A peptide-based hydrogel modified crystallized polylactic acid fiber film piezoelectric composite material and a preparation method thereof

Abstract

The application discloses a kind of crystallization polylactic acid fiber film piezoelectric composite material based on peptide-based hydrogel modification and preparation method thereof.The composite film is with electrospinning preparation left-handed polylactic acid (PLLA) film as substrate, crystallization is induced by heat treatment to form crystallization polylactic acid film, Fmoc-diphenyl phenylalanine (FmocFF) molecule is introduced in situ on its surface and induced self-assembly to form gel structure, and FF-CPLLA composite film is obtained after freeze-drying.The composite film has uniform fiber structure, good mechanical ductility, moderate surface wettability and significantly enhanced piezoelectric performance, and can stably output electric signal under external ultrasonic stimulation.The application constructs functionalized piezoelectric composite system through non-covalent interaction, significantly improves piezoelectric response performance without destroying the substrate structure, and has simple preparation process and strong controllability, and is suitable for tissue repair, nerve regulation and biological medical piezoelectric device and other fields.

Description

Technical Field

[0001] This invention relates to the field of functional polymer materials and biomedical materials technology, specifically to a peptide-based hydrogel-modified crystallized polylactic acid piezoelectric composite film, its preparation method, and its applications. Background Technology

[0002] Piezoelectric materials can generate electrical signals in response to external mechanical stimuli, and have significant applications in tissue repair, neural modulation, and bioelectronic devices. Polylactic acid (PLLA) is widely used in biomedical materials research due to its good biocompatibility and biodegradability. However, under normal conditions, the molecular chain orientation of PLLA is disordered, resulting in limited piezoelectric response performance, which makes it difficult to meet the application requirements for highly efficient piezoelectric materials.

[0003] Crystalline polylactic acid (CPLLA) can be obtained by controlling the molecular chain orientation and crystal structure. Its crystallinity is improved and its structure is more ordered, which can exhibit certain piezoelectric properties and has application potential in flexible electronics and functional thin films. However, single CPLLA materials still have limitations in terms of electrical response intensity and functional expansion, and its surface hydrophobicity is not conducive to interaction with the biological environment.

[0004] Fmoc-diphenylalanine (FmocFF) is a short peptide molecule with self-assembly capabilities, capable of forming stable nanofiber hydrogel structures with good hydrophilicity and certain electrical and mechanical properties. Introducing FmocFF hydrogels onto the surface of CPLLA matrices holds promise for improving surface wettability while maintaining substrate structural stability, and for constructing composite functional material systems that combine piezoelectric response and biocompatibility.

[0005] Therefore, developing a structurally stable and performance-controllable functional material system composed of FmocFF and crystalline polylactic acid (PLA) to achieve effective construction of the composite structure is of great technical significance for expanding the application of organic piezoelectric materials in the fields of biomedicine and flexible electronics. Summary of the Invention

[0006] To address the shortcomings of existing crystalline polylactic acid (PLA) piezoelectric materials in terms of electrical response intensity, functional tunability, and surface hydrophilicity, this invention aims to provide a structurally stable and performance-controllable fiber membrane-hydrogel composite piezoelectric material. By introducing a self-assembling Fmoc-diphenylalanine hydrogel onto the surface of a crystalline PLA fiber membrane, the piezoelectric response performance and surface wettability of the material are enhanced without damaging the fiber membrane substrate structure, thereby expanding its applications in biomedical and flexible electronics fields.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a crystallized polylactic acid (PLA) cellulose membrane-hydrogel composite piezoelectric material, comprising a crystallized PLA cellulose membrane substrate and a Fmoc-diphenylalanine self-assembled hydrogel structure loaded on the surface of the cellulose membrane. The hydrogel is fixed to the surface of the cellulose membrane through non-covalent interactions such as hydrogen bonding and π–π stacking, forming a stable composite structure with the cellulose membrane.

[0009] This invention also provides a method for preparing the above-mentioned composite piezoelectric material, comprising the following steps:

[0010] (1) A polylactic acid fiber membrane was prepared by electrospinning, and the fiber membrane was heat-treated to obtain a crystallized polylactic acid fiber membrane.

