Laser surface treatment method and application of magnesium alloy wire

Abstract

The invention relates to the technical field of biomedical materials, and particularly discloses a laser surface treatment method and application of a magnesium alloy wire. The invention discloses a laser surface treatment method of a magnesium alloy wire. The surface of the magnesium alloy wire is treated by adopting a laser surface treatment technology with the following process parameters: the scanning speed is 5-15 mm / s, the wavelength is 1050-1080 nm, the pulse width is 1 * 10 <-9 >-3 * 10 <-9 > s, the power is 5-8 W, the frequency is 18000-22,000 Hz, the light spot size is 1 / e2, the diameter is 150-175 microns, and the pulse energy density is 2.0-3.0 J / cm < 2 >. According to the scheme, in-situ tissue reconstruction is carried out through a laser surface treatment method, so that the corrosion resistance of the magnesium alloy is greatly enhanced, the reliability of the magnesium alloy wire in a cardiovascular implant is improved, the service life of the magnesium alloy wire in the cardiovascular implant is prolonged, meanwhile, the green manufacturing requirement is met, and the defects of a traditional method in the degradation control aspect are overcome.

Description

Technical Field

[0001] This application relates to the technical field of biomedical materials, specifically to a laser surface treatment method and application for magnesium alloy wire. Background Technology

[0002] Currently, magnesium alloys hold an important position in the field of biomedical materials due to their mechanical properties matching those of human bone, their complete degradability in body fluids, and their ability to promote osseointegration. Magnesium alloy biodegradable implants have made significant breakthroughs in several medical fields, including orthopedics, cardiology, and gastrointestinal anastomotic devices. Especially in the field of cardiovascular implants, magnesium alloys are a research hotspot, widely studied for the development of biodegradable implants. For example, the drug-eluting biodegradable magnesium alloy stent (Magmaris®) developed based on WE43 magnesium alloy has obtained EU CE certification (June 2016), becoming the world's first biodegradable magnesium alloy stent product.

[0003] Controlling the degradation rate is a core challenge when using magnesium alloys as raw materials for implants. This is because magnesium's high chemical reactivity and low corrosion potential lead to an often rapid and unpredictable degradation rate in body fluids (containing corrosive media such as chloride ions). The oxide film that forms on the surface of magnesium alloys is usually loose and porous, failing to provide effective and durable protection in vivo. This rapid degradation can lead to early mechanical failure of the implant; for example, biodegradable stents may lose more than 65% of their volume support within 6 to 12 months, the time required for vascular remodeling. Simultaneously, the hydrogen gas and large amounts of hydroxide ions generated during degradation can cause local pH increases and the formation of hydrogen cavities, all of which are significant factors limiting the widespread application of magnesium alloys.

[0004] To achieve the goal of controlled degradation of magnesium alloys, researchers have adopted a variety of strategies. One approach is to enhance the material's inherent corrosion resistance by optimizing alloy composition and manufacturing processes, such as by adding rare earth elements to improve mechanical strength and corrosion resistance. Simultaneously, the corrosion resistance of implants is improved by implementing end-to-end impurity control during profile processing (such as wire drawing) and inert gas protection during heat treatment. Another approach is the widespread application of surface treatment technologies aimed at forming a dense protective layer on the magnesium alloy surface. These technologies include micro-arc oxidation (MAO) and polymer coatings (such as PLA, PLGA, etc.). Furthermore, for scaffold-type implants, the maximum load-bearing capacity of the implant can be increased by appropriately increasing the wire diameter or wall thickness, thereby extending its effective support time.

[0005] However, these methods for controlling degradation also have significant limitations. Regarding alloy composition, achieving the required mechanical strength and corrosion resistance may require the addition of large proportions of rare earth elements, which could raise concerns about biocompatibility. In processing, certain rare earth elements are prone to precipitating and forming second phases during specific treatments, leading to galvanic corrosion and accelerated degradation. For surface treatment, some methods suffer from complex pretreatment processes, long protective layer formation cycles, and increased risk of surface stress cracking. Furthermore, even when increasing the wire diameter to improve mechanical properties, this design optimization can increase local and global strain in the implant, potentially accelerating its degradation rate in certain solutions. Therefore, when applying magnesium alloy wires to cardiovascular implants, these factors need to be comprehensively considered to ensure the device provides reliable mechanical support within the expected timeframe. Summary of the Invention

[0006] To address the aforementioned technical problems, this application provides a laser surface treatment method and application for magnesium alloy wire, which can effectively reduce the degradation rate of magnesium alloys with specific compositions and improve the performance and safety of the prepared endothelial products in the human body.

