Bionic compound eye structure based on double-response hydrogel as well as preparation method and application of bionic compound eye structure

Abstract

The invention discloses a bionic compound eye structure based on double-response hydrogel and a preparation method and application of the bionic compound eye structure, and belongs to the technical field of bionic optical and micro-nano optical devices. The compound eye structure comprises a base formed by pH responsive bovine serum albumin hydrogel and an aspheric small eye array formed by solution polarity or osmotic pressure responsive polyethylene glycol diacrylate hydrogel, and the base and the aspheric small eye array are integrally formed through femtosecond laser two-photon polymerization processing. The deformation of the base can be independently regulated and controlled by regulating the pH value of the environment, the spatial orientation of the ommatidium is changed, and the continuous reversible regulation of the field angle within the range of 24-36 degrees is realized; the curvature radius and the optical thickness of the ommatidium can be independently regulated and controlled by adjusting the polarity or the osmotic pressure of the solution, and continuous reversible adjustment of the focal length within the range of 20 microns to 70 microns is achieved. The two regulation and control mechanisms are based on independent response characteristics of different materials, and complete decoupling and independent regulation and control of two core optical parameters of a field angle and a focal length are achieved. The device is compact in structure, quick in response and high in regulation and control precision.

Description

Technical Field

[0001] This invention belongs to the field of biomimetic optics and micro / nano optical device technology, specifically relating to a biomimetic compound eye structure based on dual-response hydrogel, its preparation method, and its application. Background Technology

[0002] Microlens arrays (MLAs), as core micro-optical components, play an indispensable role in modern imaging systems (such as mobile phone camera modules and endoscopes), light field displays, laser beam shaping, and optical communications. Their performance directly determines key indicators of optical systems, such as field of view, resolution, and depth of field. With the rapid development of optical systems towards miniaturization, integration, and intelligence, the demand for dynamically tunable microlens arrays with environmental adaptability is becoming increasingly urgent.

[0003] Traditional tunable microlens arrays primarily rely on physical mechanisms such as electrowetting, dielectrophoresis, thermo-induced deformation, or single-material stimulus responses (e.g., thermosensitive hydrogels) to adjust focal length or field of view. However, these technologies are generally limited by a single response mechanism and driving method. Most existing technologies can only achieve a single control function; when adjusting multiple parameters (such as field of view and focal length), severe mutual interference and coupling exist between parameters, failing to meet the demands for independent, precise, and dynamically coordinated control of tunable imaging in complex scenarios. In biomimetic compound eye structures based on single-response materials, changes in field of view and focal length both originate from the same volumetric deformation of the material, leading to inevitable correlated changes that cannot be decoupled. For example, driving the overall expansion of the hydrogel by changing the pH can expand the field of view, but it simultaneously causes an uncontrollable change in focal length, resulting in defocusing of the imaging plane and severely limiting its practical application effectiveness in dynamically variable scenarios.

[0004] Existing mainstream tunable micro-optics technologies, whether based on external force drive, field-induced modulation, or single stimulus response, struggle to achieve precise, independent, and reversible control of the two core optical parameters—field angle and focal length—on a miniaturized, integrated platform. This technological bottleneck hinders the development and application of next-generation intelligent adaptive optics systems. Currently, there are no reports of biomimetic compound eye devices that can achieve true decoupled control of field angle and focal length by structurally separating the two functional units and making their response mechanisms independent through different environmental stimuli. Summary of the Invention

[0005] To address the challenges of achieving independent and decoupled control of field of view and focal length in existing tunable microlens arrays, this invention proposes a compact, fast-responding, and independently controllable biomimetic compound eye structure based on dual-response hydrogel, along with its fabrication method and applications.

[0006] This invention is achieved through the following technical solution:

[0007] In a first aspect, the present invention provides a biomimetic compound eye structure based on a dual-response hydrogel, comprising a base structure and multiple independent ommatidia structures disposed on the base structure; the base structure is composed of bovine serum albumin (BSA) hydrogel that is volume-responsive to pH; the ommatidia structures are composed of polyethylene glycol diacrylate (PEGDA) hydrogel that is volume-responsive to solution polarity and osmotic pressure; the base structure and the ommatidia structures are integrally formed using femtosecond laser processing technology to form a composite structure; by changing the pH value of the environment in which the device is located, the deformation of the base structure can be independently controlled, thereby changing the spatial orientation of the ommatidia structures fixed on the surface of the base, thus achieving the control of the overall field of view of the biomimetic compound eye; by changing the polarity or osmotic pressure of the solution environment in which the device is located, the deformation of the ommatidia structures can be independently controlled, thereby changing their radius of curvature and optical thickness, thus achieving the control of the focal length of the biomimetic compound eye.

