A method of stabilizing the remanence of an injectable magnetic fluid

Abstract

The present application relates to the field of magnetic fluid, disclose a kind of method for stabilizing injectable magnetic fluid remanence, the magnetic fluid is injectable magnetic hydrogel with three-dimensional network structure, the method comprises the following steps: after the internal magnetic moment uniformity of the magnetic hydrogel is broken, weak magnetic field is applied to the magnetic hydrogel or the object containing the magnetic hydrogel, to carry out in-situ reorientation of the magnetic hydrogel by weak magnetic field, so that the magnetic moment of the internal magnetic particle of the magnetic hydrogel is uniform, presents fluid magnetism with remanence stability.The present application realizes the remanence stability of the magnetic hydrogel is maintained within five days by using 150mT, the magnetization time is not more than 1min, the harm to organism is low, the degree of magnetic moment reduction is small, and it is easy to popularize and use.

Description

Technical Field

[0001] This invention relates to the field of magnetic fluids, and more specifically to a method for stabilizing the remanence of injectable magnetic fluids. Background Technology

[0002] Magnetic fluids are typically composed of nano-magnetic particles and a base fluid. When magnetic materials exhibit a fluid state (such as magnetorheological fluids and injectable magnetic hydrogels), the magnetic particles in the fluid cannot maintain magnetization stability due to the Brownian motion and gravitational sedimentation effects of the magnetic particles. That is, the magnetic particles in the fluid cannot form a uniform magnetism; they rotate randomly, their magnetism weakens or even disappears, and the net magnetic moment becomes zero. This prevents the exhibiting of typical hysteresis phenomena, thus limiting the biological applications of liquid electronics in magnetic materials.

[0003] Especially in applications involving the labeling and tracking of lesions / lymph nodes, traditional magnetohydrodynamic materials, being paramagnetic / superparamagnetic, are easily demagnetized. They require an external magnetic field to maintain a stable outward macroscopic net magnetic moment and induce magnetic signals. Particularly in biological applications, when magnetic particles are injected into the body, the injection process causes random orientation and domain dispersion of the magnetic particles within the fluid, leading to the loss of macroscopic magnetism. An external magnetic field is still needed to intervene with the magnetic particles. Furthermore, after the external magnetic field is removed, the magnetism of the magnetic particles weakens or even disappears again, thus limiting the biological applications of liquid electronics with magnetic materials. Summary of the Invention

[0004] The purpose of this invention is to provide a method for stabilizing the remanence of injectable magnetic fluids, so as to solve the technical problem that it is difficult to maintain the remanence of magnetic fluids after magnetization in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention specifically provides the following technical solution:

[0006] This invention provides a method for stabilizing the remanence of an injectable magnetic fluid, wherein the magnetic fluid is an injectable magnetic hydrogel with a three-dimensional network structure, and the method includes the following steps:

[0007] After the uniformity of magnetic moments inside the magnetic hydrogel is disrupted, a weak magnetic field is applied to the magnetic hydrogel or an object containing the magnetic hydrogel to perform in-situ reorientation of the magnetic hydrogel, thereby unifying the magnetic moments of the magnetic particles inside the magnetic hydrogel and exhibiting fluid magnetism with stable remanence.

[0008] As a preferred embodiment of the present invention, in the in-situ reorientation of the weak magnetic field, the strength of the weak magnetic field is 100-500 mT and the magnetization time is 0.1 min to 1 min.

[0009] As a preferred embodiment of the present invention, after in-situ reorientation in the weak magnetic field, the magnetic hydrogel maintains stable magnetism for at least 5 days.

[0010] As a preferred embodiment of the present invention, the magnetic hydrogel is prepared by crosslinking NdFeB@SiO2 magnetic nanoparticles with sodium alginate precursor solution and polyvinyl alcohol precursor.

[0011] As a preferred embodiment of the present invention, the preparation method of the magnetic hydrogel includes the following steps:

[0012] NdFeB@SiO2 magnetic nanoparticles were mixed with sodium alginate precursor solution and polyvinyl alcohol precursor solution, and stirred at high speed to obtain mixed reactant B.