[0011] (2) Fmoc-diphenylalanine was dissolved in an organic solvent and mixed with a salt-containing aqueous solution, and then dropped onto the surface of the crystallized L-polylactic acid fiber membrane to induce it to self-assemble in situ to form a hydrogel.

[0012] (3) The obtained composite system is dried to obtain a fiber membrane-hydrogel composite piezoelectric material.

[0013] Compared with the prior art, the present invention has at least the following beneficial effects:

[0014] (1) By combining hydrogel functionalization, the piezoelectric response performance of L-polylactic acid-based materials is effectively improved;

[0015] (2) The introduction of Fmoc-diphenylalanine hydrogel improves the wettability of the material surface, which is beneficial to the interaction between the material and the biological environment;

[0016] (3) The composite structure mainly relies on non-covalent interactions such as hydrogen bonds and π–π stacking to build up the structure, which maintains the flexibility and ductility of the material while ensuring structural stability;

[0017] (4) The preparation method is simple and mild, with good reproducibility and application potential. Attached Figure Description

[0018] Figure 1 SEM images of the composite films: (A) SEM image of FF gel; (B) SEM image of CPLLA film; (C) SEM image of FF-CPLLA film.

[0019] Figure 2 XRD patterns of PLLA and CPLLA

[0020] Figure 3 XPS spectra of FF gel, CPLLA film, and FF-CPLLA film

[0021] Figure 4 XPS core energy level spectra: (B) O 1s spectrum of FF; (B) O 1s spectrum of CPLLA; (C) O 1s spectrum of FF-CPLLA; (D) N 1s spectrum of FF; (E) N 1s spectrum of CPLLA; (F) N 1s spectrum of FF-CPLLA

[0022] Figure 5 Raman spectroscopy analysis of FF gel, CPLLA film, and FF-CPLLA film

[0023] Figure 6 Elongation at break of CPLLA film and FF-CPLLA film

[0024] Figure 7 Tensile strength of CPLLA film and FF-CPLLA film

[0025] Figure 8 Contact angles of FF gel, CPLLA film, and FF-CPLLA film

[0026] Figure 9 Piezoelectric microscopy (PFM) images of PLLA films: (A) AFM image of PLLA films; (B) PFM amplitude map of PLLA films; (C) PFM phase map of PLLA films; (D) AFM image of CPLLA films; (E) PFM amplitude map of CPLLA films; (F) PFM phase map of CPLLA films; (G) AFM image of FF gel; (H) PFM amplitude map of FF gel; (I) PFM phase map of FF gel; (J) AFM image of FF-CPLLA films; (K) PFM amplitude map of FF-CPLLA films; (L) PFM phase map of FF-CPLLA films.

[0027] Figure 10 Piezoelectric properties: (A) Amplitude curves and piezoelectric response phase curves of PLLA films; (B) Amplitude curves and piezoelectric response phase curves of CPLLA films; (C) Amplitude curves and piezoelectric response phase curves of FF gels; (D) Amplitude curves and piezoelectric response phase curves of FF-CPLLA films.

[0028] Figure 11 Voltage output of FF-CPLLA film under ultrasound in air, cerebrospinal fluid, and isolated rat skull. Detailed Implementation

[0029] Example 1: Preparation of FF-CPLLA composite piezoelectric thin film

[0030] (1) Preparation of PLLA film

[0031] Solid PLLA was dissolved in hexafluoroisopropanol and magnetically stirred at 20°C for 24 hours until completely dissolved, yielding a stock solution with a concentration of 100 mg / mL. 10 mL of the stock solution was loaded into a plastic syringe, connected to a passivated 20-gauge stainless steel needle (0.58 mm inner diameter), and mounted on a metering pump. Electrospinning parameters were as follows: solution flow rate 2 mL / h, distance between the spinneret and the grounded cylindrical collector 14.5 cm, collector surface wrapped with conductive aluminum foil, electric field strength 1.5 kV / cm, and collector rotation speed 100 r / min. The resulting PLLA film was vacuum dried for 24 hours to remove residual solvent.

