Intervertebral fusion cage for wireless passive strain monitoring and 4D printing method thereof

Abstract

The application provides an intervertebral fusion cage for wireless passive strain monitoring and a 4D printing method thereof, and belongs to the field of medical devices, comprising a base, a porous dot array structure and a magnetic top part connected in sequence from bottom to top, and a conductive coil arranged in the base, wherein the base is made of a shape memory polymer, and a groove is formed in the base for embedding the conductive coil; the porous dot array structure is made of a shape memory polymer and is used for compression under external force; the magnetic top part is made of a permanent magnetic ceramic material and a polymer composite and is used for generating a magnetic field, and the outside of the magnetic top part is coated with a biocompatible material. The porous dot array structure can be compressed after the intervertebral fusion cage is subjected to the pressure between adjacent vertebrae, so as to change the distance between the conductive coil and the magnetic top part, and then the voltage is generated at both ends of the conductive coil, and the wireless transmission of the voltage signal is realized by using an inductive coil arranged outside the body, and the wireless passive monitoring of the strain of the adjacent vertebrae is realized by monitoring the voltage signal.

Description

Technical Field

[0001] This invention belongs to the field of medical devices, and more specifically, relates to an interbody fusion device for realizing wireless passive strain monitoring and its 4D printing method. Background Technology

[0002] 4D printing is an additive manufacturing technology for intelligent components, whose shape, performance, or function can be controllably changed in time and space under the stimulation of external energy fields (heat, magnetism, electricity, light, force, etc.). Due to its intelligent and controllable change characteristics, 4D printing, as a disruptive manufacturing technology, has broad application prospects in aerospace, biomedicine, soft robotics, and other fields. In its early stages, the concept of 4D printing focused solely on the change in the shape of printed components; that is, 4D printing is the controllable change in the shape of additively manufactured components under the influence of external energy fields. Guided by this initial concept, researchers have conducted extensive research on shape-changing 4D printing technology, resulting in numerous inventions.

[0003] Shape memory materials, also known as shape memory materials, are materials that exhibit shape memory effects. Common examples include shape memory polymers and shape memory alloys. These materials can recover their initial shape from a temporary shape under temperature stimulation; this recovery process is known as shape change. Researchers have utilized this intelligent property of shape memory materials in additive manufacturing processes. For instance, CN115028964A discloses a method for preparing a photopolymerizable 4D-printable shape memory polymer; CN115070052A discloses a novel dual-state nickel-titanium shape memory alloy and its 4D printing preparation method; and CN114535600A discloses an optimization method for the 4D printing process of CuAlNi shape memory alloys. These inventions have successfully enabled the shaped parts to change shape under temperature stimulation, thus achieving 4D printing.

[0004] The aforementioned inventions all verify the principles of shape-changing 4D printing, primarily demonstrating the process of shape change, thus keeping 4D printing at the laboratory research stage. To address this, some researchers have explored applications of deformable 4D printing. For example, CN114601605A discloses an interbody fusion device based on a nickel-titanium shape memory alloy, which provides stable and effective fixation; CN111096829A discloses a shape memory polymer interbody fusion device; and CN111110406A discloses a shape memory negative Poisson's ratio interbody fusion device. These devices utilize highly biocompatible materials to reduce complications, promote bone repair, and deform upon temperature stimulation, compressing before implantation and expanding afterward to reduce implantation difficulty. However, this represents only a minor improvement to existing interbody fusion devices, which currently meet implantation requirements and provide good support. Furthermore, these studies only utilize the "stimulus-response" characteristics of shape memory materials, merely achieving and utilizing the controllable change in the shape of the shape memory component, offering only a single support function, and failing to realize the variation in performance and function of 4D printing. Currently, the market for interbody fusion devices is large, but postoperative recovery time is long. Monitoring the strain of the vertebrae at the surgical site has become an urgent need in this field. If the performance and function of these interbody fusion devices could be modified to sense and monitor the strain generated between adjacent vertebrae during human movement, thus guiding postoperative recovery, it would bring significant benefits to patients. This is precisely the important improvement requirement for interbody fusion devices.

