Multi-material 3D micro-printing in laminar flow

Abstract

This invention presents a method for multi-material 3D micro-printing using a microfluidic channel, where photosensitive materials are polymerized in flow by a laser. This technique removes the need for a mechanical Z-axis, with material flow in the channel serving as the Z-axis movement. The laser uses fast scanning or beam shaping to form structures in the XY plane. The channel walls are designed to be transparent to the laser wavelength for effective focusing and polymerization. The system accommodates different optical exposure configurations, such as transverse, colinear, or angular. A notable aspect is its capability for in situ multi-material printing, made possible by laminar flow that minimizes material mixing, allowing for the creation of complex, multi-material 3D structures. This method enhances the precision and complexity achievable in 3D micro-printing applications.

Description

[0001] MULTI-MATERIAL 3D MICRO-PRINTING IN LAMINAR FLOW

[0002] FIELD OF THE INVENTION

[0003] The invention relates to the field of 3D printing, in particular to a multi-material 3D micro-printing in laminar flow.

[0004] DESCRIPTION OF THE RELATED ART

[0005] The standard 3D printing process involves a three-dimensional movement system that selectively deposits or alters material to form a 3D structure. This necessitates a minimum of three axes of movement (X, Y, Z), with additional rotational axes included in certain scenarios for enhanced control. Additionally, these linear movements can be achieved through various methods, like combining linear stages with scanners, to increase speed and improve shape precision. Consequently, sophisticated 3D printing setups require numerous moving components, which brings challenges such as inertia and spatial requirements.

[0006] In areas like rapid multi-material printing using two-photon polymerization (2PP), the need for fast scanning is paramount. 2PP enables the creation of intricate microstructures with sub-micrometer accuracy and the use of various materials. While it's feasible to print a single structure using different materials, a development step between different materials is necessary. This step can be conducted either outside or within the printing setup if it has the requisite components. However, it's a time-intensive process. Moreover, 2PP's high precision makes it a slow printing method, rendering the production of multi-material 3D structures using 2PP both complex and time-consuming.

[0007] Therefore, there is a growing need for innovative approaches that streamline the multimaterial printing process, reduce time consumption, and enhance the overall efficiency and flexibility of 3D printing technologies.

[0008] The patent document EP4275869A1 (published on 15 November 2023) presents a method and apparatus for generating three-dimensional structures in a lithographic fluid using lithographic techniques, particularly suitable for creating microstructures or nanostructures. It involves focusing a writing beam, such as a laser, into the fluid to solidify it in specific regions, creating structured areas or "voxels". The apparatus includes a holding space for the fluid and a radiation source to emit the writing beam. Beam directing means define the beam path, and exit optics focus the beam in the fluid. An innovative aspect of the invention is a filling height adjustment device, which changes the lithography fluid's level in the holding space, adjusting the distance between the fluid surface and the exit optics. This design improves the writing quality, especially for structures extending along the optical axis, by maintaining a constant distance or within a specific tolerance range between the exit optics and the fluid surface, thus reducing aberration effects. Unfortunately, the following lithographic fluid method, with its reliance on precise fluid levels and beam focusing is more sensitive to environmental factors like temperature and vibrations.

[0009] In CN113977940A (published on 28 January 2022), the invention introduces a multimaterial 3D printing device based on microfluidic extrusion, aimed at overcoming the limitations of traditional single-material 3D printers. It features a complex assembly with a fuselage frame, base plate, and X, Y, Z-axis transmission mechanisms, enabling the simultaneous use of multiple materials. This design not only allows for a greater variety of printing styles and functionalities but also addresses the challenge of extruding high-viscosity materials. The precise engineering of its transmission systems ensures accuracy and quality in multi-material printing, marking a significant advancement in the 3D printing technology field. Additionally, the intricate design and multiple components, including the X, Y, and Z-axis transmission mechanisms, increase the complexity of operation.

[0010] An alternative technology of 3D multi-material printing is described in patent document Nr. US2020147865A1 (published on 14 May 2020) whereby this invention introduces a dispenser attachment for objective lenses in laser lithography devices, designed to facilitate the creation of three-dimensional structures within a lithographic fluid. The device, equipped with a laser beam source and various optical components including an objective lens, utilizes a caplike dispenser attachment that forms a fluid space around the exit lens. This setup allows for the precise application of a specially formulated lithographic fluid, which solidifies only in the focus region via a multi-photon process. The innovative design enables continuous structure generation with large depths and heights, quick substrate replacement, and high throughput. Additionally, the system can handle multiple lithographic fluids for multi-material structures and includes provisions for developer fluid introduction, compressed gas for fluid distribution, and cleaning fluid for in situ maintenance, significantly enhancing the efficiency and versatility of laser lithography in creating detailed microstructures and nanostructures. Since the printing is not done in an enclosed channel, the lithographic fluid and the printing process are more exposed to external environmental factors like dust, air currents, and humidity. This can potentially lead to contamination or inconsistencies in the printing process.

