Inhibiting platelet absorption

Abstract

The present disclosure relates to inhibition of platelet absorption. Cardiovascular grafts with highly reduced thrombosis are provided. The cardiovascular graft is an electrospun nonwoven web produced from a supramolecular polymer of large diameter fibers. The cardiovascular graft can be implanted in a human body as a vascular graft to allow blood vessel bypass / reconstruction, or repeated venous access for dialysis treatment, as well as other small diameter vascular disorders.

Description

[0001] This application is a divisional application of Chinese Patent Application No. 201880023154.9. Invention Field

[0002] This invention relates to electrospun coatings, grafts, or materials that inhibit thrombus formation. Background of the Invention

[0003] Vascular diseases involving vessels with a lumen diameter of 6 mm or less constitute the majority of cases requiring clinical intervention. In many such cases, the preferred intervention is revascularization or bypass surgery, utilizing autologous or artificial vascular grafts harvested from other parts of the patient. Such synthetic grafts come in various sizes and constructions and typically contain small amounts of medical polymers, such as polytetrafluoroethylene (PTFE) and polyethylene terephthalate (PET), within a braided or dendritic assembly.

[0004] In clinical settings, the predominantly observed failure pattern of synthetic vascular grafts is progressive intimal hyperplasia at the venous (outflow) anastomosis, leading to reduced blood flow and thrombosis. This is attributed to the connection between the graft and the natural blood vessel, differences in the mechanical properties (e.g., compliance) between the graft material and the natural tissue, and the turbulent flow caused by the foreign body nature of the graft material in contact with circulating blood, resulting in thrombus formation. However, the precise mechanisms of thrombosis remain a major focus of current research in this field.

[0005] Hemostasis encompasses a vast array of biological processes that stop bleeding from damaged tissue or blood vessels. The primary mechanism of hemostasis involves the activation and adhesion of circulating coagulation cells (also known as platelets). Within seconds of tissue damage, released proteins cause platelets to "activate," expressing adhesion structures on their surface and binding to the site of injury, initiating the formation of an "embolism" to prevent further blood loss. Additionally, activated platelets release further chemical signals in a cascade effect, recruiting and activating other circulating platelets, which can then bind to the site of injury or to other activated platelets.

[0006] Intravascular thrombosis arises from pathological interference with the hemostasis process. Typically, platelet activation, adhesion, and aggregation occur within the vessel due to turbulence, interactions between foreign bodies and circulating platelets, release of signaling proteins from the damaged vessel wall, or other reasons. When these platelets are activated and subsequently activate other circulating platelets adhering to the growing thrombus, the vessel becomes occluded, restricting or completely blocking blood flow. These conditions are exacerbated in vessels with low flow rates (typically below 600 mL / min). This is because circulating platelets remain near the growing thrombus for a longer period, and the reduced flow decreases the shear stress on the adhering platelets, thus reducing the likelihood of the activated platelets being cleared.

[0007] This invention advances the field by providing vascular grafts with significantly reduced thrombotic risk. Summary of the Invention

[0008] This invention provides cardiovascular grafts for reducing thrombosis, such as arteriovenous grafts for dialysis access or coronary artery bypass grafts. The cardiovascular graft has a tubular structure with an inner wall made of a fibrous network of supramolecular compounds having hard blocks covalently bonded to soft blocks. The hard blocks contain a 2-ureido-4[1H]-pyrimidinone (UPy) compound. The hard block may further include a chain extender, wherein the chain extender is in the range of 1 to 5 for the UPy compound, or more preferably 1.5 to 3. The soft block is a biodegradable polyester, polyurethane, polycarbonate, poly(orthoester), polyphosphate, polyanhydride, polyphosphazene, polyhydroxyalkanoate, polyvinyl alcohol, polyacrylate, or any combination thereof. The molecular weight of the soft block is between 500 and 3000 Da.

[0009] The fiber network is a bioresorbable electrospun nonwoven fiber network with fibers having an average fiber diameter of 1-10 micrometers. The tubular structure has an inner diameter between 2-8 mm and a wall thickness of 200-900 micrometers.

[0010] In one variant of this implementation, the thickness of the inner wall is at least 20 micrometers, and the average pore diameter is between 5 and 10 micrometers.