[0005] To achieve 4D printing with varying performance and functions, CN111409284A discloses a flexible piezoelectric sensor based on 4D printing and its fabrication method. This invention is based on the idea of ​​combining magnetoelectric materials, combining (splicing together) the magnetic and conductive parts manufactured by additive manufacturing. Utilizing the principle of electromagnetic induction, the change in magnetic flux of the conductive part under the action of external force leads to the generation of voltage. This newly generated piezoelectric property indicates that the performance and function have changed, thus realizing 4D printing. However, this 4D printed piezoelectric sensor still has the following problems: (1) The fabrication method adopts the unavoidable splicing process after additive manufacturing, which reduces production efficiency and fails to fully reflect the advantages of additive manufacturing technology; (2) The piezoelectric voltage is low, only at the microvolt (μV) level, which is very easy to be confused with the noise of the voltage waveform, and the sensitivity is very low; (3) The electrical signal detection of this invention requires connecting wires to both ends of the coil and then connecting the wires to the test equipment, that is, the test equipment needs to form a closed loop with the piezoelectric device, which leads to the complexity of the circuit connection. Furthermore, if piezoelectric properties are incorporated into the aforementioned intervertebral fusion device, strain sensing and monitoring between adjacent vertebrae can be achieved. However, since the piezoelectric sensor must be connected to the device via wires, it cannot be implanted into the human body, hindering its application as an implant. Therefore, to solve the above problems and promote the application of 4D-printed piezoelectric sensors in the medical field, a completely new invention is urgently needed. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide an intervertebral fusion device and its 4D printing method for achieving wireless passive strain monitoring, thereby solving the problems that existing intervertebral fusion devices cannot sense or monitor the strain generated by adjacent vertebrae during movement, and are difficult to detect electrical signals in the body.

[0007] To achieve the above objectives, the present invention provides an interbody fusion device for wireless passive strain monitoring. The device comprises, from bottom to top, a base, a porous lattice structure, and a magnetic top, and further includes a conductive coil disposed within the base. Specifically: the base is made of shape memory polymer and has internal slots for embedding the conductive coil; the porous lattice structure is also made of shape memory polymer for compression under external force; the magnetic top is made of a composite of permanent magnetic ceramic material and polymer for generating a magnetic field, and the magnetic top is externally coated with a biocompatible material.

[0008] In use, if the intervertebral fusion device is subjected to pressure between adjacent vertebrae and generates strain, the porous lattice structure is compressed under the action of external force, causing the distance between the conductive coil and the magnetic top to change, thereby changing the magnetic flux of the conductive coil and generating a voltage at its two ends. The voltage signal is wirelessly transmitted using an externally installed induction coil, and the strain of adjacent vertebrae is wirelessly and passively monitored by monitoring this voltage signal.

[0009] As a further preferred embodiment, the shape memory polymer is shape memory polyurethane, shape memory polyether ether ketone, shape memory polylactic acid, or shape memory epoxy resin; the permanent magnetic ceramic material is neodymium iron boron, barium ferrite, or strontium ferrite; and the polymer is a material whose processing temperature is 50°C below the Curie point of the permanent magnetic ceramic material.

[0010] As a further preferred embodiment, the slot in the base is located in the middle of the base and has a height of 1 to 2 mm.

[0011] As a further preferred embodiment, the mass fraction of the permanent magnetic ceramic material in the magnetic top is 40% to 60%.

[0012] As a further preferred embodiment, the conductive coil is a copper coil with 800 to 1200 turns.

[0013] As a further preferred embodiment, the porous lattice structure adopts a three-period minimal curved surface structure, the volume fraction of which is 10% to 15%, and the unit size is 2 to 5 mm.

[0014] As a further preferred embodiment, the height ratio of the base, the porous lattice structure, and the magnetic top is 1:2:1 to 1:3:1.

[0015] According to another aspect of the present invention, a 4D printing method for the above-mentioned interbody fusion device is provided, which includes the following steps:

[0016] S1 scans the area to be repaired to obtain a surface model, and then obtains the models of the upper and lower surfaces of the interbody fusion cage through reverse calculation based on the surface model. At the same time, the height of the interbody fusion cage is calculated based on the surface model to obtain the forming model of the interbody fusion cage.

[0017] S2 Based on the forming model obtained in step S1, shape memory polymer powder is used to sequentially form a slotted base and a porous lattice structure, and then permanent magnetic ceramic and polymer composite powder is used to form the magnetic top.

