Patent Application
20060008500
1. Field of the Invention
The invention relates generally to implantable medical devices and, more particularly, to implantable sensors having a biocompatible coating that controls the growth of tissue, or inhibits the growth of tissue, over and around the sensor.
2. Description of Related Art
Human implantable sensors may be used to gather important information about the body's internal environment on a regular basis. Pressure inside an artery, fluid flow inside an artery, body temperature, posture sensing and monitoring of chemical changes are among the different types of information that could be gathered by an implantable sensor.
A problem exists in that any sensor that is implanted into living tissue is subject to tissue growth over and around it. Some tissue growth may be desired in order to embed the sensor and make it a more integral part of the body. However, the sensor's calibration and sensitivity can be adversely effected by different factors of this tissue growth including, but not limited to, the type of tissue that grows over the sensor, the thickness, and the evenness of the tissue growth. For example, in the case of a pressure sensor, the sensitivity of the sensor is affected by the thickness of the tissue while sensor drift is affected by the tension exerted on the sensor by the tissue. This tension, in turn, leads to additional pressure bias that affects the accuracy of the pressure measurements provided by the sensor.
Those skilled in the art have recognized a need for providing a more consistent and predictable growth process in relation to implanted sensors to thereby mitigate the problem of unpredictable tissue growth and its impact on the sensitivity and calibration of sensors. The need for inhibiting tissue growth to further mitigate the foregoing problems has also been recognized. The invention fulfills these needs and others.
Briefly, and in general terms, the invention is directed to implantable sensors having a biocompatible coating that either controls the growth of tissue, or inhibits the growth of tissue, over and around the sensor. As used herein, “inhibit” means to substantially prevent the growth or formation of tissue. “Control” means to promote the growth or formation of a substantially even layer of tissue.
In one aspect, all or a portion of a sensor surface is covered with a biocompatible coating formed at least partially of a biomaterial matrix having properties that promote a substantially even growth of tissue cells over the surface of the coating. Additional materials, such as growth factors, agents that recruit endogenous stem cells and cell adhesion motif arginine, glycine, aspartic acid may be included in the coating. Also, autologous cells may be added to the coating prior to implantation.
In another aspect, all or a portion of a sensor surface is textured in order to promote even tissue growth over the surface. The texture may be provided by etching or abrading the surface of the interface.
In other aspects, all or a portion of a sensor surface is covered with a coating having properties that inhibit the growth of tissue. These coatings may include a biomaterial, such as polytetraflouroethylene (PTFE) and polyethylene glycol (PEG) or a biomaterial matrix having an active component that imparts growth-inhibiting properties to the coating.
These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings which illustrate by way of example the features of the invention.
a is a cross section of the sensor of
b is a cross section of the coated sensor of
c is a cross section of the coated sensor of
a is a cross section of the sensor of
b is a cross section of the coated sensor of
c is a cross section of the coated sensor of
The invention is directed to implantable sensors which are coated with a biocompatible coating that either controls or inhibits the growth of tissue over and around the sensor. The sensor may be, for example, anyone of a pressure sensor, posture sensor, chemical sensor, temperature sensor or flow sensor that is introduced temporarily or permanently into a mammal for the prophylaxis or therapy of a medical condition and that is designed to monitor physiological activity within the body. These sensors may be introduced subcutaneously, percutaneously or surgically to rest within an organ, tissue or lumen of an organ, such as arteries, veins, ventricles or atrium of the heart.
With reference to
The sensor 10 may be included as part of an implanted device, such as the lead of a cardiac rhythm management device, in which case the data gathered by the sensor is transferred to the device through a hardwire electrical connection. The sensor 10 may be configured as a wireless device, in which case the sensor interface 14 may include a transmission device for transmitting the data gathered by the sensor to a receiver remote from the sensor. For example, the sensor interface 14 may be formed of an optically compatible material that allows for certain wavelength of intra-red light to pass efficiently. In this configuration, the biocompatible coating not only serves to maintain sensor calibration and sensitivity, it also protects against interference that uneven tissue growth may impart on data transmission between transmitter and receiver. A wireless sensor may, for example, be mounted to a stent to facilitate implantation.
