Drexel University has received a three-year National Science Foundation
grant to fund another research project into crystalsomes, microscopic hollow
polymer capsules, this time to build their curved, responsive walls without
help from an outside template.
The project is led by
Christopher Li, PhD, professor of materials science and engineering, who coined the name
crystalsome in 2016 by combining "crystal" and "liposome." His group,
including PhD student Carl Furner, is working with Bin Zhao, PhD, a
chemistry professor at the University of Tennessee, Knoxville. The award
begins in August, runs through July 2029, and extends research that
also drew NSF support in 2025.
Crystalsomes matter
because of how they're made. Most polymer capsules have walls of tangled, disordered chains, leaving
weak points where heat, pressure or time can open a path for their contents
to leak out. Crystalsome walls are ordered instead, like a crystal, which
makes them stronger, more uniform, and programmable.
The challenge to spontaneously form crystalsomes without a template is that
ordered polymers naturally form flat plates, not spheres. Li's earlier
crystalsomes got their curve by growing inside a liquid droplet, which meant
the capsule's size was locked to the droplet's size. The new project removes
that dependency by building the curvature into the polymer itself, using a
bristly molecule called a bottlebrush, a long backbone with shorter chains,
or bristles, grafted densely along its length. As the bristles crystallize
and crowd against one another, the strain of being tethered so tightly to
the backbone forces the growing layer to arch into a capsule.
Freed from the droplet, the capsules could in principle be made at a broad
size range, with other materials such as metals or dyes built into the wall
as it forms.
The grant funds three lines of research: understanding how these capsules
form with a single type of bristle, extending that to bottlebrushes with two
different bristle types, and designing capsules that respond to their
environment, such as opening when acidity changes.
"What we want is a general set of rules for how these materials assemble
themselves," Li said. "Once we understand the mechanism well enough to
program it, we can design a particle to do a specific job, and that's what
makes this useful for various applications."
The project also supports graduate student mentoring, classroom instruction
and community outreach at both universities.