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A guide wire with a distal portion having adjustable flexibility. The guide wire may include a distal polymeric member and a heat source. The heat source may be activated to cause the polymeric member to increase in temperature and increase in flexibility. The increase in flexibility of the distal

A guide wire with a distal portion having adjustable flexibility. The guide wire may include a distal polymeric member and a heat source. The heat source may be activated to cause the polymeric member to increase in temperature and increase in flexibility. The increase in flexibility of the distal portion of the guide wire enhances the ability of the guide wire to navigate tortuous vasculature to a target site. After the guide wire has been navigated to the target site, the heat source may be deactivated to cause the polymeric member to decrease in temperature and increase in stiffness. The increase in stiffness of the distal portion of the guide wire enhances support provided for devices (e.g., catheters) advanced thereon.

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What is claimed is: 1. A variable stiffness guide wire, comprising: a shaft having a proximal portion and a distal portion, the distal portion having a flexibility; a polymeric member disposed on and non-releasably attached to the distal portion of the shaft, the polymeric member having a first fle

What is claimed is: 1. A variable stiffness guide wire, comprising: a shaft having a proximal portion and a distal portion, the distal portion having a flexibility; a polymeric member disposed on and non-releasably attached to the distal portion of the shaft, the polymeric member having a first flexibility at a first temperature and a second flexibility at a second temperature, wherein the first temperature is less than the second temperature and the first flexibility is less than the second flexibility; and a heat source disposed on the distal portion of the shaft, the heat source being in thermal communication with the polymeric member, whereby activation of the heat source causes the polymeric member to rise from the first temperature to the second temperature to thereby change the flexibility of the distal portion of the guide wire while the polymeric member remains attached to the shaft. 2. A variable stiffness guide wire as in claim 1, wherein the polymeric member comprises a shape memory polymer. 3. A variable stiffness guide wire as in claim 2, wherein the shape memory polymer has a glass transition temperature, and wherein the first temperature is below the glass transition temperature. 4. A variable stiffness guide wire as in claim 3, wherein the second temperature is above the glass transition temperature. 5. A variable stiffness guide wire as in claim 1, wherein the heat source comprises a resistive heating element. 6. A variable stiffness guide wire as in claim 5, wherein the distal portion of the shaft includes a tip portion. 7. A variable stiffness guide wire as in claim 6, wherein the tip portion includes the polymeric member and resistive heating element. 8. A variable stiffness guide wire as in claim 7, wherein the polymeric member comprises a tube. 9. A variable stiffness guide wire as in claim 8, wherein the resistive heating element comprises a coiled wire. 10. A variable stiffness guide wire as in claim 9, further comprising one or more lead wires connected to and extending proximally from the coiled wire. 11. A variable stiffness guide wire as in claim 10, wherein the polymeric tube is disposed on the coiled wire. 12. A variable stiffness guide wire as in claim 11, wherein a core wire extends through the tip portion. 13. A variable stiffness guide wire as in claim 12, wherein the proximal portion of the shaft includes a hypotube. 14. A variable stiffness guide wire as in claim 13, wherein the distal portion of the shaft includes a slotted hypotube. 15. A variable stiffness guide wire as in claim 14, wherein the coiled wire is disposed in the slots of the slotted hypotube. 16. A variable stiffness guide wire, comprising: a shaft including a proximal portion and a distal portion having a flexibility; a polymeric member disposed on and non-releasably attached to the distal portion of the shaft; a heat source in thermal communication with the polymeric member, whereby activation of the heat source causes the polymeric member to change the flexibility of the distal portion of the shaft; wherein the heat source comprises a resistive heating element; wherein the distal portion of the shaft includes a tip portion; wherein the tip portion includes the polymeric member and resistive heating element; wherein the polymeric member comprises a tube; wherein the resistive heating element comprises a coiled wire; further comprising one or more lead wires connected to and extending proximally from the coiled wire; wherein the polymeric tube is disposed on the coiled wire; and wherein a core wire extends through the tip portion. 17. A variable stiffness guide wire as in claim 16, wherein the proximal portion of the shaft includes a hypotube. 18. A variable stiffness guide wire as in claim 17, wherein the distal portion of the shaft includes a slotted hypotube. 19. A variable stiffness guide wire as in claim 18, wherein the coiled wire is disposed in the slots of the slotted hypotube. 20. A method of using a variable stiffness guide wire, comprising the steps of: providing a guide wire including a distal portion having a flexibility, a shaft, a distal polymeric member non-releasably attached to the shaft, and a heat source in thermal communication with the polymeric member; changing the flexibility of the distal portion of the guide wire by activating or deactivating the heat source; wherein the flexibility changing step comprises activating the heat source to increase the flexibility of the distal portion of the guide wire, the method further comprising the step of navigating the guide wire through a patient's vasculature to a target site; and further comprising: the step of deactivating the heat source to decrease the flexibility of the distal portion of the guide wire. 21. A method of using a variable stiffness guide wire as in claim 20, further comprising the step of advancing a device over the guide wire to the target site. 22. A variable stiffness guide wire, comprising: a shaft including a proximal portion and a distal portion having a flexibility; a polymeric member disposed on and non-releasably attached to the distal portion of the shaft; a heat source in thermal communication with the polymeric member,whereby activation of the heat source causes the polymeric member to change the flexibility of the distal portion of the shaft; wherein the polymeric member comprises a shape memory polymer; wherein activation of the heat source causes the shape memory polymer to change temperature; and wherein the shape memory polymer has a glass transition temperature, and wherein the change in temperature is across the glass transition temperature. 23. A variable stiffness guide wire, comprising: a shaft including a proximal portion and a distal portion having a flexibility; a polymeric member disposed on and non-releasably attached to the distal portion of the shaft; a heat source in thermal communication with the polymeric member, whereby activation of the heat source causes the polymeric member to change the flexibility of the distal portion of the shaft; wherein the polymeric member comprises a shape memory polymer; wherein activation of the heat source causes the shape memory polymer to change temperature; and wherein the shape memory polymer has a glass transition temperature, and wherein the change in temperature is near the melt temperature. 24. A method of using a variable stiffness guide wire, comprising: providing a guide wire including a distal portion having a flexibility, a shaft, a distal polymeric member non-releasably attached to the shaft, and a heat source in thermal communication with the polymeric member; changing the flexibility of the distal portion of the guide wire by activating or deactivating the heat source; and wherein the polymeric member comprises a shape memory polymer having a glass transition temperature, and wherein the flexibility changing step comprises heating the polymeric member near the melt temperature. 25. A method of using a variable stiffness guide wire, comprising: providing a guide wire including a distal portion having a flexibility, a shaft, a distal polymeric member non-releasably attached to the shaft, and a heat source in thermal communication with the polymeric member; changing the flexibility of the distal portion of the guide wire by activating or deactivating the heat source; and wherein the polymeric member comprises a shape memory polymer having a glass transition temperature, and wherein the flexibility changing step comprises heating the polymeric member above the glass transition temperature. 26. A variable stiffness guide wire, comprising: a hypotube having a proximal portion and a distal portion, the distal portion having a flexibility; a polymeric member disposed on and attached to the distal portion of the hypotube, the polymeric member having a first flexibility at a first temperature and a second flexibility at a second temperature, wherein the first temperature is less than the second temperature and the first flexibility is less than the second flexibility; and a heat source disposed on the distal portion of the hypotube, the heat source being in thermal communication wit the polymeric member, whereby activation of the heat source causes the polymeric member to rise from the first temperature to the second temperature to thereby change the flexibility of the distal portion of the guide wire.