Patent ID: 12245944

1—magnesium block;2—porous skeleton;3—stainless steel mold;4—fixing apparatus;5—graphite resistance furnace;6—selective laser melting device;7—titanium alloy powder;8—hot isostatic pressure sintering furnace;9—magnesium powder;10—alumina ceramic mold;11—laser powder bed device;120—hard-phase zone;121—soft-phase zone; and122—bonding zone.

DETAILED DESCRIPTION

In order to better illustrate the preparation process involved in the present disclosure and the advantages over the prior art, further explanations will be given on the basis of the above-described accompanying drawings.

Referring toFIGS.1-3, a method for preparing a heterogeneous metal composite structure for medical implantation includes the following steps.

In step 1, based on a selective laser melting technique or a laser powder bed fusion technique, titanium alloy powder7is prepared into a porous skeleton2according to different printing strategies.

In step 2, magnesium after being melted is filled into pores of the porous skeleton2.

In step 3, a titanium-magnesium interpenetrating phase composite structure prepared in step 2 is cooled to room temperature, and a surface of the titanium-magnesium interpenetrating phase composite structure is covered with a hydroxyapatite coating.

Preferably, in step 1, the porous skeleton is prepared using the selective laser melting technique by the following specific method: purging, before printing, a material molding chamber of a selective laser melting device with high-purity argon gas until oxygen content in the molding chamber is less than 0.1%, preheating a print substrate to 200° C., ensuring the dimensional accuracy for printing the porous skeleton, continuously printing the titanium alloy powder with a median diameter of 35 μm in layers using the selective laser melting technique under the conditions of a laser power of 100 W, a laser scanning speed of 1200 mm/s, and a layer thickness of 30 μm.

Referring toFIG.1, in S1, a specific method for preparing the porous skeleton2using the selective laser melting technique is as follows: prior to printing, the material forming chamber of the selective laser melting device6is purged with high-purity argon gas until the oxygen content in the forming chamber is less than 0.1% to reduce oxidation; the printing substrate is preheated to 200° C. to reduce the residual stress, avoid cracking and ensure good dimensional accuracy of the printing porous skeleton2; and the titanium alloy powder7with a median diameter of about 35 μm is continuously printed in layers by the selective laser melting technique under the conditions of a laser power of 100 W, a laser scanning speed of 1200 mm/s and a layer thickness of 30 μm.

Referring toFIG.1, in S2, a specific method for filling the inside of the pores of the porous skeleton2after the magnesium is melted is as follows: a pressureless infiltration method is used, the printed porous skeleton2is placed on a stainless steel mold3, a magnesium block1(with a purity of up to 99.99%) is placed on the porous skeleton2smoothly, the stainless steel mold3is placed on a fixing device4in a graphite resistance furnace5to complete preparation before infiltration, the actual height of the used stainless steel mold3needs to be ensured to be higher than the plane of the magnesium block1to avoid infiltration outside the stainless steel mold3during melting process, and finally, the graphite resistance furnace5is heated to 800° C. (namely, 150° C. higher than the melting point of magnesium), and heated in a flowing argon gas for 10 minutes; and during this time, the molten magnesium block1flows into the pores of the porous skeleton2by its own weight without an external load, cools and completes the infiltration process in the graphite resistance furnace5, and the porous skeleton2and the magnesium block1are ultrasonically cleaned with acetone to reduce contamination before the magnesium block1is combined with the titanium alloy powder7.

Referring toFIG.2, in S1, a specific method for preparing the porous skeleton2using the laser powder bed laser powder bed fusion technique is as follows: the titanium alloy powder7with a median diameter of about 35 m is processed by a laser powder bed laser powder bed fusion technique using a laser powder bed apparatus11at a scanning speed of 1200 mm/s and a laser power of 155 W. In the scanning process, a zigzag pattern is used to reduce the thermal stress between two adjacent layers, and the scanning angle is alternated by 90° on the previous layer, so as to prepare a porous skeleton2as shown inFIG.2.