[0011] In another variant of this embodiment, the inner wall has pores with an average pore diameter between 5 and 8 micrometers and an average porosity in the range of 50 to 80%.

[0012] In another variant of this implementation, the tubular structure has an inner diameter between 3 and 6 mm and a wall thickness of 200 to 800 micrometers.

[0013] In another variant of this implementation, the tubular structure has an inner diameter between 4 and 8 mm and a wall thickness of 300 to 900 micrometers.

[0014] In another variation of this implementation, the tubular structure has an inner diameter of 5 mm or less.

[0015] In another variant of this embodiment, the fibers have an average fiber diameter of 4-8 micrometers.

[0016] In another variant of this embodiment, the fibers have an average fiber diameter of 4-6 micrometers.

[0017] In another variant of this implementation, the inner layer of the graft is hydrophobic, with a water contact angle between 110 and 140 degrees.

[0018] In another variation of this embodiment, the tubular structure has an outer wall reinforced by a braided structure, polymer strands, compounds, or a combination thereof to provide resistance against cardiovascular graft collapse.

[0019] In yet another variation of this implementation, the cardiovascular graft may include α IIb β3 inhibitors.

[0020] In another variation of this implementation, the cardiovascular graft can be combined with α IIb β3 inhibitors are available orally, intravenously, or in combination with other administration methods. Brief description of the attached diagram

[0021] Figure 1A-1C SEM images (10,000x magnification) of platelet adhesion and activation on supramolecular polymer (SP) micron and submicron electrospun fibers according to an exemplary embodiment of the present invention are shown, compared to PTFE nonwoven fabric. Figure 1A High-magnification images of platelet adhesion and spreading behavior on SP electrospun fibers with an average diameter of 4-6 μm are shown. Figure 1B A high-magnification image of platelet adhesion and spreading behavior on SP electrospun fibers with an average diameter of <1 μm is shown. Figure 1C High-magnification images of platelet adhesion and spreading behavior on nonwoven PTFE fibers with an average diameter of <1 μm are shown.

[0022] Figure 2A -C illustrates platelets spread on SP micron and submicron fibers compared to PTFE nonwoven materials, according to an exemplary embodiment of the present invention. Figure 2A A low-magnification magnified image of platelet spreading behavior on SP electrospun fibers with an average diameter of 4-6 μm is shown. Figure 2BA low-magnification magnified image of platelet spreading behavior on SP electrospun fibers with an average diameter <1 μm is shown, and Figure 2C A low-magnification magnified image of platelet spreading behavior on nonwoven PTFE fibers with an average diameter of <1 μm is shown.

[0023] Figure 3A -C illustrates a method for analyzing the surface porosity of a test material after blood perfusion, according to an exemplary embodiment of the present invention. Figure 3A Original SEM image ( Figure 3B (From ") Figure 3A The cropped image with enhanced contrast ( Figure 3C )from" Figure 3B The generated binary image's automatic thresholding by ImageJ results in... Figure 3C The absolute black / white pixels show a total porosity of 27.35%.

[0024] Figure 4 This illustration shows a reduction in porosity observed in the test material under SEM after blood perfusion, as a percentage of the initial porosity, due to platelet aggregation / spreading, according to an exemplary embodiment of the invention.

[0025] Figure 5 An exemplary embodiment of the invention is shown, showing activated α in perfused blood from a test surface. IIb Detection of β3.

[0026] Figure 6 SEM images at various magnifications of platelet adhesion to electrospun SP materials and PTFE nonwoven materials with and without abciximab, according to exemplary embodiments of the present invention, are shown.

[0027] Figure 7A -C shows a magnified SEM image (250X) of an explanted sample from an animal treated with the following drug, according to an exemplary embodiment of the present invention: Figure 7A )heparin, Figure 7B Heparin and aspirin, and Figure 7C Heparin, aspirin, and clopidogrel (Plavix).

[0028] Figure 8A -C illustrates a 6mm ( ) 6 months after implantation according to an exemplary embodiment of the present invention. Figure 8A -B) and 7mm ( Figure 8C Angiography of the carotid artery graft, with arrows indicating distal (top) and proximal (bottom) anastomoses.

[0029] Figure 9The graft inner diameters of 6 mm and 7 mm intercarotid grafts, measured immediately before distal anastomosis within 36 weeks, are shown according to an exemplary embodiment of the present invention.

