Biomimetic mineralized porous aerogel as well as preparation method and application thereof

Abstract

The invention discloses biomimetic mineralized porous aerogel as well as a preparation method and application thereof, and belongs to the technical field of natural polymer-based composite materials. The preparation method comprises the following steps: dissolving sodium alginate powder in a weakly alkaline aqueous solution containing phosphate to obtain a uniformly dispersed precursor solution; freezing treatment is performed to form frozen gel with an ice crystal template structure; immersing the frozen gel into a solution containing calcium ions, and synchronously realizing crosslinking of a sodium alginate network and in-situ mineralization of hydroxyapatite at low temperature to obtain mineralized composite gel; finally, the mineralized composite gel is subjected to solvent replacement and normal-pressure drying treatment, and the biomimetic mineralized aerogel is prepared. According to the method, ionic crosslinking and in-situ mineralization are synergistically realized through a one-step method, the process is simple and efficient, expensive equipment is not needed, and the cost is low. The prepared aerogel has a rich pore structure, a high specific surface area and good biological activity, and has a wide application prospect in the fields of environmental adsorption materials, biological scaffold materials and the like.

Description

Technical Field

[0001] This invention belongs to the field of functional natural polymer matrix composite technology, specifically relating to a biomimetic mineralized porous aerogel, its preparation method, and its application. Background Technology

[0002] Aerogels are lightweight solid materials that use gas as a dispersion medium. They possess characteristics such as a three-dimensional continuous network structure, abundant pores, high specific surface area, and extremely low density, showing great promise for applications in high-end adsorption separation, efficient thermal insulation, catalyst carriers, and biomedical scaffolds. Compared to traditional inorganic aerogels and synthetic polymer aerogels, natural polymer-based aerogels, represented by sodium alginate, chitosan, and cellulose aerogels, have attracted much attention due to their advantages such as green, environmentally friendly, and renewable raw materials, low cost, good biocompatibility, biodegradability, and ease of functionalization.

[0003] Sodium alginate is a natural linear anionic polysaccharide extracted from brown algae. Due to its unique molecular structure, it is considered an ideal matrix material for preparing bio-based aerogels. The sodium alginate molecular chain is rich in carboxyl and hydroxyl functional groups, which not only allow it to react with polyvalent metal ions (such as Ca²⁺)... 2+ Rapid ionic cross-linking forms a stable "egg-box" structure, providing a basic three-dimensional network framework for aerogels. Furthermore, these active groups provide reaction sites for further chemical functionalization or composite with inorganic nanoparticles to enhance the performance and function of aerogels. However, pure sodium alginate aerogels have low mechanical strength and limited functionality, making them unsuitable for high-performance applications. Therefore, developing functionalized aerogels based on sodium alginate has significant scientific value and application prospects.

[0004] To endow sodium alginate aerogels with superior functionality, the construction of organic-inorganic nanocomposite aerogels by introducing inorganic nanophases is a current research trend. The main methods for constructing organic-inorganic composite aerogels and their limitations are as follows: 1. Physical mixing method The physical mixing method involves pre-dispersing inorganic nanoparticles in an organic polymer solution, then forming a composite gel through cross-linking, and finally obtaining an aerogel through freeze-drying. However, due to the inherent high surface energy of inorganic nanoparticles, irreversible aggregation is easily observed during aerogel preparation, leading to uneven spatial distribution of the inorganic phase within the aerogel framework and resulting in poor material stability.

[0005] 2. Step-by-step load method The stepwise loading method typically requires first preparing an organic aerogel matrix through freeze-drying, and then depositing inorganic nanoparticles onto the pre-formed aerogel framework through immersion adsorption. This method involves cumbersome processes, a long production cycle, and the nanoparticles are usually physically attached to the framework, resulting in weak interfacial bonding and easy detachment during use.

[0006] 3. Limitations of process technology Existing technologies generally rely heavily on freeze-drying. Freeze-drying requires expensive equipment and suffers from problems such as high energy consumption, long production cycles, and high costs, which severely restricts the large-scale production and application of aerogel materials. In addition, the sublimation process of ice crystals is difficult to control, which may lead to microscopic collapse or cracking of the gel skeleton, thereby affecting the pore structure and mechanical properties of aerogel materials.