Referring toFIG.2, in S2, a specific method for filling an inside of the pores of the porous skeleton2after the magnesium is melted is as follows: the prepared porous skeleton2is placed in an alumina ceramic mold10by a hot isostatic pressing method, magnesium powder9is fully sprinkled into the pores of the porous skeleton2, and the magnesium powder9is further fully filled into the internal pores of the porous skeleton2by means of mechanical vibration; and finally, the alumina ceramic mold10is placed in a hot isostatic pressing sintering furnace8in a stable manner, and the inside of the hot isostatic pressing sintering furnace8is evacuated and then argon is introduced. In order to form a dense and massive metal composite material, the porous skeleton2and the magnesium powder9are mixed by the hot isostatic pressing process, the hot isostatic pressing sintering furnace8is heated to 900° C. in an argon environment and heated for 4 hours under a pressure of 150 MPa, and during the heating process, the magnesium powder9melts and is tightly adhered to the porous skeleton2under the action of pressure and temperature.

Referring toFIG.3, in S3, the titanium-magnesium interpenetrating phase composite structure can be subdivided into a soft phase region121, a hard phase region120, and a bonding region122. In the face of impact, the hard phase region120bears more load due to the larger Young modulus and better mechanical properties of the material. However, in the bonding region122, due to the interpenetration of the two materials in the preparation process, MgAl, Ti2Si3and other phases will appear, and the bearing capacity of the bonding region122is slightly weak, mainly playing the role of stable deformation; and however, the magnesium phase in the soft phase region121plays a role of transition and connection, its bearing capacity is weaker than the former two phases, and the first crack occurs when it encounters severe impact. The overall three-dimensional interpenetrating phase structure, combined with the bionic concept, imitates the pearl layer brick-mud structure, its “soft and hard” characteristics can greatly improve the structure and material synergy, not only greatly reduce the Young modulus, eliminate the “stress shielding”, but also ensure the Young modulus between 10 Gpa-20 Gpa, strength over 180 Mpa, in line with human bone implantation requirements.

In S3, a specific method for covering the surface of the titanium-magnesium interpenetrating phase composite structure with a layer of hydroxyapatite coating is as follows: hydroxyapatite coating is prepared by electrophoretic deposition; andthe prepared titanium-magnesium interpenetrating phase composite structure is used as a cathode, an inert electrode graphite sheet is used as an anode, the cathode-anode two pole pieces are kept in parallel and the cathode-anode two pole spacing is kept at 20 mm, and vertically inserted into a quartz glass beaker filled with a certain concentration of HA suspension, concentrated nitric acid with a volume fraction of about 2% is added as electrolyte, and the pH value is adjusted with ammonia water to stabilize the pH value between 4 and 6; and a constant voltage mode is used to perform electrophoretic deposition at a set voltage for a certain time, and during the deposition, the hydroxyapatite coating will gradually cover the surface of the titanium-magnesium interpenetrating phase composite structure as a cathode. After the hydroxyapatite coating completely covers the surface of the titanium-magnesium interpenetrating phase composite structure, the power supply is turned off, and the sample is taken out and placed in an environment with a higher relative humidity and a lower relative temperature for drying.

Referring toFIGS.1-8, in S1, the porous skeleton2is a lattice lattice structure.

Referring toFIGS.4-6, in S1, the lattice lattice structure is a body-centered cubic lattice structure, a closed square beam-0 type structure, or a closed arc beam-0 type structure.

Referring toFIG.4, in S1, the body-centered cubic lattice structure takes eight vertices of a hexahedron as key nodes, which are connected to each other to form an outer beam, and takes face-centered positions of six faces as inner beam nodes, and the inner beam and the outer beam are connected and combined to form the body-centered cubic structure.

Referring toFIG.5, in S1, the closed square beam-0 type structure is based on a face-centered lattice to construct an italics X-shaped beam, the middle of the italics X-shaped beam is fixed by a straight column, and a base configuration is constructed by 2-3 times of mirror images, the connection between each of the italics X-shaped beams is the face-centered position of each plane, and the closed square beam-0 type structure is established by adjusting the total horizontal length a and the vertical length b.

