A high-strength fiber filament for a degradable implant and a preparation method thereof

Abstract

The present invention discloses a high-strength fiber filament for degradable implants and a preparation method thereof, belonging to the technical field of medical special materials. When preparing the high-strength fiber filament for degradable implants, primary fibers are first prepared; then the primary fibers are subjected to multiple consecutive stretches to obtain the product. Each stretch has an initial temperature at the start of the stretch and an end temperature after the stretch, and the end temperature of the previous stretch is the initial temperature of the next stretch; the initial temperature of each stretch is greater than or equal to the end temperature, and the initial temperature of the first stretch is between the glass transition temperature and the melting point of the primary fiber. In the present invention, the combined action of stretching-induced orientation crystallization, temperature-gradient-controlled qualitative crystallization, and solution-induced crystallization significantly improves the crystallization length and orientation degree of the filament in the longitudinal direction. The mechanical properties of the stretched fiber filament are improved, and the obtained fiber filament has high modulus and high toughness, and can be used to prepare human implant materials such as braided scaffolds and occluders.

Description

Technical Field

[0001] The present invention belongs to the technical field of medical devices or special medical materials, and particularly relates to a high-strength fiber filament for a degradable implant and a preparation method thereof. Background Art

[0002] Interventional cardiac occluders can be used to treat congenital heart defects and prevent cardiogenic stroke, and are mainly divided into ventricular septal defect occluders, atrial septal defect occluders, patent foramen ovale occluders, patent ductus arteriosus occluders, and left atrial appendage occluders. At present, the main body frame part of most degradable occluders is woven by degradable filaments or fibers. The main function of the frame in the degradable occluder is to be firmly anchored at the heart defect site of the lesion, so as to resist the impact of blood flow during heart beating and prevent the occluder from slipping out of the defect site during implantation. In addition, the frame material should also meet the requirements of interventional delivery, be able to be compressed and held in the delivery catheter for delivery, and be able to recover its initial shape after release. At present, medical suture threads are mainly used for weaving degradable occluders. Medical suture threads are relatively soft and have a low modulus. When high-modulus filaments are used for suturing, the tissue is subjected to greater stress, which is not conducive to suturing. After the existing suture threads are woven into a degradable implant, due to the low modulus of the degradable fibers, the mechanical support performance is poor. The frame of the degradable occluder cannot be firmly anchored at the defect site. Moreover, when the suture thread is prepared from a degradable polymer, it will gradually degrade after being implanted in the body, further reducing its mechanical support performance, and there is a risk of early detachment, which cannot meet the use requirements of woven implants such as lumen stents and occluders. To make up for this defect, it is generally improved by increasing the fiber diameter or increasing the weaving density. However, this will increase the volume of the occluder, which is not conducive to being compressed and held in the catheter for delivery, resulting in an overly large delivery volume and being unable to pass through thinner blood vessels. At the same time, due to the low modulus, the occluder is also prone to bending in the axial direction. When it is compressed and held and delivered in the catheter, it is easy to produce wrinkles and curls, resulting in delivery failure. At present, the strength and modulus of polymers are generally improved by heat treatment-induced crystallization. However, the polymer crystals obtained by this method have no orientation, and the modulus improvement of the suture thread is limited, and it is easy to cause a significant reduction in toughness. In addition, the suture preparation process usually involves stretching above the glass transition temperature. This process can also induce crystallization orientation, but generally uses a constant temperature, and the crystallization orientation and length are both insufficient. Summary of the Invention

[0003] In view of the above-mentioned prior art, the present invention provides a high-strength fiber filament for a degradable implant and a preparation method thereof to solve the technical problem that the strength of the woven filament used for implants in the prior art cannot meet the use requirements.

