Ureteral stent for reducing urine reflux and bladder spasms

Abstract

A ureteral stent includes a proximal end region including a first retention coil with a lumen; a straight, hollow tubular stent body; a retention element at the distal end of the stent, wherein the retention element comprises a semi-spherical, conical, or other ovoid shapes shell; a collapsible tube at the distal end, where the collapsible tube tip has a distinct shape at both the proximal and distal sides with either same or different diameters; such as straight tube, tapered inward or tapered outward; and a plurality of side ports along the stent, extending from the proximal end to distal end, either spaced uniformly or non-uniform such that distance between the holes is less on the proximal end compare to distance between holes on the distal end.

Description

URETERAL STENT FOR REDUCING URINE REFLUX AND BLADDER SPASMSRELATED APPLICATION DATA

[0001] The present application claims benefit of and priority to co-pending U.S. provisional applications Serial Nos. 63 / 666,061, filed June 28, 2024, 63 / 706,581, filed October 11, 2024, and 63 / 712,060, filed October 25, 2024, the entire disclosures of which are expressly incorporated by reference herein.TECHNICAL FIELD

[0002] This disclosure relates generally to the Urology field, and more specifically, relates to ureteral stents, an improved system for reducing Stent Related Complications, namely, urine reflux and bladder spasms.BACKGROUND

[0003] Ureteral stents are vital medical devices employed within the urinary tract to facilitate the urine flow, typically from the kidney to the bladder, and to provide support to compromised ureters. These tubular structures, terminating in opposing ends — a proximal end in the kidney and a distal end in the bladder- play a crucial role in alleviating ureteral obstructions, injuries, or ensuring the integrity of the ureter during surgical procedures.SUMMARY

[0004] The present application is directed to the field of urology and, more specifically, to a ureteral stent. Despite their therapeutic significance, ureteral stents are associated with notable challenges. One of the primary issues is urine reflux, a phenomenon where urine flows backward from the bladder into the kidneys. This reflux, triggered by the presence of the stent in ureter, disrupts the natural urinary flow dynamics. In addition to urine reflux, bladder discomfort is a major concern experienced by patients due to the length, size, and mass of the stent, which is exacerbated by the presence of retention members designed to secure the stent within the urinary tract. While the stent is intended to maintain ureteral patency, its design inadvertently aggravates urinary reflux and patient discomfort, necessitating for more precise solution.

[0005] The conventional approach to addressing discomfort caused by ureteral stents often involves administering antispasmodic drugs to alleviate symptoms such as urinary bladder musclecontractions and flank pain. However, while these pharmaceutical interventions offer temporary relief, they do not address the root cause of urine reflux associated with stent placement.Similarly, attempts to modify stent design by reducing the mass of retention members or using softer materials overlook the complex biomechanics underlying urine reflux, making such solutions inadequate for providing lasting relief to patients.

[0006] A particularly problematic design feature is the distal pigtail coil, which rests on the bladder mucosa and continuously irritates the lining. This mechanical irritation often leads to increased involuntary bladder contractions, or spasms, resulting in suprapubic pain, hematuria, and irritative voiding symptoms such as urgency, frequency, and dysuria. This issue is further compounded by anatomical variation, as ureteral length varies among individuals and current stent lengths are fixed, which may lead surgeons inadvertently leave a longer segment of the distal pigtail in the bladder when stent exceeds the ureteral length, contributing to increased stimulation of the bladder wall mucosa and subsequent bladder spasms.

[0007] The persistent challenges in addressing ureteral stent discomfort, particularly concerning urine reflux and bladder spasms, emphasize the need for an innovative solution. A deeper understanding of the biomechanics and physiological dynamics involved in urinary flow and stent placement is essential for developing more effective interventions.

[0008] Exemplary ureteral stents are disclosed herein that are designed for implantation in the ureter between the kidney and the bladder. The ureteral stent facilitates urine drainage from the kidney to the bladder while mitigating common complications such as urine reflux and bladder spasms, which are associated with conventional ureteral stents.

[0009] In one example, the novel ureteral stent comprises an elongated tubular body made from a flexible polymer material. The stent includes several innovative design elements: a) a distal tip (where 'distal' refers to the end positioned in the bladder when the stent is implanted) with a collapsible tube, b) a flexible semi -spherical shell, and c) an extendable segment. These features enhance the ureteral stent's functionality and patient comfort.

[0010] The distal tip of the Ureteral stent may include a collapsible tube that expands under radial tension. This design allows for unidirectional antegrade urine flow from the kidney to the bladder while preventing backflow of urine under retrograde bladder pressure.

[0011] The flexible semi -spherical shell structure at the distal end ensures secure retention at the ureterovesical junction. This feature helps reduce retrograde urine flow around the stent in the ureter, thereby decreasing the risk of urine reflux into the kidney and associated flank pain.

[0012] The Ureteral stent may feature a small extendable segment designed to accommodate variability in ureteral length among patients. This segment ensures a precise and secure fit, enhancing the stent's retention and reducing the risk of migration.

[0013] The polymer material of the Ureteral stent is biocompatible, ensuring compatibility with the urinary tract tissues and minimizing the risk of adverse reactions. The stent is designed to be flexible enough to navigate the anatomical curves of the ureter while being firm enough to maintain patency and support urine drainage.

[0014] Overall, the Ureteral stents herein may address one or more of the primary drawbacks of conventional ureteral stents, e.g., by incorporating features that minimize patient discomfort and complications. The collapsible tube tip and flexible semi-spherical shell structure function as a one-way valve, effectively preventing urine reflux through and around the stent. Additionally, the presence of a short distal tip inside the bladder reduces bladder irritation and spasms. These innovations make the Ureteral stent a significant advancement in ureteral stent technology, offering improved clinical outcomes and enhanced patient comfort.

[0015] Other aspects and features of the present invention will become apparent from consideration of the following description taken in conjunction with the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0016] It is believed the present invention will be better understood from the following description of certain examples taken in conjunction with the accompanying drawings, in which like reference numerals identify the same elements and in which:

[0017] FIG. 1 illustrates a urinary system with a ureteral stent placed inside the ureter;

[0018] FIG. 2A illustrates a novel ureteral stent with proximal retention element, tubular element, distal retention element, and an extendable segment as an element; FIG. 2B shows a sectional view of the tubular segment, depicting the stent lumen at a given cross-section; FIG. 2C and FIG. 2D illustrate the extendable segment positioned according to second and third alternatives;

[0019] FIG. 3 A illustrates a ureteral stent conduit according to first element; FIG. 3B illustrates the stent conduit according to another alternative with equal space side holes, and FIG. 3C third alternative with unequally spaced side holes, such as small distance between the holes in proximal end compared to distal end;

[0020] FIGS. 4Aa-4Ib illustrate examples of an extendable segment. FIGS. 4Aa-4Ac and 4Ba-4Bc depict exemplary segments with reduced wall thickness compared to the main stent body; FIGS. 4Ca and 4Cb shows a corrugated pattern with wave-like folds that act as mechanicalsprings; FIGS. 4Da-4Db and 4Ea-5Eb illustrate linear cut patterns in longitudinal and helical orientations; FIGS. 4Fa and 4Fb show a ribbon-like extension that unfurls when active / under tension; FIGS. 4Ga and 4Gb show circular perforations, FIGS. 4Ha and 4Hb show polygonal (diamond, square or rectangular) openings that promote extension under tension. FIGS. 41a and 41b show optional elliptical cut-outs that may be optimized for elongation and mechanical integrity. FIGS. 4Ja and 4Jb are cross-sections showing an exemplary extendable segment for a ureteral stent that includes a telescoping tube structure including two or more concentric sleeves;

[0021] FIGS. 5Aa-5Db illustrate exemplary features of a distal retention element. FIGS. 5Aa and 5Ab show a first element with a semi -spherical shell, while FIGS. 5B and 5C shows a varying thickness of spherical shell from center to edges that may be included in the FIG. 5 Aa configuration. FIGS. 5Da and 5Db show another alternative with a conical shell;

[0022] FIGS. 6Aa to 6Cb show exemplary features of a collapsible tube. FIGS. 6Aa and 6Ab show a collapsible tube element in its initial collapsed state (FIG. 6Aa) and its final dilated state (FIG. 6Ab) with a circular opening. FIGS. 6Ba and 6Bb show a second alternative with an inward tapered collapsible tube tip in the initial collapsed state (FIG. 6Ba) with an elliptical opening, transitioning to circular openings when dilated (FIG. 6Bb). FIGS. 6Ca and 6Cb show an outward tapered collapsible tube tip in an elliptical shape during the collapsed state (FIG. 6Ca), which expands to circular openings when dilated (FIG. 6Cb). FIG. 6D and FIG. 6E show optional varying thickness of collapsible tube from the distal end to the proximal end of the example shown in FIG. 6Aa and 6 Ab.

[0023] FIGS. 7 A and 7B show exemplary features of a combined extendable segment with distal retention element including a semispherical shell and collapsible tube, highlighting the potential for single component design and manufacturing.

[0024] FIGS. 8 A to 8C illustrate a method for preventing urine reflux according to a first element. FIG. 8A shows the distal retention element inside the bladder in a resting state. FIG. 8B depicts urine flowing through the stent into the bladder and around the stent through the ureter when the pressure inside the bladder is less than the pressure in the upper urinary tract, such as in the kidney. FIG. 8C demonstrates how increased bladder pressure pushes the distal retention structure against the bladder, closing the intramural opening and thereby preventing urine reflux through and around the stent;

[0025] FIGS. 9 A to 9C illustrate a method for preventing urine reflux according to a first configuration, when stent with or without extendable segment is placed inside the urinary tract. FIG. 9A shows the stent with the distal retention element inside the bladder at ureterovesical junction when there is no difference between kidney pressure and the bladder pressure. FIG. 9Bdepicts urine flowing through the stent into the bladder and around the stent through the ureter into the bladder, when the pressure inside the bladder is less than the pressure inside the upper urinary tract, such as in the kidney. FIG. 9C demonstrates how increased bladder pressure pushes the distal retention element of the stent against the bladder, closing the intramural opening and thereby preventing urine reflux through and around the stent.

