Piezoelectric enhanced poly-L-lactic acid fiber membrane and preparation method thereof
By using electrospinning and heat treatment on a metal substrate, the crystal structure of PLLA fiber membranes was transformed from α-crystal to α'-crystal, solving the problem of insufficient piezoelectric properties of PLLA. This resulted in a significant improvement in piezoelectric properties while maintaining the material's flexibility, making it suitable for biomedical applications.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-28
- Publication Date
- 2026-03-31
AI Technical Summary
The existing PLLA has weak piezoelectric properties, and conventional methods are insufficient to significantly improve its piezoelectric response without affecting the material's flexibility and porous structure.
PLLA fiber membranes prepared by electrospinning are brought into contact with a metal substrate and subjected to heat treatment, which induces the crystal structure to change from α crystal form to α' crystal form with high net polarization intensity.
It significantly improves the piezoelectric properties of PLLA fiber membranes while maintaining their flexibility and biocompatibility, making them suitable for flexible wearable electronics and implantable biomedical applications.
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Figure CN121760133A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of biomedical materials technology, specifically relating to a piezoelectrically reinforced poly-L-lactic acid fiber membrane and its preparation method. Background Technology
[0002] Poly(L-lactic acid) (PLLA) is an important biodegradable aliphatic polyester widely used in biomedical fields such as surgical sutures, tissue engineering scaffolds, and drug delivery systems due to its good biocompatibility, processability, and tunable degradation rate. In addition to these properties, PLLA exhibits intrinsic piezoelectricity due to the non-centrosymmetric arrangement of carbonyl dipoles in its molecular chains, meaning it can generate charge under mechanical stress. This makes it promising for constructing self-powered sensors, energy harvesters, and bioelectronic devices. However, the piezoelectric properties of untreated PLLA are typically weak, severely limiting its practicality. The piezoelectric response of PLLA mainly stems from the degree of orientation of molecular dipoles in its crystalline regions. During conventional processing (such as melt molding or solution casting) and heat treatment, PLLA tends to form a thermodynamically stable α-crystalline form. In this α-crystalline form, the molecular chains are stacked in an antiparallel manner, causing the dipole moments on adjacent chains to partially cancel each other out, thereby reducing the net polarization intensity and macroscopic piezoelectric output. Therefore, PLLA films or fibers prepared directly using conventional methods often have low piezoelectric coefficients, making it difficult to generate sufficiently strong electrical signals to meet the needs of many application scenarios.
[0003] To enhance the piezoelectric properties of PLLA, a common strategy is to combine high-voltage electric field polarization, i.e., applying a strong DC electric field near the material's glass transition temperature to attempt to orient the dipoles along the electric field direction. However, this method is difficult to operate on insulating polymer films, carries the risk of breakdown, and the polarization effect is difficult to achieve uniformly and maintain long-term in flexible, porous fiber structures. Another strategy is mechanical stretching, which enhances the piezoelectricity in a specific direction by orienting the molecular chains and crystalline regions along the stretching direction. However, single stretching treatment has limited effect on changing the polarity of the crystal structure and may sacrifice the material's flexibility or introduce anisotropy.
[0004] Therefore, developing a simple method to effectively control the crystal structure of PLLA, especially to induce the formation of crystal forms with higher net polarization intensity, thereby significantly improving its piezoelectric response without significantly affecting its bulk material properties (such as flexibility and degradability), has become an important and unresolved technical problem in this field. Summary of the Invention
[0005] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide a poly-L-lactic acid (PLLA) fiber membrane with significantly enhanced piezoelectric properties and a simple and efficient preparation method thereof. This invention utilizes a unique metal-substrate interface-induced heat treatment process to successfully modulate the crystal structure of PLLA from the relatively weak α-crystal form to a metastable α'-crystal form with higher net polarization intensity, thereby achieving an order-of-magnitude improvement in piezoelectric properties.
