Methods for the diagnosis and treatment of articular disorders comprising the use of fluorocarbons are disclosed. The methods provide for the introduction of a fluorocarbon into an articular region to replace or augment natural synovial fluid. The introduced fluorocarbons, which may be in various forms including liquids, gels or emulsions, provide articular lubrication and cushioning which is effective for the treatment of disorders such as osteoarthritis and rheumatoid arthritis. Additionally, the methods of the present invention may be used to provide high resolution articular images, reduce articular inflammation and introduce bioactive agents to the articular region.

The present invention relates to therapeutic and diagnostic methods for the management of orthopedic disorders. More particularly, the present invention relates to the administration of fluorocarbons for the treatment or diagnosis of various articular disorders.
One of the most significant events in the evolution of animal physiology was the internalization of the skeletal framework. In a broad sense, it allowed for substantial increases in size while retaining the mobility necessary to exploit new environments. Moreover, in higher organisms the skeletal system carries out several important functions. Fundamentally, it provides mechanical support for the tissues of the body and assists in the maintaining the body""s natural mineral balance. It also exhibits a protective nature, reducing the potential for harm to delicate internal organs. Perhaps most importantly, the skeletal system is a dynamic structure incorporating numerous joints and providing a framework on which muscles can act to allow motion. Responsive to neural signals, this coordinated interaction is the basis for all voluntary movement.
The adult human skeleton is made up of 206 individual bones. The sites where the bones come together are commonly called joints (arthroses) or points of articulation. In normal operation, joints efficiently function to provide smooth, painless, stable, force transmission between one bone and the next with little effort. For the average adult individual, the joints cycle more than one million times a year, typically without injury or mishap. The hip, knee and ankle joints transmit forces of three times body weight with the simplest of activities such as walking, and over seven times the body weight when undergoing motion related to climbing stairs. Because much of the force transmitted across a joint is due to agonistic muscle contraction, the force per unit area carried by all extremity joints is similar.
Based on the nature of their connective tissue, joints are generally classified as belonging to one of two principal groups. In the first group, connective tissues remain solid (synarthroses). These solid joints are further classified as being fibrous joints or cartilaginous joints based on the most prevalent type of connective tissue. Fibrous joints tend to be articulations in which the surfaces of the bones are fastened together by intervening fibrous tissue. Such joints, including those between cranial bones, tend to allow little appreciable motion. Cartilaginous joints include synchondroses (primary cartilaginous joints) and symphyses (secondary cartilaginous joints) each of which may allow limited movement. The former are essentially growth mechanisms and are found where two separate but adjacent regions of ossification occur within a continuous mass of hyaline cartilage. In most cases, the cartilage is converted ultimately to bone and the synchondrosis is replaced by complete bony union, i.e. a synostosis. Symphyses, including the intervertebral discs, consist of two well-defined, hyaline cartilage-covered bones bonded by a strong, solid connective tissue such as fibrocartilage.
The second major group of joints, the predominant form of joint in the human body, are termed diarthroses or synovial joints. Synovial joints, which allow for a wide range of motion, incorporate a fluid filled cavity (the articular cavity) having a membrane known as the synovium. The synoviurn (or synovial membrane), richly supplied by both blood vessels and lymphatics, terminates at the margin of articular cartilage and is supported by the fibrous tissue defining the cavity or capsule. Only a few cell layers thick under normal circumstances, the synovium helps regulate the amount of liquid in a joint by secreting and absorbing synovial fluid. The synovial fluid plays an important role in lubricating and separating the bone and cartilaginous surfaces comprising the joint. More specifically, the bone surfaces are typically covered by articular cartilage, a specialized form of hyaline cartilage, which has a very low coefficient of friction. Sliding contact is facilitated by the presence of the synovial fluid, which, among other functions, provides for lubrication and maintenance of the living cells in the cartilage. Where the congruity between the bones is low there may also be an articular disc or meniscus of fibrocartilage. The purpose of this fibrocartilage is uncertain although it has been suggested that it plays a part in shock absorption, improvement of fit between surfaces and spreading of weight over a larger area. In any case, the synovial joints allow an impressive array of movements while successfully supporting immense loads.
The presence of healthy cartilaginous tissue is critical for the effective operation of synovial joints. Bathed by synovial fluid, cartilage provides a smooth, relatively malleable surface allowing for almost frictionless movement. Histologically, articular cartilage is a vascular and lacking in nerve structures. It contains a relatively small number of cells (chondrocytes) in a stiff, gel-like extracellular matrix that is permeated by a network of collagen fibers. Synthesis, and to some extent degradation, of the cartilage matrix is undertaken by the chondrocytes. The unusual mechanical characteristics of cartilage are a result of the unique architectural combination as well as chemical interactions between the components. Mechanically, articular cartilage can be considered to be a fluid-filled, permeable, porous solid. It is efficient at resisting the large compressive forces generated by weight transmission during movement and its elasticity dissipates the effect of concussion. During normal joint operation, the cartilage is subjected to both mechanical distortion of the matrix and, as a result of movement of interstitial fluid in and out of the tissue, changes in volume. The movement of synovial fluid, both within the cartilage and in the articular cavity, is extremely important to proper joint function.
Synovial fluid is a dialysate of blood plasma into which hyaluronate, a glycosaminoglycan of high molecular weight is secreted by the synovial membrane. The high levels of hyaluronate dissolved in the synovial fluid tend to make it fairly viscous under normal physiological conditions. In humans, the volume of synovial fluid found in the joints is typically on the order of a few tenths of a milliliter to several milliliters which is deposited on, and permeates, the cartilage and other surfaces within the articular cavity. Besides providing the articular cartilage its smooth texture and appearance, synovial fluid is found in the bursa (small synovium lined cavities associated with ligaments) where it provides lubrication for the tendon sheaths. Collectively, the bursa and articular cavity are known as synovial cavities. The dispersion of the fluid on the critical parts of the joint plays a decisive role in transmuting the dry resistant surfaces into effective load bearing structures exhibiting very low friction. For instance, it has been reported that the friction between articular cartilage surfaces is one third that of ice on ice. Yet, the efficiency of the lubrication depends, at least in part, on the quality and smoothness of the cartilage. In joints exhibiting damaged or degenerate cartilage, surface irregularities impair the lubricating properties of the synovial fluid and increase the rate of wear. Accordingly, while the initial disruption of the cartilage may occur for any one of a number of reasons, destruction of the joint is often due to a reduction in lubrication efficiency and repetitive insult to the tissue.
Several mechanisms have been proposed to explain the degree of lubrication and/or cushioning provided by the synovial fluid. For example, fluid film lubrication, involving a relatively thick layer of liquid interposed between the surfaces, is generally accepted to play a role in joint function. Different forms of fluid film lubrication that act in synovial lubrication, depending on the loading of the joint, include hydrostatic, hydrodynamic, squeeze-film and elastohydrodynamic. It has also been proposed that, under certain conditions, boundary layer lubrication may occur. In this case, it is believed that a layer of water and glycoproteins adheres to each surface thus reducing the amount of direct contact. Moreover, solvent cohesion during boundary layer lubrication allows the synovial fluid to function as an adhesive, thereby promoting joint stability. Solvent cohesion is apparently the result of hydrogen bonding where the bonds have a relatively high tensile strength but little or no resistance to shear. Such a system enables opposing surfaces to slide freely across each other but limits their distraction.
Although normally functioning joints provide pain free, efficient movement, this is not generally the case when the joint has been damaged. Deterioration of joint function may lead to chronic pain, lack of mobility and, in extreme cases, total disability or even death. Unfortunately a multitude of diseases can affect the joints. Some may occur due to infection while others are the result of autoimmune disorders. In yet other cases, the joints may be functionally impaired or damaged by congenital disorders, age, trauma or repetitive mechanical stress over an extended period of time. Irrespective of the etiology, progressive and irreversible physiological degeneration often results. Quite often the synovial fluid in the joint (or joints) is lost or reduced in volume, thereby exacerbating the problem. Typically, degenerated cartilage is shed into the bursa or articular cavity where it is engulfed by the synovium. This leads to chronic reactive hyperemia in the synovial membrane with corresponding fibrosis and loss of elasticity in the subsynovial tissue. Gradually adhesions obliterate the synovial space and reduce or eliminate the synovial fluid. The loss of structural integrity leads to swelling, inflammation, and a reduction of joint mobility, a condition commonly known as rheumatism or arthritis.
In the past, rheumatism was the generic name for pain and stiffness associated with joints, muscles and related structures. Arthritis is more properly used where degeneration results in the inflammation of joints or connective tissue. However, the term is still often used generically to describe cases where inflammation does not occur. It is estimated that up to 33% of all adults are currently affected, at least temporarily, by some form of articular disorder. Of the more than 100 different types of articular disorder commonly termed xe2x80x9carthritisxe2x80x9d, the most common are osteoarthritis, rheumatoid arthritis, gout, pseudo gout and ankylosing spondylitis. These five conditions account for more than half of all types of joint disease diagnosed today. Other less common, though still serious, types of arthritis include juvenile arthritis, lupus, scleroderma, chondromalacia patellae, and infectious arthritis. Still other types of articular disorders involve inflammation or irritation of the structures supporting the joint, such as muscles, tendons and ligaments. These condition include bursitis, tendinitis, fibrositis and polymyositis.