[0008] Furthermore, the geometry of the base structure made of bovine serum albumin hydrogel is spherical, with a bottom diameter of 60 to 300 micrometers and a height of 10 to 50 micrometers.

[0009] Furthermore, the eyelet structure made of polyethylene glycol diacrylate hydrogel is an aspherical microlens, and is arranged in a concentric multi-ring array on the surface of the base structure made of bovine serum albumin hydrogel; the bottom diameter of the eyelet structure is 10 micrometers to 50 micrometers, and the conic constant is -0.5; wherein, the eyelet structure located at the center coincides with the optical axis of the base structure, forming a central eyelet; the remaining eyelet structures form at least one concentric eyelet ring at different radial positions on the surface of the base structure, thereby forming a multi-layer nested ring microlens array that is centrally symmetrical and uniformly distributed on the surface of the base.

[0010] Furthermore, the field of view of the bionic compound eye can be independently, continuously, and reversibly adjusted between 24° and 36° by changes in the pH value of the environment.

[0011] Furthermore, the focal length of the bionic compound eye can be independently, continuously, and reversibly adjusted between 20 μm and 70 μm by changes in the polarity or osmotic pressure of the solution environment.

[0012] Secondly, the present invention provides a method for preparing a biomimetic compound eye structure based on a dual-response hydrogel, comprising the following steps:

[0013] S1. Solution Preparation: Two photosensitive hydrogel precursor solutions with different stimulus response characteristics were prepared respectively; among them, pH-responsive precursor solution: bovine serum albumin (BSA) and photoinitiator were dissolved in deionized water to form a uniform BSA-based photoresist; polar and osmotic pressure-responsive precursor solution: polyethylene glycol diacrylate (PEGDA) monomer and photoinitiator were dissolved in deionized water to form a uniform PEGDA-based photoresist.

[0014] S2. Substrate preparation and coating: Select a substrate with good light transmittance and clean its surface; drop the prepared BSA-based photoresist onto the substrate surface.

[0015] S3. Direct writing of the base structure: The substrate coated with BSA-based photoresist is placed in the femtosecond laser two-photon polymerization processing system. According to the preset three-dimensional model of the base, the focused femtosecond laser beam is controlled to perform three-dimensional scanning and direct writing in the photoresist layer, so that bovine serum albumin is solidified to form the base structure.

[0016] S4. Introduce the second photoresist: After the direct writing of the base structure is completed, deionized water is used to develop it; then, without replacing the substrate, PEGDA-based photoresist is introduced into the area where the formed base structure is located by drop casting.

[0017] S5. Direct writing of small-eye structure: Using the femtosecond laser two-photon polymerization processing system again, according to the preset three-dimensional model of small-eye array, a second three-dimensional femtosecond laser scanning direct writing is performed on the top of the solidified base structure to form the small-eye structure and achieve integrated bonding with the base structure.

[0018] S6. Development and Curing: The sample that has undergone two-step direct writing is immersed in a suitable developing solution to remove all unexposed and unpolymerized precursor materials, thereby obtaining a biomimetic compound eye structure composed of a bovine serum albumin hydrogel base and a polyethylene glycol diacrylate hydrogel eyelet.

[0019] Furthermore, in step S1, the photoinitiator is capable of absorbing light energy and generating active species (free radicals or reactive oxygen species), such as riboflavin, D-π-A type two-photon absorber molecules, Irgacure 2959, methylene blue, etc.

[0020] Furthermore, in steps S3 and S5, the processing parameters of the femtosecond laser direct writing technology are as follows: the laser fundamental wavelength is 800nm, the repetition frequency is 80MHz, the laser pulse width is 120ps, the single-point exposure time is 1000µs, and the scanning interval is 300nm.

[0021] In terms of third parties, this invention provides an application of a biomimetic compound eye structure based on dual-response hydrogel in intelligent environmental perception and dynamic zoom microlens arrays.

