the enlarged article-containing vessel portion. The liguid reaction agent is heated to produce a vapor which flows into the first vessel portion to steri-lize the article. The first vessel portion may be designed to accept only a single article in which case the amount of liquid reaction agent required to generate the vapor is relatively small which in turn reduces the heating time reguired for vaporization and~the overall sterilization cycle time. The patent , , : ~
" , ~ SUBSTITUTE St~EEr W~93~18798 ~ v PCT/US93102793 suggests t~at the means for heating the liquid reac-tion agent may comprise a microwave radiator. In such a case, ~he vessel is situated such that only the narrow liquid-containing vessel portion is posi-tioned in the microwave radiation field while the article to be sterilized is situated outside the radiation field which, the patent notes, avoids the formation of spark gaps at border surfaces and seams of the article which cause surface destruction.
Although possibly reducing the time required for sterilization, the arrangement proposed in the patent has various drawbacks which have apparently prPvented adoption and commercialization of this arrangement.
For example, it requires a complicated, specially lS designed microwave generator adapted for positioning the vessel with only the liquid reaction agent-con~
taining portion in the radiation field of the micro-wave generator with the article-containing ves~el portion outside the radiation field. It reguires a specially designed rigid pressure vessel which either must be cleaned after each use to avoid crosscontami-nation or discarded at significant expense.
A discussion of the sterilization of articles, such as dental instruments, by microwave radiation is set forth in U.S. Patent No. 3,753,651 issued August 2l, 1973 to Boucher. Briefly, it is noted SUE~STITUTE SHEET

w~ 93/187g8 ~ 6 ~ 5 PCT/VS93~02793 that sterilization by microwave radiation is due to both thermal effects, such as microwave induced heat, and non-thermal effects, which the patent suggests may affect a metabolic system distinct from that of S thermal energy. It is disclosed that improved sur-face sterilization results are obtained when the articles are subjected to microwave radiation while situated in a humid atmosphere, i.e., an atmosphere having a relative humidity of at least 50~ or super-saturated with water or saline solution. To this end, the articles to be sterilized are placed on trays which are situated in a rigid, microwave-transparent container having a known volume, along with a quan-tity of water or saline solution determined by the container volume 50 as to be sufficient when vapor-ized to increase the humidity of the atmosphere - within the container to the desired value. Af~er placing the articles to be sterilized and the water or saline solution into the container, the container is sealed with a lid and then placed within the cavity of a microwave generator and subjected to microwave radiation. The electromagnetic energy penetrates through the container walls to evaporate the water or saline solution to produce the desired humidity, and at~the same~time, proceeds to sterilize the surface of the article by the thermal and non-- ~ SUBSTITUTE SHEET
, , - ~

W~ g3/18798 t ` P~T/US93/02793 - ~13~G15 thermal effects discussed above. It is indicated that this procedure results in reduced cycle time for effective sterilization compared to dry heat or steam sterilizing methods and that the localized arcing (sparking) which usually occurs when metallic objects are irradiated by microwave radiation is practically eliminated in the moist atmosphere.
The patent also points out that the container can be filled with any gas to constitute the atmos-phere to be humidified. For example, it is suggestedthat a ga~s or vapor sterilant can be introduced into th~ container ~through valves~ provided in the con-,:
tainer~ walls to take advantage of their chemical st-rilizing effects, although care should be taken to :
;-~ 15 ~avoid~heating the artifle being sterilized to a point , where it reaches the ignition or explosion point of the gas.

~fhe arrangement proposed in U.S. Patent No.

3,753,651 has drawbacks which have apparently pre-ventad it from being adopted on a practical basis.

For example, as noted in the above discussed U.S.
f', f ~ ,: , Patent No. 4,400,357, only surface sterilization is achieved by microwave irradiation and microorganisms present on surfaces located within the seams and cre-2S ~vices~of~the~article will not be killed, especiallyif b~lood~and salivary protein are deposited on those SUBSTITUTE SHEET
. , : - `

W093/187g8 ."~ g Pcr/uss3/on~

surfaces. This is true regardless of whether the container is initially filled with a gas sterilant as suggested in the patent. The procedure require5 a specially designed gas-tight rigid container having a known, fixed volume. The container must be steri lized after each use or discarded, in which case considerable expense is incurred especially where valves are provided in the container walls as dis-cussed above. To provide a truly gas-ti~ht co:ndi-tion, it is necessary to use materials, such as forgaskets and the like, which are not entirely trans-parent to microwaves. Moveover, the relatively large volume of the container which is necessary to accom-modate th~ articles ~o be sterilized in turn requires a relatively large volume of water or saline solution to achieve the desired humidity. This results in an increase in the time required for the evaporation~of the water or saline solution thereby increasing the overall sterilization cycle time. ~urthermore, it is not thought that the arrangement d scribed in this pat~nt will avoid the problem of arcing or sparking.
Applicants have developed new and improved methods and apparatus for sterilizing objects which overcome many of the drawbacks of the prior art arrangements discussed above. In particular, methods and apparatus for sterilizing objects are disclosed SUBSTITUTE SHEET

