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US researchers control biological cell behaviour using GaN conductivity

Study adds 'persistent photoconductivity' to the toolbox for developing new bioelectronic devices

Main image: Changes in photocurrent before and after exposure to UV light. Persistent photoconductivity is demonstrated even hours after the UV light has been turned off.

Researchers at North Carolina State University have developed a new approach for manipulating the behaviour of biological cells on semiconductor materials "“ in this case GaN - using light to alter the conductivity of the material.

"There's a great deal of interest in being able to control cell behaviour in relation to semiconductors "“ that's the underlying idea behind bioelectronics," says Albena Ivanisevic, a professor of materials science and engineering at NC State and corresponding author of a paper on the work. "Our work here effectively adds another tool to the toolbox for the development of new bioelectronic devices."

Wide bandgap semiconductors such as GaN exhibit what are known as persistent photoconductivity properties, whereby materials become more conductive when you shine a light on them. When the light is removed, it takes the material a long time to return to its original conductivity.

When conductivity is elevated, the charge at the surface of the material increases. And that increased surface charge can be used to direct biological cells to adhere to the surface.

"This is only one way to control the adhesion of cells to the surface of a material," Ivanisevic says. "But it can be used in conjunction with others, such as engineering the roughness of the material's surface or chemically modifying the material."

For this study, the researchers demonstrated that all three characteristics can be used together, working with a GaN substrate and PC12 cells "“ a line of model cells used widely in bioelectronics testing.

The researchers tested two groups of GaN substrates that were identical, except that one group was exposed to UV light "“ triggering its persistent photoconductivity properties "“ while the second group was not.

"There was a clear, quantitative difference between the two groups "“ more cells adhered to the materials that had been exposed to light," Ivanisevic says.

"This is a proof-of-concept paper," Ivanisevic says. "We now need to explore how to engineer the topography and thickness of the semiconductor material in order to influence the persistent photoconductivity and roughness of the material. Ultimately, we want to provide better control of cell adhesion and behaviour."

The paper, 'Persistent Photoconductivity, Nanoscale Topography and Chemical Functionalization Can Collectively Influence the Behavior of PC12 Cells on Wide Band Gap Semiconductor Surfaces' is published in the journal Small. Lead author of the paper is Patrick Snyder, a PhD student in Ivanisevic's lab. The paper was co-authored by Ronny Kirste of Adroit Materials, and Ramon Collazo, an assistant professor of materials science and engineering at NC State.

The work was done with support from the US Army Research Office, under grant number W911NF-15-1-0375, and the US National Science Foundation, under grant number DMR-1312582.

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