[0004] To achieve the above object, the technical solution adopted by the present invention is: to provide a preparation method of a high-strength fiber filament for a degradable implant, including the following steps:

[0005] S1: Prepare primary fibers;

[0006] S2: Continuously stretch the primary fibers multiple times to obtain the desired product; each stretch has an initial temperature at the start of the stretch and a final temperature after the stretch, and the final temperature of the previous stretch is the initial temperature of the next stretch; the initial temperature of each stretch is greater than the final temperature, and the initial temperature of the first stretch is between the glass transition temperature and the melting point of the primary fiber.

[0007] Based on the above technical solution, the present invention can be further improved as follows.

[0008] Furthermore, the method for preparing the primary fibers includes the following steps:

[0009] Melt the thermoplastic polymer at a temperature higher than or equal to its melting point, and then obtain filaments with a diameter of 0.5 - 5 mm by extrusion to obtain the primary fibers.

[0010] Furthermore, the stretching is carried out through a plurality of sequentially arranged rollers; the primary fibers are sequentially wound around the sequentially arranged rollers, and the end is fixed to the last roller.

[0011] Furthermore, except for the first and the last rollers among the plurality of sequentially arranged rollers, the remaining rollers are immersed in an organic solvent.

[0012] Furthermore, there are three rollers, namely the first roller, the second roller, and the third roller. The second roller is immersed in the organic solvent, and the end of the primary fiber is wound around the third roller.

[0013] Furthermore, the organic solvent is at least one of ethanol, acetone, dichloromethane, dimethylformamide, chloroform, petroleum ether, and ether.

[0014] Furthermore, the temperatures of the first roller, the second roller, and the third roller are T1, T2, and T3 respectively, where T1 is between the glass transition temperature and the melting point of the primary fiber, and T3 is less than the glass transition temperature of the primary fiber.

[0015] Furthermore, the circumferential linear velocities of the first roller, the second roller, and the third roller are V1, V2, and V3 respectively, and 1 < V2 / V1 < 15, 1 < V3 / V2 < 15.

[0016] By using the above preparation method, a high-strength fiber filament for a degradable implant with high modulus and high toughness can be prepared, and this high-strength fiber filament for a degradable implant can be used to prepare human implant materials such as woven scaffolds and occluders.

[0017] The beneficial effects of the present invention are:

[0018] 1. The preparation method in the present invention can simultaneously achieve the tensile-induced crystallization of polymer filaments and the longitudinal directional crystallization under a temperature gradient. Tensile and gradient temperature can act together to improve the crystallization orientation of the polymer in the longitudinal direction, and compared with the existing methods, it can further improve the flexural modulus, strength, and toughness of the polymer.

[0019] 2. The present invention uses liquid to control the temperature gradient during crystallization, which improves the cooling rate of polymer filaments and the temperature gradient at the solid-liquid interface compared with the temperature gradient control method; by adjusting the stretching speed, precise and wide-range control of the temperature gradient can be achieved, and the temperature gradient at the interface front can be kept stable within a relatively large growth rate range, and crystallization proceeds under relatively steady state, and relatively long single crystals can be obtained.

[0020] 3. The intermediate stretching process in the present invention is carried out in an organic solvent. The organic solvent can penetrate the polymer filaments to a certain extent, reduce the resistance of chain segment movement in the polymer filaments, and is beneficial to the formation of crystallization. At the same time, when the filaments leave the organic solvent, the organic solvent gradually volatilizes in the gas, further inducing the crystallization of the polymer.

[0021] 4. The tensile-induced orientation crystallization, temperature-gradient-controlled qualitative crystallization, and solution-induced crystallization in the present invention act together, significantly improving the crystallization length and orientation degree of the filaments in the longitudinal direction, and the mechanical properties of the stretched fiber filaments are improved. Specific Embodiments

[0022] The following will describe the specific embodiments of the present invention in detail with reference to the examples.

[0023] Example 1: Preparation of Primary Fibers

[0024] First, heat the poly(p-dioxanone) pellets to 150 °C to melt them, then extrude them through a screw extruder under a pressure of 9 MPa, the pore diameter of the spinneret is 2.0 mm, and the extruded fibers are immediately shaped in ethanol at -30 °C for 1 h to obtain primary fibers.

