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1. Controlling Porosity of 3D Bioprinted Scaffold: A Process Parameter-Based Approach

   Quigley, C.; 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 3D bioprinting is a promising method for repairing patient-specific tissues and organs due to its inherent capacity to release biocompatible materials containing living cells in a preset area. The filament geometry and width mostly determine the scaffold architecture. Extrusion pressure, print speed, print distance, nozzle diameter, and material viscosity are just a few of the process variables that can be carefully chosen to affect the filament shape and width, ultimately verifying the user-defined scaffold porosity. To maintain defined filament width variation for various hydrogels within an acceptable range and to confirm the overall geometric fidelity of the scaffold, in this paper, filament width for a set of biomaterial compositions was determined using an image processing technique and an analytical relationship, including various process parameters, was developed. 

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2. Process monitoring and control strategies in extrusion-based bioprinting to fabricate spatially graded structures

   AA Armstrong, A Pfeil (April 2021, Bioprinting)

   null (Ed.)

   Extrusion-based bioprinting is the most common printing technology used in regenerative medicine. Despite recent technological advances, a pressing challenge for extrusion printing is low spatial resolution, which limits the functionality of printed constructs. One of the reasons for the low spatial resolution is a lack of process monitoring and control strategies to monitor fabrication and correct for print errors. Few research efforts implement process control and investigate the relationship between extrusion process parameters and printing fidelity. The lack of understanding between process parameters and print results ultimately limits the complexity of the possible structures. For example, fabrication of structures whose topologies vary spatially within the part is not possible without advanced process control. Here we enable fabrication of advanced spatially graded structures by implementing process monitoring and control strategies. We develop material models to better understand the relationship between process parameters and printing outcomes. We also present an experimental procedure to generate a process map that provides insight into the regions of the processing space that produce the desired extrusion features (e.g., width of the filament). After generation of a process map and material models, we implement a process monitoring and control strategy that measures the feature error and intelligently updates the process control inputs to reduce defects and improve spatial fidelity, which will lead to better functionality of the final construct. 

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3. 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))

   Abstract 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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4. Self‐Regulative Direct Ink Writing of Frontally Polymerizing Thermoset Polymers

   https://doi.org/10.1002/admt.202200230  

   Aw, Jia_En; Zhang, Xiang; Nelson, Arif_Z; Dean, Leon_M; Yourdkhani, Mostafa; Ewoldt, Randy_H; Geubelle, Philippe_H; Sottos, Nancy_R (April 2022, Advanced Materials Technologies)

   Abstract The ability to manufacture highly intricate designs is one of the key advantages of 3D printing. Achieving high dimensional accuracy requires precise, often time‐consuming calibration of the process parameters. Computerized feedback control systems for 3D printing enable sensing and real‐time adaptation and optimization of these parameters at every stage of the print, but multiple challenges remain with sensor embedment and measurement accuracy. In contrast to these active control approaches, here, the authors harness frontal polymerization (FP) to rapidly cure extruded filament in tandem with the printing process. A temperature gradient present along the filament, which is dependent on the printing parameters, can impose control over this exothermic reaction. Experiments and theory reveal a self‐regulative mechanism between filament temperature and cure kinetics that allows the frontal cure speed to autonomously match the print speed. This self‐regulative printing process rapidly adapts to changes in print speed and environmental conditions to produce complex, high‐fidelity structures and freestanding architectures spanning up to 100 mm, greatly expanding the capabilities of direct ink writing (DIW). 

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5. A Roadmap to Fabricate Geometrically Accurate Three-Dimensional Scaffolds CO-Printed by Natural and Synthetic Polymers

   https://doi.org/10.1115/1.4055474  

   Quigley, Connor; Tuladhar, Slesha; Habib, Ahasan (June 2022, Journal of Micro and Nano-Manufacturing)

   Abstract Three-dimensional bioprinting is a promising field in regenerating patient-specific tissues and organs due to its inherent capability of releasing biocompatible materials encapsulating living cells in a predefined location. Due to the diverse characteristics of tissues and organs in terms of microstructures and cell types, a multinozzle extrusion-based 3D bioprinting system has gained popularity. The investigations on interactions between various biomaterials and cell-to-material can provide relevant information about the scaffold geometry, cell viability, and proliferation. Natural hydrogels are frequently used in bioprinting materials because of their high-water content and biocompatibility. However, the dominancy of liquid characteristics of only-hydrogel materials makes the printing process challenging. Polycaprolactone (PCL) is the most frequently used synthetic biopolymer. It can provide mechanical integrity to achieve dimensionally accurate fabricated scaffolds, especially for hard tissues such as bone and cartilage scaffolds. In this paper, we explored various multimaterial bioprinting strategies with our recently proposed bio-inks and PCL intending to achieve dimensional accuracy and mechanical aspects. Various strategies were followed to coprint natural and synthetic biopolymers and interactions were analyzed between them. Printability of pure PCL with various molecular weights was optimized with respect to different process parameters such as nozzle temperature, printing pressure, printing speed, porosity, and bed temperature to coprint with natural hydrogels. The relationship between the rheological properties and shape fidelity of natural polymers was investigated with a set of printing strategies during coprinting with PCL. The successful application of this research can help achieve dimensionally accurate scaffolds. 

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