Avian mud nest architecture by self-secreted saliva.

Mud nests built by swallows (Hirundinidae) and phoebes (Sayornis) are stable granular piles attached to cliffs, walls, or ceilings. Although these birds have been observed to mix saliva with incohesive mud granules, how such biopolymer solutions provide the nest with sufficient strength to support the weight of the residents as well as its own remains elusive. Here, we elucidate the mechanism of strong granular cohesion by the viscoelastic paste of bird saliva through a combination of theoretical analysis and experimental measurements in both natural and artificial nests. Our mathematical model considering the mechanics of mud nest construction allows us to explain the biological observation that all mud-nesting bird species should be lightweight.

Hierarchical Capillarity-Assisted Liquid Invasion in Multilayered Paper Channels for Nanoelectrokinetic Preconcentration.

A nanoelectrokinetic phenomenon called ion concentration polarization (ICP) has been recently applied to microfluidic paper-based devices for the high fold preconcentration of low-abundant analytes. The inherent microstructural characteristics of cellulose papers can sufficiently stabilize the chaotic electroconvection of ICP, which is a significant annoyance for typical engineered microfluidic channels. However, a high electrical voltage to induce ICP in a paper-fluidic channel can increase unavoidable electrophoretic forces over drag forces so that the preconcentrated plug is rapidly receded with severe dispersion. In order to enhance the hydraulic drag force that helps the preconcentration of analytes, here we introduce a multilayered paper structure into paper-fluidic channel. We theoretically and experimentally demonstrate that a hierarchical capillary structure in a multilayered paper-fluidic channel can effectively increase the hydraulic drag force. For the practical utility in the field of diagnostics, the mechanism is verified by a simple example of the immunoassay using biotin-streptavidin complexation.

Hydrogel-based strong and fast actuators by electroosmotic turgor pressure.

Hydrogels are promising as materials for soft actuators because of qualities such as softness, transparency, and responsiveness to stimuli. However, weak and slow actuations remain challenging as a result of low modulus and osmosis-driven slow water diffusion, respectively. We used turgor pressure and electroosmosis to realize a strong and fast hydrogel-based actuator. A turgor actuator fabricated with a gel confined by a selectively permeable membrane can retain a high osmotic pressure that drives gel swelling; thus, our actuator exerts large stress [0.73 megapascals (MPa) in 96 minutes (min)] with a 1.16 cubic centimeters of hydrogel. With the accelerated water transport caused by electroosmosis, the gel swells rapidly, enhancing the actuation speed (0.79 MPa in 9 min). Our strategies enable a soft hydrogel to break a brick and construct underwater structures within a few minutes.

Longitudinal Spin Order Labeling on Multiple Quantum Coherences Enables NMR Analysis of Intrinsically Disordered Proteins at Ultrahigh Resolution.

Intrinsically disordered proteins (IDPs) play an important role in cell signaling, and NMR is well-suited to study conformational ensembles and dynamics of IDPs. However, the intrinsic flexibility of IDPs often results in severe spectral overlap, which hampers accurate NMR data analysis. By labeling the longitudinal spin order of an α proton (i.e., Hαz) on multiple quantum coherences of backbone nuclei (e.g., NyC'xCαy), we were able to apply pre-homonuclear decoupling (PHD) to transverse relaxation-optimized spectroscopy (TROSY). The proposed scheme provides ultrahigh resolution in both amide proton and nitrogen dimensions, as illustrated in the analysis of Tau and alpha-synuclein (α-Syn) proteins. The PHD-TROSY readout enabled complete backbone resonance assignment of α-Syn using a single 3D HNCA experiment performed on a 600 MHz NMR spectrometer.