[0007] Therefore, developing a low-cost preparation method that can simultaneously achieve in-situ composite of inorganic phases and construction of organic porous network structures without relying on freeze-drying equipment is of great significance for promoting the practical application of sodium alginate-based composite aerogels. Summary of the Invention

[0008] The purpose of this invention is to overcome the problems of complex processes, uneven dispersion of inorganic phases, extreme dependence on expensive freeze-drying equipment, and high costs in the preparation of composite aerogels, especially sodium alginate-based composite aerogels, in existing technologies. This invention provides a simple and low-cost method for preparing biomimetic mineralized porous aerogels. Inspired by natural biomineralization processes, this invention proposes a biomimetic mineralization strategy. A one-step method simultaneously achieves in-situ mineralization of sodium alginate organic network crosslinking and inorganic nano-hydroxyapatite (nHA) to prepare porous aerogel materials. Specifically, an ice-templating method is used to construct a continuous, interconnected porous structure, combined with solvent displacement and atmospheric pressure drying techniques, to prepare a biomimetic mineralized aerogel material with abundant pores and uniform dispersion of nano-hydroxyapatite.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for preparing biomimetic mineralized porous aerogel, comprising the following steps: (1) Prepare a phosphate solution of a certain concentration. Add sodium alginate powder to the phosphate-containing aqueous solution and stir until the sodium alginate powder is completely dissolved. Adjust the resulting mixed solution to weak alkalinity and continue stirring to obtain a uniformly dispersed precursor solution. (2) The precursor solution is subjected to ultrasonic treatment to remove air bubbles, and then transferred to a freezing mold for low-temperature freezing treatment to obtain a cryogel; (3) The cryogel is immersed in a solution containing calcium ions and cross-linked and in-situ mineralized at low temperature to obtain a mineralized composite gel; (4) The mineralized composite gel is washed, dehydrated and solvent replaced in sequence, and then dried under normal pressure to obtain biomimetic mineralized porous aerogel.

[0010] Furthermore, the mass percentage concentration of sodium alginate in the precursor solution in step (1) is 1 wt%-5 wt%.

[0011] Furthermore, the phosphate in step (1) is selected from one or both of sodium dihydrogen phosphate or disodium hydrogen phosphate, and the molar concentration of the phosphate in the precursor solution is 0.01 M-0.20 M.

[0012] Furthermore, the total stirring time in step (1) is 1 h to 24 h, and the stirring speed is 100 rpm to 800 rpm.

[0013] Furthermore, the reagent used to adjust the pH of the mixed solution in step (1) is a dilute inorganic acid or dilute inorganic alkali solution that does not introduce interfering ions, preferably a dilute solution of sodium hydroxide, potassium hydroxide, hydrochloric acid or nitric acid; the pH of the mixed solution is adjusted to a weakly alkaline state, preferably pH 7.0-8.5.

[0014] Furthermore, the ultrasonic defoaming treatment in step (2) takes 10 min to 60 min and has a frequency of 40 kHz to 120 kHz, preferably 40 kHz.

[0015] Furthermore, the freezing mold in step (2) is selected from an integrated low-temperature resistant freezing mold or a combined directional freezing mold; wherein, the integrated low-temperature resistant freezing mold is made of a low-temperature resistant material, the low-temperature resistant material includes organosilicon material, preferably silicone rubber or polydimethylsiloxane; the combined directional freezing mold includes a cylinder made of heat-insulating material and a base made of heat-conducting material, the material of the cylinder includes at least one of polytetrafluoroethylene and polystyrene, and the material of the base includes one or more of copper, aluminum and other metals.

[0016] Furthermore, the temperature of the low-temperature freezing treatment in step (2) is from -20 ℃ to -196 ℃, the low-temperature freezing treatment method is mechanical refrigeration equipment freezing (such as a low-temperature refrigerator) or deep cryogenic medium freezing (such as liquid nitrogen), and the low-temperature freezing treatment time is at least 2 min.

[0017] Preferably, when mechanical refrigeration equipment is used for freezing, the freezing temperature is -20 ℃ to -80 ℃, and the freezing time is not less than 1 hour; Preferably, when using a cryogenic medium for freezing, the freezing temperature is -81 ℃ to -196 ℃, and the freezing time is 2 min or more.

[0018] Furthermore, the calcium ion-containing solution in step (3) is selected from anhydrous ethanol solution of calcium chloride or acetone solution of calcium chloride, the molar concentration of calcium ions in the calcium ion-containing solution is 0.05 M - 0.20 M, and the volume ratio of the cryogel to the calcium ion-containing solution is 1:(10-50).

[0019] Furthermore, the temperature for the synchronous crosslinking and in-situ mineralization reaction described in step (3) is preferably -10 ℃ to -20 ℃, and the reaction time is 2 h to 72 h.