W~93/18798 c ~ , PCT/US93/0~93 ~ i. 3 ~ ~ 1 3 g in applicants' prior U.S. patents 5,019,344 issued May 28, 1991 and 5,039,495 issued August 13, 1991, the descriptions of which are hereby incorporated herein in their entirety. These patents describe arrangements in which an object to be sterilized and a quantity of liquid are introduced into a pouch formed of flexible vapor-impermeable sheet material whereupon the pouch is sealed to form a gas-tight assembly. The liquid is introduced into the pouch in a quantity sufficient to create an over-pressure within the pouch when it is vaporized which expands the pouch, whereupon the object becomes sterilized under the effect of the hot vapor under pressure.
The liquid within the pouch may be vaporized by irradiating the gas-*ight assembly with microwave radiation in which case the object being sterilized is preferably surrounded by shielding which presen~s a barrier to the transmission of microwave radiation to thereby avoid arcing or sparking. The arrange-men~s developed by the applicants which are disclosedin the above-mentioned patents are advantageous in that the time required for a sterilizing cycle is substantially reduced relative to prior techniques, ~- a visual indication that the process is proceeding is provided by virtue of the expanding pouch, the arrangements are inexpensive in manufacture and use, SUBSTITUTE SHEET

w~ g3~l8798 ~ 6 I ~- PCT/US93~02793 . `

and they allow the subsequent handling and storage of the sterilized object without the danger of reconta-mination. The arrangements may be used for steriliz-ing a wide variety of objects including medical and dental instruments, medical waste material, contact lenses, and the like.

SUMMARY OF THE NVENTION
A general object of the present invention is to provide new and improved methods and apparatus for sterilizing objeots, such as dental and medical instruments.
Another object of the present invention is to provide new and improved methods and apparatus for ~terilizing objects by hot vapor under pressure which ,~ ~
require less time and which are simpler in construc-tion and more economical in use then prior art arrangements.
Still another object of the present invention is to provide additional ~mprovements in the methods and apparatus for sterilizing objects described in appli-cants' patents mentioned above.
Briefly, in accordance with one aspect of the - present invention, these and other obiects are attained by providing an arrangement in which a quantity of liquid and one or more objects to be : ,-SUBSTITUTE SHEET
'':

wo93/11~7ss ~ ti'i3 Pcr/uss~l sterili~ed are introduced into a pouch formed offlexible sheet material at least partially trans-parent to microwave radiation, the quantity of liquid being sufficient so that when the pouch is sealed to S form a gas-tight assembly and the liquid is vaporized by irradiating it with microwave radiation, an over-pressure is created within the pouch which causes the pouch to expand. The gas-tight assembly is thereupon situated in an inner rigid cavity of an enclosure which is at least partially formed of material that is substantially transparent to microwave radiation.
The enclosure is irradiated with microwave radiation which~passes into the cavity and then into the gas-tight assembly situated therein to vaporize the liquid thereby producing an atmosphere of hot vapor under pressure in the pouch. The pouch expands under pressure until the sheet material of which it ~s formed presses against the rigid inner surfaces of the enclosure that define the enclosure cavity where-upon further expansion of the pouch is preventedwhile the shape o~ithe pouch substantially conforms to the shape of the cavity. The enclosure may be adapted with means for providing a visual indication that the sterilizing process is proceeding.
.
According~to another as~ect of the invention, prior to irradiation, at least part of the gas-tight : SU8STITUTE SHEET

W~s3/18798 ;~ 3 PCT~US93/02793 assembly is surrounded with microwave radiation shielding means which divide the interior of the pouch into a first interior portion which will be substantially free of microwave radiation during thé
irradiation step, and a second interior portion which will be exposed to the microwave radiation during ir-radiation. Tho at lease one ob~ect to be sterilized is situated in the first shielded interior pouch por-tion~while the liquid to be vaporized is situated in ~0 the second unshielded interior portion of the pouch.
The shielding means may take the form of one or - ~ .
more~ shield members which are themselves situated within, or may form, the interior cavity of the enclosure, to surround at least a part of the gas-tight pouch assembly which is also situated in the . ~ :
-- enalosure cavity.
- The method and apparat~s of the invention pro-vide all of the advantages of the basic arrangements disclosed in Applicants' U.S. Patents 5,019,344 and 5,039,495. Moreover, higher temperatures and pres-sures may be obtained using the arrangement of the present invention and therefore cycle times are reduced still further. Thé invention facilitates handling and set-up, increases reliability and improves safety.

