Low-frequency response degradable self-reinforced piezoelectric composite material and preparation method thereof

Abstract

The invention relates to the technical field of high polymer materials, in particular to a low-frequency response degradable self-reinforced piezoelectric composite material and a preparation method thereof. The self-reinforced piezoelectric composite material is prepared from the following components: stereocomplex polylactic acid and hydroxyapatite, the content of the hydroxyapatite is 5-30 wt% of the content of the stereocomplex polylactic acid; the low-frequency response degradable self-reinforced piezoelectric composite material has a mesoporous structure. The crystal of the degradable self-reinforced piezoelectric composite material with low-frequency response is a 100% stereocomplex crystal, and has excellent piezoelectric property.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a low-frequency response degradable self-reinforced piezoelectric composite material and its preparation method. Background Technology

[0002] Existing low-frequency response biodegradable self-reinforced piezoelectric composites lack biodegradability in applications in dental materials and bioengineering, and their biosafety requires further systematic verification. Some natural molecules, such as collagen, amino acids, and cellulose, have also been shown to possess piezoelectricity and exhibit good biocompatibility and biodegradability; however, these materials have low piezoelectric activity, and their application research is still in its early stages. The carbonyl group "C=O" in the L-polylactic acid (PLLA) molecular chain can act as a dipole. When the molecule is deformed under mechanical stress, the centers of positive and negative charges shift, thereby generating a piezoelectric potential. Furthermore, PLLA has good biocompatibility and biodegradability and has been approved for biomedical applications by the Food and Drug Administration (FDA) of several countries. Current literature reports the use of piezoelectric PLLA for bone defect repair and demonstrates good bone regeneration effects; however, PLLA's piezoelectricity is relatively weak, requiring high-intensity ultrasound excitation or doping with non-degradable piezoelectric materials such as barium titanate to enhance the piezoelectric response. In addition, biosafe piezoelectric materials, after processing, are expected to be used as fillers for acrylic denture base resins in 3D printed dental prostheses. The monomer-polymer conversion rate can be improved through the thermal effect and inverse piezoelectric effect generated by microwave post-processing, thereby enhancing the mechanical strength and biocompatibility of the dental prosthesis base resin. Summary of the Invention

[0003] In view of the shortcomings of the prior art, the purpose of this invention is to provide a low-frequency response degradable self-reinforced piezoelectric composite material and its preparation method, aiming to improve the piezoelectricity of the low-frequency response degradable self-reinforced piezoelectric composite material.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: The first aspect of the present invention provides a low-frequency response degradable self-reinforced piezoelectric composite material, comprising a rough surface and a smooth surface; the components of the low-frequency response degradable self-reinforced piezoelectric composite material include: stereocomposite polylactic acid and hydroxyapatite; the content of hydroxyapatite is 5-30 wt% of stereocomposite polylactic acid; the low-frequency response degradable self-reinforced piezoelectric composite material has a mesoporous structure.

[0005] The low-frequency response biodegradable self-reinforced piezoelectric composite material, wherein the raw materials for preparing the stereocomposite polylactic acid include L-polylactic acid and D-polylactic acid.

[0006] The low-frequency response biodegradable self-reinforced piezoelectric composite material, wherein the mass ratio of L-polylactic acid to D-polylactic acid is 1:1.

[0007] A second aspect of the present invention provides a method for preparing a low-frequency response degradable self-reinforced piezoelectric composite material, which is used to prepare the low-frequency response degradable self-reinforced piezoelectric composite material as described above, comprising the following steps: S1. Dissolve L-polylactic acid and D-polylactic acid in solvents respectively to obtain PLLA solution and PDLA solution; S2. Mix the PLLA solution and PDLA solution evenly, add hydroxyapatite and PEG, and stir until fully mixed; S3. The mixture is poured into a container and subjected to temperature-induced phase separation at 35°C; S4. Immerse the material obtained after temperature-induced phase separation in deionized water for non-solvent-induced phase separation. Soak and wash thoroughly to remove PEG and leave mesoporous structures on the material. S5. Dry the material at 60°C to obtain the low-frequency response degradable self-reinforced piezoelectric composite material.

