DEGRADABLE MAGNESIUM ALLOY IN-SITU COMPOSITE ANASTOMOTIC STAPLE AND A PREPARATION METHOD THEREOF

Abstract

The present disclosure relates to the technical field of biomedical materials, more particularly to a degradable magnesium alloy in-situ composite anastomotic staple and a preparation method thereof. The anastomotic staple, with a composite structure, is mainly composed of Mg—Zn—Nd magnesium alloy with high strength and good plasticity (internal part), and corrosion-resistant MgF.sub.2 (external part), and is formed by in-situ synthesis of MgF.sub.2 with the outer layer of Mg—Zn—Nd magnesium alloy anastomotic staple. The magnesium alloy composite anastomotic staple provided by the present disclosure has good plastic deformation ability and mechanical strength, a low degradation rate, and a high biosafety level, which can meet the in-vivo implantation requirements. In addition, it can gradually degrade in vivo after achieving the medical effects in vivo, avoiding a second operation for removal.

Claims

1. A degradable magnesium alloy in-situ composite anastomotic staple, mainly comprising the internal and external parts with the former made of the Mg—Zn—Nd magnesium alloy with high strength and good plasticity, and the latter of corrosion-resistant MgF.sub.2, characterized in that it has a composite structure formed by the in-situ synthesis of MgF.sub.2 with the outer layer of the Mg—Zn—Nd magnesium alloy anastomotic staple; by weight percentage, the chemical components of the Mg—Zn—Nd magnesium alloy anastomotic staple and their contents are described as follows: Zn (0.2%-3.0%), Nd (0.2%-2.3%), and Mg (the rest).

2. The degradable magnesium alloy in-situ composite anastomotic staple according to claim 1, characterized in that by weight percentage, the chemical components of the Mg—Zn—Nd magnesium alloy anastomotic staple and their contents are described as follows: Zn (1.0%-3.0%), Nd(0.2%-1.0%), and Mg (the rest).

3. The degradable magnesium alloy in-situ composite anastomotic staple according to claim 1, characterized in that by weight percentage, the technical indicators of the Mg—Zn—Nd magnesium alloy anastomotic staple are described as follows: a tensile strength range of 260-320 MPa, a yield strength range of 170-240 MPa and an elongation of 20-33%.

4. The degradable magnesium alloy in-situ composite anastomotic staple according to claim 1, characterized in that the thickness of the corrosion-resistant MgF.sub.2 in the outer layer is 1.0 .Math.m-3.3 .Math.m.

5. The preparation method of a degradable magnesium alloy in-situ composite anastomotic staple according to one of claim 1, characterized in that it includes the following operating steps: (1) Melt the pure Mg, Zn and Nd in proportion into magnesium alloy, cast it into ingots and homogenize the ingots at 300-450° C. for 3-7 h; (2) Remove the surface defects and impurities of the magnesium alloy ingots from Step (1), and extrude them into bars with a diameter of 8-10 mm as per an extrusion ratio of 60-80:1 at a temperature of 390-470° C.; (3) Cold-draw the magnesium alloy bars from Step (2) into wires with a diameter of 0.2-0.6 mm, and anneal them at a temperature of 280-330° C. for 30 min-120 min; (4) Make U-shaped anastomotic staples out of the magnesium alloy wires from Step (3); (5) Electropolish the magnesium alloy anastomotic staples from Step (4) to remove surface defects, and then ultrasonically clean and dry them; (6) Immerse the magnesium alloy anastomotic staples from Step (5) into the hydrofluoric acid with a weight concentration of 20%-60% for in-situ synthesis with MgF.sub.2 at 20-35° C. for 3 h-200 h; (7) Ultrasonically clean and dry the in-situ composite magnesium alloy anastomotic staples from Step (6), and vacuum-seal them.

6. The preparation method of a degradable magnesium alloy in-situ composite anastomotic staple according to claim 5, characterized in that in Step (4), the U-shaped anastomotic staple is 10-15 mm long and 3-6 mm high with an elliptical bending part and an end face diameter of 0.20-0.35 mm.

7. The preparation method of a degradable magnesium alloy in-situ composite anastomotic staple according to claim 5, characterized in that in Step (5), fine electropolishing is carried out with the polishing solution, a mixture with the volume ratio of 2-ethoxyethanol: absolute ethanol: phosphoric acid = 1:2:2, and the weight concentration of phosphoric acid of 85% for 1-10 min under the voltage of 10-20 V.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Solo the FIGURE is an SEM micrograph of the magnesium matrix composites. Wherein, layer 2 is the in-situ composite MgF.sub.2, layer 3 is the magnesium alloy matrix, and layer 1 is the epoxy resin required to prepare the sample.

DETAILED DESCRIPTION

[0031] In the detailed description of the preferred embodiment, the present disclosure provides a degradable anastomotic staple with a high biosafety level, good mechanical properties and plasticity, and excellent corrosion resistance through alloying combined with drawing and in-situ synthesis.

[0032] The embodiments of the present disclosure will be further described in detail as follows with reference to the drawings. The embodiments are implemented based on the technical solution of the disclosure with the specific implementation method and procedures given. However, the protection scope of the disclosure is not limited to the following embodiments.