[0013] The mixed reactant B was subjected to vacuum degassing to improve the cross-linking tightness of the three-dimensional network in the hydrogel, thus obtaining the hydrogel precursor;

[0014] The hydrogel precursor is magnetized under a magnetization field of 2-3T, and then subjected to repeated freeze-thaw treatment to promote the tight cross-linking of sodium alginate chains and polyvinyl alcohol chains, forming polymer aggregation regions and promoting the formation of hydrogen bonds and crystals, providing a three-dimensional network for the directional linking of magnetic particles, so as to obtain the magnetic colloidal fluid.

[0015] As a preferred embodiment of the present invention, the repeated freeze-thaw treatment includes the following steps:

[0016] The magnetized hydrogel precursor was frozen at -20°C for 12-48 hours and thawed at 25°C for 2-4 hours, and the cycle was repeated 3-5 times.

[0017] In a preferred embodiment of the present invention, the high-speed stirring time is 15-30 minutes;

[0018] The vacuum degassing time is 15-30 minutes.

[0019] As a preferred embodiment of the present invention, the preparation steps of the NdFeB@SiO2 magnetic nanoparticles are as follows:

[0020] The NdFeB particles were mixed with an aqueous ethanol solution and stirred for 15-30 minutes to obtain an NdFeB dispersion.

[0021] Ammonia and tetraethyl orthosilicate were added dropwise to the NdFeB dispersion to prepare mixed reactant A;

[0022] The mixed reactant A was repeatedly washed with ethanol and water to obtain a precipitate;

[0023] The precipitate was dried to obtain the NdFeB@SiO2 magnetic nanoparticles.

[0024] As a preferred embodiment of the present invention, the amount of ethanol aqueous solution is 100-200 ml per 1 g NdFeB;

[0025] In the NdFeB dispersion, for every 1g of NdFeB, the amount of ammonia is 4-8ml and the amount of tetraethyl orthosilicate is 2-4ml.

[0026] The drying temperature is 50-60℃;

[0027] The concentration of the sodium alginate precursor solution is 0.5-2%;

[0028] The concentration of the polyvinyl alcohol precursor solution is 5-10%.

[0029] As a preferred embodiment of the present invention, the magnetic hydrogel is used for biological tissue labeling and in vivo tracing.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] This invention reorients a magnetic hydrogel with a densely cross-linked three-dimensional network in situ, stabilizes the disrupted magnetic orientation links by a weak magnetic field, and restores its outward macroscopic net magnetic moment. This achieves stable residual magnetization of the magnetic fluid after the external magnetic field is removed, enabling it to be used as a tracer and applied in biological tissue labeling, biosignal measurement, and other applications.

[0032] The in-situ reorientation magnetic field disclosed in this invention is weak. It can achieve stable magnetic hysteresis of the magnetic hydrogel within five days at 150 mT, and the magnetization time is no more than 1 min. When the magnetic hydrogel with a three-dimensional network structure is injected into a biological body, the remanence of the magnetic hydrogel can be restored by in-situ reorientation with a weak magnetic field. The magnetic field strength requirement is low, the damage to the object is low, the safety is good, and it has the characteristic of stable remanence, which makes it easy to promote its use as a tracer in biological bodies. Attached Figure Description

[0033] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0034] Figure 1 This invention provides a method for stabilizing the remanence of injectable magnetic fluids;

[0035] Figure 2 This invention provides a process for preparing magnetic hydrogels;

[0036] Figure 3 This invention provides a preparation process for NdFeB@SiO2 magnetic nanoparticles;

[0037] Figure 4 Electron micrograph of the remanent magnetized stable magnetic hydrogel shown in Example 1 is provided for the present invention;

[0038] Figure 5 Statistical graphs of magnetic moment changes of magnetic hydrogels after in-situ reorientation in Examples 1 to 6 are provided for the present invention. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] like Figure 1 As shown, this invention provides a method for stabilizing the remanence of an injectable magnetic fluid, wherein the magnetic fluid is an injectable magnetic hydrogel with a three-dimensional network structure, and the method includes the following steps:

[0041] After the uniformity of magnetic moments inside the magnetic hydrogel is disrupted, a weak magnetic field is applied to the magnetic hydrogel or an object containing the magnetic hydrogel to perform in-situ reorientation of the magnetic hydrogel, thereby unifying the magnetic moments of the magnetic particles inside the magnetic hydrogel and exhibiting fluid magnetism with stable remanence.

