Nickel-titanium alloy urethral stent with anti-calculus and anti-bacterial dual-function coating and preparation method of nickel-titanium alloy urethral stent

Abstract

The invention provides a nickel-titanium alloy urethral stent with an anti-calculus and antibacterial dual-function coating and a preparation method, and belongs to the technical field of medical instruments. The zwitterionic molecular chain and the cationic molecular chain are covalently grafted on the surface of the nickel-titanium alloy urethral stent to form a bifunctional coating, so that synergistic integration of anti-calculus and antibacterial properties is realized. The dynamic hydration layer of the zwitterionic chain can efficiently block crystal deposition, the cationic chain plays a bactericidal role by destroying bacterial cell membranes, and the coating is firmly combined with the substrate and has excellent biocompatibility. According to the technology, the problems that an existing urethral stent is prone to scaling and infection are remarkably solved, and the medical nickel-titanium stent which has clinical application prospects and has the anti-calculus and antibacterial functions is provided.

Description

Technical Field

[0001] This invention belongs to the field of medical device technology, and in particular relates to a nickel-titanium alloy urethral stent with a dual-function coating that has anti-stone and antibacterial properties, and its preparation method. Background Technology

[0002] Urethral stents are key medical devices used in urological clinical practice to treat urethral stricture. Urethral stricture can be caused by various factors such as trauma, infection, or iatrogenic injury, leading to difficulty urinating, urinary retention, and even kidney damage. Implanting a urethral stent can effectively open the narrowed lumen, restoring and maintaining urethral patency, and is one of the important treatment methods.

[0003] Among the materials used in the manufacture of urethral stents, nickel-titanium (NiTi) shape memory alloys are highly favored due to their unique superelasticity and shape memory effect. These properties enable them to withstand changes in body position and external pressure in the narrow and dynamic urethral environment without breaking or shifting, while also facilitating implantation via minimally invasive methods, greatly improving the service performance of the device and patient comfort.

[0004] However, despite the excellent mechanical properties of nickel-titanium alloys, their implantation in the urethra presents two major clinical challenges: stent surface stones and bacterial infection.

[0005] First, urine is a complex, supersaturated biological fluid rich in inorganic ions such as calcium, oxalate, and phosphate, as well as organic macromolecules such as proteins and mucopolysaccharides. When a nickel-titanium alloy stent is implanted as a foreign body, its bio-inert surface rapidly adsorbs organic matter such as proteins from the urine, forming a "conditioning film." This film provides ideal nucleation sites for the crystallization of inorganic salts, leading to the rapid deposition and growth of crystals such as calcium phosphate and calcium oxalate on the stent surface, eventually forming a hard stone layer. These stones not only block the channels inside and outside the stent, causing it to lose its drainage function, but also irritate the urethral mucosa, causing complications such as pain and bleeding, and greatly increasing the difficulty of subsequent surgical removal.

[0006] Secondly, the presence of urethral stents disrupts the natural barrier of the urethra, providing an ideal surface for retrograde bacterial infection and colonization. Because the urethra is directly connected to the outside world, bacteria (especially Proteus mirabilis) easily adhere to the protein-covered stent surface, multiply rapidly, and secrete extracellular polysaccharide matrix, ultimately forming a dense and difficult-to-remove bacterial biofilm. The bacteria within this biofilm exhibit extremely high resistance to antibiotics and the host's immune system, which is the root cause of persistent and recurrent urinary tract infections (CAUTI). More seriously, the colonization of certain urease-producing bacteria decomposes urea, leading to an increase in urine pH, which drastically accelerates the formation of phosphate stones, creating a vicious cycle where stone and infection problems intertwine.

[0007] A search revealed that existing technologies mainly construct bifunctional coatings on material surfaces through several pathways. One type is the physical adhesion method, represented by patent CN107987578A. This method utilizes the strong adhesiveness of polydopamine to fix antifouling and bactericidal monomers onto the substrate surface using a "one-pot" method. Although this method is simple and has broad substrate applicability, the functional layer and the substrate are not firmly covalently bonded, and there is a risk of peeling under long-term rinsing by bodily fluids. Another type is covalent grafting, but the specific path has limitations: for example, the technology of patent CN110669242B requires the substrate surface to contain epoxy groups in advance, which is not suitable for metals; the core of patent CN102307955B is to "absorb" the initiator into the swellable polymer substrate, which is also difficult to apply efficiently to the dense nickel-titanium alloy surface; and although the silane coupling agent grafting technology proposed by patent CN111686310B is suitable for metal surfaces, its functional combination is "thermosensitive + antibacterial", which fails to achieve the high-efficiency anti-stone / anti-fouling performance required in urethral stent coatings.

[0008] The present invention aims to provide a nickel-titanium alloy scaffold with anti-calculi and antibacterial functions by grafting stable covalent bonds, and its preparation method, thereby solving the above two major technical problems. Summary of the Invention

[0009] Based on this, the purpose of this invention is to provide a nickel-titanium alloy scaffold with a dual-functional coating. A chemical pathway involving surface activation and silane coupling agent anchoring is employed to form a uniform, high-density polymerization reaction site layer on the surface of the nickel-titanium alloy substrate. This pathway provides a stable covalent bonding basis for subsequent grafting of functional layers, effectively improving the coating's stability. Furthermore, through a one-step copolymerization grafting reaction, an amphoteric polymer with anti-calculi properties and a cationic polymer with antibacterial properties are integrated at the molecular chain level. This achieves the synergistic effect of the two functions while ensuring a strong covalent bond between the coating and the substrate, resulting in a nickel-titanium alloy scaffold with both stable and long-lasting anti-calculi and antibacterial functions.

