Magnesium alloy anastomosis nail and processing method thereof

Abstract

The application discloses a magnesium alloy anastomosis nail and a processing method thereof. The method comprises the following steps: applying a limited parameter electric pulse to a stress concentration area of a nail shoulder; a peak current density is 300-800 A / mm2, a pulse width is 30-50 microseconds, a pulse frequency is 10-50 hertz, and a continuous processing time is 8-25 seconds. The method can release residual stress of bending, homogenize microelectrochemical performance of the nail body, and convert local stress corrosion of the nail shoulder into overall uniform degradation, so that controlled and complete degradation absorption is realized. The method can guarantee mechanical stability of the nail body in a postoperative wound healing window period, reduce clinical complications such as anastomotic fistula and infection, and does not need secondary surgery for removal. The method can meet the clinical anastomosis demand, reduce physiological and psychological burden of patients, and has an excellent application prospect.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy preparation technology, specifically relating to a magnesium alloy staple and its processing method. Background Technology

[0002] Magnesium alloys are currently a highly promising absorbable metal substrate for medical implants. Their mechanical modulus closely matches human soft and bone tissues, exhibiting excellent biocompatibility. After implantation, they degrade spontaneously, eliminating the need for secondary surgery for removal.

[0003] Medical staples are core implantable consumables for suturing the digestive tract and soft tissues. The mainstream suturing consumables on the market are divided into two main categories: non-absorbable titanium staples and absorbable polymer staples. Titanium staples remain permanently in the body, easily causing chronic inflammation and rejection; polymer staples have weaker mechanical load-bearing capacity, resulting in a higher risk of early postoperative anastomotic dehiscence. Magnesium alloy absorbable staples combine mechanical strength with biodegradability, making them suitable for minimally invasive surgical suturing scenarios, and their clinical suitability is far superior to the two traditional types of staples.

[0004] Despite the aforementioned advantages of magnesium alloys in biomedical applications, their degradation process in vivo is difficult to predict and control. This uncontrollability stems from the interaction between the inherently reactive chemical properties of magnesium alloys and the complex human body environment. In body fluids rich in chloride ions, magnesium alloys undergo violent electrochemical reactions. More critically, their inherent hexagonal close-packed structure, along with microscopic defects such as coarse grains, strong texture, grain boundary second phases, and dislocations generated during subsequent processing, collectively form countless microscopic electrochemical cells. This causes corrosion to not proceed uniformly and slowly, but rather to spread rapidly in the form of highly damaging localized pitting and intergranular corrosion. This results in implants having a much shorter actual lifespan than expected, leading to catastrophic consequences.

[0005] Specifically, regarding magnesium alloy absorbable anastomotic staples, during implantation, their bending areas (such as the staple shoulder formed by pressing wire into a U-shape, etc.) Figure 1 The area shown in the box is the first to degrade, which is closely related to the stress corrosion mechanism induced by its processing history. During the molding process, the bending points of the anastomotic staples undergo severe plastic deformation, leading to internal lattice distortion and the accumulation of extremely high dislocation density and residual stress. In the body fluid environment containing high concentrations of chloride ions, these high-stress areas exhibit extremely high thermodynamic activity, becoming preferential anodic regions in the electrochemical reaction. At this time, the stress accelerates the physical rupture of the surface passivation film (such as magnesium hydroxide or calcium phosphate deposits), causing the base metal to be repeatedly exposed to the corrosive medium, forming a vicious cycle of "stress-induced fracture - electrochemical dissolution". This localized corrosion mode makes the thinning rate at the bending points far exceed that of the straight areas, becoming the first site of failure for the integrity of the entire implant structure.

[0006] During surgery, the U-shaped Mg2Zn staples bend into a B-shaped staple to suture the wound. To simulate human use, the U-shaped Mg2Zn staples were bent into a B-shape and then immersed in PBS solution for 4 weeks, resulting in the following degradation morphology: Figure 2 As shown, anastomotic staples often break between the staple shoulder and staple back where stress is concentrated. This localized accelerated degradation poses significant clinical risks. The core function of anastomotic staples is to provide reliable mechanical closure force during the early stages of tissue healing (usually the "golden window" of 1-2 weeks post-surgery). Since the bend is a critical structural part bearing mechanical loads, if it thins prematurely due to stress corrosion or even breaks early, the staple will lose its ability to restrain the tissue. In gastrointestinal anastomosis surgery, this can directly lead to poor anastomotic healing, or even induce fatal anastomotic leakage or leakage of contents. Furthermore, rapid local corrosion is accompanied by a rapid burst of hydrogen gas release. If the surrounding tissue cannot metabolize it sufficiently, the resulting gas cavity may compress microvessels, interfering with local blood perfusion and granulation tissue growth, thereby delaying the healing process and increasing the risk of infection.

[0007] Currently, the conventional modification methods used in the industry to control the degradation rate of magnesium alloys include the following three: The first type is matrix alloying modification. This involves doping with rare earth elements, calcium, and zinc to optimize the corrosion resistance of the matrix. However, this method has a low upper limit for modification, only slightly reducing the corrosion rate. Furthermore, the doping with rare earth elements is cytotoxic and does not meet the standards for medical implant materials. Additionally, alloying modification cannot eliminate the stress gradient caused by bending, and therefore still cannot solve the problem of preferential corrosion at the staple shoulder.

