DE102016110410B4 - Stent, manufacturing process and treatment system - Google Patents

Abstract

Stent (10) for implantation in a blood vessel, in particular a neurovascular one, with a substantially tubular, self-expandable lattice structure (11) which can be converted from a radially fully expanded expansion diameter to a radially fully compressed compression diameter, the lattice structure (11) exerting the diameter Radial pressure forms a hysteresis with a compression pressure RRF and an expansion pressure COF, and where the following applies for the compression pressure RRF and the expansion pressure COF in a diameter range from x1 to x2:[(RRF(x1)−RRF(x2))−(COF(x1)−COF (x2))]/[COF(x1)−COF(x2)]≥A where A = 10% and x2 > x1.

Description

The invention relates to a stent for implantation in a blood vessel, in particular a neurovascular one. Furthermore, the invention relates to a manufacturing method and a treatment system for such a stent.

Stents are well known and are commonly used to treat stenoses in blood vessels. The task of the stent is to widen the narrowed blood vessel in the area of the stenosis in order to ensure adequate blood flow. The stent is usually placed by feeding the stent through a catheter to the treatment site. During delivery through the catheter, the stent, which has a tubular lattice structure, is in a radially compressed state. At the treatment site, the stent is released from the catheter. Self-expanding stents expand automatically after being released from the catheter and exert a radial force on the vessel wall. Such stents are made, for example U.S. 2013/0197617 A1 and U.S. 2010/0087913 A1 known. This maintains the cross-section of the blood vessel through which the blood can flow.

A balloon catheter is often used in practice to widen a stenosis and thus largely restore the original cross-sectional diameter of a blood vessel through which flow can flow. The balloon catheter includes an inflatable balloon that is guided into the area of the stenosis and expanded there. This widens the stenosis. For medical reasons, the stenosis is usually not expanded by the balloon to the full original vessel diameter, i.e. to the diameter of the blood vessel in a healthy state. A partial expansion is preferred so that the vascular tissue is not overstretched and thus injured.

Injury can lead to the ablation of the endothelial tissue. As a result, blood flowing through the blood vessel can come into contact with subendothelial tissue. The subendothelial tissue is highly thrombogenic and increases the risk of blood clot formation.

Nevertheless, in the medium and long term, the aim is to completely expand the blood vessel in the area of the stenosis up to the original vessel diameter. However, the expansion should be done slowly so that the tissue of the blood vessel can adapt to the expansion and thus reduce the risk of injury. A stent is therefore desirable which continuously and slowly, in particular over a period of several days, causes the blood vessel to expand further.

A radial force is therefore required for the functioning of a stent in the blood vessel, which ensures that the stent exerts pressure radially outwards. At the same time, this radial force is problematic for the delivery of the stent, since the stent presses against the inner wall of the catheter. This increases the frictional forces when pushing the stent through the catheter.

This is problematic because a user has to apply a relatively high force to overcome the static friction between the stent and the catheter, which makes it difficult to place the stent exactly in the blood vessel.

It is also known to preload self-expanding stents directly onto a catheter tip so that the stent does not have to be pushed through the entire catheter. This solves the problem of increased static friction when advancing the stent through the catheter. At the same time, however, it is accepted that the catheter tip is stiffened by the stent arranged therein. This in turn makes it difficult to navigate through curved sections of blood vessels, which are particularly common in neurovascular blood vessels.

Out of U.S. 2012/0101572 A1 a mitral valve prosthesis is known which has an expandable support structure. A similar prosthesis, namely an aortic valve prosthesis, is disclosed US 2012/0116496 A1 . Such valve prostheses require a high radial force, but are also conveyed to the treatment site through large blood vessels, so that the problem of frictional forces in small catheters does not arise.

The object of the invention is to provide a stent that can be easily fed through a catheter and at the same time effectively widens a stenosis. Furthermore, it is the object of the invention to specify a manufacturing method for such a stent.

According to the invention, this object is achieved by the subject matter of patent claim 1 with regard to the stent, by the subject matter of patent claim 20 with regard to the production method and by the subject matter of patent claim 23 with regard to the treatment system.

Specifically, the invention is based on the idea of specifying a stent for implantation in a blood vessel, in particular a neurovascular one, with an essentially tubular, self-expanding lattice structure. The lattice structure is convertible from a radially fully expanded expansion diameter to a radially fully compressed compression diameter. The radial pressure exerted by the lattice structure forms a hysteresis with a compression pressure RRF and an expansion pressure COF. The following applies to the compression pressure RRF and the expansion pressure COF in a diameter range from x ₁ to x ₂ : $$\left[\left(\text{RRF}\left({\text{x}}_1\right)-\text{RRF}\left({\text{x}}_2\right)\right)-\left(\text{COF}\left({\text{x}}_{\text{1}}\right)-\text{COF}\left({\text{x}}_{\text{2}}\right)\right)\right]/\left[\text{COF}\left({\text{x}}_{\text{1}}\right)-\text{COF}\left({\text{x}}_{\text{2}}\right)\right]\ge \text{A}$$

Furthermore, A=10% and x ₂ >x ₁ .

