WO1985002111A1

WO1985002111A1 - Acoustic-assisted cleaning apparatus

Info

Publication number: WO1985002111A1
Application number: PCT/US1984/001818
Authority: WO
Inventors: Don Schmadel; Edward Cornfeld
Original assignee: Medical Physics Corporation
Priority date: 1983-11-08
Filing date: 1984-11-08
Publication date: 1985-05-23
Also published as: EP0160696A1; AU3619384A

Abstract

A cleaning apparatus which permits the use of a potentially non-sterile acoustic generating apparatus (8) to activate an anti-infective solution (3) for the disinfection of live tissue by the use of a readily mountable/demountable acoustic coupling (4) and an enclosure apparatus (5) which fluidically isolates the generating apparatus (8) from both the solution (3) and the tissue. The disclosed apparatus permits the reuse of the potentially non-sterile acoustic genertaing apparatus (8) with a sterilized enclosure apparatus (5) and a fluid membrane (1) so that the acoustic generating apparatus (8) does not have to be sterilized after every use.

Description

ACOUSTIC-ASSISTED CLEANING APPARATUS

Background of the Invention

As it is a principle object of the invention to provide method and means for sterilization or disinfection of human tissue prior to surgery, background information in this area as well as the area of ultrasonic cleaning will be discussed.

In the area of medicine it is a constant concern to thoroughly sterilize a patient's skin at and adjacent to the site at which incision is to be made. This is because incomplete sterilization can cause maladies ranging from irritating localized infections to fatal septicemia. Currently, the medical profession uses sponges' glued to the end of plastic sticks and saturated with an antiseptic solution. • The procedure amounts to opening a sealed, sterilized package containing the sticks, sponges, and antispetic; removing the stick with the saturated sponge; and rubbing the sponge portion at and around the anticipated incision site. This present method and means, for reasons discussed below, do not always render the skin completely sterile.

A microscopic examination of skin reveals an irregular surface typically comprising narrow pores, cavities, and wrinkles each of which is a potential haven- for infecting organisms such as bacteria. Even though the antiseptic solutions used with the current method often contain surfactants to reduce their surface tension, the remaining surface tension still can inhibit complete penetration by the solution into these skin irregularities. The result in such cases would be a skin pore or cavity possibly with bacteria at the bottom, antispetic solution at the top, and a separating air bubble

iΕ f PI in between. Although other mechanisms like the above are also responsible for the failure of the present method and means it should be clear at this point that a better cleaning method is needed. It is, however, the very special nature of sterilization and medicine in general which render most enhanced cleaning methods of the present art unmanagable, ineffective, or self-defeating. For example, CH. Prange in patent #2,970,073 entitled "Method for Ultrasonic Surgical Cleaning of Human Body Members" demonstrates the efficacy of ultrasound for sterilizing, but teaches the use of a tank into which the anticipated incision site should be emersed. This is difficult in many situations particularly when the site is located on the torso. Further, the tank solution would need to e changed after each use which could be quite costly for a larg.e tank.

The idea of using a portable ultrasonically activated applicator to assist in cleaning human tissue by placing the applicator adjacent to the area to be cleaned is well known and is discussed by, for example, Seymour Robinson in patent #3,645,255. Another example which eliminates the need for an immersion tank was invented by Frank Massa and described in patent #4,183,011 entitled "Ultrasonic Cleaning Systems". Massa's system uses a spacing means, a flat permeable wall, and an inlet to form a hand-held unit which can be rubbed against a surface to be cleaned. However, the device has at least three major deficiencies. First, most skin surfaces are contoured and are not easily cleaned by a flat surface. Second, the fluid supply hose is a potential source of cross-contamination. For example, although the hose may be sterile initially. as the device is used, the outside of the hose is likely to touch a nonsterile surface and become contaminated. The usual back and forth motion used for cleaning can, by surface to surface transfer, slowly carry the contamination closer and closer to the area being sterilized. Therefore, without extremely judicious control of the hose, the device may actually further contaminate the site. A third deficiency is that the device must be cleaned before reuse. The permeable membrane, inlet means, hose, etc. are nearly as difficult to clean and sterilize as the skin itself. Such a device therefore does not address the particular requirements and problems of sterilization. In the area of ultrasonics or more generally, acoustics, the present art provides and .describes many transducers and electronic circuits which would be helpful to one wishing to implement the present invention. In particular, Kuris et al, patent #3,980,906 entitled "Ultrasonic

Motor-Converter Systems" offers a convenient and novel type of circuit which could be used with the present invention. William L. Puskas, patent #3,651,352 discloses and explains transducers and circuits which could also be used in the present invention.

Brief Summary of the Invention

The present invention is a device which incorporates an acoustic generator and a fluid delivery system in a unique design which is easy to fabricate and allows acoustic agitation for cleaning, disinfection, or fluid coating of objects which by their size or location cannot readily be immersed in an ultrasonic bath. In particular, the design eliminates the need for the spacing means.

OMPI the inlet opening, an external reservoir, and the means for transferring the liquid from the external reservoir to the confined space of PAT #4,183,011. It is a further object of the invention to provide novel method and means for easy nondestructive mounting and dismounting of a fluid shield means between the acoustic generator and the surface to be cleaned. The shield means is used to avoid cross-contamination between the acoustic generator and the surface being cleaned.

It is a further object of the invention to provide a self-contained acoustic generator and power source module. The design of the module eliminates the need for an electric wire connecting the acoustic generator to an external power source. Such a provision in particular allows acoustic agitation to be used routinely in the sterilization preparation of a patient before and during surgery by eliminating the electric wire which by its motion may act as a vehicle in transferring germs from, for example, non-sterile surfaces to the patient.

It is further an object of the invention to provide a novel method and means to fully enclose the self-contained acoustic generator and power source in a potentially disposable container during use. This eliminates the need for sterilizating the acoustic generator apparatus. The method and means offers two particular advantages. First, only one person is required to seal the acoustic generator withing the enclosure means and no additional tools are required. Second, if implemented properly, the process of enclosing the potentially non-sterile acoustic generating apparatus, using the means of the invention, will not contaminate the hands of said person.

OMPI It is a further object of the invention to provide a flexible, protruding permeable surface through which both acoustic waves and the fluid may pass to an irregular surface. It is a further object of the invention to provide a scrubbing surface on said membrane to further facilitate the cleaning or coating of a surface.

