Multilayer polymer composite vascular graft

Abstract

The invention relates to a multilayer polymer composite vascular graft and a method for its manufacturing The said vascular graft comprises a first layer containing PCL-Heparin, a second layer containing PCL, a third layer containing PVA-Chitosan and a fourth layer containing TPU. The electrospinning method is used to prepare the vascular graft in question. In the vascular graft subject to the invention, both biodegradable (PCL, chitosan) and non-biodegradable polymer materials (TPU) are used. By supporting the biodegradable materials (PCL, chitosan), which lose their mechanical properties during the endothelialisation process, with the non-biodegradable polymer material (TPU), the problem caused by the potential loss of mechanical strength is eliminated. Thanks to the heparin additive in the inner layer of the vascular graft subject to the invention, clotting, which is commonly encountered in vascular graft applications, is also prevented.

Description

[0001] MULTILAYER POLYMER COMPOSITE VASCULAR GRAFT

[0002] Technical Field

[0003] The invention relates to a multilayer polymer composite vascular graft and a method for its manufacturing. The vascular graft in question is a synthetic artificial vascular model produced by the electrospinning method, which is used for small diameter (<6 mm) vessels that have lost their function due to vascular occlusion or other reasons. Polycaprolactone (PCL), polyvinyl alcohol (PVA), chitosan, thermoplastic polyurethane (TPU) and heparin are used in the production of the inventive vascular graft.

[0004] Background of the Technique

[0005] Cardiovascular diseases are one of the most common diseases faced by many people today. The group of diseases related to the heart or blood vessels is called cardiovascular diseases. Coronary arteries are located in the cardiovascular system that supply the heart. Coronary artery disease is the most common form of heart disease. It is the leading cause of death in men and women worldwide. The narrowing of the coronary arteries results in less blood passing through the vessel. As a standard medical procedure, the blocked or narrowed artery is replaced with a new one. The first choice here is the method in which a blood vessel obtained from the patient's own body is transferred to the area of the heart where the disease is usually present. However, if the patient does not have a blood vessel of sufficient quality, artificial vessels are used to replace the blood vessels.

[0006] In cardiovascular diseases, such as dialysis and heart surgeries, vascular replacement is required in the event of plaque formation and blockages in the blood flow. The clinical success of these vascular replacement applications is limited, and the cost is relatively high. For this reason, synthetic artificial vessels have been studied for many years [1].

[0007] Grafting is a surgical procedure to move tissue that does not have its own blood circulation from one part of the body to another or from one living organism to another. After the graft is implanted, it is supplied by new blood vessels. In some cases, the graft can be artificially produced. Artificial blood vessel grafts are examples of these grafts, and if these grafts are used in the vascular system, these artificial blood vessels are called vascular grafts. An ideal vascular graft material should have high biocompatibility, not have toxic, antigenic and carcinogenic effects, be easily obtainable and low cost, and be resistant to local inflammation [2],

[0008] In vascular graft manufacturing, various materials are used for different vascular applications. One of the main features of a vascular graft is that the mechanical properties should be compatible with real vessels. The vascular graft should also be able to provide the proper biological functions, obtain the right surface properties and be produced reliably.

[0009] While the natural vessel is a living organ, the currently most commonly used type of vascular grafts are non-biodegradable products made of synthetic polymers. These products are expected to mimic the mechanical properties of natural vessels besides being biocompatible [3]-

[0010] After the biodegradable vascular grafts used in the current technique are transplanted into the body, new endothelial cell layers settle in their place as they dissolve in the body, which is called endothelialisation. The mechanical strength of vascular grafts decreases during endothelialisation as their dissolution rate cannot be controlled. Thus, the operation may fail before the transplanted vessel can fulfil its function. Therefore, mechanical instabilities during endothelialisation, starting after the vascular graft is transplanted into the body, cannot be prevented.

[0011] In another known case of the technique, a common condition with small diameter (<6mm) vascular grafts is clot formation when vascular transplantation is necessary. The vascular graft is rendered inoperable due to clot formation and requires clot removal operations to make it reusable. In this case, the risks for the patient due to clot formation that may occur after the operation cannot be prevented.