[0010] To achieve the above objectives, the present invention provides the following technical solution: A nickel-titanium alloy urethral stent with a dual-functional coating for both anti-stone and antibacterial purposes includes a nickel-titanium alloy urethral stent body and a dual-functional coating covalently grafted onto the outer surface of the body body. The nickel-titanium alloy urethral stent body is made of medical-grade nickel-titanium shape memory alloy, wherein the mass fraction of nickel in the medical-grade nickel-titanium shape memory alloy is 54.5% to 57.0%, and the mass fraction of titanium is 43.0% to 45.5%; the outer diameter of the stent body is 2.0 mm to 6.0 mm.

[0011] Preferably, the bifunctional coating comprises zwitterionic molecular chains and cationic molecular chains; wherein the zwitterionic molecular chains have anti-stone properties, and the cationic molecular chains have antibacterial properties. The zwitterionic molecular chains inhibit the adsorption and crystallization nucleation of inorganic ions such as calcium and oxalate, as well as proteins in urine, by forming a dense dynamic hydration layer; the cationic molecular chains disrupt the integrity of bacterial cell membranes and inhibit the formation of bacterial biofilms through electrostatic interactions.

[0012] Preferably, the thickness of the bifunctional coating is 50–500 nm, and the surface roughness Ra ≤ 0.2 μm.

[0013] Preferably, the bifunctional coating is anchored to the outer surface of the substrate by covalent bonds; the bifunctional coating is a three-dimensional network structure formed by copolymerization and crosslinking of a polymerization system containing zwitterionic monomers, cationic monomers and crosslinking agents.

[0014] More preferably, the zwitterionic monomer is at least one of methacrylate zwitterionic monomers, imidazolonium zwitterionic monomers, amino acid zwitterionic monomers, and phosphocholine zwitterionic monomers.

[0015] More preferably, the methacrylate zwitterionic monomer is at least one of sulfobetaine methacrylate (SBMA), carboxybetaine methacrylate (CBMA), phosphate betaine methacrylate (PBMA), sulfobetaine ethyl acrylate (SBEA), and carboxybetaine propyl methacrylate (CBPMA); the imidazodium zwitterion is at least one of 1-vinyl-3-(3-sulfopropyl)imidazodium inner salt (VSI) and 1-methacryloyloxyethyl-3-(3-sulfopropyl)imidazodium inner salt (MSI); the amino acid zwitterion is at least one of N-methacryloyl-L-alanine (MAPA) and N-methacryloyl-L-serine (MAS); and the phosphorocholine zwitterion is at least one of 2-methacryloyloxyethyl phosphorylcholine (MPC) and 2-acryloyloxyethyl phosphorylcholine (APC).

[0016] The zwitterionic monomers in this invention can generate strong spatial repulsion and hydration layer barrier effect by constructing a dense hydration layer on the surface of the scaffold, thereby achieving an efficient anti-adhesion effect on organic matter (proteins, mucopolysaccharides) and inorganic salts (calcium, oxalate, phosphate) in urine. Among them, phosphorocholine-based (such as MPC) and imidazoline-based zwitterionic monomers can further optimize the anti-crystallization performance by adjusting the surface charge distribution.

[0017] More preferably, the cationic monomer is at least one of quaternized methacrylate cationic monomers, quaternized heterocyclic cationic monomers, and guanidine salt methacrylate cationic monomers.

[0018] More preferably, the quaternized methacrylate cationic monomer is at least one of quaternized 2-dimethylaminoethyl methacrylate (Q-DMAEMA), quaternized 2-diethylaminoethyl methacrylate (Q-DEAEMA), quaternized 3-dimethylaminopropyl methacrylamide (Q-DMAPMA), methacryloyloxyethyltrimethylammonium chloride (DMC), and methacryloyloxypropyltrimethylammonium chloride (TMC); the quaternized heterocyclic cationic monomer is at least one of quaternized vinylimidazole (Q-VI), quaternized 4-vinylpyridine (Q-4VP), and 1-vinyl-3-alkylimidazolium chloride (such as 1-vinyl-3-butylimidazolium chloride, VBIC); and the guanidine salt methacrylate cationic monomer is at least one of 2-guanidinoethyl methacrylate hydrochloride (GEMA) and 3-guanidinopropyl methacrylamide hydrochloride (GPMA) (the guanidinium group binds to the bacterial cell membrane through stronger electrostatic interaction, disrupting cell membrane stability).

[0019] More preferably, the crosslinking agent is at least one selected from polyethylene glycol dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetramethacrylate, dipentaerythritol hexamethacrylate, N,N'-bis(acryloyl)cysteine, and N,N-methylenebisacrylamide.

[0020] More preferably, the dimethacrylate crosslinking agent is at least one of polyethylene glycol dimethacrylate (PEGDMA, with different molecular weights such as PEG200DMA and PEG400DMA, which can adjust the coating flexibility), ethylene glycol dimethacrylate (EGDMA), diethylene glycol dimethacrylate (DEGDMA), triethylene glycol dimethacrylate (TEGDMA), and 1,4-butanediol dimethacrylate (BDDMA); the polymethacrylate crosslinking agent is at least one of trimethylolpropane trimethacrylate (TMPTMA), pentaerythritol tetramethacrylate (PETMA), and dipentaerythritol hexamethacrylate (DPHA); and the amino / ether bond-containing crosslinking agent is at least one of N,N'-bis(acryloyl)cysteine ​​(BAC, which can form a reduction-responsive crosslinking structure and has both stability and biocompatibility) and N,N-methylenebisacrylamide (MBA).

