Patent Publication Number: US-9415010-B2

Title: Ingestible circuitry

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/527,403, entitled IDENTIFIER CIRCUITS FOR GENERATING UNIQUE IDENTIFIABLE INDICATORS AND TECHNIQUES FOR PRODUCING SAME, filed on Jul. 27, 2010, now U.S. Pat. No. 8,540,633, which application is a 371 National Stage Entry of International Patent Application No. PCT/US2009/053721, entitled INGESTIBLE CIRCUITRY, filed on Aug. 13, 2009, which application, pursuant to 35 U.S.C. §119 (e), claims priority to the filing date of U.S. Provisional Application Ser. No. 61/088,355 entitled INGESTIBLE CIRCUITRY, filed on Aug. 13, 2008, the disclosures of which are herein incorporated by reference. 
    
    
     BACKGROUND 
     Ingestible devices that include electronic circuitry have been proposed for use in a variety of different medical applications, including both diagnostic and therapeutic applications. 
     Examples of such ingestible devices are ingestible electronic capsules which collect data as they pass through the body, and transmit the data to an external receiver system. An example of this type of electronic capsule is disclosed in U.S. Pat. No. 5,604,531 Iddan et al., which describes what is called an in vivo video camera. The swallowable capsule includes a camera system and an optical system for imaging an area of interest onto the camera system. The transmitter transmits the video output of the camera system and the reception system receives the transmitted video output. U.S. Pat. No. 7,009,634 also issued to Iddan et al discloses an ingestible imaging device that obtains images from within body lumens or cavities. The electronic circuit components of the device are enclosed by an inert indigestible housing (e.g. glass housing) that passes through the body internally. U.S. Pat. No. 6,800,060 issued to Marshall discloses an ingestible data recorder capsule medical device. The electronic circuits of the disclosed device (e.g. sensor, recorder, etc.) are housed in a capsule made of inert materials, and therefore ingestible and passable through the digestive tract without being consumed by the body. 
     In these devices, the electronic circuits are protected in a housing or capsule that prevents damage to the device&#39;s electronic circuits during the process of ingestion and elimination in the human body. 
     Recently, U.S. Patent Application Publication No. 2007/0008113 by Spoonhauer et al. disclosed fragile radio frequency identification (RFID) tags for use in drug ingestion monitoring applications. The RFID tags disclosed in this application are simple antenna structures that are configured to break down during transit through the body. 
     In certain instances, more complex circuitry suitable for use in ingestible devices is needed. 
     SUMMARY 
     The present invention provides for robust ingestible circuitry, where the components of the ingestible circuitry are ingestible, and in some instances digestible. As the ingestible circuitry is made up of ingestible, and even digestible, components, the ingestible circuitry results in little, if any, unwanted side effects, even when employed in chronic situations. The ingestible circuitry is particularly suited for use in signal identifiers, e.g., as may be found in ingestible event markers (IEMs), which include pharma-informatics enabled compositions. 
     Embodiments of ingestible circuitry of the invention include a solid support of an ingestible material, which support has on a surface thereof one or more electronic components. Components that may be present on the surface of the support may vary, and include but are not limited to: logic and/or memory elements, e.g., in the form of an integrated circuit; a power device, e.g., battery, fuel cell or capacitor; an effector, e.g., sensor, stimulator, etc.; a signal transmission element, e.g., in the form of an antenna, electrode, coil, etc.; a passive element, e.g., an inductor, resistor, etc. The one or more components on the surface of the support may be laid out in any convenient configuration. Where two or more components are present on the surface of the solid support, interconnects may be provided. All of the components and the support of the ingestible circuitry are ingestible, and in certain instances digestible. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  shows diagrammatically an ingestible identifier that includes ingestible circuitry in accordance with the invention. 
         FIGS. 2A to 2D  provide views of assembly of an ingestible identifier that includes ingestible circuitry in accordance with the invention. 
         FIGS. 3A and 3B  provide views of assembly of an ingestible identifier that includes ingestible circuitry in accordance with the invention. 
         FIG. 4  provides a view of assembly of an ingestible identifier that includes ingestible circuitry in accordance with the invention. 
         FIG. 5  provides a view of assembly of an ingestible identifier that includes ingestible circuitry in accordance with the invention. 
         FIGS. 6A and 6B  provide views of assembly of an ingestible identifier that includes ingestible circuitry in accordance with the invention. 
         FIGS. 7A to 7B  provide views of a bifurcated laminate process employed to fabricate devices according to one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention provides for ingestible circuitry, where the components of the circuitry are ingestible, and in some instances digestible. As the ingestible circuitry is made up of ingestible, and even digestible, components, the ingestible circuitry results in little, if any, unwanted side effects, even when employed in chronic situations. 
     Embodiments of ingestible circuitry of the invention include a solid support of an ingestible material, which support has on a surface thereof one or more electronic components. Components that may be present on the surface of the support may vary, and include but are not limited to: logic and/or memory elements, e.g., in the form of an integrated circuit; a power device, e.g., battery, fuel cell or capacitor; an effector, e.g., sensor, stimulator, etc.; a signal transmission element, e.g., in the form of an antenna, electrode, coil, etc.; a passive element, e.g., an inductor, resistor, etc. The one or more components on the surface of the support may be laid out in any convenient configuration. Where two or more components are present on the surface of the solid support, interconnects may be provided. 