[0030] Figure 10 Data on pore size in incremental infusion on small-diameter grafts according to an exemplary embodiment of the invention are shown, demonstrating that the size of most pores is between 5 and 10 micrometers. The average pore size of cardiovascular grafts according to the invention differs from that observed or expected in pulmonary valves.

[0031] Figure 11 The arrangement of fibers according to an exemplary embodiment is shown to increase fatigue resistance, expressed as the number of cycles until the supramolecular polymer valve fails in an accelerated wear tester (AWT) under aortic conditions according to ISO 5840. Detailed Implementation

[0032] This invention relates to cardiovascular grafts with significantly reduced thrombotic activity, produced by electrospun webs made from supramolecular polymers (SPs). Preferably, the vascular grafts are nonwoven webs and / or large-diameter fibers. The invention also relates to methods for producing such grafts by electrospinning. Furthermore, the invention relates to implanting vascular grafts into the human body to allow for vascular bypass / reconstruction, or re-establishment of venous access for dialysis, and other small-diameter vascular disorders.

[0033] By designing cardiovascular grafts as defined below, the inventors have demonstrated and described in this paper the unexpected platelet behavior of vascular grafts produced by SP. In stark contrast to widely used "biocompatible" materials (such as PTFE), platelet activation and adhesion were observed without significant spreading, aggregation, or pseudopodia formation. Such results demonstrate that this material is well-suited for small-diameter grafts, where thrombosis and / or stenosis is a critical concern. Furthermore, the SP material used is bioresorbable and allows for tissue infiltration and regrowth. This ensures a significant reduction in the risk of long-term remodeling, neointimal formation, and persistent inflammatory responses leading to vascular stenosis.

[0034] Limitations on the antithrombotic effect of cardiovascular grafts

[0035] The thrombolytic effect of this cardiovascular graft is defined by a tubular structure with an inner wall made of a fibrous network of supramolecular compounds having hard blocks covalently bonded to soft blocks. The hard blocks include 2-ureido-4[1H]-pyrimidinone (UPy) compounds. The fibrous network is a bioresorbable electrospun nonwoven fiber network with fibers having an average fiber diameter of 1-10 micrometers. The tubular structure has an inner diameter between 2-8 mm and a wall thickness of 200-900 micrometers.

[0036] Changes in cardiovascular grafts can be defined by the following structural aspects, whether used alone or in combination (if applicable): ● The inner wall has a thickness of at least 20 micrometers and the average pore diameter is between 5 and 10 micrometers.

[0037] ● The inner wall has pores with an average pore diameter between 5 and 8 micrometers and an average porosity in the range of 50 to 80%.

[0038] ● Tubular structure with an inner diameter between 3 and 6 mm and a wall thickness of 200 to 800 micrometers.

[0039] ● Tubular structure with an inner diameter between 4 and 8 mm and a wall thickness of 300 to 900 micrometers.

[0040] ● Tubular structure with an inner diameter of 5 mm or less.

[0041] ● Fibers with an average fiber diameter of 4-8 micrometers or an average fiber diameter of 4-6 micrometers.

[0042] ● Soft blocks, including biodegradable polyesters, polyurethanes, polycarbonates, poly(orthoesters), polyphosphates, polyanhydrides, polyphosphazenes, polyhydroxyalkanoates, polyvinyl alcohol, polyacrylates, or any combination thereof.

[0043] ● Soft blocks, with molecular weights between 500 and 3000 Da.

[0044] ● Hard blocks, comprising chain extenders, wherein the chain extender is in the range of 1 to 5 for the UPy compound, or more preferably 1.5 to 3.

[0045] ● The inner layer of the graft is hydrophobic, with a water contact angle between 110 and 140 degrees.

[0046] ● Cardiovascular grafts, which are arteriovenous grafts or coronary artery bypass grafts used in dialysis access.

[0047] ● A tubular structure with an outer wall reinforced by braided structures, polymer strands, compounds, or combinations thereof to provide resistance against cardiovascular graft collapse.

[0048] ● Cardiovascular grafts, containing α IIb β3 inhibitors are more likely to exhibit non-thrombotic effects.