[0042] Generally, when a magnetic fluid is injected into an object, the particles move randomly due to the pushing action, causing the magnetic domains to become scattered and the magnetic moment to weaken. Eventually, the fluid loses its magnetism. If the fluid is to regain its magnetism, a strong magnetic field needs to be applied to the object. However, a strong magnetic field requires a large coil device, which is impractical. Furthermore, a strong magnetic field poses a risk of accidental injury to personnel when used in a medical environment. Therefore, it is difficult for magnetic fluids to retain residual magnetism in existing applications.

[0043] In order to achieve the goal of maintaining remanent magnetism within an object after injecting a magnetic fluid (macroscopic magnetic moment disappears), this invention proposes a magnetic fluid and its application method. In particular, after being injected into a biological body, the magnetic fluid in the biological body can achieve magnetic moment unification and maintain remanent magnetism under a weak magnetic field environment due to its stable structure. This allows it to perform in vivo tracking, biometry, and other tasks without the intervention of an external magnetic field.

[0044] Specifically, this magnetic fluid is an injectable magnetic hydrogel with a three-dimensional network structure. Optionally, this magnetic hydrogel is prepared by cross-linking NdFeB@SiO2 magnetic nanoparticles with sodium alginate precursor solution and polyvinyl alcohol precursor.

[0045] In addition, similar hydrogels include SmCo, AlNiCo, and FeCrCo magnetic hydrogels. These hydrogels share the common characteristic of having a three-dimensional network structure. The network structure can maintain the stability of magnetic particles and at the same time maintain injectability. Moreover, after preparation, they have remanence, that is, after being magnetized by a strong magnetic field, they can retain their magnetism for a certain period of time without the intervention of an external magnetic field.

[0046] However, when this type of hydrogel is injected into an object, the injection process essentially disrupts all the fluid particles, causing the internal magnetic moment uniformity to be disrupted, resulting in the loss of magnetism and difficulty in maintaining remanent magnetism. To solve this problem, the present invention applies a weak magnetic field to the magnetic hydrogel whose internal magnetic moment uniformity has been disrupted, or applies a weak magnetic field to an object containing the injectable magnetic hydrogel whose internal magnetic moment uniformity has been disrupted. The magnetic moments of the magnetic particles inside the magnetic hydrogel become unified, and the outward macroscopic net magnetic moment is restored, exhibiting remanence within a week.

[0047] The above steps are referred to as weak magnetic field in-situ reorientation. This invention utilizes an external magnetic field to intervene in magnetic fluids, and is used in conjunction with magnetic fluids having a three-dimensional network structure. Its purpose is to restore the magnetism within the magnetic fluid. Weak magnetic field in-situ reorientation is a technique that adds a weak magnetic field. It applies small amounts of energy, but can help the magnetic fluid regain its magnetism. Even after the magnetism disappears, the magnetism within the magnetic fluid remains, and it can persist for a period of time without an external magnetic field.

[0048] Generally, a strong magnetic field is needed to magnetize liquid magnetic particles. However, this invention uses a magnetic fluid with a three-dimensional network structure of magnetic directional linkage. The network structure can maintain the stability of the magnetic particles. Its inherent characteristic is that it has remanence, meaning that after the intervention of an external magnetic field, this magnetic fluid can acquire magnetism. However, when the external magnetism disappears, the magnetism of the magnetic fluid will not disappear immediately and can still be maintained for a period of time.

[0049] In practical applications, taking the magnetic hydrogel prepared by crosslinking NdFeB@SiO2 magnetic nanoparticles with sodium alginate precursor solution and polyvinyl alcohol precursor as an example, the strength of the weak magnetic field is 100-500mT, the magnetization time is 0.1min to 1min, and the retention time of the fluid magnetism is one week (the fluid magnetism will slowly decay over time).

[0050] In this invention, a preferred embodiment of the magnetic fluid is a magnetic hydrogel prepared by crosslinking NdFeB@SiO2 magnetic nanoparticles with sodium alginate precursor solution and polyvinyl alcohol precursor.