[0008] The second category involves surface coating modification. An inert protective coating is prepared on the surface of the staple to isolate the substrate from body fluids. The coating adheres to the substrate surface through mechanical bonding. Dynamic peristalsis of human organs and tissue compression can cause the coating to crack due to impact. Damage points in the coating form single-point strong anodic zones, resulting in twice the pitting corrosion penetration rate compared to an uncoated substrate. Miniature U-shaped staples have many bending dead angles, making uniform coating application extremely difficult and resulting in a very low yield rate in mass production.

[0009] The third type is grain refinement modification under high plastic deformation. This relies on strong extrusion and rolling to reconstruct the matrix grains and weaken microscopic electrical dipoles. This process has a high processing load and is only suitable for large-size plates and bars. Since the staple substrate is made of 0.2-0.4mm ultrafine wire, high plastic deformation easily causes wire breakage and deformation, resulting in high processing costs and making it completely unsuitable for mass industrial production of staples.

[0010] Chinese invention patent CN116179976A discloses a method for re-optimizing the microstructure of magnesium alloy ultrafine wire. The method is characterized by changing the traditional heat treatment process of metal wires and using high-energy pulsed current to pass through the magnesium alloy wire. By adjusting the current density, frequency and duty cycle, the microstructure of the magnesium alloy wire is re-optimized, thereby improving the mechanical properties and corrosion resistance of the wire. The specific steps include: (1) Magnesium alloy is prepared into wires of 0.20mm to 0.30mm by batching, smelting, casting, hot extrusion and cold drawing processes; (2) The magnesium alloy wires in step (1) are polished on a wire drawing machine, cleaned with alcohol by ultrasonic cleaning and dried; (3) The magnesium alloy wires in step (2) are subjected to high-energy pulsed current treatment with an output current of 0 to 20A, a frequency of 100HZ to 3000HZ and a duty cycle of 5% to 80%. The high-energy pulsed current treatment mentioned above is not suitable for use on magnesium alloy staples because the high-energy pulse will cause an excessive local micro temperature gradient, resulting in tissue heterogeneity and superficial corrosion spots. Although the local corrosion is increased, the staple surface is discolored and the overall corrosion rate is uneven, which poses a risk of premature thinning or breakage during the critical window period of tissue healing.

[0011] In summary, existing modification processes cannot simultaneously meet the requirements of medical safety and uniform corrosion performance of the anastomosis staples. How to achieve "uniform thinning of the entire magnesium alloy anastomosis staple during use" has become a major pain point restricting the development of magnesium alloy anastomosis staples. Summary of the Invention

[0012] This invention addresses the problem of inconsistent overall degradation rates in magnesium alloy staples by providing a magnesium alloy staple and its processing method. During their research on electro-pulse technology for treating magnesium alloy staples, the inventors discovered that excessively low energy input (e.g., peak current density ≤ 150 A / mm²) cannot provide sufficient driving force to induce effective slip and climb of dense dislocations, resulting in incomplete release of residual stress at the staple shoulder bend and failing to mitigate local pitting corrosion. Conversely, when ultra-high energy or excessively long processing times are introduced (e.g., peak current density ≥ 1200 A / mm²), drastic macroscopic temperature rise and Joule heat accumulation can lead to severe grain coarsening, even causing surface oxidation discoloration and thermal cracking, which in turn exacerbates corrosion damage due to the formation of numerous micro-galvanic cells. Furthermore, while high transient energy combined with low frequency processing can forcibly release stress, it can also easily cause microstructural inhomogeneity due to excessively large local microscopic temperature gradients, leading to shallow corrosion spots.

[0013] Therefore, through continuous exploration, the inventors have obtained an "optimal energy zone": utilizing medium-to-high intensity transient current and a balanced pulse frequency, not only can a powerful electroplastic driving force be provided instantaneously to untangle dislocation tangles in high-stress areas and induce micro-dynamic recrystallization at the most severely deformed nail shoulder, but also the overall heat accumulation can be effectively controlled through the pulse gap to avoid abnormal grain growth. Based on the above exploration logic and verification through multiple sets of embodiments, this invention has determined the optimal EPT processing parameter range for improving the corrosion resistance of magnesium alloy staples to be: peak current density 300~800A / mm², pulse width 30~50 microseconds, pulse frequency 10~50 Hz, and continuous processing time 8~25 seconds. Within this process window, the staples not only eliminate the lattice distortion caused by cold working, but also achieve the homogenization of the overall electrochemical state. This successfully reverses the degradation mode of the staples in the body fluid environment from "stress-induced local early fracture" to "controlled overall uniform thinning". In other words, the magnesium alloy staples achieve "overall uniform thinning" during use, avoiding the risk of premature thinning or fracture of the staples during the critical window period.

