Negative spring rate compliance-enhancement implants

Abstract

Spring devices are disclosed that may be used for cyclical blood vessel reshaping for vascular compliance enhancement. Such devices can include a first tissue-contact pad, a second tissue-contact pad oriented in a parallel with the first tissue-contact pad, and a spring mechanism coupled to the first tissue-contact pad and the second tissue-contact pad, the spring mechanism being configured to compress between the first tissue-contact pad and the second tissue-contact pad according to a negative spring rate.

Description

Attorney Docket No.: ADV-24166WO01 NEGATIVE SPRING RATE COMPLIANCE-ENHANCEMENT IMPLANTS RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 689,071, filed August 30, 2024, the complete disclosure of which is hereby incorporated by reference in its entirety. BACKGROUND

[0002] The present disclosure generally relates to the field of medical implant devices. Insufficient or reduced compliance in certain blood vessels, including arteries such as the pulmonary artery and the aorta, can result in hypertension, vascular remodeling, increased arterial pressures, increased ventricular afterload, reduced perfusion, reduced stroke volume, impaired gas exchange, reduced cardiac output, and other health complications. Restoring compliance and / or otherwise controlling / managing flow in such blood vessels can improve patient outcomes. SUMMARY

[0003] Described herein are devices, methods, and systems that facilitate the restoration of compliance characteristics to undesirably stiff blood vessels. Devices associated with the various examples of the present disclosure can include certain negative spring rate spring mechanisms / components and can be configured to be implanted within a target blood vessel, wherein forcible compression of the spring mechanism, can store energy in the spring mechanism that can be returned to the target blood vessel in a manner as to reshape / remodel the blood vessel and increase blood flow in low-pressure conditions, thereby mimicking natural compliance of the blood vessel.

[0004] In some implementations, spring implant devices of the present disclosure can be implanted within a target blood vessel segment, wherein a biased shape of the spring implant device can have a long- / major-axis dimension that forces a non-circular shape in the blood vessel, such as by pushing outward on opposite sides of the blood vessel wall by tissue-contact pads of the spring device to cause long-axis elongation thereof; as luminal pressure increases in the blood vessel, the blood vessel walls, at two or more contact points with the spring implant device, press radially-inwardly on the spring mechanism, thereby compressing the spring mechanism to store spring energy in the implant and to allow the blood vessel to assume a more- circular shape. As luminal blood pressures decrease, the biased, elongated shape the spring mechanism can overcome the hoop stress / force in the blood vessel wall to once againAttorney Docket No.: ADV-24166WO01 reshape / remodel the blood vessel to the non-circular (e.g., oval) shape, wherein such cyclic reshaping / remodeling of the blood vessel can increase low-pressure (e.g., diastolic) flow / pressure and / or decrease high-pressure (e.g., systolic) flow / pressure.

[0005] In some implementations, aspects of the present disclosure relate to spring implant devices that have a negative spring rate, such that initial / early-stage compression of the spring mechanism, such as may occur in the presence of minimum / low pressure conditions within a blood vessel, requires greater compressive force compared to spring compression when the spring mechanism is compressed to a greater degree (e.g., as may occur in higher-pressure conditions where the blood vessel wall has compressed the spring device beyond the initial low- pressure compressive state). Accordingly, the minimum pressure condition within a blood vessel may advantageously cause only minimal compression of the spring, whereas changes in pressure between the minimum pressure condition (e.g., diastole) and the maximum pressure condition (e.g., systole) may cause relatively greater spring compression due to the decreasing resistive force of the spring mechanism as the spring is compressed. Therefore, devices of the present disclosure can advantageously provide relatively high spring compression, and therefore a relatively high amount of blood vessel volume change, over the cardiac / circulatory cycle between the minimum and maximum pressure states, thereby providing a greater increase in compliance of the blood vessel compared to similar spring implant devices that have a positive spring rate coefficient.

[0006] Example devices of the present disclosure can comprise two or more parallel tissue-contact surfaces / pads coupled by any type of negative spring rate spring mechanism, which may be configured to compress in a manner that approximates the tissue-contact pads by shortening the compression / expansion dimension of the spring mechanism, thereby shortening the distance between the tissue-contact pads. In some implementations, such a spring mechanism can comprise a plurality of linkages arranged in an overlapping and / or scissor-type configuration. The plurality of linkages may be each coupled at one or more ends to other(s) of the linkages in a pivotable coupling. One or more springs may be connected, directly or indirectly, to respective linkages of the spring mechanism in parallel with the tissue-contact pads and perpendicular to the compression / expansion dimension. The linkages of the spring mechanism may be configured to stack in a manner as to allow for a compact delivery configuration having a reduced contact-pad- to-contact-pad distance, and therefore a reduced profile in such dimension. The reduced profile can accommodate transportation within a delivery sheath / system. In some implementations, the negative spring rate spring mechanism comprises one or more deflectable bars connected between the tissue-contact pads.Attorney Docket No.: ADV-24166WO01

[0007] For purposes of summarizing the disclosure, certain aspects, advantages and novel features have been described. It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular example. Thus, the disclosed examples may be carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.

[0008] Methods and structures disclosed herein for treating a patient also encompass analogous methods and structures performed on or placed on a simulated patient, which is useful, for example, for training; for demonstration; for procedure and / or device development; and the like. The simulated patient can be physical, virtual, or a combination of physical and virtual. A simulation can include a simulation of all or a portion of a patient, for example, an entire body, a portion of a body (e.g., thorax), a system (e.g., cardiovascular system), an organ (e.g., heart), or any combination thereof. Physical elements can be natural, including human or animal cadavers, or portions thereof; synthetic; or any combination of natural and synthetic. Virtual elements can be entirely in silica, or overlaid on one or more of the physical components. Virtual elements can be presented on any combination of screens, headsets, holographically, projected, loudspeakers, headphones, pressure transducers, temperature transducers, or using any combination of suitable technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Various examples are depicted in the accompanying drawings for illustrative purposes and should in no way be interpreted as limiting the scope of the inventions. In addition, various features of different disclosed examples can be combined to form additional examples, which are part of this disclosure. Throughout the drawings, reference numbers may be reused to indicate correspondence between reference elements.

[0010] FIG.1 illustrates example cardiac and vascular anatomy.

[0011] FIGS.2A and 2B show side and axial cross-sectional views, respectively, of a blood vessel experiencing compliant expansion and retraction.

[0012] FIGS.3A and 3B show a blood vessel in circular and non-circular shapes, respectively.

[0013] FIG.4 shows a perspective view of a non-circular blood vessel reshaping stent in accordance with some examples.

[0014] FIGS.5A, 5B, and 5C provide images of a non-circular stent in various configurations according to some examples.Attorney Docket No.: ADV-24166WO01

[0015] FIGS.6A and 6B show a diametrical vessel-reshaping spring device in expanded and compressed configurations, respectively, in accordance with some examples.

[0016] FIG.7A shows a graph representing a positive spring rate response of an implant device in accordance with some examples.

[0017] FIGS.7B and 7C show an example spring implant within a blood vessel in states corresponding to points on the graph 700 of FIG.7A in accordance with some examples.

[0018] FIG.8A shows a graph representing a negative spring rate response of an implant device in accordance with some examples.

[0019] FIGS.8B and 8C show an example spring implant within a blood vessel in states corresponding to points on the graph 800 of FIG.8A in accordance with some examples.

[0020] FIGS.9A and 9B show a buckling beam negative spring rate implant device according to some examples, in extended and compressed states, respectively.

[0021] FIGS.10A and 10B show a parallel-contact scissor expansion device in expanded and compressed configurations, respectively, in accordance with some examples.

[0022] FIGS.11A and 11B show plan and perspective views, respectively, of a negative spring rate expander device in accordance with some examples.

[0023] FIG.12 shows a negative spring rate expander implant device in a compressed configuration within a delivery system in accordance with some examples.

[0024] FIGS.13, 14, 15, and 16 show a negative spring rate expander implant in various states of expansion / compression within a blood vessel in accordance with some examples.

[0025] FIG.17 shows a negative spring rate expander device in accordance with some examples.

[0026] FIG.18 shows a negative spring rate expander device including living hinge features in accordance with some examples. DETAILED DESCRIPTION

[0027] The headings provided herein are for convenience only and do not necessarily affect the scope or meaning of the claimed invention.

[0028] Although certain preferred examples are disclosed below, it should be understood that the inventive subject matter extends beyond the specifically disclosed examples to other alternative examples and / or uses and to modifications and equivalents thereof. Thus, the scope of the claims that may arise herefrom is not limited by any of the particular examples described below. For example, in any method or process disclosed herein, the acts or operationsAttorney Docket No.: ADV-24166WO01 of the method or process may be performed in any suitable sequence and are not necessarily limited to any particular disclosed sequence. Various operations may be described as multiple discrete operations in turn, in a manner that may be helpful in understanding certain examples; however, the order of description should not be construed to imply that these operations are order dependent. Additionally, the structures, systems, and / or devices described herein may be embodied as integrated components or as separate components. For purposes of comparing various examples, certain aspects and advantages of these examples are described. Not necessarily all such aspects or advantages are achieved by any particular example. Thus, for example, various examples may be carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other aspects or advantages as may also be taught or suggested herein.

[0029] Certain reference numbers are re-used across different figures of the figure set of the present disclosure as a matter of convenience for devices, components, systems, features, and / or modules having features that may be similar in one or more respects. However, with respect to any of the examples disclosed herein, re-use of common reference numbers in the drawings does not necessarily indicate that such features, devices, components, or modules are identical or similar. Rather, one having ordinary skill in the art may be informed by context with respect to the degree to which usage of common reference numbers can imply similarity between referenced subject matter. Use of a particular reference number in the context of the description of a particular figure can be understood to relate to the identified device, component, aspect, feature, module, or system in that particular figure, and not necessarily to any devices, components, aspects, features, modules, or systems identified by the same reference number in another figure. Furthermore, aspects of separate figures identified with common reference numbers can be interpreted to share characteristics or to be entirely independent of one another.

[0030] Where an alphanumeric reference identifier is used that comprises a numeric portion and an alphabetic portion (e.g., ‘10a,’ where ‘10’ is the numeric portion and ‘a’ is the alphabetic portion), references in the written description to only the numeric portion (e.g., ‘10’) may refer to any feature identified in the figures using such numeric portion (e.g., ‘10a,’ ‘10b,’ ‘10c,’ etc.), even where such features are identified with reference identifiers that concatenate the numeric portion thereof with one or more alphabetic characters (e.g., ‘a,’ ‘b,’ ‘c,’ etc.). That is, a reference in the present written description to a feature ‘10’ may be understood to refer to either an identified feature ‘10a’ in a particular figure of the present disclosure or to an identifier ‘10’ or ‘10b’ in the same figure or another figure, as an example.Attorney Docket No.: ADV-24166WO01

[0031] Certain standard anatomical terms of location are used herein to refer to the anatomy of animals, and namely humans, with respect to various examples. Although certain spatially relative terms, such as “outer,” “inner,” “upper,” “lower,” “below,” “above,” “vertical,” “horizontal,” “top,” “bottom,” and similar terms, are used herein to describe a spatial relationship of one device / element or anatomical structure to another device / element or anatomical structure, it is understood that these terms are used herein for ease of description to describe the positional relationship between element(s) / structures(s), as illustrated in the drawings. It should be understood that spatially relative terms are intended to encompass different orientations of the element(s) / structures(s), in use or operation, in addition to the orientations depicted in the drawings. For example, an element / structure described as “above” another element / structure may represent a position that is below or beside such other element / structure with respect to alternate orientations of the subject patient or element / structure, and vice-versa. It should be understood that spatially relative terms, including those listed above, may be understood relative to a respective illustrated orientation of a referenced figure.