[0008] The method for preparing the low-frequency response degradable self-reinforced piezoelectric composite material, wherein the amount of PEG is 40 wt% of the stereocomposite polylactic acid.

[0009] The method for preparing the low-frequency response degradable self-reinforced piezoelectric composite material, wherein the concentrations of the PLLA solution and the PDLA solution are 10 g / 100 mL.

[0010] The method for preparing the low-frequency response degradable self-reinforced piezoelectric composite material, wherein the solvent is selected from dichloromethane.

[0011] The method for preparing the low-frequency response degradable self-reinforced piezoelectric composite material, wherein in step S2, hydroxyapatite and PEG are added and stirred for 1-4 hours.

[0012] Beneficial Effects: This invention provides a low-frequency response degradable self-reinforced piezoelectric composite material. The crystals of this low-frequency response degradable self-reinforced piezoelectric composite material contain 100% stereocomposite crystals, exhibiting superior piezoelectric properties and generating electrical signals even under low-frequency stimulation. Furthermore, the low-frequency response degradable self-reinforced piezoelectric composite material of this invention retains a strong piezoelectric signal after degradation. The material possesses dual-sided characteristics; the smooth surface acts as a barrier, while the rough surface promotes biological effects.

[0013] The present invention also provides a method for preparing a low-frequency response biodegradable self-reinforced piezoelectric composite material. The method uses a synergistic phase separation method to obtain a low-frequency response biodegradable self-reinforced piezoelectric composite material in which the content of stereocomposite crystals reaches 100%, thereby ensuring superior piezoelectric performance. Attached Figure Description

[0014] Figure 1 The crystallinity of the material after stirring under different conditions.

[0015] Figure 2 This is the result of DSC analysis.

[0016] Figure 3 This is an XRD pattern.

[0017] Figure 4 The FTIR spectrum is for the 1700–1800 Hz band.

[0018] Figure 5 The FTIR spectrum is for the 2820–3050 GHz band.

[0019] Figure 6 The FTIR spectrum is for the 890–950 GHz band.

[0020] Figure 7 This is a schematic diagram of SEM (10000x).

[0021] Figure 8 For surface elemental content analysis.

[0022] Figure 9 This is the result of the open-circuit voltage test.

[0023] Figure 10 The piezoelectric output response results of the material under different frequency stimuli are shown.

[0024] Figure 11 The piezoelectric output response results of scPLA@10%HA at different frequencies.

[0025] Figure 12 The degradation rate of the material after 12 weeks of degradation.

[0026] Figure 13 This refers to the piezoelectric output of the material under low-frequency stimulation after degradation.

[0027] Figure 14 Pore ​​size distribution curves for different groups of materials. Detailed Implementation

[0028] This invention provides a low-frequency response, biodegradable, self-reinforced piezoelectric composite material and its preparation method. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0029] This invention provides a low-frequency response biodegradable self-reinforced piezoelectric composite material, comprising a rough surface and a smooth surface; the components of the low-frequency response biodegradable self-reinforced piezoelectric composite material include: stereocomposite polylactic acid and hydroxyapatite; the content of hydroxyapatite is 5-30 wt% of stereocomposite polylactic acid; the low-frequency response biodegradable self-reinforced piezoelectric composite material has a mesoporous structure. Stereocomposite polylactic acid has better piezoelectric properties than pure L-polylactic acid. Simultaneously, by incorporating an appropriate amount of hydroxyapatite, the crystallinity of the stereocomposite crystal can be increased, further improving the piezoelectric properties of the material.

[0030] Furthermore, the rough surface of the low-frequency response degradable self-reinforced piezoelectric composite material of this invention has more hydroxyapatite (HA) deposition, which promotes biological effects, while the smooth surface has a barrier function. EDS analysis shows that the Ca and P content of the rough surface is significantly higher than that of the smooth surface, indicating that HA tends to accumulate on the rough surface during phase separation. This selective distribution may further promote the specific response of osteoblasts on the rough surface.

[0031] The porous structure of the material is crucial to its biological function. SEM results ( Figure 7 The low-frequency response biodegradable self-reinforced piezoelectric composite material exhibits a unique asymmetric pore structure: dense, smooth surfaces coexist with porous, rough surfaces. This structure originates from the synergistic effect of temperature-induced and solvent-inducible phase separation: during SC crystal formation, strong hydrogen bonding promotes rapid enrichment of the surface polymer, forming a dense skin layer; as phase separation proceeds, the change in the lower polymer concentration gradient leads to a gradual increase in pore size, ultimately forming a hierarchical pore structure.