[0014] The specific technical solution is as follows: A magnesium alloy staple, wherein the magnesium alloy staple is composed of the following components by mass percentage: zinc 1.0~6.0%, iron ≤0.02%, aluminum ≤0.02%, silicon ≤0.02%, copper ≤0.02%, nickel ≤0.002%, other impurity elements total ≤0.05%, and the balance being magnesium; The processing method of the magnesium alloy staples includes the following steps: S1 obtains a U-shaped magnesium alloy staple and fixes the U-shaped magnesium alloy staple in a U-shaped clamp. The U-shaped clamp has a total of 4 electrical contact points, A, B, C, and D, which form electrical contact with the staple body through the electrical contact points. Points A and B are located on the two vertical sides of one side of the staple shoulder, and points C and D are located on the two vertical sides of the other side of the staple shoulder. S2 performs electrical pulse treatment on the U-shaped magnesium alloy staples. First, points A and B are connected to concentrate the electrical pulse current to conduct the bending area of ​​one staple shoulder. After the treatment is completed, points C and D are connected to concentrate the electrical pulse current to conduct the bending area of ​​the other staple shoulder. The processing parameters of the electrical pulse include: peak current density 300~800A / mm², pulse width 30~50 microseconds, pulse frequency 10~50 Hz, and continuous processing time 8~25 seconds.

[0015] Furthermore, the magnesium alloy staples exhibit an average degradation rate of 0.2-0.4 mm / y after immersion in PBS solution for 4 weeks; during the 1-2 week postoperative tissue healing window, the magnesium alloy staples maintain mechanical closure force and do not exhibit any breakage issues in the bending area.

[0016] This invention also protects a method for processing the magnesium alloy staples, comprising the following steps: S1 obtains a U-shaped magnesium alloy staple and fixes the U-shaped magnesium alloy staple in a U-shaped clamp. The U-shaped clamp has a total of 4 electrical contact points, A, B, C, and D, which form electrical contact with the staple body through the electrical contact points. Points A and B are located on the two vertical sides of one side of the staple shoulder, and points C and D are located on the two vertical sides of the other side of the staple shoulder. S2 performs electrical pulse treatment on the U-shaped magnesium alloy staples. First, points A and B are connected to concentrate the electrical pulse current to conduct the bending area of ​​one staple shoulder. After the treatment is completed, points C and D are connected to concentrate the electrical pulse current to conduct the bending area of ​​the other staple shoulder. The processing parameters of the electrical pulse include: peak current density 300~800A / mm², pulse width 30~50 microseconds, pulse frequency 10~50 Hz, and continuous processing time 8~25 seconds.

[0017] Furthermore, the peak current density of the electrical pulse processing is 450~600A / mm².

[0018] Furthermore, the pulse width of the electrical pulse processing is 35-45 microseconds.

[0019] Furthermore, the frequency of the electrical pulse processing pulse is 20~40 Hz.

[0020] Furthermore, the continuous processing time of the electrical pulse processing is 15 to 20 seconds.

[0021] Furthermore, the U-shaped magnesium alloy staple mentioned in step S1 is a Mg-2Zn binary alloy with a wire diameter of 0.2~0.4mm and a surface roughness Ra≤0.8μm. The preparation process of the U-shaped magnesium alloy staple includes: melting and preparing magnesium-zinc alloy ingots, hot extrusion of the ingots, multi-pass drawing at 120~180℃, intermediate annealing at 250~350℃ and surface polishing to obtain alloy wires, which are then bent into U-shaped staples.

[0022] Furthermore, during the electrical pulse processing described in step S2, the impedance and current waveform of the nail body are monitored in real time, and adaptive dynamic adjustments are made to address processing abnormalities to ensure consistent energy absorption of the workpiece. Specifically, this includes: when an abnormal increase in impedance occurs in the initial stage of the pulse, the clamping force of the fixture is increased and a "precursor electrical pulse" with a frequency > 50Hz and a peak current density < 300A / mm² is instantaneously inserted to break down the oxide layer, thereby quickly restoring the original processing parameters for electrical pulse processing; if a sudden drop in impedance or waveform divergence is detected in the middle or later stages, indicating a risk of local overheating and softening / melting, the pulse width is adaptively compressed and the pulse frequency is lowered while maintaining the preset total energy unchanged, providing a solid-state heat dissipation window for the nail shoulder stress area, thereby protecting the macroscopic morphology and mechanical strength of the nail body; for waveform distortion caused by electrode wear or system mismatch, an online impedance compensation algorithm is activated to reshape the waveform, and a cut-off alarm is triggered when five corrections are ineffective or an absolute short circuit is encountered.

[0023] Beneficial effects This invention significantly eliminates residual stress accumulated at the shoulder of the U-shaped staples during cold working by applying precise electrical pulse treatment. Utilizing the unique non-thermal effect (electroplastic effect) of electrical pulses, dislocation rearrangement and stress relaxation in high-stress areas can be induced in a very short time, achieving atomic-level lattice repair. Compared to traditional overall high-temperature annealing processes, this invention can precisely target localized distortion areas, effectively avoiding grain coarsening and loss of matrix mechanical strength caused by prolonged heat accumulation. While maintaining the original high strength and toughness of the magnesium alloy, this process eliminates the chemical potential differences caused by uneven deformation, achieving uniformity of the staple's electrochemical properties and ensuring corrosion resistance during subsequent service.

[0024] In terms of corrosion resistance and structural stability, this invention demonstrates superior improvement, essentially solving the technical bottleneck of deep pitting corrosion and early stress corrosion cracking at bends. After optimized EPT parameter treatment, the degradation mode of the anastomosis staples in a chloride-rich physiological environment changes from the original "preferential corrosion at the staple shoulder, leading to early fracture" to the ideal "uniform thinning of the staple body as a whole." Experimental data confirms that the average corrosion rate of the treated sample significantly decreases in the initial immersion stage, and the corrosion resistance at the staple shoulder increases to a level similar to that of the straight areas. This optimization of the degradation morphology prolongs the maintenance time of the mechanical integrity of the anastomosis staples within the implant, ensuring that the implant can provide stable and durable mechanical support during the critical window of tissue healing.

