3D Digital Grayscale Print (G-DLP), High Functional Materials (FGM)

Three-dimensional printing (3-D) or additive manufacturing (AM) is a popular technique that is currently attracting keen interest as a promising method for revolutionizing design and manufacturing. Researchers have expanded applications from rapid prototyping to tissue engineering to electronics, soft robotics, and high-performance metamaterials, but most 3D printing techniques rely on just one material to print parts or form components using multiple discrete properties with complex mechanical gradients. can not be controlled in a cohesive way.

In contrast, most natural structures, such as fish scales and bone-on tendon, are made in a variety of materials with very different properties that work together. As an alternative, functional grade materials (FGMs) have attracted substantial interest from recent research to improve the mechanical robustness and flow tolerance of substrates. This allows 3-D FGM printing with widely adjustable print properties in a single process, which is of increasing importance in materials science.

In a recent study, now published in Progress of science, Xiao Kuang and colleagues from interdisciplinary mechanical engineering, nanobiomechanics, and advanced structural engineering departments in China and Canada presented a grayscale text-based (gDLP) text-based 3D printing method. In the course of their work, they used grayscale light patterns and a two-step ink to obtain high resolution functional quality materials (FGM) and mechanical gradients up to three orders of magnitude. To demonstrate the method, they developed complex 2D and 3D arrays with controlled deformation and deformation sequences, metamaterials with a negative Poisson's ratio, pre-surgical models with variable rigidity, composites for printing 4- D and a method of fighting counterfeit 3 ​​-D printing.

3D printing techniques at a glance

For advanced 3D printing applications, the researchers demonstrated that the PolyJet method with multiple inkjet print heads allows for simultaneous filing of different materials on the print bed. However, the method had some notable disadvantages, including high equipment cost, stringent resin requirements, limited choice of materials, and a relatively low resolution multimaterial printing mode.

Researchers have therefore used many other 3D printing methods, including the manufacture of molten filaments and direct ink writing, although these techniques have not been pursued further in the past. because of the slow speeds of printing. When they used digital micromirror (DMD) -based digital light processing (DLP) as a fast, high resolution AM approach, the polymer resins hardened abruptly and were too fast in comparison. While the methods used in the past demonstrated a limited ability to practically manufacture functional grade materials with tunable properties. In a more recent technique, scientists have developed continuous liquid interface production (CLIP) as a breakthrough in delivering the fastest 3D printing technology close to the production level; also relevant to this work.

Introducing g-DLP (digital grayscale printing) to develop digital media

In this work, Kuang et al. Developed a new two-step cured hybrid ink system in a single tank to achieve 3D digital grayscale (g-DLP) printing. They synthesized the hybrid ink using bisphenol A ethoxylate diacrylate (BPADA), glycidyl methacrylate (GMA), a diamine-based crosslinking agent, n-butyl acrylate (BA), photoinitiators and photoabsorbents. In the experimental setup, they used monochromatic light intensity settings to cure the resin, layer by layer, in a manner similar to the CLIP technique.

For this, they used an oxygen permeable membrane to separate the hardened section of the window for faster printing. Scientists first cut out the designed structure into images corresponding to individual print layers, and then processed each image with MATLAB code to generate the grayscale distribution containing the desired properties. They then transmitted the images of individual layers with greyscale patterns to the UV projector for printing.

During the experiments, they induced a radical-based photopolymerization to form the polymer network and the printed structure, and showed that the crosslinking density and the modulus of the material decreased with the increase in the percentage of particles. gray scale. In the work, the GMA monomer and the diamine crosslinking agent played a crucial role in the thermal curing process and determined the effects of grayscale photopolymerization of the hybrid ink.

Kuang et al. showed the nonlinear dependence of the method at light intensity and developed models of kinetics of reaction to examine the curation of light as a function of time. Scientists have prevented the reduction of resolution based on light loss in the configuration by adjusting the software using a lower magnification optical system or by increasing the photoabsorbent content to improve the resolution of documents printed.

