A water-retention and toughening type degradable block copolymer for nerve repair and a preparation method thereof

Abstract

The present application relates to a kind of water-retention toughening type degradable block copolymer for nerve repair and preparation method, solve the technical problems that traditional acetylated chitosan material has poor water-retention performance, insufficient mechanical properties and uncontrolled degradation period in clinical application.The acetylated chitosan is prepared by homogeneous acetylation modification of chitosan, grafting methoxypolyethylene glycol hydrophilic branch on the prepared acetylated chitosan backbone, ring-opening polymerization polytrimethylene carbonate flexible block, to prepare water-retention toughening type degradable block copolymer, the water-retention rate of the material still maintains at 38% or more after 2 hours of exposure in air, and the water-retention performance is good;Mechanical properties are good, and physiological mechanics demand of different parts of nerve is adapted after being prepared into sleeve pipe without being compressed and collapsed by surrounding soft tissue;Degradation mode is the synergistic effect of enzymolysis and hydrolysis, and by adjusting acetylation degree of substitution and PTMC block ratio, controllable degradation is realized, and the problem of large individual difference of existing material degradation period is solved.

Description

Technical Field

[0001] This invention belongs to the field of nerve repair technology, specifically relating to a water-retaining and toughening biodegradable block copolymer for nerve repair and its preparation method. Background Technology

[0002] Peripheral nerve injury is a common traumatic disease in clinical practice, with more than 5 million new cases worldwide each year. More than 60% of these patients have nerve defects. The traditional gold standard for treatment is autologous nerve transplantation, but it has unavoidable drawbacks such as donor site damage, limited nerve sources, and donor site dysfunction.

[0003] Biodegradable peripheral nerve repair cannulas represent a core direction for replacing autologous nerve transplantation. They guide nerve axon growth through a closed regenerative microenvironment, avoiding the need for secondary surgery for removal. These cannulas are made from acetylated chitosan, but acetylated chitosan materials have the following drawbacks in clinical applications: Poor water retention: The free amino and hydroxyl groups on the acetylated chitosan molecular chain easily form strong hydrogen bonds. After opening the packaging, it quickly dehydrates within 3-5 minutes, and the molecular chains are tightly packed. The material changes from a flexible state to a hard and brittle state, and it is very easy to crack when bent. It is completely unsuitable for the slow-paced operation requirements of microsurgery. Insufficient mechanical properties: Acetylated chitosan has weak resistance to compression and tension. After being prepared into a cannula, it is easily compressed and collapsed by the surrounding soft tissue, blocking the nerve regeneration channel. At the same time, it has poor resistance to bending fatigue and is very easy to break during intraoperative adjustment. Uncontrollable degradation cycle: The degradation of acetylated chitosan depends entirely on the enzymatic action of human lysozyme. The concentration of lysozyme varies greatly among different patients and at different injury sites, resulting in a degradation cycle that fluctuates between 3 and 18 months, which cannot be precisely matched with the 3-6 month regeneration cycle of peripheral nerves. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a water-retaining and toughening biodegradable block copolymer for nerve repair and its preparation method, thereby solving the technical problems of poor water retention, insufficient mechanical properties and uncontrollable degradation cycle of traditional acetylated chitosan materials in clinical applications.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A water-retaining and toughening biodegradable block copolymer for nerve repair includes an acetylated chitosan backbone, a hydrophilic methoxy polyethylene glycol (mPEG) branch grafted onto the acetylated chitosan backbone, and a flexible polytrimethylene carbonate (PTMC) block ring-opened polymerized onto the acetylated chitosan backbone.

[0006] Furthermore, the degree of acetylation substitution of acetylated chitosan is 45%-55%, the number average molecular weight of mPEG is 2000 Da and the grafting degree is 15%-20%, and the number average molecular weight of PTMC is 5000 Da and the block mass ratio is 10%-15%.

[0007] Furthermore, the viscosity-average molecular weight of acetylated chitosan is 100 kDa.

[0008] A method for preparing a water-retaining, toughening, biodegradable block copolymer for nerve repair includes the following steps: Step 1: Homogeneous acetylation modification of chitosan to obtain acetylated chitosan with an acetylation degree of 45%-55%; Step 2: Graft mPEG hydrophilic side chains and ring-opening polymerize PTMC flexible blocks onto the acetylated chitosan obtained in Step 1; Step 3: After removing impurities based on Step 2, the water-retaining and toughening biodegradable block copolymer is obtained.

