Two-photon photoresist composition for preparing narrow particle size distribution microspheres based on femtosecond laser direct writing and ultraviolet light auxiliary curing and microsphere preparation method

Abstract

The invention belongs to the technical field of two-photon photoresist compositions, and particularly discloses a two-photon photoresist composition for preparing narrow particle size distribution microspheres based on femtosecond laser direct writing and ultraviolet light auxiliary curing and a microsphere preparation method. The photoresist composition comprises the following components in parts by weight: 0 to 50 parts of light-cured resin, 50 to 100 parts of an active monomer, 0.01 to 5 parts of a two-photon photoinitiator, 0.1 to 5 parts of a thixotropic agent and 0.01 to 3 parts of a polymerization inhibitor. The obtained two-photon photoresist composition has a remarkable thixotropic characteristic and efficient two-photon polymerization efficiency, femtosecond laser direct writing can be efficiently carried out to prepare suspended shell microspheres in batches, the microspheres can be easily separated from a substrate after development, and then the interiors of the shell microspheres are thoroughly cured by adopting an ultraviolet light auxiliary curing technology, so that the two-photon photoresist composition is obtained. The problem of relatively long inscribing period caused by limited femtosecond laser inscribing flux is effectively improved, rapid and thorough curing of the interiors of large-batch shell microspheres can be realized, and batch preparation of extremely narrow particle size distribution microspheres with any particle size in the range of 2-500 microns can be easily realized.

Description

Technical Field

[0001] This invention relates to the field of two-photon photoresist composition technology, and more specifically, to a two-photon photoresist composition and a method for preparing microspheres with narrow particle size distribution based on femtosecond laser direct writing and ultraviolet light-assisted curing. Background Art

[0002] Monodisperse polymer microspheres, as an important class of functional materials, have broad application prospects in fields such as electronic packaging, precision optics, and biomedicine. For example, in the biomedical field, microspheres, as sustained-release drug carriers, can effectively improve the precise and controllable release of drugs in vivo due to their narrow particle size distribution, thereby enhancing therapeutic effects. In electronic packaging and precision optics, this material can serve as a high-precision gap control medium, reducing equipment investment costs while ensuring production efficiency and product yield.

[0003] Currently, common methods for preparing polymer microspheres include emulsification-evaporation and microfluidics. Emulsification-evaporation has an inherent drawback of a wide particle size distribution range. Although the uniformity of particle size can be improved by optimizing the raw material ratio, adjusting process parameters, and improving equipment (for example, the Chinese patent application CN202310844765.2 filed on July 11, 2023, proposes a multi-stage membrane emulsification device that uses pressure difference control to achieve multiple membrane emulsification of the emulsion), it is still difficult to obtain microspheres with excellent monodispersity. Although microfluidics can prepare microspheres with better particle size uniformity (such as the novel microfluidic device developed by Szu-I Yeh et al., which successfully prepared monodisperse PLGA microspheres, Microfluid Nanofluid 2023, 27(47)), its fixed channel diameter results in a lack of flexibility in particle size adjustment. Microfluidic chips need to be redesigned and processed for different particle size requirements, which significantly restricts the universality of the technology.

[0004] Femtosecond laser direct writing technology, with its advantages of submicron-level processing precision (<200nm) and three-dimensional forming, achieves precise control of voxels at the hundred-nanometer level inside photosensitive materials through two-photon polymerization effect, enabling high-precision fabrication of arbitrary 3D models. This technology provides a new approach for the preparation of monodisperse microspheres. However, the existing technology for preparing monodisperse microspheres still has the following problems: (1) Most existing femtosecond laser direct writing equipment adopts a single-channel writing mode, and its low processing rate (<200mm / s) and the low two-photon polymerization efficiency of commercial photoresists together lead to an excessively long preparation cycle; (2) Most existing photoresists are liquids and do not have thixotropic properties, which forces the microsphere model to rely on a substrate support structure, making it impossible to achieve levitation writing in three-dimensional space. The model can only be mass-produced on a two-dimensional plane of the substrate, and there are problems such as difficulty in separating the microsphere from the substrate. In addition, when levitation writing is performed directly without support, the displacement of the microsphere caused by gravity in the liquid environment will directly lead to writing failure.

