A method for preparing a porous bio-based chitin film using crayfish shells and application in a triboelectric nanogenerator

Abstract

This invention discloses a method for preparing porous bio-based chitin films using crayfish shells and their application in triboelectric nanogenerators, belonging to the field of implantable medical devices. Cleaned crayfish shells are sequentially treated with hydrochloric acid, sodium hydroxide solution, and poloxamer aqueous solution. These shells are then alternately placed in a mold with an ethyl cellulose acetone solution, and pressure-molded to prepare an ethyl cellulose-modified porous bio-based chitin film. A non-contact triboelectric nanogenerator system constructed externally generates and outputs triboelectric charges by utilizing the relative motion between in vivo and external triboelectric materials. This invention systematically examines key factors such as material composition, implantation structure, and operating frequency, providing systematic guidance for optimizing the application of triboelectric nanogenerator devices in different scenarios. The application potential of the prepared triboelectric nanogenerator device in flexible electronics, implantable medical monitoring, and other fields is expected to be significantly expanded.

Description

Technical Field

[0001] This invention belongs to the field of implantable medical devices, specifically relating to a method for preparing porous bio-based chitin films using crayfish shells and their application in triboelectric nanogenerators. Background Technology

[0002] The rapid development of implantable medical devices has led to significant breakthroughs in chronic disease management, long-term physiological signal monitoring, and tissue repair. However, a stable and continuous power supply remains a key challenge, limiting the clinical translation and functional expansion of these devices. Traditional implantable power sources (such as lithium polymer batteries) play a crucial role in clinical treatment. They provide continuous power to pacemakers to maintain a stable heart rhythm, power deep brain stimulators for treating Parkinson's disease movement disorders, and drive implantable blood glucose monitors and tumor-targeted therapy devices. Despite their significance, these devices still have significant limitations: limited battery capacity requires periodic surgical replacement, increasing patient discomfort and medical costs, and introducing risks of surgical complications such as infection and tissue damage. Furthermore, the bulky and rigid nature of chemical batteries hinders the requirements for minimally invasive implantation, while issues such as electrolyte leakage and electromagnetic interference severely restrict the miniaturization and long-term stable operation of these devices.

[0003] To address this challenge, self-powered technologies have attracted significant attention. Among them, triboelectric nanogenerators (TENGs), through the coupling effect of contact charging and electrostatic induction, convert the mechanical energy of the human body into electrical energy, providing a sustainable energy source for implantable devices and showing great promise. Multiple studies have confirmed the potential of TENGs for in vivo applications. However, the energy source of such devices is often uncontrollable and easily affected by fluctuations in the body's condition, making output performance difficult to predict. This invention proposes implanting triboelectric materials inside a biological body and constructing a non-contact triboelectric generator by coordinating the relative motion and structural configuration of external materials, thereby achieving controllable power generation from implanted biomaterials.

[0004] Meanwhile, the deep processing and utilization of agricultural waste has become a key issue in resource recycling and environmental protection. According to the "China Crayfish Industry Development Report (2025)," as of 2024, the crayfish farming area in China reached 30.5 million mu (approximately 2 million hectares), with a yield of 3.4476 million tons, representing average annual growth rates of 3.39% and 9.07%, respectively. Non-edible components (such as crayfish shells) account for over 50% of the total weight, generating nearly 1.72 million tons of solid shell waste annually, posing a significant challenge to urban waste management and environmental protection. Crayfish shells mainly contain calcium carbonate, protein, chitin, and trace impurities. Among these, chitin and its derivative chitosan serve as high-quality electron donor triboelectric materials, providing natural raw materials for triboelectric nanogenerators. Current processing techniques include acid-base treatment (decalcification and deproteinization to extract chitin) and environmentally friendly deep eutectic solvent treatment. The extracted chitin and chitosan have been applied in biomedicine, food industry, and environmental remediation, but their application in implantable triboelectric nanogenerators has not yet been studied. Summary of the Invention

[0005] To overcome the aforementioned deficiencies in existing technologies, this invention proposes a method for preparing porous bio-based chitin films using crayfish shells and their application in triboelectric nanogenerators. This invention uses crayfish shells as raw material and employs an acid-base treatment method to remove inorganic impurities and proteins, thereby preparing a porous bio-based chitin film. Subsequently, its barrier properties against body fluids are enhanced through sequential modification with poloxamer and ethyl cellulose (EC).

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing porous bio-based chitin films using crayfish shells involves treating cleaned crayfish shells sequentially with hydrochloric acid, sodium hydroxide solution, and poloxamer aqueous solution. Subsequently, the shells are alternately placed in a mold with an ethyl cellulose acetone solution, and the ethyl cellulose-modified porous bio-based chitin film is prepared by pressure molding.

[0008] As a preferred embodiment of the present invention, in the preparation method, the cleaned crayfish shells are first treated sequentially with 3% (volume ratio) hydrochloric acid, 5% (mass ratio) sodium hydroxide solution, and 5% (mass ratio) poloxamer aqueous solution. Subsequently, poloxamer-modified porous bio-based chitin films and 3% (mass ratio) ethyl cellulose (EC) acetone solution are alternately filled into a mold.

[0009] This invention also proposes the application of porous bio-based chitin films in triboelectric nanogenerators. A silver paste layer is uniformly sprayed onto the back of an ethyl cellulose-modified porous bio-based chitin film as an electrode. After the silver paste is completely cured, a bio-based chitin film-triboelectric nanogenerator device is obtained.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0011] 1. This invention utilizes crayfish shells as raw material to prepare triboelectric materials exhibiting excellent biocompatibility. A non-contact triboelectric nanogenerator system constructed externally generates and outputs triboelectric charges through the relative motion of the in vivo and external triboelectric materials. Furthermore, this invention systematically examines key factors such as material composition, implantation structure, and operating frequency by analyzing the core characteristics and working principle of EC-modified porous bio-based chitin films, providing systematic guidance for optimizing the application of triboelectric nanogenerator devices in different scenarios. The application potential of the prepared triboelectric nanogenerator device in fields such as flexible electronics and implantable medical monitoring is expected to be significantly expanded.