[0022] The working principle of the biomimetic compound eye structure based on dual-response hydrogel of this invention lies in the differential response mechanism of different materials to specific external physicochemical stimuli. By independently driving the two functional materials, independent and non-interfering control of the two key optical parameters of the device, namely the field of view and focal length, is achieved, as follows:

[0023] The pH response mechanism of the bovine serum albumin (BSA) hydrogel is as follows: the volume change of BSA with pH is due to the change in net charge, which dominates the alteration of intramolecular electrostatic repulsion and hydration, thereby regulating the conformational expansion and contraction of the protein molecules. When the environmental pH changes, the structure of the BSA hydrogel base 1 undergoes isotropic swelling or contraction, thereby changing the spatial pointing angle of the polyethylene glycol diacrylate microlens array 2 supported on it, especially the peripheral small eye units, thus achieving independent control of the field of view of the entire device, while the morphology of the polyethylene glycol diacrylate lens 2 remains basically unchanged during this process.

[0024] The response mechanism of the polyethylene glycol diacrylate (PEGDA) hydrogel to solution polarity and osmotic pressure is as follows: In calcium chloride solution, the PEGDA hydrogel dehydrates and shrinks due to the external osmotic pressure difference; in ethanol solution, it shrinks due to the collapse of the polymer network caused by the decrease in solvent polarity. When the polarity or osmotic pressure of the environmental solution changes, the PEGDA hydrogel orifice 2 structure undergoes a reversible volume change mainly along its optical axis, directly altering the radius of curvature and thickness of the orifice, thereby achieving independent control of the focal length of the entire device. During this process, the morphology of the BSA base 1 remains largely unaffected.

[0025] Compared with the prior art, the advantages of the present invention are as follows:

[0026] 1. Achieved true decoupled control: By leveraging the independent response mechanisms of two materials to different chemical stimuli (pH, polarity / osmotic pressure), independent and non-interfering control of two key optical parameters, field of view and focal length, was achieved for the first time on a single device.

[0027] 2. Highly integrated and miniaturized structure: It adopts advanced femtosecond laser direct writing technology to form a single piece, avoiding complex assembly processes and ensuring high precision, high consistency and good mechanical stability of micro-nano scale structures, resulting in a compact device structure.

[0028] 3. Excellent dynamic response performance: This bionic compound eye not only has a wide range of adjustment (field of view 24°–36°, focal length 20–70 μm), but also has a fast response (about 15 seconds), good reversibility and high cycle stability, meeting the adaptive imaging requirements in dynamic environments.

[0029] 4. It expands the design ideas of functional optical devices: It provides innovative device prototypes and feasible technical paths for developing a new generation of miniaturized intelligent optical systems with independent adjustment of multiple parameters and environmental adaptability (such as real-time monitoring in microfluidic chips, miniature endoscopes, etc.). Attached Figure Description

[0030] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0031] Figure 1 This is a schematic diagram of the overall structure of a biomimetic compound eye structure based on dual-response hydrogel according to the present invention.

[0032] Among them, the base structure 1 is made of bovine serum albumin hydrogel, and the eye structure 2 is made of polyethylene glycol diacrylate hydrogel;

[0033] Figure 2 This is a schematic diagram illustrating the field of view and focal length tuning of the bionic compound eye of the present invention:

[0034] Figure 3 This is a schematic diagram showing the quantitative test results of the tuning performance of the dual-response regulated hydrogel biomimetic compound eye structure of the present invention;

[0035] Where, a is the focal length tuning characteristic curve of the bionic compound eye, and b is the field of view tuning characteristic curve of the bionic compound eye.

[0036] Figure 4 This is a schematic diagram showing the test results of the decoupling regulation performance of the dual-response regulated hydrogel biomimetic compound eye structure of the present invention;

[0037] Wherein, a is the response curve of the system focal length and base size as a function of pH; b is the perturbation test curve of the field of view change when different concentrations of focal length tuning solution are introduced.

[0038] Figure 5 This is a schematic diagram showing the quantitative test results of the optical performance of the dual-response regulated hydrogel biomimetic compound eye structure of the present invention.

[0039] Where, a is the dynamic response time characteristic curve of the bionic compound eye to pH stimulation, b is the gray intensity distribution curve of the focus of the bionic compound eye, c is the full width at half maximum test curve of the Gaussian fitting of the focus of the compound eye structure under pH response, and d is the curve corresponding to the diffusion function of different axial points of the small eye focus.

[0040] Figure 6This is a schematic diagram illustrating the functional verification of the dual-response modulated hydrogel biomimetic compound eye structure of the present invention in terms of field of view and focal length tuning.