[0021] Crosslinking agents form covalent crosslinks between functional molecular chains to construct a three-dimensional network structure, thereby improving the adhesion between the coating and the scaffold substrate, mechanical strength, and resistance to body fluid erosion. Among them, multifunctional methacrylate crosslinking agents can further optimize coating stability by increasing the crosslinking density, while PEG-based crosslinking agents can balance coating flexibility and biocompatibility.

[0022] Another object of the present invention is to provide a method for preparing a nickel-titanium alloy urethral stent with a dual-functional coating for both anti-stone and antibacterial purposes, comprising the following steps: (1) Surface pretreatment and functionalization of nickel-titanium alloy support The nickel-titanium alloy urethral stent was cleaned and dried, and then subjected to plasma activation treatment to introduce hydroxyl active groups, resulting in an activated stent. The activated stent was then immersed in an alcohol solution of silane coupling agent and impregnated at room temperature to construct a covalent anchoring layer containing carbon-carbon double bonds on the stent surface. After washing and drying, the surface-functionalized nickel-titanium alloy stent was obtained. (2) Preparation of photosensitive coating precursor solution Weigh out the zwitterionic monomer, cationic monomer and crosslinking agent in proportion, dissolve them in solvent, add photoinitiator, stir in the dark until dissolved and uniform; place the mixed solution in the dark for aeration and deoxygenation treatment to obtain the photosensitive polymerization reaction precursor solution. (3) Ultraviolet light-induced in-situ grafting polymerization The photosensitive polymerization precursor liquid is uniformly attached to the surface of the surface-functionalized nickel-titanium alloy support by dip-coating or ultrasonic atomization spraying, forming a liquid film on the support surface. Then, it is placed in a sealed curing chamber filled with inert gas and irradiated with ultraviolet light to form a solid dual-functional coating. (4) Cleaning and drying of the support After the reaction is complete, the scaffold is ultrasonically cleaned with a good solvent to remove unreacted monomer residues and non-covalently bonded polymers from the surface. It is then equilibrated by soaking in buffer solution and dried to obtain the finished product.

[0023] Preferably, the cleaning and drying in step (1) involves ultrasonic cleaning with an organic solvent and deionized water in sequence, followed by drying; the organic solvent is selected from one or more combinations of acetone, ethyl acetate, diethyl ether, n-hexane, anhydrous ethanol, isopropanol, and ethylene glycol; the ultrasonic cleaning is performed 2 to 10 times, with each cleaning session lasting 5 to 20 minutes and the ultrasonic power being 80 to 200 W; the drying conditions are vacuum drying at 60 to 80°C for 1 to 3 hours, with a vacuum degree ≤ -0.08 MPa.

[0024] Preferably, the plasma treatment gas in step (1) is selected from one or more combinations of oxygen, argon, and air; the plasma treatment power is 80-180W and the treatment time is 10-25min.

[0025] Preferably, the silane coupling agent in step (1) is selected from one or more combinations of 3-(methacryloyloxy)propyltrimethoxysilane, 3-(methacryloyloxy)propyltriethoxysilane, and vinyltrimethoxysilane; the mass fraction of the silane coupling agent in the alcohol solution is 0.5% to 3%, and the solvent is selected from one or more combinations of anhydrous ethanol, isopropanol, and n-butanol; the pH value of the alcohol solution of the silane coupling agent is 3.5 to 5.5, and the pH value is adjusted by using 0.05% to 1.0% glacial acetic acid or citric acid by mass fraction. The soaking time in step (1) is 3 to 8 hours.

[0026] Preferably, the molar ratio of zwitterionic monomer, cationic monomer, and crosslinking agent in step (2) is 40-85:15-50:0.5-8; the total monomer concentration of zwitterionic monomer and cationic monomer is 0.5-2.5 mol / L; and the solvent is selected from ultrapure water, deionized water, anhydrous ethanol, or isopropanol.

[0027] Preferably, the photoinitiator in step (2) is selected from one or more combinations of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone (Irgacure 2959), phenyl-2,4,6-trimethylbenzoyl lithium phosphine oxide (LAP), 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO), and 1-hydroxycyclohexylphenyl ketone (Irgacure 184); the mass-volume concentration of the photoinitiator in the reaction system is 0.1 w / v% to 2.0 w / v; and the pH of the polymerization precursor solution is 6.0 to 8.0.

[0028] Preferably, the lifting speed of the immersion lifting method in step (3) is 1.0 to 10.0 mm / s, and after the lifting is completed, the container is left to stand for 5 to 30 seconds and the liquid accumulated at the bottom of the support is removed; the spraying flow rate of the ultrasonic atomization spraying method is 0.5 to 5.0 mL / min.

[0029] Preferably, the inert gas in step (3) is selected from one or a combination of nitrogen and argon; the wavelength of the ultraviolet light source is 365nm or 405nm, and the light intensity is 20-100 mW / cm². 2 The irradiation time is 30s to 300s; during the irradiation process, the support rotates at a speed of 10 to 60 r / min to ensure uniform curing of the coating.

[0030] Preferably, the good solvent in step (4) is selected from pure water and ethanol aqueous solution, the number of cleaning times is 2 to 5, and the ultrasonic cleaning time for each time is 2 to 10 min; the buffer is selected from one or more combinations of PBS buffer, Tris-HCl buffer and HEPES buffer, and the soaking time is 8 to 15 h.