[0012] 2. Given that material composition, implantation structure, and operating frequency significantly influence the device's output performance, this invention provides systematic guidance for optimizing the application of triboelectric nanosheets in various scenarios. When the external material is polytetrafluoroethylene (PTFE), the device, implanted 0.4 cm deep in subcutaneous tissue, generates an open-circuit voltage of 592 mV and a short-circuit current of 45.7 nanocoulombs at a motion frequency of 0.7 Hz. This technology represents a major breakthrough in the field of self-powered medical devices and holds promise for solving the energy constraints faced by implantable pacemakers and other bioelectronic devices used for treatment and sensing. Attached Figure Description

[0013] Figure 1 This is a schematic diagram illustrating the fabrication process of a triboelectric nanogenerator device.

[0014] Figure 2 Structural characteristics analysis of ethyl cellulose-modified lobster chitin. (a) Schematic diagram of the fabrication process of the triboelectric nanogenerator device. (b) Scanning electron microscopy (SEM) images of raw, acid-base treated, and EC-modified lobster chitin. (c) Contact angle measurement and (d) Surface morphology characterization. (e) Schematic diagram of the hydrophobic modification mechanism. (f) Stress-strain curves of acid-base treated lobster shells. (g) X-ray diffraction (XRD) and (h) Flexibility analysis. (i) Calculation of HOMO, LUMO, and electrostatic potential distribution of the triboelectric material.

[0015] Figure 3 Optical photographs of crayfish shells after raw, acid-base treated, poloxamer treated, and EC treated.

[0016] Figure 4 X-ray photoelectron spectroscopy (XPS) of raw and acid-base treated thin films.

[0017] Figure 5 Thermogravimetric analysis (TG) curves of the original and acid-base treated films.

[0018] Figure 6 The working principle of the prepared triboelectric nanogenerator device is shown in the following figures: (a) Experimental setup; (b) Comparison of device output performance at different (c) subcutaneous thicknesses and (d) test frequencies; (e) Basic principle of non-contact charging.

[0019] Figure 7 This is a schematic diagram of the output performance test of the triboelectric nanogenerator device.

[0020] Figure 8 (a)–(d) Simulated schematic diagrams and potential distributions of the triboelectric material surface when the device is implanted subcutaneously at different thicknesses. (e) Simulated parameters of the surface of the PDMS and bio-based chitin triboelectric nanogenerator.

[0021] Figure 9 To illustrate the mechanism of enhanced output performance after device implantation in subcutaneous tissue. (a) Triboelectric output sequence. (b) Calculation of the band gaps of the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals (HOMO-LUMO). (c) Electrostatic potential distribution of the triboelectric material. (d) Comparison of device output performance under different test materials; (e) Corresponding potential distribution.

[0022] Figure 10 (a)-(d) Simulated schematic diagrams and potential distributions of the surface of the triboelectric material when the external materials are PTFE, PDMS, PVC and PP in sequence. (e) Simulated parameters of the surface of the external material and the bio-based chitin triboelectric nanogenerator.

[0023] Figure 11 To (a) demonstrate the ability of the fabricated triboelectric nanogenerator device to identify material types. (b) Characterization analysis of triboelectric signals when a tactile sensor based on a triboelectric nanogenerator is used to identify different materials.

[0024] Figure 12 Biocompatibility analysis of bio-based chitosan tablets. (a) Schematic diagram of bio-based chitosan tablet implantation. (b) Observation of wound healing 21 days after implantation. (c) H&E stained tissue section of the implantation site in SD rats.

[0025] Figure 13 (a) Schematic diagram of bio-based chitosan tablet implantation. (b) Wound recovery status 21 days post-implantation. (c) H&E stained tissue section of the implantation site in C57BL rats.

[0026] Figure 14 The following are application scenarios for the triboelectric nanogenerator device. (a) Schematic diagram of its application in the human body to promote the recovery of bodily functions. (b) and (c) diagrams of the triboelectric nanogenerator in operation, simulated by a toy mouse. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0028] Example 1

[0029] 1.1. Preparation of porous bio-based chitin films and their triboelectric nanogenerators

[0030] Crayfish shell waste was pretreated to remove surface impurities and residual tissue. The crayfish shells were sequentially immersed in 3% (volume) hydrochloric acid and 5% (mass) sodium hydroxide solutions for 12 hours each to remove calcium carbonate, protein, and lipids. They were then repeatedly rinsed with deionized water until the solution reached a neutral pH value, and dried to obtain porous bio-based chitin.

[0031] To enhance moisture resistance, porous bio-based chitin was immersed in a 5% (by mass) poloxamer aqueous solution and repeatedly pulled up and down three times to ensure full immersion of the poloxamer aqueous solution. After removal and drying, a poloxamer-modified porous bio-based chitin film was prepared.

[0032] Poloxamer-modified porous bio-based chitin film (1 g) and 3% (mass ratio) ethyl cellulose (EC) acetone solution (10 mL) were alternately filled into a 4×4 cm mold and pressurized for 120 h. Due to the non-sealed state of the mold, acetone evaporated during the pressurization process, resulting in an EC-modified porous bio-based chitin film with dimensions of 4×4×0.1 cm.

[0033] Subsequently, silver paste was uniformly sprayed onto the back of the EC-modified porous bio-based chitin film as an electrode. After the silver paste had completely cured, a bio-based chitin film-triboelectric nanogenerator device was obtained.

[0034] 1.2. Materials and Characterization

[0035] Frozen crayfish were purchased from Hanyi Aquatic Technology Co., Ltd. (China). All other chemical reagents were supplied by Aladdin Reagent Co., Ltd. (China).