[0012] In the present technique, when using polyester-based and non-biodegradable vascular grafts, the non-biodegradable vascular graft is stored in the human body as a foreign body and inhibits the regeneration of blood vessel cells. In addition, these polyester-based vascular grafts can also cause aneurysm, explained as the weakening and expansion of the vessel walls and the formation of bubbles in these areas after long-term use. Therefore, in non-biodegradable vascular graft applications, negative effects on the regeneration function of blood vessel cells, storage of these structures as foreign bodies in the body and the risk of aneurysm formation due to vascular graft use cannot be prevented. The limitations and inadequacies of the solutions in the current technique, the inability to prevent the mechanical weakness of biodegradable vascular grafts during endothelialisation, the possibility of clot formation in the vascular graft, the negative effect of polyester-based vascular grafts on the regeneration function of blood vessel cells, the storage of these structures as foreign bodies in the body and the risk of aneurysm formation due to the use of vascular grafts have made further development in this field necessary.

[0013] Brief Description and Objectives of the Invention

[0014] The invention discloses a multilayer polymer composite vascular graft and the method of manufacturing the graft. The vascular graft subject to the invention has a 4-layered polymeric structure. The said vascular graft comprises a first layer containing PCL-Heparin, a second layer containing PCL, a third layer containing PVA-Chitosan and a fourth layer containing TPU.

[0015] One object of the invention is to provide a vascular graft with high mechanical strength properties for use in coronary artery vascular replacement applications. Polyvinyl alcohol (PVA), chitosan and thermoplastic polyurethane (TPU) materials in the said vascular graft provide strengthening properties to the vascular graft in order to reduce mechanical strength losses that may occur during endothelialisation. Since TPU is a material that does not dissolve in the body, it is added to the product to maintain the mechanical strength of the vessel after transplantation. The mechanical properties of the vascular graft are strengthened thanks to its multilayer polymeric structure formed with both biodegradable and non-biodegradable polymers.

[0016] Another object of the invention is to prevent clot formation, which is frequently encountered in vascular graft applications, especially in small diameter synthetic vessels. Using heparin additive in the inner layer of the vascular graft subject to the invention prevents clot formation within the vessel during the endothelialisation process.

[0017] A further object of the invention is to develop a biocompatible vascular graft that does not interfere with the regeneration function of blood vessel cells. Since the vascular graft subject to the invention contains biodegradable polycaprolactone (PCL) and chitosan, it is a vascular graft with high biocompatibility and prevents the issue of foreign body storage in the human body caused by vascular graft application.

[0018] Unlike vascular grafts in the current technique, this vascular graft utilises both biodegradable (PCL, chitosan) and non-biodegradable polymer materials (TPU). By reinforcing the biodegradable materials (PCL, chitosan), which lose their mechanical properties during the endothelialisation process, with non-biodegradable polymer material (TPU), it aims to eliminate potential problems caused by mechanical strength loss. Additionally, the multilayered polymeric structure of the vascular graft aims to provide high mechanical strength, prevent clotting issues thanks to the heparin present in its inner layer, and serve as a replacement for small-diameter vessels that have lost functionality due to vascular blockage or other causes. Furthermore, the production of this vascular graft is intended to be achieved through the electrospinning method.

[0019] Description of the Figures

[0020] Figure 1. The layer structure of the vascular graft: (1 ) first layer containing PCL-Heparin, (2) second layer containing PCL, (3) third layer containing PVA-Chitosan, (4) fourth layer containing TPU.

[0021] Figure 2. (A) Tensile results of sample H5, (B) Tensile results of sample H10.

[0022] Figure 3. Comparison of FTIR results of PCT, H5 and H10 samples.

[0023] Figure 4. (A) Tensile test results of PCLT sample, (B) tensile test results of PPCT sample.

[0024] Figure 5. (A) Tensile results of specimen H5, (B) Tensile results of specimen H10.

[0025] Figure 6. Nanofibre structure of PCL layer at (A) 1000X and (B) 30000X magnification.

[0026] Figure 7. SEM image of TPU layer.