[0031] Preferably, the drying method in step (4) is selected from vacuum freeze drying or vacuum hot air drying; the freezing temperature of the vacuum freeze drying is ≤-40℃, the drying time is 10~30h, and the vacuum degree is ≤-0.09MPa; the vacuum hot air drying is 30~50℃, the drying time is 8~20h, and the vacuum degree is ≤-0.08MPa.

[0032] This invention offers the following advantages: By covalently grafting zwitterionic and cationic molecular chains onto the surface of a nickel-titanium alloy urethral stent to form a bifunctional coating, it achieves a synergistic integration of anti-stone and antibacterial properties. The dynamic hydration layer of the zwitterionic chains effectively prevents crystal deposition, while the cationic chains exert a bactericidal effect by disrupting bacterial cell membranes. Furthermore, the coating adheres firmly to the substrate and exhibits excellent biocompatibility. This technology significantly improves the problems of scale buildup and infection-proneness in existing urethral stents, providing a promising medical nickel-titanium stent with both anti-stone and antibacterial functions for clinical application. Detailed Implementation

[0033] Example 1 A method for preparing a nickel-titanium alloy urethral stent with a dual-functional coating for anti-stone and antibacterial properties, comprising the following steps: (1) Surface pretreatment and functionalization of nickel-titanium alloy support A medical-grade nickel-titanium alloy urethral stent (outer diameter 2.0 mm, Ni mass fraction 55.2%, Ti mass fraction 44.7%, balance being unavoidable impurities) was ultrasonically cleaned sequentially with acetone, anhydrous ethanol, and deionized water for 12 min each, at an ultrasonic power of 120 W, to remove surface oil and impurities. It was then dried in a vacuum drying oven at 70℃ and -0.092 MPa for 2 h. The dried stent was then placed in a plasma cleaner and treated with oxygen (flow rate 20 sccm) at a power of 130 W for 16 min to introduce hydroxyl active groups. A 1.5% (mass fraction) solution of 3-(methacryloyloxy)propyltrimethoxysilane in anhydrous ethanol was prepared, and 0.3% (mass fraction) glacial acetic acid was added to adjust the pH to 4.5. The plasma-activated stent was immersed in this solution at room temperature for 5.5 h to achieve silane coupling agent grafting. It was then washed three times with anhydrous ethanol for 8 min each time and dried with nitrogen gas at a rate of 5 L / min for later use. The structural formula is as shown in formula (1): (1) (2) Preparation of photosensitive coating precursor solution A mixed solvent of ultrapure water and anhydrous ethanol in a volume ratio of 1:1 was prepared. 0.65 mol of sulfobetaine methacrylate (SBMA), 0.30 mol of quaternized 2-dimethylaminoethyl methacrylate (Q-DMAEMA, 92% purity), and 0.05 mol of N,N-methylenebisacrylamide (MBA) were weighed out in a molar ratio of 65:30:5. The monomers and crosslinking agent were added to the mixed solvent and stirred to dissolve, preparing a mixed solution with a total monomer concentration of 1.5 mol / L. The photoinitiator 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone (Irgacure 2959, 0.5% (w / v)) was added to the mixed solution. The solution was magnetically stirred for 20 min under light-protected conditions until completely dissolved. The solution was then filtered through a 0.45 μm filter membrane to remove insoluble particles. The filtrate was placed in the dark and bubbled with high-purity nitrogen for 30 min to remove dissolved oxygen, yielding a clear and transparent photosensitive coating precursor solution. (3) UV-induced in-situ grafting polymerization The surface-functionalized nickel-titanium alloy scaffold prepared in step (1) was fixed on a precision dip-coating machine. The scaffold was completely immersed in the aforementioned photosensitive coating precursor solution, and then vertically pulled upwards at a constant speed of 5 mm / s to remove it from the liquid surface, forming a uniform prepolymerized liquid film on the scaffold surface. After the pull-up was completed, the scaffold was suspended for 10 seconds under nitrogen protection, and the bottom of the scaffold was gently touched with a dust-free absorbent sponge to remove the accumulated "teardrop" liquid. The scaffold with the liquid film was immediately transferred to a quartz curing chamber filled with high-purity nitrogen (oxygen content <0.1%), and a 365nm UV-LED light source was turned on, with the light intensity set to 50mW / cm². 2 Under the condition that the scaffold rotates at a speed of 30 r / min, it is irradiated and cured for 60 s. The photoinitiator in the liquid film is excited to generate free radicals, which initiate rapid in-situ grafting and cross-linking of functional monomers at the double bond sites on the scaffold surface. The reaction formula is as shown in formula (2): (2) In the formula: n: represents the number of repeating units of the sulfobetaine methacrylate monomer. m: represents the number of repeating units of the quaternized 2-dimethylaminoethyl methacrylate monomer. p: represents the number of repeating units of the N,N-methylenebisacrylamide monomer. (4) Cleaning and drying of the support After the reaction was completed, the stent was removed and first ultrasonically cleaned three times with 50% (volume fraction) ethanol aqueous solution for 12 min each time; then ultrasonically rinsed once with ultrapure water (10 min) to replace residual ethanol. The stent was then immersed in PBS buffer solution with pH 7.3 and osmotic pressure of 300 mOsm / kg for 11 h to allow the coating to fully swell and stabilize; then it was placed in a vacuum freeze dryer and dried at -55℃ and vacuum degree of -0.096 MPa for 18 h to obtain a nickel-titanium alloy urethral stent with a bifunctional coating.