[0032] Mercury intrusion porosimetry data further confirmed that the low-frequency response degradable self-reinforced piezoelectric composite material of the present invention possesses superior porosity characteristics, with significantly improved cumulative pore volume, specific surface area, and porosity. More importantly, the low-frequency response degradable self-reinforced piezoelectric composite material exhibits a multi-level pore size distribution ranging from 10 nm to 1000 nm. This structure is particularly beneficial for osteoblast behavior regulation: micropores (<10 nm) promote protein adsorption; mesopores (10-100 nm) enhance cell adhesion; and macropores (>100 nm) provide channels for blood vessel ingrowth.

[0033] Specifically, the stereocomposite polylactic acid is a stereocrystalline composite of L-polylactic acid and D-polylactic acid.

[0034] A second aspect of the present invention provides a method for preparing a low-frequency response degradable self-reinforced piezoelectric composite material, which is used to prepare the low-frequency response degradable self-reinforced piezoelectric composite material as described above, comprising the following steps: S1. Dissolve L-polylactic acid and D-polylactic acid in solvents respectively to obtain PLLA solution and PDLA solution; S2. Mix the PLLA solution and PDLA solution evenly, add hydroxyapatite and PEG, and stir until fully mixed; the PEG is used to adjust viscosity and create pores; S3. The mixture is poured into a container and subjected to temperature-induced phase separation at 35°C; S4. Immerse the material obtained after temperature-induced phase separation in deionized water for non-solvent-induced phase separation. Soak and wash thoroughly to remove PEG and leave mesoporous structures on the material. S5. Dry the material at 60°C to obtain the low-frequency response degradable self-reinforced piezoelectric composite material.

[0035] This invention discloses a method for preparing a low-frequency response biodegradable self-reinforced piezoelectric composite material. After mixing PLLA solution, PDLA solution, hydroxyapatite, and PEG, a temperature-induced phase separation is first performed. As the solvent continues to evaporate at 35°C, the overall polymer concentration of the solution continuously increases, and phase separation begins. Then, the obtained material is immersed in deionized water for non-solvent-induced phase separation. During phase separation, the surface solvent rapidly diffuses, leading to a surge in polymer concentration and the formation of a dense layer. Meanwhile, the internal solvent exchange rate slows down, reducing the phase separation rate and forming a porous sublayer with larger pore sizes. Hydrogen bonds between PLLA and PDLA enhance interchain interactions, accelerating surface polymer enrichment and forming a denser skin layer. Simultaneously, hydrogen bonds may also restrict the free movement of polymer chains during phase separation, leading to rapid surface solidification and further intensifying the formation of asymmetric structures. Finally, the material is thoroughly soaked and washed to remove PEG, leaving a mesoporous structure. After drying, the low-frequency response biodegradable self-reinforced piezoelectric composite material is obtained. The low-frequency response degradable self-reinforced piezoelectric composite material prepared by this method has 100% stereocomposite crystals (SC crystals).

[0036] The following examples further illustrate the present invention.

[0037] Experiment 1 By adding different amounts of HA and different stirring times after addition, the effect of HA addition on the formation of SC crystals in PLA was preliminarily explored, including the following steps: Step A1. Dissolve PLLA and PDLA separately in dichloromethane (10g / 100mL) and stir overnight at room temperature to ensure complete dissolution; then take equal amounts of PLLA and PDLA solutions, mix them, and stir overnight at room temperature to ensure complete mixing and formation of hydrogen bonds. Step A2. Then, according to Table 1, different amounts of hydroxyapatite (HA) were added to the above solution to prepare different groups of materials. After adding HA, the mixture was stirred continuously (1h, 2h or 4h), and an appropriate amount of the mixed solution was taken to test its crystallinity and compared with the traditional solution method.

