Systems and methods for use and manufacture of an adaptably dynamic stent

Abstract

A stent extends in a longitudinal direction and a circumferential direction to define a lumen extending therethrough. The stent includes a first series of unit cells extending from a first end to a second end along the longitudinal direction of the stent to define a longitudinal length of each unit cell. The stent a second series of unit cells extending along the longitudinal direction parallel to the first series of unit cells. Each unit cell of the second series of unit cells has a substantially similar longitudinal length to each unit cell in the first series of unit cells. A given unit cell includes at least one node flange at an intersection point between the given unit cell and an adjacent unit cell that causes asymmetrical folding of the given unit cell and the adjacent unit cell.

Description

SYSTEMS AND METHODS FOR USE AND MANUFACTURE OF AN ADAPTABLY DYNAMIC STENTSTATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0001] Not Applicable.FIELD OF THE INVENTION

[0002] Stent design that controls internal stress distribution to reduce peak stress and minimize microstructural ordering impact.BACKGROUND

[0003] Bioresorbable stents (BRS) were conceived to revolutionize the treatment of cardiovascular diseases. However, their significant benefits - such as enhanced mechanical compliance, improved vascular remodeling, and reduced long-term complications - were overshadowed by a two- to three-fold higher clotting rate compared to permanent implants. This clinical failure is closely linked to strain-induced microstructural disruptions during fabrication and implantation, resulting in a heterogeneous loss of structural integrity. The non-gradual loss of support, combined with faster, non-uniform, localized polymer deterioration, directly contributes to the acute clinical failure observed in BRS.

[0004] Therefore, there is a need for stents that overcome these and other limitations and enable precise control of the stress distribution during both crimping and expansion phases of the polymeric stent.

[0005] Concern remains that stent thrombosis is a price paid for reducing short-and long-term complications related to permanent metallic cardiovascular implants. Fear of clotting discriminates against polymeric stent usage in multiple scenarios, such as coronary, aortic and peripheral artery disease, among others. Nonetheless, undesired bioresorbable scaffold’s clinical outcomes point to design oversights rather than technique limitations. Although serving the same ultimate purpose, bioresorbable and permanent stents’ present completely different working principles. As such, stent configuration must be defined according to each type of structure [1].

[0006] The structural lifespan of bioresorbable stents dictates their clinical safety. Risk of thrombosis exponentially increases well before polymer fragmentation. Focal lossof structural integrity can enable greater recoil and malapposition of segments of the scaffold with critical effects on hemodynamics and healing. Protruding struts activate platelets, enable clot formation, delay reendothelization, and could well be responsible for the high risk of thrombosis and myocardial infarction seen with bioresorbable scaffolds. This highlights the importance of accurately balancing degradation dynamics with scaffold integration within the arterial wall. Prolonged structural lifespan provides a broader margin for consistent reendothelization. A stent configuration that matches polymer tubing microstructural properties with geometrical design implantation-related strain extends the structural lifespan of the device by reducing the occurrence of localized microstructural disruption. Highly-impacted microstructural regions in localized scaffold areas point to critical points for crack formation and propagation. Material degradation further enhances the sensitivity of such mechanical events.SUMMARY OF THE DISCLOSURE

[0007] The present disclosure addresses the aforementioned drawbacks by providing systems and methods for use and manufacture of adaptably dynamic stents. In some non-limiting examples, an adaptably dynamic stent may be configured to move between an expanded and a contracted state asymmetrically. Such an adaptably dynamic stent that undertakes asymmetrical expansion and contraction may use one or more node flanges selected or positioned to achieve asymmetrical expansion and contraction.

[0008] In accordance with one aspect of the present disclosure, a stent is provided that may extend in a longitudinal direction and a circumferential direction to define a lumen extending therethrough. The polymeric stent includes a first series of unit cells extending from a first end to a second end along the longitudinal direction of the polymeric stent to define a longitudinal length of each unit cell. The polymeric stent further includes a second series of unit cells extending along the longitudinal direction parallel to the first series of unit cells. Each unit cell of the second series of unit cells has a substantially similar longitudinal length to each unit cell in the first series of unit cells. A given unit cell includes at least one node flange at an intersection point between the given unit cell and an adjacent unit cell that causes asymmetrical folding of the given unit cell and the adjacent unit cell.

[0009] In one aspect, a polymeric stent extends in a longitudinal direction and acircumferential direction to define a lumen extending therethrough. The polymeric stent includes an exterior structure that surrounds the lumen, the exterior structure defining a plurality of first segments extending from a first end to a second end along the longitudinal direction, a plurality of second segments extending along the longitudinal direction and spaced from the first segments along the circumferential direction, and a plurality of third segments extending along the circumferential direction that connect the first segments and the second segments. The polymeric stent further includes a plurality of joints that define an intersection point between the first segments and the third segments, and an intersection point between the second segments and the third segments. Additionally, at least one of the plurality of joints includes at least one node flange configured to cause asymmetrical folding of the polymeric stent when in a compressed state.

[0010] In one aspect, a polymeric stent extends in a longitudinal direction and a circumferential direction to define a lumen extending therethrough. The polymeric stent includes a plurality of flexible joints. Each joint includes a first strut, a second strut, and a third strut meeting at a node. In an uncompressed state of the polymeric stent, the first strut and the second strut extend away from the node generally along the longitudinal direction (e.g. in opposite directions along the longitudinal direction), and the third strut extends away from the node generally along the circumferential direction. The third strut is at least one of angled or curved relative to the circumferential direction to define a preferred bending direction of the third strut during circumferential compression of the polymeric stent. The first strut and the second strut transmit a circumferential compression force to the third strut during compression for bending the third strut, such that the first strut and the second strut each bend relative to the longitudinal direction in reaction to the bending of the third strut, thereby distributing stress across the first strut, the second strut, and the third strut.

[0011]

[0012] In one aspect, a method of manufacturing a polymeric stent is provided. The polymeric stent extends in a longitudinal direction and a circumferential direction to define a lumen extending therethrough. The method includes forming an exterior structure that surrounds the lumen. The exterior structure includes a plurality of first segments extending from a first end to a second end along the longitudinal direction, a plurality of second segments extending along the longitudinal direction parallel to thefirst segments, a plurality of third segments extending along the circumferential direction that connect the first segments and the second segments, a plurality of joints that define an intersection point between the first segments and the third segments, and between the second segments and the third segments, and at least one of the plurality of joints includes at least one node flange configured to cause asymmetrical folding of the polymeric stent when in a compressed state.

[0013] In one aspect, a method is provided for manufacturing a polymeric stent that extends in a longitudinal direction and a circumferential direction to define a lumen extending therethrough. The method includes forming a plurality of flexible joints. Each joint includes a first strut, a second strut, and a third strut meeting at a node. In an uncompressed state of the polymeric stent, the first strut and the second strut extend away from the node generally along the longitudinal direction, and the third strut extends away from the node generally along the circumferential direction. The third strut is at least one of angled or curved relative to the circumferential direction to define a preferred bending direction of the third strut during circumferential compression of the polymeric stent. The first strut and the second strut transmit a circumferential compression force to the third strut during compression for bending the third strut, such that the first strut and the second strut each bend relative to the longitudinal direction in reaction to the bending of the third strut, thereby distributing stress across the first strut, the second strut, and the third struts.

[0014] These aspects are nonlimiting. Other aspects and features of the systems and methods described herein will be provided below.

[0015] The application of auxetic structures for large strain environments, such as stents, requires the modification of the design to allow the compression of the geometry in a confined space (as is the case for stents). This is not possible with conventional auxetic designs. The study of tubular auxetic structures is limited to the field of small deformations, and it has not been considered how the stress distribution affects the microstructure of the material, especially in polymeric constructs. This limited working range is what we take into account in our invention. The design is based on the improvement of a re-entrant auxetic structure. Such improvement allows to control the stress distribution across the different structural components to enhance the design’s deformation capacity. This has the ultimate purpose of reducing peak stresses and minimizing their impact on the material’s microstructural ordering -polymer alignmentand crystallinity (this impact is also dependent on the initial microstructural ordering of the as-manufactured tubing). The applied modifications cause the geometry to lose, to a certain extent, its auxetic properties. Indeed, it becomes what is known as an anepirretic structure, with a Poisson's ratio close to 0.BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is a perspective view of one non-limiting example of a stent in accordance with the present disclosure.

[0017] FIG. 2 is a front view of the stent of FIG. 1.

[0018] FIG. 3 is a top view of the stent of FIG. 1.

[0019] FIG.4 is a partial view of a unit cell of the stent of FIG. 1

[0020] FIG. 5 is a series of unit cells illustrating the unit cell’s shape throughout stent crimping in accordance with the present disclosure.

[0021] FIG. 6 is a series of functional diagrams that illustrate the stress distribution of an intersection point between the unit cell during the stent crimping process for a conventional design.

[0022] FIG. 7 is a set of functional diagrams and correlated graphs showing stress progression throughout a stent crimping process in accordance with the present disclosure.

[0023] FIG. 8 is a set of functional diagrams illustrating peak stress management based on a load-bearing distribution of a unit cell for a conventional design and a design in accordance with the present disclosure.

[0024] FIG. 9 is a set of schematic diagrams and correlated functional diagrams and graphs illustrating stress distribution management in accordance with the present disclosure.

[0025] FIG. 10 is an illustration of a unit cell in accordance with some aspects of the present disclosure showing some variables of a flexible joint design that may be adjusted to tune the joint for different stress distribution management in accordance with the present disclosure.

[0026] FIG. 11 shows: Cell unit geometry definition. Top: sketch. Bottom: contour.

[0027] FIG 12 shows: Working principle of the invention; Stress distribution of the intersection between vertical and horizontal struts during the crimping process for A) aconventional design and B) the balanced design. Colored regions correspond to peak stress regions (green: low stress; yellow: low-to-medium stress; orange: medium-to-high stress; red: high stress).

[0028] FIG 13 shows: Working principle of the invention; Stress progression throughout the crimping process for A) a conventional design and B) the balanced design. The chart represents vertical and horizontal struts’ stress (y axis) with respect to scaffold’s crimping diameter (x axis). Dark red: conventional design’s vertical strut’s stress. Light red: conventional design’s horizontal strut’s stress. Dark green: balanced design’s vertical strut’s stress. Light green: balanced design’s horizontal strut’s stress.

[0029] FIG.14 shows: Working principle of the invention.

[0030] FIG. 15 shows: Description of cell unit's structural components. Left: basic auxetic re-entrant design. Right: balanced design.

[0031] FIG. 16 shows: Working principle overview.