[0018] S3 embeds a conductive coil at the slotted position of the base to obtain an integrated magnetoelectric device;

[0019] S4 magnetizes the integrated magnetoelectric device to give the magnetic top a permanent magnet, and then coats the outside of the magnetic top with a biocompatible material to obtain the intervertebral fusion device.

[0020] As a further preferred option, in step S4, the magnetization voltage is 1800–2000V.

[0021] In summary, the technical solutions conceived by this invention have the following beneficial effects compared with the prior art:

[0022] 1. This invention, by setting a porous lattice structure between the conductive coil and the magnetic top, can compress the intervertebral fusion device when it is subjected to pressure between adjacent vertebrae, thereby changing the distance between the conductive coil and the magnetic top, and thus generating a voltage across the conductive coil. The voltage signal is wirelessly transmitted using an externally installed induction coil. By monitoring this voltage signal, wireless passive monitoring of the strain of adjacent vertebrae can be achieved, thereby guiding the patient's postoperative rehabilitation and promoting the application of 4D printed devices with improved performance and function in the medical field. At the same time, because the conductive coil and the magnetic top are designed to be in the same direction and on the same axis, the voltage generated by the intervertebral fusion device under external force is greatly increased, thereby avoiding confusion with noise in the voltage waveform and effectively improving the reliability of the monitoring results.

[0023] 2. At the same time, by optimizing the structural parameters of the base, the porous lattice structure and the magnetic top, this invention can significantly increase the output voltage of the piezoelectric sensor from the traditional microvolt level to the millivolt level.

[0024] 3. In addition, the present invention also provides a 4D printing method for intervertebral fusion devices, which adopts a multi-material additive manufacturing process, enabling integral continuous printing, eliminating the splicing process, and thus effectively improving production efficiency. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of the interbody fusion device for realizing wireless passive strain monitoring provided in an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram illustrating the principle of wireless passive strain monitoring using the interbody fusion device provided in this embodiment of the invention.

[0027] Figure 3 This is a schematic diagram of the 4D printing process of the interbody fusion device provided in an embodiment of the present invention;

[0028] Figure 4 This is a partial enlarged view of the spine and adjacent vertebrae provided in an embodiment of the present invention;

[0029] Figure 5These are schematic diagrams and photographs of the intervertebral fusion device provided in the embodiments of the present invention placed in a vertebral model, (a) being a schematic diagram and (b) being a photograph;

[0030] Figure 6 These are photographs of the interbody fusion device testing process provided in Embodiment 1 of the present invention;

[0031] Figure 7 This is a voltage curve diagram of the intervertebral fusion device provided in Embodiment 1 of the present invention under different strains.

[0032] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0033] 1-Base, 2-Porous dot matrix structure, 3-Magnetic top, 4-Conductive coil, 5-Induction coil, 6-Voltage signal testing equipment. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0035] like Figure 1 As shown, the present invention provides an interbody fusion device for wireless passive strain monitoring. The interbody fusion device includes a base 1, a porous lattice structure 2, and a magnetic top 3 connected sequentially from bottom to top. It also includes a conductive coil 4 disposed inside the base 1. The base 1 is made of shape memory polymer and has slots inside for embedding the conductive coil 4. The porous lattice structure 2 is made of shape memory polymer and is used for compression under external force. The magnetic top 3 is made of permanent magnetic ceramic material and polymer composite material and is used to generate a magnetic field. The magnetic top 3 is coated with a biocompatible material.

[0036] Because the base 1 and porous lattice structure 2 of the intervertebral fusion device are made of shape memory polymer, it possesses a heat-driven, self-supporting, and adaptive function. Before implantation, the intervertebral fusion device is compressed to its limit and cooled to fix this deformation. When implanted at the site of the vertebral injury, the stimulation of body temperature causes it to return to its original height, thereby supporting the vertebrae in a healthy position, which is beneficial for postoperative repair. During use, the magnetic top 3 generates a magnetic field, and the conductive coil 4 is located in this magnetic field. When the intervertebral fusion device is subjected to pressure between adjacent vertebrae and undergoes strain, the porous lattice structure 2 is compressed under the action of external force, causing a change in the distance between the conductive coil 4 and the magnetic top 3. This changes the magnetic flux of the conductive coil 4, causing a voltage to be generated at its two ends, thus converting mechanical energy into electrical energy. The performance and function change simultaneously, enabling 4D printing. By establishing the relationship between the strain of the intervertebral fusion device and the in vitro induced voltage through previous in vitro experimental data, the strain at the lesion site inside the body can be obtained through the voltage measured in vitro.

