High-toughness plastic for medical needle tube and preparation method of high-toughness plastic

Abstract

The invention discloses a high-toughness plastic for a medical needle tube and a preparation method of the high-toughness plastic, and belongs to the technical field of polymer composite materials. The product comprises the following components: polycaprolactone, maleic anhydride grafted polylactic acid, a chitosan modified hydroxypropyl methyl cellulose derived carbon dot bacteriostatic agent and the like. The preparation method comprises the steps of preparation of the carbon dot bacteriostatic agent, pretreatment of raw materials, preparation of the functionalized master batch, segmented temperature control twin-screw extrusion melt blending and the like. The composite carbon dot bacteriostatic agent is constructed by hydrothermal carbonization-two-step amidation grafting, and is matched with the functionalized master batch preparation and interface regulation and control technology, so that the problems that the bacteriostatic agent of the existing medical needle tube material is easy to migrate, poor in compatibility and insufficient in toughness are solved, the synergistic improvement of long-term bacteriostasis and high toughness is realized, the biocompatibility is guaranteed, and the medical needle tube material has a good application prospect. The device is suitable for intrusive medical instruments such as medical needle tubes.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, and in particular to a high-toughness plastic for medical needle tubes and its preparation method. Background Technology

[0002] As invasive medical devices that come into direct contact with bodily fluids, medical needles must be made of materials that simultaneously meet core requirements such as high toughness, excellent biocompatibility, and long-lasting antibacterial properties. Currently, most commonly used needle materials in clinical practice are traditional plastics or ordinary biodegradable polymers. These materials generally lack antibacterial function, making them prone to cross-infection due to bacterial adhesion and growth on their surface. Furthermore, some materials lack sufficient toughness, posing a risk of breakage during use and making them unsuitable for complex clinical applications.

[0003] To address these issues, existing technologies often employ methods such as adding antibacterial agents to the polymer matrix, including nano-metal particles and small-molecule antibacterial agents; simultaneously, they attempt to improve the biocompatibility of materials by blending with biodegradable polymers. In addition, some studies have explored surface modification to introduce antibacterial groups onto the material surface, thereby enhancing the antibacterial effect.