[0009] Furthermore, step 1 specifically includes: Step 11: Add chitosan to a homogeneous solvent system of acetic acid and dimethyl sulfoxide, and stir at room temperature for 12-24 hours until completely dissolved to obtain a homogeneous chitosan solution; Step 12: Add acetic anhydride dropwise to the homogeneous chitosan solution, and stir at a constant temperature of 25-30℃ for 4-6 hours to obtain the reaction solution; Step 13: Pour the reaction solution into anhydrous ethanol to precipitate the precipitate. After filtering out the precipitate, wash the precipitate 3-5 times with anhydrous ethanol and dry it under vacuum at 35°C for 24 hours to obtain acetylated chitosan with a degree of acetylation of 45%-55%.

[0010] Further, in step 11, the volume ratio of acetic acid to dimethyl sulfoxide is 1:3 to 1:5.

[0011] Furthermore, step 2 specifically involves: Step 21: Add the acetylated chitosan prepared in step 1 to anhydrous dimethyl sulfoxide and stir at room temperature until completely dissolved to obtain a homogeneous solution; Step 22: Add the catalyst stannous octoate to the homogeneous solution, and under nitrogen protection, add monomethoxy polyethylene glycol glycidyl ether. Stir and react at a constant temperature of 60-65℃ for 6-8 hours to complete the grafting of the hydrophilic side chain of mPEG. Step 23: Continue to add trimethylene carbonate (TMC) monomer to the reaction system, and stir at a constant temperature of 65-70℃ for 12-16 hours to complete the ring-opening polymerization of PTMC flexible block.

[0012] Furthermore, step 3 specifically involves: Step 31: Cool the solution after the reaction in step 23 to room temperature, pour it into a mixed solvent of anhydrous ethanol and diethyl ether (volume ratio 3:1) to precipitate, filter out the precipitate to obtain the crude product; Step 32: After preliminary removal of impurities from the crude product using dichloromethane, the crude product solid after preliminary removal of impurities is extracted with anhydrous ethanol for 24 hours to obtain a semi-finished solid. The semi-finished solid is then vacuum dried at 35°C for 48 hours to obtain purified acetylated chitosan-mPEG-PTMC ternary block copolymer. This acetylated chitosan-mPEG-PTMC ternary block copolymer is the water-retaining and toughening biodegradable block copolymer.

[0013] Compared with the prior art, the present invention has the following beneficial effects: This invention involves homogeneous acetylation modification of chitosan to achieve a uniform distribution of acetylated groups on the chitosan molecular chain, preventing dehydration caused by localized amino enrichment. Simultaneously, the grafted hydrophilic mPEG side chains form a permanent hydration layer around the acetylated chitosan molecular chain, locking in a large amount of free water. Combined with an external composite moisturizing and preservative solution, the material maintains a water retention rate of over 38% after 2 hours of exposure to air, demonstrating excellent water retention performance. Furthermore, this invention introduces PTMC flexible blocks into the acetylated chitosan molecular chain, and by adjusting the proportion of PTMC blocks, the material's tensile strength is improved. The strength and elastic modulus can be controlled, thereby improving the radial compressive strength of the material. After being made into a sleeve, it will not collapse due to pressure from the surrounding soft tissue. It has good mechanical properties and is suitable for the physiological and mechanical needs of nerves in different parts of the body. The ternary block copolymer of this invention is degraded by a combination of enzymatic hydrolysis and hydrolysis. It no longer relies entirely on the enzymatic hydrolysis of lysozyme. By adjusting the degree of acetylation substitution and the proportion of PTMC blocks, controllable degradation is achieved. The degradation cycle fluctuates within ≤1 month, which solves the problem of large individual differences in the degradation cycle of existing materials. It can match the nerve regeneration cycle of different parts of the body and different populations. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0015] Example 1: This Example 1 provides a water-retaining and toughening biodegradable block copolymer, comprising an acetylated chitosan backbone, a hydrophilic methoxy polyethylene glycol (mPEG) branch grafted onto the acetylated chitosan backbone, and a flexible polytrimethylene carbonate (PTMC) block ring-opened polymerized onto the acetylated chitosan backbone.

[0016] The specific parameters are as follows: the degree of acetylation substitution of acetylated chitosan is 50%, and the viscosity-average molecular weight is 100 kDa; the number-average molecular weight of mPEG is 2000 Da, and the grafting degree is 18%; the number-average molecular weight of PTMC is 5000 Da, and the block mass ratio is 12%.

