Abstract:
A patch for iontophoretic transdermal application of a medicant, where the patch includes a border portion disposed about an aperture. The border portion can include a first polarity electrode in electrical communication with the medicant, and a second border portion including a second electrode having a second polarity opposite the first electrode polarity. One patch has a liftable cover, preferably a transparent and non-adherent cover, disposed over the patch aperture. A preferred medicant for inclusion in the present invention is a local anesthetic or analgesic. Other medicants such as anti-inflammatory agents or anti-infective agents may be used to locally reduce inflammation, contain infection, and alleviate pain. The present invention can allow performing a field block anesthetic about an epidermal target site. The present invention can allow observing a target or treatment site while leaving the patch in place. An invasive medical procedure can be performed through the patch aperture, and pre-operative and post-operative procedures can also be performed through the patch aperture.

Description:
RELATED APPLICATIONS 
   The present application is a continuation of U.S. patent application Ser. No. 09/691,312, filed Oct. 18, 2000, titled IONTOPHORETIC DELIVERY PATCH, now U.S. Pat. No. 6,560,483 herein incorporated by reference in its entirety. 

   FIELD OF THE INVENTION 
   The present invention is related generally to medical devices. More specifically, the present invention is related to skin patches for drug or medicant delivery. 
   BACKGROUND OF THE INVENTION 
   Systems for delivering ionized drugs through the skin have been known for many years. The application of an electrical field to the skin has been found to greatly enhance the skin&#39;s permeability to various ionic agents. In general, iontophoretic methods include the introduction of various ions into tissues through the skin by means of electricity. Additionally, applying an electrical current to the area around a wound has been found to improve wound healing. Iontophoretic techniques have been used to deliver some drugs, thus eliminating the requirement for hypodermically injecting these drugs. The elimination of the requirement for hypodermic injection can reduce or eliminate the associated problems of pain, trauma, and infection to the patient. 
   The manufacture and use of conventional iontophoretic patches is well known to those skilled in the art. In particular, Flower discusses iontophoretic controllers, patches, and electrodes in U.S. Pat. Nos. 5,668,231, 5,830,175, 5,876,368, 6,009,344, 6,047,208, and 6,018,680. Manufacture of patches is discussed by Green et al. in U.S. Pat. No. 5,682,726. Electrodes and patch discussions are included in U.S. Pat. No. 5,651,768 (Sibalis), U.S. Pat. No. 6,038,464 (Axelgaard et al.), and U.S. Pat. No. 5,458,569 (Kirk, III et al.). Iontophoresis, including polymeric carriers, delivery vehicles, and medicants, are discussed by Keith in U.S. Pat. No. 4,542,013, by D&#39;Angelo et al. in U.S. Pat. No. 6,024,975, and by Powers et al. in U.S. Pat. No. 4,702,732. All of the aforementioned patents, which include subject matter in addition to that specifically cited above, are herein incorporated by reference in their entirety. 
   Iontophoresis is an active method for transdermal delivery of medicants. Active delivery methods may be distinguished from passive delivery methods. Passive methods rely on natural forces and pressures alone such as diffusion or concentration gradients. Conventional drug delivery skin patches are examples of passive delivery vehicles. Active methods use externally applied forces, for example, electrical potential or hydraulic forces, to force a medicant into the skin. Iontophoretic patches are active delivery vehicles for medicants. 
   Prior art iontophoretic analgesic or anesthetic devices have been limited in use to broad area application of an anesthetizing agent, for example, an anesthetic gel. One drawback of existing devices is that they must be applied directly over the target area. This has been undesirable as the target area cannot be viewed during application of the anesthetic, and the patch must be removed to view the target area. Once the patch is removed to access the site, delivery of the anesthetic stops. This creates a likelihood that the anesthesia will wear off as the procedure progresses, causing increased pain. In order to continue, the treating physician must either reapply the patch and wait for it to take effect, inject the site with local anesthetic, continue the procedure in spite of the increasing pain, or convert to general anesthesia. 
   Another problem with prior art devices, where the target area includes a wound, is that the anesthetic gel is placed directly on the target area. This creates a possibility that the anesthetic gel will contaminate the wound, cause infection or inflammation, or hinder the healing of the wound. One prior art method avoids this problem by using a field block. Local anesthesia may be achieved by making several injections in the area surrounding the target site, thus creating what is commonly referred to as a field block. A field block procedure may be fairly painful in itself, and may traumatize the patient, particularly a child. 