[0026] FIGS. 10A to 10C illustrate the functionality of the ureteral stent with a corrugated extendable segment for preventing urine reflux. In FIG. 10A, the distal retention part of the stent effectively closes the intramural opening at the trigone region of the bladder, assisting in retention and preventing urine reflux. FIG. 10B demonstrates how the stent facilitates antegrade urine flow when bladder pressure is lower than kidney pressure, aided by the extendable segment, inward folding of the hemispherical shell, and dilation of the collapsible tube. FIG. 10C shows the retraction of the extendable segment and the closure of the intramural opening when bladder pressure exceeds kidney pressure, with the collapsible tube collapsing to prevent retrograde flow.

[0027] FIGS. 11 A and 1 IB illustrates potential configurations of the stent’s side holes at active configuration. FIG. 11 A shows a configuration with holes spaced equally along the entire length of the stent, while FIG. 1 IB depicts a variation where the distance between the holes is smaller at the proximal end compared to the distal end. This design is aimed at optimizing antegrade flow while minimizing urine reflux.

[0028] FIGS. 12 A, 12B and 12Ca depict various examples of the ureteral stent without holes. FIG. 12Cb is a close-up view of the distal tip of the ureteral stent in FIG. 12Ca.

[0029] FIG. 13 A is a schematic view an exemplary testing assembly for a ureteral stent. FIG. 13B is a table of results showing antegrade and retrograde pressure differences, with flow rates in ml / s, from the testing of the ureteral stent using the testing assembly in FIG. 13 A with the ureteral stent in FIG. 12Ca.

[0030] FIG. 14 presents experimental flow results for other examples of the ureteral stent configurations (6 Fr size), comparing designs with and without distal end holes and incorporating a flexible or semi-flexible retention element. The table shows antegrade and retrograde flow rates (in mL / s) measured under defined pressure conditions, highlighting the influence of design variations on unidirectional flow performance.

[0031] FIGS. 15A and 15B are a schematic depiction and photograph of another example of an exemplary ureteral stent with side holes.

[0032] The drawings are not intended to be limiting in any way, and it is contemplated that various examples of the invention may be carried out in a variety of other ways, including those not necessarily depicted in the drawings. The accompanying drawings incorporated in andforming a part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention; it being understood, however, that this invention is not limited to the precise arrangements shown.DETAILED DESCRIPTION

[0033] Before the examples are described, it is to be understood that the invention is not limited to particular examples described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular examples only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.

[0034] Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention.

[0035] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, some potential and exemplary methods and materials are now described.

[0036] It must be noted that as used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a compound” includes a plurality of such compounds and reference to “the polymer” includes reference to one or more polymers and equivalents thereof known to those skilled in the art, and so forth.

[0037] Certain ranges are presented herein with numerical values being preceded by the term “about.” The term “about” is used herein to provide literal support for the exact number that it precedes, as well as a number that is near to or approximately the number that the term precedes. In determining whether a number is near to or approximately a specifically recitednumber, the near or approximating unrecited number may be a number which, in the context in which it is presented, provides the substantial equivalent of the specifically recited number.

[0038] The following description of the elements is not intended to limit the disclosure to these elements, but rather to enable any person skilled in the art to make and use the various examples described herein. FIG. 1 illustrates the human urinary tract 100, which includes ureters 102 that facilitate urine transport from the kidney 101 to the bladder 103 through intramural opening 104. If a ureter is obstructed due to, for example, post-ureteroscopy procedures, strictures, or stone fragments, urine drainage is restricted. Ureteral stents are medical devices implanted within the ureters to restore urine drainage. These ureteral stents can be a primary cause of morbidity, with stent-related complications occurring in over 80% within the first few days after placement. The system and methods disclosed herein aim to reduce stent-related complications, such as, urine reflux and bladder spasms, and to decrease overall patient discomfort.

[0039] As shown in FIGS. 1, 2A, 2C and 2D, an exemplary ureteral stent is shown, which may implanted in a patient for reducing urine reflux and bladder spasms, and includes a proximal retention element 200, positioned in the kidney 101 (proximal relative to patient); a tubular element 300, located inside the ureter 102; and a distal retention element 400, placed in the bladder 103 (distal relative to patient). The tubular element 300 has a longitudinal lumen 301 (FIG. 2B) that facilitates fluid passage from the proximal retention element 200 to the distal retention element 400 of the stent. Another element may include an extendable segment 500 along with the tubular element 300 to facilitate the stent's extension, such that the proximal retention element 200 remains in the kidney and the distal retention element 400 closes off the port of the intramural opening 104.

[0040] The proximal retention structure 200 may have shapes suitable to adapt the placement within the kidney and to stabilize the stent in the ureter, such as spiral, pigtail, hook, barbs, protrusions, hemispherical shell, subject-specific shell and similar (no figures shown). The proximal retention element has sometimes an inlet, eyelets or plurality of openings providing fluid communication from kidney into its lumen.

[0041] The tubular element 300 includes an elongated lumen 301 extending between proximal 200 and distal 400 retention elements (FIGS. 2A-D). The lumen 301 may be any shape that allows flow including, round, oblong, elliptical, hexagonal, D shaped, crescent shaped, or square in cross-section (no figures shown). Ureteral stent 300 in present disclosure may have a non-extended length of 8 cm to 36 cm as measured between the retention members. Alternate element includes extendable segment 500 on the stent to facilitate the stent extension such that,the proximal retention element 200 retains at the kidney 101, and the distal retention element 400 close the intramural opening 104. The extendable element 500 can vary in length ranging from 5 mm to 50 mm and may be located along the tubular element 300 at specific locations relative to the stent’s total length, including: at 75-95% of the total length from the proximal end for the distal positioning (FIG. 2A); at 50-75% of the total length from the proximal end for the middle positioning (FIG. 2C); and at 25-50% of the total length from the proximal end for the proximal positioning (FIG. 2D). The extendable segment 500 may increase the stent's length by 5 mm to 50 mm, depending on the application. The extension capability can be classified into three functional ranges: a narrow or optimized extension range of approximately 5-15 mm, which is suitable for precise positioning in relatively straight or short anatomical paths; a medium extension range of approximately 15-30 mm, useful in moderately curved ureters or transitional anatomies where small length adjustments help optimize placement; and a wide extension range of approximately 30-50 mm, which is particularly advantageous for tortuous or atypical anatomy, especially in pediatric or complex clinical cases. These range of extension corresponds to approximately 6- 15% of the total stent length in typical adult configurations (e.g., 24-36 cm stents), and up to 30- 60% in shorter pediatric stents (e.g., 8-15 cm). The extendable element may be particularly beneficial in pediatric or atypically shaped anatomies, where a compact stent may need to bridge a longer functional path due to curvature or tortuosity. For example: a. A 24 cm adult stent with a 20 mm extendable segment may reach up to 26 cm after deployment, enabling precise distal retention at the intramural orifice. b. A 10 cm pediatric stent with a 10 mm extendable segment may reach 11 cm, achieving full bladder entry while minimizing excess stent in the renal pelvis.This proportional extension capability ensures optimal placement without oversizing or changing the retention element geometry.

[0042] Also, the tubular element 300 (FIG. 3 A) may have plurality of openings 310 providing fluid passage from ureter into the stent lumen (FIG. 3B). The position and presence of these side holes, particularly at the distal end of the stent, play a significant role in regulating both antegrade and retrograde flow under varying conditions of ureteral obstruction.

[0043] In situations where the ureter is occluded, the antegrade flow — the movement of urine from the kidney to the bladder — remains largely unaffected by the presence or absence of side holes at the distal end of the stent. This is because the primary fluid passage continues to occur through the proximal portion of the stent. Conversely, the presence of side holes at the distal end increases retrograde flow — the movement of fluid from the bladder back towards the kidney — compared to stents that lack side holes. This configuration may allow some fluid tobypass the obstruction, which can lead to increased pressure buildup in the kidney. Therefore, minimizing the retrograde flow is crucial to preventing complications associated with obstruction.

[0044] When the ureter is unoccluded, the absence of side holes at the distal end leads to a decrease in antegrade flow compared to stents with side holes at the distal end, which facilitate more efficient urine drainage from the ureter to the bladder. In terms of retrograde flow, the presence of distal holes in unoccluded conditions did not show a significant effect compared to stents without holes.

[0045] Based on experimental findings, the ureteral stent is optimized with multiple holes 310 extending along the entire length 311 of the tubular element (FIG. 3B), including the distal end, to enhance overall drainage performance. The holes may vary in shape, commonly being round or elliptical, with diameters ranging from approximately 0.2 mm to 1.0 mm, in order to maximize fluid passage while preserving the structural integrity of the stent. The hole density along the tubular surface may range from approximately 1% to 10% porosity, defined as the total open hole area relative to the external surface area of the stent in that region. In certain configurations, the stent may include 1 to 5 holes per centimeter of length, with spacing optimized to avoid mechanical weakening of the wall. This strategic hole distribution enables the stent to maintain a balance between antegrade flow under both occluded and unoccluded conditions, and to regulate retrograde flow effectively, particularly under occluded conditions. To further improve drainage efficiency, a high density of inlet holes is provided on the proximal portion of the stent, which resides in the renal pelvis when deployed, for example, a porosity of approximately 5%- 10%, compared to the mid or distal portions. This increased proximal hole density 312 promotes greater urine entry into the stent lumen directly from the kidney (FIG. 3C). Additionally, the holes are distributed at varying circumferential positions around the stent wall, rather than being aligned on a single side. This non-uniform hole pattern reduces the likelihood of tissue contact or compression occluding all inlet holes, which could otherwise severely limit urine flow. Such a configuration supports consistent and reliable fluid communication into the lumen even in the presence of anatomical variations or external pressure from surrounding tissue.