[0005] Therefore, there is an urgent need to develop microsphere processing technology based on femtosecond laser direct writing technology, which has the ability to write suspended structures and has the characteristics of efficient mass production. This is of great significance for promoting the commercial application of monodisperse polymer microspheres. Summary of the Invention

[0006] To address the problems existing in the prior art, the first objective of this invention is to provide a two-photon photoresist composition. The photoresist composition provided in this application possesses high single / two-photon polymerization efficiency and extremely high thixotropic properties. It enables the mass suspension and writing of microsphere structures by femtosecond lasers within the photoresist without substrate support, and the microsphere structures are not affected by gravity and do not drift. Furthermore, the written microspheres can be easily detached from the substrate through development.

[0007] A second objective of this invention is to provide a method for preparing microspheres with a narrow particle size distribution using femtosecond laser direct writing and ultraviolet light secondary curing. In this application, the microsphere preparation process involves using femtosecond laser direct writing technology to inscribe a shell microsphere model, followed by complete curing of the microsphere interior using ultraviolet light secondary curing technology. This method can prepare microspheres with different particle size ranges and extremely narrow particle size distributions, while significantly shortening the microsphere preparation time.

[0008] To solve the above problems, the present invention adopts the following technical solution:

[0009] A two-photon photoresist composition comprises the following components in parts by weight: 0-50 parts of photocurable resin, 50-100 parts of active monomer, 0.01-5 parts of two-photon photoinitiator, 0.1-5 parts of thixotropic agent, and 0.01-3 parts of polymerization inhibitor. Preferably, it comprises the following components in parts by weight: 0-45 parts of photocurable resin, 70-100 parts of active monomer, 0.05-4 parts of two-photon photoinitiator, 0.3-4 parts of thixotropic agent, and 0.02-2.5 parts of polymerization inhibitor.

[0010] Furthermore, the photocurable resin is one or more selected from polyurethane acrylate, polyester acrylate, epoxy acrylate, and polyether acrylate resin. Preferably, the photocurable resin is a product with the brand names CN8888, 621A-80, FSP8967, or HP6206.

[0011] Furthermore, the active monomer comprises one or more of dipentaerythritol hexaacrylate (DPHA), ethoxylated trimethylolpropane triacrylate (TMP(EO)nA), pentaerythritol triacrylate (PETA), tricyclodecanediethanol diacrylate (TCDDA), neopentyl glycol diacrylate (NPGDA), isobornyl acrylate (IBOA), and tetrahydrofuran acrylate (THFA). Further, ethoxylated trimethylolpropane triacrylate (TMP(EO)nA) is preferably 3(ethoxy)trimethylolpropane triacrylate (TMP(EO)3TA).

[0012] Furthermore, the two-photon photoinitiator includes one or more of the compounds shown in formulas (1) to (24), 1-chloro-4-propoxythionanone, (2,4,6-trimethylbenzoyl)diphenylphosphine oxide, and 1-[4-(phenylthio)phenyl]-1,2-octanedione 2-(O-benzoyl oxime); preferably, the two-photon photoinitiator includes one or more of the compounds shown in formula (11), (10), (15), (17), (4), (7), and (24).

[0013] The chemical structural formulas of the compounds shown in formulas (1)-(24) are as follows:

[0014]

[0015]

[0016]

[0017]

[0018] Furthermore, the thixotropic agent is one or more selected from polyamide-modified hydrogenated castor oil derivatives, polyurea compounds, and polyamides. The polyamide-modified hydrogenated castor oil derivative is preferably a product with the brand name Crayvallac MT, OPTIMA, or LA-150; the polyurea compound is preferably a product with the brand name BYK-7410, BYK-D410, BYK-4410, or BYK-4420; and the polyamide is preferably a product with the brand name KMT-4006 or SNF7010.

[0019] Furthermore, the polymerization inhibitor is selected from one or more of p-hydroxyanisole, hydroquinone, 1,3,5-triphenol, 2,5-dihydroxytoluene, 2,6-di-tert-butyl-p-methylphenol, tert-butylhydroquinone, tris(N-nitroso-N-phenylhydroxylamine) aluminum salt, and tetramethylpiperidine oxide (TEMPO).