     The ingestible circuitry is particularly suited for use in signal identifiers, e.g., as may be found in ingestible event markers and pharma-informatics enabled compositions. One example includes use of the ingestible circuitry in association with a specific pharmaceutical product, such as a pill, to determine when a patient takes the pharmaceutical product. As the pill is consumed, the ingestible circuit is activated and generates a signal that is detected thereby signifying that the pharmaceutical product has been taken by a patient. 
     Ingestible Circuitry and Fabrication Thereof 
     As summarized above, the present invention provides ingestible circuitry. Ingestible circuitry of the invention includes a solid support fabricated from an ingestible material, and one or more electronic components displayed on a surface thereof. Where two or more components are present on a given solid support, conductive interconnecting elements are also present that electrically couple the two or more components. A variety of different types of components may be present on the support, as reviewed in greater detail below. In addition, one or more optional elements, such as a protective layer, etc., may be provided. 
     Ingestible circuitry of the invention can be a standalone unit or it can be incorporated into another structure, e.g., an ingestible identifier, such as may be found in an ingestible event marker, including a pharma-informatics enabled pharmaceutical composition. 
     As summarized above, circuitry of the invention is ingestible, where the disparate components of the circuitry are fabricated from ingestible materials. In certain embodiments, one or more of the ingestible materials of the circuits are digestible materials. As such, the amounts of the materials are below chronic ingestion limits if the circuitry is present in a device that is going to be ingested chronically. If the circuitry is incorporated into a device that is going to be ingested less frequently, materials may be chosen based on the anticipated dosage schedule. 
     As reviewed above, elements of the ingestible circuitry of the invention include a solid support, one or more electronic components, and interconnects, among other elements. 
     The solid support is the structure on which all of the components are present. The solid support is fabricated from an ingestible material, where the material is a dielectric or insulating material. It can be fabricated from a variety of materials. Materials that provide mechanical strength and may be employed as an insoluble component of the solid support include, but are not limited to: Ethyl cellulose (e.g. Hercules Aqualon or Dow Ethocel), cellulose acetate, Agar, Gelatin. Insoluble materials of interest include ethylcellulose, a copolymer of acrylic acid and methacrylic acid esters, having from about 5 to 10% functional quaternary ammonium groups, polyethylene, polyamide, polyvinylchloride, polyvinyl acetate and any mixtures thereof. Fillers, such as, starch, glucose, lactose, inorganic salts such as sodium or potassium chloride, carbonates, bicarbonates, sulfates, nitrates, silicates (e.g., magnesium silicate) and alkali metals phosphates and oxides (e.g., titanium dioxide, magnesium oxide), may also be present. Soluble materials that may be employed, e.g., as disintegrating agents, in the solid support include, but are not limited to: Hydroxypropyl cellulose, hydroxyethylcellulose, carboxymethylcellulose, croscarmellose, hypromellose, hydroxypropyl methyl cellulose, methyl cellulose, Polysaccharides (starch, different sugars); Polyvinyl alcohol; Gums (guar, xanthan, acacia); Alginates (sodium or calcium alginate); povidone; etc. Also of interest are Plasticizing agents, e.g., Dibutyl sebacate, triacetin, triethyl citrate, polyethylene glycol, polyethylene oxide. Soluble materials of interest include proteins, polysaccharides, polyacrylates, hydrogels, polyvinyl alcohol, polyvinyl pyrrolidone, and derivatives of such polymers. In certain embodiments, plasticizers may be present, where plasticizers make it easier to process and modulate the strength so that it is not stiff and brittle. Also of interest are surfactants. Environmentally sensitive materials may also be present in the support, such as environmentally sensitive polymers, e.g., temperature sensitive polymers, ph sensitive polymers (e.g., Polymethacrylates (e.g. Degussa Eudragit®)), oxygen sensitive polymers, enzyme sensitive polymers (e.g., Starch, Chitosan, etc.), that will make it insoluble in certain physiological locations, such as the stomach, and soluble in other physiological locations, such as the intestine. Embodiments of such supports are supports that retain their shape in the stomach and then fall apart upon entry/transit through the intestine. Also present may be foaming agents, e.g., sodium carbonate, swelling agents, e.g., hydrogel polymers, or cross linking agents, e.g., glutaraldehyde. In certain embodiments, the support is fabricated from a foodstuff which has suitable properties. Foodstuffs of interest include, but are not limited to: soy, whey, wheat glutein, rice starch, tapioca starch, rice paper, nori, corn chips, potato, pasta, filo, fruit roll-ups, haw flakes, crackers, gelatin and gummy. The solid supports can be fabricated via any convenient protocol, such as through deposition via a number of methods such as solvent cast, or melt extrusion. 
     Also present in ingestible circuitry is one or more conductive elements which serve to interconnect two or more distinct components on a surface(s) of the support. In certain embodiments, this conductive element, e.g., interconnect or wire, is a thin layer or strip of a homogenous conductive and ingestible material, such as gold, silver, graphite, titanium, copper, etc. The material making up the conductive element may be any material whose total amount is below chronic ingestion limits (i.e., how often one is ingesting the ingestible device) where the conductivity is within a desired range. Table 1 below provides examples of ranges. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                   
                 Resistivity 
                 Dimension 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Metal 
                 (Ωm) 
                 Length 
                 Width 
                 Thickness 
               
