HHMI Faculty Research Award (FRA)
Cover Sheet
Title
Thermally reversible polymers for patterning self-oscillating gels
Name of PI
Matthew Smith
Department of PI
Engineering
Name(s) of collaborators NA
Undergraduates
Minchul Kim plus 1 more student to be determined
Associated with Project:
(Give names if known or
simply numbers if
students are not yet
identified)
Projected start date
Projected end date
Total Budget
Requested
January 2014
December 2014
$14,850
ABSTRACT (keep the abstract under ½ of a page)
Self-oscillating hydrogels, have gained increasing attention for their unique biomimetic
qualities, namely the direct conversion of chemical energy to mechanical work. These gels
display swell-deswell (mechanical) oscillations driven by the Belousov-Zhabotinsky (BZ)
reaction, which is catalyzed by metal ions such as ruthenium. The intrinsic oscillations that
characterize these materials are made possible by direct incorporation of the metal catalyst
into the polymer network, causing the BZ reaction to occur only within the gel. The ability to
precisely pattern arrays of reactive BZ patches suggests a promising avenue for arranging
reactive patches much like modular building blocks to form composite actuators with the
ability to perform complex functions. Key challenges to producing functional devices are
developing effective BZ gel materials with robust patterning processes. Herein we propose
developing a printable self-oscillating gel based on thermally reversible synthetic polymers.
Patternable, self-oscillating hydrogels such as those proposed here hold potential for
advancing the state of the art in smart materials for biomimetic soft robotics, signal
amplification in chemomechanical sensors, and chemical encryption.
1 Project Description
1.1 Significance of Work
The significance of this work is, first, to develop a new patternable, self-oscillating (autonomous)
gel material with the potential for advancing the state of the art in smart materials for biomimetic
sensing and actuating applications. This work will provide the preliminary results required to
successfully pursue external funding. Second, the proposed line of research presents a unique
opportunity for engineering students and specifically those pursuing the chemical engineering
emphasis. Students will gain a distinctive interdisciplinary perspective because the proposed
project spans topics including chemical synthesis, material science and engineering, and
engineering mechanics. This broad exposure will prepare engineering students for the
multifaceted science and technology challenges they will face as STEM researcher leaders.
1.2 Objectives
Hydrogels are a class of soft matter consisting of lightly cross linked polymer networks that
swell in aqueous environments. A particular subset of these materials, self-oscillating hydrogels,
have gained increasing attention for their unique biomimetic qualities, namely the direct
conversion of chemical energy to mechanical work (See Ref. 1 for a useful review of these
materials). These gels display swell-deswell (mechanical) oscillations driven by the BelousovZhabotinsky (BZ) reaction, which is catalyzed by metal ions such as iron or ruthenium. The
intrinsic oscillations that characterize these materials are made possible by direct incorporation
of the metal catalyst into the polymer network, causing the BZ reaction to occur only within the
gel (Fig. 1). The chemical wave length of the oscillating reaction is approximately 1mm. As a
result homogeneous gels whose maximum dimension is less than 1mm display uniform swelldeswell oscillations, while those with dimensions above 1mm exhibit traveling waves. Traveling
wave behavior is useful, for example, for mass transport applications or for chemomechanical
sensors.2,3 However, we wish to significantly expand the current realm of functional design
possibilities by considering composite gels composed of arrays of sub-millimeter BZ-gel patches
Figure 1 (a) Ruthenium tris(bipyridine) complex covalently bound to a cross linked polyacrylamide polymer
network. (b) Gels with length scales around 1mm display swell-deswell oscillations that are nearly in phase
with oscillations in the oxidation state of the ruthenium catalyst.
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fixed in a non-oscillating gel matrix (Fig. 2a).
These patches have the potential to form
networks of coupled oscillators in which the
patches can achieve a range of synchronous
behavior. The control afforded by precise
patterning suggests a promising avenue for
designing and arranging reactive patches much
like modular building blocks to form composite
actuators with the ability to perform complex and
cooperative functions. In addition, we envision
the potential for modifying the supporting matrix
to enjoy a third level of responsiveness such as
thermal or photo sensitivity which would enable
multi-positioning of the autonomously oscillating
devices (Fig. 2b) or an external switch for locally
turning synchrony on or off.