[0032] Any of the various systems, devices, apparatuses, etc. in this disclosure can be sterilized (e.g., with heat, radiation, ethylene oxide, hydrogen peroxide, etc.) to ensure they are safe for use with patients, and the methods herein can comprise sterilization of the associated system, device, apparatus, etc. (e.g., with heat, radiation, ethylene oxide, hydrogen peroxide, etc.). Vascular Anatomy and Compliance

[0033] Certain examples are disclosed herein in the context of vascular implant devices, and in particular, compliance-enhancing spring implant devices implanted / implantable in the pulmonary artery or aorta. However, it should be understood that compliance-enhancement implant devices in accordance with the present disclosure may be implanted in, or configured for implantation in, any suitable or desirable blood vessels or other anatomy, such as the inferior vena cava.

[0034] The anatomy of the heart and vascular system is described below to assist in the understanding of certain inventive concepts disclosed herein. In humans and other vertebrate animals, the heart generally comprises a muscular organ having four pumping chambers, wherein the flow thereof is at least partially controlled by various heart valves, namely, the aortic, mitral (or bicuspid), tricuspid, and pulmonary valves. The valves may be configured to open and close in response to a pressure gradient present during various stages of the cardiac cycle (e.g., relaxation and contraction) to at least partially control the flow of blood to a respective region ofAttorney Docket No.: ADV-24166WO01 the heart and / or to blood vessels (e.g., ventricles, pulmonary artery, aorta, etc.). The contraction of the various heart muscles may be prompted by signals generated by the electrical system of the heart.

[0035] FIG.1 illustrates an example representation of a heart 1 and associated vasculature having various features relevant to one or more examples of the present inventive disclosure. The heart 1 includes four chambers, namely the left atrium 2, the left ventricle 3, the right ventricle 4, and the right atrium 5. In terms of blood flow, blood generally flows from the right ventricle 4 into the pulmonary artery via the pulmonary valve 9, which separates the right ventricle 4 from the pulmonary artery 11 and is configured to open during systole so that blood may be pumped toward the lungs and close during diastole to prevent blood from leaking back into the heart from the pulmonary artery 11. The pulmonary artery 11 carries deoxygenated blood from the right side of the heart to the lungs. The pulmonary artery 11 includes a pulmonary trunk and left and right pulmonary arteries that branch off of the pulmonary trunk, as shown.

[0036] The tricuspid valve 8 separates the right atrium 5 from the right ventricle 4. The tricuspid valve 8 generally has three cusps / leaflets and may generally close during ventricular contraction (i.e., systole) and open during ventricular expansion (i.e., diastole). The mitral valve 6 generally has two cusps / leaflets and separates the left atrium 2 from the left ventricle 3. The mitral valve 6 is configured to open during diastole so that blood in the left atrium 2 can flow into the left ventricle 3, and, when functioning properly, closes during systole to prevent blood from leaking back into the left atrium 2. The aortic valve 7 separates the left ventricle 3 from the aorta 12. The aortic valve 7 is configured to open during systole to allow blood leaving the left ventricle 3 to enter the aorta 12, and close during diastole to prevent blood from leaking back into the left ventricle 3. A wall of muscle 17, referred to as the septum, separates the left 2 and right 5 atria and the left 3 and right 4 ventricles.

[0037] The vasculature of the human body, which may be referred to as the circulatory system, cardiovascular system, or vascular system, contains a complex network of blood vessels with various structures and functions and includes various veins (venous system) and arteries (arterial system). Generally, arteries, such as the aorta 16 and the pulmonary artery 11, carry blood away from the heart, whereas veins, such as the inferior 19 and superior 18 venae cavae, carry blood back to the heart.

[0038] The aorta 16 is a compliant arterial blood vessel that buffers and conducts pulsatile left ventricular output and contributes the largest component of total compliance of the arterial tree. The aorta 16 includes the ascending aorta 12, which begins at the opening of the aortic valve 7 in the left ventricle of the heart. The ascending aorta 12 and pulmonary trunk 11Attorney Docket No.: ADV-24166WO01 twist around each other, causing the aorta 12 to start out posterior to the pulmonary trunk 11, but end by twisting to its right and anterior side. Among the various segments of the aorta 16, the ascending aorta 12 is relatively more frequently affected by aneurysms and dissections, often requiring open heart surgery to be repaired. The transition from ascending aorta 12 to aortic arch 13 is at the pericardial reflection on the aorta. At the root of the ascending aorta 12, the lumen has three small pockets between the cusps of the aortic valve and the wall of the aorta, which are called the aortic sinuses or the sinuses of Valsalva. The left aortic sinus contains the origin of the left coronary artery and the right aortic sinus likewise gives rise to the right coronary artery. Together, these two arteries supply the heart.

[0039] The ascending aorta 12 and gives rise to the innominate artery 27, the left common carotid artery 28, and the left subclavian artery 26 along the aortic arch 13 before continuing as the descending thoracic aorta 14 and further the abdominal aorta 15. References herein to the aorta may be understood to refer to the ascending aorta 12 (also referred to as the “ascending thoracic aorta”), aortic arch 13, descending or thoracic aorta 14 (also referred to as the “descending thoracic aorta”), abdominal aorta 15, or other arterial blood vessel or portion thereof.

[0040] The pulmonary artery 11 emerges from the right ventricle 4 and bifurcates into the left 23 and right 24 pulmonary arteries, each leading to the respective lung. Functionally, the pulmonary artery 11 is responsible for transporting deoxygenated blood from the right ventricle 4 to the lungs. In the lungs, the blood undergoes gas exchange, where carbon dioxide is expelled, and oxygen is absorbed into the bloodstream. This oxygen-rich blood then returns to the heart via the pulmonary veins 25, for circulation throughout the body.

[0041] Arteries, such as the aorta 16 and pulmonary artery 11, may utilize blood vessel compliance to store and release energy through the stretching of blood vessel walls. The term “compliance” is used herein according to its broad and ordinary meaning, and may refer to the ability of an arterial blood vessel or prosthetic implant device to distend, expand, stretch, or otherwise deform in a manner as to increase in volume in response to increasing transmural pressure, and / or the tendency of a blood vessel (e.g., artery) or prosthetic implant device, or portion thereof, to recoil toward its original dimensions as transmural pressure decreases.

[0042] As referenced above, the systolic phase of the cardiac cycle is associated with the pumping phase of the ventricles, while the diastolic phase of the cardiac cycle is associated with the resting or filling phase of the ventricles. FIGS.2A and 2B show example representations of an arterial blood vessel 21, such as the pulmonary artery 11 or ascending aorta 12, wherein the artery 21 manifests healthy arterial compliance such that an increase in volume Δv occurs whenAttorney Docket No.: ADV-24166WO01 the pressure in the artery is increased from diastole to systole. As blood is pumped into the artery 21 through the upstream valve 22 (e.g., aortic valve 7 or pulmonary valve 9), the pressure in the artery 21 increases and the diameter of at least a portion thereof expands. A first portion of the blood entering the artery 21 during systole may pass through the artery 21 during the systolic phase, while a second portion (e.g., approximately half of the total blood volume) may be stored in the expanded volume Δv caused by compliant stretching of the blood vessel 21 from a non- expanded diameter d1 to an expanded diameter d2, thereby storing energy for contributing to perfusion during the diastolic phase. A compliant aorta may generally stretch with each heartbeat, such that the diameter of at least a portion of the aorta expands.

[0043] The tendency of the arteries to stretch in response to pressure as a result of arterial compliance may have a significant effect on perfusion and / or blood pressure in some patients. For example, arteries with relatively higher compliance may be conditioned to more easily deform than lower-compliance arteries under the same pressure conditions. Compliance (C) may be calculated using the following equation, where Δv is the change in volume (e.g., in mL) of the blood vessel, and Δp is the pulse pressure from systole to diastole (e.g., in mmHg): ^^^^ ^^ (1)

[0044] and patients suffering from various health conditions,compliance of the aorta, pulmonary artery, and other arteries can be diminished to some degree or lost. For example, reduced pulmonary artery compliance can occur in patients suffering from pulmonary hypertension, wherein chronic elevated pressure in the pulmonary arteries can cause their walls to stiffen, reducing compliance. Chronic obstructive pulmonary disease (COPD), left heart failure, interstitial lung disease, aging, pulmonary fibrosis, congenital heart defects, pulmonary embolism, systemic sclerosis, sleep apnea, and chronic thromboembolic pulmonary hypertension (CTEPH) can also contribute to changes in the structure and function of the pulmonary arteries, leading to reduced compliance and associated complications.

[0045] Health complications associated with reduced pulmonary artery compliance can include increased pulmonary artery pressure, wherein stiff arteries lead to higher resistance to blood flow, causing elevated pressures, which can result in pulmonary hypertension. Other complications from a non-compliant pulmonary artery include increased right ventricular afterload, decreased right ventricular stroke volume, impaired gas exchange, vascular remodeling, and right heart failure. Example compliance-enhancing implant devices as disclosed herein, when implanted in the pulmonary artery / arteries, can improve one or more of the above conditions / risks.Attorney Docket No.: ADV-24166WO01

[0046] With regard to reduced aortic compliance, such condition can cause a reduction in the supply of blood to the organs of the body due to the decrease in blood flow during diastole. Among the risks associated with insufficient aortic compliance, a significant risk presented in such patients is a reduction in blood supply to the heart muscle itself. For example, during systole, generally little or no blood may flow in the coronary arteries and into the heart muscle due to the contraction of the heart, which holds the heart at relatively high pressures. During diastole, the heart muscle generally relaxes and allows flow into the coronary arteries. Therefore, perfusion of the heart muscle relies on diastolic flow, and therefore on aortic compliance. Insufficient perfusion of the heart muscle can lead to and / or be associated with heart failure. Heart failure may be accompanied by certain signs, including elevated jugular venous pressure, pulmonary crackles and peripheral edema, for example, which may be caused by structural and / or functional cardiac abnormality. Such conditions can result in reduced cardiac output and / or elevated intra-cardiac pressures at rest or during stress. Compliance-Enhancing, Vessel-Reshaping Implants

[0047] The present disclosure relates to systems, devices, and methods for adding- back and / or increasing compliance in a blood vessel, such as the pulmonary artery or the aorta, to provide improved perfusion and / or other health benefits. Examples of the present disclosure can include spring implant devices that, when implanted, are configured to decrease the cross- sectional area / volume of the target blood vessel segment in which the spring implant device is implanted during low-pressure conditions, such as diastole, which serves to force blood through the blood vessel segment by pushing the blood through the vessel as the vessel volume reduces in connection with spring expansion induced by cyclical drops in blood pressure.

[0048] The spring implant devices of the present disclosure can advantageously be configured to generate a differential cross-sectional area or volume of the target blood vessel(s) between high- and low-pressure phases of the cardiac cycle to increase and smooth circulatory flow. The spring implant devices of the present disclosure produce complaint blood vessel volume change by manipulating / reshaping the native blood vessel walls. Compared to blood flow solutions involving blood vessel grafting / resection, examples of the present disclosure can provide a solution that avoids the risks that may be associated with cutting of the vessel and / or devices grafted in / to such vessels, which may present risk of rupture and blood leakage outside of the circulatory system. Hazards associated with extravascular arterial blood leakage, such as within the abdominal and / or chest cavity, can include the risk of serious injury or death.Attorney Docket No.: ADV-24166WO01

[0049] Desirable diastolic flow in arterial blood vessels can be enabled by the decrease in cross-sectional area / volume of the blood vessels when transitioning from higher- pressure conditions (e.g., systole) to lower-pressure conditions (e.g., diastole). Where the relevant blood vessel has become stiff and non-compliant, stretching / expanding and subsequent contraction / shrinking of the blood vessel to cause the desired change in area / volume of the blood vessel may be limited due to the perimeter / wall of the blood vessel being resistant to stretching. Examples of the present disclosure provide implants that cause a change in cross-sectional area / volume of a target blood vessel without requiring stretching in the blood vessel wall. Rather, such cyclical change in blood vessel area / volume can be achieved through manipulation of the shape (e.g., cross-sectional shape) of the target blood vessel, wherein a transition between blood vessel shapes occurring in response to changing pressure conditions can reduce and increase the area / volume of the blood vessel in a cyclical manner to promote more even flow of blood through the blood vessel throughout the cardiac cycle.