[0041] Among them, a is the optical imaging result of the compound eye structure in the short focal state and the reconstructed image of the monocular imaging, b is the optical imaging result of the compound eye structure in the long focal state and the reconstructed image of the monocular imaging, and c is a comparison of the experimental verification results of reversible variable focal length tuning achieved by chemical stimulation. Detailed Implementation

[0042] To clearly and completely describe the technical solution and its specific working process of the present invention, the specific embodiments of the present invention are as follows, in conjunction with the accompanying drawings:

[0043] Example 1

[0044] like Figure 1 As shown, this embodiment provides a biomimetic compound eye structure based on dual-response hydrogel. It is a multi-layer integrated structure, including a tunable microlens layer (micro-eye structure), a deformable canopy layer (base structure), and a glass substrate layer stacked sequentially from top to bottom. Its core is a composite microstructure composed of two types of hydrogels.

[0045] The biomimetic compound eye structure of this embodiment 1 includes a base structure and multiple independent micro-eye structures disposed on the base structure; the base structure is composed of bovine serum albumin (BSA) hydrogel that is volume-responsive to pH value; the micro-eye structures are composed of polyethylene glycol diacrylate (PEGDA) hydrogel that is volume-responsive to solution polarity and osmotic pressure; the base structure and the micro-eye structures are integrally formed by femtosecond laser processing technology to form a composite structure;

[0046] In this embodiment, the base structure 1, composed of bovine serum albumin hydrogel, is spherical with a bottom diameter of 60-300 micrometers and a height of 10-50 micrometers. The eyelet structure 2, composed of polyethylene glycol diacrylate hydrogel, is polymerized onto the upper surface of the base structure 1 using femtosecond laser direct writing. This eyelet structure is composed of polyethylene glycol diacrylate (PEGDA) hydrogel that is responsive to solution polarity and osmotic pressure. The eyelet structure 2 is an aspherical microlens with a bottom radius of 10-50 micrometers and a conic constant of -0.5. In a preferred embodiment, the bottom diameter of the bovine serum albumin spherical base 1 is selected to be 60 micrometers, and the height is 10 micrometers; the bottom diameter of the polyethylene glycol diacrylate eyelet 2 is 10 micrometers, and the conic constant is -0.5. There are two layers and seven eyelets of polyethylene glycol diacrylate 2.

[0047] Multiple eyelet structures 2, made of polyethylene glycol diacrylate hydrogel, are arranged in a concentric multi-ring array on the surface of the base structure 1, made of bovine serum albumin hydrogel. Specifically, the eyelet structure 2 at the center of the array is coaxial with the optical axis of the base structure 1, forming a central eyelet; the remaining eyelet structures 2 are arranged radially at different positions along the surface of the base structure 1, forming at least one annular eyelet unit group concentric with the central eyelet, and there are 2-5 annular eyelet unit groups; each annular unit group is centrally symmetrical and uniformly distributed on the surface of the spherical base, together forming an annular microlens array with a multi-layer nested structure.

[0048] In this embodiment, the swelling behavior of the polyethylene glycol diacrylate (PEGDA) hydrogel originates from the hydrogen bonding between the polyethylene glycol (PEG) segments and water molecules in its molecular chain structure. This bonding promotes the adsorption and retention of water molecules within the polymer network. By actively adjusting the parameters of the hydrogel's environment (osmotic pressure and polarity of the external solution), the strength and number of hydrogen bonds between the PEG segments and water molecules can be reversibly affected. This regulation directly alters the hydrophilic-hydrophobic balance and thermodynamic state of the hydrogel network, thereby achieving precise control over the water absorption and swelling volume of the hydrogel. The apparent volume of bovine serum albumin (BSA) is regulated by the environmental pH value. The mechanism is that changes in pH reversibly alter the ionization state of amino acid residues on the surface of BSA molecules, specifically the carboxyl groups of acidic amino acid residues (glutamic acid, aspartic acid) and the amino groups of basic amino acid residues (lysine, arginine, histidine), thereby leading to a change in the net charge of the protein molecule. The change in net charge directly affects the balance of intramolecular and intermolecular electrostatic interactions, thus determining the conformational expansion and hydrodynamic volume of BSA molecules in aqueous solution, thereby controlling their apparent volume. Near the isoelectric point (pH 4.8-5.0), the net charge of BSA molecules is zero, intramolecular electrostatic attraction is enhanced, and intermolecular electrostatic repulsion is weakest, resulting in the most compact conformation and the smallest apparent volume. When the ambient pH is below the isoelectric point, the carboxyl group protonates (-COOH) and the amino group protonates, becoming positively charged (-NH3⁺), causing the BSA molecule to carry a large net positive charge. When the ambient pH is above the isoelectric point, the carboxyl group deprotonates, becoming negatively charged (-COO⁻) and the amino group deprotonates, causing the BSA molecule to carry a large net negative charge. In these two states deviating from the isoelectric point, strong intramolecular repulsion of like charges causes protein conformational expansion, while enhanced hydration further leads to a significant increase in its apparent volume.