Key challenges to producing functional
devices are developing effective BZ gel materials
with
robust
patterning
processes
and
characterizing the coupled oscillatory response
Figure 2 (a) Example of a patterned array. Reactive BZ
patches are fused with a non-reactive gel. The spacing
across various geometric and chemical regimes.
between patches effects overall synchrony between the
We recently demonstrated a facile route to
individual oscillators. If they are spaced closely then the
patches have potential to oscillate in concert. (b) A basic patterned composite gels composed of ruthenium
conceptual actuator design. The top responsive layer
functionalized and non-functional gelatin.4 A
could be used to position the arch in the up or down
chief advantage of gelatin for patterning is its
position and the patches will oscillate near that stable
ability to be melted, printed, and then solidified in
configuration. Alternately, the top layer could be used
to balance the arch near its point of instability so that
place by cooling. Unfortunately these materials
patches could drive periodic up and down motions.
also suffer from several disadvantages. (1) Swelldeswell amplitudes are limited by the high cross
link density (physical and chemical) in gelatin. (2) The peptide bonds in gelatin appear to be
unstable in the harsh BZ environment with material properties deteriorating after several hours.
(3) Polymer network composition cannot be easily modulated to vary material properties.
A primary objective of the proposed research is to determine viable alternatives to gelatin
that share its thermogelling properties but that exhibit greater chemical stability, allow for more
control of material properties (e.g. tailoring cross link density or network architecture), and
potentially allow for coupling with other kinds of responsive gels (e.g. thermally responsive).
Once a new patternable gel material is identified, and its thermogelling and self-oscillating
properties characterized, a host of new experiments and design efforts can proceed. The
proposed effort will be used to produce preliminary data that will be used to apply for external
funding.
1.3 Methods
Starting January 2014, one student will search the literature for polymers that exhibit
thermogelling properties and assess their suitability for the proposed project. At the same time a
second student will begin to refine the Smith lab process for synthesizing a vinyl functionalized
ruthenium catalyst. Once a subset of polymer candidates is identified, both students will be
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required to produce a set of mock figures for a future publication. These figures will then serve
to guide our approach to synthesizing, characterizing, and comparing the alternate selfoscillating gel materials. In this way the students will be trained in how to develop and enact a
focused research effort. During the summer the second student will continue synthesis and
characterization work on the ruthenium catalyst and will also be involved in the polymerizations
involving the catalyst. The first student will work to synthesize the alternate polymers and test
their suitability for patterning. Factors indicating material suitability will include the temperature
at which gelation occurs, continued ability to gel after incorporation of ruthenium complexes, the
ability to chemically fix the material after gelation, and the ability of the material to form
composite sheets layer by layer (that is, will gelled and melted polymer solution fuse upon
printing). If a successful candidate is identified then the students will attempt to incorporate a
ruthenium complex into the polymer and catalyze the BZ reaction. The students will continue
working into Fall 2014 and present their findings at a regional undergraduate conference.
The initial search for suitable materials will focus on polymers with constituent monomers
that can be readily purchased and easily produced through free radical polymerization. This will
hopefully enable straight forward synthesis of the polymers and accelerate the material
characterization phase. Particular attention will be paid to polymers exhibiting lower critical
solution temperatures, such as, poly(2-dimethylamino)ethyl methacrylate) and poly(Nisopropylacrylamide).5 However, other polymers such as those that have upper critical solution
temperatures will also be considered.6 Various routes to thermal gelation will be explored
including using the thermally gelling polymer as the sole constituent or grafting thermally
gelling polymer chains onto a secondary polymer backbone. Preliminary characterization of
gelation will be performed using simple tube inversion tests. If a suitable polymer is identified a
vinyl functionalized ruthenium complex will be used to incorporate the catalyst during radical
polymerization. The gel will be permanently fixed by introducing a small fraction of primary
amine pendants via a monomer such as aminopropyl methacrylamide and then crosslinking with
glutaraldehyde. Swell-deswell oscillations will be monitored under a stereomicroscope, time
lapse images will be recorded, and the images analyzed using the image analysis toolbox in
MatLab. Oscillation amplitude and period will be recorded and compared to current results in
the self-oscillating gel literature.