[0037] like Figure 2 As shown, to ensure voltage signals can still be detected after implantation in the human body, an induction coil 5 with an area and number of turns no less than that of the conductive coil 4 needs to be placed externally and positioned close to the body surface, ideally as close as possible to the surgical site. The induction coil 5 is then connected to a voltage signal testing device 6. When the magnetic flux of the conductive coil 4 changes, the magnetic flux of the induction coil 5 also changes, generating an induced voltage that is detected by the voltage signal testing device 6. The intervertebral fusion device inside the body has no power source and possesses self-driven sensing capabilities. The externally placed induction coil 5 enables wireless testing, eliminating the need for the testing device to be connected to the internal intervertebral fusion device. This successfully achieves wireless and passive monitoring of the intervertebral fusion device's strain.

[0038] Furthermore, the shape memory polymer is shape memory polyurethane, shape memory polyetheretherketone, shape memory polylactic acid, or shape memory epoxy resin; the permanent magnetic ceramic material is neodymium iron boron, barium ferrite (BaO·6Fe2O3), and strontium ferrite (SrO·Fe2O3); the polymer is a material with a processing temperature 50°C below the Curie point of the permanent magnetic ceramic material, such as nylon 12 (PA12), nylon 6 (PA6), nylon 66 (PA66), polycarbonate (PC), and polypropylene (PP); the mass fraction of the permanent magnetic ceramic material in the magnetic top 3 is 40% to 60%; and the conductive coil is a copper coil.

[0039] Furthermore, because the conductive coil and the magnetic top are designed to be in the same direction and coaxial, and the number of turns of the conductive coil is preferably 800 to 1200, the voltage generated by the intervertebral fusion device under external force is greatly increased, and the piezoelectric voltage can reach the millivolt (mV) level. Compared with the microvolt (μV) level of previous additive manufacturing piezoelectric sensors, this represents a significant improvement, thereby avoiding confusion with noise in the voltage waveform and effectively improving the reliability of the monitoring results.

[0040] Furthermore, the porous lattice structure 2 adopts a three-period minimal surface structure, which is formed by an array of a minimum unit cell (similar to a crystal cell) in three-dimensional space. It has two important parameters: volume fraction and unit size. The volume fraction of the porous lattice structure 2 is preferably 10%–15%, and its unit size is preferably 2–5 mm. Within this range, the three-dimensional lattice structure can achieve an elastic modulus matching that of human bone, effectively avoiding stress shielding effects and ensuring the normal use of the intervertebral fusion device. Furthermore, by adjusting these two parameters, the compressive modulus of the lattice structure can be precisely controlled, allowing for personalized and precise adaptation to the elastic modulus of bones at different locations.

[0041] Furthermore, the height ratio of the base 1, the porous lattice structure 2, and the magnetic top 3 is 1:2:1 to 1:3:1, that is, the base 1 and the magnetic top 3 have the same height, the porous lattice structure is 2 to 3 times the height of the two, and the slot of the base 1 is located in the middle of the base with a height of 1 to 2 mm.

[0042] like Figure 3 As shown, according to another aspect of the present invention, a 4D printing method for the above-mentioned interbody fusion device is provided, which includes the following steps:

[0043] S1 performs a CT scan on the site to be repaired to obtain a surface model. Then, based on this surface model, the upper and lower surface models of the interbody fusion cage are obtained through reverse calculation. The remaining cross-sections are squares, and the size of the squares does not exceed the size of the upper and lower surfaces. At the same time, the height of the interbody fusion cage is calculated based on this surface model to obtain the forming model of the interbody fusion cage, thereby ensuring the personalization of the prepared interbody fusion cage.

[0044] S2 The forming model obtained in step S1 is imported into the powder bed laser melting device. The grooved base 1 and the porous lattice structure 2 are formed sequentially using biocompatible shape memory polymer powder. Then, the magnetic top 3 is formed using permanent magnetic ceramic and polymer composite powder.

