Abstract:
A transponder assembly for use in identifying surgical implements such as sponges comprises a transponder substantially encased in a plastic body to which a base having an exposed adhesive surface is attached. The assembly may be fastened directly to a rigid implement or may be securely attached to a sponge by a supporting body embodying a pin-head clutch.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a transponder particularly designed to identify individual surgical sponges or implements, and to a method for making it.  
       BACKGROUND OF THE INVENTION  
       [0002]     Surgical operations involve the use of implements and blood-absorbing sponges which are placed within the wound necessarily created by the operation, there to remain for a period of time during the operation before being removed. Obviously it is essential that all such objects be removed from the patient&#39;s body before the incision is closed. If a sponge, clamp or other implement is left behind in the patient&#39;s body it will be a source of infection and trouble, potentially fatal. Accordingly one major task in any operation is to keep track of the sponges and implements used so as to make sure that the operation is terminated in an effective and medically wholesome manner. Over the years many proposals have been made for accomplishing this desired result with as high a degree of certainty as possible.  
         [0003]     One such general approach is to so modify the sponges or implements used as to make them radiation-sensitive—receiving radiation directed at them and reacting in some manner capable of being sensed by appropriate equipment so as to indicate their presence in the patient&#39;s body, thus enabling the operating team to interrogate by means of radiation and to receive some signal indicating that a foreign object is present. More specifically, it has been proposed that each implement, be it sponge, clamp or whatever, that is placed within the patient&#39;s body, thus identify itself with a signal unique to each implement, such as by a unique serial number or the like. In this way the operating team, using available circuitry and computers, can record the identification of each item placed within the patient&#39;s body, can later record the identification of each item removed from the patient&#39;s body, and can then compare the lists of identifications to determine whether something is unaccounted for, and if it is what it is, thereby to facilitate the finding and retrieval of the foreign object in question.  
         [0004]     Known devices, called transponders, are capable of receiving a transmitting radiation signal and of transmitting in response their own unique identification radiation signal. However, means must be provided for the transponders to be attached to such disparate objects as surgical sponges, clamps and other surgical instruments in such a manner that they remain with such items throughout their use during the operation, since leaving a transponder behind would in all likelihood be just as dangerous as leaving a sponge behind. The problem is intensified by the fact that a given operation will involve the use of a large number of items that must be kept track of.  
       SUMMARY OF THE INVENTION  
       [0005]     In accordance with the present invention, a transponder assembly is produced which is suitable for relatively inexpensive quantity production, which is readily attachable to such diverse surgical impedimenta as fabric sponges and metal implements, and which will reliably remain in position once appropriately attached. In such an assembly the transponders are initially substantially completely encased within a plastic body preferably having significant adhesive properties, and a base is secured to that plastic body. An exposed surface of that base is itself adhesive in character, as by applying to the plastic body a double-faced adhesive strip. In certain circumstances the double-faced adhesive strip may constitute the base, but in other circumstances the base may comprise an additional part, such as a thin steel piece, to which the double-sided adhesive strip is attached.  
         [0006]     The exposed adhesive surface on the base may be applied directly to a rigid tool such as a clamp, thereby to reliably secure the transponder in place of that tool, but to attach the transponder to a flexible fabric such as a surgical sponge is another matter. For that purpose a supporting body is provided for each transponder to an exposed surface of which the transponder assembly is adhesively fastened. That supporting body has a pin extending therefrom which is adapted to penetrate and project from the sponge, and a retaining element is frictionally fastened to the extending portion of the pin, this being the well-known pin-clutch assembly.  