[0036] The surface morphology of the samples was observed using a scanning electron microscope (SEM, JEOL JSM-5600LV). The chemical structure was characterized using X-ray diffraction (XRD, Rigaku D / max-2550V) and X-ray photoelectron spectroscopy (XPS, Shimadzu AXIS ULTRADLD). The water contact angle was measured using a contact angle analyzer (KRÜSS DSA100), and the mechanical properties were evaluated using a universal testing machine (DRS-10KG). Surface morphology was analyzed using a three-dimensional stereomicroscope (Hirox KH-7700).

[0037] The output signal of the triboelectric nanogenerator was recorded using an oscilloscope and a galvanometer. Finite element simulations of stress-strain distribution were performed using Abaqus software, and the potential difference caused by triboelectric charging was analyzed using COMSOL Multiphysics 6.1.

[0038] 1.3. Equipment Output Performance Test

[0039] To investigate the relationship between the device's output performance and external conditions, the effects of implantation depth, motion frequency, and type of external material on the output characteristics were systematically examined. The fabricated triboelectric nanogenerator was implanted into biological tissue (using pork as a simulation in this invention). A push rod drives the external material to generate reciprocating motion, forming a non-contact triboelectric power generation system. The minimum and maximum distances between the external material and the surface of the biological tissue were maintained at 0.5 cm and 10.5 cm, respectively, to ensure stable motion trajectories and no physical contact.

[0040] To assess the impact of external parameters on energy harvesting, the actuator movement frequency (0.7 Hz, 1.0 Hz, 1.4 Hz), the implantation depth of the device within biological tissue (0.4 cm, 1.6 cm, 2.4 cm), and the type of external material were systematically varied. Silver electrodes on the back of the device were connected to an oscilloscope and a galvanometer to record the output signals (including voltage and charge).

[0041] 1.4. Biocompatibility Testing

[0042] To evaluate the in vivo biocompatibility of EC-modified porous bio-based chitosan films, SD and C57BL rats were used as animal models. The material was implanted subcutaneously into the back, abdomen, and legs of the rats. During a 21-day dynamic observation period, wound swelling, crust formation, suture dehiscence, and overall healing progress were monitored at multiple postoperative time points. On postoperative day 21, tissue samples were collected from the implantation site for histological evaluation using hematoxylin and eosin (H&E) staining, and the microstructure of the tissue sections was observed using an optical microscope.

[0043] Example 2

[0044] 2.1. Design and preparation of porous bio-based chitin triboelectric materials

[0045] As an emerging research direction in the field of biological resources, crayfish shells have enormous potential for development and utilization. This invention utilizes crayfish shells from solid waste as raw materials to prepare chitin and chitosan for triboelectric materials. Figure 1As shown, the cleaned crayfish shells of this invention were sequentially treated with 3% (v / v) hydrochloric acid, 5% (w / v) sodium hydroxide solution, and 5% (w / v) poloxamer aqueous solution. Subsequently, the treated porous bio-based chitin membrane and 3% (w / w) ethyl cellulose (EC) acetone solution were alternately placed into a 4×4 cm mold to prepare an EC-modified porous bio-based chitin membrane (4×4×0.1 cm). Figure 1 As shown in the figure. Subsequently, a silver paste layer was uniformly sprayed onto the back of the film as an electrode. After the silver paste was completely cured, a bio-based chitin film-triboelectric nanogenerator device was obtained.

[0046] In this preparation process, an acid-base dissolution method is used to improve extraction efficiency, processing crayfish shells into high-purity chitin and chitosan (such as...). Figure 2 (As shown in a). First, inorganic minerals such as calcium carbonate in the shell are removed by etching with hydrochloric acid solution. Then, organic impurities such as proteins and lipids are removed with sodium hydroxide solution. See the corresponding sample photo. Figure 3 The prepared chitin and chitosan possess excellent structural properties, such as superior biocompatibility, biodegradability, and good processing performance, making them highly suitable for use in triboelectric energy converter implants within the human body.

[0047] To analyze the surface structure of the prepared materials, scanning electron microscopy (SEM), contact angle measurement, and optical interferometry three-dimensional profilometry were used. Morphological analysis showed that the original crayfish shell surface had a dense structure, indicating that the surface was covered with minerals and lipids. Figure 2 After acid treatment, the surface structure of the resulting chitin becomes relatively rough (bi). Figure 2 b ii). After alkali treatment, clearly visible pores and fiber bundles appear on the surface ( Figure 2 b iii), combined with XPS ( Figure 4 ) and TG analysis ( Figure 5 This indicates that the minerals and organic matter gradually dissolved, leaving only the chitinous skeleton. The contact angle increased from 86.1° in the original shell. Figure 2 The temperature dropped to 80.9° (ci) Figure 2 c ii), while the surface roughness decreased from 81.8 μm ( Figure 2 di increased to 241.9 μm ( Figure 2 d ii), further confirming that acid-base treatment forms a porous structure on the shell surface, ultimately generating a porous bio-based chitin film ( Figure 3 ).

[0048] Figure 3Optical photographs of crayfish shells after initial treatment, acid-base treatment, poloxamer treatment, and EC treatment are presented. These optical micrographs were acquired in transmission mode. After acid-base treatment, organic substances such as astaxanthin were removed from the shells. The shell color changed from red to white, and light transmittance increased, revealing a wrinkled surface under the microscope—this is due to the removal of organic matter and calcium carbonate. Because the poloxamer coating is extremely thin, no significant changes in microstructure were observed after coating. Conversely, EC treatment resulted in a clear EC film on the surface, effectively enhancing the hydrophobicity of the sample.

[0049] like Figure 4 As shown, characteristic peaks corresponding to C, Ca, N, and O were observed in the XPS spectra of crayfish shells before and after acid-base treatment. The presence of N on the sample surface indicates a high content of chitin and chitosan. Notably, a calcium peak was also detected in the XPS spectrum of the film after acid-base treatment, which may originate from amorphous calcium carbonate compounds remaining on the surface or adsorbed in the pore structure and interchain gaps of chitin and chitosan. It should be particularly noted that these amorphous calcium carbonate compounds are chemically stable and do not easily precipitate after implantation in the human body.

