Magnetic responsive artificial cartilage for passive wireless monitoring and method of making the same

Abstract

This invention discloses a magnetically responsive artificial cartilage for passive wireless monitoring and its preparation method, belonging to the field of artificial cartilage technology. The method includes the following steps: S1, dissolving hydrogel material in deionized water to prepare a uniform hydrogel precursor solution; S2, pre-crosslinking a portion of the hydrogel precursor solution to prepare a hydrogel support matrix; S3, mixing magnetic powder into the remaining hydrogel precursor solution to prepare a magnetically responsive composite solution; S4, uniformly spreading the magnetically responsive composite solution on the upper surface of the hydrogel support matrix, and sequentially performing freeze-thaw treatment, heat treatment, and hydration treatment, followed by magnetization treatment to obtain the final product. This invention, through layered construction and specific post-processing techniques, endows the artificial cartilage with excellent mechanical stability, interfacial bonding strength, and sensitive magnetic response signal output capability, possessing both tissue support and intelligent monitoring functions, thus achieving passive wireless monitoring.

Description

Technical Field

[0001] This invention belongs to the field of artificial cartilage technology, specifically providing a magnetically responsive artificial cartilage for passive wireless monitoring and its preparation method. Background Technology

[0002] Articular cartilage has extremely limited self-repair capabilities after injury, and currently used clinical repair methods are insufficient to achieve structural and functional reconstruction. Hydrogel materials, due to their high water content, good biocompatibility, and mechanical properties similar to natural cartilage, are considered ideal candidates for artificial cartilage replacement. Existing research indicates that hydrogels such as polyvinyl alcohol and polyacrylamide can form three-dimensional network structures through freeze-thaw crosslinking or chemical crosslinking, providing certain load-bearing and cushioning functions.

[0003] However, existing hydrogel artificial cartilage faces two technical challenges after implantation. Firstly, under prolonged cyclic compressive loads on joints, hydrogels are prone to localized structural damage, cumulative deformation, or mechanical property degradation, leading to decreased load-bearing stability. Secondly, existing hydrogel artificial cartilage lacks the ability to monitor its own stress state and deformation behavior in real time, making it difficult for doctors to know the implant's working status and to quantitatively assess the postoperative recovery process. A few studies have attempted to introduce conductive fillers into the hydrogel to achieve mechanical-electrical signal conversion, but such electrical sensing systems typically require external electrodes or power sources, resulting in complex implantation structures. Furthermore, their electrical performance is susceptible to interference from ions in the body fluid environment, and their long-term stability and biosafety fail to meet clinical application requirements.

[0004] Therefore, how to construct a mechanical state monitoring function that requires no external power supply, no electrode connection, and can work stably for a long time under physiological conditions while maintaining the good mechanical support properties of hydrogel is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the challenges of long-term stable mechanical state monitoring of existing artificial cartilage materials after implantation, and the technical problems of existing sensor-type artificial cartilages relying heavily on electrical connections, having complex structures, and limited stability in vivo, this invention provides a magnetic response sensing artificial cartilage with passive wireless monitoring capabilities and its preparation method.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing magnetically responsive sensing artificial cartilage, comprising the following steps: S1. Mix and dissolve the hydrogel material with deionized water to prepare a uniform hydrogel precursor solution; S2. Pre-crosslinking treatment is performed on a portion of the hydrogel precursor solution to prepare a hydrogel support matrix; S3. Mix the magnetic powder into the remaining hydrogel precursor solution to prepare a magnetically responsive composite solution; S4. The magnetically responsive composite solution is uniformly spread on the upper surface of the hydrogel support matrix, and then subjected to freeze-thaw treatment, heat treatment and hydration treatment in sequence, followed by magnetization treatment to obtain the final product.

[0007] In one embodiment, in step S1, the hydrogel material is selected from one or more of polyvinyl alcohol, polyacrylamide, polyacrylic acid, alginate, chitosan, and gelatin; the mass ratio of the hydrogel material to deionized water is 0.05~0.2:1. Preferably, the hydrogel material is polyvinyl alcohol.

[0008] As one implementation method, in step S2, the pre-crosslinking treatment is one or more of low-temperature freeze-thaw treatment, chemical crosslinking treatment, and photocrosslinking treatment; the pre-crosslinking treatment is preferably low-temperature freeze-thaw treatment, and the low-temperature freeze-thaw treatment conditions are: freezing temperature -25~-20 ℃, freezing time 6 h.

[0009] In one implementation, in step S3, the magnetic powder is selected from one or more of iron oxide particles and neodymium iron boron particles; the mass fraction of the magnetic powder in the magnetically responsive composite solution is 30wt%~60wt%. In one embodiment, the volume ratio of a portion of the hydrogel precursor solution to the remaining hydrogel precursor solution is 2:1 to 10:1, preferably 3:1 to 5:1.

[0010] As one implementation method, in step S4, the freeze-thaw treatment conditions are: freezing temperature -20~-5 ℃, freezing time 3~10 h, thawing temperature 20~30 ℃, and freeze-thaw cycle number 3~11 times; The heat treatment conditions are: temperature 35~75 ℃, treatment time 12~24 h; The hydration treatment conditions are: soaking in deionized water for 6 to 24 hours, preferably 12 hours; The magnetic field strength for magnetization is 0.1~3 T, preferably 0.5~2 T.

[0011] In one implementation, step S4, after the freeze-thaw treatment is completed and before the heat treatment begins, also includes covering the outer side of the composite structure with a restrictive layer.