[0007] In a first aspect, this application provides a laser surface treatment method for magnesium alloy wire, which uses laser surface treatment technology with the following process parameters to treat the surface of magnesium alloy wire: Scanning speed 5-15mm / s, wavelength 1050-1080nm, pulse width 1×10 -9 -3×10 -9 s, power 5-8W, frequency 18000-22000Hz, spot size 1 / e 2 With a diameter of 150-175 μm and a pulse energy density of 2.0-3.0 J / cm², [the pulse energy density is not specified]. 2 .

[0008] Laser surface treatment (LST) technology, as an emerging surface treatment technology, has shown many advantages in improving the degradation performance of magnesium alloy wire and its internal components. Firstly, LST can significantly improve the corrosion resistance of the material and reduce the degradation rate, thus solving the problem of excessively rapid degradation of magnesium alloys within the bulk. This performance improvement is mainly attributed to the LST-induced changes in surface microstructure and rapid passivation. After treatment, a dense and uniform remelted layer forms on the material surface. This remelted layer effectively refines the grains, reduces corrosion defects, and inhibits galvanic corrosion caused by second-phase particles, thereby providing a more compact and protective corrosion product layer. Secondly, as a non-contact physical processing method, LST has a relatively simple processing procedure, is highly efficient and convenient, cost-effective, and meets the requirements of green manufacturing, making it an environmentally friendly processing technology.

[0009] The core of the laser surface treatment method in this application lies in using a laser beam as a high-energy heat source to induce the reconstruction of the microstructure and structure of the magnesium alloy surface layer in situ without adding any foreign substances, thereby fundamentally improving its degradation performance. The basic principle of laser surface treatment is that when a high-power-density laser beam irradiates the metal surface, the surface material absorbs energy and rapidly heats up to above the melting point in a very short time, forming a molten pool. Due to the narrow laser action area, heat is rapidly conducted to the interior of the matrix, and the molten pool then undergoes an extremely high cooling rate and undergoes rapid solidification. This unconventional "rapid heating-rapid cooling" process leads to significant changes in the surface microstructure, mainly reflected in the following aspects: (1) Grain refinement: Rapid solidification inhibits grain growth, forming equiaxed crystals or dendrites that are much smaller than the matrix structure. (2) Redistribution of alloying elements: The solid solubility of alloying elements in the α-Mg solid solution matrix increases, and the distribution is more uniform. (3) Second phase reconstruction: The original coarse and discontinuous intermetallic compounds in the matrix are dissolved in the molten pool and then re-precipitated in a fine and diffuse form during the subsequent rapid solidification process. They are evenly distributed at the refined α-Mg grain boundaries to form a nearly continuous network structure.

[0010] In laser surface treatment process parameters, the laser wavelength affects the material's absorption rate of the laser; for magnesium alloys, CO2 lasers with wavelengths of 1050-1080 nm have good absorption effects. Scanning speed is a crucial parameter for controlling heating time and cooling rate. Lower scanning speeds can achieve thicker fused layers but may lead to grain coarsening; while higher scanning speeds, although resulting in thinner fused layers, yield finer grain structures. Experimental analysis shows that as the scanning speed increases, the hardness of the fused layer decreases, but corrosion resistance improves. This is because rapid scanning reduces the heat-affected zone, avoiding grain coarsening. Increasing laser power leads to a corresponding increase in fused layer thickness, more pronounced grain refinement, and significantly improved corrosion resistance. However, excessive power can cause severe evaporation on the material surface, forming defects such as pits and pores, thus reducing surface quality. Therefore, this application selects a suitable power range of 5-8 W. Pulse width determines the duration of laser energy application; a shorter pulse width of 1×10⁻⁶ is preferred. -9 -3×10 -9The laser beam allows for faster heating and cooling rates, which is beneficial for obtaining ultrafine grain structures and significantly improving hardness and corrosion resistance. The pulse frequency affects the number of pulses applied per unit time; a suitable frequency ensures processing quality while avoiding excessive thermal effects. The spot size directly affects the energy density distribution; a smaller spot size yields higher energy density, which is beneficial for fine machining and surface modification. The choice of spot size needs to be matched with the power and scanning speed to obtain the ideal energy density. Pulse energy density is the core parameter determining the material modification effect. Experimental analysis shows that a pulse energy density of 2.0-3.0 J / cm² is optimal. 2 Within a certain range, good surface modification effects can be obtained. Too low an energy density will prevent sufficient melting and solidification, while too high an energy density will lead to material evaporation and surface defects. This application, through reasonable optimization of various parameters of laser surface treatment, can achieve grain refinement and improved corrosion resistance of magnesium alloy wire surfaces, while controlling the degradation rate within an acceptable range for the human body.