[0027] Figure 8. Nanofibre structure of PVA-Chitosan layer at (A) 100X and (B) 5000X magnification.

[0028] Figure 9. SEM image of H5 layer at (A) 100X, (B) 1000X, (C) 5000X and (D) 1000X magnification.

[0029] Figure 10. SEM image of sample H5

[0030] Figure 11. (A), (B), (C), (D) SEM image of sample H10

[0031] Figure 12. SEM image of 10% Heparin / PCL (4% solid solution) solution Detailed Description of the Invention

[0032] The invention relates to a multilayer polymer composite vascular graft and to the method of manufacturing the graft. The inventive vascular graft has a 4-layered polymeric structure.

[0033] The vascular graft in question comprises a first layer of PCL-Heparin, a second layer of PCL, a third layer of PVA-Chitosan and a fourth layer of TPU from the inside out. The so-called inner part of the vascular graft is the first part of the vascular graft that directly contacts the blood.

[0034] The thickness of the first layer containing PCL-Heparin is in the range of 25-150 microns, preferably 75 microns. The thickness of the second layer containing PCL is in the range of 50-200 microns, preferably 125 microns. The thickness of the third layer containing PVA- Chitosan is in the range of 25-150 microns, preferably 75 microns. The thickness of the fourth layer containing TPU is in the range of 50-200 microns, preferably 125 microns. The vascular graft subject to the invention comprises a cylindrical structure with an outer thickness of 5 mm, an inner thickness of 4 mm, and a wall thickness of 1 mm. The heparin supplementation in the innermost layer of the vascular graft prevents the risk of clot formation that may occur after the vascular graft is transplanted into the human body. The PCL polymer contained in the vascular graft dissolves in the body during endothelialisation, which begins after the vessel is transplanted into the body. The PVA and chitosan polymers in the third layer of the vascular graft act as a reinforcing layer to reduce the loss of mechanical strength that may occur during the endothelialisation of the vascular graft. The outer layer of the vascular graft containing TPU also prevents the loss of mechanical strength that may occur in the vascular graft.

[0035] The electrospinning method is used in the production of this vascular graft. The vessel form is created by coiling on a collector shaft of suitable diameter in the electrospinning device. Solid polymer materials are dissolved in suitable solvents to form a solution and then subjected to spinning. In the production of vascular grafts, the graft components are dissolved with the help of solvents and then woven into thin fibres in an electrospinning machine.

[0036] The production process of the inventive vascular graft comprises the following steps:

[0037] ^Preparation of PCL solution, ii) Preparation of TPU solution, iii) Preparation of PVA solution, iv) Preparation of chitosan solution, v)Preparation of chitosan / PVA solution, vi) Preparation of PCL / Heparin solution, vii)Coiling of the first layer of PCL / Heparin solution in the electrospinning device, vii i) Coi li ng of the second layer of PCL over the first layer, ix)Coiling of the third layer of PVA / Chitosan solution over the first and second layers, x)Coi li ng of the fourth and last layer of TPU over the first, second and third layers, xi)Dropping PCL in solution on the intersection points and glueing.

[0038] In one implementation of the invention, the manufacturing of the vascular graft is comprised of the following steps:

[0039] ^Preparation of 5-8% PCL solution, ii) Preparation of 5-8% TPU solution, iii) Preparation of 5-8% PVA solution, iv) Preparation of 1 -4% Chitosan solution, v)Preparation of Chitosan / PVA solution in a ratio of 1 -2:2-5, vi) Preparation of PCL / Heparin solution, vii)Coiling the first layer of PCL / Heparin solution in the electrospinning device at 20-40 kV voltage, 2-8 ml / h feed rate, 100-500 rpm and 10-20 cm distance, viii)Coiling the second layer of PCL on the first layer at a distance of 10-20 cm at 15-30 kV voltage, 2-5 ml / h feed rate and 100-500 rpm, ix)Coiling the third layer of PVA / Chitosan solution on the first and second layers at a voltage value of 20-40 kV, a feed rate of 1 -4 ml / h, 100-500 rpm and a distance of 10-20 cm, x)Coiling the fourth and last layer of TPU on the first, second and third layers at 20-40 kV voltage, 1 -5 ml / h feed rate, 100-500 rpm and a distance of 15 cm, xi)Dropping PCL in solution on the intersection points and glueing.