[0046] In certain examples, the circumferential hole distribution may follow a helical or staggered pattern 312 to further reduce occlusion risk and improve flow uniformity. The combined effect of proximal high-density holes and circumferential distribution enhances overall stent performance by optimizing urine drainage, preventing urine retention, and minimizing the risk of backflow into the kidney. These features contribute to improved clinical outcomes by reducing complications such as hydronephrosis, bladder spasms, or infection due to stagnant urine (FIG. 3).

[0047] The spacing between holes along the longitudinal (axial) direction may vary depending on the patient population and intended clinical application. In certain examples, such as shown in FIG. 3B, the holes are distributed in a helical pattern around the circumference of the stent, with uniform axial spacing between successive holes along the helix. The axial spacing in such configurations may range from approximately 5 mm to 25 mm, with preferred ranges of 10 mm to 25 mm for adult stents, and 5 mm to 15 mm for pediatric stents, balancing drainage performance with stent flexibility. In other examples, such as FIG. 3C, the stent exhibits a helical hole pattern with variable axial spacing along its length. The proximal portion of the stent (positioned in the renal pelvis) has a higher density of holes, with axial spacing in the range of 5 mm to 10 mm, to promote efficient urine inflow. Conversely, the distal portion of the stent (near the bladder) has lower hole density, with axial spacing ranging from 10 mm to 25 mm, minimizing the risk of excessive retrograde flow while preserving drainage. This non-uniform spacing strategy enables the stent to adapt to regional flow demands and anatomical constraints, improving clinical performance

[0048] To further enhance performance, the spacing between the holes 312 may vary along the length of the stent. In another alternative, the proximal end (near the kidney) features a higher number of closely spaced holes compared to the distal end (near the bladder) hole number, where the holes are fewer and spaced farther apart (FIG. 3C). For example, the spacing between holes may be closer on the proximal end, ranging from 5 mm to 10 mm, while at the distal end, the spacing may range from 10 mm to 25 mm. This configuration ensures that the proximal side, which handles a greater volume of fluid, facilitates more efficient drainage while the distal end maintains adequate control over retrograde flow. Hole sizes may also vary, with diameters ranging from 0.5 mm to 3 mm, adjusted based on their position and stent size to optimize flow dynamics (no figure shown).

[0049] Overall, the ureteral stent is designed with these varied hole spacings and distributions to optimize fluid dynamics, ensuring that the stent functions effectively under different physiological conditions. This tailored approach allows the stent to meet the specific needs of each patient, resulting in improved overall performance and clinical outcomes.

[0050] The extendable segment 500 of the stent is designed to accommodate variations in length to adapt the anatomical changes. The ureteral stent may be configured with various engineered cuts or micro-patterns along its tubular wall to provide targeted mechanical flexibility, elongation capability, and fluid management features. These modifications can be implemented using precision techniques such as laser cutting, photolithography, or mechanical micro-machining, depending on the stent’s material composition (e.g., thermoplastics, elastomers, or super elastic alloys like nitinol).

[0051] In certain examples, the stent comprises a segment of reduced wall thickness relative to the standard tubular body (FIGS. 4Aa and 4Ba). This locally thinned region (FIGS. 4Ab and 4Bb) may have a wall thickness of 50 to 300 microns, compared to adjacent thicker regions with wall thickness of 300 to 800 microns. This locally thinned region allows the stent to undergo axial elongation of 10-30% when tension of 0.1-0.5 N is applied, facilitating easier deployment or repositioning. It also enables passive elongation in response to physiological movements of the ureter without inducing excessive stress (FIGS. 4Ac and 4Bc). These thinner segments may be integrally formed during extrusion or selectively thinned using laser ablation, micro-machining or etching techniques.

[0052] The corrugated pattern (FIG. 4Ca) consists of wave-like undulations or accordion folds with an amplitude (peak to trough depth) of 0.5 mm to 1mm and a pitch (peak to peak spacing) of 1 mm to 5 mm along a portion of the stent wall. This design enhances axial elongation up to 20% and radial compressibility by 10-25%, while preserving structural integrity. The corrugations act as mechanical springs, allowing the stent to compress or elongate (FIG. 4Cb) in response to ureteral motion. This pattern is especially beneficial in areas where peristalsis or anatomical curvature requires the stent to flex without kinking or migration. Corrugations can be formed by thermal molding, mechanical pressing, or 3D printing techniques.

[0053] Linear cuts along the stent wall (FIGS. 4Da, 4Ea) are another example may be 0.2 mm to 1 mm in width, 2 mm to 10 mm in length, and spaced 1 mm to 5 mm apart, to improve flexibility and promotes directional expansion. These cuts may be aligned longitudinally, diagonally, or in a helical orientations. When appropriately spaced, they allow the stent to bend without forming sharp angles, reduce the radial stiffness by 15-25%, and enable controlled elongation of up to 20% (FIGS. 4Db, 4Eb). Such cuts also serve to relieve localized stress and can enhance fluid egress through secondary pathways. Laser micromachining is the preferred technique for fabricating these features with high precision and consistency.

[0054] A specialized example includes a ribbon-like extension (FIG. 4Fa), where a segment of the stent unfurls (FIG. 4Fb) into a flat or helically wound strip. The ribbon width may range from 0.5 mm to 3 mm, with a thickness of 50 to 150 micron, and a coil pitch of 1 mm to 3 mm. The unfurling length may extend 10 mm to 40 mm depending on deployment force or anatomical requirement. This design provides enhanced conformity to narrow or irregular ureteral segments and may also reduce mucosal irritation. The ribbon may act as a tension-bearing segment or provide auxiliary flow pathways through spaces between the coils. This feature can bemanufactured by cutting specific portions of the tubular body to unfurl or by integrating a multilayered laminate that delaminates under deployment stress.

[0055] To further improve fluid dynamics and surface interaction, a variety of cut-out patterns may be incorporated into the stent wall. These include:1. Circular 560 perforations (FIGS. 4Ga, 4Gb): These are ideal for uniform stress distribution and minimal disruption to wall integrity. The smooth geometry reduces the likelihood of stress concentrations and encrustation formation. Circular perforations may range from 0.3 mm to 1 mm in diameter, with a porosity of 1 to 10% surface area.2. Polygonal 570 (Square, rectangular) openings (FIGS. 4Ha,4Hb): These allow for more aggressive fluid exchange and potentially increased flexibility. However, corners may introduce stress risers and require additional structural compensation. Polygonal openings may have a side length of 0.5 mm to 2 mm, with 3-6 sides and porosity of 1 to 10% of surface area.3. Elliptical or oval-shaped slots (FIGS. 41a, 41b): These offer a balance between flow area and mechanical robustness, allowing elongation along the long axis while resisting collapse. Elliptical or oval shaped slots may have major axis 1.5 mm to 3 mm, minor axis of 0.5 mm to 1 mm, facilitating elongation while retaining strength.

[0056] These cut-based modifications provide key advantages over traditional stent designs by allowing greater mechanical adaptability of stent with the ureteral length and enhancing urine flow through multiple entry and exit paths. By tuning the geometry, spacing, and placement of these features, the stent can accommodate varying ureteral morphologies and motion demands.

[0057] In one example, the extendable segment 500 of the ureteral stent comprises a telescoping tube structure (FIGS. 4Ja, 4 Jb) composed of two or more concentric sleeves, each with interlocking ribs or nested grooves. The inner segment fits within the outer with a clearance of 50 -150 microns, and elongates under tensile force of 0.1 and 0.5 N. The segment provides an extension range of 5 to 20 mm while maintaining internal lumen patency. The rib or groove height may range from 0.2 mm to 1 mm, with interlock pitch of 1 to 3 mm to regulate elongation rate and prevent kinking. .

[0058] Overall, the lumen 301 of the ureteral stent may have walls of either constant or varying thickness from 100 microns to 2 mm, depending on design. The stent is designed to have a length ranging from approximately 8 cm to 36 cm, depending on the specific anatomical location and clinical need. In many cases, stents are designed with lengths in the range of 10 cm to 28 cm, which can accommodate a variety of patient anatomies and clinical scenarios. The outerdiameters of the stents typically range from 3.5 Fr to 14 Fr to accommodate various ureteral sizes. Stents with diameters between 4.8 Fr and 8.5 Fr are commonly used for adult patients, while smaller diameters, ranging from 3 Fr to 4.7 Fr, may be more appropriate for pediatric patients or delicate ureters. The extendable segment 500 is designed to preserve the functional lumen of the stent during and after axial extension. In its collapsed or unextended state, the segment maintains a wall thickness between 100 microns to 2 mm, with the capacity to thin by up to 50% upon full extension depending on the material used. The internal lumen diameter through the extendable segment is maintained within ±10% of the lumen diameter of the adjacent tubular element to ensure consistent flow and avoid obstruction.

[0059] The second retention element at the distal end includes two elements. The first alternative comprises a collapsible tube 410 and a semi-spherical shell element 420 (FIGS. 5Aa, 5Ab). The semi -spherical shell 420 is characterized by a diameter ranging from approximately 3 mm to 15 mm, with a radius of curvature between 3 mm and 20 mm. The depth of the shell typically ranges from 3 mm to 15 mm. The wall thickness ranges from 5 micron to 2 mm, sufficiently flexible to close the intramural opening based on selected material. The semi- spherical shell is formed from an elastomeric material such as polyurethane, silicone, hydrogels or a thermoplastic elastomer. These materials are selected for their combination of flexibility, biocompatibility, and shape retention. This geometry also provides inherent structural stiffness due to its curvature, similar to the structural behavior of a contact lens. Even with wall thicknesses as thin as 50 microns, the semi-spherical shell maintains its domed shape in the absence of external forces due to curvature-induced resistance to inversion or collapse. Under antegrade- pressure from kidney, the shell is designed to elastically deform or fold inward, allowing it to function as a passive one-way valve in the ureteral lumen. Once the pressure subsides, the shell returns to its original shape without requiring a shape-memory alloy or actuator, purely relying on elastic recovery. In contrast, a multi panel element such as in quadra, penta, hexa and octa, with the same material and thickness would collapse more readily under gravity or mild pressure. Thus, the spherical geometry offers a unique balance of collapsibility and shape resilience that enhances device function in dynamic physiological conditions.