[0032] FIG. 17 shows: Schematic representation of the polymer stent. A) Cell unit view. B) Top view. C) Isometric view. D) Front view.DETAILED DESCRIPTIONGeneral Overview

[0033] The application of auxetic structures for large strain environments requires the modification of the design to allow the compression of the geometry in a confined space (as is the case for stents). This is not possible with conventional auxetic designs. The study of tubular auxetic structures is limited to the field of small deformations [2], and it has not been considered how the stress distribution affects the microstructure of the material, especially in polymeric constructs [1].

[0034] This limited working range is what we take into account in our invention. The design is based on the improvement of a re-entrant auxetic structure. Such improvement allows to control the stress distribution across the different structural components to enhance the design’s deformation capacity. This has the ultimate purpose of reducing peak stresses and minimizing their impact on the material’s microstructural ordering -polymer alignment and crystallinity (this impact is also dependent on the initial microstructural ordering of the as-manufactured tubing). The applied modifications cause the geometry to lose, to a certain extent, its auxetic properties. Indeed, it becomeswhat is known as an anepirretic structure, with a Poisson's ratio close to 0.

[0035] A polymeric stent having a longitudinal direction and a circumferential direction, the polymeric stent comprising: a plurality of flexible joints, each joint being configured to flex between a first configuration and a second configuration as the polymeric stent is changed respectively from an uncrimped state to a crimped state in which a circumferential size of the stent is reduced by forces applied along the circumferential direction, each joint comprising: at least three struts arranged to meet at a node, wherein in the first configuration a first longitudinal strut and a second longitudinal strut of the at least three struts each extend away from the node within 45° of the longitudinal direction, the first longitudinal strut extending away from the node generally along one of the positive longitudinal direction and the negative longitudinal direction with respect to the node and the second longitudinal strut extending away from the node generally along the other of the positive longitudinal direction and the negative longitudinal direction with respect to the node, and wherein a first circumferential strut of the at least three struts extends away from the node within 45° of the circumferential direction, the first circumferential strut extending along a direction between the circumferential direction and the first longitudinal strut and / or having a shape that is asymmetric with respect to a length direction of the circumferential strut to define a preferred flexing direction of the joint; wherein the fist and / or second longitudinal strut extends away from the node and meets a second circumferential strut extending in the opposite circumferential direction to the first circumferential strut, such that in the second configuration the first circumferential strut and the first and / or second longitudinal struts of the flexible joint are each bent compared to the first configuration.

[0036] Figure 11 shows: Cell unit geometry definition. Top: sketch. Bottom: contour.Reduced Peak Stress

[0037] This invention reduces the maximum stresses by splitting them among the various structural component. Thus, there is not a single strut bearing all the load (as is the case with vertical struts in conventional auxetic re-entrant structures), but the load is distributed among the vertical and horizontal struts. This translates into reduced risk of crack formation and loss of structural integrity after stent compression and expansion throughout the implantation process.

[0038] Figures 12 to 14 show: working principle of the invention.Minimized microstructural ordering impact

[0039] The invention allows controlling the stress distribution of the structure throughout the implantation process. This is achieved by modifying the parameters that control the shapes and sizes of the vertical and horizontal struts separately. As a result, the stress distribution can be fine-tuned to range from a state where vertical struts bear the higher loads to one where horizontal struts present the highest stress. Such enhanced control over internal stresses can be used to achieve an even stress distribution among the structural components of the device or a stress distribution that matches the microstructural properties of the base material. This is crucial to minimize implantation-induced impact on microstructural properties across localized regions of the scaffold. Microstructural ordering heterogeneity between stent regions yields unforeseeable outcomes in vivo, such as non-uniform accelerated degradation and early loss of scaffold integrity, which translate into increased risk of thrombosis.

[0040] Optimal macroscopic performance depends on the microscopic properties of the post-implanted scaffold. In turn, the microstructural ordering of the postimplanted device depends on the interaction between the stress distribution and the polymer alignment and crystallinity of the as-manufactured device. Obtaining a postimplanted microstructure with uniform polymeric chain alignment and crystallinity relies on being able to cast a tube with such properties and preserving them with a purposedly adjusted stress distribution. In other words, polymer tubing and stent design must be developed synergistically. Consequently, being able to modify the design to adjust the implantation-related stent distribution to the microstructure properties of the as-cut device is a powerful tool to improve clinical outcomes.Anepirretic behavior

[0041] The mechanical performance of the stent is of critical importance for the efficient functional recovery of blood vessels. The anepirretic design enhances the radial expansion ability while reducing the axial foreshortening of the structure.

[0042] More precisely, the anepirretic behavior benefits the scaffold from the following aspects [3], [4], [5], [6], [7]:• Reducing the radial size of the stent without increasing its length when the stent is crimped. This feature is beneficial to minimally invasive implantation. Small radial and longitudinal sizes of the stent facilitate deliverability and reduce the occurrence of complications due to potentialinjury in the process of catheter navigation through the tortuous vessels of the child.• Maintain luminal patency by expanding in the radial direction without foreshortening. This characteristic reduces the probability of stent malapposition and allows good anchorage with arterial walls, thus avoiding the problem of stent migration.• Arterial endothelium is subjected to both wall shear stress and cyclic circumferential stress due to pulsatile blood flow, so it exhibits concurrent axial and transverse expansion, contrary to a non-auxetic structure. Thus, the anepirretic stent better integrates with native tissues, which helps reduce the potential injury to the arterial intimal surface and enhances compliance, resulting in lower ST and 1SR.

[0043] Reducing the structure’s Poisson ratio can also improve the stent’s mechanical performance, reduce the happening of stent fracture, and enhance its ability to withstand fatigue and vibration.Crimped-based geometry

[0044] The polymeric stent design has been optimized through a reverse engineering process. This optimization consists of adjusting the initial geometry configuration to the desired geometry at the end of the crimping process. This adjustment prompts the design to transition into the desired shape during the crimping process and minimizes the effort that the structure must undertake to carry out this adaptation from the expanded to the crimped state. This reduced effort allows the stent to achieve a lower crossing profile without presenting structural damage. Low crossing profiles are of critical importance for smooth, eased navigation during minimally invasive cardiovascular interventions.Design versatilityThis invention provides a singular structure with enhanced mechanical behavior. The advantages of such invention are meant to be leveraged for the development of cardiovascular polymeric stents. However, non-cardiovascular and / or non-polymeric stents could also benefit from such characteristics. Actually, any type of structure based on the invented unit cell design could use its unique features to present improved mechanical performance.Geometry features outline

[0045] The following tables are intended to provide an overview of the unit cell design for the proposed structure compared to the basic re-entrant auxetic geometry. Details, specifications and values are not provided, as this is not the scope of this section. Rather, the main features and their contribution to the working principle of each design are highlighted.<Table 1: Geometry OverviewTable 2: Working principle overviewConcept

[0046] This invention concerns a polymeric stent design that enables precise control of the stress distribution across the various components of the structure during both the crimping and expansion phases of the implantable device. By effectively managing these stresses, the design provides two fundamental benefits: (1) reduced peak stress for minimized risk of crack formation; and (11) adjustable stress distribution for reduced microstructural disruption; as described in more detailed in section ‘Relevance’. As a result, this approach contributes to improved clinical performance of the device. The following sections describe this technology, focusing on the precise control of stress distribution across the various components of the structure through the specificpolymeric stent design, and highlight its importance for the field.Background

[0047] Bioresorbable stents (BRS) were conceived to revolutionize the treatment of cardiovascular diseases. However, their significant benefits — such as enhanced mechanical compliance, improved vascular remodeling, and reduced long-term complications — were overshadowed by a two- to three-fold higher clotting rate compared to permanent implants. This clinical failure is closely linked to strain-induced microstructural disruptions during fabrication and implantation, resulting in a heterogeneous loss of structural integrity. The non-gradual loss of support, combined with faster, non-uniform, localized polymer deterioration, directly contributes to the acute clinical failure observed in BRS (Wang et al., 2018). Leveraging this understanding marks a significant advancement toward their safe clinical reintroduction. We have built upon the current state of the art in BRS to conceive a polymeric stent design that overcomes their limitations.Description

[0048] The technology consists of a polymeric stent. The polymeric stent is made of a cylindrical tube with a repetitive pattern cut along its perimeter and length. This pattern is referred to as a cell unit, as shown in Figure 17. This stent undergoes a crimping process, where its diameter is reduced from its initial state to a crimped state, allowing it to be introduced into a catheter. Afterward, the structure goes through an expansion process, increasing its diameter from the crimped state to an expanded state that fits the size of the target vessel. Throughout both the crimping and expansion processes, the structure is subjected to different loads, which generate varying stresses across its components. The distribution of these stresses is dependent on the design of the cell unit, making it a crucial factor in the stent's performance.

[0049] Figure 17 shows: Schematic representation of the polymer stent. A) Cell unit view. B) Top view. C) Isometric view. D) Front view.

[0050] The invention advantageously provides the specific design of the cell unit, and how it behaves during the crimping and expansion process. The balanced design was achieved by modifying a basic auxetic re-entrant structure, as depicted in Figure 15.

[0051] Figure 15 shows: Description of cell unit’s structural components. Left: basic auxetic re-entrant design. Right: balanced design.

[0052] Regarding the basic auxetic re-entrant design, the cell unit consists of threeprimary components: A, B, and C. This unit cell is contained within a perfect square, providing a structured framework for the design. Component A represents the straight struts oriented in the circumferential direction of the tubular structure, while component B comprises the straight struts that are predominantly aligned in the longitudinal direction of the tubular structure. The struts in B are positioned at a specific angle relative to a vertical plane. This strategic angling allows the vertical struts to rotate in the desired direction when force is applied. Notably, both A and B are established with the same width, ensuring uniformity in their dimensions. The intersection of A and B is represented by component C. All three components — A, B, and C — exhibit symmetry with respect to both horizontal and vertical planes, contributing to the overall balance and stability of the cell unit design.