         [0007]     Large numbers of transponder assemblies of the present invention will be required since significant numbers of items, particularly sponges, are placed within the patient&#39;s body during a typical operation. The particular construction of the transponder assembly of the present invention is well suited to relatively inexpensive quantity production. The transponder unit itself is embedded within and essentially completely surrounded by a self-sustaining plastic mass, preferably inherently of adhesive character but at any rate having an exposed surface which is, inherently or otherwise, of adhesive character. A base is secured to the transponder, the exposed surface of that base exhibiting adhesive properties. The base itself may be constituted by a double-sided adhesive strip or, if additional structural strength is required, may comprise two layers, the first layer, adhesively secured to the transponder-plastic combination, being structural in character such as a metal strip, with the second layer preferably being the aforementioned double-sided adhesive strip. The thus-constructed transponder assembly may be very conveniently manufactured by means of an open-topped mold preferably in the form of a flexible sheet having multiple open-topped cavities of appropriate size and shape. A transponder and an appropriate quantity of unset plastic material is inserted into each open-topped cavity, the desired base is applied thereto, the plastic mass is caused to set, and then the individual transponder assemblies can be removed from their respective cavities merely by flexing the mold sheet. In order to ensure that the plastic material properly engages and protects the transponder with which it is associated, it is preferred that the unset plastic material is inserted into a mold cavity in two stages, a preliminary amount first being placed in the cavity, the transducer then being pushed into that plastic, and a second quantity of plastic then being added to fill the cavity and preferably substantially completely cover the transducer, before the base is applied.  
         [0008]     Thus the transponders are substantially insulated and protected from external problems while at the same time are readily manipulatable and capable of reliably functioning in the external environment to which they will be subjected in the course of a surgical operation. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     To the accomplishment of the above, and to such other objects as may hereinafter appear, the present invention relates to the construction of a transponder assembly and the method of making same as defined in the appended claims and as described in this specification and disclosed in the following drawings:  
         [0010]      FIG. 1  is a perspective exploded view of the attachment of the transponder assembly of the present invention to a surgical sponge;  
         [0011]      FIG. 2  is an exploded view of one embodiment of the transponder assembly of the present invention;  
         [0012]      FIG. 3  is an exploded view of a second embodiment of the transponder assembly of the present invention;  
         [0013]      FIG. 4  is a three-quarter exploded view of that part of the assembly of  FIG. 1  that carries the sponge-engaging pin;  
         [0014]      FIG. 5  is a three-quarter view showing a first step in the preferred method of formation of the assembly of the present invention;  
         [0015]      FIGS. 6, 7 ,  8  and  9  are three-quarter views similar to  FIG. 5  but showing successive steps in the preferred formation of the transponder assembly;  
         [0016]      FIG. 10  is a three-quarter perspective fragmentary view of a typical mold sheet that may be used in the preferred formation method, with the individual mold cavities filled with assemblies of  FIG. 2 ;  
         [0017]      FIG. 11  is a cross-sectional view taken along the line  11 - 11  of  FIG. 10 ; and  
         [0018]      FIG. 12  is a view similar to  FIG. 11  but showing transponder assemblies of  FIG. 3  in the mold cavities.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]     Transponder—devices capable of receiving a radiation signal and transmitting a radiation signal in response—are readily available in sizes capable of being used in connection with this invention. The basic transponder assembly of the present invention comprises a transponder  2 , here shown as a small cylinder, embedded in and substantially covered by a plastic mass  4  attached to a base  6  the exposed surface of which is adhesive in character. The base  6  preferably comprises a double-faced adhesive strip  8  secured either directly or indirectly to an exposed surface of plastic mass  4 . If desired for improved structural reliability, and as shown in  FIG. 2 , a strip  10  of suitable structural material such as metal may be interposed between the adhesive strip  8  and the plastic mass  4 , being secured to the plastic. Alternatively, and as illustrated in  FIG. 3 , the metal strip  10  may be omitted, the adhesive strip  8  being applied directly to the plastic mass  4 .  
         [0020]     These individual assemblies may readily be formed on a quantity basis by utilizing a mold sheet  12  having a plurality of appropriately sized and shaped open-topped cavities  14 . The mold sheet  12  is preferably formed of flexible material to facilitate ejection of the assemblies from the sheet. A typical sheet may have a hundred rows of a hundred cavities  14  each.  
         [0021]     As illustrated in  FIG. 5 , the first step in the preferred method of fabrication of the transponder assembly  2  is to place, usually by pouring, a first quantity  4   a  of that plastic material into a cavity  14  so as to partially but not completely fill that cavity. Next, as shown in  FIG. 6 , a transponder  2  is inserted into the plastic mass  4   a  in a cavity  14  so as to be at least partially submerged, this procedure tending to insure that there is a layer of the plastic material  4   a  between the transponder  2  and the bottom of the cavity  14 . Next, as shown in  FIG. 2 , a second mass of plastic material  4   b  is poured or otherwise placed within the cavity  14  to substantially fill that cavity and substantially completely cover the transponder  2 . Next, as shown in  FIG. 8 , the assembly&#39;s base  6  may be placed on top of the unset plastic mass  4 , preferably fitting relatively snugly within the cavity  14  so as to effectively close the open top thereof. As indicated above, the base  6  may be constituted by a double-sided adhesive sheet of conventional construction the lower and upper surfaces of which, as the name implies, exhibit adhesive properties. Alternatively and as shown in  FIG. 2 , the base  6  may be in two parts, a structurally strong strip  10  of metal such as steel lying directly on the plastic mass  4  with the double sided adhesive strip  8  adhesively secured to the upper surface of the strip  10 .  