[0006] To achieve the above objectives, a specific embodiment of the present invention provides the following technical solution: In a first aspect, the present invention provides a method for preparing a piezoelectrically reinforced poly-L-lactic acid cellulose membrane, comprising the following steps: Provides poly-L-lactic acid fiber membranes manufactured by electrospinning; The poly-L-lactic acid cellulose membrane is brought into contact with a metal substrate and subjected to heat treatment to induce crystallization of the cellulose membrane under the interface of the metal substrate, thereby obtaining a piezoelectrically reinforced poly-L-lactic acid cellulose membrane with metastable α' crystal form.
[0007] In one or more embodiments of the present invention, the metal substrate is a single metal or multi-metal substrate such as aluminum, copper, iron, magnesium, tin, or titanium.
[0008] In one or more embodiments of the present invention, the metal substrate is an aluminum substrate with an oxide layer on its surface.
[0009] In one or more embodiments of the present invention, the temperature of the heat treatment is 65°C to 160°C.
[0010] In one or more embodiments of the present invention, the heat treatment time is from 2 hours to 20 hours.
[0011] Secondly, the present invention provides a piezoelectrically reinforced poly-L-lactic acid cellulose membrane prepared by the above-described preparation method, wherein the cellulose membrane has a metastable α' crystal form.
[0012] In one or more embodiments of the present invention, the X-ray diffraction pattern of the fiber membrane has a characteristic diffraction peak at 16.3°±0.5°.
[0013] Compared with the prior art, the present invention has the following beneficial effects: This invention creatively utilizes the interfacial induction effect of a metal substrate to successfully transform the crystal structure of PLLA from the low-net-polarity α-type to the high-net-polarity α'-type during heat treatment, fundamentally improving the intrinsic piezoelectricity of the material. The resulting fiber film exhibits a significantly enhanced piezoelectric coefficient and can generate a stronger electrical signal under mild external mechanical stimulation. The preparation method requires no complex and expensive equipment, nor does it require the application of a strong external electric field, thus avoiding the risk of electrical breakdown. The crystal structure can be oriented and effectively controlled simply by controlling the heat treatment conditions and selecting a specific substrate. The process has good repeatability, is safe to operate, and is easy to scale up for production.
[0014] This invention significantly improves piezoelectric properties while maintaining the inherent flexibility, porous structure, biodegradability, and biocompatibility of PLLA fiber membranes. The fiber membrane remains flexible, suitable for conformal contact with biological tissues, laying the material foundation for its application in flexible wearable electronics and implantable biomedicine. Furthermore, the enhanced piezoelectric fiber membrane can efficiently convert external mechanical energy into electrical energy, providing an ideal material platform for wireless, non-invasive energy transfer, self-powered sensing, and bioelectric signal modulation, demonstrating significant application value in smart implants, tissue engineering, and bioelectronic medicine. Attached Figure Description
[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0016] Figure 1 This is a schematic flowchart of a method for preparing a piezoelectrically reinforced poly(L-lactic acid) cellulose membrane according to an embodiment of the present invention. Detailed Implementation
[0017] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.
[0018] Example 1: Preparation and structural characterization of CPLLA piezoelectric fiber membranes This embodiment details the preparation process and key structural features of the piezoelectrically reinforced poly-L-lactic acid (PLLA) fiber membrane (CPLLA) of the present invention.
[0019] raw material: Poly-L-lactic acid (PLLA) has an intrinsic viscosity of approximately 2.0 dL / g.
[0020] Solvent: Isopropanol (analytical grade).
[0021] Aluminum plate (1 mm thick, with a naturally formed oxide layer on the surface, ultrasonically cleaned with ethanol and dried before use).
[0022] instrument: Electrospinning apparatus (including high voltage power supply, injection pump, and metal roller receiver).
[0023] Vacuum drying oven.
[0024] Polytetrafluoroethylene sheet (used to prepare a comparative example).
[0025] like Figure 1 As shown, the preparation method is as follows: (1) Preparation of spinning solution: Dissolve PLLA particles in isopropanol and stir magnetically in a 50°C water bath for 6 hours to prepare a uniform transparent spinning solution with a mass fraction of 8 wt%.