[0017] The preparation method is as follows: Step 1: Homogeneous acetylation modification of chitosan to obtain acetylated chitosan with a degree of acetylation substitution of 50%; Step 2: Graft mPEG hydrophilic side chains and ring-opening polymerize PTMC flexible blocks onto the acetylated chitosan obtained in Step 1; Step 3: After removing impurities based on Step 2, the water-retaining and toughening biodegradable block copolymer is obtained.

[0018] Specifically, step 1 involves preparing 10g of chitosan (95% degree of deacetylation, viscosity-average molecular weight 120kDa), adding the prepared chitosan to a mixed solvent of 1L acetic acid and dimethyl sulfoxide (volume ratio 1:4), stirring at room temperature for 18h until completely dissolved to obtain a homogeneous chitosan solution; adding 8mL of acetic anhydride dropwise to the homogeneous chitosan solution, stirring at 30℃ for 5h; after the reaction is complete, pouring the reaction solution into 5L of anhydrous ethanol to precipitate, filtering out the precipitate, washing the precipitate 4 times with anhydrous ethanol, and vacuum drying the washed precipitate at 35℃ for 24h to obtain acetylated chitosan with a degree of acetylation substitution of 50%.

[0019] Step 2 is as follows: Take 8g of the acetylated chitosan obtained in Step 1, add it to 100mL of anhydrous dimethyl sulfoxide, stir at room temperature until completely dissolved to obtain a homogeneous solution; add 0.4g of stannous octoate catalyst to the homogeneous solution, add 3g of mPEG glycidyl ether under nitrogen protection, stir at 60℃ for 7h to complete the grafting of the hydrophilic side chain of mPEG, and the grafting degree of the hydrophilic side chain of mPEG is 18%; add 2g of TMC monomer, stir at 65℃ for 14h to complete the ring-opening polymerization of PTMC flexible block, and the mass ratio of PTMC block is 12%.

[0020] Step 3 is as follows: After the reaction in step 2 is completed, the solution is cooled to room temperature, poured into 500 mL of a mixed solvent of anhydrous ethanol and diethyl ether (volume ratio 3:1) to precipitate, and the precipitate is filtered out to obtain the crude product. After initial purification of the crude product by dissolving it in dichloromethane, the crude product solid after initial purification was extracted with anhydrous ethanol by Soxhlet extraction for 24 hours to obtain a semi-finished solid. The semi-finished solid was then vacuum dried at 35°C for 48 hours to obtain purified acetylated chitosan-mPEG-PTMC ternary block copolymer. This acetylated chitosan-mPEG-PTMC ternary block copolymer is the water-retaining and toughening biodegradable block copolymer.

[0021] Example 2 provides a water-retaining and toughening biodegradable block copolymer, comprising an acetylated chitosan backbone, a hydrophilic methoxy polyethylene glycol (mPEG) branch grafted onto the acetylated chitosan backbone, and a flexible polytrimethylene carbonate (PTMC) block ring-opened polymerized onto the acetylated chitosan backbone.

[0022] The specific parameters are as follows: the degree of acetylation substitution of acetylated chitosan is 45%, the viscosity-average molecular weight is 100kDa, the grafting degree of mPEG is 20%, the number-average molecular weight is 2000Da, and the proportion of PTMC blocks is 10%, with a number-average molecular weight of 5000Da.

[0023] The preparation method is as follows: Step 1: Homogeneous acetylation modification of chitosan to obtain acetylated chitosan with a degree of acetylation substitution of 45%; Step 2: Graft mPEG hydrophilic side chains and ring-opening polymerize PTMC flexible blocks onto the acetylated chitosan obtained in Step 1; Step 3: After removing impurities based on Step 2, the water-retaining and toughening biodegradable block copolymer is obtained.

[0024] Step 1 specifically involves: preparing 10g of chitosan (95% degree of deacetylation, viscosity-average molecular weight 120kDa), adding the prepared chitosan to a mixed solvent of 1L acetic acid and dimethyl sulfoxide (volume ratio 1:5), stirring at room temperature for 12h until completely dissolved to obtain a homogeneous chitosan solution; adding 8mL of acetic anhydride dropwise to the homogeneous chitosan solution, stirring at 30℃ for 4h; after the reaction is complete, pouring the reaction solution into 5L of anhydrous ethanol to precipitate, filtering out the precipitate, washing the precipitate three times with anhydrous ethanol, and vacuum drying the washed precipitate at 35℃ for 24h to obtain acetylated chitosan with a degree of acetylation substitution of 45%.