[0011] Preferably, the magnesium alloy wire is selected from any one of AZ91 magnesium alloy wire, WE43 magnesium alloy wire, and magnesium-zinc-calcium alloy wire.

[0012] Preferably, the chemical composition of the magnesium-zinc-calcium alloy wire, by weight percentage, is: zinc 2.0-6.2 wt%, calcium 1-2 wt%, and the balance being magnesium; The chemical composition of the AZ91 magnesium alloy wire is: 9.0% aluminum, 1.0% zinc, 0.15-0.5% manganese, and the balance is magnesium; The chemical composition of the WE43 magnesium alloy wire is: 4.0% yttrium, 3.3% rare earth elements, and the balance is magnesium.

[0013] Preferably, the chemical composition of the magnesium-zinc-calcium alloy wire, by weight percentage, is: zinc 3.2-5.1 wt%, calcium 1.3-1.8 wt%, with the balance being magnesium.

[0014] Preferably, the diameter of the magnesium alloy wire is 1-5 mm.

[0015] Preferably, before laser surface treatment, the magnesium alloy wire needs to be pretreated. The specific method is as follows: the magnesium alloy wire is pretreated by sanding with sandpaper, and then ultrasonically cleaned and dried with acetone, anhydrous ethanol and deionized water in sequence.

[0016] Preferably, the sandpaper is 1000-2000 mesh SiC.

[0017] Preferably, the process parameters for the laser surface treatment are: scanning speed 7-13 mm / s, wavelength 1060-1070 nm, and pulse width 1.3 × 10⁻⁶. -9 -2.7×10-9 s, power 5.5-7.5W, frequency 18500-21500Hz, spot size 1 / e 2 With a diameter of 155-170 μm and a pulse energy density of 2.2-2.8 J / cm², 2 .

[0018] Preferably, the process parameters for the laser surface treatment are: scanning speed 8-12 mm / s, wavelength 1060-1070 nm, and pulse width 1.5 × 10⁻⁶. -9 -2.5×10 -9 s, power 5.9-6.9W, frequency 19000-21000Hz, spot size 1 / e 2 With a diameter of 158-165 μm and a pulse energy density of 2.4-2.6 J / cm², 2 .

[0019] In one specific implementation, the process parameters for the laser surface treatment are: scanning speed 10 mm / s, wavelength 1064 nm, and pulse width 2 × 10⁻⁶. -9 s, power 6.4W, frequency 20000Hz, spot size 1 / e 2 With a diameter of 163 μm and a pulse energy density of 2.5 J / cm², 2 .

[0020] Experimental analysis shows that this application controls the various process parameters of laser surface treatment to the above-mentioned range, which further improves the performance of magnesium alloy wire products.

[0021] Secondly, this application provides a magnesium alloy wire product prepared using the laser surface treatment method described above.

[0022] Thirdly, this application provides an application of the aforementioned magnesium alloy wire product in the preparation of biomedical materials. In summary, the technical solution of this application has the following effects: In exploring magnesium alloys as raw materials for cardiovascular stents and implants, the main challenge faced in this application is the excessively rapid degradation rate of magnesium alloys in bodily fluid environments, which may lead to premature loss of mechanical support by the implants. The laser surface treatment technology proposed in this application, through its unique energy input and processing characteristics, brings significant technical advantages to improving the degradation performance of magnesium alloys, providing a technical path to solve the inherent problem of poor corrosion resistance in magnesium alloys.