SUBSTITUTE SHEET

:

,~,, WO93t18798 ;~ PCTtUS93/02793 DESCRIPT~ OF THE D~AWIN~GS
A more complete appreciation of the present invention and many of the attendant advantages there-of will be readily understood by reference to the .:
S following detailed description when considered in connection with the accompanying drawings in which: `
Fig. l is a perspective view af an enclosure in its closed condition in accordance with the inven- :
tion;
Fig. 2 is an exploded perspective view of the enclosure shown in Fig. l, and illustrating shielding means received theriPin;
Fig. 3 i a partial perspective view from the r~ar of a closure slide forming a part of the en-clo~ure of Fig. l;
Fig. 4 is a partia1 perspective view o~ theenclosure of Fig~ l illustrating detent-indicator means for locking the clo~ure slide in its locked position during operation and for visually indicating that the sterilizing process is proceeding;
Fig. 5A is a section view taken along line 5-5 of Fig. l illustxating the inner cavity of the en-closure and the shielding means and gas-tight pouch assembly cantaining objects to be sterilized situated - 25 . within the ca~ity, prior to irradiation;

Sl)BSTITUTE SHEET

WO 93tl~79~ S Pr/US93102793 . ~

14 ::
Fig. 5B is a view similar to Fig. 5A, during irradiation;
Fig. 6~ is a section view ~aken along line 6-6 of Fig. 1, prior to irradiation;
Yig. 6B is a view similar to Fig. 6A, during irradiation;
Fig. 7A is a section view taken along line 7-7 of Fig. 1, prior to irradiation; and Fig. 7B is a view similar to Fig. 7A, during 10irradiation.

DETAILED DESC~IPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings wherein like reference characters designate identical or corres-15ponding parts throughout ~he several views, and more particularly to Fig~. 1, 2 and 5A, apparatus in accordance with the present invention, generally designated 10, comprise an enclosure 12 and a gas-tight assembly 14 (Fig. 5A) including a sealed pouch 2016 formed of flexible sheet material 18 and, sealed therein, a quantity of liquid 20 and at least one object 22 to be disinfected. In the illustrated embodiment, enclosure 12 also comprises microwave radiation shield means 24.
25The fundamental principles of the arrangement of the present invention are similar to those descri~ed SIJ8STITUTE SHEE~

W~93/1~98 ~ PCT/US93~02793 in the aforementioned applicants~ U.S. patents Nos.
5,0l9,344 and 5,039,495. Generally, referring to Fig.
5A, the pouch 16 is formed of flexible substantially vapor-impermeable sheet material which is at least partial~y transparent to microwave electromagnetic radiation. For example, the sheet material l8 of pouch 16 may comprise a laminate of polypropylene and polyester film material. Initially, the pouch has a sealable opening (not shown) through which the at least one object 22 to be disinfected is introduced into the pouch interior. ~he liquid 20 in the illus- :
trated embodiment comprises water but may also com-prise other liquid disinfectants or sterilants such, ~or example, as hydrogen peroxide~ The liquid 20 is provided in a quantity sufficient such that when the pouch i8 sealed and the liquid is vaporized, an over-preæsure is created within the pouch ~0 which w~
cause it to expand. For example, about lO ml. of water may be used in a pou~h ha~ing a volume of about 50cc. The microwave shielding means 24, as described in greater detail below, are associated with the pouch 16 in a manner such that the interior of the pouch is divided into a first interior portion which is substantially free of microwave radiation during irr~diation of the sealed pouch assembly, and a second interior portion which is exposed to the SU8ST~TUTE~ SHEET

WO93/18798 ~`~ 4~ 2615 PCT~US93/On93 radiation during irradiation. As in the case of the method disclosed in the prior patents, in accordance with the present invention, the at least one object 22 to be sterilized is situated in the first shielded interior portion of the pouch and the liquid 20 is situated in the second unshielded interior pouch portion. The pouch is irradiated with microwave radiation at which time the liquid situated in the unshielded portion of the pouch is irradiated, heated and vaporized. At the same time, however, the at least one object 22 situated in the shielded portion of the pouch is not exposed to the radiation so that ~parking or arcing is avoided. An overpressure is cseated within the pouch through the vaporization of the liquid whereupon the at least one object 22 is sterilized under the effect of the hot vapor under pressure.
The present invention provides improvements in the methods and apparatus disclosed in applicants' prior patents. Referring now to Figs. 1, 2, and 5A, in accordance with one aspect of the present inven-tion, thë enclosure 12 defines an inner cavity 26 (Fig. 5A) in which the gas-tight assembly comprising the pouch 16, liquid 20, and the object or objects 22 - - - 25 to be disinfected, is recèived. Enclosure 12 com-, , ~ prises a pair of substantially rectangular-shaped - :
: ~
~ ~ SUBSTllIJTE SHEET