[0060] The spherical shell material hardness is defined by a Shore A durometer in the range of 10A to 70A, with optimized configurations between 20A and 40A, balancing collapsibility with shape retention. Displacement force required to collapse the shell is in the range of 0.01 N to 1 N, with preferred values between 0.05 N and 0.2 N, ensuring responsiveness to physiological flow while preventing premature closure or retrograde seepage.The spherical shell has a radius of curvature between 3 mm and 15 mm and an apex angle from 60° to 180°, which may be tuned to achieve hemispherical or more conical geometries, depending on deployment site and performance goals. The elastic modulus of the shell material falls within the range of 0.1 MPa to 10 MPa. However, for optimized performance balancing tissue compliance and anti-reflux behavior, a range of 0.3 MPa to 2 MPa is preferred. This modulus ensures sufficient collapsibility under antegrade pressure while resisting deformation under retrograde pressure. Materials falling outside of this range may not provide the appropriate balance between flexibility and retention strength, leading to either leakage or excessive irritation. Additional mechanical criteria include a tear resistance of at least 10 N / mm, a collapsibility force threshold under antegrade flow of < 0.2 N, and a recovery time of <2 seconds after deformation, ensuring rapid sealing and reopening behavior during dynamic flow conditions.

[0061] The wall thickness of the shell varies radially 421, 422 to optimize deformation behavior (FIGS. 5B, 5C). The central portion of the shell may have a thickness ranging from 5 to 50 microns, with optimized examples at 15-30 microns, to permit collapse under low intra- ureteral pressure (<5 cm H2O), simulating the dynamic responsiveness of shell. The peripheral edge may have a thickness ranging from 0.5 mm to 2 mm, with optimized examples around 1-1.5 mm, to provide anchoring strength and resistance to inversion or prolapse under backpressure.

[0062] The second alternative, shown in FIGS. 5Da, 5Db, consists of a collapsible tube 410 and a conical shell 420. In one example, the distal retention element comprises a conical shell structure designed to anchor the stent at the intramural ureteral orifice and regulate fluid flow. The conical shell may be formed as a truncated or full cone with a centrally open or closed apex. The base diameter of the conical shell may range from approximately 3 mm to 15 mm, depending on patient anatomy (e.g., pediatric vs adult use). The axial height of the cone (measured from base to apex) may range from 3 mm to 15 mm, providing sufficient wall surface for flow control and anatomical engagement. The cone angle — defined as the angle between the cone wall and the central axis — may range from 30° to 70°, with preferred angles between 40° and 60° to balance sealing pressure and compliance. A wider angle enhances conformability with the bladder floor and reduces the risk of migration, while narrower angles improve intrusion into the intramural orifice to resist reflux. The conical shell wall may exhibit a tapered thickness profile to optimize mechanical performance. In some examples, the wall thickness is approximately 1 mm at the base and tapers gradually to 100-300 microns at the apex, allowing for controlled flexure and pressure response. This design provides a gradient stiffness profile, wherein the thicker base region offers structural stability while the thinner apex permits limited dynamic deformation under bladder pressure. In some variations, the conical shell may be formed from elastic or super-elasticmaterials (e.g., silicone, polyurethane, or nitinol-based composites), enabling radial expansion or deformation under load and restoration of original shape upon pressure normalization. Fabrication may include molding, 3D printing, or thermoforming depending on material choice. The conical shell may further incorporate fluidic or structural features, such as radial cut-outs, slotted apertures, or microtextured surfaces to enhance flow dispersion, improve tissue interface, and reduce encrustation (Figures not shown).

[0063] The curved geometry of the semispherical or conical structure is designed to provide uniform stress distribution during deformation, minimizing the risk of material fatigue, rupture, or delamination under physiologic cyclic loading. Finite element modeling and empirical testing suggest that a wall thickness ranging from 5 microns to 2 mm, depending on the material’s elastic modulus (e.g., 0.1-5 MPa), achieves a balance between flexibility and fatigue resistance. The radius of curvature of the shell structure may range from 1 mm to 5 mm, tailored to conform to the bladder wall while maintaining deformation thresholds below 100 cm JLO. This continuous, seamless form factor is distinguishable from multi-panel, ribbed, or umbrella-like geometries that rely on segmented deformation and often require mechanical hinges or struts. The integrated design avoids points of concentrated stress, which can serve as initiation sites for cracking or delamination during long-term indwelling.

[0064] In terms of attachment, the shell structure may be coupled to the ureteral stent using a variety of mechanical or chemical methods including: a. Press-fit or friction-fit interfaces, where the shell inner diameter is 0.1 to 0.5 mm smaller than the stent outer diameter, ensuring a compressive retention force of at least 0.5 to 2 N. b. Over-molding with the stent body during fabrication using thermoplastic elastomers, enabling material continuity and uniform bonding. c. Medical-grade adhesives with tensile shear strengths exceeding 1 MPa, applied in a band width of 0.5 to 2 mm around the coupling interface.

[0065] The mechanical interface is designed to maintain structural integrity and positional stability even under cyclic bladder contractions with frequencies up to 20 cycles per hour and pressures up to 80-120 cm H2O, typical of detrusor activity during voiding and storage phases. Placement of the shell element is targeted at or just proximal to the intramural ureter segment or vesicoureteral junction, typically located less than 0.5 cm from the ureteral orifice, to optimize reflux prevention while minimizing bladder irritation.

[0066] The shell element may be fabricated from flexible or semi-rigid materials, including but not limited to elastomers, silicones, shape-memory polymers, super-elastic alloys(e.g., nitinol), polyurethane blends, or thermoplastic elastomers, and may optionally incorporate surface coatings or treatments to improve biocompatibility, hydrophobicity, or biofilm resistance. When the semi-spherical element is made of a rigid material, the shell resists inversion but may not seal the ureteral orifice effectively during episodes of bladder pressure elevation, leading to increased retrograde urine flow. Conversely, when composed of flexible or elastic materials, the shell is capable of undergoing elastic outward deformation under retrograde pressure, effectively sealing the ureteral opening by collapsing onto intramural tissue, thereby reducing or eliminating reflux. Overall, the spherical element rigidity resulted in less effective sealing at the bladder junction, allowing more retrograde flow. Thus, the choice of material and thickness may be useful for balancing rigidity and flexibility to achieve optimal stent performance.

[0067] The shell is composed of high-density polyethylene (HDPE), low-density polyethylene (LDPE), or a composite of LDPE with nylon (PA) to enhance performance characteristics. Alternatively, materials such as silicone, silicone, EVA, PTFE, polyurethane, polyethylene, and their copolymers or elastomers similar to ureteral stent materials may be utilized for the semi-spherical shell. These materials provide excellent biocompatibility, flexibility, and durability, further enhancing the retention and anti-reflux properties of the stent.

[0068] Additionally, the semi -spherical structure can take other shapes, such as semi- oblate spheroid, semi-prolate spheroid, ovoid, subject-specific, conical, truncated cone, or similar structures, to ensure proper contact at the intramural part inside the bladder. The urine surrounding the ureter exerts pressure on the shell structure 420, causing it to fold inward into the bladder, allowing urine flow into the bladder. When the bladder pressure increases, the surface of the shell structure expands outward towards the bladder wall, closing the intramural opening and thereby preventing fluid reflux.

[0069] The figures FIGS. 6Aa to 6E show an exemplary element of a collapsible tube 410. In its initially collapsed state 411 A (FIG. 6Aa), the collapsible tube opens radially to state 41 IB under positive pressure, such as when the pressure inside the kidney is higher than the pressure inside the bladder (FIG. 6Ab). When the pressure outside the tube exceeds or equals the internal pressure, the tube collapses to state 411 A, thereby preventing antegrade fluid flow through the stent lumen. The lumen of the collapsible tube may have various internal cross-sectional shapes that support fluid flow, including round, oblong, elliptical, or polygonal geometries (e.g., hexagonal). The maximum outer diameter may range from 3.5 French (Fr) to 14 Fr, depending on the diameter of the stent body. The collapsible tube is designed to have a functional length between 3 mm and 15 mm to ensure responsive deformation under physiological conditions. To support its unidirectional flow function, the collapsible tube’s material is engineered to exhibitcontrolled distensibility — expanding radially under positive pressure while returning to a collapsed state under neutral or negative pressure. This behavior is enabled by using materials with an elastic modulus in the range of 0.1 to 10 MPa, which allows for reversible elastic deformation without material fatigue. The rigidity-to-flexibility ratio is further optimized by varying the wall thickness, with a range of 5 microns to 2 mm, depending on the material selected.

[0070] Common materials used include silicone, EVA, PTFE, polyurethane, polyethylene, and their copolymers — chosen for their high flexibility, biocompatibility, and tear resistance. For example, in one example, the collapsible tube is fabricated from medical-grade polyurethane with a wall thickness of approximately 5 mil (0.127 mm). Polyurethane of this type typically exhibits an elastic modulus in the range of 2 to 10 MPa, which provides sufficient flexibility to deform under intraluminal pressure while maintaining structural resilience to prevent kinking or collapse during normal ureteral compression. These material and dimensional properties enable reliable, repeatable opening and closing cycles under physiological flow conditions.

[0071] The collapsible tube can be integrated into the stent in two ways: (1) manufactured as a separate element and affixed to the elongated member, or (2) co-molded or co-extruded with the elongated member using variable wall thickness strategies that support collapsibility in response to physiological pressure changes.