[0038] Table 1

[0039] The traditional solution-based preparation method, referring to the paper "Study on the Influence of Ordered Mixing of Molecular Chains on the Melt Stability of Stereoscopic Polylactic Acid Composites", Zhang Wei, Sichuan University, Master's Thesis, includes the following steps: First, PLLA and PDLA were dissolved separately in dichloromethane at room temperature. Then, equal volumes of PLLA and PDLA solutions (ensuring a 1:1 mass ratio of PLLA to PDLA) were taken and thoroughly mixed. The mixed solution was poured into excess methanol to obtain a flocculent precipitate. The precipitate was separated from the solution using vacuum filtration, and the precipitate was the prepared sample. Finally, the sample was naturally dried in a fume hood for 48 h and then vacuum dried in a 60°C oven for 24 h to remove residual solvent. The prepared sample had a SC crystallinity of only 10.6% and contained a large amount of HC crystals (accounting for 37.3%), with an overall low crystallinity.

[0040] like Figure 1 As shown, under appropriate concentrations and stirring times, the addition of HA can promote the formation of SC crystals in PLA. The highest SC crystallization, reaching 47.2%, was observed in the 10% HA group with stirring for 2 hours. Compared with the traditional solution method sample, which had the lowest SC crystallization at only 10.6%, the HC crystal content was significantly improved.

[0041] Experiment 2 The preparation of a low-frequency response degradable self-reinforced piezoelectric composite material includes the following steps: A1. Dissolve PLLA and PDLA separately in dichloromethane (10g / 100mL) and stir overnight at room temperature to ensure complete dissolution; then take equal amounts of PLLA and PDLA solutions, mix them, and stir overnight at room temperature to ensure complete mixing and formation of hydrogen bonds; A2. Then, according to Table 1, different amounts of hydroxyapatite (HA) were added to the above solution to prepare different groups of materials. After adding HA, the mixture was stirred for 2 hours and then a suitable amount of the mixed solution was taken for material preparation. A3. Take an appropriate amount of the above mixed solution, pour it into a glass dish, and then place it in a 35℃ oven for temperature-induced phase separation. After 5 minutes, immerse the material in deionized water for non-solvent-induced phase separation. At the same time, remove PEG through a thorough soaking and washing process, leaving a mesoporous structure. Place the prepared material in a 60℃ oven and dry for 8 hours to obtain low-frequency response degradable self-reinforced piezoelectric composite material samples PLLA, scPLA@0%HA, scPLA@5%HA, scPLA@10%HA, scPLA@15%HA, scPLA@20%HA, scPLA@25%HA, and scPLA@30%HA.

[0042] Test 1: Crystal Configuration Analysis The crystal configurations of the low-frequency response degradable self-reinforced piezoelectric composite materials PLLA, scPLA@0%HA, scPLA@5%HA, scPLA@10%HA, scPLA@15%HA, scPLA@20%HA, scPLA@25%HA, and scPLA@30%HA prepared in Experiment 2 were analyzed. The DSC analysis results are as follows: Figure 2 As shown, the XRD patterns of each group of materials are as follows: Figure 3 As shown.

[0043] DSC analysis showed that ( Figure 2 PLLA exhibits a single melting peak at approximately 172°C, which is attributed to the melting behavior of homogeneous crystals (HC crystals); while all scPLA materials show a melting peak that migrates significantly to the high-temperature region (approximately 222°C), confirming the formation of stereocomposite crystals (SC crystals).

[0044] XRD patterns ( Figure 3 Further supporting this conclusion: the diffraction peaks appearing at 12.1°, 20.9° and 24.0° (marked by red reference lines in the figure) correspond to the (110), (300 / 030) and (220) crystal planes of the SC crystal, respectively; while the diffraction peaks appearing near 16.8° and 18.9° (marked by gray reference lines) belong to the (200 / 110) and (203) crystal planes of the HC crystal.

[0045] The above results collectively indicate that HC crystals are formed in the PLLA samples, while SC crystals are the main crystal structure in the scPLA group. Among them, the samples with low concentrations of HA (0%, 5%, 10%) only show the characteristic peaks of the (110), (300 / 030), and (220) crystal planes corresponding to SC crystals at 12.1°, 20.9°, and 24.0°, respectively, and 100% SC crystal polylactic acid was obtained.