[0020] This invention also provides a method for preparing narrow-size distribution microspheres, the preparation steps of which are as follows:

[0021] S1: Use 3D modeling software to create a three-dimensional model of the hollow shell microsphere array in STL format, and then import the model into the femtosecond laser direct writing equipment software for size setting, slice layering processing and setting femtosecond laser writing parameters.

[0022] S2: Drop the two-photon photoresist composition according to any one of claims 1-6 onto the sample stage and fix it. Adjust the writing focus to be inside the photoresist composition using the focus locking software. According to the femtosecond laser writing parameters set in step S1, start the femtosecond laser direct writing system to print microspheres.

[0023] S3: After the writing is completed, the sample is immersed in the developing solution, centrifuged and filtered to obtain microspheres with solidified shells. Then, ultraviolet light-assisted exposure is used to completely solidify the inside of the microspheres to obtain microspheres with uniform particle size.

[0024] Furthermore, in step S2, the wavelength of the femtosecond laser marking is 500-1000nm, preferably one of the femtosecond lasers with wavelengths of 517nm, 532nm, and 780nm; in step S3, the ultraviolet light source is a mercury lamp or an LED light source with a wavelength of 365-405nm. Preferably, the ultraviolet light source is one of a mercury lamp, a 365nm LED light source, and a 405nm LED light source.

[0025] Furthermore, according to claim 1, the two-photon photoresist composition is characterized in that: in step S3, the developer is one or more of isopropanol, propylene glycol methyl ether acetate, N-methylpyrrolidone, acetone, xylene, and acetonitrile.

[0026] Compared with the prior art, the advantages of this invention are:

[0027] I. The two-photon photoresist composition provided by this invention effectively solves the technical bottlenecks of traditional liquid photoresists in suspended structure printing, which require starting the writing process from the substrate to avoid structural deformation or drift, and the difficulty in separating the written model from the substrate. By introducing a thixotropic agent, the system acquires high thixotropy and extremely high viscosity in a static state or at low shear rates. It enables the femtosecond laser to suspend and write microsphere structures in a large quantity within the photoresist in three-dimensional space without substrate support, and the written structure is not affected by gravity and will not drift. Furthermore, the written microspheres can be easily detached from the substrate through development; most traditional two-photon photoresist compositions do not possess this characteristic.

[0028] II. The two-photon photoresist composition provided by the present invention, by introducing a thixotropic agent, increases the viscosity of the system dramatically. The femtosecond laser direct writing process can effectively suppress the diffusion of active free radicals and further improve the accuracy of writing microspheres. Most traditional two-photon photoresist compositions do not have this characteristic.

[0029] Third, the two-photon photoresist composition provided by the present invention has high single / two-photon polymerization efficiency. Through the reasonable combination of photocurable resin, active monomer and two-photon photoinitiator, microspheres with different hardness can be prepared to meet the needs of different application scenarios.

[0030] IV. The narrow particle size distribution microspheres provided by this invention are prepared by femtosecond laser direct writing and ultraviolet light-assisted curing. This preparation method combines the high-precision writing advantages of femtosecond laser direct writing technology, and can quickly adjust the particle size of microspheres in the range of 2-500μm by simply changing the size parameters of the printing model. The process is simple and the resulting microspheres have a uniform particle size distribution. Most traditional microsphere preparation processes do not have this feature.

[0031] V. The narrow-size microspheres provided by this invention are prepared by femtosecond laser direct writing and ultraviolet-assisted curing. This preparation method first uses a femtosecond laser direct writing device to print hollow shell-shaped microspheres, and then uses ultraviolet light-assisted secondary exposure to completely solidify the interior of the microspheres. This effectively improves the problem that most existing femtosecond laser direct writing devices are single-channel writing modes with low processing speeds (<200 mm / s) and that commercial photoresists have low two-photon polymerization efficiency, both of which lead to excessively long preparation cycles for solid microspheres. This method can further shorten the microsphere preparation cycle. Compared with microspheres prepared by traditional emulsification and microfluidic methods, this process is simpler and produces microspheres with a narrower particle size distribution, showing great application potential. Attached Figure Description

[0032] Figure 13D modeling schematic diagram and microsphere cross-section diagram of hollow microsphere arrays printed by femtosecond laser direct writing suspension printing in Test Example 1 and Example 6;

[0033] Figure 2 The graph shows the viscosity data of the two-photon photoresist compositions of Examples 1-5 and Comparative Examples 1-2 at different shear rates.

