CN118161647A - A method for preparing a silk fibroin-based ultrafine monofilament suture - Google Patents

Abstract

The present invention discloses a method for preparing a silk fibroin-based ultrafine monofilament suture, wherein ultrafine fibers are obtained by drafting a silk fibroin/polyvinyl alcohol/silk fibroin nanofibril composite fiber, and chitosan is coated on the surface of the ultrafine fibers to prepare the ultrafine monofilament suture. The suture has a smooth surface and a uniform structure, a diameter of 36.6 to 42.9 μm, and a breaking strength of 0.25 to 0.31 N, which meets the strength requirements for suture, and has good antibacterial properties, can effectively inhibit bacterial growth, and reduce wound infection. In addition, the silk fibroin, polyvinyl alcohol, and chitosan used in the suture all have excellent biocompatibility, can promote wound healing, and reduce scar hyperplasia, and have great application potential in the field of medical suture materials.

Description

A method for preparing a silk fibroin-based ultrafine monofilament suture

Technical Field

The invention belongs to the technical field of biomedical materials and relates to a method for preparing a silk fibroin-based ultra-fine monofilament suture thread.

Background technique

Surgical sutures are a type of medical material used to suture wounds and connect tissues in surgical operations. They are also the most common materials that can be implanted in the human body. In surgical operations, different types of sutures are generally selected according to the size of the wound and the different suture sites. The diameter, toughness, strength, damage caused by penetrating tissues, and tissue reactions caused by each type of suture are different. Sutures with larger diameters have high tensile strength and are easy to operate, but they are prone to cause tissue inflammation and rejection reactions, and are prone to scarring. They are suitable for areas with large wounds and high strength requirements, such as epidermal sutures on the trunk and limbs; sutures with smaller diameters cause less tissue damage, cause less capillary phenomena, and recover faster, but have high requirements for suture technology. They are suitable for areas with small wounds and low strength requirements, such as sutures of the eyes, mouth, blood vessels, and organs. In general, sutures with smaller diameters are a better choice in surgical operations on the premise of meeting the strength required for wound sutures.

Silk, as a natural protein fiber, is rich in glycine, alanine, serine and other amino acids. It has good mechanical properties, biocompatibility and low immunogenicity, and is one of the most important suture materials at home and abroad. Medical silk sutures have excellent hygroscopicity, softness and knot stability, and are widely used in wound suture, tissue fixation and vascular ligation. According to the preparation method, they can be mainly divided into twisted sutures, braided sutures, barbed sutures and monofilament sutures. In patent CN101244288A, the inventors disclosed a method for preparing a twisted silk surgical suture, which has a simple preparation process, a smooth surface, and high strength, but an unstable shaping effect, and is prone to kinking and deformation during use; in patent CN103816564A, the inventors disclosed a method for preparing a braided silk suture, which is easy to operate and tie a knot, has a stable structure and is not easy to deform, but has a large diameter and a large number of gaps on the surface, which can easily harbor bacteria and increase the risk of postoperative surgical wound infection; in patent CN113197705A, the inventors disclosed a method for preparing a barbed silk suture, which is simple to operate and does not require knotting, but the barb formation process is immature, the overall strength of the suture is uneven, and there is a risk of breakage during and after surgery. Compared with the above three types of sutures, monofilament sutures have a smooth surface, a small diameter, and weak friction resistance when penetrating tissues. They can effectively avoid larger wounds, reduce pain reactions, slow down inflammation, avoid the risk of wound infection, and are less likely to produce scars and subcutaneous lumps. However, the strength of monofilament sutures is relatively low, and there is a risk of wound rupture.

Therefore, how to develop an ultra-fine monofilament suture that is smooth, uniform, strong enough to meet suturing requirements, and biodegradable is a problem that needs to be solved at present.

Summary of the invention

The present invention aims to provide a method for preparing a silk fibroin-based ultrafine monofilament suture thread, so as to solve the problems that the existing monofilament suture thread has relatively low strength and the hidden danger of wound rupture.

