Bionic electronic skin based on liquid metal and shape memory microneedle and preparation method and application thereof

Abstract

The application belongs to the field of biomaterials and flexible electronic technology, and particularly relates to a kind of bionic electronic skin based on liquid metal and shape memory microneedle and its preparation method and application;The electronic skin is integrated by shape memory microneedle array and liquid metal flexible circuit.The microneedle array is prepared by casting forming and thermal mechanical programming, and has temperature response shape memory function: vertical form at room temperature to facilitate painless penetration into skin, automatically bent into barb shape at body temperature and mechanically interlocked with tissue, which significantly improves dynamic adhesion reliability.Liquid metal circuit is patterned on flexible substrate using magnetic control iron bead transfer printing technology, can withstand more than 700% tensile strain, and ensures signal acquisition stability.The preparation method of the application is simple, low in cost, the obtained electronic skin has good biocompatibility, can monitor joint movement in real time, and has wide application prospect in the field of personalized health monitoring, rehabilitation tracking and human-computer interaction.

Description

Technical Field

[0001] This invention belongs to the field of biomaterials and flexible electronics technology, specifically relating to a biomimetic electronic skin based on liquid metal and shape memory microneedles, its preparation method, and its applications. This electronic skin, through biomimetic design, can achieve dynamic and firm adhesion to human skin and can be used in fields such as physiological signal monitoring, joint motion sensing, and human-computer interaction. Background Technology

[0002] Flexible electronic devices have shown great application potential in fields such as medical and health monitoring, wearable devices, and human-computer interaction. Unlike traditional rigid electronic devices, flexible electronic devices can maintain functional stability under deformations such as stretching, bending, and twisting. In order to achieve stable integration with human skin, an ideal electronic skin not only needs to have good flexibility and conductivity, but also needs to be able to adhere firmly to dynamic and irregular skin surfaces, especially in moving parts such as joints.

[0003] Currently, researchers have developed various flexible substrates based on materials such as polymers and hydrogels, and constructed sensing circuits by incorporating conductive fillers such as carbon nanotubes, graphene, and liquid metals. However, achieving reliable adhesion between flexible devices and dynamic skin surfaces remains a core challenge. Although microneedle arrays have been introduced as a physical anchoring method, the fixed upright structure of traditional vertical microneedles is prone to detachment from the tissue when the skin undergoes dynamic deformations such as stretching or rotation, leading to device displacement or signal interruption, making it difficult to maintain long-term, stable monitoring.

[0004] Therefore, developing a novel microneedle that can adaptively change its structure and enhance tissue mechanical interlocking after insertion into the skin is of great significance for improving the adhesion reliability and sensing stability of electronic skin in dynamic environments. Summary of the Invention

[0005] Purpose of the Invention: This invention aims to solve the technical problem of existing flexible electronic skins being poorly adhered to dynamic skin surfaces (such as joints), easily detaching, and causing unstable signal acquisition. To this end, this invention provides a biomimetic electronic skin based on liquid metal and shape memory microneedles, along with its preparation method and applications.

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

[0007] A method for fabricating biomimetic electronic skin based on liquid metal and shape memory microneedles, wherein the electronic skin is obtained by integrating a shape memory microneedle array with temperature-responsive deformation capability with a liquid metal flexible circuit, specifically including the following steps:

[0008] (1) Preparation of shape memory microneedle array: Dissolve shape memory polymer material in organic solvent, cast the resulting solution into a mold with micron-sized cavity, vacuum process the solution to fill the mold cavity, and obtain vertically oriented microneedle array after drying and demolding;

[0009] (2) Shape programming of microneedle array: The vertical microneedle array obtained in step (1) is subjected to mechanical external force to produce a predetermined angle of tilt deformation, and heat treatment is performed under the condition of fixing the deformation state so that the tilt state becomes the permanent memory shape of the material. After cooling and releasing the external force, the microneedles return to the vertical state.