[0034] Figure 3 Images of the liquid formulations of Example 1 and Comparative Example 2 after being inverted and left to stand for 4 hours in sample bottles;

[0035] Figure 4 This is a comparison chart showing the precision of femtosecond laser etched lines using the two-photon photoresist compositions of Example 1 and Comparative Example 1.

[0036] Figure 5 SEM images of microspheres with different particle sizes (2μm, 5μm, 8μm, 10μm, 20μm) were prepared using the two-photon photoresist compositions prepared in Examples 1-5, respectively. Detailed Implementation

[0037] The products involved in the light-curing resins in the following examples are: CN8888 purchased from Sartoma (Guangzhou) Chemical Co., Ltd.; 621A-80 purchased from Changxing Chemical Industry (China) Co., Ltd.; FSP8967 purchased from Guangzhou Runao Chemical Materials Co., Ltd.; and HP6206 purchased from Guangdong Haohui New Materials Co., Ltd.

[0038] The thixotropic agents used in the following examples are: BYK-7410, BYK-D410, BYK-4410 and BYK-4420, all purchased from BYK Additives (Shanghai) Co., Ltd.; Crayvallac MT, OPTIMA and LA-150, all purchased from Arkema Chemicals, France; KMT-4006, purchased from Gansu Kaimet Materials Technology Co., Ltd.; and SNF7010, purchased from Foshan Xinruixiang New Materials Co., Ltd.

[0039] Example 1:

[0040] A two-photon photoresist composition for preparing narrow-size microspheres based on femtosecond laser direct writing and ultraviolet light-assisted curing is shown below:

[0041] In a yellow light chamber, 1.5 parts by weight of the two-photon initiator as shown in formula (11), 0.1 parts by weight of tert-butylhydroquinone, and 1 part by weight of BYK-7410 are added to a mixture of 40 parts by weight of PETA and 50 parts by weight of DPHA. The mixture is stirred for 2 hours in the dark. Then, impurities are removed by filtration through a filter membrane with a pore size of 0.45 μm to obtain a two-photon photoresist composition.

[0042] Example 2:

[0043] In a yellow light chamber, 0.5 parts by weight of a two-photon initiator as shown in formula (11), 1 part by weight of a two-photon initiator as shown in formula (18), and a mixture of 0.2 parts by weight of a two-photon initiator as shown in formula (24), 0.75 parts by weight of a mixture of tert-butylhydroquinone and 0.75 parts by weight of TEMPO are added to 90 parts by weight of PETA. After stirring for 2 hours, 10 parts by weight of 621A-80, 1 part by weight of SNF7010, and 0.5 parts by weight of Crayvallac MT are added. Stirring is continued for 2 hours in the dark. Then, impurities are removed by filtration through a filter membrane with a pore size of 0.45 μm to obtain a two-photon photoresist composition.

[0044] Example 3:

[0045] In a yellow light chamber, 0.75 parts by weight of a mixture of two-photon initiators as shown in formula (10) and 0.25 parts by weight of a mixture of two-photon initiators as shown in formula (4), 0.3 parts by weight of tris(N-nitroso-N-phenylhydroxylamine) aluminum salt, and 35 parts by weight of TMP(EO)3TA were added. After stirring for 2 hours, 45 parts by weight of HP6206, 0.5 parts by weight of BYK-7410, and 1.5 parts by weight of SNF7010 were added. Stirring was continued for 2 hours under dark conditions. Then, impurities were removed by filtration through a filter membrane with a pore size of 0.45 μm to obtain a two-photon photoresist composition.