[0025] From a clinical application perspective, this invention improves the safety and reliability of absorbable magnesium alloy staplers. By inhibiting premature thinning at the staple shoulder, the staples ensure the stability of the anastomotic closure force within 1-2 weeks post-surgery, effectively reducing the risk of serious postoperative complications such as anastomotic leakage and effusion caused by staple failure. Simultaneously, the gradual and uniform degradation process effectively avoids the explosive release of local hydrogen gas and its resulting compressive effect, improving the biochemical microenvironment around the anastomosis. Ultimately, the staples achieve controlled and complete degradation and absorption, eliminating the need for secondary surgery for removal, thus meeting clinical anastomotic needs while reducing the physiological and psychological burden on patients. Attached Figure Description

[0026] To more clearly and intuitively illustrate the technical solution and performance advantages of the present invention, the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the following drawings are only preferred embodiments of the present invention and are not intended to limit the overall scope of protection of the present invention.

[0027] Figure 1 A schematic diagram of the shoulder of a staple; Figure 2 The degradation morphology of untreated type B staples in the background art after soaking in PBS solution for 4 weeks shows that the staples often break between the stress concentration point of the staple shoulder and the staple back. Figure 3 This is a schematic diagram of the staples being fixed in the clamp; Figure 4 This is a schematic diagram of the wiring for the electrical pulse processing of the anastomosis staples; Figure 5 This is a degradation morphology image of the anastomotic staples after immersion in PBS solution for 1 week in Example 1; Figure 6 This is a degradation morphology image of the anastomotic staples after soaking in PBS solution for 1 week in Example 2; Figure 7 This is a degradation morphology image of the anastomotic staples after soaking in PBS solution for 1 week in Example 3; Figure 8 This is a degradation morphology image of the anastomotic staples after soaking in PBS solution for 1 week in Example 4; Figure 9 The image shows the degradation morphology of the anastomotic staples in Comparative Example 1 after 4 weeks of immersion in PBS solution. Figure 10 This is a diagram of the oxidation and discoloration morphology of the anastomosis staple surface after electrical pulse treatment in Comparative Example 2. Figure 11 This is a degradation morphology image of the anastomotic nails in Comparative Example 3 after soaking in PBS solution for 1 week. Detailed Implementation

[0028] Preferred embodiments of the present invention will now be described in more detail. While preferred embodiments of the present invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products. In the following embodiments, unless otherwise explicitly stated, "%" refers to weight percentage.

[0029] The following examples and comparative examples use U-shaped absorbable staples with a diameter of 0.35 mm prepared from Mg-2Zn medical magnesium alloy as the substrate. This substrate does not constitute a limitation on the method provided by this invention. The method provided by this invention is applicable to absorbable magnesium alloy staples with a diameter of 0.2~0.4 mm and a surface roughness Ra≤0.8μm. The above-mentioned substrate can be commercially available or self-made.

[0030] As an example, the method for preparing this magnesium alloy staple can be as follows: First, a high-purity magnesium-zinc binary alloy (chemical composition shown in Table 1 below) is induction melted under vacuum and high-purity argon protection to obtain an alloy ingot with a diameter of approximately 100 mm. Then, the ingot is processed into a dense coarse wire with a diameter of 2-3 mm by hot extrusion to refine the grains through dynamic recrystallization. Next, a multi-pass temperature drawing process (120-180℃) combined with intermediate annealing (250-350℃) is used to eliminate work hardening and restore plasticity. After gradual diameter reduction, precision drawing, and surface polishing, the coarse wire is processed into a high-precision fine wire with a diameter of 0.2-0.4 mm and a surface roughness Ra≤0.8μm. Finally, it is bent into a U-shaped staple using a bending machine. It should be noted that the above preparation method is an example and does not constitute a limitation on the application of the method described in this invention.

[0031] Table 1 Raw Material Composition Table

[0032] In the following examples and comparative cases, the degradation rate of the magnesium alloy staples was determined according to the weight loss method specified in the ASTM standard. The specific calculation logic and formula are as follows: Record the mass of each group (100 staples) of anastomotic nails before and after soaking in PBS solution, and calculate the weight loss value. = Initial weight - Residual weight after 1 week of soaking), in mg.

[0033] Calculate corrosion rate (Characterizing daily weight loss per unit area), this index is used to assess the basic dissolution rate of a material under specific solution conditions, and the calculation formula is:

[0034] Where A: the total surface area of ​​100 staples, i.e., 10.22 cm².

[0035] t: The duration of the immersion test, i.e., 7 days.

[0036] The final result is expressed in mg / cm²·d.

[0037] To more intuitively assess the structural maintenance time and lifespan of staples in the human implantation environment, mass loss needs to be converted into thickness reduction rate, i.e., corrosion rate. The average annual thinning depth is represented by the following formula:

[0038] in The actual density of the magnesium alloy substrate is set to 1.767 g / cm³.

[0039] k: A constant that converts t to year, k = 87600.

[0040] The final result is in mm / y (millimeters per year).