[0050] like Figure 5 As shown, the thermogravimetric analysis (TG) curves reveal three distinct weight loss stages, corresponding to dehydration, chitin decomposition, and CaCO3 decomposition, respectively. Compared to the TG curve of the original crayfish shell, the curve of the acid-alkali treated crayfish shell exhibits two significant differences: First, the ash content decreases significantly at high temperatures, from 38.6% to 3.7%, indicating that only a small amount of CaCO3 remains after acid-alkali treatment. Second, the decomposition temperature of CaCO3 decreases from 600℃ to 400℃, which may be due to the adsorption of a small amount of amorphous CaCO3 by the porous structure of chitin and chitosan after acid-alkali treatment.

[0051] Due to the hydrophilicity of chitin-chitosan, water molecules easily form a conductive film on the surface, leading to charge dissipation and altering the triboelectric properties of the chitin-chitosan-based triboelectric nanogenerator. To mitigate the impact of human body moisture on device performance, this invention employs poloxamer and ethyl cellulose (EC) for sequential modification of porous bio-based chitin films. The modification mechanism is as follows: Figure 2 As shown in EI: The poloxamer ethylene oxide segment (-O-CH2-CH2-) first forms a complex system with the hydroxyl and amino groups of chitin and chitosan through hydrogen bonds, and then binds to ethyl cellulose through intermolecular forces, ultimately constructing a hydrophobic chitin-chitosan composite structure. After surface modification, the porous bio-based chitin film is encapsulated by an EC film (…). Figure 2 e ii), the contact angle increased to 96.2° ( Figure 2 c iii), the surface roughness decreased to 158.4 μm ( Figure 2 (d iii). These changes indicate that the EC layer was successfully formed on the chitin-chitosan composite surface, significantly enhancing its hydrophobicity.

[0052] To investigate the potential mechanisms underlying the structure-property variations, crystallographic characterization was performed. For example... Figure 2 As shown in f, the XRD pattern of the original crayfish shell exhibits weak characteristic peaks at 29.1° and 47.5°, corresponding to the (104) and (018) diffraction peaks of calcium carbonate, respectively. In contrast, the porous bio-based chitin film modified with acid, alkali, and EC showed a new characteristic peak at 19.3°, corresponding to the chitin (110) diffraction plane, while the characteristic peak of calcium carbonate disappeared. By comparing the XRD characteristic peaks of the original crayfish shell and the EC-modified porous bio-based chitin film, it was found that after acid-alkali treatment and EC modification, the mineral components in the original shell were effectively removed, while the crystal structure of chitin was completely preserved and stabilized.

[0053] The mechanical properties of materials are crucial to the practical application of medical devices, directly determining their ability to withstand the mechanical stress generated by physiological activities after implantation in the human body, thereby ensuring the stability and service life of the devices. Figure 2 The stress-strain curves of g show that the tensile strength of the EC-modified porous bio-based chitin film reaches 32.1 MPa, while the tensile strengths of the original chitin and the porous bio-based chitin film are only 11.8 MPa and 20.1 MPa, respectively. These data indicate that acid-base treatment combined with EC modification can enhance the material strength, further confirming that acid-base treatment can effectively remove calcium from the pores of chitin.

[0054] Both porous bio-based chitin films and EC-modified porous bio-based chitin films can be freely bent. Figure 2 (h i-iii) exhibits excellent flexibility, making it highly adaptable to the mechanical deformation requirements of implant applications. Due to the electron-rich nature of the -NH- group in the chitin molecule, this material exhibits strong electron-donating ability, making it an ideal positively charged material. To elucidate the influence of the chitin-chitosan mixture on the generation of triboelectric signals, Gaussian calculations were used to simulate the monomeric molecular properties of both. For example... Figure 2 As shown in ii, Gaussian calculations reveal that chitin's highest occupied molecular orbital (HOMO) energy level is -6.955 eV, while its lowest unoccupied molecular orbital (LUMO) energy level differs from chitosan's by only 0.123 eV. The HOMO-LUMO band gaps of chitin and chitosan are 6.92 eV and 6.11 eV, respectively, placing them on the same order of magnitude. This indicates that the residual chitosan and chitin have minimal differences in terms of electronic excitation difficulty and molecular stability. During charge transfer with the anodic material, their electron-accepting abilities are comparable, avoiding fluctuations in electron transfer efficiency caused by chitosan's energy level anomalies. More importantly, as... Figure 2As shown in ii, the electrostatic potentials of chitin and chitosan exhibit more extreme distributions (-1.9 eV to 2.0 eV and -1.6 eV to 2.1 eV) and a wider range (3.9 eV and 3.7 eV), indicating their superior charge delocalization and local dipole formation capabilities. This endows the materials with overall electron donor properties and lays the foundation for charge transfer in the generation of triboelectric signals.

[0055] 2.2. Output performance of the bio-based chitin sheet-triboelectric nanogenerator device

[0056] EC-modified porous bio-based chitin films, with their stable crystal structure, excellent hydrophobicity, and electron donor properties, have become the core functional carrier for implantable triboelectric nanogenerator devices. These inherent properties not only determine the basic performance limits of the devices but also directly affect their adaptability and output stability in different application scenarios. To systematically investigate the influence of external conditions on the output performance of prefabricated triboelectric nanogenerator devices, this invention conducts multi-dimensional tests focusing on "external structure and material properties." Figure 6 and Figure 9 The characterization series shown comprehensively analyzes the impact of factors such as external material selection, implantation structure, and operating frequency on device output performance, providing a theoretical and experimental basis for device optimization and scenario-based applications.