[0046] Example 4:

[0047] In a yellow light chamber, 0.5 parts by weight of a mixture of two-photon initiators as shown in formula (7) and 1 part by weight of a mixture of two-photon initiators as shown in formula (15), 0.5 parts by weight of tert-butylhydroquinone, and 40 parts by weight of a mixture of DPHA, 10 parts by weight of TCDDA, and 25 parts by weight of IBOA were added. After stirring for 2 hours, 15 parts by weight of HP6206, 10 parts by weight of FSP8967, 1.5 parts by weight of BYK-7410, and 1.5 parts by weight of Crayvallac MT were added. Stirring was continued for 2 hours in the dark. Then, impurities were removed by filtration through a filter membrane with a pore size of 0.45 μm to obtain a two-photon photoresist composition.

[0048] Example 5:

[0049] In a yellow light chamber, 0.5 parts by weight of a mixture of two-photon initiator as shown in formula (10), 0.5 parts by weight of a mixture of two-photon initiator as shown in formula (15) and 1 part by weight of a mixture of two-photon initiator as shown in formula (24), and 0.3 parts by weight of TEMPO are added to a mixture of 5 parts by weight of DPHA, 10 parts by weight of TCDDA and 35 parts by weight of THFA. After stirring for 2 hours, 10 parts by weight of HP6206, 40 parts by weight of FSP8967, 2 parts by weight of BYK-7410 and 3 parts by weight of CrayvallacMT are added. Stirring is continued for 2 hours under dark conditions. Then, impurities are removed by filtration through a filter membrane with a pore size of 0.45 μm to obtain a two-photon photoresist composition.

[0050] The following is Comparative Example 1 without thixotropic agents:

[0051] In a yellow light chamber, 1.5 parts by weight of the two-photon initiator as shown in formula (11) and 1.5 parts by weight of tert-butylhydroquinone are added to a mixture of 40 parts by weight of PETA, 50 parts by weight of DPHA and 10 parts by weight of IBOA. The mixture is stirred for 2 hours in the dark. Then, impurities are removed by filtration through a filter membrane with a pore size of 0.45 μm to obtain a two-photon photoresist composition.

[0052] Test Example 1:

[0053] The performance of the two-photon photoresist composition involved in Examples 1-5 and Comparative Example 1, as well as the commercial two-photon photoresist IP-DIP (Comparative Example 2), was tested. The test methods and test contents are as follows:

[0054] (1) Viscosity test

[0055] The viscosity of the two-photon photoresist composition was determined using an Anton Paar MCR302e rheometer. A PP25 parallel plate was used, and the programmed temperature was set to 25°C. The sample was coated onto a substrate with a fixed plate spacing of 0.3 mm. After loading, the sample was allowed to stand for equilibration for 30 minutes. The viscosity data of the photoresist at different shear rates were then measured, and the thixotropic value (Ti) of the two-photon photoresist composition was calculated. The formula for calculating the thixotropic value is: Ti = η1 / η2

[0056] In the formula, η1 and η2 represent the photoresist at a shear rate of 0.1 s⁻¹. -1 10s -1 The viscosity value is Ti, which represents the levitation writing ability of the photoresist. The higher the Ti value, the stronger the levitation writing ability.

[0057] (2) Shore hardness test

[0058] The Shore hardness tester was used according to GB / T 2411-2008 standard. The photoresist was placed in a circular polytetrafluoroethylene mold with a thickness of 4 mm and a diameter of 2 cm, and tested using a 365 nm LED light source at 500 mw / cm². 2 Irradiate the sample with light for 20 seconds, then remove it and allow it to stand at room temperature. Place the sample on a table, hold the hardness tester vertically, and ensure the tip of the indenter is at least 9 mm away from any edge of the sample. Immediately apply pressure to bring the indenter into close contact with the sample, and read the maximum value of the hardness tester within 1 second. Measure 5 hardness values ​​on the same sample at least 6 mm apart and calculate their average value.

