We study theoretically the surface response of a semi-infinite viscoelastic polymer network using the two-fluid model. We focus on the overdamped limit and on the effect of the network's intrinsic length scales. We calculate the decay rate of slow surface fluctuations, and the surface displacement in response to a localized force. Deviations from the large-scale continuum response are found at length scales much larger than the network's mesh size. We discuss implications for surface scattering and microrheology. We provide closed-form expressions that can be used for surface microrheology -the extraction of viscoelastic moduli and intrinsic length scales from the motions of tracer particles lying on the surface without doping the bulk material. arXiv:2003.09048v1 [cond-mat.soft]
We study theoretically the velocity cross-correlations of a viscous fluid confined in a slit between two viscoelastic media. We analyze the effect of these correlations on the motions of particles suspended in the fluid. The compliance of the confining boundaries gives rise to a long-ranged pair correlation, decaying only as 1/r with the interparticle distance r. We show how this long-ranged effect may be used to extract the viscoelastic properties of the confining media without embedding tracer particles in them. We discuss the remarkable robustness of such a potential technique with respect to details of the confinement, and its expected statistical advantages over standard two-point microrheology.
Electrophysiological investigations of intact neural circuits are challenged by the gentle and complex nature of neural tissues. Bi-directional electrophysiological interfacing with the retina, in its intact form, is particularly demanding and currently there is no feasible approach to achieve such investigations. Here we present the use of novel soft multi electrode arrays for bi-directional electrophysiological study of the intact retina. To this aim, soft electrode arrays, suitable for stable electrical interfacing with the retina, were developed and tested. The soft probes were designed to accommodate the curvature of the retina in the eye and offer a unique opportunity to study the retina in its intact form. For the first time, we show both electrical recording and stimulation capabilities from the intact retina. In particular, we demonstrate the ability to map retina responses to electrical stimulation in order to reveal conspicuously, stable, direct and indirect responses. These results suggest that intact retinas retain better stability and robustness than ex-vivo retinas.
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