Session: 16-01-01: Government Agency Student Poster Competition

Paper Number: 149944

149944 - Spatiotemporal Dynamics of Focused Ultrasound-Induced Actuation in 4d-Printed Shape Memory Polymers 

4D printing integrates time into traditional 3D printing, enabling the creation of complex structures using smart materials like shape memory polymers (SMPs). These materials can be programmed to dynamically change shape and properties in response to external triggers, marking a significant advance in additive manufacturing. However, achieving precise actuation and dynamic shape transformations in these 4D-printed polymers remains challenging using conventional stimuli such as regular heating, light, chemical reactions, etc. Here, we report on the spatiotemporal capabilities of focused ultrasound (FUS) in actuating 4D-printed SMPs and evaluate the influence of various printing parameters on shape recovery performance. Our experiments demonstrate that FUS provides a unique, non-invasive mechanism for inducing controlled localized heating, triggering multiple intermediate shape transformations, and achieving complete shape recovery in SMPs. By optimizing key parameters—such as sample size, ultrasound frequency, exposure duration, intensity, and focal positioning—FUS exhibits enhanced precision in controlling both the temporal and spatial aspects of shape recovery.

We systematically examine how different 3D printing parameters, including printing temperature, speed, infill density, and infill architecture, impact the thermo-mechanical shape recovery properties of thermoplastic polyurethane SMPs exposed to FUS irradiation. Our investigation reveals that higher printing temperatures and moderate printing speeds improve layer bonding, reduce impedance mismatches for efficient propagation of acoustic waves in SMPs, and enhance shape recovery capabilities. Infill density and structure, including designs like tri-hexagonal patterns, significantly influence flexibility, deformation resistance, and shape recovery capabilities. Additionally, optimal sample sizes and higher ultrasound frequencies enhance spatial resolution in shape recovery. Optimal exposure duration and intensity are critical for balancing heating rate and preventing thermal damage. Focal positioning of ultrasound waves is crucial for achieving uniform shape transformation across SMP structures.

By leveraging acoustical principles and thermo-mechanical experimental data, we have established a systematic relationship between additive manufacturing settings and the viscoelastic deformation properties of SMPs exposed to ultrasound. Using these results, we demonstrate the dynamic transition of a 4D-printed gripper-like structure under FUS. Upon FUS irradiation using optimized parameters, the gripper exhibited both opening and closing motions, showcasing the potential for complex, programmable actuation using FUS. This example highlights the practical applications of our research, particularly in fields requiring precise, controllable movements. It paves the way for precise spatiotemporal and localized actuation of SMPs via FUS, with significant implications for advanced medical applications, including minimally invasive surgical tools, targeted drug delivery systems, and adaptive prosthetics. The ability to control SMPs with such high precision opens new possibilities for innovation in various other fields.

Presenting Author: Hrishikesh Kulkarni Virginia Tech

Presenting Author Biography: Hrishikesh Kulkarni is a third-year Mechanical Engineering PhD student in the MInDS Lab at Virginia Tech. He holds a master's degree in mechanical engineering from the University of Florida and a bachelor's degree from Visvesvaraya Technological University in India. Before transitioning to academia for his PhD, Hrishikesh gained four years of industry experience with Toshiba-Mitsubishi Electric, working in their Automation and Computational Modeling group in Virginia. His current research focuses on acoustics, wave manipulation, the dynamics of smart materials, and additive manufacturing. Hrishikesh has one publication under review and actively collaborates with experts at the Swiss Federal Laboratories for Materials Science and Technology and the Soft Dynamics Lab at USC, aiming to produce an impactful PhD thesis through interdisciplinary research. His research broadly aims to create an innovative framework that combines 4D printing and acoustics to facilitate medical applications, including minimally invasive surgical tools, targeted drug delivery, and advanced neuromodulation techniques.

Authors:

Hrishikesh Kulkarni Virginia Tech
David Safranski Enovis Foot & Ankle
Shima Shahab Virginia Tech