While the sensor 10 shown in
With reference to
In one embodiment, the biocompatible coating consists of a biomaterial matrix favorable to tissue growth allowing for formation of a substantially even neointimal layer of tissue over the sensor. The biomaterial matrix comprises a polymer, oligomer or co-polymer for coating the sensor from various types and sources, including, natural or synthetic polymers, which are at least biocompatible. The polymers may also be biodegradable and/or bioabsorbable. For example, a natural polymer such as an extracellular matrix (ECM) material may be used, including, for example, intestine submucosa (SIS) and urinary bladder matrix (UBM) substances. Such ECMs are composed of three major classes of biomolecules including structured proteins, e.g., collagen and elastin, specialized proteins, e.g., fibrillin, fibronectin and laminin and proteoglycans. Proteoglycans are composed of a protein core to which is attached long chains of repeating disaccharide units termed of glycosaminoglycans (GAGs) forming extremely complex high molecular weight components of the ECM. Independent of their inclusion in the ECMs, both proteoglycans and proteins, including collagen, fibrin, elastin, fibrillin, fibronectin, and laminin, may themselves be used as the polymer. Another example of a natural polymer which may be used as a coating is phosphytidyl choline.
Synthetic polymers may be selected from polyhydroxyvalerate, poly(L)lactic acid, polycaprolactone, polylactide-co-glycolide, polyhydroxybutyrate, polyhydroxybutyrate-co-valerate, polydioxanone, polyorthoesters, polyanhydrides, polyacetic or polyglycolic acid and derivatives thereof, poly(D,L)lactic acid, polyglycolic acid-co-trimethylene carbonate, polysebacic acid, polylactic-co-sebacic acid, polyglycolic-co-sebacid acid, polyphosphoesters, polyphosphoester urethanes, polyamino acids, such as polylysine, lactic/glycolic acid copolymers, and ion exchange resins such as sulfonated polytetrafluorethylene, or combinations thereof; cyanoacrylates, polytrimethylene carbonate, polyiminocarbonate, copolyether-esters (e.g., PEO/PLA), polyalkylene oxalates and polyphosphazenes. Polymers with a relatively low chronic tissue response such as polyurethanes, silicones, and polyesters could be used.
Other polymers could also be used if they can be dissolved and cured or polymerized on the sensor such as polyolefin, polyisobutylene and ethylene-alphaolefin copolymers; acrylic polymers and copolymers, vinyl halide polymers and copolymers, such as polyvinyl chloride; polyvinyl ethers, such as polyvinyl methyl ether; polyvinylidene halides, such as polyvinylidene fluoride and polyvinylidene chloride; polyacrylonitrile; polyvinyl ketones; polyvinyl aromatics, such as polystyrene; polyvinyl esters, such as polyvinyl acetate; copolymers of vinyl monomers with each other and olefins, such as ethylene-methyl methacrylate copolymers, acrylonitrile-styrene copolymers, ABS resins, and ethylene-vinyl acetate copolymers; polyamides, such as Nylon 66 and polycaprolactam; alkyd resins; polycarbonates; polyoxymethylenes; polyimides; polyethers; epoxy resins; rayon and rayon-triacetate.
The polymer coating may be applied to the sensor is any one of several ways known in the art including those disclosed in the following U.S. patents, the disclosures of which are hereby incorporated by reference: U.S. Pat. No. 6,713,119, titled “Biocompatible Coating for a Prosthesis and a Method of Forming the Same,” U.S. Pat. No. 6,673,385, titled “Methods for Polymeric Coating Stents,” U.S. Pat. No. 6,616,765, titled “Apparatus and Method for Depositing a Coating onto a Surface of a Prosthesis,” U.S. Pat. No. 6,555,157, titled “Method for Coating an Implantable Device and System for Performing the Method,” U.S. Pat. No. 6,544,582, titled “Method and Apparatus for Coating an Implantable Device” and U.S. Pat. No. 6,506,437, titled “Methods of Coating an Implantable Device Having Depots Formed in a Surface Thereof.”