WO 93/l~g8 ~ - ~ r~ PCT/US93/02793 ~:

cover members 28, 30 which are hinged to each other along corresponding ones of their long sides by inter-meshing piano hinges 32a, 32b and a pin 34.
Referring to Figs. 2 and 5A, similarly-shaped depressions 36 and 38 are formed in cover members 28, 30 respectively which together form the inner ca~ity 26 when the enclosure 12 is in its closed condition.
Vertical walls 40 and 42 project a limited distance into each of the respective depressions 36, 38 to divide them into respective sub-depressions 36a, 36b;
38a, 38b. ~A first horizontal shoulder 44 extends around three sides of the periphery of sub-depression 38a while a second horizontal shoulder 46 extends around three sides of the periphery of sub-depression 38b. Similar shoulders 48 and 50 are formed around corresponding sides of the sub-deprassions 36a and 36b in cover member 28. As seen in Figs. 5A and ~B, when the enclosure 12 is closed with the cover mem-bers 28, 30 in the positions shown, sub-depressions 36a and 3~a cooperate to define an inner sub-cavity 26a while sub-depressions 36b and 38b cooperate to define an interior sub-cavity 26b which communicates ~- with sub-cavity 26a through the space between walls - 40 and 42.
-~ 25 : Shield means 24 comprise a pair of shield ~ ~ .
members 52 and~54 ~ormed of aluminum sheet material.

W~93~18798 PCT/US93/02793 Any other suitable material which is opaque to micro-wave radiation may be usied. The shield members 52-and 54 comprise substantially rectangular, concave members which correspond in shape to the shape of the sub-depressions 36a and 38a respectively so that each fits snugly into to be held within a corresponding sub-depression. Each of the shield members has a horizontal peripheral rim 56 extending around three of its sides which become clamped between correspond-ing shoulders 44, 48 when enclosure 12 is in `its closed condition. The fourth side of each of the shield members 52, 54 is shaped to define a substan-: tially vertical radiation barrier wall 58 which ter-minates at a straight outer edge 60 that engages the inner surface of the divider walls 40 and 42. The ~- ~ inner boundaries of the radiation barrier walls 58 comprise arcuate siurfaces 62 shaped such that the radiation ~arrier walls 58 increase in height towards the transverse central regions thereof as seen in Fi~ure 2. Thus, the inner surfaces 62 of radiation barrier :walls 58 approach sach other towards the center regions, but remain spaced from each other even at the region at which they are closest to each other, as seen in Fig. 5A, so that the sub-cavities : 25 ~26a~and 26b remain in communication with each other.

SUBSTITUTE SHEET

WQ 93/1~98 ~ ~ " ~ ~j PCT/US93/02793 An upwardly facing channel 64 is formied in the upper surface of the region of t~e free, i.e. the unhinged, long side of cover member 28 and a down- :
wardly facing channel (not shown~ is formed in its lower surface. A plurality of longitudinally spaaed projections 66 extend from the end surface of the corresponding long side of cover member 30~ each projection having a bottom surface 67 which is angled upwardly to the right as viewed in Fig. 2. Referring to Figs. 1-4 and 6A, a closure slide 68 has a down-wardly directed flange 70 formed along its upper edge and a plurality of inwardly directed spaced tabs 72 projecting inwardly from its lower edge. ~ short up-wardly directed lower flange 74 ii formed at each end of the closure slide midway between its upper and lower edges, and a handle 76 is fixed to the slide by tabs 77. The closure slide is coupled to the c~er memb~r 28 by its upper and lower flanges 70 and 74 being slidingly received in channel 64 and in the downwardly facing channel (not shown). With the clo-surei slide 6~ positioned towards the right as viewed (but not shown) in Fig. l, the tabs 72 are situated so that they will pass through the spaces between the projections 66 of cover member 30 when the cover mem-bers are pivoted to close enclosure 12. After the cover members have been pivoted t~ close enclosure SUBSTITUTE SHEE~

WQ93/187gX PCT/US93/02793 ~ 6 13 `~

12, the closure slide 68 is moved to the left as viewed in Fig. 1 to its left-most position, shown in Fig. 1, until the end 68a of closure slide 68 en-gages an abutment wall 78 formed on the cover member 28. This movement results in the tabs 72 of the slide gradually engaging the bottom surfaces 67 of projections 66 until each tab is tightly engaged with and situated beneath a corresponding projection 66 of cover pember 30 to thereby lock the cover mem~ers tightly together, i.e., to lock enclosure 12 in its closed ~ondition.
~ It will be seen from the foregoing that thc en-closure 12 constructed in the manner described above including the shield me~bers 52 and 54 received in the respective sub-depressions 36a and 38a defines a first sub-cavity 26a which, upon placing enclosure 12 on a ~icrowave radiation field, is substantially shielded from the radiation, and a second sub-cavity 26b which is not so shielded. In other words, upon aubjecting the enclosure 12 to microwave radiation, radiation will pass into the unshielded sub-cavity 26b but will be prevented from passing into the shielded sub-cavity 26a by the shield members S2 and 54.~The inner cavity 26 comprising sub-cavities 26a 25 ~ and~6b are of;fixed size~and shape being defined by rigid~inwardly facing surfaces. For reasons dis-; ~ ~ : SUBSTITUTE SHEET
,:
-~