It is further object of the invention to provide a sterile enclosure apparatus which comprises a potentially disposable container configured as a cylinder which, before use, contains the fluid to be applied to the surface. The fluid contained by means of a piston and a removable film seal at one end of the cylinder. The piston configured to serve as a fluid shield and the cylinder also fitted with a cap over the film seal. The cap may be fitted internally with a recepticle configured to connect to and temporarily hold the said self-contained module. The cylinder is also externally fitted with an acoustic barrier to permit it being hand held while in use without transmitting significant acoustic energy to the operator. The container apparatus is used by: removing the cap from the cylinder using the receptacle to pick up potentially non-sterile self-contained module, depositing the module into cylinder so the acoustic generating surface contacts the piston, pushing the cap against a spring on the module until the cap contacts the end of cylinder opposite the film seal, fastening the cap onto the end thus enclosing the module in the cylinder, finally by removing the film seal to expose a permeable membrane and placing the membrane against the surface to be cleaned. It is a further object of the invention to provide an electric coil located internally to the

OMPI - o -

module configured to convert an alternating magnetic field into electricity for replenishing a power source. The alternating magnetic field is caused by a charging apparatus. This provision eliminates the need for direct electrical connection to the module which is sometimes undesirable around aqueous liquids.

It is a still further object of the invention to provide a switch internal to the module which is activated by knocking or jarring the module which electrically connects or disconnects the power source to the acoustic generator. Using such a switch simplifies the design and lowers the fabrication expense of the enclosure apparatus since it need not be fitted with a means to allow switch activation.

Brief Discription of the Drawings

Fig 1 is an end view of a preferred embodiment of the invention; Fig 2 is a cross-sectional view of the disposable portion of the preferred embodiment on line 2-2 of Fig 1 ;

Fig 3 is a cross-sectional view like that illustrated in Fig 2 with the non-disposable portion of the device installed within the disposable portion and the disposable portion partially used; Fig 4 is an end view of the non-disposable portion of a device of the present invention; Fig 5 is a section on line 5-5 of the structures illustrated in Fig 4;

Fig 6 is an fragmentary cross-sectional view of a modified form of the present invention;

Fig 7 is a view like Fig 6 of a spent disposable portion; Fig 8 is a fragmentary enlarged cross- sectional view of another form of the present invention;

Fig 9 is an end view of the structure shown in Fig 8; Fig 10 is a partially sectional view of a further form of the present invention;

Fig 11 is a perspective view of still a further form of the present invention;

Fig 12 is a fragmentary sectional view of a portion of the acoustic generating apparatus showing a form of switch means and charging means therefore; and

Fig 13 is a sectional view of a modified form of acoustic coupling means of the present invention.

Detailed Description of the Invention

. The invention encompasses both methods and means for acoustic-assisted cleaning, sterilizing, and/or coating of surfaces. The invention is particularly useful for small areas of surfaces which are large, irregular, or attached to some object so that they cannot be submerged in an ultrasonic tank and cleaned, coated, and/or sterilized by the usual methods. In the description and claims which follow, cleaning will be used to also include coating, disinfecting, and sterilizing unless otherwise noted.

A specific application involving such surfaces, which has been unable to benefit from ultrasonic agitation in view of the prior art, is the cleaning and preparation of human or animal skin ^•prior to surgery. Since it is a particular object of the invention to serve this application and because its specific requirements have not been addressed in the prior art, it is therefore necessary to explain some of the requirements.

First, all implements which touch the skin either during or after sterilization near where an incision is to be made must themselves be sterile. Therefore, such implements should be either replaceable and disposable after use or else they must .be easily cleanable and sterilizable.

Second, all implements .which are fluidically connected to a surface which at some time may be nonsterile must be replaceable and disposable, or easily cleanable and sterilizable after use. As an example, a sudden, possible unnoticed backflow of liquid may contaminate a tube and reservoir which supply liquid to a scrubber which is in contact with a surface to be sterilized. Because of the existence of this possibility of contamination, the tube and reservoir must be either emptied and cleaned or else disposed of and replaced before reuse. Therefore, although a part of an apparatus may not come into direct contact with the surface being cleaned or sterilized, it may still become contaminated if it is fluidically connected to such unclean or nonsterile surfaces. When such possibilities exist, all such parts should be cleanable and sterilizable or disposable.

Finally, if any part of an apparatus is removable and if replacement may be required in the operating room, then electrical contact should not be required between the part and the apparatus. Eliminating electrical contact reduces the possibility of igniting the occasionally flammable anesthesia gases.

The present invention in its preferred embodiment meets all of these requirements without adding unacceptable complication or monetary expense. Basically, the preferred embodiment consists of an ultrasonic generator and energy source which are intended to be inserted into and fully enclosed by a potentially disposable apparatus which contains the cleaning fluid and a fluid delivery means.

The invention provides a method and means by which the acoustic coupling between an acoustic generating surface and another surface is readily mountable/demountable i.e., the coupling can actually be established and then broken without requiring the use of matching gells or tools such as wrenches and without waiting for epoxies to cure. This feature is then used to fluidically isolate the acoustic generator from the cleaning fluid by containing the fluid in a readily mountable/demountable enclosure which is potentially diposable. The monetary expense of the potentially disposable part is kept low by a unique feature which allows integrating the fluid enclosure with the fluid delivery means. The preferred embodiment of all these features, consists of an enclosure apparatus and an acoustic generating apparatus and is shown in various parts and sections in figs 1 through 7. Figure 1 is an end view of the preferred embodiment and contains the cutting plane line for the cross-sectional view of figure 2. Fig 2 is a sectional view of the enclosure apparatus without the generator apparatus inserted. Referring to fig 2, 5 designated a hollow cylinder which could be made of a plastic such as polypropylene and 4 designates a piston which fits within cylinder 5 sufficiently tight to contain the cleaning or disinfecting fluid 3. The fluid may be for example Betadine which is manufactured by Purdue Frederick in Norwalk, CT. A fluid permeable membrane 1 is sealed to the end of cyliner 5 at 9. The fluid permeable membrane 1, cylinder 5, and piston 4 form boundaries of the fluid space. The membrane could be a fabric woven from polypropylene fibers and the seal at 9 could be accomplished by glueing or melting the fabric to the walls of cylinder 5.