[0051] like Figure 2 As shown, the present invention provides a preparation process for a magnetic colloidal fluid, comprising the following steps:

[0052] (1) Mix NdFeB@SiO2 magnetic nanoparticles with sodium alginate precursor solution and polyvinyl alcohol precursor solution, stir at high speed for 15-30 min to obtain mixed reactant B, wherein the concentration of sodium alginate precursor solution is 0.5-2% and the concentration of polyvinyl alcohol precursor solution is 5-10%.

[0053] (2) Vacuum degassing treatment was performed on the mixed reactant B for 15-30 min to obtain the hydrogel precursor. Vacuum degassing treatment can improve the cross-linking tightness of the three-dimensional network in the hydrogel and improve the stability of the directional linking of magnetic particles.

[0054] (3) The hydrogel precursor is magnetized under a magnetization field of 2-3T to achieve magnetization of magnetic particles. Then, the hydrogel precursor is subjected to repeated freeze-thaw treatment to promote the tight cross-linking of sodium alginate chains and polyvinyl alcohol chains, forming a polymer aggregation region and promoting the formation of hydrogen bonds and crystals, providing a three-dimensional network for the directional linking of magnetic particles, so as to obtain magnetic hydrogel.

[0055] Magnetic hydrogels possess high remanence, coercivity, and fluidity.

[0056] This invention involves mixing sodium alginate, polyvinyl alcohol precursor solution, and neodymium iron boron particles at high speed, followed by vacuum degassing. Vacuum degassing enhances the cross-linking tightness of the hydrogel's three-dimensional network and improves the stability of the directional linkages of magnetic particles.

[0057] This invention uses a freeze-thaw cycle physical cross-linking method to prepare permanent magnetic fluids, since physical cross-linking can form a biosafe and stable modulus hydrogel structure.

[0058] This invention constructs a three-dimensional network through a hydrogel crosslinking network, employs micron-sized permanent magnetic particles to mitigate the effects of Brownian motion, and exhibits hysteresis. After the hydrogel precursor is magnetized by a magnetic field, the magnetic particles in the matrix exhibit directional linkages within the three-dimensional network structure while maintaining a fluid state, resulting in a material with high remanence, coercivity, and fluidity.

[0059] Sodium alginate precursor solution and polyvinyl alcohol precursor form a three-dimensional network. Micron-sized magnetic particles are structurally fixed in the three-dimensional network structure of the matrix in the hydrogel cross-linking network. After being structurally fixed, the micron-sized magnetic particles are difficult to disperse, so they can maintain magnetism for a long time and are not easily affected by external forces, exhibiting a certain degree of permanent magnetism.

[0060] It is worth noting that the permanent magnetism described in this invention refers to the ability of magnetic particles to maintain magnetism for a long time after being structurally fixed within the hydrogel matrix. The magnetic fluid prepared by the above method, through structural design, weakens the free movement of magnetic particles within the fluid, thus preserving magnetism while remaining injectable. After in-situ reorientation and magnetization, it can maintain magnetism for a long time without the need for an additional external magnetic field. This significantly enhances its versatility and ease of use when performing lesion tracing and localization, or injecting it into tissue surfaces for physiological function testing.

[0061] In particular, the permanent magnetic fluid disclosed in this invention, based on high remanence, coercivity and fluidity, can be used for continuous tissue labeling and biosignal measurement in living organisms.

[0062] The principle is that the above preparation process ensures that the internal network structure of the magnetic fluid material is not completely destroyed after injection (such as the breakage of polymer monomer links), so a weak magnetic field can be used to promote the unification of the magnetic moments of the internal magnetic particles.

[0063] When a magnetic hydrogel with a conventional structure is injected, its internal structure becomes completely disordered. Therefore, to remagnetize it, a relatively high magnetic field (2T to 3T, far exceeding the safe magnetic field) is required during the initial magnetization process. The difference in magnetic field strength is significant: generating 2T to 3T requires a very large coil with a high current, resulting in a very strong magnetic attraction, which limits its application scenarios and safety.

[0064] The network structure of the magnetic colloid prepared by this invention has certain functions and inherently possesses remanent magnetism. However, after injection, the remanent magnetism is lost because the internal magnetic moment uniformity is disrupted when the colloid is drawn into the syringe and then injected through the needle.