[0050] With respect to a blood vessel having a relatively fixed perimeter, wherein the blood vessel wall does not expand sufficiently due to stiffness and / or other factors of non- compliance, generally, the greatest area / volume of the blood vessel may be present / achieved when the blood vessel wall forms a circular cross-sectional shape, which may maximize the cross-sectional area and volume of the blood vessel. FIG.3A shows an example blood vessel 31a having a blood vessel wall 32 forming a generally circular cross-sectional shape, such that the area Ac thereof is maximized for the given perimeter / wall-length Pa. In the circular configuration, the diameter d1is substantially constant at every angle about the axis of the vessel.

[0051] Diverging from a circular cross-sectional shape can produce a cross-sectional area / volume for a blood vessel that is less than the maximum area Acshown in FIG.3A. For example, FIG.3B shows the blood vessel 31b having a shape that resembles an oval / ellipse, which produces the cross-sectional area Aothat is less than the area Acwith the same blood vessel wall / perimeter length Pa. The oval shape of the vessel 31b may have a major axis am having a dimension d3that is greater than a dimension d2of the minor axis anthereof.

[0052] With further reference to FIGS.3A and 3B, due to the area Ao of the oval vessel of FIG.3A being less than the area Ac of the circular configuration shown in FIG.3A, transitioning from the circular shape 31a to the non-circular shape 31b, can produce a reduction in area / volume of the blood vessel, and therefore solutions that cause transitions between circular and non-circular blood vessel shapes between cardiac phases can provide compliance characteristics without the need for elasticity in the blood vessel wall tissue. For example, where a mechanism is implemented to cause a blood vessel to transition between circular and non-Attorney Docket No.: ADV-24166WO01 circular shapes in response to changing pressure conditions, such manipulation of the blood vessel shape can introduce volumetric change in the blood vessel in response to the typical changes in pressure experienced during the cardiac cycle, thereby mimicking natural compliance to increase cardiac efficiency and reduce pulsatile load.

[0053] Examples of the present disclosure provide spring implant devices and associated processes configured to transition the shape / area of a blood vessel from circular / more- circular to non-circular / less-circular shapes, and vice versa, to enhance compliance. Such spring implant devices / processes may cause vessel reshaping through dynamic compression / expansion of the spring mechanism of the spring implant in a way that produces a change in shape of the blood vessel in which it is implanted between the systolic and diastolic phases of the cardiac cycle.

[0054] Examples of the present disclosure provide for spring-type implants that are biased to a shape that has an expanded dimension, wherein such implant devices are configured to transition to a compressed dimension / length when forcibly remodeled by the blood vessel overcoming the spring bias of the spring to some degree and causes the spring mechanism(s) to be compressed. The ability of spring implant devices of the present disclosure to reshape the target blood vessel in the manner described above to produce the desired oval cross-section of the blood vessel can be achievable due to stiff / non-compliant blood vessels, which may be unable to stretch to a substantial degree, still retaining the ability to bend to a sufficient degree to allow for such shaping of the blood vessel. That is, the bending stiffness of a non-compliant blood vessel may be relatively lower compared to the stretching stiffness thereof. Therefore, examples of the present disclosure achieve compliance through bending energy with respect to the blood vessel wall, as opposed to stretching energy. When spring implant devices of the present disclosure are forced to a compressed / modified shape corresponding more closely to a circular shape of the target blood vessel, energy may be stored in the structure of the spring(s) of the device, wherein recoil / expansion of the spring mechanism towards its biased, expanded configuration can return / release energy to the blood circulation.

[0055] FIG.4 shows a perspective view of a spring-like non-circular stent 400 in accordance with one or more examples, which may be configured to produce cyclical reshaping of a target blood vessel as described above. The description of the stent 400 may be understood to relate to, and / or describe aspects of, any of the spring implant devices described herein.

[0056] The stent 400 may be formed of a tubular frame 431, which may form a wall around an axial channel 449, thereby defining the channel 449. The stent frame 431 may be considered to comprise sidewall segments 425 that run along relatively long sides of the stentAttorney Docket No.: ADV-24166WO01 400 that are aligned generally with the orientation of the major axis / dimension Amajof the stent, as well as end wall segments 427, which may connect the side walls 425 on major-axis ends of the stent 400. The end walls 427 may be outwardly-curved / concave with respect to an axis Asof the stent 400 and may provide primary tissue-contact surfaces / portions for reshaping the target blood vessel. The sidewalls 425 may be generally straight over at least a portion of a length thereof, and / or may bow / deflect inward and / or outward, either in a resting, unpressurized state, or in conditions of hoop / wall stress on the frame 431.

[0057] The stent 400 may be elastically deformable between a first, non-circular configuration, as shown in FIG.4, and more-circular configurations (see FIGS.5B, 5C), with the stent 400 biased toward the first configuration. In some examples, the stent frame 431 may comprise a shape-memory material, such as Nitinol. Although shown as an oval-shaped stent, the stent 400 may be any non-circular shape in a resting state thereof, such as a triangle, peanut, figure-8, and / or kidney shape.

[0058] FIGS.5A, 5B, and 5C provide axial views of the blood vessel reshaping stent 400 of FIG.4 in a biased, neutral shape, in a low-pressure deformed shape, and a high-pressure deformed state, respectively. FIG.5A shows the stent 400 in its natural, biased shape, wherein the major axis Amaj is in its fully-expanded length do in the absence of compressive force. The stent 400 may be configured to be percutaneously delivered to a blood vessel in a compressed delivery configuration. Once within the blood vessel lumen at the target deployment site, the stent 400 may be configured to be radially expanded into direct surface contact with the blood vessel wall. In some examples, the stent 400 may be configured to be expanded such that the perimeter of the stent 400 approximates and / or exceeds a perimeter of the blood vessel portion where the stent 400 is implanted.

[0059] FIG.5B shows the stent 400 deployed within a target blood vessel 31, wherein a minimum amount of baseline blood pressure in the blood vessel 31 causes the blood vessel wall to apply some minimum amount of force against the end walls 427 of the stent 400 along the major axis Amajof the stent 400, thereby partially deforming the stent 400 towards a more circular shape. For example, the cells of the frame 431 may provide openings in the frame 431 that allow blood in the blood vessel 31 to transfer pressure through the frame 431 and load the inner diameter / surface of the blood vessel 31 with a force commensurate with the circulatory pressure state.

[0060] FIG.5C shows the stent 400 circularized to a greater degree in response to a maximum pressure conditions within the blood vessel 31. Luminal pressure forces against the blood vessel wall increase the hoop stress on the blood vessel, which may force the blood vessel,Attorney Docket No.: ADV-24166WO01 and with it the stent 400, to assume a more-circular shape. The resulting hoop stress, also referred to as “tangential stress” or “circumferential stress,” from luminal pressure increase exerts radially-outward force along the blood vessel’s inner circumference, such stresses / forces being tensile in nature, which can tend to cause the blood vessel to increase in diameter. However, where the elasticity of the blood vessel wall is compromised, the expansion of the blood vessel diameter is limited, and therefore, the pressure increase reshapes the blood vessel without substantially increasing the circumference thereof. The blood pressure force on the blood vessel wall and resulting inward deflection of the blood vessel walls (due to outward deflection of the vessel wall portions in the area of the minor axis Amin) at the major-axis-ends 427 of the stent 400 cause inward deflection of the ends 427 of the stent 400 to form a desired geometric change to a more-circular shape of the blood vessel and stent 400.

[0061] The transition of the stent from oval to the more-circular stent shape causes energy to be stored in the stent frame 431 (e.g., in the elasticity and / or shape memory thereof), such that energy is returned to the blood vessel walls 31, and therefore to the blood circulation within the blood vessel segment, when the frame transitions back to the oval shape as pressure decreases. The shape memory forces of the stent 400 are advantageously sufficient to overcome the pressure forces within the blood vessel 31 to return the stent 400 to a near oval configuration as in FIG.5B in the presence of minimum diastolic pressure conditions, thereby reshaping the blood vessel 31 to a non-circular (e.g., generally-oval) cross-sectional shape. However, due to the baseline pressure of the circulation, the stent 400 may not fully extend, but may be partly compressed even in the lowest-pressure condition.

[0062] Because the amount of compliance added to the blood vessel 31 is proportional to the amount of shape change of the stent 400 and blood vessel 31 between the low-pressure and high-pressure conditions, the initial transitional deflection of the stent as shown in FIG.5B, which is caused by the baseline pressure of the circulation, robs the stent 400 and blood vessel 31 of some amount of volume / shape change that would occur if the cyclical reshaping of the stent was between the fully-elongated shape of FIG.5A and the fully-shortened shape of FIG.5C. Therefore, blood vessel reshaping stents and other spring-type devices of the present disclosure may advantageously be designed in a manner as to minimize the major-axis compression of the device caused by baseline pressure conditions and / or maximize the major- axis compression of the device between the baseline pressure condition (e.g., diastole) and the maximum pressure condition (e.g., systole). For example, in accordance with aspects of the present disclosure, the stent 400 may be configured such that the compression spring rate alongAttorney Docket No.: ADV-24166WO01 the major axis Amajis negative, such that compression resistance decreases as the stent is compressed along the major axis Amaj. Longitudinally-Compressible Intravascular Spring Implants

[0063] In addition to stent-type blood vessel reshaping devices, various other types of spring devices can be implemented to reshape a target blood vessel through direct contact between the implant device and one or more portions of an inner or outer blood vessel wall. In some examples, spring implant devices can be designed in a manner such that they are not only effective with respect to the blood vessel reshaping effects thereof, but also provide reduced or minimized contact between the implant device and the native blood vessel anatomy. For example, contact between reshaping implant devices and native blood vessel anatomy, over many heart cycles, can produce abrasion, irritation, and / or other damage to the blood vessel anatomy, depending on the type of contact, the number of contact points, the contact surface(s), and / or the like. In some implementations, examples of the present disclosure provide spring-type implants that are configured to reshape a target blood vessel through contact in only two interior blood vessel contact points or areas, such as points / areas on opposite diametrical sides of the target blood vessel. In some implementations, aspects of the present disclosure relate to intravascular implant devices that comprise longitudinally-compressible spring mechanisms, wherein such spring mechanisms are configured to cause stretching / reshaping of the target blood vessel from within the blood vessel by elongating a major axis of the blood vessel, thereby shaping the blood vessel into a stretched-out, ovalized shape.

[0064] FIGS.6A and 6B show a diametrical vessel-reshaping spring device 50 in expanded and compressed configurations, respectively, in accordance with one or more examples. The implant 50 shown in FIGS.6A and 6B represents an example blood-vessel- reshaping device comprising one or more spring-biased elements or mechanisms 51, wherein the device 50 is implantable within, for example, a non-compliant blood vessel segment 31. The example implant 50 is an example of a type of implant of the present disclosure that is designed to facilitate transition of a target blood vessel segment between oval and more-circular configurations, thereby restoring and / or increasing compliance characteristics thereof, while advantageously maintaining only two points of contact between the implant and the inner wall of the target blood vessel.

[0065] The spring mechanism 51 includes one or more springs dimensioned such that a lengthwise dimension dl can extend across a blood vessel lumen in a biased shape thereof. The spring mechanism 51 can comprise any type of compression, extension, or torsion spring(s). TheAttorney Docket No.: ADV-24166WO01 spring mechanism 51 is designed to assume a biased elongated or extended state, represented by the illustrated elongated configuration 50e, by default.

[0066] The tissue-contact pads 53a, 53b at the lengthwise ends of the device 50 can have any shape or form, such as any type of paddles or sled / ski form. The tissue-contact pads 53a, 53b are configured to press against opposite sides of the inner wall of the blood vessel 31, effectively reshaping the blood vessel 31 to an oval shape by expanding the vessel along its major axis when the blood pressure within the blood vessel 31 is insufficient to fully overcome the compression resistance of the spring mechanism. Descriptions of spring implant devices with spring elements / mechanisms in a relaxed configuration should be understood to relate to a configuration that the spring element naturally assumes in the absence of tension / force on the tissue-contact portions / pads of the implant device from external forces (e.g., ambient fluid pressure, physical contact forces, etc.).