The technical solution of the present invention is:

A method for preparing a silk fibroin-based ultrafine monofilament suture thread comprises the following steps:

(1) unwinding the silk fibroin/polyvinyl alcohol/silk fibroin nanofibril primary composite fiber from a winding roller, drawing it, immersing it in a bath liquid to moisten and soften it, then pulling it out of the bath liquid, passing through a yarn guide device into a drawing device, and drawing it between two rollers of the drawing device, and finally evenly winding it onto a collecting device under the guidance of a cyclic reciprocating yarn guide device to obtain the drawn fiber;

(2) Using deionized water as solvent, weigh chitosan powder and dissolve it in ascorbic acid solution to prepare a chitosan solution, fix the two ends of the stretched fiber, completely immerse it in the chitosan solution, take out the soaked fiber and place it in a vacuum oven to dry, so as to obtain a silk fibroin-based ultrafine monofilament suture thread.

Furthermore, in step (1), the method for preparing the silk fibroin/polyvinyl alcohol/silk fibroin nanofibril primary composite fiber comprises the following steps:

(1.1) boiling the waste silk in a sodium carbonate aqueous solution with a bath ratio of 1:400 for 25 minutes, stirring appropriately to fully degummed the waste silk, placing the degummed waste silk in a 9.3 mol/L lithium bromide aqueous solution, dissolving it at a mass ratio of 1:10 at 60° C., and then dialyzing, centrifuging, removing impurities, and concentrating to obtain a silk fibroin aqueous solution with a concentration of 20 wt.%;

(1.2) cutting the degummed waste silk into short fibers of 5 mm in length, soaking them in deionized water at a mass ratio of 1:100, mechanically grinding them for 30 to 90 min, and then filtering the silk slurry through a 100 to 500 mesh filter, centrifuging, and secondary filtering to finally obtain a silk fibroin nanofibril aqueous solution with a concentration of 1 wt.%, wherein the length distribution range of the silk fibroin nanofibril in the silk fibroin nanofibril aqueous solution is 10 to 150 μm, and the diameter distribution range is 20 to 250 nm;

(1.3) The silk nanofibrils are added into the silk fibroin aqueous solution in an amount of 0.1-0.4wt.%, and ultrasonic treatment is performed to make them evenly dispersed. The ultrasonic time is 20min, the temperature is 5°C, and the power is 120W. A polyvinyl alcohol aqueous solution with a concentration of 20wt.% is added into the solution after ultrasonic treatment. The mass ratio of polyvinyl alcohol to silk fibroin is 1:1. After stirring evenly, a silk fibroin/polyvinyl alcohol/silk nanofibril composite aqueous solution is obtained. Silk fibroin/polyvinyl alcohol/silk nanofibril primary composite fibers are prepared by dry-jet wet spinning. The propulsion speed of the dry-jet wet spinning method is 2.8ml/h, the inner diameter of the needle used for extrusion is 0.21mm, the distance of the air section is 2cm, the length of the coagulation bath is 90cm, and the winding speed of the winding device is 92.3m/h.

Furthermore, in step (1), the bath liquid is an ethanol solution, the concentration of the ethanol solution is 50 wt.%, and the immersion time is 30 to 60 s.

Furthermore, in step (1), when the silk fibroin/polyvinyl alcohol/silk fibroin nanofibril primary composite fiber is evenly wound onto a collecting device under the guidance of a cyclic reciprocating yarn guiding device, it is necessary to regulate the fiber unwinding speed and the final collecting speed so that the drafting multiple is 130 to 200%.

Furthermore, in step (2), the concentration of the ascorbic acid solution is 1 wt.%.

Furthermore, in step (2), the chitosan viscosity of the chitosan powder is ≥400 mPa·s.

Furthermore, in step (2), the concentration of the chitosan solution is 0.5 to 3 wt.%.

Furthermore, in step (2), the soaking time is 1 to 5 minutes and the number of times is 1 to 5 times.

Furthermore, in step (2), the drying temperature is 60° C. and the drying time is 3 minutes.

Furthermore, in step (2), the diameter of the silk fibroin-based ultrafine monofilament suture thread is 36.6-42.9 μm, and the breaking strength is 0.25-0.31N.