[0065] However, since the hydrogel disclosed in this invention has a stable three-dimensional network structure, even after injection, its magnetic orientation link can be quickly restored and remanent magnetism can be re-exhibited under the support of a weak magnetic field for a short time (not exceeding 1 minute).

[0066] The safety of the magnetic colloidal fluids disclosed in this invention has been verified through biosafety testing, including histological results.

[0067] Furthermore, in order to further ensure the structural stability of the magnetic fluid and facilitate its rapid recovery to a state of uniform magnetic moment after reorientation, the repeated freeze-thaw treatment includes the following steps:

[0068] The magnetized hydrogel precursor was frozen at -20°C for 12-48 hours and thawed at 25°C for 2-4 hours, and the cycle was repeated 3-5 times.

[0069] Repeated freeze-thaw cycles can help make the hydrogel structure more compact and reduce the impact of injection and other actions.

[0070] See Figure 3 The preparation steps of NdFeB@SiO2 magnetic nanoparticles are as follows:

[0071] (1) Mix 1-20 μm NdFeB particles with an ethanol aqueous solution and stir for 15-30 min to obtain NdFeB dispersion. The amount of ethanol aqueous solution is 100-200 ml per 1 g NdFeB.

[0072] (2) Ammonia and tetraethyl orthosilicate are added dropwise to the NdFeB dispersion to prepare mixed reactant A. In the NdFeB dispersion, for every 1g of NdFeB, the amount of ammonia is 4-8ml and the amount of tetraethyl orthosilicate is 2-4ml.

[0073] (3) The mixed reactant A was washed repeatedly with ethanol and water to obtain a precipitate;

[0074] (4) The precipitate is dried at a temperature of 50-60℃ to obtain NdFeB@SiO2 magnetic nanoparticles.

[0075] In this invention, the permanent magnetic particles are 1-20 μm neodymium iron boron particles, which are coated with silicon using the stobber process to improve the dispersibility of the magnetic particles in the hydrogel matrix and the stability in the liquid environment.

[0076] The magnetic particles provided by this invention are oriented and linked in a three-dimensional network structure. The internal structure is tightly cross-linked and has remanent magnetism. After operations such as injection that cause the fluid magnetism to disappear, a stable fluid structure can be restored by applying a weak magnetic field (greater than 150 mT). The remanent magnetism can be stabilized for at least five days, which is convenient for application in the fields of in vivo tracking and biometry, thus broadening its application scope.

[0077] This invention constructs a three-dimensional network structure by crosslinking sodium alginate and polyvinyl alcohol. Sodium alginate, polyvinyl alcohol precursor solution and NdFeB particles are mixed at high speed and then a physical crosslinking method of freeze-thaw cycle is used to prepare permanent magnetic fluid. This promotes the tight crosslinking of sodium alginate chains and polyvinyl alcohol chains, forming polymer aggregation regions, promoting the formation of hydrogen bonds and crystals, and providing a three-dimensional network for the directional linking of magnetic particles, further forming a biosafe and stable modulus hydrogel structure.

[0078] The preferred application of this invention for stabilizing remanent magnetization is as a tracer. Specifically, before orientation, there must be an operation that disrupts the uniformity of the magnetic moments within the magnetic fluid. That is, the freshly prepared magnetic fluid possesses remanent magnetization because its preparation process involves magnetization. However, due to its wide applicability and the fact that it is a fluid intended for injection, its remanent magnetization is lost after injection. This is because the uniformity of the internal magnetic moments is disrupted when the fluid is drawn into a syringe and injected through a needle.

[0079] Therefore, since it needs to be applied into a living organism, magnetic domain straying and magnetic moment weakening will occur when the magnetic fluid is injected. In order to regain the magnetism in the living organism, the present invention performs in-situ reorientation on the living organism during the application process, so that the magnetic fluid regains its remanent magnetism and stability.

[0080] In this invention, the reorientation magnetic field is relatively low, only above 100mT is required. The applied magnetic field is weak, which has little impact on organisms and ensures the safety and wide applicability of the application.

[0081] The following examples are provided for further illustration:

[0082] Example 1:

[0083] 1. Preparation of magnetic hydrogels:

[0084] Take 2g of 5µm NdFeB particles and mix them with 300ml of ethanol aqueous solution. Stir for 15-30min to obtain NdFeB dispersion.