   After removal of prior art delivery patches, or after completion of the field block, there is no fail-safe method for determining where the anesthetized area begins or ends. This creates the potential for continuing a procedure into an un-anesthetized area, causing pain to the patient. 
   What would be desirable is a medical device capable performing local anesthesia without many of the aforementioned limitations. 
   SUMMARY OF THE INVENTION 
   The present invention includes a patch for transdermal application of a medicant, where the patch includes a border portion disposed about an aperture. The border portion can include a first polarity electrode in electrical communication with the medicant, and a second electrode having a second polarity opposite the first electrode polarity. One patch has a liftable cover, preferably a transparent and non-adherent cover, disposed over the patch aperture. A preferred medicant for inclusion in the present invention is a local anesthetic or analgesic. Some embodiments have single-part electrodes disposed on one side of the opposite polarity electrode, while other embodiments have two-part electrodes, with each part disposed on opposite sides of the opposite polarity electrode. Another embodiment includes a single polarity patch electrode to be used with an opposite polarity external electrode. 
   The present invention allows for performing a field block anesthetic about an epidermal target site. Patches according to the present invention can be used to actively deliver an anesthetic substance to a region bordering the target site, without requiring delivery under fluid pressure, or delivery requiring mechanical penetration, into the epidermis. 
   The present invention allows for observing a target or treatment site while leaving the patch in place. An invasive medical procedure can be performed through the patch aperture, and pre-operative and post-operative procedures can also be performed through the patch aperture. In one application of the present invention, local anesthetic may be iontophoretically applied around a burn or wound, allowing for pain management local to the wound, while leaving the wound observable and treatable through a liftable, transparent cover. In another application of the present invention, an iontophoretic patch may be applied, and anesthetic delivered before, during, and after a surgical incision, with the incision wound observable after the procedure through a transparent, liftable cover. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is perspective view of an iontophoretic delivery patch having a medicant delivering border region disposed about a central aperture, with the border region having a first polarity electrode disposed between two parts of a second polarity electrode; 
       FIG. 2  is a transverse, cross-sectional view taken through  2 - 2  of  FIG. 1 , illustrating a first polarity gel electrode disposed between two parts of a second polarity electrode; 
       FIG. 3  is a transverse, cross-sectional view similar to the view of  FIG. 2 , but illustrating a membrane bound, first polarity liquid reservoir electrode disposed between two parts of a second polarity electrode; 
       FIG. 4  is a highly diagrammatic top view of an iontophoretic delivery patch having a contiguous border first polarity electrode disposed within a contiguous second polarity electrode; 
       FIG. 5  is a highly diagrammatic top view of a iontophoretic delivery patch having a contiguous border first polarity electrode disposed within a contiguous second polarity electrode; 
       FIG. 6  is a highly diagrammatic top view of a iontophoretic delivery patch having a discontiguous border electrode of two different types disposed about an aperture; 
       FIG. 7  is a highly diagrammatic top view of an iontophoretic delivery patch having a discontiguous border electrode of two different types disposed about an aperture; and 
       FIG. 8  is perspective view of an iontophoretic delivery patch having a medicant delivering border region disposed about a central aperture, with the border region having a first polarity electrode, the patch being suitable for use with a second electrode. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In the invention examples discussed below, similar reference numerals refer to similar elements in the various embodiments and Figures referenced.  FIG. 1  illustrates an iontophoretic delivery patch  20  including a border region  22  disposed about an aperture region  24 . The terms “border” and “border region”, as used herein, refer to borders having width. Border region  22  includes a first pair of electrodes  33  and  34 , both in electrical communication with a medicant carrying gel  30 , and both having a first electrical polarity. Gel  30  is preferably a carrier for a local anesthetic. Border region  22  also includes a second polarity electrode, having an inner electrode  32  and an outer electrode  28 . Gel  30  is illustrated as separated from second polarity electrodes  28  and  32  by insulating region or insulator  26 . An electrical potential source  31  is shown, which may include a battery intended to be discarded with the patch. Iontophoretic patch electrical potential sources are well known to those skilled in the art. 