[0053] In terms of the balanced design, the cell unit is composed of several key components: A’, B’, C, D, E, and F. A’ represents the curved struts, which are primarily oriented in the circumferential direction of the tubular stent. These struts are confined within specific margins, labeled A, and their curvature is defined to fit the final crimped shape of the stent. Similarly, B’ represents the struts that are predominantly vertical within the structure. These are enclosed within margins B, with their curvature tailored to accommodate the final crimped shape as well. Notably, B is set at a specific angle relative to a vertical plane. This angle is crucial, as it ensures that vertical struts rotate in the intended direction when force is applied. A’ and B’ differ in width, a deliberate design choice to modify the stiffness of each member, allowing for controlled stress distribution across the structure. C marks the intersection point of A’ and B’, confined within its own margins, C. D represents the rounding radius between A’ and B’. E represents the rounding radius between A’ and C. F represents the rounding radius between B’ and C’. Importantly, B’ and C are symmetric along both horizontal and vertical planes, creating balance within the structure. However, A’, D, E, and F are asymmetric with respect to both horizontal and vertical planes. This vertical plane asymmetry is particularly significant, as it ensures that all A’ struts rotate in the same direction, thereby enhancing the compression capability of the stent. A’ and B’ are tangentially connected to C, with the tangency designed to align with the desired rotation direction of C. Lastly, the relationship between D, E, and F, where D is smaller than E and approximately equal to F, plays a critical role in ensuring that the stress distribution between A’ and B’ is achieved as intended.

[0054] One description of the cell unit reads as follows: A polymeric stent having a longitudinal direction and a circumferential direction, the polymeric stent comprising: a plurality of flexible joints, each joint being configured to flex between a first configuration and a second configuration as the polymeric stent is changed respectively from an uncrimped state to a crimped state in which a circumferential size of the stent is reduced by forces applied along the circumferential direction, each joint comprising: at least three struts arranged to meet at a node, wherein in the first configuration a first longitudinal strut and a second longitudinal strut of the at least three struts each extend away from the node within 45° of the longitudinal direction, the first longitudinal strut extending away from the node generally along one of the positive longitudinal direction and the negative longitudinal direction with respect to the node and the second longitudinal strut extending away from the node generally along the other of the positive longitudinal direction and the negative longitudinal direction with respect to the node, and wherein a first circumferential strut of the at least three struts extends away from the node within 45° of the circumferential direction, the first circumferential strut extending along a direction between the circumferential direction and the first longitudinal strut and / or having a shape that is asymmetric with respect to a length direction of the circumferential strut to define a preferred flexing direction of the joint; wherein the fist and / or second longitudinal strut extends away from the node and meets a second circumferential strut extending in the opposite circumferential direction to the first circumferential strut, such that in the second configuration the first circumferential strut and the first and / or second longitudinal struts of the flexible joint are each bent compared to the first configuration.Working Principle

[0055] The working principle refers to the behavior of the cell unit during the implantation process of the device. The very specific behavior of the balanced design, with respect to other conventional structures, allows for precise control of the stress distribution across the various components of the structure, as illustrated in Figure 12.

[0056] Figure 12 shows: Stress distribution of the intersection between vertical and horizontal struts during the crimping process for A) a conventional design and B) the balanced design. Colored regions correspond to peak stress regions (green: low stress; yellow: low-to-medium stress; orange: medium-to-high stress; red: high stress).

[0057] The conventional design is characterized by an implantation stressdistribution in which the axial stress of the vertical struts predominates, leading to well-defined regions of stress concentration within the structure. In contrast, the balanced design features a two-phase stress distribution. Initially, the vertical struts bear the highest stresses, which are subsequently transferred to the horizontal struts as the scaffold diameter decreases. This results in lower peak stresses and a more evenly distributed strain throughout the structure.

[0058] The primary difference between the two designs lies in their load-bearing behavior. In conventional structures, only the vertical struts bend to accommodate the loads applied to the structure. However, in the balanced design, both the horizontal and vertical struts bend, effectively sharing the load-bearing responsibilities. The degree of bending for each structural component can be fine-tuned by adjusting the specific attributes of the cell unit design, allowing for tailored stress distributions that meet particular performance requirements. This is further illustrated in Figure 13.

[0059] Figure 13 shows: Stress progression throughout the crimping process for A) a conventional design and B) the balanced design. The chart represents vertical and horizontal struts’ stress (y axis) with respect to scaffold’s crimping diameter (x axis). Dark red: conventional design’s vertical strut’s stress. Light red: conventional design’s horizontal strut’s stress. Dark green: balanced design’s vertical strut’s stress. Light green: balanced design’s horizontal strut’s stress.Relevance

[0060] This section develops the two main benefits of employing the balanced design, in the context described in section ‘Background’.Reduced peak stress for minimized risk of crack formation

[0061] As described in section ‘Working Principle’, this distinct cell unit design reduces the maximum stresses experienced during implantation by splitting them among the various structural components of the scaffold. Thus, there is not a single strut bearing all the load (as is the case with vertical struts in conventional structures), but the load is distributed among the vertical and horizontal struts. This translates into reduced risk of crack formation and loss of structural integrity after stent crimping and expansion throughout the delivery process in the target vessel.Adjustable stress distribution for minimized microstructural ordering impact

[0062] As described in section ‘Working Principle’, the invention allows controlling the stress distribution of the structure throughout the implantation process.This is achieved by modifying the parameters that control the shapes and sizes of the vertical and horizontal struts of the cell unit. As a result, the stress distribution can be fine-tuned to range from a state where vertical struts bear the higher loads to one where horizontal struts present the highest stress. Such enhanced control over internal stresses can be used to achieve an even stress distribution among the structural components of the device or a stress distribution that matches the microstructural properties of the base material. This is crucial to minimize implantation-induced impact on microstructural properties across localized regions of the scaffold. Microstructural ordering heterogeneity between stent regions yields unforeseeable outcomes in vivo, such as non-uniform accelerated degradation and early loss of scaffold integrity, which translate into increased risk of thrombosis (Wang et al., 2018).

[0063] Optimal macroscopic performance depends on the microscopic properties of the post-implanted scaffold. In turn, the microstructural ordering of the postimplanted device depends on the interaction between the stress distribution and the polymer alignment and crystallinity of the as-manufactured device. Obtaining a postimplanted microstructure with uniform polymeric chain alignment and crystallinity relies on being able to cast a tube with such properties and preserving them with a purposedly adjusted stress distribution. In other words, polymer tubing and stent design must be developed synergistically. Consequently, being able to modify the design to adjust the implantation-related stent distribution to the microstructure properties of the as-cut device is a powerful tool to improve clinical outcomes.

[0064] Wang, P .-J. et al. (2018) ‘Strain-induced accelerated asymmetric spatial degradation of polymeric vascular scaffolds’, Proceedings of the National Academy of Sciences, 115(11), pp. 2640-2645. Available at: https: / / doi.org / 10.1073 / pnas.1716420115.

[0065] The present disclosure provides systems and methods for stents. In some non-limiting configurations, a stent is provided that can provide precise control of the stress distribution across various components of the structure during both the crimping or retracted and expansion phases. By managing these stresses, the stent provides reduced peak stress for minimized risk of crack formation and adjustable stress distribution for reduced microstructural disruption. As will be described, movement between the retracted and expansion states or phases, may be asymmetrical. As will be further described, one non-limiting system for such movement may include joints and / ornode flanges that are designed and arranged to effectuate a particular, desired motion, asymmetrical or otherwise.

[0066] FIGS. 1-3 illustrate a stent 100 that extends in a longitudinal direction 104 and a circumferential direction 108. The stent 100 may be a polymeric stent. The stent 100 defines a lumen 112 that extends therethrough from a first end 116 to a second end 120.

[0067] In this way, the stent can define an exterior structure 124 that surrounds the lumen 112. In one non-limiting example and referring to FIG. 2, the stent 100 can be formed from a plurality of first segments 128, a plurality of second segments 140, and a plurality of third segments 152. The plurality of first segments 128 extend from the first end 116 to the second end 120 along the longitudinal direction 104. The first segments 128 include a first side 132 and a second side 136. The exterior structure 124 also includes a plurality of second segments 140. The plurality of second segments 140 extend from the first end 116 to the second end 120 along the longitudinal direction 104 parallel to the first segments 128. The second segments 140 include a first side 144 and a second side 148. The exterior structure 124 further includes a plurality of third segments 152. The plurality of third segments 152 also extend along the circumferential direction 108 to connect the first segments 128 and the second segments 140. The third segments 152 define a first end 156, a second end 160 opposite the first end 156, a first side 164, and a second side 168 opposite the first side 164. The plurality of third segments 152 are parallel to one another along the longitudinal direction 104 between a corresponding segment of the plurality of first segments 128 and a corresponding segment of the plurality of second segments 140. For example, the third segments 152A, 152B are parallel along the longitudinal direction 104 between the first segment 128A and the second segment 140A. In another example, the third segments 152H, 1521 are parallel along the longitudinal direction 104 between a first segment 128B and the second segment 140A.

[0068] A plurality of first segments 128, a plurality of second segments 140, and a plurality of third segments 152 can define a series of unit cells. For example, a first segment 128 extends in the longitudinal direction 104, a second segment also extends in the longitudinal direction 104, and two third segments 152 extend in the circumferential direction 108 to define a unit cell 170. Referring to FIG. 2, for example, a first segment 128A, a second segment 140A, and third segments 152A-G define a firstseries of unit cells172. The first series of unit cells 172 define a longitudinal length 176 and a circumferential length 180 of each unit cell 172. In the illustrated, non-limiting example, the longitudinal length 176 may be longer than the circumferential length 180. However, in other configurations the longitudinal length 176 may be less than or the same as the circumferential length 180, is some or all of the unit cells 172. The second segment 140A, a first segment 128B, and third segments 152H-N define a second series of unit cells 184. In the illustrated, non-limiting example, the second series of unit cells 184 are parallel to the first series of unit cells 172. However, other, non-parallel configurations are also contemplated. In the illustrated, non-limiting example, each unit cell 184 has a substantially similar longitudinal length 188 and circumferential length 192 to each unit cell 172 in the first series of unit cells 172. In one, non-limiting example, “substantially similar” may be within an acceptable manufacturing or functional tolerance, which may include less than 1% or 1% or 2% or 3% or 4% or 5% or 6% or 7% or 8% or 9% or 10% or 11% or 12% or 13% or 14% or 15% or greater, or values between these integers. In other configurations, non-similar configurations may also be used. In the illustrated, nonlimiting example, the second series of unit cells 184 are offset relative to the first series of unit cells 172. However, other offsets or non-offsets are also contemplated. In the illustrated, non-limiting example, a first end 196 and a second end 200 of each unit cell in the first series of unit cells 172 is offset relative to a first end 204 and a second end 208 of each unit cell 184 in the second series of unit cells 184. In some non-limiting configurations, the first series of unit cells 172 and the second series of unit cells 184 may be repeated in the circumferential direction 108, for example, to be sized for pediatrics. In some other non-limiting examples, the first series of unit cells 172 and the second series of unit cells 184 may be repeated in the circumferential direction 108, for example, to be sized for adults.