[0004] However, existing solutions still have significant shortcomings: nano-metal particles are prone to dissolution and produce biotoxicity; small molecule antibacterial agents are prone to migration, resulting in short-lasting antibacterial effects; simple blending of antibacterial agents will damage the polymer matrix structure, leading to a significant decrease in material toughness; surface-modified antibacterial layers are prone to peeling off and it is difficult to achieve overall uniform antibacterial action; at the same time, the poor compatibility of biodegradable polymer blend systems further exacerbates the deterioration of mechanical properties, making it impossible to meet the core requirements of high toughness and long-lasting safe antibacterial action. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a high-toughness plastic for medical needles and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a high-toughness plastic for medical needles includes the following steps: S1. Preparation of carbon dot antibacterial agent: S101. Hydroxypropyl methylcellulose is dissolved in a water-ethanol mixed solvent with a volume ratio of 5:1, and the temperature is raised to 180℃ at a rate of 5℃ / min to carry out a hydrothermal reaction to obtain a crude carbon dot solution. Hydroxypropyl methylcellulose (HPMC) has a backbone of cellulose-derived (1→4)-β-D-glucose units with methyl ether bonds (-O-CH3) and hydroxypropyl ether bonds (-O-CH2CH(OH)CH3) branched on the sides. The molecular chains form a stable aggregated structure through hydrogen bonds. In a 5:1 water-ethanol mixed solvent and a high-temperature, high-pressure hydrothermal environment at 180°C, the mixed solvent plays a key regulatory role: water, as a polar solvent, can penetrate into the interstices of HPMC molecular chains, causing them to swell and weakening the hydrogen bonding between the molecular chains; ethanol, on the other hand, adjusts the dielectric constant of the system, reduces the pressure inside the hydrothermal reactor, and avoids uneven carbonization caused by local overheating. During this process, high temperature and high pressure cause two key breaks in the HPMC molecular chain: first, the (1→4)-β-D-glycosidic bond of the main chain is hydrolyzed and broken, and second, the ether bond of the side chain is cracked. Ultimately, the long-chain polymer is degraded into simple small-molecule polysaccharide fragments, which provide low-molecular-weight precursors for the uniform formation of carbon cores and avoid the problem of uneven carbon dot particle size caused by direct carbonization of macromolecular polymers. Meanwhile, in a hydrothermal environment, water produces a small amount of reactive oxygen at high temperatures. The terminal hydroxyl groups (-CH2OH) of small molecule polysaccharide fragments are first oxidized to aldehyde groups (-CHO). Under continuous high-temperature hydrothermal conditions, the aldehyde groups are further oxidized and eventually converted into carboxyl groups (-COOH). The C-C bonds of some side chain hydroxypropyl groups are broken, and the resulting terminal methylene hydroxyl groups are also converted into carboxyl groups through a similar oxidation pathway. The carboxyl content is usually in the range of 1.5-2.0 mmol / g. ; Under continuous hydrothermal conditions at 180℃, the small molecule polysaccharides generated by degradation undergo spontaneous dehydration condensation reactions of intramolecular and intermolecular hydroxyl groups (-OH). This is the core step in the formation of carbon dots and carbon cores. Intramolecular dehydration preferentially occurs between adjacent hydroxyl groups of polysaccharide molecules, removing one molecule of water and forming a carbon-carbon double bond (C=C). Intermolecular dehydration occurs between hydroxyl groups of different polysaccharide molecules, forming ether bonds (COC) and initiating moderate cross-linking of the small molecule polysaccharides. As the dehydration condensation reaction progresses, the number of oxygen-containing functional groups (-OH, -O-) in the polysaccharide molecules gradually decreases, while the carbon content continues to increase. The carbon-carbon double bonds form a stable large π-bond structure through conjugation. These conjugated structures further aggregate and undergo mild graphitization, eventually forming nanoscale graphitized carbon cores. At the same time, the mild hydrothermal environment can retain a large number of oxygen-containing active functional groups such as hydroxyl and carboxyl groups on the surface of the carbon cores, providing binding sites for the subsequent amidation grafting reaction with chitosan, ultimately resulting in a well-dispersed crude carbon dot solution. The aforementioned carbon dots are hydroxypropyl methylcellulose-derived carbon dots. In the high-toughness antibacterial plastic system for medical needles, these derived carbon dots are not a single functional component, but rather exist as antibacterial activity carriers, covalent grafting core mediators, and sites for enhancing mechanical properties. As an antibacterial active carrier, its surface is rich in primary amino groups (≥0.8mmol / g) and has a zeta potential ≥+20mV after being modified with chitosan. It can destroy the negatively charged bacterial cell membrane through electrostatic interaction to achieve non-toxic and long-lasting physical contact antibacterial action. The nanoscale size (5-20nm) can also improve the antibacterial efficiency. As a covalent grafting core medium, its surface carboxyl groups can be covalently combined with chitosan and maleic anhydride-grafted polylactic acid through a two-step amidation reaction to form a core-shell structure and anchor it on the polymer chain, thus solving the problem of aggregation and precipitation of traditional antibacterial agents. As a site for enhancing mechanical properties, its nanoscale size can serve as a physical cross-linking point, and combined with covalent effects to disperse stress, synergistic modification of nano-hydroxyapatite with low addition amount (1-3 parts) can improve the impact strength and flexural modulus of materials, thereby achieving synergistic improvement of antibacterial function and mechanical properties. S102. After activating the crude carbon dot solution with 1-ethyl-(3-dimethylaminopropyl)carbodiimide / N-hydroxysuccinimide, dissolve low molecular weight chitosan hydrochloride with a molecular weight of 1000-4000 Da in an acetate-sodium acetate buffer solution at pH 5.5. Gradually add the activated crude carbon dot solution to the chitosan hydrochloride solution and carry out an amidation reaction at pH 5-6 and 70°C. The mass ratio of hydroxypropyl methylcellulose to low molecular weight chitosan hydrochloride is 2:1. The surface of the coarse carbon dots has a large number of oxygen-containing functional groups (-COOH, -OH), among which the carboxyl group is the active site for the grafting reaction. In a weakly acidic environment of pH 5-6, 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC) acts as a carboxyl activator and first undergoes a nucleophilic addition reaction with the carboxyl group on the surface of the carbon dots to generate an unstable O-acyl isourea intermediate. This intermediate is readily hydrolyzed, while the addition of N-hydroxysuccinimide (NHS) can react rapidly with the intermediate to generate a stable N-hydroxysuccinimide ester intermediate (-CO-O-NHS), which significantly reduces the activation energy of the reaction between the carboxyl group and the amino group, providing a highly active site for the subsequent amidation reaction. When low molecular weight chitosan hydrochloride (molecular weight 1000-4000 Da) is dissolved in an acetate-sodium acetate buffer solution at pH 5.5, the amino (-NH2) groups on its molecular chain are partially protonated to -NH3. +However, sufficient free amino groups still possess reactivity. The activated carbon dot solution is slowly added dropwise to the chitosan hydrochloride solution. Under constant temperature of 70℃, the N-hydroxysuccinimide ester intermediate on the carbon dot surface undergoes a nucleophilic substitution reaction with the free amino groups of chitosan, removing NHS molecules and forming stable amide bonds (-CONH-). This achieves covalent grafting of chitosan onto the carbon dot