[0020] Furthermore, the washing, dehydration, and solvent replacement treatment in step (4) includes: firstly, washing and dehydrating the mineralized composite gel once or multiple times with a washing solvent, with each washing time not less than 20 min; then, soaking and replacing the washed mineralized composite gel once or multiple times with a low surface tension solvent, with each replacement time not less than 1 h. Preferably, the washing solvent includes at least one of anhydrous ethanol, acetone, and isopropanol; and the replacement solvent includes at least one of tert-butanol, cyclohexane, and n-hexane.

[0021] Furthermore, the atmospheric pressure drying is atmospheric pressure drying under air at 25 ℃-80 ℃, preferably at a drying temperature of 30 ℃-60 ℃.

[0022] This invention provides a biomimetic mineralized porous aerogel, which is prepared by any of the methods described above.

[0023] Furthermore, the biomimetic mineralized porous aerogel has a three-dimensional network structure of sodium alginate and nano-hydroxyapatite grown in situ in the network structure; the X-ray diffraction (XRD) pattern of the mineralized aerogel retains the amorphous diffuse peaks of sodium alginate and has characteristic diffraction peaks belonging to hydroxyapatite crystals.

[0024] Furthermore, the XRD pattern of the biomimetic mineralized porous aerogel has sharp diffraction peaks at 26.7°, 31.7°, 45.6° and 53.9° representing the (002), (211), (222) and (004) crystal planes of hydroxyapatite.

[0025] Furthermore, in the infrared spectrum of the biomimetic mineralized porous aerogel, at 561 ± 5 cm⁻¹... -1 and 601 ±5cm -1 It exhibits an absorption peak due to the bending vibration of phosphate at 1030 ± 5 cm⁻¹. -1 Up to 1100 ±5 cm -1 The range contains an absorption band attributable to the stretching vibration of phosphate.

[0026] Furthermore, the specific surface area of ​​the biomimetic mineralized porous aerogel is 10-40 m². 2 / g, apparent density is 30-50 mg / cm³ 3 .

[0027] This invention provides the application of the biomimetic mineralized porous aerogel in the preparation of bone tissue engineering scaffolds, wound repair dressings, heavy metal ion adsorbents or anion adsorbents.

[0028] In summary, compared with the prior art, the present invention achieves the following technical effects: (1) This invention employs a "one-step simultaneous crosslinking and mineralization" strategy to prepare biomimetic mineralized porous aerogels. In a low-temperature organic solvent reaction system containing calcium ions, sodium alginate molecular chains react with Ca... 2+ Ions coordinate and crosslink to form a three-dimensional network structure. Simultaneously, phosphates pre-dispersed uniformly within the sodium alginate network can interact with Ca... 2+ In-situ ion mineralization reaction simultaneously generates nano-hydroxyapatite. Low-temperature conditions effectively control the slow progress of crosslinking and mineralization, which is conducive to the formation of structurally stable and uniformly sized nano-hydroxyapatite. This process integrates the traditionally stepwise crosslinking and mineralization processes into a one-step simultaneous process, overcoming the particle agglomeration problem in physical blending methods and the composition gradient problem in stepwise methods, simplifying the operation process and improving preparation efficiency.

[0029] (2) This invention uses the ice template method to precisely construct an aerogel framework with a continuous, interconnected pore structure, and combines solvent displacement and atmospheric pressure drying techniques to avoid the reliance on expensive freeze-drying equipment in traditional aerogel preparation. This method can maintain the porous structure of the aerogel material under atmospheric pressure. This technology significantly reduces the equipment and energy costs of aerogel production, providing a feasible low-cost approach for large-scale production.

[0030] (3) This invention uses natural and renewable high-molecular-weight sodium alginate as the aerogel matrix material. The reaction conditions are mild, green and environmentally friendly, and meet the requirements of sustainable development. Through a biomimetic mineralization strategy, nano-hydroxyapatite is generated in situ and uniformly distributed in the three-dimensional network aerogel framework, so that the surface of the composite aerogel has abundant active sites and high efficiency of bioactivity. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 The images shown are scanning electron microscope (SEM) images of the aerogel materials prepared in Examples 1 and 2.

[0033] Figure 2 The X-ray diffraction (XRD) patterns of the aerogel materials prepared in Examples 1 and 2 are shown.

[0034] Figure 3 The images show the infrared (FTIR) spectra of the aerogel materials prepared in Examples 1 and 4.

[0035] Figure 4 The X-ray photoelectron spectroscopy (XPS) full scan spectra of the aerogel materials prepared in Examples 1 and 3 are shown.