By far, the most prevalent articular disorders are rheumatoid arthritis and osteoarthritis which is also known as degenerative joint disease. Rheumatoid arthritis, thought to be an autoimmune disorder, is the result of an inflammation of the synovial membrane. Peak onset of the disorder occurs in the 30s and 40s and afflicts women three times more often than men. In extreme cases, chronic inflammation erodes and distorts the joint surfaces and connective tissue resulting in severe articular deformity and constant pain. Moreover, rheumatoid arthritis often leads to osteoarthritis, further compounding the destruction of the joint. The most common articular disorder, osteoarthritis is characterized by degenerative changes in the surface of the articular cartilage. Alterations in the physicochemical structure of the cartilage make it less resistant to compressive and tensile forces. Finally complete erosion occurs, leaving the subchondral bone exposed and susceptible to wear. Joints of the knees and hands are most often affected, followed by the spine, hips, ankles and shoulder. In both rheumatoid arthritis and osteoarthritis, degeneration of the weight bearing joints such as the hips and knees can be especially debilitating and often requires surgery to relieve pain and increase mobility.
No means currently exist for halting or reversing the degenerative changes brought about by these disorders. At the same time, approximately 37 million Americans seek symptomatic relief in the form of prescription drugs. In such cases nonsteroidal, anti-inflammatory drugs (NSAIDS) are most often prescribed. While these compounds often alleviate the arthritic symptoms, they are not without side effects such as nausea and gastrointestinal ulceration. Another class of commonly prescribed compounds are corticosteroid such as triamcinolone, prednisolone and hydrocortisone. Yet, the long term use of such measures increases the chance of undesirable side effects and is often contraindicated. In addition to difficulties in determining effective dosages, a number of adverse reactions have been reported during intra-articular steroid treatment. As a result, the use of corticosteroid treatments in the management of articular disorders is currently being reassessed.
Formulations of hyaluronic acid, including gels and slurries as described in U.S. Pat. No. 5,143,724, have also been proposed for use in the treatment of arthritis. However, the use of such treatments has been limited as hyaluronic acid is reported to lubricate only the soft tissues of the joint which are not subject to heavy loading. Further, as with more conventional treatments, adverse side effects have been observed following the intra-articular administration of the formulation. Significantly, patients with clinical histories of local adverse reactions to the hyaluronic acid treatment are reportedly susceptible to severe permanent joint damage. Accordingly, widespread use of the disclosed formulations has yet to be achieved.
In addition to the intra-articular injection of natural polymers such as hyaluronan, the administration of synthetic polymers has also been used for the management of articular disorders. For example, U.S. Pat. No. 4,828,828 discloses methods of treating degenerative joint disease through the intra-articular injection of meth(acrylamide) (co)-polymers in the form if a gel. However, acrylamide monomers are known to be potent neurotoxins making such gels undesirable for long term therapeutic administration. Questions involving breakdown products and bioincorporation of the constituent material complicate necessary regulatory approval. Similarly, U.S. Pat. No. 3,697,653 describes a method of treating osteoarthritic joints with polysiloxanes. While the disclosed materials possess some of the desired qualities for the proposed use, the presence of free silicone and silicone derivatives have recently been associated with immune disorders and connective tissue disease. In particular, silicone breast implants incorporating polysiloxanes have been implicated in the etiology of autoimmune disorders, immune suppression, connective tissue disease and, perhaps most importantly, rheumatoid arthritis. As such, it is possible that the intra-articular administration of siloxane polymers will exacerbate any preexisting arthritic condition.
Accordingly, it is an object of the present invention to provide methods for the treatment of articular disorders.
It is another object of the present invention to provide methods for the reduction of articular inflammation.
It is yet another object of the present invention to provide methods for the articular administration of therapeutic compounds.
It is still another object of the present invention to provide methods of imaging an articular region providing enhanced contrast.
These and other objects and advantages are accomplished by the methods of the present invention that, in a broad aspect, provide for the improved diagnosis and treatment of articular disorders. More particularly, the present invention comprises the introduction of fluorocarbons into an articular region for the purpose of treating a disorder, or symptoms thereof including articular inflammation, or delivering a bioactive agent. During the course of therapy, the presence and distribution of the fluorocarbon can be monitored using imaging techniques such as computed tomography, conventional radiography, magnetic resonance imaging and ultrasound. Similarly, high resolution imaging of the articular region, and in particular the synovial cavities, may be achieved using the aforementioned techniques following administration of a neat fluorocarbon liquid to the articular region.
Besides promoting physiological improvements in the articular condition and reduction of pain, the methods of the present invention also act to provide enhanced bioavailability and target specificity for co-introduced bioactive agents as well as improving resolution and clarity of diagnostic images. Unlike prior art compounds introduced into the articular region for management of a disorder, the fluorocarbons of the present invention are safe, nonreactive and extremely biocompatible. Such characteristics, when combined with the efficacious physical properties of the disclosed compounds, allow for the long term therapeutic treatment of articular disorders, or symptoms arising therefrom, without provoking undesirable responses from the patient. Similarly, the enhanced bioavailability and target specificity provided by the present invention prolongs the time a drug may be administered and allows higher doses while lowering the risk of side effects. Additionally, imaging techniques according to the present invention may be used to monitor the progress of the therapy during the normal course of treatments. Other embodiments of the present invention provide for the generation of high resolution images following the administration of a neat fluorocarbon liquid.
In accordance with one aspect of the present invention fluorocarbons may be administered to an articular region to treat an articular disorder or the symptoms thereof. In preferred embodiments the articular disorder is osteoarthritis or rheumatoid arthritis and the fluorocarbon is a liquid fluorocarbon having low water solubility, relatively high density and low surface tension. Upon introduction to the articular region, preferably through intra-articular injection, the fluorocarbon acts to replace or augment the synovial fluid normally found in the joint. Low water solubility acts to retard diffusion out of the synovial space and promotes long residence time at the target site. Low surface tension and an effective coefficient of spreading allows the fluorocarbon to spread evenly over the articular surfaces and provide the desired lubrication and surface uniformity. Similarly, the relatively high density of fluorocarbons provide a natural cushion between opposing surfaces to reduce contact force and attendant pain. In other embodiments, the fluorocarbon may comprise a gel, emulsion or other viscous composition to improve the natural cushioning effect. Moreover, the fluorocarbon may comprise a bioactive agent such as an anti-inflammatory pharmaceutical compound. In preferred embodiments, the method further comprises the step of imaging at least a portion of the articular region following administration of the fluorocarbon. More particularly, as discussed above, the position, amount and condition of the introduced fluorocarbon, as well as the progress of the treatment, may be monitored using conventional imaging techniques during the course of therapy.
Another aspect of the present invention comprises the introduction of a therapeutically effective amount of a fluorocarbon into an articular region to reduce inflammation. In particular, the methods of the present invention provide for the introduced fluorocarbon to reduce inflammation without the use of additional bioactive agents. That is, the administered fluorocarbon itself possesses anti-inflammatory properties. Of course, it is contemplated that the fluorocarbon may further comprise a bioactive agent such as steroidal compounds or antibiotics. In particularly preferred embodiments, the selected fluorocarbons may be used to reduce the cellular and molecular events associated with chronic immune cell infiltration which provoke synovial inflammation. As with other aspects of the invention, the form, or state, of the introduced fluorocarbon is not critical and may comprise, for example, a liquid, a gel, an emulsion or the like. Similarly, the present invention may be used without regard as to the cause of the articular inflammation and, further, may be used in any articular region comprising an inflamed joint. In preferred embodiments the fluorocarbon, in any form, will be introduced intra-particularly using an injection. Conversely, the fluorocarbon may be a gel or other preparation that may be introduced using conventional surgical or arthroscopic techniques. Preferably, the method further comprises imaging at least a portion of the articular region following administration of the fluorocarbon to monitor the course of therapy.
Yet another aspect of the present invention involves methods for administering a bioactive agent to an articular region using a bioactive preparation comprising a fluorocarbon and at least one bioactive agent. In these methods, a therapeutically effective amount of the bioactive preparation is introduced to the selected articular region. The selection of the bioactive agent is limited only by the ability to incorporate it in the chosen preparation. Preferred embodiments may incorporate a radioactive element or compound that can act as a radiation synovectomy agent. As with the fluorocarbon in other aspects of the present invention, the bioactive preparation may comprise any one of a number of forms or states including, but not limited to, liquids, solids, gels, sols, suspensions, micelles, emulsions, inverse emulsions and reverse emulsions. Selection of which form to use may be based on factors concerning desired drug delivery profiles, retention times, characteristics of the bioactive agent and type of articular disorder. In a preferred embodiment, the bioactive preparation comprises a plurality of biodegradable polymeric microspheres, associated with the selected bioactive agent, in liquid perfluorocarbon. In other preferred embodiments the biological preparation may be in the form of a gel having a fluorocarbon matrix with a bioactive agent incorporated therein. Such preparations substantially increase bioavailability and target specificity of the bioactive agent while simultaneously reducing undesirable systemic side effects and toxicity. Administration of the bioactive agent may be monitored as described above.
In addition to the aforementioned advantages, the present invention also provides improved methods for imaging an articular region comprising the administration of an effective contrast enhancing amount of a neat liquid fluorocarbon to the selected area. Preferred embodiments comprise the administration of a neat liquid fluorocarbon to the synovial cavities. It will be appreciated that the articular region may be imaged using the same techniques used to monitor the presence or condition of the fluorocarbon during a course of therapy or dosing regimen. In particular, the low water solubility, high density and low surface tension of the neat liquid fluorocarbon serve to provide long lasting, high resolution images of the tissues in the region of interest using magnetic resonance imaging (MRI), computed tomography (CT), conventional radiography and ultrasound. Accordingly, the present invention may be used to obtain enhanced resolution images of the articular region including the joint and the surrounding connective tissue. With respect to CT, conventional radiography and ultrasound, the density and radiopacity of the fluorocarbon contrasts sharply with the water filled tissue. In the case of MRI, the fluorocarbon may be used as a negative contrast agent when imaged using proton weighted MRI or as a positive contrast agent when used in conjunction with F19 weighted MRI. Any free flowing, neat liquid fluorocarbon may be used as long as it possesses the necessary contrast enhancing characteristics and any articular region may be imaged using the methods disclosed herein.