[0085] 12 ml of ammonia and 6 ml of tetraethyl orthosilicate were added dropwise to the NdFeB dispersion to obtain mixed reactant A;

[0086] Mixed reactant A was repeatedly washed with ethanol and water to obtain a precipitate;

[0087] The precipitate was dried at 50-60℃ to obtain NdFeB@SiO2 magnetic nanoparticles;

[0088] NdFeB@SiO2 magnetic nanoparticles were mixed with a 1% sodium alginate precursor solution and a 7% polyvinyl alcohol precursor solution, and stirred at high speed for 15-30 minutes to obtain mixed reactant B.

[0089] The mixed reactant B was subjected to vacuum degassing for 15-30 min to obtain the hydrogel precursor.

[0090] The hydrogel precursor was magnetized under a magnetizing field of 2.5T, and then frozen at -20℃ for 12-48h and thawed at 25℃ for 2-4h. This process was repeated 3-5 times to obtain a magnetic hydrogel.

[0091] The electron micrograph of the magnetic hydrogel in Example 1 is shown below. Figure 4 As shown.

[0092] 2. In vitro experiments

[0093] The magnetic hydrogel obtained in Example 1 was injected into an object, which was a biological simulation sample. A magnetic field of 60 mT was applied to the object for 0.5 min, and the change in magnetic moment of the material was continuously detected by a vibrating sample magnetometer (VSM).

[0094] Example 2:

[0095] The other steps are the same, except that the applied magnetic field is 80mT.

[0096] Example 3:

[0097] The other steps are the same, except that the applied magnetic field is 100mT.

[0098] Example 4:

[0099] The other steps are the same, except that the applied magnetic field is 150mT.

[0100] Example 5:

[0101] The other steps are the same, except that the applied magnetic field is 200mT.

[0102] Example 6:

[0103] The other steps are the same, except that the applied magnetic field is 500mT.

[0104] See results Figure 5 By detecting the change in magnetic moment of the material after in-situ reorientation, it was found that the magnetic moment of the material could be stably detected within 5 days, with a small degree of reduction.

[0105] As illustrated in the embodiments, this invention proposes a technical solution for stabilizing the remanent magnetization of magnetic fluids in living organisms through in-situ reorientation. Specifically, after injecting an injectable magnetic fluid with a three-dimensional network structure into a living organism, remanent magnetization stabilization (approximately one week) is achieved through in-situ reorientation using a weak magnetic field. This method can be applied to various biological systems.

[0106] This invention represents a significant breakthrough in achieving remanent magnetic stability of fluid materials for biological applications. It essentially eliminates the need for a continuous external magnetic field, and its five-day remanent magnetic stability offers immense potential for biological applications such as in vivo tracing and biometry. This breakthrough is challenging in biological applications and has high application value.

[0107] The preparation method of the magnetic colloidal fluid in this embodiment is simple, with the entire preparation temperature not exceeding 60°C and the minimum preparation temperature not lower than -20°C. The reactants are common and readily available, making preparation easy. At the same time, a three-dimensional network is constructed by a hydrogel crosslinking network. After being magnetized by a magnetic field, the magnetic particles exhibit directional linkage in the three-dimensional network structure and still maintain a flow state. The permanent magnetic particles are structurally fixed in the matrix, exhibiting hysteresis, and realizing the long-term existence of magnetism in the magnetic fluid after the external magnetic field disappears.

[0108] The magnetic colloidal fluid in this embodiment has a stable structure that is easy to recover. After the magnetic moment disappears, the stable fluid structure can be restored by applying a weak magnetic field (greater than 150 mT), and it can exhibit remanent magnetic stability for at least a few days. This makes it easy to apply to in vivo tracking and biometry, thus broadening its application scope.

[0109] This invention discloses a method for stabilizing the remanence of injectable magnetic fluids. By reorienting a structurally stable magnetic hydrogel in situ, a weak magnetic field is used to stabilize the magnetic orientation links disrupted by injection and other operations, allowing it to exhibit an outward macroscopic net magnetic moment again. This enables the long-term existence of magnetism within the magnetic fluid after the external magnetic field is removed. The magnetic hydrogel can be used for continuous tissue labeling and biosignal measurement in biological organisms. Furthermore, the in-situ reorientation magnetic field is weak, resulting in low harm to organisms and easy promotion and use.