A removable file seal 2, such as "Safe-Guard" currently used to seal plastic bottles and supplied by 3 M Corporation in St. Paul, Minnesota, is fastened at 10 to maintain the fluid within the cylinder prior to use. A cap 7 is fitted to the end of the cylinder with for example screw threads. The cap is fitted internally with a hook 6. An ultrasonic barrier material such as a closed cell silicone rubber foam is formed around the cylinder 5 and is designated 33. This barrier allows the user to manually grasp the cylinder without receiving an uncomfortable amount of acoustic energy when the fluid 3 is ultrasonically agitated.

Fig 4 shows an end view of the acoustic generator apparatus designated 8 with the cutting plane line for the cross-sectional view of fig 5. Referring to fig 5, 26 designates a hollow cylinder into which is placed a bolted assembly consisting of: a longitudinal mode piezoelectric transducer designated 15 which may be a 1 inch diameter, longitudinal mode C 5400 transducer manufactured by Channel Industries, Inc. in Santa Barbara, CA; a bolt designated 17; a sleeve 60 insulating the bolt from the transducer; and a steel cylinder designated 18, which helps direct the acoustic energy to the aluminum cylinder designated 14. The electrode 29 of the transducer is contacted by the steel cylinder which is electrically.connected to wire 23, electrode 28 is connected to wire 24 and insulated from cylinder 14 by an insulating sheet of, for example, plastic. The aluminum cylinder is provided with a convex surface 13 which serves as an acoustic generating surface. The bolted assembly can be cemented in the cylinder 26 using RTV 156 silicone rubber manufactured by General Electric Corp. in Waterford, NY. This material designated 27 will form a waterproof seal yet, because of its location and its low shear strength, will not adversely affect the operation of the transducer.

Also located within the tube is the energy source 21 which may be a nickel-cadmium battery made of, for example, six VB10 button cells distributed by SAFT AMERICA INC. in St. Paul, MN and the electronic circuitry 20 which converts the battery power into alternating current at preferably 90 kHz at about 2 watts which is carried to the transducer by wires 24 and 23. The transducer will convert the alternating current into acoustic power having essentially the same frequency. The electronic circuitry, together with the transducer, forms the transducer means. An ultrasonic barrier 19 is provided to isolate the electronic circuitry from the acoustic energy and to ease assembly by providing a positive stop for the insertion of the bolted assembly in the cylinder 26. The barrier 19 could be made from closed cell silicone rubber. 22 designates a wire which connects the far pole of the battery through a unique electrical switch, located in housing 32, to the electronic circuit 20. The opposite pole of the battery is connected to the electronic circuit by a wire not shown. The housing 32 is cemented to cylinder 26 and serves as the waterproof and closure. Finally, a spring 11 is fastened to the housing 32 and serves the dual purpose as a receptacle for the hook 6 and as the pressure generating means for the fluid 3.

The anticipated procedure for the operation of the preferred embodiment is as follows: First, the sterile enclosure apparatus of fig 2 is removed from its package and placed on the surgical instrument cart. Second, the enclosure apparatus is picked up by sterile hands, one of which removes the cap 7 and using hook 6 picks up the possibly nonsterile generator apparatus by the spring and inserts it into the cylinder 5. Third, the cap 7 is screwed onto the cylinder 5 thus fully enclosing the generator apparatus and simultaneously causing pressure in the fluid 3 by virtue of the spring force causing the piston 4. to slide. Notice that all exposed surfaces, including the forementioned hands, and all surfaces hydronically connected to exposed surfaces are still sterile even without requiring the acoustic generator to be sterile. Fourth, the assembled apparatus is bumped against a sterile Surface to turn on the unique electric switch thus activitating the acoustic transducer. Fifth, the film seal is removed allowing the fluid to flow through the membrane 1. Sixth, the assembled apparatus is used as a swab to clean, sterilize, and/or coat a surface by rubbing membrane 1 against the surface.

Fig 3, a cut-away view, illustrates the assembled apparatus after following this procedure. It can be seen from the figure 2 that in the preferred embodiment the membrane is formed with extra material, shown as folds, so that the flexible membrane protrudes from the cylinder 5 in response to the fluid pressure as shown in fig 3. This protrusion of the membrane allows it to conform to irregular surfaces, thus enhancing its operation. The tightness of the weave of the fabric from which the membrane is made could be chosen so as to limit the fluid flow to desirable rates. Alternatively, the membrane 1 could be a stretchable material such as silicone rubber formed with one or more small holes having,, for example, about .003 inch diameter. Such holes are sufficiently small to make possible the maintenance of internal fluid pressure. The invention provides that the stretchable material can also be configured with small holes and be sufficiently thin or structurally weak so as to bulge in response to the internal pressure which can be maintained with the small holes. If the membrane bulges an amount equal to about one-third or more of its diameter then the bulge can.-perform the additional task of supplying pressure ballast by acting as a hydraulic accumulator. A pressure ballast will help maintain fluid pressure by compensating for the possibly slow motion of the piston 4 or any other interuption in the fluid pressure supply.

The invention also provides that the membrane may be supplied to the operator initially without holes. The operator can then use a needle to poke holes of the size and number desired so as to control the fluid flow for the particular use at the time.

The invention also provides that the membrane 1 may be formed with bristles designated 50 which would serve as an additional means for scrubbing. The bristles could be formed from silicone rubber in the case of a silicone rubber membrane or the bristles could be, in the case of a woven fabric membrane, woven in with fabric as is done in corduroy fabric. The invention also provides that the cap 7 may have a hole to allow air to flow into the cylinder 5 as the piston moves in response to the spring force. The invention also provides that the hole can be made small so as to limit the flow of air which would control the rate at which fluid 3 passes through the membrane 1. Alternatively, instead of a hole, the operator could tighten or loosen cap 7 to control the flow rate. It can also be seen from fig 3 that the piston 4 has deformed so as to more fully contact the acoustic generating surface 13. The readily mountable and demountable acoustic coupling formed by the surface 13 and the surface of piston 4 allows acoustic energy to flow from the acoustic generating surface 13 and through piston 4 thus causing the opposite surface 61 of the piston to become an acoustic generating surface. Acoustic generating surface 61 can then deliver acoustic energy into fluid 3. Because the acoustic coupling depends on considerations and features not explained in the prior art, it will be explained and expanded on below.

