Mapping 2D- and 3D-distributions of metal/metal oxide nanoparticles within cleared human ex vivo skin tissues.

An increasing number of commercial skincare products are being manufactured with engineered nanomaterials (ENMs), prompting a need to fully understand how ENMs interact with the dermal barrier as a major biodistribution entry route. Although animal studies show that certain nanomaterials can cross the skin barrier, physiological differences between human and animal skin, such as the lack of sweat glands, limit the translational validity of these results. Current optical microscopy methods have limited capabilities to visualize ENMs within human skin tissues due to the high amount of background light scattering caused by the dense, ubiquitous extracellular matrix (ECM) of the skin. Here, we hypothesized that organic solvent-based tissue clearing ("immunolabeling-enabled three-dimensional imaging of solvent-cleared organs", or "iDISCO") would reduce background light scattering from the extracellular matrix of the skin to sufficiently improve imaging contrast for both 2D mapping of unlabeled metal oxide ENMs and 3D mapping of fluorescent nanoparticles. We successfully mapped the 2D distribution of label-free TiO2 and ZnO nanoparticles in cleared skin sections using correlated signals from darkfield, brightfield, and confocal microscopy, as well as micro-spectroscopy. Specifically, hyperspectral microscopy and Raman spectroscopy confirmed the identity of label-free ENMs which we mapped within human skin sections. We also measured the 3D distribution of fluorescently labeled Ag nanoparticles in cleared skin biopsies with wounded epidermal layers using light sheet fluorescence microscopy. Overall, this study explores a novel strategy for quantitatively mapping ENM distributions in cleared ex vivo human skin tissue models using multiple imaging modalities. By improving the imaging contrast, we present label-free 2D ENM tracking and 3D ENM mapping as promising capabilities for nanotoxicology investigations.

Robotic fluidic coupling and interrogation of multiple vascularized organ chips.

Organ chips can recapitulate organ-level (patho)physiology, yet pharmacokinetic and pharmacodynamic analyses require multi-organ systems linked by vascular perfusion. Here, we describe an 'interrogator' that employs liquid-handling robotics, custom software and an integrated mobile microscope for the automated culture, perfusion, medium addition, fluidic linking, sample collection and in situ microscopy imaging of up to ten organ chips inside a standard tissue-culture incubator. The robotic interrogator maintained the viability and organ-specific functions of eight vascularized, two-channel organ chips (intestine, liver, kidney, heart, lung, skin, blood-brain barrier and brain) for 3 weeks in culture when intermittently fluidically coupled via a common blood substitute through their reservoirs of medium and endothelium-lined vascular channels. We used the robotic interrogator and a physiological multicompartmental reduced-order model of the experimental system to quantitatively predict the distribution of an inulin tracer perfused through the multi-organ human-body-on-chips. The automated culture system enables the imaging of cells in the organ chips and the repeated sampling of both the vascular and interstitial compartments without compromising fluidic coupling.

A Switch and Wave of Neuronal Activity in the Cerebral Cortex During the First Second of Conscious Perception.

Conscious perception occurs within less than 1 s. To study events on this time scale we used direct electrical recordings from the human cerebral cortex during a conscious visual perception task. Faces were presented at individually titrated visual threshold for 9 subjects while measuring broadband 40-115 Hz gamma power in a total of 1621 intracranial electrodes widely distributed in both hemispheres. Surface maps and k-means clustering analysis showed initial activation of visual cortex for both perceived and non-perceived stimuli. However, only stimuli reported as perceived then elicited a forward-sweeping wave of activity throughout the cerebral cortex accompanied by large-scale network switching. Specifically, a monophasic wave of broadband gamma activation moves through bilateral association cortex at a rate of approximately 150 mm/s and eventually reenters visual cortex for perceived but not for non-perceived stimuli. Meanwhile, the default mode network and the initial visual cortex and higher association cortex networks are switched off for the duration of conscious stimulus processing. Based on these findings, we propose a new "switch-and-wave" model for the processing of consciously perceived stimuli. These findings are important for understanding normal conscious perception and may also shed light on its vulnerability to disruption by brain disorders.