| Pulsed current sintering for surfaces of medical implants -> Monitor Keywords |
|
|
  Pulsed current sintering for surfaces of medical implantsUSPTO Application #: 20060015187Title: Pulsed current sintering for surfaces of medical implants Abstract: A porous medical implant and a method of making same is described. The medical implant comprises a porous surface formed by application of pulsed electrical energy ins such a way as to cause a localized heating in the surface of the material comprising portions of the implant. The method comprises a pulsed current sintering technique. (end of abstract) Agent: Smith & Nephew, Inc. - Memphis, TN, US Inventors: Gordon Hunter, Vivek Pawar, Daniel A. Heuer, Abraham Salehi, Michael B. Cooper USPTO Applicaton #: 20060015187 - Class: 623023500 (USPTO) Related Patent Categories: Prosthesis (i.e., Artificial Body Members), Parts Thereof, Or Aids And Accessories Therefor, Implantable Prosthesis, Bone, Having Textured Outer Surface The Patent Description & Claims data below is from USPTO Patent Application 20060015187. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority to U.S. provisional application Ser. No. 60/589,143, filed on Jul. 19, 2004. TECHNICAL FIELD [0002] The present invention is directed toward the fabrication of a porous sintered surface for medical implants. BACKGROUND OF THE INVENTION [0003] For a variety of reasons, it is sometimes necessary to surgically correct an earlier implanted medical implant (most commonly a prosthetic joint) or replace it with an entirely new medical implant. Typically, this results from either a loosening of the implant in the implant site, or the deterioration of the implant due to forces such as abrasion. Ideally, an medical implant is often formed from a high-strength material which is not only able to accommodate the various loading conditions that it may encounter, but is also non-toxic to, and otherwise biocompatible with, the human body. It is also preferable to implant the device in such a way as to enhance fixation over the long term. [0004] A number of advances have been made to increase service life of medical implants by increasing their resistance to forces such as abrasion. The advent of oxidized zirconium, first described by Davidson in U.S. Pat. No. 5,037,438 has provided a surface with superior hardness which is also resistance to brittle fracture, galling, fretting and attack by bodily fluids. A similar advance in the area of fixation stability will address the other major source of implant failure and would represent a significant advance in implant service life. [0005] In cases of extreme loading conditions as is often the case for artificial hips, prosthetic joints may be made from metal alloys such as titanium, zirconium, or cobalt chrome alloys. Not only are these metal alloys of sufficient strength to withstand relatively extreme loading conditions, but due to their metallic nature, a metallic porous coating typically of titanium or cobalt chrome may be secured to the metal alloy by a metallic bond. Such metallic porous coatings are useful for providing initial fixation of the implant immediately after surgery, but also serve to facilitate long-term stability by enhancing bone ingrowth and ongrowth. [0006] While medical implant devices made from biocompatible metal alloys are effective, they may lack certain desirable characteristics. For example, metal alloys have poor flexibility and therefore do not tend to distribute load as evenly as would be desired. Uneven loads tend to result in a gradual loosening of the implant. As such loosening becomes more severe, revision or replacement becomes necessary. For this reason, it is desirable to design medical implants generally and prosthetic joints specifically in such a way as to improve their in vivo fixation stability. [0007] One way this problem has historically been addressed in the past is through the use of modified surfaces for medical implants which increase surface contact area and promote bone ingrowth and ongrowth. Another more recent technique involves the use of depositing material onto the surface of an implant, the material being the emission of a plasma spray source. This is discussed in U.S. Pat. Nos. 5,807,407, 6,087,553, and 6,582,470, among others, which are incorporated by reference as though fully disclosed herein. [0008] A promising way to form porous products involves fusing materials in such as way as to effect a porous finished material. Such approaches have been the subject of past work. Electrical discharge is one mechanism by which this has been performed, as in U.S. Pat. Nos. 5,294,769, 5,352,385, and 5,421,943. Sintered materials have also been the subject of investigation as a potential solution to the issue of fixation stability improvement through the use of porous materials which allow for tissue ingrowth and ongrowth. For example, Chowdhary in U.S. Pat. No. 5,104,410, describes a prosthesis having a metallic substrate and multiple sintered layers. The sintered layers were formed by conventional methods of sintering, using temperatures of 1100.degree. C. for one hour at 10.sup.-5-10.sup.