[0110] The above embodiments are merely exemplary embodiments of this application and are not intended to limit this application. The scope of protection of this application is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to this application within its substance and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of this application.

Claims

1. A method for stabilizing the remanence of an injectable magnetic fluid, wherein the magnetic fluid is an injectable magnetic hydrogel with a three-dimensional network structure, characterized in that... The method includes the following steps: After the uniformity of magnetic moments inside the magnetic hydrogel is disrupted, a weak magnetic field is applied to the magnetic hydrogel or an object containing the magnetic hydrogel to perform in-situ reorientation of the magnetic hydrogel, thereby unifying the magnetic moments of the magnetic particles inside the magnetic hydrogel and exhibiting fluid magnetism with remanent magnetism stability. The preparation method of the magnetic hydrogel includes the following steps: NdFeB@SiO2 magnetic nanoparticles were mixed with sodium alginate precursor solution and polyvinyl alcohol precursor solution, and stirred at high speed to obtain mixed reactant B. The mixed reactant B was subjected to vacuum degassing to improve the cross-linking tightness of the three-dimensional network in the hydrogel, thus obtaining the hydrogel precursor; The hydrogel precursor is magnetized under a magnetization field of 2-3T, and then subjected to repeated freeze-thaw treatment to promote the tight cross-linking of sodium alginate chains and polyvinyl alcohol chains, forming polymer aggregation regions and promoting the formation of hydrogen bonds and crystals. This provides a three-dimensional network for the directional linking of magnetic particles, thereby obtaining a magnetic colloidal fluid.

2. The method for stabilizing the remanence of an injectable magnetic fluid according to claim 1, characterized in that, In the in-situ reorientation of the weak magnetic field, the strength of the weak magnetic field is 100-500 mT and the magnetization time is 0.1 min to 1 min.

3. The method for stabilizing the remanence of an injectable magnetic fluid according to claim 2, characterized in that, After in-situ reorientation in the weak magnetic field, the magnetic hydrogel maintains stable magnetism for at least 5 days.

4. The method for stabilizing the remanence of an injectable magnetic fluid according to claim 1, characterized in that, The magnetic hydrogel was prepared by crosslinking NdFeB@SiO2 magnetic nanoparticles with sodium alginate precursor solution and polyvinyl alcohol precursor.

5. The method for stabilizing the remanence of an injectable magnetic fluid according to claim 1, characterized in that, The repeated freeze-thaw treatment includes the following steps: The magnetized hydrogel precursor was frozen at -20°C for 12-48 hours and thawed at 25°C for 2-4 hours, and the cycle was repeated 3-5 times.

6. The method for stabilizing the remanence of an injectable magnetic fluid according to claim 1, characterized in that, The high-speed stirring time is 15-30 minutes; The vacuum degassing time is 15-30 minutes.

7. The method for stabilizing the remanence of an injectable magnetic fluid according to claim 1, characterized in that, The preparation steps of the NdFeB@SiO2 magnetic nanoparticles are as follows: NdFeB dispersion was prepared by mixing NdFeB particles with an aqueous ethanol solution and stirring for 15-30 min. Ammonia and tetraethyl orthosilicate were added dropwise to the NdFeB dispersion to prepare mixed reactant A; The mixed reactant A was repeatedly washed with ethanol and water to obtain a precipitate; The precipitate was dried to obtain the NdFeB@SiO2 magnetic nanoparticles.

8. The method for stabilizing the remanence of an injectable magnetic fluid according to claim 7, characterized in that, For every 1g of NdFeB, the volume of the ethanol aqueous solution is 100-200ml; In the NdFeB dispersion, for every 1g of NdFeB, the amount of ammonia is 4-8ml and the amount of tetraethyl orthosilicate is 2-4ml. The drying temperature is 50-60℃; The concentration of the sodium alginate precursor solution is 0.5%–2%; The concentration of the polyvinyl alcohol precursor solution is 5-10%.

9. The method for stabilizing the remanence of an injectable magnetic fluid according to any one of claims 1-8, characterized in that, The magnetic hydrogel is used for biological tissue labeling and in vivo tracing.

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