Gregory F. , Ph.D
Professor, University of Maryland College Park
gpayne@umd.edu
Biography:
Greg Payne did his
B.S./M.S/PhD and postdoctoral training at Cornell University and The University
of Michigan, and is a Professor at the University of Maryland. His group does
research at the intersection of material science, biology and information
sciences, and he is currently Principal Investigator of a prestigious Materials
Genome Initiative project awarded by the National Science Foundation with the
aim of understanding how to integrate biology and electronics. His work is
internationally recognized by invitations to be keynote speaker at several
scientific conferences and he currently holds Guest or Chair Professor
positions at several universities around the world.
Topic title: ENLISTING BIOLOGY’S “EXCITABLE
MEDIA” TO CREATE COMPLEX, DYNAMIC AND SUSTAINABLE MATERIALS
Abstract:Traditionally, materials scientists have focused on developing
repeatable methods to organize matter into stable structures with reliable functional
properties. For example, current polymer
processing methods allow a diverse range of products to be generated using somewhat
generic methods that cue mesoscale organization in response to controlled thermal,
mechanical (e.g., printing) and optical (e.g., photolithography) inputs. Biology uses a somewhat different approach: starting
from a small number of “bio-generic” materials (e.g., collagen and cellulose), biology
often uses chemical cues to guide the assembly of mesoscale structure with an
emphasis on balancing stability with dynamic-responsiveness (e.g., reconfigurability)
and degradability (e.g., resorbability). Converging theories from physics, biology and information
science emphasize the importance of “excitable” media: mesoscale structure emerges
in response to the set of spatiotemporal cues that induce interactions among “excitable”
components. To extend these theories to polymer
manufacturing we focus on: (i) stimuli-responsive self-assembling biological
polymers as excitable media; (ii) inputs that provide the cues to direct the
emergence of mesoscale structure; and (iii) the interaction mechanisms responsible
for converting the “information” in the imposed input cues into structural
outputs.
Imposed electrical inputs provide a versatile means to “cue”
the emergence of hierarchical organization.1 Specifically, an imposed electric field provides
a driving force for charged biopolymers (e.g., proteins and polysaccharides) to
migrate and align to form oriented and anisotropic mesoscale structure. In addition, electrode-induced reactions can
yield gradients in concentration (e.g., in pH) which can, in some cases, induce
self-assembly. The best-studied example
of biopolymer electrodeposition is the cathodic deposition of the pH-responsive
aminopolysaccharide chitosan through a neutralization mechanism (the high pH
adjacent to the cathode induces chitosan’s reversible sol-gel transition). The versatility of electrical signals is
illustrated by two studies. First, when
the electrical input was provided in an oscillatory fashion, a segmented hydrogel
structure emerged with the segment regions controlled by the “ON” signal and
the boundary regions controlled by the “OFF” signal.2 Second, when chitosan’s electrodeposition was
performed in 2 steps with low salt in the first step and high salt in the second
step, a Janus structure emerged with one face being dense and non-porous and the
other face being highly porous.3
Electrofabrication is versatile and can be coupled with other
emerging methods. For instance, 3D
printing also allows chemical stimuli to be imposed to induce spatiotemporally
controlled transitions in: interaction mechanisms, structure, and properties. For
instance, printing of acidic SDS micellar solutions onto an electrodeposited
chitosan film yielded adjacent regions that were crosslinked through different physical
mechanisms: one region is crosslinked by electrostatic interactions between SDS
and cationic chitosan chains while an adjacent region is crosslinked through crystalline
network junctions of neutral chitosan chains.4 These gradients in structure are stable due
to a structure-induced shift in pKa but these crosslinking mechanisms can be
reversibly switched. 5
In conclusion, nature provides the materials, mechanisms and
inspiration for the sustainable manufacturing of high performance materials.
1.Li et al. 2019. Electrobiofabrication:
Electrically-Based Fabrication with Biologically-Derived Materials. Biofabrication, 11 (2019)
032002.
2.Yan et al. 2018.
Electrical Programming of Soft Matter: Using Temporally Varying Electrical
Inputs to Spatially Control Self Assembly. Biomacromolecules, 19, 364.
3.Lei et. al.
2019. Programmable Electrofabrication of Porous Janus
Films with Tunable Janus Balance for Anisotropic Cell Guidance and Tissue Regeneration. Advanced
Functional Materials, In Press.
4.He et. al. 2017.
Reversible Programing of Soft Matter with Reconfigurable Mechanical
Properties. Advanced Functional Materials, 27,605665.
5.Tsai et. al. 2018. Exploring
pH-Responsive, Switchable Crosslinking Mechanisms for Programming
Reconfigurable Hydrogels Based on Aminopolysaccharides. Chemistry of Materials, 30, 8597.