The first consideration is that by using the interface shapes which are provided by the invention, the coupling for the acoustic powers and frequencies involved can actually be much higher than 60%, for example, 80% repeatedly. The significance of the shapes are understood as follows: as the convex surface 13 first contacts piston 4, the area of contact is small, essentially a point or small circular patch near the center of the two surfaces. As the contact force increases the circular patch of contact grows outward, pushing air ahead of it as it grows. This action of pushing the air ahead of the contact area is an important

OMPI achievement of the invention and signi icantly aids in preventing the formation of air pockets which lessen acoustic coupling. The invention provides that either one or both of the surfaces could be convex for the purpose of preventing gas pockets.

The second consideration is that the spring 11 together with end cap 7 form a reversible fastening means which develops the pressure within the fluid 3 and also supplies a force which maintains the contact between surface 13 and piston 4. The fastening means is considered reversible because the coupling can be separated without substantial damage as would occur if hardening epoxies were used. The third consideration is that the piston, if made of a resilient material, also helps to maintain contact in the interface between surface 13 and itself -in particular by supplying a higher contact pressure near its center than at the edges.. This gradient in contact pressure will have a vector component parallel to the interface. The gas pockets will tend to travel in the direction opposite that which the vector component points. The surfaces should therefore be configured so that the vector components point opposite an escape route for gas pockets. For fig 3 if vector components point towards the center they will continually help to eliminate the gas pockets even while the apparatus is in use by causing them to be ejected from the interface at the edges of the convex surface 13. Alternatively, the piston 4 could be formed from a nonflexible material and instead the cylinder 14 could be of a composite structure as shown in fig 13 as 13-14. Referring to fig 13, 13-63 could be aluminum and geometrically shaped as cylinder 14. Disc 13-61 is a soft, resilient material like silicone rubber whose concave surface is bonded to 13-63. The flat surface of 13-61 is pressed against piston 13-4 to form the acoustic coupling. However, since there is less resilient material near the center of contact in the structure 13-14 than at the edges the effective conpressive strength is higher near the center than at the edges. This gradient in compressive strength will produce a gradient in coupling pressure which will point towards the center.

A fourth consideration is that fabricating surface 13 to be very smooth and fabricating the piston from a material which exhibits a surface wetting property will result in a more complete contact as the piston surface flows on a microscopic scale to conform to the microscopic irregularities of surface 13. No direct treatment of such a wetting property has been found iri the prior art. However, experimentation by the inventors has revealed that this property is related in a rather complex manner to other material properties such as: Poisson's ratio, elasticity, and the chemical structure of the material. In addition, such considerations as: surface smoothness, cleanliness, and treatment also influence whether or not a material exhibits the wetting property. For example, silicone rubber generally exhibits the wetting property; however, some- commercial preparations of the rubber as sheets have surfaces which are coated with a powder and do not exhibit the property. Further, various chemicals classified as silanes when used to treat a surface can enhance the ability of a material to exhibit the wetting property. Rather than present a theoretical treatment of the wetting property, the invention provides a method and means to test a particular preparation of a material for the existence of the property. The test consists of first, preparing a sample of the material with a flat exposed surface leaving the same microscopic smoothness, cleanliness, and treatment as the particular preparation in question; second, placing a 1.5.inch diameter double convex lens having a surface radius of curvature of 4 inches on top of the exposed surfaces; third, viewing the area of contact of the lens and material surfaces by looking through and supplying light through the lens from an angle of about 10" from the normal to the material surface, using a microscope if necessary. The actual contact area will appear slightly darker than the surrounding areas since the surface reflectivity of the lens is lower in the contact area. If the diameter of the circumference of the contact area is greater than or equal to 1/16 of an inch and if the contact area is contiguous within the circumference and occupies at least 90% of the area within the circumference, then the material exhibits the wetting property. Do not confuse the contact area with the Newton's rings which may be present and will be seen to surround the central .contact area. These Newton's rings should not be included in the measurement of diameter of the contact area. For a further discussion of Newton's rings see Principles of ^' Optics by Max Born and Emil Wolf. It should be emphasized that some materials will not exhibit the wetting property in some forms but will in others. The sample for the above test, except for requiring a flat surface, should approximate as much as possible the particular preparation in question. For example, if the particular preparation in question is a sandwich structure of several materials then the sample should have the sandwich structure.

Some materials which have been found to exhibit the wetting property in 1/4 inch thick slabs are: cured RTV 630A, plasticized vinyl, and the material from which R-3603 Tygon tubing is made. Tygon tubing is manufactured by Norton Plastics and Synthetics Division located in Worcester, MA. Some materials which do not exhibit the wetting property in 1/4 inch thick slabs are nylon and high density polyethylene. The provision for a wetting property is the feature which eliminates the need for messy acoustic matching gells, greases, or oils as taught in the prior art. A fifth consideration is that forming the piston 4 from a flexible material will allow the hydraulic force, supplied by the fluid 3 against the^surface of the piston opposite the interface, to deform- the piston' to more uniformly contact the acoustic generating surface. It is still a further consideration that the piston 4 is acoustically thin, i.e., its thickness is small compared to the transmission characteristics of the acoustic wave. In particular, the thickness is such as to not significantly attenuate the acoustic wave as it passes through the piston since in the preferred embodiment the piston is also an acoustic transmission wall. In other words, the thickness of the piston 4 is much less than the skin depth for the wave under consideration. For the power and frequencies already stated a thickness of 1/4 inch is suitable.

It is another consideration that the piston be configured so that activation of the coupled acoustic generator surface does not unacceptably increase leakage of fluid 3 between the piston 4 and the inside wall of the cylinder 5. The invention provides two features to minimize the leakage. The features can be used separately or together to reduce leakage as desired. The first feature is the inclusion of a sleeve extension.-

This sleeve extension of the piston works well if it is formed with an outer diameter which is an amount larger than the inside diameter of the cylinder 5 but not so large as to cause a ripple in the extension. The actual amount is a function of the piston material and is best determined empirically. For silicone rubber the initial sleeve diameter could be larger than the tube diameter by approximately 3%. The second feature is the addition of a spring intensifier ring embedded in the piston which acts to force the sides of the piston against the cylinder walls. In addition, the piston may. be fitted with^* intensifier ridges as are currently used on medical syringe pistons. For additional useful piston features the reader is referred to the prior art dealing with pistons and cylinders which contains numerous additional considerations.