[0046] Test 2: FTIR spectral analysis The hydrogen bonding interactions and crystal structures of the low-frequency response biodegradable self-reinforced piezoelectric composite materials PLLA, scPLA@0%HA, scPLA@5%HA, scPLA@10%HA, scPLA@15%HA, scPLA@20%HA, scPLA@25%HA, and scPLA@30%HA, prepared in Experiment II, were analyzed by FTIR spectroscopy. The results are as follows: Figures 4-6 As shown.

[0047] In scPLA, the main side groups of PLLA and PDLA molecular chains are –CH3 and C=O, respectively. The hydrogen atoms on the –CH3 group and the oxygen atoms in the C=O group can form intermolecular hydrogen bonds, and this interaction significantly enhances the overall properties of scPLA. To further understand the mechanism of enhanced orderliness in PLLA / PDLA molecular chains, this study used an FTIR transmission method to analyze the formation and changes of hydrogen bonds in scPLA samples.

[0048] The formation of hydrogen bonds can usually be identified by the frequency shifts and intensity variations of characteristic absorption peaks in infrared spectra. These variations reflect the type and strength of the hydrogen bonds. In the FTIR spectrum, the peak at 1745 cm⁻¹... -1 The absorption peak at this position is attributed to the C=O stretching vibration. The scPLA sample shows a significant shift at this peak position, indicating the presence of C=O. H-type hydrogen bonding. Furthermore, in the CH stretching vibration region (2800-3000 cm⁻¹). -1 Corresponding changes were also observed: the scPLA group was located at 2995 cm. -1 (CH3 asymmetric stretching) and 2944 cm -1 The absorption peaks of (CH2 symmetric stretching) were red-shifted to 2993 cm⁻¹. -1 and 2942cm -1 This further confirms CH The formation of O=C hydrogen bonds. The above results indicate that homogeneous blending of PLLA and PDLA at the molecular level promotes the formation of highly ordered chain structures, increases hydrogen bond density, and thus causes a red shift of the characteristic absorption peak. Figure 4 and Figure 5 ).

[0049] In addition, such as Figure 6 As shown, the FTIR spectrum of the scPLA sample at 908 cm⁻¹ 1 An absorption peak appears at a certain point, which is identified as a characteristic signal of the 31-helix conformation, indicating the formation of an asymmetric β-type crystal structure, namely a stereocomplex crystal (SC crystal).

[0050] Test 3: Characterization of Surface Morphology and Elemental Composition The surface morphology of the low-frequency response degradable self-reinforced piezoelectric composite material was observed by SEM, and the elemental composition of the material surface was analyzed by energy dispersive spectroscopy (EDS).

[0051] SEM results show ( Figure 7 The scPLA material exhibits a distinctly asymmetric porous structure, while both surfaces of the pure PLA group show a relatively dense morphology. This structural difference mainly stems from the strong hydrogen bonding between the PLLA and PDLA molecular chains during sc crystal formation, which promotes rapid enrichment of the surface polymer and facilitates the rapid diffusion of the surface solvent into the non-solvent, thus forming a dense epidermal layer. Over time, PLLA and PDLA undergo phase separation, the hydrogen bonding gradually weakens, leading to a decrease in the concentration of the lower polymer layer, ultimately forming a porous sublayer structure with a larger pore size. In contrast, pure PLA, lacking this type of hydrogen-bonded phase separation behavior, forms a relatively uniform dense structure.

[0052] In addition, energy dispersive spectroscopy (EDS) results showed that ( Figure 8 ), Figure 8 a represents the surface Ga content analysis of each group of materials. Figure 8 b represents the surface P content analysis of each group of materials. Figure 8 c represents the Ga / P surface analysis of each group of materials. Figure 8 d represents the performance spectrum of the scPLA@15%HA group. From... Figure 8 The results show that the calcium (Ca) and phosphorus (P) content on the rough surface of the material is significantly higher than that on the smooth surface. This is because the hydrogen bonds between the PLLA and PDLA molecular chains enhance the inter-chain interactions of the polymers, accelerate the enrichment of surface polymers, and form a denser skin structure. This promotes the selective deposition of hydroxyapatite (HA) in the rough layer, resulting in rough and smooth surfaces on both sides of the scPLA material.

