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1. Nanoclay Suspension-Enabled Extrusion Bioprinting of Three-Dimensional Soft Structures

   https://doi.org/10.1115/1.4051010  

   Jin, Yifei; Xiong, Ruitong; Antonelli, Patrick J.; Long, Christopher J.; McAleer, Christopher W.; Hickman, James J.; Huang, Yong (December 2021, Journal of Manufacturing Science and Engineering)

   Abstract Three-dimensional (3D) extrusion printing of cellular/acellular structures with biocompatible materials has been widely investigated in recent years. However, the requirement of a suitable solidification rate of printable ink materials constrains the utilization of extrusion-based 3D printing techniques. In this study, the nanoclay yield-stress suspension-enabled extrusion-based 3D printing system has been investigated and demonstrated to overcome solidification rate constraints during printing. Utilizing the liquid–solid transition property of nanoclay suspension, two fabrication approaches, including nanoclay support bath-enabled printing and nanoclay-enabled direct printing, have been proposed. For the former approach, nanoclay (Laponite® EP) has been used as a support bath material to fabricate alginate-based tympanic membrane patches. The constituents of alginate-based ink have been investigated to have the desired mechanical property of alginate-based tympanic membrane patches and facilitate the printing process. For the latter approach, nanoclay (Laponite® XLG) has been used as an internal scaffold material to help print poly (ethylene glycol) diacrylate (PEGDA)-based neural chambers, which can be further cross-linked in air. Mechanical stress analysis has been performed to explore the geometric limitation of printable Laponite® XLG-PEGDA neural chambers. 

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2. 3D Printing of Monolithic Proteinaceous Cantilevers Using Regenerated Silk Fibroin

   https://doi.org/10.3390/molecules27072148  

   Mu, Xuan; Gonzalez-Obeso, Constancio; Xia, Zhiyu; Sahoo, Jugal Kishore; Li, Gang; Cebe, Peggy; Zhang, Yu Shrike; Kaplan, David L. (April 2022, Molecules)

   Silk fibroin, regenerated from Bombyx mori, has shown considerable promise as a printable, aqueous-based ink using a bioinspired salt-bath system in our previous work. Here, we further developed and characterized silk fibroin inks that exhibit concentration-dependent fluorescence spectra at the molecular level. These insights supported extrusion-based 3D printing using concentrated silk fibroin solutions as printing inks. 3D monolithic proteinaceous structures with high aspect ratios were successfully printed using these approaches, including cantilevers only supported at one end. This work provides further insight and broadens the utility of 3D printing with silk fibroin inks for the microfabrication of proteinaceous structures. 

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3. Advanced Design and 3D Printing Strategies With Alginate‐Nanoclay Nanocomposites: From Microstructure to Bioprinting

   https://doi.org/10.1002/admt.202401167  

   Hua, Weijian; Zhang, Cheng; Mitchell, Kellen; Raymond, Lily; Hensley, Dale_K; Coulter, Ryan; Bandala, Erick; Chen, Jihua; Do, Changwoo; Zhao, Danyang; et al (October 2024, Advanced Materials Technologies)

   Abstract Nanocomposites made from alginate and nanoclay are extensively applied for diverse biomedical applications. However, the lack of a clear understanding of the interactions between alginate and nanoclay makes it difficult to rationally design the nanocomposites for different material extrusion‐based 3D bioprinting strategies. Here, a combined analytical model is proposed to accurately predict the interaction mechanisms between alginate and nanoclay through small‐angle neutron scattering. These mechanisms are summarized into a phase diagram that can guide the design of alginate‐nanoclay nanocomposites for different bioprinting applications. The rheological properties of various nanocomposites are measured to validate the proposed interaction mechanisms at the macroscale. Accordingly, three representative extrusion‐based bioprinting strategies are linked with the nanocomposite design and applied to freeform fabricate complex structures. A roadmap is summarized to bridge the gap between biomaterial design and bioprinting processes, enabling the rapid and rational selection of biomaterial formula based on available 3D printing methods, and vice versa. 

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4. Particle–polymer interactions for 3D printing material design

   https://doi.org/10.1063/5.0179181  

   Mitchell, Kellen; Hua, Weijian; Bandala, Erick; Gaharwar, Akhilesh K; Jin, Yifei (March 2024, Chemical Physics Reviews)

   Embedded ink writing (EIW) and direct ink writing (DIW) constitute the primary strategies for three-dimensional (3D) printing within the realm of material extrusion. These methods enable the rapid fabrication of complex 3D structures, utilizing either yield-stress support baths or self-supporting inks. Both these strategies have been extensively studied across a range of fields, including biomedical, soft robotics, and smart sensors, due to their outstanding print fidelity and compatibility with diverse ink materials. Particle additives capable of forming volume-filling 3D networks are frequently incorporated into polymer solvents. This integration is crucial for engineering the requisite microstructures essential for the formulation of successful support bath and ink materials. The interplay between the particle additives and polymer solvents is critical for achieving rheological tunability in various 3D printing strategies, yet this area has not been systematically reviewed. Therefore, in this critical review, we examined various mechanisms of particle–polymer interactions, the resulting microstructures, and their subsequent impact on mechanical and rheological properties. Overall, this work aims to serve as a foundational guideline for the design of next-generation materials in the field of extrusion additive manufacturing, specifically for EIW and DIW. 

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5. 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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