[0010] (3) Preparation of liquid metal flexible circuit: Liquid metal alloy is deposited or coated on a flexible polymer substrate by patterning technology to form a conductive layer with a specific circuit pattern, and then encapsulated with another layer of flexible polymer to obtain a liquid metal flexible circuit;

[0011] (4) The shape-programmed microneedle array obtained in step (2) is integrated and bonded with the liquid metal flexible circuit obtained in step (3) to obtain biomimetic electronic skin.

[0012] As a preferred embodiment, the shape memory polymer material mentioned in step (1) is polylactide-trimethylene carbonate copolymer (PLATMC); the organic solvent is chloroform (CHCl3), and the concentration of polylactide-trimethylene carbonate copolymer (PLATMC) in the solvent is 5%-15% (w / v). This material has good biocompatibility and an adjustable shape memory transition temperature.

[0013] As a preferred embodiment, the mold described in step (1) is a polydimethylsiloxane (PDMS) mold with a micron-sized cavity height of 800-1200 µm and a bottom diameter of 300-400 µm. The microneedles formed within this size range can effectively penetrate the stratum corneum of the skin without touching the pain nerve endings, achieving painless or minimally painful insertion.

[0014] As a preferred embodiment, the predetermined angle in step (2) is 30°-90°; the heat treatment temperature is 35-50°C, and the treatment time is 5-15 minutes; the mechanical external force is achieved by pressing and clamping the microneedle array to both sides. By adjusting the pressing angle and heat treatment conditions, the final bending angle of the microneedles can be precisely controlled to adapt to different tissue locations and adhesion requirements.

[0015] As a preferred embodiment, the liquid metal alloy mentioned in step (3) is gallium-indium alloy (EGaIn); the flexible polymer substrate is polydimethylsiloxane (PDMS). EGaIn has extremely high conductivity and fluidity, is liquid at room temperature, and is an ideal stretchable conductor.

[0016] As a further preferred option, the patterning technique described in step (3) is magnetron magnetization transfer (MST), specifically: a template with a predetermined microchannel pattern is placed on a PDMS substrate, and ferromagnetic microspheres impregnated with liquid metal are guided by an external magnetic field to roll within the channels of the template, thereby transferring the liquid metal to the substrate surface to form conductive lines. This method can rapidly and cost-effectively prepare high-precision (linewidth up to 200-300µm) and highly complex liquid metal patterns without damaging the surface properties of PDMS.

[0017] This invention also protects biomimetic electronic skin based on liquid metal and shape memory microneedles prepared according to any of the above preparation methods.

[0018] Preferably, in the biomimetic electronic skin, the microneedle array can spontaneously deform from a vertical state to a pre-programmed tilted state at body temperature (37°C), forming a barbed structure that mechanically interlocks with the tissue. The height of the microneedles is 900-1100 µm, the base diameter is 300-400 µm, and the tip diameter is 10-50 µm; the tilt angle after deformation is 25°-35°.

[0019] Preferably, in the biomimetic electronic skin, the linewidth of the liquid metal conductive layer is 200-300 µm, which can maintain the continuity of the conductive path under at least 700% tensile strain.

[0020] Preferably, in the bionic electronic skin, the microneedle array is composed of PLATMC, whose shape memory triggering temperature is between 36-40℃, which is highly matched with the normal human body temperature, and can achieve self-triggered deformation without external stimulation.

[0021] Beneficial effects:

[0022] Compared with the prior art, the present invention has the following significant advantages:

[0023] (1) This invention uses shape memory polymer PLATMC to prepare microneedle arrays. Through simple casting and thermomechanical programming processes, intelligent microneedles with temperature-triggered deformation capabilities can be obtained. This method is simple to operate, low in cost, easy to scale up, and can precisely control the geometry and bending angle of the microneedles.

[0024] (2) This invention draws inspiration from the predation strategy of the mantis's forelegs with their spiny structure and designs a biomimetic barbed microneedle. The microneedle experiences minimal resistance when inserted vertically into the skin; upon entering a body temperature environment, the microneedle automatically bends into a pre-set inclined barb shape, forming a mechanical interlock with the skin tissue. Experiments show that this structure exhibits more than 60% greater adhesion to dynamic skin compared to traditional vertical microneedles, and can withstand repeated joint movements and skin stretching without detaching, significantly improving the long-term monitoring reliability of the electronic skin in dynamic environments.