[0049] Bovine serum albumin (BSA) spherical base 1: Serving as a field-of-view control unit, it is composed of bovine serum albumin (BSA) hydrogel with volume-responsive properties to pH. Its morphological changes directly determine the spatial orientation of the upper ommatidia structure, thus determining the field of view of the compound eye device; Polyethylene glycol diacrylate (PEGDA) aspherical ommatidia 2: Serving as a focal length control unit, it is composed of polyethylene glycol diacrylate (PEGDA) hydrogel with volume-responsive properties to solution polarity and osmotic pressure. Its axial dimensions and curvature changes directly determine the focal length of a single microlens.

[0050] Example 2

[0051] This embodiment provides a method for preparing a biomimetic compound eye structure based on a dual-response hydrogel, including the following steps:

[0052] S1. Solution Preparation: Two photosensitive hydrogel precursor solutions with different stimulus response characteristics were prepared. The pH-responsive precursor solution consisted of bovine serum albumin (BSA) and methylene blue dissolved in deionized water at a volume ratio of 1.8:0.0099:3. After aging at 4°C in the dark for 72 hours, a uniform BSA-based photoresist was formed. The polar and osmotic pressure-responsive precursor solution consisted of polyethylene glycol diacrylate (PEGDA) monomer and methylene blue dissolved in deionized water at a volume ratio of 1:0.001:0.3. After ultrasonic mixing in the dark for 30 minutes, a uniform PEGDA-based photoresist was formed.

[0053] S2. Substrate preparation and coating: Select a substrate with good light transmittance and clean its surface; drop the prepared BSA-based photoresist onto the substrate surface.

[0054] S3, Direct Writing of Base Structure: The substrate coated with BSA-based photoresist is placed in the femtosecond laser two-photon polymerization processing system. According to the preset three-dimensional model of the base, the focused femtosecond laser beam is controlled to perform three-dimensional scanning and direct writing in the photoresist layer, so that bovine serum albumin is solidified to form base structure 1.

[0055] S4. Introduce the second photoresist: After completing the direct writing of the base structure, develop it with deionized water; then, without replacing the substrate, introduce the PEGDA-based photoresist into the area where the formed base structure 1 is located by drop casting.

[0056] S5. Direct writing of small-eye structure: Using the femtosecond laser two-photon polymerization processing system again, according to the preset three-dimensional model of small-eye array, a second three-dimensional femtosecond laser scanning direct writing is performed on the top of the solidified base structure to form small-eye structure 2, and integrated bonding is achieved with the base structure;

[0057] S6. Development and Curing: The sample that has undergone two-step direct writing is immersed in a suitable developing solution to remove all unexposed and unpolymerized precursor materials, thereby obtaining a biomimetic compound eye structure composed of bovine serum albumin hydrogel base 1 and polyethylene glycol diacrylate hydrogel eyelet 2.

[0058] In steps S3 and S5, the processing parameters of the femtosecond laser direct writing technology are as follows: the laser fundamental wavelength is 800nm, the repetition frequency is 80MHz, the laser pulse width is 120ps, the single-point exposure time is 1000µs, and the scanning interval is 300nm.

[0059] Example 3

[0060] This embodiment demonstrates the control performance and working principle of the biomimetic compound eye structure of Embodiment 1 through experimental testing.

[0061] like Figure 2 As shown, the working process of the biomimetic compound eye structure device presents a dynamic and reversible cycle. Specifically, the initial state 1 corresponds to the device's morphology when the ambient pH is 5 and there is no calcium chloride or ethanol stimulation solution. When a pH stimulus is applied, the BSA base 1 undergoes a volume-responsive deformation, and the device transitions from state 1 to state 2. Based on state 2, when a calcium chloride or ethanol stimulation solution is applied, the PEGDA eyelet 2 exhibits a volume response, and the device further transitions to state 3. If the pH stimulus is removed in state 3, the morphology of the BSA base 1 recovers, and the device enters state 4. Finally, after the calcium chloride and ethanol stimulation solution is removed in state 4, the PEGDA eyelet 2 returns to its original state, and the device reversibly returns to state 1, thus completing a complete and reversible dual-stimulation response cycle. The four state cycles visually demonstrate the device's reversible working process and state switching capability under dual stimulation, proving its good cycle stability.