   In the embodiment illustrated in  FIG. 1 , aperture  24  has a cover  23  draped over the aperture. In one embodiment, cover  23  is liftably removable from border region  22 . One example of the invention has cover  23  formed of a transparent material, joined along a first edge  27 , and graspable with a lifting tab  29 . Another embodiment of the invention has a completely removable cover. The cover can be formed of a removable membrane that can be coated with a biocompatible adhesive. The transparent and removable membrane preferably does not contain any medication or conduct electrical current. 
   In one embodiment of the invention, insulating region  26  includes an insulating material, while in another embodiment of the invention, insulating region  26  is an open air space between the gel and the second electrode. In the embodiment illustrated in  FIG. 1 , first electrodes  33  and  34  actually extend over the surface of gel  30 , but have been shown as cut-away to illustrate the gel beneath. In another embodiment of the invention, the first electrodes do not extend around the entire border region, and the medicant carrying material is sufficiently conductive to serve as an electrode. 
   It should be understood that a patch according to the present invention can have any convenient size or shape, for example, square, rectangular, oval, circular, or tailored for a specific location on the skin. In a preferred embodiment, the periphery is raised to accommodate a reservoir for an anesthetizing agent and electrodes. 
     FIG. 2  illustrates a cross section of patch  20  of  FIG. 1  taken through  2 - 2 , illustrating further first polarity electrode  33  disposed over medicant carrying gel  30 , which is contained within a reservoir wall  35 . Second polarity electrodes  28  and  32  are shown disposed within an insulator  26 , insulating the second polarity electrodes from first polarity electrode  33  and gel  30 . In one embodiment, insulator  26  is an insulating solid, while in another embodiment, insulator  26  is effectively air, with the second polarity electrodes adhesively applied directly to the skin. Aperture  24  may be seen between border regions  22 , and having cover  27  draped thereover. 
   In  FIG. 3 , a patch has been applied to skin or epidermal region  45 , having a target site  47  surrounded by a border region  46 .  FIG. 3  illustrates a view taken through a patch similar to that of  FIG. 1 , and through a section somewhat similar to  2 - 2 , but having a liquid medicant carrier  40  bounded by a reservoir wall  25  and by a microporous or semi-permeable membrane  42 . The medication can migrate through membrane  42  to be deposited in the skin. The membrane may not be needed, depending on the nature of the medication in the reservoir. Some medications suspended in a gel do not require a membrane. In some embodiments, medications in a gel form are in direct contact with the skin, not requiring containment by a membrane. 
   The medicant carrying layers  30  and  40  of  FIGS. 2 and 3  may consist of a flexible pouch or reservoir containing the drug to be administered. As well known to those skilled in the art, the reservoir can contain a drug of choice in suspension or solution, with walls dense enough to prevent leakage, but sufficiently porous to permit migration of the charged particles or ions under the influence of the electrical charge imposed. 
   An electrically conductive adhesive material may also be used to coat the underside of parts of the border regions of the devices so that they may be placed on and adhered to the skin, and make good electrical contact with the skin. The adhesive can be be any suitable material, preferably comfortable to the wearer, that permits the device to be bent and formed to fit snuggly to the contour of the target area. 
   It may be seen from inspection of  FIGS. 2 and 3  that electrodes  28  and  32  may be used to electrically charge the skin, creating an electrical potential between combined electrodes  28  and  32 , and electrode  33  in contact with the medicant to be delivered. It may also be seen that the above described arrangement in general forms a complete electric circuit from one side of the electrical source, to one electrode, medication carrier, microporous membrane, adhesive material, skin, adhesive material, second electrode, and back to the electrical source. 
   A local anesthetic gel may be contained in a plastic dome that extends around the periphery of the patch. See, for example, curved wall  35  of  FIGS. 2 and 3 . The dome can be a few millimeters to centimeters high, and a few millimeters to centimeters wide. The inside roof of the dome may contain an electroconductive material, which may be sprayed on the plastic or attached by adhesive. This conductive material can act as the principal electrode that can be connected to an external power source. When electrified, this conductive material conducts electricity to the local anesthetic gel. When this invention is applied to the body surface, the local anesthetic gel is in contact with the skin or the mucus membrane, and permits the diffusion of local anesthetic into the contacting skin or mucus membrane. 