[0069] A plurality of first segments 128 and a plurality of third segments 152 include a plurality of joints 212. Referring to FIG. 2, the plurality of first segments 128 and the plurality of third segments 152 define a plurality of joints 212. For example, the first segment 128A and the third segment 152B define a joint 212A. The plurality of joints 212 define an intersection point 216.

[0070] A plurality of second segments 140 and a plurality of third segments 152 include a plurality of joints 220. Referring to FIG. 2, the plurality of second segments 140 and the plurality of third segments 152 define a plurality of joints 220. For example, thesecond segment 140A and the third segment 152B define a joint 220A. The plurality of joints 220 define an intersection point 224.

[0071] Each joint may also be considered to comprise a first strut, a second strut, and a third strut, each strut arranged to meet at a node. For example, the second segment 140A of joint 220A defines a first strut extending generally in a first longitudinal direction away from the intersection point 224, and the second segment 140A of joint 220A also defines a second strut extending generally in the opposite longitudinal direction away from the intersection point 224. Meanwhile, the third segment 152B of the joint 220A defines a third strut extending away from the intersection point 224 generally along the circumferential direction. In the present disclosure, the first and second struts may also be referred to as longitudinal struts, and the third struts may be referred to as circumferential struts. Each first segment and each second segment may also be considered to define a respective plurality of first and second struts in the present context, while the third segments may define a plurality of third struts.

[0072] At select ones of the plurality of joints 212, 220, a node flange 228 can be formed. A node flange 228, as will be described, can be used to help cause and / or manage asymmetrical folding of a stent when in a compressed state and effectuate asymmetrical movement between the compressed and expanded states of the stent 100. Referring to FIG. 4, one non-limiting example of a node flange 228 formed at the joint 212, 220 is illustrated. More particularly, the plurality of joints 212, 220 form a corner 232, which may or many not have a node flange 228 formed thereabout, as illustrated.

[0073] In the non-limiting configuration illustrated in FIG. 4, the first segments 128 include node flanges 228 formed in an alternating pattern between the first side 132 and the second side 136 of the first segments 128. The second segments 140 can, but need not necessarily, also include node flanges 228 formed in an alternating pattern between the first side 144 and the second side 148 of the second segments 140. In this illustrated, non-limiting configuration, the intersection point 216 between the first segment 128A and the first end 156 of the third segment 152A can have a first node flange 228A formed therein. In the illustrated, non-limiting example, the first node flange 228A is also at the intersection point 216 between the first segment 128A and the first side 164 of the third segment 152A. As also provided in the illustrated, non-limiting example, the intersection point 224 between the second segment 140A and the second end 160 of the third segment 152A includes a second node flange 228B, and the second node flange228B is also arranged at the intersection point 224 between the second segment 140A and the second side 168 of the third segment 152A.

[0074] Viewed differently, in the non-limiting example provided in FIG. 4, a given unit cell 172 of the first series of unit cells 172 includes at least one node flange 228 at the intersection points 216, 224 between the given unit cell 172 and an adjacent unit cell 184 of the second series of unit cells 184. For example, the unit cell 172 illustrated in FIG.4 includes two node flanges 228B, 228C. The two node flanges 228B, 228C are formed at the intersection points 216, 224 that are arranged diagonally from one another in the unit cell 172.

[0075] FIG. 5 illustrates a unit cell 172 moving between a crimped or retracted state and an extended or expanded state. The left most unit cell 172 illustrates the unit cell 172 in an extended state 236. The right most unit cell 172 illustrates the unit cell 172 in a compressed state 240. As illustrated, the arrangement of the struts and the node flanges 228 cause asymmetrical folding of the unit cell 172. As further illustrated, though asymmetrical, the folding is consistent and predictable. That is a unit cell 172 folds and unfolds in the same way each time when moving between the expanded and contracted states. Also, as shown in Figure 5, this folding may involve bending of both the circumferential struts / third segments and the first and second struts / first and second segments, which more evenly distributes the stresses associated with crimping of the stent through the structure.

[0076] As illustrated in FIG. 5, the unit cell 172 may be rectangular and extend longer in a first direction 244 than in a second direction 248. In the extended state 236, a first side 252 in the first direction 244 of the unit cell 172 is offset relative to a second side 256 in the first direction 244 of the unit cell 172. Further, in the extended state 236, a first side 260 in the second direction 248 of the unit cell 172 has the same shape as a second side 264 in the second direction 248 of the unit cell 172. In the compressed state 240, the first side 252 in the first direction 244 of the unit cell 172 is offset relative to the second side 256 in the first direction 244 of the unit cell 172. Further, in the compressed state, the first side 260 in the second direction 248 of the unit cell 172 has the same shape as the second side 264 in the second direction 248 of the unit cell 172.

[0077] Referring back to FIG. 2, the node flanges 228 between the unit cell 172 in the first series of unit cells 172 and the adjacent unit cell 184 in the second series of unit cells 184 causes asymmetrical folding of the given unit cell 172 and the adjacent unit cell184. The offset of the second series of unit cells 184 relative to the first end 196 and the second end 200 of each unit cell 172 in the first series of unit cells 172 causes the given unit cell 172 to influence compression or extension of adjacent unit cells 184 to cause the first series of unit cells 172 and the second series of unit cells 184 to move asymmetrically as the stent moves between the extended or expanded state 236 and the compressed or retracted state 240.

[0078] The design of the stent 100 allows for precise control of the stress distribution across the stent 100 as illustrated in FIGS. 6 and 7. Comparative stent designs 300, e.g. which have a stress distribution in which the axial stress of vertical struts 304 predominates, lead to well-defined stress concentration regions within the stent. Whereas the stent 100 of the present disclosure features a two-phase stress distribution. Initially, the first segments 128 bear the highest stresses, which are subsequently transferred to the third segments 152 as the stent 100 transitions to the compressed / retracted state 240. This results in lower peak stresses and a more evenly distributed strain through the stent 100. Further, the comparative stent designs 300 experience a different load-bearing behavior. The vertical struts 304 bend to accommodate the loads applied to the stent 300. Whereas, in the stent 100 of the present disclosure, the first segments 128, the second segments, and the third segments 152 can bend, effectively sharing the load-bearing capacities.

[0079] Referring to FIG. 6, the stress distribution of the comparative stent design 300 and the stent 100 are compared. Beginning with the comparative stent design 300 in the expanded state 236, there is no stress and the stent 300 exhibits an evenly distributed polymer chain alignment. At an intermediate stage 308, the vertical struts 304 bear the entirety of the initial load acting on the stent 300. This results in moderate vertical stress, causing a mild shift of the polymer chains toward the longitudinal axis within the vertical struts 304. In the compressed state 240, the vertical struts 304 sustain the entire increased load acting on the stent 300. This leads to high vertical stress, causing a pronounced shift of the polymer chains toward the longitudinal axis in the vertical struts 304. Consequently, this increases the risk of microcrack formation and microstructural heterogeneity. Continuing with the stent 100 of the present disclosure, FIG. 6 illustrates the first segment 128 and the third segment 152. It can be appreciated that this same analysis can be conducted for the second segment 140 and the third segment 152. In the expanded state 236 for the stent 100 of the present disclosure, thereis no stress and the stent 300 exhibits an evenly distributed polymer chain alignment. At an intermediate stage 308, the first segment 128 carries a significant portion of the initial load acting on the structure, leading to moderate vertical stress and a mild shift of the polymer chains toward the longitudinal axis in the first segments 128. In contrast, the third segments 152 bear a smaller portion of the initial load, resulting in a negligible impact on polymer chain alignment within the third segments 152. In the compressed state 240, both the first segment 128 and the third segment 152 share the increased load uniformly. This results in a mild shift of polymer chains toward the longitudinal direction 104 in the first segment 128 and toward the circumferential direction 108 in the third segment 152. This reduces the risk of microcrack formation and minimizes microstructural heterogeneity.

[0080] FIG. 7 illustrates the stress progression of the comparative stent 300 and one non-limiting configuration of the stent 100 in accordance with the present disclosure. The chart represents the stress in the vertical (e.g., first and second segments) and horizontal struts (e.g. third segments) on the y-axis with respect to the crimping diameter of the stent. In the comparative stent 300, the stress in the vertical struts 304 increases sharply as the vertical struts 304 bend during compression. In contrast, the stress in horizontal struts 312 remains constantas the horizontal struts 312 do not bend during compression. This results in high peak stress and a significant disparity between the stress in the vertical struts 304 and horizontal struts 312. In the stent 100, the stress in the firstand second segments 128, 140 and the third segments 152 increases gradually as the first segments 128, the second segments 140, and the third segments 152 bend during compression. This results in low peak stress and minimal disparity between the stresses in the first and second segments 128, 140, and the third segments 152.

[0081] The design of the stent 100 reduces the maximum stresses experienced during implantation by splitting the stresses among the first segments 128, the second segments 140, and the third segments 152. Therefore, the load is distributed among the first segments 128, the second segments 140, and the third segments 152. This reduces the risk of crack formation and loss of structural integrity after stent crimping and expansion through the delivery process of the stent 100. FIG. 8 illustrates a schematic representation of peak stress management based on the load-bearing distribution of the unit cell for the comparative stent 300 where only vertical struts 304 bend, resulting in high peak stress, the stent 100 where the first segments 128 and the third segments 152bend, significantly reducing peak stress, and the comparative stent 300 where only horizontal struts 312 bend, also resulting in high peak stress.

[0082] The design of the stent 100 also manages the stress distribution by modifying the parameters that control the shapes and sizes of the first segments 128, the second segments 140, and the third segments 152. As a result, the stress distribution can be fine-tuned to range from a state where the first segments and the second segments 140 bear the higher loads to one where the third segments 152 present the highest stress. Such enhanced control over internal stresses can be used to achieve an even stress distribution among the structural components of the stent of a stress distribution that matches the microstructural proposed of a base material. This is crucial to minimize implantation-induced impact on microstructural properties across localized regions of the stent. Microstructural ordering heterogeneity between stent regions yields unforeseeable outcomes in vivo, such as non-uniform accelerated degradation and early loss of stent integrity, which translate into increased risk of thrombosis.

[0083] Optimal macroscopic performance depends on the microscopic properties of the post-implanted stent. In turn, the microstructural ordering of the post-implanted stent depends on the interaction between the stress distribution and the polymer alignment and crystallinity of the as-manufactured stent. Obtaining a post-implanted microstructure with uniform polymeric chain alignment and crystallinity relies on being able to cast a tube with such properties and preserving them with a purposely adjusted stress distribution. In other words, polymer tubing and stent design must be developed synergistically. Consequently, being able to modify the design to adjust the implantation-related stress distribution to the microstructure properties of the as-cut stent is a powerful tool to improve clinical outcomes.