[0072] The collapsible tube configurations are designed to optimize fluid flow within the ureteral stent system while accommodating variations in anatomical size. Each configuration includes a proximal opening that is equal to the inner lumen diameter of the stent, typically ranging from 1 mm to 8 mm, depending on stent size. For adult applications, proximal diameter is typically 2 mm to 4 mm, and for pediatric cases, 1 mm to 2 mm. The geometries illustrated in FIGS. 6Aa, 6Ba, 6Ca correspond to the passive or collapsed state of the collapsible tube, while FIGS. 6 Ab, 6Bb, 6Cb show active state or expanded state under pressure from antegrade urine flow. Each configuration maintains a proximal diameter that corresponds to the stent size, with the distal end differing in size to achieve specific functional goals.(a) Configuration with equal distal and proximal opening: In this design, the proximal end diameter of the collapsible tube matches the stent diameter, and the distal opening is also equal to the stent diameter (FIGS. 6Aa, 6Ab). In the collapsed state (FIG. 6Aa), the tip is folded or tapered but designed to open under physiological pressure into a shape with a distal opening that matches the proximal / stent lumen diameter. The cross-section of the opening may be circular or oval, with oval openings having a major axis ranging from 2 mm to 6 mm and minor axis from 1 mm to 4 mm. This symmetric design enablesconsistent flow in both the collapsed and expanded states and may be optimized to maintain alignment with stent walls to minimize resistance. In the expanded state (FIG. 6Ab), the tube resumes an open lumen configuration for urine passage. At active state, the distal opening diameters for this configuration may range from 1 mm to 8 mm, accommodating anatomical variation across the patient population. In certain examples, the diameter may range from 2 mm to 4 mm, representing values optimized for adult patients based on testing outcomes and clinical relevance. For pediatric applications, a diameter range of 1 mm to 2 mm may be used to align with the anatomical scale of younger individuals.(b) Configuration with smaller distal opening: This configuration also maintains a proximal end equal to the stent diameter, with the distal opening narrower than the proximal end in both collapsed and active states (FIGS. 6Ba, 6Bb). In this example, the collapsed distal tip (FIG. 6Ba) has an inward-tapered or pinched configuration, forming a narrowed outlet in the passive state. The distal opening expands under fluid pressure (FIG. 6Bb) to allow flow but remains smaller than the proximal opening. The collapsed oval shape typically has a major axis ranging from 0.5 mm to 3 mm, and a minor axis of 0.3 mm to 2 mm. Preferred adult configurations use 1 mm to 2 mm major axes, while pediatric versions may be as small as 0.5 mm. The taper angle in the collapsed state may range from 10° to 45°, facilitating opening in the flow direction while resisting retrograde pressure. In the active (expanded) state, the distal diameter ranges from 0.5 mm to 3 mm, with 1 mm to 2 mm optimized for adult anatomy and 0.5 mm to 1 mm for pediatric use.(c) Configuration with larger distal opening: In this configuration, the proximal end diameter of the collapsible tube is equal to the stent diameter, while the distal opening is designed to expand beyond the proximal diameter in active state, while still remaining functionally collapsible (FIGS. 6Ca, 6Cb). In the collapsed state, the distal tip typically assumes an elliptical or conical shape with a long axis of 1 mm to 2 mm and a short axis of 0.5 mm to 1.5 mm, restricting reverse flow from the bladder. In the expanded state, the distal opening may range from 2 mm to 5 mm, allowing adaptability across a broad spectrum of anatomical sizes. In specific examples optimized for adult patients, the distal diameter may range between 3 mm and 4 mm, which has shown favorable outcomes in performance testing. Additionally, a range of 2 mm to 4 mm may be used in cases where design performance and functional reliability are validated across varied clinical scenarios.The use of a 3 mm to 15 mm collapsible tip inside the bladder minimizes the length of the ureteral stent within the bladder, reducing episodes of bladder irritation and abrasions. This, in turn, decreases bladder spasms, hematuria, urinary urgency, and dysuria.

[0073] Inward tapering at the tip (FIG. 6Ba) enhances collapsibility and facilitates pressure-driven opening during active state (FIG. 6Bb), while outward tapering (FIG. 6Ca) may aid in anchoring or directing flow opening during increased pressures or active state (FIG. 6Cb). To further enhance functional asymmetry, the proximal and distal openings of the tube may have differential wall thickness, promoting preferred collapse from one end to the other (FIG. 6D, E). This ensures that flow directionality is maintained with minimal backflow.

[0074] The extendable segment and distal retention element can be sometime manufactured within single design. A configuration of corrugated extendable segment (FIG. 4C) with distal retention element (FIG. 5A) can be simplified to FIG.7A (FIG.7B, is sectional view), potentially minimize the number of manufacturing steps or subcomponents assembly time.

[0075] Overall, the semi -spherical shell 420, in conjunction with the collapsible tube 410, functions as a dynamic retention and reflux-prevention element located at the intramural ureteral opening. This configuration creates a mechanical valve that prevents retrograde fluid passage from the bladder to the ureter while still permitting antegrade flow from the kidney to the bladder. Unlike traditional stents that rely on passive flow channels or flaps, the proposed design utilizes pressure-responsive deformation enabled by engineered material properties and geometry.

[0076] As illustrated in FIGS. 8A to 8C, the mechanism for preventing urine reflux is pressure-driven and involves structural response to differential pressures across the distal end of the stent. FIG. 8A shows the semi -spherical shell 420 in a neutral, resting state inside the bladder. In FIG. 8B, when the pressure in the upper urinary tract (e.g., renal pelvis or ureter) exceeds bladder pressure, antegrade urine flow proceeds normally through the stent lumen and around the stent wall. The semi -spherical shell remains partially collapsed or deformed, maintaining patency. In FIG. 8C, when bladder pressure rises — such as during voiding — the increased pressure acts on the exterior of the shell, causing it to expand radially outward against the bladder wall. This deformation blocks the intramural ureteral opening, preventing retrograde flow through and around the stent.

[0077] This pressure-responsive behavior is governed by the shell’s structural and material characteristics. The semi -spherical shell is fabricated from biocompatible elastomers such as silicone hydrogel or polyurethane, chosen for their reversible elastic deformation properties. The shell features a variable wall thickness, with a central membrane as thin as 5 microns to 500 microns at the central membrane, and a thicker peripheral edge (up to 2 mm),though certain examples may employ central thickness of 10-100 microns and peripheral regions of 0.3- 1.5 mm, depending on anatomical site and stent diameter. The elastic modulus of the shell material is generally in the range of 0.05 MPa to 20 MPa, with preferred ranges between 0.1 to 10 MPa for adult anatomical pressures. This enables deformation in response to pressure differentials ranging from 5 cm H2O to 150 cm H2O. In certain pediatric or low-pressure variants, the modulus may be as low as 0.01 MPa, while high-retention examples may use moduli up to 30 MPa with structural reinforcement. The deformation ratio — defined as the change in shell height under pressure relative to its resting height, is typically between 0.1 and 0.9, indicating the shell may compress by 10% to 90% under physiologic voiding conditions.

[0078] This pressure-responsive, dome-like structure differs mechanistically from conventional anti-reflux stent tips, which often incorporate rigid or semi-rigid flaps, slit valves, or pre-formed fixed geometries that do not conform to local anatomy or dynamically adapt to changing pressures. In contrast, the present configuration leverages curvature-controlled deformation, similar to soft contact lenses, to achieve a smooth and continuous seal that conforms to bladder wall movement without requiring additional anchoring or tension. The dome-like element comprises a semi-spherical or ellipsoidal shell integrally or fixedly coupled to the distal end of the ureteral stent. This shell comprises a central membrane with a wall thickness of less than 250 microns, and a peripheral edge with a thickness equal to or greater than 0.5 mm, thereby enabling localized flexure under physiological pressure differentials.

[0079] The shell is fabricated from biocompatible elastomeric materials (e.g., silicone hydrogel or polyurethane) with a Young’s modulus in the range of 0.05 MPa to 20 MPa, allowing reversible elastic deformation under pressure differentials ranging from 10 to 150 cm ILO, typically 40-90 cm ILO during bladder voiding. In a preferred configuration, the dome exhibits a resting radius of curvature between 3 mm and 20 mm, and a base diameter between 2 mm and 10 mm. Under elevated bladder pressure, the dome undergoes radial expansion of at least 20% of its base diameter and a reversible deformation ratio of at least 0.2, defined as the ratio of vertical displacement (height reduction) to the initial dome height. These deformation characteristics enable the structure to form a seal against the intramural ureter during retrograde pressure spikes while maintaining antegrade patency during normal flow.

[0080] To distinguish eligible examples, dome structures falling within the scope of the invention are those that exhibit a reversible deformation ratio of at least 0.2 when subjected to bladder pressures in the range of 40-90 cm ILO, and achieve a radial expansion equal to or greater than 20% of the base diameter during the closure state.

[0081] Additionally, the combination of the semi -spherical geometry and collapsible tube provides bidirectional control, a feature not seen in prior art, which typically addresses either retention or reflux prevention — not both simultaneously. This adaptive sealing mechanism thus offers a unique, dual-functional benefit: anchoring the distal end of the stent within the bladder while preventing bladder-to-ureter urine reflux through a material-responsive, anatomically conforming interface.

[0082] During the placement of the novel ureteral stent, it is positioned such that the proximal retention 200 is located in the kidney pelvis, and the distal end is placed inside the bladder 103. The stent without extendable segment and with extendable segment 500 assists in retaining the distal retention part, effectively closing the intramural opening at the trigone region of the bladder (FIGS. 9 A, 10 A). The ureteral stent facilitates urine flow in such a way that, when the pressure inside the bladder is lower than the pressure inside the kidney, urine flows antegrade (FIGS. 9B, 10B), with synergy of proximal end 510, extendable segment 500, semi-spherical shell 420 inward folding and collapsible tube 410 dilation. Conversely, when urine accumulates in the bladder and its pressure exceeds that of the kidney, the extendable segment 531 retracts, such that distal retention part 400 closes the intramural opening 104, and the collapsible tube 410 collapses at the distal end of the stent preventing urine reflux or retrograde urine flow both through and around the stent (FIGS. 9C, 10C). For the stent with or without extendable segment, the presence or absence of holes 310 impacts both antegrade and retrograde fluid flow rates. FIGS. 11A,11B illustrates possible configurations of these holes 310, either spaced at equal distances 311 along the length of the stent or with a smaller distance between holes 312 at the proximal end compared to the distal end. This variation in spacing is designed to facilitate higher antegrade flow while mitigating urine reflux.

