Gaëlle Piret

Neurite outgrowth and synaptophysin expression of postnatal CNS neurons on GaP nanowire arrays in long-term retinal cell culture.

We have established long-term cultures of postnatal retinal cells on arrays of gallium phosphide nanowires of different geometries. Rod and cone photoreceptors, ganglion cells and bipolar cells survived on the substrates for at least 18 days in vitro. Glial cells were also observed, but these did not overgrow the neuronal population. On nanowires, neurons extended numerous long and branched neurites that expressed the synaptic vesicle marker synaptophysin. The longest nanowires (4 μm long) allowed a greater attachment and neurite elongation and our analysis suggests that the length of the nanowire per se and/or the adsorption of biomolecules on the nanowires may have been important factors regulating the observed cell behavior. The study thus shows that CNS neurons are amenable to gallium phosphide nanowires, probably as they create conditions that more closely resemble those encountered in the in vivo environment. These findings suggest that gallium phosphide nanowires may be considered as a material of interest when improving existing or designing the next generation of implantable devices. The features of gallium phosphide nanowires can be precisely controlled, making them suitable for this purpose.

Support of Neuronal Growth Over Glial Growth and Guidance of Optic Nerve Axons by Vertical Nanowire Arrays.

Neural cultures are very useful in neuroscience, providing simpler and better controlled systems than the in vivo situation. Neural tissue contains two main cell types, neurons and glia, and interactions between these are essential for appropriate neuronal development. In neural cultures, glial cells tend to overgrow neurons, limiting the access to neuronal interrogation. There is therefore a pressing need for improved systems that enable a good separation when coculturing neurons and glial cells simultaneously, allowing one to address the neurons unequivocally. Here, we used substrates consisting of dense arrays of vertical nanowires intercalated by flat regions to separate retinal neurons and glial cells in distinct, but neighboring, compartments. We also generated a nanowire patterning capable of guiding optic nerve axons. The results will facilitate the design of surfaces aimed at studying and controlling neuronal networks.

Fluid and highly curved model membranes on vertical nanowire arrays.

Sensing and manipulating living cells using vertical nanowire devices requires a complete understanding of cell behavior on these substrates. Changes in cell function and phenotype are often triggered by events taking place at the plasma membrane, the properties of which are influenced by local curvature. The nanowire topography can therefore be expected to greatly affect the cell membrane, emphasizing the importance of studying membranes on vertical nanowire arrays. Here, we used supported phospholipid bilayers as a model for biomembranes. We demonstrate the formation of fluid supported bilayers on vertical nanowire forests using self-assembly from vesicles in solution. The bilayers were found to follow the contours of the nanowires to form continuous and locally highly curved model membranes. Distinct from standard flat supported lipid bilayers, the high aspect ratio of the nanowires results in a large bilayer surface available for the immobilization and study of biomolecules. We used these bilayers to bind a membrane-anchored protein as well as tethered vesicles on the nanowire substrate. The nanowire-bilayer platform shown here can be expanded from fundamental studies of lipid membranes on controlled curvature substrates to the development of innovative membrane-based nanosensors.

Surface nanostructures for fluorescence probing of supported lipid bilayers on reflective substrates

The fluorescence interference contrast (FLIC) effect prevents the use of fluorescence techniques to probe the continuity and fluidity of supported lipid bilayers on reflective materials due to a lack of detectable fluorescence. Here we show that adding nanostructures onto reflective surfaces to locally confer a certain distance between the deposited fluorophores and the reflecting surface enables fluorescence detection on the nanostuctures. The nanostructures consist of either deposited nanoparticles or epitaxial nanowires directly grown on the substrate and are designed such that they can support a lipid bilayer. This simple method increases the fluorescence signal sufficiently to enable bilayer fluorescence detection and to observe the recovery of fluorescence after photobleaching in order to assess lipid bilayer formation on any reflective surface.