A team has developed a theoretical model to design soft materials that demonstrate autonomous oscillating properties that mimic biological functions. The work could advance the design of responsive materials used to deliver therapeutics as well as for robot-like soft materials that operate autonomously.
The design and synthesis of materials with biological functions require a delicate balance between structural form and physiological function. During embryonic development, for instance, flat sheets of embryonic cells morph through a series of folds into intricate three-dimensional structures such as branches, tubes, and furrows. These, in turn, become dynamic, three-dimensional building blocks for organs performing vital functions like heartbeat, nutrient absorption, or information processing by the nervous system.
Such shape-forming processes, however, are controlled by chemical and mechanical signaling events, which are not fully understood on the microscopic level. To bridge this gap, researchers designed computational and experimental systems that mimic these biological interactions. Hydrogels, a class of hydrophilic polymer materials, have emerged as candidates capable of reproducing shape changes upon chemical and mechanical stimulation observed in nature.
The researchers developed a theoretical model for a hydrogel-based shell that underwent autonomous morphological changes when induced by chemical reactions. The chemicals modified the local gel microenvironment, allowing swelling and de-swelling of materials via chemo-mechanical stresses in an autonomous manner. This generated dynamic morphological change including periodic oscillations reminiscent of heartbeats found in living systems.
The team designed a chemical-responsive polymeric shell meant to mimic living matter. They applied the water-based mechanical properties of the hydrogel shell to a chemical species — a chemical substance that produces specific patterned behavior (in this case, wavelike oscillations) — located within the shell. After conducting a series of reduction-oxidation reactions — a chemical reaction that transfers electrons between two chemical species — the shell generated microcompartments capable of expanding, contracting, or inducing buckling-unbuckling behavior when mechanical instability was introduced.
If the level of chemicals goes past a certain threshold, water gets absorbed, swelling the gel. When the gel swells, the chemical species gets diluted, triggering chemical processes that expel the gel’s water, therefore contracting the gel.
The model could be used as the basis to develop other soft materials demonstrating diverse, dynamic morphological changes. This could lead to new drug delivery strategies with materials that enhance the rate of diffusion of compartmentalized chemicals or release cargos at specific rates. The work could also inform the future development of soft materials with robot-like functionality that operate autonomously. These soft robotics have emerged as candidates to support chemical production, tools for environmental technologies, or smart biomaterials for medicine. Yet the materials rely on external stimuli, such as light, to function.
The new soft material operates autonomously, so there is no external control involved.
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