Self-expanding stents have the property that they have different radial forces during the transition from the compressed state to the expanded state than during the transition from the expanded state to the compressed state. In addition, the radial force or the pressure exerted radially by the lattice structure differs for each cross-sectional diameter of the lattice structure.

It has been found that a self-expanding lattice structure resists a radial compression process more than it does itself when radially expanding. In other words, the compression pressure required to compress the self-expanding stent is higher than the expansion pressure that the lattice structure exerts automatically when expanding.

The invention now proposes adjusting the lattice structure in such a way that in a predetermined diameter range the difference between the increase in the compression pressure and the increase in the expansion pressure corresponds to at least 0.1 times the increase in the expansion pressure.

In other words, it is intended to contrast the increase in pressure that occurs when the lattice structure is compressed with the reduction in pressure that occurs when the lattice structure is expanded. The expansion pressure decreases as the lattice structure expands, the decrease being smaller than the increase in compression pressure as the lattice structure compresses.

Surprisingly, it has been shown that when the compression pressure and the expansion pressure are set according to the above formula, a particularly good compromise is achieved between the ability to deliver the stent through a catheter and the therapeutic effectiveness of the stent for widening a stenosis. It is believed that the therapeutic efficacy is improved because the stenosis attempts to compress the stent, and the stent opposes the relatively higher compressive pressure to this compression. When the stent is fed in, the lattice structure automatically presses outwards, so that the expansion pressure, which is lower than the compression pressure, acts on the inner surface of the catheter.

The invention provides that the compression pressure RRF is not constantly greater than the expansion pressure COF, but varies as a function of the current cross-sectional diameter of the lattice structure. The smaller the cross-sectional diameter of the lattice structure, the higher the difference between the compression pressure RRF and the expansion pressure COF.

As a result, the lattice structure exerts a relatively low but constant force, namely the expansion pressure COF, on a stenosis. The expansion pressure decreases over time as the lattice structure slowly expands, thus increasing the cross-sectional diameter of the lattice structure. In this way, it is ensured that the stenosis is expanded continuously over a long period of time, in particular over several days, in a manner that is gentle on the vascular tissue.

The different progression of the compression pressure RRF and the expansion pressure COF consequently has particular advantages with regard to the behavior of the stent in the blood vessel. A high difference between the compression pressure RRF and the expansion pressure COF leads to a relatively rigid behavior of the stent. The stent thus withstands compression by the blood vessel, but due to the comparatively lower expansion pressure itself only has a moderate effect on the blood vessel. So avoid On the one hand, the stent causes a further narrowing of the blood vessel and, on the other hand, causes a moderate and slow expansion at the same time. This is particularly advantageous in the area of a stenosis, because rapid expansion of the stenosis can lead to damage to the vascular tissue.

This advantage of the invention is particularly evident in the treatment of neurovascular blood vessels in the intracranial area. Such blood vessels have a relatively large number of vascular outlets, so-called perforators. In the treatment of stenoses with stents, these perforators extending from the main vessel represent particularly critical areas. In particular, there is a risk that parts of the vascular area affected by a stenosis will break open and be pushed into the perforators. This can lead to further vascular occlusions.

As the lattice structure acts continuously on the stenosis due to the low expansion pressure COF, the blood vessel in this area is slowly expanded. This avoids rupture of the vascular area affected by the stenosis and thus reduces the risk of further vascular occlusions.

The invention places great value on a comparatively high compression pressure RRF of the lattice structure with a relatively low or moderate expansion pressure COF at the same time. However, a small difference between the compression pressure RRF and the expansion pressure COF promotes the compliance of the stent in the blood vessel. Such a small difference is achieved with comparatively larger cross-sectional diameters of the lattice structure, since the compression pressure RRF and the expansion pressure COF converge with increasing cross-sectional diameter of the lattice structure.

Especially in the pulsatile cycle of blood flow, a small difference between the compression pressure RRF and the expansion pressure COF is advantageous since the force of the stent is similar in systole (expansion of the stent) and in diastole (compression of the stent). The vessel wall of the blood vessel is thus exposed to a similar pressure during expansion in systole and during compression in diastole. This pressure adds up to the dynamic pressure of the bloodstream, which varies between systole and diastole. The smaller the difference between compression pressure RRF and expansion pressure COF, the smaller the difference in the load on the vessel wall between systole and diastole. The physiological, pulsatile expansion of the vessel is not affected as much.

The aforementioned behavior is particularly advantageous in the edge areas of the stent, which are in direct contact with the vessel wall in the implanted state. The good compliance behavior of the stent avoids the pulse wave being interrupted at the edge of the stent, which can otherwise lead to vascular injuries and restenosis.

Particularly good results can be achieved if one of the following values is substituted for the value A in the above formula. In particular, it is preferred if A=15%, in particular A=20%, in particular A=25%, in particular A=30%, in particular A=35%, in particular A=40%.