The present invention provides a method for preparing a silk fibroin-based ultrafine monofilament suture. The method obtains an antibacterial ultrafine monofilament suture by subjecting silk fibroin/polyvinyl alcohol/silk nanofibril primary composite fibers to a wet post-drawing treatment and surface coating with chitosan. The fibers prepared by the method can meet the requirements of No. 9-0 sutures in the national standard "YY0167-2020 Non-absorbable Surgical Sutures". Compared with conventional surgical sutures, the fibers can reduce the suture wound surface, alleviate pain reactions, reduce inflammatory reactions, promote wound healing, and reduce scar hyperplasia during actual application. The sutures are particularly suitable for fine sutures of tissue parts such as the face, eyes, and mouth.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a diagram showing the distribution change of the silk fibroin nanofibrils in the silk fibroin/polyvinyl alcohol/silk fibroin nanofibril primary composite fiber prepared in Example 1 before and after the drawing treatment, wherein (a) is before the drawing and (b) is after the drawing;

FIG2 is a surface morphology of a silk fibroin-based ultrafine monofilament suture prepared in Example 1 according to the method for preparing a silk fibroin-based ultrafine monofilament suture of the present invention before and after coating treatment, wherein (a) is before coating treatment and (b) is after coating treatment;

FIG3 is a diagram showing the antibacterial effect of the silk fibroin-based ultrafine monofilament suture prepared in Example 1 according to the method for preparing a silk fibroin-based ultrafine monofilament suture of the present invention on Escherichia coli and Staphylococcus aureus, wherein (a) is Escherichia coli and (b) is Staphylococcus aureus;

FIG4 is a diagram showing the in vitro degradation of the silk fibroin-based ultrafine monofilament suture prepared in Example 1 according to the method for preparing a silk fibroin-based ultrafine monofilament suture of the present invention in PBS simulated body fluid, wherein (a) is 5 days, (b) is 10 days, (c) is 15 days, (d) is 20 days, (e) is 25 days, and (f) is 30 days;

Figure 5 is a diagram showing the application of the silk fibroin-based ultrafine monofilament suture thread prepared in Example 1 according to the preparation method of the silk fibroin-based ultrafine monofilament suture thread described in the present invention in mouse epidermal suture, wherein (a) is the immediate effect after suture, (b) is the recovery condition after 5 days, (c) is the recovery condition after 10 days, and (d) is the recovery condition after 15 days.

Detailed ways

The purpose of the present invention is to provide a method for preparing a silk fibroin-based ultrafine monofilament suture, wherein a silk fibroin/polyvinyl alcohol/silk fibroin nanofibril composite fiber with good flexibility and large elongation at break is subjected to a drawing process to obtain an ultrafine fiber, and chitosan is coated on the surface of the ultrafine fiber to prepare an ultrafine monofilament suture. The surface of the suture after only the drawing process is rough. If it is directly used for suture, the friction between the suture and the tissue is large, and the surface grooves are easy to hide bacteria. Therefore, chitosan with good film-forming effect is selected to coat it, and chitosan can additionally give the suture a certain antibacterial function.

Specific steps are as follows:

(1) The silk fibroin/polyvinyl alcohol/silk fibroin nanofibril primary composite fiber is unwound from the winding roller and drawn into a 50wt.% ethanol solution to make it wet and softened. After 30-60s of immersion, it is pulled out of the bath liquid, enters the drawing device through the yarn guide device, and is drawn between the two rollers of the drawing device. Finally, it is evenly wound onto the collecting device under the guidance of the reciprocating yarn guide device, and the fiber unwinding speed and the final collection speed are regulated. When the drawing ratio is lower than 130%, the average fiber diameter is larger, about 45μm, which exceeds the requirements of the national standard 9-0 suture; when the drawing ratio is higher than 200%, the fiber is easy to break during the actual operation, and it is difficult to achieve continuous drawing. Therefore, the more appropriate drawing ratio is 130-200%.

The preparation method of the silk fibroin/polyvinyl alcohol/silk fibroin nanofibril composite fiber mentioned in the above steps is as follows:

(1.1) Boil the waste silk in a sodium carbonate aqueous solution with a concentration of 0.25wt.% at a bath ratio of 1:400 for 25 minutes, and stir appropriately to fully degummed the waste silk. The degummed waste silk is placed in a 9.3mol/L lithium bromide aqueous solution, dissolved at a mass ratio of 1:10 at 60°C, and then dialyzed, centrifuged, impurity removed, and concentrated to obtain a silk fibroin aqueous solution with a concentration of 20wt.%.