[0032] (2) Preparation of CPLLA thin film

[0033] The film prepared in Example 1 (1) was placed in the constant temperature zone of a tube furnace and heated to 105°C at 5°C / min under nitrogen protection. The temperature was held for 600 minutes and then cooled to room temperature to obtain the CPLLA film.

[0034] (3) Preparation of FF-CPLLA composite film

[0035] FmocFF was dissolved in dimethyl sulfoxide (DMSO) to prepare a 100 mg / mL stock solution. Sodium chloride (NaCl) was dissolved in ultrapure water and ultrasonically dispersed to obtain a 0.63 mM aqueous solution. The FmocFF / DMSO stock solution and the NaCl aqueous solution were mixed at a volume ratio of 1:49, stirred thoroughly, and then uniformly drop-coated onto the surface of a CPLLA film (80 μL / cm²). The mixture was allowed to stand at room temperature for 1 hour to form a gel, and finally freeze-dried to obtain the FF-CPLLA composite film.

[0036] The morphology of FF gel, CPLLA fiber membrane, and FF-CPLLA composite film was observed using scanning electron microscopy. The results are as follows: Figure 1 FF gel exhibits a dense nanofiber network structure; CPLLA film exhibits a relatively uniform micron-scale fiber structure; while maintaining the original fiber continuity, the surface roughness of the FF-CPLLA composite film is significantly increased.

[0037] Test Example 1: XRD analysis of the material

[0038] X-ray diffraction was used to analyze the crystal structure of PLLA and CPLLA films. The results are as follows: Figure 2 Compared with PLLA film, CPLLA film shows obvious diffraction peak at about 16.4°, indicating that the crystallinity of the material is improved after heat treatment and the molecular chain orientation is more ordered, which provides a structural basis for the subsequent improvement of piezoelectric properties.

[0039] Test Example 2: XPS Verification of Materials

[0040] XPS global spectral analysis was performed on FF gel, CPLLA film, and FF-CPLLA composite film. Results are as follows: Figure 3 A significant nitrogen signal was observed in the composite film, with the nitrogen content increasing from 0.82% in the CPLLA film to 1.80%, confirming the successful loading of FmocFF hydrogel onto the CPLLA fiber membrane surface. Further analysis of the O 1s and N 1s core energy level spectra was conducted. The results are as follows... Figure 4 The characteristic peaks of C=O, C–O and CO–NH in the FF-CPLLA composite film showed slight chemical shifts compared to the single component, and the −NH3⁺ content increased from 19.16% in the FF gel to 26.54%, indicating that there are non-covalent interactions such as hydrogen bonding and π–π stacking between the FF hydrogel and the CPLLA fiber membrane.

[0041] Test Example 3: Raman Spectroscopy Analysis of Materials

[0042] The chemical structures of FF gel, CPLLA film, and FF-CPLLA composite film were analyzed using Raman spectroscopy. The results are as follows: Figure 5 The FF-CPLLA composite film retains both the amide I characteristic peak of FmocFF molecules and the C–H characteristic peak of CPLLA, indicating that the chemical structures of the two components were not damaged during the composite process.

[0043] Test Example 4: Mechanical Property Testing of Materials

[0044] Tensile tests were performed on CPLLA films and FF-CPLLA composite films to determine their elongation at break. The results are as follows: Figure 6 The elongation at break of the CPLLA film was approximately 85%, while that of the FF-CPLLA composite film increased to approximately 167%, indicating that the introduction of hydrogel significantly improved the material's ductility and toughness. Further testing of the tensile strength of the material yielded the following results: Figure 7 The tensile strength of the FF-CPLLA composite film shows an increasing trend compared to the CPLLA film, indicating that the composite structure improves ductility without significantly weakening the overall strength of the material.

[0045] Test Example 5: Surface wettability testing of the material

[0046] The surface wettability of FF gel, CPLLA film, and FF-CPLLA composite film was characterized by contact angle testing. The results are as follows: Figure 8 The CPLLA film surface exhibits strong hydrophobicity, while the contact angle of the composite film is significantly reduced after the introduction of FF hydrogel, indicating that the introduction of hydrogel effectively improves the hydrophilicity of the material surface, which is beneficial for its application in biological environments.

