(6hx) Multiscale Structure and Dynamics of Polymers and Biological Soft Matter

A grand challenge in polymer engineering lies in integrating the design, characterization, analysis, and prediction of polymer structure and dynamics from nanometers to meters. My research addresses this need by investigating the molecular-scale mechanisms that underlie macroscopic properties of soft materials. Polymers exhibit disparate behaviors across a broad range of length and time scales, such that molecular properties intertwine with microstructure and non-equilibrium dynamics to dictate a material’s macroscopic response and applicability. My work probes materials across time and length scales by integrating bioinspired polymer engineering with molecular theory, coarse-grained simulation, and multiscale experimental characterization, including single molecule fluorescence microscopy, light and neutron scattering, and opto-mechanical testing. This approach enables strategic iterations through the materials design loop to develop responsive and functional soft materials. Initial research areas in my proposed research program include programmable bio-coordinated polymer hydrogels, responsive biopolymer brushes, and muscle-mimetic recombinant protein materials.

Research Experience:

Nucleoporin-based materials for selective biomolecular separations, Department of Chemical Engineering, Massachusetts Institute of Technology (advised by Bradley D. Olsen)

My postdoctoral research has focused on engineering materials with selective biomolecular transport properties. Controlling biomolecular transport is central to numerous technologies including bio-sensing, bio-separations, and tissue engineering. Natural systems such as nuclear pores routinely regulate molecular transport with remarkable specificity (>99.9% of proteins rejected) and speed (1,000 proteins per second per pore), which inspired the development of a molecular transport theory to identify design criteria for synthetic polymers with selective biomolecular permeability. A quantitative transport model predicted two key principles for specific biomolecular transport by a polymer network: (1) entropic repulsion of non-interacting molecules and (2) affinity-mediated permeation of interacting molecules through a walking mechanism. The model guided the design and synthesis of artificial nucleopore-inspired polymer hydrogels that replicate the selective transport function of nuclear pore proteins. Biophysical characterization of nucleopore-inspired hydrogels using small-angle neutron scattering, protein permeability assays, and fluorescence recovery after photobleaching (FRAP) confirmed the importance of entropic size exclusion, moderate binding affinity, and bound-state diffusive mechanisms in selective hydrogel permeability and transport, in agreement with the model predictions. This work presents a new paradigm for selective transport that critically enables the design of polymer hydrogels to control the transport of multi-receptor biomolecules including therapeutic proteins, immunoglobulins, and broad classes of biotoxins.

Single molecule studies of branched polymer dynamics, Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign (advised by Charles M. Schroeder)

My dissertation research extended the field of single polymer dynamics to include DNA comb polymers, effectively bridging a knowledge gap between molecular-scale structure and behavior of topologically complex polymers. The vast majority of single polymer studies focus on linear DNA molecules, but branched polymers generally exhibit more complex flow behavior compared to their linear counterparts. Comb-shaped polymers consist of a main polymer backbone with grafted side chains (branches), and this molecular topology enables chemical versatility for drug delivery, biodegradable sutures, and antifouling coatings. My Ph.D. work included the design, synthesis, characterization, single molecule visualization, and coarse-grained simulation of DNA comb polymers. Microfluidic devices were used to manipulate comb-shaped DNA molecules in extensional flow fields, which are common in polymer processing, while directly visualizing the conformational dynamics of single polymers during flow-induced stretching and relaxation. Single molecule experiments revealed the impact of local constraints (branches) on global behavior (conformations, longest relaxation time), in agreement with Brownian dynamics simulations of DNA comb polymers. This research provided fundamental understanding of branched polymers in flow, as well as an unexpected comb polymer stretching mechanism that suggests a major role of dynamic heterogeneity in the known macroscopic features of topologically complex polymers, including enhanced strain hardening and stress overshoots in the startup of shear flow.