[0012] In one embodiment, the material of the limiting layer is selected from at least one of polyimide, Ecoflex silicone, polyamide, and polyester materials; Preferably, the limiting layer is a polyimide film with a thickness of 80-520 μm. More preferably, the limiting layer is a polyimide film with different thickness gradients, the film thicknesses being 80-120 μm, 280-320 μm, and 480-520 μm respectively.

[0013] Secondly, the present invention provides a magnetically responsive artificial cartilage prepared by the above preparation method, comprising a hydrogel support matrix and a magnetically responsive functional layer composited on the upper surface of the hydrogel support matrix.

[0014] Thirdly, the present invention provides the application of the magnetically responsive artificial cartilage prepared by the above-described preparation method or the magnetically responsive sensing artificial cartilage prepared by the above-described preparation method in the preparation of implants for articular cartilage repair and passive wireless monitoring of postoperative status.

[0015] Compared with the prior art, the present invention has at least the following beneficial effects: (1) This invention divides the hydrogel precursor solution into two parts to prepare a hydrogel support matrix and a magnetically responsive composite solution, respectively. The magnetically responsive composite solution is then laid only on the upper surface of the support matrix to form a magnetically responsive functional layer. This structure allows the hydrogel support matrix to be dedicated to providing load-bearing and buffering functions, while the magnetically responsive functional layer is located only in the top region where the stress is most direct. When the artificial cartilage is subjected to compressive load, the magnetic particles in the top functional layer undergo relative displacement, causing a change in the local magnetic field distribution. This change in magnetic field can be read non-contactly by an external detection device. Thus, passive wireless monitoring without the need for an internal power supply or electrode connection is achieved, avoiding the stability risks and infection hazards of electrical sensing systems in the in vivo environment.

[0016] (2) After the hydrogel is laid, it undergoes freeze-thaw treatment, heat treatment, and hydration treatment in sequence. The freeze-thaw treatment causes physical cross-linking and interpenetration of polymer chains at the interface between the supporting matrix and the top functional layer, forming an integrated structure. This effectively avoids common problems in layered splicing structures, such as interface peeling, functional layer detachment, or sensor signal instability. The subsequent heat treatment further enhances the overall mechanical strength and fatigue resistance of the hydrogel, enabling it to withstand long-term cyclic compression of the joint without irreversible damage. The final hydration treatment restores the artificial cartilage to a stable water-containing state, ensuring its flexibility and cushioning properties are similar to natural cartilage. The three post-treatment methods work synergistically to endow the artificial cartilage with structural stability and sensor reliability under long-term service conditions.

[0017] (3) In the artificial cartilage prepared by the present invention, the hydrogel support matrix occupies the main volume and has high water content, good flexibility and biocompatibility. It can provide effective buffering and load-bearing during joint movement, disperse local load concentration, and reduce the risk of damage to the implanted structure and surrounding tissues. At the same time, since the magnetic response functional layer is only located on the top surface, the mechanical properties of the support matrix are not affected by magnetic particle doping, thus achieving state monitoring capability while maintaining excellent support function.

[0018] (4) The artificial cartilage prepared by this invention has both tissue support and passive wireless monitoring functions. After implantation, it can not only replace or assist natural cartilage in playing a mechanical buffering role, but also reflect its own stress state and deformation behavior in real time. By reading the magnetic response signal non-contactly through an external detection device, the working state of the artificial cartilage can be quantitatively evaluated, providing objective data for judging the postoperative rehabilitation process, early warning of abnormal load, and formulation of personalized rehabilitation plans, making up for the shortcomings of traditional implants that cannot know the working state in the body.

[0019] (5) The preparation process used in this invention has good versatility and scalability, and is applicable to a variety of hydrogel material systems and different types of magnetic response materials. It can perform structural design and functional regulation according to different implantation sites and mechanical requirements, thereby meeting the application needs of different tissue repair and health monitoring scenarios. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0021] Figure 1 This is a schematic diagram illustrating the preparation process and working principle of the magnetically responsive sensing artificial cartilage prepared in Example 1. Figure 2 This is a schematic diagram illustrating the working principle of the magnetically responsive sensing artificial cartilage prepared in Example 1. Figure 3 A photograph of the magnetically responsive sensing artificial cartilage prepared in Example 1; Figure 4 This is a comparison of the electrical signals of magnetically responsive sensing artificial cartilage under different magnetic particle contents in Examples 1-4. Figure 5 The electrical signal response diagrams of the magnetically responsive sensing artificial cartilage prepared in Example 5 under different pressure conditions (20 N~1000 N) are shown. Figure 6 This is a test image of the cyclic compression stability of the magnetically responsive sensing artificial cartilage prepared in Example 5. Figure 7This is a test image of the long-circulation sensing performance of the magnetically responsive sensing artificial cartilage prepared in Example 5. Figure 8 The image shows the electrical signal response of the magnetically responsive sensing artificial cartilage prepared in Example 5 in PBS solution, deionized water (DI), simulated body fluid (SBF), and saline solution. Figure 9 This is a photograph of the external wireless monitoring device after the magnetic response sensing artificial cartilage prepared in Example 5 was implanted into the prosthetic knee joint.