[0083] Overall, the ureteral stent may be placed using various clinically accepted techniques, depending on physician preference and the clinical scenario. The procedure is performed under sterile conditions. The patient is prepped and draped using standard sterile technique. A cystoscope or ureteroscope is introduced transurethrally into the bladder to visualize the ureteral orifice. A guidewire is inserted through the orifice and advanced into the renal pelvis under fluoroscopic or direct endoscopic guidance. The stent — preloaded on a proprietary or commercially available stent pusher or delivery catheter — is then advanced over the guidewire into the ureter. Delivery tools may include polymeric or metallic pusher tubes, flexible introducers, or telescoping deployment systems designed to facilitate controlled expansion of the retention ends. In cases involving the extendable segment, the delivery catheter may include an inner lumen for guiding the segment extension and retraction during placement. After theproximal retention element is deployed within the renal pelvis, and the distal retention element is confirmed to rest within the bladder, the delivery tool is withdrawn, allowing the stent to fully expand and settle into place. In post-ureteroscopy scenarios, the stent may be passed through the working channel of the ureteroscope using a guidewire and the pusher assembly. Throughout the procedure, fluoroscopy or endoscopic visualization is used to confirm correct placement of the stent. Final imaging may be performed to verify positioning and assess drainage from the kidney to the bladder.

[0084] FIGS. 12A and 12B depict various examples of the ureteral stent. In FIG. 12 A, the stent comprises a J-shaped proximal end, and thin long conical retention structure enclosing J- shaped coil for the distal end. In FIG. 12B, the proximal end comprises a pig-tail configuration while the distal end comprises a smaller tapered collapsible tube-like structure (made from polyethylene / polyurethane 1-5 mils thickness) with a smaller convex / concave disc retention structure made of silicone (2 mm thickness, acting as semi-flexible material), as illustrated in detail in FIG. 12Ca. Close-up view of the distal tip of the ureteral stent FIG. 12Ca is shown in FIG. 12Cb.

[0085] FIG. 13 A is a schematic view an exemplary testing assembly for a ureteral stent, comprising a constant pressure head fluid reservoir with an inlet, an upper outlet, and a lower outlet. The lower outlet is coupled to a fluid line with a stopcock valve and 3D printed upper urinary tract. The ureteral stent of FIG.12 Ca, was compared to the double-J stent (Olympus Sof- Curl, 8.5Fr, 22 cm) using an in-vitro testing apparatus consisting of a renal pelvis chamber connected to a bladder chamber by a conduit simulating the ureter. Antegrade flow rates were measured with the renal pelvic pressure set to 15 cm H2O and bladder pressure set to 0 cm H2O. Retrograde flow rates were measured at variable bladder pressures (15, 30, 50, and 70 cm H2O) with the renal pelvic pressure consistently 0 cm H2O. In-vitro testing demonstrated that, stented ureteral antegrade flow rates were similar for the novel ureteral stent and the traditional double-J stent (7.53 + / - 0.14 v 7.01 + / - 0.16). In contrast, the novel ureteral stent significantly minimized retrograde urine flow, exhibiting a reduction of over 95% in flow rates compared to the traditional double J stent (2 -tail test, * p<0.001) (FIG.13B). The results demonstrate the functional performance of the distal retention element, which includes the semi-flexible semi -spherical shell, and the collapsible tube on flow regulation. The collapsible tube acts as a one-way flow resistor, while the flexible shell conforms to pressure changes to prevent reverse flow without occluding antegrade flow.

[0086] FIG. 14 provides test results with other examples of ureteral stent (6 Fr size) with (A) with side holes along the stent and a semi-flexible retention element, (B) with side holes alongthe stent and a flexible retention element, (C) with side holes only at proximal end of the stent and a semi-flexible retention element), and were compared to the JJ stent (Olympus Sof-Curl, 6Fr). Flow rates were measured in the in-vitro testing apparatus consisting of two cavities (renal pelvis and bladder) connected by a 5mm conduit simulating the ureter. Pressure differentials were set for antegrade flow (renal pelvis = 15 cm H2O, bladder = 0 cm H2O) and retrograde flow (renal pelvis = 0 cm H2O, bladder = 50 cm H2O) with the stent in place. In-vitro testing showed that ureteral stent configuration A (4.7 ± 0.1 ml / s, p < 0.001) and ureteral stent configuration C (4.8 ± 0.2 ml / s, p < 0.001) reduced antegrade flow compared to the JJ stent (15.0 ± 0.6 ml / s), and reduced retrograde flow by 75% compared to the JJ stent (Table). In contrast, ureteral stent configuration B had the highest antegrade flow (13.9 ± 0.2 ml / s), and significantly reduced retrograde flow by 85% compared to JJ stent, offering the ideal stent characteristics.

[0087] In vitro testing of these examples allowed to isolate the contributions of individual design elements, particularly the collapsible tip, the distal retention element and side holes, to urine flow regulation. Our observations demonstrated that: a. While the semi-flexible retention element effectively reduced retrograde flow compared to standard stents, its rigidity may introduce challenges during cystoscopic placement and has the potential to cause bladder irritation postimplantation. b. The flexible retention element effectively modulated retrograde flow under simulated bladder pressure conditions, offering improved compatibility during placement, and a reduced risk of post-implantation irritation. c. Incorporation of distal side holes influenced flow rates significantly. Stents with side holes only at proximal end exhibited reduced antegrade and retrograde flow compare to standard stent. This trade-off suggests the potential to fine-tune flow properties via hole configuration, which may be valuable for personalized stent designs.These results confirmed the functional advantages of incorporating the flexible retention element and collapsible tube at the distal end of ureteral stents, particularly in reducing the urine reflux and optimizing urine drainage.

[0088] In some examples, a ureteral stent comprises: a coil section defining a lumen at the proximal end; a straight hollow stent body; a collapsible tube tip at the distal end, where the collapsible tube tip has a distinct shape at both the proximal and distal sides; a semi -spherical retention element at the distal end; a plurality of side ports along the semi -spherical retention element and straight hollow stent body, extending from the proximal end to either the middle ordistal end of the stent; Wherein the collapsible tube tip comprises a proximal end and distal ends with either same or different diameters; such as straight tube, tapered inward or tapered outward (FIGS. 15A,15B).

[0089] In some examples, when the stent has higher pressures inside the kidney and lower pressures inside the bladder, then urine flow from the kidney to the bladder through: (a) intralumen, enabling urine to pass directly through the hollow core of the stent from the kidney to the bladder; (b) extra-lumen, allowing urine to flow along the outer surface of the stent within the ureter, through side ports or channels, ensuring continued drainage even in the presence of partial obstructions or high-pressure differentials.

[0090] In some examples, the proximal retention element, such as a curled or pigtail shape, is configured to securely anchor the stent within the upper portion of the ureter, preventing migration or dislodgement.

[0091] In some examples, the stent, wherein the straight hollow stent body, further comprising an extendable section to facilitate elongation inside the ureter due to urine pressure, enabling antegrade flow. The stent, wherein the extendable section comprises elongation structures selected from a list consisting of variations in wall thickness, spiral or ribbon patterns, micro-cut patterns with circular, square, diamond or elliptical holes.

[0092] In some examples, the ureteral stent comprises a plurality of side holes distributed along its length, and the spacing between the holes may be equal or unequal along different portions of the stent to optimize fluid drainage and minimize reflux. The distal portion of the stent features a configuration where the distance between the holes is optimized for unidirectional flow, while the proximal portion of the stent is configured for enhanced fluid passage from the ureter into the stent lumen.

[0093] In some examples, the collapsible tube tip distal end has a circular or elliptical shape. The stent, wherein the collapsible tube tip has the hydraulic diameter of the distal end equal to, greater or less than the outer diameter of the stent body.

[0094] In some examples, the collapsible tube, opens or closes radially in response to a pressure differential, such that: (a) it remains closed under no kidney to bladder pressure difference, maintaining a no through flow; (b) it opens when the pressure within kidney exceeds the pressure inside the bladder, allowing urine to flow through the stent lumen into the bladder, such that the radial opening occurs only when the pressure differential between the kidney and bladder is greater than 0 cm ILO, ensuring that urine is expelled effectively from the stent; (c) it contracts radially, preventing the flow of urine from the bladder into the stent lumen when the pressure differential between the kidney and bladder is less than or equal to 0 cm ILO, such thattube remains closed when the bladder pressure is higher, thereby preventing reflux or backflow of urine from the bladder into the ureter. This pressure driven opening and closing of collapsible tube mechanism ensures unidirectional flow, optimizing urine drainage during normal physiological conditions and reducing the risk of infections or ureteral damage, or urinary tract complications.

[0095] In some examples, the distal retention structure is designed to provide secure anchorage within the ureter, ensuring proper placement and minimizing migration or dislodgement. The distal semi -spherical element folds inward into the bladder to facilitate urine flow from the kidney to the bladder through the outer lumen of the stent when the pressure inside the kidney exceeds the pressure inside the bladder (i.e., when the pressure differential is greater than 0 cm H2O). The inward folding of the semi -spherical shell enhances urine flow by ensuring a clear path through the ureter and minimizing obstruction. This inward folded configuration supports efficient antegrade flow, allowing for unobstructed drainage of urine from the kidney to the bladder under normal physiological conditions.

[0096] In some examples, the semi -spherical element expands outward radially within the bladder to close the ureteral orifice and reduce urine flow entering the ureter when the pressure inside the kidney is less than or equal to the pressure inside the bladder (i.e., when the pressure differential is less than or equal to 0 cm H2O). The expansion of the semi -spherical element effectively reduces or prevents retrograde flow of urine from the bladder into the ureter by sealing the ureteral orifice. This radially expanded configuration helps to regulate urine flow and maintain proper function of the stent by preventing the backflow of urine and associated complications such as infection or inflammation.