[0025] (3) This invention uses liquid metal EGaIn as the conductive material and combines it with magnetron transfer technology (MST) to construct a high-precision, stretchable circuit on a PDMS substrate. The circuit can maintain stable conductivity even under strain of up to 700%, which is far beyond the normal stretching range of human skin (about 30%), ensuring the accuracy and reliability of signal acquisition of the electronic skin under severe deformation.

[0026] (4) The PLATMC, PDMS and EGaIn materials used in this invention all have good biocompatibility and comply with the ISO 10993-5 international standard. This electronic skin can be directly attached to human skin to achieve real-time, high-fidelity monitoring of the movement angles of multiple joints such as the thumb, wrist and elbow. It has broad application prospects in personalized medicine, rehabilitation training, motion monitoring and advanced human-computer interaction. Attached Figure Description

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0028] Figure 1 A schematic diagram illustrating the design concept and working principle of a biomimetic electronic skin based on liquid metal and shape memory microneedles.

[0029] Figure 2 This is a schematic diagram of the preparation of liquid metal using the magnetic transfer technology (MST) of the present invention.

[0030] Figure 3 The figures show the shape memory function of PLATMC, the shape memory material of this invention. Figures (a), (b), and (c) respectively represent the deformation process of the butterfly shape, flower shape, and microneedle array at 37°C.

[0031] Figure 4 The images shown are physical images of shape memory microneedle arrays at different angles obtained in an example of the present invention; wherein, Figures (a) to (e) correspond to microneedle arrays at 90 degrees, 75 degrees, 60 degrees, 45 degrees and 30 degrees respectively.

[0032] Figure 5Physical images of liquid metal substrates and shape memory microneedles integrated using magnetron transfer technology (MST) were prepared.

[0033] Figure 6 This is a comparison of the peeling curves of the shape memory microneedles and vertical microneedles of the present invention on agarose and pigskin.

[0034] Figure 7 This is a diagram demonstrating the motion monitoring performance of biomimetic electronic skin based on liquid metal and shape memory microneedles. Detailed Implementation

[0035] The present invention can be better understood from the following embodiments.

[0036] Example 1: Fabrication and Programming of Shape Memory Microneedle Array

[0037] like Figure 1 The diagram shown illustrates the design concept and working principle of the biomimetic electronic skin based on liquid metal and shape memory microneedles of this invention.

[0038] (1) Fabrication of shape memory microneedle array:

[0039] Polylactide-trimethylene carbonate copolymer (PLATMC) was dissolved in chloroform (CHCl3) to prepare a 10% (w / v) solution. 2 mL of this solution was carefully pipetted into a pre-cleaned silicone microneedle mold. The mold had micropores arranged in an array, each pore being 1000 μm high, 360 μm in bottom diameter, and 700 μm between tips. The mold was placed in a vacuum desiccator and vacuumed for 2 minutes to ensure the polymer solution completely filled the bottom of each micropore without any air bubbles. The mold was then removed and placed in a fume hood to dry at room temperature for 24 hours. After the solvent had completely evaporated, the cured PLATMC microneedle array was carefully peeled off from the mold to obtain a vertically oriented microneedle array. This microneedle array was approximately 1000 μm high, approximately 360 μm in bottom diameter, and approximately 30 μm in tip diameter.

[0040] (2) Shape memory programming of microneedles:

[0041] Place the vertical microneedle array obtained in step (1) on a heating stage. Gently press the microneedle array from one side using a clean glass slide to tilt it at approximately 60°. Secure the microneedle array and glass slide in this tilted state using metal clamps. Then, place the entire device in a 40°C water bath for heat annealing for 10 minutes to allow the polymer molecular chains to rearrange under the tilting stress. After treatment, remove the device and allow it to air cool at room temperature for 30 minutes before finally removing the clamps. At this point, the microneedle array macroscopically returns to its initial vertical state, but its internal structure has "memorized" the 60° tilt. When heated again to 37°C (human body temperature), the microneedles will revert to their 60° barbed structure.

