A swelling self-assembled gelma / cnts-agnps hydrogel microcrack sensor and a preparation method thereof

Abstract

This invention discloses a swelling self-assembled GelMA / CNTs-AgNPs hydrogel microcrack sensor and its preparation method. Using photocrosslinked GelMA as a flexible substrate, CNTs as a conductive filler, and AgNPs as a conductive layer, the photocrosslinked GelMA and CNTs solutions are mixed and shaped using a double-exposure technique. Subsequently, a uniform layer of AgNPs is attached to the surface of the pre-crosslinked GelMA / CNTs hydrogel. This GelMA / CNTs-AgNPs hydrogel is then immersed in water, allowing it to absorb water and swell. Utilizing the negative correlation between the degree of crosslinking and the degree of swelling of the photosensitive hydrogel, local tensile stress is generated on the hydrogel surface. The AgNPs conductive layer is subjected to this stress, generating microcracks, resulting in an isotropic microcrack sensor. The sensor of this invention exhibits ultra-high sensitivity and ultra-low detection limit, isotropic strain sensing capability, and excellent flexibility and biocompatibility, ensuring long-term monitoring of the contraction and relaxation movements of cardiomyocytes under natural conditions. This invention is expected to advance the development of microcrack sensors towards real-time, quantitative monitoring of complex and minute biomechanical systems.

Description

Technical Field

[0001] This invention belongs to the field of mechanical bionics and biomanufacturing, and relates to a stress sensor, and more particularly to a swellable self-assembled hydrogel microcrack sensor with isotropic ultra-high sensitivity and ultra-low detection limit made of biocompatible materials. Background Technology

[0002] Cardiac cardiomyocytes are the fundamental power units of the heart, and exploring their function is beneficial for understanding the pathogenesis of heart diseases. Cardiac cardiomyocyte contractility is an important indicator for assessing its function. The contractile force and deformation of a single mature cardiomyocyte along the heart wall are approximately 1 μN and 1 μm, respectively. These extremely small contractile forces and deformations pose significant challenges to the detection of cardiomyocyte contractility. Traditional strain sensors suffer from low-response sensitivity, limiting their application to relatively large-amplitude joint movements and failing to meet the requirements for detecting the minute, multi-directional contractile forces of cardiomyocytes. However, existing microcrack sensors exhibit significant differences in measurement accuracy across different directions.

[0003] In 2014, inspired by the spider-like slit-like sensory organs, Choi's team developed the first microcrack strain sensor based on pre-stretching and molding, publishing their work in Nature, which attracted widespread attention. Its ultra-high strain sensitivity makes it a promising method for quantifying cellular contractile forces. To detect the complex and diverse strains during myocardial contraction, microcrack sensors should be able to accurately detect minute strains in all directions. However, limited by microcrack fabrication methods, existing microcrack sensors exhibit significant differences in measurement accuracy across different directions. How to generate isotropic microcracks has become crucial for solving the problem of high-precision isotropic sensing and overcoming the bottleneck in the biological applications of microcrack sensors. The microcrack swelling molding method based on the difference in swelling properties between flexible membranes and conductive layers is an important innovative approach for generating isotropic microcracks. Among these, biocompatible hydrogels, with their excellent water absorption and swelling properties, are the best choice for flexible substrates for isotropic microcrack sensors. Therefore, this project proposes a microcrack design scheme based on the isotropic water absorption and swelling properties of hydrogels to solve the problems of poor controllability of microcrack formation, large differences in multi-directional detection accuracy, and poor biocompatibility, so as to obtain a high-precision isotropic microcrack sensor and realize the detection of small and complex biomechanical parameters such as myocardial cell contractile force. Summary of the Invention

[0004] Measuring myocardial contractility is crucial for assessing cardiac function and exploring the pathogenesis of heart-related diseases. However, the extremely small contractile force and minute deformation of a single mature cardiomyocyte along the heart wall pose a significant challenge to its detection. Therefore, there is an urgent need for a sensor that meets the aforementioned mechanical performance requirements. Furthermore, this sensor should be biocompatible to ensure long-term monitoring of the natural contraction and relaxation movements of cardiomyocytes.

[0005] This invention selects photocrosslinked GelMA as a flexible substrate, highly conductive and flexible CNTs as the conductive filler, and silver nanoparticles (AgNPs) as the conductive layer. A highly sensitive isotropic microcrack sensor of AgNPs is prepared using a swelling self-assembly method. The experiment first fabricated a hydrogel solution using 10 wt% GelMA, 0.5–1.5 wt% CNTs, and 0.5 wt% 12959 photoinitiator. Using a double-exposure technique, the GelMA / CNTs solution was first fully exposed to ultraviolet light to pre-form the entire GelMA / CNTs hydrogel. Then, a custom-designed mask was placed on the pre-crosslinked hydrogel, and it was irradiated again with ultraviolet light to achieve localized differential crosslinking of the GelMA / CNTs hydrogel material, resulting in differences in the degree of local crosslinking. The GelMA / CNTs hydrogel was placed in a 25 mg / ml AgNO3 solution, and 1.0–1.5 ml of 15 mg / ml ascorbic acid was added. After waiting 0.5–5 hours, silver ions were reduced and deposited on the hydrogel surface, yielding a GelMA / CNTs-AgNPs sensor. Solvent-assisted swelling molding is a typical method for isotropic microcrack formation. Because the hydrogel layer absorbs water and swells in a liquid environment, and the degree of water absorption and swelling is inversely proportional to the degree of cross-linking, different degrees of swelling will cause tensile stress in the GelMA / CNTs-AgNPs composite film layer. This leads to instability and cracking of the conductive layer on the surface of the micropatterned hydrogel due to differences in swelling deformation. Since the cracks are generated by a large-scale isotropic volume change resulting from a swelling-deswelling process in response to environmental stimuli, this method can generate isotropic cracks. In summary, an isotropic microcrack sensor was fabricated using this method.

