DE20019429U1 - Double helix stent with particularly high radial force and flexibility - Google Patents

Description

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Dr. med. Alexander Rübben Aachen, 11.02.01

Gut Steeg 20
52074 Aachen
Germany

Double helix stent with particularly high radial force and flexibility.

Reference number 200 19 429.1

Summary:

So-called "minimally invasive procedures" are becoming increasingly important in medicine. In the context of radiology, interventional radiology is mentioned here, which has contributed significantly to the development of minimally invasive techniques and the necessary devices and prostheses made of suitable materials. Today, small metal grids are inserted into arteriosclerotic vessels as vascular endoprostheses, so-called stents, by both cardiologists and radiologists in order to keep them open.

Background:

Stents, based on an idea by Charles T. Dotter, have been known in medicine since 1969 as vascular endoprostheses. The first stents consisted of a stainless steel spiral and were inserted endovascularly using a guide wire and a suitable catheter. In a further development, a stent made of Nitinol, a special alloy with "memory" behavior, was later developed, which, when inserted at room temperature, expands to the desired full size, originally specified during production, at body temperature. While the first applications were carried out as animal experiments, the first clinical trials began in the 1980s using an elastic, self-expanding spiral made of two stainless steel bands (double-threaded helix) from

Dr. Alexander Rübben
Reference number 200 19 429.1

0.10-0.15mm thick, which could expand up to 35mm. Due to their large diameter, they could only be used to treat large vessels such as the aorta or vena cava. However, since they had to be positioned using a relatively large, flexible introduction instrument, a surgical arteriotomy or venotomy was required. Later, smaller spirals (diameter 10-15mm) were developed, which required a smaller introduction kit and could be introduced percutaneously.

Today's stents usually consist of spirals or metal mesh structures of various designs and are inserted percutaneously using an appropriate catheter.

There are three basic types of stents: stents with thermal memory (memory stents), balloon-expanding stents and mechanically self-expanding stents. The memory stents and the mechanically self-expanding stents are also grouped together as self-expanding stents.

With regard to their areas of application, the following comparison is limited to peripheral applications and the stent types suitable for this purpose.

Stents with thermal memory (memory stents)

These "memory stents" or more precisely "shape memory alloy stents" are made of nitinol, a nickel-titanium alloy that has the property of regaining a shape that was given at high temperature after cooling and reheating to body temperature. This makes it possible to reduce the stent diameter for insertion into the sheath or vessels and thus use smaller, less traumatic insertion sheaths.

This type of stent, the Rabkin stent, was used on a larger clinical scale, initially successfully in the areas of the iliac and renal arteries. However, its use in the femoral and popliteal vessels was problematic with regard to keeping the vessels open. It had a spiral-shaped metal structure, which

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However, percutaneous introduction and precise positioning proved to be quite difficult.

A further development of this type, the Cragg® stent, with a zigzag metal structure, has already been used with good success in stenosing lesions of the iliac vessels. This type of stent is characterized by good longitudinal flexibility due to the polypropylene connections between the individual meshes and was therefore much easier to handle.

Another stent that is often used today is the Memotherm® stent, a stent with a diamond-shaped lattice structure that is made from a nitinol tube using a laser beam. It is characterized by its very high flexibility, very low complication rate (embolisms) and ease of use. It is used successfully in the treatment of stenotic vascular occlusions. The main areas of application are the iliac and femoral vessels. Another stent that should be mentioned here is the Symphony® stent, which is similar to the Memotherm stent but is easier to manufacture. A zigzag-shaped wire is welded to form a lattice structure.

Balloon-expanding stents

Stents of this type are mounted on a balloon catheter and expanded to the desired diameter in the vessel. The stenoses to be treated are usually expanded beforehand using angioplasty to reduce the risk during stent insertion. Once the stent has been positioned, the balloon catheter is removed. The following types of stent are currently being used on an increasing scale.

The Palmaz® stent is made of stainless steel with an initially rectangular grid structure without welding points, which takes on a diamond shape when installed. Stents of this type are not flexible and therefore cannot be positioned in highly tortuous vessels. The "cross-over" technique, i.e. pushing the stent from one iliac artery across the aortic bifurcation into the opposite iliac artery, is not possible with this type of stent. The main areas of application are stenoses of the iliac and renal arteries, and less frequently of the femoral and carotid arteries.

Dr. Alexander Rübben
Reference number 200 19 429.1

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The Strecker® stent was first discovered in 1988 for the treatment of iliac arteries. It consists of a single, very close-meshed thin lattice (0.10-015mm) made of tantalum with great elasticity and flexibility in both the radial and longitudinal directions. It is attached to a balloon catheter using a very thin silicone sheath. The areas of application correspond to those of the Palmaz stent.

Mechanically self-expanding stents

Compressed tightly with the help of a plastic sleeve that is retracted during positioning, these stents slowly expand to the predetermined diameter. Depending on their location and degree of stenosis, vascular stenoses are stented directly or pre-dilated if necessary. The final diameter of the dilated vessel is only reached after days, depending on the deformability of the vascular lesion and the radial expansion force of the stent.

Two types of stent are worth mentioning here: the Gianturco Expandable Wire Stent (GEWS)® or Z-Stent and the Wallstent®. The GEWS, with a zigzag-shaped grid structure made of stainless steel, wire diameter 0.45 mm, was initially used to treat occlusions of the vena cava. It is compressed tightly and inserted through a corresponding catheter with a Teflon sheath and then positioned by pulling back the sheath. The expansion force depends on the diameter of the catheter, the number and shape of the meshes and the length of the endoprosthesis. Due to their relatively high rigidity, these stents are essentially only used in large-caliber vessels such as the aorta and vena cava. The Wallstent, a stent made of stainless steel with diamond-shaped meshes without welds, is characterized by good compressibility and good longitudinal flexibility. It has a special introduction kit and is currently used for peripheral vascular stenoses (iliac, renal and carotid arteries). As a result of its relatively large radial expansion force, the stent tends to shorten longitudinally.