         [0022]     The substance used for the plastic mass  4  is one which can readily be inserted into the cavity  14 , as by pouring, yet in the finished product will have form, solidity and shape so as to carry and protect the transponder  2 . Thus a thermosetting resin is preferred for this purpose. Moreover, it is desirable that the material  4  when set itself have adhesive properties. When the base  6  comprises the metal strip  10  it is preferable that the strip  10  is applied to the plastic mass  4  before the latter has set, particularly when the mass  4  itself is adhesive, so that adhesion of the strip  6  with the remainder of the assembly will be reliably and permanently obtained. However, if needed, a separate adhesive layer may be interposed between the metal strip  6  and the plastic  4 . The double-sided adhesive strip  8  whether used with or without the metal strip  10  may be applied to the assembly either before or after the plastic mass  4  has set. I prefer, when the metal strip  10  is used, to apply the adhesive strip  8  to the metal strip  10  to form the base  6  and then apply the thus-formed base  6  to the plastic mass  4  before the latter is subjected to setting conditions.  
         [0023]     I have found that epoxy adhesives, and particularly those of the room temperature curable type, are very effective. I have used such epoxy adhesives as those sold by Loctite under the designations M-31CL, 3981, E-20EP and E-120HP, as well as the epoxy adhesives sold by MasterBond under the designations EP42HT and EP42HT-2. For double-sided adhesive strips I have used those sold by 3M under the designations 468MP and 9469-PC.  
         [0024]     After the cavities  14  have been filled as thus described the sheets  12  may then be subjected to such external conditions as will cause the particular material  4  to set. With the materials specified above, letting the filled trays stand at room temperature for twenty-four hours provides the desired setting condition.  
         [0025]     After the plastic material  4  in the cavity  14  has set the individual transponder assemblies can readily be removed from the sheet  12  because all of the cavities  14  have open tops. One convenient way in which the assemblies may thus be removed is by flexing the sheet  12 , causing the individual transponder assemblies to pop out from their respective cavities  14  in the same way that ice cubes may be popped out of flexible ice cube trays.  
         [0026]     The exposed adhesive surface of the double-sided adhesive strip functions satisfactorily when attaching the assemblies to a rigid operating tool such as a clamp. However, the flexible and usually loosely-woven material of a surgical sponge  18 , more or less schematically shown in  FIG. 1 , makes impractical the adhesive attachment of the assemblies of the present invention directly to the sponge. Therefore, as shown in  FIGS. 1 and 4 , the complete transponder assembly  20  is attached to a supporting body  22  in the form of a preferably metal disc by means of its exposed adhesive surface, here shown as constituted by the exposed surface of the double-sided adhesive strip  8 . Projecting from the opposite surface of the supporting body  22  is a pin  24  designed to penetrate and extend beyond the body of the sponge  18 , and a retaining element  26  is designed to slide over the pin  24  and resist removal therefrom. This type of device is well-known, and often designated a pin-head clutch. The action of this type of device to secure a transponder assembly  20  to a sponge  18  has the advantage that the same transponder assembly  2  with pin-head clutch  22 ,  26  may be removed from the sponge  18  to which it is connected before that sponge is discarded, with the assembly  20 ,  22 ,  26  being ready for use with another sponge  18  as is required.  
         [0027]     With the present arrangement readily available transponders can be adapted to be secured to virtually any type of implement and device used in connection with surgical operations so as to perform vitally needed identification functions. The resulting assemblies may be manufactured in a simple, reliable and relatively inexpensive manner, and when made will protect the transponder while making it readily manipulatable and effectively operable.  
         [0028]     While only a limited number of embodiments have been here specifically disclosed, it will be apparent that many variations may be made therein, all within the scope of the invention as defined in the following claims.