Embodiment 1

[0033] In this embodiment, the anastomotic staples are prepared in the following way: melt pure magnesium, 1% Zn and 1% Nd into liquid based on weight percentage; cast the liquid metal into ingots and remove their surface defects and impurities; homogenize the ingots at 400° C. for 4 h and make magnesium alloy bars with a diameter of 10 mm (extrusion ratio of 70:1) by hot extrusion at 430° C.; cold-draw the bars to make wires with a diameter of 0.3 mm and anneal the wires at 300° C. for 60 min. Make U-shaped anastomotic staples out of magnesium alloy wires with an elliptical bending part, a total length of 10-15 mm, a height of 3-6 mm, and an end face diameter of 0.20-0.35 mm. Electropolish the anastomotic staples for 5 min under a voltage of 15 V to remove surface defects and impurities with a mixture of 2-ethoxyethanol, absolute ethanol, and phosphoric acid at a volume ratio of 1:2:2 (the weight concentration of phosphoric acid being 85%). Then ultrasonically clean and dry the anastomotic staples, and immerse them into hydrofluoric acid with a weight concentration of 35% for in-situ synthesis with magnesium fluoride at room temperature for 6 h. Finally, ultrasonically clean, dry and vacuum-seal the anastomotic staples.

[0034] Mechanical properties and cytotoxicity data of the anastomotic staples in this embodiment are presented in Table 1 and corrosion resistance data is provided in Table 2.

Embodiment 2

[0035] In this embodiment, the anastomotic staples are prepared in the following way: melt pure magnesium, 1.73% Zn and 0.68% Nd into liquid based on weight percentage; cast the liquid metal into ingots and remove their surface defects and impurities; homogenize the ingots at 380° C. for 6 h and make magnesium alloy bars with a diameter of 10 mm (extrusion ratio of 60:1) by hot extrusion at 420° C.; cold-draw the bars to make wires with a diameter of 0.3 mm and anneal the wires at 280° C. for 120 min. Make U-shaped anastomotic staples out of magnesium alloy wires with an elliptical bending part, a total length of 10-15 mm, a height of 3-6 mm, and an end face diameter of 0.20-0.35 mm. Electropolish the anastomotic staples for 3 min under a voltage of 20 V to remove surface defects and impurities with a mixture of 2-ethoxyethanol, absolute ethanol, and phosphoric acid at a volume ratio is 1:2:2 (the weight concentration of phosphoric acid being 85%). Then ultrasonically clean and dry the anastomotic staples, and immerse them into hydrofluoric acid with a weight concentration of 40% for in-situ synthesis with magnesium fluoride at room temperature for 7 h. Finally, ultrasonically clean, dry, and vacuum-seal the anastomotic staples.

[0036] Mechanical properties and cytotoxicity data of the anastomotic staples in this embodiment are presented in Table 1 and corrosion resistance data is provided in Table 2.

Embodiment 3

[0037] In this embodiment, the anastomotic staples are prepared in the following way: melt pure magnesium, 1.6% Zn and 0.7% Nd into liquid based on weight percentage; cast the liquid metal into ingots and remove their surface defects and impurities; homogenize the ingots at 420° C. for 5 h and make magnesium alloy bars with a diameter of 10 mm (extrusion ratio of 80:1) by hot extrusion at 410° C.; cold-draw the bars to make wires with a diameter of 0.3 mm and anneal the wires at 320° C. for 30 min. Make U-shaped anastomotic staples out of magnesium alloy wires with an elliptical bending part, a total length of 10-15 mm, a height of 3-6 mm, and an end face diameter of 0.20-0.35 mm. The anastomotic staples are electropolished to remove surface defects and impurities. The electropolishing solution used is a mixture with the volume ratio of 2-ethoxyrethanol: absolute ethanol: phosphoric acid = 1:2:2 and the weight concentration of phosphoric acid of 85%. The electropolishing lasts for 6 min under a voltage of 10 V. Then the anastomotic staples are ultrasonically cleaned, dried and immersed into hydrofluoric acid with a weight concentration of 45% for in-situ synthesis with magnesium fluoride at room temperature for 8 h. Finally, the anastomotic staples are ultrasonically cleaned, dried and vacuum-sealed.

[0038] Mechanical properties and cytotoxicity data of the anastomotic staples in this embodiment are presented in Table 1 and corrosion resistance data is provided in Table 2.

TABLE-US-00001 MECHANICAL PROPERTIES AND CYTOTOXICITY OF ANASTOMOTIC STAPLES Tensile Strength (MPa) Yield Strength (MPa) Elongation (%) Cytotoxicity EMBODIMENT 1 310.2 236.2 25 Grade 0 EMBODIMENT 2 296.4 221.6 27 Grade 0 EMBODIMENT 2 314.2 239.7 29 Grade 0

TABLE-US-00002 CORROSION RESISTANCE OF ANASTOMOTIC STAPLES E.sub.0(V) I.sub.c (A/cm.sup.2) R.sub.p(Ω/cm.sup.2) EMBODIMENT 1 -1.56 5.23×10.sup.-7 3.65×10.sup.5 EMBODIMENT 2 -1.53 6.59×10.sup.-8 5.3×10.sup.5 EMBODIMENT3 -1.49 3.59×10.sup.-8 6.8×10.sup.5

[0039] From Table 1 and Table 2, it can be concluded that the anastomotic staples of the present disclosure have high tensile strength and excellent plasticity that meet the requirements for mechanical properties, and that the cytotoxicity of the anastomotic staples is Grade 0, indicating that the anastomotic staples have high cytocompatibility.