[0062] Specifically, the working principle and regulation process of the bionic compound eye. The regulation function of the device is based on the volume phase change of two materials: the bovine serum albumin (BSA) hydrogel base has pH-responsive characteristics. When the environmental pH value deviates from the isoelectric point of the BSA material, the BSA base 1 swells or shrinks. Since the PEGDA ommatidia 2 are fixed on this base, the change in the radial dimension of the base will change the angle between the optical axis of the outer ommatidia 2 and the central optical axis, thereby realizing the adjustment of the viewing angle of the entire device. During this process, the material volume and optical morphology of the PEGDA ommatidia 2 themselves basically remain unchanged, so the system focal length of the device is not significantly affected by this regulation process; when the polarity or osmotic pressure of the environmental solution (such as ethanol concentration, salt ion concentration) changes, the PEGDA ommatidia 2 mainly undergo reversible water absorption expansion or dehydration shrinkage along their optical axes. This axial deformation directly changes the curvature radius and optical thickness of the microlens, thereby realizing independent regulation of the focal length. During this process, the BSA base 1 as the support structure maintains a stable shape, so the viewing angle of the device remains unchanged.

[0063] Independent regulation of the viewing angle: When the pH value of the environment where the device is located changes (for example, in the environment of the bionic compound eye, a pH buffer solution is applied, resulting in the pH changing from 5 to the range of pH = 1 or pH = 12), the BSA base 1 undergoes volume swelling or shrinkage. Since the PEGDA ommatidia 2 are bonded to the BSA base 1 by femtosecond laser direct writing, the deformation of the BSA base 1 will change the spatial pointing angle of the optical axis of the outer ommatidia 2, thereby directly regulating the viewing angle of the entire device, while the pH has very little effect on the focal length of the PEGDA ommatidia 2. It is experimentally measured that through pH stimulation, the viewing angle can be reversibly adjusted within the range of 24° to 36°, see Figure 3 of b; Independent regulation of the focal length: When the polarity or osmotic pressure of the solution contacted by the device changes (for example, contacting a mixed solution of different proportions of ethanol and saturated calcium chloride), the PEGDA ommatidia 2 mainly undergo water absorption swelling or dehydration shrinkage along their optical axes, thereby changing their curvature radius and optical thickness to achieve the adjustment of the focal length. This process is mainly completed by the deformation of the PEGDA ommatidia 2 themselves, and has basically no interference on the shape of the BSA base 1 and the viewing angle determined thereby. It is experimentally measured that the focal length can be tuned within the range of 20 microns to 70 microns, and the maximum tuning amplitude can reach 32.8 ± 2% of the initial focal length, see Figure 3 of a.

[0064] Verification of decoupling performance: To prove the independence of the regulation of the viewing angle and the focal length, a special decoupling test was carried out, as Figure 4 shown:

[0065] In an environment with a fixed pH = 7, the solution polarity was changed to drive the change in the focal length. It was measured that as the focal length changed, the change in the viewing angle was only about 0.01 ± 0.005°, as Figure 4b indicates that the effect of the focus adjustment process on the field of view is negligible within the error range; when adjusting the field of view in different pH environments, the measured system focus will change slightly, such as Figure 4 Further analysis confirmed that this focal length change originated entirely from the additional optical power generated by the deformation of the BSA base 1 itself, consistent with the theoretical expectation of the formula f=R1 / (n−1), while the focal length of the PEGDA small eye 2 remained stable during this process. This proves that the focal length adjustment function of the PEGDA small eye 2 was not disturbed in the field of view control mode.

[0066] Dynamic response and optical performance: Figure 5 Figure a shows the dynamic response time characteristics of the compound eye structure to pH stimulation. When the ambient pH value switches between 5 and 11, the device volume change is mainly concentrated in the first 10 seconds and reaches a steady state in about 15 seconds, indicating that it has a rapid stimulus response and shape recovery capability; Figure 5 b shows the gray intensity distribution curve at the cross section of the central small eye 2, and its light intensity distribution conforms to the Gaussian distribution characteristics; Figure 5 Figure c shows the angle sensitivity function curves of the compound eye under different pH conditions. Measurements showed that the full width at half maximum (FWHM) of the angle sensitivity function was 17.95 μm, 16.79 μm, and 17.62 μm at pH values ​​of 9, 7, and 2, respectively, which is consistent with the trend of the compound eye BSA base under different pH stimuli. Figure 5 Figure d shows the point spread function curve of the central ommatidia 2. The full width at half maximum (FWHM) of the light spot in the x and y directions are 4.44 μm and 4.34 μm, respectively, demonstrating the uniformity of the convergent light spot in the compound eye. The change in the FWHM of the angle sensitivity function is consistent with the volume change trend of the BSA base 1 under PH stimulation, directly confirming the effectiveness of field-of-view modulation from an optical perspective.