surface, constructing a core-shell composite carbon dot. The mass ratio of hydroxypropyl methylcellulose to low molecular weight chitosan hydrochloride is 2:1, which can precisely control the amino grafting density on the carbon dot surface, ensuring that the primary amino content on the composite carbon dot surface is not less than 0.8 mmol / g. The reaction temperature of 70℃ can increase the molecular collision frequency, accelerate the amidation reaction rate, and at the same time avoid the degradation of chitosan molecular chains caused by high temperature, ensuring the structural integrity of the grafted product. ; S103. The reaction solution was purified by ultrafiltration and centrifugation, and then freeze-dried to obtain carbon dot antibacterial agent. The core of ultrafiltration centrifugation is to achieve separation by utilizing the pore size sieving effect of the ultrafiltration membrane: by selecting an ultrafiltration membrane with a molecular weight cutoff smaller than that of chitosan, small molecule impurities in the reaction solution (unreacted EDC, NHS, sodium acetate, free chloride ions, etc.) can pass through the ultrafiltration membrane under centrifugal force, while larger core-shell carbon dots are retained. Freeze-drying involves first freezing the purified carbon dot dispersion below its freezing point, causing the water in the dispersion to transform into solid ice crystals. Then, under vacuum, the ice crystals sublimate directly into gaseous water vapor and leave the system, ultimately yielding a loose and porous solid carbon dot antibacterial agent. This low-temperature drying method avoids the decomposition of active functional groups such as amino and amide bonds on the surface of the composite carbon dots due to high temperatures, while maintaining the nano-dispersion of the carbon dots and preventing agglomeration. S2. Raw material pretreatment: Maleic anhydride-grafted polylactic acid, polycaprolactone, modified nano-hydroxyapatite, and carbon dot antibacterial agent were dried in a vacuum drying oven at 60-80℃ for later use. The vacuum environment is used to lower the boiling point of water and accelerate the evaporation of water adsorbed on the surface of raw materials: the temperature of 60-80℃ can provide the heat energy for water evaporation, and the vacuum conditions (usually vacuum degree ≥-0.09MPa) allow the water on the surface of the raw materials to evaporate and fall off rapidly at low temperature, thereby achieving the drying of the raw materials. S3. Preparation of functionalized masterbatch: Maleic anhydride-grafted polylactic acid was dissolved in dimethyl sulfoxide, and its carboxyl group was activated by 1-ethyl-(3-dimethylaminopropyl)carbodiimide / N-hydroxysuccinimide. Then, a carbon dot antibacterial agent was added, and the temperature was raised to 70°C to carry out an amidation grafting reaction in the solution. Subsequently, the reaction solution was poured into 3 times the volume of anhydrous ethanol for precipitation, filtration, washing, and drying to obtain functionalized masterbatch with a carbon dot mass fraction of 10%-30%. Maleic anhydride-grafted polylactic acid (PLA) molecular chains have maleic anhydride groups grafted onto them. Upon ring opening, these groups generate a large number of free carboxyl groups (-COOH). In dimethyl sulfoxide (DMSO) solvent, 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC) acts as a carboxyl activator, preferentially undergoing a nucleophilic addition reaction with the carboxyl groups on the maleic anhydride-grafted PLA molecular chains to generate an unstable O-acyl isourea intermediate. This intermediate is highly susceptible to hydrolysis and degradation. However, the addition of N-hydroxysuccinimide (NHS) can rapidly react with the intermediate to generate a stable N-hydroxysuccinimide ester active intermediate, significantly reducing the activation energy of the reaction between the carboxyl and amino groups and providing highly active sites for subsequent amidation grafting. When the carbon dot antibacterial agent is added to the above activation solution and heated to 70°C, the primary amino groups on the surface of the carbon dots will launch a nucleophilic attack on the N-hydroxysuccinimide ester active intermediate on the maleic anhydride-grafted polylactic acid molecular chain, resulting in a nucleophilic substitution reaction, removing the NHS small molecule, and finally forming a stable amide bond (-CONH-) between the carbon dots and the maleic anhydride-grafted polylactic acid molecular chain, thus achieving covalent anchoring between the two. ; A reaction temperature of 70℃ can increase the frequency of molecular collisions and accelerate the amidation reaction rate, while avoiding the degradation of polymer molecular chains caused by high temperature. After the reaction is completed, the reaction solution is poured into 3 times the volume of anhydrous ethanol. The addition of anhydrous ethanol destroys the dissolution environment of dimethyl sulfoxide on maleic anhydride-grafted polylactic acid carbon dot graft products. Ethanol is used as a poor solvent to precipitate the covalent graft products. After filtration and washing to remove residual EDC, NHS and unreacted raw materials, functionalized masterbatch with a carbon dot mass fraction of 10%-30% can be obtained after drying. S4, melt blending: Functionalized masterbatch and polycaprolactone are added to a high-speed mixer at 400-500 rpm and mixed at room temperature for 10 min. Then, modified nano-hydroxyapatite and other additives are added and mixed. The mixture is then melt-blended in a twin-screw extruder. The temperatures of each section are set as follows: feeding section 90-110℃, compression section 140-160℃, homogenization section 160-170℃, and die head 160-170℃. The screw speed is 150-250 rpm. The mixture is cooled in a cooling water tank, pelletized, and dried to obtain a high-toughness antibacterial plastic for medical syringes. When the high-speed mixer mixes functionalized masterbatch and polycaprolactone (PCL) at a speed of 400-500 rpm and at room temperature, it relies on mechanical shearing and impact forces to break up the agglomerated particles of functionalized masterbatch, so that the PCL particles and masterbatch are initially uniformly mixed. After the addition of modified nano-hydroxyapatite (n-HA) and additives, the continuous mechanical action can further disperse the modified n-HA into the mixture, forming a premix with a relatively uniform component distribution. The segmented temperature control of the twin-screw extruder (feeding section 90-110℃, compression section 140-160℃, homogenization section 160-170℃) enables the gradual melting of materials: the temperature in the feeding section is lower than the melting point of PCL (58-60℃), ensuring stable material conveying; the increased temperature in the compression section causes the PCL and functionalized masterbatch to gradually melt, and the screw shear force further refines the premix into a molecular-level dispersion system; the high temperature in the homogenization section and the die head maintains the molten state of the material, ensuring uniform dispersion; The KH-550 silane reagent grafted onto the surface of modified n-HA can undergo an amidation reaction with the residual carboxyl groups (-COOH) in the functionalized masterbatch to form stable amide bonds. At the same time, the residual silanol groups (-SiOH) after KH-550 hydrolysis can undergo a dehydration condensation reaction with the terminal hydroxyl groups (-OH) of the polycaprolactone molecular chain to form ether bonds. These interfacial chemical reactions eliminate interfacial defects between the organic polymer matrix and the inorganic n-HA filler, enhance the binding force between components, and avoid interfacial delamination under stress. Meanwhile, the strong shear force provided by the screw speed of 150-250 rpm can further refine the dispersed particle size of n-HA, ultimately endowing the material with excellent toughness and mechanical strength. After being cooled in a cooling water tank, the molten material changes from a molten state to solid particles. The pelletizing and drying processes only remove moisture from the surface of the particles, ultimately yielding a high-toughness antibacterial plastic for medical syringes with uniform performance.