[0059] (3) Precision and speed test of femtosecond laser engraving lines

[0060] Two-photon photoresist composition / commercial two-photon photoresist IP-DIP was dropped onto a sample stage and fixed. The photoresist was exposed using a femtosecond laser with a spot scanning speed of 50-800 mm / s and a scanning energy of 0-100% for line array writing. After femtosecond laser exposure, the photoresist was developed and sputtered with gold. The writing line array was observed using a scanning electron microscope to obtain the maximum writing speed (SMax) and optimal writing line accuracy of the photoresist formulation.

[0061] (4) Processing time test of 20-micron monodisperse shell-shaped microspheres

[0062] First, a three-dimensional model of the hollow shell microsphere in STL format is created using 3D modeling software. Then, the model is imported into the femtosecond laser direct writing device software, the size is set to 20μm and sliced, and the femtosecond laser writing parameters (such as femtosecond laser wavelength, writing energy, writing speed, etc.) are set.

[0063] Then, the two-photon photoresist composition / commercial two-photon photoresist was dropped onto the sample stage and fixed. The writing focus was adjusted to the interface between the photoresist composition and the glass substrate by the focus locking software. The femtosecond laser direct writing system was started, and monodisperse microspheres were written and printed according to the set writing parameters. The printing time was recorded at the same time.

[0064] (5) Femtosecond laser writing test of suspended shell microsphere array

[0065] A. Femtosecond laser direct writing processing

[0066] A three-dimensional model of the hollow shell microsphere array in STL format was created using 3D modeling software (e.g., Figure 1 As shown in the figure, the model is then imported into the femtosecond laser direct writing device software for size setting and slicing, and the femtosecond laser writing parameters (such as femtosecond laser wavelength, writing energy, writing speed, etc.) are set.

[0067] The prepared two-photon photoresist composition is dropped onto the sample stage and fixed. The writing focus is adjusted to be inside the photoresist composition by the focus locking software. The femtosecond laser direct writing system is started, and the microspheres are written and printed according to the set writing parameters to obtain a microsphere array with a solidified shell.

[0068] B. Ultraviolet-assisted curing

[0069] After the writing is completed, the sample is immersed in the developing solution, centrifuged and filtered to obtain microspheres with solidified shells. Then, ultraviolet light-assisted exposure is used to completely solidify the inside of the microspheres to obtain microspheres with uniform particle size.

[0070] The test results of the above performance tests are shown in Table 1:

[0071] Table 1 shows the performance test results of the two-photon photoresist composition involved in Examples 1-5 and Comparative Example 1, as well as the IP-DIP of Comparative Example 2.

[0072]

[0073] Note: In the table, “~A” indicates that the value is near A, representing “A±1”.

[0074] As shown in Table 1, the two-photon photoresist compositions involved in Examples 1-5 can be directly written using femtosecond lasers. Furthermore, through the rational combination of photocurable resin, active monomers, and two-photon photoinitiators, microspheres of varying hardness can be prepared, meeting the needs of different application scenarios. Moreover, compared to commercially available two-photon photoresist IP-DIP, Examples 1-5 exhibit faster line writing speeds, all exceeding 200 mm / s. When processing 20 μm shell-shaped microspheres using femtosecond lasers with the same writing power, the processing time is shorter than that of IP-DIP, demonstrating that the two-photon photoresist compositions provided by this invention possess high two-photon polymerization efficiency.

[0075] Depend on Figure 2 It can be seen that the two-photon photoresist compositions obtained by using thixotropic agents in Examples 1-5 all exhibit significant viscosity thixotropy.

[0076] Test Example 2:

[0077] Using Example 1, which has relatively low thixotropy, as the research object, the flowability of the two-photon photoresist composition prepared in Example 1 and the commercially available two-photon photoresist composition IP-DIP from Comparative Example 2 were tested by inverting the components for 4 hours. The test results are as follows. Figure 3 As shown.

[0078] Depend on Figure 3 It can be seen that in Example 1, the sample bottle can still maintain its shape and not flow even when inverted for 4 hours, while the IP-DIP will flow due to gravity when inverted.