               
                   
               
               
                   
                 Cu 
                 1.68 × 10 −8   
                 1 cm 
                 100 μm 
                 1 μm 
               
               
                   
                 Mg 
                 4.39 × 10 −8   
                 1 cm 
                 100 μm 
                 10 μm  
               
               
                   
                 Au 
                 2.21 × 10 −8   
                 1 cm 
                 100 μm 
                 100 μm  
               
               
                   
                 Ag 
                 1.59 × 10 −8   
                 1 cm 
                  10 μm 
                 1 μm 
               
               
                   
                 Fe 
                 9.61 × 10 −8   
                 1 cm 
                 100 μm 
                 0.1 μm   
               
               
                   
               
            
           
         
       
     
     The conductive elements (i.e., interconnects) can be deposited on a surface of the support to provide interconnection between two or more components as a homogeneous layer, for example a layer of gold. Any convenient deposition protocol may be employed, such as but not limited to: evaporation, plating, electrolysis plating, galvanic deposition, screen or ink jet printing, or other thin layer deposition techniques. Alternatively, a lamination method may be employed, where various elements are positioned as sheets. In yet other embodiments, a decal transfer process may be employed, where each of the distinct elements is on a separate backing layer. The distinct elements are transferred to the solid support, and then the backing layer is removed. With each of the above protocols, a patterning technique may be employed. The choice of patterning technique will depend on the choice of deposition process and the dimensional control required of the final pattern, for example evaporation or plating is very compatible with photo lithography. For laminate protocols, laser patterning might be employed, e.g., where a layer is deposited and the unwanted portions are cut out. In certain embodiments, purely additive techniques, such as ink jet or screen printing, are employed. 
     Instead of having a conductive element fabricated from a homogenous material, the conductive element can be a heterogenous material that is a paste or an ink. For example, a suspension of a conductive filler of the conductive materials, e.g., gold, silver, graphite, etc., with an ingestible binder material, such as a polymer, a thermoset or thermoplastic polymer, may be employed. This heterogenous material can contain other polymeric components such as plasticizers, surfactants to make the ink and the paste flow better, be more processable etc. In yet other embodiments, the conductive element is an isotropic conductive film, e.g., a film of inert particles, such as of a material like glass, that have been coated with a conductive material, e.g., a metal. 
     Electrical connection between the conductive element and components on the support may be achieved in a number of different ways. For example, interconnects and various components may be positioned on a surface of the solid support, and a layer of conductive material that covers the disparate components and conductive elements can be deposited in a manner that provides the desired connection. Alternatively, ingestible conductive glues, pastes and adhesives may be employed. In certain embodiments, of interest is the use of a combination of two (or more) glues, where one of the glues provides for desired conductive properties and one of the glues provides mechanical strength. In addition, mechanical attachment protocols such as pressing different components together, e.g., where the components have suitable shape interfaces that make it easier for them to bond under mechanical force, pressure, and temperature, may be employed. Also of interest is laser welding, sonic welding, etc. The components can be immobilized relative to a surface of the solid support by mechanically holding the components on to the solid support, e.g., via deposition of a conductive overlay, as reviewed above, by way of a glue, such as a thermoplastic glue that physically holds items in place or thermosetting glue that is cross linked. Lasers may be employed with mixtures of some metals or conductive elements and locally sintered to make an electrical contact at the sintered point (e.g., where the laser removes or densifies an organic material in a binder, leaving a more thermally stable conductive material behind). 
     In addition to the above components, the ingestible circuitry of the invention also includes one or more electronic components. Electrical components of interest include, but are not limited to: logic and/or memory elements, e.g., in the form of an integrated circuit; a power device, e.g., battery, fuel cell or capacitor; an effector, e.g., sensor, stimulator, etc.; a signal transmission element, e.g., in the form of an antenna, electrode, coil, etc.; a passive element, e.g., an inductor, resistor, etc. 
     The various components may be produced on a surface of a solid support using a variety of different protocols. For example, where the components are electrode elements that make up a battery which is activated upon contact with stomach fluid, e.g., as described below, the battery components can be deposited directly onto the solid support. For example, a magnesium layer can be evaporated onto a surface of the solid support, where the solid support is fabricated from a material(s) that withstands the temperature and pressure that occurs during that deposition process. The different components of the electrodes can be deposited onto a conductor layer that is then attached to the solid support. For example, one can have a thin sheet of gold, and a layer of CuCl can be deposited onto the gold, with the resultant product being attached to the solid support. The different layers can also be deposited via an ink or a paste. For example, a structure of CuCl deposited on gold can be broken up into small particles, and an ink material can be fabricated from the particles. The resultant ink material can be used to either print or silk screen the desired electrode pattern onto the solid support. Also of interest are protocols that employ screen printing or ink jet printing techniques. In yet other embodiments, an unpatterned slurry is deposited. In yet other embodiments, “roll-to-roll” or “continuous web” protocols are employed. 