[0097] In some examples, the semi -spherical element is made of: (a) semi-flexible material, but the rigidity may result in less effective sealing at the bladder junction, allowing more retrograde flow; (b) flexible material, when it is positioned within the bladder, antegrade flow increases, likely due to decreased resistance at the ureteral -bladder junction; and but, when it is positioned within the ureter, antegrade flow decreases, facilitating inefficient urine flow into the bladder.

[0098] In some examples, the collapsible tube tip and the semi -spherical element at the distal end are either: (a) integrally formed with the stent body as a single continuous piece, providing a unified structure that enhances durability and simplifies manufacturing; or (b) mounted separately onto the stent body at the distal end, wherein the collapsible tube tip and semi -spherical element are distinct components that can be assembled or disassembled, offering flexibility in design and replacement.

[0099] In some examples, the semi -spherical element at the distal end of the stent is either: (a) integrally formed with the collapsible tube tip as a single continuous structure, providing enhanced structural integrity and reducing the potential for disjointed assembly; or (b) mounted separately onto the collapsible tube tip at the distal end, allowing for modular design where the semi -spherical element and collapsible tube tip can be individually assembled or replaced, offering flexibility in manufacturing and maintenance.

[0100] In some examples, the stent is made of a biocompatible, flexible material selected from the group consisting of silicone elastomer, polyurethane, polytetrafluoroethylene (PTFE), ethylene-vinyl acetate (EVA), polyethylene, or their copolymers. Material must: (a) have flexibility, allowing the stent to conform to the natural curvature of the ureter; (b) possesses durability, enabling the stent to remain functional for extended indwelling periods without significant degradation or material fatigue; (c) resists biofilm formation and encrustation, thereby reducing the likelihood of infection or obstruction; (d) has low friction properties to minimize trauma during both insertion and removal from the ureter; (e) maintain chemical stability in the presence of urine and other bodily fluids, ensuring prolonged use without breakdown or deterioration.

[0101] In some examples, the semi -spherical element of the stent, is made from elastic materials selected from the group consisting of rubbers, shape-memory alloys, super-elastic materials, or their combinations, and wherein said materials are characterized by: (a) elasticity and shape retention, allowing the semi-spherical element to expand outward radially in response to pressure conditions and return to its original shape when pressures normalize; (b) rigidity and structural integrity, which affect the semi -spherical element’s ability to effectively seal the ureteral orifice and regulate urine flow, while impacting the rate of decrease of antegrade and retrograde flow; (c) biocompatibility, ensuring that the material does not induce adverse reactions or irritation when in contact with ureteral or bladder tissues; and (d) durability, providing longterm performance without significant degradation or loss of functional properties.

[0102] In some examples, the stent is manufactured using one or more of the following processes: (a) casting, for creating complex shapes with high precision and uniformity; (b) injection molding, to produce detailed and consistent stent components in large volumes; (c) blow molding, enabling the formation of hollow and flexible stent sections; (d) die drawing, for producing elongated stent bodies with controlled thickness and strength; (e) 3D printing, allowing for custom designs and rapid prototyping of stent components; and (f) extrusion, to create continuous and uniform stent bodies with consistent properties.

[0103] While the stent with its mechanism is primarily intended for urological applications, it can also be adapted for other suitable applications, both clinical and non-clinical. For instance, similar one-way flow facilitation systems may be used in: cardiovascular applications such as endovenous stents-treating chronic venous insufficiency or varicose veins by ensuring proper blood flow and preventing backward flow; Gastroenterology applications such as biliary stent ensuring bile flows in one direction from liver to the intestine; Gastrointestinal applications such as one-way stents can be used in colon to ensure flow of intestinal contents in one direction and to prevent obstructions or strictures from causing backflow; and others.

[0104] The examples and illustrations included herein show, by way of illustration and not of limitation, specific elements in which the subject matter may be practiced. Other elements may be utilized and derived therefrom, such that structural and logical substitutions and changes may be made without departing from the scope of this disclosure. Such elements of the inventive subject matter may be referred to herein individually or collectively by the term “disclosure” merely for convenience and without intending to voluntarily limit the scope of this application to any single invention or inventive concept, if more than one is in fact disclosed. Thus, although specific elements have been illustrated and described herein, any arrangement calculated to achieve the same purpose may be substituted for the specific elements shown. This disclosure is intended to cover any and all adaptations or variations of various elements. Combinations of the above elements, and other elements not specifically described herein, will be apparent to those of skill in the art upon reviewing the above description.

Claims

We claim:

1. A ureteral stent, comprising: a straight, hollow tubular stent body comprising a proximal end and a distal end; a proximal end region on the proximal end including a first retention coil with a lumen; a retention element on the distal end, wherein the retention element comprises one of a semi -spherical, conical, or other ovoid shapes shell; a collapsible tube on the distal end; and a plurality of side holes spaced apart substantially uniformly along the stent body at least partially between the proximal end and the distal end.

2. A ureteral stent, comprising: a straight, hollow tubular stent body comprising a proximal end and a distal end; a proximal end region on the proximal end including a first retention coil with a lumen; a retention element on the distal end, wherein the retention element comprises one of a semi -spherical, conical, or other ovoid shapes shell; a collapsible tube on the distal end; and a plurality of side holes spaced apart non-uniformly along the stent body at least partially between the proximal end and the distal end such that a distance between the side holes is smaller on the proximal end compared to a distance between the side holes on the distal end.

3. A ureteral stent, comprising: a straight, hollow tubular stent body comprising a proximal end and a distal end; a proximal end region on the proximal end including a first retention coil with a lumen; a retention element on the distal end, wherein the retention element comprises one of a semi -spherical, conical, or other ovoid shapes shell; a collapsible tube on the distal end; and a plurality of side ports spaced apart substantially uniformly along the stent body at least partially between the proximal end and the distal end4. A ureteral stent, comprising: a straight, hollow tubular stent body comprising a proximal end and a distal end; a proximal end region on the proximal end including a first retention coil with a lumen; a retention element on the distal end, wherein the retention element comprises one of a semi -spherical, conical, or other ovoid shapes shell;a collapsible tube on the distal end; and a plurality of side ports spaced apart non-uniformly along the stent body at least partially between the proximal end and the distal end such that a distance between the side ports on the proximal end is smaller than a distance between the side ports on the distal end.

5. The ureteral stent of anyone of claims 1-4, wherein the collapsible tube comprises a distinct shape at both its proximal and distal sides with either same or different diameters.

6. The ureteral stent of claim 5, wherein the collapsible tube comprises one of a straight tube, tapers inwardly, or tapers outwardly.

7. The stent of claim 1 or 2, wherein the side holes having diameters ranging from 0.5 mm to 3 mm, configured to allow fluid entry into the lumen from the surrounding ureteral environment.

8. The stent of claim 7, wherein the side holes are arranged along the entire length of the stent body, including both the proximal end and the distal end.

9. The stent of claim 7, wherein the distance between adjacent side holes varies along the length of the stent, such that: a. On the proximal portion of the stent (configured to reside in the renal pelvis), the spacing between adjacent holes ranges from 5 mm to 10 mm, and b. On the distal portion (configured to reside in the bladder), the spacing ranges from 10 mm to 25 mm.

10. The stent of claim 7, wherein the proximal end has a higher density of holes compared to the distal end, facilitating increased urine inflow from the kidney during both occluded and unoccluded ureteral conditions.

11. The stent of claim 7, wherein the side holes are arranged in a circumferentially distributed pattern around the stent body, with each circumferential group of holes separated by at least 90 degrees, to minimize the risk of full obstruction from surrounding tissue compression.

12. The stent of claim 11, wherein the circumferentially distributed pattern of the side holes follows a helical or staggered configuration, reducing fluid stagnation and promoting uniform drainage from multiple orientations.

13. The ureteral stent of any one of claims 1-4, wherein the retention element comprises a semi -spherical retention element formed from material having a modulus of elasticity and having dimensions effective to allow inward and outward folding based on urine pressures.

14. The ureteral stent of claim 13, wherein the retention element is formed from a flexible material selected from the group consisting of polyurethane, silicone, thermoplastic elastomers, or combinations thereof, optionally, having a radius of curvature ranging from 3 mm to 20 mm, a maximum diameter ranging from 3 mm to 15 mm, a shell height (apical rise from the base plane) between 3 mm and 15 mm, and and a wall thickness ranging from 5 microns to 2 mm, such that the shell maintains its dome-like structure in the absence of pressure and collapses in response to fluidic pressure exerted from within the urinary tract.

15. The ureteral stent of claim 13, wherein the retention element comprises a geometry that mimics a contact lens structure (convex shape), providing inherent curvature-induced stiffness that resists collapse under gravity or resting conditions, while remaining sufficiently flexible to deform under transient back-pressure.

16. The ureteral stent of claim 13, wherein the retention element has a variable wall thickness ranging from approximately 5 microns to 2 mm, wherein the wall thickness is greater at a central region of the retention element and thinner at a periphery of the retention element to balance structural integrity and flexibility.

17. The ureteral stent of claim 13, wherein the retention element has a variable wall thickness ranging from approximately 5 microns to 2 mm, wherein the wall thickness is greater at a periphery of the retention element and thinner at a central region of the retention element to balance structural integrity and flexibility.

18. The ureteral stent of claim 13, wherein a central region of the retention element is configured to collapse under antegrade pressure but remain open under increased bladder pressure.

19. The ureteral stent of claim 13, wherein a thickness of a central region of the retention element is optimized to collapse under antegrade pressure but remain open under increased bladder pressure, mimicking the mechanical behavior of a flexible contact lens.

20. The ureteral stent of claim 13, wherein the material of the retention element comprises thermoplastic elastomer having a Shore A hardness between 10 and 70.

21. The ureteral stent of claim 13, wherein the material of the retention element has an elastic modulus between 0.1 MPa and 10 MPa, enabling reversible folding and unfolding in response to pressure changes.