[0067] The tissue-contact features 53 associated with opposite ends of the device 50 may have atraumatic tissue-contact surfaces facing longitudinally outward with respect to the lengthwise dimension dl of the spring mechanism 51, such that the tissue-contact ends 53 are opposite-facing with respect to one another. For example, the tissue-contact ends 53 may comprise curved sleds or other curved surfaces, as illustrated, wherein the curvature of the surfaces may advantageously provide reduced risk of damage to the inner wall of the blood vessel 31, while providing sufficient tissue contact surface to allow the implant 50 to stretch-out the blood vessel as in FIG.6A. The curvature of the ends 53 may further allow sidewalls 33 of the blood vessel to curve in an oval-shaped manner, as shown, without being unduly impeded in such shaping by the presence of the ends 53.

[0068] With the device 50 deployed within the target blood vessel 31, the tissue- contact pads 53a, 53b man be oriented to exert outward radial force against the vessel walls. The spring mechanism 501 is preloaded to generate a continuous force, causing the blood vessel 31 to deform from its natural circular cross-section to an oval shape. This deformation is achieved by elongating the major axis Amajof the blood vessel 31 and compressing the minor axis Aminof the blood vessel’s cross-section. When blood pressure within the vessel increases, it exerts an outward radial tensile stress on the vessel walls, which counteracts the intrinsic force of the spring mechanism 51. As blood pressure rises, it compresses the spring mechanism 51, allowing the vessel to approach its natural circular shape.

[0069] FIG.6B shows the spring device 50 compressed due to high-pressure dynamics. Under high blood pressure, the spring mechanism 51 compresses, enabling the blood vessel 31 to return to a more circular cross-section. The compressive force from the bloodAttorney Docket No.: ADV-24166WO01 pressure must exceed the intrinsic force of the spring for this to occur, which may occur in connection with the systolic phase of the cardiac cycle. When blood pressure decreases (in a cyclical pattern), the tensile stress on the vessel walls decreases, such that the intrinsic force of the spring mechanism 51 once again becomes dominant, causing the tissue-contact elements 53a, 53b to press outward and re-expand the major axis Amaj of the blood vessel 31, thus restoring the oval shape. This mechanism operates cyclically, with the blood vessel alternating between oval and more-circular cross-sections in response to varying blood pressures.

[0070] The action the device 50 and blood vessel 31 can be understood in terms of force vectors. Prior to any deployment or compression, the spring mechanism 51 generally assumes its expanded state 50e. When deployed within the blood vessel 31, this behavior exerts a radial outward force on the blood vessel walls through the contact pads 53. This force can be represented as vectors pointing perpendicularly outward from the vessel’s inner surface at the points of contact. The inner walls of the blood vessel 31 exert an equal and opposite reaction force inward, balancing the outward force of the spring. As blood pressure increases, it generates an outward radial tensile stress on the vessel walls. These forces act uniformly around the inner circumference of the vessel 31, represented as vectors pointing outward from the center of the vessel. Initially, the outward radial force due to blood pressure and the outward force from the spring are balanced, with the vessel maintaining its ovalized shape. As blood pressure continues to rise, the outward radial tensile stress increases. The vectors representing this force become larger, indicating a greater force exerted on the vessel walls (see FIG.6B). The spring mechanism 51 further compresses under this increased outward force. The net force on the vessel wall is the difference between the outward tensile stress from the blood pressure and the diminishing outward force from the spring. This resultant force causes the vessel walls to move outward, compressing the spring further. At peak blood pressure, the outward radial tensile stress vectors are at their maximum, indicating a strong force pushing outward uniformly along the vessel walls. The extent of resulting circularization of the blood vessel 31 depends on the magnitude of the blood pressure relative to the spring mechanism’s intrinsic force.

[0071] Although a two-dimensional representation of the spring implant device 50 is presented in FIGS.6A and 6B, it should be understood that the implant 50 may have an axial width dimension that is parallel with an axis of the blood vessel 161. That is, with respect to the illustrated orientations of FIGS.6A and 6B, the implant 50 may extend in and / or out of the page some distance, such as a length of between 1–10 cm, or longer. In such implementations, the implant 50 may effectively span a longitudinal segment of the target blood vessel, thereby potentially enhancing the reshaping effect of the implant device on the blood vessel 31.Attorney Docket No.: ADV-24166WO01

[0072] In the low-pressure state of FIG.6A (e.g., diastole), although the pressure is lower, the force vectors 35 from the tensile force on the blood vessel wall that that are directed radially inward, and thus act on the tissue-contact pads 53, are aligned to a high degree with the lengthwise dimension dlof the spring mechanism 51, and therefore a non-trivial amount of compression of the device 50 may occur even during the lowest-pressure state. Such initial compression decreases the amount of shape change between the low-pressure state and the high- pressure state (see FIG.6B), and therefore negatively impacts the compliance-enhancement function of the device 50. Furthermore, in the high-pressure state, where the blood vessel 31 is more circularized, the force vectors 35 acting against the tissue-contact pads 53 may be less oriented in parallel with the length dimension dlof the spring, and therefore, in spite of the higher blood pressure, the resulting force against the tissue-contact pads 53 may not be commensurate with the level of pressure increase compared to the low-pressure state. These undesired low- pressure compression and reduced high-pressure force vector alignment issues can be exacerbated when the spring mechanism 51 has a positive spring rate, such that compression resistance is less in the low-pressure state where the spring is more expanded and higher in the high-pressure state where the spring is more compressed. Therefore, it may be desirable to implement negative spring rate spring mechanisms as described in detail below to account for the undesired low-pressure compression and reduced high-pressure force vector alignment issues addressed above.

[0073] FIG.7A shows a graph 700 representing a positive spring rate response of an implant device 50 in accordance with one or more examples. FIGS.7B and 7C show an example spring implant 50 within a blood vessel in states corresponding to points on the graph of FIG. 7A.

[0074] In the illustrated graph 700, the x-axis represents spring compression. Moving from left to right indicates increasing compression of the spring, which may be measured in millimeters, for example. The y-axis represents the force required to compress the spring at each compression state, wherein higher values indicate a greater force required to further compress the spring mechanism of the implant device 50.

[0075] The graph 700 represents a spring implant 50 having a positive spring rate, represented by the positively sloped line / curve 701. Elastic spring mechanisms of implant devices of the present disclosure may generally conform to Hooke’s Law, wherein compression / expansion force (F) of the spring mechanism conforms to the equation F = KX, where ‘K’ is the spring constant and ‘X’ is the spring compression. With respect to the positive spring rate implant represented by the graph 700, as the spring compression increases, the forceAttorney Docket No.: ADV-24166WO01 required to compress the spring also increases. The steeper the slope 702, the higher the spring rate represented thereby. Although the example line 701 is shown as straight / linear, it should be understood that spring implant devices can have varying spring rates, wherein the curve 701 may be nonlinear, such as by curving upwards as displacement increases. The compression range shown in the graph 700 may correspond to the elastic range within which the spring returns to its original shape after the force is removed; beyond the limits of the illustrated range, the spring may be incompressible and / or permanent deformation may occur.

[0076] FIG.7B shows a minimal compression state of the spring implant 50, wherein the spring is only slightly compressed from its natural length and exerting its intrinsic outward force. Generally, since the resistive force of the spring is low in the low compression state, the force required to cause and / or maintain the illustrated compression state. FIG.7C shows the maximum compression state of the implant 50 within the circularized blood vessel 31. Due to the positive spring rate, the force required to compress the spring increases as indicated by the upward slope of the graph. This means that more force is needed to achieve and / or maintain the greater spring compression shown in FIG.7B. After maximum compression as blood pressure drops, the force exerted by the blood vessel walls decreases, and the spring begins to re-expand, wherein the compression of the spring decreases, moving leftward on the graph, and the force required to maintain that compression also decreases. Due to the positive spring rate, it takes progressively more force to compress the spring 51 as displacement increases. This means that at higher blood pressures, the spring 51 is harder to compress, requiring significant force to reduce the vessel’s ovalization.

[0077] With regard to effective reshaping of the blood vessel to enhance blood vessel compliance, for maximum change in the cross-sectional area of the blood vessel, the spring mechanisms can advantageously be designed to exert significant outward force at low blood pressures and be sufficiently compressible at high blood pressures. Unfortunately, for positive spring rate implants, the increasing force requirement means that as blood pressure rises, it becomes increasingly difficult to compress the spring and reduce the vessel’s ovalization. Therefore, examples of the present disclosure relate to systems that are designed to promote sufficient spring compression at high pressures without being overly stiff. For example, the spring mechanism of the implant may be designed to exhibit a spring rate that balances the need for substantial compression under high pressure while maintaining enough force to re-ovalize the vessel at low pressure. Such designs can provide a significant change in the vessel’s cross- sectional area between low and high pressure conditions, maximizing the change in blood vessel volume.Attorney Docket No.: ADV-24166WO01

[0078] Spring implant examples of the present disclosure may further be designed to minimize the compression of the spring under low-pressure conditions, as such initial compression can effectively rob the implant of its reshaping ability, at least in part. For example, because blood pressure does not ever go to 0 mmHg in a living person, the implant’s cross- sectional area change from low pressure (e.g., diastole) to high pressure (e.g., systole) is reduced due to initial, low-pressure compression. This reduced cross-sectional area change also means reduced effectiveness and compliance. For spring implant examples having positive spring rates, a substantial amount of cross-sectional area may be lost between a zero-pressure environment and a diastolic blood pressure environment within a blood vessel. Conversely, as pressure increases from diastole to systole, such springs may become stiffer, and therefore the ratio of area change may be substantial, or even greater, from zero pressure to diastolic pressure compared to the change in pressure from diastolic pressure to systolic pressure due to the increasing stiffness of the spring.

[0079] Furthermore, in the early stages of compression, the force vectors from the blood pressure are more aligned with the axis of the spring, which means that a significant portion of the outward radial force is directed towards compressing the spring. Therefore, even the minimal diastolic pressure can cause a noticeable compression of the spring. This early compression uses up some of the spring’s capacity to expand and compress, reducing the overall range of motion available for subsequent higher-pressure states (systolic pressure). As a result, the device loses some of its potential to create significant changes in the blood vessel’s cross- sectional area. Negative spring rate implant examples of the present disclosure can improve blood vessel reshaping by reducing the degree to which the spring mechanism is compressed by the diastolic pressure, which otherwise limits the additional compression possible during systolic pressure increase. Negative Spring Rate Spring Implants

[0080] In some implementations, examples of the present disclosure comprise spring mechanisms that have a negative spring rate. Such examples can be designed with a linkage configuration, or other mechanism, that actually decreases in stiffness as the implant is compressed, such that less cross-sectional area change occurs from a near-zero-pressure condition to a minimal blood pressure (e.g., diastolic) condition, such that most of the cross- sectional area change of the blood vessel occurs between the low-pressure and high-pressure phases.Attorney Docket No.: ADV-24166WO01

[0081] FIG.8A shows a graph 800 representing a negative spring rate response of an implant device 80 in accordance with one or more examples. FIGS.8B and 8C show spring configurations associated with aspects of the graph 800 of FIG.8A in accordance with one or more examples. As the spring implant device 80 is a negative spring rate device, as the spring mechanism 81 of the device 80 is compressed, instead of becoming more resistive to compression, compression becomes easier. The implant 80 is designed for minimal deflection in diastole, and more compression, and therefore more blood vessel area / volume change, from diastole to systole.

[0082] When the device 80 is first placed in the blood vessel 31, even the diastolic pressure exerts a force on the spring mechanism 81. The force exerted by the blood pressure acts radially outward on the vessel walls, which in turn produces inward deflection of the major-axis portions 33 of the blood vessel walls, which applies compression force to the tissue-contact pads 83 of the device 80, causing compression of the spring mechanism 81. Initially, the spring mechanism 81 provides relatively high compression resistance due to the negative rate spring constant, resisting movement towards its natural circular shape in the presence of low pressures.