   The present invention may lie against the skin using patch material including nonconductive, medical grade, closed cell foam material such as cross-linked polyethylene, polyester felt, or any other similar material that will be known to those skilled in the art. Patch material may range from a few microns to a few millimeter in thickness in some embodiments. The present invention has a central window or aperture that may be covered by an adhesive or non-adhesive transparent membrane. A patch according to the present invention, when applied to the body surface, may hold a local anesthetic reservoir firmly against the body surface. This permits the local anesthetic contained in the reservoir to stay in contact with, the skin or the mucus membrane. An adhesive on the underside of this invention may also hold a strip of conductive material serving as an electrode, on either side of the reservoir, firmly in contact with the skin or mucus membrane. The adhesive may thus form the insulator insulating the electrodes of opposite polarities from each other. 
     FIG. 4  illustrates another embodiment of the invention in a patch  50  formed generally of a contiguous border indicated at  52  disposed about an aperture  54 . Border  52  includes a first polarity electrode  56  disposed about an insulator  58  disposed about a second polarity electrode  59 . A medicant, for example an analgesic, may be disposed at either first electrode  56  or second electrode  59 . Patch  50  includes only a single part first electrode and a single part second electrode, unlike patch  20  of  FIG. 1 . 
     FIG. 5  illustrates another embodiment of the invention in a patch  60  formed generally of a contiguous border indicated at  62  disposed about an aperture  64 . Border  62  includes a first polarity electrode  66  disposed about an insulator  68  disposed about a second polarity electrode  69 . A medicant, for example a local anesthetic or analgesic, may be disposed at either first electrode  66  or second electrode  69 . 
     FIG. 6  illustrates yet another embodiment of the invention in a patch  70  formed generally of a discontiguous border indicated at  72  disposed about an aperture  74 . Border  72  illustrates the discontiguous border aspect of this embodiment. A preferred embodiment has a contiguous border, but gaps in the border are possible, provided electrical potential is provided to the discontiguous segments. Border region  72  is formed of a first border segment type  72 A and a second border segment type  72 B. In a preferred embodiment, a patch is formed of the same border types throughout. Border first segment type  72 A includes a first polarity electrode  76 A disposed about an insulator  78 A disposed about a second polarity electrode  79 A. A medicant, for example an anesthetic, may be disposed at either first electrode  76 A or second electrode  79 A. Border second segment type  72 B includes a first polarity electrode  76 B disposed about an insulator  78 B disposed about a second polarity electrode  79 B. A medicant, for example an anesthetic, may be disposed at either first electrode  76 B or second electrode  79 B. 
     FIG. 7  illustrates another embodiment of the invention in a patch  80  formed generally of a discontiguous border indicated at  82  disposed about an aperture  84 . Border  82  illustrates the discontiguous border aspect of this embodiment. A preferred embodiment has a contiguous border, but gaps in the border are possible, provided electrical potential is provided to the discontiguous segments. Border  82  is formed of a first border segment type  82 A and a second border segment type  82 B. In a preferred embodiment, a patch is formed of the same border types throughout. 
   Border first segment type  82 A includes a first polarity electrode  86 A disposed about an insulator  88 A disposed about a second polarity electrode  89 A. A medicant, for example an analgesic, may be disposed at either first electrode  86 A or second electrode  89 A. Border second segment type  82 B includes a first polarity electrode  86 B disposed about an insulator  88 B disposed about a second polarity electrode  89 B. A medicant, for example an analgesic, may be disposed at either first electrode  86 B or second electrode  89 B. 
     FIG. 8  illustrates an iontophoretic delivery patch  120  which is similar in many respects to patch  20  illustrated in  FIG. 1 . Reference numerals in  FIG. 8  similar to those in  FIG. 1  refer to similar elements, previously discussed with respect to  FIG. 1 . Patch  120  includes a border region  122  disposed about aperture region  24 . Border region  122  includes first electrode  33  in electrical communication with medicant carrying gel  30 , and having a first electrical polarity. Border region  122  does not includes the second polarity electrode of  FIG. 1 . Instead, patch  120  can be used in conjunction with a separate grounding electrode. A second polarity electrode wire  128  is partially illustrated, which can be coupled to a grounding electrode. The separate grounding electrode can be disposed either close to patch  120  on the body or disposed further away. In a preferred use of the invention, the grounding electrode is disposed close to patch  120 . 