(1.2) The degummed waste silk fibers were cut into short fibers of 5 mm in length, immersed in deionized water at a mass ratio of 1:100, and mechanically ground for 30 to 90 min. The silk slurry was then filtered through a 100 to 500 mesh filter, centrifuged, and filtered again to finally obtain a 1 wt.% silk nanofibril aqueous solution, wherein the length distribution range of the silk nanofibrils was 10 to 150 μm, and the diameter distribution range was 20 to 250 nm.

(1.3) Add 0.1-0.4wt.% of silk nanofibrils to the silk protein aqueous solution, and perform ultrasonic treatment to make it dispersed evenly, the ultrasonic time is 20min, the temperature is 5°C, and the power is 120W. Add 20wt.% of polyvinyl alcohol aqueous solution to the solution after ultrasonic treatment, the mass ratio of polyvinyl alcohol to silk protein is 1:1, stir evenly to obtain a silk nanofibril/silk protein/polyvinyl alcohol composite aqueous solution, and prepare silk nanofibril/silk protein/polyvinyl alcohol composite fiber by dry-jet wet spinning. Among them, the propulsion speed of the solution is 2.8ml/h, the inner diameter of the needle used for extrusion is 0.21mm, the distance of the air section is 2cm, the length of the coagulation bath is 90cm, and the winding speed of the winding device is 92.3m/h.

(2) Using deionized water as solvent, prepare an ascorbic acid solution with a concentration of 1 wt.%, weigh different masses of chitosan powder (chitosan viscosity is ≥ 400 mPa·s) and dissolve it in the ascorbic acid solution to prepare a chitosan solution with a concentration of 0.5-3 wt.%. Fix both ends of the drawn fiber and completely immerse it in the chitosan solution for 1-5 min and 1-5 times. Take out the soaked fiber and dry it in a vacuum oven at 60°C for 3 min.

In this step, different masses of chitosan powder are weighed because the concentration of the prepared chitosan solution is between 0.5 and 3 wt.%, and different concentrations correspond to different masses of chitosan powder. Chitosan solutions of different concentrations all have good antibacterial effects, and the width of the inhibition zone increases with the increase of chitosan concentration. The antibacterial effect of the chitosan solution with the lowest concentration of 0.5 wt.% reaches a better level.

The silk fibroin-based ultrafine monofilament suture prepared by the above method has a smooth surface, uniform structure, a diameter of 36.6-42.9 μm, and a breaking strength of 0.25-0.31 N, which meets the requirements of No. 9-0 suture in the national standard "YY0167-2020 Non-absorbable Surgical Suture" and has good antibacterial, anti-inflammatory, and healing functions.

In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, the technical solutions of the present invention are further described below in conjunction with specific embodiments. However, the present invention is not limited to the embodiments listed, and should also include any other known changes within the scope of the rights claimed by the present invention.

The term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

Example 1

The following example shows a method for preparing a silk fibroin-based ultrafine monofilament suture, and the specific steps are as follows:

(1) The fibroin/polyvinyl alcohol/silk nanofibril primary composite fiber is unwound from the winding roller and drawn into a 50wt.% ethanol solution to make it wet and softened. After 30s of immersion, it is pulled out of the bath liquid, enters the drawing device through the yarn guide device, and is drawn between two rollers of the drawing device. Finally, it is evenly wound onto the collecting device under the guidance of the cyclic reciprocating yarn guide device, and the fiber unwinding speed and the final collection speed are adjusted to make the drawing multiple 150%. Please refer to Figure 1, which is a diagram of the distribution change of the silk fibroin/polyvinyl alcohol/silk nanofibril primary composite fiber before and after the drawing treatment of the fibroin/polyvinyl alcohol/silk nanofibril primary composite fiber prepared in Example 1 of the preparation method of a fibroin-based ultrafine monofilament suture according to the present invention. It can be seen from Figure 1 that before the drawing treatment, the fibrils inside the fiber are unevenly dispersed, entangled with each other, and have a disordered orientation. After the drawing treatment, the fibrils inside the fiber are evenly dispersed, arranged regularly, and oriented neatly. The fiber crystallinity increases, the strength and toughness increase, and the overall mechanical properties of the fiber are enhanced.