[0022] Figure 10 This is a comparison chart showing the cyclic compression stability and magnetic response sensing performance of the magnetically responsive artificial cartilage prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0023] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0024] This invention provides a method for preparing magnetically responsive sensing artificial cartilage, comprising the following steps: S1. Mix and dissolve the hydrogel material with deionized water to prepare a uniform hydrogel precursor solution; S2. Pre-crosslinking treatment is performed on a portion of the hydrogel precursor solution to prepare a hydrogel support matrix; S3. Mix the magnetic powder into the remaining hydrogel precursor solution to prepare a magnetically responsive composite solution; S4. The magnetically responsive composite solution is uniformly spread on the upper surface of the hydrogel support matrix, and then subjected to freeze-thaw treatment, heat treatment and hydration treatment in sequence, followed by magnetization treatment to obtain the final product.

[0025] In some embodiments, in step S1, the hydrogel material is selected from one or more of polyvinyl alcohol, polyacrylamide, polyacrylic acid, alginate, chitosan, and gelatin; the mass ratio of the hydrogel material to deionized water is 0.05~0.2:1. Preferably, the hydrogel material is polyvinyl alcohol.

[0026] In some embodiments, in step S2, the pre-crosslinking treatment is one or more of low-temperature freeze-thaw treatment, chemical crosslinking treatment, and photocrosslinking treatment; the pre-crosslinking treatment is preferably low-temperature freeze-thaw treatment, and the low-temperature freeze-thaw treatment conditions are: freezing temperature -25~-20 ℃, freezing time 6 h.

[0027] Specifically, the present invention uses a pre-crosslinking treatment to make the obtained hydrogel support matrix in an incompletely crosslinked state, and its upper surface area still retains a certain amount of polymer chain segment activity, which is beneficial to the formation of a stable bond between the subsequent top magnetic response functional layer and the hydrogel support matrix.

[0028] In some embodiments, the present invention does not specifically limit the specific steps of chemical crosslinking and photocrosslinking treatments, as long as the resulting hydrogel support matrix is ​​in a partially crosslinked state. It should be noted that when the hydrogel material is polyvinyl alcohol, the pre-crosslinking treatment is preferably a low-temperature freeze-thaw process; when the hydrogel material is a chemically crosslinkable or photocrosslinkable material such as polyacrylamide, polyacrylic acid, alginate, chitosan, or gelatin, the pre-crosslinking treatment can employ a chemical crosslinking or photocrosslinking treatment matched to the corresponding material system.

[0029] Specifically, the chemical crosslinking treatment includes: adding a crosslinking agent or initiator to the hydrogel precursor solution, mixing thoroughly, injecting into a mold, and allowing it to react statically at room temperature or under heating conditions to form a pre-crosslinked hydrogel support matrix. The photocrosslinking treatment includes: adding a photoinitiator to the hydrogel precursor solution, mixing thoroughly, injecting into a mold, and carrying out a crosslinking reaction under ultraviolet light irradiation to form a pre-crosslinked hydrogel support matrix.

[0030] In some embodiments, in step S3, the magnetic powder is selected from one or more of magnetite particles and neodymium iron boron particles; the mass fraction of the magnetic powder in the magnetically responsive composite solution is 30 wt% to 60 wt%, based on the total mass of the magnetic powder and the remaining hydrogel precursor solution used to prepare the magnetically responsive composite solution. Magnetite has excellent biocompatibility and chemical inertness, making it suitable for long-term implantation; neodymium iron boron has high remanence and can generate stronger magnetic field changes under relatively small compressive deformation, making it suitable for scenarios requiring high detection sensitivity.

[0031] In some embodiments, the volume ratio of a portion of the hydrogel precursor solution to the remaining hydrogel precursor solution is 2:1 to 10:1, preferably 3:1 to 5:1. This ratio ensures that the hydrogel support matrix occupies the main volume of the artificial cartilage, providing sufficient load-bearing and cushioning capacity; while the top magnetically responsive functional layer is a relatively thin surface layer, which can generate a sensitive magnetic response signal to compression deformation without affecting the overall flexibility due to excessive magnetic particles.

[0032] In some embodiments, in step S4, the freeze-thaw treatment conditions are: freezing temperature -20~-5 ℃, freezing time 3~10 h, thawing temperature 20~30 ℃, and freeze-thaw cycle number 3~11 times.

[0033] Specifically, the present invention uses freeze-thaw treatment to form sufficient physical cross-linking and interpenetration of chain segments at the interface between the hydrogel support matrix and the functional layer, thereby preventing the top magnetic response functional layer from peeling or falling off during subsequent pressure or cyclic deformation.

[0034] In some embodiments, the heat treatment conditions are: temperature 35~75 ℃, treatment time 12~24 h.

[0035] In some embodiments, the hydration treatment conditions are: soaking in deionized water for 6 to 24 hours, preferably 12 hours.

[0036] In some embodiments, the magnetic field strength for magnetization is 0.1~3 T, preferably 0.5~2 T.

[0037] Specifically, heat treatment temperatures of 35–75 °C promote increased crystallinity of polyvinyl alcohol, enhancing overall compressive strength and fatigue resistance. Temperatures below 35 °C have little effect, while temperatures above 75 °C may cause polymer degradation. Hydration treatment allows the hydrogel, which lost water after heat treatment, to reabsorb water to an equilibrium state, restoring its flexibility to similar levels to natural cartilage. Magnetization treatment requires a sufficiently strong external magnetic field to saturate the magnetic particles, ensuring the repeatability and stability of the magnetic response signal during use.

[0038] To further improve the buffering performance, stress dispersion ability, and structural stability of the hydrogel support matrix under compression, a space confinement treatment is applied to the outer side of the resulting composite structure. In some embodiments, step S4, after the freeze-thaw treatment and before the heat treatment begins, further includes covering the outer side of the composite structure with a confinement layer.