WOg3/1~98 P~T/US93~02793 6 1 ~

cussed below, a pair of short legs 79 are formed at the left end (as viewed in Fig. 5A) of ~nclosure 12 so that when the enclosure is placed on a horizontal surface, the shielded sub-cavity 26z will be elevated 5 with respect to the unshielded sub-cavity 26b.
In operation, at least one object 22 to be sterilized is placed within the pouch 16 along with a quantity of liquid 20 whereupon the pouch 1~ is sealed to form the gas-tight assembly 14. The enclo-sure 12 is opened and the gas-tight assembly~ is placed into the inner cavity 26 thereof. The o~ject or objects 22 ~o be sterilized are situated in the portion of the pouch interior which is received with-in the first shielded sub-ca~ity 26a of enclosure 12 while the liquid 20 is situated in the portion of the pouch 16 which is received within the second un-shielded sub-cavity 26b of enclosure 12. In ~his manner, the shielding means 24 substanti~lly surround a part of the pouch to thereby shield a first inter 2Q ior portion thereof from microwave radiation when the enclosure is placed in a microwave radiation field.
In other words, when the gas-tight assembly 14 is situated within enclosure 12 as described above, the shielding means 24 are associated with the pouch 16 . to di~ide the interior thereof into a first interior portion, situated in the shielded su~-cavity 26a, SUBSTITUTE SHEET

wog3~187g8 ~ 6~ PCrl~lS93~027g3 ~

which is substantially free of microwave radiation and a second interior portion, situated in the un-shielded sub-cavity 26b, which is exposed to micro-wave radiation when the enclosure containing the ~as-tight assembly is exposed to a microwave radiationfield. The shielding means 24 surround at least a part of the pouch to divide the interior thereof into the first shielded interior portion and the second .
unshielded interior portion.
After the gas-tight assembly 14 has been situated as described above, the enclosure is closed and locked. The marginal edges of the part of the pouch 16 that is situated in the shielded sub-cavity 26a are clamped between the rims 56 of the shield members 52 and 54 while the marginal edges of the part of the pouch that is situated in the unshielded sub-cavity 26b are clamped between shoulders 46'and 50. The enclosure is then placed into the ca~ity of a microwave generator whereupon it is irradiated.
The radiation, designated 90 in Figs. 5B, 6B and 7B, passes into the unshielded sub-cavity 26b and then into the unshielded interior portion of pouch 16 whereupon the liquid 20 is heated and vaporized.
As the liquid 20 is vaporized, the hot vapor travela into~the entire pouch and an overpressure is creàted within both the shielded and unshielded ~, ~ , ~ ~ ~ SUBSTITUTE StlEET

W~93/1~98 PCT/US93/02793 b i ~ :

~ 3 interior portions of the pouch c~using the pouch to expand. Expansion continues until the sheet material 18 of which the pouch 16 is formed pre~ses against the inner surfaces of the shield members 52 and 54 defining the shielded ~ub-cavity 26a and the inwardly facing surfaces defining the unshielded sub-cavity 26b as seen in Figs. 5B, 6B and 7B. Engagement of the rigid cavity surfaces by the pouch restricts `
further expansion of the pouch. This has the ~ene-ficial effect of not only assuring that the pouch will not rupture but, additionally, enables the final volume of the expanded pouch to be precisely def ? ned and limited to achieve higher pressures and tempera-tures in a more precise manner than had been possible heretofore. `.
As irradiation continues, the object or objects 22 are sterilized under the effect of hot vapor unaer pressure. The vapor present in the shielded interior portion of the pouch eventually cools and condenses on the inner surface of the pouch. Since the pouch is tilted by legs 79, the condensate will flow into the unshielded portion of the pouch interior where it can be again vaporized by continued irradiation.
In accordance with another feature of the invention, referring to Figs~ 1, 2, 4, 7A and 7B, a through bore 80 is formed through the wall of the SUBSTITUTE SHEET

W093/1~98 PCT/US93/02793 ~ 4 cover member 28 communicating with the unshielded sub-cavity 26b, and a slide member 82 is received therein. A lug 84 is formed on the inner end of slide member 82 while a detent-indicator 86 ic formed on its outer end. Referring to Figs. 7A and 7B, after the gas-tight assembly 14 has been positioned within the interior cavity of enclosure 12 and the enclosure has been locked by moving the closure slide to its locking position, and prior to initiation of irradiation, the slide member 82 is in an inner position under the force of gravity with the lug 84 engaging the unexpanded pouch 16. In this inner position, the detent-indicator 86 is retracted within the bore 80. Upon irradiation with the consequent vaporization of li~uid 20 and expansion of pouch 16 to the configuration illustrated in Fig. 7B, the expanding pouch engages the lug 84 of slide member 82 thereby pushing it outwardly through bore 80 until the detent-indicator 86 reaches the extended position æeen in Fig. 7B. The extended condition of the d~tent-indicator 86 provides a visual indication that the interior of the pouch is at an appropriate over-pressure to achieve effective sterilization of the object contained within pouch 16. Furthermore, as best seen in Fig. 4, the detent-indicator in its extended position is situated in the path of a SUBSTITUTE SHEE~

