A method of polishing medical grade metal tubing and uses thereof

Abstract

This application relates to the field of medical devices, specifically disclosing a polishing method for medical-grade metal tubing and its application. The method sequentially includes surface pretreatment, mechanical rough polishing, mechanical fine polishing, and final cleaning steps. Specifically, the mechanical rough polishing uses a first polishing fluid to reduce the surface roughness of the tubing to Ra 0.4–0.8 μm. This polishing fluid contains diamond abrasive and a dispersant. The mechanical fine polishing uses a second polishing fluid to further reduce the surface roughness to Ra 0.05–0.1 μm. This polishing fluid contains diamond abrasive, modified boron nitride particles, modified alumina particles, a dispersant, and a lubricant. Through this process, an ultra-smooth, low-damage surface can be obtained while maintaining the original dimensional accuracy of the tubing. Furthermore, the entire process is environmentally friendly and pollution-free, resulting in a clean tubing surface free of harmful residues. This method is particularly suitable for the mass production of medical-grade metal tubing with stringent requirements for dimensional and surface quality.

Description

Technical Field

[0001] This application relates to the field of medical devices, and more specifically, to a polishing method for medical-grade metal tubing and its application. Background Technology

[0002] Medical-grade metal tubing is widely used in critical medical fields such as orthopedic implants, cardiovascular stents, surgical instruments, and minimally invasive interventional catheters. These tubing materials not only require excellent biocompatibility and mechanical properties, but their dimensional accuracy and surface quality directly impact the safety and effectiveness of medical devices. Specifically, medical-grade metal tubing typically requires micron-level dimensional accuracy, including strict tolerance control for outer diameter, inner diameter, wall thickness, roundness, and straightness. Simultaneously, its inner and outer surfaces must achieve an ultra-smooth surface (surface roughness Ra is typically required to be ≤0.4 μm, or even lower), and any visible scratches, pits, microcracks, or other defects are not permitted. Furthermore, extremely high cleanliness and the absence of harmful residues are also fundamental requirements for ensuring its biocompatibility.

[0003] Currently, the mainstream processes for surface polishing of metal pipes in the industry mainly include mechanical polishing and electrolytic polishing.

[0004] Mechanical polishing typically utilizes polishing wheels, polishing belts, or centrifugal polishing equipment, along with polishing media containing hard abrasives (such as alumina or silicon carbide), to remove surface material through physical friction, thereby improving gloss and reducing roughness to some extent. However, for thin-walled, dimensionally precise medical tubing, the continuous grinding action during mechanical polishing can easily lead to uneven material removal, causing uncontrollable variations in the tubing's outer diameter, inner diameter, or wall thickness, making it difficult to meet the stringent requirements of micron-level dimensional tolerances. Furthermore, improper process control can easily introduce new scratches or embed abrasive particles into the surface.

[0005] Electropolishing is a surface treatment technology based on the principle of electrochemical anodic dissolution. It places the pipe as the anode in a specific electrolyte, dissolving microscopic protrusions on the surface by passing an electric current, thus obtaining a smooth and clean surface. Theoretically, this method can achieve good surface quality with minimal impact on dimensions. However, in practical applications, electropolishing has limited ability to level deep scratches, pits, and other severe defects on the pipe surface. More importantly, the electrolytes used in traditional electropolishing processes often contain high concentrations of highly corrosive and toxic chemicals such as phosphoric acid, sulfuric acid, and chromic acid. This not only poses significant safety and health risks during production but also makes wastewater treatment extremely difficult, easily causing serious environmental pollution. If cleaning is not thorough after polishing, harmful ions (such as chromium ions) remain on the pipe surface, posing serious biocompatibility risks and failing to meet the cleanliness and safety standards for medical materials.

[0006] Therefore, existing polishing technologies cannot simultaneously meet the multiple stringent requirements of medical-grade metal tubing for "maintaining ultra-high dimensional accuracy," "obtaining an ultra-smooth, defect-free surface," and "environmentally friendly process with clean, residue-free results." In view of this, this application is hereby submitted. Summary of the Invention

[0007] To address the aforementioned issues, this application provides a polishing method for medical-grade metal tubing and its application.

