PRODUCTS

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to applying an outer layer to shape memory materials and, more particularly, but not way of limitation, to anodizing shape memory materials such as Nitinol.

2. Description of the Related Art

Anodizing of metals and metal alloys produces useful benefits including an outer layer that provides protection and an application of color for use in color coding of parts. While many metals and metal alloys may be anodized, certain shape memory materials such as Nitinol, which is an alloy containing substantially equal mixtures of nickel and titanium, cannot be anodized using standard anodizing processes due to its high nickel content. Nitinol products, such as Nitinol medical implants, therefore are not anodized and thus do not incorporate a protective outer layer.

Moreover, Nitinol products are not color anodized such that the Nitinol products may be color coded for product identification, aesthetics, and quality control.

Accordingly, anodizing of shape memory materials and, in particular, Nitinol will beneficially create Nitinol products that incorporate an outer layer and that may be color coded for product identification, aesthetics, and quality control.

SUMMARY OF THE INVENTION

In accordance with the present invention, a shape memory material product or part is anodized as follows. The shape memory material product or part is polished, thereby producing a polished shape memory material product or part The polished shape memory material product or part then is anodized. The polishing of the shape memory material product or part includes mechanical polishing thereof. The mechanical polishing includes but is not limited to paste polishing, polishing with emery paper, or abrasive blasting.

The polishing of the shape memory material product or part includes electrochemical polishing thereof. The electrochemical polishing includes placing the shape memory material product or part in an electrolyte and applying a voltage to the shape memory material product or part for a predetermined time period. The voltage for the electrochemical polishing is an anodic voltage between 10V and 60V. The predetermined time period for the electrochemical polishing includes but is not limited to between 1 and 60 seconds. Applying the voltage for the electrochemical polishing includes placing a cathode in the electrolyte with the shape memory material product or part therebetween, connecting a negative terminal of a voltage source with the cathode, and connecting a positive terminal of the voltage source with the shape memory material product or part.

The anodizing of the polished shape memory material product or part includes placing the polished shape memory material product or part in an electrolyte and applying a voltage to the polished shape memory material product or part for a predetermined time period. The electrolyte for the anodizing includes phosphoric acid, acetic acid, sulphuric acid, or mixtures thereof in a concentration between 0.1% and 5% total volume of the electrolyte. The electrolyte for the anodizing includes distilled water as a remainder thereof. The voltage for the anodizing is an anodic voltage between 10V and 40V. The predetermined time period for the anodizing includes but is not limited to between 1 and 120 seconds. Applying the voltage for the anodizing includes placing a cathode in the electrolyte adjacent the polished shape memory material product or part, connecting a negative terminal of a voltage source with the cathode, and connecting a positive terminal of the voltage source with the shape memory material product or part. As an illustration, a voltage for the anodizing between 29V and 31V and a predetermined time period for the anodizing of 120 seconds produces a gold hue on the polished shape memory material product or part, whereas a voltage for the anodizing between 24V and 26V and a predetermined time period for the anodizing of 120 seconds produces a blue hue on the polished shape memory material product or part.

It is therefore an object of the present invention to facilitate the anodizing of a shape memory material product or part

It is a further object of the present invention to facilitate the anodizing of a shape memory material product or part through a polishing of the shape memory material product or part prior to the anodizing thereof.

Still other objects, features, and advantages of the present invention will become evident to those of ordinary skill in the art in light of the following. Also, it should be understood that the scope of this invention is intended to be broad, and any combination of any subset of the features, elements, or steps described herein is part of the intended scope of the invention.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a block diagram illustrating electrochemical polishing of a shape memory material industrial or medical product or part.

Figure 2 is a block diagram illustrating anodizing of the shape memory material industrial or medical product or part. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Figures are not necessarily to scale, and some features may be exaggerated to show details of particular components or steps.

Shape memory materials such as Nitinol, due to their superelastic or temperature dependent shape changing properties, include many industrial and medical uses. Illustratively, Nitinol, which is an alloy containing substantially equal mixtures of nickel and titanium, is utilized in golf club inserts, frames for glasses, cell phone antennae, springs, temperature controls, stents, orthodontic equipment, and the like, and, in particular, orthopedic implants. Nitinol orthopedic implants are important in affixing bone, bones, or bone pieces to promote a healing thereof due to their ability to transition between a natural shape and an insertion shape. Nitinol orthopedic implants when deformed from their natural shapes to their insertion shapes store energy deliverable to bone, bones, or bone pieces. In accordance with their manufacture from shape memory materials, Nitinol orthopedic implants begin in their natural shapes, are transitionable to their insertion shapes, and, once implanted in bone, bones, or bone pieces, attempt to transition from their insertion shapes to their natural shapes whereby the Nitinol orthopedic implants deliver the energy stored therein to the bone, bones, or bone pieces in order to affix the bone, bones, or bone pieces and promote a healing thereof.