[0011] In US 11693311B2 (published on 4 July 2023) the disclosed invention is a multi-material bioprinting system utilizing stereolithographic technology for precision fabrication of biological constructs. Central to the system is a microfluidic device comprising multiple reservoirs containing different inks. The microfluidic chip, made from polydimethylsiloxane (PDMS), includes a chamber with multiple inlets and outlets, and an elastic membrane, facilitating the sequential introduction and photo crosslinking of various inks. This setup, combined with a digital micromirror device (DMD) in the printing apparatus, allows for rapid, automated fabrication of high-fidelity biological constructs. The system's design effectively overcomes traditional challenges in bioprinting, such as ink switching and system decontamination, making it particularly suitable for producing constructs for biological in vivo use. But nozzles in bioprinting systems are prone to clogging, especially when working with complex biological materials that may solidify or aggregate. This can lead to frequent maintenance requirements and potential downtimes in the printing process.

[0012] Accordingly, it is desired to provide an innovative 3D printing technology capable of efficiently and precisely handling multiple materials in a single, streamlined process is essential.

[0013] This description provides an advanced in-flow 3D micro-printing method, where photosensitive materials flow through a microfluidic channel and are selectively polymerized by a laser beam, creating 3D structures as the material flows. This process, which can use either single or multiple materials, eliminates the need for mechanical Z-axis movement, offering flexibility and efficiency in creating complex microstructures with high precision.

[0014] SUMMARY OF THE INVENTION

[0015] The invention presents a novel approach to multi-material 3D micro-printing using a microfluidic channel where photosensitive materials are selectively polymerized by a laser beam during flow. This technique eliminates the need for a mechanical Z-axis, as the material flow inside the channel represents the Z-axis movement, while the laser beam, through fast scanning or beam shaping, constructs the structure in the channel's cross-section in the XY plane. The microfluidic channel's walls are partially or completely transparent to the laser wavelength, facilitating effective focusing and polymerization. The system accommodates various optical exposure configurations, including transverse, colinear, or angular, to suit different application needs. Additionally, light can be introduced into the channel either through direct focusing or using additional optical elements like mirrors or specialty optical fibers, adaptable for any configuration.

[0016] Central to this invention is its capacity for in situ multi-material printing. The laminar flow within the micro fluidic channel ensures minimal mixing of different materials, enabling the creation of complex multi-material structures. This can be achieved either through a static approach, introducing materials at different times, or a dynamic multi-channel arrangement, allowing simultaneous material supply. This advanced method offers significant potential in precision manufacturing and complex micro-structuring in 3D micro-printing.

[0017] BRIEF DESRCIPTION OF DRAWINGS

[0018] FIG. 1: Principle of in-flow printing methodology.

[0019] FIG. 2: Configurations of channel and focusing optics.

[0020] FIG. 3: Multi-focal point application in in-flow printing.

[0021] FIG. 4: Introducing light to the channel using additional optical elements.

[0022] FIG. 5: Multi-focal point application in in-flow printing.

[0023] FIG. 6: Introducing light to the channel using additional optical elements.

[0024] DETAILED DESCRIPTION OF THE INVENTION

[0025] The proposed multi-material 3D micro-printing in laminar flow technology finds its groundbreaking application in the realm of biomedical engineering, particularly in the development of intricate tissue structures and organoid models. Its unparalleled precision in multi-material printing at the sub-micrometer level stands to revolutionize tissue engineering, allowing for the creation of highly complex and functional artificial tissues and organ replicas. These could be used for advanced medical research, drug testing, and potentially in the future, organ transplants. This technology's ability to seamlessly integrate different materials within a single printing process ensures the production of structures that closely mimic the natural composition of human tissues, offering significant advancements in personalized medicine and paving the way for innovative treatments and medical solutions.

[0026] To accelerate the process of multi-material 3D micro-printing, an in-flow printing technique is synchronized with rapid scanning or beam shaping mechanisms, as illustrated in Fig. 1. This innovative approach involves the flow of photosensitive material(s) through a meticulously designed microfluidic channel (1) where the flow remains laminar due to the confined nature of the space. As the material progresses through the channel (1), a strategically directed laser beam (4) interacts with it, inducing selective polymerization in real-time. This action effectively replaces the need for a mechanical Z-axis, with the material flow serving as a substitute. The simultaneous action of the laser's fast scanning or beam shaping capabilities constructs the structure in the XY plane, layer by layer.