[0034] Example 2 A method for preparing a nickel-titanium alloy urethral stent with a dual-functional coating for anti-stone and antibacterial properties, comprising the following steps: (1) Surface pretreatment and functionalization of nickel-titanium alloy support A medical-grade nickel-titanium alloy urethral stent (outer diameter 3.0 mm, Ni mass fraction 56.0%, Ti mass fraction 43.9%, the remainder being unavoidable impurities) was ultrasonically cleaned sequentially with acetone, anhydrous ethanol, and deionized water for 10 min each, with an ultrasonic power of 110 W; then vacuum-dried at 70℃ and a vacuum degree of -0.09 MPa for 2 h. The stent was placed in a plasma cleaner and treated with oxygen as the treatment gas at a flow rate of 25 sccm and a power of 140 W for 15 min to introduce hydroxyl active groups. A 2.0% (mass fraction) solution of 3-(methacryloyloxy)propyltrimethoxysilane in anhydrous ethanol was prepared, and 0.4% glacial acetic acid was added to adjust the pH to 4.2; the stent was immersed in the solution at room temperature for 6 h, washed three times with anhydrous ethanol (10 min each time), and dried with nitrogen gas at 8 L / min for later use. The structural formula is the same as formula (1).

[0035] (2) Preparation of photosensitive coating precursor solution Prepare a mixed solvent of ultrapure water and isopropanol in a volume ratio of 4:6. Weigh out 0.35 mol of carboxybenzene betaine methacrylate (CBMA), 0.35 mol of sulfobetaine methacrylate (SBMA), 0.25 mol of quaternized vinylimidazolium (Q-VI, 91% purity), and 0.05 mol of MBA according to a copolymerization molar ratio of (CBMA+SBMA):Q-VI:MBA = 70:25:5, and add them to ultrapure water to prepare a mixed solution with a total monomer concentration of 1.2 mol / L. Add the photoinitiator phenyl-2,4,6-trimethylbenzoyl lithium phosphine (LAP) to the solution to a concentration of 0.8% (w / v). After dissolving by stirring in the dark, place the solution in the dark and bubble it with high-purity nitrogen for 30 min to remove dissolved oxygen, obtaining the photosensitive coating precursor solution.

[0036] (3) UV-induced in-situ grafting polymerization The bracket processed in step (1) is fixed on the rotating shaft of the ultrasonic atomizing spraying equipment. The photosensitive coating precursor liquid is loaded into the injection pump, and the ultrasonic generator (power 2.0W) and the focusing ultrasonic nozzle (frequency 120kHz) are turned on. The spraying parameters are set as follows: solution inlet flow rate is 0.8mL / min, nitrogen carrier gas pressure is 0.05MPa, nozzle moving speed is 10mm / s; bracket rotation speed is 60r / min. During the spraying process, the nozzle reciprocates along the bracket axis for 4 cycles, so that the precursor liquid forms a uniform and micron-sized liquid film on the bracket surface. After the spraying is completed, the bracket with the liquid film is immediately placed in a UV curing chamber filled with high-purity nitrogen (oxygen content <0.1%). The 365nm UV-LED light source is turned on, and the light intensity is set to 60mW / cm. 2 The functional monomers were in-situ grafted onto the scaffold surface and cured by irradiation for 90 seconds under continuous scaffold rotation (40 r / min). The reaction formula is as shown in formula (3): (3) The symbols in the formula are defined as follows: n: represents the number of repeating units (degree of polymerization) of carboxybetaine methacrylate monomer in the copolymer, reflecting the molar proportion of this anti-stone hydrophilic monomer in the polymer.

[0037] m: represents the number of repeating units (degree of polymerization) of sulfobetaine methacrylate monomer in the copolymer, reflecting the molar proportion of this antifouling and hydrophilic monomer in the polymer.

[0038] p: represents the number of repeating units (degree of polymerization) of the quaternized vinylimidazolium monomer in the copolymer, reflecting the molar proportion of this antibacterial quaternary ammonium salt functional monomer in the polymer.

[0039] q: represents the number of repeating units of N,N-methylenebisacrylamide crosslinking agent in the crosslinked polymer network: written as q-1 in the product because the crosslinking agent molecule contains two active double bonds.

[0040] (4) Cleaning and drying of the support The stent was washed three times with ultrapure water (15 min each time), and then soaked in PBS buffer with pH 7.4 and osmotic pressure 310 mOsm / kg for 12 h. Subsequently, it was freeze-dried under vacuum (-50℃, -0.095 MPa) for 20 h to obtain a bifunctional coated nickel-titanium alloy urethral stent.

[0041] Comparative Example Medical-grade nickel-titanium alloy urethral stents (without any coating) of the same material as those in Examples 1 and 2 were selected. Comparative Example 1 corresponds to the stent specifications of Example 1 (outer diameter 2.0 mm), and Comparative Example 2 corresponds to the stent specifications of Example 2 (outer diameter 3.0 mm). After surface cleaning and drying treatment in the same manner as in the examples, they were directly used for performance testing.

[0042] 1. Coating basic property test Test methods Coating thickness: The cross-section of the support was observed using a field emission scanning electron microscope (FE-SEM, model: SU8010). Five different fields of view were randomly selected, and the coating thickness was measured using image analysis software. The average value was taken.

[0043] Surface roughness (Ra): The surface of the support was scanned using an atomic force microscope (AFM, model: DimensionIcon) in tapping mode. The scanning range was 5μm×5μm. Three different regions were randomly selected, and the average roughness was calculated.

