Self-Assembly of Shape-Defined Micro-Hydrogels: Top-Down Meets Bottom-Up

Nature uses a genetic code to dictate the structures of proteins which, in turn, underpin their functions. However, there is no analog to a genetic code when fabricating synthetic materials. The goal of this project is to create a platform for fabricating materials by assembling soft, polymeric microparticles (particles whose sizes are in the 1-1000 micrometer range) with specific shapes into precisely controlled arrangements.

The research idea is that that the molecular information necessary to guide the assembly of the polymeric microparticles can be embedded into the particles themselves. The particles will be formed in a microfluidic system equipped with flow lithography, which is a particle synthesis method for fabricating microparticles by exposing polymers to UV light under precise control.

Then, the assembly of the particles into structures will be guided by molecules that are patterned onto the microparticle surfaces. Once established, the platform could be used to construct a variety of innovative structures, such as healable and recyclable tissue-mimetic materials, self-assembled micromachines that harvest waste energy, or soft micro-robots that execute complex tasks in biological environments.

To broaden participation in STEM research, the project will support several research and education experiences for underrepresented high school and undergraduate students in collaboration with campus organizations.

Programmable self-assembly on the mesoscale is limited to periodic lattices, one-dimensional chains, and small high-symmetry clusters. It is not yet possible to program the self-assembly of particles at the level of sophistication that is achieved in biology or using certain top-down approaches such as 3-D printing. This dearth of methodology limits bottom-up access to anisotropic or highly detailed structures.

Despite the emergence of many preparation methods and applications of shape-defined microgels, research on their hierarchical self-assembly into ordered superstructures is limited. Using custom-built flow lithography devices, researchers on this project will control how various functional molecule pairs (e.g., charge-pairing and host-guest motifs) are localized within sequence-defined, one-dimensional and shape-defined two-dimensional polymer microgels.

This synthetic method will encode information that governs where and how the particles interact and how they respond to stimuli. The assemblies will be large enough for direct observation in a microscope, facilitating the development of an empirical framework to understand and predict the information-structure-property-behavior relationships. This combination of top-down and bottom-up fabrication techniques will enable a versatile strategy for scaling up molecular-level work to the mesoscale and beyond, the high-throughput synthesis of complex geometries for soft colloids, and a more diverse library of motifs and stimuli for building and actuating soft micro-machines.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.