In another embodiment, the biocompatible coating includes a biomaterial matrix having an added growth factor, agent, cytokine or the like, which stimulates local cell growth to promote a substantially even tissue growth. The coating is preferably formed to provide a sustained release of the agent. The biomaterial matrix may be either a natural or synthetic polymer like those previously listed. The added growth factor may include one or more of vascular endothelial cell growth factor (VEGF) and isoforms, basic fibroblast growth factor (bFGF), platelet-induced growth factor (PDGF), transforming growth factor beta (TGF.b), acidic fibroblast growth factor (aFGF), osteonectin, angiopoietin 1, angiopoietin 2, insulin-like growth factor (IGF), platelet-derived growth factor AA (PDGF-AA), platelet-derived growth factor BB (PDGF-BB), platelet-derived growth factor AB (PDGF-AB), granulocyte-macrophage colony-stimulating factor (GM-CSF), and the like, or functional fragments thereof.
In another embodiment, the biocompatible coating includes a biomaterial matrix having an added agent, cytokine or the like, which recruits endogenous stem cells to promote a substantially even tissue growth. The coating is preferably formed to provide a sustained release of the agent. The biomaterial matrix may be either a natural or synthetic polymer like those previously listed. The added agent may include one or more of granulocyte colony-stimulating factor (G-CSF), stem cell factor (SCF-1), stromal-derived factor (SDF-1), insulin-like growth factor (IGH) or hepatocyte growth factor (HGF).
In another embodiment, the biocompatible coating includes a biomaterial matrix having attached thereto a cell adhesion motif arginine, glycine, aspartic acid (RGD), which is a ligand for integrin cell adhesion receptors. RGD recruits the adhesion of cells and thus forms a type of neointimal layer of endothelia cells to thereby promote a substantially even tissue growth. The biomaterial matrix may be either a natural or synthetic polymer like those previously listed.
In each of the preceding three embodiments, the biocompatible coating, i.e., biomaterial matrix plus added growth factor, agent and/or RGD, may be formed and applied to the sensor is any one of several ways known in the art including those disclosed in the previously cited U.S. patents and the following U.S. patents, the disclosures of which are also hereby incorporated by reference: U.S. Pat. No. 6,743,462, titled “Apparatus and Method for Coating Implantable Devices,” U.S. Pat. No. 6,716,444, titled “Barriers for Polymer-Coated Implantable Medical Devices and Method for Making the Same” and U.S. Pat. No. 6,712,845, titled “Coating for a Stent and a Method of Forming the Same.”
In another embodiment, the biocompatible coating is formed to provide a sustained release of an active component that inhibits tissue growth. The coating is formed of a biomaterial matrix, like those previously listed, and an active component. The active component may include, for example, a sirolimus or a steroid. The coating may be formed and applied to the sensor in any one of the ways described in the previously cited U.S. patents.
Alternatively, the active component may include an anti-thrombotic substance and an anti-inflammatory substance. Possible anti-thrombotic substances include heparin, sodium heparin, low molecular weight heparin, hirudin, argatroban, forskolin, vapiprost, prostacyclin and prostacyclin analogs, D-phe-pro-arg-chloromethylketone, dipyridamole, glycoprotein IIb/IIa platelet membrane receptor antibody, and recombinant hirudin. Possible anti-inflamatory substance includes aspirin, diclofenac, etodolac, ibuprofen, ketoprofen, ketorólac, nabumetone, naproxen, oxaprozin, clobetasol, diflucortolone, flucinolone, halcinolonide, halobetasol, dexamethasone, betamethasone, corticol, cortisone, prednisone, and prednisolone.