[0039] The spatial confinement treatment in this step is mainly used to improve the mechanical adaptability of the hydrogel support matrix under pressure. Through the above spatial confinement treatment and heat treatment, different regions of the hydrogel support matrix can form certain differences in mechanical response, thereby helping to improve the buffering capacity and stress dispersion capacity of artificial cartilage under complex compressive loads.

[0040] In some embodiments, the material of the limiting layer is selected from at least one of polyimide, Ecoflex silicone, polyamide, and polyester materials; In some embodiments, the limiting layer is a polyimide film with a thickness of 80-520 μm; In some embodiments, the confinement layer is provided with a gradient thickness distribution along the axial direction of the hydrogel support substrate. Specifically, the hydrogel support substrate is divided into an upper region, a middle region, and a lower region along the axial direction, and the outer walls of the corresponding regions are covered with polyimide films of different thicknesses; wherein, the upper region is covered with a polyimide film with a thickness of 80–120 μm, the middle region is covered with a polyimide film with a thickness of 280–320 μm, and the lower region is covered with a polyimide film with a thickness of 480–520 μm. Preferably, the bottom surface of the hydrogel support substrate is closed by a polyimide film, while the top surface remains open.

[0041] The present invention provides a magnetically responsive artificial cartilage prepared by the above preparation method, comprising a hydrogel support matrix and a magnetically responsive functional layer composited on the upper surface of the hydrogel support matrix.

[0042] Specifically, the magnetic response functional layer of this invention is disposed on the upper layer of the hydrogel support matrix, rather than dispersed throughout the entire hydrogel support matrix. The hydrogel support matrix mainly serves to provide flexible support, buffering, and load-bearing functions, while the top magnetic response functional layer mainly serves to generate magnetic response signals under pressure or deformation. The two are structurally layered and functionally complementary, thereby enabling the artificial cartilage to possess both mechanical support and condition monitoring capabilities.

[0043] The magnetic response functional structure contains distributed magnetic particles. When the artificial cartilage is compressed, bent, or deformed, the relative spatial positions between the magnetic particles change, thereby altering the local magnetic field distribution and generating a corresponding magnetic response signal. This magnetic response signal can be read non-contactly by an external detection device and converted into an electrical signal output, enabling passive wireless monitoring of the artificial cartilage's stress state, deformation behavior, and usage status. To improve the structural stability and mechanical adaptability of the artificial cartilage under complex stress environments, the hydrogel support matrix may optionally have a microstructure or mechanical property distribution that varies along at least one direction. Specifically, the hydrogel support matrix may have a gradually varying pore structure, network density, crystallinity, and compressive modulus distribution along the axial direction to improve the stress dispersion and buffering performance of the artificial cartilage under compressive loads.

[0044] The present invention provides the application of the magnetically responsive artificial cartilage prepared by the above preparation method or the magnetically responsive sensing artificial cartilage prepared by the above preparation method in the preparation of implants for articular cartilage repair and passive wireless monitoring of postoperative status.

[0045] The technical solution of the present invention will be further described below with reference to specific embodiments. The present invention does not impose any special restrictions on the source of reagents used in the following embodiments; commercially available products well known to those skilled in the art can be used.

[0046] Example 1 This embodiment provides a method for preparing a basic magnetically responsive sensing artificial cartilage, which includes the following steps: (1) Weigh polyvinyl alcohol powder and add it to deionized water. Stir and heat at 90 °C until the polyvinyl alcohol is completely dissolved to obtain a polyvinyl alcohol precursor solution with a volume of 30 mL and a mass fraction of 20 wt%.

[0047] (2) Pour the above 20 mL of polyvinyl alcohol precursor solution into a cylindrical mold with a diameter of 3 cm and a height of 4 cm, and place it in a container. Freezing at 20 ℃ causes the polyvinyl alcohol molecular chains to undergo preliminary physical cross-linking, forming a hydrogel support matrix with a certain shape retention capability.

[0048] In this step, the resulting hydrogel support matrix is ​​in an incompletely cross-linked state, and its upper surface area still retains a certain amount of polymer chain segment activity, which is beneficial for the subsequent formation of a stable bond between the top magnetic response functional layer and the hydrogel support matrix.

[0049] (3) Add 50 wt% of the magnetic particles of iron oxide to 6 mL of polyvinyl alcohol precursor solution. Through mechanical stirring and ultrasonic dispersion treatment, the magnetic particles of iron oxide are uniformly dispersed in the precursor solution to form a magnetic response composite solution.

[0050] (4) The magnetic response composite solution obtained in step (3) is uniformly spread on the upper surface of the hydrogel support substrate obtained in step (2) so that a magnetic response functional layer is formed on the top of the hydrogel support substrate.

[0051] (5) Place the resulting composite structure as a whole in Freeze at 20 °C and thaw at room temperature to complete one freeze-thaw cycle; repeat the freeze-thaw process three times to form a stable interface between the top magnetic response functional layer and the hydrogel support matrix.

[0052] Through this process, the polyvinyl alcohol segments in the top magnetic response functional layer undergo physical cross-linking and a certain degree of interpenetration with the polyvinyl alcohol segments on the surface of the hydrogel support matrix, thereby preventing the top magnetic response functional layer from peeling off or falling off during subsequent pressure or cyclic deformation.

[0053] (6) After the freeze-thaw treatment, a polyimide film with a thickness of 100 μm is sequentially placed from top to bottom on the composite structure.

