Session: 20-17-01: Rising Stars of Mechanical Engineering

Paper Number: 173777

Fundamental Investigations of Laser-Induced Forward Transfer (Lift) Printing 

Laser-Induced Forward Transfer (LIFT) is an innovative additive manufacturing method offering precise, non-contact deposition of biomaterials, holding significant potential in tissue engineering, regenerative medicine, and biomedical device fabrication. Despite the notable advantages of LIFT, there remains limited fundamental understanding of the intricate physical processes involved, particularly the interactions between short-pulse, high-frequency lasers and bio-compatible hydrogels.

This study systematically investigates these fundamental phenomena, focusing on bubble dynamics, jet formation, and droplet deposition processes, which occur at extremely short timescales (sub-microsecond) and sub-micron spatial resolutions. Such phenomena pose significant challenges for experimental characterization and numerical modeling, necessitating advanced methodologies to achieve reliable understanding and control.

A key component of our research involved developing a comprehensive computational fluid dynamics (CFD) model to accurately predict the complex jet flow dynamics central to the LIFT process. The developed CFD model captures critical physical phenomena including phase changes, bubble formation and growth, fluid jetting dynamics, and droplet breakup, providing valuable insights into the intricate relationships between laser parameters, material properties, and resultant printing outcomes. The CFD model's predictive capabilities were rigorously validated through experiments utilizing high-speed imaging and laser diagnostics, ensuring robust model accuracy.

Our previous experimental studies investigated the influence of different energy-absorbing layer materials and varying sodium alginate viscosities on LIFT performance. By evaluating commonly employed energy-absorbing layer materials, including metallic thin films and polymer layers, we observed significant variations in bubble formation characteristics and subsequent jetting behaviors. Metallic thin films demonstrated distinct jet formation dynamics compared to polymeric layers, highlighting the crucial role of energy absorption mechanisms and thermal properties of the absorbing layer. Additionally, varying the sodium alginate viscosities revealed substantial impacts on jet stability, droplet formation, and printing resolution, emphasizing the importance of rheological properties of hydrogels in optimizing bioprinting performance.

Further investigations were conducted to enhance printing quality by combining numerical modeling with targeted experimental validation. Through this integrated approach, we identified critical operational parameters, such as laser fluence, pulse duration, and hydrogel absorption characteristics, that significantly influence jetting stability and reproducibility. Adjusting these parameters led to marked improvements in printing resolution, structural consistency, and cellular viability of printed constructs. The synergistic use of modeling and experiments provided a robust framework for systematically optimizing LIFT bioprinting processes.

Overall, our research delivers foundational insights into the fundamental physics governing the LIFT process, offering essential knowledge required for optimizing printing performance and extending its applications. This work emphasizes critical considerations for scaling LIFT from laboratory research to industrial applications, highlighting current limitations and outlining strategies to achieve broader implementation. Future research will focus on further expanding the material compatibility database, refining computational models to accommodate complex material behaviors, and exploring the potential for printing multilayered, multimaterial constructs with enhanced precision and functionality. These advancements are pivotal for unlocking the full potential of LIFT technology within the biomedical field.

Presenting Author: Ben Xu University of Houston

Presenting Author Biography: Dr. Ben Xu is an Assistant Professor and Presidential Frontier Faculty Fellow in the Department of Mechanical and Aerospace Engineering at the University of Houston. His research expertise lies in advanced additive manufacturing, particularly laser-induced forward transfer (LIFT) bioprinting, and computational modeling of multiphase fluid dynamics. His research has been supported by prominent funding agencies, including NSF, DOE, NASA, and DoD. Dr. Xu is actively involved in promoting STEM education and workforce development initiatives, particularly in clean energy and advanced manufacturing technologies.

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