W~93~18Js~ PCT/US93~02793 ~5 :
locking tab 88 formed on the closure slide 68. This prevents the slide 6~ from movement towards the right as viewed in Fig. 1 and 4. In this manner, it becomes impossible to unlock the enclosure 12 while the pouch 16 is pressurized, thereby providing another measure of security.
It is seen from the foregoing that the present invention provides an improvement in the methods and apparatus disclosed in applicants' prior patents.
The inner cavity 26 of enclosure 12 need not be pres-sure-tight, since the pressure is maintained within the pouch 16. This enables the enclosure 12 to be constructed in an inexpensive fashion. The provision of the shield means to surround the gas-tight assem-bly simplifies the shielding of the obje ts beingsterilized from microwave radiation, and the pro-vi~ion of the rigid enclosure cavity enables hig~er pressures to ~e achieved in a more precise fashion.
All of these benefits are obtained while still 20 retaining the benefits of the basic method and apparatus, namely quick sterilizing cycle time, elimination of the possi~ility of recontamination, and providing a visual indication that the steriliza-- tion process is proceeding. In cases where arcing in a microwave radiation field is not a problem, for example, in certain cases where sharp edges are not SUBSTITUTE SHEET

WO93/18798 PCT~US93/02793 1 S i ~"`

26 ;~
present on the object being sterilized, it may be ``
possible to utilize the method and apparatus of the invention without the shielding means which are ;
normally required. In tests that have been con~
ducted, using 10 ml. of water in a bag having a --volume of about 50cc, temperatures of about 295-F at pressures of 48.3 psig have been obtained in steri- `.`
lizing objects i~n times of about two minutes.
Obviously, numerous modifications and variations -~
of the present invention are possible in the light of the above teachings. For example, the shielding ;.
means may comprise~ a metallic coating applied directly to the surfaces defining the sub depressions ~
36a and 38a. It is therefore to:be understood that ~ `
within the scope of tbe claims appended hereto, the invention may be practiced otherwise than as speci- ~.
fically disclosed herein.

. .

:: :

SUBSTITUTE SHEET `:

Claims

WHAT IS CLAIMED IS:

1. Apparatus for sterilizing at least one object by vapor under pressure, comprising:
a pouch formed of flexible, substantially vapor-impermeable sheet material at least partially transparent to microwave radiation, said pouch being receivable of said at least one object;
liquid receivable within said pouch;
means for irradiating said pouch with microwave electromagnetic radiation to vaporize said liquid to produce an atmosphere of hot vapor under pressure;
and shielding means associated with said pouch for dividing the interior of said pouch into a first interior portion which is substantially free of said microwave radiation during irradiation of said pouch by said irradiating means and a second interior portion which is exposed to said microwave radiation during irradiation of said pouch by said irradiating means, said first interior portion being receivable of said at least one object to be sterilized and, said second interior portion being receivable of said liquid, whereby upon irradiating said pouch with micro-wave radiation, said at least one object situated in said first interior portion of said pouch is substan-tially entirely shielded from said radiation, and said liquid situated in said second interior portion is exposed to said radiation whereupon it is heated and then vaporized thereby, whereupon said at least one object is sterilized under the effect of vapor under pressure.

2. Apparatus as recited in Claim 1 wherein said shielding means are formed of microwave radiation shielding material, and are adapted to substantially surround at least part of said pouch to shield said first interior portion thereof from said microwave electromagnetic radiation upon irradiating said pouch with said radiation.

3. Apparatus as recited in Claim 2 wherein said shielding means comprise at least one shield member formed of microwave radiation shielding material.

4. Apparatus as recited in Claim 3 wherein said shielding means comprise a pair of said shield members.

5. Apparatus as recited in Claim 2 further includ-ing means for positioning said shielding means to substantially surround at least part of said pouch to shield said first interior portion thereof.

6. Apparatus as recited in Claim 5 wherein said means for positioning said shielding means comprise an enclosure having an interior cavity for receiving said pouch.

7. Apparatus as recited in Claim 6 wherein said shielding means comprise at least one shield member.

8. Apparatus as recited in Claim 7 wherein said shielding means comprise a pair of shield members.

9. Apparatus as recited in Claim 6 wherein said enclosure comprises means for holding said pouch in said interior cavity.

10. Apparatus as recited in Claim 9 wherein said shielding means comprise at least one shield member, and said enclosure further comprises means for holding said at least one shield member to surround at least a part of said pouch to shield said first interior portion thereof.

11. Apparatus as recited in Claim 5 wherein said shielding means positioning means comprise a pair of cover members operatively associated with each other and defining a closed interior space between them, and means for holding said pouch in said interior space.