[0023] In this application, laser surface treatment technology, through its unique "rapid heating-rapid cooling" process, achieves intense refinement and homogenization of the microstructure by relying on an extremely fast cooling rate. This induces the formation of a dense and uniform remelted layer on the surface of magnesium alloy wire, thereby significantly improving its degradation performance. This approach effectively suppresses galvanic corrosion and corrosion defects through microstructural changes such as grain refinement, redistribution of alloying elements, and second-phase reconstruction, resulting in a significant enhancement of the corrosion resistance of the magnesium alloy. From a microstructural perspective, laser treatment generates novel microstructures in situ on the magnesium alloy surface. For example, on the AZ31 magnesium alloy of Example 1, laser treatment can refine the average grain size from approximately 7.45 µm to 1.43 µm, significantly improving corrosion resistance. It allows harmful second-phase particles such as Al-Mn-Fe to redissolve into the magnesium matrix, greatly suppressing rapid degradation caused by galvanic corrosion.

[0024] In addition, laser surface treatment, as a non-contact physical processing method, has the advantages of high efficiency, convenience and environmental protection. It does not rely on chemical additives or complex pretreatment, and avoids the biocompatibility problems that may be caused by adding rare earth elements in existing technologies, or the risk of stress cracking caused by surface treatment.

[0025] The proposed solution achieves precise control of degradation rate through in-situ tissue reconstruction, improving the reliability and service life of magnesium alloy wire in cardiovascular implants, while meeting green manufacturing requirements and overcoming the shortcomings of traditional methods in degradation control. Detailed Implementation

[0026] The present application will be further described in detail below with reference to embodiments, comparative examples and performance test results. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0027] Example

[0028] Examples 1-6 Examples 1-6 provide a laser surface treatment method for magnesium alloy wire.

[0029] The object of treatment in Example 1 was AZ91 magnesium alloy wire with a diameter of 0.3 mm.

[0030] Example 2 involves processing WE43 magnesium alloy wire with a diameter of 0.3 mm.

[0031] The object of treatment in Example 3 was a magnesium-zinc-calcium alloy wire with a diameter of 0.3 mm; the chemical composition of the magnesium-zinc-calcium alloy wire was: zinc 3.2 wt%, calcium 1.8 wt%, and the balance being magnesium.

[0032] The object of treatment in Example 4 was a magnesium-zinc-calcium alloy wire with a diameter of 0.3 mm; the chemical composition of the magnesium-zinc-calcium alloy wire was: zinc 5.1 wt%, calcium 1.3 wt%, and the balance being magnesium.

[0033] The object of treatment in Example 5 was a magnesium-zinc-calcium alloy wire with a diameter of 0.3 mm; the chemical composition of the magnesium-zinc-calcium alloy wire was: zinc 2.0 wt%, calcium 2.0 wt%, and the balance being magnesium.

[0034] The object of treatment in Example 6 was a magnesium-zinc-calcium alloy wire with a diameter of 0.3 mm; the chemical composition of the magnesium-zinc-calcium alloy wire was: zinc 6.2 wt%, calcium 1.0 wt%, and the balance being magnesium.

[0035] Before laser surface treatment, magnesium alloy wire needs to be pretreated. The specific method is as follows: the magnesium alloy wire is pretreated by grinding with 1000-2000 grit SiC sandpaper, and then ultrasonically cleaned with acetone, anhydrous ethanol and deionized water for 15 minutes each, and then dried.

[0036] The surface of magnesium alloy wire was treated using laser surface treatment technology with the following process parameters: scanning speed 10 mm / s, wavelength 1064 nm, pulse width 2 × 10⁻⁶. -9 s, power 6.4W, frequency 20000Hz, spot size 1 / e 2 With a diameter of 163 μm and a pulse energy density of 2.5 J / cm², 2 .

[0037] Examples 7-10 Examples 7-10 provide a laser surface treatment method for magnesium alloy wire.

[0038] The difference between the above embodiments and Embodiment 3 is that the process parameters of the laser surface treatment technology are different, as shown below.

[0039] In Example 7: scanning speed 5 mm / s, wavelength 1064 nm, pulse width 3 × 10 -9 s, power 5W, frequency 22000Hz, spot size 1 / e 2 A pulse with a diameter of 150 μm and a pulse energy density of 3.0 J / cm² 2 .

