UV filters can initiate redox reactions of oxygen and water when exposed to sunlight, generating reactive oxygen species (ROS) that deteriorate the products containing them and cause biological damages. This photochemical reactivity originates from the high chemical potential of UV filters, which also determines the optical properties desirable for sunscreen applications. We hypothesize that this dilemma can be alleviated if the photochemical pathway of UV filters is altered to coupling with redox active molecules. Here, we employ tannic acid (TA) as a key molecule for controlling the photochemical properties of titanium dioxide nanoparticles (TiO NPs). TA provides an unusual way for layer-by-layer assembly of TiO NPs by the formation of a ligand-to-metal charge transfer complex that alters the nature of UV absorption of TiO NPs. The galloyl moieties of TA efficiently scavenge ROS due to the stabilization of ROS by intramolecular hydrogen bonding while facilitating UV screening through direct charge injection from TA to the conduction band of TiO. The TiO-TA multilayers assembled in open porous polymer microspheres substantially increased sun protection while dramatically reducing ROS under UV exposure. The assembled structure exhibits excellent in vivo anti-UV skin protection against epidermal hyperplasia, inflammation, and keratinocyte apoptosis without long-term toxicity.
Many technical challenges
exist in the co-culture of multiple types
of cells, including medium optimization, cell-to-cell connection,
and selective data acquisition of cellular responses. Particularly,
mixed cellular responses limit the precise interpretation of intercellular
signal transduction. Here, we report the formation of an agarose gel
skin on neurons closely assembled with gustatory cells to selectively
stimulate gustatory cells by retarding the diffusion of tastants to
neurons. The signal transmission, triggered by denatonium benzoate,
from gustatory cells to neurons was monitored using intracellular
calcium ion concentrations. The agarose gel skin efficiently suppressed
the direct transfer of tastants to neurons, decreasing the number
of responsive neurons from 56 to 13% and the number of calcium ion
signals per neuron from multiple to single. The assembly of neurons
with gustatory cells induced the high level of neuronal responses
through taste signal transduction from gustatory cells to neurons.
However, the calcium ion signal peaks of free neurons coated with
agarose gel were much shorter and weaker than those of neurons closely
assembled with gustatory cells. This work demonstrated that agarose
gel skin is a simple, fast, and effective means to increase the signal
selectivity of cellular responses in the co-culture of multiple types
of cells.
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