Medical stent with increased diameter after intervention

Abstract

The stent device 10 includes a primary stent body 12 configured to expand when placed at a treatment site in a patient, the primary stent body being configured to expand to a first diameter D1 at a first time and to expand to a second diameter D0 at a later second time, the second diameter being larger than the first diameter.

Description

[Technical field]

[0001] TECHNICAL FIELD The following relates generally to the fields of vascular stents, vascular stent delivery, and related art. [Background technology]

[0002] Arteries and veins can develop stenosis, i.e., the lumen is occluded, resulting in a blockage of blood flow. A common treatment is to increase the lumen by balloon angioplasty, followed by the implantation of a stent to ensure that the patency created is maintained. The diameter of the selected stent should be large enough to ensure good contact with the vessel wall with enough pressure to maintain patency and ensure that migration does not occur. On the other hand, the stent diameter should not be too large so as to generate excessive pressure on the tissue, causing either damage to the tissue or disruption of blood flow due to a sudden increase in lumen diameter. Summary of the Invention [Problem to be solved by the invention]

[0003] After stent placement, there is also some measure of in-stent restenosis that typically develops over the first few months that must be taken into account when selecting the diameter of the stent. In-stent restenosis can be the result of injury to tissue and disruption of blood flow.

[0004] The following discloses specific improvements that overcome these and other problems. [Means for solving the problem]

[0005] In some embodiments disclosed herein, a stent device includes a primary stent body configured to expand when placed at a treatment site in a patient, the primary stent body configured to expand to a first diameter (D1) at a first time and to a second diameter (D0) at a later second time, the second diameter being larger than the first diameter.

[0006] In some embodiments disclosed herein, a stent device includes an expandable stent configured to expand to a second diameter, and a bioabsorbable constraining structure secured to the expandable stent and constraining the expandable stent to a first diameter that is smaller than the second diameter, the bioabsorbable constraining structure being made from a bioabsorbable material.

[0007] In some embodiments disclosed herein, a stent device includes an outer stent having a bioabsorbable material configured to expand to a first diameter D1 and an inner stent disposed within the outer stent and configured to expand to a second diameter D0, the second diameter D0 being greater than the first diameter D1.

[0008] One advantage is in providing a self-expanding stent device that expands in diameter in two steps separated by a designed time interval that can be on the order of hours, days, or longer.

[0009] One advantage is in providing a self-expanding stent device that gradually expands in diameter over a designed time interval, which may be on the order of hours, days, or longer.

[0010] Another advantage resides in providing a stent device having multiple stent layers or materials that have different absorption rates in the patient's tissue.

[0011] Another advantage resides in providing a stent device that exerts a gradually increasing radial force on the patient's tissue.

[0012] Another advantage would be to provide a stent device that automatically increases its nominal diameter over time.

[0013] A given embodiment may provide none, one, two, more, or all of the aforementioned advantages, and / or other advantages that will become apparent to those of ordinary skill in the art upon reading and understanding this disclosure.

[0014] The disclosure may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the disclosure. [Brief description of the drawings]

[0015] [Figure 1] 1 illustrates a schematic representation of a stent device according to the present disclosure;

[0016] (A) A perspective view of a self-expanding main stent body having an expanded diameter D0;

[0017] (B) A perspective view of a bioabsorbable self-expanding stent having an expanded diameter D1 smaller than D0.

[0018] (C) A perspective view of a self-expanding stent device having a self-expanding main stent body of portion (A) coaxially disposed inside a bioabsorbable self-expanding stent of portion (B); and

[0019] (D) End view of the self-expanding stent device of part (C); Includes. [Diagram 2] 2 shows a schematic diagram of a graph of data for the stent device of FIG. 1. [Diagram 3] 2 illustrates a schematic diagram of another embodiment of the stent device of FIG. [Figure 4] 2 illustrates a schematic diagram of another embodiment of the stent device of FIG. [Diagram 5] 2 illustrates a schematic diagram of another embodiment of the stent device of FIG. [Figure 6] 2 illustrates a schematic diagram of another embodiment of the stent device of FIG. [Figure 7] 2 illustrates a schematic diagram of another embodiment of the stent device of FIG. [Figure 8] 2 shows an exemplary flowchart of operations performed in a medical procedure using the stent device of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] When a vascular stent is deployed, it is set in place either by self-expanding, in the case of a self-expanding stent, or by the action of an internal balloon that is inflated to expand the stent. In either case, stent deployment places significant stress on the treatment site, which is typically already weakened due to plaque buildup and potentially due to previous treatment actions such as balloon angioplasty. Thus, there is a desire to fix the stent with a high degree of force, which must be balanced by concerns about overstressing the site. Stent diameter and stiffness are the two design parameters that most strongly control deployment force.