Nitinol industrial and medical products and parts such as Nitinol orthopedic implants cannot be anodized using standard anodizing processes due to their high nickel content although

Nitinol industrial and medical products and parts would benefit from anodizing. Illustratively, anodized Nitinol industrial and medical products and parts such as Nitinol orthopedic implants would include an outer layer capable of providing protection and, if color anodized, could be color coded for product identification, aesthetics, and quality control. Moreover, with respect to Nitinol orthopedic implants, an anodized Nitinol orthopedic implant would include an outer layer due to process changes at its surface layer such that the anodized Nitinol orthopedic implant becomes more biocompatible for patients with nickel allergies due to the outer layer that forms a protective barrier between the nickel of the Nitinol orthopedic implant and the patients experiencing nickel allergies.

Anodizing shape memory materials, and, in particular, the shape memory material Nitinol, includes a preparation step involving polishing of the Nitinol employing a chemical/electrochemical polishing technique or a mechanical polishing technique including but not limited to paste polishing, polishing with emery paper, and abrasive blasting with a suitable abrasive media such as sand. Polishing the Nitinol prepares its surface such that the Nitinol is compatible for application of an anodizing technique that generates an oxide on its surface. More particularly, polishing the Nitinol removes from its surface residual oxides that may interfere with the anodizing technique. After polishing, the Nitinol exhibits a generally bright finish on its surface indicating residual oxides have been removed.

After polishing the Nitinol, an anodizing step generates an oxide on the surface of the

Nitinol to form an outer layer that may include a specific color for product identification, aesthetics, and quality control. In the preferred embodiment, the thickness of the oxide layer may be between 10 nm (nanometers) and 200 nm (nanometers). More particularly, in anodizing the

Nitinol, the Nitinol forms an anode for application of an anodizing technique, which may include the Nitinol being fixtured to a titanium rack for electrical contact. The cathode for the anodizing technique is any suitable metal such as stainless steel that typically includes a larger surface area than the anode, which, in the preferred embodiment is the Nitinol. The electrolyte for the anodizing technique is any suitable electrolyte used in anodizing including but not limited to an electrolyte of phosphoric acid and distilled water with the phosphoric acid in a concentration between 0.5% and 5% total volume of the electrolyte and the remainder of the electrolyte consisting of the distilled water. Other electrolytes may include sulfuric acid or acetic acid in distilled water in similar concentration ranges to the phosphoric acid and distilled water. The anodizing technique includes applying an anodic voltage between 20 V and 40 V for a predetermined time period including but not limited to between 1 second and 120 seconds, depending on the size of the Nitinol to be anodized and the current limitation of the voltage source. The electrolyte may be stirred during application of the anodic voltage although stirring of the electrolyte is not a necessity.

During the anodizing technique, the temperature of the electrolyte is maintained between

68°F/20°C and 77°F/25°C utilizing a water bath, although a higher or lower temperature may produce a successful anodized layer on the Nitinol. Upon the expiration of the predetermined time period, the Nitinol will include a homogenous and adherent outer layer of oxide with a thickness between 10-200 nm. Moreover, depending upon the voltage level applied at the anode, the Nitinol will be colored whereby the colors range among blue and gold. As an illustration, a voltage level between 24V and 26V will produce a blue hue on the Nitinol, and a voltage level between 29V and 31V will produce a gold hue on the Nitinol.

In order to illustrate the present invention and aid in the understanding thereof, the following example of anodizing a shape memory material industrial or medical product or part and, in particular, a Nitinol orthopedic implant is provided. The Nitinol implant is mechanically polished until the Nitinol implant exhibits a desired level of polishing using one of the following techniques including but not limited to paste polishing, polishing with emery paper, and abrasive blasting with a suitable abrasive media such as sand. Illustratively, the Nitinol implant undergoes fine polishing employing emery paper until a mirror finish is achieved.

Alternatively, as illustrated in Figure 1, a Nitinol implant 10 may be electrochemically polished. An electrolyte 11 is prepared and then placed in a container 12 suitable to hold the electrolyte 11. The electrolyte 11 for the electrochemical polishing technique is any suitable electrolyte used in electrochemical polishing including but not limited to an electrolyte containing methanesulfonic acid in a concentration range of 75%-100% and, if included, sulfuric acid in a concentration range of 2.5%- 10%, whereby the density of the electrolyte is 1.5 g/cm ³ at 68°F/20°C with a pH between 0-1. In a particular example, the electrolyte 11 may be a commercially available electrolyte used in electrochemical polishing such as the electrolyte sold by ElpoChem AG,