[0054] (7) The composite structure after spatial confinement treatment was subjected to heat treatment at 50 °C for 12 h. After heat treatment, the sample was immersed in deionized water for 12 h to restore it to a stable hydrated state, thus obtaining a composite hydrogel artificial cartilage with stable hydrated state.

[0055] (8) The above-mentioned composite hydrogel artificial cartilage is placed in an external magnetic field environment (magnetic field strength is 1T) for magnetization treatment, so that the ferric oxide magnetic particles in the top magnetic response functional layer form a stable magnetization state, thereby obtaining artificial cartilage with magnetic response sensing function.

[0056] like Figure 1 As shown, the preparation process of the magnetically responsive sensing artificial cartilage in Example 1 mainly includes the following steps: preparation of precursor solution, construction of hydrogel support matrix, construction of top magnetically responsive functional layer, freeze-thaw interface bonding, heat treatment and hydration, and magnetization treatment. The resulting artificial cartilage includes a lower hydrogel support matrix and a top magnetically responsive functional layer disposed on its upper surface.

[0057] like Figure 2 The diagram illustrates the working principle of the magnetically responsive sensing artificial cartilage prepared in Example 1. When the artificial cartilage is compressed, bent, or deformed, the relative positions of the magnetic particles in the top magnetically responsive functional layer change, causing a change in the local magnetic field distribution. This change in magnetic field is read non-contactly by an external magnetic signal detection device, enabling passive wireless monitoring of the stress state and deformation behavior of the artificial cartilage. Compared to traditional electrical sensing systems, this invention requires no electrode connection or built-in power supply, offering advantages such as simple structure, high stability, and suitability for implantable applications.

[0058] like Figure 3 The image shown is a physical diagram of the magnetically responsive sensing artificial cartilage prepared in Example 1. The resulting artificial cartilage has a regular cylindrical structure, with the top magnetically responsive functional layer located on the upper surface of the artificial cartilage, and the lower hydrogel support matrix maintaining a high water content and good flexibility. The bonding between the top magnetically responsive functional layer and the hydrogel support matrix is ​​stable, and no obvious interface delamination or peeling was observed. This indicates that the present invention can achieve a stable integrated construction between the top magnetically responsive functional layer and the hydrogel support matrix, thereby ensuring that the artificial cartilage still has good structural stability and magnetic response monitoring capability under pressure and cyclic deformation conditions.

[0059] Example 2 The difference between this embodiment and Embodiment 1 is that the mass fraction of the magnetite particles is 60 wt%, while the rest of the formulation and preparation method are the same as in Embodiment 1.

[0060] Compared with Example 1, this example increases the content of magnetic particles in the top magnetic response functional layer to enhance the amplitude of magnetic field changes generated by the artificial cartilage during compression or deformation, thereby improving the ability of external detection devices to identify magnetic response signals.

[0061] The artificial cartilage obtained in Example 2 exhibits a more pronounced change in magnetic field due to the higher content of magnetic particles in the top magnetic response functional layer, resulting from the change in the relative position of the magnetic particles. Therefore, this example is suitable for force monitoring scenarios involving artificial cartilage where high sensing sensitivity is required.

[0062] Example 3 The difference between this embodiment and Example 1 is that the mass fraction of the magnetite particles is 40 wt%. The rest of the formulation and preparation method are the same as in Example 1.

[0063] Example 4 The difference between this embodiment and Example 1 is that the mass fraction of the magnetite particles is 30 wt%. The rest of the formulation and preparation method are the same as in Example 1.

[0064] like Figure 4 The figure shows a comparison of the magnetic response electrical signals of artificial cartilage under different magnetic particle contents. Specifically, the artificial cartilage in Example 2 with a magnetite magnetic particle content of 60 wt% in the top magnetic response functional layer exhibits a significantly higher electrical signal intensity under the same compressive load than the artificial cartilage in Example 1 with a content of 50 wt%. This indicates that as the content of magnetic particles in the top magnetic response functional layer increases, the magnetic field change of the artificial cartilage under pressure becomes more significant, thereby improving the recognition ability and detection sensitivity of the external detection device for the magnetic response signal.

[0065] Example 5 This embodiment provides a method for preparing mechanically enhanced magnetically responsive sensing artificial cartilage, which includes the following steps: (1) Weigh polyvinyl alcohol powder and add it to deionized water. Stir and heat at 90 °C until the polyvinyl alcohol is completely dissolved to obtain a polyvinyl alcohol precursor solution with a volume of 30 mL and a mass fraction of 20 wt%.

[0066] (2) Pour the above 20 mL of polyvinyl alcohol precursor solution into a cylindrical mold with a diameter of 3 cm and a height of 4 cm, and place it in a container. Freezing at 20 ℃ causes the polyvinyl alcohol molecular chains to undergo preliminary physical cross-linking, forming a hydrogel support matrix with a certain shape retention capability.

[0067] (3) Add 60 wt% of magnetite magnetic particles to 6 mL of polyvinyl alcohol precursor solution, and disperse the magnetic particles evenly in the precursor solution by mechanical stirring and ultrasonic dispersion to form a magnetic response composite solution.

[0068] (4) The magnetic response composite solution obtained in step (3) is uniformly spread on the upper surface of the hydrogel support matrix obtained in step (2) to form a top magnetic response functional layer.

[0069] (5) Place the resulting composite structure as a whole in Freeze at 20 °C and thaw at room temperature to complete one freeze-thaw cycle; repeat the freeze-thaw process three times to form a stable bond between the top magnetic response functional layer and the hydrogel support matrix.

