METHOD FOR PREPARING ANISOTROPIC CELLULOSE-BASED HYDROGEL

Abstract

A method for preparing anisotropic cellulose-based hydrogel is provided. The method comprises ammoniating the dialdehyde cellulose obtained by oxidizing cellulose using sodium periodate to obtain ammoniated cellulose derivatives; performing Schiff reaction using the ammoniated cellulose derivatives and dopamine to obtain cellulose-based nanosheets; depositing Fe.sub.3O.sub.4 nanoparticles on a surface of the cellulose-based nanosheets by a deposition method to obtain magnetic cellulose-based nanosheets; and forming the anisotropic cellulose-based hydrogel using the magnetic cellulose-based nanosheets by a polymerization method.

Claims

1. A method for preparing anisotropic cellulose-based hydrogel, comprising: (1) obtaining dialdehyde cellulose by oxidizing cellulose using sodium periodate; (2) ammoniating the dialdehyde cellulose to obtain ammoniated cellulose derivatives; (3) performing Schiff reaction using the ammoniated cellulose derivatives and dopamine to obtain cellulose-based nanosheets; (4) depositing Fe.sub.3O.sub.4 nanoparticles on a surface of the cellulose-based nanosheets by a deposition method to obtain magnetic cellulose-based nanosheets; and (5) forming the anisotropic cellulose-based hydrogel using the magnetic cellulose-based nanosheets by a polymerization method.

2. The method according to claim 1, wherein: the obtaining dialdehyde cellulose by oxidizing cellulose using sodium periodate in the step 1 comprises: mixing the cellulose and the sodium periodate in a water system, stirring while preventing light exposure, then washing in deionized water, and freeze-drying to obtain the dialdehyde cellulose; and heating the dialdehyde cellulose to be dissolved in water to obtain a dialdehyde cellulose aqueous solution.

3. The method according to claim 1, wherein: the ammoniating the dialdehyde cellulose to obtain ammoniated cellulose derivatives in the step 2 comprises: mixing the dialdehyde cellulose obtained in the step 1 with NH.sub.3.Math.H.sub.2O and methanol, reacting in a reaction kettle while heating under catalyst and H.sub.2 pressure to obtain the ammoniated cellulose derivatives, wherein the catalyst is selected from at least one of an iron-based catalyst, a cobalt-based catalyst, a nickel-based catalyst, an Ru/C catalyst, or a Pd/C catalyst.

4. The method according to claim 3, wherein, in the step 2, the H.sub.2 pressure is more than 2.0 MPa, a temperature for the reacting is 100-150 C., and a time for the reacting is more than 2 hours.

5. The method according to claim 1, wherein: the performing Schiff reaction using the ammoniated cellulose derivatives and dopamine to obtain cellulose-based nanosheets in the step 3 comprises: adding the ammoniated cellulose derivatives obtained in the step 2 to a mixture of methanol and water, stirring, then adding the dopamine, and reacting to obtain a reaction solution; and adjusting pH of the reaction solution to be alkaline, further reacting, centrifuging, and drying to obtain the cellulose-based nanosheets.

6. The method according to claim 1, wherein: the depositing Fe.sub.3O.sub.4 nanoparticles on a surface of the cellulose-based nanosheets by a deposition method to obtain magnetic cellulose-based nanosheets in the step 4 comprises: dispersing the cellulose-based nanosheets obtained in the step 3 into a mixture of water and methanol, stirring, then adding a mixture solution containing FeCl.sub.2.Math.4H.sub.2O and FeCl.sub.3.Math.6H.sub.2O , stirring under N.sub.2 atmosphere, then adding NH.sub.3.Math.H.sub.2O, reacting while heating, centrifuging, and washing to obtain the magnetic cellulose-based nanosheets.

