(4bu) Multifunctional Soft Robots Enabled By Complex Material Response and Collective Interactions

Characterizing material properties is essential when designing functionality. Specifically, soft materials modulate their properties in situ with external stimuli due to their nonlinear nature. A soft robot uses this complex response to morph its shape, move in heterogeneous environments, and perform multiple tasks. However, the complexity of a soft robot makes it challenge to program its response, as its material properties are highly nonlinear. To address this challenge and build a fully controllable soft robot from the bottom up, my research program focuses on novel soft actuators and robotic materials based on one of the simplest geometric designs: a drop shape. This simple system is an excellent model for understanding the complex behavior of soft robots and their interactions with their surroundings. These drop-shaped units have a magnetic, liquid core (ferrofluid) and are encased by a wide range of shells (powders with diverse microstructures and thin gel films), allowing for a broad range of functionalities. By altering the unit’s core and shell, my team will design and calibrate its properties, enhancing and optimizing functionalities for specific environments or tasks. Ultimately, using these soft units as a foundation, we will engineer them to form a soft robot capable of performing multiple tasks simultaneously.

During my postdoctoral work, I discovered a unique way to drive a drop using a rotating magnetic field, enabling precise and remotely-controlled speed and direction control (ref. 1). I demonstrated that these drops can perform a variety of tasks, such as climbing a curved surface and picking up and transporting cargo. Moreover, I dramatically altered its locomotion mechanism and realized a new form of soft actuator by adding a shell to the drop, for example, with hydrophobic powder. These soft actuators exhibit multiple translation modes, and I can capture their behavior using a simple mechanical model capable of extending to more complicated scenario. While these actuators are simple in both shape (a drop) and moving mechanism (rotation), the interaction of these actuators with various surroundings brings about complex behavior, which we must understand at a fundamental level to integrate these actuators into realistic environments. To overcome this challenge, my team will study swarms of these soft actuators, and how collective interactions can enhance functionality.

I have demonstrated that a wide range of motion strategies and functionalities can be created with a simple actuated system: a magnetic liquid core coated with a powder shell. To enable a more diverse set of behaviors, and create a more robust platform, my team will build upon this base system, for example replacing the powder shell with a thin film, replacing the Newtonian fluid core with a viscoelastic solution, or fully switching to gels embedded with magnetic particles. These new forms of actuators will be more resilient and move faster by storing deformation energy. We will further design more functionalities to the actuators using various types of gels that react differently to external stimuli. Since we control the actuator’s properties with the external stimuli, we must understand how and when to apply external stimuli and control its nonlinear response. My team will engineer various types of actuators and employ them as a base unit, connecting various types of actuators to form a complex soft robot that achieves multiple tasks simultaneously.

Future goals:

My research focuses on developing novel, magnetically-driven soft robots, and leverages my strengths in fabrication. To set a comprehensive understanding and blueprint for building complex soft robots, my research group will initially focus on three main objectives:

1. Manufacturing a diverse set of actuators and characterizing how modifications to actuator shape and surface coating modulate their functionality.
2. Exploring how collective swarms of actuators can accomplish new functions, and better navigate heterogenous and structured environments.
3. Incorporating stimuli-responsive functionalities into actuators by transitioning from water/oil-based ferrofluids to viscoelastic cores.

Teaching interests:

My teaching philosophy is rooted in two fundamental principles: (1) collaborative learning with students as partners and (2) a comprehensive assessment of students' abilities. My teaching philosophy has its roots in my own experience. After I received my bachelor's degree, I was a teaching assistant at my alma mater for the sophomore class Experimental Physics II. This course enables students to design and improve an experiment that replicates the results of a cutting-edge scientific paper. Due to the difficulty of this course, the students and I collaborated intensively to navigate all the challenges, and I gained valuable experience in motivating students. During my graduate career, I assisted my PI to develop an online class, Introduction to Scientific Computing, and was the teaching assistant for it during Covid. As a postdoc, I led a summer tutorial focused on image analysis, and designed a hands-on class for the participants to practice image analysis with ImageJ and Python including Fourier transformation, morphology, convolution, etc. My teaching experiences have equipped me with the skill to design courses that cater to different forms of interaction, whether in-person or online, and that are tailored to diverse audiences including physicists, mathematicians, and engineers.

In addition to my standard teaching, I look forward to connecting with local schools and teaching young people outside the university. During both my PhD and postdoc, I have mentored a diverse group of research students, including measuring the rheology of grains mixed with larvae, testing the fatigue of a swelling hydrogel, and synthesizing ferrofluid liquids and colloidal gels. I also have mentored four high school interns over three summers which has resulted in the preliminary data for my core-shell actuator system. I aspire to connect with local schools as a faculty member, designing summer workshops to inspire future scientists by guiding them on the cutting edge of scientific discovery.

In addition to teaching standard courses such as Mechanics and Thermodynamics, I look forward to developing specialized courses related to soft matter topics such as non-Newtonian fluid mechanics, granular materials, or rheology. Additionally, I plan to organize summer workshops at local schools to introduce my research to a broader community; these efforts are rewarding, and often lead to unexpected scientific discoveries.

Selected Publications:

1. (in review) Aaveg Aggarwal*, Shih-Yuan Chen*, Eleftherios Kirkinis, Mohammed Imran Khan, Bei Fan, Michelle M Driscoll, Monica Olvera de la Cruz, Wobbling and Migrating Ferrofluid Droplets, preprint: arXiv:2406.08289 (* equal contribution)
2. Shih-Yuan Chen, Hector Lopez-Rios, Monica Olvera de la Cruz, and Michelle M. Driscoll, Restructuring a passive colloidal suspension using a rotationally driven particle, Soft Matter (2023)
3. Aaron Bardall, Shih-Yuan Chen, Karen E Daniels, and Michael Shearer, Gradient-induced droplet motion over soft solids, IMA Journal of Applied Mathematics 85, 495–512 (2020).
4. Shih-Yuan Chen, Aaron Bardall, Michael Shearer, and Karen E. Daniels, Distinguishing deformation mechanisms in elastocapillary experiments, Soft Matter 15, 9426–9436 (2019)

Selected Awards:

• DSOFT Future Investigator Travel Award (2024)
• MRSEC Symposium, Best Poster Award (2023)

Professional Service:

• Co-chair, GRS Complex Active and Adaptive Material Systems (2025)
• Physics with a Bang! (UChicago annual outreach event) (2022-2023)
• Judge, Rapid Fire Research, Department of Physics and Astronomy, Northwestern University (2024)
• Lecturer, Soft Matter Summer Workshop, Department of Physics and Astronomy, Northwestern University (2023)
• Session chair, N11: Active Colloids II, APS March meeting (2022)
• Journal reviewer: Nature Communications, Frontiers in Physics.