[0070] (6) After freeze-thaw treatment, polyimide films with thicknesses of 100 μm, 300 μm and 500 μm are sequentially placed from top to bottom on the composite structure to control the moisture migration conditions and local deformation constraints in different regions of the composite structure during subsequent heat treatment.

[0071] (7) The composite structure after space confinement treatment was subjected to heat treatment at 70 °C for 24 h. After heat treatment, the sample was immersed in deionized water for 12 h to restore it to a stable water content state.

[0072] (8) The above composite structure is placed in an external magnetic field environment (magnetic field strength is 1T) for magnetization treatment, so that the magnetic particles in the top magnetic response functional layer form a stable magnetization state, thereby obtaining mechanically enhanced magnetic response sensing artificial cartilage.

[0073] The artificial cartilage obtained in Example 5 is suitable for cartilage replacement or repair scenarios with high requirements for load-bearing capacity and buffering performance. Its lower gradient hydrogel support matrix primarily bears compressive loads and achieves stress dispersion and buffering through variations in the mechanical properties of different regions, thereby reducing damage to the artificial cartilage structure caused by concentrated local loads. The top magnetic response functional layer generates corresponding magnetic response signals during compression, achieving synergy between mechanical support and condition monitoring functions.

[0074] like Figure 5The figure shows the electrical signal response results of the magnetically responsive sensing artificial cartilage prepared in Example 5 under different pressure conditions. Under different compressive loads ranging from 20 N to 1000 N, the artificial cartilage was able to generate stable and distinguishable magnetically responsive electrical signal outputs. As the external pressure gradually increases, the relative position changes between the magnetic particles in the top magnetically responsive functional layer become more obvious, resulting in more significant magnetic field changes and demonstrating good pressure response capability. At the same time, the gradient hydrogel support matrix can achieve stress dispersion and buffering during compression, thereby improving the structural stability and magnetic response stability of the artificial cartilage under different pressure conditions.

[0075] like Figure 6 The figure shows the mechanical stability test results of the magnetically responsive sensing artificial cartilage prepared in Example 5 under cyclic compression conditions. During multiple cyclic compression processes, the artificial cartilage maintained a relatively stable structural state and mechanical response, without significant structural collapse or irreversible damage. This is because the gradient hydrogel support matrix can achieve stepwise buffering and stress dissipation during compression, thereby improving the overall compressive stability and fatigue resistance of the artificial cartilage.

[0076] like Figure 7 As shown, during the long-term cyclic sensing performance test, the artificial cartilage prepared in Example 5 maintained a stable magnetic response signal output without significant signal attenuation or fluctuation. This indicates that the top magnetic response functional layer and the gradient hydrogel support matrix have good interfacial and structural stability, thus laying the foundation for long-term in vivo state monitoring and long-term signal sensing applications of the artificial cartilage.

[0077] like Figure 8 The image shows the magnetic response electrical signal test results of the artificial cartilage prepared in Example 5 in PBS solution, deionized water (DI), simulated body fluid (SBF), and saline solution environments. The results show that the artificial cartilage can maintain stable electrical signal output in different liquid environments, indicating that the top magnetic response functional layer constructed in this invention has good environmental adaptability and liquid stability, and can meet the application requirements of long-term sensing and monitoring in implantation environments.

[0078] like Figure 9The image shown is an in vitro wireless monitoring diagram of the magnetic response sensing artificial cartilage prepared in Example 5 after implantation into the prosthetic knee joint. The artificial cartilage is placed in the joint contact area of ​​the prosthesis. During joint movement and compression, the magnetic particles in the top magnetic response functional layer undergo relative position changes, thereby generating corresponding magnetic field changes. An external detection coil can non-contactly read this magnetic response signal, enabling real-time wireless monitoring of the artificial cartilage's stress and operational status. The results show that the artificial cartilage prepared in this invention not only possesses excellent load-bearing and buffering performance but also meets the requirements for implantable status monitoring, demonstrating promising application prospects in intelligent prostheses and cartilage repair.

[0079] Example 6 This embodiment provides a method for preparing interface-stabilized magnetically responsive sensing artificial cartilage, which includes the following steps: (1) Weigh polyvinyl alcohol powder and add it to deionized water. Stir and heat at 90 °C until the polyvinyl alcohol is completely dissolved to obtain a polyvinyl alcohol precursor solution with a volume of 30 mL and a mass fraction of 20 wt%.

[0080] (2) Pour the above 20 mL of polyvinyl alcohol precursor solution into a cylindrical mold with a diameter of 3 cm and a height of 4 cm, and place it in a container. Freezing at 20 ℃ causes the polyvinyl alcohol molecular chains to undergo preliminary physical cross-linking, forming a hydrogel support matrix with a certain shape retention capability.

[0081] (3) Add 60 wt% of the magnetite particles to 6 mL of polyvinyl alcohol precursor solution. Through mechanical stirring and ultrasonic dispersion treatment, the magnetite particles are uniformly dispersed in the precursor solution to form a magnetic response composite solution.

[0082] (4) The magnetic response composite solution obtained in step (3) is uniformly spread on the upper surface of the hydrogel support matrix obtained in step (2) to form a top magnetic response functional layer.

[0083] (5) Place the resulting composite structure as a whole in Freeze at 20 °C and thaw at room temperature to complete one freeze-thaw cycle; repeat the freeze-thaw process 5 times to form a more stable physical cross-linking and interpenetrating chain structure between the top magnetic response functional layer and the hydrogel support matrix.