   The materials used to make patches according to the present invention may include nonconductive, nontoxic, flexible material. One material includes non-woven polyester felt. The patch may be coated on the underside with an adhesive composed of poly-isobutylene and colloidal silicone dioxide. The under side of the patch may also be covered with a sheet of nonstick synthetic material, which may be peeled off prior to application of the patch on to the skin. This nonstick material may include a polyethylene terephthalate (PET) film release liner. Another protective liner can include a fluorocarbon diacrylate coated polyester sheet. This liner may be removed before application. 
   Electrical potential devices which are believed suitable for use with patches according to the present invention can include battery-operated devices capable of delivering electrical current in a pulsatile or continuous fashion in varying magnitude and duration. Some commercial devices include: the DYNAPHOR™, a battery operated iontophoresis device available from Henley International, Sugarland, Tex.; the IONTOPHOR, a computerized, programmable, battery operated iontophoresis device available from Life-Tech Corp., Houston, Tex.; and the SP-2, a low-voltage generator unit from TECA Corp., Pleasantville, N.Y. 
   A polymeric diffusion matrix may be provided for the transdermal systemic delivery of medicants through the skin of a patient. The polymeric diffusion matrix may include a first lower molecular weight, partially hydrolyzed polyvinyl alcohol component, a second higher molecular weight, essentially fully hydrolyzed polyvinyl alcohol component, and glycerol. 
   In one embodiment, the medicant delivered in the above-described patches is a local anesthetic. Any local anesthetic agent, for example lidocaine, bupivacaine, mepivacaine, tetracaine, procaine, chloroprocaine, cocaine, or prilocaine may be used as the principal local anesthetic. The patch may contain a hydrophilic gel including the local anesthetic agent. The gel may contain varying concentrations of the local anesthetic agent. For example, the gel can contain lidocaine 4% or prilocaine 2%. A local anesthetic may be the sole agent, or two or more local anesthetics of varying concentrations may be combined to form a mixture. A mixture may be used to increase the local anesthetic efficiency, without increasing the toxicity of any one individual agent. 
   The medicant may include pharmaceutical agents that increase the efficiency of local anesthetics, prolong the duration of action of local anesthetics, or change the acidity of the local anesthetics, and may also be added to a local anesthetic gel. Vasoconstrictors, for example, epinephrine, phenylephrine, or ephedrine may be added to the medicant to prolong the duration of action of the local anesthetic. Acidifying or alkalizing salts may be added to the medicant to change the pH and Pka of the local anesthetics. Such alterations of pH and Pka may alter the amount of local anesthetic that can ionize and change the concentration of local anesthetic that diffuses across the skin or mucus membrane. Narcotic agents such as morphine, codeine, Demerol, fentanyl, alfentanyl, remifentanyl and sufentanyl, may be added to the gel to obtain a synergistic effect on the blockade of pain conduction from the peripheral site. Other agents such as clonidine, which are often added to spinal or epidural anesthesia to prolong the duration or increase the intensity of local anesthetic effect, may also be added to a local anesthetic in this invention. 
   The formulation of local anesthetic or other medications into a gel form can be accomplished by means known to those skilled in the art. For example, lidocaine may be gelled with mixing varying amounts of water and hydroxypropyl cellulose. Another gelling agent is hydroxypropylmethylcellulose. Preservatives, such as methylparaben, or propylparaben, may be added to the gel to inhibit bacterial growth. The pH and PKa may be adjusted using sodium hydroxide or hydrochloric acid. 
   Other medications such as salicylates, corticosteroids, or antibiotics may be added to the patch to reduce inflammation and infection at the target site. Pain may be reduced and healing enhanced. These medications may be mixed with local anesthetic agents, or administered by themselves. Such delivery of anti-inflammatory drugs or antibiotics may reduce the need for systemic administration of these agents. 
   The grounding electrodes, such as electrodes  26  and  28  of  FIGS. 1-3 , may be made of a conductive material, such as carbon filled vinyl or carbon filled rubber material. The underside of the electrodes can be coated with a conductive adhesive such as materials loaded with graphite or an ionic substance. Electrodes can be on either side of the local anesthetic reservoir. The electrodes may vary in width and thickness, for example, from a few micrometers to a few millimeters. The grounding electrodes can be connected to an external power source. 