[0025] Step 2 is as follows: Take 8g of the acetylated chitosan obtained in Step 1, add it to 100mL of anhydrous dimethyl sulfoxide, stir at room temperature until completely dissolved to obtain a homogeneous solution; add 0.4g of stannous octoate catalyst to the homogeneous solution, add 3g of mPEG glycidyl ether under nitrogen protection, stir at 60℃ for 8h to complete the grafting of mPEG hydrophilic branches, the grafting degree of mPEG hydrophilic branches is 20%; add 2g of TMC monomer, stir at 65℃ for 12h to complete the ring-opening polymerization of PTMC flexible block, the mass ratio of PTMC block is 10%.

[0026] Step 3 is as follows: After the reaction in step 2 is completed, the solution is cooled to room temperature, poured into 500 mL of a mixed solvent of anhydrous ethanol and diethyl ether (volume ratio 3:1) to precipitate, and the precipitate is filtered out to obtain the crude product. After preliminary purification of the crude product with dichloromethane, the crude product solid was subjected to Soxhlet extraction with anhydrous ethanol for 24 hours to obtain a semi-finished solid. The semi-finished solid was then vacuum dried at 35°C for 48 hours to obtain purified acetylated chitosan-mPEG-PTMC ternary block copolymer. This acetylated chitosan-mPEG-PTMC ternary block copolymer is the water-retaining and toughening biodegradable block copolymer.

[0027] Example 3 provides a water-retaining and toughening biodegradable block copolymer, comprising an acetylated chitosan backbone, a hydrophilic methoxy polyethylene glycol (mPEG) branch grafted onto the acetylated chitosan backbone, and a flexible polytrimethylene carbonate (PTMC) block ring-opened polymerized onto the acetylated chitosan backbone.

[0028] The specific parameters are as follows: the degree of acetylation substitution of acetylated chitosan is 55%, the viscosity-average molecular weight is 100kDa, the grafting degree of mPEG is 15%, the number-average molecular weight is 2000Da, and the proportion of PTMC blocks is 15%, with a number-average molecular weight of 5000Da.

[0029] The preparation method is as follows: Step 1: Homogeneous acetylation modification of chitosan to obtain acetylated chitosan with a degree of acetylation substitution of 55%; Step 2: Graft mPEG hydrophilic side chains and ring-opening polymerize PTMC flexible blocks onto the acetylated chitosan obtained in Step 1; Step 3: After removing impurities based on Step 2, the water-retaining and toughening biodegradable block copolymer is obtained.

[0030] Specifically, step 1 involves preparing 10g of chitosan (95% degree of deacetylation, 120kDa viscosity-average molecular weight), adding the prepared chitosan to a mixed solvent of 1L acetic acid and dimethyl sulfoxide (volume ratio 1:3), stirring at room temperature for 24h until completely dissolved to obtain a homogeneous chitosan solution; adding 8mL of acetic anhydride dropwise to the homogeneous chitosan solution, stirring at 30℃ for 6h; after the reaction is complete, pouring the reaction solution into 5L of anhydrous ethanol to precipitate, filtering out the precipitate, washing the precipitate 5 times with anhydrous ethanol, and vacuum drying the washed precipitate at 35℃ for 24h to obtain acetylated chitosan with a degree of acetylation substitution of 55%.

[0031] Step 2 is as follows: Take 8g of the acetylated chitosan obtained in Step 1, add it to 100mL of anhydrous dimethyl sulfoxide, stir at room temperature until completely dissolved to obtain a homogeneous solution; add 0.4g of stannous octoate catalyst to the homogeneous solution, add 3g of mPEG glycidyl ether under nitrogen protection, stir at 60℃ for 6h to complete the grafting of mPEG hydrophilic branches, with a grafting degree of 15%; add 2g of TMC monomer, stir at 65℃ for 16h to complete the ring-opening polymerization of PTMC flexible blocks, with a block mass ratio of 15%.