[0083] As the pressure rises, and the spring mechanism further compresses, the force required to compress the device 80 decreases. That is, the spring 81 offers more resistance to initial compression and less resistance as it is further compressed. Since the spring mechanism 81 offers more resistance at initial compression and less resistance at higher compression, it effectively uses the full range of blood pressure changes to maximize the vessel’s volume change. The decreasing force requirement with increased compression means the spring can maintain the vessel in an ovalized shape at lower pressures and allow significant spring compression, and therefore blood vessel reshaping / circularization, at higher pressures, optimizing the cyclical volume change.

[0084] With regard to the graph 800, the x-axis represents the compression of the spring 81, whereas the y-axis represents the force required to compress the spring 81. The initial part of the graph on the left side is associated with starts with higher force levels, indicating substantial resistance to initial compression. As spring compression increases moving left to right, the slope 802 of the graph 800 being negative, causes the force value to decrease, showing that less force is required for further compression. That is, at systolic pressure, the force required for further compression is lower. The area under the curve / line 800 from diastolic to systolic pressure shows an extended range of compression. Because the spring 81 offers less resistance as it compresses, the full pressure range can be effectively utilized.Attorney Docket No.: ADV-24166WO01

[0085] When the blood vessel 31 is ovalized as in FIG.8B, the force vectors associated with the blood vessel acting inward against the contact pads 83 are relatively aligned with the compression axis of the spring mechanism, and so even in low pressure conditions, strong compression forces may act to compress the spring mechanism 81. Conversely, when the blood vessel 31 is more circularized as in FIG.8C, the force vectors acting against the contact pads 83 to compress the spring mechanism 81 are less aligned with the spring compression axis, and so in spite of the higher-pressure levels, the compression forces may not be commensurate with the increase in blood pressure. Therefore, the ability to provide increased compression resistance at lower pressure and reduced compression at higher pressure can be critical in terms of maximizing blood vessel shape chance from oval to more circular as pressure rises from diastole to systole and reduces from systole to diastole.

[0086] With reference back to the graph 800, line 801 does not continue to the left fully to the vertical axis as the minimum pressure condition in the blood vessel and / or the dimensions of the blood vessel relative to the spring implant device 80 may be such that the spring mechanism 81 is prevented from expanding fully beyond a certain point, and therefore an initial pre-load force may be maintained even at low pressures. As external force is applied (e.g., from blood pressure), the spring mechanism begins to buckle at the point associated with the configuration of FIG.8B, which is the beginning of a range where additional force leads to decreased resistance due to the buckling action.

[0087] The spring mechanism 81 may have any suitable or desirable configuration that provides a negative spring rate behavior. For example, leaf springs or torsional springs may be used that exhibit bi-stable behavior, providing an initial resistance followed by a reduction in force required for further compression.

[0088] In some implementations, a negative spring rate implant device as disclosed herein may be configured as a buckling beam spring device, as shown in FIGS.9A and 9B in extended and compressed states, respectively.

[0089] FIGS.9A and 9B show a negative rate spring implant device 90 with a slender, elastic beam 91, which acts as a spring and is fixed at both ends to respective tissue- contact pads / bars 93, which may have any suitable or desirable length. The device 90 may be deployed within a blood vessel as with other examples shown and described in connection with the present disclosure.

[0090] In minimal pressure conditions (e.g., diastole), the spring / beam 91 may be under initial tension from tensile forces associated with the minimal pressure conditions, as shown in FIG.9A. Under initial tension / force, the spring / beam 91 may advantageously resistAttorney Docket No.: ADV-24166WO01 compression, thereby maintaining the blood vessel’s oval shape. In the initial tension / force condition, the bar 91 may be substantially straight, or may have a slight bowing / curvature, as shown in FIG.9A.

[0091] As blood pressure increases, the beam 91 begins to buckle, transitioning to a state shown in FIG.9B in which the beam is more inclined to bend and offers less resistance to further compression. The buckling action results in a negative spring rate where increased compression requires decreasing levels of force. The implementation of a buckling beam, as shown in FIGS.9A and 9B may represent a relatively simple mechanical mechanism to achieve a negative spring rate. The description below provides additional, more complex, mechanical devices for use as negative spring rate spring mechanisms for blood-vessel-reshaping spring implant devices disclosed herein.

[0092] FIGS.10A and 10B show a parallel-contact scissor expansion device 100 in expanded and compressed configurations, respectively, in accordance with one or more examples. The device 100 includes tissue-contact pads / bars 103a, 103b in a parallel configuration, as with other examples disclosed herein. Generally, the force separating the contact pads 103 may be considered a mechanical spring mechanism, which can be configured to operate such that when the contact pads 103 are farther apart (e.g., in diastole), the compression force in the lengthwise / compression dimension dl is relatively high, wherein as the contact pads 103 are compressed together (e.g., in systole), the compression resistance force is relatively lower. That is, the spring mechanism 101 can be part of a negative spring rate spring mechanism.

[0093] The two parallel tissue-contact pads / bars 103a 103b, in the orientation illustrated in FIGS.10A and 10B, are positioned one above the other and serve as the primary components that make contact with the inner blood vessel wall tissue. The pads 103a, 103b can move relative to each other, expanding and contracting the distance between them.

[0094] The spring mechanism 101 can be configured as a linkage system, wherein each end of both the upper and lower tissue contact pads 103a, 103b is connected to a pair of hinge / pivot joints 107, forming the basis of a scissor-like arrangement of pivotably-connected linkages, as shown. Four elongate linkages / arms 105 can create the main scissor mechanism of the spring mechanism 101. For example, one linkage 105a can be pivotably attached to the left end of the bottom contact bar 103b at a pivot connection 107a and cross diagonally to pivotably attach to another of the linkages 105c at a pivot connection 106b that is pivotably coupled to the left end of the top contact bar 103a at a pivot connection 107c. Another linkage 105b can be pivotably attached to the right end of the bottom contact bar 103b at a pivot connection 107b and cross diagonally to pivotably attach to another of the linkages 105d, at a pivot connection 106a,Attorney Docket No.: ADV-24166WO01 the linkage 105d being pivotably coupled to the right end of the top contact bar 103a at a pivot connection 107d. The pairs of linkages 105 coupled to the respective ones of the top and bottom contact bars 103 can cross in an ‘X’ configuration, as shown, with bottom and top ‘X’ pairs 105 coupled together at end portions thereof at central pivot connections 106, allowing the contact bars 103 to move closer or further apart through rotation of the linkages at the respective pivot connections 106, 107.

[0095] The spring mechanism 101 may further include two additional shorter linkages 108a, 108b that are configured to enhance the stability and functionality of the spring mechanism. For example, a left medial linkage 108a (with respect to the arbitrary illustrated orientation) connects the pivot connection 106a of the primary linkages 105b, 105d to a medial pivot connection 109a on the primary linkage 105c. A right medial linkage 108b can connect the pivot connection 106b the primary linkages 105a, 105c to a medial pivot connection 109b on the primary linkage 105b. The medial linkages 108 can help ensure that the scissor spring mechanism 101 operates smoothly, maintaining parallelism and adding to the mechanical stability of the system.

[0096] When the tissue-contact bars 103a, 103b are farthest apart in an expanded state, as shown in FIG.10 A, the primary linkages 105 form a wider angle θ1, such as up to 45 degrees or more, but less than 90 degrees. This creates the ‘X’ shapes with the crossing linkages 105. In such state, the distance between the contact bars 103 is maximized, and the system provides significant resistance to further expansion due to the mechanical advantage created by the scissor mechanism. Therefore, in the configuration of FIG.10A, with the addition of certain springs as described in greater detail below, the contact bars 103 can exert an outward force on the blood vessel tissue, maintaining an expanded configuration which helps to achieve the desired ovalization effect.

[0097] FIG.10B shows a compressed configuration of the device 100, wherein the tissue-contact bars 103 are positioned close together. In such state, the primary linkages are at a smaller angle relative to the contact bars 103, closer to being parallel but still forming an ‘X’ configuration. The crossing of the linkages 105 ensures that the contact bars 103 can move closer together while maintaining stability. Collectively, the various pivot connections 106, 107, 109 and crossing linkages 105 provide mechanical stability and facilitate smooth, uniform movement of the tissue-contact bars 103 between the states shown in FIGS.10A and 10B. The shorter medial linkages 108 contribute to maintaining the parallelism of the tissue-contact bars 103, preventing skewing or misalignment during operation.Attorney Docket No.: ADV-24166WO01

[0098] The scissor-type design of the device 100 can achieve a negative spring rate constant by leveraging the unique mechanical properties of the scissor (or pantograph) mechanism. For example, the pivotable connection of the primary linkages 105 in an ‘X’ shape can allows the linkages 105 to extend and retract in a controlled manner. When the bars 103 are far apart (expanded state), the linkages are at wider angles. The force required to compress the bars initially is higher because the linkages must overcome the mechanical advantage created by the wide angle θ1. As the bars 103 move closer together, the angle between the linkages decreases. This results in a mechanical configuration where the linkages offer less resistance to further compression. The crossing linkages can interact in such a way that their combined mechanical properties create a variable resistance profile. The configuration of the linkages 105, 106 can be stacked to allow a compact package when fully closed for transcatheter delivery, as shown in FIG.10B.

[0099] Although figures and description of the present disclosure show pin-type pivot / hinge joints, it should be understood that such disclosure is for convenience and example only, and any pivoting components of examples of the present disclosure can instead be implemented as false pivots, such as shape-memory compliant hinges. For example, any of the pivoting components disclosed herein can be implemented as a single, continuous piece of nitinol or other shape memory material that can flex and return to its original shape, mimicking the function of a pin joint / pivot without the need for separate pin pieces. Such configurations may be more suitable for implantation in a blood vessel due to more simple mechanics thereof, and therefore it may be desirable to implement any of the examples herein using compliant hinges, at least in part. Such a mechanism can rely on the material’s ability to undergo deformation and then return to its preset shape, providing the rotational or bending motion typically achieved by a pivot. Any of the examples disclosed herein can be implemented as a hybrid nitinol implant that mimics the pivoting action shown and described herein.

[0100] FIGS.10A and 10B show the scissor mechanism of an example negative spring rate blood vessel reshaping implant device, wherein additional spring components are omitted for visual and descriptive clarity. It should be understood that additional components may be implemented with the device 100 to achieve desirable negative spring rate functionality. FIGS.11A and 11B show plan and perspective views, respectively, of a negative spring rate expander implant 110 in accordance with one or more examples.

[0101] The device 110 includes the scissor mechanism 100 of FIGS.10A and 10B, as well as certain additional features that facilitate negative spring rate functionality. Each end of the upper and lower tissue-contact bars 103 is connected to a plurality of primary linkages 105 atAttorney Docket No.: ADV-24166WO01 pivot joints 107. Four elongate primary linkages / arms 105 create the main scissor mechanism, as described in detail above. Two additional shorter medial linkages 108 enhance stability and promote alignment.

[0102] In addition to the mechanics shown in FIGS.10A and 10B, the negative spring rate device 110 of FIGS.11A and 11B include two additional pairs of outer guide linkages 118, including a first pair of guide linkages 118a, 118b that connect between the left end of the upper bar 103a to the left end of the lower bar 103b. The ends of these linkages are pivotably coupled to one another at a pivot connection 116, forming an outward-pointing ‘V’ shape. The angle of the ‘V’ is wider when the tissue-contact bars 103 are expanded apart and narrows when the bars 103 are compressed together. A similar pair of guide linkages 118c, 118d is connected in the same manner on the right side of the tissue-contact bars 103. As with any example disclosed herein, the apparatus 110 can be considered a device or a system of a plurality of assembled sub- components. The device / system 110 can be used in connection with any blood vessel reshaping process or method disclosed herein to increase compliance of a target blood vessel by modulating vessel wall motion in response to pulsatile intravascular pressure.

[0103] The device 110 further comprises a guide bar 111, which runs parallel to the tissue-contact bars 103 and is positioned between them (e.g., halfway between the contact bars 103). The pivot connection 116 of the left guide linkages 118a, 118b is connected to one end / portion of the guide bar 111. The pivot connection 117 of the right guide linkages 118c, 118d is a sliding pivot within a guide slot / channel 112 that runs along an end length of the right side of the guide bar 111, as shown. The guide slot / channel 112 allows the pivot connection 117 of the right guide linkages 118c, 118d to slide, accommodating the varying distance between the guide linkage apices as the device expands and contracts.