[0036] Figure 5 Macroscopic images of the mineralized aerogel materials prepared in Examples 3 and 7. Detailed Implementation

[0037] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention are clearly and completely described. 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 should fall within the scope of protection of the present invention.

[0038] Example 1 (1) Weigh a certain amount of sodium alginate powder, slowly add it to deionized water, and stir continuously for 4 hours. The magnetic stirring speed is 300 rpm. After the powder is completely dissolved, a uniform 2 wt% sodium alginate precursor solution is obtained.

[0039] (2) The sodium alginate precursor solution was subjected to ultrasonic defoaming treatment for 10 min at a frequency of 40 kHz; then it was transferred to a silicone rubber mold and placed in an ultra-low temperature freezer at -80 ℃ for 6 h to form a stable ice crystal template. The cryogel was obtained by freezing and molding.

[0040] (3) The formed cryogel was immersed in a pre-cooled 0.1 M calcium chloride anhydrous ethanol solution and reacted at -18 ℃ for 12 h to carry out the cross-linking reaction and obtain the cross-linked gel.

[0041] (4) Take out the cross-linked gel and wash it with anhydrous ethanol three times for 30 min each time. Then transfer it to tert-butanol for displacement twice for 1 h each time. Finally, place the sample in a 50 ℃ oven and dry it at normal pressure for 12 h to obtain a white, light sodium alginate aerogel.

[0042] The sodium alginate aerogel sample prepared in Example 1 was named Alg and used as a comparative example.

[0043] Example 2 (1) Weigh a certain amount of sodium alginate powder and slowly add it to deionized water that has dissolved sodium dihydrogen phosphate (final concentration of 0.10M). Stir continuously for 2 h at a magnetic stirring speed of 300 rpm. After the powder is completely dissolved, use NaOH solution to adjust the pH of the mixture to 7.8 under stirring. Continue stirring for 2 h to obtain a uniform 2 wt% sodium alginate-phosphate mixed precursor solution.

[0044] (2) The sodium alginate-phosphate mixed precursor solution was subjected to ultrasonic defoaming treatment for 10 min at a frequency of 40 kHz; then it was transferred to a silicone rubber mold and placed in an ultra-low temperature freezer at -80 ℃ for 6 h to form a stable ice crystal template. The cryogel was obtained by freezing and molding.

[0045] (3) The formed cryogel was immersed in a pre-cooled 0.1 M calcium chloride anhydrous ethanol solution and reacted at -18 ℃ for 12 h to carry out cross-linking and in-situ mineralization reaction to obtain mineralized composite gel.

[0046] (4) The mineralized composite gel was removed and washed and dehydrated three times with anhydrous ethanol for 30 min each time. Then it was transferred to tert-butanol for displacement twice, for 1 h each time. Finally, the sample was placed in a 50 ℃ oven and dried at normal pressure for 12 h to obtain biomimetic mineralized aerogel.

[0047] Example 3 (1) Weigh a certain amount of sodium alginate powder and slowly add it to deionized water that has dissolved sodium dihydrogen phosphate (final concentration of 0.05M). Stir continuously for 2 h at a magnetic stirring speed of 300 rpm. After the powder is completely dissolved, use NaOH solution to adjust the pH of the mixture to 7.8 under stirring. Continue stirring for 2 h to obtain a uniform 2 wt% sodium alginate-phosphate mixed precursor solution.

[0048] (2) The sodium alginate-phosphate mixed precursor solution was subjected to ultrasonic defoaming treatment for 10 min at a frequency of 40 kHz; then it was transferred to a silicone rubber mold and placed in an ultra-low temperature freezer at -80 ℃ for 6 h to form a stable ice crystal template. The cryogel was obtained by freezing and molding.

[0049] (3) The formed cryogel was immersed in a pre-cooled 0.1 M calcium chloride anhydrous ethanol solution and reacted at -18 ℃ for 12 h to carry out cross-linking and in-situ mineralization reaction to obtain mineralized composite gel.

[0050] (4) The mineralized composite gel was removed and washed and dehydrated three times with anhydrous ethanol for 30 min each time. Then it was transferred to tert-butanol for displacement twice, for 1 h each time. Finally, the sample was placed in a 50 ℃ oven and dried at normal pressure for 12 h to obtain biomimetic mineralized aerogel.