[0021] The following discloses an improvement in which the stent is designed to expand to an initial diameter D1 upon deployment and then expand again some time later to a larger diameter D0>D1. In this way, the stress applied to the treatment site is delivered in two stages. In some embodiments where the expansion from D1 to D0 occurs gradually, the additional stress is applied gradually.

[0022] In some embodiments disclosed herein, this two-stage stent expansion is implemented by including bioabsorbable structural features within the stent. The bioabsorbable structure(s) initially restrict the expanded stent to an initial D1 diameter. For example, in one embodiment, the stent has an inner Nitinol self-expanding stent designed to expand to a diameter D0, which is coaxially positioned within an outer bioabsorbable stent designed to expand to a smaller diameter D1. The initial deployment of this two-part stent expands to the smaller diameter D1. Once the outer stent is absorbed by the patient's body, the inner Nitinol stent is released and expands to a larger final diameter D0. The target time interval between expansion from D1 to D0 can be designed by designing the composition and geometry of the outer bioabsorbable stent to be absorbed over the target time interval.

[0023] In other embodiments, the bioabsorbable expansion limiting structures may include bioabsorbable strut braces, encircling loops, etc. that initially restrain the stent to expand to a smaller D1 diameter and then are absorbed over a designed time interval, thereby allowing the stent to subsequently expand to a larger final diameter D0.

[0024] In some alternative embodiments, the primary stent having a natural expanded diameter D0 is also bioabsorbable, but at a slower rate than the bioabsorbable structure that initially limits expansion to diameter D1. In this case, the primary stent can also eventually be absorbed after the treatment site has healed.

[0025] In any of the foregoing embodiments, the designed time interval for expansion from the initial smaller diameter D1 to the final larger diameter D0 can be designed using appropriate experiments on calibration stents with different bioabsorbable structures, differing in the choice of bioabsorbable material and / or bioabsorbable structure geometry (e.g., bioabsorbable structures with different wire thicknesses). By way of non-limiting illustration, the calibration stent can be placed in an environment such as being deployed in a segment of porcine blood vasculature of appropriate lumen diameter placed in a saline-based solution that mimics the salinity, pH, and other properties of human blood and is maintained at human body temperature (e.g., about 36.5-37.0° C.) over the experimental time interval. In a more realistic experimental environment, the saline-based solution may contain white and red blood cells or may be real blood (porcine, human, etc.) and / or may be flowed through the porcine vasculature segment at a flow rate comparable to the expected blood flow rate at the target treatment site in the human vasculature. The calibration stents can then be observed over time to determine the time interval for expansion of each calibration stent from the initial diameter D1 to the final diameter D0. Such experimental testing can be used to optimize the time interval during which the bioabsorbable structure degrades sufficiently to release the constraint, allowing the stent to expand from the initial diameter D1 to the final diameter D0.

[0026] In some examples, the resorption rate of a bioabsorbable structure can be performed to characterize the resorption rate under various conditions as a material parameter. This data can then be used in combination with a computational physics model of the stent device and its intended environment (i.e., tissue) to calculate the resorption time of a particular stent device. When using a parametric model, the design can be adapted manually or automatically to arrive at the desired behavior.