[0104] When the tissue-contact bars 103 are expanded apart (e.g., the configuration of FIG.11A), the guide linkages 118 form a relatively wider ‘V’ shape. The sliding connection within the guide slot / channel 112 allows the guide bar 111 to maintain stability and parallel alignment of the tissue-contact bars 103. When the tissue-contact bars 103 are brought closer together, the guide linkages 118 form a narrower ‘V’ shape. The sliding connection 117 in the guide slot / channel 112 of the guide bar 111 accommodates the reduced distance between the guide linkage apices, ensuring smooth contraction of the device 110. The guide slot 112 can advantageously serve as a stopper that prevents the guide linkages 118 from inverting inward or becoming co-linear in a manner that would potentially prevent the device 110 from compressing on the next cardiac cycle.Attorney Docket No.: ADV-24166WO01

[0105] The additional guide linkages 118 maintain parallelism of the tissue-contact bars 103, preventing skewing and facilitating uniform movement. The sliding pivot 117 in the guide slot / channel 112 allows the device 110 to adjust dynamically as it expands and contracts, providing additional stability and flexibility. The guide slot / channel 112 allows the connection point 117 of the right-side guide linkages 118 to slide, accommodating the varying distance between the guide linkage apexes as the device expands and contracts.

[0106] The device 110 further comprises a plurality of flat wing features 114 that are pivotably coupled / connected to the pivoting connections 116, 117 associated with the guide linkages 118 and guide bar 111. In particular, each of the pivot connections 116, 117 includes a pair of wings 114 extending away from the medial line 1101 of the guide bar 111. The left-side pair of wings 114a, 114b can have a form and orientation of a right-facing curve and a left-facing flat edge. The right-side pair of wings 114c, 114d may have a form and orientation of a left- facing curve and a right-facing flat edge. The outer tips 119 of the wings 114 extend away from the guide bar 111 on the outside of the guide linkages 118 and can have stoppers 121 to prevent rotation of the stopper portion of the wing past the outer edge of the corresponding one of the guide linkages 118. The wings 114 can advantageously decrease the profile of the device 110 for delivery to the target location (see FIG.12).

[0107] Multiple transverse springs 113 can be included to create a negative spring rate constant. The springs 113 can include a pair of springs on one or both sides (i.e., front and back sides with respect to the illustrated orientation of FIG.11A) of the linkage system. The springs 113 can connect in the lengthwise dimension 1101 of the contact bars 103 and the guide bar 111 between wingtips 119 of two of the wings 114. For example, the spring 113a may connect between wingtips 119 of the wings 114b and 114c and the spring 113b may connect between wingtips 119 of the wings 114a, 114d.

[0108] In some implementations, each of the springs 113 is implemented with a coiled spring portion 113s and a spring tie portion 113t. For example, each coiled spring portion 113s can be connected to one wing, and a coupled tie 113t (e.g., suture, wire) connects the spring portion 113s to the opposite-facing wing. Such arrangement may alternate between top and bottom springs 113, as shown. For example, the top spring 113s and tie 114t can be ordered with either the spring or the tie on the left and the other on the right, whereas the bottom spring 113b can have the opposite arrangement from the top spring.

[0109] The springs 113 connected to the wings 114 provide high initial resistance to compression, maintaining the expanded state shown in FIG.11A. As the wings 114 pivot and theAttorney Docket No.: ADV-24166WO01 springs 113 compress, the force required to compress the springs further decreases. This creates a negative spring rate, where less force is needed for additional compression.

[0110] Adjusting the stiffness of the springs 113 can change the initial resistance and the rate at which the force decreases with compression. For example, use of relatively stiff springs can provide high initial resistance, making the system more resistant to initial compression, whereas use of softer springs can decrease initial resistance, allowing easier initial compression, but still providing a negative spring rate effect. Furthermore, changing the relative lengths of the coiled spring portions 113s and spring tie portions 113t can affect the overall force-displacement behavior. For example, longer springs can provide a more gradual decrease in force required for compression, enhancing the negative spring rate effect over a longer range, whereas shorter springs can create a steeper decrease in force required for compression, making the transition to a negative spring rate more abrupt. In addition, adjusting the position of the stoppers 121on the wings 114 can control the maximum range of motion of the springs. In some implementations, pre-loaded spring elements can be adjustable via wires, leadscrews, etc., (e.g., using a transcatheter tool) to adjust the desired stiffness of the implant prior to deployment or release of the device 110 from the delivery system.

[0111] Any of the spring devices disclosed herein, including the negative spring rate implant device 110, can be implemented within a vacuum- or fluid-sealed balloon or other enclosure 191. In such implementations, the balloon device with a negative spring rate expander mechanism disposed therein can be placed within a blood vessel, wherein increased blood pressure causes compression of the spring mechanism and balloon in a manner that stores spring energy and expands as pressure decreases, thereby pushing blood through the blood vessel and increasing flow in a compliant manner. FIG.11A shows an example balloon 191 configured to fully encase the spring device 110 inside of a closed outer layer. The balloon device (or other spring implant devices of the present disclosure) may be configured to be fully expanded at external pressure of around 80 mmHg, or less, and collapse to a lower volume at pressures higher than 80 mmHg. The internal chamber 145 of the balloon 191 may advantageously lose as much volume as possible when reaching around 120 mmHg, for example. As used herein, references to blood pressure values in units of millimeters of mercury (mmHg) may refer to pressure relative to the surrounding atmospheric pressure, which is 760 mmHg at sea level. Therefore, a described change from 120 mmHg to 80 mmHg may represent an actual change from 880 mmHg (i.e., 760 mmHg + 120 mmHg) to 840 mmHg (i.e., 760 mmHg + 80 mmHg) at sea level, which represents a change of less than 5% in absolute pressure. In embodiments comprising a gas- or fluid-filled balloon as a compliance-enhancing volume, the balloon 191 may be free, or emptied, of gasAttorney Docket No.: ADV-24166WO01 and / or fluid, such as through the application of a vacuum thereto. The chamber 145 may remain in an expanded state using the spring device 110. Certain embodiments of compliance restoration devices in accordance with the present disclosure comprise a collapsible, hollow chamber, such as a balloon-type chamber, that may be inserted into the target blood vessel in an at least partially collapsed state using a catheter delivery system. Compliance restoration devices of the present disclosure may further be deployed and / or anchored in the target blood vessel (e.g., aorta) using, for example, a stent or other structure.

[0112] Negative spring rate blood vessel reshaping implant devices of the present disclosure can be delivered, deployed, implanted, utilized, and / or maintained according to various processes and methods, some of which are described below in connection with FIGS. 12–16. For example, FIG.12 shows a negative spring rate expander implant device 110 in a compressed configuration within a delivery system 150, which may comprise a sheath or the like, in accordance with one or more examples. The device 110 in FIG.12 may be similar in one or more respects to the device shown in FIGS.11A and 11B, discussed in detail above. In the delivery configuration shown in FIG.12, the implant device 110 can be folded for low profile delivery, as shown. In the compressed delivery configuration, the linkages 105, 108 can be pivoted to tighter angles as shown in the compressed scissor-type mechanism shown in FIG.10B and described above. Further, the guide linkages 118 and spring-connection wings 114 can be extended in the axial dimension of the sheath 150 to accommodate the compression / approximation of the tissue-contact pads 103. In the delivery configuration, the pivot connection 117 of the right-side guide bars 118 may be slid towards a right end of the channel / slot of the guide bar 111.

[0113] FIGS.13–16 show the negative spring rate expander implant 110 in various states of expansion / compression as deployed within a blood vessel 31 in accordance with one or more examples. In particular, FIG.13 shows the device 110 in an expanded configuration corresponding to a low-pressure state within the blood vessel 31, such as diastole. Due to the negative spring rate characteristic of the device 110, the spring assembly thereof, comprising a plurality of linkages and / or springs as shown, can advantageously provide high initial resistance to compression in the low-pressure conditions, which helps the tissue-contact bars 103 maintain their expanded length / separation deagainst tensile forces imposed on the tissue-contact pads 103 by the blood vessel wall. The squeezing force Fb on the device 110 may be relatively greater at diastole when the device 110 is expanded due to the flatness / stretch of the blood vessel, whereas the squeezing force Fb on the device 110 from the vessel at systole, in spite of the higher blood vessel tensile force from the relatively high blood pressure, may be equal or less than the force FbAttorney Docket No.: ADV-24166WO01 during diastole due to the circular shape of the blood vessel, which reduces the ratio of force aligned in the dimension of the force Fb.

[0114] The tension springs 113 are used to generate forces Fsperpendicular to the contact pad separation dimension de. Reaction forces Fofrom the springs 113 are applied to the tissue-contact pads 103 via the connected guide linkages 118 at the pivot connection 117, which forces resist compression of the contact pads 103 in the expanded configuration. In the expanded configuration, the pivot connection 117 of the guide linkages 118 and the spring support wings 114 is positioned within the guide bar channel 112 at a position relatively close to the center of the guide bar 111 and / or contact pads 103. A relationship between the spring force Fs and the contact pad force Fomay be represented as a sum of the bending moments at the pivot connection 107. For example, the moment generated by the springs 113 may generally conform to the relationship: Fs*Ls= Fo*Lo. According to the mechanical configuration of the device 110, as the tissue contact pads 103 compress inward (e.g., as pressure rises from diastole to systole), the moment arm for the spring force, Ls, becomes / approaches zero. Therefore, the contact pad force Fo also becomes / approaches zero. At low pressure tissue contact pad forces Fb represented in FIG.13, the contact pad force Fo can be represented according to equation (1) below: Fo = Fs*Ls / Lo (1)

[0115] Therefore, as the contact pads 103 compress, the force Fo becomes smaller, providing a negative spring rate. The geometry of the linkages and spring rate of the springs all contribute to the actual end performance of the device 110.

[0116] FIG.14 shows the expansion state of the device 100 after the intraluminal pressure has increased from the low-pressure condition (e.g., diastole), but has not reached the maximum pressure condition (e.g., systole). That is, FIG.14 shows the device 110 response in an intermediate pressure environment, which produces sufficient tensile force Fb in the blood vessel wall to overcome the initial high-resistance range of the device 110. As compression forces Fbfrom the blood vessel wall increase, the angle between the linkages decreases, reducing the force required to compress the tissue-contact bars 103 further. The device 110 responds dynamically to changes in blood pressure due to the changing forces Fb, promoting effective expansion and contraction of device 110 and blood vessel 31. In the intermediate compression configuration of FIG.14, the pivot connection 117 has slid to the right, away from the center of the guide bar 111 and / or contact pads 103, by some amount, increasing the dimension Lo, and therefore decreasing the compression force Foof the contact pads 103. As the intravascular pressure increases, the contact pad separation dimension di is altered / decreases in a dimension orthogonal to a lengthwise dimension of the tissue-contact pads 103 according to the negative spring rate, suchAttorney Docket No.: ADV-24166WO01 that the further the pads 103 are compressed toward one another, the less the outward spring resistance of the spring mechanism of the device 110 over at least a portion of the operational range of the spring mechanism, thereby promoting re-circularization of the blood vessel and increasing the delta in cross-sectional area of the blood vessel between low and high pressure states.

[0117] FIG.15 shows the compression state of the device 100 after the intraluminal pressure has increased to the maximum pressure condition (e.g., systole). That is, FIG.15 shows the device 110 response in a high-pressure environment, which produces sufficient tensile force Fb in the blood vessel wall to approach or achieve a circular cross-sectional shape of the blood vessel. In the compressed configuration of FIG.15, the pivot connection 117 has slid to a point 172 in the guide bar channel 112 even farther to the right and away from the center of the guide bar 111 and / or contact pads 103, further increasing the dimension Lo, and therefore further decreasing the compression force Fo of the contact pads 103. After blood pressures again subside, as shown in FIG.16, the springs 113 cause the pivot connection 117 to slide back to the left towards the center of the guide bar 111 and / or contact pads 103, thereby pushing the contact pads 103 back out to again ovalize the blood vessel. The mechanics of the device described help maintain a balance between initial resistance and ease of compression, optimizing the cyclical volume change of blood vessels and enhancing their functional performance.