7. The method according to claim 1, wherein: the depositing Fe.sub.3O.sub.4 nanoparticles on a surface of the cellulose-based nanosheets by a deposition method to obtain magnetic cellulose-based nanosheets in the step 4 comprises: dispersing 10 mg of the cellulose-based nanosheets obtained in the step 3 into 30 mL of a mixture of water and methanol, stirring for 30 minutes, then adding 20 mL of a mixture solution containing 3 mg of FeCl.sub.2.Math.4H.sub.2O and 8 mg of FeCl.sub.3.Math.6H.sub.2O , stirring for 1 hour under N.sub.2 atmosphere, then adding 0.1 mL of 28% NH.sub.3.Math.H.sub.2O, reacting while heating, and repeatedly centrifuging and washing to obtain the magnetic cellulose-based nanosheets coated with the Fe.sub.3O.sub.4 nanoparticles, wherein a volume/volume (v/v) ratio of the water and the methanol is 2:1.

8. The method according to claim 1, wherein: the forming hydrogel using the magnetic cellulose-based nanosheets by a polymerization method in the step 5 comprises: mixing tetramethylethylenediamine, allyl monomer, initiator, N,N-methylene diacrylamide, and the magnetic cellulose-based nanosheets obtained in the step 4, stirring, pouring into a mold, and performing the polymerization method to obtain the anisotropic cellulose-based hydrogel.

9. The method according to claim 8, wherein: the allyl monomer is acrylamide or acrylic acid; and the initiator is ammonium persulfate or potassium persulfate.

10. The method according to claim 8, wherein: the forming hydrogel using the magnetic cellulose-based nanosheets by a polymerization method in the step 5 further comprises: leaving the mold to stand at 60-70 C. for 1-3 hours.

11. The method according to claim 3, wherein, in the step 2, the H.sub.2 pressure is 2.0-3.0 MPa, a temperature for the reacting is 120 C., and a time for the reacting is 3-5 hours.

12. The method according to claim 5, wherein: a volume/volume (v/v) ratio of the methanol and the water is 1:4, and the adjusting pH of the reaction solution to be alkaline comprises adjusting pH of the reaction solution to be 8.0-9.0.

13. The method according to claim 6, wherein: a weight/volume ratio of cellulose-based nanosheets and the mixture of the water and the methanol is 1 mg: 2-4 mL, a volume/volume (v/v) ratio of the water and the methanol of the mixture is 1-3:1, a weight ratio of the FeCl.sub.2.Math.4H.sub.2O and FeCl.sub.3.Math.6H.sub.2O in the mixture solution is 3:5-12, the NH.sub.3.Math.H.sub.2O is 28% NH.sub.3.Math.H.sub.2O, a temperature for the reacting while heating is 80-100 C., and a time for the reacting while heating is 1-5 hours.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0029] FIG. 1 illustrates X-ray diffraction (XRD) patterns of samples at various stages in Embodiment 1.

[0030] FIGS. 2A and 2B illustrate transmission electron microscope (TEM) images of magnetic cellulose-based nanosheets obtained in Embodiment 1, and FIG. 2B illustrates Fe.sub.3O.sub.4 magnetic nanoparticles loaded on a sheet carrier.

[0031] FIGS. 3A and 3B illustrate good stability of a magnetic PFeDAC nanosheet prepared in Embodiment 1 in water, and FIG. 3C illustrates good magnetism of the magnetic PFeDAC nanosheet in water.

[0032] FIGS. 4A and 4B illustrate a principle for forming various hydrogels.

[0033] FIGS. 5A, 5B, and 5C illustrate adhesion and tensile results of the hydrogel prepared in Embodiment 1, and a content of magnetic PFeDAC hybrid in the various hydrogels is 8 wt %.

[0034] FIG. 6 illustrates a compression experiment of the hydrogel prepared in Embodiment 1, and the content of the magnetic PFeDAC hybrid in the various hydrogels is 8 wt %.

[0035] FIGS. 7A and 7B illustrate good adhesion properties of the hydrogel prepared in Embodiment 1 relative to various substrates as follows: iron sheet (56 kPa), glass (48 kPa), stainless steel (53 kPa), rubber (31 kPa), wood (13 kPa), polytetrafluoroethylene (PTFE) (39 kPa), plastic (17 kPa), paper (11 kPa), and skin (63 kPa). The content of the magnetic PFeDAC hybrid in the various hydrogels is 8 wt %.