[0007] Preferably, the carbon dot antibacterial agent is a chitosan-modified hydroxypropyl methylcellulose-derived carbon dot, with a surface primary amino content of not less than 0.8 mmol / g and a zeta potential of not less than +20 mV, and the carbon dot antibacterial agent is covalently grafted onto the molecular chain of maleic anhydride-grafted polylactic acid via amide bonds.

[0008] Preferably, the grafting rate of maleic anhydride-grafted polylactic acid is 1.0-3.0 wt%; the modified nano-hydroxyapatite is nano-hydroxyapatite surface-modified with silane coupling agent KH-550, with a particle size of 50-200 nm.

[0009] Preferably, the mass ratio of hydroxypropyl methylcellulose to low molecular weight chitosan hydrochloride in the carbon dot antibacterial agent is 2:1, the molecular weight of low molecular weight chitosan hydrochloride is 1000-4000 Da, the water-ethanol mixed solvent is water and anhydrous ethanol mixed at a volume ratio of 5:1, and the hydrothermal reaction temperature is 180℃.

[0010] Preferably, the antioxidant is a compound of hindered phenolic antioxidant 1010 and phosphite antioxidant 168, with a mass ratio of 1:1; the ultraviolet absorber is a benzotriazole derivative.

[0011] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention employs a composite modification method combining hydrothermal carbonization of hydroxypropyl methylcellulose with directional grafting of chitosan, along with a two-step amidation covalent grafting mechanism, to solve the problems of easy aggregation, easy migration, biotoxic residues, and short-lasting antibacterial effect of traditional antibacterial agents. At the same time, it achieves molecular-level integration of antibacterial function with polymer matrix, thereby improving the long-lasting antibacterial effect while ensuring the biocompatibility of the material.

[0012] 2. This invention employs a pre-preparation method of functionalized masterbatch, combined with a purification mechanism of dimethyl sulfoxide dissolution-anhydrous ethanol precipitation, to solve the problem of uneven dispersion of carbon dot antibacterial agents in the polymer matrix, achieving precise control of carbon dot mass fraction, and laying the foundation for the uniformity of components in subsequent melt blending.

[0013] 3. This invention employs the interface control method of modifying nano-hydroxyapatite with silane coupling agent KH-550, combined with the dual interface reaction mechanism of amino-carboxyl amidation and silanol-hydroxy dehydration condensation, to solve the problems of poor compatibility and deterioration of mechanical properties in biodegradable polymer blend systems, and achieves strong interfacial bonding between inorganic fillers and organic matrix, thereby synergistically improving the toughness and rigidity of materials.

[0014] 4. This invention employs a hydrothermal carbonization method controlled by a water-ethanol mixed solvent, combined with a polymer chain controllable degradation-oxidation-dehydration condensation synergistic mechanism, to solve the problems of uneven particle size and insufficient surface active functional groups during carbon dot preparation, thereby achieving the retention of sufficient carboxyl and hydroxyl groups on the carbon dot surface, providing ample active sites for subsequent grafting reactions. Detailed Implementation

