(2jw) Design Principles for Active Matter Materials

Active matter is an emerging perspective to describe non-equilibrium biological or artificial systems that convert chemical energy to directed mechanical motion. Whether a flock of birds or a swarm of bacteria or Janus particles, their collective behaviors are governed by similar underlying principles. What if we bring living active matter into colloidal materials? Swimming algae can inspire better micro-robots; doping bacteria into cement can enhance its strength. My research group will focus on the intersection of chemical engineering and active matter physics to push the frontiers of non-equilibrium materials design.

Aim 1: Active Microfluidic Robots
In many important applications like targeted drug delivery, we need to transport cargo through such complex porous flow environments as the human blood vessels and tissues. Microscopic
navigation and maneuver of the transport is highly desirable for such problems but is far from a mature technology. Our group will push forward the field of microfluidic transport engineering by designing composite active swimmers that perform multi-modal swim strategy, configurational transformation, and swarming. We will systematically investigate swimmer mobility considering complex boundary shape, porosity of the tissue medium, and time-varying flow fields.

Aim 2: Herding Bacteria for drug delivery

Genetically modified microbes have been successfully used in many industrial and medical applications. Precise control of the microbial swarm mobility may open new technological possibilities. We will advance quantitative models of active matter swarms incorporating the quorum sensing behavior and hydrodynamic interactions, as well as the swarming-biofilm transition. We will then investigate the mobility of drug-secreting microbes mixed with artificial active particles or genetically modified magnetotactic bacteria. Finally, we will perform microfluidic experiments to demonstrate the design principles.

Aim 3: Active Doping Colloids
The enemy of self-assembly is kinetic arrest. The long sought-after colloidal crystals as novel photonic band gap materials have been difficult to manufacture due to the many meta-stable states arising from colloidal interactions. Meanwhile, kinetically arrested colloidal gels also have wide applications in food, medicine, and cosmetics industries. It will be powerful to control the gel-crystal phase transition and accelerate the manufacturing process. We will use active matter embedded in colloidal gels to control gel structural properties and overcome kinetic arrest barriers. We apply external fields to turn on or change activity. We treat ‘dry’ active matter using the standard Active Brownian Particle (ABP) and Active Levy Swimmer (ALS) models, and for ‘wet’ active matter we incorporate hydrodynamic interactions. We will expand the current state-of-art computational treatment for passive colloidal hydrodynamics, the Stokesian Dynamics technique, to adapt to the active swimmers. In parallel to the theoretical development, our team will perform proof-of-concept microfluidic experiments using bacteria and Janus particles.

Aim 3: Active Computing Meta-Materials
An important part of autonomous soft robotics or smart architecture is the ‘brain’, i.e., control and decision-making system. It is desirable to evaluate the practical potential of active matter in computing circuits, as well as to understand fundamentally how information flows and transforms in such non-equilibrium systems. We will explore microfluidic meta-materials to interact with active matter for computing capability. We will first focus on designing the individual logical gates (AND, OR, etc.) and units (diodes, triodes, etc.), leveraging current studies on active matter ratchets and rectification. To achieve these computing units, the state of the activity can be controlled by feedback circuits to vary the activity parameters, such as run time distribution or self-propelling force. We will build microfluidic versions of Maxwell’s demon. Then we will combine these gates and units to design circuits integrated on microfluidic chips.

Teaching interests:

Philosophy: I believe the best quality of a teacher is patience. To be a patient teacher, I strive to (1) sense
the progress of the students and adjust the pace and presentation of lectures; (2) actively listen
to students’ questions and feedback to meet them at their perspective instead of forcing a specific
approach to a problem. To be able to adjust to students’ needs, I will be flexible when designing
the curriculum, so that later I can choose to spend more time elaborating certain parts in response
to the students’ reaction. The learning styles of students also vary a lot; for example, some students
prefer verbal presentations (written or spoken), while others prefer visual presentations (graphs,
pictures, etc.). To accommodate to all of them, I will combine different teaching methods, such as
mixing lecturing with videos and live demonstrations. I also believe that teaching is the best way
to learn. ‘While we teach, we learn.’ as ancient Roman philosopher Seneca said. To achieve my
goal, it is important to understand the subject deeply from multiple perspectives so that one can
adapt to different students. In this sense, I will grow together with the students. When I was TAing, I realized that a lot of times the students’ performance is limited not by capability, but by their emotional fear of the topic, or lacking family or friends knowledgeable in that field. This intellectual loneliness and isolation leads to loss of interest or motivation. These interactions are good supplement to support the students’ needs for discussions on complex subjects. Small group study sessions are also more private and students feel more secure and build up confidence in the topic, without feeling ashamed of their current level of knowledge. The goal of my teaching is for the students to feel motivated about the subject and overcome learning obstacles, by making new materials a natural extension of their current knowledge domain.

Course design: My theoretical training background has lay down a solid foundation to elaborate fundamental ideas and techniques. I have been working with faculty members from Chemical Engineering departments at MIT (Martin Bazant) and Caltech (John Brady and Zhen-Gang Wang), and have taken various classes from each of them, from electro-chemical systems to transport phenomena to polymer physics. All these training experiences have well prepared me to teach any core course for both undergraduate and graduate students. I am very excited to teach classes such as fluid mechanics, electrochemistry, polymer physics, statistical mechanics. I am also passionate to design my own courses, such as introduction to active matter physics, and computational modeling of porous materials.