1.4 Expected Outcomes
This project will provide essential training for engineers with a chemical emphasis as it will
require them to consider factors in polymer synthesis, concepts in rheology, and challenges
inherent in materials processing. These students will also be well trained in research
methodology, experiment design, laboratory skills, data collection and analysis, and the effective
reporting of results. This training will enable them to effectively perform research as soon as
they enter graduate school and will facilitate them quickly moving into research leadership
positions within their groups. In addition, it is expected that we will identify and characterize a
suitable thermogelling polymer and observe swell-deswell oscillations when the ruthenium
complex is incorporated into the polymer network and the gel immersed in BZ solution. This
initial effort will provide the necessary preliminary data and proof of concept to allow us to
pursue multi-responsive autonomous actuator design, which will be the subject of an external
grant proposal.
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1.5 Potential Difficulties
It may be that none of the polymer systems we identify prove suitable for the intended
application. For example, the polymers may not form robust enough gels or they may not gel
after we incorporate the ruthenium or primary amine co-monomers. However, there are
numerous thermally gelling systems reported in the literature that appear to have robust material
properties. We believe it is likely we will be able to identify one or more satisfactory materials.
In the event that we cannot produce a suitable synthetic polymer system we will also consider
other biopolymer based gels such as chitosan. These biopolymers could constitute the primary
polymer system or they could potentially be used as a temporary support matrix.
1.6 Connection to other HHMI Programs
Students will be trained in research methodology including literature searches, experiment
design, data collection and analysis, and the reporting of results. The current returning student to
the Smith lab is a junior engineering major. Every effort will be made to recruit a sophomore
engineer with a chemical emphasis who has not yet had a research experience. This will enable a
new student to engage in STEM research for the first time. In addition it will provide the junior
student with an opportunity to mentor an inexperienced researcher in the standard practices of
the Smith lab. In addition, these students will be required to produce an attractive self-guided 510 minute PowerPoint presentation describing self-oscillating gels and how they work. The
presentation will feature animation and video that is at a suitable level for middle and high
school students. This presentation will be used for high school visit days at Hope and made
publicly accessible online. The sophomore student will be encouraged to pursue another summer
of research and participate in the training of a novice researcher the following year. As a result
both students will progress toward becoming future research leaders by honing their ability to
mentor and train other researchers and by refining their ability to increase the accessibility of
scientific knowledge through communication with the non-specialist.
1.7 Plans for External Funding To Continue Work
The Smith group plans to apply for an NSF RUI to support this work under the Materials
Engineering and Processing program in January 2015.
1.8 Timeline
January 14
April 7-May 12
May 12-July 18
July18-January15
Literature search begins. Each pertinent paper will be summarized on one
PowerPoint slide.
Purchase chemicals and supplies and begin preliminary polymer synthesis
Begin summer research. Students synthesize polymers. Test gelation.
Synthesize self-oscillating gels and characterize swell-deswell amplitudes.
Students will make an internal oral presentation of their results and
prepare a poster for a regional conference.
Students will present at a regional undergraduate conference. NSF RUI
proposal will be prepared.
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2 Bibliography/References
1. Yoshida, R. “Self-Oscillating Gels Driven by the Belousov-Zhabotinsky Reaction as
Novel Smart Materials,” Advanced Materials, 2010, 22(31), 3463-3483.
2. Murase, Y., Maeda, S., Hashimoto, S., Yoshida, R. “Design of a Mass Transport Surface
Utilizing Peristaltic Motion of a Self-Oscillating Gel,” Langmuir, 2009, 25, 483-489.
3. Kuksenok, O., Yashin, V. V., Balazs, A. C. “Mechanically induced chemical oscillations
and motion in responsive gels,” Soft Matter, 2007, 3, 1138-1144.
4. Smith, M. L., Slone, C., Heitfeld, K., Vaia, R. A. “Designed Autonomic Motion in
Heterogeneous Belousov-Zhabotinsky (BZ)-Gelatin Composites by Synchronicity,”
Advanced Functional Materials, 2013, 23(22), 2835-2842.
5. Liu, R., Fraylich, M., Saunders, B. R., “Thermoresponsive copolymers: from
fundamental studies to applications,” Colloid and Polymer Science, 2009, 287, 627-643.
6. Seuring, J., Agarwal, S. “Polymers with Upper Critical Solution Temperature in Aqueous
Solution,” Macromolecular Rapid Communications, 2012, 33, 1898-1920.
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4 Biographical Sketches
Matthew L. Smith
A. Professional Preparation
Cedarville University
Cedarville University
Cornell University
Mechanical Engineering
Mathematics
Theoretical & Applied Mechanics
B.S., 2003
B.A., 2003
Ph.D., 2009
B. Appointments
Assistant Professor or Engineering, Hope College, 2012-Present.
