Light-guided hydrogels direct cell growth

Researchers in the US have developed a gel-like material whose structural and chemical properties can change in response to laser light, providing a highly adaptable environment for work in areas ranging from cell culture to tissue engineering.

Hydrogels (polymer networks swollen by water) are already used in a range of biomedical applications, from cell cultures to drug release. Currently, the user determines the properties of the hydrogel material during the gelation process, and these remain fixed during the hydrogel’s use. Kristi Anseth’s group at the University of Colorado, however, has now found a way to use light to manipulate the structural and chemical properties of formed hydrogels, with living cells still inside.

Anseth and her team used a nitrobenzyl ether molecule as the light-degradable unit for their experiments. This particular molecule was chosen based on its proven sensitivity to the light the researchers planned to use, and its history of use with living cells. 

Using this light-sensitive building block as a structural unit of their hydrogels, Anseth and her coworkers demonstrated that they could carve new channels and connections into the hydrogel network, allowing cells that were previously locked in to migrate to different, precisely defined locations. 

In a second type of experiment, the authors showed that with the same approach they can also switch the chemical environment that the cells experience inside the hydrogel.   They trapped stem cells inside the gel, together with an important signal peptide that guides the differentiation of the cells during embryonal development. Using light-sensitive linkers, they attached the signal peptide inside the cavities of the hydrogel. 

After 10 days, the researchers selectively cleaved this link in certain parts of the sample and allowed the peptide to diffuse away. Monitoring the characteristic changes that stem cells undergo during differentiation and development, the researchers could show that they successfully switched their cells from one development path to another by applying light to the hydrogel. Importantly, the cells in both experiments did not suffer any adverse effect as a result of the changes to the hydrogel. 

’These light degradable hydrogels offer the experimentalist the ability to tune the physical and chemical microenvironment of cells at any point in space and time,’ says first author April Kloxin. ’We believe that these gels will be useful tool for many researchers to dynamically examine the influence of the microenvironment on cell functions, such as differentiation, migration, and communication, and to direct them for tissue regeneration.’

Paul Fairchild, co-director of the Oxford Stem Cell Institute, James Martin 21st Century School at the University of Oxford, welcomed the new addition to the tool kit. ’The ability to control with precision the three-dimensional interactions between stem cells, while fine tuning their differentiation and function, will doubtless elevate tissue engineering and regenerative medicine to a whole new level of sophistication,’ he told Chemistry World.

Michael Gross