[0084] FIG. 9 illustrates a schematic representation of the stress distribution management adapted to the stent’s microstructural ordering for the stent 100 with predominantly circumferentially oriented polymer chains 316, matched with a cell unit design adjusted for predominant circumferential stress; the stent 100 with polymer chains 320 aligned along a diagonal direction, matched with the unit cell 172, 184 adjusted for equally distributed stress; and the stent 100 with predominantly axially oriented polymer chains 324, matched with a cell unit design adjusted for predominant axial stress.

[0085] FIG. 10 illustrates the variables that may be adjusted within each joint to fine tune for different stress distributions. In particular, while it is preferred for stents in accordance with the present disclosure to have a net orientation direction generally between the longitudinal and circumferential directions, alignments closer to either the longitudinal or circumferential directions can also be tolerated by tuning of the joint design.

[0086] In FIG. 10, two joints 220A, 220B are shown fully, and four joints 2200-220E are shown only partially. As explained above, considering the joint 220A, this is formed by a second segment 140, which provides the joint 220A with a first strut 140A’ extending away from the intersection point 224 in one generally longitudinal direction and a second strut 140A” extending away from the intersection point 224 in the opposite generally longitudinal direction, and is formed by a third segment 152B, which provides the third strut 152B’ extending in the generally circumferential direction away from the intersection point 224. It will also be noted that each joint 220A-220E has the same design, being rotated and / or mirrored relative to the other joints. FIG. 10 firstly shows that each joint may be configured by adjusting the angle between adjacent nodes at intersection points 224 along the circumferential direction, illustrated as A in FIG. 10. In many embodiments, this is substantially 0°. Additionally, the shape of the two circumferential struts A’, including the width, curvature and angle of the struts, may be configured as they each extend away from their respective node. Similarly, the adjacent nodes along the longitudinal direction may define an angle relative to the longitudinal direction, labelled B in the Figure, which may be configured. The shape of the two longitudinal struts B’ between the adjacent nodes, including their width, curvature and angle, may also be configured. C / C’ illustrate the resulting intersection position and size of the struts and therefore are dependent upon and vary with the other parameters. Where the circumferential strut 152B’ meets the node, its opposing edges 153B, 154B transition into longitudinal struts 140 A’, 140A” extending in opposite directions. A small radius of curvature D is defined on one edge 153B of the third strut 152B’, defining a sharp transition into the edge 141A’ associated longitudinal strut 140A’. On the opposing edge 154B of the circumferential strut 152B’ a larger radius of curvature is defined by the edge 154B as it transitions into the edge 141A” of longitudinal strut 140A”, and this large radius of curvature defines the node flange described above. This large radius of curvature, in this embodiment, is formed by two discrete radii of curvature E and F;however, this could instead be embodied as a single radius of curvature, a continuously changing radius of curvature, or any number of discrete radii of curvature. In this embodiment, the two discrete radii of curvature E and F may be adjusted independently to tune the response of the flexible joint 220A.

[0087] If the joint design is being tuned for balanced stresses, e.g. as may be desired when polymer chains have a net orientation generally between the longitudinal and circumferential directions, then the circumferential and longitudinal struts may have substantially the same widths and radius of curvature within a tolerance of 10% and 15%, respectively. The angle A between adjacent circumferential nodes is 0° and the angle between adjacent longitudinal nodes B is between 5-10° relative to the longitudinal direction such that the struts define angles to their respective directions that differ by no more than 5-10°. The radius of curvature D is preferably in the range 50-75 pm and the radius of curvature E should be approximately equal to F within a tolerance of 5%, their radius of curvature preferably being in the range 250-325 pm.

[0088] If the joint design is being adjusted so that the longitudinal struts bear higher stresses, e.g. when the polymer chains are more closely aligned with the longitudinal direction, then improved performance may be obtained by configuring the shape A’ of the circumferential struts to have a greater width than that of the longitudinal struts B’, including up to 50% wider, and / or to have a larger radius of curvature than the longitudinal struts, including up to 25% greater. The angle between adjacent longitudinal nodes B should be between 0-5° relative to the longitudinal direction, while it is still preferred that the angle A between adjacent circumferential nodes is 0°. The radius of curvature D would preferably be in the range 5-75 pm and the radius of curvature E should be greater than F, their radii of curvature preferably being in the ranges 325-350 pm and 225-250 pm, respectively.

[0089] If the joint design is being adjusted so that the circumferential struts bear higher stresses, e.g. when the polymer chains are more closely aligned with the circumferential direction, then improved performance may be obtained by configuring the shape A’ of the circumferential struts to have a lower width than that of the longitudinal struts B’, including the longitudinal struts being up to 50% wider, and / or the longitudinal struts may have a greater radius of curvature than the circumferential struts, including 25% greater. The angle between adjacent longitudinal nodes B should be between 10-20° relative to the longitudinal direction, while it is still preferred that theangle A between adjacent circumferential nodes is 0° so that the angle of the longitudinal struts to the longitudinal direction is greater than the angle of the circumferential struts to the circumferential direction. The radius of curvature D would preferably in the range 75-150 pm, and the radius of curvature E should be less than F, their radii of curvature preferably being in the ranges 225-250 pm and 325-350 pm, respectively.

[0090] The polymeric stents according to the present disclosure may be manufactured by providing an extruded cylindrical tube, e.g. as shown in FIG. 9, and cutting the tube into the desired stent shape. In one embodiment, the material used for the tubing was Purasorb® PLC 9538 (Corbion, Netherlands), with a 95:5 poly(L-lactide):polycaprolactone molar ratio, a viscosity of 3.8 dl / g, a molecular weight of 700,000 g / mol, a glass transition temperature of 55°C, and a melting temperature of 180°C. The extruded cylindrical construct was Absorv™ PLC 95L / 5C Extruded Special XSE (Zeus Inc., USA), with a diameter of 7.493 mm and a wall thickness of 127 pm.

[0091] In one aspect, a polymeric stent extends in a longitudinal direction and a circumferential direction to define a lumen extending therethrough, the polymeric stent comprising: a plurality of flexible joints, wherein each joint comprises: a first strut, a second strut and a third strut arranged to meet at a node, wherein in an uncompressed state of the polymeric stent, the first strut and the second strut extend away from the node generally along opposite longitudinal directions, and the third strut extends away from the node generally along the circumferential direction, wherein the third strut is angled and / or curved relative to the circumferential direction so as to define a preferred bending direction of the third strut during circumferential compression of the polymeric stent, wherein the first and second struts are arranged to transmit a circumferential compression force to the third strut during compression for bending the third strut, such that the first and second strut each bend relative to the longitudinal direction in reaction to the bending of the third strut, thereby distributing stress across the first, second and third struts.

[0092] Embodiments of the invention have been described in detail above. Further embodiments of the invention will also be understood from the following description.

[0093] As described above, in certain embodiments, a polymeric stent extends in a longitudinal direction and a circumferential direction to define a lumen extending therethrough. The polymeric stent includes a plurality of flexible joints. Each jointincludes a first strut, a second strut, and a third strut meeting at a node. In an uncompressed state of the polymeric stent, the first strut and the second strut extend away from the node generally along the longitudinal direction (e.g. in opposite directions along the longitudinal direction), and the third strut extends away from the node generally along the circumferential direction. The third strut is at least one of angled or curved relative to the circumferential direction to define a preferred bending direction of the third strut during circumferential compression of the polymeric stent. The first strut and the second strut transmit a circumferential compression force to the third strut during compression for bending the third strut, such that the first strut and the second strut each bend relative to the longitudinal direction in reaction to the bending of the third strut, thereby distributing stress across the first strut, the second strut, and the third strut.

[0094] It is preferred in these embodiments that a first of the flexible joints is adjacent to a second of the flexible joints along the longitudinal direction, wherein the respective third struts of the adjacent flexible joints extend generally along opposite circumferential directions, such that the adjacent flexible joints induce the bending of the first and second struts between first and second flexible joints during circumferential compression of the polymeric stent. In the present context, the first strut may be considered to be the strut extending from the node in a positive longitudinal direction and the second strut may be considered to be the strut extending in the negative longitudinal direction, in which case the first strut of one flexible joint may transition into the second strut of the adjacent flexible joint along the positive longitudinal direction. In this way, the first and second struts between adjacent nodes along the circumferential direction may each bend during circumferential compression. This may, for example, be because of the respective third struts extending generally along opposite circumferential directions, the first and second struts between adjacent nodes experience reaction forces in opposite directions during circumferential compression, which may therefore cause bending. In some examples, the third struts of the adjacent flexible joints are angled and / or curved relative to the circumferential direction so that the preferred bending direction of the adjacent flexible joints is such that the third struts bend towards the same direction in the longitudinal direction during compression.

[0095] In some examples, the nodes of adjacent flexible joints along the longitudinal direction are offset from one another along the circumferential direction, inparticular in an uncompressed state. Preferably each node is offset along the circumferential direction compared to the adjacent node in a direction opposite to the direction that its third strut extends along the circumferential direction. This may define a Z-shaped arrangement of third struts, and the intervening first / second struts. This may mean that the first and / or second struts between the adjacent nodes define an angle relative to the longitudinal direction. This may contribute to an auxetic behavior of the stent. For example, when the nodes are brought into alignment along the longitudinal direction, this corresponds to a straightening of the first / second struts, which increases the length of the stent at the same time that the circumference increases.

[0096] In some embodiments, three or more flexible joints are arranged in series along the longitudinal direction, wherein the direction of extension of the third struts alternates from each flexible joint to the next along the longitudinal direction. This may further extend the advantages conferred by the flexible joint along a greater length of the polymeric stent.

[0097] In some embodiments, a first of the flexible joints is adjacent to a second of the flexible joints along the circumferential direction, wherein the third strut of the first flexible joint transitions into the third strut of the second flexible joint. In this way, the advantages conferred by the flexible joint may be extended around the circumferential direction of the polymeric stent.

[0098] In some embodiments, a first of the flexible joints is offset from a second of the flexible joints along the circumferential direction, wherein the respective third struts of the offset flexible joints along the circumferential direction are angled and / or curved relative to the circumferential direction towards opposite longitudinal directions, such that the third struts of the offset flexible joints along the circumferential direction bend towards opposite longitudinal directions during compression. In this way, the adjacent nodes may move relative to one another in the longitudinal direction during compression. This may allow for the nodes to move closer to one another along the circumferential direction without imposing very high stresses on the intervening third struts. This may also cause an asymmetrical folding of the polymeric stent when in a compressed state.