Referring toFIG.6, in S1, the closed arc-shaped beam-0 structure is based on a quadrilateral, and four sides are cut with an arc to construct an arc-shaped beam and form a circular array to establish the closed arc-shaped beam-0 structure, the porosity of the closed arc-shaped beam-0 structure is regulated with the horizontal arc diameter C1and the vertical arc C2as variable parameters.

Referring toFIG.1orFIG.2, the titanium alloy powder7used in S1 is Ti-6Al-4V powder.

Referring toFIG.7, in S1, the body-centered cubic lattice structure is arranged in an acetabular region.

Referring toFIG.7, in S1, the closed square beam-0 type structure is arranged in a iliac region.

Referring toFIG.7, in S1, the closed arc beam-0 type structure is arranged in a sacral region.

The present invention includes the following operation principles.

Pelvis can be considered as a three-dimensional columnar structure formed by multiple bone connections, which can be subdivided into the posterior sacrum, coccyx and bilateral arc-shaped hip bone according to different positions, which is mainly used for bearing load, connecting and protecting internal organs in human body. Once the pelvic bone is damaged due to severe impact, the action of a person will be greatly limited. Therefore, in the completion of bone repair and bone replacement, it is necessary to pay attention to the impact resistance and vibration damping performance of implanted bone so as to avoid secondary postoperative trauma. At the same time, according to the existing research, when the pelvic bone is impacted, the stress mainly passes through the sacroiliac joint from the upper end of the sacrum and then passes along the lower edge of the ilium, the stress distribution on both sides is mainly distributed near the greater notch of the ischium, the stress around is small, and finally the stress is transmitted to the acetabulum and anterior ring region on both sides. Obviously, different regions of the pelvic bone are subjected to different forces when they face the impact. So far, it is difficult to simultaneously meet the force-bearing standard of multiple regions of the pelvic bone by designing a single lattice lattice structure. Therefore, as shown inFIG.7, the idea of designing and filling the lattice lattice structure specifically according to different positions of the pelvic bone is put forward. A variety of lattice lattice structures suitable for different impact conditions as shown inFIGS.4-6can be prepared by printing, and filled according to different stress regions of the pelvis, for example, the closed arc-shaped beam-O structure has the largest bearing capacity among the three lattice structures, and can be set in the sacral region where the pelvis first encounters impact load; similarly, the body-centered cubic lattice structure has good vibration damping performance and can be set in the acetabular region; and the closed tetragonal beam-0 construct is stable in deformation and can effectively transmit loads, and can be placed in the iliac region to join the sacral and acetabular regions. Due to the different filling positions, the lattice lattice structures of the three regions play the role of mechanical locking, which can make full use of advantages thereof and make up for the deficiency of a single structure.

As shown inFIG.8, when the human pelvic bone or hip joint is subjected to significant impact or trauma, the bone surface may generate cracks or even gaps, and in order not to affect the normal life, it is necessary to perform hip joint and pelvic bone replacement for bone repair. The titanium-magnesium interpenetrating phase composite structure prepared by the above two methods is used to replace or fill the gaps and injuries, and suture after filling. After implantation into the human body, the hydroxyapatite coating on the surface of titanium-magnesium interpenetrating phase composite structure can effectively slow down the corrosion of magnesium and prevent the premature degradation of the implant due to the corrosion of body fluids, thus affecting the bone repair process; on the other hand, the calcium and phosphorus plasma released after the degradation of hydroxyapatite coating can help promote the development of chondrocytes and the formation of bone trabeculae; the surface of hydroxyapatite coating will induce the deposition of new bone new bone promote the reaction between osteoblasts and osteoclasts, make them adhere to the surface of hydroxyapatite coating for growth, induce the growth of bone tissues along the implantation interface, and cooperate with rehabilitation training after implantation. The damaged bone gap can gradually heal, compared with the previous single metal implant material, shorten the bone formation cycle and greatly reduce the suffering of patients.