It is also clear from the anticipated procedure for using the appartus of the invention that the hook need not be shaped exactly as shown in the'drawing. In fact, the hook may be replaced with any fastener such as a clothes snap, valcra, etc. which can function as a lifting fastening means to pick up the generator apparatus and which is shaped such that any portion of its surface which comes into contact with the acoustic generator apparatus can be fully enclosed within the enclosure apparatus leaving only a sterile surface exposed to the operator. Likewise, the acoustic generating apparatus can be fitted with any receptical which

-g REAT OMPI will allow the generator to be lifted and which can be enclosed so as to prevent it from contaminating exterior surfaces.

The enclosure apparatus need not be formed from a cylinder or a tube of circular cross-section. The cylinder could be a tube having a rectangular, oval, or other cross-section with the piston shaped accordingly. In such cases, the cap 7 could snap onto the tube rather than use screw threads. As stated above, the transducer will convert the alternating current to acoustic power of essentially the same frequency. The resulting acoustic power is usually specified in Watts/cm2. For a 2.54 cm diameter transducer having an efficiency of about 50% to 70% the acoustic power is about 0.2 Watts/cm2. This power is delivered into the fluid space and'eventually to the surface being cleaned. The invention provides for the use of a range of frequencies and powers. The most useful frequency range is 10 kHz to 400 kHz. When the surface being cleaned is living tissue, the most useful power range is from about 0.03 to 0.5 Watts/cm2 at the tissue surface. The upper limit of 0.5 Watts/cm--^*- is not absolute but is chosen to prevent tissue damage. It could be raised to 3- Watts/cm-2 and higher if the tissue is carefully monitored. The other limits can also be extended but with lesser gains in utility. For cleaning surfaces other than living tissue, power ranges and frequencies equal to those of the prior art could be used.

The foregoing described various features and considerations of the preferred embodiment. It is recognized that a usable cleaning, sterilizing, and/or coating device will result from various combinations and adaptations of the foregoing.

- -UXξr OMPI fr IPO _y The most straight foreward implementation of the invention would consist of a membrane and an acoustic generating surface both forming at least a portion of the boundary of a fluid space and arranged to facilitate the pressurizing of the fluid space by a direct displacement of the boundary into the fluid space. Clearly such an inward displacement could be caused by a variety of means, e.g., spring and piston and other means yet to be discussed.

In the examples to follow, the readily mountable/demountable acoustic coupling feature has been included to show its general application. However, it is not essential in all implementations of the inventions and anyone skilled in the art will recognize that physically the coupling attaches an acoustic generating surface to another surface thus creating one more additional acoustic -generating surfaces. ^' Further, since the prior art provides numerous means which establish acoustic generating surfaces, i.e. piezoelectric transducers, magnetostrictive etc., often including 1/4 wave matching transformers and the like; the present invention allows that such devices can be used whenever there is called for an acoustic generating surface. For example, in fig 3 the aluminum cylinder 14 could be fitted with an "0" ring to form a seal to the inside wall of cylinder 5 thus serving as the piston itself. Piston 4 could thus be eliminated. This device though still useful lacks the readily mountable/demountable coupling feature. Alternatively, the piston 4 could be made of plastic and firmly and permanently bonded to the cylinder 14 with Eastman 910 adhesive available from Eastman KODAK in Rochester, NY. Under such a condition, the. device of fig 3 would not have a readily mountable/demountable acoustic coupling.

An example of another adaptation provided by the invention is shown in figs 6 and 7. Referring to fig 6, 6-8 designates a partial view of the sectional view of the acoustic generator apparatus of fig 5. However, in fig 6, the aluminum cylinder 6-14, unlike cylinder 14, is fitted with threads 6-35 as shown. Screwed onto the threads is shown a cup—like device 6-4, which is fitted with internal threads 6-36. The cup-like device may be made of a semi-resilient inexpensive plastic such as polyethylene or plasticized vinyl. The wall of the device 6-4 which contacts convex surface 6-13 and serves as an acoustic transmission wall should be flat prior to contacting. When the device 6-4 is screwed onto cylinder 6-14, the resulting distortion of the surface and wall of 6-4 will supply the restoring force to keep acoustic contact between 6-14 and 6-4 thus causing the opposite surface of device 6-4, i.e., the surface which is one of the boundaries of the fluid space, to become an acoustic generating surface. This will cause.the acoustic energy to flow into the fluid 6-3 which is held under pressure in the fluid space by resilient, stretched wall boundary 6-5. The cylindrical wall 6-5 is fastened to device 6-4 by ring clamp 6-34 or glueing. The cylindrical wall 6-5 could be made of rubber. The device is used by activating the acoustic generating surface, removing the film seal 6-2, and then using the device as a swab as previously described. When the liquid 6-3 is expelled, the device 6-4 may be removed, and owing to low fabrication cost may be discarded. A new device 6-4 may be screwed onto the acoustic generator apparatus. The spent device 6-4 would appear as shown in fig 7 which shows how wall 6-5 has contracted, shown as 6-5, causing an inward displacement of membrane 6-1 which expelled the fluid. Of course, alternatively, the wall 6-5 could be clamped or glued directly to cylinder 6-14. Such a device would lack the readily mountable/ demountable coupling but would still be useful as an acoustic-assisted cleaning apparatus. A still further adaptation of the device of figs 6 and 7 is shown expanded in size in figs 8 and 9. Referring to fig 8, again is shown a partial view of an acoustic generator apparatus 8-8. However, instead of screw threads to maintain acoustic coupling to the fluid 8-3, the reversible fastening means is a nonhardening pressure sensitive adhesive designated 8-42. The adhesive could be the same type as that produced by 3 M Corporation and currently used on their "Scotchtab" product. The adhesive could initially be coated on the mounting surface of the acoustic transmission wall 8-4 of the thin, flexible .002 inch thick polyethylene or plasticized vinyl sheet designated 8-5. The adhesive layer could be protected with a waxed paper prior to use. The permeable membrane 6-1 could be replaced by the structure shown as 8-41 in profile in fig 8 and in front view in fig 9. The structure is seen to consist of a single hole 8-44 for the fluid 8-3 to escape, concentric ridges 8-43, with alternating slots 8-45. The concentric ridges can help to both scrub the surface to be cleaned as well as retain the fluid between the membrane 8-41 and the said surface. The slots allow fluid to flow outward from the inner ridges to help keep the spaces between the outer ridges filled even with low fluid pressure. In fact, for this adaptation. pressing the device against, for example, the surface to be cleaned can develop sufficient pressure for fluid flow by collapsing a portion of the fluid space boundary, i.e., wall 8-5 causing an inward displacement of the boundary portion 8-41 shown in front view as 8-41. By using the external force applied by the surface being cleaned, the need for a portion of the boundary of the fluid space to be a stretched resilient material can be eliminated. It would only be necessary that the portion of the boundary be flexible.