The advantages described above are particularly evident in the diameter range between 1.5 mm and 2.5 mm. In this respect, it is preferred if x ₂ =2.5 mm and x ₁ =1.5 mm.

wobei d_exp den Expansionsdurchmesser der Gitterstruktur bezeichnet.In general, it is advantageous in the invention if the relatively larger cross-sectional diameter x ₂ corresponds to the expansion diameter of the lattice structure minus 0.5 mm. The relatively smaller cross-sectional diameter x ₁ is preferably 1 mm smaller than the relatively larger cross-sectional diameter x ₂ . Expressed mathematically, the following preferably applies: $${\text{x}}_{\text{2}}={\text{i.e}}_{\text{ex}}-0.5{\text{mm and x}}_{\text{1}}={\text{x}}_{\text{2}}-1\text{mm},$$

where d _exp denotes the expansion diameter of the lattice structure.

$${\text{x}}_{\text{1}}=\mathrm{3,5}\text{mm}-\mathrm{1,}\text{0mm}=\mathrm{2,5}\text{mm}$$

For a stent with an expansion diameter of 4.0 mm this results in: $${\text{x}}_{\text{2}}=4.0\text{mm}-\mathrm{0,}\text{5mm}=3.5\text{mm}$$

$${\text{x}}_{\text{1}}=3.5\text{mm}-\mathrm{1,}\text{0mm}=2.5\text{mm}$$

The lattice structure of the stent can have an implantation diameter and an expansion diameter. The implantation diameter is also referred to as the intended use diameter. This diameter indicates the preferred value for the diameter of the blood vessel in which the stent is to be inserted. For the compromise between compression pressure and expansion pressure described above, it has proven to be advantageous if the implantation diameter of the lattice structure is less than 3.5 mm, in particular between 3.4 mm and 1.0 mm.

The expansion diameter of the lattice structure is when the lattice structure is fully expanded. The expansion diameter thus describes the force-free state of the lattice structure. Preferably, the expansion diameter of the lattice structure in the present invention is more than 2.5 mm and at most 4.0 mm. In particular, it can be provided that the expansion diameter is at least 3.0 mm and at most 3.5 mm. Concretely, the expansion diameter of the lattice structure can be 3.0 mm.

The lattice structure preferably has a length of between 8 mm and 35 mm, in particular between 8 mm and 20 mm, in particular between 10 mm and 15 mm.

In this context, it is pointed out that the radial pressure described here acts on the environment via the outer contact surface of the lattice structure. The outer contact area of the lattice structure is determined by the outer surfaces of the structural elements, in particular webs or wires, of the lattice structure. The sum of the outer surfaces of all structural elements of the lattice structure essentially forms the outer contact surface of the lattice structure with the environment, for example a vessel wall.

The radial pressure exerted across the outer contact surface of the grating structure can be measured with a device which essentially has some kind of iris diaphragm. The stent is inserted into the iris diaphragm, with the iris diaphragm being coupled to a load cell or strain gauge. The iris absorbs the pressure of the lattice structure over the entire circumference of the lattice structure, so that the corresponding radial pressure can be measured with the pressure cell connected to the iris.

The outer contact area of the stent is preferably between 7.5 mm ² and 16.75 mm ² . For a stent with an implantation diameter of 3.0 mm and a length between 15 mm and 35 mm, the contact area is preferably between 8.2 mm ² and 18.7 mm ² . A stent with an implantation diameter of 4.0 mm and with a length between 15 mm and 35 mm can have a contact area between 7.5 mm ² and 16.7 mm ² .

For a stent with an implantation diameter between 4.5 mm and 5.5 mm and a length between 15 mm and 35 mm, the outer contact area is preferably between 9.5 mm ² and 24.6 mm ² .

In particular for the treatment of stenoses in neurovascular blood vessels, for example blood vessels in the intracranial area of the head, it has proven to be advantageous if the compression pressure RRF is increased at an expansion diameter of between 1.0 mm and 3.0 mm, in particular between 1.5 mm and 2 .5 mm is at least 30 mmHg. It is also possible that the compression pressure RRF for the aforementioned expansion diameters is at least 40 mmHg, in particular at least 50 mmHg, in particular at least 60 mmHg.

The compression pressure RRF can be at most 150 mmHg, in particular at most 120 mmHg, in particular at most 100 mmHg, in particular at most 80 mmHg, in particular for the expansion diameters described above.

During self-expansion, the lattice structure of the stent exerts an expansion pressure COF which, with an expansion diameter of between 1.0 mm and 3.5 mm, in particular between 1.5 mm and 2.5 mm, can be at least 10 mmHg and at most 70 mmHg. It is preferred if the expansion pressure COF at the aforementioned diameter values is between 20 mmHg and 60 mmHg, in particular between 30 mmHg and 50 mmHg.

The lattice structure of the stent can have or consist of a nickel-titanium alloy, in particular nitinol. Such nickel-titanium alloys are suitable for the production of self-expanding stents and have corresponding material properties which, together with further optimization measures, lead to the effects desired according to the invention.

