Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Treating electrolytic or nonelectrolytic coating after it is...
Reexamination Certificate
2001-06-21
2003-03-04
Nguyen, Nam (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Treating electrolytic or nonelectrolytic coating after it is...
C205S322000, C205S640000, C205S675000, C205S705000, C205S717000, C427S002100, C427S002240, C427S002250, C427S002260, C427S331000, C427S343000
Reexamination Certificate
active
06527938
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates broadly to medical articles and devices. More particularly, this invention relates to methods of treating the surface of the medical article or devices to affect the surface structure thereof, and medical articles and devices having such modified surface structure.
2. State of the Art
Metals and metal alloys, and particularly titanium and titanium alloys, are used for a great variety of implantable articles for medical applications. Among these applications are: structural articles which are used to repair or replace or reinforce bones or to reconstruct joints; structural articles to expand and reinforce arterial, vascular, and other body structures with lumens; wire embolization coils for occluding arteries; enclosures for pacemakers, defibrillators, and implantable infusion pumps; pacing leads; wire sutures and ligatures; staples; filters to catch thrombi and emboli; and, so forth. All implantable articles suffer from some degree of bio-incompatibility, which may be manifested as tissue inflammation, necrosis, hyperplasia, mutagenicity, toxicity, and other reactions, such as attack by giant cells and leukocytes, and macrophages. While titanium and its alloys are generally considered inert when implanted, some biological and biochemical interactions still may occur, and others have found it desirable to provide various coatings on the surface of titanium and titanium alloy implants for certain purposes. The same holds true for many other metals and metal alloys.
In the area of vascular stents others have coated stents (whether made of titanium or other materials) with biological agents (such as genetic material or cellular material) or chemical agents (such as anti-proliferation reagents or cell-growth factors) to reduce problems associated with hyperplasia or inflammation. In order to attach these biological or chemical agents to the surface of a metallic stent, the agents have been mixed with binders such as elastomers or bio-resorbable polymers. These binders can also create problems in that they can cause inflammation, and they can cause the surface of the stent to have more friction, which reduces the ease of stent delivery.
In the field of dental and orthopedic implants, there are sometimes problems associated with acceptance of the implant by body tissues. These problems may be ameliorated by adding anti-inflammatory agents to the surface of the implant. Also, it has been shown that for some implants, it is advantageous for the surface of the implant to be microporous to allow ingrowth of either soft tissue or hard tissue (bone) to enhance the anchoring of the implant in the body. Such microporous surfaces are generally created by attaching a layer of sintered spherical powders to selected surfaces of the implant in areas where tissue ingrowth is desired.
However, attachment of these sintered-powder layers requires additional processing steps, and there is a practical limit to the size of pores that can be achieved. Also, the temperature at which the powders must be sintered approaches the melting point of the material, and the implant is left in a fully-annealed condition, which may be lower in strength than desired. Also, sintered-powder coatings on titanium articles must be applied in a high-temperature, high-vacuum furnace, which is necessarily an expensive and labor-intensive process.
In the field of implanted electrodes, it has been found that sintered powder coatings enhance the attachment of the electrodes and help them to retain a low-impedance connection to the tissue. Such electrodes are generally manufactured by machining an electrode component, applying a multiple-layer coating of powdered metal in an organic binder, and sintering the coated electrode in a controlled-atmosphere (or high vacuum) furnace.
Other medical implants, such as vena-cava filters, aneurism clips, staples, and sutures, are constructed of wire and thus have a relatively large surface area for their size. Accordingly, methods which allow the addition of biological and biochemical agents to the surface of the implant may be advantageous in minimizing the adverse reactions of body tissues with the implant.
Another type of implant, embolization coils, are intended to cause thrombosis so that arteries may be blocked off to mitigate the danger of an aneurism or to deny the blood supply to a tumor. In such devices it may be advantageous to apply biological or chemical agents to the surface of the coils in order to enhance the formation of thrombus.
In the field of arterial stents, coatings have been applied to stainless steel and titanium alloys (e.g., TiNi alloys) to retard tissue reactions such as thrombosis, inflammation, and hyperplasia. Such coatings have been based upon stable bio-compatible polymers (such as styrene-isobutylene-styrene (SIBS)) and bio-resorbable polymers, such as polyglycolic acid. In the work known to date, the active chemical or biological agent is mixed with the polymeric coating material, and the agent then elutes from the coating once the implant is placed in the body.
U.S. Pat. No. 5,972,027 relates to a stent formed of graded layers of powdered metal, with some of the surface layers formed of powder made of larger particle sizes. Once the stent has been sintered, the major portion of the stent is consolidated to a substantially solid form, but that portion of the surface that was made with larger particle-size powder remains microporous. In this way, a stent is manufactured so that at least some parts of the surface are microporous and can be infiltrated with a biological or chemical agent. Such a process is very difficult, since the stent must be made from a “green” preform that is very thin. The finished thickness of an arterial stent ranges from approximately 50 to 125 microns (or approximately 0.002 to 0.005 inches), and the microporous surface layer would be only a fraction of that thickness. Such a thin preform would be very fragile and difficult to handle prior to being sintered.
Other techniques have been described for creating a micro-microporous surface on a metallic article, and such processes might be used for creating a microporous coating on a metallic implant. Such processes include ion milling, photo-chemical machining, electro-discharge machining, and micro-machining using conventional cutting tools.
Of these methods, only the first two are suitable for creating a large number of very small pores (micropores), in the range of 1 to 50 microns in size. Such methods are more suitable for application to flat substrates because they rely on optical or quasi-optical processes. It would be difficult and expensive to apply these processes to small non-flat articles, such as stents, bone screws, dental implants, and clips.
The last three methods are suitable for creating larger pores or pockets in the surface of implants, but such larger pores would require the chemical or biological agent to be bound to the article by means of some binding agent, usually a polymer.
Thus, all of the known methods require either very expensive processes to produce a fine microporous structure, or else it is necessary to use a binding material to attach the biological or chemical agent to the implant article.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a process for modifying the surface of a metal or metal alloy implant to create a microporous surface layer thereon.
It is another object of the invention to provide a process for particularly modifying the surface of a titanium or titanium alloy implant to create a microporous surface layer thereon.
It is a further object of the invention to provide a process for creating a microporous surface on an implant article that could be preferentially applied to only a desired portion of the surface of the implant.
It is also an object of the invention to provide an efficient process which would create a fine microporous structure on the surface of an implant article that would allow a biological or chemical agent to be
Bales Thomas O.
Jahrmarkt Scott L.
Gallagher Thomas A.
Gordon David P.
Jacobson David S.
Leader William T.
Nguyen Nam
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