[0044] Coating adhesion: According to the national standard GB / T9286-1998 "Cross-cut test of paint and varnish film", a cross-cut tester is used to make a grid on the coating surface (grid spacing 1mm, grid depth to the substrate). After sticking the grid area with transparent tape, it is quickly peeled off. The coating peeling is observed and the adhesion grade is evaluated (5B is the best, 0B is the worst).

[0045] Test Results The basic properties of the coating are shown in Table 1.

[0046] Table 1. Test results of basic coating properties

[0047] 2. Anti-calculus performance test Test methods Simulated urine preparation: Based on the main components of human urine, a simulated urine system was prepared, containing Ca. 2+ 5 mmol / L, oxalate 3 mmol / L, protein (bovine serum albumin) 2 mg / mL, and pH adjusted to 6.5–7.0 with Tris-HCl buffer.

[0048] Incubation treatment: Each test sample (Examples 1, 2 and comparative examples) was placed in 50 mL of simulated urine, sealed and placed in a 37°C constant temperature shaking incubator (shaking rate 100 r / min) for 7 days.

[0049] Crystal deposition detection: After incubation, the sample was taken out and gently rinsed three times with deionized water. After drying, the amount of Ca deposited on the sample surface was determined by inductively coupled plasma optical emission spectrometry (ICP-OES, model: iCAP7400), and the amount of crystal deposition was calculated. At the same time, the crystal morphology on the sample surface was observed by FE-SEM, and the crystal coverage was calculated (five fields of view were randomly selected, and the proportion of the crystal coverage area to the total field of view area was calculated).

[0050] Anti-stone efficiency calculation: Anti-stone efficiency (%) = (Comparative example crystal deposition amount - Example crystal deposition amount) / Comparative example crystal deposition amount × 100%.

[0051] Test Results The anti-calculi properties are shown in Table 2.

[0052] Table 2 Results of Anti-calculi Performance Test

[0053] 3. Antibacterial performance test Test methods Test strains: Common pathogenic bacteria of the clinical urinary system, Escherichia coli (ATCC25922) and Proteus mirabilis (ATCC13315), were selected and activated in LB medium to the logarithmic growth phase (OD600 = 0.6–0.8). The cultures were then diluted with PBS buffer to a bacterial concentration of 1 × 10⁻⁶. 6 CFU / mL was used as a standard bacterial suspension for later use.

[0054] Viable bacterial count detection: Each test sample (Examples 1, 2, and comparative examples) was cut into 1cm × 1cm pieces, aseptically treated, and placed in a 24-well cell culture plate. 1 mL of the above-mentioned standard bacterial suspension was added to each well, ensuring complete immersion of the sample. After incubation at 37℃ for 24 h, 2 mL of PBS buffer containing 0.05% Tween-80 was added to each well, and the plate was sonicated for 10 min (80 W) to thoroughly wash away viable bacteria from the sample surface and adhering to it, yielding the eluent.

[0055] The viable bacterial count in the eluent was determined using the serial dilution plating method: the eluent was serially diluted 10-fold, and 100 μL of the appropriately diluted bacterial solution was plated onto LB agar plates. After incubation at 37°C for 18–24 h, the colony count was calculated and converted to the viable bacterial concentration (CFU / mL) per milliliter of eluent. Three replicates were set up for each sample group, and the average value was taken.

[0056] Viable bacteria change factor calculation: Viable bacteria change factor = viable bacteria concentration after 24 hours / initial viable bacteria concentration, which can be used to intuitively characterize the proliferation or decline trend of bacteria on the sample surface.

[0057] Biofilm inhibition rate test: Crystal violet staining was used. After 24 hours of culture, the samples were gently rinsed three times with PBS buffer to remove airborne bacteria, stained with 0.1% crystal violet solution for 30 minutes, rinsed with distilled water until the eluent was colorless, air-dried, and then dissolved in 33% glacial acetic acid solution. The absorbance (OD value) was measured at 570 nm using a microplate reader (Model: Multiskan FC). Biofilm inhibition rate (%) = (Comparative example OD value - Example OD value) / Comparative example OD value × 100%.

[0058] Long-lasting antibacterial test: The samples from Examples 1 and 2 were placed in PBS buffer and soaked at 37°C for 7 days. The above steps for detecting the number of viable bacteria were repeated to determine the concentration of viable bacteria and the fold change of viable bacteria in the samples after 24 hours of soaking.

[0059] Test Results The antibacterial properties are shown in Table 3, and the results of the long-lasting antibacterial test are shown in Table 4.

[0060] Table 3. Antibacterial performance test results (live bacteria count index)

[0061] Table 4. Results of long-lasting antibacterial test (after 7 days of soaking)

[0062] 4. Coating stability test Test methods Sterilization treatment: The samples of Examples 1 and 2 were sterilized by gamma rays (dose 25 kGy) and then placed at room temperature for 24 hours.

[0063] Performance retention rate test: For the sterilized samples, the amount of crystal deposition and sterilization rate were determined according to the above-mentioned methods for "anti-stone performance test" and "antibacterial performance test", and the performance retention rate was calculated: Performance retention rate (%) = performance index after sterilization / performance index before sterilization × 100%.

[0064] Coating integrity observation: FE-SEM was used to observe the morphology of the coating on the surface of the sterilized sample to determine whether there was peeling or cracking.

[0065] Test Results The results of the coating stability test are shown in Table 5.