[0049] ●Cardiovascular grafts and α IIb When administered in combination with a β3 inhibitor, the inhibitor is more likely to exhibit non-thrombotic effects.

[0050] The supramolecular polymers (SPs) mentioned herein may include a ureido-pyrimidinone (UPy) tetrahydrobonded motif and polymer backbone, such as those selected from biodegradable polyesters, polyurethanes, polycarbonates, poly(orthoesters), polyphosphates, polyanhydrides, polyphosphazenes, polyhydroxyalkanoates, polyvinyl alcohol, and polyfumarate. Examples of polyesters are polycaprolactone, poly(L-lactide), poly(DL-lactide), poly(valerol), polyglycolic acid, polydioxanone, and their copolyesters. Examples of polycarbonates are poly(trimethylene carbonate), poly(dimethyltrimethylene carbonate), and poly(hexamethylene carbonate).

[0051] If materials are carefully selected and processed to ensure the desired surface properties, reduced platelet adhesion can also occur with alternative non-supramolecular polymers. These polymers can be biodegradable or non-biodegradable polyesters, polyurethanes, polycarbonates, poly(orthoesters), polyphosphates, polyanhydrides, polyphosphazenes, polyhydroxyalkanoates, polyvinyl alcohol, and polyfumarate. Examples of polyesters are polycaprolactone, poly(L-lactide), poly(DL-lactide), poly(valerol), polyglycolic acid, polydioxanone, and their copolyesters. Examples of polycarbonates are poly(trimethylene carbonate), poly(dimethyltrimethylene carbonate), and poly(hexamethylene carbonate).

[0052] Furthermore, the morphology of the graft cavity surface also plays an important role in thrombotic characteristics. In vitro experiments using human blood have shown that the fiber diameter of the nonwoven mesh is critical, with larger diameter fibers of 4-6 µm being preferred over smaller fibers.

[0053] Platelet aggregation on scaffolds made of supramolecular polymers

[0054] Samples of electrospun SP materials with various surface morphologies were coated onto PET plates coated with indium tin oxide (ITO). These samples were exposed to human blood perfusion fluid containing 3.2% citrate via a flow cell at a constant shear rate to inhibit thrombin activation, allowing for a specific study of platelet behavior. After 30 minutes of perfusion, the flow cell was removed, and the material surfaces were fixed using ethanol dehydration and characterized by scanning electron microscopy (SEM). A negative control on bare PET-ITO sheets showed no significant platelet adhesion. A positive control on collagen-coated PET-ITO sheets showed significant platelet cluster formation. All experiments were performed in triplicate with multiple healthy blood donors.

[0055] Compared to commercially available PTFE nonwoven materials, electrospun SP webs exhibited significantly reduced platelet activity. This effect was most pronounced on larger diameter fibers, but the reduction in spreading was also evident on submicron fibers, with a morphology similar to PTFE nonwovens. SEM images of platelet adhesion to SP fibers and nonwoven PTFE at high magnification (10000 X) are shown. Platelet adhesion and activation to the fibers are clearly observed, but platelet aggregation and spreading are significantly reduced compared to PTFE nonwovens. SEM images of all substrates at lower magnification (1000 X) are also shown, indicating reduced platelet spreading and aggregation over a larger area.

[0056] Compared to commercially available biocompatible materials with similar morphology, UPy-based electrospun fibers exhibited reduced platelet spreading and aggregation in human blood. The observed platelet behavior was anomalous and highly correlated with bioresorbable devices intended to achieve tissue remodeling. The presence of an activated platelet coating stimulated subsequent remodeling phases and epidermal regeneration. However, the presence of an active platelet layer was frequently accompanied by severe thrombotic reactions, leading to rapid occlusion of small-diameter conduits composed of synthetic materials. Therefore, the demonstrated platelet reaction represents an ideal scenario for the formation of new tissue on a bioresorbable substrate, theoretically leading to a completely thrombosis-free biological surface. Furthermore, the supramolecular chemistry allows for a degree of flexibility in the mechanical properties of the synthetic polymer, thereby increasing the tunability of device performance to further improve blood reactivity.