[0040] In one implementation of the invention, the manufacturing of the vascular graft is comprised of the following steps:

[0041] ^Preparation of 6.5% PCL solution, ii) Preparation of 6.5% TPU solution, iii) Preparation of 6.5% PVA solution, iv) Preparation of 2% Chitosan solution, v)Preparation of Chitosan / PVA solution in a ratio of 1 :3, vi) Preparation of PCL / Heparin solution, vii)Coiling the first layer of PCL / Heparin solution in the electrospinning device at 30 kV voltage,

[0042] 5 ml / h feed rate, 300 rpm and 15 cm distance, viii)Coiling the second layer of PCL on the first layer at a distance of 15 cm at 25 kV voltage, 3 ml / h feed rate and 300 rpm, ix)Coiling the third layer of PVA / Chitosan solution on the first and second layers at a voltage value of 35 kV, a feed rate of 1 -1 .5 ml / h, 300 rpm and a distance of 15 cm, x)Coi li ng the fourth and last layer of TPU on the first, second and third layers at 30 kV voltage, 3 ml / h feed rate, 300 rpm and a distance of 15 cm, xi)Dropping PCL in solution on the intersection points and glueing.

[0043] In the process step (i) of the vascular graft subject to the invention, 6.5% PCL solution is prepared by placing the solid PCL granules in chloroform solvent and mixing at 600 rpm on a magnetic stirrer at room temperature for 24 hours. The solution obtained is taken into a syringe for spinning. In the process step (ii) of the method subject to the invention, during the preparation of 6.5% TPU solution, TPU granules are taken into N,N-Dimethylformamide solvent and mixed at 60°C and 600 rpm on a magnetic stirrer for 24 hours. Before preparing the PVA-chitosan mixture, which is the process step (v), separate solutions of PVA and chitosan are first prepared. In the process step (iii), PVA particles are preheated to 40°C in an oven to prepare the 6.5% PVA solution. It is then taken into pure water heated to 80°C and stirred in a magnetic stirrer at 600 rpm at 80°C for 24 hours. The resulting solution is kept in an oven preheated to 120°C for 120 minutes, then taken out and allowed to cool to room temperature. These steps are essential for the complete dissolution of PVA. In the process step (iv), 2% chitosan solution is prepared in 2% aqueous acetic acid solvent. The solution is obtained by stirring on a magnetic stirrer at 600 rpm for 24 hours at room temperature. In the process step (v), PVA and chitosan solutions are obtained by stirring on a magnetic stirrer at a 1 :3 Chitosan / PVA ratio for 24 hours at room temperature. In the process step (vi), PCL / Heparin solution is prepared in a solvent prepared from 2% distilled water, 28% methanol, and 70% dichloromethane. PCL and heparin solid materials are taken directly into the solvent and obtained by stirring on a magnetic stirrer for 24 hours at room temperature. For the preparation of the graft, the collector part of the static spinning device is covered with aluminium foil for easier removal of the material obtained. Table 3 shows the electrospinning conditions of the layers. After the samples taken from the aluminium foil are circularised to give a vein form, PCL is dropped as a solution on the intersection points, and the glueing process is applied.

[0044] Table 1 describes the composition ratios of the graft samples.

[0045] Table 1. Sample composition table in solid state after spinning

[0046] *(%by w): percentage by weight

[0047] PCLT and PPCT are control samples of the vascular graft subject of the invention. PCLT has two layers and contains PCL and TPU. PPCT has three layers and contains PCL, TPU, PVA and Chitosan.

[0048] In another application of the invention, the multilayer polymer vascular graft in the PPCT sample contains 32% PCL, 32% PVA, 4% chitosan and 32% TPU. In another implementation of the invention, in sample H5, the multilayer polymer vascular graft comprises 47% PCL, 1 .5% heparin, 24% PVA, 3.5% chitosan and 24% TPU.