[0079] As demonstrated in Test Examples 1 and 2, the thixotropic properties of this application enable the photoresist to maintain extremely high viscosity at low shear rates or under static conditions. This effectively prevents the etched structure from shifting during femtosecond laser-assisted levitation microsphere array writing, ensuring a smooth levitation writing process and ultimately yielding microspheres with uniform particle size and a solidified shell. In contrast, the IP-DIP in Comparative Example 2, lacking thixotropic properties, experienced structural drift during the levitation writing process, leading to the failure of the levitation microsphere writing.

[0080] Furthermore, experiments revealed that the line writing precision of Example 1 and Comparative Example 1 was approximately 120 nm and 150 nm, respectively. Figure 4 The only difference between the two formulations is the thixotropic agent, indicating that adding the thixotropic agent can further improve the writing accuracy. The main reason for this is that after adding the thixotropic agent in Example 1, the system has extremely high viscosity. The diffusion effect of the active free radicals generated during the writing process in the high viscosity formulation is effectively suppressed, thereby improving the writing accuracy. This characteristic has a better advantage for processing microspheres with smaller particle sizes.

[0081] Example 6:

[0082] Using the two-photon photoresist compositions described in Examples 1-5, shell-shaped microspheres with particle sizes of 2μm, 5μm, 8μm, 10μm, and 20μm were fabricated by femtosecond laser direct writing suspension. The preparation methods are as follows:

[0083] Step 1: After creating a 3D model of the suspended hollow shell microsphere array in STL format using 3D modeling software, import the model to be printed into the femtosecond laser direct writing device software; and set the size, slice and layer processing, and femtosecond laser writing parameters as needed.

[0084] Step 2: Select a certain mass of the two-photon photoresist composition prepared in the example according to the parameters in Step 1, drop it onto the sample stage and fix it. Adjust the writing focus to be inside the two-photon photoresist composition by the focus locking software. According to the writing parameters set in Step 1, start the femtosecond laser direct writing system to print microspheres.

[0085] Step 3: After the writing is completed, the sample is immersed in isopropanol for development, centrifuged and filtered to obtain microspheres with solidified shells. Then, a 365nm LED ultraviolet light source is used to assist in exposure to completely solidify the inside of the microspheres, thus obtaining microspheres with uniform particle size.

[0086] The microspheres obtained in step three were imaged using a scanning electron microscope. The imaging results are as follows: Figure 5 As shown.

[0087] Figure 5SEM images of microspheres with different particle sizes (2μm, 5μm, 8μm, 10μm and 20μm) prepared using the two-photon photoresist compositions prepared in Examples 1-5 were obtained. (1), (2), (3), (4) and (5) represent microspheres prepared using the two-photon photoresist composition prepared in Example 1, the two-photon photoresist composition prepared in Example 2, the two-photon photoresist composition prepared in Example 3, the two-photon photoresist composition prepared in Example 4 and the two-photon photoresist composition prepared in Example 5, respectively.

[0088] Depend on Figure 5 It is evident that the processed microspheres exhibit excellent monodispersity, uniform size, and narrow particle size distribution. Compared to traditional emulsification methods, the microfluidic method utilizes the high-precision processing characteristics of femtosecond laser direct writing. By simply setting different model processing dimensions, microspheres with varying diameters can be obtained, and the microspheres possess excellent monodispersity, further demonstrating the effectiveness of the microsphere preparation method provided by this invention.

[0089] Furthermore, the femtosecond laser direct writing suspension fabrication of a 10μm solid microsphere array using Example 1 takes approximately 5 hours. However, the microsphere fabrication method provided by this invention first uses femtosecond laser direct writing suspension fabrication of a 10μm hollow-shell microsphere array, requiring only about 2 hours. Then, through development, filtration, and 365nm LED ultraviolet light-assisted curing, the microspheres are completely solidified, and the entire process takes only about 3 hours. This further demonstrates that the microsphere preparation method provided by this invention has higher processing efficiency and can effectively improve the problems of existing femtosecond laser direct writing equipment, which mostly uses a single-channel writing mode, and the long writing cycle caused by printing solid microspheres.