[0027] The printing process can be executed continuously or can pause after the completion of each layer or structural component, thereby obviating the necessity for traditional Z-axis movement. It is crucial to recognize that the choice of the XYZ coordinate system is a matter of convenience and does not limit the orientation or configuration of the printing process. For optimal focus and light transmission, the channel walls (2) — or at least the sections through which the laser is focused — should be transparent to the specific wavelength employed for printing. Other sections of the channel (1) can be constructed from materials that do not interfere with the flow, chemical properties, or optical characteristics essential to the printing process.

[0028] In scenarios where beam shaping is employed to selectively polymerize the materials within the channel's cross-section, the printing setup benefits from the absence of moving parts, enhancing stability and precision. Beam shaping can be adeptly managed by a spatial light modulator (SLM) or a dynamic mirror device (DMD), with the former being the preferred method due to its precise control capabilities. When multiple materials are introduced into the channel (1), the laminar flow ensures they remain distinct with only minimal intermixing, a phenomenon that is typically inconsequential when using standard photopolymers. This characteristic allows for the simultaneous printing of multi-material structures directly within the channel (1), circumventing the need for additional development processes. Upon completion, the printed structures are transported through the microfluidic system to a developer for post-processing. The general principle of in-flow printing methodology is depicted in Fig. 1. The process is depicted at three sequential stages: the beginning of the printing process, midway through, and at the end.

[0029] In the upper row of Fig. 1 the printing of a cylindrical component within a microfluidic channel using beam shaping technology is shown. The sequence demonstrates how the structure is developed as the photosensitive material flows through the channel (1).

[0030] The photosensitive material enters the microfluidic channel (1), flowing in the direction indicated by the arrows (3). The focused laser beam (4) is directed into the channel (1), and by manipulating its shape (beam shaping), it begins to selectively polymerize a specific region of the photosensitive material, initiating the formation of the printed component (5). As the material continues to flow, the laser beam (4) selectively polymerizes additional material. This stepwise polymerization corresponds to the XY layering in traditional 3D printing, effectively 'drawing' the subsequent layers of the cylindrical shape. The continuous flow and laser polymerization conclude with the formation of a complete cylinder. The flow of material effectively serves as the Z-axis progression in traditional 3D printing, while the laser beams (4) movement or shaping controls the XY plane construction.

[0031] In the bottom row of Fig. 1, the same cylindrical printing process is illustrated, but with the use of a scanner instead of beam shaping. In the beginning of the print, the scanner directs the laser beam (4) in a pattern over the flowing photosensitive material, starting the polymerization process for the cylinder's first layer. The laser scanner continues to move, layering the material and building up the cylinder's structure as the photosensitive material flows through the channel (1). The final shape of the cylinder is achieved as the scanning process completes the necessary layers to form the final 3D structure. Beam shaping and scanners can be used separately, or combined solution, using scanner and beam shaping simultaneously is also possible.

[0032] Throughout both processes, the channel walls (2) contain the material flow and the laser interaction. It's important that at least the wall (6) through which the laser enters is transparent to the laser light to allow for effective polymerization. Other walls can be transparent or opaque.

[0033] When configuring the setup for in-flow 3D micro-printing, the methodology can utilize transverse, colinear, or angular exposure techniques, as depicted in Fig. 2. The choice of configuration is determined by the specific requirements of the application and the setup design.

[0034] In the transverse configuration, the laser exposure occurs at a right angle to the material flow within the channel (1). This setup features the optical axis of the laser intersecting the material flow at a perpendicular angle, hence a right angle between the optical axis (8) and the flow direction (3). The transparency of the channel wall (6) is crucial for the laser to penetrate and interact with the material flow. The focusing optic (7), possibly a lens, objective, or an F- theta lens, is aligned so that the laser beam (4) converges sharply onto the material in the channel. The working distance (9) is determined by the space between the focusing optic and the point of convergence on the channel cross-section (10). This setup promotes simplicity in the microfluidic system's design, as the perpendicular interaction between the laser and material flow is straightforward and easy to construct.

[0035] Conversely, the colinear configuration aligns the optical axis of the laser with the flow direction of the photosensitive material. In this arrangement, the optical axis of the laser is parallel to the flow direction of the material. It allows the laser to focus along the Z-axis with simplicity, as the laser beam (4) travels in the same direction as the material flow. The focusing is achieved over a specific working distance (9), maintaining a consistent interaction between the laser and the flowing material throughout the length of the channel.