[0051] Example 4 (1) Weigh a certain amount of sodium alginate powder and slowly add it to deionized water that has dissolved sodium dihydrogen phosphate (final concentration of 0.03M). Stir continuously for 2 h at a magnetic stirring speed of 300 rpm. After the powder is completely dissolved, use NaOH solution to adjust the pH of the mixture to 7.8 under stirring. Continue stirring for 2 h to obtain a uniform 2 wt% sodium alginate-phosphate mixed precursor solution.

[0052] (2) The sodium alginate-phosphate mixed precursor solution was subjected to ultrasonic defoaming treatment for 10 min at a frequency of 40 kHz; then it was transferred to a silicone rubber mold and placed in an ultra-low temperature freezer at -80 ℃ for 6 h to form a stable ice crystal template. The cryogel was obtained by freezing and molding.

[0053] (3) The formed cryogel was immersed in a pre-cooled 0.1 M calcium chloride anhydrous ethanol solution and reacted at -18 ℃ for 12 h to carry out cross-linking and in-situ mineralization reaction to obtain mineralized composite gel.

[0054] (4) The mineralized composite gel was removed and washed and dehydrated three times with anhydrous ethanol for 30 min each time. Then it was transferred to tert-butanol for displacement twice, for 1 h each time. Finally, the sample was placed in a 50 ℃ oven and dried at normal pressure for 12 h to obtain biomimetic mineralized aerogel.

[0055] Example 5 (1) Weigh a certain amount of sodium alginate powder and slowly add it to deionized water that has dissolved sodium dihydrogen phosphate (final concentration of 0.05M). Stir continuously for 1.5 h at a magnetic stirring speed of 200 rpm. After the powder is completely dissolved, use NaOH solution to adjust the pH of the mixture to 8.0 under stirring. Continue stirring for 2.5 h to obtain a uniform 1 wt% sodium alginate-phosphate mixed precursor solution.

[0056] (2) The sodium alginate-phosphate mixed precursor solution was subjected to ultrasonic defoaming treatment for 20 min at a frequency of 40 kHz; then it was transferred to a polytetrafluoroethylene-copper base directional freezing mold and placed in an ultra-low temperature freezer at -80 ℃ for 12 h to form a stable ice crystal template. The frozen gel was obtained by freezing and molding.

[0057] (3) The formed cryogel was immersed in a pre-cooled 0.05 M calcium chloride anhydrous ethanol solution and reacted at -18 ℃ for 12 h to carry out cross-linking and in-situ mineralization reaction to obtain mineralized composite gel.

[0058] (4) The mineralized composite gel was taken out and washed and dehydrated three times with anhydrous ethanol for 30 min each time. Then it was transferred to tert-butanol for displacement twice, for 1 h each time. Finally, the sample was placed in a 60 ℃ oven and dried at normal pressure for 12 h to obtain biomimetic mineralized aerogel.

[0059] Example 6 (1) Weigh a certain amount of sodium alginate powder and slowly add it to deionized water containing dissolved disodium hydrogen phosphate (final concentration of 0.10M). Stir continuously for 4 h at a magnetic stirring speed of 500 rpm. After the powder is completely dissolved, use HCl solution to adjust the pH of the mixture to 8.0 under stirring. Continue stirring for 2 h to obtain a uniform 3 wt% sodium alginate-phosphate mixed precursor solution.

[0060] (2) The sodium alginate-phosphate mixed precursor solution was subjected to ultrasonic defoaming treatment for 30 min at a frequency of 40 kHz; then it was transferred to a polytetrafluoroethylene-copper base directional freezing mold and frozen with liquid nitrogen for 5 min to form a stable ice crystal template. The frozen gel was obtained by freezing.

[0061] (3) The formed cryogel was immersed in a pre-cooled 0.20 M calcium chloride anhydrous ethanol solution and reacted at -10 ℃ for 12 h to carry out cross-linking and in-situ mineralization reaction to obtain mineralized composite gel.

[0062] (4) The mineralized composite gel was removed and washed and dehydrated three times with anhydrous ethanol for 1 h each time. Then it was transferred to tert-butanol for displacement twice for 2 h each time. Finally, the sample was placed in a 50 ℃ oven and dried at normal pressure for 18 h to obtain biomimetic mineralized aerogel.

[0063] Example 7 (1) Weigh a certain amount of sodium alginate powder and slowly add it to deionized water that has dissolved sodium dihydrogen phosphate (final concentration of 0.03M). Stir continuously for 2 h at a magnetic stirring speed of 300 rpm. After the powder is completely dissolved, use NaOH solution to adjust the pH of the mixture to 7.8 under stirring. Continue stirring for 2 h to obtain a uniform 2 wt% sodium alginate-phosphate mixed precursor solution.