[0045] S3 embeds the conductive coil 4 into the slot of the base 1 to obtain an integrated magnetoelectric device. The thickness of the conductive coil 4 is similar to the height of the slot to ensure smooth embedding.

[0046] S4 sets the integrated magnetoelectric device parallel to the horizontal plane, so that the magnetic top 3 is in close contact with the magnetizer. The magnetization voltage is set to 1800~2000V. At the moment the magnetizer is started, the magnetic top 3 acquires permanent magnetism. Then, the magnetic top 3 is coated with a biocompatible material to make it have the biological conditions for implantation in the human body, thereby producing an intervertebral fusion device.

[0047] The technical solution provided by the present invention will be further described below with reference to specific embodiments.

[0048] Example 1

[0049] S1 performs a CT scan on the site to be repaired to obtain a surface model. Then, based on this surface model, the upper and lower surfaces of the interbody fusion cage are obtained through reverse calculation. At the same time, the height h of the interbody fusion cage is calculated to be 20mm based on this surface model, thus obtaining the forming model of the interbody fusion cage.

[0050] S2 imports the forming model obtained in step S1 into the powder bed laser melting device, and uses shape memory polyurethane powder printing to first form a grooved base 1 with a forming height of 4mm, wherein the groove is located in the middle of the base with a height of 2mm. Above the base, a porous lattice structure 2 is formed with a forming height of 12mm, a volume fraction of 10%, and a unit size of 5mm. The powder feeding cylinder is replaced with neodymium iron boron and nylon 12 (PA12) composite powder, with a neodymium iron boron mass fraction of 60%. At the same time, the process parameters of the device are adjusted to suit the new powder material. The above-mentioned polymer magnetic composite powder material is used to form a magnetic top 3 with a forming height of 4mm.

[0051] S3 embeds a conductive coil 4 into the slot of the base 1 to obtain an integrated magnetoelectric device. The thickness of the conductive coil 4 is equivalent to the height of the slot to ensure smooth embedding. The number of turns of the conductive coil is 1000.

[0052] S4 sets the integrated magnetoelectric device parallel to the horizontal plane, so that the magnetic top 3 is in close contact with the magnetizer. The magnetization voltage is set to 1920V. At the moment the magnetizer is started, the magnetic top 3 acquires permanent magnetism. Then, the magnetic top 3 is coated with a biocompatible material to make it have the biological conditions for implantation in the human body, thereby producing an intervertebral fusion device.

[0053] Example 2

[0054] S1 performs a CT scan on the site to be repaired to obtain a surface model. Then, based on this surface model, the upper and lower surfaces of the interbody fusion cage are obtained through reverse calculation. At the same time, the height h of the interbody fusion cage is calculated to be 20mm based on this surface model, thus obtaining the forming model of the interbody fusion cage.

[0055] S2. The forming model obtained in step S1 is imported into the powder bed laser melting device. Shape memory polyetheretherketone powder is used for printing. First, a grooved base 1 is formed with a forming height of 5mm, wherein the groove is located in the middle of the base with a height of 1mm. A porous lattice structure 2 is formed above the base with a forming height of 10mm, a volume fraction of 15%, and a unit size of 2mm. The powder feeding cylinder is replaced with barium ferrite and nylon 6 (PA6) composite powder, with a barium ferrite mass fraction of 40%. At the same time, the process parameters of the device are adjusted to suit the new powder material. The above polymer magnetic composite powder material is used to form a magnetic top 3 with a forming height of 5mm.

[0056] S3 embeds a conductive coil 4 into the slot of the base 1 to obtain an integrated magnetoelectric device. The thickness of the conductive coil 4 is equivalent to the height of the slot to ensure smooth embedding. The number of turns of the conductive coil is 1200.

[0057] S4 sets the integrated magnetoelectric device parallel to the horizontal plane, so that the magnetic top 3 is in close contact with the magnetizer. The magnetization voltage is set to 1800V. At the moment the magnetizer is started, the magnetic top 3 acquires permanent magnetism. Then, the magnetic top 3 is coated with a biocompatible material to make it have the biological conditions for implantation in the human body, thereby producing an intervertebral fusion device.