Other objects, features and advantages of the present invention will be apparent to those skilled in the art from a consideration of the following detailed description of preferred exemplary embodiments thereof.
While the present invention may be embodied in many different forms, disclosed herein are specific illustrative embodiments thereof that exemplify the principles of the invention. It should be emphasized that the invention is not limited to the specific embodiments illustrated.
It will be appreciated that, in a broad aspect, the present invention comprises the administration or introduction of a fluorocarbon into an articular region for a variety of purposes. Among other applications, the methods disclosed herein are particularly useful for treating articular disorders, or the symptoms arising therefrom, due to the excellent lubricating and cushioning properties provided by the selected fluorocarbons. More specifically, preferred embodiments of the invention allow for the replacement or augmentation of natural synovial fluid. This, in turn, provides for the efficient and uniform dispersion of forces placed on the articular region while, at the same time, reducing the forces generated by articular surface opposition. Besides enhancing mobility, the improvement in articular function will result in a reduction of pain and a reduction in the rate of tissue degeneration.
When a fluorocarbon is introduced or administered to an articular region in accordance with the present invention some or all of it preferably adheres the surfaces of the tissue to provide a slick, smooth fluorocarbon coat that minimizes friction. As with natural synovial fluid, it is believed that the introduced fluorocarbon improves the surface homogeneity of the underlying bone or cartilage and, through any one of a number of hydrodynamic mechanisms (depending on the loading of the joint), allows the surfaces to move easily past one another. In addition, the introduced fluorocarbon acts as a cushion to prevent, or at least reduce, the destructive forces generated by contact between opposing surfaces. That is, the introduced fluorocarbon will act to simultaneously separate the surfaces and uniformly dissipate any applied stress or force within the entire articular region. The even dissipation of forces acts to relieve concentrated stress points and, when combined with the fluorocarbon lubrication, retard the further degeneration of the articular tissue. It is also contemplated that the methods of the present invention may also be used to cushion and lubricate prosthetic joints such as those currently employed in artificial hips and knees.
In addition to the unexpected physio-mechanical benefits provided by the present invention, several other advantages are afforded by the disclosed methods. For example, in preferred embodiments the invention may be used to reduce the articular inflammation often associated with joint disorders. More specifically, in selected embodiments fluorocarbons compatible with the present invention may be used to reduce the cellular and molecular events associated with chronic immune cell infiltration, particularly in the synovial cavities, which provoke inflammation. Accordingly, the immunosuppressive aspects of the present invention are preferably employed to reduce synovial inflammation. In particularly preferred embodiments, the treatments are enhanced by the addition of an anti-inflammatory bioactive agent to the fluorocarbon to form a biological preparation which is then administered as provided for herein. As will be discussed further below, the bioactive preparations of the present invention may be used to deliver any compatible bioactive agent to the articular region.
For the purposes of this application, the term xe2x80x9cbioactive agentxe2x80x9d is defined to mean any pharmaceutical compound or composition, including diagnostic and therapeutic agents as well as live cells, microorganisms and physiologically acceptable gases such as oxygen or nitric oxide, which may be administered to an animal to treat a disorder. Accordingly, a bioactive preparation comprising nutrients, live cartilage producing cells (chondrocytes) and oxygen in a liquid fluorocarbon could be introduced into an articular region according to the present invention. In addition, the contrast enhancing properties of the compatible fluorocarbons allow the tissues of the articular region to be readily delineated during such treatments by imaging at least a portion of the articular region following administration of the fluorocarbon.
The methods of the present invention may be used to treat, alleviate, retard, prevent diagnose, monitor or cure any articular disorder or symptoms arising therefrom. For the purposes of this disclosure the term xe2x80x9cparticular disorderxe2x80x9d shall be held to mean any affliction (congenital, autoimmune or otherwise), injury or disease of the articular region which causes degeneration, pain, reduction in mobility, inflammation or physiological disruption of the articular tissue or connective tissue in the articular region. Specific articular disorders include, but are not limited to, osteoarthritis, rheumatoid arthritis, juvenile arthritis, lupus, scleroderma, chondromalacia patellae, infectious arthritis, bursitis, tendinitis, fibrositis, fibromyositis and polymyositis. Moreover, the methods of the present invention could be used as a prophylactic measure to prevent future damage or degeneration. For example, fluorocarbons could be administered intra-particularly to athletes intermittently throughout their career to minimize the risk of stress related injury or cartilage degeneration.
Those skilled in the art will appreciate that the methods of the present invention are applicable to more than just the joint itself; i.e. more than the point of articulation. By way of example only, the methods of the present invention could be used in the region of the knee to administer fluorocarbon to the subcutaneous infrapatellar bursa (below the kneecap) to lubricate the patellar ligament and reduce inflammation in the surrounding tissue. Accordingly, while the methods of the present invention may be practiced by administering fluorocarbons directly into the articular cavity, it is not limited to such embodiments. Rather, the methods of the present invention are directed to the administration or introduction of the fluorocarbons to the articular region. As defined herein the xe2x80x9carticular regionxe2x80x9d includes the joint itself (the point of articulation), the articular cavity, any ligaments required for joint articulation, any bursa associated with the joint or attendant ligaments and any immediately surrounding tissue. For example, the articular region in the knee extends from the point where the quadriceps femoris tendon attaches to the rectus femoris muscle (below the thigh) to the point where the patellar ligament is affixed to the tibia (above the shin) and comprises all intervening ligaments, cavities, bursa and joints. By way of comparison, xe2x80x9cintra-articularxe2x80x9d administration (or injection) will be held to mean the introduction of material into any cavity (including bursa and synovial) in proximity to the designated joint.
Furthermore, the present invention is not limited to use in any particular articular region but may be used in conjunction with any selected joint. Exemplary joints that are compatible with the methods of the present invention include, but are not limited to, knee, hip, ankle, shoulder, elbow, tarsal, carpal, interphalangeal and intervertebral. In preferred embodiments the present invention will be used in conjunction with synovial joints. Even more preferably the methods of the present invention are used in conjunction with weight bearing joints such as the hip or the knee. It must be emphasized that, as previously discussed, the present invention provides for the introduction or administration of compatible fluorocarbons to any articular region associated with the aforementioned joints rather than just the point of articulation.
This is especially true with respect to embodiments directed to the reduction of inflammation. As alluded to earlier, the methods of the present invention are particularly beneficial at reducing articular inflammation associated with the synovium. Accordingly, while useful for all articular disorders, the anti-inflammatory aspects of the invention make it very effective for the treatment or prophylaxis of acute inflammation associated with autoimmune articular disorders such as rheumatoid arthritis and ankylosing spondyloarthritis. In such cases, administration of the fluorocarbon to the afflicted joint region may be used to suppress cellular responses such as phagocytosis and molecular activity such as the secretion of cytokines and adhesion molecules. Of course, the anti-inflammatory features disclosed herein are not limited to synovial inflammation. Rather, the methods of the present invention can be used to reduce the inflammation in any tissue (including musculature) associated with the articulation. Administration of the selected fluorocarbon, which in preferred embodiments is perfluorooctylbromide, may be intra-articular, subcutaneous or intramuscular depending on the site of the inflammation to be treated.
Similarly, use of the methods of the present invention to provide high resolution images of an articular region is not limited to administration of the selected fluorocarbon in the synovial cavities. To the contrary the invention may be used to delineate any or all of the tissue desired within the articular region. However, in preferred embodiments, the area to be imaged will comprise at least one synovial cavity.
When used to monitor the course of therapy or determine the placement of fluorocarbon used in such treatments, any form of fluorocarbon (i.e. gels, liquids etc.) may be imaged. However, in order to produce high resolution images of the articular region for the purposes of diagnosis, neat fluorocarbon liquids are used. Generally, the imaging methods of the present invention comprise administering a effective contrast enhancing amount of a neat fluorocarbon liquid to an articular region and imaging the at least a portion of the region. As used herein the term xe2x80x9cneat fluorocarbon liquidxe2x80x9d shall mean a liquid or liquid preparation that possesses approximately the same flow and spreading characteristics as the liquid in a pure state. Thus, neat fluorocarbon liquids may contain relatively small amounts of additives, including solutes and particulates, as long as the flow characteristics are not impaired. The high density and relatively low surface tension of neat, liquid fluorocarbons allows them to efficiently disperse throughout the selected tissue or cavity providing superior resolution with respect to other forms of fluorocarbon. Preferably the enhanced resolution image will be generated using MRI, radiography (including CT) or ultrasound. The term xe2x80x9ceffective contrast enhancing amountxe2x80x9d shall be held to mean an amount of neat fluorocarbon liquid that improves the definition of the tissue in the imaged area. While this amount may vary, effective ranges for liquid fluorocarbons are between about 0.01 ml and about 20 ml depending on the size of the articular region and type of imaging employed. Preferred regions are on the order of approximately 0.5 ml to approximately 10 ml.