[0064] (2) The sodium alginate-phosphate mixed precursor solution was subjected to ultrasonic defoaming treatment for 10 min at a frequency of 40 kHz; then it was transferred to a silicone rubber mold and placed in an ultra-low temperature freezer at -80 ℃ for 6 h to form a stable ice crystal template. The cryogel was obtained by freezing and molding.

[0065] (3) The formed cryogel was immersed in a pre-cooled 0.1 M calcium chloride anhydrous ethanol solution and reacted at 4 °C for 12 h to carry out cross-linking and in-situ mineralization reaction to obtain mineralized composite gel.

[0066] (4) The mineralized composite gel was removed and washed and dehydrated three times with anhydrous ethanol for 30 min each time. Then it was transferred to tert-butanol for displacement twice, for 1 h each time. Finally, the sample was placed in a 50 ℃ oven and dried at normal pressure for 12 h to obtain biomimetic mineralized aerogel.

[0067] Example 8: Structural Characterization and Performance Testing of Aerogel Materials To verify the effect of the preparation method described in this invention on the microstructure and macroscopic properties of aerogel materials, the composite aerogel materials prepared in Examples 1-6 above were characterized and tested as follows: 1. Microscopic morphology and composition characterization The morphology, crystal structure and chemical composition of the aerogel were characterized and analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS).

[0068] (1) Scanning electron microscope (SEM) The surface microstructure of the aerogel was observed using scanning electron microscopy, and the results are as follows: Figure 1 As shown. Among them, Figure 1 (a) shows the morphology of the pure sodium alginate aerogel (Alg) prepared in Example 1. It was found that it exhibits a typical three-dimensional porous network structure. The surface of the sodium alginate framework is relatively smooth, and the pores are continuously interconnected. This indicates that the sodium alginate network and Ca 2+ The ions successfully cross-linked to form a stable structure. In contrast, Figure 1 (b) SEM image of the in-situ mineralized aerogel (Alg / nHA) in Example 2. The Alg / nHA aerogel not only retains the original three-dimensional network framework, but also shows obvious nanoparticle aggregation on the framework surface, making the surface relatively rough. This fully demonstrates that nHA is successfully formed and loaded in situ in the sodium alginate network structure, which not only endows the mineralized aerogel with a higher specific surface area and abundant surface active sites, but also provides a structural basis for the enhancement of its mechanical properties.

[0069] (2) X-ray diffraction (XRD) The crystal structures of the aerogel materials prepared in Example 1 (Alg) and Example 2 (Alg / nHA) were analyzed by X-ray diffraction pattern analysis, and the results are as follows: Figure 2 As shown. The results show that the Alg aerogel prepared in Example 1 only has a broad and diffuse "bun peak" around 20°, which is a characteristic peak of typical amorphous polymers. However, the XRD pattern of the Alg / nHA mineralized aerogel still retains the amorphous diffuse peak of sodium alginate, while a series of sharp diffraction peaks appear at positions such as 26.7°, 31.7°, 45.6°, and 53.9°. These diffraction peaks are attributed to the (002), (211), (222), and (004) crystal planes of hydroxyapatite (HA), respectively. This indicates that nano-hydroxyapatite with a crystalline structure was successfully synthesized in the sodium alginate network structure by in-situ mineralization.

[0070] (3) Fourier transform infrared spectroscopy (FTIR) The chemical structure of the aerogel materials prepared in Example 1 (Alg) and Example 4 (Alg / nHA) was characterized by Fourier transform infrared spectroscopy, and the results are as follows: Figure 3 As shown. The results show that in the infrared spectrum of the Alg aerogel prepared in Example 1, at 3434 cm⁻¹... -1 The broad peak nearby is attributed to the stretching vibration absorption peak of the -OH group, 1630 cm⁻¹. -1 and 1420 cm -1 The nearby absorption peaks correspond to the asymmetric and symmetric stretching vibrations of the carboxylate group (-COO-), respectively, at 1039 cm⁻¹. -1 The nearby broad peaks originate from the stretching vibrations of COC in the sodium alginate structure. In contrast, the infrared spectrum of the Alg / nHA aerogel prepared in Example 4 retains the aforementioned characteristic peaks of sodium alginate, with a peak at 561 cm⁻¹. -1 and 601 cm -1 The typical bending vibration characteristic peak of phosphate appears at 1030 cm⁻¹. -1 Up to 1100 cm -1 A broad and strong absorption band appeared within the range, which is attributed to the characteristic peak of phosphate stretching vibration. The appearance of these characteristic peaks fully demonstrates the successful synthesis of nHA in the mineralized aerogel.