[0036] FIG. 8 illustrates tensile stress-strain curves of three hydrogels prepared in Embodiment 1 under forces in different directions, the three hydrogels are as follows: (*) represents a first hydrogel prepared under no external magnetic field, the first hydrogel is isotropic and has a same force in all directions; (//) represents a second hydrogel prepared under an applied force parallel to a magnetic field direction; () represents a third hydrogel prepared under the applied force perpendicular to the magnetic field direction. The content of the magnetic PFeDAC hybrid in the various hydrogels is 8 wt %. FIG. 8 illustrates results of Embodiment 1, the tensile stress-strain test are performed by the conventional method.

[0037] FIG. 9 illustrates compressive stress-strain curves of the three hydrogels prepared in Embodiment 1 under the forces in the different directions, the three hydrogels are as follows: (*) represents the first hydrogel prepared under no external magnetic field, the first hydrogel is isotropic and has a same force in all directions; (//) represents the second hydrogel prepared under an applied force parallel to the magnetic field direction; () represents the third hydrogel prepared under the applied force perpendicular to the magnetic field direction. The content of the magnetic PFeDAC hybrid in the various hydrogels is 8 wt %.

[0038] FIG. 10 illustrates the tensile stress-strain curves of the second hydrogel prepared in Embodiment 1 during a loading-unloading cycle, the applied force is parallel to the magnetic field direction, and the content of the magnetic PFeDAC hybrid in the second hydrogel is 8 wt %.

[0039] FIG. 11 illustrates electric conductivity of the three hydrogels prepared in Embodiment 1 with different concentrations of PFeDAC under the applied force parallel to the magnetic field direction.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] The technical solution of the present disclosure will be further described below in combination with the accompanying embodiments and drawings, and the scope of the present disclosure is not limited thereto.

Embodiment 1

[0041] The embodiment is performed in the following steps. [0042] (1) 100 mL of a wood pulp cellulose suspension with a concentration of 0.55 wt %, 0.6 g of NaIO.sub.4, and 2 mL of isopropyl alcohol are mixed in a conical bottle and reacted at 65 C. while preventing light exposure for 12 hours at a mixing speed of 500 revolutions per minutes (rpm). Dialdehyde cellulose is then obtained by centrifugation, washing in deionized water, and freeze-drying. The dialdehyde cellulose is added into a round-bottled flask containing 100 mL of deionized water and reacted at 100 C. for 2 hours at a stirring speed of 300 rpm. Dialdehyde cellulose aqueous solution is obtained by centrifugation and concentration, and a concentration of the dialdehyde cellulose aqueous solution is tested to be 3.3 g/10 g. [0043] (2) The dialdehyde cellulose aqueous solution (10 g) obtained in the step 1 is centrifuged to remove water and then fully mixed with NH.sub.3.Math.H.sub.2O (6 mL) and methanol (30 mL) to obtain a first mixture. The first mixture is reacted in a 100 mL reactor under a Ru/C catalyst (0.1 g) and 2 MPa of H.sub.2 pressure for 2 hours at 100 C. to obtain ammoniated cellulose derivatives. [0044] (3) The ammoniated cellulose derivatives (5 mL) obtained in the step 2 are added into a mixture of methanol/water with a volume/volume (v/v) ratio of 1:4 and stirred for 1 hour, and dopamine (0.02 g) is then added and reacted for 2 hours at room temperature (e.g., 20-25 C.) to obtain a reaction solution. pH of the reaction solution is adjusted to 8.2 by NaOH. After the reaction solution is further reacted, centrifuged at 8000 rpm for 5 minutes, and dried at 50 C. for 48 hours to obtain cellulose-based nanosheets. [0045] (4) 10 mg of the cellulose based nanosheets obtained in the step 3 are dispersed into 30 mL of water/methanol with a v/v ratio of 2:1 and stirred for 30 minutes to obtain a dispersing solution. 20 mL of a mixture solution containing 3 mg of FeCl.sub.2.Math.4H.sub.2O and 8 mg of FeCl.sub.3.Math.6H.sub.2O is added into the dispersing solution and stirred for 1 hour under N.sub.2 atmosphere to obtain a second mixture. Then, 0.1 mL of 28% NH.sub.3.Math.H.sub.2O is added into the second mixture and reacted for 3 hours at 80 C., and centrifuged and washed repeatedly to obtain cellulose-based nanosheets (i.e., cellulose-dopamine nanosheets) coated with magnetic Fe.sub.3O.sub.4 nanoparticles. [0046] (5) 2.6 g of acrylamide, 0.026 g of N,N-methylene diacrylamide, 15 L of tetramethylethylenediamine, 0.03 g of ammonium persulfate, and 0.052 g of the cellulose based nanosheets coated with magnetic Fe.sub.3O.sub.4 nanoparticles (i.e., magnetic PFeDAC nanosheets or magnetic cellulose-dopamine nanosheets) prepared by the step 4 are mixed, stirred, and poured into a mold. The mold is then left to stand at 60 C. for 3 hours to be polymerized to obtain a cellulose-based hydrogel.