[0049] In another application of the invention, in sample H10, the multilayer polymer vascular graft comprises 42% PCL, 2.5% heparin, 26% PVA, 2.5% chitosan and 26% TPU. Table 2 describes the components of the vascular graft, the solvents of the components and the solubilisation conditions of the components.

[0050] Table 2 Preparation conditions of the solutions

[0051] Table 3. Electrospinning conditions of solutions

[0052] Tensile tests were performed on the vascular graft subject to the invention. In order to test the mechanical properties of the vascular graft, the specimens were cut into rectangular thin films. Tensile tests were performed at room temperature using a Universal Testing Machine (INSTRON). The standard gauge length is 25 mm, and the thickness of the specimens is in the range of 0.100 mm-0.150 mm. Cross head speed is 1 mm / min. According to the tensile test results, Figures 4 (a) and (b) show the tensile stress-tensile strain data of PCT (PCL- PU), PCLT (PCL-CHITOSAN-PU) and PPCT (PCL-CHITOSAN-PVA-PU) specimens. The maximum tensile strength of the PCLT specimen is around 4 MPa, the elastic modulus value is 35 MPa, and the maximum elongation value is 100%. On the other hand, the maximum tensile strength of the PPCT specimen is 1.2 MPa, the elastic modulus value is 5.5 MPa, and the maximum elongation value is around 200%. According to these results, adding a PVA layer to the PCLT sample makes the sample more flexible, decreases the maximum tensile and elastic modulus values, and increases the maximum elongation rate.

[0053] Figures 5 (a) and (b) show the tensile stress-tensile strain data of specimens H5 and H10. The maximum tensile strength of specimen H5 is around 5.2 MPa, the elastic modulus value is 20 MPa, and the maximum elongation value is 140%. On the other hand, the maximum tensile strength of specimen H10 is around 5.5 MPa, the elastic modulus value is 35 MPa, and the maximum elongation value is around 80%. According to these results, adding 5% more heparin to the H5 specimen makes the specimen more rigid, the maximum tensile and elastic modulus values increase, and the maximum elongation rate decreases. Table 4 shows the results of the mechanical properties of the specimens. Table 4. Mechanical properties of the specimens

[0054] Sample Tensile Strength (MPa) Elastic Modulus (MPa) % elongation (E)

[0055] Fourier transform infrared spectroscopy (FTIR) analyses of the vascular graft subject to the invention were performed using a Bruker Tensor 27 type spectrometer. The produced samples were analysed in the 500-4500 cm -1 range. FTIR spectra were recorded at room temperature. The functions of the absorption bands obtained from the samples were analysed.

[0056] According to the results of the FTIR analysis, the FT-IR graph of the PCL / PVA- Chitosan / TPU (PCT) sample is given in Figure 2 (a). IR (ATR) vmax(cm-1 ): 1721 -1722 (C=O and C-O-C voltage bands), 1239 (CO-NH2 voltage band).

[0057] The distinct characteristic peaks of PCL at 1722 cm-1 were assigned to the C=O and C-O- C bands in ester bonds at 1721 cm-1 , respectively. While the intensity of the amide II and -NH- bands decreased as the PCL content increased, the C=O and C-O-C bands from the ester clearly increased. The FTIR results confirm that the ratio of TPU and PCL varies in scaffolds with different material combinations. The main differences in the FTIR spectrum of chitosan are the bands at 1239 cm-1 , which can be attributed to the CO-NH2 stretching vibration. These bands indicate the presence of phosphate groups in chitosan particles.

[0058] As shown in Figure 2 (a) and (b), the TPU curves indicated that the intensity of different characteristic-NH- bands of polyurethane decreased, while C=O and C-O-C bands from ester increased obviously. The FTIR results confirmed that the ratio of TPU and PCL varied in the structure with different material combinations. IR (ATR) vmax(cm-l ): 2937-2863 (asymmetric and symmetric CH2 tension bands), 1720 (C=O tension band), 1363 -1 164 (COO carboxyl acid tension bands), 1 164-1037 (SO3 tension bands)

[0059] Figure 2 (b) shows the FT-IR plot of sample H5. Characteristic peaks for PCL's amino and amine groups were observed at 1723 and 2937 cm-1 , respectively. Distinctive peaks for one carboxylic acid heparin group were detected at 1363 and 1 164 cm-1 in H-10 and H-5 vascular grafts, respectively. In addition, these signals disappear after heparin conjugation, with the amines forming amide bonds with the carboxyl groups of heparin. The characteristic SO3- peaks attributed to heparin are observed at 1 164 and 1037 cm -1 .

