Coating processes – Medical or dental purpose product; parts; subcombinations;... – Implantable permanent prosthesis
Reexamination Certificate
2001-07-24
2003-05-20
Meeks, Timothy (Department: 1762)
Coating processes
Medical or dental purpose product; parts; subcombinations;...
Implantable permanent prosthesis
C427S002260, C427S525000, C427S531000, C427S533000, C427S537000, C427S577000, C427S249700, C427S250000, C427S255700, C204S192160, C204S192320
Reexamination Certificate
active
06565913
ABSTRACT:
FIELD OF THE INVENTION
The present invention provides a coating and a method of making an antimicrobial coating which strongly adheres to surfaces of medical implants and is relatively well-tolerated by the body. When a medical implant bearing the coating is exposed to an solution or alcohol, or is implanted into the body, the coating provides an effective zone of inhibition for a period of about 12 hours or more, preferably for about 24 hours or more, even more preferably for about 3 days or more, and most preferably for about 10 days or more.
BACKGROUND OF THE INVENTION
A common cause of failure of implanted biomedical devices is infection. The attachment of bacteria to medical implants and in-dwelling catheters, and the proliferation of such bacteria, is a major cause of infection during or after the implantation process. Treating an implant with antibiotics has not proven very effective to combat infections, and has sometimes resulted in development of resistant strains of bacteria.
Silver coatings are effective to combat infections; however, contact with a non-leaching silver surface tends to cause tissue irritation. If a coating does leach silver, then the tissue irritation may be somewhat alleviated, but the rate of release of the silver must be controlled. If the silver leaches too slowly, then the coating does not form a zone of inhibition that is effective to prevent infection. If the silver leaches too rapidly, then the zone of inhibition disappears after too short a period of time to prevent infection.
An antimicrobial coating for a medical implant is needed which maintains good adhesion to the implant surface and produces a zone of inhibition that is effective to prevent infection, at least during a sufficient immediate post-operative or post insertion period.
SUMMARY OF THE INVENTION
The invention provides a method of forming an adherent antimicrobial coating on a surface of a substrate, said method comprising:
exposing said surface to initial conditions effective to convert at least some atoms of said surface to activated atoms;
condensing a carbonaceous vapor consisting essentially of carbonaceous precursor material onto said surface under condensing conditions effective to induce the formation of covalent bonds between said activated atoms and carbon atoms in said carbonaceous vapor, producing a bonding region comprising hydrogenated amorphous carbon covalently bonded to said substrate;
exposing an antimicrobial metal to physical vapor deposition techniques, thereby producing a metallic stream consisting essentially of an antimicrobial metal selected from the group consisting of Ag, Au, Pt, Pd, Ir, Sn, Cu, Sb, Bi, Zn, and combinations thereof;
condensing a combination comprising said carbonaceous vapor and said metallic stream onto said hydrogenated amorphous carbon at a ratio and under incorporation conditions effective to produce an antimicrobial region comprising hydrogenated amorphous carbon having dispersed therein an antimicrobially effective load of antimicrobial metal ions.
The invention also provides a substrate comprising an adherent antimicrobial coating comprising an outer surface, said antimicrobial coating comprising:
a bonding region immediately adjacent to said substrate consisting essentially of hydrogenated amorphous carbon comprising carbon atoms covalently bonded to atoms in said substrate; and
an antimicrobial region extending from said bonding region to said outer surface, said antimicrobial region comprising hydrogenated amorphous carbon comprising an antimicrobially effective load of ions of an antimicrobial metal dispersed therein, said antimicrobial metal being selected from the group consisting of Ag, Au, Pt, Pd, Ir, Sn, Cu, Sb, Bi, Zn, and combinations thereof.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention, a substrate is provided with a film of hydrogenated amorphous carbon in which ions of at least one antimicrobial metal, preferably silver, are disposed. The method used to make the film is ion beam assisted deposition (IBAD).
The ion beam imparts a substantial amount of energy to both the substrate and to the carbonaceous precursor materials as they are deposited onto the substrate. The ion beam activates the substrate so that atoms of the substrate covalently bond with carbon atoms in the carbonaceous precursor material. The result is an interlayer of hydrogenated amorphous carbon comprising carbon atoms covalently bonded to atoms in the substrate. The covalently bonded interlayer prevents delamination of the antimicrobial coating from the substrate surface.
In a preferred embodiment, where the substrate material is a polymer, the covalent bonding comprises carbon-carbon and carbon-hydrogen bonds formed between the carbon in the polymer and the carbon in the hydrogenated amorphous carbon film. In this embodiment. bombardment of the surface of the polymeric component with a beam of energetic ions is believed to disrupt carbon-carbon bonds in the polymer, leaving reactive carbon atoms “dangling” at the surface of the polymer. The carbonaceous precursor material is deposited onto the surface under continued ion bombardment, causing carbon atoms in the precursor material to react with the reactive or “dangling” carbon atoms at the surface of the substrate, thereby forming stable carbon-carbon bonds. The result is a hydrogenated amorphous carbon coating that is bonded to the polymeric substrate by a substantial amount of covalent carbon-carbon bonding.
After the covalently bonded interlayer is produced, a stream of an antimicrobial metal is produced using vapor deposition techniques and introduced essentially simultaneously into the stream of carbonaceous precursor material. Ion bombardment of the combined streams—of carbonaceous precursor material and antimicrobial metal—produces a dispersion of ions of the antimicrobial metal in the hydrogenated amorphous carbon. The form of the dispersion may vary from a substantially uniform dispersion, to a graded dispersion, to actual multilayers of substantially pure hydrogenated amorphous carbon and substantially pure antimicrobial metal. The form of the dispersion depends upon a number of factors, a most important factor being the rate at which the antimicrobial metal is introduced with the stream of carbonaceous precursor material. Preferably, the dispersion is a gradient in which the concentration of antimicrobial metal increases from the covalently bonded interlayer, which consists essentially of hydrogenated amorphous carbon, to the outer surface of the antimicrobial coating. An optional outer film of substantially pure antimicrobial metal also may be deposited.
Suitable Substrates
The antimicrobial coating of the invention is useful on a large variety of substrates, with preferred substrates being those that inherently form covalent bonds with carbon. Most preferred substrates are organic substrates, preferably polymeric substrates. Other suitable substrates include, but are not necessarily limited to metal alloys that have been treated, for example with silicon, to form an outer surface of a material that does covalently bond with carbon.
The antimicrobial coating preferably is applied to the surface of a medical device which comes into contact with alcohol or a water based electrolyte, including a body fluid (for example blood, urine or saliva) or body tissue (for example skin, muscle or bone), for a period of time sufficient for microorganism to grow on the device surface. The term “alcohol or water based electrolyte” also includes alcohol or water based gels. The devices typically are in-dwelling devices (sometimes called medical implants) or other medical devices that contact human tissue during use. Such medical devices include, but are not necessarily limited to catheters, implants, tracheal tubes, orthopedic pins, insulin pumps, wound closures, drains, dressings, shunts, connectors, prosthetic devices, pacemaker leads, needle, surgical instruments, dental prostheses, ventilator tubes and the like. However, the invention is not limited to such devices
Arps James
Dearnaley Geoffrey
Meeks Timothy
Paula D. Morris & Associates P.C.
Southwest Research Institute
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