[0099] As noted above, the third strut may be angled and / or curved. While the first and second struts may be linear and / or could be aligned along the longitudinal direction, preferably the first and / or second struts are angled and / or curved relative tothe longitudinal direction. In particularly preferred embodiments, the first and second struts of any one flexible joint are angled and / or curved relative to the longitudinal direction towards the same circumferential direction. This may, for example, provide the flexible joint with an arrowhead shape.

[0100] In some embodiments, the stent is predominantly defined by the same flexible joint design that is repeated across the stent, including rotations and mirroring of the flexible joint design.

[0101] In some embodiments, a set of four flexible joints is provided defining a rectangular unit cell. For example, the set of four flexible joints may comprise two pairs of flexible joints, wherein within each pair, a first of the flexible joints is adjacent to a second of the flexible joints along the longitudinal direction, wherein the respective third struts of the adjacent flexible joints extend generally along opposite circumferential directions, and wherein the two pairs of flexible joints are offset from one another along the circumferential direction, wherein a third strut of one of the pairs transitions into a third strut of the other pair.

[0102] In some embodiments, a set of six flexible joints is arranged such that the struts of the flexible joints define a substantially rectangular or hourglass-shaped opening through the circumferential surface of the polymeric stent. In some embodiments, this arrangement of six flexible joints may be repeated across the stent such that the stent comprises an array of said substantially rectangular or hourglassshaped openings. For example, the arrangement of six flexible joints may define a unit cell, in which two of the joints of the unit cell are shared with a previous unit cell along the longitudinal direction and two of the joints of the unit cell are shared with a subsequent unit cell along the longitudinal direction.

[0103] As noted above, the first and second struts each extend generally along the longitudinal direction, but they may define a small angle relative to the longitudinal direction. For example, the first and second struts may be considered to be struts defining an angle of less than 45° to the longitudinal direction. However, preferably, for each flexible joint, the first and second struts each extend away from the node along a direction within 30° of the longitudinal direction, preferably within 25°, more preferably within 20°, more preferably within 15°, most preferably within 10°.

[0104] Similarly, the third strut extends generally along the circumferential direction, but may define a small angle relative to the circumferential direction. Forexample, the third strut may be considered to be a strut defining an angle of less than 45° to the circumferential direction. However, preferably, for each flexible joint, the third strut extends away from the node along a direction within 30° of the circumferential direction, preferably within 25°, more preferably within 20°, more preferably within 15°, most preferably within 10°.

[0105] In some embodiments, the third strut widens asymmetrically with respect to the circumferential direction and / or an elongate direction of the third strut as it approaches the node so as to define a node flange between the third strut and either the first or second strut. Preferably, the node flange is located so as to be between third strut and the one of the first or second strut that the third strut bends towards when it bends in accordance with the preferred bending direction. In this way, the node flange may provide a region of polymeric material about which the struts bend to further improve the distribution of stresses within the joint.

[0106] The inventors have found that the extent of disruption of a polymeric stent, in many cases, depends not merely on the magnitude of stress, but also on the degree of misalignment between polymer chain orientation and stress direction. Achieving minimized disruption in polymeric chains alignment and uniform crystallinity across layers requires harmonized interaction between the microstructural ordering of the as-manufactured device and the implantation-related stress distribution of the design. Reducing the mismatch between these features is as critical as adjusting their properties to the scaffold's intended application. Greater uniformity across regions enables sustained and controlled crack formation during degradation, which extends the structural lifespan of BRS — a critical factor for clinical safety, as the risk of thrombosis rises sharply well before polymer fragmentation occurs. Therefore, in some embodiments, the polymeric stent is formed of a polymeric material having polymer chains defining a net orientation direction, the net orientation direction preferably extending along a direction of the polymeric stent between the longitudinal direction and the circumferential direction, more preferably extending along a direction between 20° and 70° from the longitudinal direction, more preferably between 30° and 60° from the longitudinal direction, most preferably between 40° and 50° from the longitudinal direction. In the present context, the net orientation angle of the polymer chains may be considered to be defined in cylindrical coordinates, in which an angle of 0° would be aligned with the longitudinal direction, whereas an angle of 90° would be aligned withthe circumferential direction. It will be appreciated that this does not require that every polymer chain is oriented along the stated direction, but only that there is a tendency towards this direction such that the average orientation lies along the stated direction. An oblique net orientation direction means that the microstructure of the polymeric stent is particularly suited to tolerating both circumferential and longitudinal stresses, and so works well in a stent comprising joints that distribute stresses to both longitudinal and circumferential struts, as set out in these embodiments.

[0107] There are a number of further parameters that may be adjusted to balance the stresses between longitudinal and circumferential struts. Preferably, the first, second and third struts are configured to relatively evenly bear stresses by one or more of the following: 1) the first and / or second struts have substantially the same width as the third strut to within a tolerance of 25%, preferably 20%, more preferably 15%, most preferably 10%, 2) the third strut defines an angle relative to the circumferential direction that is equal to an angle defined by the first and / or second struts relative to the longitudinal direction to within 20°, preferably within 10°, preferably within 5°, 3) the first and / or second struts are curved with substantially the same radius of curvature as the third strut to within a tolerance of 50%, preferably 40%, preferably 30%, preferably 20%, preferably 15%, 4) the larger of a radius of curvature of a first edge of the third strut as it transitions into an edge of the first strut and a radius of curvature of a second edge of the third strut as it transitions into an edge of the second strut is in the range 2 to_8 times that of the smaller radius of curvature, preferably 3 to 7 times, preferably 4 to 6 times, preferably 4.5 to 5.5 times, and 5) the first edge of the third strut that transitions into an edge of the first strut and the second edge of the third strut that transitions into an edge of the second strut that has the larger overall radius of curvature comprises a radius of curvature that remains substantially constant to within a tolerance of 30% as the edge of the third strut transitions into the edge of the first and / or second, preferably within 20%, more preferably within 10%, more preferably within 5%. In this context, the width may be the median width. Tolerances in the present context are calculated as the difference between two values as a percentage of the smaller value. These embodiments are particularly preferred where the net orientation direction of the polymer chains extends along a direction of the polymeric stent between the longitudinal direction and the circumferential direction, e.g. between 20° and 70° from the longitudinal direction, more preferably between 30° and 60° from the longitudinaldirection, most preferably between 40° and 50° from the longitudinal direction, as this orientation of polymer chains is able to better tolerate stresses in both the longitudinal and circumferential directions,

[0108] In some circumstances, it may be preferred for a stent to be configured more for longitudinal stresses. Therefore, in some embodiments, the polymeric stent is formed of a polymeric material having polymer chains defining a net orientation direction, the net orientation direction extending along a direction within 30° of the longitudinal direction. This microstructure would be configured for higher longitudinal stresses. Therefore, preferably the joint is designed to bear higher stresses in the longitudinal struts. In particular, preferably the first and / or second struts are configured to bear higher stresses than the third strut by one or more of the following: 1) the third strut is wider than the first and / or second struts, preferably at least 10% wider, more preferably at least 20% wider, more preferably at least 30% wider, more preferably at least 40% wider, most preferably at least 50% wider, 2) the first and / or second struts define an angle relative to the longitudinal direction that is no more 20° more than an angle defined by the third strut relative to the circumferential direction, preferably no more than 10° more, preferably no more than 5° more, most preferably wherein the first and / or second struts define an angle relative to the longitudinal direction that is less than an angle defined by the third strut relative to the circumferential direction, 3) the third strut is curved with a greater radius of curvature than the first and / or second struts , preferably at least 10% greater, preferably at least 15% greater, preferably at least 20% greater, preferably at least 25% greater, 4) the larger of a radius of curvature of a first edge of the third strut as it transitions into an edge of the first strut and a radius of curvature of a second edge of the third strut as it transitions into an edge of the second strut is at least 5 times that of the smaller radius of curvature, preferably at least 7 times, more preferably at least 8 times, most preferably at least 10 times, 5) the first edge of the third strut that transitions into an edge of the first strut and the second edge of the third strut that transitions into an edge of the second strut that has the larger overall radius of curvature comprises a radius of curvature that decreases as the edge of the third strut transitions into the edge of the first and / or second strut.

[0109] In some circumstances, it may be preferred for a stent to be configured more for circumferential stresses. Therefore, in some embodiments, the polymeric stent is formed of a polymeric material having polymer chains defining a net orientationdirection, the net orientation direction extending along a direction within 30° of the circumferential direction. In this case, the microstructure would be configured for higher circumferential stresses. Therefore, preferably the joint is designed to bear higher stresses in the circumferential struts. In particular, preferably, the third strut is configured to bear higher stresses than the first and / or second struts by one or more of the following: 1) the first and / or second struts are wider than the third strut, preferably at least 10% wider, more preferably at least 20% wider, more preferably at least 30% wider, more preferably at least 40% wider, most preferably at least 50% wider, 2) the first and / or second struts define an angle relative to the longitudinal direction that is greater than an angle defined by the third strut relative to the circumferential direction, preferably at least 5° more, more preferably at least 10° more, more preferably at least 20° more than an angle defined by the third strut relative to the circumferential direction, 3) the first and / or second struts are curved with a greater radius of curvature than the third strut, preferably at least 10% greater, preferably at least 15% greater, preferably at least 20% greater, preferably at least 25% greater, 4) the larger of a radius of curvature of a first edge of the third strut as it transitions into an edge of the first strut and a radius of curvature of a second edge of the third strut as it transitions into an edge of the second strut is no more than 5 times that of the smaller radius of curvature, preferably no more than 4 times, preferably no more than 3 times, preferably no more than two times, and 5) the first edge of the third strut that transitions into an edge of the first strut and the second edge of the third strut that transitions into an edge of the second strut that has the larger overall radius of curvature comprises a radius of curvature that increases as the edge of the third strut transitions into the edge of the first and / or second strut.

[0110] In one aspect, a method of manufacturing a stent is provided. The polymeric stent extends in a longitudinal direction and a circumferential direction to define a lumen extending therethrough. The method comprises: forming a plurality of flexible joints, wherein each joint comprises: a first strut, a second strut and a third strut arranged to meet at a node, wherein in an uncompressed state of the polymeric stent, the first strut and the second strut extend away from the node generally along opposite longitudinal directions, and the third strut extends away from the node generally along the circumferential direction, wherein the third strut is angled and / or curved relative to the circumferential direction so as to define a preferred bending direction of the third strut during circumferential compression of the polymeric stent , wherein the first andsecond struts are arranged to transmit a circumferential compression force to the third strut during compression for bending the third strut, such that the first and second strut each bend relative to the longitudinal direction in reaction to the bending of the third strut, thereby distributing stress across the first, second and third struts.