The partially fluorinated or perfluorinated compounds comprising the fluorocarbons of the present invention are typically chosen for their low water solubility, toxicity, high density or viscosity, surface tension and spreading coefficient. Water solubility, density and viscosity are readily determined for any liquid fluorocarbon and may provide an initial screen if the fluorocarbon is to be administered neat. Of course, amixtures of fluorocarbons may be used to provide the desired characteristics. Preferably the fluorocarbons will be capable of delivering therapeutically significant amounts of gases including nitric oxide or oxygen to facilitate treatment. At the same time, it is preferred that the fluorocarbons have vapor pressures sufficiently low to prevent significant liquid loss caused by evaporation during storage or delivery. Lower vapor pressures also promote retention of the fluorocarbon in the articular region where it is introduced and are generally associated with higher viscosity and density. In addition, the ability of the fluorocarbon to spread evenly over the articular surfaces or xe2x80x9cwetxe2x80x9d the joint is desirable as the uniform distribution will maximize lubrication and dissipation of applied force. Liquid fluorocarbons typically have low surface tension values on the order of 20 dynes/cm and, as they have a relatively high density, spread fairly easy. Accordingly, in this respect almost all liquid fluorocarbons are compatible with the present invention.
Generally, highly fluorinated or perfluorinated compounds having the desired physical properties may be linear, branched or cyclic, saturated or unsaturated fluorinated compounds. Conventional structural derivatives of these fluorocarbons are also contemplated as being within the scope of the present invention. In addition, these totally or partially fluorinated compounds may contain one or more hetero-atoms and/or atoms of bromine or chlorine. As used herein, the term xe2x80x9cpartially fluorinatedxe2x80x9d indicates that approximately half or more of the hydrogen atoms in the hydrocarbon oil or derivative thereof have been replaced with fluorine atoms. Preferably, these fluorocarbons comprise from 2 to 16 carbon atoms and include, but are not limited to, linear, cyclic or polycyclic fluorinated alkanes, bis(perfluoroalkyl)alkenes, perfluoroethers, perfluoroamines, perfluoroalkyl bromides and perfluoroalkyl chlorides. With respect to the disclosed methods, the aforementioned compounds may be used either alone or in combination. Moreover, mixtures of the same or different species of fluorocarbons are specifically contemplated as being within the scope of the invention.
In selected embodiments of the invention the fluorinated compound may comprise perfluorooctylbromide, C8F17Br (PFOB or perflubron). Other preferred alkyl fluorocarbons include perfluoroctane C8F18, perfluorodecane C10F22, perfluorodecylbromide C10F21Br (PFDB) and bis(perfluorobutyl) ethene (F-44E). In addition to the these compounds, exemplary fluorocarbons contemplated for use in the present invention generally include halogenated fluorocarbons (i.e. CnF2n+1X, XCnF2nX, where n=2-10, X=Br, Cl or I) and, in particular, 1 -bromo-F-butane n-C4F9Br, 1 -bromo-F-hexane (n-C6F13Br), 1-bromo-F-heptane (n-C7F15Br), 1,4-dibromo-F-butane and 1,6-dibromo-F-hexane. Other useful brominated fluorocarbons are disclosed in US Pat. No. 3,975,512 to Long and are incorporated herein by reference. Specific fluorocarbons having chloride substituents, such as perfluorooctyl chloride (n-C8F17Cl), 1,8-dichloro-F-octane (n-ClC8F16Cl), 1,6-dichloro-F-hexane (n-ClC6F12Cl), and 1, 4-dichloro-F-butane (n-ClC4F8Cl) may also be used.
Polycyclic and cyclic fluorocarbons, such as C10F18 (F-decalin or perfluorodecalin) are generally useful in the present invention due to their low vapor pressure. Preferred cyclic fluorocarbons include perfluorodecalin and its fluoroalkyl substituents, perfluoroperhydrophenanthrene and its isomers and perfluoroalkyl substituents. Such compounds tend to have a long residence time and provide therapeutic effects in the articular region for an extended period. In this respect, other fluorocarbons which may be useful include, but are not limited to, perfluoro n-butyldecalin, perfluorotetramethylcyclohexane (AP-144), perfluoromethyladamantane, perfluorodimethyladamantane, perfluoro-6,7 H-undec-6-ene, perfluoromethyldecalin, perfluorodimethyl-ethylcyclohexane, perfluorodimethyldecalin, and perfluorodiethyldecalin. Such fluorocarbons, in addition to possessing extended residence times, tend to exhibit desirable viscosity and density characteristics for use in the present invention.
Fluorocarbons, fluorocarbon-hydrocarbon oil compounds and halogenated fluorocarbons containing other linkage groups, such as esters, thioethers and amines are also suitable for use in forming the compositions and bioactive preparations of the present invention. For instance, compounds having the general formula, CnF2n+1OCmF2m+1, or CnF2n+1CHxe2x95x90CHCmF2m+1, (as for example C4F9CHxe2x95x90CHC4F9 (F-44E), i-C3F9CHxe2x95x90CHC6F13 (F-i36E), and C6F13CHxe2x95x90CHC6F13 (F-66E)) where n and m are the same or different and n and m are integers from about 2 to about 12 are compatible with teachings herein. Useful fluorocarbon-hydrocarbon diblock and triblock compounds include those with the general formulas CnF2n+1xe2x80x94CmH2m+1 and CnF2n+1xe2x80x94CmH2mxe2x88x921, where n=2-12; m=2-16 or CpH2p+1xe2x80x94CnF2nxe2x80x94CmH2m+1, where p=1-12, m=1-12 and n=2-12. Preferred compounds of this type include C8F17C2H5, C6F13C10H,21, C8F17C8H17, C6F13CHxe2x95x90CHC6H13 and C8F17CHxe2x95x90CHC10H21. Substituted ethers or polyethers (i.e. XCnF2nOCmF2mX, XCFOCnF2nOCF2X, where n and m=1-4, X=Br, Cl or I) and fluorocarbon-hydrocarbon ether diblocks or triblocks (i.e. CnF2n+1xe2x80x94Oxe2x80x94CmH2m+1, where n=2-10; m=2-16 or CpH2p+1xe2x80x94Oxe2x80x94CnF2nxe2x80x94Oxe2x80x94CmH2m+1, where p=2-12, m=1-12 and n=2-12) may also used as well as CnF2n+1Oxe2x80x94CmF2mOCpH2p+1, wherein n, m and p are from 1-12. Furthermore, perfluoroalkylated ethers or polyethers may be compatible with the methods of the present invention.
Additional fluorocarbons that may be used in accordance with the teachings herein include perfluorinated amines, such as F-tripropylamine (xe2x80x9cFTPAxe2x80x9d) and F-tributylamine (xe2x80x9cFTBAxe2x80x9d). F-4-methyloctahydroquinolizine (xe2x80x9cFMOQxe2x80x9d), F-N-methyl-decahydroisoquinoline (xe2x80x9cFMIQxe2x80x9d), F-N-methyldecahydroquinoline (xe2x80x9cFHQxe2x80x9d), F-N-cyclohexylpyrrolidine (xe2x80x9cFCHPxe2x80x9d) and F-2-butyltetrahydrofuran (xe2x80x9cFC-75xe2x80x9d or xe2x80x9cFC-77xe2x80x9d) may also be incorporated. Other contemplated fluorocarbons having nonfluorine substituents, such as, perfluorooctyl hydride, and similar compounds having different numbers of carbon atoms are also contemplated as being within the scope of the invention. Mixtures of any fluorocarbons compatible with the methods disclosed herein are also contemplated for use in the present invention. Further, those skilled in the art will appreciate that other variously modified fluorocarbons are encompassed within the broad definition of xe2x80x9cfluorocarbonsxe2x80x9d and are suitable for use in the present invention.
While some preferred embodiments of the present invention comprise liquid fluorocarbons, it must be emphasized that it is within the scope of the invention to administer or introduce the fluorocarbon to the desiginated articular region in any form. Accordingly, other preferred embodiments of the present invention comprise introducing the fluorocarbon in the form of a liquid, solid, foam, micelle, gel, sol, slurry, dispersion, suspension, emulsion, microemulsion, reverse emulsion and combinations thereof. The selection of which state to use in administering the fluorocarbon will depend, to a large extent, on the type of disorder or symptom being treated and the articular region of interest. For example, in the large articular cavity of the weight bearing knee it may be appropriate to insert a fluorochemical gel or biocompatible sponge soaked with a liquid fluorocarbon to provide extra cushioning. Conversely, in the relatively small, non-weight bearing carpal joints it may be preferred to administer the fluorocarbon as a sol or microemulsion wherein a bioactive agent is suspended as nanometer size particles. In each case, optimization of various aspects of the present invention allows increased bioavailability and maximizes the therapeutic effects of the treatment. For certain embodiments, the methods of the present invention comprise the introduction or administration of a selected, neat fluorocarbon liquid to the designated articular region. In a particularly preferred embodiment, the liquid fluorocarbon is perfluorooctylbromide (PFOB). As alluded to earlier, the neat liquid fluorocarbon may be used to provide beneficial cushioning and lubrication, reduce articular inflammation and act as a contrast agent for real time monitoring of the treatment. The amount of liquid fluorocarbon (or liquid fluorocarbon based preparations such as sols, suspensions, emulsions, etc.) administered is preferably enough to effectively perform the desired function whether it be cushioning, contrast enhancement, anti-inflammation or drug delivery. For mechanical benefits it is contemplated to administer an amount sufficient to replace or augment natural synovial fluid allowing lubrication and cushioning of the afflicted joints. The exact amount administered is generally a function of the joint involved (particularly cavity volume), severity of the articular degradation and other factors related to the disorder. Typically the amount administered may range from approximately 0.01 ml or less for small joints to approximately 10 ml or more for large joints such as the knee. In preferred embodiments, the amount of fluorocarbon administered will range from approximately 0.1 ml to approximately 5 ml.