[0040] As shown in solo figure, it can be seen from the SEM micrograph of magnesium matrix composites that there is no obvious delamination between the matrix of the composites and in-situ composite MgF.sub.2, which is different from conventional coatings. The in-situ composite MgF.sub.2 layer ensures the structural and property stability of the material, and improves the corrosion resistance of the alloy.

[0041] The embodiment results show that the magnesium alloy composite anastomotic staple provided by the present disclosure has good plastic deformation ability and mechanical strength, a low degradation rate, and a high biosafety level, which can meet the requirements of in vivo implantation. In addition, it can gradually degrade in vivo after achieving the medical effects in vivo, avoiding a second operation for removal.

Embodiment 4

[0042] In this embodiment, the anastomotic staples are prepared in the following way: melt pure magnesium, 2.0% Zn and 0.5% Nd into liquid based on weight percentage; cast the liquid metal into ingots and remove their surface defects and impurities; homogenize the ingots at 380° C. for 6 h and make magnesium alloy bars with a diameter of 10 mm (extrusion ratio of 60:1) by hot extrusion at 410° C.; cold-draw the bars to make wires with a diameter of 0.3 mm and anneal the wires at 280° C. for 120 min. Make U-shaped anastomotic staples out of magnesium alloy wires with an elliptical bending part, a total length of 10-15 mm, a height of 3-6 mm, and an end face diameter of 0.20-0.35 mm. Electropolish the anastomotic staples for 3 min under a voltage of 20 V to remove surface defects and impurities with a mixture of 2-ethoxyethanol, absolute ethanol, and phosphoric acid at a volume ratio is 1:2:2 (the weight concentration of phosphoric acid being 85%). Then ultrasonically clean and dry the anastomotic staples, and immerse them into hydrofluoric acid with a weight concentration of 40% for in-situ synthesis with magnesium fluoride at room temperature for 7 h. Finally, ultrasonically clean, dry, and vacuum-seal the anastomotic staples.

[0043] The wires used for the anastomotic staples in this embodiment have a tensile strength of 265 Mpa, a yield strength of 173 Mpa, a cytotoxicity grade of 0, and a corrosion current density of 6.18 × 10.sup.-7, making them good materials for forming staples.

Comparative Example 5

[0044] In this embodiment, the anastomotic staples are prepared in the following way: melt pure magnesium, 6.0% Zn and 0.5% Nd into liquid based on weight percentage; cast the liquid metal into ingots and remove their surface defects and impurities; homogenize the ingots at 380° C. for 6 h and make magnesium alloy bars with a diameter of 10 mm (extrusion ratio of 60:1) by hot extrusion at 410° C.; cold-draw the bars to make wires with a diameter of 0.3 mm and anneal the wires at 280° C. for 120 min. Make U-shaped anastomotic staples out of magnesium alloy wires with an elliptical bending part, a total length of 10-15 mm, a height of 3-6 mm, and an end face diameter of 0.20-0.35 mm. Electropolish the anastomotic staples for 3 min under a voltage of 20 V to remove surface defects and impurities with a mixture of 2-ethoxyethanol, absolute ethanol, and phosphoric acid at a volume ratio is 1:2:2 (the weight concentration of phosphoric acid being 85%). Then ultrasonically clean and dry the anastomotic staples, and immerse them into hydrofluoric acid with a weight concentration of 40% for in-situ synthesis with magnesium fluoride at room temperature for 7 h. Finally, ultrasonically clean, dry, and vacuum-seal the anastomotic staples.

[0045] The wires used for the anastomotic staples in this comparative example have a tensile strength of 368 Mpa, a yield strength of 256 Mpa, an elongation of 4%, a cytotoxicity grade of 0, and a corrosion current density of 9.59 × 10.sup.-7. It is found in this comparative example that magnesium alloy anastomotic staples are difficult to form when the wire elongation is 4%. This is mainly because of the increase of Zn content in the alloy. Although the tensile strength and yield strength of the alloy increase, its elongation drops dramatically.

[0046] Therefore, massive studies have found that the content of Zn and Nd should be controlled within a certain range in order to form staples, for example, within the following ranges: Zn 0.2%-3.0%, Nd 0.2%-2.3%, and the rest is Mg, or preferably within such ranges: Zn 1.0%-3.0%, Nd 0.2%-1.0%, and the rest is Mg. The alloy has a high strength-plasticity matching ratio and a low degradation rate and forms staples easily especially when the elongation of magnesium alloy wires ranges from 20%-33%.