[0041] Through the standardized conversion steps described above, the minor quality fluctuations recorded in the original experiment can be transformed into objective, rigorous degradation rate indicators with clinical significance, as shown in Table 3.

[0042] Example 1 Take a U-shaped staple substrate, such as Figure 3 As shown, the staples are fixed in a U-shaped clamp with a U-shaped groove. The staples are inserted into the groove and clamped in place. There are four electrical contact points (A, B, C, and D) within the U-shaped groove, which form electrical contact with the staple body. Points A and B are located on the two vertical sides of one side of the staple's shoulder, and points C and D are located on the two vertical sides of the other side of the staple's shoulder.

[0043] During electrical pulse processing, first connect points A and B with a wire, allowing current to enter from point A and exit from point B, thus applying electrical pulse processing to the left nail shoulder. Then connect points C and D with a wire, allowing current to enter from point C and exit from point D, thus applying electrical pulse processing to the right nail shoulder. See the wiring diagram. Figure 4 By using the above method, it can be ensured that the current can effectively cover and concentrate through the nail shoulder area where stress accumulation is most severe.

[0044] The specific electrical pulse processing method is described below, employing high current density and extremely short pulse duration for multi-frequency cyclic processing. This energy application method ensures that energy is precisely applied to grain boundaries and dislocation aggregation sites, while limiting macroscopic temperature rise and preventing excessive surface oxidation or loss of mechanical strength due to the high chemical reactivity of magnesium alloys. The pin impedance and current waveform are monitored in real time during the processing to ensure consistent energy absorption by the workpiece. Specifically, if an abnormal increase in transient impedance of the pin is detected at the initial stage of pulse application, or if the peak value of the current waveform drops significantly, this is usually determined to indicate poor contact between the electrical contact points of the fixture (such as points A, B, C, and D) and the surface of the low-melting-point magnesium alloy staple, or that a slight non-conductive oxide film has formed on the staple surface due to exposure to ambient air. Faced with this situation of high impedance, the first step is to increase the physical clamping force of the drive fixture to enhance the quality of electrical contact. If the current peak still does not rise back to the set threshold, the controller will adaptively insert a set of ultra-high frequency, low energy (i.e., frequency > 50Hz, peak current density < 300A / mm²) "precursor high voltage pulses" within milliseconds before the standard pulse train is fired. This utilizes the local micro-area discharge effect to instantly break down and peel off the non-conductive oxide layer on the contact surface. When the system detects that the impedance has instantly dropped back to the intrinsic conductivity range of the substrate, it indicates that the problem has been solved. The original processing parameters are then immediately restored for pulse processing, thereby avoiding problems such as localized arcing or insufficient energy input caused by excessive contact resistance.

[0045] Conversely, if the monitoring system detects a sharp, non-linear drop in the impedance of the staple during the mid-to-late stages of pulsed energy injection, or if the current waveform exhibits an abnormal upward and divergent trend during the plateau phase, this indicates severe localized Joule overheating has occurred, and the matrix is ​​on the verge of degrading from solid-state to localized micro-area softening or even melting. In response to this high-risk state of low impedance and localized overheating, the process control program immediately initiates heat dilution intervention. Without altering the preset total energy input control logic, it instantaneously adjusts the pulse waveform generator, for example, adaptively compressing the duration (pulse width) of subsequent pulses from a predetermined 50 microseconds to 30 microseconds, and simultaneously lowering the pulse frequency to 10 Hz. By lengthening the power-off gap between pulses, sufficient solid-state heat dissipation windows are provided for the staple shoulder area. This dynamic coupling and reduction of frequency and pulse width can promptly curb heat flow concentration, prevent abnormal grain coarsening, and protect the macroscopic geometry and mechanical strength of the staple while ensuring deep release of internal residual stress.

[0046] Furthermore, if severe asymmetric distortion or time lag occurs on the rising edge of the current waveform, it indicates impedance matching drift in the external transformer module or physical wear and metal adhesion on the surface of the clamp electrodes. In this case, an online impedance compensation algorithm is activated to dynamically boost and reshape the pulse waveform by adjusting the discharge time constant of the capacitor array. If the waveform fails to correct itself within five consecutive pulse cycles, or if the transient impedance drops below the set absolute short-circuit safety limit, the closed-loop control system will immediately implement microsecond-level emergency cut-off protection and issue an alarm. This multi-scenario, quantitative waveform adaptive correction and shutdown mechanism effectively prevents localized burning of low-melting-point, highly reactive magnesium alloys during mass automated nail production and ensures highly consistent energy absorption at the nail shoulder of each finished staple in the warehouse.

[0047] Specifically, this embodiment employs a high-energy, low-frequency, short-time processing strategy. The equipment parameters are set as follows: peak current density up to 800 A / mm², pulse width 50 microseconds, pulse frequency reduced to 10 Hz, and continuous processing time of 8 seconds. The extremely high instantaneous current density provides a powerful electron wind driving force, forcibly releasing stress within seconds. The low frequency setting allows sufficient heat dissipation time between pulses, preventing overall melting.