[0025] Example 2: Stretching Process

[0026] The primary fibers obtained in Example 1 were successively wound around three rollers, all with a diameter of 30 cm, and the ends were fixed to the last roller. There was friction between the surface of the roller and the wire material, so that the wire material could be driven to move with the roller during rotation. Among them, the rollers were the first roller, the second roller, and the third roller in sequence, and their temperatures were T1, T2, and T3 respectively. The rollers rotated at a certain speed, and the circumferential point-line speeds were V1, V2, and V3 respectively. Among them, the second roller was immersed in ethanol, and the temperatures of both the ethanol and the roller were T2. By adjusting the number of winding turns of the wire material on the roller, the residence time of the wire material on the second roller was 6 h (the maintenance time at temperature T2 was 6 hours). The wire material was first stretched after passing through the first roller and the second roller, and was secondarily stretched after passing through the second roller and the third roller. Finally, the stretched wire material was collected from the third roller. By adjusting the temperatures of the rollers and the liquid, as well as the rotation speed, Samples 1-4 were obtained, and the specific stretching conditions of Samples 1-4 are shown in Table 1.

[0027] Example 3: Aqueous solution stretching

[0028] The primary fibers obtained in Example 1 were successively wound around three rollers, all with a diameter of 30 cm, and the ends were fixed to the last roller. There was friction between the surface of the roller and the wire material, so that the wire material could be driven to move with the roller during rotation. Among them, the rollers were the first roller, the second roller, and the third roller in sequence, and their temperatures were T1, T2, and T3 respectively. The rollers rotated at a certain speed, and the circumferential point-line speeds were V1, V2, and V3 respectively. Among them, the second roller was immersed in water, and the temperatures of both the water and the roller were T2. By the number of winding turns of the wire material on the roller, the maintenance time of the wire material at temperature T2 was set at 6 hours. The wire material was first stretched after passing through the first roller and the second roller, and was secondarily stretched after passing through the second roller and the third roller. Finally, the stretched wire material was collected from the third roller. By adjusting the temperatures of the rollers and the liquid, as well as the rotation speed, Sample 5 was obtained, and the specific stretching conditions of Sample 5 are shown in Table 1.

[0029] Example 4: Stretch without liquid

[0030] Consistent with the process of Example 2, the primary fiber is wound around three rollers in sequence. The diameters of the rollers are all 30 cm, and the end is fixed on the last roller. There is friction between the roller surface and the wire material, so that the wire material can be driven to move with the roller during rotation. Among them, the rollers are the first roller, the second roller, and the third roller in sequence, and their temperatures are T1, T2, and T3 respectively. The rollers rotate at a certain speed, and the circumferential point-line speeds are V1, V2, and V3 respectively. All the rollers are exposed to the air, and the residence time of the wire material on the second roller is 6 h. The wire material is stretched for the first time after passing through the first roller and the second roller, and is stretched for the second time after passing through the second roller and the third roller. Finally, the stretched wire material is collected from the third roller to obtain Sample 6. The specific stretching conditions of Sample 6 are shown in Table 1.

[0031] Example 5: Isothermal stretching

[0032] The primary fiber prepared in Example 1 is wound around three rollers in sequence. The diameters of the rollers are all 30 cm, and the end is fixed on the last roller. There is friction between the roller surface and the wire material, so that the wire material can be driven to move with the roller during rotation. Among them, the rollers are the first roller, the second roller, and the third roller in sequence, and their temperatures are T1, T2, and T3 respectively. The rollers rotate at a certain speed, and the circumferential point-line speeds are V1, V2, and V3 respectively. The three rollers are all immersed in ethanol, and the liquid and roller temperatures are the same. The residence time of the wire material on the second roller is 6 h. The wire material is stretched for the first time after passing through the first roller and the second roller, and is stretched for the second time after passing through the second roller and the third roller. Finally, the stretched wire material is collected from the third roller, and then annealed at 70 degrees Celsius for 6 hours to anneal the polymer, obtaining Sample 7. The specific stretching conditions of Sample 7 are shown in Table 1.