[0060] IR (ATR) vmax(cm-l ): 1687-1226-1099 (CO stretching vibration bands), 1 141 (crystallinity tension band), 1687 (amide I tension band), 1226 (amide II and amide III tension bands), 3300 (-NH- tension band), 1160 (C-O-C tension band).

[0061] Figure 2 (c) shows the FT-IR graph of sample H-10. It is possible to conclude that intermolecular hydrogen bonds are formed between OH and NH groups in chitosan and OH groups in PVA. Among the characteristic bands of PVA, the band's intensity at 1 141 cm-1 is known to be sensitive to crystallinity. The bands generated at 1687-1226-1099 cm-1 represent CO stretching vibrations. TPU curves showed different characteristic peaks of polyurethane (amide I, amide II and amide III bands at 1687 cm -1 and 1226 cm -1 , respectively). Peaks at 3300 cm -1 and 1160 cm -1 were assigned to -NH- and C-O-C bands in urethane bonds, respectively.

[0062] Figure 3 shows the comparison of the FT-IR results of Sample 2 (PCT), Sample 3 (H5) and Sample 4 (H10). It was found that the intensity of the 3300 cm-1 band decreased with the presence of chitosan; this may be due to the tension vibrations of the secondary NH groups in the structure of chitosan and OH atoms in the structure of PVA. When two or more polymers are mixed, the formation of chemical bonds and chemical interactions cause changes in characteristic peaks. Therefore, the peak differences in the 3300cm-1 band of the H5 / 10 samples and the PCT sample are evidence of the presence of PVA and chitosan.

[0063] SEM analysis of the vascular graft subject to the invention was performed. In SEM analysis, the pore structures of the samples were observed with a Scanning Electron Microscope (SEM) (JEOL, MODEL: JSM 7001 F). In the experiments with EDS Oxford Instruments, an SE detector, HV mode and accelerating voltages of 5-15 kV were used. All layers were observed and photographed separately. According to the results of SEM analysis, Figures 6 (a) and (b) show the SEM image of the electrospun PCL solution and the diameter of the nanofibres. Figure 7 shows the SEM image of the electrospun TPU solution. The nanofibre morphology of the TPU sample is more irregular and distorted than that of the PCL sample. Figure 8 shows the SEM image of the electrospun PVA / Chitosan solution. The nanofibre morphology of this sample is more regular and homogeneous than the TPU and PCL samples. Figure 9 shows the SEM images of the innermost layer of the electrospun sample 3. In Figure 9, the images in (B) and (D) were taken from different regions of the same sample. The nanofibre morphology of this sample is more regular and homogeneous than that of the TPU, PCL and PVA / chitosan samples. Figure 10 shows the SEM image of the electrospun 5% Heparin-PCL solution of sample 3. The nanofibre morphology of this layer is observed to be more irregular and inhomogeneous than the innermost layer nanofibre morphology. It is observed that the nanofibre morphology in this sample is more degraded and irregular compared to sample 3 with the addition of 5% more heparin.

[0064] Figure 12 shows the SEM image of the electrospun test sample of 10% Heparin-PCL solution (containing 4% solid solution). The nanofibre morphology in this sample is more regular and homogeneous since it is prepared from a more dilute solution than the 10% Heparin-PCL (containing 7% solid solution) sample, which is the innermost layer of sample 4, and the nanofibre diameters are smaller and have a more homogeneous average numerical value among themselves. All these results show that the main factor determining the nanofibre morphology's homogeneity and regularity is the electrospin solution concentration and the optimised adjustment of the electrospin parameters according to the solution viscosity.

[0065] A flow test was performed on the vascular graft subject to the invention. A device has been developed to perform flow tests on the vascular graft. Arduino UNO R3 CH340, mini submersible water pump, water flow sensor, two silicone hoses with a diameter of 4mm, plastic hose with a diameter of 1 cm, 1000 ml beaker and measuring plastic container were used in the device prepared for the flow test.