In order to use the material properties of the lattice structure to provide the desired effect, namely improved feedability with good therapeutic effectiveness of the stent at the same time, the nickel-titanium alloy can have between 50 atom % and 60 atom % nickel. It is particularly preferred if the nickel-titanium alloy contains between 55 atom % and 56 atom %, in particular concretely 50.8 atom %, nickel.

In particularly preferred embodiments, the lattice structure is formed in one piece from webs. For example, the lattice structure can be produced in one piece by laser cutting a tube or by building up in layers using a deposition method, in particular a vacuum deposition method, for example a physical vacuum deposition method (PVD) or a sputtering method. However, it is conceivable that the lattice structure is formed by a mesh of wires.

In order to enable the stent to be fed into small blood vessels, in particular through a correspondingly thin catheter, the lattice structure can be compressible to a compression diameter of 0.4 mm.

It is also preferred if the lattice structure has closed cells, in particular a closed-cell design. The closed cells facilitate delivery of the stent through a catheter. In particular, the webs of closed cells support one another, so that the stent can be moved well as a unit through a through-lumen of the catheter.

A distinction is made between a closed-cell design and an open-cell design, which, however, can lead to a distortion of the lattice structure when it is released. In particular, in an open-cell design, free-standing bar connectors can lead to additional irritation or damage to the tissue. A closed-cell design, on the other hand, has advantages in that it does not have free-standing bar connectors and typically does not distort during release from a catheter.

Furthermore, a lattice structure with a closed-cell design can be pulled back into the catheter after partial release from the catheter. This can be useful to correct misplacement of the stent.

Advantageously, the invention provides that a central section of the lattice structure in the implanted state causes a sufficient expansion of a stenosis and edge areas of the lattice structure generate a radial pressure that is sufficient to hold the lattice structure in the blood vessel without causing injury to the vascular tissue.

The lattice structure is usually placed in the blood vessel in such a way that a middle section of the lattice structure covers the stenosis. The edge sections or edge areas of the lattice structure, on the other hand, are located in healthy vessel sections that border on the stenosis. In the area of the healthy vessel sections, i.e. in the edge areas, the lattice structure has a larger cross-sectional diameter in the implanted state than in the central section, whose cross-sectional diameter is limited by the stenosis.

Because of the relationship between the compression pressure RRF and the expansion pressure COF with respect to the cross-sectional diameter, as described in detail above, the lattice structure is more stable in the middle section than in the edge areas. Therefore, the lattice structure can better follow a deformation of the blood vessel by the pulsating blood flow, i.e. a pulse wave, in the edge areas than in the middle section.

In concrete terms, it can be provided that the edge areas of the lattice structure avoid a vessel injury or reduce its effect by reducing the amplitude of the pulse wave deformation of the blood vessel in the edge areas by at most 10%, in particular at most 20%, in particular at most 30%, in particular at most 40%, in particular at most 50%, based on the state without inserted stent is reduced.

At the same time, the radial pressure of the middle section of the lattice structure causes the stenosis to dilate. This expansion preferably takes place very slowly in order to prevent stenosis particles from becoming detached. Otherwise, detached stenosis particles could be washed into smaller blood vessels and lead to an occlusion there.

The expansion of the stenosis by the middle section of the lattice structure is preferably so slow that a period of at least 12 hours is required for the diameter of the blood vessel to expand to 110% of the original diameter value, ie before the implantation of the stent. The expansion of the blood vessel to a diameter that is 10% greater than the original diameter can also last for at least one day, in particular at least 2 days, in particular at least 3 days, in particular at least 1 week, in particular at least 2 weeks, in particular at least 1 month. last for.

It is also possible, particularly when using a lattice structure that provides an increased expansion pressure COF, that the stenosis expands to a diameter that exceeds the original diameter by 20% within the aforementioned periods of time. In any case, it is planned that the expansion of the stenosis up to a diameter of 110% of the original diameter will not take longer than 6 months.

In particular, the middle section of the lattice structure can expand the stenosis so slowly that perforator vessels branching off in the area of the stenosis are not closed by the expansion of the stenosis. In particular, an expansion of 10% or 20% of the original diameter can take place in the aforementioned time periods. This ensures that the perforator vessels have sufficient time to adapt to the changed cross-sectional diameter of the main vessel.

The adaptation of the perforating vessels to the changing cross-sectional diameter of the main vessel is referred to as "remodeling".

Adequate remodeling ensures adequate blood flow into the perforator vessels, which is adapted to the (energy) requirements of the subsequent tissue. The remodeling takes several hours, sometimes even several days or weeks. If a stenosis widens too quickly, the tissue of the stenosis, called plaque tissue, slowly bulges into the perforator vessels and can lead to flow restriction or occlusion. This is avoided by slowly expanding the stenosis.

One aspect of the invention relates to a stent for implantation in a blood vessel, in particular a neurovascular one, with an essentially tubular, self-expanding lattice structure which can be converted from a radially fully expanded expansion diameter to a radially fully compressed compression diameter. The stent is formed according to the previous statements. It is provided within the framework of the secondary aspect of the invention that the lattice structure has at least one edge cell with a first length and at least one middle cell with a second length. The ratio between the first length and the second length is preferably between 0.5 and 2.5, in particular between 1.0 and 2.0, in particular between 1.25 and 1.75. In a specific embodiment it can be provided that the ratio between the first length and the second length is 1.5.