[0118] FIG.17 shows a negative spring rate expander implant 210 in accordance with one or more examples. The implant device 210 is similar to the device 110 described above, with the exception that, rather than including the elongate guide linkages 118 and spring-support wings 114 as in the device 110, the device 210 includes combined spring-support guide linkages / forms 218 that connect to one another in pairs between the tissue-contact pads 203. The left and right pairs of guide linkages / forms 218 connect to one another at respective ends thereof at pivot connections 217. In some implementations, the guide forms 218 have a triangular shape, with an inwardly-facing straight edge, and angled edges that meet in a peak / apex that points outward, as shown. However, it should be understood that the guide forms 218 may have any suitable or desirable shape or form.

[0119] FIG.18 illustrates an alternative implementation of a negative spring rate expander implant device 310, which may have any of the features of other negative spring rate devices disclosed herein, wherein living hinge features are implemented in place of some or all of the pin-type pivot connections described above with respect to other examples. For example, various mechanical linkages, struts, and / or spring elements of the device 310 can be implemented in a unitary, monolithic structure formed from one or more layers of a suitable material, such asAttorney Docket No.: ADV-24166WO01 nitinol or a suitable polymer (e.g., PEEK, urethane, nylon, or elastomeric thermoplastic), rather than from multiple mechanically-coupled subcomponents.

[0120] Whereas the pivotable joints in some examples of the present disclosure are defined by pins, bushings, or discrete articulating elements, at least some of the pivoting struts / bars of the device 310 are instead formed by integrally molded or machined living hinges 301. The living hinges 301 can be formed as flexural elements defined by narrowed or necked- down regions between adjacent struts or bars, configured to provide localized bending during articulation while preserving structural integrity and fatigue life. In some examples, the living hinges 301 may be formed by locally reducing the cross-sectional thickness (e.g., by etching, laser thinning, or co-molding) at targeted inflection points along each strut / bar.

[0121] The overall geometry of device 310 in FIG.18 preserves the fundamental parallel-bar ovalization architecture described above, including the upper and lower tissue contact elements (e.g., sleds or skis) 303 that move apart and together to engage and reshape an inner wall of a blood vessel between an expanded (ovalized) configuration and a collapsed (circularized) configuration in response to changing intravascular pressures. These tissue- contacting sleds 303 can be connected by a set of cross-linking struts arranged in a parallelogram-like or scissor-type mechanism, each set of struts being pivotably connected at intersections by one or more superimposed living hinges.

[0122] The device 310 of FIG.18 can include components that correspond functionally and structurally to the various struts, bars, sleds, or the like of the previously described examples, wherein such analogous features of the device 310 may be realized as integral portions of one or more monolithic structures comprising interconnected struts, hinges, and / or spring forms. For example, the tissue-contact sleds 303 can comprise elongate, tissue- contacting elements that span transversely across the device and are configured to contact diametrically opposed inner wall regions of a target vessel. The elements 303 can be biased apart to expand the cross-section of the vessel into an oval shape, and move closer together when vessel pressure increases. In FIG.18, the contact elements 303 are shown as integrally formed with the linkage assembly via living hinges 301 positioned at either end, eliminating the need for mechanical fasteners or separate subcomponents.

[0123] The elements 305, 308 in FIG.18 are crossed struts or linkage arms that correspond to the scissor-type members described previously. These struts / bars can be pivotably joined via co-planar or vertically offset living hinges that allow each linkage to rotate independently despite overlapping or converging at common nominal pivot locations. The linkages 305, 308 can be configured to transform relative vertical movement between the upperAttorney Docket No.: ADV-24166WO01 and lower contact elements 303 into horizontal movement of associated guide or spring linkages 311, 313, thereby producing the nonlinear, negative spring rate behavior of the overall assembly.

[0124] The wing struts 318 shown in FIG.18 are analogous to the spring-coupled wings 114 of previous figures. These struts / elements can have a hinged coupling to longitudinal spring elements 313, which may be implemented as integrated struts that are formed as zig-zag or serpentine forms cut or otherwise formed into the unitary body of the device 310. The compliant elements 313 are designed to deflect and store strain energy during compression and to provide a restoring force that biases the device toward the expanded configuration. Because these spring struts 313 are integrally formed, they may include tapered cross-sections, curved webs, or variable-width beams to tailor local stiffness and / or dynamic response.

[0125] The element 311 of the device 310 provides a central longitudinal guide structure analogous to the guide bar or rail or other examples disclosed herein. In the illustrated implementation, the guide structure 311 is centrally located between the upper and lower tissue contact elements 313 and includes an integrated linear channel or track to constrain the horizontal travel of portions of the linkage assembly. In some versions, a slotted aperture or longitudinal groove may be formed in the body of the guide 311, into which integral extensions or protrusions, which may be associated with the connection of the wing struts 319, are received. In other versions, the guide constraint may be provided by elastic or curved track features that restrict lateral deflection without requiring a discrete mechanical guide channel.

[0126] At locations where multiple struts or bars intersect at a common pivot axis, such as the crossover regions of the scissor linkages or the connection points between crossbars and guide elements, the individual struts may be laterally offset or staggered / offset in an out-of- plane dimension (i.e., the z-axis dimension into / out of the page with respect to the illustrated orientation / reference of FIG.18). Such offsetting can enable each strut to rotate independently about shared pivot areas / locations while maintaining a unitary construction. In some configurations, the device may be fabricated from stacked or multilayer sheets of material, selectively bonded or processed to allow selective flexure in a z-axis direction.

[0127] The living hinges 301 of the device 310 may be formed with predefined mechanical limits, including integrated hard stops or flexure-limiting features designed to prevent over-rotation or fatigue-induced failure. Such features may include thicker hinge shoulders, stiffening ribs, or tab-style protrusions that come into contact with adjacent structure when a predefined angle of deflection is reached. The device 310 of FIG.18 advantageously can provide some or all of the mechanical behavior described in other examples herein, including a non-linear, negative-rate force-displacement relationship during cyclic vessel loading, whileAttorney Docket No.: ADV-24166WO01 offering substantial benefits in terms of manufacturability, miniaturization, fatigue resistance, and implantability, owing to its unitary construction and elimination of multi-component joints or assemblies. Additional Description of Examples

[0128] Provided below is a list of examples, each of which may include aspects of any of the other examples disclosed herein. Furthermore, aspects of any example described above may be implemented in any of the numbered examples provided below.

[0129] Example 1: A spring device comprising a first tissue-contact pad, a second tissue-contact pad oriented in a parallel with the first tissue-contact pad, and a spring mechanism coupled to the first tissue-contact pad and the second tissue-contact pad, the spring mechanism being configured to compress between the first tissue-contact pad and the second tissue-contact pad according to a negative spring rate.

[0130] Example 2: The spring device of any example herein, in particular example 1, wherein the spring mechanism comprises a deflectable bar extending between the first tissue- contact pad and the second tissue-contact pad.

[0131] Example 3: The spring device of any example herein, in particular example 1, wherein the spring mechanism comprises a plurality of pivotably-connected linkages.

[0132] Example 4: The spring device of any example herein, in particular example 3, wherein the plurality of pivotably-connected linkages comprises first and second linkages pivotably-connected to the first tissue-contact pad, and third and fourth linkages pivotably- connected to the second tissue-contact pad.

[0133] Example 5: The spring device of any example herein, in particular example 4, wherein the first and second linkages are in a crossing arrangement, and the third and fourth linkages are in a crossing arrangement.

[0134] Example 6: The spring device of any example herein, in particular example 4, wherein an end portion of the first linkage is pivotably connected to an end portion of the third linkage, and an end portion of the second linkage is pivotably connected to an end portion of the fourth linkage.

[0135] Example 7: The spring device of any example herein, in particular example 6, further comprising a first medial linkage pivotably coupled to the end portions of the first and third linkages and a medial portion of the second linkage.

[0136] Example 8: The spring device of any example herein, in particular example 1, wherein the spring mechanism comprises one or more transverse springs that are configured toAttorney Docket No.: ADV-24166WO01 expand and compress in a dimension parallel with lengths of the first and second tissue-contact pads and perpendicular with an expansion dimension of the spring mechanism.

[0137] Example 9: The spring device of any example herein, in particular example 8, wherein the spring mechanism further comprises first and second linkages coupled to first and second end portions, respectively, of the first tissue-contact pad, and third and fourth linkages coupled to first and second end portions, respectively, of the second tissue-contact pad, the first and third linkages are pivotably coupled together at a first pivot joint and the second and fourth linkages are pivotably coupled together at a second pivot joint.

[0138] Example 10: The spring device of any example herein, in particular example 9, wherein the first pivot joint and the second pivot joint are coupled to a guide bar that runs in parallel with the first and second tissue-contact pads.

[0139] Example 11: The spring device of any example herein, in particular example 10, wherein the first pivot joint is slidingly coupled within a lengthwise slot formed in the guide bar.

[0140] Example 12: The spring device of any example herein, in particular example 10, wherein the guide bar is positioned halfway between the first tissue-contact pad and the second tissue-contact pad.

[0141] Example 13: The spring device of any example herein, in particular example 10, wherein the spring mechanism further comprises a first pair of wings coupled to the first pivot joint, a second pair of wings coupled to the second pivot joint, and a pair of springs, each coupled at a first end to one of the first pair of wings and at a second end to one of the second pair of wings.

[0142] Example 14: The spring device of any example herein, in particular example 9, wherein the spring mechanism further comprises a first spring coupled between the first linkage and the third linkage, and a second spring coupled between the second linkage and the fourth linkage.

[0143] Example 15: A method of reshaping a blood vessel, the method comprising disposing a spring device in a target blood vessel, contacting an inner wall of the target blood vessel with first and second tissue-contact pads of the spring device, in a low-pressure condition of the blood vessel, resisting compression of the spring device at a first resistance when the spring device has a first expansion length, and in a high-pressure condition of the blood vessel, resisting compression of the spring device at a second resistance that is less the first resistance when the spring device has a second expansion length that is shorter than the first expansion length.Attorney Docket No.: ADV-24166WO01

[0144] Example 16: The method of any example herein, in particular example 15, wherein the spring device comprises a deflectable bar extending between the first tissue-contact pad and the second tissue-contact pad.

[0145] Example 17: The method of any example herein, in particular example 15, wherein the spring device comprises a plurality of pivotably-connected linkages.

[0146] Example 18: The method of any example herein, in particular example 15, wherein the spring device comprises one or more transverse springs that are configured to expand and compress in a dimension parallel with the first and second tissue-contact pads and perpendicular with an expansion dimension of the spring device.

[0147] Example 19: The method of any example herein, in particular example 15, wherein the spring device further comprises first and second linkages coupled to first and second end portions, respectively, of the first tissue-contact pad, and third and fourth linkages coupled to first and second end portions, respectively, of the second tissue-contact pad, wherein the first and third linkages are pivotably coupled, at a first pivot joint, together and to a first end portion of a guide bar that runs in parallel with, and between, the first and second tissue-contact pads, and the second and fourth linkages are pivotably coupled, at a second pivot joint, together and to a lengthwise channel in the guide bar.

[0148] Example 20: A spring device comprising a first contact pad, a second contact pad oriented in a parallel with the first contact pad, and a spring mechanism coupled to the first contact pad and the second contact pad, the spring mechanism being configured to compress between the first contact pad and the second contact pad according to a negative spring rate, the spring mechanism comprising a plurality of transverse springs arranged in parallel with the first and second contact pads and perpendicular to an expansion dimension of the spring mechanism, first and second linkages pivotably-connected to the first contact pad in a crossing arrangement, and third and fourth linkages pivotably-connected to the second contact pad in a crossing arrangement. An end portion of the first linkage is pivotably connected to an end portion of the third linkage, and an end portion of the second linkage is pivotably connected to an end portion of the fourth linkage.