[0047] Longitudinal tensile strength of a directional hydrogel (i.e., the cellulose-based hydrogel or various hydrogels) prepared under these conditions is about 0.22 MPa, 1.7 times the longitudinal tensile strength of a random directional hydrogel. Conductivity of the directional hydrogel is 41 S.Math.m.sup.1, and an adhesion force of the directional hydrogel to the skin can reach 63 kPa. Material properties are tested using conventional methods (referring to K. Liu, L. Han, P. Tang, K. Yang, D. Gan, X. Wang, K. Wang, F. Ren, L. Fan, Y. Xu, Z. Lu, X. Lu, Nano Lett. 2019, 19, 8343-83).

[0048] FIG. 4 illustrates a principle for forming a hydrogel. When power supply is not connected, the magnetic PFeDAC nanosheets are in disordered states. When the power supply is connected, the magnetic nanosheets are arranged in a direction of the magnetic field under an action of the magnetic field to form an ordered anisotropic structure.

Embodiment 2

[0049] Embodiment 2 is performed as follows. [0050] (1) The dialdehyde cellulose aqueous solution is obtained according to the step of the Embodiment 1. [0051] (2) An operation of step 2 in this embodiment is performed in accordance with the step 2 in Embodiment 1. The step 2 in this embodiment differs from the step 2 in Embodiment 1 in that the first mixture is reacted for 3 hours. [0052] (3) An operation of step 3 in this embodiment is performed in accordance with the step 3 in Embodiment 1. The step 3 in this embodiment differs from the step 3 in Embodiment 1 in that 0.03 g of the dopamine is added, and pH of the reaction solution is adjusted to 8.2. [0053] (4) An operation of step 4 in this embodiment is performed in accordance with the step 4 in Embodiment 1. The step 4 in this embodiment differs from the step 4 in Embodiment 1 in that 0.1 mL of 28% NH.sub.3.Math.H.sub.2O is added into the second mixture and reacted for 5 hours at 80 C. [0054] (5) An operation of step 5 in this embodiment is performed in accordance with the step 5 in Embodiment 1. The step 5 in this embodiment differs from the step 5 in Embodiment 1 in that 0.026 g of magnetic hybrids (i.e., the cellulose based nanosheets coated with magnetic Fe.sub.3O.sub.4 nanoparticles) is added.

[0055] The longitudinal tensile strength of the directional hydrogel prepared under these conditions is about 0.19 MPa, 1.5 times the longitudinal tensile strength of the random directional hydrogel. Conductivity of the directional hydrogel is 37 S.Math.m.sup.1, and an adhesion force of the directional hydrogel to the skin can reach 54 kPa.

