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1. Influence of Short Fiber Encapsulated in Hybrid Hydrogel For 3d Bioprinting Process: Aspect of Rheological Properties

   Tuladhar, S. ; Clark, S. ; & Habib, M. A. ( May 2023 , Proceedings of the IISE Annual Conference & Expo 2023)

   Babski-Reeves, K ; Eksioglu, B ; Hampton, D. (Ed.)

   Extrusion-based three-dimensional (3D) bio-printing is one of the several 3D bioprinting methods that is frequently used in current times. This method enables the accurate deposition of cell-laden bio-ink while ensuring a predetermined scaffold architecture that may allow living tissue regeneration. Natural hydrogels are a strong choice for bio-ink formulation for the extrusion-based 3D bioprinting method because they have a combination of unique properties, which include biocompatibility, reduced cell toxicity, and high-water content. However, due to its low mechanical integrity, hydrogel frequently struggles to retain structural stability. To overcome this challenge, we evaluated the rheological characteristics of distinct hybrid hydrogels composed of carboxymethyl cellulose (CMC), a widely used alginate, and nanofibers generated from cellulose (TEMPO-mediated nano-fibrillated cellulose, TONFC). Therefore, to examine the rheological properties, a set of compositions was developed incorporating CMC (1%–4%), alginate (1%–4%), and higher and lower contents of TONFC (0.5%) and (0.005%) respectively. From the flow diagram, the shear thinning coefficients of n and K were calculated, which were later linked to the 3D printability. With the guidance of diverse nanofiber ratios, it is possible to regulate the rheological properties and create 3D bioprinted scaffolds with well-defined scaffold architecture. 

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2. An Effort to Fabricate Clinically Relevant Scaffold Using 3D Bioprinting Processes

   Nelson, Cartwright ; Tuladhar, Slesha ; Habib, Ahasan ( May 2022 , Proceedings for IISE Annual Conference & Expo 2022)

   Ellis, K ; Ferrell, W ; Knapp, J. (Ed.)

   Three-dimensional bio-printing is a rapidly growing field attempting to recreate functional tissues for medical and pharmaceutical purposes. Development of functional tissues and organs requires the ability to achieve large full-scale scaffolds that mimic human organs. It is difficult to achieve large scaffolds that can support themselves without damaging printed cells in the process. The high viscosity needed to support large prints requires high amounts of pressure that diminishes cell viability and proliferation. By working with the rheological, mechanical, and microstructural properties of different compositions, a set of biomaterial compositions was identified to have high structural integrity and shape fidelity without needing a harmful amount of pressure to extrude. Various large scale-scaffolds were fabricated (up to 3.0 cm, 74 layers) using those hybrid hydrogels ensuring geometric fidelity. This effort can ensure to fabricate large scaffolds using 3D bio-printing processes ensuring proper internal and external geometries. 

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3. Systemic Control of 3D Bioprinting Process Parameters to Achieve Defined Scaffold Porosity

   https://doi.org/10.1115/msec2023-104235  

   Quigley, Connor ; Tuladhar, Slesha ; Adhikari, Samrat ; Habib, MD Ahasan ( June 2023 , Proceedings of the ASME 2023 18th International Manufacturing Science and Engineering Conference (MSEC2023))

   Due to its inbuilt ability to release biocompatible materials encapsulating living cells in a predefined location, 3D bioprinting is a promising technique for regenerating patient-specific tissues and organs. Among various 3D bioprinting techniques, extrusion-based 3D bio-printing ensures a higher percentage of cell release, ensuring suitable external and internal scaffold architectures. Scaffold architecture is mainly defined by filament geometry and width. A systematic selection of a set of process parameters, such as nozzle diameter, print speed, print distance, extrusion pressure, and material viscosity, can control the filament geometry and width, eventually confirming the user-defined scaffold porosity. For example, carefully selecting two sets of process parameters can result in a similar filament width. However, the lack of availability of sufficient analytical relations between printing process parameters and filament width creates a barrier to achieving defined scaffold architectures with available resources. In this paper, filament width was determined using an image processing technique and an analytical relationship was developed, including various process parameters to maintain defined filament width variation for different hydrogels within an acceptable range to confirm the overall geometric fidelity of the scaffold. Proposed analytical relations can help achieve defined scaffold architectures with available resources.

    

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4. Controlling Rheological Properties of Hybrid Hydrogel Using Short Fiber for Extrusion-Based 3D Bioprinting Process

   https://doi.org/10.1115/msec2023-104233  

   Tuladhar, Slesha ; Clark, Scott ; Habib, MD Ahasan ( June 2023 , Proceedings of the ASME 2023 18th International Manufacturing Science and Engineering Conference (MSEC2023))

   Among various available 3D bioprinting techniques, extrusion-based three-dimensional (3D) bio-printing allows the deposition of cell-laden bio-ink, ensuring predefined scaffold architecture that may offer living tissue regeneration. With a combination of unique characteristics such as biocompatibility, less cell toxicity, and high-water content, natural hydrogels are a great candidate for bio-ink formulation for the extrusion-based 3D bioprinting process. However, due to its low mechanical integrity, hydrogel faces a common challenge in maintaining structural ty. To tackle this challenge, we characterized the rheological properties of a set of hybrid hydrogels composed of cellulose-derived nanofiber (TEMPO-mediated nano-fibrillated cellulose, TONFC), carboxymethyl cellulose (CMC) and commonly used alginate. A total of 46 compositions were prepared using higher (0.5% and 1.0%) and lower percentages (0.005% and 0.01%) of TONFC, 1%–4% of CMC, and 1%–4% of alginate to analyze the rheological properties. The shear thinning coefficients of n and K were determined for each composition from the flow diagram and co-related with the 3D printability. The ability to control rheological properties with various ratios of a nanofiber can help achieve a 3D bio-printed scaffold with defined scaffold architecture.

    

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5. Engineered assistive materials for 3D bioprinting: support baths and sacrificial inks

   https://doi.org/10.1088/1758-5090/ac6bbe  

   Brunel, Lucia G ; Hull, Sarah M ; Heilshorn, Sarah C ( May 2022 , Biofabrication)

   Abstract Three-dimensional (3D) bioprinting is a promising technique for spatially patterning cells and materials into constructs that mimic native tissues and organs. However, a trade-off exists between printability and biological function, where weak materials are typically more suited for 3D cell culture but exhibit poor shape fidelity when printed in air. Recently, a new class of assistive materials has emerged to overcome this limitation and enable fabrication of more complex, biologically relevant geometries, even when using soft materials as bioinks. These materials include support baths, which bioinks are printed into, and sacrificial inks, which are printed themselves and then later removed. Support baths are commonly yield-stress materials that provide physical confinement during the printing process to improve resolution and shape fidelity. Sacrificial inks have primarily been used to create void spaces and pattern perfusable networks, but they can also be combined directly with the bioink to change its mechanical properties for improved printability or increased porosity. Here, we outline the advantages of using such assistive materials in 3D bioprinting, define their material property requirements, and offer case study examples of how these materials are used in practice. Finally, we discuss the remaining challenges and future opportunities in the development of assistive materials that will propel the bioprinting field forward toward creating full-scale, biomimetic tissues and organs. 

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