New hydrogel-based 4D material changes shape in response to psychological stimuli and could be used to bioengineer organs.
As published in the journal Advanced Functional Materials, the hydrogel-based material, developed by a research team at the University of Illinois, Chicago, USA, can curl into tubes in response to water, making the materials good candidates for bioengineering blood vessels or other tubular structures.
For tissue engineering, traditional techniques have involved culturing biodegradable polymer scaffolds with cells in biochambers filled with liquid nutrients that keep the cells alive. Over time the cells multiply and produce new tissue that takes on the shape of the scaffold as the scaffold degrades. For example, a scaffold in the shape of an ear seeded with cells capable of producing cartilage and skin tissue may eventually become a transplantable ear.
A geometrically static scaffold cannot enable the formation of tissues that dynamically change shape over time or facilitate interactions with neighbouring tissues that change shape. A high density of cells is also typically not used and/or supported by the scaffolds.
Eben Alsberg, a professor at UIC and leader of the project, said: “Using a high density of cells can be advantageous in tissue engineering as this enables increased cell-cell interactions that can promote tissue development.”
Taking advantage of advanced materials
4D materials are similar to 3D materials, however, they change shape when they are exposed to specific environmental cues, such as light or water. These materials have drawn the attention of biomedical engineers as potential new structural substrates for tissue engineering, but most currently available 4D materials are not biodegradable or compatible with cells.
To take advantage of the promise of 4D materials for bioengineering applications, Alsberg and colleagues developed the new hydrogel-based material that change shape over time in response to the addition of water. The cell-compatible and biodegradable material is an excellent candidate for advanced tissue engineering.
In the paper, the researchers describe how exposure to water causes the hydrogel scaffolds to swell as the water is absorbed. The amount of swelling can be tuned by changing aspects of the hydrogel material such as its degradation rate or the concentration of cross-linked polymers – strands of protein or polysaccharide in this case – that comprise the hydrogels.
The researchers found that by layering hydrogels with different properties, the difference in water absorption between the layers will cause the hydrogel stack to bend into a ‘C’ shaped conformation. If the stack bends enough, a tubular shape is formed, which resembles structures like blood vessels and other tubular organs.