[0057] This invention uses EC-modified porous bio-based chitin film as the core functional material and designs a testing system that meets the requirements for bio-implantation. The relevant results are as follows: Figure 6 a i-iii and Figure 7 As shown (using pork to simulate biological tissue). A three-layer test structure was constructed, and the prepared triboelectric nanogenerator device was implanted at depths of 0.4 cm, 1.6 cm, and 2.3 cm to simulate different implantation depths. Figure 6 ai). It should be noted that the electrode preparation was completed by spraying silver paste onto the back of the EC-modified sheet ( Figure 6 aii). Simultaneously, the push rod causes the external material to reciprocate on the surface of the pork ( Figure 6 aiii ①-④). It is worth noting that the external material did not contact the pork surface, and the minimum distance between the push rod and the pork skin was controlled at 0.5 cm, with a maximum distance of 10.5 cm, to ensure a stable trajectory. Polydimethylsiloxane (PDMS) was selected as a representative external material (to match the electron gain characteristics of bio-based chitin films). The experiment first investigated the effects of implantation depth and operating frequency on output characteristics. For example... Figure 6As shown in bi and ii, when the triboelectric nanogenerator is implanted subcutaneously at a frequency of 0.7 Hz at a depth of 0.4 cm, both the output charge and voltage decrease with increasing implantation depth. The optimal output performance occurs in the first layer (0.4 cm subcutaneously), generating approximately 500 mV of voltage and 35 nC of charge. To further clarify the effect of frequency, the output performance at frequencies of 0.7 Hz, 1 Hz, and 1.4 Hz was tested at three depths (0.4 cm, 1.6 cm, and 2.3 cm). Figure 6 ci, ii). The results show that the output voltage increases with frequency, reaching a peak of approximately 700mV at 1.4Hz in the first layer (0.4cm). Figure 6 ci); while the charge output shows a "low-frequency optimal" trend, with the first layer reaching 35 nanocoulomb charge at 0.7 Hz ( Figure 6 c ii). Combined Figure 6 Results b and 2c show that, under the synergistic effect of implantation depth and operating frequency, this triboelectric nanogenerator achieves optimal performance at a subcutaneous depth of 0.4 cm: the voltage is maximum at 1.4 Hz, and the charge output is maximum at 0.7 Hz. This pattern provides direct guidance for adjusting device operating parameters according to application requirements.

[0058] Besides the electronic structure of the material, the interfacial spacing, a key spatial parameter for contactless power generation, and its impact on the potential distribution of the bio-based chitin film and the device output also require further verification. To this end, the potential distribution of the bio-based chitin film at four different subcutaneous tissue thicknesses was simulated when PDMS was used as the external material. Figure 6 d i①-④、ii①-④、 Figure 8 As shown, when the implantation depth of the triboelectric nanogenerator is 0 cm, 0.4 cm, 1.6 cm, and 2.3 cm, the potential difference between the device and the PDMS surface is 4.16 × 10⁻⁶. 4 V, 3.99×10 4 V, 3.62×10 4 V and 3.20×10 4 V. Clearly, the potential distribution is positively correlated with the electrode implantation depth in pork: the shallower the implantation, the greater the potential difference. This result is consistent with the device's optimal output performance at a subcutaneous thickness of 0.4 cm. Figure 6 (b) This aligns with the findings, further confirming the correlation between the implanted structure and the actual output performance of the device. Furthermore, the study demonstrates that acid-base treatment and EC surface modification effectively maintain the excellent electron donor properties of chitin, laying the foundation for subsequent device structural design and expanded applications.

[0059] Figure 8 AI-DI presents a simulated schematic diagram of the surface potential distribution of the triboelectric material when the device is implanted at different subcutaneous depths. The corresponding simulation parameters are shown in [link to simulation parameters]. Figure 8e. To eliminate the influence of the spacing between triboelectric materials on the simulated potential, the spacing between the device and the PDMS is kept constant during the simulation, such as... Figure 8 As shown in aii-dii. When the spacing is fixed at 2.8 cm, the simulated surface voltage of the device is: 4.16 × 10⁻⁶. 4 V (implantation depth: 0 cm), 3.99×10 4 V (implantation depth: 0.4 cm), 3.62×10 4 V (implantation depth: 1.6 cm) and 3.20×10 4 V (implantation depth: 2.3 cm). These results indicate that the surface voltage gradually decreases with increasing implantation depth. The surface potential of the device decreases accordingly as the separation distance between the triboelectric materials increases. Clearly, the potential distribution is correlated with the electrode implantation depth: the shallower the implantation depth, the greater the potential difference generated.

[0060] To elucidate the working mechanism of non-contact power generation in the fabricated triboelectric nanogenerator device, the energy harvesting phenomenon can be explained by applying the basic principle of triboelectricity using a superimposed electron cloud model. For example... Figure 6 As shown in e i-iv, the electron clouds of the two materials remain separated before atomic-scale contact or proximity. Under mechanical pressure, the atoms of the two phases gradually approach each other, causing the outer electron clouds to form an adjacent arrangement. Driven by an electric field, the charges within the electron clouds undergo directional movement. Unlike the direct overlap of electron clouds in traditional triboelectric nanogenerators, this triboelectric nanogenerator expands the interaction range of the electron clouds by shortening the interatomic spacing and reducing the interatomic potential barrier, ultimately promoting interatomic electron transfer. Furthermore, the larger the interaction range of the electron clouds, the more significant the reduction in the potential barrier, thus promoting more electron transfer. Specifically, the deeper the device is implanted in the human body and the closer it is to the epidermis, the better the device's output performance.