The adaptation of figs 8 and 9 might be used as follows: first, the waxed paper is removed from the adhesive layer on the fluid chamber. Second, the adhesive layer is brought into contact with the acoustic generating surface 8-13. Third, using a needle the membrane is pierced within the innermost ridge to form a hole. Fourth, the acoustic generator is activated and the device is used as a swab.

Alternatively, the membrane may be formed with a flexible protrusion shown as 8-44. Such a structure can act as a one-way valve which will allow fluid 8-3 to escape in response to pressure but stop air or fluids which may interfere with the acoustic transmission from entering the fluid space.

Fig. 8 and 9 also show a partial view of an alternative enclosure means designated 8-64. This alternative means is a flexibel material e.g., 0.002 inch polyethylene sheet formed into a bag or tube one end of which is bonded to wall 8-5 as shown and the other end of which is initially left open for insertion of the acoustic generator apparatus 8-8. After insertion of the acoustic generator apparatus the open end of the tube can be closed by means of a - 25 -

draw string or rubber band.

A still further adaptation of the invention is shown in fig 10. Referring to fig 10, 10-15 designates a longitudinal mode transducer which together with cylinders 10-18 and 10-14 and bolt

10-17 forms the forementioned bolted assembly. The said assembly is cemented into the cylindrical cavity in handle 10-48 using for example RTV silicone rubber 10-27. An acoustic barrier 10-19, which may be closed cell silicone rubber, is used to reduce the amount of acoustic energy which enters the handle 10-48 to acceptable levels. It also serves as a positive stop which simplifies insertion of the bolt assembly during manufacture. The electronics and energy source may be located in that part of the handle designated 10-49. Attached to the cylinder 10-14 by perhaps screw threads is a cup-like .device 10-4 which functions in principle like device 6-4. Attached to the device 10-4, perhaps with glue, is a fluid retaining material

10-1 which by virtue of its internal pores and tiny passages can temporarily retain a fluid with which it has been saturated. Suitable fluid retaining materials could be sponge, thick felt, etc. The fluid retaining material may be partly surrounded by a flexible sleeve 10-37 which stops fluid from escaping out the sides of the fluid retaining material thus reducing nonuseful fluid loss. Leading through said sleeve and into the sponge 10-1 is a tube 10-38 which serves as an inlet means and is connected to a fluid supply 10-39 which is pressurized by the squeeze arm 10-40 and spring 10-11.

For this adaptation the device 10-4 and sponge 10-1 may be replaced as a unit after use.

This replaceable unit may also include the tube and reservoir. Alternatively, the tube 10-38 could be extended in length and the reservoir could be enlarged and located a distance away. The reservoir could contain sufficient fluid for application on several different surfaces. This alternative could also be useful in sterilization if some mechanism were provided to avert the possibility of cross-contamination between different surfaces. Such a mechanism might be for example a flow sensor and warning device which sounds an alarm in the event of a backflow which might contaminate the reservoir. On hearing the alarm, the operator would clean or dispose of the reservoir. Another mechanism might be a oneway valve located in the entended tube which could prevent fluid backflow and even prevent back diffusion of chemicals or particles within the fluid.

Such a device as in fig 10 with an extended tube and enlarged reservoir as detailed above is- also particularly useful for coating surfaces where sterility is not a consideration, such as iriditing aluminum too large to be submerged in a tank. In an adaptation of fig 10 the fluid retaining material can be glued directly to the aluminum cylinder. This adaptation lacks the readily mountable/demountable acoustic coupler.

A still further adaptation of the readily mountable/demountable acoustic coupling means is shown in fig 11 wherein a rectangular block 11-14 is substituted for the aluminum cylinder 6-14. A cup-like device 11-4 which may be made of polyethylene and which shares the purpose of cup-like device 6-4 is shown to slide rather than screw onto the block. The arrow marked A in fig 11 shows the direction of the slide. Cup-like device 11-4 is initially configured to have a flat surface

OMPI on that portion which is to contact surface 11-13 and serves as the acoustic transmission wall. It is the bending of this initially flat surface which develops the forementioned pressure gradient which the invention provides to enhance acoustic coupling by eliminating air pockets between 11-14 and 11-4. The surface of 11-4 opposite that surface which contacts the block 11-14 will be rendered an acoustic generating surface and can be used for mounting the fluid retaining means, scrubbers, sponges, etc. consistent with the invention. If the device 11-4 is snapped onto block 11-14 instead of the forementioned slide it becomes apparent that the shapes will initially contact in a region resembling a line or stripe. As the surfaces are brought closer the stripe will grow in width pushing air ^■ ahead of it as it grows, thus implementing the principle explained previously in conjunction with a circular patch of contact. The invention provides that any shapes which initially contact in a small area and are configured so that the area grows in a manner which helps to prevent gas pockets by pushing air in a direction away from the contact region, may be used for a readily mountable/demountable acoustic coupling.

A possible design for the forementioned unique electric switch is shown in fig 12 which is an expanded partial view of fig 5. The bounce switch is inside of housing 32 and consists of: a magnet 54 embedded in a potting epoxy 59 such as

EPON 828 epoxy resin and V25 curing agent available from Read Plastics in Rockville, MD; a contact arm 51 made of spring metal such as berylium copper supplied by Kawecki Berylco Industries Inc. in Reading, PA; an iron block 53 fastened to the contact arm, said iron block together with magnet 54 forms a holding means; an electrical contact 52 also fastened to arm 51 and electrically connected to wire 22; and contact 55 fastened to the potting epoxy as shown and electrically connected to battery 21 by a wire as shown. The operation of the switch can be understood as follows: when the switch is open the contact arm, which is a spring, is held by its own spring force in the position shown in the figure by dashed lines. If the entire device is suddenly accelerated upward, i.e. a bump on a hard surface, the mass of iron will fall towards the magnet where it will be held by the magnetic force thus holding the contacts 55 and 52 together and electrically connecting the battery 21 to wire 22 which leads to the acoustic generator circuit. To open the switch one simply turns the device upside down and again-bumps it on a hard surface thus causing the arm 51 to return to the dashed line position. An improvement in the design above consists of forming the contacts 52 and 55 so they touch before the magnet and iron block touch. This feature allows the iron block to accelarate to a higher speed before the contacts 52 and 55 separate during the process of electrically opening the switch. This higher speed reduces the time during which the contacts can electrically arc thus protecting their surfaces.