[0048] The processed sample was bent into a B-shape to simulate a usage scenario and then soaked in PBS solution for one week. (See below for further details.) Figure 5 From the degradation morphology, the stress corrosion at the staple shoulder has basically disappeared, and the overall structure remains consistent. However, due to the excessively high transient energy, the temperature gradient in the local micro-regions led to a very small amount of microstructural heterogeneity, resulting in a few superficial micro-corrosion spots in the straight areas. However, these did not pose a substantial threat to the overall mechanical support of the staple. Calculations showed that the average degradation rate of the workpiece immersed in PBS solution for one week was 0.38 mm / y.

[0049] Example 2 The substrate, processing device, fixture fixing method, wiring method, and electrical monitoring method in this embodiment are consistent with those in Embodiment 1. The electrical pulse processing adopts a parameter configuration of medium-high energy and balanced frequency, with the peak current density set at 500 A / mm², pulse width at 40 microseconds, pulse frequency at 30 Hz, and continuous processing time at 20 seconds. Under these ideal conditions, the strong non-thermoelectric plastic effect and localized micro Joule heating work well together, instantly penetrating high-stress areas. This not only unravels dense dislocation entanglements but also induces micro-dynamic recrystallization at the most severely deformed local shoulder, thus homogenizing the electrochemical state of the material.

[0050] The processed sample was bent into a B-shape to simulate a usage scenario. After a one-week immersion test in PBS solution, the overall structure remained intact without any breakage. (See attached image) Figure 6In terms of microstructure, chloride ion erosion is uniformly distributed across the entire nail surface, with the degradation depth in the nail shoulder area and the straight area being almost identical. This essentially eliminates the risk of stress-induced fracture and achieves ideal controlled and uniform degradation. Calculations show that the average degradation rate of the workpiece immersed in PBS solution for one week is 0.21 mm / y.

[0051] Example 3 The substrate, processing device, fixture fixing method, wiring method, and electrical monitoring method in this embodiment are the same as in Embodiment 1. The parameters for the electrical pulse processing are: peak current density 300 A / mm², pulse width 30 microseconds, pulse frequency 10 Hz, and continuous processing time 8 seconds. After processing, the workpiece is ultrasonically cleaned with pure water to remove trace impurities from the surface.

[0052] The processed sample was bent into a B-shape to simulate a usage scenario, and a one-week immersion test was performed using PBS to simulate body fluid. See [link / reference]. Figure 7 As can be seen, the overall structure remains intact, and most of the staples did not break. The average degradation rate of the workpiece after immersion in PBS solution for one week was calculated to be 0.36 mm / y. The residual stress on the staple shoulder was fully released, the lattice distortion was completely repaired, the corrosion rate of the staple shoulder and the staple body was synchronized, no deep pitting was formed, and the overall structure of the workpiece remained intact, meeting the mechanical requirements for use during the clinical window period.

[0053] Example 4 The substrate, processing device, clamping method, wiring method, and electrical monitoring method in this embodiment are the same as in Embodiment 1. The parameters for the electrical pulse processing are: peak current density 800 A / mm², pulse width 50 microseconds, pulse frequency 50 Hz, and continuous processing time 25 seconds. Segmented heat dissipation is used during pulse intervals to control the overall Joule heat accumulation. The finished product is then ultrasonically cleaned after processing.

[0054] The processed sample was bent into a B-shape to simulate a usage scenario, and a one-week immersion test was performed using PBS to simulate body fluid. See [link / reference]. Figure 8 The average degradation rate of the workpiece was 0.37 mm / y. High-frequency long-duration pulses did not induce grain coarsening or surface oxidation. The electrochemical properties of the nail body were homogeneous, with no localized preferential corrosion sites. It exhibited excellent overall corrosion resistance and could maintain mechanical closure force during the 1-2 week postoperative tissue healing window, without any fracture issues in the bending area.

[0055] Example 5 The substrate, processing device, clamping method, wiring method, and electrical monitoring method in this embodiment are consistent with those in Embodiment 1. The parameters for the electrical pulse processing are: peak current density 450 A / mm², pulse width 35 microseconds, pulse frequency 25 Hz, and continuous processing time 15 seconds. Real-time closed-loop electrical monitoring ensures balanced and controllable energy input. After processing, the device is cleaned and ready for use.

[0056] The processed sample was bent into a B-shape to simulate a usage scenario. After soaking in PBS for one week, the average degradation rate was 0.26 mm / y. It is compatible with the batch processing of standard-sized medical staples and can maintain mechanical closure force during the tissue healing window period of 1-2 weeks after surgery, without the problem of breakage in the bending area.

[0057] Example 6 The substrate, processing device, fixture fixing method, wiring method, and electrical monitoring method in this embodiment are consistent with those in Embodiment 1. The parameters for the electrical pulse processing are: peak current density 600 A / mm², pulse width 45 microseconds, pulse frequency 40 Hz, and continuous processing time 18 seconds. The rearrangement of shoulder dislocations is achieved based on the electron wind effect, with micro-Joule heating assisting grain boundary migration.

[0058] The processed sample was bent into a B-shape to simulate usage. After soaking in PBS for one week, the average degradation rate was 0.24 mm / y. There was no stress corrosion in the bending area, the surface passivation film was dense and uniform, and the long-term service stability was excellent.

[0059] Example 7 The substrate, processing device, fixture fixing method, wiring method, and electrical monitoring method of this comparative example are consistent with those of Example 1. The parameters of the electrical pulse processing are: peak current density 300 A / mm², pulse width 30 microseconds, pulse frequency increased to 50 Hz, and processing time extended to 15 seconds. The moderately increased current density and the cumulative effect of the high-frequency pulse provide sufficient momentum for dislocation climb and rearrangement at the spike shoulder, resulting in a significant repair of lattice distortion without causing abnormal grain growth.