(2) Using deionized water as solvent, prepare an ascorbic acid solution with a concentration of 1 wt.%, weigh different masses of chitosan powder (chitosan viscosity ≥ 400 mPa·s) and dissolve it in the ascorbic acid solution to prepare a chitosan solution with a concentration of 0.5 wt.%. Fix both ends of the drawn fiber and completely immerse it in the chitosan solution for 1 min and 3 times. Take out the soaked fiber and dry it in a vacuum oven at 60°C for 3 min.

The diameter of the silk fibroin-based ultrafine monofilament suture prepared by the above preparation method and process parameters is 39.4 μm, and the breaking strength is 0.31 N. Please refer to Table 1, which is a performance comparison table of sutures prepared in Example 1 and other related patents.

Table 1:

As shown in Table 1, the suture obtained in Example 1 has many advantages such as ultra-fine, antibacterial, good biocompatibility and degradability. Please refer to Figure 2, which is a surface morphology of the suture before and after coating treatment of the suture without coating treatment in Example 1 of the preparation method of a suture based on silk protein protein. It can be seen from Figure 2 that the surface of the suture without coating treatment is rough, the friction with the skin tissue is large during the suture process, and the groove is easy to hide bacteria; while the surface of the suture after coating treatment is smooth, the friction resistance is small when penetrating the tissue during the suture process, and the pain reaction caused is light. Please refer to Figure 3, which is a suture based on the preparation method of a suture based on silk protein ... Please refer to Figure 4, which is a diagram of the in vitro degradation of the silk fibroin-based ultrafine monofilament suture prepared in Example 1 of the preparation method of the silk fibroin-based ultrafine monofilament suture of the present invention in PBS simulated body fluid. As can be seen from Figure 4, as the immersion time increases, the chitosan on the surface of the suture is first dissolved and falls off, and then the silk fibroin-based ultrafine fibers inside are gradually degraded. When the immersion time is 30 days, the weight loss rate of the suture reaches 43.09%. Please refer to Figure 5, which is a diagram of the application of the silk fibroin-based ultrafine monofilament suture thread prepared in Example 1 according to the preparation method of the silk fibroin-based ultrafine monofilament suture thread described in the present invention in mouse epidermal suture. It can be seen from Figure 5 that the suture thread can firmly fix the skin tissue during the suturing process to avoid wound cracking; 5 days after suturing, the wound has recovered to a large extent, and no wound infection and tissue inflammation have occurred; 10 days after suturing, the wound has almost completely recovered without obvious needle holes; 15 days after suturing, the wound has completely recovered without leaving obvious scars, indicating that the suture thread has a good effect of promoting wound healing and reducing scar hyperplasia.

Example 2

The following example shows a method for preparing a silk fibroin-based ultrafine monofilament suture, and the specific steps are as follows:

(1) The silk fibroin/polyvinyl alcohol/silk fibroin nanofibril primary composite fibers are unwound from a winding roller and stretched and immersed in a 50wt.% ethanol solution to make them wet and softened. After 40 seconds of immersion, they are pulled out of the bath liquid, enter a stretching device through a yarn guide device, and are stretched between two rollers of the stretching device. Finally, they are evenly wound onto a collecting device under the guidance of a reciprocating yarn guide device, and the fiber unwinding speed and the final collecting speed are adjusted to make the stretching multiple 130%.

(2) Using deionized water as solvent, prepare an ascorbic acid solution with a concentration of 1wt.%, weigh different masses of chitosan powder (chitosan viscosity ≥ 400mPa·s) and dissolve them in the ascorbic acid solution to prepare a chitosan solution with a concentration of 2wt.%. Fix the two ends of the drawn fiber and completely immerse it in the chitosan solution for 3 minutes and once. Take out the immersed fiber and dry it in a vacuum oven at 60°C for 3 minutes.

The antibacterial silk fibroin-based ultrafine monofilament suture thread prepared by the above-mentioned preparation method and process parameters has a diameter of 42.9 μm and a breaking strength of 0.25N.