Embodiment 3

[0056] Embodiment 3 is performed as follows. [0057] (1) The dialdehyde cellulose aqueous solution is obtained according to the step of the Embodiment 1. [0058] (2) An operation of step 2 in this embodiment is performed in accordance with the step 2 in Embodiment 1. The step 2 in this embodiment differs from the step 2 in Embodiment 1 in that the first mixture is reacted in 3 MPa of the H.sub.2 pressure. [0059] (3) An operation of step 3 in this embodiment is performed in accordance with the step 3 in Embodiment 1. The step 3 in this embodiment differs from the step 3 in Embodiment 1 in that 0.03 g of the dopamine is added, and pH of the reaction solution is adjusted to 8.5. [0060] (4) An operation of step 4 in this embodiment is performed in accordance with the step 4 in Embodiment 1. The step 4 in this embodiment differs from the step 4 in Embodiment 1 in that 0.1 mL of 28% NH.sub.3.Math.H.sub.2O is added into the second mixture and reacted for 1 hour at 90 C. [0061] (5) An operation of step 5 in this embodiment is performed in accordance with the step 5 in Embodiment 1. The step 5 in this embodiment differs from the step 5 in Embodiment 1 in that 0.1 g of magnetic hybrids (i.e., the cellulose based nanosheets coated with magnetic Fe.sub.3O.sub.4 nanoparticles) is added.

[0062] The longitudinal tensile strength of the directional hydrogel prepared under these conditions is about 0.3 MPa, 2.3 times the longitudinal tensile strength of the random directional hydrogel. Conductivity of the directional hydrogel is 45 S.Math.m.sup.1, and an adhesion force of the directional hydrogel to the skin can reach 66 kPa.

Embodiment 4

[0063] Embodiment 4 is performed as follows. [0064] (1) The dialdehyde cellulose aqueous solution is obtained according to the step of the Embodiment 1. [0065] (2) An operation of step 2 in this embodiment is performed in accordance with the step 2 in Embodiment 1. The step 2 in this embodiment differs from the step 2 in Embodiment 1 in that the first mixture is reacted at 110 C. [0066] (3) An operation of step 3 in this embodiment is performed in accordance with the step 3 in Embodiment 1. The step 3 in this embodiment differs from the step 3 in Embodiment 1 in that pH of the reaction solution is adjusted to 9.0. [0067] (4) An operation of step 4 in this embodiment is performed in accordance with the step 4 in Embodiment 1. The step 4 in this embodiment differs from the step 4 in Embodiment 1 in that 0.1 mL of 28% NH.sub.3.Math.H.sub.2O is added into the second mixture and reacted for 3 hours at 80 C. [0068] (5) An operation of step 5 in this embodiment is performed in accordance with the step 5 in Embodiment 1.

[0069] The longitudinal tensile strength of the directional hydrogel prepared under these conditions is about 0.2 MPa, 1.5 times the longitudinal tensile strength of the random directional hydrogel. Conductivity of the directional hydrogel is 39 S.Math.m.sup.1, and an adhesion force of the directional hydrogel to the skin can reach 58 kPa.

Embodiment 5

[0070] Embodiment 5 is performed as follows. [0071] (1) The dialdehyde cellulose aqueous solution is obtained according to the step of the Embodiment 1. [0072] (2) An operation of step 2 in this embodiment is performed in accordance with the step 2 in Embodiment 1. The step 2 in this embodiment differs from the step 2 in Embodiment 1 in that the first mixture is reacted at 140 C. [0073] (3) An operation of step 3 in this embodiment is performed in accordance with the step 3 in Embodiment 1. The step 3 in this embodiment differs from the step 3 in Embodiment 1 in that 0.03 g of the dopamine is added, and pH of the reaction solution is adjusted to 8.0. [0074] (4) An operation of step 4 in this embodiment is performed in accordance with the step 4 in Embodiment 1. The step 4 in this embodiment differs from the step 4 in

[0075] Embodiment 1 in that 20 mL of the mixture solution containing 3 mg of FeCl.sub.2.Math.4H.sub.2O and 8 mg of FeCl.sub.3.Math.6H.sub.2O is added into the dispersing solution and stirred for 3 hours under the N.sub.2 atmosphere, and 0.1 mL of 28% NH.sub.3.Math.H.sub.2O is added into the second mixture and reacted for 3 hours at 90 C. [0076] (5) An operation of step 5 in this embodiment is performed in accordance with the step 5 in Embodiment 1.