[0111] Preferably, in this aspect, the method comprises providing a polymeric tube defining a substantially continuous cylindrical surface, and wherein forming the plurality of flexible joints comprises selectively removing areas of the polymeric tube so as to define the plurality of flexible joints. Material may be removed by laser cutting, for example. The polymeric tube may have polymer chains defining a preferred net orientation direction, e.g. between 20° and 70° from the longitudinal direction, more preferably between 30° and 60° from the longitudinal direction, most preferably between 40° and 50° from the longitudinal direction, or within 30° of the longitudinal direction, or within 30° of the circumferential direction, as explained above.

[0112] The present disclosure has described one or more preferred embodiments, and it should be appreciated that many equivalents, alternatives, variations, and modifications, aside from those expressly stated, are possible and within the scope of the invention.REFERENCES:[1] P. J. Wang, N. Ferralis, C. Conway, J. C. Grossman, and E. R. Edelman, “Straininduced accelerated asymmetric spatial degradation of polymeric vascularscaffolds,” Proceedings of the National Academy of Sciences, vol. 115, no. 11, pp.2640-2645, 2018, doi: 10.1073 / pnas.1716420115.[2] X. Ren, J. Shen, A. Ghaedizadeh, H. Tian, and Y. M. Xie, “A simple auxetic tubular structure with tuneable mechanical properties,” Smart Mater Struct, vol. 25, no. 6,May 2016, doi: 10.1088 / 0964-1726 / 25 / 6 / 065012.[3] H. Xue, Z. Luo, T. Brown, and S. Beier, “Design of Self-Expanding Auxetic Stents Using Topology Optimization,” Front Bioeng Biotechnol, vol. 8, Jul. 2020, doi:10.3389 / fbioe.2020.00736.[4] D. B. Camasao and D. Mantovani, “The mechanical characterization of blood vessels and their substitutes in the continuous quest for physiological -relevant performances. A critical review,” Mar. 01, 2021, Elsevier B.V. doi:10.1016 / j.mtbio.2021.100106.[5] S. K. Bhullar, H. Lekesiz, A. A. Karaca, Y. Cho, S. M. Willerth, and M. B. G. Jun,“Characterizing the Mechanical Performance of a Bare-Metal Stent with an Auxetic Cell Geometry,” Applied Sciences (Switzerland) , vol. 12, no. 2, Jan. 2022, doi: 10.3390 / appl2020910.[6] F. Amin, M. N. Ali, U. Ansari, M. Mir, M. A. Minhas, and W. Shahid, “Auxetic coronary stent endoprosthesis: Fabrication and structural analysis,” J Appl Biomater Funct Mater, vol. 13, no. 2, pp. E127-E135, Apr. 2015, doi:10.5301 / jabfm.5000213.[7] Z. Wu etal., “Radial compressive property and the proof-of-concept study for realizing self-expansion of 3D printing polylactic acid vascular stents with negative poisson’s ratio structure,” Materials, vol. 11, no. 8, Aug. 2018, doi:10.3390 / mal 1081357.

Claims

36CLAIMS1. A polymeric stent extending in a longitudinal direction and a circumferential direction to define a lumen extending therethrough, the polymeric stent comprising:a plurality of flexible joints, wherein each joint comprises:a first strut, a second strut, and a third strut meeting at a node, wherein in an uncompressed state of the polymeric stent, the first strut, and the second strut extend away from the node generally along the longitudinal direction, and the third strut extends away from the node generally along the circumferential direction,wherein the third strut is at least one of angled or curved relative to the circumferential direction to define a preferred bending direction of the third strut during circumferential compression of the polymeric stent,wherein the first strut and the second strut transmit a circumferential compression force to the third strut during compression for bending the third strut, such that the first strut and the second strut each bend relative to the longitudinal direction in reaction to the bending of the third strut, thereby distributing stress across the first strut, the second strut, and the third strut.

2. A polymeric stent according to claim 1, wherein a first of the plurality of flexible joints is adjacent to a second of the plurality of flexible joints along the longitudinal direction to define adjacent flexible joints, wherein respective third struts of the adjacent flexible joints extend generally in opposite directions along the circumferential direction, such that the adjacent flexible joints induce the bending of the first and second struts between the first of the plurality of flexible joints and the second of the plurality of flexible joints during circumferential compression of the polymeric stent.

3. A polymeric stent according to claim 2, wherein the nodes of adjacent flexible joints of the plurality of flexible joints along the longitudinal direction are offset from one another along the circumferential direction.

4. A polymeric stent according to claim 2, wherein three or more flexible joints are arranged in series along the longitudinal direction, and wherein a direction of extension of the third strut of each of the three or more flexible joints alternates from each flexible joint to an adjacent flexible joint along the longitudinal direction.

5. A polymeric stent according to claim 1, wherein a first of the plurality of flexible joints is adjacent to a second of the plurality of flexible joints along the circumferential direction, and wherein the third strut of the first of the plurality of flexible joints transitions into the third strut of the second of the plurality of flexible joints.

6. A polymeric stent according to claim 1, wherein a first of the plurality of flexible joints is offset from a second of the plurality of flexible joints along the circumferential direction, wherein a respective third strut of each of the first flexible joint and second flexible joint are at least one of angled or curved relative to the circumferential direction towards opposite directions of the longitudinal direction, such that the third strut shared long the circumferential direction bends towards the longitudinal direction during compression.

7. A polymeric stent according to claim 1, wherein the first strut and the second strut of any one the plurality of flexible joints are at least one of angled or curved relative to the longitudinal direction towards the circumferential direction.

8. A polymeric stent according to claim 1, wherein a set of six flexible joints is arranged such that all struts of the six flexible joints define a substantially rectangular or hourglass-shaped opening through the circumferential surface of the polymeric stent.

9. A polymeric stent according to claim 1, wherein, for each of the plurality of flexible joints, the first strut and the second strut each extend away from the node along a direction within 30° of the longitudinal direction, or within 25° of the longitudinal direction, or within 20° of the longitudinal direction, or within 15° of the longitudinal direction, or within 10° of the longitudinal direction.

10. A polymeric stent according to claim 1, wherein, for each flexible joint of the plurality of flexible joints, the third strut extends away from the node along a direction within 30° of the circumferential direction, or within 25° of the circumferential direction, or within 20° of the circumferential direction, or within 15°, or within 10° of the circumferential direction.

11. A polymeric stent according to claim 1, wherein the third strut widens asymmetrically with respect to at least one of the circumferential direction or an elongate direction of the third strut as it approaches the node to define a node flange between the third strut and either the first strut or the second strut.

12. A polymeric stent according to claim 1, wherein the third strut comprises a first edge that transitions into an edge of the first strut and a second edge that transitions into an edge of the second strut, and wherein a radius of curvature of the first edge as it transitions into the edge of the first strut is different from a radius of curvature of the second edge as it transitions into the edge of the second strut.

13. A polymeric stent according to claim 1, wherein the polymeric stent is formed of a polymeric material having polymer chains defining a net orientation direction, the net orientation direction preferably extending along a direction of the polymeric stent between the longitudinal direction and the circumferential direction, or extending along a direction between 20° and 70° from the longitudinal direction, or extending along a direction between 30° and 60° from the longitudinal direction.

14. A polymeric stent according to claim 1, wherein the first, second and third struts are configured to relatively evenly bear stresses by one or more of the following: 1) the first and / or second struts have substantially the same width as the third strut to within a tolerance of 25%, preferably 20%, more preferably 15%, most preferably 10%, 2) the third strut defines an angle relative to the circumferential direction that is equal to an angle defined by the first and / or second struts relative to the longitudinal direction to within 20°, preferably within 10°, preferably within 5°, 3) the first and / or second struts are curved with substantially the same radius of curvature as the third strut to within a tolerance of 50%, preferably 40%, preferably 30%, preferably 20%, preferably 15%, 4)the larger of a radius of curvature of a first edge of the third strut as it transitions into an edge of the first strut and a radius of curvature of a second edge of the third strut as it transitions into an edge of the second strut is in the range 2 to 8 times that of the smaller radius of curvature, preferably 3 to 7 times, preferably 4 to 6 times, preferably 4.5 to 5.5 times, and 5) the first edge of the third strut that transitions into an edge of the first strut and the second edge of the third strut that transitions into an edge of the second strut that has the larger overall radius of curvature comprises a radius of curvature that remains substantially constant to within a tolerance of 30% as the edge of the third strut transitions into the edge of the first and / or second, preferably within 20%, more preferably within 10%, more preferably within 5%.

15. A polymeric stent according to claim 1, wherein the polymeric stent is formed of a polymeric material having polymer chains defining a net orientation direction, the net orientation direction extending along a direction within 30° of the longitudinal direction, wherein the first and / or second struts are configured to bear higher stresses than the third strut by one or more of the following: 1) the third strut is wider than the first and / or second struts, preferably at least 10% wider, more preferably at least 20% wider, more preferably at least 30% wider, more preferably at least 40% wider, most preferably at least 50% wider, 2) the first and / or second struts define an angle relative to the longitudinal direction that is no more than 20° more than an angle defined by the third strut relative to the circumferential direction, preferably no more than 10° more, preferably no more than 5° more, most preferably wherein the first and / or second struts define an angle relative to the longitudinal direction that is less than an angle defined by the third strut relative to the circumferential direction, 3) the third strut is curved with a greater radius of curvature than the first and / or second struts , preferably at least 10% greater, preferably at least 15% greater, preferably at least 20% greater, preferably at least 25% greater, 4) the larger of a radius of curvature of a first edge of the third strut as it transitions into an edge of the first strut and a radius of curvature of a second edge of the third strut as it transitions into an edge of the second strut is at least 5 times that of the smaller radius of curvature, preferably at least 7 times, more preferably at least 8 times, most preferably at least 10 times, 5) the first edge of the third strut that transitions into an edge of the first strut and the second edge of the third strut that transitions into an edge of the second strut that has the larger overall radius ofcurvature comprises a radius of curvature that decreases as the edge of the third strut transitions into the edge of the first and / or second strut.