Example 3

The following example shows a method for preparing a silk fibroin-based ultrafine monofilament suture, and the specific steps are as follows:

(1) The silk fibroin/polyvinyl alcohol/silk fibroin nanofibril primary composite fibers are unwound from a winding roller and stretched and immersed in a 50wt.% ethanol solution to make them wet and softened. After 50s of immersion, they are pulled out of the bath solution, enter a stretching device through a yarn guide device, and are stretched between two rollers of the stretching device. Finally, they are evenly wound onto a collecting device under the guidance of a reciprocating yarn guide device, and the fiber unwinding speed and the final collecting speed are adjusted to make the stretching multiple 200%.

(2) Using deionized water as solvent, prepare an ascorbic acid solution with a concentration of 1 wt.%, weigh different masses of chitosan powder (chitosan viscosity is ≥ 400 mPa·s) and dissolve it in the ascorbic acid solution to prepare a chitosan solution with a concentration of 1 wt.%. Fix the two ends of the drawn fiber and completely immerse it in the chitosan solution for 5 min and 5 times. Take out the soaked fiber and place it in a vacuum oven for drying at 60°C for 3 min.

The antibacterial silk fibroin-based ultrafine monofilament suture thread prepared by the above-mentioned preparation method and process parameters has a diameter of 36.6 μm and a breaking strength of 0.28N.

Example 4

The following example shows a method for preparing a silk fibroin-based ultrafine monofilament suture, and the specific steps are as follows:

(1) The silk fibroin/polyvinyl alcohol/silk fibroin nanofibril primary composite fibers are unwound from a winding roller and stretched and immersed in a 50wt.% ethanol solution to make them wet and softened. After 60s of immersion, they are pulled out of the bath solution, enter a stretching device through a yarn guide device, and are stretched between two rollers of the stretching device. Finally, they are evenly wound onto a collecting device under the guidance of a reciprocating yarn guide device, and the fiber unwinding speed and the final collecting speed are adjusted to make the stretching multiple 180%.

(2) Using deionized water as solvent, prepare an ascorbic acid solution with a concentration of 1wt.%, weigh different masses of chitosan powder (chitosan viscosity ≥ 400mPa·s) and dissolve them in the ascorbic acid solution to prepare a chitosan solution with a concentration of 3wt.%. Fix the two ends of the stretched fiber and completely immerse it in the chitosan solution for 3 minutes and 3 times. Take out the immersed fiber and place it in a vacuum oven for drying at 60°C for 3 minutes.

The antibacterial silk fibroin-based ultrafine monofilament suture thread prepared by the above-mentioned preparation method and process parameters has a diameter of 39.9 μm and a breaking strength of 0.28N.

In summary, the preparation method of a silk fibroin-based ultrafine monofilament suture thread described in the present invention is to obtain ultrafine fibers by drawing silk fibroin/polyvinyl alcohol/silk fibroin nanofibril composite fibers, and then coat chitosan on the surface of the ultrafine fibers to prepare ultrafine monofilament suture threads. The suture thread has a smooth surface, a uniform structure, a diameter of 36.6 to 42.9 μm, and a breaking strength of 0.25 to 0.31 N, which meets the strength requirements for suture, and has good antibacterial properties, which can effectively inhibit bacterial growth and reduce wound infection. In addition, the silk fibroin, polyvinyl alcohol, and chitosan used in the suture thread all have excellent biocompatibility, can promote wound healing, and reduce scar hyperplasia, and have great application potential in the field of medical suture materials.

It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims (10)

1. The preparation method of the silk fibroin-based superfine monofilament suture is characterized by comprising the following steps of:

(1) Unwinding silk fibroin/polyvinyl alcohol/silk fibroin nano fibril primary composite fibers from a winding roller, drafting, immersing in bath liquid for wetting and softening, then drawing the bath liquid, entering a drawing device through a yarn guide device, drafting between two rollers of the drawing device, and finally uniformly winding the silk fibroin/polyvinyl alcohol/silk fibroin nano fibril primary composite fibers on a collecting device under the guidance of a circulating reciprocating yarn guide device to obtain drawn fibers;

(2) Taking deionized water as a solvent, weighing chitosan powder, dissolving the chitosan powder in an ascorbic acid solution to prepare a chitosan solution, fixing two ends of the drawn fiber, completely immersing the fiber in the chitosan solution for soaking, taking out the soaked fiber, and drying in a vacuum oven to obtain the silk fibroin-based superfine monofilament suture.

