Guidewire device and method

The present invention is a multi-layer guidewire which has a first core metal and a secondary metal formed on the outer periphery of the core. During manufacture the composite structure is twisted providing superior mechanical properties to the finished guidewire.

DETAILED DESCRIPTION The concept of operator “feel” is difficult to describe and more difficult to quantify. However, in the field of interventional cardiology it is widely recognized that solid nitinol guidewires react differently in vessels than more conventional stainless steel guidewires. Although nitinol guidewires excel at such properties as “push” and “torque” ability, the drag on the wire as well as the ability to feel the tip is reduced when compared to stainless steel wires. For this reason there is a continuing need to improve guidewires. 
 DETAILED DESCRIPTION OF THE INVENTION The invention is disclosed in the context of a guide wire which is a common interventional device. It should be appreciated that a similar construction for any intervention device. FIG. 1 shows a guidewire 10 having a super elastic nitinol core 12 surrounded by a cladding 14 of stainless steel or other metal. Material of this type can be prepared by drawing clad material through progressively smaller dies. This process is well known in the industry. The distal tip of the device 16 may include a coil 20 placed over a centerless ground taper 22 which exposes the nitinol core 12 . The coil is attached be a weld glue or solder joint 24 . The atrumatic tip 26 may be formed of the core material or it may be a separate piece. 28 . FIG. 2 shows the cross section of the wire where D is the total diameter. It is preferred to have the cladding depth range between about 5% and 25% of the diameter D. The optimal dimension of cladding stainless steel onto nitinol is difficult to determine analytically, but it is believed that on a standard 0.014 to 0.018 guidewire approximately 10 to 15 percent of the total diameter should be stainless steel. In general it is easier to make thickly clad material which may influence the design choice. FIG. 3 shows a schematic representation of the two metal material that has been twisted as indicated by arrow 42 resulting in a twist 40 in the wire. Although stainless steel material is preferred as the clad, other metals may be used as a substitute for stainless steel. In each instance, however, the core should be super elastic nitinol. A non-exhaustive list of alternative cladding materials includes titanium, tungsten, MP35N, gold and platinum. Returning to the process of treating the coaxial wire it has been determined that a twist of five to 12 turns per inch followed by a heat soak at 900° F. for 5 to 20 minutes simultaneously results in both stress relief for the stainless steel layer and straightening or set the nitinol wire. The heater 45 depicts the heat treatment process. In general there