[0026] (2) Electrospinning: Inject the spinning solution into a 10 mL syringe and attach it to the syringe pump. Set the spinning parameters: feed rate 1.0 mL / h, applied voltage 15 kV, and distance from the needle (inner diameter 0.51 mm, 21 G) to the receiver 15 cm. The receiver is a metal roller wrapped in aluminum foil, and the roller speed is set to 1600 rpm. The ambient temperature is controlled at 25±2℃, and the relative humidity is controlled at 40±5%. Continue spinning for about 4 hours to collect a uniform PLLA fiber membrane with a certain orientation on the receiver.
[0027] (3) Substrate-guided heat treatment (restricted crystallization): The collected PLLA fiber film was carefully peeled off from the aluminum foil and then flatly sandwiched between two aluminum plates. It was placed in a vacuum drying oven and heat-treated at 105°C for 10 hours. After the heat treatment, the heating was turned off and the furnace was allowed to cool naturally to room temperature to obtain a crystallized PLLA fiber film, which is the piezoelectric reinforced product of the present invention, denoted as CPLLA.
[0028] (4) Preparation of control group: As a comparison, the PLLA fiber membrane prepared by electrospinning in the same way was placed on a polytetrafluoroethylene (PTFE) plate and subjected to conventional free thermal crystallization treatment under the same temperature and time conditions (105℃, 10 hours). The resulting sample was denoted as HT-PLLA.
[0029] Structural characterization and results: (1) Morphological observation: The fiber morphology was observed using a scanning electron microscope. The results showed that the CPLLA fibers after heat treatment on the aluminum substrate still maintained good continuity and orientation. The fiber surface was smooth and there was no obvious melting phenomenon. The average diameter was about 1.4 μm, which was not significantly different from the original PLLA fibers and HT-PLLA. This indicates that the method optimized the crystal structure without destroying the macroscopic morphology of the fibers.
[0030] (2) Crystal structure analysis: X-ray diffraction was used for testing. The results showed that the conventionally heat-treated HT-PLLA exhibited a sharp diffraction peak near 16.7°, which corresponds to the thermodynamically stable α crystal form (110 / 200 crystal plane). However, the CPLLA, after heat treatment guided by the aluminum substrate, showed a significant shift of its main diffraction peak to a lower angle, appearing at 16.3°, which is the characteristic diffraction peak of the metastable α' crystal form. This result conclusively proves that the interfacial interaction of the aluminum substrate effectively induced a fundamental change in the crystallization behavior of PLLA, successfully realizing the transformation from the low-piezoelectric α phase to the high-piezoelectric α' phase.
[0031] (3) Molecular chain conformation analysis: Fourier transform infrared spectroscopy was used for testing. The results showed that CPLLA has a molecular chain conformation at approximately 1758 cm⁻¹. -1 The peak shape of the carbonyl (C=O) stretching vibration at 1180-1080 cm⁻¹ undergoes a significant change, with an increased full width at half maximum (FWHM). Simultaneously, the peak shape changes noticeably in the 1180-1080 cm⁻¹ range. -1 Slight shifts and intensity changes were also observed in the COC skeletal vibration peaks within the range. These changes in spectral characteristics confirm that the conformation, interchain stacking, and dipole interactions of the CPLLA molecular chain have significantly changed compared to HT-PLLA (α crystal), which is consistent with the formation of the α' crystal form and its different molecular chain conformation, further corroborating the conclusions of XRD.
[0032] Piezoelectric property characterization: (1) Piezoelectric microscopy (PFM) test: The local piezoelectric response of the material was directly observed by PFM. The PFM amplitude and phase responses of HT-PLLA were weak and non-uniform, indicating that its piezoelectricity was weak and its polarization direction was disordered. In contrast, CPLLA showed strong and uniform amplitude and phase response signals, indicating that it had significantly enhanced and directional macroscopic piezoelectric polarization.
[0033] (2) Effective piezoelectric coefficient measurement: PFM was used to quantitatively test the sample. The results showed that the effective piezoelectric coefficient of HT-PLLA was only about 12 pm V. -1 The CPLLA fiber membrane prepared by this invention has an effective piezoelectric coefficient as high as approximately 44 pm V. -1This represents an improvement of nearly three times. This quantitatively demonstrates that the α'-crystalline PLLA fiber membrane obtained by the method of this invention possesses extremely superior piezoelectric output performance.
