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1. Nanoclay Suspension-Enabled Extrusion Printing of 3D Soft Structures for Biomedical Applications

   https://doi.org/10.1115/MSEC2020-8330  

   Jin, Yifei; Antonelli, Patrick J.; Long, Christopher J.; McAleer, Christopher W.; Hickman, James J.; Xiong, Ruitong; Huang, Yong (September 2020, ASME 2020 15th International Manufacturing Science and Engineering Conference)

   null (Ed.)

   Three-dimensional (3D) extrusion printing of cellular/acellular structures with biocompatible materials has been widely investigated in recent years. However, the requirement of suitable solidification rate of printable ink materials constrains the utilization of extrusion-based 3D printing technique. In this study, the yield-stress nanoclay 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. Multiscale embedded printing of engineered human tissue and organ equivalents

   https://doi.org/10.1073/pnas.2313464121  

   Zhang, Cheng; Hua, Weijian; Mitchell, Kellen; Raymond, Lily; Delzendehrooy, Fatemeh; Wen, Lai; Do, Changwoo; Chen, Jihua; Yang, Ying; Linke, Gabe; et al (February 2024, Proceedings of the National Academy of Sciences)

   Creating tissue and organ equivalents with intricate architectures and multiscale functional feature sizes is the first step toward the reconstruction of transplantable human tissues and organs. Existing embedded ink writing approaches are limited by achievable feature sizes ranging from hundreds of microns to tens of millimeters, which hinders their ability to accurately duplicate structures found in various human tissues and organs. In this study, a multiscale embedded printing (MSEP) strategy is developed, in which a stimuli-responsive yield-stress fluid is applied to facilitate the printing process. A dynamic layer height control method is developed to print the cornea with a smooth surface on the order of microns, which can effectively overcome the layered morphology in conventional extrusion-based three-dimensional bioprinting methods. Since the support bath is sensitive to temperature change, it can be easily removed after printing by tuning the ambient temperature, which facilitates the fabrication of human eyeballs with optic nerves and aortic heart valves with overhanging leaflets on the order of a few millimeters. The thermosensitivity of the support bath also enables the reconstruction of the full-scale human heart on the order of tens of centimeters by on-demand adding support bath materials during printing. The proposed MSEP demonstrates broader printable functional feature sizes ranging from microns to centimeters, providing a viable and reliable technical solution for tissue and organ printing in the future. 

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