[0006] Therefore, the beneficial effects of this invention are as follows: By utilizing self-assembled GelMA / CNTs-AgNPs and changing process parameters, the polymerization degree and swelling degree of the GelMA / CNTs hydrogel can be altered, thereby changing the morphology of the composite film surface and achieving the desired effect of the fabricated microcrack sensor. Compared with traditional microcrack sensors, the newly invented sensor has ultra-high sensitivity and ultra-low detection limit, capable of capturing minute mechanical deformations under myocardial contraction, and can also be used in other fields of fine force measurement. Most importantly, the newly invented sensor has isotropic strain sensing capability, enabling it to understand the complex multidirectional contraction motion in cardiac tissue, a capability not found in other microcrack sensors. Finally, this sensor possesses excellent flexibility and biocompatibility, ensuring long-term monitoring of the contraction and relaxation motions of myocardial cells under natural conditions. This invention is expected to advance the development of microcrack sensors towards real-time, quantitative monitoring of complex micro-biomechanics. Attached Figure Description

[0007] Figure 1 This is a schematic diagram of the fabrication process of a microcrack sensor based on a swelling self-assembly process.

[0008] Figure 2 This provides an explanation of the anisotropic swelling and microcrack formation mechanism of hydrogels.

[0009] Figure 3 The equivalent sensing circuit and strain-crack size mathematical model for GelMA / CNTs-AgNPs microcracks.

[0010] Figure 4 Microscopic morphology of the GelMA / CNTs-AgNPs microcrack sensor. Detailed Implementation Plan

[0011] Example 1

[0012] like Figure 1 As shown, a hydrogel solution was first prepared with 10 wt% GelMA and 1 wt% CNTs, and then photoinitiator 12959 with a concentration of 0.5 wt% was added to obtain a hydrogel prepolymer. Subsequently, a first indiscriminate exposure was performed under ultraviolet light, followed by selective exposure under the cover of a patterned mask, thereby obtaining a GelMA / CNTS hydrogel with different crosslinking characteristics between regions.

[0013] Next, AgNPs self-assembly was performed. The GelMA / CNTs hydrogel was immersed in a 25 mg / ml AgNPs solution and gently stirred at room temperature. Then, 1.0 ml of 15 mg / ml ascorbic acid was added to the solution to reduce AgNO3 to AgNPs. After one hour, the reduced AgNPs gradually self-assembled onto the surface of the GelMA / CNTs hydrogel. Finally, the composite membrane was thoroughly washed several times with deionized water to remove free, unadhered AgNPs, yielding the GelMA / CNTs-AgNPs hydrogel.

[0014] The swelling and anisotropic swelling formation mechanism of the hydrogel and microcracks prepared by this invention are as follows: Figure 2 As shown, the hydrogel layer absorbs water and swells in a liquid environment, and the degree of water absorption and swelling of the hydrogel is inversely proportional to the degree of cross-linking. Different degrees of swelling will lead to tensile stress in the GelMA / CNTs-AgNPs composite film layer, thereby causing the conductive layer on the surface of the micropatterned hydrogel to become unstable and crack due to differences in swelling deformation. Since the cracks are generated by a large-scale isotropic volume change due to the swelling-de-swelling process in response to environmental stimuli, this method can generate isotropic cracks.

[0015] Finally, the GelMA / CNTs-AgNPs composite membrane was placed in water to allow it to absorb water and swell. Due to the negative correlation between the degree of crosslinking of the hydrogel and its water absorption, protrusions formed on the hydrogel surface, thereby inducing stress on the surface AgNPs and forming isotropic cracks. Thus, an isotropic microcrack sensor was obtained, with a micromorphology as shown in the figure. Figure 4 As shown.

[0016] The equivalent sensing circuit and strain-crack size mathematical model for GelMA / CNTs-AgNPs microcracks are as follows: Figure 3 As shown, assuming the resistance of the AgNPs conductive layer is R0 and the resistance of the GelMA / CNT substrate layer is R1, due to the difference in conductivity between the conductive layer and the hydrogel substrate layer, R1 is much larger than R0. Figure 3 From (i), it can be seen that when the invented microcrack sensor is not subjected to force, the current is mainly conducted by AgNPs in the conductive layer, and the resistance at this time is R = R0.