     In certain embodiments, the ingestible circuitry includes a coating layer. The purpose of this coating layer can vary, e.g., to protect the circuitry, the chip and/or the battery, or any components during processing, during storage, or even during ingestion. For example, one may not desire the circuitry to be exposed to the body fluids after it is ingested. In such instances, it may be desirable to only have the battery and transmit antennas be exposed to body fluids, with the rest of the circuitry being protected. In such instances, a coating on top of the circuitry that is ingestible but does not dissolve until the device is finished doing its transmission may be provided. Also of interest are coatings that are designed to protect the ingestible circuitry during storage, but dissolve immediately during use. For example, coatings that dissolve upon contact with an aqueous fluid, e.g., stomach fluid. Also of interest are protective processing coatings that are employed to allow the use of processing steps that would otherwise damage certain components of the device. For example, in embodiments where a chip with battery material deposited on the top and bottom is produced, the product needs to be diced. However, the dicing process can scratch off the battery material, and also there might be liquid involved which would cause the battery materials to discharge or dissolve. In such instances, a protective coating on the battery that prevents mechanical or liquid contact with the battery component during processing can be employed. Another purpose of the edible coatings would be to control the activation of the device. For example, an edible coating that sits on the battery electrodes and takes a certain period of time, e.g., five minutes, to dissolve upon contact with stomach fluid may be employed. The coating can also be an environmentally sensitive coating, e.g., a temperature or pH sensitive coating, or other chemically sensitive coating that provides for dissolution in a controlled fashion and allows one to activate the device when desired. Coatings that survive the stomach but dissolve in the intestine are also of interest, e.g., where one desires to delay activation until the device leaves the stomach. An example of such a coating is a polymer that is insoluble at low pH, but becomes soluble at a higher pH. Also of interest are pharmaceutical formulation protective coatings, e.g., a gel cap liquid protective coating that prevents the circuit from being activated by liquid of the gel cap. 
     Another component present in certain embodiments of the ingestible circuit is an activation mechanism, e.g., where the activation mechanism is distinct from the power source (e.g., battery). An example of such an alternative activation element is a patch of circuit that closes upon contact with fluid and activates the device. Another example is the reactive removal of a patch of the circuit that, before it is removed, keeps the circuit from operating. 
     As indicated above, ingestible circuitry devices in accordance with the invention may be fabricated in a variety of different ways. Any of a variety of different protocols may be employed in manufacturing the circuitry structures and components thereof. For example, molding, deposition and material removal, e.g., planar processing techniques, such as Micro-Electro-Mechanical Systems (MEMS) fabrication techniques, including surface micromachining and bulk micromachining techniques, may be employed. Deposition techniques that may be employed in certain embodiments of fabricating the structures include, but are not limited to: electroplating, cathodic arc deposition, plasma spray, screen or ink jet printing, sputtering, e-beam evaporation, physical vapor deposition, chemical vapor deposition, plasma enhanced chemical vapor deposition, etc. Material removal techniques included, but are not limited to: reactive ion etching, anisotropic chemical etching, isotropic chemical etching, sacrificial lift-off etching, planarization, e.g., via chemical mechanical polishing, laser ablation, electronic discharge machining (EDM), etc. Also of interest are lithographic protocols. Of interest in certain embodiments is the use of planar processing protocols, in which structures are built up and/or removed from a surface or surfaces of an initially planar substrate using a variety of different material removal and deposition protocols applied to the substrate in a sequential manner. Illustrative fabrication methods of interest are described in greater detail in PCT application serial nos. PCT/US2006/016370; PCT/US2007/022257; PCT/US2007/082563; PCT/US2008/052845; PCT/US2008/053999; and PCT/US2008/077753; the disclosures of which are herein incorporated by reference. 
     In certain embodiments, of interest is a bifurcated laminate process for preparing a device made up of ingestible circuitry. In this bifurcated laminate process, a laminate component is made separate from a circuitry component, allowing greater freedom in terms of processing protocols than may be employed to fabricate the disparate components together, since protocols may be employed to fabricate a first component that cannot be used to fabricate the other, and vice versa. In such bifurcated laminate protocols, the circuitry and laminate components are combined into a single device following separate fabrication of the two components. To combine the two components, any convenient protocol may be employed. In certain embodiments, the circuitry component is fixed into receiving feature of the laminate component, and fixed in place with a suitable adhesive, such as a conductive adhesive. An example of the use of this protocol for the fabrication of an ingestible event marker according to an embodiment of the invention is provided below in connection with a description of  FIGS. 7A to 7B . 
     In  FIG. 7A , an initial laminate sheet which includes battery elements and a virtual dipole element (e.g., skirt) of an ingestible event marker is shown being prepared using a “continuous web” or “roll-to-roll process”. The initial laminate sheet is characterized by having exposed battery layers, e.g., upper and lower exposed battery layers, and includes a first battery layer  708 , e.g., CuCl layer (e.g., produced by evaporation, electrodeposition, slurry deposition, silkscreen, or inkjet, etc.), a second virtual dipole layer  710  positioned on top of the battery layer (i.e., skirt), a third current collector layer  712 , e.g., Au, Cu, or graphite, etc., which may be a sheet or printed on the skirt, on top of the virtual dipole layer, and a fourth battery layer  714 , e.g., Mg foil. Where desired, one or more of the layers can be made separately before lamination, so each process need not be compatible with all the layers e.g., current collector can be graphite-based, made with a high temperature process, which may be incompatible with processes and/or materials used to fabricate the other layers. Layers may be glued together with edible, cellulose adhesive or other safe pressure sensitive adhesives (including but not limited to, silicon materials, etc.). 
     Fabricated separate from the laminate component is the circuitry component. The circuitry component may be fabricated using any convenient protocol, e.g., as summarized above. 