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How it works:

The endoprosthesis described here, a double helix stent, is characterized by the fact that it is particularly flexible due to its special shape and at the same time develops a very strong radial force. This makes it particularly suitable for use in small, twisted vessels, such as coronary vessels. The shape of the individual helix is distinguished by the fact that each element of the helix can deform both transversely and longitudinally. In the longitudinal direction, the double helices are movably connected to one another at certain points.

This special shape gives the stent a high degree of mobility in the longitudinal and transverse direction, adaptation to curved hollow organs and at the same time a high degree of radial stability. Due to the mobility in the longitudinal direction, the stent is shorter than conventional spiral stents.

The special shape of the stent beginning and end also ensures a closed, straight finish.

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Description of the invention:

Stent shape characterized by double helices arranged one behind the other in the longitudinal direction, which are connected to each other at certain points via stent struts.

Here, two helix bands are arranged opposite each other in a mirror image and are connected to each other in a joint-like manner via short transition pieces, see illustration. The double helices form deformable diamonds that lie on top of each other in a spiral shape. In the longitudinal direction, the double helices are connected to each other by connecting elements similar to double-S.

This design, see Fig. 1, ensures that each element of the double helix can deform both transversely and longitudinally and that the stent as a whole can adapt to any vessel curvature.

Fig. 1 View of the stent (not to scale).

The basic lattice structure of the stent is shown.

Annotation:

The shape of the lattice structure is dimension-dependent, i.e. with different dimensions (shorter or longer, smaller or larger diameter) dimension-dependent changes occur without changing the basic design principle.

This special shape gives the stent a high degree of mobility in the longitudinal and transverse direction, adaptation to curved hollow organs and at the same time a very high radial stability through the formation of diamonds in the unfolded state. Due to the mobility in the longitudinal direction, the stent has a lower shortening compared to other stents than with conventional spiral stents. The double-S-like connecting pieces nestle diagonally in a curved shape between the elements of the double helix when compressed, so that

Dr. Alexander Rübben

the stent can be optimally and tightly mounted onto the balloon catheter, while still maintaining mobility.

The stent consists of a lattice structure that is cut from a circular cylinder with a diameter of 1.0-30 mm (depending on the location) using laser technology. The circular cylinder can be made of a variety of materials, such as stainless steel, tanalum, nitinol, copper-gold alloy, other metals, alloys, composite materials, polylactides and other polymers. The wall thickness of the cylinder varies between 0.06 and 0.4 mm (depending on the location). The length of the endoprosthesis varies between 0.5 cm and 15 cm (depending on the location).

To improve biocompatibility, the implants can be coated. Polymers such as parylene or precious metals and their alloys can be used as coatings.

Claims (46)

1. Stent for use in the human body, the shape of which is characterized by the fact that the stent consists of double helices arranged one behind the other in the longitudinal direction and connected to one another at certain points by stent struts. In this case, two helix bands are arranged opposite one another in a mirror image and are connected to one another in a joint-like manner by short transition pieces. The double helices form deformable diamonds that lie on top of one another in a spiral shape. In the longitudinal direction, the double helices are connected to one another by connecting elements similar to double-S. 2. Like 1, and made from a circular cylinder of stainless steel. 3. As 2 with a coating of a polymer material. 4. As 2 with a coating of Parylene. 5. Like 2 with a coating of a precious metal. 6. As 2 with a coating of a precious metal alloy. 7. How 1 is prepared from a circular cylinder of polylactide. 8. As 7 with a coating of a polymer material. 9. Like 7 with a coating of Parylene. 10. Like 7 with a coating of a precious metal. 11. As 7 with a coating of a precious metal alloy. 12. How 1 is made from a circular cylinder made of a polymer. 13. As 12 with a coating of a polymer material. 14. As 12 with a coating of Parylene. 15. Like 12 with a coating of a precious metal. 16. As 12 with a coating of a precious metal alloy. 17. How 1 is made from a circular cylinder of Nitinol. 18. As 17 with a coating of a polymer material. 19. As 17 with a coating of Parylene. 20. Like 17 with a coating of a precious metal. 21. As 17 with a coating of a precious metal alloy. 22. How 1 is made from a circular cylinder of tantalum. 23. As 22 with a coating of a polymer material. 24. Like 22 with a coating of Parylene. 25. Like 22 with a coating of a precious metal. 26. As 22 with a coating of a precious metal alloy. 27. How 1 is made from a circular cylinder of copper/gold alloy. 28. As 27 with a coating of a polymer material. 29. Like 27 with a coating of Parylene. 30. Like 27 with a coating of a precious metal. 31. As 27 with a coating of a precious metal alloy. 32. How 1 is made from a circular cylinder of an alloy. 33. As 32 with a coating of a polymer material. 34. Like 32 with a Parylene coating. 35. Like 32 with a coating of a precious metal. 36. Like 32 with a coating of a precious metal alloy. 37. How 1 is made from a circular cylinder made of composite materials. 38. As 37 with a coating of a polymer material. 39. Like 37 with a coating of Parylene. 40. Like 37 with a coating of a precious metal. 41. Like 37 with a coating of a precious metal alloy. 42. How 1 is made from a circular metal cylinder. 43. As 42 with a coating of a polymer material. 44. Like 42 with a Parylene coating. 45. Like 42 with a coating of a precious metal. 46. Like 42 with a coating of a precious metal alloy.