Successful Proposals: Oak Ridge National Laboratory High Flux Isotope Reactor, Bio-SANS CG-3 (September 2017, May 2018); NIST Center for Neutron Research, NG-7 SANS (March 2018)

Selected Publications:

• D. J. Mai, Y. J. Yang, A. C. Huske, S. Li, B. S. Souza, B. D. Olsen, in prep., (2018).
• R. K. Avery, A. Velmahos, D. J. Mai, B. D. Olsen, in prep., (2018).
• C. E. R. Edwards,* D. J. Mai,* S. Tang, B. D. Olsen, in prep., (2018). *equal contributions
• D. J. Mai,* Y. J. Yang,* T. J. Dursch, B. D. Olsen. “Nucleopore-inspired polymer hydrogels for selective biomolecular transport”, submitted, (2018).
• D. J. Mai,* A. Saadat,* B. Khomami, C. M. Schroeder. “Stretching dynamics of single comb polymers in extensional flow”, Macromolecules, 51(4), 1507-1517, (2018).
• D. J. Mai, C. M. Schroeder. “Single polymer dynamics of topologically complex DNA”. Current Opinion in Colloid and Interface Science, 26, 28-40, (2016).
• D. J. Mai, A. B. Marciel, C. E. Sing, C. M. Schroeder. “Topology-controlled relaxation dynamics of single branched polymers”. ACS Macro Letters, 4, 446-452, (2015).
• A. B. Marciel, D. J. Mai, C. M. Schroeder. “Template-directed synthesis of structurally defined branched polymer architectures”. Macromolecules, 48(5), 1296-1303, (2015).
• D. J. Mai, C. A. Brockman, C. M. Schroeder. “Microfluidic systems for single DNA dynamics”. Soft Matter, 8, 10560-10572, (2012).

Selected Awards:

• Arnold O. Beckman Postdoctoral Fellows Award (2017 – present)
• ACS Polymeric Materials Science and Engineering Future Faculty Scholar (2018)
• 1st Place Poster Prize, APS Division of Polymer Physics (2018)
• National Science Foundation Graduate Research Fellowship (2013 – 2016)
• Illinois Distinguished Fellowship (2011 – 2016)
• Mavis Future Faculty Fellowship (2013 – 2015)
• Excellence in Graduate Research Travel Award, APS FGSA (2016)
• AIChE Women's Initiative's Committee (WIC) Travel Award (2015)
• Lam Research Outstanding Graduate Student Award (2015)

Teaching Interests:

As a formally trained chemical engineer, I am excited and qualified to teach core coursework in thermodynamics, fluid mechanics, transport phenomena, separations, chemical kinetics and reactor design, and process dynamics and control. I also look forward to leveraging my research experience and interests to develop and teach electives in polymer science and engineering, soft matter physics, biomolecular engineering, non-Newtonian fluid dynamics, and/or applied mathematics for chemical engineers. My teaching extends beyond the classroom into the laboratory, such that students and postdoctoral researchers in my research group will engage in an interdisciplinary approach toward polymer science and engineering by drawing from expertise in chemical engineering, materials science, biology, chemistry, and physics.

Teaching Experience:

• Structure of Soft Matter (MIT ChemE), Guest Lecturer (2016)
• Applied Mathematics in Chemical Engineering (Illinois ChBE), Teaching Assistant and Guest Lecturer (2012, 2015)
• Polymer Science and Engineering (Illinois ChBE), Guest Lecturer (2013)
• Thermodynamics (Illinois ChBE), Teaching Assistant (2013)
• Chemical Engineering Thermodynamics (Michigan ChE), Undergraduate Instructor (2010)

Service:

I am passionate about recruiting the world’s top talent to pursue careers in engineering and science in order to solve society’s most pressing needs. To this end, I am committed to broadening access to mentorship for talented individuals from all walks of life. At the University of Illinois, I co-founded a campus-wide program to provide support, resources, and advocacy for prospective STEM-field faculty candidates. This program cultivated a community of scholars through a series of faculty-led seminars, panels, and facilitated group discussions. At least seven alumnae have earned tenure-track positions since the program began in 2014, and the program continues to operate under new student leadership. I have also shared my experiences with the next generation of engineers by participating in panels for the AIChE Women's Initiative's Committee (2015 Annual Meeting in Salt Lake City) and the Multi-Cultural Engineering Recruitment for Graduate Education (MERGE) Program at Illinois. At MIT, I supervised under-represented students at the high school, community college, and undergraduate levels, with aims to provide mentorship and to support the students’ continued engagement with the scientific method in their careers. Finally, in my pursuit to recognize the contributions of diverse researchers in polymer physics, I accepted a role as co-chair of the 2018 Polymer Physics Gordon Research Seminar. Overall, I deeply value the richness of scientific communities, and I hope to contribute to their sustained growth and diversity.