     Next, a hole or passage  720  configured to receive the circuitry component (e.g., integrated circuit (IC)) is punched in the resultant laminate component  722  to receive the circuitry component  724 , as shown in  FIG. 7B . The circuitry component is then positioned in the passageway and fixed in place with a conductive adhesive  726 , e.g., as shown in  FIG. 7B . A variety of conductive adhesives may be employed, e.g., a polymer filled with conductive particles or a reactive (2-part) glue. The conductivity of the adhesive may be moderate. Where desired, the adhesive can be covered with a final layer of insulating adhesive. 
     In a variation of the above protocol, a pre-punched lower laminate is employed. In this embodiment, the IC is placed onto a pre-punch hole, where prior to placement, the sheet may be covered with a pressure sensitive adhesive material that is removed prior to chip placement during punching but is removed prior to chip placement. A second laminate is applied over the top of the chips and then opened, e.g., with a laser, over the chips and the top conductor (e.g., battery material) is additively applied, e.g., by screen printing. A final non-conductive layer, such as treated paper or plastic, is used in a roll-to-roll process after this step to isolate the two sides of the battery before the IEMs are finally punched out of the roll for assembly into tablets or capsules. 
     Finally, a disc shaped device  740 , e.g., shown by dashed lines in  FIG. 7B , is punched out to produce the desired IEM. 
     The above bifurcated laminate protocol finds use in, among other applications, fabricating IEMs that have a virtual dipole, e.g., as described in greater detail in pending U.S. Provisional Application Ser. No. 60/975,108 titled “Virtual Dipole Signal Amplification For Pharma-Informatics System” and filed on Sep. 25, 2007, the disclosure of which is herein incorporated by reference. 
     Devices Comprising Ingestible Circuitry 
     Ingestible circuitry of the invention finds use in a variety of different types of devices. One example of a device that can include ingestible circuitry of the invention is an ingestible identifier. Ingestible identifiers are described in PCT application serial no. PCT/US2006/016370 published as WO/2006/116718; PCT application serial no. PCT/US2007/082563 published as WO/2008/052136; PCT application serial no. PCT/US2007/024225 published as WO/2008/063626; PCT application serial no. PCT/US2007/022257 published as WO/2008/066617; PCT application serial no. PCT/US2008/052845 published as WO/2008/095183; PCT application serial no. PCT/US2008/053999 published as WO/2008/101107; PCT application serial no. PCT/US2008/056296 published as WO/2008/112577; PCT application serial no. PCT/US2008/056299 published as WO/2008/112578; PCT application serial no. PCT/US2008/077753 published as WO2009/042812; PCT application serial no. PCT/US2008/085048 published as WO 2009/070773; and PCT application serial no. PCT/US2009/36231; as well as pending U.S. application Ser. Nos. 12/126,792 and 12/126,798; the disclosures of which are incorporated herein by reference. 
     An example of such an ingestible identifier is an identifier that includes battery. The battery includes, when completed, a cathode, an anode, and an electrolyte, where the electrolyte component is provided by a physiological fluid, e.g., stomach acid. When the identifier is ingested and reaches the stomach, the cathode and anode are exposed to stomach fluid. The stomach fluid (either by itself or when combined with a dried conductive precursor medium component of the identifier, e.g., as described in pending PCT application serial no: PCT/US2007/082563 the disclosure of which is herein incorporated by reference) acts as the electrolyte component of the battery. Completion of the battery powers the circuitry of the identifier which, in turn broadcasts a detectable signal. 
     Identifiers of interest include two dissimilar electrochemical materials which constitute the two electrodes (e.g., anode and cathode) of the battery. When the electrode materials are exposed and come into contact with the body fluid, such as stomach acid or other types of fluid (either alone or in combination with a dried conductive medium precursor), a potential difference, that is, a voltage, is generated between the electrodes as a result of the respective oxidation and reduction reactions incurred to the two electrode materials. A voltaic cell, or battery, can thereby be produced. Accordingly, in embodiments of the invention, such batteries are configured such that when the two dissimilar materials are exposed to the target site, e.g., the stomach, the digestive tract, etc., during the physical and chemical erosion of the composition in which the signal generation element is present, a voltage is generated. The two dissimilar materials in an electrolyte are at different potentials. As an example, copper and zinc when put into a cell have different potentials. Similarly, gold and magnesium have different potentials. As a result, a potential difference between the two dissimilar materials is generated. 
     In certain of these embodiments, the battery power source may be viewed as a power source that exploits electrochemical reaction in an ionic solution such as gastric fluid, blood, or other bodily fluids and some tissues.  FIG. 1  provides a diagrammatic representation of an ingestible identifier  10  having a battery that is completed by stomach fluid. First and second electrode materials ( 12  and  13 ) are present in an ionic solution  16  (which may be made up of target site fluid alone or target site fluid combined with a dried conductive medium precursor). This configuration creates a low voltage (V−) and a high voltage (V+) as applied to corresponding inputs of an electronic circuit  14 . The polarity of the electrodes is determined by the connection needs of the electronic circuit  14  and the design as illustrated is just one embodiment. Thus, it will be apparent to one skilled in the art that the scope of the present invention includes reversal of the polarity of the electrodes, such that electrode  13  represents the low voltage and electrode  12  represents high voltage. The two outputs of that electronic circuit  14  are EU  11  and El  15 , which are the signal-transmission electrodes on the top surface. 
     Electrodes  12  and  13  can be made of any two materials appropriate to the environment in which the identifier  10  will be operating. The active materials are any pair of materials with different electrochemical potentials, as long as they are ingestible, e.g., as described above. For instance, in some embodiments where ionic solution  16  comprises stomach acids, electrodes  12  and  13  may be made of a noble metal (e.g., gold, silver, platinum, palladium or the like) so that they do not corrode prematurely. Suitable materials are not restricted to metals, and in certain embodiments the paired materials are chosen from metals and non-metals, e.g., a pair made up of a metal (such as Mg) and a salt (such as CuCl or CuI). With respect to the active electrode materials, any pairing of substances—metals, salts, or intercalation compounds—with suitably different electrochemical potentials (voltage) and low interfacial resistance are suitable. 
     Materials and pairings of interest include, but are not limited to those reported in Table 2 below. 
     