22. The ureteral stent of claim 13, wherein the material of the retention element exhibits shape memory or viscoelastic behavior that prevents permanent deformation following repeated pressure cycles.

23. The ureteral stent of claim 13, wherein the retention element comprises a curvature and wall thickness configured to generate a pressure-dependent sealing effect at the ureterovesical junction to reduce reflux without impeding antegrade flow.

24. The ureteral stent of claim 13, wherein the retention element is configured to exhibit directional flexibility that resists retrograde flow while permitting antegrade flow.

25. The ureteral stent of claim 13, wherein the retention element is elastically deformable under bladder pressures of 5-50 cm JLO and returns to its original shape when pressure normalizes, functioning as a passive bidirectional flow-regulating element.

26. The ureteral stent of any one of claims 1-4, wherein the retention element comprises a conical shell having an apex oriented toward the ureter and a base oriented toward the bladder, and, optionally, wherein the conical shell comprises a base diameter ranging from 3 mm to 15 mm, an axial height ranging from 3 mm to 15 mm, and a cone angle between 30° and 70°, wherein the conical shell is oriented such that its apex points distally and forms a compliant barrier at the intramural orifice.

27. The ureteral stent of claim 26, wherein a wall thickness of the conical shell varies to provide gradient stiffness, including configurations in which: a. the thickness tapers from approximately 2 mm at the base to approximately 5 microns at the apex; and / or b. the thickness is greater at the apex of the shell and decreases toward the peripheral edge or at the base.

28. The ureteral stent of claim 26, wherein the conical shell is configured to collapse along its longitudinal axis when subjected to antegrade pressures between 10 and 50 cm JLO.

29. The ureteral stent of claim 26, wherein the conical shell comprises a cone angle is between 30° and 70°, configured to allow the base to form a sealing surface against the bladder mucosa.

30. The ureteral stent of claim 26, wherein the conical shell includes circumferential reinforcement near its base to maintain ureteral orifice sealing under bladder backpressure.

31. The ureteral stent of any one of claims 1-4, wherein the retention element has a smooth, continuous curvature and is free of pleats or ribs, providing uniform deformation characteristics under pressure.

32. The ureteral stent of any one of claims 1-4, wherein the retention element is configured without corrugations to minimize reduce tissue irritation at the ureterovesical junction.

33. The ureteral stent of any one of claims 1-4, wherein the retention element exhibits a radial stiffness of less than 0.3 N / mm.

34. The ureteral stent of any one of claims 1-4, wherein the collapsible tube is formed from material having modulus of elasticity and dimensions effective to allow radial expansion and radial contraction based on urine pressures inside stent and bladder.

35. The ureteral stent of claim 34, wherein the collapsible tube has a wall thickness ranging from 5 microns to 2 mm and comprises a biocompatible elastomer selected from the group consisting of silicone, polyurethane, or SEBS.

36. The ureteral stent of claim 34, wherein the collapsible tube deforms radially outward under antegrade pressure exceeding 5 cm JLO and re-collapses when pressure falls below 5 cm JLO, thereby creating a pressure-sensitive valve-like behavior.

37. The ureteral stent of claim 34, wherein the collapsible tube is shaped as (a) a straight-walled cylinder, (b) a tube tapered inward toward the distal end, or (c) a tube flared outward toward the distal end, and wherein each configuration modulates flow resistance and deformation response to bladder pressure.

38. The ureteral stent of claim 34, wherein the collapsible tube comprises anisotropic material zones, with longitudinal stiffness greater than radial stiffness, enabling preferential radial collapse without significant axial shortening.

39. The ureteral stent of claim 34, wherein the collapsible tube has a functional length between 3 mm and 15 mm, and a maximum outer diameter ranging from 3.5 French (Fr) to 14 Fr, depending on the diameter of the stent body.

40. The ureteral stent of claim 34, wherein the collapsible tube has an internal cross- sectional geometry selected from the group consisting of round, oblong, elliptical, or polygonal (e.g., hexagonal) shapes.

41. The ureteral stent of claim 34, wherein the collapsible tube is formed from a material having an elastic modulus between 0.1 MPa and 10 MPa, allowing for reversible elastic deformation under physiological pressure conditions.

42. The ureteral stent of claim 34, wherein the collapsible tube is formed from a material selected from the group consisting of silicone, EVA, PTFE, polyurethane, polyethylene, and their copolymers.

43. The ureteral stent of claim 34, wherein the collapsible tube comprises medicalgrade polyurethane with a wall thickness of approximately 0.127 mm (5 mil) and an elastic modulus in the range of 2 MPa to 10 MPa.

44. The ureteral stent of claim 34, wherein collapsible tube has an elliptical crosssection in an inactive state, the collapsible tube having a major axis between 1.2 mm and 2.0 mm, and a minor axis between 0.2 mm and 0.6 mm; wherein the collapsible tube expands under antegrade fluid pressure to assume a generally circular cross-section with a diameter between 1.2 mm and 2.0 mm at both its proximal and distal openings, and wherein the collapsible tube collapses under retrograde fluid pressure to return to an elliptical or flattened shape that resists reverse flow.

45. The ureteral stent of claim 34, wherein the collapsible tube has an elliptical crosssection in an inactive state, the collapsible tube having a major axis between 1.5 mm and 2.5 mm, and a minor axis between 0.3 mm and 0.6 mm; wherein the collapsible tube expands under antegrade fluid pressure to form a conically tapering shape with a proximal opening diameter between 1.5 mm and 2.5 mm, and a distal opening diameter between 0.5 mm and 1.0 mm, and wherein the collapsible tube collapses under retrograde pressure to restrict flow by reducing the distal opening diameter below 0.3 mm.

46. The ureteral stent of claim 34, wherein collapsible tube has an elliptical or flattened cross-section in an inactive state, and, optionally, wherein the collapsible tube has a major axis between 1.2 mm and 2.0 mm, and a minor axis between 0.2 mm and 0.6 mm; wherein, under antegrade flow conditions, the collapsible tube expands into a flared configuration with a proximal opening diameter between 1.2 mm and 1.8 mm, and a distal opening diameter between 2 0 mm and 3.0 mm; and wherein, under retrograde pressure, the distal opening collapses to a diameter less than 0.5 mm to resist reflux.

47. The ureteral stent of claim 34, wherein the collapsible tube is configured with a proximal and distal opening diameter selected from the group consisting of: (a) a configuration where both proximal and distal openings range from 1 mm to 8 mm; (b) a configuration where the distal opening ranges from 0.5 mm to 3 mm; (c) a configuration where the distal opening ranges from 2 mm to 5 mm, with the proximal end matching the stent diameter.

48. The ureteral stent of claim 34, wherein the collapsible tube incorporates an inward or outward taper to facilitate pressure-driven flow or anchoring, and wherein wall thickness varies along the tube to promote directional collapse from the distal to the proximal end.

49. The ureteral stent of any one of claims 1-4, wherein the stent body includes an extendable segment, either at the distal end, the proximal end, or an intermediate region of the tubular segment, configured to extend the stent body along the ureteral length, and place the distal retention element at the bladder, closing the intramural opening.

50. The ureteral stent of claim 49, wherein the extendable segment is integrated along the tubular element, wherein the stent body has a non-extended length of 8 cm to 36 cm; wherein the extendable segment is configured to increase the length of the stent by between 5 mm and 50 mm upon deployment.

51. The ureteral stent of claim 49, wherein the extendable element is located at the proximal end, the distal end, or an intermediate region of the tubular segment, to enable length adjustment for optimal placement of the retention element at the bladder opening.

52. The ureteral stent of claim 49, wherein the extendable segment is located at a position between 75% and 95% of the total non-extended stent length from the proximal end, providing distal extension.

53. The ureteral stent of claim 49, wherein the extendable segment is located at a position between 50% and 75% of the total non-extended stent length from the proximal end, providing mid-body extension.

54. The ureteral stent of claim 49, wherein the extendable segment is located at a position between 25% and 50% of the total non-extended stent length from the proximal end, providing proximal extension.

55. The ureteral stent of claim 49, wherein then extendable segment is configured to elongate axially in response to mechanical or physiological forces, wherein the segment includes engineered cuts or micro-pattern.

56. The ureteral stent of claim 49, wherein the engineered cuts comprise linear slits aligned longitudinally, diagonally, or helically, enabling directional elongation and flexibility.

57. The ureteral stent of claim 49, wherein the micro-patterns comprise corrugations or accordion-like folds configured to provide both axial and radial compliance.

58. The ureteral stent of claim 49, wherein the extendable segment includes a locally thinned region, having a wall thickness that is reduced by at least 30% compared to adjacent sections, allowing passive elongation.

59. The ureteral stent of claim 49, wherein the extendable segment comprises a ribbonlike structure that unfurls into a flat or helically wound strip during deployment to accommodate ureteral irregularities.

60. The ureteral stent of claim 49, wherein the micro-patterns are fabricated using laser cutting, photolithography, or mechanical micro-machining.

61. The ureteral stent of claim 49, wherein the tubular wall includes circular perforations for uniform stress distribution.

62. The ureteral stent of claim 49, wherein the tubular wall includes polygonal openings to enhance fluid exchange.

63. The ureteral stent of claim 49, wherein the tubular wall includes elliptical or ovalshaped slots configured to permit axial elongation while maintaining radial support.

64. The ureteral stent of claim 49, wherein the extendable segment comprises a telescoping tube structure with interlocking ribs that maintain patency and allow axial elongation under traction force between 0.1 and 0.5 N.

65. The ureteral stent of claim 49, wherein the wall thickness of the extendable segment ranges from 50 microns to 2 mm and remains within ±10% of the adjacent tubular wall thickness after extension.

66. The ureteral stent of claim 49, wherein an internal lumen diameter of the extendable segment remains within ±10% of the lumen diameter of the adjacent tubular element before and after extension.

67. The ureteral stent of claim 49, wherein the extendable segment or collapsible tube is over molded or integrally formed with the stent body using a dual-material extrusion or comolding process to ensure mechanical continuity and fluid-tight sealing.

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