Those skilled in the art will appreciate that, one major advantage of the present invention is that compounds or materials, including bioactive agents, may be introduced to the articular region in combination with the selected fluorocarbon. In the case of liquid fluorocarbons, selected embodiments comprise the formation of a molecular solution where the bioactive agent or other additive is solubilized in a fluorocarbon carrier. Techniques for forming such solutions are provided by co-pending application U.S. Ser. No. 08/843,468 which is incorporated herein by reference. Other exemplary embodiments of the present invention comprise sols, colloidal dispersions of solid microparticulates on the order of nanometers, or suspensions and dispersions of slightly larger particulates in a fluorocarbon liquid. By increasing the concentration of the suspended particulates, slurries may be obtained. The formation of fluorocarbon based suspensions are well known in the art as evidenced by U.S. Pat. No. 5,496,535 which is incorporated herein by reference. A particularly preferred method of forming sols by driving a bioactive agent or additive out of a fluorocarbon solution is disclosed in co-pending application U.S. Ser. No. 08/482,176 which is also incorporated herein by reference. In forming the aforementioned preparations, those skilled in the art will appreciate that the concentration of the bioactive agents or additives may be adjusted and optimized without undue experimentation to provide a therapeutically effective dosages.
In other embodiments, hydrolytically active (bioerodable) or hydrolytically stable (non-bioerodable) polymeric compounds, typically in the form of microcapsules or microparticulates, may be suspended in the selected fluorocarbon. Preferably, hydrolytically active particulates will themselves act as a bioactive agent, wetting and lubricating the articular region. It is further contemplated as being within the scope of the invention to associate a bioactive pharmaceutical agent with the polymeric microparticulates or microcapsules used in the dispersion or suspension. The selected polymeric drug delivery vehicles may either be hydrolytically stable or bioerodable depending on the dosing regimen. Preferably, the polymeric microparticulates are sized on the order of approximately 0.02 xcexcm to 200 xcexcm, while the microcapsules are sized on the order of approximately 2 xcexcm to 200 xcexcm.
Suspensions and sols of non-active or non-bioerodable hydrolytically stable materials such as fluoropolymers (i.e. polytetrafluoroethylene or PTFE), engineering plastics and the like are particularly compatible with the methods of the present invention. In addition to PTFE, other exemplary hydrolytically stable polymers which are suitable for use in the bioactive preparations of the present invention include acrylate, ethylene vinylacetate, polyurethanes, and polysulfones. Such particulates may be used to enhance the beneficial properties of the administered fluorocarbon when coadministered. For example, the inclusion of non-bioerodable nanometer sized particles comprising a hydrolytically inactive polymer in a bioactive preparation may be used to enhance the lubricating characteristics of a cointroduced liquid fluorocarbon. In a particularly preferred embodiment of the present invention, a suspension of PTFE microparticulates in perfluorooctylbromide will be administered to the articular cavity of weight bearing joint. Of course, those skilled in the art will appreciate that the hydrolytically inactive particulates may be associated with a pharmaceutical compound so as to act as a polymeric drug delivery vehicle. Moreover, mixtures of different sizes and/or and different kinds of particulates (i.e. PTFE and acrylate particulates) can be administered in accordance with the teachings herein.
Conversely, exemplary polymers which will erode at the chosen articular site to provide lubrication or wetting of the surface comprise poly(methylvinylether/maleic anhy-dride), carboxy vinyl polymers, polyfumaric acid/sebacic acid, collagen, gelatin, polyvinyl alcohol, methylcelluloses, polyorthoesters, polyglycolic acid, polylactic acid, polyvinylpyrrolidone, polysebacic acid anhydride, polycarboxyphenoxypropane anhy-dride, polyterephthalic acid anhydride, and polyphosphazine. Preferred embodiments will comprise poly(methylvinylether/maleic anhydride) particulates or microcapsules. As previously mentioned, particulates and microcapsules comprising such polymers may be associated with pharmaceutical compounds to form polymeric drug delivery vehicles. Such embodiments are especially useful as particulates made from these hydrolytically active polymer provide a long shelf life, do not prematurely erode and are very effective at drug release and lubrication when delivered to the aqueous target environment.
It is also within the scope of the present invention to provide bioactive preparations comprising a mixture of particle sizes or mixtures of microcapsule and microparticulates with varying erosion rates or hydrophobicity profiles. Mixtures of hydrolytically active particles and hydrolytically stable particles are also contemplated. Such combinations can be designed to provide specific drug release profiles, including high initial concentrations or so-called zero order deliveries which may be used to provide combinations of different bioactive agents. However, those skilled in the art will appreciate that particulates or microcapsule prepared from polymers which are hydrolytically labile are especially well suited for use with fluorocarbons of the present invention. In particular, they may be used to form stable preparations having long shelf lives and yet will erode in the aqueous environment of the target site thereby eliminating themselves from the body.
In addition to the liquid fluorocarbon preparations described above, thixotropic preparations may be used in present invention. As is known in the art, a thixotropic composition or compound is one that becomes fluid or less viscous when disturbed or shaken. When the internal shearing force is removed, the viscosity returns to its original xe2x80x9cat-restxe2x80x9d value. Natural synovial fluid is a thixotropic material. A suspending aid incorporated in the fluorocarbon is used to impart the desired thixotropic characteristics. Exemplary suspending aids comprise commercially available surfactants, dispersants, suspending agents, and excipients. In preferred embodiments, fluorocarbon-hydrocarbon diblocks may be used. Which suspending aids are used can be determined utilizing routine testing procedures and will, to some extent, be dependent upon the selected pharmaceutical compound, fluorocarbon, form of preparation and method of administration.
Thus, in accordance with the teachings of the present invention, the disclosed preparations may be formed to be relatively viscous or gelatinous when in an undisturbed state yet are capable of liquid like administration or introduction when exposed to the shearing forces associated with a needle or cannula. The high viscosity of the preparation at rest maintains a substantially homogeneous dispersion of a suspended bioactive agent during storage. Yet, when stress is applied to the compositions such as during administration by injection or other methods, the viscosities are greatly reduced, allowing the thixotropic preparations to act as free flowing liquids. In this low viscosity state, the thixotropic preparations behave similarly to a neat liquid fluorocarbon thereby allowing the preparation to spread throughout the articular cavity or other voids. Following administration to the articular target site and removal of the delivery stress, the thixotropic preparations rapidly return to their original higher or xe2x80x9cat-restxe2x80x9d viscosities.
Those skilled in the art will appreciate that such thixotropic characteristics may improve the lubricating and cushioning properties of the administered material. In addition to providing a lubricating or wetting function, the increase in viscosity following administration causes the compositions to behave as viscoelastic materials at the target site thereby confining any incorporated bioactive agent and cushioning the articulation. The confinement of the drug provides sharply enhanced bioavailability through a reduction in drug migration or drainage. Moreover, the thixotropic preparations of the present invention can alter the local environment of the target site thereby promoting the adhesion and retention of any incorporated agents on the surface of the tissue. The resultant high localized bioavailability provides increased efficacy and substantially reduces undesirable systemic side effects.
Conversely, the fluorocarbons and bioactive preparations of the present invention may be made dilatant in that the viscosity of the material will increase as the shear rate increases. The increase in viscosity upon the application of dynamic force may be used to increase the cushioning effect of the administered fluorocarbon at the times the force on the point of articulation is the greatest. It will be appreciated that fluorocarbons compatible with the present invention may be made dilatant through established techniques such as providing a concentrated suspension of colloidal particles. These concentrated sols may be formed in the same manner as the previously describe sol preparations. Administration is preferably be effected using a larger bore needle or arthroscopically.
In still other preferred embodiments the administered fluorocarbon or bioactive preparation will be in the form of an emulsion. These emulsions may be thixotropic or dilatant as previously described. Except as otherwise provided or as required by context, the term xe2x80x9cemulsionxe2x80x9d shall include liposomes, micelles, microemulsions, reverse emulsions, multiple emulsions and gels. As is well known in the art, fluorocarbon emulsions can be prepared using conventional techniques. U.S. Pat. Nos. 4,865,836, 4,927,623 and 4,987,154 all incorporated herein by reference, disclose the formation of fluorocarbon emulsions suitable for use in the present invention. Preferably, one or more surfactant(s), which may be fluorinated or non-fluorinated, are dispersed in an aqueous phase that may contain other additives. Thereafter, fluorocarbons compatible with the teachings herein are provided as, or as a part of, an oily phase which is added to the aqueous phase, followed by dispersion of the whole utilizing conventional techniques. Of course those skilled in the art will appreciate that other, equally effective techniques may be used to form emulsions compatible with the present invention. In other embodiments reverse emulsions, where the continuous phase is the oil phase and the discontinuous or dispersed phase is the aqueous or polar liquid phase, may be administered to the articular region. Reverse emulsions, micelles, microemulsions and multiple emulsions comprising fluorocarbons are described in co-pending application U.S. Ser. No. 08/487,612 which is incorporated herein by reference. Similarly, hydrocarbon-in-fluorocarbon emulsions suitable for use in the present invention are described in co-pending application U.S. Ser. No. 08/572,859 that is also incorporated herein by reference. Of course bioactive agents may be combined with the emulsions to provide bioactive emulsion preparations in accordance with the teachings herein.
In those cases where the emulsion comprises an aqueous phase, additives may be included to achieve certain, desired effects, such as particle size stability, osmolarity, thermal stability, and the like. Therefore, additives such as mineral salts, buffers, osmotic agents, oncotic agents, anti-oxidants such as alpha-tocopherol, and pharmaceutical and/or nutritive products, chosen according to the application of the emulsion are contemplated, as well as other agents. Hydrophilic bioactive agents may also be added to the aqueous phase of articular compatible emulsions.