[0067] Example 4

[0068] This embodiment provides an application of a biomimetic compound eye structure based on dual-response hydrogel in intelligent environmental sensors and dynamic zoom microlens arrays.

[0069] To verify the actual imaging function and control effect of the device described in this invention, an optical imaging system was constructed, and the following embodiments were performed for verification:

[0070] like Figure 6As shown in a and b, this embodiment demonstrates the process of active field-of-view tuning through pH stimulation. At the start of the experiment, the compound eye was in an environment with pH=5. At this time, the BSA base 1 relatively contracted in volume, causing the PEGDA micro-eyes 2 fixed on it to converge towards the center, resulting in a small field-of-view state. After image acquisition, stitching, and digital reconstruction of the monocular view for each micro-eye 2, a pattern containing three concentric square outlines was obtained. Subsequently, the ambient pH was adjusted to 2. Under this acidic condition, according to the pH response mechanism of BSA hydrogel, its molecular chains generate stronger electrostatic repulsion due to the increase in net charge, causing the base to swell, recover its volume, and slightly expand. This deformation caused the optical axis of the peripheral PEGDA micro-eyes 2 to deflect outwards. After reconstruction using the same image processing method, the obtained monocular view contained four concentric square outlines. The significant change from three-frame rings to four-frame rings in the reconstructed image visually confirms that altering the morphology of the BSA base 1 through pH stimulation can effectively control the spatial orientation of the peripheral micro-eyes 2, thereby achieving active widening of the field of view.

[0071] like Figure 6 As shown in Figure c, this embodiment demonstrates the process of achieving reversible focal length tuning through chemical stimulation. The experiment involved two target objects at different object distances: a nested box template at a closer distance and a letter "F" template at a farther distance. First, a specific chemical stimulation solution (such as a mixture of calcium chloride and anhydrous ethanol) was introduced into the system. Based on the response mechanism of PEGDA hydrogel to solution polarity and osmotic pressure, the high external osmotic pressure difference and reduced solvent polarity caused by the mixed solution drove the PEGDA micro-eye 2 network to dehydrate and undergo axial contraction, causing the compound eye to enter a short focal length state. In this state, both the near and far target objects were within the effective imaging depth of the device, thus the system could simultaneously form clear images of both. Subsequently, the chemical stimulation solution was removed, restoring the environment to its initial state. The PEGDA hydrogel network reabsorbed water and swelled, the micro-eye 2 returned to its original shape along the optical axis, and the device returned to a long focal length state. At this point, only the distant letter "F" target object remained within the clear imaging range, therefore the reconstructed image only showed a clear image of the letter "F". The reversible switching between clear imaging of two targets and imaging of distant targets only directly proves that active and reversible tuning of the focal length can be achieved by changing the axial size and curvature of PEGDA micro-eye 2 through chemical stimulation.

[0072] In summary, the above embodiments not only intuitively demonstrate the device's ability to independently control the field of view and focal length, but also show that the experimental phenomena are completely consistent with the stimulus-response mechanisms of the aforementioned BSA and PEGDA hydrogel materials, thus fully verifying the correctness of the design principle and the feasibility of the invention. This device successfully achieves dual, independent, and reversible control of the field of view and focal length, and has clear application potential in fields such as microscale imaging, motion monitoring, biomedical sensing, and integrated microfluidic optical systems.

[0073] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0074] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0075] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A biomimetic compound eye structure based on dual-response hydrogel, characterized in that, The device includes a base structure and multiple independent eye structures mounted on the base structure. The base structure is composed of bovine serum albumin (BSA) hydrogel that is volume-responsive to pH. The eye structures are composed of polyethylene glycol diacrylate (PEGDA) hydrogel that is volume-responsive to solution polarity and osmotic pressure. Both the base structure and the eye structures are integrally formed using femtosecond laser processing technology, forming a composite structure. By changing the pH value of the environment in which the device is located, the deformation of the base structure can be independently controlled, thereby changing the spatial orientation of the eye structures fixed on the base surface, thus achieving the control of the overall field of view of the bionic compound eye. By changing the polarity or osmotic pressure of the solution environment in which the device is located, the deformation of the eye structures can be independently controlled, thereby changing their radius of curvature and optical thickness, thus achieving the control of the focal length of the bionic compound eye.