[0008] The technical solution adopted in this application is as follows:

[0009] In a first aspect, this application provides a polishing method for medical-grade metal tubing, comprising:

[0010] Ultrasonic cleaning is performed on the medical-grade metal tubing to be treated.

[0011] The ultrasonically cleaned pipe was mechanically rough-polished using a first polishing solution to achieve a surface roughness of Ra 0.4 μm to 0.8 μm.

[0012] The pipe is further mechanically polished using a second polishing solution until its surface roughness reaches Ra 0.05 μm to 0.1 μm.

[0013] The pipes after the mechanical polishing step are cleaned and dried.

[0014] Both the first polishing liquid and the second polishing liquid are water-based polishing liquids containing hard abrasives, polycarboxylate dispersants and surfactants, and the second polishing liquid also contains a lubricant.

[0015] Furthermore, the aforementioned hard abrasive includes at least one of diamond abrasive, modified boron nitride particles, and modified alumina particles.

[0016] The modified boron nitride particles are prepared by sintering cubic boron nitride with a binder (such as TiN or AlN) to form polycrystalline cubic boron nitride; the modified alumina particles are α-Al₂O₃ particles obtained by adding suitable additives and controlling the calcination process. Both can be commercially available products.

[0017] Furthermore, the aforementioned first polishing liquid comprises, by weight percentage:

[0018] Diamond abrasive 30%~50%,

[0019] Secondary alcohol ethoxylates 2%~10%,

[0020] Non-foaming surfactant 1%~4%,

[0021] Polycarboxylate dispersants 1%~5%,

[0022] The remainder is water.

[0023] In this technical solution, diamond abrasive, with its extremely high hardness, serves as the primary abrasive, responsible for rapidly and efficiently removing macroscopic unevenness, oxide layers, and deep defects from the pipe surface, laying the foundation for subsequent fine polishing. A high content of diamond abrasive ensures a high material removal rate during the rough polishing stage. Secondary alcohol ethoxylates primarily function as wetting and cleaning agents. A non-foaming surfactant, preferably HNF1-8, is used to specifically control foam and ensure process stability (during high-speed centrifugal polishing, mechanical stirring easily generates a large amount of foam, which reduces polishing efficiency, affects the uniformity of abrasive distribution, and may lead to uneven polishing). A polycarboxylate dispersant primarily works through steric hindrance, ensuring the high concentration of diamond micropowder remains stably suspended in water for a long period, preventing sedimentation and agglomeration, and guaranteeing uniform abrasive distribution during polishing, thereby achieving consistent material removal and surface roughness.

[0024] Using a polishing slurry with this composition for rough polishing, the high-concentration diamond abrasive, under a stable dispersion system, can quickly and uniformly reduce the surface roughness of medical-grade metal tubing to the Ra range of 0.4-0.8μm, effectively eliminating macroscopic defects.

[0025] Furthermore, the aforementioned second polishing slurry, by weight percentage, comprises:

[0026] Diamond abrasive 20%~30%,

[0027] Modified boron nitride particles 2%~10%,

[0028] Modified alumina particles 1%~12%,

[0029] Lubricant 1%~4%,

[0030] Polycarboxylate dispersants 1%~5%,

[0031] Nonionic surfactants 1%~4%,

[0032] The remainder is water.

[0033] This technical solution employs three types of abrasives: diamond abrasive, with a lower content than coarse polishing fluid and typically finer particle size, continues to perform the main micro-cutting function, further reducing surface roughness; modified boron nitride particles effectively fill and smooth finer scratches; simultaneously, their excellent lubricity reduces frictional heat, preventing surface burns or plastic deformation, which is crucial for protecting precision dimensions; modified alumina particles, with a hardness between diamond and boron nitride, primarily assist diamond in finer cutting; their unique hardness and shape allow them to work synergistically with boron nitride, providing cutting force while promoting plastic flow of surface material rather than brittle fracture, thus achieving higher surface integrity. Polycarboxylate dispersants play the same role as described above. Lubricants (such as polyethylene glycol) further reduce the coefficient of friction, provide buffering, and aid in the adhesion and film formation of the polishing fluid. Nonionic surfactants enhance the ability to wet, clean, and emulsify residual oil.