[0036] The angular configuration represents any setup where the laser's optical axis intersects the material flow direction at an arbitrary angle. Here, the laser's optical axis is set at an arbitrary angle relative to the flow direction. This setup provides a versatile middle ground between transverse and colinear configurations. The angular arrangement can be tailored to the specific geometric or optical requirements of a given application.

[0037] Each configuration has its own merits: the transverse setup is favored for its microfluidic simplicity, while the colinear setup is beneficial for ease of focusing in the Z direction. Ultimately, the preferred configuration will hinge on the intended application, taking into account factors such as the complexity of the microfluidic design and the specific focusing requirements of the laser within the channel (1). The key aspect across all configurations is the transparent nature of the channel wall (6) through which the laser exposure occurs. This wall must be at least partially, ideally completely, transparent to the wavelength of the laser to ensure effective polymerization.

[0038] To enhance the efficiency of the in-flow 3D micro-printing system, multi-beam exposure techniques are employed, as illustrated in Fig. 3. This approach increases throughput by enabling the simultaneous polymerization of multiple sections of a structure, or even distinct structures, within the microfluidic channel.

[0039] The process involves splitting a single laser beam (4) and then refocusing it into the channel (1) through a common set of optical elements, or by employing multiple sets of focusing optics. The flexibility of this system allows for the focal points of these beams to be aligned at uniform or varied distances from the channel walls. Moreover, the laser beams (4) can be directed into the channel (1) from the same side or from different sides, depending on the complexity and requirements of the printed structure.

[0040] Multi-focal point application in in-flow printing facilitates two modes of operation - synchronized and desynchronized.

[0041] In synchronized printing (left side of Fig. 3) all laser beams (4) function in harmony to construct different sections of a single structure concurrently. This is depicted by a shared focal point (11) where multiple beams (4) converge from a single optical element, enabling the simultaneous printing of various parts of the structure.

[0042] In desynchronized mode, different laser beams (4) operate independently to print separate structures within the same channel (1). This allows for the parallel creation of multiple components, which can be particularly advantageous when manufacturing parts that differ in design or function.

[0043] Both synchronized and desynchronized modes can utilize the same XY positioning techniques or different ones, such as combining scanner and beam shaping technologies. This versatility means that the same structure, or multiple distinct structures, can be printed in the same channel (1) either in a fully coordinated manner or with each beam working on a separate task.

[0044] Such multi-focal point strategies not only multiply the system's productivity but also expand its capability to produce complex multi-material components with high precision and at a faster rate. This technology opens up the possibility of intricate design executions within a single, continuous flow, marking a significant advancement in micro-manufacturing processes.

[0045] Fig. 4 demonstrates the versatility in the method of introducing light into the microfluidic channel, a critical step in the 3D micro -printing process. Direct focusing of the laser beam (4) is the standard approach, yet the inclusion of additional optical elements — such as mirrors (12) and specialty optical fibers (13) — offers alternative techniques that can be adapted to different configurations and focal arrangements.

[0046] An integrated mirror (12) (top left of Fig. 4) redirects the laser beam (4) post its emergence from the focusing optic (7). This arrangement facilitates the light's entry into the channel (1) from a direction that may better suit the specific requirements of the printing application. Such a use of mirrors can streamline the design of the optical path, proving advantageous in constrained spaces or when specific angles of incidence are necessary.

[0047] Using specialty optical fibers (13) (top right of Fig. 4) which offer a means to transport the focused light to the desired location within the channel (1). This technique enables the focusing optic (7) to be placed at a distance from the channel (1) or in a different orientation, providing greater flexibility in the layout of the printing apparatus. Optical fibers (13) also permit the channel walls (2) to be completely non-transparent, as the light is delivered directly to the point of polymerization.

[0048] Employing a hybrid approach, the system integrates both mirrors (12) and specialty fibers (13), as showcased in the lower portion of the Fig. 4. This method permits the concurrent use of colinear and transverse orientations, paving the way for desynchronized printing within the channel (1). The advantage of this setup lies in its ability to print separate structures or different sections of the same structure simultaneously, which significantly streamlines the utilization of space and time during the printing process.

[0049] The adaptability of these optical introductions means that synchronized and desynchronized printing can be achieved with precision. This enables complex multi-focal arrangements and the simultaneous execution of multiple printing tasks within the same channel (1), greatly enhancing the throughput and efficiency of the micro-printing system. Whether using mirrors (12), fibers (13), or a combination of both, these methods can be tailored to the unique requirements of each printing task, ensuring optimal delivery of light for the polymerization process.