[0057] The quantification of the surface coverage of blood products on test materials was based on the analysis of the decrease in total surface porosity observed under SEM. The analysis was performed using ImageJ software, and its stages were... Figure 3A The process is outlined in section -D. In short, SEM images are prepared by cropping, contrast enhancement, and conversion to a binary image (containing only black or white pixels). This binary image is then analyzed using ImageJ's "thresholding" function, which calculates the total number of black pixels in the image. This process was performed on three characteristic SEM images of the sample surface before blood perfusion, and surface SEM images after blood perfusion are also reported, along with changes in porosity. Figure 4 The study showed a decrease in porosity in all material samples after surface perfusion due to the surface being covered by blood products.

[0058] In addition to using thrombin-inactivated human blood for blood flow experiments, static experiments were also performed using whole blood. In these experiments, blood from healthy donors was placed in 96-well plates along with the test material samples. The sample chambers were incubated at 37°C for 20 minutes in a shaking incubator before the blood was removed by pipette and characterized by flow cytometry.

[0059] These experiments showed that, compared to blood samples exuded from nonwoven PTFE, the levels of glycoprotein α in blood incubated with electrospun SP materials were significantly lower. IIb β3 unexpectedly reduced cell adhesion by 50%, while no reduction was observed in another adhesion glycoprotein, P-selectin. Figure 5 ).

[0060] By making integrin α IIb β3 inactivation effectively inhibits the adhesion of platelets to supramolecular polymer fibers.

[0061] Based on cell counting results from whole blood experiments on various samples, it is speculated that platelets are activated and adhere to electrospun SP fibers, exhibiting a strong and particularly independent dependence on integrin, α. IIb β3.

[0062] To determine the adhesion mechanism, abciximab (ReoPro), an alpha-123 α-glucanone, was used. IIb A β3 inhibitor was added to healthy citric acid-contaminated blood at a clinically relevant dose of 10 µg / ml. Blood was then perfused for 30 minutes onto samples of electrospun nonwoven SP material with fiber diameters of 4–6 µm and nonwoven PTFE samples using a controlled shear rate flow chamber. After flow, the samples were fixed and imaged using scanning electron microscopy to directly observe platelet adhesion. Compared to the control, the addition of abciximab (ReoPro) resulted in a significant reduction in platelet adhesion. Figure 6 Furthermore, this effect is significantly amplified compared to PTFE nonwoven fiber materials. The ability to almost completely inhibit platelet adhesion to synthetic polymer materials (XP) with a single clinically available drug (ReoPro) at physiologically relevant doses is considered a novel finding with potential applications in a range of blood contact applications.

[0063] The platelet counts calculated from the SEM images above onto the test materials showed a 97% reduction in SP electrospun materials (226 to 6) and a 78% reduction in PTFE nonwovens (236 to 51) after the addition of abciximab. Based on the apparent specific efficacy of abciximab as a platelet uptake inhibitor on electrospun SP materials, and the above data regarding glycoprotein IIb / IIIa levels after perfusion and in vitro thrombosis assays, it is proposed that any antiplatelet chemotherapeutic agent with a mechanism of action targeting glycoprotein IIb / IIIa will have a similar amplification effect on SP electrospun materials. The mechanism of this amplification is unclear, but it is presumed to be driven by the dissimilarity of apparent surface charge density and / or associated hydrophobicity of SP electrospun materials. It is known that surface charge density, or the charge per unit area of ​​material surface, affects protein binding. This effect arises from the attraction / repulsion generated from surfaces with different / similar charges due to the charge distribution within these proteins. Furthermore, materials exhibiting significant surface roughness may further amplify or exacerbate this effect, as the total charge density increases in curvature regions, such as microscale protrusions from flat surfaces and the nanoscale roughness of these surfaces and protrusions. This effect of surface charge on platelet activation has been established in the literature on dendritic synthetic polymers (Dobrovolskaia et al., 2012, Nanoparticle size and surface charge determine effects of PAMAM dendrimers on human platelets). in vitro ). Molecular pharmaceutics .2012;9(3):382-393. doi:10.1021 / mp200463e).