[0034] Traditional fine polishing often uses only a single, finer abrasive. This application employs a ternary composite abrasive system of diamond, modified boron nitride, and modified alumina. Diamond ensures a basic micron / submicron level material removal rate, modified boron nitride introduces a "solid lubrication" and "flattening" mechanism, and modified alumina achieves performance transition and synergy between abrasives of different hardness. This composite abrasive system can achieve ultra-low roughness and extremely high surface quality with extremely high efficiency.

[0035] Furthermore, the lubricant mentioned above is polyethylene glycol, and the nonionic surfactant is fatty alcohol polyoxyethylene ether.

[0036] Furthermore, the average size of the diamond abrasive is 1.0~1.4mm; the average size of the modified boron nitride particles and modified alumina particles is 0.1~0.25mm.

[0037] Furthermore, the above-mentioned mechanical rough polishing process is carried out using high-speed centrifugal polishing, with a polishing speed of 200~230 r / min and a polishing time of 90~150 min.

[0038] Furthermore, the above-mentioned mechanical polishing process is carried out using high-speed centrifugal polishing with a polishing speed of 280~320 r / min and a polishing time of 90~200 min.

[0039] Secondly, this application provides an application of the polishing method for the above-mentioned medical-grade metal tubing, which is made of stainless steel or titanium alloy and is used in the fields of cardiovascular stents, minimally invasive surgical instruments, and orthopedic implant catheters.

[0040] In summary, this application has the following beneficial effects:

[0041] The medical-grade metal tubing polishing method provided in this application, through a two-step mechanical polishing process and a specially formulated water-based polishing fluid system, solves multiple technical problems in traditional technologies, such as difficulty in maintaining dimensional accuracy, insufficient surface quality, environmental pollution, and harmful residues, achieving the following significant beneficial effects:

[0042] 1. Traditional mechanical polishing, due to uneven abrasive distribution and improper cutting force control, easily leads to uncontrollable changes in key dimensions such as pipe wall thickness and diameter. This invention, through optimized formula and process parameters, achieves continuous control from macroscopic leveling to nanoscale precision polishing, simultaneously maintaining ultra-high dimensional accuracy (no deformation) and ultra-smooth surface quality (Ra≤0.1μm) of medical-grade metal pipes, far exceeding medical standards (typically Ra≤0.4μm).

[0043] 2. In the rough polishing stage, the first polishing fluid effectively eliminates significant defects on the original surface (such as scratches and pits), providing a uniform base for fine polishing. In the fine polishing stage, the second polishing fluid uses a composite abrasive system of "diamond abrasive + modified boron nitride + modified alumina," which can form a "nanoscale rolling polishing" effect during the polishing process. This mechanism can effectively smooth out micro-scratches, reducing the surface scratch depth by up to 90%, thereby obtaining a perfect surface with high gloss, minimal defects, and low residual stress, which is beneficial to improving the fatigue life and biocompatibility of medical devices. At the same time, through the combination of "abrasive (diamond, etc.)" and "polycarboxylate dispersant," the abrasive dispersion stability is greatly improved, and the centrifugal sedimentation rate is reduced by more than 50%, ensuring the uniformity of abrasive action during the polishing process and preventing dimensional deviations caused by local over-cutting.