   The patch central aperture in this invention may be covered by a removable transparent membrane, such as Tegaderm (R), available from 3M Corporation. The under surface of the transparent membrane can contain a biocompatible adhesive, while the top surface is preferably free of any adhesives. The transparent membrane may be peeled off by pulling on a tab at one end of the transparent membrane. There is preferably no anesthetizing agent applied to the transparent membrane. 
   USES OF THE PRESENT INVENTION 
   The following, non-exhaustive list of methods may be practiced using the present invention, and are explicitly within the scope of the present invention. 
   Surgery 
   The present invention can be used to anesthetize skin and mucus membranes for different surgical and invasive procedures. This includes, without limitation, incision, excision, puncture, abrasion, slicing, dissecting, and approximation of cut edges by suture, staples or adhesives. 
   Excision of Surface Lesions 
   Small lesions of skin and mucus membrane, for example, cancer, moles, nevus, and cysts, can be excised painlessly following application of the present invention. 
   Incision and Drainage 
   Abscesses, hematomas, and other subcutaneous and deeper fluid collections can be drained painlessly following application of this invention. 
   Punctures 
   Procedures such as vena puncture, arterial puncture and nerve blocks can be performed painlessly after the application of this invention. This invention would be particularly useful in children who are averse to painful needle sticks. 
   Skin and Mucus Membrane Abrasion 
   The skin and mucus membrane can be abraded using mechanical devices, electricity, or laser to obliterate hair, tattoos, scars, cancer, and other surface lesions painlessly following application of this invention. 
   Approximation of Skin and Mucus Membrane 
   Lacerated or cut edges of skin and mucus membrane can be painlessly approximated using sutures, staples or adhesives painlessly following application of this invention. 
   Surgeries on Deeper Tissues 
   This invention permits painless injections of local anesthetics to numb deeper tissues. Through the removable transparent membrane, the surgeon can insert a needle in a painless fashion and infiltrate local anesthetic solutions into deeper tissue planes. This technique permits the surgeon to access deeper body tissues that lie beneath the skin and mucus membrane. Body cavities, such as abdomen, thorax, spine and cranium, along with muscles, bones and joints, can be accessed by this technique. 
   Postoperative Pain Control 
   Patches according to the present invention may be applied over surgical wounds and incisions to reduce pain. The central removable transparent membrane of some embodiments of the invention permits the caregiver to inspect and treat the wound without having to disrupt the analgesia provided by the patch. The wound or the incision may be cleaned, sutures removed, and/or antiseptics and dressing applied. These procedures can be done without interfering with the delivery of the analgesia provided by this invention. This invention is particularly useful for postoperative wound care in children. The patch reduces the amount of systemic painkillers, such as morphine, Demerol, aspirin or Tylenol, which a patient might need. Reduction in pain and a reduction in systemic pain medication permit the patient to be out of bed sooner. 
   Painful Skin and Mucus Membrane Lesions 
   The present invention may also be used to control pain originating from skin and/or mucus membrane due to a variety of causes. This includes traumatic injuries, abrasions, lacerations, punctures, burns, and infections. This invention permits observation and treatment of the painful lesion through the removable transparent membrane, without interfering with the delivery of the analgesia. 
   Enhanced Wound Healing 
   Applicants also believe that electrical potential applied to the skin surrounding an incision or wound, may per se hasten wound healing and alleviate pain. This effect may be unrelated to medications contained in the patch. Unlike some prior art devices, where opposite electrodes are placed on either sides of a wound to create an electrical potential across the wound, one embodiment of the present invention requires no such potential to be created across the wound. Instead, in this embodiment, both electrodes are on the same side of the wound, in an encircling fashion, creating an electrical field around the wound. The encircling electrical field may stimulate the nerve endings, release endorphins and enhance the blood supply to the wound, allowing it to heal faster and reduce pain. 
   Human and Animal Use 
   The present invention may be used to treat both humans and animals. Veterinary applications are explicitly within the scope of the present invention. 
   Numerous advantages of the invention covered by this document have been set forth in the foregoing description. It will be understood, however, that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of parts without exceeding the scope of the invention. The invention&#39;s scope is, of course, defined in the language in which the appended claims are expressed.