[0061] Given that EC-modified porous bio-based chitin films possess electron-donating properties, they require pairing with suitable external materials to achieve maximum output. This experiment further investigated the influence of the electronegativity of the external materials on device performance. Differences in electronegativity between materials lead to changes in both the amount of triboelectric charge generated and the charge separation efficiency. Figure 9 a), which in turn affects output performance. The corresponding experimental configuration is as follows: Figure 6 As shown in a and iii. Ten external materials (PTFE, PDMS, PVC, PP, PE, PU, ​​PF, CuO, PA, and POM) were selected and their output performance was tested at a frequency of 0.7 Hz. To explore the fundamental reason for the difference in output performance when paired with EC-modified porous bio-based chitin films, and to clarify the influence of material electronic structure on non-contact triboelectric signals, the HOMO-LUMO band gap of each material was calculated using Gaussian software. Figure 9 b) and electrostatic potential distribution ( Figure 9 c). For example Figure 9 As shown in b, the HOMO-LUMO band gaps differ among different materials. This band gap can be used to estimate the excitation energy of electrons: a larger band gap indicates higher molecular stability and lower reactivity; a smaller band gap indicates stronger reactivity. PDMS, with its narrow band gap (HOMO-LUMO gap of 5.5 eV), facilitates electron excitation. When paired with chitin, its strong electron acceptor properties combined with the electron donor properties of the bio-based chitin film result in efficient charge transfer. Although PTFE has a wide band gap (HOMO-LUMO gap of 7.5 eV) and higher molecular stability, its good orbital energy matching (small gap difference between the two materials) still allows it to produce excellent output performance when paired with chitin. Further analysis shows that the orbital energy difference between the material and chitin affects the charge separation efficiency: polytetrafluoroethylene and polydimethylsiloxane have smaller band gaps (6.1-6.9 eV) with chitin, resulting in strong charge transfer driving force and excellent output performance. This indicates that materials with strong electron acceptor capabilities can achieve more efficient charge transfer with chitin-based electron donor materials (bio-based chitin films). Furthermore, the electrostatic potential distributions of ten materials were analyzed. Figure 9 c). Based on Figure 2 Analysis of i showed that chitin and chitosan had higher electrostatic potential extrema and total amount compared to the ten external materials. This phenomenon indicates that charge delocalization is more likely to occur.

[0062] Based on tribological sequence diagrams, HOMO-LUMO band gaps, and electrostatic potential distributions, the output performance of ten external materials was tested at a frequency of 0.7 Hz. Figure 9 As shown in diagram di, the output voltages of PTFE, PDMS, PVC, PP, PE, PU, ​​PF, CuO, PA, and POM are 592 mV, 525 mV, 424 mV, 408 mV, 352 mV, 272 mV, 280 mV, 280 mV, 296 mV, and 264 mV, respectively. Charge output mode and voltage distribution ( Figure 9The results are consistent with d and ii), with corresponding charge values ​​of 45.7 nC, 35.3 nC, 32.9 nC, 26.9 nC, 26.6 nC, 1.0 nC, 0.4 nC, 0.8 nC, 2.3 nC, and 1.1 nC, respectively. Among these, PTFE, due to its extremely high electronegativity, forms the optimal charge transfer pair with the EC-modified porous bio-based chitin film (electron donor material), achieving a voltage of nearly 600 mV and a charge of nearly 46 nC, exhibiting the best output performance. Materials following PE (such as PU, PF, CuO, etc.) possess electron-accepting capabilities, but their electronegativity differences are smaller than those of the EC-modified porous bio-based chitin film. When these external materials interact with the implanted triboelectric nanogenerator under the action of a push rod, the changes in charge transfer and induced charge separation efficiency generated by surface interactions are minimal. Therefore, their output performance tends to be similar and relatively weak. Figure 6 The structural and frequency optimization conclusions in b and c further clarify the collaborative optimization path: device characteristics - external material selection - structural and frequency parameters.

[0063] Simultaneously, COMSOL Multiphysics 6.1 software was used to simulate and analyze the surface potential of the device and external materials. For example... Figure 9 ei、 Figure 10 As shown, the surface potential values ​​of the bio-based chitin film are 5.18 × 10⁻⁶. 4 V ( Figure 9 eii ①) When the external materials are PTFE, PDMS, PVC and PP respectively, their surface potential values ​​are 3.99×10 4 V ( Figure 9 eii ②), 3.71×10 4 V ( Figure 9 eii ③) and 3.04×10 4 V ( Figure 9 eii ④). Simulation regularity and Figure 9The experimental data shown in d are consistent. The simulation results and the relationship between output voltage and charge difference reveal the non-contact triboelectric phenomenon, indicating that the material-related potential distribution and its position in the triboelectric output sequence (i.e., the material's ability to gain or lose electrons) have a decisive influence on the output of the triboelectric nanogenerator. This phenomenon is directly related to the electron donor characteristics of the bio-based chitin film. Its surface carbon atoms form a positive potential region through oxygen-nitrogen bonds, which must establish a potential difference with the negative potential region of the external material to drive charge transfer. In addition, the hydrophobic surface of the bio-based chitin film can reduce the interference of interfacial water molecules on the potential distribution and maintain stable interfacial dipole interactions. The significant difference between output voltage and charge originates from the difference in positive and negative properties of the external material, further highlighting the importance of potential matching between the bio-based chitin film and the external material. In summary, based on the research results of molecular orbital analysis, potential distribution simulation, and interfacial parameter verification, the charge transfer mechanism between different polymers in the non-contact triboelectric process is explained in depth. This mechanism is not only applicable to mechanical energy harvesting, but can also be extended to the field of sensing. Figure 11 ).

[0064] Figure 10 ai-di shows simulated schematic diagrams of the surface potential distribution of triboelectric materials when the external materials are PTFE, PDMS, PVC and PP. Figure 10 e provides the corresponding simulated parameters for the external material and the surface of the bio-based chitin triboelectric nanogenerator. When the distance between the device and the PDMS is fixed at 2.8 cm, the simulated surface voltage of the device is: 5.18 × 10⁻⁶. 4 V (external material: PTFE), 3.99 × 10 4 V (external material: PDMS), 3.71 × 10 4 V (external material: PVC) and 3.04×10 4 V (External material: PP), see details Figure 10 These results demonstrate that the surface voltage decreases progressively with decreasing electronegativity of the external material. Simulation results, combined with the relationship between output voltage and charge difference, confirm the existence of a non-contact triboelectric effect. This finding indicates that the material-dependent potential distribution and its position within the triboelectric series (i.e., the ability to gain or lose electrons) jointly have a decisive influence on the output performance of the triboelectric nanogenerator.