The invention also provides method and means for charging the battery located within the acoustic generating apparatus without requiring electrical contact to the exterior of the acoustic generating apparatus. Referring to fig 12, basically the means consists of a coil of wire 31 shown in cross-section, preferably wound around a ferromagnetic core 30 shaped as shown and sealed inside the cylinder 26. This coil when placed into an. alternating magnetic field whose lines of flux encircle the windings, will deliver AC electricity at its output leads 58. This AC electricity can then be rectified, regulated, and used to charge the battery. When this means is used to charge the battery, the cylinder 26 should be neither ferromagnetic nor electrically conductive.

A possible configuration of a means for generating the alternating magnetic field is also shown in cross-section in fig 12 as a coil of wire 57 which is preferably wound inside of a channel formed in a ferromagnetic ring 56 also as shown. The number of turns in each winding, the frequency of the alternations, and the voltage applied to the coil 57 can be determined empirically. Alternatively, by assuming the core 30 and ring 56 to form .a pot core, these parameters may be calculated as shown in Linear Ferrite Magnetic Design Manual available from Ferroxcube in Saugerties, NY.

Claims

1. An acoustically assisted cleaning apparatus comprising: an acoustic generating surface which is a boundary of a pressurizeable fluid space and which can deliver acoustic energy into the fluid space, and a membrane which is also a boundary of the fluid space and though which fluid, if placed within the fluid space may flow when said membrane is provided with a hole, said acoustical generating surface and said membrane arranged so pressure within the fluid space is caused by an inward displacement of at least a portion of at least one of the boundaries.

2. The invention of claim 1 wherein at least a portion of at least one of the boundaries is formed from a^* flexible material arranged so that it may collapse in response to an exterior force directed at a portion of said boundary and directed inward to the fluid space so as to cause pressure in a fluid when said fluid is placed in the fluid space.

3. The invention of claim 1 wherein at least a portion of at least one of the boundaries is formed from a resilient material arranged so as to cause pressure within a fluid locatable within the fluid - space when said resilient material is under tension.

4. The invention of claim 1 wherein a portion of a boundary of the fluid space is formed as a tube and the acoustic generating surface is located on a piston within said tube wherein the said inward displacement is accomplished by the sliding of the piston.

5. The invention of claim 1 wherein the membrane is a woven fabric arranged so that the tightness of the weave can control the rate of flow of a fluid out of the fluid space.

6. The invention of claim 1 wherein the membrane is configured to protrude in response to pressure within the fluid space.

7. The invention of claim 1 wherein the membrane is provided with a hole through which fluid, placed within the fluid space, may flow.

8. The invention of claim 7 further comprising a one-way valve located to only allow flow through the said hole in a direction out of the fluid space.

9. The invention of claim 1 wherein the membrane is provided with at least one ridge which is provided with at least one slot.

10. The invention of claim 1 wherein the membrane is provided with bristles.

11. A readily mountable/demountable acoustic coupling comprising: two surfaces and a reversible fastening means which provides a force to hold the two surfaces in contact, said surfaces configured so that, as they are brought together to form the acoustic coupling, initially a small area of contact is established and as the force bringing the surfaces together is increased the initial area of contact increases in size to thereby reduce the formation of gas pockets.

OMPI

12. The invention of claim 11 wherein the reversible fastening means is a nonhardening pressure sensitive adhesive.

13. The invention of claim 11 wherein at least one of the surfaces is convex.

14. The invention of claim 11 wherein at least one of the surfaces is formed onto a material which exhibits a surface wetting property so as to enhance the ability of the two surfaces to contact on a microscopic scale.

15. The invention of claim 14 wherein one of the surfaces is convex.

16. The invention of claim 11 wherein the reversible fastening means supplies a hydraulic ^' forc 'and at least one of the surfaces is formed on a flexible wall.

17. A readily mountable/demountable acoustic coupling comprising: two surfaces and a reversible fastening means which provides a force to hold the two surfaces in contact, said surfaces configured and said fastening means is arranged so that there will result a gradient in the coupling pressure which has a vector component parallel to the interface and pointing, so as to enhance the ejection of gas pockets.

18. The invention of claim 17 wherein the pressure gradient vector component parallel to the interface is caused by configuring at least one of the surfaces to be convex.

19. The invention of claim 17 wherein the vector component parallel to the interface is caused by forming at least one of the surfaces onto a composite structure which causes that surface to have an effective co pressive strength which is greater at a contact point from which a vector component points, than the effective compressive strength at contact points to which that vector is pointing.

20. A readily mountable/demountable acoustic coupling comprising: a reversible fastening means and two surfaces at least one of which is formed onto a material which exhibits a surface wetting property so as to enhance the ability of the two surfaces to contact on a microscopic scale.

21. The invention of claim 20 wherein the surfaces are configured and the fastening means is arranged so that there will result a gradient in the coupling pressure which has a vector component parallel to the interface and pointing so as to enhance the ejection of gas pockets.

22. A readily mountable/demountable acoustic coupling comprising: two surfaces at least one surface of which is formed on a flexible wall and a reversible fastening means which supplies hydraulic force against the side of the flexible wall opposite the one surface so as to better ensure uniform contact between the two surfaces.

23. A readily mountable/demountable acoustic coupling comprising:' two surfaces and a nonhardening pressure sensitive adhesive applied initially to at least one of the surfaces to maintain acoustic coupling between the two surfaces.

24. A mechanically activated electric switch which can be both turned on and off by a brief acceleration comprising: two electrical contacts, a spring, a holding means, and a mass; said spring, mass, and holding means arranged so that a nondestructive sudden acceleration to an instrument containing said switch will overpower the holding force or the spring so as to reverse the state of the switch.

25. The invention of claim 24 wherein the holding force is supplied by a magnet and piece of a ferro-magnetic material;

26. The invention of claim 24 wherein"the spring, holding means, and mass are also configured so as^' to allow the mass to accelerate in speed before -electrical contact is broken to thereby reduce electrical arcing.

27. An acoustically assisted cleaning apparatus comprising an acoustic generating surface to which is attached a fluid retaining material.

28. The invention of claim 27 further comprising an inlet means and a fluid supply arranged to feed fluid into the fluid retaining material.