[0058] Example 3

[0059] S1 performs a CT scan on the site to be repaired to obtain a surface model. Then, based on this surface model, the upper and lower surface models of the interbody fusion cage are obtained through reverse calculation. At the same time, the height h of the interbody fusion cage is calculated to be 17.5 mm based on this surface model, thus obtaining the forming model of the interbody fusion cage.

[0060] S2 imports the forming model obtained in step S1 into the powder bed laser melting device, and uses shape memory polylactic acid powder for printing. First, a grooved base 1 is formed with a forming height of 4mm, wherein the groove is located in the middle of the base with a height of 1.5mm. Above the base, a porous lattice structure 2 is formed with a forming height of 10mm, a volume fraction of 12.5%, and a unit size of 4mm. The powder feeding cylinder is replaced with strontium ferrite and polypropylene (PP) composite powder, with a mass fraction of 50% strontium ferrite. At the same time, the process parameters of the device are adjusted to suit the new powder material. The above-mentioned polymer magnetic composite powder material is used to form a magnetic top 3 with a forming height of 4mm.

[0061] S3 embeds a conductive coil 4 into the slot of the base 1 to obtain an integrated magnetoelectric device. The thickness of the conductive coil 4 is similar to the height of the slot to ensure smooth embedding. The number of turns of the conductive coil is 800.

[0062] S4 sets the integrated magnetoelectric device parallel to the horizontal plane, so that the magnetic top 3 is in close contact with the magnetizer. The magnetization voltage is set to 2000V. At the moment the magnetizer is started, the magnetic top 3 acquires permanent magnetism. Then, the magnetic top 3 is coated with a biocompatible material to make it have the biological conditions for implantation in the human body, thereby producing an intervertebral fusion device.

[0063] Example 4

[0064] S1 performs a CT scan on the site to be repaired to obtain a surface model. Then, based on this surface model, the upper and lower surfaces of the interbody fusion cage are obtained through reverse calculation. At the same time, the height h of the interbody fusion cage is calculated as 16mm based on this surface model, thus obtaining the forming model of the interbody fusion cage.

[0065] S2 imports the forming model obtained in step S1 into the powder bed laser melting device, and uses shape memory epoxy resin powder printing to first form a grooved base 1 with a forming height of 4mm, wherein the groove is located in the middle of the base with a height of 2mm. Above the base, a porous lattice structure 2 is formed with a forming height of 8mm. The powder feeding cylinder is replaced with neodymium iron boron and polycarbonate (PC) composite powder, with a mass fraction of 55% and a volume fraction of 13% for neodymium iron boron, and its unit size is 3mm. At the same time, the process parameters of the device are adjusted to suit the new powder material, and the above-mentioned polymer magnetic composite powder material is used to form a magnetic top 3 with a forming height of 4mm.

[0066] S3 embeds a conductive coil 4 into the slot of the base 1 to obtain an integrated magnetoelectric device. The thickness of the conductive coil 4 is similar to the height of the slot to ensure smooth embedding. The number of turns of the conductive coil is 900.

[0067] S4 sets the integrated magnetoelectric device parallel to the horizontal plane, so that the magnetic top 3 is in close contact with the magnetizer. The magnetization voltage is set to 1950V. At the moment the magnetizer is started, the magnetic top 3 acquires permanent magnetism. Then, the magnetic top 3 is coated with a biocompatible material to make it have the biological conditions for implantation in the human body, thereby producing an intervertebral fusion device.

[0068] The sensing and strain monitoring functions of the intervertebral fusion device prepared in Example 1 were tested in vitro using a human vertebral model, as shown in the figure. Figure 4 As shown, the intervertebral fusion cage was replaced between adjacent vertebrae. (See diagram and photograph.) Figure 5 As shown, the test process and results are as follows: Figure 6 , 7 As shown. When subjected to pressure from the mold, the distance between the magnetic top 3 and the conductive coil 4 changes, causing a change in the magnetic flux in the conductive coil 4, thereby generating a voltage. Different pressures cause different strains in the intervertebral fusion device, resulting in different output voltages. Figure 7The results show that when the compressive strain is 36%, 46%, 53%, 58%, 61%, and 63%, the output voltages are 3.1 mV, 4.0 mV, 5.2 mV, 6.3 mV, 6.5 mV, and 6.8 mV, respectively. Through a large amount of data, the relationship between strain and voltage can be established, and the corresponding strain can be obtained from the voltage data.

