Apparatus and Methods for Embedding a Biocompatible Material in a Polymer Bone Implant
Problems with current implant designs originate from the difference in mechanical properties between the materials used in the implant system and the bone itself.
In a first embodiment, a biocompatible material, such as a titanium coil, is initially wrapped around a polymer bone implant, as described and claimed in U.S. patent application Ser. No. 08/742,733, filed Nov. 1, 1996, which is incorporated herein by reference. The combined coil-implant is then placed in a manifold comprising a hot gas input port and a plurality of output openings. The coil-implant when in the manifold has at least one and preferably four rollers pressing against the coil; the rollers are forced against the coil through the use of a biasing means, such as a spring.
In operation, the implant is rotated while a hot gas is fed through the openings in the manifold to heat the coil-implant. When the titanium coil becomes hot and the polymer of the implant softens, the rollers and springs push the titanium coil into the surface of the implant. Stopping means are located in the rollers-springs to prevent the titanium coil from being pushed more than 1/3 to 1/2 of its diameter into the surface of the implant.
In a second embodiment, a coil of a biocompatible material, preferably titanium, is compressed to the point where almost no space remains between individual coils. The length of the coil is determined so one continuous piece will provide the coverage desired over the surface of the implant. The compressed coil is then slid onto a needle wire; the tip of the needle wire is placed against the surface of the implant; and the point of contact is spot heated to soften the implant's surface. Thereafter, the implant is rotated with the simultaneous stretching and feeding of the coil to the surface of the implant, the tip of the needle wire pushing away the softened surface to create a channel for the coil. The coil is laid in the channel and the tip of the needle wire as it passes pulls the softened surface of the implant over the bottom of the coil, thereby partially embedding the coil. As in the first embodiment, the coil should be embedded no more than from 1/3 to 1/2 of its diameter.
In the third embodiment, induction heating and a ceramic clamp are used to partially embed a biocompatible material such as a titanium coil in the surface of the polymer bone implant. As in the first embodiment, the titanium coil is initially wrapped around the implant. An optional interface means, e.g., a titanium foil slip sheet, may be used to cover the coil-implant. The ceramic clamp comprising at least two ceramic parts is then placed around the interface means, if used, and a nonconductive, elastic material, e.g., rubber or compression bands, is wrapped around the ceramic parts to hold them in place and apply pressure. The entire apparatus is then placed into an induction coil.
The titanium is inductively heated and, as a result, softens the implant with which it is in contact. The elastic material compresses the ceramic clamp parts together pushing the titanium coil into the softened surface of the implant. The interior diameter of the ceramic clamp is designed such that when it is fully compressed, i.e., the ceramic parts are in contact with each other, pressure can no longer be applied to the titanium coil, which at that point is then embedded from 1/3 to 1/2 of its diameter into the surface of the implant. Alternatively, the titanium coil may be wrapped around the implant in sufficient tension that it will embed itself when inductively heated, without using the ceramic clamp and elastic material to apply pressure.
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