Systems and methods for variable stiffness tethers
Described herein are devices and methods for guide elements configured with variable stiffness, with one or more flexible portions and one or more stiff portions. The flexible portion is be used as a tensioning element of a cinchable implant to tighten or compress tissues while the stiff portion is used to facilitate the insertion or withdrawal of portions of the implant or instruments acting on the implant. The guide element is further configured to be separated or severed between the flexible and stiff portions so that a flexible portion is left within the body as part of the implant, while the stiff portion is withdrawn from the body after implantation is completed.
1. A guidewire element comprising:
a rigid proximal portion;
a flexible distal tether portion that is less rigid than the proximal portion;
an attachment portion located between the flexible distal tether portion and the rigid proximal portion that releasably attaches the flexible distal tether portion to the rigid proximal portion; and
wherein the flexible distal tether portion is configured to be used as a tensioning element and to be detached after tensioning.
2. The guidewire element of claim 1 , wherein the flexible distal tether portion has a first torsional stiffness and the rigid proximal portion has a second torsional stiffness that is higher than the first torsional stiffness.
3. The guidewire element of claim 1 , wherein a yield force of the rigid proximal portion as determined by compression testing is greater than a yield force of the flexible distal tether portion as determined by compression testing.
4. The guidewire element of claim 1 , wherein the rigid proximal portion comprises a first portion and a second portion, wherein the first portion is more rigid than the second portion.
5. The guidewire element of claim 1 , wherein the attachment portion comprises a first clasp attached to the rigid proximal portion, a second clasp that interfits with the first clasp attached to the flexible distal tether portion, and a pull-wire slidably insertable within the first and second clasps, wherein in a first protracted configuration the pull-wire secures the engagement between the first and second clasps, and in a second retracted configuration the pull-wire releases the engagement between the first and second clasps.
6. The guidewire element of claim 1 , wherein the attachment portion comprises a temperature-sensitive polymer segment that is attached between the rigid proximal portion and the flexible distal tether portion, wherein the temperature-sensitive polymer segment is configured to weaken when heated.
7. The guidewire element of claim 1 , wherein the attachment portion comprises a metal segment that is attached between the rigid proximal portion and the flexible distal tether portion, wherein the metal segment is configured to weaken when heated.
8. The guidewire element of claim 7 , wherein the attachment portion comprises a metal segment susceptible to electrolytic dissolution that is attached between the rigid proximal portion and the flexible distal tether portion, wherein the metal segment is configured to dissolve when subjected to an electrical charge.
9. The guidewire element of claim 1 , wherein the attachment portion comprises a plug attached to the flexible distal tether portion, wherein the rigid proximal portion comprises a lumen that is sized and shaped to frictionally retain the plug.
10. The guidewire element of claim 1 , wherein the attachment portion comprises a screw joint, wherein the external thread of the screw joint is attached to the rigid proximal portion and the internal thread of the screw joint is attached to the flexible distal tether portion.
11. The guidewire element as in claim 1 , wherein the flexible distal tether portion and the rigid proximal portion are made from a same material and said rigid proximal portion is stiffened by applying a stiffening agent.
12. The guidewire element as in claim 11 , wherein the material is biodegradable.
13. The guidewire element as in claim 11 , wherein the material is non-biodegradable.
14. The guidewire element as in claim 1 , wherein the flexible distal tether portion is in the range of from about 5 cm to about 30 cm in length.
15. The guidewire element as in claim 1 , wherein a ratio of the axial length of the flexible distal tether portion to the axial length of the rigid proximal portion is in the range of from about 0.05 to about 0.5.
16. The guidewire element as in claim 1 , wherein the flexible distal tether portion is a monofilament and the rigid proximal portion is braided.
17. The guidewire element as in claim 1 , wherein the flexible distal tether portion is braided and the rigid proximal portion is monofilament.
18. The guidewire element as in claim 1 , wherein the rigid proximal portion comprises a larger outer diameter than the flexible distal tether portion.
19. The guidewire element as in claim 1 , wherein the flexible distal tether portion is made from a first material; wherein the rigid proximal portion comprises at least one filament, and wherein the filament is made from a second material stiffer than the first material.
20. The guidewire element as in claim 1 , wherein the flexible distal tether portion and the rigid proximal portion are coated with different materials.