[0077] The longitudinal tensile strength of the directional hydrogel prepared under these conditions is about 0.15 MPa, 1.2 times the longitudinal tensile strength of the random directional hydrogel. Conductivity of the directional hydrogel is 35 S.Math.m.sup.1, and an adhesion force of the directional hydrogel to the skin can reach 57 kPa.

Embodiment 6

[0078] Embodiment 6 is performed as follows. [0079] (1) The dialdehyde cellulose aqueous solution is obtained according to the step of the Embodiment 1. [0080] (2) An operation of step 2 in this embodiment is performed in accordance with the step 2 in Embodiment 1. The step 2 in this embodiment differs from the step 2 in Embodiment 1 in that the first mixture is reacted under 0.2 g of the Ru/C catalyst. [0081] (3) An operation of step 3 in this embodiment is performed in accordance with the step 3 in Embodiment 1. The step 3 in this embodiment differs from the step 3 in Embodiment 1 in that pH of the reaction solution is adjusted to 8.2. [0082] (4) An operation of step 4 in this embodiment is performed in accordance with the step 4 in Embodiment 1. The step 4 in this embodiment differs from the step 4 in Embodiment 1 in that 20 mL of the mixture solution containing 3 mg of FeCl.sub.2.Math.4H.sub.2O and 3 mg of FeCl.sub.3.Math.6H.sub.2O is added into the dispersing solution and stirred for 3 hours under the N.sub.2 atmosphere, and 0.1 mL of 28% NH.sub.3.Math.H.sub.2O is added into the second mixture and reacted for 5 hours at 80 C. [0083] (5) An operation of step 5 in this embodiment is performed in accordance with the step 5 in Embodiment 1.

[0084] The longitudinal tensile strength of the directional hydrogel prepared under these conditions is about 0.14 MPa, 1.1 times the longitudinal tensile strength of the random directional hydrogel. Conductivity of the directional hydrogel is 31 S.Math.m.sup.1, and an adhesion force of the directional hydrogel to the skin can reach 47 kPa.

Embodiment 7

[0085] Embodiment 7 is performed as follows. [0086] (1) The dialdehyde cellulose aqueous solution is obtained according to the step of the Embodiment 1. [0087] (2) An operation of step 2 in this embodiment is performed in accordance with the step 2 in Embodiment 1. [0088] (3) An operation of step 3 in this embodiment is performed in accordance with the step 3 in Embodiment 1. The step 3 in this embodiment differs from the step 3 in Embodiment 1 in that pH of the reaction solution is adjusted to 9.0. [0089] (4) An operation of step 4 in this embodiment is performed in accordance with the step 4 in Embodiment 1. The step 4 in this embodiment differs from the step 4 in Embodiment 1 in that 20 mL of the mixture solution containing 3 mg of FeCl.sub.2.Math.4H.sub.2O and 5 mg of FeCl.sub.3.Math.6H.sub.2O is added into the dispersing solution and stirred for 3 hours under the N.sub.2 atmosphere. [0090] (5) An operation of step 5 in this embodiment is performed in accordance with the step 5 in Embodiment 1.

[0091] The longitudinal tensile strength of the directional hydrogel prepared under these conditions is about 0.24 MPa, 1.9 times the longitudinal tensile strength of the random directional hydrogel. Conductivity of the directional hydrogel is 48 S.Math.m.sup.1, and an adhesion force of the directional hydrogel to the skin can reach 67 kPa.