[0034] Example 2: Effects of different metal substrates This embodiment explores the influence of different metal substrates on the induced formation of α' crystal form and piezoelectric properties.
[0035] The preparation process is the same as in Example 1, except that the aluminum plate in step (3) is replaced with a clean copper plate, a titanium plate, and a polytetrafluoroethylene (PTFE) plate as a comparative example.
[0036] All heat treatment conditions remained consistent: 105°C for 10 hours.
[0037] XRD analysis revealed that the PLLA fiber membranes heat-treated with copper and titanium plates also exhibited a main peak around 16.3°, indicating successful induction of the α' crystal form. The sample treated with PTFE plates showed a main peak at 16.7°, representing the α crystal form. PFM and d 33 Tests showed that the piezoelectric properties of copper-based and titanium-based induced samples were significantly higher than those of PTFE-based samples. Although slightly lower than the optimal alumina substrate, they still exhibited a significant piezoelectric enhancement effect. This indicates that various metal substrates have a certain interface-induced effect, with the aluminum substrate with a natural oxide layer showing the best effect.
[0038] Example 3: Effect of heat treatment temperature This embodiment explores the effect of heat treatment temperature on crystal structure and piezoelectric properties.
[0039] The preparation process is the same as in Example 1, except that the heat treatment temperature in step (3) is changed to 95℃, 105℃ and 115℃ respectively, and the time is fixed at 10 hours. The substrate is aluminum plate.
[0040] XRD results showed that samples treated at 95℃ and 105℃ successfully induced a crystal structure dominated by the α' crystal form, with the main peak at ~16.3°. The sample treated at 115℃ showed a tendency for its diffraction peaks to shift towards the higher-angle α crystal direction and exhibited double peaks, indicating that at this higher temperature, the α' crystal form tends to transform into the more stable α crystal form. 33 Tests showed that the sample treated at 105℃ had the highest piezoelectric coefficient, approximately 44 pm V. -1 The next best result was the sample treated at 95℃, with a concentration of approximately 35 pm V. -1 The sample treated at 115℃ showed a decrease, approximately 28 pm V. -1 This indicates that 95°C to 115°C is an effective temperature window, with 105°C being the preferred temperature range for obtaining the optimal α' crystal content and piezoelectric properties.
[0041] It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this disclosure. No reference numerals in the claims should be construed as limiting the scope of the claims.
[0042] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.
Claims
1. A method for preparing a piezoelectric enhanced poly-L-lactic acid fiber film, characterized by, The method comprises the following steps: providing a poly-L-lactic acid fiber film prepared by electrospinning; contacting the poly-L-lactic acid fiber film with a metal substrate and performing heat treatment, so that the fiber film is induced to crystallize at the interface of the metal substrate, thereby obtaining a piezoelectric enhanced poly-L-lactic acid fiber film with a metastable α' crystal form.
2. The method for preparing the piezoelectrically reinforced poly-L-lactic acid cellulose membrane according to claim 1, characterized in that, The metal substrate is a single metal substrate or a multi-metal substrate.
3. The method for preparing the piezoelectrically reinforced poly-L-lactic acid cellulose membrane according to claim 2, characterized in that, The metal substrate is an aluminum substrate with an oxidation layer on the surface.
4. The method for preparing the piezoelectrically reinforced poly-L-lactic acid cellulose membrane according to claim 1, characterized in that, The temperature of the heat treatment is 65-160°C.
5. The method for preparing the piezoelectrically reinforced poly-L-lactic acid cellulose membrane according to claim 1, characterized in that, The time of the heat treatment is 2-20 hours.
6. A piezoelectric enhanced poly-L-lactic acid fiber film prepared by the production method according to any one of claims 1 to 7, characterized by, The fiber film has a metastable α' crystal form.
7. The piezoelectric enhanced poly-L-lactic acid fiber film according to claim 8, wherein, The X-ray diffraction pattern of the fiber film has a characteristic diffraction peak at 16.3°±0.5°.