[0017] When the sensor is subjected to small strain (ii), the contact area between silver nanoparticles in the conductive layer of the elastic matrix decreases, and the resistance increases exponentially with the increase of the AgNPs spacing. However, in the GelMA hydrogel, CNTs can maintain the integrity of the conductive network, and the total resistance depends on the parallel resistance of the AgNPs film and the GelMA / CNTs conductive hydrogel.

[0018] As the strain amplitude increases, the crack size in the AgNPs conductive layer increases, resulting in a significantly greater resistance of the conductive layer than that of the GelMA / CNTs conductive hydrogel substrate. The GelMA / CNTs conductive hydrogel provides the only continuous conductive path for electrical signal sensing, at which point the resistance R = R1.

[0019] Therefore, this invention allows the stress value applied to the sensor to be obtained by measuring the change in the sensor's resistance. Unlike microcracks based on pre-stretched channels, the isotropic swelling characteristics of the novel hydrogel eliminate the anisotropic sensing properties caused by anisotropic cracks. When the microcrack sensor is subjected to strain in different directions, the same crack gap can be generated under the same strain in different directions. Therefore, the sensor based on GelMA / CNTs-AgNPs isotropic microcracks can achieve isotropic sensing.

[0020] Example 2

[0021] (1) Prepare a hydrogel solution with a concentration of 10wt% GelMA and 1.5wt% CNTs, and then add photoinitiator 12959 with a concentration of 0.5wt% to obtain a hydrogel prepolymer.

[0022] (2) Then, the first indiscriminate exposure was performed under ultraviolet light, and then selective exposure was performed under the cover of a patterned mask to obtain GelMA / CNTS hydrogel with crosslinking differences between regions.

[0023] (3) To perform AgNP self-assembly, the GelMA / CNTS hydrogel was immersed in a 25 mg / ml AgNP solution and gently stirred at room temperature. Then, 1.5 ml of 15 mg / ml ascorbic acid was added to the solution to reduce AgNO3 to AgNPs. After 2 hours, the reduced AgNPs gradually self-assembled on the surface of the GelMA / CNTs hydrogel.

[0024] (4) The composite membrane was thoroughly cleaned several times with deionized water to remove free and unadhered AgNPs and obtain the GelMA / CNTs-AgNPs hydrogel microcrack sensor.

Claims

1. A method for fabricating a swelling self-assembled GelMA / CNTs-AgNPs hydrogel microcrack sensor, characterized in that, The preparation method selects photocrosslinked methacryloyl gelatin (GelMA) as a flexible substrate, carbon nanotubes (CNTs) as a conductive filler, and silver nanoparticles (AgNPs) as a conductive layer. The GelMA / CNTs-AgNPs high-sensitivity isotropic microcrack sensor is prepared by swelling self-assembly method. The preparation method specifically includes the following steps: S1. A certain concentration ratio of methacrylamide gelatin (GelMA) and carbon nanotubes (CNTs) is mixed to prepare a GelMA / CNTs hydrogel solution, and then a photoinitiator is added to form a GelMA / CNTs hydrogel prepolymer. S2. A photocrosslinked GelMA / CNTs hydrogel is formed by a double exposure process; S3. GelMA / CNTs-AgNPs hydrogel microcrack sensor was prepared by self-assembly deposition of silver nanoparticles AgNPs on the surface of photocrosslinked GelMA / CNTs hydrogel. The secondary exposure process in S2 is specifically as follows: S2-1, First uniform and indiscriminate exposure: The GelMA / CNTs hydrogel solution is completely exposed to ultraviolet light to pre-crosslink the entire GelMA / CNTs hydrogel; S2-2, Second selective exposure under the cover of a patterned mask: A custom mask is placed on the pre-crosslinked hydrogel and then irradiated with ultraviolet light again to achieve localized differential crosslinking of the GelMA / CNTs hydrogel material, thereby producing localized differences in crosslinking degree and obtaining photocrosslinked GelMA / CNTs hydrogel.

2. The method for fabricating a swelling self-assembled GelMA / CNTs-AgNPs hydrogel microcrack sensor according to claim 1, characterized in that: The specific concentration ratio of methacrylamide gelatin (GelMA), photoinitiator, and carbon nanotubes (CNTs) in S1 is: 10 wt% GelMA, 0.5 wt% photoinitiator, and 0.5–1.5 wt% CNTs.

3. The method for preparing a swelling self-assembled GelMA / CNTs-AgNPs hydrogel microcrack sensor according to claim 1, characterized in that: The deposition of surface silver nanoparticles in S3 specifically involves immersing the photocrosslinked GelMA / CNTs hydrogel in a silver nitrate solution, adding 1.0–1.5 ml of ascorbic acid at a concentration of 15 mg / ml, and soaking for 0.5–5 hours.

4. A swelling self-assembled GelMA / CNTs-AgNPs hydrogel microcrack sensor prepared by the preparation method according to any one of claims 1 to 3.

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