Embodiment 8

[0092] Embodiment 8 is performed as follows. [0093] (1) The dialdehyde cellulose aqueous solution is obtained according to the step of the Embodiment 1. [0094] (2) An operation of step 2 in this embodiment is performed in accordance with the step 2 in Embodiment 1. The step 2 in this embodiment differs from the step 2 in Embodiment 1 in that the first mixture is reacted under 0.2 g of the Ru/C catalyst. [0095] (3) An operation of step 3 in this embodiment is performed in accordance with the step 3 in Embodiment 1. The step 3 in this embodiment differs from the step 3 in Embodiment 1 in that 0.03 g of the dopamine is added, and pH of the reaction solution is adjusted to 8.0. [0096] (4) An operation of step 4 in this embodiment is performed in accordance with the step 4 in Embodiment 1. The step 4 in this embodiment differs from the step 4 in Embodiment 1 in that 20 mL of the mixture solution containing 3 mg of FeCl.sub.2.Math.4H.sub.2O and 3 mg of FeCl.sub.3.Math.6H.sub.2O is added into the dispersing solution and stirred for 1 hour under the N.sub.2 atmosphere. [0097] (5) An operation of step 5 in this embodiment is performed in accordance with the step 5 in Embodiment 1.

[0098] The longitudinal tensile strength of the directional hydrogel prepared under these conditions is about 0.11 MPa, 0.9 times the longitudinal tensile strength of the random directional hydrogel. Conductivity of the directional hydrogel is 28 S.Math.m.sup.1, and an adhesion force of the directional hydrogel to the skin can reach 41 kPa.

Performance Tests

[0099] Relevant performance tests are performed using Embodiment 1 as follows.

[0100] FIG. 1 illustrates X-ray diffraction (XRD) patterns of samples at various stages in Embodiment 1. According to an analysis of the XRD patterns, sharp peaks at 30.2 C., 35.5 C., 43.2 C., 57.1 C., and 62.8 C. have characteristics of a crystal structure of Fe.sub.3O.sub.4NPs, indicating that the crystal structure of Fe.sub.3O.sub.4NPs is formed on a surface of a PFeDAC sheet. Characteristics of peaks at around 20 C. are consistent with characteristics of DAC, identifying that PDA and the DAC play an important role for forming magnetic sheets. DAC is the dialdehyde cellulose obtained by sodium periodate (i.e., the NaIO.sub.4) oxidation of the cellulose; DAC-PDA is a DAC complex modified by dopamine (PDA) grafting; the PFeDAC is magnetic cellulose-based two-dimensional nanosheets mediated by the PDA and the DAC (i.e., magnetic PFeDAC hybrid); DAC-Fe.sub.3O.sub.4 is magnetic hybrid mediated only by the DAC; and PAD-Fe.sub.3O.sub.4 is magnetic hybrid mediated only by the PDA.

[0101] FIGS. 2A and 2B illustrate transmission electron microscope (TEM) images of magnetic cellulose-based nanosheets obtained in Embodiment 1, and FIG. 2B illustrates Fe.sub.3O.sub.4 magnetic nanoparticles loaded on a sheet carrier.

[0102] FIGS. 3A, 3B, and 3C illustrate existing states of magnetic PFeDAC nanosheets prepared in Embodiment 1 in water. The magnetic PFeDAC nanosheets prepared in Embodiment 1 have no obvious sediment after being left to stand in water for 3 hours, indicating that the magnetic PFeDAC nanosheets have good stability (see FIGS. 3A and 3B). When a magnet moves close to the magnetic PFeDAC nanosheets, the Fe.sub.3O.sub.4 magnetic nanoparticles are obviously attracted by the magnet, indicating that the Fe.sub.3O.sub.4 magnetic nanoparticles have good magnetism (see FIG. 3C).

[0103] Adhesion and tensile tests of the various hydrogels prepared in Embodiment 1 are performed using conventional methods. The various hydrogels can be adhered to the skin and has good tensile properties (the adhesion and tensile results of the various hydrogels are shown in FIGS. 5A, 5B, and 5C). A content of the magnetic PFeDAC hybrid used in various hydrogels is 8 wt %.