[0065] Triboelectricity occurs at the interface of contacting materials and is the fundamental mechanism for surface charge generation. Specifically, the close contact between the EC-modified porous bio-based chitin film and the test material drives electron transfer. Different materials are known to have drastically different electron gain and loss tendencies. Therefore, when external materials approach or move away from the device surface, triboelectric charges are generated at different rates and intensities, forming characteristic electrical signal waveforms. To extract more complex features from the output of the triboelectric nanosheet-based tactile sensor, a deep learning method—R-CNN—is used for signal processing, analysis, training, and recognition. Figure 11 a) The characteristics of the output signal vary with the electronic structure of the contact material. By integrating a tactile sensor based on a triboelectric nanogenerator with R-CNN technology, accurate identification of material types can be achieved, demonstrating great potential in applications such as electronic skin. Crucially, the main difference in the triboelectric signals generated by different materials lies in the waveform characteristics rather than the absolute voltage amplitude. The waveform morphology reflects inherent material properties such as Fermi level, surface roughness, and composition, while the voltage magnitude is also affected by external environmental factors.

[0066] For example, the heatmap of feature extraction from convolutional neural networks ( Figure 11 As shown in bi), the appearance of "hot spots" indicates that the R-CNN model has accurately located the most recognizable signal feature regions. These local regions, typically surrounding the signal peak distribution, encode the crucial material-specific information required for accurate classification. Thus, the trained model efficiently extracts recognition-related information from the triboelectric signal, achieving high-precision material identification. Figure 11 As shown in bii, after training the R-CNN model with triboelectric signals collected under natural conditions, the classification accuracy of the four different materials reached 97.8%. Furthermore, the error rates of the training set and the validation set were basically consistent, with no significant differences. Figure 11 (b iii) confirms that the model has extremely low overfitting. In summary, these findings reveal a clear intrinsic correlation between the output signal characteristics and the fine features of the contact material surface, indicating that this device has broad prospects in implantable tactile sensing applications.

[0067] 2.3. Biocompatibility Verification

[0068] Biocompatibility is a core requirement for implantable medical devices. To verify the in vivo safety of bio-based chitin sheet biomaterials, this invention uses SD rats (… Figure 12 ) and C57BL rats ( Figure 13 The implantation experimental system was used to monitor the biological response and simulate material-tissue interactions under different physiological microenvironments. Porous bio-based chitosan films modified with EC were implanted into the back, abdomen, and legs of SD rats. Figure 12 a). Continuous monitoring of wound healing dynamics within 21 days post-surgery ( Figure 12(b) Key observation time points were d0 (immediately after suturing), d3, d7, d11, d15, d19, and d21. On d0, mild tissue swelling was observed at all implantation sites, a normal acute inflammatory response to surgical trauma, consistent with the initial stage of physiological repair. By day 3, swelling in the legs and abdomen had significantly subsided, but slight residual swelling remained in the back. This was attributed to the greater mechanical stress on the back tissues (such as muscle traction during rat activity), leading to delayed recovery of local blood circulation. Protective scabs formed on day 7. By day 11, sutures in the abdomen and legs had completely fallen off, while sutures in the back gradually fell off. By day 19, epithelialization began in the back, abdomen, and legs, and the wounds were essentially closed. By day 21, all implantation sites had achieved mature healing, with no signs of infection (such as suppuration or erythema) or wound dehiscence. These results indicate that the bio-based chitosan film did not hinder wound healing, and its surface properties may even have promoted the repair process.

[0069] To further assess histological biocompatibility, tissue sections from the three implantation sites on day 21 were stained with hematoxylin and eosin (H&E) and observed at magnifications of 10×10 and 10×40. Figure 12 c). The results showed the back ( Figure 12 ci), abdomen ( Figure 12 c ii) and legs ( Figure 12 (c) (iii) No tissue necrosis or skin ulceration was observed in any of the sections, confirming that the bio-based chitosan film did not cause physical damage or cytotoxicity upon contact with tissue. Furthermore, no significant inflammatory cell infiltration (such as neutrophils or macrophages) or excessive fibrous tissue proliferation was observed, further demonstrating the excellent biocompatibility of the prepared triboelectric nanogenerator device. This superior biocompatibility essentially stems from the structural and chemical modifications of the bio-based chitosan film. The physical barrier formed by ethyl cellulose on the chitosan surface minimizes direct contact between hydrophilic chitosan and tissue fluid, preventing local tissue edema caused by water absorption while preserving the inherent biocompatibility of chitosan. Figure 6 The excellent triboelectric properties of the bio-based chitin film triboelectric nanogenerator (e.g., generating an output voltage of approximately 500 mV and a charge of 35 nC at a subcutaneous depth of 0.4 cm) demonstrate that the bio-based chitin film is suitable for near-epidermal or implantable triboelectric nanogenerator devices, thereby eliminating safety concerns regarding its biomedical applications.

[0070] Figure 13 a i-iii illustrates a schematic diagram of an EC-modified bio-based chitin film implanted in the back of a C57BL rat. To assess the in vivo safety of these biomaterials, they were first implanted in the backs of C57BL / 6 mice, and biological responses were systematically monitored to conduct preliminary studies. The dynamic wound healing process was tracked for 21 days post-implantation. Figure 13 (b) Key observation points include day 0 (immediately after suturing), day 1, day 3, day 5, day 7, day 9, day 12, day 15, day 18, and day 21. On day 0, mild tissue swelling was observed at all implantation sites, reflecting a normal acute inflammatory response to surgical trauma, consistent with the initial stage of physiological repair. Residual swelling persisted until day 3, but completely subsided by day 5. A protective eschar formed on day 7, and the sutures were completely drained. Epithelialization was observed on the dorsal wound surface on day 15, accompanied by significant wound contraction and healing. By day 21, all implantation sites showed complete and mature healing, with no signs of infection (such as suppuration or erythema) or wound dehiscence.