2. The method for preparing the silk fibroin-based ultrafine monofilament suture according to claim 1, wherein the method comprises the following steps: in the step (1), the preparation method of the silk fibroin/polyvinyl alcohol/silk fibroin nano-fibril primary composite fiber comprises the following steps:

(1.1) the waste silk is processed according to the following steps: 400 in a sodium carbonate aqueous solution with the concentration of 0.25wt.% for 25min, properly stirring to fully degumm the waste silk, and placing the degummed waste silk in a lithium bromide aqueous solution with the concentration of 9.3mol/L according to the following formula 1:10, dissolving at 60 ℃, dialyzing, centrifuging, removing impurities, concentrating to obtain a silk fibroin aqueous solution with the concentration of 20 wt.%;

(1.2) shearing the degummed waste silk into short fibers with the length of 5mm according to the following steps of 1:100 mass ratio is soaked in deionized water, mechanically grinded for 30-90 min, then silk fibroin slurry is filtered through a 100-500 mesh filter screen, centrifuged and secondarily filtered, and finally silk fibroin aqueous solution with the concentration of 1wt.% is obtained, wherein the length distribution interval of silk fibroin in the silk fibroin aqueous solution is 10-150 mu m, and the diameter distribution interval is 20-250 nm;

(1.3) adding the silk fibroin nano-fibrils into the silk fibroin aqueous solution according to the addition amount of 0.1-0.4 wt.%, uniformly dispersing the silk fibroin nano-fibrils by ultrasonic treatment, wherein the ultrasonic treatment time is 20min, the temperature is 5 ℃, the power is 120W, adding a polyvinyl alcohol aqueous solution with the concentration of 20wt.% into the ultrasonic solution, and the mass ratio of the polyvinyl alcohol to the silk fibroin is 1:1, uniformly stirring to obtain a silk fibroin/polyvinyl alcohol/silk fibroin nano fibril composite aqueous solution, and preparing the silk fibroin/polyvinyl alcohol/silk fibroin nano fibril nascent composite fiber by a dry-jet wet spinning method, wherein the propelling speed of the dry-jet wet spinning method is 2.8ml/h, the inner diameter of a needle head adopted by extrusion is 0.21mm, the distance of an air section is 2cm, the length of a coagulating bath is 90cm, and the winding speed of a winding device is 92.3m/h.

3. The method for preparing the silk fibroin-based ultrafine monofilament suture according to claim 1, wherein the method comprises the following steps: in the step (1), the bath liquid is an ethanol solution, the concentration of the ethanol solution is 50wt.%, and the infiltration time is 30-60 s.

4. The method for preparing the silk fibroin-based ultrafine monofilament suture according to claim 1, wherein the method comprises the following steps: in the step (1), when the silk fibroin/polyvinyl alcohol/silk fibroin nano-fibril primary composite fiber is uniformly wound on the collecting device under the guidance of the circulating reciprocating yarn guiding device, the fiber unwinding speed and the final collecting speed need to be regulated so that the draft multiple is 130-200%.

5. The method for preparing the silk fibroin-based ultrafine monofilament suture according to claim 1, wherein the method comprises the following steps: in step (2), the concentration of the ascorbic acid solution is 1wt.%.

6. The method for preparing the silk fibroin-based ultrafine monofilament suture according to claim 1, wherein the method comprises the following steps: in the step (2), the chitosan viscosity of the chitosan powder is more than or equal to 400 mPas.

7. The method for preparing the silk fibroin-based ultrafine monofilament suture according to claim 1, wherein the method comprises the following steps: in step (2), the chitosan solution has a concentration of 0.5 to 3wt.%.

8. The method for preparing the silk fibroin-based ultrafine monofilament suture according to claim 1, wherein the method comprises the following steps: in the step (2), the soaking time is 1-5 min, and the times are 1-5 times.

9. The method for preparing the silk fibroin-based ultrafine monofilament suture according to claim 1, wherein the method comprises the following steps: in the step (2), the drying temperature is 60 ℃ and the drying time is 3min.

10. The method for preparing the silk fibroin-based ultrafine monofilament suture according to claim 1, wherein the method comprises the following steps: in the step (2), the diameter of the silk fibroin-based ultrafine monofilament suture is 36.6-42.9 mu m, and the breaking strength is 0.25-0.31N.