[0071] (4) X-ray photoelectron spectroscopy (XPS) The elemental composition of the aerogel materials prepared in Example 1 (Alg) and Example 3 (Alg / nHA) was analyzed using XPS. The XPS full spectra of pure Alg aerogel and Alg / nHA mineralized aerogel were compared, and the results are as follows: Figure 4As shown in the figure. The results show that in the XPS full spectrum of pure Alg aerogel, only carbon (C 1s), oxygen (O 1s), and calcium (Ca 2p) characteristic peaks introduced by ionic crosslinking from sodium alginate were observed. This indicates that sodium alginate has been crosslinked with Ca... 2+ The ion coordination successfully constructed a stable gel network. After in-situ mineralization, the XPS spectrum of the Alg / nHA aerogel showed significant changes, with the appearance of new characteristic peaks for phosphorus (P2p and P2s), indicating the successful in-situ synthesis and loading of nano-hydroxyapatite into the sodium alginate network. The relative intensity of the C1s peak in the Alg / nHA spectrum was significantly reduced, further demonstrating that the newly generated nHA was effectively loaded onto the surface of the sodium alginate network structure.

[0072] 2. Physical properties The specific surface area and macroscopic physical properties of aerogel materials were revealed through nitrogen adsorption-desorption experiments and apparent density measurements. The macroscopic morphology of the mineralized aerogel materials was observed through digital photographs.

[0073] (1) Nitrogen adsorption-desorption experiment The specific surface area of ​​the aerogel was analyzed by nitrogen adsorption-desorption test. The results showed that the specific surface area of ​​the sodium alginate aerogel in Example 1 was only 4.20 m². 2 / g, while after one-step in-situ mineralization treatment, the specific surface area of ​​the mineralized aerogel in Example 4 increased to 16.56 m². 2 / g, the specific surface area of ​​the mineralized aerogel in Example 2 is 33.62 m². 2 / g (an increase of nearly 8 times). This indicates that the mineralization process not only successfully loaded nano-hydroxyapatite into the sodium alginate network, but also constructed a rich hierarchical porous structure, thereby increasing the specific surface area of ​​the aerogel.

[0074] (2) Apparent density measurement The apparent density of the aerogel material is calculated by measuring its physical dimensions and mass, based on the mass-to-volume ratio.

[0075] Comparison of the apparent density of aerogels before and after mineralization revealed that the apparent density of the sodium alginate aerogel in Example 1 was 33.87 ± 4.81 mg / cm³. 3 The apparent density of the mineralized aerogel in Example 2 increased to 45.01 ± 3.55 mg / cm³. 3 This growth trend is attributed to the in-situ deposition and loading of dense hydroxyapatite within the sodium alginate network, which also helps enhance the mechanical properties of the material, while the mineralized aerogel retains its excellent lightweight properties.

[0076] (3) Macroscopic morphology The macroscopic morphology of the mineralized aerogel was observed through digital photography, and the results are as follows: Figure 5 As shown, where, Figure 5 (a) and Figure 5 (b) A macroscopic image of the mineralized aerogel material prepared in Example 3. The results show that the mineralized aerogel has lightweight properties, and the aerogel after mineralization at -18 ℃ exhibits a uniform and intact structure with no obvious shrinkage or cracking on the surface, indicating that low temperature is beneficial for the aerogel to maintain a stable porous framework during the mineralization process. In contrast, Figure 5 (c) is a macroscopic image of the mineralized aerogel material prepared in Example 7. The results show that the aerogel structure exhibits a certain degree of shrinkage or local collapse after mineralization at 4 °C. This may be due to the rapid dissolution of ice crystals and accelerated ion migration, leading to an excessively rapid cross-linking reaction between sodium alginate and calcium ions, resulting in structural stress concentration and uneven porosity, thus causing structural defects. Therefore, low-temperature mineralization is a key process condition for maintaining the structural integrity and lightweight properties of aerogels.

[0077] In summary, this invention successfully prepared a novel sodium alginate-based composite aerogel material with biomimetic mineralization characteristics. The mineralized aerogel prepared by this invention not only achieves a strong bond between the organic and inorganic phases at the microscale, but also possesses comprehensive advantages such as lightweight, high specific surface area, and tunable structure. This makes it show clear and broad application prospects in fields such as bone tissue engineering scaffolds, wound repair dressings, and heavy metal ion or anion adsorbents (such as fluoride ions).