NRC Research Associate, Air Force Research Lab, Wright-Patt. AFB, OH, 2010-2012
C. Selected Publications (* denotes non-Hope undergraduate author)
1. M. R. Shankar, M. L. Smith, V. P. Tondiglia, K. M. Lee, M. E. McConney, D. H. Wang,
L. S. Tang, T. J. White, “Contactless, Photoinitiated Snap-through in Azobenzenefunctionalized Polymers,” Accepted, Proceedings of the National Academy of Sciences.
2. J. J. Wie, K. M. Lee, M. L. Smith, R. A. Vaia, T. J. White, “Torsional Mechanical
Responses in Azobenzene Functionalized Liquid Crystalline Polymer Networks,” Soft
Matter, 2013, 9, 9303-9310.
3. M. L. Smith, C. Slone*, K. Heitfeld, R. A. Vaia, “Designed Autonomic Motion in
Heterogeneous Belousov-Zhabotinsky (BZ)-Gelatin Composites by Synchronicity,”
Advanced Functional Materials, 2013, 23(22), 2835-2842.
4. H. Koerner, R. Strong*, M. L. Smith, H. Wang, L.-S. Tan, K. M. Lee, T. White, R. A.
Vaia, “Polymer Design for High Temperature Shape Memory: Low Crosslink Density
Polyimides,” Polymer, 2013, 54(1), 391-402.
5. M. L. Smith, K. Heitfeld, C. Slone*, R. A. Vaia, “Autonomic Hydrogels through
Postfunctionalization of Gelatin,” Chemistry of Materials, 2012, 24(15), 3074-3080.
6. M. L. Smith, G. Yanega, A. Ruina, “Elastic Instability Model of Rapid Beak Closure in
Hummingbirds,” Journal of Theoretical Biology, 2011, 282, 41-51.
7. K. M. Lee, M. L. Smith, H. Koerner, N. Tabiryan, R. A. Vaia, T. J. Bunning, T. J. White,
“Photodriven, Flexural-Torsional Oscillation of Glassy Azobenzene Liquid Crystal
Polymer Networks,” Advanced Functional Materials, 2011, 21(15), 2913-2918.
D. Selected Presentations
1. M. L. Smith, C. Slone, K. Heitfeld, R. A. Vaia, “Hybrid BioGels: Amplification and
Synchronicity through Composite Design.” US-Japan Workshop on Advances in
Organic/Inorganic Hybrid Materials, Ann Arbor, Michigan, May 2012 (poster).
2. M. L. Smith, C. Slone, K. Heitfeld, R. Kramb, R. A. Vaia, “Coupling Chemomechanical
Oscillators: Patterning BZ Hydrogels.” Materials Research Society Fall Meeting, Boston,
Massachusetts, December 2011 (oral presentation).
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3. M. L. Smith, K. M. Lee, H. Koerner, R. A. Vaia, T. J. Bunnung, T. J. White, “Tuning the
Photoinduced Motion of Azobenzene Liquid Crystal Polymer Cantilevers.” ASME
Applied Mechanics and Materials Conference, Chicago, Illinois, May 2011 (oral
presentation).
4. M. L. Smith, K. Heitfeld,R. Kramb, M. Tchoul, D. Gallagher, R. Vaia,
“Chemomechanical Characterization of Autonomic Polyacrylamide Gels,” American
Physical Society March Meeting, Dallas, Texas, March 2011 (oral presentation).
5. M. L. Smith, S. Goyal, T. J. Healey, “Modeling the Effects of Chirality on DNA
Supercoiling.” 52nd Annual Biophysical Society Meeting, Long Beach, California,
February 2008 (poster presentation).
E. Collaborators and other Affiliations
Professor M. Ravi Shankar (University of Pittsburgh)
Dr. Timothy White (Air Force Research Lab, Wright-Patt. AFB, OH)
F. Graduate and Postgraduate Advisors
Graduate Thesis Advisor, Timothy Healey (Cornell University)
Postdoctoral Advisor, Richard Vaia (Air Force Research Lab, Wright-Patt. AFB, OH)
G. Undergraduate Students Supervised: 2 at Hope, 4 additional prior to employment at
Hope
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5 Current and Pending Support
Current:
Hope College Dean’s start-up funding.
Pending:
MSGC Faculty Research Seed grant. $5000 with $5000 matching from the Dean of Natural and
Applied Sciences at Hope College.
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