[0032] Step 3 is as follows: After the reaction in step 2 is completed, the solution is cooled to room temperature, poured into 500 mL of a mixed solvent of anhydrous ethanol and diethyl ether (volume ratio 3:1) to precipitate, and the precipitate is filtered out to obtain the crude product. After preliminary purification of the crude product with dichloromethane, the crude product solid was subjected to Soxhlet extraction with anhydrous ethanol for 24 hours to obtain a semi-finished solid. The semi-finished solid was then vacuum dried at 35°C for 48 hours to obtain purified acetylated chitosan-mPEG-PTMC ternary block copolymer. This acetylated chitosan-mPEG-PTMC ternary block copolymer is the water-retaining and toughening biodegradable block copolymer.

[0033] Comparative Example 1: A pure acetylated chitosan with a degree of acetylation of 50%, without grafting of mPEG hydrophilic side chains, and without ring-opening polymerization of PTMC flexible blocks.

[0034] The acetylated chitosan-mPEG-PTMC ternary block copolymers prepared in Examples 1-3 and the pure acetylated chitosan in Comparative Example 1 were subjected to performance tests. The water retention rate test results were as follows: the water retention rate of the material in Example 1 after 2 hours of exposure to air was 42%, the water retention rate of the material in Example 2 after 2 hours of exposure to air was 48%, the water retention rate of the material in Example 3 after 2 hours of exposure to air was 38%, and the water retention rate of the material in Comparative Example 1 after 2 hours of exposure to air was only 7%. The results of the elongation at break test after dehydration were as follows: the elongation at break of the material after dehydration in Example 1 was 165%, the elongation at break of the material after dehydration in Example 2 was 182%, the elongation at break of the material after dehydration in Example 3 was 152%, and the elongation at break of the material after dehydration in Comparative Example 1 was only 12%. The radial compressive strength test results are as follows: the radial compressive strength of the material in Example 1 is 3.2 MPa, the radial compressive strength of the material in Example 2 is 2.5 MPa, the radial compressive strength of the material in Example 3 is 4.1 MPa, and the radial compressive strength of the material in Comparative Example 1 is only 0.8 MPa; The tensile strength test results are as follows: the tensile strength of the material in Example 1 is 22 MPa, the tensile strength of the material in Example 2 is 18 MPa, the tensile strength of the material in Example 3 is 28 MPa, and the tensile strength of the material in Comparative Example 1 is only 12 MPa. The results of the in vitro degradation cycle fluctuation range test are as follows: the in vitro degradation cycle fluctuation range of the material in Example 1 is 5-6 months, the in vitro degradation cycle fluctuation range of the material in Example 2 is 3-4 months, the in vitro degradation cycle fluctuation range of the material in Example 3 is 7-8 months, and the in vitro degradation cycle fluctuation range of the material in Comparative Example 1 is 3-18 months. The results of the relative cell proliferation rate test were as follows: the relative cell proliferation rate of the material in Example 1 was 96%, the relative cell proliferation rate of the material in Example 2 was 98%, the relative cell proliferation rate of the material in Example 3 was 95%, and the relative cell proliferation rate of the material in Comparative Example 1 was 82%.

[0035] As can be seen from the comparison results of Examples 1-3 and Comparative Example 1, the material of the present invention improves the water retention and water locking capacity of the material by introducing mPEG hydrophilic side chains, and can maintain a high water content for a long time after being exposed to air, preventing the material from losing water and hardening rapidly; the present invention introduces PTMC flexible blocks, and the mechanical properties of the material can be controlled by adjusting the proportion of PTMC flexible blocks, which significantly improves the tensile strength, elongation at break and radial compressive strength of the material. After being prepared into a nerve conduit, it can prevent the collapse due to compression by surrounding soft tissue and adapt to the physiological and mechanical needs of nerves in different parts; The elongation at break after dehydration remains ≥150%, and there is no cracking after bending 180°, solving the problems of low operational tolerance, high brittleness and insufficient flexibility of existing materials after dehydration. This invention enables the material to achieve synergistic degradation through enzymatic and hydrolytic processes by acetylation homogeneous modification and the introduction of PTMC blocks. The degradation cycle can be controlled by adjusting the degree of acetylation substitution and the proportion of PTMC blocks, with a degradation cycle fluctuation range of ≤1 month, reducing individual differences in degradation cycle and matching the nerve regeneration cycle of different sites and different populations. At the same time, the material of this invention has excellent cell compatibility and good cell proliferation activity.