[0104] The compression experiment of the various hydrogels prepared in Embodiment 1 is performed using conventional methods. When a preset press is applied to the various hydrogels, the various hydrogels are obviously deformed. When the preset press is released, the various hydrogels reset to an original form of the hydrogel, indicating that the various hydrogels have good compression resistance (results are shown in FIG. 6). The content of the PFeDAC magnetic hybrid used in the various hydrogels is 8 wt %.

[0105] Adhesion properties of the various hydrogels prepared in Embodiment 1 are performed using conventional methods. FIGS. 7A and 7B illustrate good adhesion properties of the various hydrogels prepared in Embodiment 1 relative to various substrates as follows: iron sheet (56 kPa), glass (48 kPa), stainless steel (53 kPa), rubber (31 kPa), wood (13 kPa), polytetrafluoroethylene (PTFE) (39 kPa), plastic (17 kPa), paper (11 kPa), and skin (63 kPa). The content of the magnetic PFeDAC hybrid in the various hydrogels is 8 wt %.

[0106] Tensile performance tests of the various hydrogels prepared in Embodiment 1 are performed using conventional methods. FIG. 8 illustrates tensile stress-strain curves of three hydrogels prepared in Embodiment 1 under forces in different directions, the three hydrogels are as follows: (*) represents a first hydrogel prepared under no external magnetic field, the first hydrogel is isotropic and has a same force in all directions; (//) represents a second hydrogel prepared under an applied force parallel to a magnetic field direction; () represents a third hydrogel prepared under the applied force perpendicular to the magnetic field direction. The content of the magnetic PFeDAC hybrid in the various hydrogels is 8 wt %.

[0107] Tensile strain tests of the various hydrogels prepared in Embodiment 1 are performed by conventional methods. FIG. 9 illustrates compressive stress-strain curves of the three hydrogels prepared in Embodiment 1 under the forces in the different directions, the three hydrogels is as follows: (*) represents the first hydrogel prepared under no external magnetic field, the first hydrogel is isotropic and has a same force in all directions; (//) represents the second hydrogel prepared under an applied force parallel to the magnetic field direction; () represents the third hydrogel prepared under the applied force perpendicular to the magnetic field direction. The content of the magnetic PFeDAC hybrid in the various hydrogels is 8 wt %.

[0108] Loading-unloading tests of the second hydrogel prepared in Embodiment 1 are performed by conventional methods. FIG. 10 illustrates the tensile stress-strain curves of the second hydrogel prepared in Embodiment 1 during a loading-unloading cycle, the applied force is parallel to the magnetic field direction, and the content of the magnetic PFeDAC hybrid in the various hydrogels is 8 wt %. Referring to FIG. 10, no significant hysteresis is observed on a loading-unloading cyclic curve of the second hydrogel having 8 wt % of the magnetic PFeDAC hybrid when a constant force for 700% deformation is applied to the second hydrogel.

[0109] Conductivity tests of the various hydrogels prepared in Embodiment 1 are tested by conventional methods. FIG. 11 illustrates electric conductivity of the various hydrogels prepared in Embodiment 1 with different concentrations of the magnetic PFeDAC hybrid under the applied force parallel to the magnetic field direction. Results of the conductivity tests are as follows: with respect to the first hydrogel with 8 wt % of the magnetic PFeDAC hybrid prepared under no external magnetic field (*), the second hydrogel with 8 wt % of the magnetic PFeDAC hybrid prepared under the applied force parallel to the magnetic field direction (//), and the third hydrogel with 8 wt % of the magnetic PFeDAC hybrid prepared under the applied force perpendicular to the magnetic field direction (), a conductivity of the hydrogel increases with an increase of the content of the magnetic PFeDAC hybrid. The conductivity of the hydrogel stabilizes or even decreases slightly following with increasing of a concentration of the magnetic PFeDAC hybrid.