The emulation of synaptic functions such as potentiation and depression is of strategic importance for the development of artificial neuromorphic architectures. Memristors can qualitatively reproduce the short-term plasticity behaviour of biological synapses by exploiting the gradual relaxation of resistance levels upon the removal of the switching signals. Various types of memristors based on nanofabricated metal-oxide-semiconductor stacks have been proposed for this purpose. Here we present a different fabrication approach based on cluster-assembled nanostructured zirconia and gold films (ns-Au/ZrO _x ) deposited in a bilayer planar configuration. This device shows memristive behaviour with short-term memory and potentiation/depression. The observed relaxation can be described by a stretched-exponential function. Furthermore, the characteristic time of the short-term phenomena dynamically changes under repeated pulses application. Our nanostructured device is characterised by a substantially larger conductive path length with respect to other nanoscale memristive devices; the use of a zirconia nanostructured film makes the device compatible with neuronal cell culture.

Astrocytes’ organisation affects the functioning and the fine morphology of the brain, both in physiological and pathological contexts. Although many aspects of their role have been characterised, their complex functions remain, to a certain extent, unclear with respect to their contribution to brain cell communication. Here, we studied the effects of nanotopography and microconfinement on primary hippocampal rat astrocytes. For this purpose, we fabricated nanostructured zirconia surfaces as homogenous substrates and as micrometric patterns, the latter produced by a combination of an additive nanofabrication and micropatterning technique. These engineered substrates reproduce both nanotopographical features and microscale geometries that astrocytes encounter in their natural environment, such as basement membrane topography, as well as blood vessels and axonal fibre topology. The impact of restrictive adhesion manifests in the modulation of several cellular properties of single cells (morphological and actin cytoskeletal changes) and the network organisation and functioning. Calcium wave signalling was observed only in astrocytes grown in confined geometries, with an activity enhancement in cells forming elongated agglomerates with dimensions typical of blood vessels or axon fibres. Our results suggest that calcium oscillation and wave propagation are closely related to astrocytic morphology and actin cytoskeleton organisation.

Nanostructured films assembled by metallic nanoparticles deposited by Supersonic Cluster Beam Deposition (SCBD) have been investigated for their Resistive Switching (RS) capabilities in view of unconventional and neuromorphic computing. The physical phenomena underlying RS in nanostructured metallic films have been attributed to structural and morphological rearrangements of grain boundaries, at the nano- and meso-scale, triggered by joule heating and electromigration. The direct in operando observation in ambient condition of the structural and morphological reorganization of the nanostructured films deposited at different scales under voltage stimuli causing RS has never been reported. By means of Dark Field optical microscopy we obtained the first real-time evidence of the irreversible morphological reorganization over the entire network and reversible local ones within the nanostructured network of a gold cluster-assembled film under electrical stimulation, responsible for the emerging collective resistive switching behavior. We have identified distinct film reorganization phenomena: an irreversible roughening of the entire film network is observed during the electrical forming process, which triggers the onset of RS. After this initial modification, reversible structural rearrangements occur at both the macro- and micro-scale. These results support the proposed model relying on RS mechanism in cluster-assembled films on the modulation of the complex cluster-assembled film structural connectivity.