The length of a cell is usually determined between two connection points or crossing points of the webs, which are arranged directly adjacent to one another in the longitudinal direction of the lattice structure. The length thus runs parallel to the longitudinal axis of the lattice structure. Edge cells are cells that are located at the edge of the lattice structure along the longitudinal axis, ie close the lattice structure along the longitudinal axis.

The setting of different cell lengths between at least one edge cell and at least one middle cell has several advantages. On the one hand, the result is that comparatively low radial forces are set in the edge area, as a result of which the ability to feed the stent through a catheter is improved. On the other hand, it can be provided that each second edge cell has the first length in the circumferential direction. In contrast, the edge cell arranged in between can have a different length. This makes it possible for the edge-side tips of the edge cells to be arranged offset to one another, which ensures improved compressibility of the lattice structure.

It is particularly preferred if the edge cell with the first length has an extension that carries an X-ray marker. Particular advantages result in particular when edge cells with an extension and edge cells without an extension alternate in the circumferential direction of the lattice structure. Since the X-ray marker, which is arranged on the extension, increases the wall thickness and web width of the lattice structure, an offset arrangement of the edge-side tips of the edge cells can improve compression be achieved. This in turn contributes to the fact that the stent can easily be guided through a catheter to the treatment site despite sufficiently high therapy efficiency.

The edge cell with the first length and the middle cell with the second length can be arranged directly adjacent to one another in the longitudinal direction of the lattice structure. Alternatively or additionally, it is possible that the edge cell with the first cell and the middle cell with the second length are coupled to one another by a common cell connector.

A secondary aspect of the invention relates to a manufacturing method for a stent as described above. In the production method according to the invention, the lattice structure is preferably deposited on a substrate by a physical deposition method, in particular a sputtering method, and is then removed from the substrate.

The lattice structure can either be deposited in a tube shape or first deposited in a planar manner and then converted into a tube shape. In the case of initially planar formation of the lattice structure, it is preferably provided that the shaping to the final tube shape takes place at elevated temperatures between 450.degree. C. and 680.degree.

Provision can preferably be made for the lattice structure to be formed by depositing a supporting material and an X-ray-visible material that is different from the supporting material. In other words, the lattice structure can be formed from two different materials, with a support layer and a surface layer being provided, and with the surface layer having X-ray-visible properties.

It is also conceivable that the X-ray-visible material is applied to the supporting material in certain areas or at certain points, in particular in order not to impair the mechanical properties of the supporting material. Preferably, however, the X-ray-visible material is distributed along the lattice structure so that at least the longitudinal-axial ends of the lattice structure can be easily identified under X-ray control.

In particular, the supporting material can have or consist of a nickel-titanium alloy. As described above, the nickel-titanium alloy may contain a predetermined amount of nickel. The X-ray visible material preferably includes or consists of tantalum and/or platinum and/or gold. Such materials are particularly suitable for coating a nickel-titanium alloy to improve the X-ray visible properties.

• 1: eine entfaltete Ansicht einer Gitterstruktur des erfindungsgemäßen Stents nach einem bevorzugten Ausführungsbeispiel;
• 2: ein Diagramm zur Darstellung des Kompressionsdrucks und des Expansionsdrucks bei dem Stent gemäß 1; und
• 3: eine tabellarische Übersicht unterschiedlicher Umfangsflächen bei dem Stent gemäß 1.

The invention is explained below using an exemplary embodiment with reference to the accompanying schematic representations. Show in it:

• 1 1: an unfolded view of a lattice structure of the stent according to the invention according to a preferred embodiment;
• 2 : a diagram showing the compression pressure and the expansion pressure in the stent according to FIG 1 ; and
• 3 : a tabular overview of different circumferential areas in the stent according to FIG 1 .

1 shows a stent 10 or its lattice structure 11 in an unfolded view. The webs 13 delimit cells 12. Specifically, it is provided that the lattice structure 11 is designed as a closed lattice structure (closed cell design). In particular, four webs 13 in each case delimit a cell 12. The cells 12 essentially have a kite-shaped or diamond-shaped basic geometry.

The individual webs are connected to one another at cell connectors 15 . The cell connectors 15 are preferably aligned with one another in the longitudinal direction of the stent (from left to right in the image plane).

In 1 it can be seen that at the axial longitudinal ends of the lattice structure 11 edge cells 12a are arranged, which have a first length l ₁ . The edge cells 12a are coupled by a cell connector 15 to center cells 12b. The center cells 12b have a second length I ₂ .

Specifically, it is provided that the central cells 12b are each delimited by four webs 13 of equal length. The edge cells 12a, on the other hand, can have webs 13 of different lengths. In particular, it can be seen that a plurality of edge cells 12a are arranged adjacent to one another in the circumferential direction at the axial longitudinal ends of the lattice structure 11, with each second edge cell 12a having two longer webs 13 arranged in a V-shape relative to one another. The longer webs 13 open into an extension 14 which extends parallel to the longitudinal axis of the lattice structure 11 beyond the edge cells 12a. The extension 14 is provided to accommodate an X-ray marker. For example, an X-ray marker sleeve can be slipped onto the extension 14 and fixed by crimping.

