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Introduction Femoropopliteal artery (FPA) mechanics play a paramount role in pathophysiology and the artery’s response to therapeutic interventions, but data on FPA mechanical properties are scarce. Our goal was to characterize human FPAs over a wide population to derive a constitutive description of FPA ageing to be used for computational modeling. Methods Fresh human FPA specimens (n=579) were obtained from n=351 predominantly male (80%) donors 54±15 years old (range 13–82 years). Morphometric characteristics including radius, wall thickness, opening angle, and longitudinal pre-stretch were recorded. Arteries were subjected to multi-ratio planar biaxial extension to determine constitutive parameters for an invariant-based model accounting for the passive contributions of ground substance, elastin, collagen and smooth muscle. Nonparametric bootstrapping was used to determine unique sets of material parameters that were used to derive age-group-specific characteristics. Physiologic stress-stretch state was calculated to capture changes with ageing. Results Morphometric and constitutive parameters were derived for seven age groups. Vessel radius, wall thickness, and circumferential opening angle increased with ageing, while longitudinal pre-stretch decreased (p<0.01). Age-group-specific constitutive parameters portrayed orthotropic FPA stiffening, especially in the longitudinal direction. Structural changes in artery wall elastin were associated with reduction of physiologic longitudinal and circumferential stretches and stresses with age. Conclusions These data and the constitutive description of FPA ageing shed new light on our understanding of peripheral arterial disease pathophysiology and arterial ageing. Application of this knowledge might improve patient selection for specific treatment modalities in personalized, precision medicine algorithms and could assist in device development for treatment of peripheral artery disease.

Although aging is the dominant risk factor for femoropopliteal artery calcification and stiffening, these processes seem to be linked and can begin at a young age. Calcification is associated with the presence of certain risk factors and with elastic fiber degradation, suggesting overlapping molecular pathways that require further investigation.

We compared response patterns and electrical receptive fields (ERF) of retinal ganglion cells (RGCs) during epiretinal and subretinal electrical stimulation of isolated mouse retina. Retinas were stimulated with an array of 3200 independently controllable electrodes. Four response patterns were observed: a burst of activity immediately after stimulation (Type I cells, Vision Research (2008), 48, 1562–1568), delayed bursts beginning >25 ms after stimulation (Type II), a combination of both (Type III), and inhibition of ongoing spike activity. Type I responses were produced more often by epiretinal than subretinal stimulation whereas delayed and inhibitory responses were evoked more frequently by subretinal stimulation. Response latencies were significantly shorter with epiretinal than subretinal stimulation. These data suggest that subretinal stimulation is more effective at activating intraretinal circuits than epiretinal stimulation. There was no significant difference in charge threshold between subretinal and epiretinal configurations. ERFs were defined by the stimulating array surface area that successfully stimulated spikes in an RGC. ERFs were complex in shape, similar to receptive fields mapped with light. ERF areas were significantly smaller with subretinal than epiretinal stimulation. This may reflect the greater distance between stimulating electrodes and RGCs in the subretinal configuration. ERFs for immediate and delayed responses mapped within the same Type III cells differed in shape and size, consistent with different sites and mechanisms for generating these two response types.

Retinal prostheses are used to restore vision to individuals with vision impairments caused by the damaged photoreceptors in their retina. Despite the early successes, designing prostheses that can restore functional vision in general, continues to be a challenging problem due to the large number of design parameters that need to be customized for individual users. Gathering data using real patients in a timely and safe manner is also difficult. To address these problems, a virtual environment for realistically and safely simulating prosthetic vision is described. Besides supporting phosphenized rendering of images at different resolutions to normal users, and eye movement tracking, the environment also supports spatial distortions that are commonly perceived by prostheses users. A procedure to automatically generate such spatial distortions is developed. User corrections if any, are logged and compared with the original distortion values to evaluate distortion perception. Experimental results obtained in using this environment to perform various visual acuity tasks are described.