[0027] Referring to FIG. 1, an exemplary self-expanding stent device 10 is shown in parts (C) and (D) of FIG. 1. The self-expanding stent device 10 has a non-bioabsorbable self-expanding stent 12, also referred to herein as a primary stent body 12, shown in isolation in part (A). The primary stent body 12 is coaxially disposed inside a bioabsorbable self-expanding stent 14, shown in isolation in part (B). The primary stent body 12 may be, for example, a Nitinol stent. As seen in part (A), the primary stent body stent 12 has an expanded diameter D0. In contrast, the bioabsorbable self-expanding stent 14 has a smaller expanded diameter D1. The self-expanding stent device 10 is constructed by inserting the primary stent body stent 16 coaxially inside the bioabsorbable self-expanding stent 14. This coaxial arrangement is best seen in the end view of the self-expanding stent device 10 shown in part (D). Note that in section (D), the outer bioabsorbable stent 14 is shown in dashed lines and the inner main stent body 12 is shown in solid lines. The resulting self-expanding stent device 10 has an expanded diameter D1 with the outer bioabsorbable self-expanding stent device 14 preventing the inner main stent body 12 from self-expanding to its full diameter D0. The bioabsorbable material that makes up the bioabsorbable outer stent 14 may be materials such as polyester, poly-L-lactide (PLLA), polyglycolide (PGA), magnesium alloy, and tyrosine polycarbonate. In some examples, the stent 10 may be a drug-eluting stent. In some examples, the inner stent 16 of section (A) may be crimped and then placed inside the outer stent 14 of section (B) to form the self-expanding stent device 10 of sections (C) and (D).

[0028] In one example, the inner stent 12 (i.e., main stent body 12) can have a non-bioabsorbable material (e.g., Nitinol, nickel-titanium (Ni-Ti) alloy, cobalt-chromium-nickel (Co-Cr-Ni) alloy, steel, etc.), and the outer bioabsorbable stent 14 can have a bioabsorbable material, such as polyester, poly-L-lactide (PLLA), polyglycolide (PGA), magnesium alloy, and tyrosine polycarbonate. The outer stent 14 is configured to be absorbed by the patient's tissue to allow the inner stent 12 to expand to the second diameter D0. For example, the bioabsorbable material of the outer stent 14 is configured to be absorbed from a first time to a second time. In another example, the bioabsorbable material of the outer stent 14 has a first bioabsorbable time in a human blood vessel, and the inner stent 12 has a second bioabsorbable material that is different from the bioabsorbable material of the bioabsorbable restraining structure, and the second bioabsorbable material has a longer bioabsorbable time in a human blood vessel than the bioabsorbable material of the bioabsorbable restraining structure.

[0029] FIG. 2 shows a graph illustrating the radial force exerted by the main stent body 12 on the patient's tissue versus the diameter of the main stent body 12. The stent 10 automatically increases its nominal diameter over time. As shown in FIG. 2, the stent 10 can move from curve 1 to curve 2 to curve 3. Curve 1 shows the baseline curve of the radial force versus diameter of the stent. If the stiffness of this stent is increased, this results in curve 2. Here, the unstressed diameter remains unchanged, but a higher force is applied for all diameters below this. This will make the vessel more dilated if an oversized stent is used. If a size that is not too large is applied, the difference between the luminal increase will be smaller. Curve 3 shows the behavior of the stent proposed herein after the restrictive material has been absorbed, with a similar stiffness (slope) but a larger unstressed diameter compared to the baseline stent. For a vessel with compliance corresponding to the radial forces shown by points A, B, and C, placing the stent of curve 2 will result in an immediate increase in diameter to point B. Placing the proposed stent results in the vessel achieving the diameter of point A immediately after the procedure. Over time, the curve shifts toward curve 3, with a corresponding increase in vessel and stent diameter.

[0030] In this manner, the amount of radial force can be gradually increased over time such that the lumen size of the main stent body 12 can also increase over time. This gradual increase allows the tissue to remodel and adapt under a moderately elevated mechanical force, after which the force is increased and the remodeled tissue has time to again adapt to the new force. By allowing the tissue to adapt slowly, lower values ​​of stress are imposed and less tissue damage is introduced.