[0044] 3. This application uses water-based polishing fluid throughout the entire process, completely eliminating the strong acids, heavy metals, and other hazardous chemicals used in traditional electrolytic polishing. This eliminates environmental pollution and occupational health risks at the source, and waste liquid treatment is simple. The final stage of the process uses anhydrous ethanol for ultrasonic cleaning, which can thoroughly remove any polishing media residue from the surface. The final pipe surface is clean, free of any chemical hazards, fully meeting the stringent requirements for cleanliness and biosafety of medical materials. Attached Figure Description

[0045] Figure 1 The surface inspection results of the medical-grade metal tubing provided in Embodiment 6 of this application;

[0046] Figure 2 The surface inspection results of the medical-grade metal tubing provided in Embodiment 9 of this application. Detailed Implementation

[0047] The embodiments of the present invention will be described in detail below with reference to the examples. However, those skilled in the art will understand that the following examples are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention. Specific conditions not specified in the examples shall be carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0048] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0049] First set of embodiments

[0050] This set of embodiments provides a polishing method for medical-grade metal tubing, the polishing method comprising:

[0051] (1) Surface pretreatment: The tube with an outer diameter of 1.44 mm, an inner diameter of 1.37 mm, and a length of 5 mm is used as the medical-grade metal tube to be treated. The tube is ultrasonically cleaned with anhydrous ethanol to remove metal debris and impurities adhering to the surface of the medical-grade metal tube. After cleaning, it is rinsed clean with anhydrous ethanol.

[0052] (2) Mechanical rough polishing: Mix the medical grade metal tubing with the first polishing liquid evenly, and use a high-speed centrifugal polishing machine to perform mechanical rough polishing on the medical grade metal tubing. The rotation speed is 200 r / min and the polishing time is 120 min.

[0053] The composition of the first polishing slurry used (based on a total weight of 100%) is shown in Table 1:

[0054] Table 1.

[0055]

[0056] Wherein, secondary alcohol AEO-9 S9 is a secondary alcohol ethoxylate; HNF1-8 is a non-foaming surfactant; the average size of the diamond abrasive is 1.2 mm; the dispersant in Examples 1-3 and Comparative Example 2 is Tehosan™ 2028C, and the dispersant in Comparative Example 3 is lecithin.

[0057] (3) Mechanical polishing: Mix the medical-grade metal tubing with the second polishing liquid evenly, and use a high-speed centrifugal polishing machine to perform mechanical polishing on the medical-grade metal tubing. The speed is 300 r / min and the polishing time is 90 min.

[0058] The second polishing liquid, based on a total weight of 100%, comprises the following raw materials in parts by weight:

[0059] The composition consists of 30% diamond abrasive (average size 0.2 mm), 10% modified boron nitride particles (average size 0.15 mm), 8% modified alumina particles (average size 0.2 mm), 3% polyethylene glycol, 3% Tehosan™ 2028C, 3% fatty alcohol polyoxyethylene ether, and the balance being water.

[0060] (4) Finished product cleaning: After the medical-grade metal pipes are polished, they are ultrasonically cleaned with anhydrous ethanol and then dried.

[0061] The wall thickness and roughness of the pipes after treatment in the first set of examples were measured, and the results are shown in Table 2:

[0062] Table 2.

[0063]

[0064] As shown in Table 2, Examples 1-3 of this application exhibit excellent polishing effects, achieving a surface roughness of less than 0.8 μm after rough polishing and no deformation of the pipe with a surface roughness of less than 0.1 μm after fine polishing. In contrast, Comparative Example 1, lacking a dispersant, resulted in easy abrasive settling and caking during polishing, making it difficult to achieve a good polishing effect. Comparative Example 2, with its higher content of dispersant (Tehosan™ 2028C), also negatively impacted the polishing effect. Comparative Example 3, although containing a dispersant, exhibited poor ability to prevent abrasive settling and caking, still struggled to achieve a satisfactory polishing effect.

[0065] Second set of embodiments

[0066] This set of embodiments provides a polishing method for medical-grade metal tubing, which is consistent with the steps of the first set of embodiments, and the first polishing liquid adopts the composition ratio of Embodiment 3. The difference lies in the composition of the second polishing liquid (based on a total weight of 100%), as shown in Table 3:

[0067] Table 3.

[0068]

[0069] The diamond abrasive had an average size of 0.2 mm; the modified boron nitride had an average size of 0.15 mm; the modified alumina had an average size of 0.2 mm; the dispersant was Tehosan™ 2028C; and Comparative Example 3 used ordinary boron nitride particles and alumina particles of the same size.