[0084] (6) Polyimide films with thicknesses of 100 μm, 300 μm and 500 μm are sequentially placed on the composite structure from top to bottom to regulate the moisture migration conditions and local structural stability of different regions of the composite structure during subsequent heat treatment.

[0085] (7) The composite structure after space confinement treatment was subjected to heat treatment at 70 °C for 24 h. After heat treatment, the sample was immersed in deionized water for 12 h to restore it to a stable water content state.

[0086] (8) The above composite structure is placed in an external magnetic field environment (magnetic field strength is 1T) for magnetization treatment, so that the ferric oxide magnetic particles in the top magnetic response functional layer form a stable magnetization state, thereby obtaining an interface-stable magnetic response sensing artificial cartilage.

[0087] Compared with Examples 1 and 2, Example 6 increases the number of freeze-thaw cycles to enhance the interfacial bonding strength between the top magnetic response functional layer and the hydrogel support matrix, reducing the risk of functional layer peeling, detachment, or signal fluctuation during long-term compression, bending, or cyclic deformation.

[0088] The artificial cartilage obtained in Example 6 maintains good bonding stability between the top magnetic response functional layer and the hydrogel support matrix during repeated compression or long-term use, which is beneficial to improving the repeatability and stability of the magnetic response signal. It is suitable for implantable artificial cartilage application scenarios with high requirements for monitoring stability.

[0089] Example 7 This embodiment provides a method for preparing rare-earth magnetically responsive magnetically responsive sensing artificial cartilage, which includes the following steps: (1) Weigh polyvinyl alcohol powder and add it to deionized water. Stir and heat at 90 °C until the polyvinyl alcohol is completely dissolved to obtain a polyvinyl alcohol precursor solution with a volume of 30 mL and a mass fraction of 20 wt%.

[0090] (2) Pour the above 20 mL of polyvinyl alcohol precursor solution into a cylindrical mold with a diameter of 3 cm and a height of 4 cm, and place it in a container. Freezing at 20 ℃ causes the polyvinyl alcohol molecular chains to undergo preliminary physical cross-linking, forming a hydrogel support matrix with a certain shape retention capability.

[0091] (3) Add NdFeB magnetic particles at a mass fraction of 50 wt% to 6 mL of polyvinyl alcohol precursor solution, and disperse them uniformly in the precursor solution by mechanical stirring and ultrasonic dispersion to form a magnetic response composite solution.

[0092] (4) The magnetic response composite solution obtained in step (3) is evenly spread on the upper surface of the hydrogel support matrix obtained in step (2) to form a magnetic response functional layer on the top of the artificial cartilage.

[0093] (5) Place the resulting composite structure as a whole in Freeze at 20 °C and thaw at room temperature to complete one freeze-thaw cycle; repeat the freeze-thaw process three times to form a stable interface between the top magnetic response functional layer and the hydrogel support matrix.

[0094] (6) After the freeze-thaw treatment, polyimide films with thicknesses of 100 μm, 300 μm and 500 μm are sequentially placed from top to bottom on the composite structure to form different regions of moisture migration and local constraint conditions during subsequent heat treatment.

[0095] (7) The composite structure after spatial confinement treatment was subjected to heat treatment at 70 °C for 24 h. After heat treatment, the sample was immersed in deionized water for 12 h to restore it to a stable hydrated state, thus obtaining a composite hydrogel artificial cartilage with stable hydrated state.

[0096] (8) The above-mentioned composite hydrogel artificial cartilage is placed in an external magnetic field environment (magnetic field strength is 1T) for magnetization treatment, so that the neodymium iron boron magnetic particles in the top magnetic response functional layer form a stable magnetization state, thereby obtaining artificial cartilage with magnetic response sensing function.

[0097] Because neodymium iron boron magnetic particles possess high remanence and magnetic response capabilities, the artificial cartilage obtained in Example 7 can generate a significant magnetic response signal even under relatively small compressive deformation conditions, which is beneficial for improving the detection sensitivity of the artificial cartilage under low pressure conditions. Simultaneously, the stable bonding between the top magnetic response functional layer and the gradient hydrogel support matrix enhances the structural and magnetic response stability of the artificial cartilage during long-term cyclic compression. The artificial cartilage obtained in this example is suitable for implantable cartilage monitoring scenarios requiring high magnetic response sensitivity and can be used in fields such as intelligent prostheses, cartilage repair, and postoperative rehabilitation monitoring.

[0098] The above embodiments correspond to different technical focuses: Embodiment 1 is a basic magnetic response sensing artificial cartilage; Embodiment 2 is a high-sensitivity magnetic response sensing artificial cartilage; Embodiments 3 and 4 are low-sensitivity magnetic response sensing artificial cartilage; Embodiment 5 is a mechanically enhanced magnetic response sensing artificial cartilage; Embodiment 6 is an interface-stabilized magnetic response sensing artificial cartilage; and Embodiment 7 is a rare-earth magnetic response sensing artificial cartilage, which uses neodymium iron boron magnetic particles to construct the top magnetic response functional layer to improve the magnetic response sensitivity and wireless detection capability of the artificial cartilage under low-pressure conditions.

[0099] In the above embodiments, the hydrogel support matrix mainly provides flexible support, buffering, and load-bearing functions; the top magnetic response functional layer is mainly used to generate magnetic response signals when the artificial cartilage is compressed, bent, or deformed. By using an external detection device to read these magnetic response signals non-contactly, passive wireless monitoring of the stress state and deformation behavior of the artificial cartilage can be achieved.