-6 torr. While such sintered surface imparts desirable porosity, sintering at such extreme conditions of temperature and time fundamentally alter the nature of the substrate in undesirable ways. BRIEF SUMMARY OF THE INVENTION [0009] A porous medical implant and a method of making same is described. The medical implant comprises a porous surface formed by application of pulsed electrical energy in such a way as to cause a localized heating in the surface of the material comprising portions of the implant. [0010] In one aspect of the present invention, there is a method of making a medical implant having a porous surface and a solid substrate, comprising the steps of placing a finite number of individual bodies in continuous contact with one another, the finite number of individual bodies comprising a first material; sintering the first material by applying pulsed electrical energy across at least a portion of the aggregate mass of the individual bodies, thereby creating a cohesive porous structure and, attaching the first material to a second material, the second material comprising the solid substrate. In some embodiments, the step of attaching said first material to a second material comprises sintering said first material to said second material by applying pulsed electrical energy across at least a portion of the aggregate mass of the first material and the second material while the first material and the second material are in physical contact with one another. In some embodiments, the steps of sintering and attaching are performed simultaneously by applying pulsed electrical energy across at least a portion of the aggregate mass of the first material and the second material while the first material and the second material are in physical contact with one another. In some embodiments, the steps of sintering and attaching are performed sequentially by first applying pulsed electrical energy across at least a portion of the aggregate mass of the first material and thereafter applying pulsed electrical energy across at least a portion of the aggregate mass of the first material and the second material while the first material and the second material are in physical contact with one another. In some embodiments, the step of attaching said first material to a second material comprises a step selected from the group consisting of welding, soldering, diffusion bonding, brazing, adhering using an adhesive or grouting material or both, and any combination thereof. In some embodiments, the step of placing a finite number of individual bodies in continuous contact with one another comprises placing a finite number of individual bodies of at least two materials in continuous contact with one another. The method may further comprise the step of removing at least a portion of at least one of said at least two materials either during or after said step of sintering, thereby creating a cohesive porous structure where said material was removed. Preferably, the method further comprises the step of applying a mechanical load to at least a portion of said first material or to at least a portion of said second material or to at least a portion of both said first material and said second material. In cases where a mechanical load is applied, it is preferably applied during said step of sintering. In some embodiments, the step of sintering is performed at an elevated temperature. In some embodiments, the step of sintering comprises applying pulsed electrical energy at high frequencies. In some embodiments, the first material and said second material are selected from the group consisting of metal, ceramic, polymer, composite materials, and any combination thereof. The first material and second material may or may not be different. Preferably the first material and the second material are refractory materials. Alternatively, one or both of the first material and the second material may be non-refractory materials. In some embodiments, a portion of the individual bodies of the first material are of different composition from another portion of the individual bodies of the first material. Accordingly in some embodiments, a portion of the individual bodies of the first material comprises a refractory material and another portion of the individual bodies of the first material comprises a non-refractory material. In some embodiments, one of the first material and the second material is refractory and the other is non-refractory. In some embodiments, the first material has a form selected from the group consisting of symmetric particles, asymmetric particles, single fibers, multiple fibers, flat porous sheets, deformed porous sheets, reticulated open-celled structures, and any combination thereof. In some embodiments, the first material has a symmetric particle form and is a spherical particle. In some embodiments, the sintering step is performed in a controlled environment. The controlled environment may be one having a pressure less than atmospheric pressure. The controlled environment may be one comprising an atmosphere of an inert gas. The controlled environment may be one comprising an atmosphere of a reactive gas. In some embodiments of the method, the controlled environment is varied during the step of sintering. In some embodiments of the method, the step of placing comprises using a binder. In some embodiments, the method further comprises the step of infusing at least a portion of the porous region with a material. In some embodiments where an infusing step is used, the step of infusing comprises infusing with a method selected from the group consisting of direct compression molding, injection, solution deposition, vapor deposition, and any combination thereof. In some embodiments where an infusing step is used, the material to be infused is a polymer. In some embodiments where an infusing step is used, the material to be infused comprises a growth factor or antibiotic. In some embodiments where an infusing step is used, the material to be infused is selected from the group consisting of hydroxyapatite, fluoroapatite, chloroapatite, bromoapatite, iodoapatite, calcium sulfate, calcium phosphate, calcium carbonate, calcium tartarate, bioactive glass, and any combination thereof. [0011] In another aspect of the present invention, there is a method of making a medical implant having a porous surface comprising the steps of placing a finite number of non-spherical individual bodies in continuous contact with one another; and, sintering said individual bodies by applying pulsed electrical energy across