[0149] Example 21: A method of reshaping a blood vessel using a spring implant device in response to pulsatile intravascular pressure, the method comprising: positioning a spring implant device within a lumen of a target blood vessel such that a first contact pad and a second contact pad contact an inner diameter of the target blood vessel, expanding a spring mechanism coupled to the first contact pad and the second contact pad to cause the target blood vessel to assume an ovalized shape, and permitting increasing blood pressure within the targetAttorney Docket No.: ADV-24166WO01 blood vessel to cause a wall of the target blood vessel to apply inward force on the first and second contact pads, thereby causing the spring mechanism to compress between the first contact pad and the second contact pad according to a negative spring rate.

[0150] Example 22: The method of any example herein, in particular example 21, wherein the spring mechanism comprises a plurality of transverse springs arranged in parallel with the first and second contact pads and perpendicular to an expansion dimension of the spring mechanism, first and second linkages pivotably-connected to the first contact pad in a crossing arrangement, and third and fourth linkages pivotably-connected to the second contact pad in a crossing arrangement. An end portion of the first linkage is pivotably connected to an end portion of the third linkage, and an end portion of the second linkage is pivotably connected to an end portion of the fourth linkage.

[0151] Example 23: A system for modulating blood vessel wall motion and compliance in response to pulsatile intravascular pressure, the system comprising a plurality of outwardly convex elongate tissue-contact sleds shaped to provide atraumatic tissue-contact surfaces, and a spring mechanism formed of a set of interconnected linkages and one or more springs oriented perpendicular to an operational compression dimension of the spring mechanism, the spring mechanism being coupled between the plurality of tissue-contact sleds and adapted to exhibit a negative spring rate over at least a portion of an operational compression range of the spring mechanism, such that spring compression resistance reduces as the plurality of tissue-contact sleds come closer together over the portion of the operational compression range. The spring mechanism is adapted to bias the plurality of tissue-contact sleds apart to exert opposing forces on an internal blood vessel wall to cause ovalization of the blood vessel wall and respond to increases in intravascular pressure by permitting the plurality of tissue-contact sleds to move toward each other according to the negative spring rate to promote re-circularization of the blood vessel wall during systolic loading.

[0152] Depending on the example, certain acts, events, or functions of any of the processes or algorithms described herein can be performed in a different sequence, may be added, merged, or left out altogether. Thus, in certain examples, not all described acts or events are necessary for the practice of the processes.

[0153] Conditional language used herein, such as, among others, “can,” “could,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is intended in its ordinary sense and is generally intended to convey that certain examples include, while other examples do not include, certain features, elements and / or steps. Thus, such conditional language is not generally intended to imply that features,Attorney Docket No.: ADV-24166WO01 elements and / or steps are in any way required for one or more examples or that one or more examples necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and / or steps are included or are to be performed in any particular example. The terms “comprising,” “including,” “having,” and the like are synonymous, are used in their ordinary sense, and are used inclusively, in an open-ended fashion, and do not exclude additional elements, features, acts, operations, and so forth. Also, the term “or” is used in its inclusive sense (and not in its exclusive sense) so that when used, for example, to connect a list of elements, the term “or” means one, some, or all of the elements in the list. Conjunctive language such as the phrase “at least one of X, Y and Z,” unless specifically stated otherwise, is understood with the context as used in general to convey that an item, term, element, etc. may be either X, Y or Z. Thus, such conjunctive language is not generally intended to imply that certain examples require at least one of X, at least one of Y and at least one of Z to each be present.

[0154] It should be appreciated that in the above description of examples, various features are sometimes grouped together in a single example, Figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that any claim require more features than are expressly recited in that claim. Moreover, any components, features, or steps illustrated and / or described in a particular example herein can be applied to or used with any other example(s). Further, no component, feature, step, or group of components, features, or steps are necessary or indispensable for each example. Thus, it is intended that the scope of the inventions herein disclosed and claimed below should not be limited by the particular examples described above, but should be determined only by a fair reading of the claims that follow.

[0155] It should be understood that certain ordinal terms (e.g., “first” or “second”) may be provided for ease of reference and do not necessarily imply physical characteristics or ordering. Therefore, as used herein, an ordinal term (e.g., “first,” “second,” “third,” etc.) used to modify an element, such as a structure, a component, an operation, etc., does not necessarily indicate priority or order of the element with respect to any other element, but rather may generally distinguish the element from another element having a similar or identical name (but for use of the ordinal term). In addition, as used herein, indefinite articles (“a” and “an”) may indicate “one or more” rather than “one.” Further, an operation performed “based on” a condition or event may also be performed based on one or more other conditions or events not explicitly recited.Attorney Docket No.: ADV-24166WO01

[0156] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example examples belong. It be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0157] The spatially relative terms “outer,” “inner,” “upper,” “lower,” “below,” “above,” “vertical,” “horizontal,” and similar terms, may be used herein for ease of description to describe the relations between one element or component and another element or component as illustrated in the drawings. It be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation, in addition to the orientation depicted in the drawings. For example, in the case where a device shown in the drawing is turned over, the device positioned “below” or “beneath” another device may be placed “above” another device. Accordingly, the illustrative term “below” may include both the lower and upper positions. The device may also be oriented in the other direction, and thus the spatially relative terms may be interpreted differently depending on the orientations.

[0158] Unless otherwise expressly stated, comparative and / or quantitative terms, such as “less,” “more,” “greater,” and the like, are intended to encompass the concepts of equality. For example, “less” can mean not only “less” in the strictest mathematical sense, but also, “less than or equal to.”

Claims

Attorney Docket No.: ADV-24166WO01 WHAT IS CLAIMED IS:

1. A blood vessel reshaping spring implant device comprising: a first contact pad; a second contact pad oriented in a parallel with the first contact pad; and a spring mechanism coupled to the first contact pad and the second contact pad, the spring mechanism being designed to compress between the first contact pad and the second contact pad according to a negative spring rate, the spring mechanism comprising: a plurality of transverse springs arranged in parallel with the first and second contact pads and perpendicular to an expansion dimension of the spring mechanism; first and second linkages pivotably-connected to the first contact pad in a crossing arrangement; and third and fourth linkages pivotably-connected to the second contact pad in a crossing arrangement; wherein: an end portion of the first linkage is pivotably connected to an end portion of the third linkage; and an end portion of the second linkage is pivotably connected to an end portion of the fourth linkage.

2. The spring device of claim 1, wherein the first linkage and the third linkage are connected via a rotating pin connection.

3. The spring device of claim 1, wherein the first linkage and the third linkage are connected via a living hinge.

4. A blood vessel reshaping spring implant device comprising: a first tissue-contact pad; a second tissue-contact pad oriented in a parallel orientation with the first tissue- contact pad; and a spring mechanism coupled to the first tissue-contact pad and the second tissue- contact pad, the spring mechanism being designed to compress between the first tissue- contact pad and the second tissue-contact pad according to a negative spring rate.Attorney Docket No.: ADV-24166WO01 5. The spring device of claim 4, wherein the spring mechanism comprises a deflectable bar extending between the first tissue-contact pad and the second tissue-contact pad.

6. The spring device of claim 4 or claim 5, wherein the spring mechanism comprises a plurality of pivotably-connected linkages.

7. The spring device of claim 6, wherein the plurality of pivotably-connected linkages comprises: first and second linkages pivotably-connected to the first tissue-contact pad; and third and fourth linkages pivotably-connected to the second tissue-contact pad.

8. The spring device of claim 7, wherein: the first and second linkages are in a crossing arrangement; and the third and fourth linkages are in a crossing arrangement.

9. The spring device of claim 7, wherein: an end portion of the first linkage is pivotably connected to an end portion of the third linkage; and an end portion of the second linkage is pivotably connected to an end portion of the fourth linkage.

10. The spring device of claim 9, further comprising a first medial linkage pivotably coupled to the end portions of the first and third linkages and a medial portion of the second linkage.

11. The spring device of claim 4 or claim 5, wherein the spring mechanism comprises one or more transverse springs that are designed to expand and compress in a dimension parallel with lengths of the first and second tissue-contact pads and perpendicular with an expansion dimension of the spring mechanism.

12. The spring device of claim 11, wherein the spring mechanism further comprises: first and second linkages coupled to first and second end portions, respectively, of the first tissue-contact pad; and third and fourth linkages coupled to first and second end portions, respectively, of the second tissue-contact pad; wherein:Attorney Docket No.: ADV-24166WO01 the first and third linkages are pivotably coupled together at a first pivot joint; and the second and fourth linkages are pivotably coupled together at a second pivot joint.

13. The spring device of claim 12, wherein the first pivot joint and the second pivot joint are coupled to a guide bar that runs in parallel with the first and second tissue-contact pads.

14. The spring device of claim 13, wherein the first pivot joint is slidingly coupled within a lengthwise slot formed in the guide bar.

15. The spring device of claim 13, wherein the guide bar is positioned halfway between the first tissue-contact pad and the second tissue-contact pad.

16. The spring device of claim 13, wherein the spring mechanism further comprises: a first pair of wings coupled to the first pivot joint; a second pair of wings coupled to the second pivot joint; and a pair of springs, each coupled at a first end to one of the first pair of wings and at a second end to one of the second pair of wings.

17. The spring device of claim 12, wherein the spring mechanism further comprises: a first spring coupled between the first linkage and the third linkage; and a second spring coupled between the second linkage and the fourth linkage.

18. A blood vessel reshaping spring implant device comprising: a first tissue-contact sled oriented in a first dimension; a second tissue-contact sled oriented in the first dimension; a linkage network connected between the first tissue-contact sled and the second tissue-contact sled, the linkage network manipulable to alter a distance between the first tissue-contact sled and the second tissue-contact sled in a second dimension orthogonal to the first dimension; and one or more springs extending in the first dimension and coupled between respective pairs of struts of the linkage network, the one or more springs being designed to resist compression of the first tissue-contact sled and the second tissue-contact sled towards one another according to a negative spring rate.Attorney Docket No.: ADV-24166WO01 19. A method of reshaping a blood vessel using a spring implant device in response to pulsatile intravascular pressure, the method comprising: positioning a spring implant device within a lumen of a target blood vessel such that a first contact pad and a second contact pad contact an inner diameter of the target blood vessel; expanding a spring mechanism coupled to the first contact pad and the second contact pad to cause the target blood vessel to assume an ovalized shape; and permitting increasing blood pressure within the target blood vessel to cause a wall of the target blood vessel to apply inward force on the first and second contact pads, thereby causing the spring mechanism to compress between the first contact pad and the second contact pad according to a negative spring rate.

20. The method of claim 19, wherein the spring mechanism comprises: a plurality of transverse springs arranged in parallel with the first and second contact pads and perpendicular to an expansion dimension of the spring mechanism; first and second linkages pivotably-connected to the first contact pad in a crossing arrangement; and third and fourth linkages pivotably-connected to the second contact pad in a crossing arrangement; wherein: an end portion of the first linkage is pivotably connected to an end portion of the third linkage; and an end portion of the second linkage is pivotably connected to an end portion of the fourth linkage.

21. A system for modulating blood vessel wall motion and compliance in response to pulsatile intravascular pressure, the system comprising: a plurality of outwardly convex elongate tissue-contact sleds shaped to provide atraumatic tissue-contact surfaces; and a spring mechanism formed of a set of interconnected linkages and one or more springs oriented perpendicular to an operational compression dimension of the spring mechanism, the spring mechanism being coupled between the plurality of tissue-contact sleds and adapted to exhibit a negative spring rate over at least a portion of an operational compression range of the spring mechanism, such that spring compression resistanceAttorney Docket No.: ADV-24166WO01 reduces as the plurality of tissue-contact sleds come closer together over the portion of the operational compression range; wherein the spring mechanism is adapted to bias the plurality of tissue-contact sleds apart to exert opposing forces on an internal blood vessel wall to cause ovalization of the blood vessel wall and respond to increases in intravascular pressure by permitting the plurality of tissue-contact sleds to move toward each other according to the negative spring rate to promote re-circularization of the blood vessel wall during systolic loading.

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