12. Apparatus as recited in Claim 11 wherein said shielding means comprise a pair of shield members, and said shielding means positioning means further comprise means for holding each of said shield mem-bers on a respective one of said cover members so that when said cover members are operatively asso-ciated with each other said shield members define an interior sub-space between them to substantially surround said first interior portion of said pouch.

13. Apparatus as recited in Claim 12 wherein each of said shield members has a substantially concave con-figuration.

14. Apparatus as recited in claim 2 wherein said liquid comprises water.

15. Apparatus as recited in claim 2 wherein said liquid comprises hydrogen peroxide.

16. Apparatus as recited in claim 2 further in-cluding means for elevating said first interior portion of said pouch with respect to said second interior portion of said pouch.

17. Apparatus for sterilizing at least one object by vapor under pressure, comprising:
a pouch formed of flexible substantially vapor-impermeable sheet material at least partially trans-parent to microwave electromagnetic radiation, said pouch having a sealable opening through which said at least one object can be introduced into the interior thereof;
liquid receivable within said pouch;
means for irradiating said pouch with microwave radiation to vaporize said liquid to produce an atmosphere of hot vapor under pressure; and shielding means comprising at least one shield member formed of microwave electromagnetic radiation shield material defining a shielded space in which at least a part of said pouch is situated to define a first interior pouch portion which is substantially free of said microwave radiation during irradiation of said pouch by said irradiating means and a second interior pouch portion which is exposed to said microwave radiation during irradiation of said pouch by said irradiating means, said first interior por-tion being receivable of said at least one object to be sterilized and said second interior portion being receivable of said liquid, whereby upon irradiating said pouch with micro-wave radiation, said at least one object situated in said first interior portion of said pouch is substan-tially entirely shielded from said radiation, and said liquid situated in said second interior portion is exposed to said radiation whereupon it is heated and then vaporized thereby, whereupon said at least one object is sterilized under the effect of vapor under pressure.

18. Apparatus as recited in Claim 17 wherein said at least one shield member includes inwardly facing rigid surface means defining said shielded space, and wherein upon irradiating said pouch and vaporizing said liquid, an overpressure is created within said pouch which causes said pouch to expand such that said sheet material thereof presses against said inwardly facing surface means of said at least one shield member under pressure.

19. Apparatus as recited in Claim 18 further in-cluding means for holding said at least one shield member and pouch such that said at least one shield member defines said shielded space and divides the interior of said pouch into said first and second interior portions.

20. Apparatus as recited in Claim 18 further in-cluding enclosure means for defining an interior cavity and for holding said pouch in said cavity and positioning said at least one shield member to define said shielded space to divide the interior of said pouch into said first and second interior portions, and so that said sheet material of said pouch presses against said inwardly facing surface means of said at least one shield member upon expansion of said pouch during irradiation.

21. Apparatus as recited in Claim 20 wherein said enclosure means comprise a housing including a pair of cover members operatively associated with each other, means provided on said cover members for holding said pouch and positioning said at least one shield member.

22. Apparatus as recited in Claim 21 wherein said shielding means comprise a pair of shield members, and wherein each of said shield members is fixed to a respective one of said cover members.

23. Apparatus as recited in Claim 22 wherein each of said shield members is substantially concave.

24. Apparatus as recited in Claim 17 further in-cluding enclosure means for defining an interior cavity and for holding said pouch in said cavity and positioning said at least one shield member to divide the interior of said pouch into said first and second interior portions.

25. Apparatus as recited in Claim 24 wherein said at least one shield member includes inwardly facing, substantially rigid surface means defining said shielded space, and wherein upon irradiating said pouch and vaporizing said liquid, an overpressure is created within said pouch which causes said pouch to expand such that said sheet material thereof presses against said inwardly facing surface means of said at least one shield member.

26. Apparatus as recited in Claim 24 further in-cluding means for providing an indication visible from the exterior of said enclosure means that said pouch has expanded under pressure.

27. Apparatus as recited in Claim 2 6 wherein said indication means comprise a member movably mounted on said enclosure means and adapted to be engaged by said sheet material of said pouch as said pouch ex-pands under pressure.

28. Apparatus as recited in Claim 24 further in-cluding means for locking said enclosure means to prevent access to said interior cavity when said pouch has expanded under pressure.

29. Apparatus as recited in Claim 28 wherein said locking means comprises a member movably mounted on said enclosure means and adapted to be engaged by said sheet material of said pouch as said pouch expands under pressure.

30. Apparatus for sterilizing at least one object by vapor under pressure, comprising:
a pouch formed of flexible substantially vapor-impermeable sheet material at least partially trans-parent to microwave radiation, said pouch being receivable of said at least one object;

liquid receivable within said pouch;
means for irradiating said pouch with microwave radiation to vaporize said liquid to produce an atmosphere of hot vapor under pressure; and enclosure means formed of microwave radiation transparent material having inwardly facing substan-tially rigid surfaces defining an interior cavity, said enclosure means including means for holding said pouch in said cavity, and wherein upon irradiating said pouch with microwave radiation, said liquid receivable within said pouch is exposed to said radiation whereupon it is heated and then vaporized thereby, whereupon an overpressure is created within said pouch which causes said pouch to expand until said sheet material thereof presses against said inwardly facing surfaces of said enclosure means defining said interior cavity, to thereby prevent further expansion of said pouch.