[0040] In Example 8: scanning speed 15 mm / s, wavelength 1064 nm, pulse width 1 × 10⁻⁶. -9 s, power 8W, frequency 18000Hz, spot size 1 / e 2 With a diameter of 175 μm and a pulse energy density of 2.0 J / cm², 2 .

[0041] In Example 9: Scanning speed 7 mm / s, wavelength 1064 nm, pulse width 1.3 × 10⁻⁶. -9 s, power 5.5W, frequency 21500Hz, spot size 1 / e 2 With a diameter of 155 μm and a pulse energy density of 2.8 J / cm², 2 .

[0042] In Example 10: scanning speed 13 mm / s, wavelength 1064 nm, pulse width 2.7 × 10⁻⁶. -9 s, power 7.5W, frequency 18500Hz, spot size 1 / e 2 With a diameter of 170 μm and a pulse energy density of 2.2 J / cm², 2 .

[0043] All other process parameters in the above embodiments are the same as those in Embodiment 3.

[0044] Comparative Example Comparative Examples 1-2 Comparative Examples 1 and 2 respectively provide a laser surface treatment method for magnesium alloy wire.

[0045] The difference between the above comparative example and Example 3 is that the process parameters of the laser surface treatment technology are different, as shown below.

[0046] Comparative Example 1: Scanning speed 5 mm / s, wavelength 1064 nm, pulse width 3 × 10 -9 s, power 5W, frequency 22000Hz, spot size 1 / e 2 A pulse with a diameter of 150 μm and a pulse energy density of 3.0 J / cm² 2 .

[0047] Comparative Example 2: Scanning speed 15 mm / s, wavelength 1064 nm, pulse width 1 × 10 -9 s, power 8W, frequency 18000Hz, spot size 1 / e 2 With a diameter of 175 μm and a pulse energy density of 2.0 J / cm², 2 .

[0048] All other process parameters in the above comparative examples are the same as those in Example 3.

[0049] Performance testing Electrochemical corrosion test corrosion current density: Magnesium alloy wires before and after treatment in the examples and comparative examples were placed in simulated body fluid (SBF) for electrochemical corrosion testing. Corrosion current density is a key electrochemical parameter for measuring the corrosion rate of materials. A significant reduction in its value directly reflects a substantial improvement in the material's corrosion resistance and an effective reduction in the degradation rate.

[0050] Degradation rate was tested using the weight loss method: The degradation rate of magnesium alloy wires before and after treatment in the examples and comparative examples was tested using the corrosion method.

[0051] Test results are shown in Table 1.

[0052] Table 1. Performance test results of magnesium alloy wire products in the examples and comparative examples.

[0053] As shown in Table 1 above, the corrosion current density of the magnesium alloy decreased by nearly an order of magnitude after this process, the degradation rate measured by the weight loss method decreased significantly, and the corrosion resistance was significantly improved. For AZ91 magnesium alloy, the corrosion current density after laser treatment in Example 1 decreased from 7.22 × 10⁻⁶. -5 A / cm² decreased to 7.50×10 -6 The degradation rate decreased from 2.4 mm / y to 1.62 mm / y (A / cm²). For WE43 magnesium alloy, the corrosion current density after laser treatment in Example 2 decreased from 10.17 × 10⁻⁶. -5 A / cm² decreased to 6.14×10 -6 The degradation rate decreased from 3.16 mm / y to 1.92 mm / y (A / cm²). For magnesium-zinc-calcium alloys, the corrosion current density after laser treatment in Example 3 decreased from 3.20 × 10⁻⁶ mm / y. -5 A / cm² decreased to 4.81×10 -6 The degradation rate was reduced significantly from 1.6 mm / y to 0.23 mm / y. These results indicate that the remelted layer formed by laser treatment is more continuous, compact, and dense, effectively isolating the corrosive medium from the magnesium matrix, reducing the degradation rate by up to an order of magnitude, and providing more durable mechanical support. Laser treatment reduced the corrosion current density by nearly an order of magnitude, significantly decreasing the degradation rate and solving the long-standing problem of excessively rapid and unpredictable degradation of magnesium alloys in body fluids.