[0100] The magnetic response sensing artificial cartilage provided by this invention has both tissue support and status monitoring functions, which can provide a basis for status assessment, rehabilitation training monitoring and personalized rehabilitation program development after cartilage repair or replacement.

[0101] Comparative Example 1 The specific steps are as follows: (1) Weigh polyvinyl alcohol powder and add it to deionized water. Stir and heat at 90°C until the polyvinyl alcohol is completely dissolved to obtain a polyvinyl alcohol precursor solution with a volume of 30 mL and a mass fraction of 20 wt%.

[0102] (2) Add 50 wt% of magnetite magnetic particles directly to the above polyvinyl alcohol precursor solution. Through mechanical stirring and ultrasonic dispersion treatment, the magnetite magnetic particles are uniformly dispersed in the entire precursor solution to form a magnetic response composite solution.

[0103] (3) Pour the above magnetic response composite solution directly into a cylindrical mold with a diameter of 3 cm and a height of 4 cm.

[0104] (4) Place the mold in Freeze at 20°C and thaw at room temperature to complete one freeze-thaw cycle; repeat the freeze-thaw process three times.

[0105] (5) The freeze-thawed sample was subjected to heat treatment at 50°C for 12 h. After the heat treatment, the sample was immersed in deionized water for 12 h to restore it to a stable water content state.

[0106] (6) The above hydrogel is placed in an external magnetic field environment for magnetization treatment to obtain a magnetically responsive hydrogel material with uniformly dispersed magnetic particles.

[0107] The sample of Comparative Example 1 and the sample of Example 1 of the present invention were subjected to cyclic compression stability test and magnetic response sensing test under the same conditions. The results are as follows: Figure 10 As shown. By Figure 10As can be seen, compared with Comparative Example 1, Example 1 exhibits a higher stress retention rate and lower residual deformation after cyclic compression, while generating a more obvious and stable magnetic response signal under the same compression conditions. The results demonstrate that the present invention, by concentrating magnetic particles on the top magnetic response functional layer and having the hydrogel support matrix primarily bear the load and buffer functions, can balance the mechanical stability and magnetic response sensing performance of the artificial cartilage.

[0108] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing magnetically responsive artificial cartilage for passive wireless monitoring, characterized in that, Includes the following steps: S1. Mix and dissolve the hydrogel material with deionized water to prepare a uniform hydrogel precursor solution; S2. Pre-crosslinking treatment is performed on a portion of the hydrogel precursor solution to prepare a hydrogel support matrix; S3. Mix the magnetic powder into the hydrogel precursor solution to prepare a magnetically responsive composite solution; S4. The magnetically responsive composite solution is uniformly spread on the upper surface of the hydrogel support matrix, and then subjected to freeze-thaw treatment, heat treatment and hydration treatment in sequence, followed by magnetization treatment to obtain the final product.

2. The preparation method according to claim 1, characterized in that, In step S1, the hydrogel material is selected from one or more of polyvinyl alcohol, polyacrylamide, polyacrylic acid, alginate, chitosan, and gelatin; the mass ratio of the hydrogel material to deionized water is 0.05~0.2:

1. Preferably, the hydrogel material is polyvinyl alcohol.

3. The preparation method according to claim 1, characterized in that, In step S2, the pre-crosslinking treatment is one or more of low-temperature freeze-thaw treatment, chemical crosslinking treatment, and photocrosslinking treatment; the pre-crosslinking treatment is preferably low-temperature freeze-thaw treatment, and the low-temperature freeze-thaw treatment conditions are: freezing temperature -25~-20 ℃, freezing time 6 h.

4. The preparation method according to claim 1, characterized in that, In step S3, the magnetic powder is selected from one or more of iron oxide particles and neodymium iron boron particles; the mass fraction of the magnetic powder in the magnetic response composite solution is 30wt%~60wt%.

5. The preparation method according to claim 1, characterized in that, The volume ratio of a portion of the hydrogel precursor solution to the remaining hydrogel precursor solution is 2:1 to 10:1, preferably 3:1 to 5:

1.

6. The preparation method according to claim 1, characterized in that, In step S4, the freeze-thaw treatment conditions are: freezing temperature -20~-5 ℃, freezing time 3~10 h, thawing temperature 20~30 ℃, and freeze-thaw cycle number 3~11 times; The heat treatment conditions are: temperature 35~75 ℃, treatment time 12~24 h; The hydration treatment conditions are: soaking in deionized water for 6 to 24 hours, preferably 12 hours; The magnetic field strength for magnetization is 0.1~3 T, preferably 0.5~2 T.

7. The preparation method according to claim 1, characterized in that, In step S4, after the freeze-thaw treatment is completed and before the heat treatment begins, a confinement layer is applied to the outer side of the composite structure.

8. The preparation method according to claim 7, characterized in that, The material of the limiting layer is selected from at least one of polyimide, Ecoflex silicone, polyamide, and polyester materials; Preferably, the limiting layer is a polyimide film with a thickness of 80-520 μm. More preferably, the limiting layer is a polyimide film with different thickness gradients, the film thicknesses being 80-120 μm, 280-320 μm, and 480-520 μm respectively.

9. A magnetically responsive artificial cartilage prepared by the method according to any one of claims 1-8, characterized in that, It includes a hydrogel support matrix and a magnetically responsive functional layer composited on the upper surface of the hydrogel support matrix.

10. The application of the magnetically responsive artificial cartilage prepared by the preparation method according to any one of claims 1-8 or the magnetically responsive sensing artificial cartilage according to claim 9 in the preparation of implants for articular cartilage repair and passive wireless monitoring of postoperative status.

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