[0036] Finally, it should be noted that the above embodiments are merely preferred embodiments of the present invention used to illustrate the technical solutions of the present invention, and are not intended to limit the invention, nor are they intended to limit the patent scope of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention. That is to say, any changes or refinements made to the main design concept and spirit of the present invention that are not of substantial significance, but whose technical problems are still consistent with the present invention, should be included within the protection scope of the present invention. In addition, the direct or indirect application of the technical solutions of the present invention to other related technical fields are similarly included within the patent protection scope of the present invention.

Claims

1. A water-retaining, toughening, biodegradable block copolymer for nerve repair, characterized in that, It includes an acetylated chitosan backbone, a hydrophilic methoxy polyethylene glycol (mPEG) branch grafted onto the acetylated chitosan backbone, and a flexible polytrimethylene carbonate (PTMC) block that is ring-opened polymerized onto the acetylated chitosan backbone.

2. The water-retaining, toughening, biodegradable block copolymer for nerve repair according to claim 1, characterized in that, The degree of acetylation substitution of acetylated chitosan is 45%-55%, the number average molecular weight of mPEG is 2000 Da and the grafting degree is 15%-20%, and the number average molecular weight of PTMC is 5000 Da and the block mass ratio is 10%-15%.

3. The water-retaining and toughening biodegradable block copolymer for nerve repair according to claim 1, characterized in that, The viscosity-average molecular weight of acetylated chitosan is 100 kDa.

4. A method for preparing a water-retaining, toughening, biodegradable block copolymer for nerve repair according to any one of claims 1-3, characterized in that, Includes the following steps: Step 1: Homogeneous acetylation modification of chitosan to obtain acetylated chitosan with an acetylation degree of 45%-55%; Step 2: Graft mPEG hydrophilic side chains and ring-opening polymerize PTMC flexible blocks onto the acetylated chitosan obtained in Step 1; Step 3: After removing impurities based on Step 2, the water-retaining and toughening biodegradable block copolymer is obtained.

5. The method for preparing a water-retaining and toughening biodegradable block copolymer for nerve repair according to claim 4, characterized in that, Step 1 is as follows: Step 11: Add chitosan to a homogeneous solvent system of acetic acid and dimethyl sulfoxide, and stir at room temperature for 12-24 hours until completely dissolved to obtain a homogeneous chitosan solution; Step 12: Add acetic anhydride dropwise to the homogeneous chitosan solution, stir at 30°C for 4-6 hours to obtain the reaction solution; Step 13: Pour the reaction solution into anhydrous ethanol to precipitate the precipitate. After filtering out the precipitate, wash the precipitate 3-5 times with anhydrous ethanol and dry it under vacuum at 35°C for 24 hours to obtain acetylated chitosan with a degree of acetylation of 45%-55%.

6. The method for preparing a water-retaining and toughening biodegradable block copolymer for nerve repair according to claim 5, characterized in that, In step 11, the volume ratio of acetic acid to dimethyl sulfoxide is 1:3 to 1:

5.

7. The method for preparing a water-retaining and toughening biodegradable block copolymer for nerve repair according to claim 4, characterized in that, Step 2 is as follows: Step 21: Add the acetylated chitosan prepared in step 1 to anhydrous dimethyl sulfoxide and stir at room temperature until completely dissolved to obtain a homogeneous solution; Step 22: Add the catalyst stannous octoate to the homogeneous solution, and under nitrogen protection, add monomethoxy polyethylene glycol glycidyl ether. Stir and react at 60°C for 6-8 hours to complete the grafting of the hydrophilic side chain of mPEG. Step 23: Continue to add trimethylene carbonate (TMC) monomer to the reaction system, and stir at 65°C for 12-16 hours to complete the ring-opening polymerization of PTMC flexible block.

8. The method for preparing a water-retaining and toughening biodegradable block copolymer for nerve repair according to claim 7, characterized in that, Step 3 specifically involves: Step 31: Cool the solution after the reaction in step 23 to room temperature, pour it into a mixed solvent of anhydrous ethanol and diethyl ether (volume ratio 3:1) to precipitate, filter out the precipitate to obtain the crude product; Step 32: After preliminary removal of impurities from the crude product using dichloromethane, the crude product solid after preliminary removal of impurities is extracted with anhydrous ethanol for 24 hours to obtain a semi-finished solid. The semi-finished solid is then vacuum dried at 35°C for 48 hours to obtain purified acetylated chitosan-mPEG-PTMC ternary block copolymer. This acetylated chitosan-mPEG-PTMC ternary block copolymer is the water-retaining and toughening biodegradable block copolymer.