16. A polymeric stent according to claim 1, wherein the polymeric stent is formed of a polymeric material having polymer chains defining a net orientation direction, the net orientation direction extending along a direction within 30° of the circumferential direction, wherein the third strut is configured to bear higher stresses than the first and / or second struts by one or more of the following: 1) the first and / or second struts are wider than the third strut, preferably at least 10% wider, more preferably at least 20% wider, more preferably at least 30% wider, more preferably at least 40% wider, most preferably at least 50% wider, 2) the first and / or second struts define an angle relative to the longitudinal direction that is greater than an angle defined by the third strut relative to the circumferential direction, preferably at least 5° more, more preferably at least 10° more, more preferably at least 20° more than an angle defined by the third strut relative to the circumferential direction, 3) the first and / or second struts are curved with a greater radius of curvature than the third strut, preferably at least 10% greater, preferably at least 15% greater, preferably at least 20% greater, preferably at least 25% greater, 4) the larger of a radius of curvature of a first edge of the third strut as it transitions into an edge of the first strut and a radius of curvature of a second edge of the third strut as it transitions into an edge of the second strut is no more than 5 times that of the smaller radius of curvature, preferably no more than 4 times, preferably no more than 3 times, preferably no more than two times, and 5) the first edge of the third strut that transitions into an edge of the first strut and the second edge of the third strut that transitions into an edge of the second strut that has the larger overall radius of curvature comprises a radius of curvature that increases as the edge of the third strut transitions into the edge of the first and / or second strut.

17. A method of manufacturing a stent extending in a longitudinal direction and a circumferential direction to define a lumen extending therethrough, the method comprising:forming an exterior structure that surrounds the lumen, wherein the exterior structure comprises:a plurality of first segments extending from a first end to a second end along the longitudinal direction;a plurality of second segments extending along the longitudinal direction parallel to the first segments;a plurality of third segments extending along the circumferential direction that connect the first segments and the second segments;a plurality of joints that define an intersection point between the first segments and the third segments, and between the second segments and the third segments; andat least one of the plurality of joints includes at least one node flange configured to cause asymmetrical folding of the stent when in a compressed state.

18. A method of manufacturing a stent extending in a longitudinal direction and a circumferential direction to define a lumen extending therethrough, the method comprising:forming a plurality of flexible joints, wherein each joint comprises:a first strut, a second strut, and a third strut meeting at a node, wherein in an uncompressed state of the polymeric stent, the first strut, and the second strut extend away from the node generally along the longitudinal direction, and the third strut extends away from the node generally along the circumferential direction,wherein the third strut is at least one of angled or curved relative to the circumferential direction to define a preferred bending direction of the third strut during circumferential compression of the polymeric stent,wherein the first strut and the second strut transmit a circumferential compression force to the third strut during compression for bending the third strut, such that the first strut and the second strut each bend relative to the longitudinal direction in reaction to the bending of the third strut, thereby distributing stress across the first strut, the second strut, and the third strut.

19. A method according to claim 18, further comprising providing a polymeric tube defining a substantially continuous cylindrical surface, and wherein42forming the plurality of flexible joints comprises selectively removing areas of the polymeric tube to define the plurality of flexible joints.

20. A stent extending in a longitudinal direction and a circumferential direction to define a lumen extending therethrough, the stent comprising:a first series of unit cells extending from a first end to a second end along the longitudinal direction of the stent to define a longitudinal length of each unit cell;a second series of unit cells extending along the longitudinal direction parallel to the first series of unit cells, wherein each unit cell of the second series of unit cells has a substantially similar longitudinal length to each unit cell in the first series of unit cells; andwherein a given unit cell includes at least one node flange at an intersection point between the given unit cell and an adjacent unit cell that causes asymmetrical folding of the given unit cell and the adjacent unit cell.

21. The stent of claim 20, wherein the second series of unit cells is offset relative to a first end and a second end of each unit cell in the first series of unit cells, and wherein the offset causes the given unit cell to influence compression or extension of adjacent unit cells to cause the first series of unit cells and the second series of unit cells to move asymmetrically as the stent moves between an extended state and a compressed state.

22. The stent of claim 20, wherein each unit cell is rectangular and extending longer in a first direction than in a second direction.

23. The stent of claim 20, wherein in a compressed state, a first side in a first direction of the given unit cell is offset relative to a second side in the first direction of the given unit cell.

24. The stent of claim 20, wherein in a compressed state, a first side in a second direction of the given unit cell has the same shape as a second side in the second direction of the given unit cell.4325. The stent of claim 20, wherein in an extended state, a first side in a first direction of the given unit cell is offset relative to a second side in the first direction of the given unit cell.

26. The stent of claim 20, wherein in an extended state, a first side in a second direction of the given unit cell has the same shape as a second side in the second direction of the given unit cell.

27. The stent of claim 20, wherein the given unit cell includes two node flanges.

28. The stent of claim 27, wherein the two node flanges are arranged diagonally from one another in the unit cell.

29. The stent of claim 20, wherein the first series of unit cells and the second series of unit cells are repeated in an alternating manner in the circumferential direction.

30. A stent extending in a longitudinal direction and a circumferential direction to define a lumen extending therethrough, the stent comprising:an exterior structure that surrounds the lumen, the exterior structure defining a plurality of first segments extending from a first end to a second end along the longitudinal direction, a plurality of second segments extending along the longitudinal direction and spaced from the first segments along the circumferential direction, and a plurality of third segments extending along the circumferential direction that connect the first segments and the second segments;a plurality of joints that define an intersection point between the first segments and the third segments, and an intersection point between the second segments and the third segments; andat least one of the plurality of joints includes at least one node flange configured to cause asymmetrical folding of the stent when in a compressed state.

31. The stent of claim 30, wherein the third segments define a first end, a second end, a first side, and a second side.4432. The stent of claim 31, wherein the at least one node flange includes a first node flange formed at an intersection point between the first segment and the first end of the third segment, and a second node flange formed at the intersection point between the second segment and the second end of the third segment.

33. The stent of claim 31, wherein the at least one node flange is formed at an intersection point between the first segment and the first side of the third segment.

34. The stent of claim 31, wherein the at least one node flange is formed at an intersection point between the second segment and the second side of the third segment.

35. The stent of claim 30, wherein the first segments include a first side and a second side, and wherein the at least one node flange includes a plurality of node flanges formed in an alternating pattern between the first side and the second side of the first segments.

36. The stent of claim 30, wherein the second segments include a first side and a second side, and wherein the at least one node flange includes a plurality of node flanges formed in an alternating pattern between the first side and the second side of the second segments.

37. The stent of claim 30, wherein the third segments are parallel to one another along the longitudinal direction between a corresponding segment of the plurality of first segments and a corresponding segment of the plurality of second segments.

38. The stent of claim 30, wherein the first segments and the second segments are repeated in the circumferential direction to be sized for pediatrics.

39. A stent comprising:a plurality of interconnected cell units, each cell unit comprising:a first curved strut;a second curved strut; and45a third curved strut,wherein the first, second, and third curved struts are connected to form an asymmetric pattern within the cell unit.

40. The stent of claim 39, wherein the asymmetric pattern of the cell unit is configured to provide a non-linear stress-strain response during compression of the stent.

41. The stent of claim 39, wherein the first, second, and third curved struts have different curvatures.

42. The stent of claim 39, wherein at least one of the first, second, or third curved struts has a variable width along an extended lengthwise side.

43. The stent of claim 39, wherein the cell unit is configured to exhibit auxetic behavior during compression of the stent.

44. The stent of claim 39, wherein the asymmetric pattern of the cell unit is configured to distribute stress across the cell unit during compression of the stent.

45. The stent of claim 39, wherein the stent is formed from a polymeric material.

46. A method of manufacturing a stent, the method comprising:forming a plurality of interconnected cell units, each cell unit comprising:a first curved strut;a second curved strut; anda third curved strut,wherein the first, second, and third curved struts are connected to form an asymmetric pattern within the cell unit.

47. The method of claim 46, wherein forming the plurality of interconnected cell units comprises laser cutting a tubular structure.

48. The method of claim 46, further comprising refining the curvature of at least one of the first, second, or third curved struts to achieve a desired stress distribution during compression of the stent.

49. A stent comprising:a tubular structure formed from a plurality of interconnected cell units, each cell unit comprising:a first curved strut extending in a first direction;a second curved strut extending in a second direction different from the first direction; anda third curved strut connecting the first and second curved struts, wherein the arrangement of the first, second, and third curved struts forms an asymmetric pattern within the cell unit.

50. The stent of claim 49, wherein the asymmetric pattern of the cell unit is configured to provide a gradual decrease in stress as the stent is compressed from an initial diameter to a crimped diameter.

51. The stent of claim 49, wherein the first, second, and third curved struts have differing radii of curvature.

52. The stent of claim 49, wherein the asymmetric pattern of the cell unit is configured to reduce stress concentration at connection points between the curved struts during compression of the stent.

53. The stent of claim 49, wherein the tubular structure is configured to exhibit a non-linear stress-strain response during radial compression.

54. A method of designing a stent, the method comprising:defining a cell unit comprising first, second, and third curved struts;arranging the first, second, and third curved struts in an asymmetric pattern within the cell unit;analyzing stress distribution within the cell unit during simulated compression;adjusting at least one of curvature, width, or arrangement of the curved struts to improve stress distribution during compression.

55. The method of claim 54, further comprising:repeating the cell unit to form a tubular structure; andanalyzing global mechanical properties of the tubular structure.

56. The method of claim 54, wherein adjusting at least one of curvature, width, or arrangement of the curved struts comprises iteratively modifying the cell unit design to achieve a predetermined stress-strain response during compression.

57. The method of claim 54, further comprising selecting a polymeric material for the stent based on the cell unit design after adjusting.

58. The method of claim 54, wherein arranging the first, second, and third curved struts in an asymmetric pattern comprises positioning the curved struts to create a re-entrant geometry that exhibits auxetic behavior during compression.

59. A polymeric stent having a longitudinal direction and a circumferential direction, the polymeric stent comprising:a plurality of flexible joints, each joint being configured to flex between a first configuration and a second configuration as the polymeric stent is changed respectively from an uncrimped state to a crimped state in which a circumferential size of the stent is reduced by forces applied along the circumferential direction, each joint comprising:at least three struts arranged to meet at a node, wherein in the first configuration a first longitudinal strut and a second longitudinal strut of the at least three struts each extend away from the node within 45 degrees of the longitudinal direction, the first longitudinal strut extending away from the node generally along one of the positive longitudinal direction and the negative longitudinal direction with respect to the node and the second longitudinal strut extending away from the node generally along the other of the positive longitudinal direction and the negative longitudinal direction with respect to the node, and wherein a first circumferential strut of the at least three struts extends away from the node within 45 degrees of the circumferential direction, the first circumferential strut extending along a direction between the circumferential direction and the first longitudinal strut and / or having a shape48that is asymmetric with respect to a length direction of the circumferential strut to define a preferred flexing direction of the joint;wherein the fist and / or second longitudinal strut extends away from the node and meets a second circumferential strut extending in the opposite circumferential direction to the first circumferential strut, such that in the second configuration the first circumferential strut and the first and / or second longitudinal struts of the flexible joint are each bent compared to the first configuration.

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