From Microgel to Particle
Researchers from RWTH and Forschungszentrum Jülich have succeeded, for the first time, in determining structural processes in an adaptive hydrogel. With the help of X-ray scattering experiments and computer simulations, they were able to show the changes in size and structure of the hydrogel in reaction to external stimuli. The results could lead to new applications in technology and medicine.
Researchers from RWTH and Forschungszentrum Jülich have succeeded, for the first time, in determining structural processes in an adaptive hydrogel. With the help of X-ray scattering experiments and computer simulations, they were able to show the changes in size and structure of the hydrogel in reaction to external stimuli. The results could lead to new applications in technology and medicine.
Adaptive polymers are macromolecules whose structure adjusts to external stimuli such as temperature, pH value, and the uptake or release of molecules. Hydrogels are a distinct type of adaptive polymer; such polymers are also referred to as “smart materials,” as they allow for the preparation of responsive materials within natural biological environments.
As the Jülich biophysicist Professor Roland Winkler explains, “Typically an external stimulus induces a volume change in the hydrogel, and thus also a change in other physical properties, such as optical and mechanical characteristics.” For this reason, hydrogels are used, among other fields, in small-scale robotics or – in a biological setting – to identify and release medical substances.
Responsive micro- and nanogels are particularly interesting, as the small length scale enables very fast response times. “Their porous structure permits fast mass transfer and thus a very fast structural adaptation to the environment,” says Winkler.
The change in the microgel structure involves a unique transition from a macromolecular network, characterized by a fuzzy surface, to a colloidal particle with a homogeneous density and a sharp surface.
Structural Development Determined
In collaboration with colleagues from France and Denkar, scientists from RWTH and Forschungszentrum Jülich now succeeded in determining the structural evolution during the microgel-to-particle transition. The RWTH researchers involved in the project are Professor Walter Richtering, Otto Virtanen and Dersy M. Lugo from the Institute of Physical Chemistry and Professor André Bardow, Rico Keidel and Peter Beumers from the Chair of Technical Thermodynamics. The research results have now been published in the academic journal Science Advances. With the help of time-resolved small-angle x-ray scattering and computer simulations, a two-stage process has been detected: In an initial, very fast process, collapsed clusters form at the periphery, leading to an intermediate, hollowish core-shell structure that, in a second phase, slowly transforms to a globule.
This structural evolution is independent of the type of stimulus and thus applies to instantaneous transitions, as in a temperature jump, was well as to slower stimuli. The rapid transitions of size and shape provide unique opportunities for various applications in the fields of catalysis, sensing, and medicine, such as the uptake of medical substances.
“Using our insights, we seek to build a new, more complex microgel, which, for example, has a core-shell structure. Such microgels could be used as a transport capsule, as they protect their content and may react to their content by expanding,” explains Walter Richtering.
Another project is concerned with diseases which release toxins into the intestines: “Our colleagues are developing a microgel which can be swallowed by the patient, and which is capable of binding and removing these toxins. But this is still a long way off from becoming a reality.”
Original Publication
Time-resolved structural evolution during the collapse of responsive hydrogels: The microgel-to-particle transition
Rico Keidel, Ali Ghavami, Dersy M. Lugo, Gudrun Lotze, Otto Virtanen, Peter Beumers, Jan Skov Pedersen, Andre Bardow, Roland G. Winkler, Walter Richtering