[0064] Furthermore, the inclusion of chemotherapeutic agents, such as abciximab (US20100280594), in electrospun fibers and polymer coatings is known. Due to the significant specific interaction between SP electrospun materials and glycoprotein IIb / IIIa inhibitors (especially abciximab), this approach can achieve highly effective antithrombotic effects. Combinations of bioresorbable electrospun supramolecular constructs with abciximab or other compounds targeting glycoprotein IIb / IIIa inhibition are expected to be particularly beneficial, as such combinations can enable the regeneration of human tissue in applications such as coronary artery bypass grafting, which was previously impossible. It is foreseeable that other methods of including such chemotherapeutic agents are possible, including but not limited to covalent or otherwise incorporated into electrospun fiber materials, absorbed on the fiber surface, or contained in carrier materials coated onto nonwoven surfaces. Another possibility is the oral, intravenous, or other administration of the chemotherapeutic agent. This can be done before, during, or after implantation of cardiovascular grafts.

[0065] The role of platelets in thromboembolism of small-diameter grafts made from electrospun supramolecular polymer (SP) materials in large animal models

[0066] To demonstrate the role of platelets in thrombotic occlusion of small-diameter grafts made of electrospun SP material in vivo, 4 mm grafts were implanted as coronary artery bypass grafts in a sheep model, and various pharmacological treatment strategies targeting platelet inhibition were employed. The combination of relatively low flow rates (typically <120 mL / min), tortuous graft paths, and small diameters was expected to provide the worst-case scenario for the synthetic grafts, thus necessitating a rigorous evaluation of the efficacy of in vivo antiplatelet therapy.

[0067] Prior to surgery, animals were treated with heparin, heparin-aspirin, and heparin-aspirin-clopidogrel combinations. Since heparin is a recognized inhibitor of the thrombin-driven coagulation pathway, all observed coagulation responses could be considered platelet-driven. Both aspirin and clopidogrel act on secondary platelet activation—the ability of activated platelets to activate other circulating platelets—with clopidogrel being a more potent agent. Grafts were implanted 4 hours prior to transplantation, fixation, and histological and SEM characterization. As can be seen in Figure 7, the use of increased platelet-inhibiting therapy resulted in a significant reduction in thrombus formation on the nonwoven surface of the graft. These results suggest that platelet activation and aggregation are the primary mechanisms of thrombus formation in vivo.

[0068] Long-term thrombotic response of small-diameter grafts of SP electrospun materials in large animal models

[0069] To demonstrate the long-term thrombotic response of small-diameter grafts containing SP electrospun material, 6- and 7-mm grafts were implanted as intercarotid artery implants in sheep models (n = 4 and n = 2, respectively). Immediately after implantation, angiography and ultrasound were performed, followed by ultrasound examinations at days 0, 7, 14, 21, and 28, and then monthly, to assess graft patency. Changes in the proximal, distal, and mid-segment luminal diameter of the graft were assessed during this period. At the 6-month timepoint, half of the test animals were sacrificed and the grafts were removed for overall histological characterization; the remaining animals were scheduled for sacrifice and interpretation at 12 months.

[0070] At the start of the surgery, the animals were treated with 0.4 mL of Lovenox® enoxaparin (low molecular weight heparin) twice daily for 90 days, and with 125 mg of aspirin once daily until sacrifice.

[0071] As can be seen in Figure 8, angiography showed good patency of the graft at the 6-month time point before implantation. Figure 9 The data shows the diameter of the distal anastomosis (most prone to thrombosis) throughout the study.

[0072] Methods for preparing supramolecular polymers

[0073] In one exemplary embodiment, a supramolecular polymer can be prepared using one of the formulations described in U.S. Provisional Application 62 / 611431, filed December 28, 2017, the entire contents of which are incorporated herein by reference and priority is claimed hereof.

[0074] According to these formulations, supramolecular compounds are defined as hard blocks covalently bonded to soft blocks. The hard blocks are based on the UPy moiety. The soft blocks form the backbone of the supramolecular compound. Polycarbonate (PC) is used because it exhibits surprising benefits for the purposes and objectives of this invention, particularly compared to polycaprolactone.

[0075] The ratio between soft and hard blocks affects material properties. Here, we describe the significant impact of component ratios within the hard block portion on properties such as durability. We describe specific combinations of ratios within the hard block with the ratio of polymer lengths used to form the soft block to improve mechanical properties (durability). Specifically, polycarbonates in the molecular weight range of 500–2000 Da offer enhanced durability and reduced fatigue compared to, for example, polycaprolactone. The hard block consists of an Upy component, a diisocyanate, and a chain extender. For the ratio (R) of the 2-ureido-4[1H]-pyrimidinone (UPy) compound and the chain extender in the hard block, the chain extender to UPy compound ranges from 1.5 to 3.