Chriesbaumstr. 4, CH-8064 Volketswil, Switzerland, under the Trade name ElpoLux TI-med. A cathode 13 for the electrochemical polishing technique, which may be any suitable metal such as stainless steel, is submerged in the electrolyte 11 and connected to a voltage source 14 at its negative terminal 15. The Nitinol implant 10 is submerged in the electrolyte 11 between the cathode 13 and connected to the voltage source 14 at its positive terminal 16 thereby forming an anode 17 for application of the electrochemical polishing technique, which may include the Nitinol implant 10 being fixtured to a titanium rack for electrical contact. In the electrochemical polishing technique, the cathode 13 typically includes a larger surface area than the anode 17. The electrochemical polishing technique includes utilizing the voltage source 14 to apply an anodic voltage between 10 V and 60 V and, in particular, an anodic voltage of 25 V for a blue color and

30 V for gold color. The anodic voltage is applied for a predetermined time period of between 1 and 60 seconds and, in particular, a time period of 10 seconds. The predetermined time period depends on the ability of the voltage source 14 to supply current and the surface area of the Nitinol implant 10 whereby the predetermined time period increases as the size of the Nitinol implant 10 increases. The electrolyte 11 may be stirred during application of the anodic voltage although stirring of the electrolyte 11 is not a necessity. During the electrochemical polishing technique, the temperature of the electrolyte is maintained between 68°F/20°C and 77°F/25°C utilizing a water bath, although a higher or lower temperature may produce a successful anodized layer on the

Nitinol implant 10. The temperature could also be outside this range and produce a color anodized layer. Upon the expiration of the predetermined time period, the Nitinol implant 10 is polished and its surface prepared through a removal of residual oxides such that the Nitinol implant 10 is compatible for application of an anodizing technique whereby an oxide may be generated on its surface.

After polishing the Nitinol implant 10, anodizing of the Nitinol implant 10 as illustrated in

Figure 2 generates an oxide on the surface of the Nitinol implant 10 to form an outer layer that is protective and may include a specific color for product identification, aesthetics, and quality control. An electrolyte 20 is prepared and then placed in a container 21 suitable to hold the electrolyte 20. The electrolyte 20 for the anodizing technique is any suitable electrolyte used in anodizing including but not limited to an electrolyte of phosphoric acid, acetic acid, sulphuric acid, or mixtures thereof and distilled water with the phosphoric acid, acetic acid, sulphuric acid, or mixtures thereof in a concentration between 0.1 % and 5% total volume of the electrolyte and the remainder of the electrolyte consisting of the distilled water. More particularly, the electrolyte 20 is an electrolyte with phosphoric acid in a concentration of 0.5% total volume of the electrolyte with the remainder consisting of distilled water. A cathode 22 for the anodizing technique, which may be any suitable metal such as stainless steel, is submerged in the electrolyte 20 and connected to a voltage source 23 at its negative terminal 24. The Nitinol implant 10 is submerged in the electrolyte 20 adjacent the cathode 22 and connected to the voltage source 23 at its positive terminal 25 thereby forming an anode 26 for application of the anodizing technique, which may include the Nitinol implant 10 being fixtured to a titanium rack for electrical contact. In the anodizing technique, the cathode 22 typically includes a larger surface area than the anode 26. The anodizing technique includes utilizing the voltage source 23 to apply an anodic voltage of between

10 V and 40 V and, in particular, an anodic voltage of 25 V to produce a blue color and an anodic voltage of 30 V to produce a gold color. The anodic voltage is applied for a predetermined time period of between 1 and 120 seconds to produce the blue or gold color and, in particular, for a time period of 120 seconds. The electrolyte 20 may be stirred during application of the anodic voltage although stirring of the electrolyte 20 is not a necessity. During the anodizing technique, the temperature of the electrolyte is maintained between 68°F/15°C and 95°F/35°C utilizing a water bath. Upon the expiration of the predetermined time period, the Nitinol implant 10 will include a homogenous and adherent outer layer of oxide with a thickness between 10-200 nm and, in particular, 90 nm for a gold color. Moreover, depending upon the voltage level applied at the anode, the Nitinol will be colored whereby the colors range among gold and blue. As an illustration, a voltage level between 29 V and 31 V will produce a gold hue on the Nitinol, whereas a voltage level between 24V and 26 V will produce a blue hue on the Nitinol. In the foregoing specific example, the anodic voltage of 30 V applied for 120 seconds produces bright gold on the

Nitinol implant 10. The Nitinol implant 10 is disconnected from the voltage source 23 and removed from the electrolyte 20 whereby the Nitinol implant 10 includes an outer layer capable of providing protection as well as a color suitable to provide product identification, aesthetics, and quality control. Moreover, the anodized Nitinol implant 10 would include an outer layer due to process changes at its surface layer such that the anodized Nitinol implant 10 becomes more biocompatible for patients with nickel allergies due to the outer layer that forms a protective barrier between the nickel of the Nitinol implant 10 and the patients experiencing nickel allergies.

Although the present invention has been described in terms of the foregoing preferred embodiment, such description has been for exemplary purposes only and, as will be apparent to those of ordinary skill in the art, many alternatives, equivalents, and variations of varying degrees will fall within the scope of the present invention. That scope, accordingly, is not to be limited in any respect by the foregoing detailed description; rather, it is defined only by the claims that follow.