[0066] Table 5. Coating stability test results

[0067] 5. Test Result Analysis The above test results show that the nickel-titanium alloy urethral stent with dual anti-stone and antibacterial coating prepared in this invention exhibits excellent performance in terms of coating basic properties, anti-stone performance, antibacterial performance, and stability. (1) The coating has a uniform thickness (200-250 nm), low surface roughness (Ra≤0.18 μm), and strong adhesion to the substrate (adhesion grade ≥4B), which is superior to the surface characteristics of the uncoated substrate; (2) It has significant anti-stone properties, and the amount of crystal deposition is reduced by more than 92% compared with the uncoated stent. The crystal coverage rate is only 2.8% to 3.2%, which can effectively inhibit the adsorption and growth of inorganic salt crystals in urine. (3) It has outstanding antibacterial effect and long-lasting effect, showing strong killing and proliferation inhibition effects on Escherichia coli and Proteus mirabilis, common pathogens in the clinical urinary system. After 24 hours of culture, the change in viable bacteria on the surface of the sample in the example was only 0.0007 to 0.002, and the number of bacteria decreased by more than 3 orders of magnitude compared with the initial concentration; while the change in viable bacteria on the surface of the uncoated comparative sample was as high as 51 to 59 times, and a large number of bacteria proliferated. At the same time, the inhibition rate of bacterial biofilm by the sample in the example was ≥94.5%, which can block biofilm-mediated persistent infection from the root. After a long-term test of soaking in PBS buffer at 37℃ for 7 days, the change in viable bacteria of the sample was still controlled within the range of 0.0017 to 0.004, and the antibacterial performance did not show significant decay, which can meet the antibacterial protection requirements during the clinical implantation cycle of urethral stents; (4) The coating has good stability. After γ-ray sterilization, the retention rate of various properties is ≥93%, and there is no peeling or cracking, which meets the requirements for clinical sterilization.

[0068] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A nickel-titanium alloy urethral stent with a dual-functional coating for both anti-stone and antibacterial properties, characterized in that, Includes a nickel-titanium alloy urethral stent body and a bifunctional coating covalently grafted onto the outer surface of the body; The nickel-titanium alloy urethral stent body is made of medical-grade nickel-titanium shape memory alloy, wherein the mass fraction of nickel in the medical-grade nickel-titanium shape memory alloy is 54.5% to 57.0%, and the mass fraction of titanium is 43.0% to 45.5%; the outer diameter of the stent body is 2.0 mm to 6.0 mm.

2. The nickel-titanium alloy urethral stent with a dual-functional coating for anti-calculi and antibacterial purposes according to claim 1, characterized in that, The bifunctional coating comprises zwitterionic molecular chains and cationic molecular chains; The thickness of the bifunctional coating is 50–500 nm, and the surface roughness Ra ≤ 0.2 μm; The bifunctional coating is anchored to the outer surface of the substrate by covalent bonds; the bifunctional coating is a three-dimensional network structure formed by copolymerization and crosslinking of a polymerization system containing zwitterionic monomers, cationic monomers and crosslinking agents.

3. The nickel-titanium alloy urethral stent with a dual-functional coating for anti-calculi and antibacterial purposes according to claim 1, characterized in that, The zwitterionic monomer is at least one of methacrylate zwitterionic monomers, imidazolonium zwitterions, amino acid zwitterions, and phosphocholine zwitterions. The zwitterionic monomer of the methacrylate is at least one of sulfobetaine methacrylate, carboxybetaine methacrylate, phosphate betaine methacrylate, sulfobetaine ethyl acrylate, and carboxybetaine propyl methacrylate. The imidazolonium zwitterion is at least one of 1-vinyl-3-(3-sulfopropyl)imidazolonium inner salt and 1-methacryloyloxyethyl-3-(3-sulfopropyl)imidazolonium inner salt; the amino acid zwitterion is at least one of N-methacryloyl-L-alanine and N-methacryloyl-L-serine; the phosphorocholine zwitterion is at least one of 2-methacryloyloxyethyl phosphorylcholine and 2-acryloyloxyethyl phosphorylcholine.

4. The nickel-titanium alloy urethral stent with a dual-function coating for anti-calculi and antibacterial properties according to claim 1, characterized in that, The cationic monomer is at least one of quaternized methacrylate cationic monomers, quaternized heterocyclic cationic monomers, and guanidine salt methacrylate cationic monomers; The quaternized methacrylate cationic monomer is at least one of quaternized 2-dimethylaminoethyl methacrylate, quaternized 2-diethylaminoethyl methacrylate, quaternized 3-dimethylaminopropyl methacrylamide, methacryloyloxyethyltrimethylammonium chloride, and methacryloyloxypropyltrimethylammonium chloride. The quaternized heterocyclic cationic monomer is at least one of quaternized vinylimidazolium, quaternized 4-vinylpyridine, and 1-vinyl-3-alkylimidazolium chloride. The guanidine salt methacrylate cationic monomer is at least one of 2-guanidinoethyl methacrylate hydrochloride and 3-guanidinopropyl methacrylamide hydrochloride.

5. The nickel-titanium alloy urethral stent with a dual-functional coating for anti-calculi and antibacterial purposes according to claim 1, characterized in that, The crosslinking agent includes at least one of polyethylene glycol dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetramethacrylate, dipentaerythritol hexamethacrylate, N,N'-bis(acryloyl)cystamine, and N,N-methylenebisacrylamide.