In another configuration, instead of the anti-thrombotic substance of the active component being released, the sensor is coated with an anti-thrombogenic material which is not substantially released from the surface. Such anti-thrombogenic coatings can be made from either an active thrombin inhibitor, typically heparin, a heparin derivative, or a heparin analog, or can be made from a passively thromboresistant material, such as a hydro-gel, or any combination of active and passive thromboresistant material. Examples of useful hydro-gels include poly-ethylene oxide, albumin, hydrophilic poly-(meth)acrylates, and hydrophilic poly-urethanes. In another embodiment, an anti-thrombotic substance may also be releasably contained with the anti-inflammatory substance in the anti-thrombogenic coating. Details of these active components are disclosed in U.S. Patent Application Publication No. 20010007082, titled “Device and Active Component for Inhibiting Formation of Thrombus-Inflammatory Cell Matrix,” which is hereby incorporated by reference.
In another embodiment, the biocompatible coating is a biomaterial having properties that substantially inhibit growth of tissue cells over its surface. The biomaterial may be polytetraflouroethylene (PTFE) or polyethylene glycol (PEG). In another configuration, the biomaterial is formed of an anti-thrombogenic material, such as those described above. The material may be applied to the sensor in any one of several ways known in the art.
In another embodiment, substantially even tissue cell growth is promoted by texturing portions of the sensor. As used herein, a “textured” surface includes a surface that is roughened, unsmooth or uneven. For example, metallic portions of the sensor may be textured by etching or abrading the surface of the metal. Such texturing is intended to promote cell adhesion to the surface of the metal which will lead to the formation of a neointimal layer of endothelial cells and ECM which then inhibits the formation of thrombosis or other potential fibrotic responses.
In another embodiment, the biocompatible coating includes a biomaterial matrix that is applied during the manufacturing of the sensor (using known methods or those method described in the U.S. patents previously incorporated by reference) and an additive including autologous cells that are added to the matrix after the manufacturing process and at a pre-defined time prior to actual implantation of the sensor in the body. The autologous cells may be added to the biomaterial matrix by any standard method.
In one such embodiment, the additive includes disassociated autologous cells which may be harvested from the patient's mesenchymal stem cells (MSC), endothelial progenitor cells (EPC), smooth muscle cells (SMC), endothelial cells, hematopoietic stem cells, for instance, cells from cord blood and isolated CD34+ cells, multipotent adult progenitor cells, side population stem cells, adult stem cells and embryonic stem cells or differentiated cells derived from any of, but not limited to, the stem cells listed above. The biomaterial matrix with autologous cells is preferably cultured in vitro prior to implantation in the patient. The particular autologous cells added to the matrix may be selected based on the implantation cite. For example, EPC cells would most likely be used for intra artery implants while SMC cells would be used for intra muscle implants.
Possible biomaterial matrixes for use in this embodiment include the polymers previously listed. Other useful polymers include polymers or copolymers of caprolactones, carbonates, amides, amino acids, orthoesters, acetals, cyanoacrylates and degradable urethanes, as well as copolymers of these with straight chain or branched, substituted or unsubstituted, alkanyl, haloalkyl, thioalkyl, aminoalkyl, alkenyl, or aromatic hydroxy- or di-carboxylic acids. In addition, the biologically important amino acids with reactive side chain groups, such as lysine, arginine, aspartic acid, glutamic acid, serine, threonine, tyrosine and cysteine, or their enantiomers, may be included in copolymers with any of the aforementioned materials.
In another embodiment, the biocompatible coating includes a self-assembled monolayer (SAM) coating, such as pre-formed carboxylic acid alkanethiolate. This coating prevents cell growth and thus the growth of tissue on the sensor surface. In this embodiment, the sensor surface includes gold which allows for the attachment of the SAM coating. The gold may be an integral part of the sensor surface or, alternatively, the gold may be included in a layer of metallic material that is applied to the sensor surface prior to the application of the SAM coating.
While the sensors shown in the figures and described have only one type of biocompatible coating, i.e., either growth inhibiting or even-growth promoting, a sensor may be coated with both types of coatings. For example, it may be beneficial to apply the growth inhibiting coating only to the sensor interface and the even-growth promoting coating to the remainder of the sensor.
It will be apparent from the foregoing that while particular forms of the invention have been illustrated and described, various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited, except as by the appended claims.