[0042] Combination Figure 3 It is evident that PLATMC material can stably exhibit shape memory recovery behavior at 37°C. Figure 3 (a) and Figure 3 In (b), the pre-programmed butterfly-shaped and flower-shaped macroscopic samples gradually recover from a temporary fixed state to a preset shape during the heating process; Figure 3 In (c), the microneedle array gradually recovers from a near-vertical temporary configuration to an inclined barbed configuration at 37°C. Both the macroscopic pattern and the microneedle array can undergo controllable recovery at temperatures close to human body temperature, indicating that the shape memory trigger temperature of PLATMC matches the skin application scenario and can provide a material basis for the subsequent "vertical insertion - body temperature recovery - tissue interlocking" working mode.

[0043] Combination Figure 4 As can be seen, shape memory microneedle arrays with different memory angles, such as 90°, 75°, 60°, 45°, and 30°, can be obtained by adjusting the pressing angle during the programming process. Each group of microneedles maintains a complete array structure, with no obvious breakage, collapse, or adhesion between the needles, indicating that the above thermomechanical programming method can achieve angle adjustment without damaging the basic morphology of the microneedles. As the memory angle decreases from 90° to 30°, the tilt of the microneedles gradually increases, and the barb effect is enhanced. This facilitates the formation of directional mechanical interlocking after the microneedles penetrate the tissue, thereby improving the device's resistance to detachment during skin stretching, rotation, and joint flexion and extension.

[0044] Example 2: Fabrication of a liquid metal flexible circuit (magnetically controlled iron bead transfer technology, MST)

[0045] (1) Preparation of PDMS substrate:

[0046] Mix the PDMS prepolymer and curing agent at a mass ratio of 10:1 and stir thoroughly until homogeneous. Pour 2 mL of the mixture into a clean glass petri dish and allow it to stand to level naturally. Place the dish in a vacuum degasser for 15 minutes to remove air bubbles generated during stirring. Then transfer it to a 60°C oven for curing for 4 hours to obtain a PDMS film with a thickness of approximately 0.8 mm and a smooth surface.

[0047] (2) Circuit patterning:

[0048] The cured PDMS film was subjected to oxygen plasma treatment (100 W, 0.8 mbar, 60 s) to improve its surface hydrophilicity, facilitating the spread of liquid metal. A 3D-printed polylactic acid (PLA) mold with an internally hollowed-out serpentine pattern (250 μm linewidth, 200 μm depth) was tightly bonded to the PDMS surface. Figure 2 The diagram illustrates the fabrication of liquid metal using magnetron sputtering (MST) technology. Specifically, a 2 mm diameter iron bead is immersed in a gallium indium alloy (EGaIn) liquid, uniformly covering its surface with an EGaIn layer. This bead is then placed at the entrance of a mold channel. A neodymium magnet (N52 grade) is slowly moved beneath the PDMS substrate, guiding the iron bead to roll precisely along the mold channel. Where the iron bead rolls, the liquid metal EGaIn is continuously transferred to the PDMS surface, forming conductive lines perfectly matching the channel pattern. After removing the 3D printing mold, a thin layer of PDMS (10:1 mixture and degassed) approximately 0.5 mm thick is cast on top of the patterned liquid metal. The circuit is then cured again in a 60°C oven for 4 hours for encapsulation, resulting in a sandwich-structured liquid metal flexible circuit. The fabricated serpentine circuit maintains acceptable resistance changes and continuous conductive paths even when stretched to 700% strain. Figure 5 It is evident that the magnetron transfer printing technology can form a variety of liquid metal conductive patterns, including letter patterns, snake patterns, cross patterns, and heart patterns, on PDMS substrates, demonstrating that this method has good pattern adaptability and processing flexibility. Figure 5 The study also demonstrated that the liquid metal conductive layer, after being encapsulated with PDMS, maintains a clear and continuous circuit outline and can be integrated with a shape memory microneedle array to obtain a structurally complete biomimetic electronic skin. This indicates that the MST process can not only fabricate regular serpentine sensing circuits but also customize conductive patterns according to different monitoring locations and device configuration requirements.