       
         
           
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Anode 
                 Cathode 
               
               
                   
               
             
            
               
                 Metals 
                 Magnesium, Zinc 
                   
               
               
                   
                 Sodium (†), 
                   
               
               
                   
                 Lithium (†) 
                   
               
               
                   
                 Iron and 
                   
               
               
                   
                 alloys thereof 
                   
               
               
                 Salts 
                   
                 Copper salts: iodide, chloride, bromide, 
               
               
                   
                   
                 sulfate, formate, (other anions possible) 
               
               
                   
                   
                 Fe 3+  salts: e.g. orthophosphate, 
               
               
                   
                   
                 pyrophosphate, (other anions possible) 
               
               
                   
                   
                 Oxygen or hydrogen (††) on platinum, 
               
               
                   
                   
                 gold or other catalytic surfaces 
               
               
                 Intercalation 
                 Graphite with 
                 Vanadium oxide 
               
               
                 compounds 
                 Li, K, Ca, 
                 Manganese oxide 
               
               
                   
                 Na, Mg 
               
               
                   
               
               
                 (†) Protected anodes: certain high energy anode material such as Li, Na, and other alkali metals are unstable in their pure form in the presence of water or oxygen. These may however be used in an aqueous environment if stabilized. One example of this stabilization is the so-called “protected lithium anode” developed by Polyplus Corporation (Berkeley, CA), where a polymer film is deposited on the surface of lithium metal to protect it from rapid oxidation and allow its use in aqueous environment or air ambient. (Polyplus has IP pending on this). 
               
               
                 (††) Dissolved oxygen can also serve as a cathode. In this case, the dissolved oxygen in the bodily fluids would be reduced to OH— at a suitable catalytic surface such at Pt or gold. Also of interest dissolved hydrogen in a hydrogen reduction reaction. 
               