[0060] The processed samples were bent into a B-shape to simulate usage. After soaking in PBS solution for one week, the average degradation rate of the samples significantly decreased to 0.37 mm / y. Morphological observation showed that the highly active anodic region was effectively weakened, and preferential corrosion at the staple shoulder was greatly delayed. The entire staple surface was covered with relatively uniform, loose magnesium hydroxide products. After removing the products, the staple body exhibited relatively uniform overall thinning, with no deep localized penetrating pitting corrosion observed, and the structural integrity was well maintained.

[0061] Table 2 Summary of Electrical Pulse Parameters for Examples and Comparative Examples

[0062] Comparative Example 1 The substrate, processing device, clamping method, wiring method, and electrical monitoring method of this comparative example are the same as those of Example 1. The parameters of the electrical pulse processing are: peak current density of 150 A / mm², pulse width of 20 microseconds, pulse frequency of 20 Hz, and continuous processing time of 10 seconds. Under these parameters, the electron wind is weak and the Joule heating is low, which can only cause a very small amount of piled dislocations at the bend (nail shoulder) to slip slightly, and the residual stress is only partially released.

[0063] After the above treatment, the U-shaped staples were bent into a B-shape to simulate use. After being soaked in PBS solution for one week, the average degradation rate of the staples was calculated to be approximately 0.43 mm / y by weight loss method.

[0064] The U-shaped staple substrate from Example 1 was bent directly into a B-shape without EPT treatment and used as a blank control. After immersion in PBS solution for one week, the average degradation rate, calculated by the weight loss method, was approximately 0.68 mm / y. Therefore, the degradation rate of the sample in Comparative Example 1 was only slightly lower than that of the untreated staple. From the degradation morphology, although the overall corrosion was slowed down, high concentrations of chloride ions still preferentially attacked the staple shoulder area with higher residual stress. Macroscopically, this manifested as obvious local pitting and early thinning at the staple shoulder, indicating that the risk of structural failure still exists. The sample prepared in Comparative Example 1 was immersed in PBS solution for 4 weeks. Figure 9 As shown, most of the staples suffered structural damage, and the fracture locations of the workpieces were mostly in the bending area at the staple shoulder. This indicates that the electrical pulse processing parameters were set improperly, the residual stress at the bending area of ​​the staple shoulder was not completely released, and the pitting corrosion at the bending area of ​​the staple shoulder could not be effectively slowed down, thus leading to fracture and structural damage.

[0065] Comparative Example 2 The substrate, processing device, fixture fixing method, wiring method, and electrical monitoring method of this comparative example are the same as those in Example 1. The parameters for the electrical pulse processing are: peak current density 1200 A / mm², pulse width 60 microseconds, pulse frequency 50 Hz, and continuous processing time up to 30 seconds. The processed sample is bent into a B-shape to simulate a usage scenario.

[0066] In this comparative example, although the residual stress from cold working was eliminated under high energy input, excessive Joule heat accumulation led to a significant macroscopic temperature rise, causing severe grain coarsening in the magnesium alloy and even inducing fine hot cracks or oxidation discoloration on the surface. (See [reference]). Figure 10 .

[0067] In the PBS solution immersion test, the degradation rate of the anastomotic staples rebounded, rising to approximately 0.62 mm / y. The degradation morphology exhibited a chaotic and non-uniform corrosion characteristic. Although the staple shoulder was no longer the only weak point, the large grain size and the formation of numerous micro-galvanic cells between the surface thermal damage area and the substrate led to extensive and severe peeling and disintegration of the entire anastomotic staple surface, resulting in the loss of its ability to achieve smooth thinning.

[0068] Comparative Example 3 This comparative example is based on Example 2, with the only difference being that the peak current density is increased to 250 A / mm², while the other three parameters remain unchanged. The processed sample was bent into a B-shape to simulate usage, and its morphology was referenced after soaking in PBS for one week. Figure 11 The calculated degradation rate is 0.41 mm / y.

[0069] Analysis revealed that directional pitting corrosion still occurred on the shoulder of the dislocation in this comparative example, indicating a failure of localized corrosion control. This may be due to insufficient current driving force, preventing the shoulder dislocation from completing a full slip rearrangement.

[0070] Comparative Example 4 This comparative example is based on Example 2, with the only difference being that the pulse width was adjusted to 55 microseconds, while all other parameters remained unchanged. The processed sample was bent into a B-shape to simulate a usage scenario, and after soaking in PBS for one week, the degradation rate was 0.40 mm / y.

[0071] From the degradation morphology, shallow corrosion spots appeared at multiple points on the nail body in this comparative example, indicating that the corrosion uniformity was destroyed. This may be due to the excessive duration of single-pulse heat generation, local thermal accumulation on the nail shoulder causing slight coarsening of the grains and a rebound in the grain boundary potential difference.

[0072] Comparative Example 5 This comparative example is based on Example 2, with the only difference being that the continuous processing time was adjusted to 30 seconds, while all other parameters remained unchanged. The processed sample was bent into a B-shape to simulate usage. After one week of PBS immersion, the degradation rate was 0.39 mm / y, indicating a resurgence in the risk of localized corrosion. This may be due to the accumulated Joule heat from prolonged energization, resulting in slight oxidation marks on the workpiece surface and an increase in microscopic grain boundary defects.