[0076] Synthesis of supramolecular polymers

[0077] PCL polymer-XP1

[0078] A telechelic hydroxyl-terminated polycaprolactone with a molecular weight of 800 g / mol (30.0 g, 37.5 mmol, vacuum dried), 1,6-hexanediol (4.4 g, 37 mmol), and UPy monomer (6.3 g, 37 mmol) were dissolved in anhydrous DMSO (105 mL) at 80 °C. Hexamethylene diisocyanate (18.8 g, 111.5 mmol) was added to the reaction mixture with stirring, followed by one drop of tin dioctanoate. The reaction mixture was stirred overnight at 80 °C. The next day, the reaction mixture was cooled to 25 °C, and its viscosity was reduced by adding additional DMSO to precipitate the mixture in water. The polymer was collected as a white, elastic solid, which was redissolved in chloroform / methanol (7 / 3 v / v) and reprecipitated in excess methanol. Vacuum drying at 50 °C yielded a clear, elastic solid. SEC (THF, PS-standard): Mn = 13 kg / mol, D = 1.6. See also WO2014185779.

[0079] PC polymer

[0080] Polymers made of polycarbonate with molecular weights ranging from 500 to 3000 g / mol were synthesized in a manner similar to XP1. The ratios were varied according to the length of the polycarbonate and the desired proportions between the components. The molar ratios can be expressed as follows: A (polycarbonate) is fixed at 1; B (chain extender) varies between 0 and 3; D (upy) varies between 0.3 and 2; and C is always equal to 0.8 to 1.2 times the total molar amount of A plus B plus D. The molar ratio B / D is denoted as R. Table 1 provides a non-exhaustive list of examples of supramolecular polymers obtained according to the above description.

[0081] Table 1: List of Materials

[0082] For example, a feature that can affect durability is the arrangement of fibers within the stent. A preferred fiber arrangement is circumferentially arranged around an imaginary axis of the implant, wherein, in the case of a tubular implant, this axis points in the direction of blood flow. Figure 11 We can clearly see that this arrangement increases fatigue resistance. The arrangement, defined as having a linear elastic stiffness ratio change of up to 8:1 between the preferred fiber direction and perpendicular to the preferred fiber direction. Although... Figure 11 The example is based on an arrangement comparison in electrospun supramolecular polymer heart valves, but it can be expected that the same principle will apply to cardiovascular grafts.

[0083] Additional Information

[0084] 1. Scope (Durability Focus)

[0085] ● The ratio R varies between 0 and 3. When the ratio is higher than 1.5, enhanced / optimal fatigue resistance is achieved.

[0086] ● The PC length varies between 500 and 3000 g / mol. Enhanced / optimal fatigue resistance is achieved when the PC length is 1000.

[0087] ● The mass ratio of chain extenders varies between 0 and 15. Higher HD ratios (above 9 w%) yield enhanced / optimal fatigue resistance.

[0088] 2. Support structure

[0089] ● The thickness can vary from a few micrometers to a few millimeters, but the preferred thickness is between 200 and 800 micrometers, or even more preferably between 250 and 550 (average thicknesses of 300 and 500 provide good results).

[0090] ● Fiber diameters can be obtained in a wide range from 1 µm to 20 µm. Preferably, we operate in the range of 3-15 μm, and even more preferably in the range of 4-10 μm.

[0091] ● Fiber arrangement is another parameter for improving durability, especially when electrospinning results in a random 1:2 (circumferential:axial) distribution (meaning the axial stiffness is twice the circumferential stiffness). Fibers can be arranged from an infinite :1 to a 1:2 ratio. Ratios of 2:1 to 8:1 are preferred as they provide a good improvement in durability.

[0092] ● Pore size: The matrix material contains pores with a diameter of 1-300 micrometers, preferably 5-100 micrometers.

[0093] ●Porosity: The matrix material contains a fibrous network with a porosity between 50% and 80%.