[0070] The wall thickness and roughness of the pipes after treatment in the second set of examples were measured, and the results are shown in Table 4:

[0071] Table 4.

[0072]

[0073] As shown in Table 2, the addition of modified boron nitride and modified alumina particles during the fine polishing process helps to form a composite abrasive system with diamond abrasives, achieving synergy between abrasives of different hardness, and ensuring that the surface roughness after fine polishing is below 0.1 μm (Examples 4-6). Comparative Example 4, lacking modified boron nitride particles, and Comparative Example 5, lacking modified alumina particles, both struggled to achieve an effective composite abrasive system; while Comparative Example 6, using ordinary boron nitride and alumina particles, showed limited improvement in fine polishing and failed to meet the requirements. This is because: the polishing method of this application involves placing the workpiece and ceramic abrasive together in a container, and through high-frequency vibration or rotation, causing random, uniform rolling friction and micro-cutting between the abrasive and the workpiece. The continuous, high-frequency friction between a large number of ceramic particles and the metal surface generates heat and ultimately leads to the peeling off of fine materials, achieving workpiece polishing. The higher the hardness of the ceramic particles, the stronger the cutting ability and the better the polishing effect. Modified boron nitride and modified alumina particles have high strength, resulting in a better polishing effect than unmodified particles.

[0074] Third set of embodiments

[0075] This set of embodiments provides a polishing method for medical-grade metal tubing, which is consistent with the steps of the first set of embodiments. The first polishing liquid adopts the composition ratio of Embodiment 3, and the second polishing liquid adopts the composition ratio of Embodiment 6. The difference lies in the process parameters for rough polishing and fine polishing, as shown in Tables 5 and 6:

[0076] Table 5. Rough Polishing Process

[0077]

[0078] Note: The fine polishing process parameters for all embodiments and comparative examples in Table 5 are the same, namely a polishing speed of 300 r / min and a polishing time of 90 min.

[0079] Table 6. Fine Polishing Process

[0080]

[0081] Note: The rough polishing process parameters for all embodiments and comparative examples in Table 6 are the same, namely a polishing speed of 200 r / min and a polishing time of 120 min.

[0082] As can be seen from Tables 5 and 6, the process parameters for rough polishing and fine polishing have a significant impact on the polishing effect. Figure 1 The surface detection results are from Example 6. Figure 2The results are for surface inspection in Example 9. During the rough polishing stage, when the rotation speed exceeds 230 r / min (as in Comparative Example 7), the pipe is prone to deformation. During the fine polishing stage, when the rotation speed exceeds 320 r / min (as in Comparative Example 8), the pipe is prone to deformation; when the rotation speed is less than 280 r / min (as in Comparative Example 9), the surface roughness is relatively high and not smooth enough.

[0083] Test case

[0084] In vitro cytotoxicity test

[0085] I. Experimental Procedure:

[0086] 1.1. Blank control

[0087] Name: MEM culture medium containing 10% fetal bovine serum

[0088] Extraction conditions: 37 ℃, 24 h, 40 rpm

[0089] 1.2. Negative Control

[0090] Name: High Density Polyethylene Film

[0091] Extraction ratio 6cm 2 1 mL

[0092] Extraction conditions: 37 ℃, 24 h, 40 rpm

[0093] 1.3. Positive Control

[0094] Name: Powder-free latex gloves

[0095] Extraction ratio: 6 cm² : 1 mL

[0096] Extraction conditions: 37 ℃, 24 h, 40 rpm

[0097] 1. Experimental Design

[0098] 2.1 Extraction solution

[0099]

[0100] 2.2 Experimental Procedure

[0101] (1) L-929 cells were cultured in MEM medium containing 10% fetal bovine serum and antibiotics (penicillin 100 IU / mL, streptomycin 100 µg / mL) and placed in an incubator (5% CO2, 37℃, >90% humidity). Cells were digested with 0.25% trypsin (containing EDTA) to prepare a single-cell suspension. The cell suspension was centrifuged (200 g, 3 min), and then the cells were redispersed in the culture medium to adjust the cell density to 1×105 cells / mL. The cell suspension was seeded into a 96-well culture plate, 100 µL per well, and incubated in an incubator for 24 h.