[0050] The laser system (Fig. 5) serves as the cornerstone for providing and controlling the laser beam (4) used in in-flow printing. This system comprises a femtosecond (fs) laser (14), characterized by a pulse duration of 10-10000 femtoseconds, a repetition rate ranging from 1 kHz to 100 MHz, and a wavelength spectrum of 350-1750 nm. Accompanying the fs laser (14) in the setup are essential components such as a shutter (15), a power attenuator (16), and, optionally, a polarization control unit (17). These components can either be integrated into the laser (14) itself or function as standalone units.

[0051] Following these initial elements, the system includes either a scanner or a beam shaping unit (18). This segment of the setup is responsible for manipulating the laser beam (4) and may consist of a variety of elements based on the required configuration. The potential components include telescopes, lenses, apertures, mirrors, and beam shaping devices, along with the scanner itself.

[0052] The final stage of focusing the laser (14) into the microfluidic channel (1) is achieved using either a microscope objective lens or an f-theta lens. The chosen focusing optic (7) is characterized by a numerical aperture (NA) that falls between 0.2 to 1.45, tailored to match the requirements of the printing process. The working distance is the space between the focusing optic (7) and the channel wall (2), and it is influenced by the thickness of the channel wall (2). The cross-sectional dimensions of the channel (1) range from 1 pm to 20 mm.

[0053] It is worth noting that additional optical elements may follow the focusing optics (7) to further refine the light path. These can include mirrors (12) or specialty optical fibers (13), among others, enhancing the precision and flexibility of the laser focusing mechanism within the in-flow printing system.

[0054] In-flow 3D printing offers the versatility to work with either a single material or an array of materials, ensuring adaptability to various design requirements. When employing multiple materials, it is critical for the chosen photopolymers to have the ability to flow alongside each other within the microfluidic channel (1) without significant mixing or diffusion. This characteristic is vital for maintaining the distinct properties of each material throughout the fabrication process.

[0055] The process can be approached in two distinct manners Fig. 6. The first is a static method where different materials are introduced into the channel at separate times (19). This allows for the creation of layered structures with varying material properties. The second method involves a dynamic, multi-channel arrangement. In this setup, several channels or nozzles converge into a single main channel, enabling the simultaneous introduction of different materials (20). The materials can either be consistent throughout the printing process or varied, offering nuanced control over the final composition of the printed object.

Claims

CLAIMS1. A method for multi-material 3D micro-printing in laminar flow, characterized in that, it has the following steps: introducing one or multiple photosensitive materials into a microfluidic channel (1) to establish a laminar flow of said materials; implementing a laser system equipped with a femtosecond (fs) laser (14), characterized by a pulse duration ranging from 10 to 10000 femtoseconds, a repetition rate between 1 kHz and 100 MHz, and a wavelength spectrum spanning 350 to 1750 nm, to selectively polymerize the photosensitive materials as they continuously or intermittently flow through the microfluidic channel (1); employing fast scanning or beam shaping techniques with the laser system to create desired structures in the cross-section of the micro fluidic channel (1);2. The method of claim 1, wherein the laser system's configuration for exposing the photosensitive materials in the microfluidic channel (1) is selectable from transverse, colinear, or angular exposure options to suit different printing requirements and setups.

3. The method of claim 1, wherein the microfluidic channel incorporates walls (6) or sections of walls (6) that are at least partially, and ideally completely, transparent to the chosen wavelength of the laser.

4. The method of claim 1, wherein beam shaping can be realized using a spatial light modulator (SLM) or dynamic mirror device (DMD).

5. The method of claim 1, wherein the system can enhance throughput through the utilization of multi-beam exposure.

6. The method of claim 1, wherein various focal points can be operated either synchronously or desynchronously while utilizing multi-beam exposure to enhance throughput.

7. The method of claim 1, wherein focusing into the channel is realized using a microscope objective lens or f-theta lens.

8. The method of claim 1, wherein the numerical aperture (NA) of the used focusing optic is between 0.2 to 1.45.

9. The method of claim 1, wherein the cross-sectional dimensions of the channel (1) range from 1 pm to 20 mm.

10. The method of claim 1, wherein the shape of the channel (1) can be selected, including round, oval, rectangular, square, or any other shape, as necessitated by material flow dynamics or the experimental setup.

11. The method of claim 1, wherein in-flow 3D printing can be realized using one material or multi-materials.

12. The method of claim 1, wherein beam shaping and scanners can be used separately, or combined solution, even using simultaneously.

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