[0033] Result analysis

[0034] The properties of Samples 1-7 prepared in Examples 2-5 were tested using the test method described in GB / T 14344-2008 "Test Method for Tensile Properties of Chemical Fiber Filaments". The results are shown in Table 1.

[0035] Table 1 Tensile conditions and performance test results of samples

[0036]

[0037] As can be seen from Table 1:

[0038] Samples 1 and 2: Under the same draw ratio and temperature gradient, Sample 2 has better modulus and elongation, indicating that a slower drawing speed is beneficial to the longitudinal orientation crystallization of the fiber, thus improving the modulus and toughness. The same situation also occurs in Samples 3 and 4.

[0039] Samples 1 and 3: When other conditions are the same, a decrease in the ratio of roller speeds (the ratio of V2 to V1) will reduce the modulus but increase the toughness. The same situation also occurs with Samples 2 and 4.

[0040] Samples 1 and 5: When other conditions are the same, adding ethanol instead of water as the liquid is beneficial to improving the modulus and toughness because ethanol can better promote the movement of molecular chain segments within poly(p-dioxanone), thereby promoting the crystallization orientation in the stretched state.

[0041] Samples 1 and 6: When other conditions are the same, heating and stretching in solution are more beneficial to improving the modulus and toughness of the fiber than heating and stretching in air.

[0042] Samples 1 and 7: Stretching under isothermal conditions will significantly reduce the toughness of the fiber.

[0043] Although the specific embodiments of the present invention have been described in detail in conjunction with the examples, it should not be construed as a limitation on the scope of protection of this patent. Within the scope described in the claims, various modifications and deformations that can be made by those skilled in the art without creative efforts still fall within the scope of protection of this patent.

Claims

1. A preparation method of high-strength fiber filaments for degradable implants, characterized in that, It includes the following steps: S1: Prepare primary fibers; S2: Conduct multiple consecutive stretches on the primary fibers to obtain the product. Each stretch has an initial temperature at the start of the stretch and an end temperature after the stretch. The end temperature of the previous stretch is the initial temperature of the next stretch. The initial temperature of each stretch is greater than the end temperature, and the initial temperature of the first stretch is between the glass transition temperature and the melting point of the primary fibers. The stretch is carried out through a plurality of rollers arranged in sequence. The primary fibers are wound around the rollers arranged in sequence in turn and the end is fixed on the last roller. Except for the first and the last rollers among the plurality of rollers arranged in sequence, the remaining rollers are immersed in an organic solvent.

2. The preparation method according to claim 1, wherein The preparation method of the primary fibers includes the following steps: Melt the thermoplastic polymer at a temperature higher than or equal to its melting point, and then obtain filaments with a diameter of 0.5 - 5 mm by extrusion to obtain the primary fibers.

3. The preparation method according to claim 1, characterized in that: There are three rollers, namely the first roller, the second roller and the third roller. The second roller is immersed in the organic solvent, and the end of the primary fibers is wound around the third roller.

4. The preparation method according to claim 3, characterized in that: The organic solvent is at least one of ethanol, acetone, dichloromethane, dimethylformamide, chloroform, petroleum ether and ether.

5. The preparation method according to claim 4, characterized in that: The temperatures of the first roller, the second roller and the third roller are T1, T2 and T3 respectively, where T1 is between the glass transition temperature and the melting point of the primary fibers, and T3 is less than the glass transition temperature of the primary fibers.

6. The preparation method according to claim 4, characterized in that: The circumferential linear velocities of the first roller, the second roller and the third roller are V1, V2 and V3 respectively, and 1 < V2 / V1 < 15, 1 < V3 / V2 < 15.

7. A high-strength fiber filament for a degradable implant prepared by the preparation method according to any one of claims 1 - 6.

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