[0049] To further verify the stretchable conductivity of the liquid metal conductive layer, serpentine liquid metal conductive layers with linewidths ranging from 200 to 300 µm were fabricated. Digital multimeters were connected to both ends of each layer, and uniaxial tensile tests were performed on a tensile testing machine. During the test, the tensile displacement was gradually increased from the initial length, and the resistance change was recorded in real time, observing whether the conductive path broke or opened. The results show that when the linewidth of the liquid metal conductive layer is 200-300 µm, the conductive circuit maintains continuous electrical signal output even when stretched to at least 700% strain, without any sudden increase in resistance, signal interruption, or irreversible open circuit. This result demonstrates that the above linewidth range can balance pattern accuracy and liquid metal continuity under large deformation conditions, enabling the conductive path to adapt to tensile strains far exceeding the conventional deformation range of human skin.

[0050] Example 3: Integration and Performance Testing of Bionic Electronic Skin

[0051] The shape-programmed PLATMC microneedle array (vertical state) from Example 1 was bonded to the upper encapsulation layer surface of the liquid metal flexible circuit prepared in Example 2 using a small amount of uncured PDMS as an adhesive layer. The PDMS was then baked at 60°C for 30 minutes to fully cure, achieving a stable integration of the microneedle array and the flexible circuit, resulting in the final biomimetic electronic skin.

[0052] The microneedle array of the biomimetic electronic skin was gently pressed onto the skin surface of the test subject's forearm. The microneedles penetrated the stratum corneum painlessly in a vertical position. After several minutes, under the influence of body temperature, the tips of the microneedles gradually bent, forming a mechanical interlock with the skin tissue. Adhesion tests showed that compared with a vertical PLATMC microneedle array of the same size, the biomimetic barbed microneedles of this invention improved the lateral detachment force on the skin by approximately 65%. During the test subject's repeated flexion and extension of the wrist 100 times, the electronic skin maintained a tight fit with the skin without detachment or displacement. Simultaneously, the liquid metal serpentine circuit integrated in the electronic skin converted the strain generated by wrist flexion into a resistance change signal, which could be recorded stably and in real time by an external data acquisition system. After 8 hours of continuous operation, the device showed no significant signal drift or increase in noise. The above integrated results indicate that the shape memory microneedle array mainly provides the interface anchoring effect triggered by body temperature, while the liquid metal conductive layer mainly provides continuous conductivity and resistance response under large strain. The two work together to enable the biomimetic electronic skin to simultaneously possess stable adhesion and stable sensing capabilities. In particular, the liquid metal conductive layer with a linewidth of 200-300 µm maintains the continuity of the conductive path under at least 700% tensile strain, which can avoid the line breakage caused by large joint movements, thereby improving the signal reliability during human motion monitoring.

[0053] Comparative Example: Adhesion Stability of Traditional Vertical Microneedle Electronic Skin

[0054] A vertical PLATMC microneedle array was prepared using the same method as in Example 1 (without shape programming), and integrated with the same liquid metal flexible circuit as in Example 3 to obtain a control electronic skin. This control electronic skin was then attached to agarose and pigskin in the same manner, and the adhesion between the two was tested. Figure 6 As shown, shape memory microneedles (CM microneedles) can withstand greater loads during the peeling process on both agarose and porcine skin substrates, with their peeling curves generally higher than those of vertical microneedles, and the failure process lasting longer. On the agarose substrate, both CCM and vertical microneedles underwent initial attachment, interface expansion, and eventual detachment; however, the CCM microneedles exhibited a higher peak value in their peeling curve, indicating stronger interface locking in the homogeneous gel substrate. In contrast, the difference in peeling curves was more pronounced on the porcine skin substrate, with CCM microneedles not only showing a higher peak value but also maintaining high load for a longer period, indicating a more significant anchoring effect in real biological tissues. Quantitative results showed that the peak peel adhesion force of CCM microneedles on porcine skin was approximately 3.4 N, while that of vertical microneedles was approximately 2.1 N, with the former being about 60% higher than the latter. Therefore, CCM microneedles exhibit superior adhesion capabilities on both substrates.

