What are Nitinol stents used for?
Application of Nitinol Shape Memory Alloy in Medicine
7月 7, 2021
what is nitinol fatigue life?
8月 25, 2021
Nitinol is an indispensable material in stents. We are a professional Nitinol wire and Nitinol tube manufacture. Let us take you to understand the knowledge of Nitinol stents.
1.Stent Categories
Nitinol alloy stent according to the surface state can be divided into bare stent, drug-coated stent, polymer-coated stent,metal-coated stent, radioactive stent and artificial vascular covering stent; according to the implantation site of the stent is divided into esophageal stent, intestinal stent, tracheal stent,biliary stent, urethral stent, peripheral vascular stent,endocardial vascular stent, etc.; according to the stent implantation time is divided into permanent stent and temporary stent.
Nitinol alloy inner bracket can be divided into five kinds according to its design:
(a) bent wire stent
This stent is made by bending round wire or flat wire into a repeating sinusoidal flower cavity,rolled into a spiral ring,stitched, pressed or welded all the way.Changing the sinusoidal geometry, the number of repeating elements,the geometry of the wire, the connection between the ring and the ring can change the performance of the bracket.This bracket typically provides medium flexibility, radial ring strength and minimal size reduction.
b) braid wire stent
This bracket is made by weaving multi-strand round wire or flat wire on the mandrel.The wire forms a spiral on the mandrel, in which the clockwise wire and the counterclockwise wire are woven all the way.Changing the number of strands of wire, wire geometry, weaving flower cavity and weaving angle can change the performance of the stent.Such a bracket typically provides good flexibility,lower radial ring strength and a larger size reduction.
(c) coil wire stent
This bracket is made by spiral progressive winding of single or multi-strand round wire or flat wire on the mandrel.Change the number of wires, wire geometry, coil spacing can change the performance of the bracket.Such a bracket typically provides good flexibility, high radial ring strength(in some loading cases the lower ring is easy to collapse) and a larger size reduction.
(d) laser cut tube stent
The scaffold is formed by laser cutting a complex arrangement of“monocytes”on a small diameter pipe,which are protected to the desired geometry and shaped by heating Complex monocellular cavities require the diameter of the pipe to be as close as possible to the required stent geometry to ensure that the design of the cavity characteristics are not lost during the expansion process.The performance of the stent can be changed by changing the thickness of the tube wall, the flower cavity geometry of the cells, and the connectivity between the cells.Such brackets typically provide medium flexibility,high radial strength and small or no size shortening
(e) laser cut sheet stent
The scaffold is laser-cut on the sheet to create a complex arrangement of “cells”, rolled into a tube, welded or pressed into one.The final size of the stent is limited only by the width of the plate,the flower cavity geometry of the cell, the connection between the cells can change the performance of the stent.Such stents typically provide medium flexibility,high radial/ring strength, and smaller or no size shortening nitinol stents are divided into three categories according to their phase transition temperature
(1)self-expanding stent with a temperature around body temperature.
Implantation in a cold state, hyperelastic recovery of shape at body temperature.
(2)temperature above the body temperature of the self-expanding stent.
Implanted at body temperature, the shape does not change,heated to a temperature above body temperature, shape recovery occurs.
(3)temperature above body temperature balloon dilatation stent.
At this time, the Nitinol alloy is in martensite state,and the diameter of the stent becomes larger by ball expansion.When the stent needs to be removed, the stent is heated locally,the shape is reduced, and the hoop is placed on the sheath tube and pulled out of the body.
2.Characteristics of the bracket
In the past ten years,Nitinol alloy stent has been widely used in the treatment of narrow human lumen.Overall, the development history of various types of stents is similar,from spiral coil-like structure to grid-like braided structure,laser-cut tubular structure, from bare stents to polymer coating or polymer tube package, from shape memory effect type to superelastic self-expansion type, from long-term implantation to short-term implantation and can be recovered.
The earlier bracket products are spiral coil-like structure, made of Nitinol alloy round wire, flat wire or elongated sheet wound.It is divided into two kinds of structures,dense winding and loose winding, mostly dense winding structure, which belongs to the shape memory type.The use of ice salt water and other cooling stent, the coil diameter is reduced, implanted in the body using body temperature heating, so that the stent shape recovery occurs.
The advantages are:
① Easy to pull out,you can use the spray catheter to spray cooling liquid, so that the stent becomes soft,clamp the stent coil with a clamp, pull out of the body, suitable for temporary implantation;
(2) The tightly wound structure can avoid tumor inward growth and cause re-narrowing.
The disadvantages are:
① The spiral coil can not be wound too fine, resulting in a larger diameter of the input device;
② When the shape is restored, the length direction is shortened too much,and the shape recovery of each part is not synchronized, which is easy to cause the coil to be closed incomplete, bent, or twisted;
③ The flexibility of the stent is poor,and the adaptability of the curved cavity is poor;
④ stent expansion and extraction require special catheter injection of hot and cold salt water to achieve, operation trouble;
(5) The anti-radial tightening ability of such structural brackets is poor and is not suitable for the manufacture of larger diameter brackets.
The subsequent development of stent products for Nitinol alloy wire braided mesh stent.It is mostly made of monofilament weaving and is self-expanding Compared to nickel-titanium alloy spiral coil bracket,
The advantages are:
① Full of elasticity and flexibility, easy to pass through the narrow section;
② Can produce large diameter size and ensure sufficient support strength;
The diameter of the support becomes smaller when placed,and the system is simple to operate and the expansion rate is high.
The disadvantage is that the post-implantation meta-method prevents the growth of the tumor and causes the cavity to be narrower.One is endogenous narrowness, that is, the tumor grows inward through the stent mesh; the other is over-narrowness, that is, the tumor grows mainly to the two ends of the stent and then narrow again.
At present, the new type of nitinol alloy intravascular stent is mostly laser-cut tubular stent.
The advantages of this bracket are:
① The pillars are integrated,and the contact between the cavity wall is surface contact, which can provide high radial strength;
② Compared with other types of stents,in the case of providing the same strength,the wall thickness of the tubular stent is lower,which is conducive to the smooth flow of the cavity at the lesion site;
③ Can achieve a larger diameter size change through the flower cavity design, while the size of the length direction does not shorten
The disadvantage is that the processing process is more complex, high technical requirements,the price is more expensive.
The advantages of high-quality Nitinol alloy coated stent are:
① Can greatly reduce the probability of tumor endogenous growth;
② can play a blocking role in all kinds of fistulas.
The disadvantage is that:
① the coating surface is more creamy, it is difficult to firmly attach to the inner wall of the cavity, so the risk of displacement of the coating stent is large;
② Has an impact on the function of the inner surface of the cavity, such as affecting the secretion of mucus.