[0066] The flow test was applied to the prototype vessel, and it started to drip from the centre line between the eighth and ninth seconds. The dripping can be seen at the connection point of the hoses and 2 cm from the connection point of the vessel. The test used water as a liquid; blood or a blood-like liquid was unavailable. The vessel produced in the project is a small diameter vessel sample based on the coronary artery. The average blood flow rate in the left anterior descending coronary artery is 29.7 + / - 17.4 ml / min. In this test with water, the average volume time is 2903.35 + / - 284.21 ml / min. In this test with water, the average volume time is 2903.35 + / - 284.21 ml / min. The viscosity of blood is higher than that of water due to its components; however, considering that fluid flow in the body cannot occur at the same speed as in the setup, it can be argued that the prototype vessel would resist blood flow similar to that in the body. Since this is a simple setup, the data obtained is very limited. In order to obtain better data (pressure exerted by the blood on the prototype vessel, blood flow rate, blood clotting state, etc.), further tests should be performed.

[0067] REFERENCES

[0068] [1] Chlupac J, Filova E, Bacakova L. Blood Vessel Replacement: 50 years of Development and Tissue Engineering Paradigms in Vascular Surgery, Physiol Res 2009; 58:119-139.

[0069] [2] Eren S, lllcay Y. Yapay Tekstil Damarlan. Electronic Journal of Textile Technologies 2010; 4:35-47.

[0070] [3] Wang D, Xu Y, Li Q, Turng LS. Artificial small diameter blood vessels: materials, fabrication, surface modification, mechanical properties, and bioactive functionalities. Journal of Materials Chemistry B,1801 -1822, 2020.

Claims

CLAIMS1. It is a multi-layered polymer composite vascular graft designed for use in smalldiameter (<6 mm) vessels, consisting of a total of 4 layers with the following composition from the inside out: the first layer contains polycaprolactone (PCL)-Heparin, the second layer contains PCL, the third layer contains polyvinyl alcohol (PVA)-Chitosan, and the fourth layer contains thermoplastic polyurethane (TPU).

2. A vascular graft according to claim 1 , characterised by comprising 47% PCL, 1 .5% heparin, 24% PVA, 3.5% chitosan and 24% TPU.

3. A vascular graft according to claim 1 , characterised by comprising 42% PCL, 2.5% heparin, 26% PVA, 2.5% chitosan, and 26% TPU.

4. A vascular graft according to claim 1 , characterised by comprising a cylindrical structure.

5. A vascular graft according to claim 1 , characterised by an outer thickness of 5 mm and an inner thickness of 4 mm.

6. A vascular graft according to claim 1 , characterised by a wall thickness of 1 mm.

7. A vascular graft according to claim 1 , characterised by the thickness of the first layer being in the range of 25-150 microns, the second layer in the range of 50-200 microns, the third layer in the range of 25-150 microns, and the fourth layer in the range of 50-200 microns.

8. A vascular graft according to claim 1 , characterised by the thickness of the first layer being 75 microns, the second layer being 125 microns, the third layer being 75 microns, and the fourth layer being 125 microns.

9. A method of manufacturing a vascular graft according to any one of the preceding claims, characterised by the following processing steps:^Preparation of PCL solution, ii) Preparation of TPU solution, iii) Preparation of PVA solution, iv) Preparation of chitosan solution,v)Preparation of PVA / Chitosan solution, vi) Preparation of PCL / Heparin solution, vii)Coiling the first layer of PCL / Heparin solution in the electrospinning device, vii i) Coi li ng the second layer of PCL over the first layer, ix)Coiling the third layer of PVA / Chitosan solution over the first and second layers, x)Coi li ng the fourth and last layer of TPU over the first, second and third layers, xi)Dropping PCL in solution on the intersection points and glueing.