In 1 the difference in length between the first length I ₁ and the second length I ₂ is clearly marked. The first length I ₁ of the edge cell 12a and the second length I ₂ of the central cell 12b are measured between the cell connectors 15 that are directly adjacent in the longitudinal direction of the lattice structure 11 and aligned with one another.

Since only every second edge cell 12a is lengthened along the longitudinal axis and ends in an extension 14, the offset cell tips 16 leave a free space for the x-ray markers. In this way, the crimpability of the lattice structure 11 is improved. Since the X-ray markers can “evade” into the free spaces between two extended edge cells, the edge areas of the lattice structure 11 in the compressed state do not press disproportionately against an inner peripheral surface of a catheter.

2 shows a diagram in which the cross-sectional diameter of the stent 10 or the lattice structure 11 and the radial pressure exerted by the lattice structure 11 are compared. The values for a stent 10 are shown here as an example, the implantation diameter of which is 3.0 mm. The length of the stent 10 or the lattice structure 11 is preferably 35 mm.

are shown in 2 the change in radial pressure upon expansion of the stent 10 from a 2 mm cross-sectional diameter to a 2.5 mm cross-sectional diameter.

The radial pressure during expansion is called the expansion pressure COF. It can be seen that the expansion pressure COF decreases as the lattice structure expands. The idealized, linear course of the expansion pressure COF between the diameter values 2.0 mm and 2.5 mm has a comparatively flat gradient.

When compressed, the stent 10 resists a radial pressure referred to as the compression pressure RRF. The compression pressure RRF is in 2 also shown in the diameter range between 2 mm and 2.5 mm. It can be seen that the radial pressure of the lattice structure 11 increases sharply when the stent 10 is compressed from a cross-sectional diameter of 2.5 mm to a cross-sectional diameter of 2.0 mm. The gradient of the idealized linear change in the compression pressure RRF is comparatively large.

It is also possible that the slope of the compression pressure RRF and/or expansion pressure COF curves is not linear. For example, the gradient of the curve of the compression pressure RRF (RRF curve) or the gradient of the curve of the expansion pressure COF (COF curve) can increase with decreasing cross-sectional diameters. For the other curve, the slope may decrease as the diameter decreases. Consequently, the difference in the slope of the RRF curve and the COF curve can become more apparent in the case of relatively small or relatively large cross-sectional diameters of the lattice structure 11 .

It is also possible that the slope of both curves decreases or increases as the cross-sectional diameters become smaller. It is also possible for one curve to be nearly linear and the other curve to have a change in slope, i.e. a curved shape. By appropriately adjusting the slope of the two curves, different variations are conceivable, which are advantageous for use in different stenoses.

In particular shows 2 clearly that the expansion pressure COF is always smaller than the compression pressure RRF. At the same time, it can be seen that the course of the compression pressure RRF between two diameter values has a significantly higher slope than the course of the expansion pressure between two diameter values. This is used in the stent according to the invention in order to achieve good feedability through a catheter. Inside the catheter is particular the expansion pressure COF effective. Since this is relatively small, the stent 10 can be easily pushed through the catheter.

At the treatment site, particularly in the area of a stenosis, the stent is compressed by the stenosis. The pressure that the stent resists is the compression pressure RRF, which is relatively high. The stent can thus be used particularly effectively for keeping a blood vessel open. The advantage of the increased compression pressure RRF with a relatively smaller cross-sectional diameter comes into play in particular when the blood vessel to be treated tends towards restenosis. The renewed growth of the blood vessel leads to a compression of the stent 10, which counteracts this with the now increasing compression pressure RRF.

• Im Bereich einer Stenose ist der Stent möglicherweise in einem mittleren Abschnitt, insbesondere im Bereich der Mittelzellen 12a, stärker komprimiert als in seinen Außenabschnitten bzw. Randbereichen, insbesondere im Bereich der Randzellen 12a. Dies ergibt sich bereits daraus, da der Stent 10 üblicherweise in einer Länge eingesetzt wird, die größer ist als die Länge des durch die Stenose beeinträchtigten Blutgefäßabschnitts. Diese Überdimensionierung des Stents 10 führt dazu, dass die Randzellen 12a außerhalb der Stenose zu liegen kommen, wogegen die Mittelzellen 12b unmittelbar in Kontakt mit der Stenose gelangen.

The diagram according to 2 makes something else very clear. Since the expansion pressure and the compression pressure change over the current diameter of the stent 10 or the lattice structure 11, different radial pressures are also effective in different areas of the stent 10. This is particularly advantageous for gentle therapy of a stenosis. This is explained below:

• In the area of a stenosis, the stent may be more strongly compressed in a middle section, in particular in the area of the central cells 12a, than in its outer sections or edge areas, in particular in the area of the edge cells 12a. This is due to the fact that the stent 10 is usually used in a length that is greater than the length of the blood vessel section affected by the stenosis. This oversizing of the stent 10 means that the edge cells 12a come to lie outside the stenosis, whereas the central cells 12b come into direct contact with the stenosis.