They followed the evolution of the chemical structure during photocuration with Fourier Transform Infrared Spectroscopy (FTIR) and tested the mechanical and thermomechanical properties of the materials. Kuang et al. included Young's modulus and glass transition temperature (Tg) tests as a percentage of gray scale to characterize the new material. Since the method allowed the creation of digital materials by controlling gray levels, the scientists followed the initial experiments by printing samples of simple geometry with graded properties.

They also used finite element modeling (FEE) simulations to predict the graded properties and deformation rates of architectures to allow for a continuous gradient pattern. This allowed Kuang et al. to make a continuously sized material that bends with a continuously changing curvature when applying a point load. The scientists showed that the experimental results were consistent with the one-point bending simulation.

Graduated metamaterial printing with g-DLP (grayscale digital light printing) for multifunctional materials

The scientists then used g-DLP to explore the design and manufacture of lattice and cellular structures in the study. For this, they first printed a 2D network architecture matrix with a grayscale pattern of a triangular region and a void space underneath. During compression studies, deformation occurred only in the triangular region with a soft material, where the space under the triangular band was not deformed in order to provide a screen protecting all material located under this region. Scientists have shown that such controlled buckling could improve the ability of energy absorption – verified with the help of stable stress drop in the associated stress-strain curve. As before, the FEM simulation accurately predicted the experimental results.

Kuang et al. then designed a 3D network architecture, in which they assigned each layer a different gray scale value to obtain a clean network, printed with a high resolution. The 3D network architecture showed a sequential deformation behavior – with applications of energy absorption. Scientists can exploit the material properties of the g-DLP printing technique to make pre-surgical models.

For example, using the method, they printed fabric-like structures with a bioinspired mimicry to create a bone (with grayscale G₀), soft muscle (G₈₅) and skin (G₇₀) structures. They were also able to design a small-scale artificial limb structure with a soft muscle (G₈₅) and hard bones (G₀), which was printed using the g-DLP method. Kuang et al. proposes to use this technique to design custom architectures with patient-specific physical properties to form pre-operative models in tissue engineering for regenerative medicine.

Form-memory polymers for 4-D printing and diffusion-assisted encryption

Printed material g-DLP can be programmed or set to a temperature range (T_g) from 14⁰ C to 68⁰ C to use as a shape memory polymer (SMP), which has an actuation at different temperatures. To demonstrate this, they developed a helical model that, once heated to 60⁰ C opened to form a straight line, followed by cooling in the ice to return to the initial conformation. However, if the helical structures were printed with the same gray scale (G20), all the hinges regained their shape simultaneously at the same speed, but without recovery of the original shape. The scientists then studied the applications of such SMPs by developing a robotic arm.

As classified materials had different modules and T_gthis led to a different diffusivity in the experimental system. Scientists were able to visualize the various grayscale patterns with a variety of coloring dyes. Kuang et al. proposes to use fluorescein staining for encryption and anti-counterfeiting applications. For example, when scientists included a QR code (quick response) in a film using a grayscale pattern for printing, followed by fluorescein treatment, the pattern is only visible under UV light and invisible under visible light. In addition, when Kuang et al. printing a QR code as a grayscale pattern and analyzing it with a smartphone, scientists were able to establish a direct link with the information or site encoded via the Internet, thus avoiding the counterfeiting of 3D products .

In this way, Kuang et al. developed a g-DLP 3-D printing technique by two-step polymerization to achieve high-resolution digital fabrication with complex shapes and programmable functional gradients. Scientists are looking to optimize the components of the material for other printing applications. They were able to directly develop complex 2D networks, metamaterials, 4-D impressions with shape memory polymers, and produce anti-counterfeiting techniques embedded in the 3D material itself. Scientists Want to Further Enhance the New g-DLP Method to Design Materials for Future Applications, Including 4-D Metamaterials, Preoperative Biomechanical Models, Soft Robotics and Additive Manufacturing with Cyber ​​Security rooted.

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