at least a portion of the aggregate mass of said individual bodies, thereby creating a cohesive porous structure. In some embodiments, the step of placing a finite number of non-spherical individual bodies in continuous contact with one another further comprises placing said individual bodies in contact with at least one other material. In some embodiments, the method further comprises the step of removing at least a portion of said at least one other material either during or after said step of sintering, thereby creating a cohesive porous structure where said material was removed. The method may further comprise the step of applying a mechanical load to at least a portion of said individual bodies. In some embodiments, the step of applying a mechanical load is performed during said step of sintering. In some embodiments, the step of sintering is performed at an elevated temperature. In some embodiments, the step of sintering comprises applying pulsed electrical energy at high frequencies. In some embodiments, the individual bodies are selected from the group consisting of metal, ceramic, polymer, composite materials, and any combination thereof. In some embodiments, the composition of a portion of the individual bodies is different from the composition of another portion of the individual bodies. In some embodiments, at least a portion of said individual bodies comprise a refractory material. In some embodiments, the individual bodies have a form selected from the group consisting of symmetric particles, asymmetric particles, single fibers, multiple fibers, flat porous sheets, deformed porous sheets, reticulated open-celled structures, and any combination thereof. In some embodiments, the sintering step is performed in a controlled environment. The controlled environment may be one having a pressure less than atmospheric pressure. The controlled environment may be one comprising an atmosphere of an inert gas. The controlled environment may be one comprising an atmosphere of a reactive gas. In some embodiments of the method, the controlled environment is varied during the step of sintering. In some embodiments, the step of placing comprises using a binder. In some embodiments, the method further comprises the step of infusing at least a portion of the porous structure with a material. In some embodiments, the step of infusing comprises infusing with a method selected from the group consisting of direct compression molding, injection, solution deposition, vapor deposition, and any combination thereof. In some embodiments where an infusing step is used, the material to be infused is a polymer. In some embodiments where an infusing step is used, the material to be infused comprises a growth factor or antibiotic. In some embodiments where an infusing step is used, the material to be infused is selected from the group consisting of hydroxyapatite, fluoroapatite, chloroapatite, bromoapatite, iodoapatite, calcium sulfate, calcium phosphate, calcium carbonate, calcium tartarate, bioactive glass, and any combination thereof. [0012] The present invention also includes a medical implant comprising a solid substrate and a porous sintered surface, wherein the solid substrate possesses substantially the same bulk mechanical and tribological properties after sintering which existed prior to sintering. Preferably, the material possesses substantially the same microstructure after sintering which existed prior to sintering. [0013] There is also a medical implant having a porous surface produced by the process comprising the steps of placing a finite number of non-spherical individual bodies in continuous contact with one another; and, sintering the individual bodies by applying pulsed electrical energy across at least a portion of the aggregate mass of the individual bodies, thereby creating a cohesive porous structure. [0014] There is also a medical implant having a porous surface produced by the process comprising the steps of placing a finite number of individual bodies in continuous contact with one another, said finite number of individual bodies comprising a first material; sintering the first material by applying pulsed electrical energy across at least a portion of the aggregate mass of the individual bodies, thereby creating a cohesive porous structure; and, attaching the first material to a second material, the second material comprising said solid substrate. [0015] The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized that such equivalent constructions do not depart from the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS [0016] For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings. [0017] FIG. 1 is a demonstrating the result of the use of conventional sintering on an medical implant. [0018] FIG. 2 is a schematic illustration demonstrating the result of the use of pulsed current sintering on an medical implant. DETAILED DESCRIPTION OF THE INVENTION Continue reading... Full patent description for Pulsed current sintering for surfaces of medical implants Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Pulsed current sintering for surfaces of medical implants patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Pulsed current sintering for surfaces of medical implants or other areas of interest. ### Previous Patent Application: Implant and arrangement for especially replacing surfaces that are subject to stresses Next Patent Application: Ureteral stent with end-effector and related methods Industry Class: Prosthesis (i.e., artificial body members), parts thereof, or aids and accessories therefor ### FreshPatents.com Support Thank you for viewing the Pulsed current sintering for surfaces of medical implants patent info. IP-related news and info Results in 3.94602 seconds Other interesting Feshpatents.com categories: Tyco , Unilever , Warner-lambert , 3m |
||