[0015] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0016] Example 1: A method for preparing a high-toughness plastic for medical needles: S1. Preparation of carbon dot antibacterial agent: S101. Hydroxypropyl methylcellulose is dissolved in a water-ethanol mixed solvent with a volume ratio of 5:1, and the temperature is raised to 180℃ at a rate of 5℃ / min to carry out a hydrothermal reaction to obtain a crude carbon dot solution. S102. After activating the crude carbon dot solution with 1-ethyl-(3-dimethylaminopropyl)carbodiimide / N-hydroxysuccinimide, dissolve low molecular weight chitosan hydrochloride with a molecular weight of 2500 Da in an acetate-sodium acetate buffer solution at pH 5.5. Gradually add the activated crude carbon dot solution to the chitosan hydrochloride solution and carry out an amidation reaction at pH 5.5 and 70°C. The mass ratio of hydroxypropyl methylcellulose to low molecular weight chitosan hydrochloride is 2:1. S103. The reaction solution was purified by ultrafiltration and centrifugation, and then freeze-dried to obtain carbon dot antibacterial agent. S2. Raw material pretreatment: Maleic anhydride-grafted polylactic acid, polycaprolactone, modified nano-hydroxyapatite, and carbon dot antibacterial agent were dried in a vacuum drying oven at 60°C for later use. S3. Preparation of functionalized masterbatch: Maleic anhydride-grafted polylactic acid was dissolved in dimethyl sulfoxide. After its carboxyl group was activated by 1-ethyl-(3-dimethylaminopropyl)carbodiimide / N-hydroxysuccinimide, a carbon dot antibacterial agent was added. The mass ratio of maleic anhydride-grafted polylactic acid to carbon dot antibacterial agent was 20:1. The temperature was raised to 70°C, and an amidation grafting reaction was carried out in the solution. Subsequently, the reaction solution was poured into 3 times the volume of anhydrous ethanol for precipitation, filtration, washing, and drying to obtain a functionalized masterbatch with a carbon dot mass fraction of 20%. S4, melt blending: By mass, 10 parts of functionalized masterbatch and 60 parts of polycaprolactone were added to a high-speed mixer at 450 rpm and mixed at room temperature for 10 min. Then, 2 parts of modified nano-hydroxyapatite, 1 part of composite antioxidant, and 0.6 parts of ultraviolet absorber were added and mixed. The mixture was then melt-blended in a twin-screw extruder with the following temperatures set: feeding section 100℃, compression section 150℃, homogenization section 165℃, and die head 165℃. The screw speed was 200 rpm, and the mixture was cooled in a cooling water tank. After pelleting and drying, a high-toughness antibacterial plastic for medical syringes was obtained.

[0017] Example 2: A method for preparing a high-toughness plastic for medical needles: S1. Preparation of carbon dot antibacterial agent: S101. Hydroxypropyl methylcellulose is dissolved in a water-ethanol mixed solvent with a volume ratio of 5:1, and the temperature is raised to 180℃ at a rate of 5℃ / min to carry out a hydrothermal reaction to obtain a crude carbon dot solution. S102. After activating the crude carbon dot solution with 1-ethyl-(3-dimethylaminopropyl)carbodiimide / N-hydroxysuccinimide, dissolve low molecular weight chitosan hydrochloride with a molecular weight of 2500 Da in an acetate-sodium acetate buffer solution at pH 5.5. Gradually add the activated crude carbon dot solution to the chitosan hydrochloride solution and carry out an amidation reaction at pH 5.5 and 70°C. The mass ratio of hydroxypropyl methylcellulose to low molecular weight chitosan hydrochloride is 2:1. S103. The reaction solution was purified by ultrafiltration and centrifugation, and then freeze-dried to obtain carbon dot antibacterial agent. S2. Raw material pretreatment: Maleic anhydride-grafted polylactic acid, polycaprolactone, modified nano-hydroxyapatite, and carbon dot antibacterial agent were dried in a vacuum drying oven at 60°C for later use. S3. Preparation of functionalized masterbatch: Maleic anhydride-grafted polylactic acid was dissolved in dimethyl sulfoxide. After its carboxyl group was activated by 1-ethyl-(3-dimethylaminopropyl)carbodiimide / N-hydroxysuccinimide, a carbon dot antibacterial agent was added. The mass ratio of maleic anhydride-grafted polylactic acid to carbon dot antibacterial agent was 5:1. The temperature was raised to 70°C, and an amidation grafting reaction was carried out in the solution. Subsequently, the reaction solution was poured into 3 times the volume of anhydrous ethanol for precipitation, filtration, washing, and drying to obtain a functionalized masterbatch with a carbon dot mass fraction of 20%. S4, melt blending: By mass, 20 parts of functionalized masterbatch and 60 parts of polycaprolactone were added to a high-speed mixer at 450 rpm and mixed at room temperature for 10 min. Then, 2 parts of modified nano-hydroxyapatite, 1 part of composite antioxidant, and 0.6 parts of ultraviolet absorber were added and mixed. The mixture was then melt-blended in a twin-screw extruder with the following temperatures set: feeding section 100℃, compression section 150℃, homogenization section 165℃, and die head 165℃. The screw speed was 200 rpm, and the mixture was cooled in a cooling water tank. After pelleting and drying, a high-toughness antibacterial plastic for medical syringes was obtained.