[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a biomimetic mineralized porous aerogel, characterized in that, Includes the following steps: (1) Prepare a phosphate solution of a certain concentration. Add sodium alginate powder to the phosphate-containing aqueous solution and stir until the sodium alginate powder is completely dissolved. Adjust the resulting mixed solution to weak alkalinity and continue stirring to obtain the precursor solution. (2) The precursor solution is subjected to ultrasonic treatment to remove air bubbles, and then transferred to a freezing mold for low-temperature freezing treatment to obtain a cryogel; (3) The cryogel is immersed in a solution containing calcium ions and cross-linked and in-situ mineralized at low temperature to obtain a mineralized composite gel; (4) The mineralized composite gel is washed, dehydrated and solvent replaced in sequence, and then dried under normal pressure to obtain biomimetic mineralized porous aerogel.

2. The preparation method according to claim 1, characterized in that, The mass percentage concentration of sodium alginate in the precursor solution in step (1) is 1 wt%-5 wt%; the phosphate is selected from one or both of sodium dihydrogen phosphate or disodium hydrogen phosphate, and the molar concentration of the phosphate in the precursor solution is 0.01 M-0.20 M.

3. The preparation method according to claim 1, characterized in that, The total stirring time in step (1) is 1 h-24 h, and the stirring speed is 100 rpm-800 rpm; the reagent for adjusting the pH of the mixed solution is a dilute inorganic acid or dilute inorganic base solution that does not introduce interfering ions, preferably a dilute solution of sodium hydroxide, potassium hydroxide, hydrochloric acid or nitric acid; The pH of the mixed solution is adjusted to a slightly alkaline state, preferably between pH 7.0 and 8.

5.

4. The preparation method according to claim 1, characterized in that, The ultrasonic defoaming treatment in step (2) takes 10 min to 60 min and has a frequency of 40 kHz to 120 kHz.

5. The preparation method according to claim 1, characterized in that, The freezing mold mentioned in step (2) is selected from an integrated low-temperature resistant freezing mold or a combined directional freezing mold; wherein, the integrated low-temperature resistant freezing mold is made of a low-temperature resistant material, the low-temperature resistant material includes organosilicon material, preferably silicone rubber or polydimethylsiloxane; the combined directional freezing mold includes a cylinder made of heat-insulating material and a base made of heat-conducting material, the material of the cylinder includes at least one of polytetrafluoroethylene and polystyrene, and the material of the base includes one or more of copper, aluminum and other metals.

6. The preparation method according to claim 1, characterized in that, The temperature of the low-temperature freezing treatment in step (2) is -20 ℃ to -196 ℃, the method of low-temperature freezing treatment is mechanical refrigeration equipment freezing or cryogenic medium freezing, and the time of low-temperature freezing treatment is at least 2 min; Preferably, when mechanical refrigeration equipment is used for freezing, the freezing temperature is -20 ℃ to -80 ℃ and the freezing time is not less than 1 hour; when cryogenic medium is used for freezing, the freezing temperature is -81 ℃ to -196 ℃ and the freezing time is more than 2 minutes.

7. The preparation method according to claim 1, characterized in that, The calcium ion-containing solution in step (3) is selected from anhydrous ethanol solution of calcium chloride or acetone solution of calcium chloride. The molar concentration of calcium ions in the calcium ion-containing solution is 0.05 M - 0.20 M. The volume ratio of cryogel to calcium ion-containing solution is selected as 1:(10-50). The temperature for the simultaneous crosslinking and in-situ mineralization reaction is selected as -10 ℃ to -20 ℃, and the reaction time is 2 h - 72 h.

8. The preparation method according to claim 1, characterized in that, The washing, dehydration, and solvent replacement treatment in step (4) includes: first, washing and dehydrating the mineralized composite gel once or multiple times with a washing solvent, with each washing time not less than 20 min; then, soaking and replacing the washed mineralized composite gel once or multiple times with a low surface tension solvent, with each replacement time not less than 1 h; preferably, the washing solvent includes at least one of anhydrous ethanol, acetone, and isopropanol; the replacement solvent includes at least one of tert-butanol, cyclohexane, and n-hexane; and the atmospheric pressure drying is carried out by air drying at 25℃-80℃.

9. A biomimetic mineralized porous aerogel, characterized in that, The biomimetic mineralized porous aerogel is obtained by the preparation method described in any one of claims 1-8.

10. The application of the biomimetic mineralized porous aerogel according to claim 9 in the preparation of bone tissue engineering scaffolds, wound repair dressings, heavy metal ion adsorbents or anion adsorbents.

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