2. The biomimetic compound eye structure based on dual-response hydrogel as described in claim 1, characterized in that, The base structure, made of bovine serum albumin hydrogel, has a spherical shape with a base diameter of 60 to 300 micrometers and a height of 10 to 50 micrometers.

3. The biomimetic compound eye structure based on dual-response hydrogel as described in claim 1, characterized in that, The eyelet structure made of polyethylene glycol diacrylate hydrogel is an aspherical microlens, and is arranged in a concentric multi-ring array on the surface of the base structure made of bovine serum albumin hydrogel. The bottom diameter of the eyelet structure is 10 micrometers to 50 micrometers, and the conic constant is -0.

5. The eyelet structure located at the center coincides with the optical axis of the base structure, forming the central eyelet. The remaining eyelet structures form at least one concentric eyelet ring at different radial positions on the surface of the base structure, thereby forming a multi-layer nested ring microlens array that is centrally symmetrical and uniformly distributed on the surface of the base.

4. The biomimetic compound eye structure based on dual-response hydrogel as described in claim 1, characterized in that, The field of view of the bionic compound eye can be independently, continuously, and reversibly adjusted between 24° and 36° by changes in the pH value of the environment.

5. The biomimetic compound eye structure based on dual-response hydrogel as described in claim 1, characterized in that, The focal length of the bionic compound eye can be independently, continuously, and reversibly adjusted between 20 μm and 70 μm by changes in the polarity or osmotic pressure of the solution environment.

6. The method for preparing a biomimetic compound eye structure based on a dual-response hydrogel as described in claim 1, characterized in that, Includes the following steps: S1. Solution Preparation: Two photosensitive hydrogel precursor solutions with different stimulus response characteristics were prepared respectively; among them, pH-responsive precursor solution: bovine serum albumin (BSA) and photoinitiator were dissolved in deionized water to form a uniform BSA-based photoresist; polar and osmotic pressure-responsive precursor solution: polyethylene glycol diacrylate (PEGDA) monomer and photoinitiator were dissolved in deionized water to form a uniform PEGDA-based photoresist. S2. Substrate preparation and photoresist coating: Select a substrate with good light transmittance and clean its surface; drop the prepared BSA-based photoresist onto the substrate surface. S3. Direct writing of the base structure: The substrate coated with BSA-based photoresist is placed in the femtosecond laser two-photon polymerization processing system. According to the preset three-dimensional model of the base, the focused femtosecond laser beam is controlled to perform three-dimensional scanning and direct writing in the photoresist layer, so that bovine serum albumin is solidified to form the base structure. S4. Introducing the second photoresist: After the direct writing of the base structure is completed, deionized water is used to develop it; then, without replacing the substrate, PEGDA-based photoresist is introduced into the area where the formed base structure is located by drop casting. S5. Direct writing of small-eye structure: Using the femtosecond laser two-photon polymerization processing system again, according to the preset three-dimensional model of small-eye array, a second three-dimensional femtosecond laser scanning direct writing is performed on the top of the solidified base structure to form the small-eye structure and achieve integrated bonding with the base structure. S6. Development and Curing: The sample that has undergone two-step direct writing is immersed in a suitable developing solution to remove all unexposed and unpolymerized precursor materials, thereby obtaining a biomimetic compound eye structure composed of a bovine serum albumin hydrogel base and a polyethylene glycol diacrylate hydrogel eyelet.

7. The method for preparing a biomimetic compound eye structure based on a dual-response hydrogel as described in claim 6, characterized in that, In step S1, the photoinitiator is riboflavin, D-π-A type two-photon absorber molecule, Irgacure 2959, or methylene blue.

8. The method for preparing a biomimetic compound eye structure based on a dual-response hydrogel as described in claim 6, characterized in that, In steps S3 and S5, the processing parameters of the femtosecond laser direct writing technology are as follows: the laser fundamental wavelength is 800nm, the repetition frequency is 80MHz, the laser pulse width is 120ps, the single-point exposure time is 1000µs, and the scanning interval is 300nm.

9. The application of the biomimetic compound eye structure based on dual-response hydrogel as described in claim 1 in intelligent environmental perception and dynamic zoom microlens array.

Images