3,681 research outputs found
Tunable biohybrid hydrogels from coacervation of hyaluronic acid and PEOâbased block copolymers
Accurately tuning the macroscopic properties of biopolymerâbased hydrogels remains challenging due to the illâdefined molecular architecture of the natural building blocks. Here, we report a biohybrid coacervate hydrogel, combining the biocompatibility and biodegradability of naturally occurring hyaluronic acid (HA) with the tunability of a synthetic polyethylene oxide (PEO) âbased ABAâtriblock copolymer. Coacervation of the cationic ammonium or guanidiniumâfunctionalized copolymer Aâblocks with the anionic HA leads to hydrogel formation. Both mechanical properties and water content of the selfâhealing hydrogels can be controlled independently by altering the copolymer structure. By controlling the strength of the interaction between the polymer network and smallâmolecule cargo, both release rate and maximum release are controlled. Finally, we show that coacervation of HA and the triblock copolymer leads to increased biostability upon exposure to hyaluronidase. We envision that noncovalent crosslinking of HA hydrogels through coacervation is an attractive strategy for the facile synthesis of tunable hydrogels for biomedical applications
Thermal histories of the samples of two KOSI comet nucleus simulation experiments
Temperatures recorded during two KOSI comet nucleus simulation experiments strongly suggest that heat transport by vapor flow into the interior of the sample is very important. Two comet nucleus simulation experiments have been done by the KOSI team in a big space simulator. The thermal evolution of the sample during insolation and the results of simplified thermal evolution calculations are discussed. The observed thermal histories cannot be explained by a simple model with heat transferred by heat conduction at a constant conductivity, so a coupled heat and mass transfer problem was considered. The porous ice matrix was assumed to have a constant thermal conductivity and to be in thermal equilibrium with vapor in the pores, the internal pressure being the vapor pressure. The vapor was modelled as an ideal gas because, at the temperatures relevant to the problem, the mean free path length of the vapor molecules is large in comparison with the pore dimensions. The heat capacity at constant volume per unit mass of the two phase mixture was also assumed constant. The vapor was allowed to flow and transfer heat in response to an internal pressure gradient
Quickly fading afterimages: hierarchical adaptations in human perception
Afterimages result from a prolonged exposure to still visual stimuli. They
are best detectable when viewed against uniform backgrounds and can persist for
multiple seconds. Consequently, the dynamics of afterimages appears to be slow
by their very nature. To the contrary, we report here that about 50% of an
afterimage intensity can be erased rapidly--within less than a second. The
prerequisite is that subjects view a rich visual content to erase the
afterimage; fast erasure of afterimages does not occur if subjects view a blank
screen. Moreover, we find evidence that fast removal of afterimages is a skill
learned with practice as our subjects were always more effective in cleaning up
afterimages in later parts of the experiment. These results can be explained by
a tri-level hierarchy of adaptive mechanisms, as has been proposed by the
theory of practopoiesis.Comment: 3 pages, 3 figure
- âŠ