Similarly, a variety of surfactants, including fluorinated surfactants may be used to form emulsions in accordance with the present invention. Like additives in the aqueous phase, surfactants are chosen according to the desired properties of the emulsion. Examples of suitable surfactants for use in the present invention include lecithins, polyoxyethylene-polyoxypropylene copolymers, sorbitan polyoxy-ethylenes, phospholipids such as egg-yolk, soy or synthetic lipids, perfluoroalkyl phospholipids and the other synthetic perfluoroalkyl surfactants.
Preferred concentrations of components for selected emulsions or gels that are compatible with the present invention are generally as follows:
from 10 to 120% in weight/volume of an oily phase,
from 0.1 to 10% in weight/volume of surfactant(s), and
the aqueous phase making up the balance.
Microemulsions may be preferably prepared with the following ratios:
from 10 to 120% in weight/volume of an oily phase,
from 3 to 30% in weight/volume of surfactant(s), and
the aqueous phase making up the balance.
In general, fluorocarbon gels will comprise a higher concentration of the continuous oil phase to provide the desired viscosity. For example, fluorocarbon gels suitable for use in the present invention contain up to 98% w/v of the fluorocarbon APF 260, (Air Products) 0.2% w/v F-alkylamidopropyl dimethylamine oxide (surfactant) and distilled water to 100%. As with the other emulsions and liquid fluorocarbons, the gels may comprise bioactive agents or other additives as previously described.
The route of administration may be selected depending on the form of the fluorocarbon or bioactive preparation to be introduced to the articular region. For example, in the case of flowing materials such as liquids, emulsions or gel precursors administration by injection, including intra-articular, is preferred. In this respect, it is contemplated that gel components may be combined and injected in a fluid state and allowed to gel in the target area. It must be reiterated that, whatever the form of the fluorocarbon or bioactive preparation, introduction or administration of the material is not limited to the point of articulation or specific cavities but rather may be anywhere in the articular region. For example, a liquid fluorocarbon may be injected into the tissue or fat immediately adjacent to a tendon to reduce inflammation and provide beneficial lubrication. Similarly, a bioactive preparation may be injected directly into a single bursa in contact with a ligament to deliver oxygen and a pharmaceutical composition to that localized area. In contrast, relatively large volumes of a thixotropic fluorocarbon preparation may be introduced into each of the synovial cavities in and around the selected joint to provide mechanical cushioning and lubrication to relieve the symptoms of osteoarthritis.
Nor is the form of administration limited to specific methods. Any manner of introducing or administering the fluorocarbon or bioactive preparation to the articular region is within the scope of the invention. For example, a preformed fluorocarbon gel carrying high concentrations of oxygen may be introduced to the articular cavity of the knee through conventional surgical techniques. In this vein a solid biocompatible material, such as a lipophilic sponge, may be soaked with a selected fluorocarbon and surgically positioned in the joint to cushion the articular surfaces. Similarly, a dilatant sol comprising prednisone may be administered to the articular cavity of the elbow using arthroscopic techniques well known in the art. It will therefore be appreciated that any techniques for introducing liquids or solids to the appropriate areas of the body are within the scope of the invention.
The bioactive preparations of the present invention are capable of delivering any desired bioactive agent that may be incorporated in the introduced material. Due to the use of fluorocarbons the present invention is particularly useful in delivering lipophilic agents which otherwise exhibit poor bioavailability. In preferred embodiments, lipophilic agents are combined with the chosen fluorocarbon to form a molecular solution or with the disperse phase in conventional fluorocarbon emulsions either prior to or after formation. Similarly, the fluorophilic agent may be combined with a fluorocarbon to provide a sol or suspension. Conversely, water soluble bioactive agents may be combined with the continuous phase of regular emulsions or the disperse phase in reverse emulsions. As previously defined, the term xe2x80x9cbioactive agentxe2x80x9d means any pharmaceutical compound or composition, including diagnostic and therapeutic agents, living cells or microorganisms and physiologically acceptable gases such as oxygen or nitric oxide, which may be administered to an animal to treat a disorder. Preferred bioactive agents include hydrophilic drugs with solubility in water and lipophilic agents.
As discussed, any bioactive agent that may be incorporated in the bioactive preparations of the present invention may be used. Yet, some indication as to the general ability of an individual bioactive agent to be incorporated in a fluorocarbon (and in what form) may be derived from the measured value of its lipophilicity. The convention is to measure and report the lipophilicity of a bioactive agent using the log of the octanol/water partition coefficient (Log PO/W) In this system increasing lipophilicity corresponds to higher Log PO/W values. Preferably, lipophilic bioactive agents incorporated in the present invention will have a Log PO/W greater than about 0.5. More preferably the lipophilic bioactive agents will have a Log PO/W greater than about 2.0. As those skilled in the art will appreciate, values such as these indicate that a compound has limited solubility in an aqueous environment and are difficult to deliver using conventional vehicles. The octanol/water partition coefficients of several exemplary lipophilic bioactive agents compatible with the teachings of the present invention, are reproduced below in Table 1.
Preferably, the bioactive preparations of the present invention incorporate less than about 50% w/v of a therapeutic or diagnostic agent. Typically, diagnostic agents will be incorporated at higher concentrations. The precise amount of bioactive agent incorporated in the preparations of the present invention is dependent upon the agent of choice, the required dose, and the form of the drug actually used for incorporation. Those skilled in the art will appreciate that such determinations may be made by using well-known pharmacological techniques in combination with the teachings of the present invention. Preferred bioactive agents comprise hydrophilic and lipophilic anti-inflammatories, antibiotics, antivirals, antihistimics, anti-neoplastics, anesthetics, enzymes, active principals, nucleic acids, genetic material, viral vectors, immunoactive agents, imaging agents, immunosuppressive agents, peptides, proteins, physiological gases and combinations thereof.
Further exemplary embodiments of the present invention comprise anti-inflammatory agents such as the glucocorticosteroids (i.e. cortisone, prednisone, prednisolone, dexamethasone, betamethasone, beclomethasone diproprionate, triamcinolone acetonide, flunisolide) and non-steroidal anti-inflammatory drugs, xanthines (i.e. theophylline, caffeine), chemotherapeutics (i.e. cyclophosphamide, lomustine, methotrexate, cisplatin, carboxy platin, taxane derivatives), antibiotics (i.e. aminoglycosides, penicillins, cephalosporins, macolides, quinolones, tetracyclines, chloramphenicol), B2-agonists (i.e. adrenaline, isoprenaline, salmeterol, salbutamol, terbutaline, formoterol) and surfactants.
Still other exemplary embodiments include xcex1/xcex2adrenergic blockers (i.e. Normodyne, Trandate), calcium channel blockers, inotropic agents, anesthetics (i.e. morphine). Most preferred agents include glucocorticosteroids, non-steroidal anti-inflanmmatory drugs, taxane derivatives (i.e. Taxol, Taxotere) and the base forms of drugs typically administered as the salt derivative (i.e. Gentamicin, Ciprofloxacin). In accordance with the present invention, those skilled in the art will appreciate that various forms (different pharmaceutically acceptable salts, prodrugs, etc.) of these compounds may be used to modify the therapeutic index of the bioactive agents. Accordingly, the foregoing lists of bioactive agents are exemplary only and not intended to be limiting. As is well known, the proper amount of bioactive agent and the timing of the dosages may be determined for the preparations in accordance with already-existing information and without undue experimentation.
As alluded to earlier, the selected bioactive agent may be a radioactive compound. Such agents could be incorporated in bioactive preparations useful for performing radiation synovectomy. Conventional synovectomy is surgical removal of the damaged synovial membrane, typically to treat sufferers of rheumatoid arthritis, which is painful and often ineffective. Radiation synovectomy is ablation of the damaged synovial membrane using radioactive material injected into the afflicted area. Although this method has proven effective, it suffers from the fact that aqueous radioactive material rapidly leaks from the synovial cavities into the interstitial spaces and can become concentrated in the lymph nodes providing unacceptable radiation dosages to sites distant from the afflicted area. The present invention overcomes these drawbacks through hydrophilic retention in the synovial space and prolonged target specificity. Accordingly, alpha and/or beta emitters could be used to form bioactive preparations, preferably thixotropic, as described herein and introduced into the desired synovial cavity. Destruction of the inflamed synovium is effected without surgery or the systemic side effects and lymphatic concentration presently observed.
It will further be appreciated by those skilled in the art that the fluorocarbons and bioactive preparations of the present invention may be sterilized, for example, by heat, irradiation, ultrafiltration or combinations of any of these or equivalent techniques. The fluorocarbons and high bioavailability bioactive preparations of the present invention may advantageously be supplied to the physician in a sterile prepackaged form. More particularly, the formulations may be supplied as stable, preformed emulsions, suspensions gels, etc., ready for administration or as separate, ready to mix components. Typically, when supplied as components the fluorocarbon, optionally incorporating a bioactive agent, will be packaged separately. This bioactive dispersion or suspension could then be mixed, generally by the physician or in a hospital lab, with a sterile polar liquid phase (i.e. water) to form an emulsion, gel reverse emulsion, etc. of the present invention. In such cases, the polar liquid phase could be supplied either by the manufacturer or the final user.
Finally it will be appreciated that the methods of the present invention are not limited to use in human beings and may advantageously be used on any organism possessing articulations. For instance, the methods disclosed herein may be used on race horses to reduce inflammation and cushion the knee and ankle joints. Similarly, other farm livestock and domestic animals may benefit from the veterinary applications of the disclosed methods.