[0053] Test 4: Open Circuit Voltage Test The open-circuit voltage performance of the low-frequency response degradable self-reinforced piezoelectric composite materials PLLA, scPLA@0%HA, scPLA@5%HA, scPLA@10%HA, scPLA@15%HA, scPLA@20%HA, scPLA@25%HA, and scPLA@30%HA prepared in Experiment 2 under cyclic loading conditions was tested, and the results are as follows: Figure 9 .

[0054] The test results show that no significant electrical signal was detected in the pure PLLA low-frequency response biodegradable self-reinforced piezoelectric composite material, indicating a weak piezoelectric response. This is mainly attributed to the lack of a stereocomposite (SC) crystal structure, resulting in limited piezoelectric polarization capability. In contrast, the output voltage of the scPLA group was significantly improved, fully demonstrating the key role of the stereocomposite crystal in enhancing the piezoelectric effect. Notably, the piezoelectric performance changed further after the introduction of HA. Among them, the scPLA@10%HA group exhibited the best piezoelectric output, with an open-circuit voltage as high as 10.8V, indicating that the incorporation of an appropriate amount of HA helps to promote piezoelectric performance. However, when the HA content continued to increase, the output voltage decreased, indicating that excessive HA may lead to changes in material structure or a decrease in interfacial compatibility, thereby weakening the piezoelectric effect. This phenomenon is consistent with the trend of the SC crystallization of the material first increasing and then decreasing after adding different amounts of HA.

[0055] Test 5: Piezoelectric response under low-frequency stimulation Figure 10 The piezoelectric output responses of each group of materials under different frequency stimuli are shown in Figure 1. Here, a represents the piezoelectric response under 25Hz stimulation; b represents the piezoelectric response under 50Hz stimulation; c represents the piezoelectric response under 75Hz stimulation; and d represents the piezoelectric response under 100Hz stimulation.

[0056] from Figure 10 The results show that the piezoelectric output response of the material varies significantly under mechanical stimulation at different frequencies: the output is weak at 25 Hz and no obvious current peak is observed; when the frequency is increased to 50 Hz, a clear piezoelectric current signal appears; and when the frequency is further increased to 75 Hz and 100 Hz, the current signal strength increases accordingly.

[0057] Figure 11 The piezoelectric output response of the scPLA@10%HA group at different frequencies was demonstrated. Although high-frequency stimulation can induce stronger electrical signals, 50Hz can produce stable and effective piezoelectric output, and this frequency is far from the inherent resonant frequency range of major human organs (usually 3-10 Hz), which may have better biocompatibility. Therefore, to achieve a balance between effectiveness and biocompatibility, 50Hz was chosen as the stimulation parameter for subsequent cell experiments.

[0058] Test 6: In vitro degradation test Materials from all experimental groups were uniformly cut to a size of 2cm × 2cm, and their initial weight was recorded. Each sample was then placed in a centrifuge tube containing 10mL of PBS solution and immersed in a shaker at 37℃ and 200rpm. The PBS solution was changed weekly. At week 12, samples were taken and dried in a 37℃ oven until constant weight, and the sample weight at each time point was measured.

[0059] from Figure 12 The results show that after 12 weeks of in vitro degradation, no significant difference was observed in the degradation rate of each group of materials, with the degradation rate being around 10%.

[0060] Test 7: Piezoelectric output under low-frequency stimulation after degradation After 4, 8, and 12 weeks of in vitro degradation, the piezoelectric output of each group of low-frequency response degradable self-reinforced piezoelectric composite material samples prepared in Experiment 2 was tested under low-frequency mechanical stimulation (50 Hz). Figure 13 The piezoelectric output results under low-frequency stimulation after degradation are shown in Figure 1. a represents the piezoelectric output results after 4 weeks of degradation; b represents the piezoelectric output results after 8 weeks of degradation; c represents the piezoelectric output results after 12 weeks of degradation; and d represents the piezoelectric output results of the scPLA@10%HA low-frequency response degradable self-reinforced piezoelectric composite material at different degradation times.

