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Much of the stuff of life is made of polymers (molecules composed of strings of similar repeating units) or molecular assemblies (structures that are made when nanoscale interactions cause molecules to stick to each other). DNA, proteins, and carbohydrates are examples of biological polymers, while cell membranes, viral capsids, and collagen fibers are examples of assemblies.

The Schroeder lab is inspired by systems in biology that showcase the ability of polymers and assemblies to finely control the movement of matter, heat, or electric charge. These systems are often exquisitely complex and drive some of life’s most impressive and essential functions. Skeletons that last a lifetime are built by such processes: calcium and phosphate ions are pumped by protein-based machines into membrane-bound compartments, forced to crystallize out of solution, and deposited on collagen fibers to build bones. Another example: in “excitable” tissues such as neurons and muscles, switch-like channels made of protein and a circuit architecture made of self-assembled lipid membranes ultimately direct the bioelectrical signals that allow us to think and move.

Our group seeks to take design cues from evolution to develop new and useful configurations of matter and energy in which polymers and assemblies control transport processes.

In particular, our ongoing and future projects are as follows:

1. Controlling crystal growth via macromolecular additives

Crystalline materials from the nanoscale to the macroscale are highly valued for their favorable optical, electrical, and mechanical properties. A crystal’s morphology and growth kinetics can be affected by other particles in the crystallizing solution, which can nucleate crystallization using areas of charge density that match the periodicity of the crystal lattice or, conversely, inhibit growth by binding to the surfaces of the crystal.

Our group will seek to design macromolecular additives to exert control over crystal growth in a variety of contexts such as material fabrication, thermal energy release from phase change materials, textile finishing, and drug formulation.

2. Development of strong, sustainable materials from mineralized biopolymers

Across the animal kingdom, anatomical structures such as hair, fingernails, and feathers are composed of a protein called keratin. Some of these keratin-based materials (notably horn, tortoiseshell, and baleen) have been crafted into useful implements for most of human history. Elsewhere in animal physiology, collagen serves as a fibrous scaffold for the growth of bones, teeth, and antlers. These essential materials each consist of biopolymers that are mineralized to varying degrees: that is, they contain deposits of calcium salts that improve their mechanical properties.

Our group will seek to develop new materials, including reinforced textiles and biodegradable alternatives to petroleum-derived plastics, by experimenting with ways to combine sustainably sourced biopolymers and inorganic salts.

3. Creating neuron-like autonomous circuits in polymers and gels

The past century of technological progress has been defined by electronic circuitry made of metals and semiconductors. The most versatile and powerful computing schemes yet known, however, are the nervous systems of living beings, which are ultimately circuits based on the transport of ions through aqueous media. Such systems exhibit several advantages over traditional electronics based on the materials they are composed of: they may be soft, biocompatible, and transparent, they may leverage solution-phase chemistry, and they may derive electrical power from chemical gradients.

Taking inspiration from the form, function, and arrangement of neurons in animals, our group will seek to advance the development of synthetic ionic circuits in solvated polymer systems such as textiles and gels. An ultimate goal is to develop networked systems that couple sensors and actuators to produce complex, autonomous responses.