[0018] Example 3: A method for preparing a high-toughness plastic for medical needles: S1. Preparation of carbon dot antibacterial agent: S101. Hydroxypropyl methylcellulose is dissolved in a water-ethanol mixed solvent with a volume ratio of 5:1, and the temperature is raised to 180℃ at a rate of 5℃ / min to carry out a hydrothermal reaction to obtain a crude carbon dot solution. S102. After activating the crude carbon dot solution with 1-ethyl-(3-dimethylaminopropyl)carbodiimide / N-hydroxysuccinimide, dissolve low molecular weight chitosan hydrochloride with a molecular weight of 2500 Da in an acetate-sodium acetate buffer solution at pH 5.5. Gradually add the activated crude carbon dot solution to the chitosan hydrochloride solution and carry out an amidation reaction at pH 5.5 and 70°C. The mass ratio of hydroxypropyl methylcellulose to low molecular weight chitosan hydrochloride is 2:1. S103. The reaction solution was purified by ultrafiltration and centrifugation, and then freeze-dried to obtain carbon dot antibacterial agent. S2. Raw material pretreatment: Maleic anhydride-grafted polylactic acid, polycaprolactone, modified nano-hydroxyapatite, and carbon dot antibacterial agent were dried in a vacuum drying oven at 60°C for later use. S3. Preparation of functionalized masterbatch: Maleic anhydride-grafted polylactic acid was dissolved in dimethyl sulfoxide. After its carboxyl group was activated by 1-ethyl-(3-dimethylaminopropyl)carbodiimide / N-hydroxysuccinimide, a carbon dot antibacterial agent was added. The mass ratio of maleic anhydride-grafted polylactic acid to carbon dot antibacterial agent was 20:1. The temperature was raised to 70°C, and an amidation grafting reaction was carried out in the solution. Subsequently, the reaction solution was poured into 3 times the volume of anhydrous ethanol for precipitation, filtration, washing, and drying to obtain a functionalized masterbatch with a carbon dot mass fraction of 20%. S4, melt blending: By mass, 20 parts of functionalized masterbatch and 60 parts of polycaprolactone were added to a high-speed mixer at 450 rpm and mixed at room temperature for 10 min. Then, 2 parts of modified nano-hydroxyapatite, 1 part of composite antioxidant, and 0.6 parts of ultraviolet absorber were added and mixed. The mixture was then melt-blended in a twin-screw extruder with the following temperatures set: feeding section 100℃, compression section 150℃, homogenization section 165℃, and die head 165℃. The screw speed was 200 rpm, and the mixture was cooled in a cooling water tank. After pelleting and drying, a high-toughness antibacterial plastic for medical syringes was obtained.

[0019] Comparative Example 1: Compared with Example 3, the number of functionalized masterbatches in Comparative Example 1 was 35 parts, and other conditions remained unchanged.

[0020] Comparative Example 2: Compared with Example 3, in Comparative Example 2, the mass ratio of maleic anhydride-grafted polylactic acid to carbon dot antibacterial agent was 35:1, while other conditions remained unchanged.

[0021] Comparative Example 3: Compared with Example 3, no carbon dot antibacterial agent was added in Comparative Example 3, while other conditions remained unchanged.

[0022] Comparative Example 4: Compared with Example 3, the nano-hydroxyapatite in Comparative Example 4 was not modified, and other conditions remained unchanged.

[0023] Comparative Example 5: Compared with Example 3, Comparative Example 5 did not add maleic anhydride-grafted polylactic acid, that is, the carbon dot antibacterial agent was directly mixed with the matrix, and no functional masterbatch was prepared, while other conditions remained unchanged.

[0024] Performance testing: 1. Following the standard performance tests in GB / T 1040.2-2006 "Tension Properties of Plastics", GB / T 1843-2008 "Impact Strength Test of Plastic Cantilever Beams", GB / T 9341-2008 "Bending Properties Test of Plastics - Determination of Bending Strength", GB / T 21510-2008 "Test Method for Antibacterial Properties of Nano-Inorganic Materials", GB / T 31402-2015 "Test Method for Antibacterial Properties of Plastic Surfaces", GB / T16886.5-2017 "Biological Evaluation of Medical Devices - Part 5: In Vitro Cytotoxicity Tests", and GB / T 1633-2000 "Determination of Vicat Softening Temperature of Thermoplastic Plastics", the high-toughness plastics prepared in the above examples and comparative proportions were tested for tensile strength, elongation at break, impact strength, flexural strength, flexural modulus, antibacterial rate against Escherichia coli and Staphylococcus aureus, surface antibacterial long-term effect, biosafety, and Vicat softening point.

[0025] Table 1 below shows the mechanical and heat resistance data of the high-toughness plastics for medical needles prepared in each embodiment and comparative example, including mechanical indicators such as tensile strength and elongation at break, as well as the Vicat softening point, a heat resistance parameter. Combined with the differences in the preparation processes of each example, the differences in the materials' performance in terms of toughness, rigidity, and heat resistance can be clearly compared.