[0055] Example 4: Demonstration of Human Motion Monitoring Performance of Bionic Electronic Skin Based on Liquid Metal and Shape Memory Microneedles

[0056] like Figure 7 The image shown illustrates the performance of the biomimetic electronic skin based on liquid metal and shape memory microneedles in human joint motion monitoring.

[0057] The bionic electronic skin prepared in Example 3 was applied to the thumb, wrist, and elbow joints of the test subjects. During application, the shape memory microneedle array was positioned so that one side faced the skin surface, and gentle pressure was applied to allow the microneedles to pierce the superficial layer of the skin in a near-vertical position. Subsequently, under the influence of body temperature, the shape memory microneedles gradually returned to the preset tilted barb-like structure, thereby forming a stable mechanical interlock with the skin tissue and improving the application stability of the device during repeated joint movements.

[0058] The liquid metal conductive lines at both ends of the bionic electronic skin are connected to a digital multimeter or data acquisition system via wires to record the changes in the device's resistance in real time during joint bending. During the test, the tester performs joint bending and extension movements at preset angles and records the resistance response signals under different movement states.

[0059] In the thumb joint movement test, the test subject performed thumb bending movements of approximately 30°, 60°, and 90°. The results showed that as the thumb bending angle increased, the amplitude of the resistance change output by the device gradually increased, and the resistance signals corresponding to different bending angles showed significant differences, indicating that the bionic electronic skin of the present invention can effectively identify different degrees of thumb joint bending.

[0060] In wrist joint motion testing, a bionic electronic skin was attached to the dorsal skin surface of the wrist joint, and the test subject performed wrist flexion movements at different angles. The test results showed that the device could output a stable and repeatable resistance response signal in response to changes in the wrist flexion angle, and the signal amplitude increased with the degree of flexion. This indicates that the device can adapt to large-amplitude wrist joint deformation and achieve real-time monitoring of the wrist joint motion status.

[0061] In elbow joint motion testing, a bionic electronic skin was attached to the skin surface near the elbow joint, and the test subject performed flexion and extension movements within a range of approximately 30° to 120°. Test results showed that the device maintained stable attachment during large-angle flexion and repeated flexion and extension, without significant detachment or displacement, and was able to output a continuous and regular resistance change signal. Due to the significant deformation of the skin surface during elbow joint movement, the device exhibited a more pronounced resistance response amplitude in the elbow joint test.

[0062] The above results demonstrate that the biomimetic electronic skin based on liquid metal and shape memory microneedles prepared in this invention can maintain stable adhesion during human joint movement and convert the skin surface deformation caused by joint movement into a detectable resistance change signal. This device can be used for human motion monitoring in different parts of the body, such as the thumb, wrist, and elbow joints, and exhibits good flexibility, interface stability, and motion signal recognition capabilities. Further combined with… Figure 7 (a)- Figure 7 As shown in the attached diagram and photographs in (c), the bionic electronic skin of the present invention can be attached to skin surfaces with different curvatures and different ranges of motion, such as the thumb, wrist, and elbow; combined with Figure 7 (d)- Figure 7As shown in the resistance response curve (f), during the bending of the thumb and wrist joints at approximately 30°, 60°, and 90°, and during the flexion and extension of the elbow joint from approximately 30° to 120°, the relative change in resistance gradually increases with the increase of the bending angle, and the repeating peak shape at the same angle has good consistency. This result indicates that the liquid metal conductive layer can convert the skin stretching and bending caused by joint movement into distinguishable resistance signals, while the shape memory microneedles can suppress the lifting, slippage, or detachment of the device edges during movement. Therefore, this embodiment further verifies the beneficial effects of this application from the perspective of human motion monitoring: on the one hand, the shape memory microneedles recover to the tilted barb structure at body temperature, forming a mechanical interlock with the superficial skin tissue, improving the adhesion reliability of the dynamic interface; on the other hand, the liquid metal conductive layer with a linewidth of 200-300 µm still maintains the continuity of the conductive path under tensile strain, providing a stable electrical transmission path for large-amplitude joint movements. The combination of these two technologies enables the resulting bionic electronic skin to continuously output stable and distinguishable motion signals under repeated bending and large deformation conditions, proving its suitability for applications such as personalized health monitoring, rehabilitation training assessment, and human-computer interaction.