[0031] Figures 3-7 show different embodiments of the stent device 10. In these embodiments, the primary stent body 12 is augmented by bioabsorbable structures that constrain the initial diameter of the stent device 10 to an initial diameter D1. When the bioabsorbable structures are absorbed into the bloodstream, they cease to provide constraining of the stent diameter and the primary stent body 12 then expands to a larger second diameter D0. Figure 3 shows that the primary stent body 12 includes a bioabsorbable structure with one or more bioabsorbable strut fasteners 18. The left drawing in Figure 3 shows several struts of the primary stent body 12 with an expanded diameter D0. The center drawing in Figure 3 shows the struts constrained to a smaller diameter D1 by the bioabsorbable strut fasteners 18. To attach the strut fasteners 18, the primary stent body 12 may be crimped to the smaller diameter D1 before attachment. As the bioabsorbable strut fasteners 18 biodegrade, this constraint on the struts is removed and the main stent body 12 expands to a larger diameter D0, as shown in the right diagram of Figure 3. The struts 18 can be made from a bioabsorbable material and are added to limit migration between the outer stent 14 and the inner stent 16. Over time, the struts 18 can be absorbed by the tissue and the inner stent 16 expands to a second diameter D0.

[0032] 4, in another embodiment, the struts of the primary stent body 12 comprise a bioabsorbable structure having an additional layer of bioabsorbable material 19 added to the struts 18. The primary stent body 12 may be crimped to a smaller diameter D1 prior to application of the bioabsorbable material coating 19. As the coating 19 biodegrades, the constraint it imposes is removed and the primary stent body 12 expands to a larger diameter D0.

[0033] FIG. 5 illustrates another embodiment in which the primary stent body 12 includes one or more wires formed as loops 20. The loops 20 can be made of Nitinol and can encircle the primary stent body 12. The loops 20 are connected to the primary stent body 12 via bioabsorbable material 21 at multiple locations, as seen in the drawing on the left side of FIG. 5. In some embodiments, the bioabsorbable material 21 at different locations has different volumes of material. As a result, they are bioabsorbed at different times (i.e., a smaller mass of bioabsorbable material is absorbed first), creating a temporal sequence of "release" of the tension provided by the loops 20, and thus creating a multi-step radial force of the stent device 10 that increases over time. The drawing on the right side of FIG. 5 shows the illustrated struts of the expanded primary stent body 12 after the bioabsorbable material has been fully absorbed.

[0034] In another embodiment, the loops 20 are themselves made of a bioabsorbable material (in which case the connections 21 may be of a non-bioabsorbable material), in which case the loops 20 themselves are absorbed into the bloodstream, allowing the stent device 10 to expand from an initial diameter D1 constrained by the loops 20 to a final diameter D0 as the loops are absorbed.

[0035] FIG. 6 shows an embodiment in which the struts of the primary stent body 12 include one or more bioabsorbable springs 22 made from wires secured to the primary stent body 12. The wires (one of which is shown in FIG. 6) are secured to the stent at the distal side of the primary stent body 12 and lead through holes 24 (two of which are shown in FIG. 6) in the primary stent body 12 toward the proximal side where they are secured using a bioabsorbable material 26. The wires extend tangentially through loops in the stent body 12. Thus, the contracted diameter of the primary stent body 12 can be determined by the length of the wire of the spring 22. By releasing one or both of the secured ends, the primary stent body 12 can be allowed to expand further. In some instances, a bioabsorbable stop or plug 26 can be included to restrain the wire of the spring 22 to restrain it from moving through one of the holes 24.

[0036] 7, the wire making up the main stent body 12 can be shortened by looping it over itself and fastening with absorbable material 28. This can be done in multiple locations, again optionally with different volumes of material at the different fastening points 28, thus creating a multi-step radial force increase in the stent device over time.

[0037] 8, a stent procedure suitably performed using the stent device 10 will be described. In operation S1, the stent device is compressed and loaded into a lumen having a diameter D2 at the tip of a stent delivery catheter. In this operation S1, the stent device 10 is compressed to a lumen diameter D2 that is smaller than the initial expanded diameter D1 of the expanded stent device 10.

[0038] In operation S2, an endovascular procedure is used in which the tip of a stent delivery catheter is inserted into a vein or artery and pushed through that vein or artery until the tip of the catheter reaches the treatment site where the stent device 10 is to be deployed. This insertion may optionally be performed under the guidance of medical imaging, such as computed tomography (CT) imaging or ultrasound imaging.

[0039] In operation S3, the stent is deployed at the treatment site using the deployment control wires or other mechanism of the stent delivery catheter, which pushes the compressed stent out of the lumen of diameter D2. Upon exiting the lumen of diameter D2, the stent device 10 self-expands to an initial diameter D1, which is the diameter of the stent device 10, while being restrained by the biodegradable restraining structure. In another example, the stent can also be expanded by inflating a balloon within its lumen to a desired diameter.