[0026] Table 2 below shows the antibacterial and biosafety performance data of the high-toughness plastics for medical needles prepared in each example and comparative example. It covers the antibacterial rate against Escherichia coli and Staphylococcus aureus, as well as the surface antibacterial longevity and cytotoxicity level after 7 days. Combined with the differences in the preparation process of each example, the antibacterial effect and biosafety performance can be compared intuitively:

[0027] Data Analysis: As shown in Tables 1 and 2, the plastic prepared in Example 3 exhibits balanced and excellent mechanical and antibacterial properties. Mechanistically, the amount of functionalized masterbatch added in this example is within a reasonable range. The carbon dot antibacterial agent achieves stable bonding with the polymer molecular chain through a two-step amidation grafting process, while the modified nano-hydroxyapatite forms a good interfacial bond with the matrix. This synergistic effect ensures both uniform dispersion and long-lasting effect of the antibacterial agent, while also enhancing the interaction between matrix molecular chains and effectively dispersing stress, thus achieving a balance between high toughness and antibacterial function, with all performance indicators reaching optimal equilibrium.

[0028] Compared to Example 3, the mechanical properties of Example 1 showed a certain degree of decline, and the antibacterial performance was also slightly weakened. The core reason is that the amount of functionalized masterbatch added in Example 1 was insufficient, resulting in a lower effective content of carbon dot antibacterial agent in the system, and a reduced proportion of maleic anhydride-grafted polylactic acid. On the one hand, the role of carbon dots as physical cross-linking points was weakened, failing to effectively enhance the binding force between matrix molecular chains, resulting in poor stress dispersion and a decline in mechanical properties; on the other hand, the insufficient number of antibacterial active sites weakened the adsorption and destruction ability against bacteria, thus leading to a slight reduction in antibacterial performance.

[0029] Compared to Example 3, Comparative Example 1 showed significantly deteriorated mechanical properties, with only a slight improvement in antibacterial properties. Mechanistic analysis revealed that the excessive addition of functionalized masterbatch in Comparative Example 1 resulted in an excessively high proportion of maleic anhydride-grafted polylactic acid in the system. Excessive grafted polymers easily lead to molecular chain entanglement, forming stress concentration points in the matrix, which are prone to fracture under stress, significantly reducing the material's toughness and tensile properties. Simultaneously, the excessive functionalized masterbatch increased the density of antibacterial active sites, slightly improving antibacterial performance, but this improvement came at the cost of sacrificing mechanical properties, failing to meet the comprehensive performance requirements of medical needle materials.

[0030] Compared to Example 3, Example 2 showed a significant improvement in antibacterial performance, but a slight decrease in toughness-related mechanical properties. Mechanistically, in the preparation of the functionalized masterbatch in Example 2, the ratio of maleic anhydride-grafted polylactic acid to carbon dot antibacterial agent was more biased towards carbon dots, resulting in increased carbon dot grafting density, a significant increase in antibacterial active sites, and enhanced antibacterial effect. However, excessively high carbon dot grafting density increases steric hindrance between molecular chains, weakening the flexibility of the matrix molecular chains. Simultaneously, the uniformity of carbon dot dispersion in the matrix slightly decreased, leading to a slight reduction in material toughness.

[0031] Compared with Example 3, Comparative Example 2 showed a significant weakening of antibacterial performance, while its mechanical properties remained essentially the same. The core mechanism lies in the fact that during the preparation of the functionalized masterbatch in Comparative Example 2, the proportion of carbon dots in the ratio of maleic anhydride-grafted polylactic acid to carbon dot antibacterial agent was too low. This resulted in insufficient numbers of carbon dots grafted onto the polymer chain, leading to a significant reduction in the density of antibacterial active sites in the system, thus failing to effectively exert its antibacterial effect. However, the low amount of carbon dots added had little impact on the flexibility and dispersibility of the molecular chain; therefore, the mechanical properties did not fluctuate significantly and remained largely consistent with Example 3.

[0032] Compared to Example 3, Comparative Example 3 almost completely lost its antibacterial properties, while its mechanical properties showed no significant difference. From a mechanistic perspective, Comparative Example 3 did not contain any carbon dot antibacterial agent; therefore, the system lacked components with antibacterial activity, making it impossible to adsorb and destroy bacteria, resulting in near-zero antibacterial performance. In contrast, carbon dots primarily function as antibacterial agents and auxiliary reinforcing agents in the system. Their absence did not affect the molecular chain bonding state of the polymer matrix itself, nor did it alter the interfacial interaction between the modified nano-hydroxyapatite and the matrix. Therefore, its mechanical properties remained similar to those of Example 3.

[0033] Compared to Example 3, Comparative Example 4 showed a significant decline in all mechanical properties, while its antibacterial properties remained essentially the same. Mechanistically, Comparative Example 4 used unmodified nano-hydroxyapatite, whose surface lacks silane coupling agent-modified active groups, preventing interfacial chemical reactions with the polymer matrix. This resulted in significant interfacial defects between the inorganic filler and the organic matrix. Under stress, these defects easily become stress concentration points, triggering interfacial delamination and drastically reducing the material's mechanical properties. However, the antibacterial properties were unaffected by filler modification and remained consistent with Example 3.