[0073] Table 3. Calculation of degradation rate of anastomotic staples after one week of PBS immersion.

[0074] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0075] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0076] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A magnesium alloy staple, characterized in that, The magnesium alloy staples are composed of the following components by mass percentage: zinc 1.0~6.0%, iron ≤0.02%, aluminum ≤0.02%, silicon ≤0.02%, copper ≤0.02%, nickel ≤0.002%, other impurity elements total ≤0.05%, and the balance is magnesium. The processing method of the magnesium alloy staples includes the following steps: S1 obtains a U-shaped magnesium alloy staple and fixes the U-shaped magnesium alloy staple in a U-shaped clamp. The U-shaped clamp has a total of 4 electrical contact points, A, B, C, and D, which form electrical contact with the staple body through the electrical contact points. Points A and B are located on the two vertical sides of one side of the staple shoulder, and points C and D are located on the two vertical sides of the other side of the staple shoulder. S2 performs electrical pulse treatment on the U-shaped magnesium alloy staples. First, points A and B are connected to concentrate the electrical pulse current to conduct the bending area of ​​one staple shoulder. After the treatment is completed, points C and D are connected to concentrate the electrical pulse current to conduct the bending area of ​​the other staple shoulder. The processing parameters of the electrical pulse include: peak current density 300~800A / mm², pulse width 30~50 microseconds, pulse frequency 10~50 Hz, and continuous processing time 8~25 seconds.

2. The magnesium alloy staple according to claim 1, characterized in that: The magnesium alloy staples exhibited an average degradation rate of 0.2-0.4 mm / y after being immersed in PBS solution for one week.

3. The magnesium alloy staple according to claim 2, characterized in that: The magnesium alloy staples maintain mechanical closure force during the 1-2 week postoperative tissue healing window and do not have the problem of breakage in the bending area.

4. A method for processing magnesium alloy staples according to any one of claims 1-3, characterized in that: Includes the following steps: S1 obtains a U-shaped magnesium alloy staple and fixes the U-shaped magnesium alloy staple in a U-shaped clamp. The U-shaped clamp has a total of 4 electrical contact points, A, B, C, and D, which form electrical contact with the staple body through the electrical contact points. Points A and B are located on the two vertical sides of one side of the staple shoulder, and points C and D are located on the two vertical sides of the other side of the staple shoulder. S2 performs electrical pulse treatment on the U-shaped magnesium alloy staples. First, points A and B are connected to concentrate the electrical pulse current to conduct the bending area of ​​one staple shoulder. After the treatment is completed, points C and D are connected to concentrate the electrical pulse current to conduct the bending area of ​​the other staple shoulder. The processing parameters of the electrical pulse include: peak current density 300~800A / mm², pulse width 30~50 microseconds, pulse frequency 10~50 Hz, and continuous processing time 8~25 seconds.

5. The processing method of the magnesium alloy staple according to claim 4, characterized in that: The peak current density of the electrical pulse processing is 450~600A / mm².

6. The processing method of the magnesium alloy staple according to claim 4, characterized in that: The pulse width of the electrical pulse processing is 35~45 microseconds.

7. The processing method of the magnesium alloy staple according to claim 4, characterized in that: The pulse frequency of the electrical pulse processing is 20~40 Hz.

8. The processing method of the magnesium alloy staple according to claim 4, characterized in that: The continuous processing time for the electrical pulse processing is 15-20 seconds.

9. The method for processing magnesium alloy staples according to any one of claims 4-8, characterized in that: The U-shaped magnesium alloy staple mentioned in step S1 is a Mg-2Zn binary alloy with a wire diameter of 0.2~0.4mm and a surface roughness Ra≤0.8μm; The manufacturing process of the U-shaped magnesium alloy staple includes: melting and preparing magnesium-zinc alloy ingots, hot extrusion, multi-pass drawing at 120~180℃, intermediate annealing at 250~350℃ and surface polishing to obtain alloy wires, which are then bent into U-shaped staples.

10. The method for processing magnesium alloy staples according to any one of claims 4-8, characterized in that: During the electrical pulse processing described in step S2, the impedance and current waveform of the nail body are monitored in real time, and adaptive dynamic adjustments are made to address processing abnormalities to ensure consistent energy absorption of the workpiece. Specifically, this includes: when an abnormal increase in impedance occurs in the initial stage of the pulse, the clamping force of the fixture is increased and a "precursor electrical pulse" with a frequency > 50Hz and a peak current density < 300A / mm² is instantaneously inserted to break down the oxide layer, thereby quickly restoring the original processing parameters for electrical pulse processing; if a sudden drop in impedance or waveform divergence is detected in the middle or later stages, indicating a risk of local overheating and softening and melting, the pulse width is adaptively compressed and the pulse frequency is lowered while maintaining the preset total energy unchanged, providing a solid-state heat dissipation window for the nail shoulder stress area, thereby protecting the macroscopic morphology and mechanical strength of the nail body; for waveform distortion caused by electrode wear or system mismatch, an online impedance compensation algorithm is activated to reshape the waveform, and a cut-off alarm is triggered when five corrections are ineffective or an absolute short circuit is encountered.

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