As in 2 is clearly visible, with a smaller diameter of the stent 10 a comparatively higher compression pressure RRF counteracts a compression of the stent. The middle section of the stent 10, which is arranged in the area of the stenosis, is usually compressed more than the edge areas. The more heavily compressed stent in the area of the stenosis can therefore prevent the blood vessel from further narrowing due to its regionally higher compression pressure RRF. Thus, the central portion of the stent 10 effectively acts on the stenosis.

In contrast, in the edge sections of the stent, which are arranged outside the stenosis, it is expedient if the stent can follow a movement of the vessel walls. Areas of a blood vessel that are free of stenosis are very flexible and constantly in motion due to the pulsating blood flow. In particular, the vessel diameter of a blood vessel changes constantly depending on the pulse rate. This effect is significantly reduced in the area of a stenosis, since the stenosis leads to a stiffening of the blood vessel.

The edge sections of the stent follow a temporary widening of the blood vessel, for example as a result of a pulse wave, with the expansion pressure COF being relatively low. In particular, the expansion pressure COF is lower than in the middle section of the stent, which is more compressed because of the stenosis. At the same time, in the edge sections of the stent, the compression pressure RRF is relatively lower than in the central section. In particular, because of the different slopes of the compression pressure RRF and the expansion pressure COF, the difference between these two pressures is smaller for larger cross-sectional diameters than for smaller cross-sectional diameters.

In other words: the larger the cross-sectional diameter in a section of the stent 10 or the lattice structure 11, the more the compression pressure RRF and the expansion pressure COF equal each other. The edge portions of the stent 10, which are placed in healthy vascular portions, can well follow the movement of the vascular wall due to the pulse waves of the blood. In contrast, in the middle section, which has a relatively smaller cross-sectional diameter because of the narrowing caused by the stenosis, the lattice structure 11 is stabilized by the greater difference between the compression pressure RRF and the expansion pressure COF.

Concrete will be off 2 and the dependency of the radial pressure of the lattice structure 11 on the current local cross-sectional diameter of the lattice structure 11 that the stent 10 has a higher flexibility in the edge sections than in the more heavily compressed central section that supports the stenosis.

wobei A = 10 % und x₂ > x₁.This effect is particularly effective when the difference between the slope of the compression pressure curve RRF and the expansion pressure curve COF is between two predetermined averages measured values x ₁ , x ₂ , this difference corresponds to at least 0.1 times the slope of the expansion pressure curve COF. Expressed mathematically, the following applies: $$\left[\left(\text{RRF}\left({\text{x}}_1\right)-\text{RRF}\left({\text{x}}_2\right)\right)-\left(\text{COF}\left({\text{x}}_{\text{1}}\right)-\text{COF}\left({\text{x}}_{\text{2}}\right)\right)\right]/\left[\text{COF}\left({\text{x}}_{\text{1}}\right)-\text{COF}\left({\text{x}}_{\text{2}}\right)\right]\ge \text{A}$$

where A = 10% and x ₂ > x ₁ .

3 1 shows a table with different area values for the outer peripheral area of the stent 10. To calculate the radial pressure in the unit mmHg, the force values recorded in the measuring device are converted over the cylindrical peripheral area of the stent. The cylindrical peripheral surface or cylindrical surface is idealized.

It is assumed here that the stent 10 is a solid cylinder with a diameter which corresponds to the implantation diameter. The height of the cylinder corresponds to the length of the stent. This results in the lateral cylinder surface, which is used as the ideal conversion variable (cylindrical surface). However, the pressure is actually effective over a contact area that results from the number of webs. The contact area of the stent corresponds to the cylindrical area minus the cell openings.

According to the stent 1 , whose radial pressure values in 2 shown, the cylindrical area is 288.4 mm ² and the contact area is 16.64 mm ² . The stent has a stent length of 35 mm and an implantation diameter of 3.0 mm.

Reference List

10

stent

11

lattice structure

12

cell

12a

edge cell

12b

center cell

13

web

14

extension

15

cell connector

16

cell top

RRF

compression pressure

COF

expansion pressure

I1

first length

I2

second length

Claims (24)

