Researchers have devised design principles for building silicon-based interfaces for light-induced biological processes that do not use genetic modification to facilitate light-based control. The design principles quantify and differentiate the capacitive, Faradaic,, and thermal outputs from about 30 different silicon materials in saline. A flexible silicon mesh can adapt to the soft surface of the brain for stimulating neural activity. Courtesy of Jiang et al./University of Chicago. Using mouse models, the research team showed that the interfaces could be used for the light-controlled nongenetic modulation of intracellular calcium dynamics, of cytoskeletal structures and transport, of cellular excitability, of neurotransmitter release from brain slices, and of brain activity in vivo. The principles, developed by a team at the University of Chicago, provide a guide to working with silicon to develop interfaces to control biology using light on three levels — from individual organelles within cells, to tissues, to whole limbs. They map the best methods to craft silicon devices depending on the intended task, and the scale and the mechanical properties of the object. For example, to interface with individual brain cells, silicon can be crafted to respond to light by emitting a tiny ionic current, which encourages neurons to fire. In order to stimulate limbs, a stronger interface would be needed, such as one that uses a gold-coated silicon material. “We want this to serve as a map, where you can decide which problem you would like to study and immediately find the right material and method to address it,” said professor Bozhi Tian. The team tested its system in cells and in mice. It found that in mice, limb movements could be stimulated by shining light on brain implants. The team believes that this is the first time that light has been used to control mice behavior without genetic modification. The method does not require a wired-in power supply, because the silicon can be fashioned to generate its own power. “We don’t have answers to a number of intrinsic questions about biology, such as whether individual mitochondria communicate remotely through bioelectric signals," said researcher Yuanwen Jiang. "This set of tools could address such questions as well as point the way to potential solutions for nervous system disorders.” The research was published in Nature Biomaterials (doi:10.1038/s41551-018-0230-1). Photostimulation from implanted nanowires (in blue) helps these neurons fire. Photostimulation of internalized nanowires can elicit calcium wave propagations to adjacent glial cells and neurons. This technique could be adapted to glial-cell-mediated deep brain photostimulations. Courtesy of Jiang et al./University of Chicago.