[0071] For histological evaluation, tissue sections were collected from the implantation site on day 21, stained with hematoxylin and eosin (H&E), and observed under a light microscope. Figure 13 (ci and ii). The results showed no tissue necrosis or skin ulceration in the dorsal implantation area, confirming the excellent biocompatibility of the EC-modified bio-based chitin film.

[0072] 2.4. Validation of the bio-based chitin sheet-triboelectric nanogenerator device in in vitro mechanical energy harvesting

[0073] Based on the biocompatibility and triboelectric properties of bio-based chitin films, this invention further explores their potential applications in the biomedical field. Compared to traditional implantable stimulation devices, the core advantage of the fabricated triboelectric nanogenerator device lies in its ability to generate electricity autonomously through non-contact motion, requiring no external power source, significantly expanding its potential application scenarios. In implantable applications ( Figure 14 a) After being implanted in the human body, this triboelectric nanogenerator can induce non-contact mechanical interaction between the device and surrounding tissues / external materials through daily activities (such as leg muscle contraction or limb joint movement during walking), thereby generating triboelectric current. This current exhibits multi-organ physiological regulation capabilities.

[0074] To simulate the implantation state in the human body, the present invention fixes the prepared triboelectric nanogenerator device to the palm of the hand. Figure 14 When the bi display device is attached to the palm of the hand, the output voltage reaches 40 mV. Figure 14 b ii), the response time is 110 ms ( Figure 14 (biii). Continuous power supply is achieved through hand movements, fully demonstrating its excellent flexibility (conforming to the curvature of the palm) and ability to harvest kinetic energy from the human body. To further verify its feasibility under dynamic physiological conditions, Figure 14 The study used a toy mouse model to simulate in vivo movement. Experimental results confirmed that the triboelectric nanogenerator maintained stable power generation during simulated physiological movement, with an output voltage reaching 38 mV. Figure 14 c ii), the response time is 109 ms ( Figure 14 (c iii) This provides an experimental reference for the mechanical design of implantable self-powered devices. From a clinical application perspective, this self-generating triboelectric nanogenerator device overcomes the fundamental bottleneck of traditional implantable devices: it eliminates the medical risks of secondary surgery for battery replacement and reduces the economic costs of long-term treatment. In the future, it can be further integrated with external intelligent medical systems to power micro-sensors using self-generated power. These sensors will enable continuous monitoring of physiological indicators such as heart rate, blood pressure, and nerve electrical signals, transmitting data wirelessly to terminals to provide real-time support for precision medicine.

[0075] In summary, this invention utilizes implantable triboelectric nanosheets to construct a self-powered medical device that effectively harvests external mechanical energy. The core advantage of the fabricated triboelectric nanogenerator lies in its ability to generate electricity autonomously through non-contact motion, thus eliminating the need for an external power source. This performance benefits from the synergistic biocompatibility and triboelectric properties of the bio-based chitin film.

[0076] This invention uses crayfish shells as raw material and removes inorganic impurities and proteins through a combination of acid-base treatment and electrochemical modification to prepare a hydrophobic bio-based chitin film. This film is integrated into an externally constructed non-contact triboelectric nanogenerator system, where triboelectric charges are generated and transferred through the relative motion of the in-body and external triboelectric materials. The effects of material composition, implantation structure, and operating frequency on output performance were systematically analyzed.

[0077] Unlike traditional triboelectric nanogenerators where electron clouds directly overlap, this device effectively expands the range of electron cloud interactions by shortening the interatomic spacing and reducing the potential energy barrier, thereby promoting electron transfer. When polytetrafluoroethylene (PTFE) is used as the external material and implanted subcutaneously at a depth of 0.4 cm, the device generates an open-circuit voltage of 592 mV and a short-circuit charge of 45.7 nC at a motion frequency of 0.7 Hz. Notably, the shallow implantation depth, closer to the skin surface, actually improves the output performance.

[0078] Furthermore, the bio-based chitin film exhibits excellent biocompatibility, does not inhibit wound healing, and its surface properties may even promote tissue repair. To further verify the device's performance, the triboelectric nanogenerator was tested in the palm of a human hand and in a toy mouse model, achieving stable self-powered operation with an output voltage of 380mV and a response time of 109 milliseconds.

[0079] In summary, these findings highlight the potential of bio-based chitin film-triboelectric nanogenerator systems in driving a new generation of long-term self-powered implantable medical devices, opening up broad application prospects in the fields of personalized medicine and advanced medical technologies.

Claims

1. A method for preparing porous bio-based chitin films using crayfish shells, characterized in that, The cleaned crayfish shells were treated sequentially with hydrochloric acid, sodium hydroxide solution, and poloxamer aqueous solution. Then, they were alternately placed in a mold with ethyl cellulose acetone solution and pressurized to prepare ethyl cellulose modified porous bio-based chitin films.

2. The method as described in claim 1, characterized in that, The cleaned crayfish shells were treated sequentially with 3% (volume ratio) hydrochloric acid, 5% (mass ratio) sodium hydroxide solution, and 5% (mass ratio) poloxamer aqueous solution.

3. The method as described in claim 1, characterized in that, Poloxamer-modified porous bio-based chitin films were alternately filled into the mold with 3% (by mass) ethyl cellulose (EC) acetone solution.

4. The application of the porous bio-based chitin thin film prepared by the method according to any one of claims 1-3 in a triboelectric nanogenerator, characterized in that, A silver paste layer was uniformly sprayed onto the back of an ethyl cellulose-modified porous bio-based chitin film as an electrode. After the silver paste was completely cured, a bio-based chitin film-triboelectric nanogenerator device was obtained.

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