[0040] In operation S4, the delivery catheter is withdrawn to complete the endovascular procedure.

[0041] In operation S5, the bioabsorbable constraint is absorbed into the bloodstream over time, allowing the stent device to expand to its final larger diameter D0.

[0042] The present disclosure has been described with reference to the preferred embodiment. Modifications and alterations may occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiments be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

1. a primary stent body configured to expand when placed at a treatment site in a patient, the primary stent body configured to expand to a first diameter at a first time and to a second diameter at a subsequent second time, the second diameter being greater than the first diameter; A stent device having:

2. The stent device of claim 1 , wherein the main stent body comprises Nitinol.

3. The main stent body has an inner stent, an outer stent configured to expand to the first diameter; Further comprising: the inner stent is disposed within the outer stent and configured to expand to the second diameter. A stent device according to any one of claims 1 and 2.

4. the inner stent comprises a non-bioabsorbable material; the outer stent comprises a bioabsorbable material; 4. The stent device of claim 3.

5. The stent device of claim 4 , wherein the outer stent is configured to be absorbed by the patient's tissue to allow the inner stent to expand to the second diameter.

6. the bioabsorbable material of the outer stent has a first bioabsorption time in a human vessel; the inner stent has a second bioabsorbable material different from the bioabsorbable material of the bioabsorbable restraining structure; the second bioabsorbable material has a longer bioabsorption time in a human vasculature than the bioabsorbable material of the bioabsorbable restraint structure. A stent device according to any one of claims 4 and 5.

7. 7. The stent device of claim 5, wherein the bioabsorbable material of the outer stent is configured to be absorbed from the first time to the second time.

8. 8. The stent device of claim 1, wherein the main stent body has one of a strut anchor or a loop, the strut anchor or loop comprising Nitinol.

9. 2. The stent device of claim 1, wherein the primary stent body comprises a bioabsorbable material configured to constrain the primary stent body to the first diameter, and the primary stent body expands to the second diameter upon absorption of the bioabsorbable material.

10. The stent device of claim 8, wherein the bioabsorbable material comprises polyester, poly-L-lactide (PLLA), polyglycolide (PGA), magnesium alloy, and tyrosine polycarbonate.

11. an expandable stent configured to expand to a second diameter; a bioabsorbable constraining structure secured to the expandable stent and constraining the expandable stent to a first diameter smaller than the second diameter, the bioabsorbable constraining structure being made of a bioabsorbable material; A stent device having:

12. The stent device of claim 11 , wherein the bioabsorbable constraining structure comprises an outer stent that includes the expandable stent, the outer stent being made of a bioabsorbable material and configured to expand to the first diameter.

13. The stent device of claim 11 , wherein the bioabsorbable restraining structure comprises a bioabsorbable spring secured to the expandable stent.

14. The stent device of claim 11 , wherein the bioabsorbable constraining structure comprises bioabsorbable struts of the expandable stent.

15. The stent device of claim 11 , wherein the bioabsorbable constraining structure comprises a plurality of bioabsorbable loops having the first diameter that encircle the expandable stent.

16. 16. The stent device of any one of claims 11 to 15, wherein the bioabsorbable material comprises polyester, poly-L-lactide (PLLA), polyglycolide (PGA), magnesium alloy, and tyrosine polycarbonate.

17. 17. The stent device of any one of claims 11 to 16, wherein the expandable stent comprises a self-expanding Nitinol stent.

18. the bioabsorbable material of the bioabsorbable constraining structure has a first bioabsorption time in a human blood vessel; the expandable stent has a second bioabsorbable material different from the bioabsorbable material of the bioabsorbable restraining structure; the second bioabsorbable material has a longer bioabsorption time in a human vasculature than the bioabsorbable material of the bioabsorbable restraint structure.

17. A stent device according to any one of claims 11 to 16.

19. an outer stent having a bioabsorbable material configured to expand to a first diameter D1; an inner stent disposed within the outer stent and configured to expand to a second diameter D0; 1. A stent device comprising: The second diameter D0 is greater than the first diameter D1. Stent device.

20. 20. The stent device of claim 19, wherein the inner stent comprises a non-bioabsorbable material.

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