[0054] Comparing the test results of Examples 3-6, it can be seen that for magnesium-zinc-calcium alloys, the amount of chemical composition of the magnesium-zinc-calcium alloy wire has a significant impact on the performance of the alloy wire products after laser treatment. Compared with Examples 5-6, this application uses a magnesium-zinc-calcium alloy with a chemical composition of 3.2-5.1 wt% zinc, 1.3-1.8 wt% calcium, and the balance magnesium as the sample to be treated. The alloy wire products prepared after laser treatment have excellent performance.

[0055] By comparing the detection results of Examples 3 and 7-10 with those of Comparative Examples 1 and 2, it can be seen that the process parameters for laser surface treatment in this application are optimized as follows: scanning speed 5-15 mm / s, wavelength 1050-1080 nm, and pulse width 1×10⁻⁶. -9 -3×10-9 s, power 5-8W, frequency 18000-22000Hz, spot size 1 / e 2 With a diameter of 150-175 μm and a pulse energy density of 2.0-3.0 J / cm², [the pulse energy density is not specified]. 2 This can refine the grains on the surface of magnesium alloy wire, thereby effectively improving its corrosion resistance.

[0056] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A laser surface treatment method for magnesium alloy wire, characterized in that, The surface of magnesium alloy wire was treated using laser surface treatment technology with the following process parameters: Scanning speed 5-15mm / s, wavelength 1050-1080nm, pulse width 1×10 -9 -3×10 -9 s, power 5-8W, frequency 18000-22000Hz, spot size 1 / e 2 With a diameter of 150-175 μm and a pulse energy density of 2.0-3.0 J / cm², [the pulse energy density is not specified]. 2 .

2. The laser surface treatment method for magnesium alloy wire according to claim 1, characterized in that, The magnesium alloy wire is selected from any one of AZ91 magnesium alloy wire, WE43 magnesium alloy wire, and magnesium-zinc-calcium alloy wire.

3. The laser surface treatment method for magnesium alloy wire according to claim 2, characterized in that, The chemical composition of the magnesium-zinc-calcium alloy wire, by weight percentage, is: zinc 2.0-6.2 wt%, calcium 1-2 wt%, with the balance being magnesium; The chemical composition of the AZ91 magnesium alloy wire is: 9.0% aluminum, 1.0% zinc, 0.15-0.5% manganese, and the balance is magnesium; The chemical composition of the WE43 magnesium alloy wire is: 4.0% yttrium, 3.3% rare earth elements, and the balance is magnesium.

4. The laser surface treatment method for magnesium alloy wire according to claim 1, characterized in that, The diameter of the magnesium alloy wire is 1-5 mm.

5. The laser surface treatment method for magnesium alloy wire according to claim 1, characterized in that, Before laser surface treatment, magnesium alloy wire needs to be pretreated. The specific method is as follows: the magnesium alloy wire is pretreated by sanding with sandpaper, and then ultrasonically cleaned and dried with acetone, anhydrous ethanol and deionized water in sequence.

6. The laser surface treatment method for magnesium alloy wire according to claim 1, characterized in that, The sandpaper is 1000-2000 mesh SiC.

7. The laser surface treatment method for magnesium alloy wire according to claim 1, characterized in that, The process parameters for the laser surface treatment are: scanning speed 7-13 mm / s, wavelength 1060-1070 nm, and pulse width 1.3 × 10⁻⁶. -9 -2.7×10 -9 s, power 5.5-7.5W, frequency 18500-21500Hz, spot size 1 / e 2 With a diameter of 155-170 μm and a pulse energy density of 2.2-2.8 J / cm², 2 .

8. The laser surface treatment method for magnesium alloy wire according to claim 7, characterized in that, The process parameters for the laser surface treatment are: scanning speed 8-12 mm / s, wavelength 1060-1070 nm, and pulse width 1.5 × 10⁻⁶. -9 -2.5×10 -9 s, power 5.9-6.9W, frequency 19000-21000Hz, spot size 1 / e 2 With a diameter of 158-165 μm and a pulse energy density of 2.4-2.6 J / cm², 2 .

9. A magnesium alloy wire product, characterized in that, It is prepared using the laser surface treatment method as described in any one of claims 1-8.

10. The application of the magnesium alloy wire product as described in claim 9 in the preparation of biomedical materials.

Images