Responsive Soft Materials Inspired by Morphogenesis

Innovation: Academia

Northwestern University

2021

Image: Timothy Dykes / Unsplash / CC BY SA - Creative Commons Attribution + ShareAlike

Chemically Generate Flow of Electrons (Redox)

Electron flows, or electron transport, is a critical step in numerous biochemical pathways. For example, the flow of electrons along the electron transport chain between membrane-bound proteins of mitochondria during cellular respiration or the chloroplast during photosynthesis triggers a flow of protons across the same membrane. This flow provides the energy for cellular processes similar to the flow of water across a hydroelectric dam.

Search this Function

Modify Material Characteristics

The materials found in living systems are variable, yet often made from the same basic building blocks. For example, all insect exoskeletons consist of a material called chitin. Because material resources are limited, each material within or used by a given living system must frequently serve multiple purposes. Therefore, living systems have strategies to modify materials’ softness, flexibility, and other characteristics. To ensure survival, the benefits of these modifications must outweigh the living system’s energy and material expenditure to generate them. For example, spiders store the liquid components of spider silk in a gland, converting them into silk thread when needed. Some threads have different characteristics, such as elasticity and UV reflectance, than others.

Search this Function

Modify Size/Shape/Mass/Volume

Many living systems alter their physical properties, such as size, shape, mass, or volume. These modifications occur in response to the living system’s needs and/or changing environmental conditions. For example, they may do this to move more efficiently, escape predators, recover from damage, or for many other reasons. These modifications require appropriate response rates and levels. Modifying any of these properties requires materials to enable such changes, cues to make the changes, and mechanisms to control them. An example is the porcupine fish, which protects itself from predators by taking sips of water or air to inflate its body and to erect spines embedded in its skin.

Search this Function

Physically Assemble Structure

Living systems use physical materials to create structures to serve as protection, insulation, and other purposes. These structures can be internal (within or attached to the system itself), such as cell membranes, shells, and fur. They can also be external (detached), such as nests, burrows, cocoons, or webs. Because physical materials are limited and the energy required to gather and create new structures is costly, living systems must use both conservatively. Therefore, they optimize the structures’ size, weight, and density. For example, weaver birds use two types of vegetation to create their nests: strong, a few stiff fibers and numerous thin fibers. Combined, they make a strong, yet flexible, nest. An example of an internal structure is a bird’s bone. The bone is comprised of a mineral matrix assembled to create strong cross-supports and a tubular outer surface filled with air to minimize weight.

Search this Function

Soft materials from Northwestern University autonomously morph when induced by a chemical reaction.

Benefits

Autonomous
Versatile
Dynamic

Applications

Medical implants
Medical treatment

UN Sustainable Development Goals Addressed

Goal 3: Good Health & Wellbeing
Goal 9: Industry Innovation & Infrastructure

The Challenge

Numerous chemical and mechanical signaling events help to dictate a variety of shape-forming biological processes, from the growth of a single cell to the functioning of an entire organ. However, many of these process are unknown or not wel understood. In order to better understand how theses processes work at a microscopic level, scientists must design experimental systems that mimic these biological interactions. Hydrogels, a class of hydrophilic materials, are excellent at reproducing shape changes with chemical and mechanical stimulation. These can be used to mimic the biological interactions found in nature, to better understand natural shape-forming processes.

Innovation Details

The researchers designed a chemical-responsive polymeric shell that mimics living matter. It undergoes autonomous morphological changes when induced by chemical reactions. If the level of chemicals goes past a certain threshold, water within the gel gets absorbed, swelling the gel. When this occurs, the chemical species gets diluted, triggering chemical processes that expel the water, contracting the gel. This allows the researchers to create dynamic morphological changes, such as periodic oscillations reminiscent of heartbeats.

Autonomous responsive polymer shells undergo morphological changes when triggered by an initial deformation. Photo: Monica Olvera de la Cruz/Northwestern University.

Biological Model

Morphogenesis is the differentiation of cells, tissues, and organs that occurs when an organism is first growing, giving rise to various organ systems. Numerous chemical and mechanical signaling events tightly control this process to ensure that an organism grows correctly.

References

Journal article

Chemically controlled pattern formation in self-oscillating elastic shells

PNAS

embedly preview

AskNature