[0034] Compared to Example 3, Comparative Example 5 showed a significant deterioration in mechanical properties, and its antibacterial performance and long-lasting effect also decreased markedly. The core reason is that Comparative Example 5 did not prepare a functionalized masterbatch; the carbon dot antibacterial agent was directly mixed with the matrix and could not be covalently grafted and anchored onto the polymer chain. On the one hand, the carbon dots easily aggregated, forming stress concentration points and disrupting the matrix continuity; on the other hand, the unanchored carbon dots were prone to migration, which reduced both the long-lasting antibacterial effect and weakened the interfacial bonding force, ultimately leading to a double decline in both mechanical and antibacterial properties.

[0035] The above embodiments and comparative examples illustrate that the appropriate addition amount of functionalized masterbatch, the suitable ratio of carbon dot antibacterial agent and maleic anhydride-grafted polylactic acid, the modification of nano-hydroxyapatite, and the preparation process of functionalized masterbatch are key to ensuring the synergistic effect of high toughness and long-lasting antibacterial effect in materials. Deviation from optimal parameters or the absence of key processes / components will lead to performance imbalance and failure to meet medical requirements.

[0036] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A high-toughness plastic for medical syringes, characterized in that, Includes the following components by weight: 50-70 parts polycaprolactone, 10-30 parts functionalized masterbatch, 1-3 parts modified nano-hydroxyapatite, 0.5-2 parts composite antioxidant, and 0.3-1 parts ultraviolet absorber; The functionalized masterbatch is prepared by reacting maleic anhydride-grafted polylactic acid with a carbon dot antibacterial agent at a mass ratio of 5-30:1, linked by amide bonds. The carbon dot antibacterial agent is chitosan-modified hydroxypropyl methylcellulose-derived carbon dots with a surface primary amino content of not less than 0.8 mmol / g and a zeta potential of not less than +20 mV. The preparation method of the carbon dot antibacterial agent is characterized by including the following steps: S1. Hydroxypropyl methylcellulose was dissolved in a water-ethanol mixed solvent and subjected to a hydrothermal reaction to obtain a crude carbon dot solution; S2. The crude carbon dot solution is activated with 1-ethyl-(3-dimethylaminopropyl)carbodiimide / N-hydroxysuccinimide, and then subjected to an amidation reaction with low molecular weight chitosan hydrochloride at pH 5-6 and 70°C. S3. The reaction solution is purified by ultrafiltration and centrifugation, and then freeze-dried to obtain the carbon dot antibacterial agent.

2. The high-toughness plastic for medical needle tubes according to claim 1, characterized in that, The grafting rate of the maleic anhydride-grafted polylactic acid is 1.0-3.0 wt%; the modified nano-hydroxyapatite is nano-hydroxyapatite with a particle size of 50-200 nm, which has been surface-modified with silane coupling agent KH-550.

3. The high-toughness plastic for medical needle tubes according to claim 1, characterized in that, The mass ratio of hydroxypropyl methylcellulose to low molecular weight chitosan hydrochloride in the carbon dot antibacterial agent is 2:

1. The molecular weight of low molecular weight chitosan hydrochloride is 1000-4000 Da. The water-ethanol mixed solvent is water and anhydrous ethanol mixed at a volume ratio of 5:

1. The hydrothermal reaction temperature is 180℃.

4. The high-toughness plastic for medical needle tubes according to claim 1, characterized in that, The antioxidant is a compound of hindered phenolic antioxidant 1010 and phosphite antioxidant 168, with a mass ratio of 1:1; the ultraviolet absorber is a benzotriazole derivative.

5. A method for preparing a high-toughness plastic for medical needles as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Raw material pretreatment: Maleic anhydride-grafted polylactic acid, polycaprolactone, modified nano-hydroxyapatite, and carbon dot antibacterial agent were dried in a vacuum drying oven at 60-80℃. S2. Preparation of functionalized masterbatch: Maleic anhydride-grafted polylactic acid was dissolved in dimethyl sulfoxide, and its carboxyl group was activated by 1-ethyl-(3-dimethylaminopropyl)carbodiimide / N-hydroxysuccinimide. Then, it was subjected to an amidation grafting reaction with carbon dot antibacterial agent in solution. The mass ratio of maleic anhydride-grafted polylactic acid to carbon dot antibacterial agent was 5-30:

1. Subsequently, the mixture was precipitated, filtered, washed, and dried to obtain carbon dot-grafted functionalized masterbatch. S3, melt blending: The functionalized masterbatch, polycaprolactone, modified nano-hydroxyapatite and other additives are mixed and melt-blended in a twin-screw extruder, cooled in a cooling water tank, pelletized and dried to obtain a high-toughness antibacterial plastic for medical needle tubes.

6. The method for preparing a high-toughness plastic for medical needle tubes according to claim 1, characterized in that, The mass fraction of carbon dot antibacterial agent in the functionalized masterbatch is 10%-30%.

7. The method for preparing a high-toughness plastic for medical needle tubes according to claim 1, characterized in that, The set temperatures for each section of the twin-screw extruder in S3 are: feeding section 90-110℃, compression section 140-160℃, homogenization section 160-170℃, and die head 160-170℃; screw speed 150-250rpm.

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