31. Apparatus as recited in Claim 30 further including shielding means associated with said pouch for dividing the interior of said pouch into a first interior portion which is substantially free of said microwave radiation during irradiation of said pouch by said irradiating means and a second interior portion which is exposed to said microwave radiation during irradiation of said pouch by said irradiating means, said first interior portion being receivable of said at least one object to be sterilized and said second interior portion being receivable of said liquid.

32. Apparatus as recited in Claim 31 wherein said shielding means is associated with said enclosure means and substantially surrounds at least part of said pouch to shield said first interior portion thereof from said microwave radiation during irra-diation of said pouch by said irradiating means.

33. Apparatus as recited in Claim 32 wherein said shielding means comprise at least one shield member associated with said enclosure means, said at least one shield member having inwardly facing surfaces comprising at least in part said inwardly facing surfaces of said enclosure means which define said interior cavity.

34. Apparatus as recited in Claim 33 wherein said shielding means comprise a pair of substantially concave shield members having end portions which cooperate to substantially divide said first and second interior pouch portions from each other.

35. Apparatus for use in sterilizing objects by vapor under pressure, comprising:
an enclosure which is selectively openable and closable and defining an interior cavity in its closed condition; and shielding means for dividing said interior cavity into a first sub-cavity which is substantially shielded from microwave radiation and a second sub-cavity which is substantially unshielded from microwave radiation.

36. Apparatus as recited in Claim 35 further in-cluding means for locking said enclosure in said closed condition.

37. Apparatus as recited in Claim 35 wherein said shielding means comprise at least one shield member formed of microwave radiation shielding material.

38. Apparatus as recited in Claim 35 wherein said enclosure comprises a pair of cover members opera-tively associated with each other, at least one of said cover members having a depression formed therein for defining said interior cavity.

39. Apparatus as recited in Claim 38 wherein said shielding means comprise at least one shield member, each shield member being situated in a respective one of said depressions to define said first shielded sub-cavity when said enclosure is in said closed condition.

40. Apparatus as recited in Claim 39 wherein said shielding means comprise a pair of shield members.

41. Apparatus as recited in Claim 40 wherein each of such shield members is substantially concave.

42. Apparatus as recited in Claim 35 wherein said shielding means comprise a coating of microwave radiation shield material deposited on inner surfaces of said enclosure defining said first sub-cavity.

43. A method for sterilizing at least one object by vapor under pressure comprising the steps of:
introducing at least one object to be sterilized and a quantity of liquid into a pouch formed of material at least partially transparent to microwave radiation through a sealable opening therein, said quantity of liquid being sufficient so that when said pouch opening is sealed to form a gas-tight assembly and said liquid is vaporized, an overpressure is created within said pouch which will cause said pouch to expand;
sealing said pouch opening to form a gas-tight assembly;
introducing said gas-tight assembly into an interior cavity of an enclosure which is formed of material substantially transparent to microwave radiation, said interior cavity being defined by inwardly facing surfaces; and irradiating said gas-tight assembly with micro-wave electromagnetic radiation to vaporize said liquid to produce an atmosphere of hot vapor under pressure in said pouch so that said pouch expands until said material of which said pouch is formed presses against said inwardly facing surfaces which define said interior cavity whereupon further expan-sion of said pouch is prevented, whereby said at least one object situated within said gas-tight assembly is sterilized under the effect of vapor under pressure.

44. A method for sterilizing at least one object by vapor under pressure comprising the steps of:
introducing at least one object to be sterilized and a quantity of liquid into a pouch formed of material at least partially transparent to microwave radiation through a sealable opening therein, said quantity of liquid being sufficient so that when said pouch opening is sealed to form a gas-tight assembly and said liquid is vaporized, an overpressure is created within said pouch which will cause said pouch to expand;
sealing said pouch opening to form a gas-tight assembly;
surrounding at least part of said gas-tight assembly with shielding means for dividing the inter-ior of said pouch into a first interior portion which is substantially free of said microwave radiation during irradiation of said pouch by irradiating means and a second interior portion which is exposed to microwave radiation during irradiation of said pouch by irradiating means, said first interior portion being receivable of said at least one object to be sterilized, and said second interior portion being receivable of said liquid; and irradiating said gas-tight assembly with micro-wave radiation while said at least one object is shielded from said radiation to vaporize said liquid which is unshielded from said radiation to produce an atmosphere of hot vapor under pressure in said pouch, whereby said at least one object situated within said gas-tight assembly is sterilized under the effect of vapor under pressure.