[0061] The results showed that the material still exhibited significant electrical signal output after 4, 8, and 12 weeks of in vitro degradation. The scPLA@10%HA group showed even stronger electrical signal output at longer degradation times (12 weeks). This may be because the degradation of scPLA occurs first in the non-crystalline amorphous region, while the degradation of SC crystals is slower. This biodegradable material can provide stable piezoelectric output at all stages of bone defect repair, thereby promoting bone defect repair. This material can also be used as a filler for 3D-printed acrylic denture base resin after liquid nitrogen embrittlement. Through microwave post-treatment, the piezoelectric composite material can respond to the alternating electromagnetic field in the microwave, increasing the molecular kinetic energy in the polymerization system through thermal and inverse piezoelectric effects, thereby increasing the monomer-polymer conversion rate and improving the strength and biocompatibility of the denture base resin.

[0062] Test 8: Orifice Diameter Detection Using the Pump Pressure Method Table 2

[0063] From Table 2 and Figure 14 The results show that the scPLA group has superior pore characteristics, with significantly higher cumulative pore volume, specific surface area, and porosity than the PLA group. More importantly, the scPLA group exhibits a multi-level pore size distribution ranging from 10 nm to 1000 nm, a structure that is particularly beneficial for osteoblast behavior regulation: micropores (<10 nm) promote protein adsorption; mesopores (10-100 nm) enhance cell adhesion; and macropores (>100 nm) provide channels for blood vessel ingrowth.

[0064] It is understood that those skilled in the art can make equivalent substitutions or modifications to the technical solution and inventive concept of the present invention, and all such substitutions or modifications should fall within the protection scope of the appended claims.

Claims

1. A low frequency responsive degradable self-reinforced piezoelectric composite material, characterized in that, The components of the low-frequency response degradable self-reinforced piezoelectric composite material include stereocomplex polylactic acid and hydroxyapatite; the content of the hydroxyapatite is 5-30 wt% of the stereocomplex polylactic acid; and the low-frequency response degradable self-reinforced piezoelectric composite material has a mesoporous structure.

2. The low frequency responsive degradable self-reinforced piezoelectric composite of claim 1, wherein, The stereocomplex polylactic acid is prepared from L-polylactic acid and D-polylactic acid.

3. The low frequency responsive degradable self-reinforced piezoelectric composite of claim 2, wherein, The mass ratio of the L-polylactic acid to the D-polylactic acid is 1:

1.

4. The low frequency responsive degradable self-reinforced piezoelectric composite of claim 1, wherein, The content of the hydroxyapatite is 10 wt% of the stereocomplex polylactic acid.

5. A method for producing a low frequency responsive degradable self-reinforced piezoelectric composite material, characterized by, The method for preparing the low-frequency response degradable self-reinforced piezoelectric composite material as claimed in any one of claims 1-4 comprises the following steps: S1. dissolving the L-polylactic acid and the D-polylactic acid in a solvent respectively to obtain PLLA solution and PDLA solution; S2. mixing the PLLA solution and the PDLA solution uniformly, adding hydroxyapatite and PEG, and stirring until fully mixed; S3. casting the mixed solution into a container and performing temperature-induced phase separation at 35°C; S4. immersing the material obtained after the temperature-induced phase separation in deionized water to perform non-solvent-induced phase separation, fully immersing and washing with water to remove the PEG, so that the material is left with a mesoporous structure; S5. drying the material at 60°C to obtain the low-frequency response degradable self-reinforced piezoelectric composite material.

6. The method of claim 5, wherein the low frequency responsive degradable self- reinforcing piezoelectric composite is prepared by the steps of: The amount of the PEG is 40 wt% of the stereocomplex polylactic acid.

7. The method for preparing the low-frequency response degradable self-reinforced piezoelectric composite material according to claim 5, characterized in that, The concentration of the PLLA solution and the PDLA solution is 10 g / 100 mL.

8. The method for preparing the low-frequency response degradable self-reinforced piezoelectric composite material according to claim 5, characterized in that, The solvent is dichloromethane.

9. The method for preparing the low-frequency response degradable self-reinforced piezoelectric composite material according to claim 5, characterized in that, In S2, after adding the hydroxyapatite and the PEG, the stirring is performed for 1-4 h.

10. The method for preparing the low-frequency response degradable self-reinforced piezoelectric composite material according to claim 6, characterized in that, In S2, after adding the hydroxyapatite and the PEG, the stirring is performed for 2 h.

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