[0047] Test Example 6: Piezoelectric stress microscopy evidence of the material

[0048] The piezoelectric properties of PLLA films, CPLLA films, FF gels, and FF-CPLLA composite films were tested using piezoelectric response force microscopy. The results are as follows: Figure 9 The composite film exhibits typical piezoelectric response characteristics under an applied electric field. Atomic force microscopy (AFM) results show that the FF-CPLLA composite film possesses a uniform fibrous structure. Piezoelectric response force microscopy (PFM) amplitude maps reveal significant piezoelectric response signals in different regions of the FF-CPLLA composite film, with the response intensity varying with differences in microstructure, suggesting a certain degree of anisotropic piezoelectric behavior on the material surface. Simultaneously, the PFM phase map shows obvious brightness contrast, indicating phase contrast differences in different regions, reflecting variations in the internal polarization orientation of the material.

[0049] Test Example 7: Detection of Butterfly Amplitude Curve and Phase Diagram of Material

[0050] The piezoelectric response force microscopy test results are as follows Figure 10 The FF-CPLLA films exhibited a typical butterfly curve and a significant phase reversal, indicating excellent piezoelectric response. The piezoelectric response coefficient of the PLLA film was 8.32±0.88 pm / V, that of the CPLLA film increased to 27.24±2.04 pm / V, that of the FF gel was 26.73±2.6 pm / V, and that of the FF-CPLLA composite film was further improved to 34.10±5.48 pm / V. These results demonstrate that crystallization and hydrogel functionalization have a synergistic effect in improving piezoelectric properties.

[0051] Test Example 8: Electrical Signal Output Test of Materials under Ultrasonic Stimulation

[0052] At 1 MHz, 50% duty cycle, 0.3 W / cm 2 The FF-CPLLA composite film was placed in simulated environments of air, cerebrospinal fluid, and isolated rat skulls, and its voltage output performance was tested under ultrasonic stimulation. Results are as follows: Figure 11 In different media environments, the composite film can generate stable electrical signal output under ultrasonic stimulation, indicating that the material has good acoustic response piezoelectric properties and environmental adaptability, and is suitable for biomedical applications.

Claims

1. A crystalline polylactic acid piezoelectric composite film modified with peptide-based hydrogel, characterized in that, The composite film includes a crystallized polylactic acid (CPLLA) fiber film substrate and a Fmoc-diphenylalanine (FmocFF) self-assembled structure loaded on the surface of the substrate.

2. The composite film according to claim 1, characterized in that, The FmocFF undergoes in-situ self-assembly on the surface of the CPLLA in a saline aqueous solution environment to form a gel network structure, wherein the self-assembled peptide functional component is selected from diphenylalanine or its derivatives.

3. The composite film according to claim 2, characterized in that, The salt is sodium chloride, and the concentration of the sodium chloride solution is 0.1–5 mM.

4. The composite film according to claim 1, characterized in that, The FmocFF self-assembled structure forms a continuous or semi-continuous nanofiber network layer on the surface of CPLLA fibers.

5. A method for preparing a crystalline polylactic acid piezoelectric composite film modified with peptide-based hydrogel as described in any one of claims 1-4, characterized in that, Includes the following steps: (1) PLLA fiber films were prepared by electrospinning and heated to 90–130 °C at 3–10 °C / min under an inert atmosphere, held for 4–12 h and then cooled to room temperature to obtain crystallized polylactic acid (PLLA) films. (2) Fmoc-diphenylalanine was dissolved in dimethyl sulfoxide to form a stock solution, which was then mixed with a salt-containing aqueous solution at a volume ratio of 1:(30–80) and drop-coated onto the surface of the CPLLA film at a drop volume of 60–120 μL / cm². The solution was then allowed to stand at 20–30 °C for 0.5–3 h to form a hydrogel. (3) The obtained material is dried to obtain FF-CPLLA composite film.

6. The application of the composite film according to any one of claims 1–4 in biomedical piezoelectric materials, tissue repair materials or ultrasonic response electrical signal generators.

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