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1. Rapid, continuous projection multi-photon 3D printing enabled by spatiotemporal focusing of femtosecond pulses

   https://doi.org/10.1038/s41377-021-00645-z  

   Somers, Paul; Liang, Zihao; Johnson, Jason E.; Boudouris, Bryan W.; Pan, Liang; Xu, Xianfan (December 2021, Light: Science & Applications)

   null (Ed.)

   Abstract There is demand for scaling up 3D printing throughput, especially for the multi-photon 3D printing process that provides sub-micrometer structuring capabilities required in diverse fields. In this work, high-speed projection multi-photon printing is combined with spatiotemporal focusing for fabrication of 3D structures in a rapid, layer-by-layer, and continuous manner. Spatiotemporal focusing confines printing to thin layers, thereby achieving print thicknesses on the micron and sub-micron scale. Through projection of dynamically varying patterns with no pause between patterns, a continuous fabrication process is established. A numerical model for computing spatiotemporal focusing and imaging is also presented which is verified by optical imaging and printing results. Complex 3D structures with smooth features are fabricated, with millimeter scale printing realized at a rate above 10 −3 mm 3 s −1 . This method is further scalable, indicating its potential to make fabrications of 3D structures with micro/nanoscale features in a practical time scale a reality. 

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2. 3D nanoprinting via spatially controlled assembly and polymerization

   https://doi.org/10.1038/s41467-022-29432-z  

   Pattison, Thomas G.; Wang, Shuo; Miller, Robert D.; Liu, Gang-yu; Qiao, Greg G. (April 2022, Nature Communications)

   Abstract Macroscale additive manufacturing has seen significant advances recently, but these advances are not yet realized for the bottom-up formation of nanoscale polymeric features. We describe a platform technology for creating crosslinked polymer features using rapid surface-initiated crosslinking and versatile macrocrosslinkers, delivered by a microfluidic-coupled atomic force microscope known as FluidFM. A crosslinkable polymer containing norbornene moieties is delivered to a catalyzed substrate where polymerization occurs, resulting in extremely rapid chemical curing of the delivered material. Due to the living crosslinking reaction, construction of lines and patterns with multiple layers is possible, showing quantitative material addition from each deposition in a method analogous to fused filament fabrication, but at the nanoscale. Print parameters influenced printed line dimensions, with the smallest lines being 450 nm across with a vertical layer resolution of 2 nm. This nanoscale 3D printing platform of reactive polymer materials has applications for device fabrication, optical systems and biotechnology. 

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3. Temperature-Controlled 3D Cryoprinting Inks Made of Mixtures of Alginate and Agar

   https://doi.org/10.3390/gels9090689  

   Lou, Leo; Rubinsky, Boris (September 2023, Gels)

   Temperature-controlled 3D cryoprinting (TCC) is an emerging tissue engineering technology aimed at overcoming limitations of conventional 3D printing for large organs: (a) size constraints due to low print rigidity and (b) the preservation of living cells during printing and subsequent tissue storage. TCC addresses these challenges by freezing each printed voxel with controlled cooling rates during deposition. This generates a rigid structure upon printing and ensures cell cryopreservation as an integral part of the process. Previous studies used alginate-based ink, which has limitations: (a) low diffusivity of the CaCl2 crosslinker during TCC’s crosslinking process and (b) typical loss of print fidelity with alginate ink. This study explores the use of an ink made of agar and alginate to overcome TCC protocol limitations. When an agar/alginate voxel is deposited, agar first gels at above-freezing temperatures, capturing the desired structure without compromising fidelity, while alginate remains uncrosslinked. During subsequent freezing, both frozen agar and alginate maintain the structure. However, agar gel loses its gel form and water-retaining ability. In TCC, alginate crosslinking occurs by immersing the frozen structure in a warm crosslinking bath. This enables CaCl2 diffusion into the crosslinked alginate congruent with the melting process. Melted agar domains, with reduced water-binding ability, enhance crosslinker diffusivity, reducing TCC procedure duration. Additionally, agar overcomes the typical fidelity loss associated with alginate ink printing. 

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4. An exploration of 3D printed freeform kerf structures

   https://doi.org/10.1117/12.2658554  

   Darnal, Aryabhat; Poluri, Kamal; Deshpande, Himani; Kim, Jeeeun; Kalantar, Negar; Muliana, Anastasia (April 2023, PROCEEDINGS OF SPIE)

   Wissa, Aimy; Gutierrez Soto, Mariantonieta; Mailen, Russell W. (Ed.)

   This study presents the use of a 3D printing method to create kerf structures that can be formed into complex geometries. Kerfing is a subtractive manufacturing method to create flexible surfaces out of stiff planar materials such as metal or wood sheets by removing portions of the materials. The kerf structures are characterized by the kerf pattern, such as square interlocked Archimedean spiral and hexagon spiral domain, cell size, and cut density. By controlling the kerf pattern, spatial density, cell size, and material, the local properties of the structure can be controlled and optimized to achieve the desired local flexibility while minimizing the stresses developed in the kerf structure. Since subtractive manufacturing limits the patterns and materials that can be considered in kerf structures, FDM 3D printing is explored to fabricate kerf structures using polymers, such as Polylactic acid (PLA) and Thermoplastic polyurethane (TPU), where it is possible to vary microstructural topology and materials within the kerf structures. 3D printing enables the combination of the two different polymers and tuning printing factors to create multifunctional kerf structures. The multifunctional kerf structures can then be actuated using non-mechanical stimulations, such as thermal, to shape them into complex geometries. 

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5. High‐Precision Printing of Complex Glass Imaging Optics with Precondensed Liquid Silica Resin

   https://doi.org/10.1002/advs.202105595  

   Hong, Zhihan; Ye, Piaoran; Loy, Douglas_A; Liang, Rongguang (April 2022, Advanced Science)

   Abstract 3D printing of optics has gained significant attention in optical industry, but most of the research has been focused on organic polymers. In spite of recent progress in 3D printing glass, 3D printing of precision glass optics for imaging applications still faces challenges from shrinkage during printing and thermal processing, and from inadequate surface shape and quality to meet the requirements for imaging applications. This paper reports a new liquid silica resin (LSR) with higher curing speed, better mechanical properties, lower sintering temperature, and reduced shrinkage, as well as the printing process for high‐precision glass optics for imaging applications. It is demonstrated that the proposed material and printing process can print almost all types of optical surfaces, including flat, spherical, aspherical, freeform, and discontinuous surfaces, with accurate surface shape and high surface quality for imaging applications. It is also demonstrated that the proposed method can print complex optical systems with multiple optical elements, completely removing the time‐consuming and error‐prone alignment process. Most importantly, the proposed printing method is able to print optical systems with active moving elements, significantly improving system flexibility and functionality. The printing method will enable the much‐needed transformational manufacturing of complex freeform glass optics that are currently inaccessible with conventional processes. 

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