Certain materials exist as solids, but become thinner and flow like liquids when they are put under stress. This property, called thixotropy, is found in natural substances including honey, human bodily tissues and some clays—making it an important and dangerous factor in earthquakes and landslides.

Now thixotropy could have a new application in cell biology, thanks to Jackie Ying, Andrew Wan, Shona Pek and co-workers at the Institute of Bioengineering and Nanotechnology in Singapore.1 The researchers have developed artificial thixotropic gels that could provide an excellent new medium for cell culturing in laboratories.

Fig. 1: A new ‘thixotropic’ gel for creating cell cultures. When the gel is stirred, it turns to liquid so that cells can be added. It then resolidifies to trap the cells in a three-dimensional culture.Copyright © Institute of Bioengineering and Nanotechnology, Singapore 2008

Their new gel turns to liquid when stirred, so that cells and other biological components can be added. It then resolidifies to trap the cells, but allows the flow of nutrients and gases, enabling the development of cell culture. This is the first example of a cell culture that can be manipulated without heating the gel or adding enzymes and chemicals, which can affect cell quality.

“When the thixotropic properties of the gel were discovered in our laboratory, we realized that it could become a new medium for 3D cell culture,” says Wan. “Our gel offers better stability and convenience of use than existing systems.” The researchers created the gel by reacting polyethylene glycol (PEG) with silica. This produced a gel composed of PEG/silica nanoparticles, which tend to stick together but are easily broken apart by stirring.

Thixotropic gels have been used before for delivering gel-cell composites into living creatures, but this is the first example of their use for in vitro studies outside the body. The researchers are hopeful about potential applications of their gel.

For example, they found that cells cultivated in the gel secreted extracellular matrix (ECM) proteins such as collagen, which made the gels stiffer. By monitoring the stiffness of the gel, scientists could learn how the ECM changes in response to disease conditions such as fibrosis.

“A fibrosis model would allow us to study various factors that promote or attenuate related diseases,” says Wan. “The gel could also be useful for studying the effects of chemical gradients, such as those that guide the growth of nerve cells.”