Use of fluorocarbons for diagnosis and treatment of articular disorders


A process for cleaning an electrically conducting surface (3) by arranging for the surface to form the cathode of an electrolytic cell in which the anode (1) is maintained at a DC voltage in excess of 30V and an electrical arc discharge (electro-plasma) is established at the surface of the workpiece by suitable adjustment of the operating parameters, characterized in that the working gap between the anode and the cathode is filled with an electrically conductive medium consisting of a foam (9) comprising a gas/vapor phase and a liquid phase. The process can be adapted for simultaneously coating the metal surface by including ions of the species required to form the coating in the electrically conductive medium. Apparatus for carrying out the process is also disclosed and, in particular, an anode assembly (1) which comprises a perforated anode plate (2) which is in communication with a chamber (4) adapted to receive a flow of a liquid electrolyte, means to supply the liquid electrolyte to the chamber, and means (7) to convert the liquid electrolyte received in the chamber into a foam.

The present invention relates to an improved process and apparatus for cleaning and/or coating metal surfaces using electro-plasma technology.
Metals, notably, steel in its many forms, usually need to be cleaned and/or protected from corrosion before being put to their final use. As produced, steel normally has a film of mill-scale (black oxide) on its surface which is not uniformly adherent and renders the underlying material liable to galvanic corrosion. The mill-scale must therefore be removed before the steel can be painted, coated or metallised (e.g. with zinc). The metal may also have other forms of contamination (known in the industry as xe2x80x9csoilxe2x80x9d) on its surface including rust, oil or grease, pigmented drawing compounds, chips and cutting fluid, and polishing and buffing compounds. All of these must normally be removed. Even stainless steel may have an excess of mixed oxide on its surface which needs removal before subsequent use.
Traditional methods of cleaning metal surfaces include acid pickling (which is increasingly unacceptable because of the cost and environmental problems caused by the disposal of the spent acid); abrasive blasting; wet or dry tumbling; brushing; salt-bath descaling; alkaline descaling and acid cleaning. A multi-stage cleaning operation might, for example, involve (i) burning-off or solvent-removal of organic materials, (ii) sand- or shot-blasting to remove mill-scale and rust, and (iii) electrolytic cleaning as a final surface preparation. If the cleaned surface is to be given anti-corrosion protection by metallising, painting or plastic coating, this must normally be done quickly to prevent renewed surface oxidation. Multi-stage treatment is effective but costly, both in terms of energy consumption and process time. Many of the conventional treatments are also environmentally undesirable.
Electrolytic methods of cleaning metal surfaces are frequently incorporated into processing lines such as those for galvanising and plating steel strip and sheet. Common coatings include zinc, zinc alloy, tin, copper, nickel and chromium. Stand-alone electrolytic cleaning lines are also used to feed multiple downstream operations. Electrolytic cleaning (or xe2x80x9celectro-cleaningxe2x80x9d) normally involves the use of an alkaline cleaning solution which forms the electrolyte while the workpiece may be either the anode or the cathode of the electrolytic cell, or else the polarity may be alternated. Such processes generally operate at low voltage (typically 3 to 12 Volts) and current densities from 1 to 15 Amps/dm2. Energy consumptions thus range, from about 0.01 to 0.5 kWh/m2. Soil removal is effected by the generation of gas bubbles which lift the contaminant from the surface. When the surface of the workpiece is the cathode, the surface may not only be cleaned but also xe2x80x9cactivatedxe2x80x9d, thereby giving any subsequent coating an improved adhesion. Electrolytic cleaning is not normally practicable for removing heavy scale, and this is done in a separate operation such as acid pickling and/or abrasive-blasting.
Conventional electrolytic cleaning and plating processes operate in a low-voltage regime in which the electrical current increases monotonically with the applied voltage. Under some conditions, as the voltage is raised, a point is reached at which instability occurs and the current begins to decrease with increasing voltage. The unstable regime marks the onset of electrical discharges at the surface of one or other of the electrodes. These discharges (xe2x80x9cmicro-arcsxe2x80x9d or xe2x80x9cmicro-plasmasxe2x80x9d) occur across any suitable non-conducting layer present on the surface, such as a layer of gas or vapour. This is because the potential gradient in such regions is very high.
GB-A-1399710 teaches that a metal surface can be cleaned electrolytically without over-heating and without excessive energy consumption if the process is operated in a regime just beyond the unstable region, the xe2x80x9cunstable regionxe2x80x9d being defined as one in which the current decreases with increasing voltage. By moving to slightly higher voltages, where the current again increases with increasing voltage and a continuous film of gas/vapour is established over the treated surface, effective cleaning is obtained. However, the energy consumption of this process is high (10 to 30 kWh/m2) as compared to the energy consumption for acid pickling (0.4 to 1.8 kWh/m2).
SU-A-1599446 describes a high-voltage electrolytic spark-erosion cleaning process for welding rods which uses extremely high current densities, of the order of 1000 A/dm2, in a phosphoric acid solution.
SU-A-1244216 describes a micro-arc cleaning treatment for machine parts which operates at 100 to 350 V using an anodic treatment. No particular method of electrolyte handling is taught.
Other electrolytic cleaning methods have been described in GB-A-1306337 where a spark-erosion stage is used in combination with a separate chemical or electro-chemical cleaning step to remove oxide scale; in U.S. Pat. No. 5,232,563 where contaminants are removed at low voltages from 1.5 to 2V from semi-conductor wafers by the production of gas bubbles on the wafer surface which lift off contaminants; in EP-A-0657564, in which it is taught that normal low-voltage electrolytic cleaning is ineffective in removing grease, but that electrolytically oxidisable metals such as aluminum may be successfully degreased under high voltage (micro-arc) conditions by acid anodisation.
The use of jets of electrolyte situated near the electrodes in electrolytic cleaning baths to create high speed turbulent flow in the cleaning zone is taught for example in JP-A-08003797 and DE-A-4031234.
The electrolytic cleaning of radioactively contaminated objects using a single jet of electrolyte without overall immersion of the object, is taught in EP-A-0037190. The cleaned object is anodic and the voltage used is between 30 to 50V. Short times of treatment of the order of 1 sec are recommended to avoid erosion of the surface and complete removal of oxide is held to be undesirable. Non-immersion is also taught in CA-A-1165271 where the electrolyte is pumped or poured through a box-shaped anode with an array of holes in its base. The purpose of this arrangement is to allow a metal strip to be electro-plated on one side only and specifically to avoid the use of a consumable anode.
DE-A-3715454 describes the cleaning of wires by means of a bipolar electrolytic treatment by passing the wire through a first chamber in which the wire is cathodic and a second chamber in which the wire is anodic. In the second chamber, a plasma layer is formed at the anodic surface of the wire by ionisation of a gas layer which contains oxygen. The wire is immersed in the electrolyte throughout its treatment.
EP-A-0406417 describes a continuous process for drawing copper wire from copper rod in which the rod is plasma cleaned before the drawing operation. The xe2x80x9cplasmatronxe2x80x9d housing is the anode and the wire is also surrounded by an inner co-axial anode in the form of a perforated U-shaped sleeve. In order to initiate plasma production the voltage is maintained at a low but unspecified value, the electrolyte level above the immersed wire is lowered, and the flow-rate decreased in order to stimulate the onset of a discharge at the wire surface.
Whilst low voltage electrolytic cleaning is widely used to prepare metal surfaces for electro-plating or other coating treatments, it cannot handle thick oxide deposits such as mill-scale without an unacceptably high expenditure of energy. Such electrolytic cleaning processes must normally be used, therefore, in conjunction with other cleaning procedures in a multi-stage operation.
WO-A-97/35052 describes an electrolytic process for cleaning electrically conducting surfaces using an electro-plasma (arc discharge) in which a liquid electrolyte flows through one or more holes in an anode held at a high DC voltage and impinges on the workpiece (the cathode) thus providing an electrically conductive path. The system is operated in a regime in which the electrical current decreases or remains substantially constant with increase in the voltage applied between the anode and the cathode and in a regime in which discrete bubbles of gas and/or vapour are present on the surface of the workpiece during treatment.
WO-A-97/35051 describes an electrolytic process for cleaning and coating electrically conducting surfaces which is similar to the process as described in WO-A-97/35052 except that the anode comprises a metal for metal-coating of the surface of the workpiece.
In operating the processes of WO-A-97/35051 and WO-A-97/35052 an arc discharge or electro-plasma is formed on the surface of the workpiece and is established within the bubble layer. The plasma has the effect of rapidly removing mill-scale and other contaminants from the surface of the work-piece, leaving a clean metal surface which may also be passivated (resistant to further oxidation).
If, additionally, the anode is constructed from a non-inert material, such as a non-refractory metal, then metal atoms are transferred from the anode to the cathode, providing a metal coating on the cleaned surface.
Coating may also be achieved under the regime of operation described above by using an inert anode and an electrolyte containing ions of the metal to be coated as described in WO-A-99/15714. In this case the process becomes a special form of electroplating, but because it occurs at high voltage in the presence of an arc discharge the plating is faster than normal electroplating and the coating has better adhesion to the substrate metal.
WO-A-98/32892 describes a process which operates essentially in the manner described above but uses a conductive gas/vapour mixture as the conductive medium. This gas/vapour mixture is generated within a two- or multi-chambered anode before being ejected into the working gap through holes in the anode. The gas/vapour mixture is generated by heating an aqueous electrolyte within the anode chambers to boiling point or above, and the anode chambers may be heated either by the main electric current or by independent electrical heaters.