[0102] (2) After the cells grow into a monolayer, discard the original culture medium and add 100µL of different concentrations of test sample extract (100%, 75%, 50%, 25%), blank control solution, positive control (100%) and negative control solution (100%) respectively. Incubate for 24h at 37℃, 5%CO2 and >90% humidity. Perform 6 replicates for each group.

[0103] (3) After 24 h, take out the 96-well plate and observe the cell morphology. Then discard the original culture medium, add 50 µL MTT (1 mg / mL) to each well, and incubate for 2 h (5% CO2, 37℃, >90% humidity). Discard the supernatant and add 100 µL isopropanol to each well to dissolve the crystals.

[0104] (4) Measure the absorbance value on an ELISA reader with 570 nm as the main absorption wavelength and 650 nm as the reference wavelength.

[0105] II. Experimental Results:

[0106] The cell morphology results are shown in Table 7:

[0107] Table 7.

[0108]

[0109] The cell viability results are shown in Table 8:

[0110] Table 8.

[0111]

[0112] As can be seen from Tables 7 and 8, the metal tubing obtained by the polishing method of this application did not show potential cytotoxicity to L-929 cells and is biosafety.

[0113] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A polishing method for medical-grade metal tubing, characterized in that, It includes: Ultrasonic cleaning is performed on the medical-grade metal tubing to be treated. The ultrasonically cleaned pipe was mechanically rough-polished using a first polishing solution to achieve a surface roughness of Ra 0.4μm~0.8μm. The pipe is further mechanically polished using a second polishing solution until its surface roughness reaches Ra 0.05μm~0.1μm; The pipes after the mechanical polishing step are cleaned and dried. Both the first polishing liquid and the second polishing liquid are water-based polishing liquids containing hard abrasives, polycarboxylate dispersants and surfactants, and the second polishing liquid also contains a lubricant.

2. The polishing method for medical-grade metal tubing according to claim 1, characterized in that, The hard abrasive includes at least one of diamond abrasive, modified boron nitride particles, and modified alumina particles.

3. The polishing method for medical-grade metal tubing according to claim 2, characterized in that, The first polishing slurry comprises, by weight percentage: Diamond abrasive 30%~50%, Secondary alcohol ethoxylates 2%~10%, Non-foaming surfactant 1%~4%, Polycarboxylate dispersants 1%~5%, The remainder is water.

4. The polishing method for medical-grade metal tubing according to claim 2, characterized in that, The second polishing slurry comprises, by weight percentage: Diamond abrasive 20%~30%, Modified boron nitride particles 2%~10%, Modified alumina particles 1%~12%, Lubricant 1%~4%, Polycarboxylate dispersants 1%~5%, Nonionic surfactants 1%~4%, The remainder is water.

5. The polishing method for medical-grade metal tubing according to claim 4, characterized in that, The lubricant is polyethylene glycol, and the nonionic surfactant is fatty alcohol polyoxyethylene ether.

6. The polishing method for medical-grade metal tubing according to any one of claims 2-4, characterized in that, The diamond abrasive has an average size of 1.0~1.4 mm; the modified boron nitride particles and modified alumina particles have an average size of 0.1~0.25 mm.

7. The polishing method for medical-grade metal tubing according to claim 1, characterized in that, The mechanical rough polishing process is carried out using high-speed centrifugal polishing, with a polishing speed of 200~230 r / min and a polishing time of 90~150 min.

8. The polishing method for medical-grade metal tubing according to claim 1, characterized in that, The mechanical polishing process is carried out using high-speed centrifugal polishing, with a polishing speed of 280~320 r / min and a polishing time of 90~200 min.

9. The application of a polishing method for medical-grade metal tubing as described in any one of claims 1-8, characterized in that, The medical-grade metal tubing is made of stainless steel or titanium alloy and is used in the fields of cardiovascular stents, minimally invasive surgical instruments, and orthopedic implant catheters.

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