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1. Designing an Interchangeable Multi-Material Nozzle System for the 3D Bioprinting Process

   https://doi.org/10.1115/1.4055249  

   Nelson, Cartwright; Tuladhar, Slesha; Habib, MD (August 2022, Journal of Medical Devices)

   Abstract Three-dimensional bioprinting is a rapidly growing field attempting to recreate functional tissues for medical and pharmaceutical purposes. Development of functional tissue requires deposition of multiple biomaterials encapsulating multiple cell types i.e. bio-ink necessitating switching ability between bio-inks. Existing systems use more than one print head to achieve this complex interchangeable deposition, which decreases efficiency, structural integrity, and accuracy. In this research, we developed a nozzle system capable of switching between multiple bio-inks with continuous deposition ensuring the minimum transition distance so that precise deposition transitioning can be achieved. Finally, the effect of rheological properties of different bio-material compositions on the transition distance is investigated by fabricating the sample scaffolds. 

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2. Inhouse Multi-Material Nozzle System Design and Fabrication for 3D Bioprinting Process: Next Step

   https://doi.org/10.1115/msec2023-104454  

   Quigley, Connor; Hurd, Warren; Clark, Scott; Sarah, Rokeya; Habib, MD Ahasan (June 2023, Proceedings of the ASME 2023 18th International Manufacturing Science and Engineering Conference (MSEC2023))

   Abstract Three-dimensional (3D) bio-printing is a rapidly growing field attempting to recreate functional tissues for medical and pharmaceutical purposes. The printability of multiple materials encapsulating various living cells can take this emerging effort closer to tissue regeneration. In our earlier research, we designed a Y-like nozzle connector system capable of switching materials between more than one filament with continuous deposition. The device had a fixed switching angle, was made from plastic, and was suitable for one-time use. This paper presents the extension of our previously proposed nozzle system. We considered 30°, 45°, 60°, and 90° angles (vertical and tilted) between the two materials and chose stainless steel as a material to fabricate those nozzle connectors. The overall material switching time was recorded and compared to analyze the effects of those various angles. Our previously developed hybrid hydrogel (4% Alginate and 4% Carboxymethyl Cellulose, CMC) was used as a test material to flow through the nozzle system. These in-house fabricated nozzle connectors are reusable, easy to clean, and sterile, allowing smooth material transition and flow. 

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3. Tuning Process Parameters for Multi-Material Extrusion Through In-house Nozzle System for 3D Bio-printing Process

   Quigley, C.; Hurd, W.; Clark, S.; Sarah, R.; & Habib, M. A. (May 2023, Proceedings of the IISE Annual Conference & Expo 2023)

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

   The emerging field of three-dimensional bio-printing seeks to recreate functional tissues for medical and pharmaceutical purposes. With the ability to print diverse materials containing different living cells, this growing area may bring us closer to achieving tissue regeneration. In previous research, we developed a Y-shaped nozzle connection device that facilitated the continuous deposition of materials across multiple filaments. This plastic device had a fixed switching angle and was intended for single use. In this study, we present an extension of our previous nozzle system. To fabricate the nozzle connectors, we chose stainless steel and considered angles of 300, 450, and 900 (both vertical and tilted) between the two materials. The total material switching time was recorded and compared to analyze the effects of these angles. We used our previously developed hybrid hydrogel (4% Alginate and 4% Carboxymethyl Cellulose, CMC) as a test material to flow through the nozzle system. These in-house fabricated nozzle connectors are reusable, and sterile and enable smooth material transition and flow. 

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4. Tuning of ultraviolet ‐curable ink printability via in situ ultraviolet irradiation during direct ink write applications

   https://doi.org/10.1002/app.55360  

   Jackson, Sean; Zaragoza, Lysette; Kumar, Balaji Krisna; Dickens, Tarik (May 2024, Journal of Applied Polymer Science)

   Abstract Direct ink write deposition facilitates line‐by‐line extrusion of inks spanning wide viscoelastic ranges. Following deposition, post processing technologies permit tuning of the extrudate's material property characteristics—ultraviolet (UV) irradiation, facilitating the photopolymerization of UV‐reactive catalyst solutions, permits targeted modification of the extrudate's microstructure and in situ tuning of extrudate macrostructure. This report analyzes the morphological, rheological, and microstructural property relationships governing the printability, and processivity, of extruded UV‐curable resin inks for delineation of sufficiency and optimization of ink printability utilizing direct ink write technologies. A design‐of‐experiments approach is implemented to quantify significance regarding an extrudate's dimensional response to extrusion parameter variation and in situ processing parameters, identifying proportionally of nozzle velocity, nozzle height, and UV irradiation exposure with extrudate aspect ratio, reflected by respective maximum extrudate aspect ratio increases of 158% and 109%, regarding 121 and 123K resin inks. Finally, the relationship between extrudate morphology and microstructure variation was assessed via dielectric cure monitoring, whereby an extrudate's ion viscosity was calculated in relation to its rheological modulus, reflecting the relationship between an extrudate's morphology, rheological response, and printability, regarding its microstructural variation. 

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5. Process Control for Direct Ink Writing of Composite Materials Via Reinforcement Learning

   https://doi.org/10.1115/1.4069011  

   Li, Zebin; Chen, Wuyang; Guo, Zipeng; Zhou, Chi; Sun, Hongyue (September 2025, Journal of Manufacturing Science and Engineering)

   Abstract Material-extrusion-based additive manufacturing is a versatile technology attracting interest across multiple industries in energy, semiconductor, biomedical, and construction. It has several unique merits including material variety, the ability to produce complex and customized geometries, and cost-effectiveness. The feedstock material, commonly referred to as the feedstock ink, is a viscous elastomeric fluid (i.e., a kind of composite material). Extrusion of such feedstock inks is a dynamic process governed by multiple interdependent process parameters. The intrinsic interactions within the process often lead to ink flow heterogeneity, resulting in unpredictable under-extrusion and over-extrusion. This ultimately affects the consistency of ink deposition. Traditional control strategies rely on open-loop, empirically derived methods that are often material-specific and nontransferable. Lacking a generic control strategy poses significant challenges with composite material-based inks. In this work, a data-driven reinforcement learning (RL)-based controller is developed to address the challenge. The stochastic state transition technique is adopted to generate the offline data set for the RL-based controller training and reduce the physical experimentation needs. The RL-based controller adjusts the printing in real-time to compensate for the over-extrusion and under-extrusion when such undesired phenomena occur. Several validation material extrusion (i.e., direct ink writing) experiments demonstrate the effectiveness of the RL-based controller. Besides, the RL-based controller is transferable and can be adapted to new process conditions with limited experiments at new process conditions, showing its generalization ability and broadening the application scenarios of the RL-based controller. 

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