Stent (10) for implantation in a blood vessel, in particular a neurovascular one, with a substantially tubular, self-expandable lattice structure (11) which can be converted from a radially fully expanded expansion diameter to a radially fully compressed compression diameter, the lattice structure (11) exerting the diameter Radial pressure forms a hysteresis with a compression pressure RRF and an expansion pressure COF, and where the following applies to the compression pressure RRF and the expansion pressure COF in a diameter range from x ₁ to x ₂ : $$\left[\left(\text{RRF}\left({\text{x}}_1\right)-\text{RRF}\left({\text{x}}_2\right)\right)-\left(\text{COF}\left({\text{x}}_{\text{1}}\right)-\text{COF}\left({\text{x}}_{\text{2}}\right)\right)\right]/\left[\text{COF}\left({\text{x}}_{\text{1}}\right)-\text{COF}\left({\text{x}}_{\text{2}}\right)\right]\ge \text{A}$$

where A = 10% and x ₂ > x ₁ . stent (10) after claim 1 , characterized in that A=15%, in particular A=20%, in particular A=25%, in particular A=30%, in particular A=35%, in particular A=40%. stent (10) after claim 1 or 2 , characterized in that x ₂ = 2.5 mm and x ₁ = 1.5 mm. Stent (10) according to one of the preceding claims, characterized in that an implantation diameter of the lattice structure (11) is less than 3.5 mm, in particular between 3.4 mm and 1.0 mm. Stent (10) according to one of the preceding claims, characterized in that the expansion diameter of the lattice structure (11) is greater than 2.5 mm and is at most 4.0 mm, in particular at least 3.0 mm and at most 3.5 mm, in particular 3.0mm. Stent (10) according to one of the preceding claims, characterized in that the lattice structure (11) has a length of between 8 mm and 35 mm, in particular between 8 mm and 20 mm, in particular between 10 mm and 15 mm. Stent (10) according to one of the preceding claims, characterized in that the compression pressure RRF at an expansion diameter between 1.0 mm and 3.0 mm, in particular between 1.5 mm and 2.5 mm, is at least 30 mmHg, in particular at least 40 mmHg, in particular at least 50 mmHg, in particular at least 60 mmHg. Stent (10) according to one of the preceding claims, in particular according to claim 7 , characterized in that the compression pressure RRF is at most 150 mmHg, in particular at most 120 mmHg, in particular at most 100 mmHg, in particular at most 80 mmHg. Stent (10) according to one of the preceding claims, characterized in that the lattice structure (11) exerts an expansion pressure COF during self-expansion which, with an expansion diameter of between 1.0 mm and 3.5 mm, in particular between 1.5 mm and 2 5 mm, at least 10 mmHg and at most 70 mmHg, in particular between 20 mmHg and 60 mmHg, in particular between 30 mmHg and 50 mmHg. Stent (10) according to one of the preceding claims, characterized in that the lattice structure (11) has or consists of a nickel-titanium alloy, in particular nitinol. stent (10) after claim 10 , characterized in that the nickel-titanium alloy has between 50 atom % and 60 atom %, in particular between 55 atom % and 56 atom %, in particular 50.8 atom %, nickel. Stent (10) according to one of the preceding claims, characterized in that the lattice structure (11) is formed in one piece from webs (13) or from a mesh of wires. Stent (10) according to one of the preceding claims, characterized in that the lattice structure (11) can be compressed to a compression diameter of at most 0.5 mm, in particular at most 0.4 mm. Stent (10) according to one of the preceding claims, characterized in that the lattice structure (11) has closed cells (12), in particular a closed-cell design. Stent (10) according to one of the preceding claims, characterized in that a central section of the lattice structure (11) in the implanted state causes a sufficient dilatation of a stenosis and edge regions of the lattice structure (11) generate a radial pressure which is sufficient for the lattice structure (11 ) in the blood vessel without causing damage to the vascular tissue. stent (10) after claim 15 , characterized in that the central section of the lattice structure expands the stenosis so slowly that branching perforator vessels in the area of the stenosis are not closed by the expansion of the stenosis. Stent (10) according to one of the preceding claims, wherein the lattice structure (11) has at least one edge cell (12a) with a first length I ₁ and at least one middle cell (12b) with a second length I ₂ , and wherein a ratio between the first Length I ₁ and the second length I ₂ is between 0.5 and 2.5, in particular between 1.0 and 2.0, in particular between 1.25 and 1.75, in particular 1.5. stent (10) after Claim 17 , characterized in that the edge cell (12a) has an extension (14) which carries an X-ray marker. stent (10) after Claim 17 or 18 , characterized in that the edge cell (12a) and the central cell (12b) are arranged directly adjacent to one another in the longitudinal direction of the lattice structure (11) and/or are coupled to one another by a common cell connector (15). Method of manufacturing a stent (10) according to one of the preceding claims, in which the lattice structure (11) is deposited on a substrate by a physical deposition method, in particular a sputtering method, and is subsequently removed from the substrate. manufacturing process claim 20 , characterized in that the lattice structure (11) is formed by depositing a supporting material and an X-ray visible material different from the supporting material. manufacturing process Claim 21 , characterized in that the supporting material is a nickel-titanium alloy, in particular after claim 11 , comprises or consists of, and that the X-ray visible material comprises or consists of tantalum and/or platinum and/or gold. Treatment system, in particular for the treatment of stenoses in intracranial blood vessels, with a balloon catheter and a stent (10) according to one of Claims 1 until 19 wherein the balloon catheter has a catheter tube which carries an inflatable balloon, and wherein the catheter tube has a through lumen in which the stent is arranged in a longitudinally displaceable manner. treatment system Claim 23 , characterized in that the through lumen has an inner diameter of 0.4 mm.

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