[0063] This invention provides a concept and method for biomimetic electronic skin based on liquid metal and shape memory microneedles, its preparation method, and its application. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for fabricating biomimetic electronic skin based on liquid metal and shape memory microneedles, characterized in that, Includes the following steps: (1) Preparation of shape memory microneedle array: Dissolve shape memory polymer material in organic solvent, cast the resulting solution into a mold with micron-sized cavity, vacuum process the solution to fill the mold cavity, and obtain vertically oriented microneedle array after drying and demolding; (2) Shape programming of microneedle array: The vertical microneedle array obtained in step (1) is subjected to mechanical external force to produce a predetermined angle of tilt deformation, and heat treatment is performed under the condition of fixing the deformation state so that the tilt state becomes the permanent memory shape of the material. After cooling and releasing the external force, the microneedles return to the vertical state. (3) Preparation of liquid metal flexible circuit: Liquid metal alloy is deposited or coated on a flexible polymer substrate by patterning technology to form a conductive layer with a specific circuit pattern, and then encapsulated with another layer of flexible polymer to obtain a liquid metal flexible circuit; (4) The shape-programmed microneedle array obtained in step (2) is integrated and bonded with the liquid metal flexible circuit obtained in step (3) to obtain biomimetic electronic skin.

2. The preparation method according to claim 1, characterized in that, The shape memory polymer material mentioned in step (1) is polylactide-trimethylene carbonate copolymer, the organic solvent is chloroform, and the concentration of polylactide-trimethylene carbonate copolymer in the solvent is 5%-15% (w / v).

3. The preparation method according to claim 1, characterized in that, The mold mentioned in step (1) is a polydimethylsiloxane mold; the height of the micron-sized cavity is 800-1200 µm and the bottom diameter is 300-400 µm.

4. The preparation method according to claim 1, characterized in that, The predetermined angle in step (2) is 30°-90°; the heat treatment temperature is 35-50°C and the treatment time is 5-15 minutes; the mechanical external force is achieved by pressing and clamping the microneedle array to both sides.

5. The preparation method according to claim 1, characterized in that, The liquid metal alloy mentioned in step (3) is a gallium-indium alloy, and the flexible polymer substrate is polydimethylsiloxane.

6. The preparation method according to claim 1 or 5, characterized in that, The patterning technique described in step (3) is a magnetically controlled iron bead transfer technique, specifically: a template with a predetermined microchannel pattern is placed on a polydimethylsiloxane substrate, and ferromagnetic microbeads wetted with liquid metal are guided by an external magnetic field to roll in the channels of the template, thereby transferring the liquid metal to the substrate surface to form conductive lines.

7. The biomimetic electronic skin based on liquid metal and shape memory microneedles prepared by the preparation method according to any one of claims 1-6.

8. The bionic electronic skin according to claim 7, characterized in that, The microneedle array can spontaneously deform from a vertical state to a pre-programmed tilted state under body temperature conditions, forming a barbed structure that is mechanically interlocked with the tissue; the height of the microneedle is 900-1100 µm, the bottom diameter is 300-400 µm, and the tip diameter is 10-50 µm; the tilt angle after deformation is 25°-35°.

9. The bionic electronic skin according to claim 7, characterized in that, The liquid metal conductive layer has a linewidth of 200-300 µm and is able to maintain the continuity of the conductive path under at least 700% tensile strain.

10. The bionic electronic skin according to claim 7, characterized in that, The microneedle array is composed of poly(lactic acid-co-trimethylene carbonate), and its shape memory triggering temperature is between 36-40°C.

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