6. The method for preparing the nickel-titanium alloy urethral stent with a dual-functional coating for anti-calculi and antibacterial properties according to claim 1, characterized in that, Includes the following steps: (1) Surface pretreatment and functionalization of nickel-titanium alloy support The nickel-titanium alloy urethral stent was cleaned and dried, and then subjected to plasma activation treatment to introduce hydroxyl active groups, resulting in an activated stent. The activated stent was then immersed in an alcohol solution of silane coupling agent and impregnated at room temperature to construct a covalent anchoring layer containing carbon-carbon double bonds on the stent surface. After washing and drying, the surface-functionalized nickel-titanium alloy stent was obtained. (2) Preparation of photosensitive coating precursor solution Weigh out the zwitterionic monomer, cationic monomer and crosslinking agent in proportion, dissolve them in solvent, add photoinitiator, stir in the dark until dissolved and uniform; place the mixed solution in the dark for aeration and deoxygenation treatment to obtain the photosensitive polymerization reaction precursor solution. (3) Ultraviolet light-induced in-situ grafting polymerization The photosensitive polymerization precursor liquid is uniformly attached to the surface of the surface-functionalized nickel-titanium alloy support by dip-coating or ultrasonic atomization spraying, forming a liquid film on the support surface. Then, it is placed in a sealed curing chamber filled with inert gas and irradiated with ultraviolet light to form a solid dual-functional coating. (4) Cleaning and drying of the support After the reaction is complete, the scaffold is ultrasonically cleaned with a good solvent to remove unreacted monomer residues and non-covalently bonded polymers from the surface. It is then equilibrated by soaking in buffer solution and dried to obtain the finished product.

7. The method for preparing the nickel-titanium alloy urethral stent with a dual-functional coating for anti-calculi and antibacterial properties according to claim 6, characterized in that, The cleaning and drying in step (1) involves ultrasonic cleaning with an organic solvent and deionized water in sequence, followed by drying. The organic solvent is selected from one or more combinations of acetone, ethyl acetate, diethyl ether, n-hexane, anhydrous ethanol, isopropanol, and ethylene glycol. The ultrasonic cleaning is performed 2 to 10 times, with each cleaning session lasting 5 to 20 minutes and an ultrasonic power of 80 to 200 W. The drying conditions are vacuum drying at 60 to 80°C for 1 to 3 hours, with a vacuum degree ≤ -0.08 MPa. The plasma treatment gas in step (1) is selected from one or more combinations of oxygen, argon, and air; the plasma treatment power is 80-180W, and the treatment time is 10-25min. The silane coupling agent in step (1) is selected from one or more combinations of 3-(methacryloyloxy)propyltrimethoxysilane, 3-(methacryloyloxy)propyltriethoxysilane, and vinyltrimethoxysilane; the mass fraction of the silane coupling agent in the alcohol solution of the silane coupling agent is 0.5% to 3%, and the solvent is selected from one or more combinations of anhydrous ethanol, isopropanol, and n-butanol; the pH value of the alcohol solution of the silane coupling agent is 3.5 to 5.5, and the pH value is adjusted by using 0.05% to 1.0% glacial acetic acid or citric acid by mass fraction. The soaking time in step (1) is 3 to 8 hours.

8. The method for preparing the nickel-titanium alloy urethral stent with a dual-functional coating for anti-calculi and antibacterial properties according to claim 6, characterized in that, The molar ratio of zwitterionic monomer, cationic monomer, and crosslinking agent in step (2) is 40-85:15-50:0.5-8; the total monomer concentration of zwitterionic monomer and cationic monomer is 0.5-2.5 mol / L; the solvent is selected from ultrapure water, deionized water, anhydrous ethanol, or isopropanol. The photoinitiator in step (2) is selected from one or more combinations of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone, phenyl-2,4,6-trimethylbenzoyl lithium phosphine, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and 1-hydroxycyclohexylphenyl ketone; the mass-volume concentration of the photoinitiator in the reaction system is 0.1 w / v% to 2.0 w / v; and the pH of the precursor solution for the polymerization reaction is 6.0 to 8.

0.

9. The method for preparing a nickel-titanium alloy urethral stent with a dual-functional coating for anti-calculi and antibacterial properties according to claim 6, characterized in that, In step (3), the lifting speed of the immersion lifting method is 1.0 to 10.0 mm / s, and after the lifting is completed, it is left to stand for 5 to 30 seconds and the liquid accumulated at the bottom of the support is removed; the spraying flow rate of the ultrasonic atomization spraying method is 0.5 to 5.0 mL / min. The inert gas in step (3) is selected from one or a combination of nitrogen and argon; the wavelength of the ultraviolet light source is 365nm or 405nm, and the light intensity is 20-100 mW / cm². 2 The irradiation time is 30s to 300s; during the irradiation process, the support rotates at a speed of 10 to 60 r / min to ensure uniform curing of the coating.

10. The method for preparing a nickel-titanium alloy urethral stent with a dual-functional coating for anti-calculi and antibacterial properties according to claim 6, characterized in that, The good solvent in step (4) is selected from pure water and ethanol aqueous solution. The number of cleaning times is 2 to 5, and the ultrasonic cleaning time for each time is 2 to 10 min. The buffer is selected from one or more combinations of PBS buffer, Tris-HCl buffer, and HEPES buffer. The soaking time is 8 to 15 h. The drying method in step (4) is selected from vacuum freeze drying or vacuum hot air drying; the freezing temperature of the vacuum freeze drying is ≤-40℃, the drying time is 10~30h, and the vacuum degree is ≤-0.09MPa; the drying temperature of the vacuum hot air drying is 30~50℃, the drying time is 8~20h, and the vacuum degree is ≤-0.08MPa.

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