10. A method of manufacturing a vascular graft according to any one of the preceding claims, characterised by the following processing steps: ^Preparation of 5-8% PCL solution, ii) Preparation of 5-8%TPU solution, iii) Preparation of 5-8% PVA solution, iv) Preparation of 1 -4% chitosan solution, v)Preparation of Chitosan / PVA solution in a ratio of 1 -2:2-5, vi) Preparation of PCL / Heparin solution vii)Coiling the first layer of PCL / Heparin solution in an electrospinning device at a voltage of 20-40 kV, a feed rate of 2-8 ml / h, 100-500 rpm and a distance of 10-20 cm, viii)Coiling the second layer of PCL on the first layer at a distance of 10-20 cm at 15-30 kV voltage, 2-5 ml / h feed rate and 100-500 rpm, ix)Coiling the third layer of PVA / Chitosan solution on the first and second layers at a voltage of 20-40 kV, a feed rate of 1 -4 ml / h, 100-500 rpm and a distance of 10-20 cm, x)Coiling the fourth and last layer of TPU on the first, second and third layers at 20-40 kV voltage, 1 -5 ml / h feed rate, 100-500 rpm and 15 cm distance, xi)Dropping PCL in solution on the intersection points and glueing.

11. A method of manufacturing a vascular graft according to any one of the preceding claims, characterised by the following processing steps:^Preparation of 6.5% PCL solution, ii) Preparation of 6.5% TPU solution, iii) Preparation of 6.5% PVA solution, iv) Preparation of 2% Chitosan solution, v)Preparation of 1 :3 chitosan / PVA solution, vi) Preparation of PCL / Heparin solution, vii)Coiling the first layer of PCL / Heparin solution in the electrospinning device at 30 kV voltage, 5 ml / h feed rate, 300 rpm and a distance of 15 cm, viii)Coiling the second layer of PCL on the first layer at a distance of 15 cm at 25 kV voltage, 3 ml / h feed rate and 300 rpm, ix)Coiling the third layer of PVA / Chitosan solution on the first and second layers at a voltage of 35 kV, 1 -1 .5 ml / h feed rate, 300 rpm and a distance of 15 cm, x)Coi li ng the fourth and last layer of TPU on the first, second and third layers at 30 kV voltage, 3 ml / h feed rate, 300 rpm and 15 cm distance, xi)Dropping PCL in solution on the intersection points and glueing.

12. A method of manufacturing a vascular graft according to any one of Claims 9-1 1 , characterised by step (i) in which solid PCL granules are placed into a chloroform solvent and stirred at 600 rpm on a magnetic stirrer at room temperature for 24 hours to obtain a 6.5% PCL solution.

13. A method of manufacturing a vascular graft according to any one of Claims 9-1 1 , characterised by step (ii) in which TPU granules are placed into an N,N-Dimethylformamide solvent and stirred at 600 rpm on a magnetic stirrer at 60°C for 24 hours to obtain a 6.5% TPU solution.

14. A method of manufacturing a vascular graft according to any one of Claims 9-1 1 , characterised by step (iii) in which PVA particles are first heated in an oven to 40°C, thenplaced into deionised water preheated to 80°C and stirred on a magnetic stirrer at 600 rpm at 80°C for 24 hours. The resulting solution is then placed in an oven preheated to 120°C for 120 minutes, removed, and allowed to cool to room temperature to obtain a 6.5% PVA solution.

15. A method of manufacturing a vascular graft according to any one of Claims 9-1 1 , characterised by step (iv) in which a 2% chitosan solution is prepared by stirring in a 2% aqueous acetic acid solvent on a magnetic stirrer at 600 rpm at room temperature for 24 hours.

16. A method of manufacturing a vascular graft according to any one of Claims 9-1 1 , characterised by step (v) in which PVA and chitosan solutions are mixed at a 1 :3 chitosan / PVA ratio on a magnetic stirrer at room temperature for 24 hours.

17. A method of manufacturing a vascular graft according to any one of Claims 9-1 1 , characterised by step (vi) in which solid PCL and heparin materials are placed into a solvent prepared from 2% deionised water, 28% methanol, and 70% dichloromethane, and stirred on a magnetic stirrer at room temperature for 24 hours.

18. A multilayer polymer composite vascular graft is produced using a method according to any one of Claims 9-17.

Images