29. The invention of claim 28 further comprising a one way valve located fluidically between the fluid supply and fluid retaining material so as to stop fluid and contaminants from traveling from the fluid retaining means to the fluid supply.

30. The invention of claim 27 further comprising a flexible fluid retaining sleeve placed around the fluid retaining material to reduce nonuseful fluid loss.

31. An acoustic assisted cleaning apparatus comprising: an acoustic generating surface and a membrane formed from a woven fabric said surface and membrane arranged to form boundaries for a fluid space and the acoustic generating surface also arranged to deliver acoustic energy into the fluid space, and the membrane also arranged so fluid placed within the fluid space will flow through the membrane at a rate which can be controlled by the tightness of the weave of said fabric.

32. The invention of claim 31 wherein the membrane is configured to protrude in response to pressure within the fluid space.

33. The invention of claim 31 further comprising at least one ridge with at least one slot fixed to the membrane and arranged so as to partially retain the fluid between the membrane and the surface being ^• cleaned.

34. The invention of claim 3^'1 further comprising bristles fixed to the membrane.

35. The invention of claim 31 further comprising an antiseptic solution located within the fluid space.

36. An acoustic generator apparatus comprising: a transducer means; a battery; and an exposed flat acoustic generating surface all of which are held in an arrangement which can fit into a cylindrical container with the acoustic generating surface at one end of said container with said surface held oriented essentially perpendicular to the axis of said container.

37. The invention of claim 36 wherein the acoustic generating surface is convex.

38. The invention of claim 36 further comprising an electrical switch said switch including two electrical contacts, a spring, a holding means, and a mass; said spring, mass, and holding means arranged so that a nondestructive sudden acceleration reverses the electrical state of the switch.

39. The invention of claim 36 further comprising a coil of wire arranged so as to convert an externally generated alternating magnetic field into electricity.

40. The invention of claim 36 further comprising a spring located at the end of the arrangement opposite the acoustic generating surface.

41. The invention of claim 36 further comprising a receptical for a fastener capable of lifting the arrangement.

42. The invention of claim 41 wherein the spring is the said receptical.

43. A cleaning apparatus readily mountable/ demountable from an acoustic generating surface comprising: an acoustic transmission wall and a membrane which form boundaries for a fluid" space. said ^'wall arranged so acoustic energy can be transmitted through said wall into, the fluid space.

44. The invention of claim 43 wherein the acoustic transmission wall is provided with a nonhardening pressure sensitive adhesive located on the surface opposite the surface which forms a boundary for the fluid space so that the adhesive may serve as a reversible fastening means for maintaining acoustic coupling between the said wall and an acoustic generating surface.

45. The invention of claim 43 wherein the acoustic transmission wall is configured so that when the wall is acoustically coupled to an acoustic generating surface there exists a pressure gradient in the coupling pressure which has a vector component parallel to the interface and pointing so as to enhance the ejection of gas pockets.

46. The invention of claim 43 wherein the acoustic transmission wall is configured so that as the wall is brought together with an acoustic generating surface to form an acoustic coupling, initially a small area of contact is established and as the force, bringing the wall and the acoustic generating surface together, is increased the initial area of contact increases in size in a manner which helps to prevent the formation of gas pockets.

47. The invention of claim 43 wherein the surface of the acoustic transmission wall opposite the fluid space is convex.

48. The invention of claim 43 wherein the surface of the acoustic transmission wall which is opposite the fluid space is formed from a solid material which exhibits the fluid wetting property.

49. The invention of claim 43 wherein the acoustic transmission wall is formed from a flexible material

5 so that hydraulic pressure in the fluid space will distort the wall to cause more uniform contact with an acoustic generating surface.

50. The invention of claim 43 further comprising an enclosure means arranged so as to allow enclosure of

10 a potentially non-sterile acoustic generator apparatus thus reducing the possibility of said generator from further contaminating areas exterior to the enclosure means while permitting the generator apparatus to deliver acoustic energy ^"to

15. the fluid space.

51.. The invention of claim 50 further comprising a fastening means capable of lifting a potentially non-sterile acoustic generator apparatus for insertion into the enclosure means, said fastening 20 means located so it is also enclosed within the enclosure means with the generator apparatus so as to reduce the possibility of lifting the fastening means from contaminating areas external to the enclosure.

25 52. The invention of claim 51 wherein the lifting fastening means is a hook.

53. The invention of claim 51 further comprising a piston and a cylinder wherein the enclosure means is formed by an extension of the cylinder which is 30 fitted with an end cap to which is attached the lifting fastening means.

OMPI

•_

54. The invention of claim 43 wherein at least a portion of at least one of the boundaries of the fluid space is formed of a flexible material arranged so that said portion may collapse in response to a force directed at said portion and directed toward the fluid space so as to cause pressure within a fluid located in the fluid space.

55. The invention of claim 43 wherein at least a portion of at least one of the boundaries of the fluid space is formed from a resilient material arranged to cause pressure within a fluid located within the fluid space when said resilient material is under tension.

56. The invention of claim 43 wherein a portion of a boundary of the fluid space is formed as a cylinder and .the acoustic transmission wall is configured as a- piston within the cylinder.

57. The invention of claim 43 wherein the membrane is a woven fabric with the tightness of the weave controlling the rate of flow of a fluid out of the fluid space.

58. The invention of claim 43 wherein the membrane is configured to protrude in response to pressure within the fluid space.

59. The invention of claim 43 wherein the membrane is provided with a hole through which fluid, within the fluid space, may flow.

60. The invention of claim 59 further comprising a one-way valve located to only allow flow through the said hole in a direction out of the fluid space.

61. The invention of claim 43 wherein the membrane is provided with at least one ridge which is provided with at least one slot.

62. The invention of claim 43 wherein the membrane is provided with bristles.

63. The invention of claim-43 wherein at least a portion of the membrane is covered with a film seal.

64. The invention of claim 43 further comprising an inlet means and a fluid supply apparatus arranged to supply a fluid to the fluid space.

65. The invention of claim 64 further comprising a one way valve located fluidically between the fluid space and the fluid supply so as to stop fluid and contaminants from traveling from the fluid space to the fluid supply.

66. The invention of claim 43 wherein a fluid retaining material is substituted for the membrane and is attached to the acoustic transmission wall.

67. The invention of claim 43 further comprising a disinfectant located within the fluid space.