            
           
         
       
     
     In certain embodiments, one or both of the metals may be doped with a non-metal, e.g., to enhance the voltage output of the battery. Non-metals that may be used as doping agents in certain embodiments include, but are not limited to: sulfur, iodine and the like. 
     In certain embodiments, the electrode materials are cuprous iodine (CuI) or cuprous chloride as the cathode and magnesium (Mg) metal or magnesium alloy as the anode. Embodiments of the present invention use electrode materials that are not harmful to the human body. 
     In certain embodiments, the batteries have a small form factor. Batteries may be about 20 mm 3  or smaller, e.g., about 10 mm 3  or smaller, such as 1.0 mm 3  or smaller, including 0.1 mm 3  or smaller, including 0.02 mm 3  or smaller. In certain embodiments, the battery element is dimensioned to have a width ranging from about 0.01 mm to about 100 mm, e.g., from about 0.1 mm to about 20 mm, including from about 0.5 mm to about 2 mm; a length ranging from about 0.01 mm to about 100 mm, e.g., from about 0.1 mm to about 20 mm, including from about 0.5 mm to about 2 mm, and a height ranging from about 0.01 mm to about 10 mm, e.g., from about 0.05 mm to about 2 mm, including from about 0.1 mm to about 0.5 mm. 
     The ingestible identifier  10  uses the voltage potential difference to power up electronic circuit  14 . In one embodiment, the electronic circuit  14  modulates conductance to create a unique and identifiable current signature. 
     In certain embodiments, the battery has a laminate structure. As indicated above, a laminate process may be employed to fabricate ingestible circuitry in accordance with the invention. An example of such a laminate process is illustrated in  FIGS. 2A to 2D . In  FIG. 2A , structure  21  is made up of circular metallic foil  22 , e.g., gold, and has patterned areas of an electrode material, such as CuCl, patterned on its surface in the form of four distinct quadrants  24 . The CuCl regions  24  may be produced on the surface of the foil via any convenient protocol, such as evaporation. Also shown is area  26  which lacks electrode material and is configured to receive an integrated circuit. In  FIG. 2B , structure  21  placed onto solid support  23 , which support is made of an ingestible material, e.g., as described above. Structure  21  may be placed onto support  23  in a manner such that the two components are stably associated with each other, e.g., by press-fitting the structure  21  onto support  23  or gluing structure  21  onto support  23 , among other ways to immobilize structure  21  onto support  23 . While the sequence shown in  FIGS. 2A and 2B  illustrate a protocol in which structure  21  is produced before placement on support  23 , in another embodiment the metallic foil  22  is first placed on support  23 . Following placement of metallic foil  22  on support  23 , the patterned areas of electrode material  24  are produced on the surface of metallic foil  22 . In  FIG. 2C , integrated circuit  25  is positioned in area  26  and connected to metallic foil  22 . Finally, in  FIG. 2D , a cover layer  27  (e.g., fabricated from the same material as the support) having electrode cutout areas  28  is stably positioned (e.g., with an ingestible adhesive) over structure  21  to produce a final ingestible circuit device that includes a solid support, an integrated circuit and four distinct surface electrodes. In this structure, the metallic foil layer  22  serves as the conductive interconnect between the different electronic components, i.e., the integrated circuit and electrodes, that are positioned on the surface of the support. 
       FIG. 3A  illustrates another embodiment of a laminate process that may be employed to construct an ingestible circuit device of the invention. In  FIG. 3A , structure  30  has been produced by first providing a release layer  31  on a backing layer  32 . Metallic layer (e.g., gold)  33  has been deposited on the surface of release layer  31 . Next, electrode material  34 , e.g., CuCl, is deposited on surface of metallic layer  33 . Finally, insulating layer  35  is positioned over electrode layer  34 , which insulating layer may have cutout regions (not shown), e.g., as described in connection with the description of  FIGS. 2A to 2D . 
     In  FIG. 3B , an integrated circuit  36  having a layer of a second electrode material  37 , e.g., Mg, on a surface thereof, is positioned in ingestible support  38 . To assemble the final device, the release layer  31  and backing layer  32  are removed from structure  30 , providing exposed metallic layer  33 . This exposed metallic layer  33  is then positioned over circuit  36  and support  38  to yield the final desired device. 
       FIG. 4  illustrates a transfer protocol that may be employed to fabricate ingestible circuits in accordance with the invention. In  FIG. 4 , a circuit structure  40  that includes integrated circuit  41  connected to five different electrodes  42  via interconnecting conductive lines  43  is first produced on a removable backing  44 . After production of circuit structure  40 , backing  44  is removed and the circuit structure  44  is positioned on the surface of ingestible support  45 . The protocol illustrated in  FIG. 4  may be employed in processes where parameters of circuit structure production (e.g., chemicals, temperatures, pressures) are incompatible with the solid support material. 
       FIG. 5  illustrates a variation in which a conductive ink is employed to provide conductive interconnects between different components of an ingestible circuit device. In the device shown in  FIG. 5 , ingestible support  51  has displayed on its surface four different electrodes (made up of electrode material)  52 . Positioned at a center region of support  51  are four contact pads  53 . Interconnecting each electrode to a contact pad is a line of conductive ink material  54 . To complete the structure, an integrated circuit is bonded to pads  53  and then a layer of protection material is positioned over the surface leaving exposed electrode elements, analogous to that shown in  FIG. 2D . 
