475758 Polymer Science As a Tool for Materials Design and Biological Discoveries

Sunday, November 13, 2016
Continental 4 & 5 (Hilton San Francisco Union Square)
Liheng Cai, School of Engineering and Applied Sciences, Harvard University, Cambridge, MA

Research Interests: I envision a research group focusing on emerging questions at the interface of polymer science and biology, with the vision to push the boundary of classical polymer science as well as to solve challenges in energy, environmental science and healthcare. Empowered by the knowledge of polymer science, I will focus on the development of new functional soft (bio) materials for energy harvesting and healthcare, elucidating the roles of biological gels in health and disease, and exploiting the use of synthetic biology in creating designer biomaterials.

Soft materials with extreme mechanical properties and their mechanics under large deformation. In the course of evolution, biological systems have optimized themselves with extraordinary properties. For instance, cells and tissues are extremely soft with typical Young’s modulus lower than 100kPa, muscles change their stiffness at will, and skins accommodate large deformation easily and self-heal upon damage. Seamlessly interfacing with them offers approaches to solve challenges in healthcare and improving the quality of life, but often requires materials with properties that are comparable, if not the same, to biological objects. Using relatively well-established polymer science as a tool, I will adopt a bottom-up approach to design materials on the molecular-level, enabling new materials with extraordinary mechanical properties and functions. Initially I will focus on (i) extremely soft, yet dry gels and (2) malleable, tough, self-healing polymers. In parallel, I will develop new, fundamental understanding of the mechanics of such compliant materials under large deformation and explore their applications in stretchable electronics and biomedical scaffolds from 3D printing.

Biological gels in health and disease. Biological gels, such as mucus and extracellular matrix, are the major components of mucosal surfaces that line respiratory, gastrointestinal and reproductive tracts. Small changes in biophysical and biochemical properties of these gels result in their abnormal functions that are associated with chronic obstructive pulmonary disease (COPD), cystic fibrosis, inflammatory bowel disease and reproductive tract infection. Restoring the functions of biological gels is critical to treatment of these diseases; this requires elucidating their complex biophysical and biochemical origin. To this end, I will harness relatively well-established knowledge and tools in physical and chemical science to answer emerging clinically and therapeutically important questions related to these biological gels. Using the concept of polymer brush established in polymer physics enables my recent discovery of a new paradigm for mucus clearance, the primary innate defense system for mammalian lungs. I will adapt this unique interdisciplinary approach to elucidate the biophysics and biochemistry of native rather than reconstituted mucus, to study the interaction between mucus and epithelial cells, and to explore the roles of mucus on functionalities of microbiome.

Synthetic biology as a tool for designer biomaterials. Classical polymer science is largely enabled by precise chemical synthesis the can create polymers with controlled structure and thus properties. Yet biopolymers such polypeptides not only have a prescribed structure, but also consist of motifs that possess different strength of interactions such hydrogen bonds, electrostatic and hydrophobic-hydrophilic interactions. Such interactions are relatively weak, yet enable biopolymers with robust and deterministic functions. Due to the diversity and complexity of these interactions, it is challenging to understand how they determine the properties of biopolymers; yet this offers opportunities to classical polymer science. In parallel, emerging synthetic biological techniques allow precise control over both the structure of biopolymers and the types of weak interactions. Harnessing the power of synthetic biology, I will design and create biopolymers with prescribed structure and weak interactions to explore the fundamental polymer science of such systems. Initial research will focus on amphiphilic biopolymers with ionic crosslinkable domains; the amphiphilic nature will allow the polymer to self-assemble to useful structures such as vesicles, whereas the crosslinkable sites can be used to fix the structures after self-assembly. In parallel, I will explore the application of such structures as synthetic vaccines.


Teaching Interests: With my diverse background, B.S. in Physics, Ph.D. in Materials Science, and Postdoctoral experience in Chemistry, Materials Science and Biology, I am well prepared to teach a broad range of topics in materials science. Examples of specific undergraduate courses include polymer chemistry, thermodynamics, mechanics, solid-state physics, and applied mathematics. Examples of advanced undergraduate or graduate courses include polymer physics and chemistry, advanced thermodynamics, materials characterization, biological physics and soft condensed matter physics.

I am also dedicated to develop interdisciplinary courses to contribute to the diversity of curriculum in classical Materials Science, Chemistry, or Chemical Engineering. As modern materials science and engineering is growing into interdisciplinary areas, the emphasis in materials science education should alter accordingly. In addition to fundamental courses, focuses should also be placed on interdisciplinary areas where materials science is coupled with physics, chemistry, and biology; an example of such area is soft matter and polymer science. Knowing the essential concepts and techniques in soft matter and polymer science greatly broadens the view and expertise of students and benefit to their research; according to my experience, however, there is almost no such course dedicated to provide students with an overview of essential techniques through hands-on experience, and only through research projects in laboratories students will have a chance to learn some of them. As a start, I would like to introduce a new course to cover a wide range of techniques and concepts in soft matter and polymer science in combination with hands-on experience. Specific course subjects will cover chemical synthesis, chromatography, light scattering, osmotic measurements, rheology, microscopy, wetting and de-wetting, cell culture, and computer simulation. Each topic will be covered by a two-week lecture; one week focuses on in-class discussion and the other focuses on laboratory training. Students will be required write a short scientific report about each topic and use the knowledge learned during the course to complete a collaborative final project selected from the frontiers of research.

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