[0069] The strain monitoring function of the interbody fusion device can be achieved wirelessly and passively, as shown in the schematic diagram below. Figure 2 As shown, the intervertebral fusion device is implanted within a closed space. Outside this closed space, i.e., externally, an induction coil 5 is placed near the conductive coil inside the body. When the magnetic flux of the internal conductive coil 4 changes, the corresponding external induction coil 5 also experiences a change in magnetic flux, and the resulting voltage can be recorded by an external voltage signal testing device 6. The sensor inside the body can operate without a power source; therefore, this invention achieves wireless, passive detection and output of electrical signals.

[0070] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An intervertebral fusion cage for enabling wireless passive strain monitoring, the intervertebral fusion cage comprising: The intervertebral fusion cage comprises a base (1), a porous lattice structure (2) and a magnetic top (3) connected in sequence from bottom to top, and further comprises an electrically conductive coil (4) arranged inside the base (1), wherein: the base (1) is made of shape memory polymer, and is internally slotted for embedding the electrically conductive coil (4); the porous lattice structure (2) is made of shape memory polymer and is used for compression under external force; the magnetic top (3) is made of permanent magnetic ceramic material and polymer composite, is used for generating a magnetic field, and the outer part of the magnetic top (3) is coated with a biocompatible material. In use, if the intervertebral fusion cage is strained by the pressure between adjacent vertebrae, the porous lattice structure (2) is compressed under external force, resulting in a change in the distance between the electrically conductive coil (4) and the magnetic top (3), and thus the magnetic flux of the electrically conductive coil (4) is changed to generate a voltage at both ends of the electrically conductive coil (4), and an externally arranged induction coil (5) is used to realize wireless transmission of the voltage signal, so as to realize wireless passive monitoring of the strain of adjacent vertebrae by monitoring the voltage signal. The intervertebral fusion cage is manufactured by using a 4D printing method, specifically: S1, scanning the position to be repaired to obtain a surface model, then obtaining the models of the upper and lower surfaces of the intervertebral fusion cage by inverse operation according to the surface model, and calculating the height of the intervertebral fusion cage according to the surface model to obtain a forming model of the intervertebral fusion cage; S2, according to the forming model obtained in step S1, using shape memory polymer powder to successively form the base (1) with a slot and the porous lattice structure (2), and then using permanent magnetic ceramic material and polymer composite powder to form the magnetic top (3); S3, embedding the electrically conductive coil (4) in the slotted position of the base (1) to obtain an integrated magnetoelectric device; S4, magnetizing the integrated magnetoelectric device to make the magnetic top (3) have permanent magnetism, and then coating the outer part of the magnetic top (3) with a biocompatible material to obtain the intervertebral fusion cage.

2. The wireless passive strain monitored intervertebral fusion cage of claim 1, wherein, The shape memory polymer is shape memory polyurethane, shape memory polyether ether ketone, shape memory polylactic acid or shape memory epoxy resin; the permanent magnetic ceramic material is neodymium iron boron, barium ferrite or strontium ferrite; and the polymer is a material with a processing temperature 50 ℃ below the Curie point of the permanent magnetic ceramic material.

3. The wireless passive strain monitored intervertebral fusion cage of claim 1, wherein, The slot of the base (1) is located in the middle of the base, and has a height of 1-2 mm.

4. The wireless passive strain monitored intervertebral fusion cage of claim 1, wherein, The mass fraction of the permanent magnetic ceramic material in the magnetic top (3) is 40%-60%.

5. The wireless passive strain monitored intervertebral fusion cage of claim 1 wherein, The electrically conductive coil is a copper coil, and the number of turns of the electrically conductive coil is 800-1200.

6. The wireless passive strain monitored intervertebral fusion cage of claim 1, wherein, The porous lattice structure (2) adopts a three-period minimal surface structure, the volume fraction of the porous lattice structure (2) is 10%-15%, and the unit size thereof is 2-5 mm.

7. The wireless passive strain monitored intervertebral fusion cage of any one of claims 1 to 6, wherein, The height ratio of the base (1), the porous lattice structure (2) and the magnetic top (3) is 1: (2-3):

1.

8. The wireless passive strain monitored intervertebral fusion cage of claim 7, wherein, In step S4, the magnetizing voltage is 1800-2000 V.

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