We have now developed an improved process in which an electro-plasma (arc discharge) is employed to clean and/or to apply a metal coating to an electrically conductive surface, for example, steel, in which the electrically conductive pathway is provided by a foaming electrolyte which fills the space between the anode and the cathode and provides advantages with respect to lower power consumption, more uniform surface treatment and greater latitude in the size of the gap between anode and workpiece.
Accordingly in a first aspect the present invention provides a process for cleaning an electrically conducting surface by arranging for the surface to form the cathode of an electrolytic cell in which the anode is maintained at a DC voltage in excess of 30V and an electrical arc discharge (electro-plasma) is established at the surface of the workpiece by suitable adjustment of the operating parameters, characterised in that the working gap between the anode and the cathode is filled with an electrically conductive medium consisting of a foam comprising a gas/vapour phase and a liquid phase.
In a second aspect the present invention provides a process for coating an electrically conducting surface by arranging for the surface to form the cathode of an electrolyte cell in which the anode is maintained at a DC voltage in excess of 30V and an electrical arc discharge (electro-plasma) is established at the surface of the workpiece by suitable adjustment of the operating parameters, characterised in that the working gap between the anode and the cathode is filled with an electrically conductive medium containing positive ions of the (one or more) species required to form the coating and consisting of a foam comprising a gas/vapour phase and a liquid phase.
In a further aspect the present invention provides an anode assembly which comprises a perforated anode plate which is in communication with a chamber adapted to receive a flow of liquid electrolyte, means to supply the liquid electrolyte to the said chamber and means to convert the liquid electrolyte received in the said chamber into a foam.
In a still further aspect the present invention provides apparats for cleaning and/or coating an electrically conducting surface which comprises
(i) a sealed treatment zone having one or more anode assemblies as described above suitably disposed with respect to the surface or surfaces to be treated;
(ii) means to continuously move a workpiece to be treated through the treatment zone between the anode assemblies,
(iii) means to open and close the treatment zone, and
(iv) means to control the supply of a foam to and removal of the foam from the treatment zone.
The foam may suitably be produced by boiling an aqueous electrolyte, although other methods of foam production may also be used. If the foamed electrolyte contains only ions of metals that react with water, such as sodium or potassium, the workpiece is cleaned. If other metal ions are present they will, additionally, be deposited to form a coating on the cleaned workpiece.
The operating parameters that can be adjusted to provide the necessary conditions for the establishment of an electro-plasma include; the voltage; the chemical composition of the foam; the density of the foam; the temperature of the foam; the rate at which the foam is supplied to the working gap; and the width of the working gap (the distance between the anode and the cathode).
This invention also provides for an anode assembly containing one or more heated chambers in which an electrolyte may be converted into a foam before being injected into the working gap, together with means for removing the foam from the working gap, filtering, rejuvenating and recirculating spent foam.
This invention further provides for the containment of the foam within the working gap by means of an enclosure through which the workpiece can move without significant leakage of foam.
The present invention represents an improvement on the prior art methods of cleaning and/or coating in that the conductive medium between the anode and cathode is neither a liquid electrolyte nor a gas/vapour mixture, but an electrically conductive foam which fills the entire working gap. Generally, the term xe2x80x9cfoamxe2x80x9d refers to a medium containing at least 20% by volume, preferably 30% by volume of gas and/or vapour in the form of bubbles or cells, the remainder of the medium being liquid. More preferably at least 50% by volume of the foam is gas and/or vapour in the form of bubbles or cells. The foam used in the present invention is generally formed from an aqueous electrolyte.
Such a foam may conveniently be formed by boiling an aqueous electrolyte such as a solution of metal salts in water. Foaming agents and stabilisers may be added to optimise the properties of the foam, in terms of foam density, and bubble or cell size, for example.
However, other methods of foam production may also be employed, such as the incorporation in an electrolyte of thermally-activated blowing agents; the release of pressure from a liquid electrolyte super-saturated with a volatile substance (as when a bottle of champagne is shaken and opened); the mechanical injection of a liquid electrolyte with steam or another vapour or gas; the mechanical xe2x80x98whippingxe2x80x99 of a relatively viscous electrolyte; or the combination of two liquid streams which react together chemically to produce a gas causing the mixture to xe2x80x98blowxe2x80x99 into a foam; or other means known in the art for creating liquid foams.
The use of a foam as the conductive medium has the following advantages over liquid electrolytes.
a) The foam, by virtue of its gas/vapour content, has a lower conductivity than the corresponding liquid electrolyte. This reduces the current flow during cleaning/coating and thus reduces power consumption and improves the economics of the process.
b) Because the bubble size and overall gas/vapour content of the foam may be varied, it provides an additional means of control over the power consumption of the process and the intensity of the process. This in turn permits control over the smoothness or roughness (the topography or profile) of the cleaned or coated surface.
c) Since the foam fills the entire working gap, electrical conduction involves the whole surface of the anode and the whole surface of the work-piece under the anode. This contrasts with the use of a liquid electrolyte where independent streams of electrolyte impinge on the work-piece. The use of foam thus improves the uniformity of the process, both as regards the treated surface and (where applicable) the erosion of any sacrificial anode. The current flow is also more uniform being unaffected by the interruption of liquid streams which can occur when a liquid electrolyte is used and, for example, anode holes become blocked.
d) When liquid streams impinge on the work-piece there is a limit to the size of the working gap that can be used in practice because the liquid streams break up and destroy the conductive pathway. This does not occur when foam fills the working gap uniformly, so that both smaller and larger working gaps can be used. This has great practical importance in, for example, the on-line cleaning of steel sheet where it is not practicable to maintain a uniform working gap. The greater tolerance of the foam method towards variations in the working gap provides a practical advantage under such conditions.
The advantages listed above are not intended to be exhaustive but to illustrate that the use of foam rather than liquid or gas/vapour as the conductive medium represents a genuine advance in the technology of electro-plasma cleaning and coating technology.
The foam may conveniently be produced by injecting an aqueous electrolyte into the working gap through holes in a heated anode so that the electrolyte boils and foams in the process. Preferably, the electrolyte is heated to its boiling point before passing into the working gap.
This advance foaming may be suitably be achieved by arranging for the anode assembly to contain one or more heated chambers through which the electrolyte passes in succession, the chambers being separated by perforated plates to allow passage of the electrolyte from one chamber to another and finally into the working gap.
The chambers themselves may be heated by the operating current passing through the anode but preferably by one or more independent heaters situated within the chamber(s).
In an alternative embodiment of the invention, a voltage is applied to the anode and an electrolyte is injected into the working gap at any convenient point other than through holes in the anode. The electrolyte is converted into foam in the working gap by being caused to boil by its own resistive heating (or otherwise) and contact with the hot surfaces of anode and/or cathode. Preferably, however, the electrolyte is converted into foam by suitable means outside the working gap and then injected thereinto.
Whether the foam is introduced into the working gap through holes in the anode or otherwise, it is necessary to provide means for the used foam to be removed from the working region. If the system is open, this will occur naturally as foam runs off the workpiece into a collecting tank. If the working gap is enclosed, an exhaust port is provided to drain away used foam. In most cases the used foam can be condensed to liquid, cleaned, filtered, rejuvenated (e.g. by adjustment of pH or salt concentration), reheated, and recirculated.
The process of the present invention is operated in a manner such that an electrical arc discharge (electro-plasma) is established at the surface of the workpiece. This is achieved by suitable adjustment of the operating parameters such as the voltage, the inter-electrode separation, the electrolyte flow rate into the working zone (whether in the form of liquid or foam) and the electrolyte temperature. It may also be advantageous to initiate the plasma discharge in an aqueous (non-foam) environment and then to introduce the foamed electrolyte into the working gap. For example, in a closed working chamber (see below) a pool of liquid electrolyte may be allowed to form between the anode and the workpiece (cathode) which provides a conductive bridge for the initiation of the process and the establishment of the desired plasma regime.
A further embodiment of the invention is achieved by arranging for the anode, and the area of the workpiece undergoing treatment, to lie within a sealed enclosure which has the effect of containing the foam. This makes it easier to ensure that the foam fully fills the working gap at all times and allows the foam-injection rate to be reduced. It also allows a pressure somewhat higher than atmospheric pressure to be maintained in the working region. An elevated pressure has the effect of reducing bubble size both in the foam and on the workpiece surface and can produce smoother cleaned or coated surfaces.
Since one important application of the invention is its use in continuous processes, where the workpiece moves continuously through the treatment zone, the enclosure must allow the workpiece to move while maintaining a reasonable seal. This can be achieved by using flexible rubber seals around the moving workpiece.
The cleaning effects achieved by the process of the present invention are believed to occur largely (though not exclusively) through micro-zonal melting of the workpiece surface. Small bubbles of hydrogen and steam form on the cathode and undergo electrical breakdown due to the high potential gradient developed across them. As each bubble undergoes breakdown, a micro-arc forms briefly, raising the temperature of the surface within a micro-region (a region measured in microns) and causing localised melting of the surface. That is, the micro-zonal melting of the surface occurs through microelectric plasma discharges between positive ions in the foam which are concentrated near to the surface of the workpiece and the surface of the workpiece. After the micro-discharge has occurred, the surface rapidly solidifies again.
The process of the present invention may be used in various ways to clean or coat one side or both sides of an article simultaneously by the use of multiple anodes suitably positioned with respect to the workpiece. Any shape or form of workpiece such as sheet, plate, wire, rod, tube, pipe or complex shapes may be treated, using if necessary shaped anode surfaces to provide a reasonably uniform working distance. Both static and moving workpieces may be treated in accordance with the present invention.
The present invention will be further described with reference to FIGS. 1 to 4 of the accompanying drawings, in which:

Process and apparatus for cleaning and/or coating metal surfaces using electro-plasma technology