[0094] Methods for manufacturing cardiovascular grafts

[0095] In one exemplary embodiment of the fabrication of cardiovascular grafts, a supramolecular polymer (SP) material, such as that obtained in one of the formulations described below, is dissolved to a concentration of 11.5% by weight in a solvent mixture of chloroform and hexafluoroisopropanol. This solution is delivered via a syringe pump to a blunt-tipped stainless steel needle maintained between 5 and 10 kV, creating an electrostatically driven agitating nozzle. This nozzle is drawn into a cylindrical collector, which is charged to a negative voltage between 1 and 4 kV, thereby forming a highly porous fibrous nonwoven coating. After depositing an electrospun polymer material to a thickness of 0.5 mm, it can be removed from the collector device by separation with a soft-tipped scraper, resulting in an electrospun tubular graft with a wall thickness of 0.5 mm.

[0096] in conclusion

[0097] The data described herein demonstrate the unexpected effects of the cardiovascular grafts of the present invention on platelet activation, adhesion, and spreading. Platelet-driven thrombosis is quantitatively reduced on cardiovascular grafts compared to known biocompatible synthetic polymers (e.g., Figure 4 For electrospun SP materials, porosity was reduced by 27%, and for PTFE, by 59%. Furthermore, a previously unknown and unexpected dependence on single-cell adhesion proteins glycoproteins IIb / IIIa was proposed. It is speculated that this unexpected interaction is based on the surface charge of the SP electrospun fibers. This dependence of platelet adhesion on specific glycoproteins means that platelet-driven thrombosis is strongly influenced by a single chemotherapeutic agent, in contrast to known biocompatible synthetic polymers (e.g., PTFE), which require broader inhibition of cell adhesion molecules. Further investigation is needed to propose combining this chemotherapeutic approach with the electrospun fibers of SP materials or for surface absorption to provide site-specific and highly effective platelet inhibition.

Claims

1. Use of cardiovascular grafts in the preparation of grafts with reduced platelet adhesion, the cardiovascular grafts comprising: a tubular structure having an inner wall made of a fibrous network of a supramolecular compound having hard blocks covalently bonded to soft blocks, wherein the hard blocks comprise 2-ureido-4[1H]-pyrimidinone (UPy) compounds, wherein the fibrous network is a bioresorbable electrospun nonwoven fiber network having fibers with an average fiber diameter of 1-10 micrometers, and wherein the tubular structure has an inner diameter of 2-8 mm and an inner wall thickness of 20-900 micrometers, wherein the soft blocks comprise polyurethane, polycarbonate, poly(orthoester), polyphosphate, polyanhydride, polyphosphazene, polyhydroxyalkanoate, polyvinyl alcohol, polyacrylate, or any combination thereof.

2. The use as claimed in claim 1, wherein the cardiovascular graft further comprises α IIb β3 inhibitors.

3. The use as claimed in claim 1, wherein the inner wall has a thickness of 200-900 micrometers and pores with an average pore size between 5 and 10 micrometers.

4. The use as claimed in claim 1, wherein the inner wall has pores with an average pore diameter between 5 and 8 micrometers and an average porosity in the range of 50 to 80%.

5. The use as claimed in claim 1, wherein the tubular structure has an inner diameter of 3-6 mm and a wall thickness of 200-800 micrometers.

6. The use as claimed in claim 1, wherein the tubular structure has an inner diameter of 4-8 mm and a wall thickness of 300-900 micrometers.

7. The use as claimed in claim 1, wherein the average fiber diameter of the fiber is 4-8 micrometers.

8. The use as claimed in claim 1, wherein the average fiber diameter of the fiber is 4-6 micrometers.

9. The use as described in claim 1, wherein the molecular weight of the soft block is in the range of 500 to 3000 Da.

10. The use as claimed in claim 1, wherein the hard block further comprises a chain extender, the chain extender being in the range of 1 to 5 for the UPy compound.

11. The use as claimed in claim 1, wherein the hard block further comprises a chain extender, the chain extender being in the range of 1.5 to 3 for the UPy compound.

12. The use as claimed in claim 1, wherein the inner wall of the graft is hydrophobic, with a water contact angle between 110 degrees and 140 degrees.

13. The use as claimed in claim 1, wherein the tubular structure has an outer wall reinforced by a braided structure, polymer strands, a compound, or a combination thereof to provide resistance against collapse of the cardiovascular graft.

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