[0090] In summary, the two-photon photoresist composition provided by this invention exhibits excellent single / two-photon polymerization performance. Its significant thixotropic properties enable excellent resistance to gravitational deformation during femtosecond laser processing of three-dimensional structures, achieving good morphological stability of microspheres during suspension processing without the need for additional support structures. This technical characteristic not only ensures the dimensional accuracy of microsphere manufacturing but also enables non-destructive separation of microspheres from the substrate. Finally, the fabrication process of this invention employs a synergistic processing strategy of femtosecond laser-induced shell solidification and ultraviolet light-assisted exposure to thoroughly solidify the interior of the microspheres, significantly shortening the microsphere fabrication cycle and greatly improving production efficiency. It is worth emphasizing that the microspheres of this invention have advantages such as extremely narrow particle size distribution and precise controllability of microsphere size over a wide range (2-500 μm), and the fabrication process is economical, showing broad application potential in fields such as electronic packaging materials, precision optical devices, and biomedical engineering.

[0091] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A two-photon photoresist composition, characterized in that: It includes the following components in parts by weight: 0-50 parts of photocurable resin, 50-100 parts of active monomer, 0.01-5 parts of two-photon photoinitiator, 0.1-5 parts of thixotropic agent, and 0.01-3 parts of polymerization inhibitor.

2. The two-photon photoresist composition according to claim 1, characterized in that: The photocurable resin is one or more of polyurethane acrylate, polyester acrylate, epoxy acrylate, and polyether acrylate resin.

3. The two-photon photoresist composition according to claim 1, characterized in that: The active monomers include one or more of the following: pentaerythritol hexaacrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol triacrylate, tricyclodecanediethanol diacrylate, neopentyl glycol diacrylate, isobornyl acrylate, and tetrahydrofuran acrylate.

4. The two-photon photoresist composition according to claim 1, characterized in that: The two-photon photoinitiator includes one or more of the compounds shown in formulas (1) to (24), 1-chloro-4-propoxythionanone, (2,4,6-trimethylbenzoyl)diphenylphosphine oxide, and 1-[4-(phenylthio)phenyl]-1,2-octanedione-2-(O-benzoyl oxime); The chemical structural formulas of the compounds shown in formulas (1)-(24) are as follows:

5. The two-photon photoresist composition according to claim 1, characterized in that: The thixotropic agent is one or more of polyamide-modified hydrogenated castor oil derivatives, polyurea compounds, and polyamides.

6. The two-photon photoresist composition according to claim 1, characterized in that: The polymerization inhibitor is selected from one or more of p-hydroxyanisole, hydroquinone, 1,3,5-triphenol, 2,5-dihydroxytoluene, 2,6-di-tert-butyl-p-methylphenol, tert-butylhydroquinone, tris(N-nitroso-N-phenylhydroxylamine) aluminum salt, and tetramethylpiperidine oxide.

7. A method for preparing narrow-size microspheres, characterized in that: The preparation steps are as follows: S1: Use 3D modeling software to create a three-dimensional model of the hollow shell microsphere array in STL format, and then import the model into the femtosecond laser direct writing equipment software for size setting, slice layering processing and setting femtosecond laser writing parameters. S2: Drop the two-photon photoresist composition according to any one of claims 1-6 onto the sample stage and fix it. Adjust the writing focus to be inside the photoresist composition using the focus locking software. According to the femtosecond laser writing parameters set in step S1, start the femtosecond laser direct writing system to print microspheres. S3: After the writing is completed, the sample is immersed in the developing solution, centrifuged and filtered to obtain microspheres with solidified shells. Then, ultraviolet light-assisted exposure is used to completely solidify the inside of the microspheres to obtain microspheres with uniform particle size.

8. The method for preparing narrow particle size distribution microspheres according to claim 1, characterized in that: In step S2, the wavelength of the femtosecond laser marking is 500-1000nm. In step S3, the ultraviolet light source is a mercury lamp or an LED light source with a wavelength of 365-405nm.

9. The method for preparing narrow particle size distribution microspheres according to claim 1, characterized in that: According to claim 1, a two-photon photoresist composition is characterized in that: in step S3, the developer is one or more of isopropanol, propylene glycol methyl ether acetate, N-methylpyrrolidone, acetone, xylene, and acetonitrile.

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