     In certain instances, laser patterning may be employed during fabrication of ingestible circuits of the invention, e.g., as illustrated in  FIGS. 6A and 6B . In  FIG. 6A , a blanket (i.e., non-patterned) layer of metal  61  is deposited on a surface of an ingestible support  62 . Positioned on a portion of metal layer  61  is integrated circuit  63 . Next, laser patterning is employed to remove portions of metal layer  61  to produce antenna structure  64  and  65  on surface of support  62 . 
     Ingestible identifiers that include ingestible circuitry of the invention find use in a variety of different applications. One application of interest is the use of the ingestible identifiers as ingestible event markers (IEMs). Ingestible event markers can be used in both therapeutic and non-therapeutic applications, and are described in PCT application serial no. PCT/US2006/016370 published as WO/2006/116718; PCT application serial no. PCT/US2007/082563 published as WO/2008/052136; PCT application serial no. PCT/US2007/024225 published as WO/2008/063626; PCT application serial no. PCT/US2007/022257 published as WO/2008/066617; PCT application serial no. PCT/US2008/052845 published as WO/2008/095183; PCT application serial no. PCT/US2008/053999 published as WO/2008/101107; PCT application serial no. PCT/US2008/056296 published as WO/2008/112577; PCT application serial no. PCT/US2008/056299 published as WO/2008/112578; PCT application serial no. PCT/US2008/077753 published as WO2009/042812; PCT application serial no. PCT/US2008/085048 published as WO 2009/070773; and PCT application serial no. PCT/US2009/36231; as well as pending U.S. application Ser. Nos. 12/126,792 and 12/126,798; the disclosures of which are incorporated herein by reference. 
     The disclosure of these ingestible event markers and applications for the same therein is specifically incorporated herein by reference. Therapeutic applications of ingestible identifiers are embodiments where, at least in some instances, the identifier is associated with a pharmaceutical composition. Medical embodiments of the present invention provide the clinician an important new tool in their therapeutic armamentarium: automatic detection and identification of pharmaceutical agents actually delivered into the body. The applications of this new information device and system are multi-fold. Applications include, but are not limited to: (1) monitoring patient compliance with prescribed therapeutic regimens; (2) tailoring therapeutic regimens based on patient compliance; (3) monitoring patient compliance in clinical trials; (4) monitoring usage of controlled substances; and the like. Each of these different illustrative applications is reviewed in greater detail in PCT application serial no. PCT/US2006/016370 published as WO/2006/116718; PCT application serial no. PCT/US2007/082563 published as WO/2008/052136; PCT application serial no. PCT/US2007/024225 published as WO/2008/063626; PCT application serial no. PCT/US2007/022257 published as WO/2008/066617; PCT application serial no. PCT/US2008/052845 published as WO/2008/095183; PCT application serial no. PCT/US2008/053999 published as WO/2008/101107; PCT application serial no. PCT/US2008/056296 published as WO/2008/112577; PCT application serial no. PCT/US2008/056299 published as WO/2008/112578; PCT application serial no. PCT/US2008/077753 published as WO2009/042812; PCT application serial no. PCT/US2008/085048 published as WO 2009/070773; and PCT application serial no. PCT/US2009/36231; as well as pending U.S. application Ser. Nos. 12/126,792 and 12/126,798; the disclosures of which are incorporated herein by reference. 
     It is to be understood that this invention is not limited to particular embodiments described, as such may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims. 
     Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and are also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention, representative illustrative methods and materials are now described. 
     All publications and patents cited in this specification are herein incorporated by reference as if each individual publication or patent were specifically and individually indicated to be incorporated by reference and are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. The citation of any publication is for its disclosure prior to the filing date and should not be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed. 
     It is noted that, as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation. 
     As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present invention. Any recited method can be carried out in the order of events recited or in any other order which is logically possible. 
     Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it is readily apparent to those of ordinary skill in the art in light of the teachings of this invention that certain changes and modifications may be made thereto without departing from the spirit or scope of the appended claims. 
     Accordingly, the preceding merely illustrates the principles of the invention. It will be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples and conditional language recited herein are principally intended to aid the reader in understanding the principles of the invention and the concepts contributed by the inventors to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents and equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure. The scope of the present invention, therefore, is not intended to be limited to the exemplary embodiments shown and described herein. Rather, the scope and spirit of present invention is embodied by the appended claims.