Haemostasis occurs at sites of vascular injury, where flowing blood forms a clot, a dynamic and heterogeneous fibrin-based biomaterial. Paramount in the clot’s capability to stem haemorrhage are its changing mechanical properties, the major driver of which are the contractile forces exerted by platelets against the fibrin scaffold 1. However, how platelets transduce microenvironmental cues to mediate contraction and alter clot mechanics is unknown. This is clinically relevant, as overly softened and stiffened clots are associated with bleeding 2 and thrombotic disorders 3. Here, we report a high-throughput hydrogel based platelet-contraction cytometer that quantifies single-platelet contraction forces in different clot microenvironments. We also show that platelets, via the Rho/ROCK pathway, synergistically couple mechanical and biochemical inputs to mediate contraction. Moreover, highly contractile platelet subpopulations present in healthy controls are conspicuously absent in a subset of patients with undiagnosed bleeding disorders, and therefore may function as a clinical diagnostic biophysical biomarker.

Fire ants link their bodies to form aggregations; these can adopt a variety of structures, they can drip and spread, or withstand applied loads. Here, by using oscillatory rheology, we show that fire ant aggregations are viscoelastic. We find that, at the lowest ant densities probed and in the linear regime, the elastic and viscous moduli are essentially identical over the spanned frequency range, which highlights the absence of a dominant mode of structural relaxation. As ant density increases, the elastic modulus rises, which we interpret by alluding to ant crowding and subsequent jamming. When deformed beyond the linear regime, the aggregation flows, exhibiting shear-thinning behaviour with a stress load that is comparable to the maximum load the aggregation can withstand before individual ants are torn apart. Our findings illustrate the rich, collective mechanical behaviour that can arise in aggregations of active, interacting building blocks.

THE physiological importance of acetylcholine in the nervous system has made it very desirable to secure further knowledge of the details of acetylcholine metabolism in the body. Little is known as yet of the mode of production of this choline ester in the tissues. Beznak [1934] has reported that the ester is formed in minced frog heart muscle when sufficient eserine is present to prevent its destruction by choline esterase. Chang [1935] states that it is formed in vitro from placenta. Much more is known [Plattner & Galehr, 1928; Ammon & Voss, 1935; Stedman & Stedman, 1935, 1] of the breakdown of acetylcholine by an esterase which has recently been isolated and purified by Stedman & Stedman [1935, 2]. The reader is referred to summaries of recent literature on the subject in articles by Gaddum [1935] and by Ammon [1935].Experiments have been undertaken by the authors to determine whether acetylcholine is formed as a normal product of metabolism of tissues examined in vitro by the Warburg manometric technique, and the following paper is concerned with a description of the results which have been found so far.Technique. Thin slices of tissue were cut from the organs freshly dissected from the animal and placed in a manometric vessel containing Ringer solution or a phosphate saline solution. The vessel was filled with oxygen, and determinations of the oxygen consumption of the tissue were made, using the well-known manometric methods of Warburg. The experimental period varied from 1 to 3 hours at 370 or at 38.40, at the termination of which the solution in the manometric vessel was tested for its acetylcholine activity, and the tissue slices were removed, washed, dried and weighed.Media. Solutions were all made up so as to have an osmotic pressure approximately equal to 0-16 M NaCl. The final volume of the medium was made up to 3-0 ml. with 0-16 M NaCl after all other desired substances had been added. The hydrogen ion concentration was maintained at pH 7-4 in the experiments to be reported here.Tissue slices. The thickness of the slices varied from one experiment to another but usually lay between 0-2 and 0-4 mm. Several slices were employed, the total dry weight in each vessel varying from 10 to 20 mg.Neutralization of acids. All acids were neutralized before use, solutions of sodium salts being prepared.Estimation of choline ester. The choline ester was estimated by measuring the contraction of the eserinized longitudinal muscle from the dorsum of a leech. The muscle, after dissection, was immersed at room temperature in an oxygenated saline medium of the following composition: NaCl=0-71 %, KCl=0-032%, CaCl2=0-018%, NaHCO3=0-012 %, glucose=0-077 %. The final volume of ( 1668 )

Solid polymer electrolytes (SPEs) have the potential to enhance the safety and energy density of lithium batteries. However, poor interfacial contact between the lithium metal anode and SPE leads to high interfacial resistance and low specific capacity of the battery. In this work, we present a novel strategy to improve this solid–solid interface problem and maintain good interfacial contact during battery cycling by introducing an adaptive buffer layer (ABL) between the Li metal anode and SPE. The ABL consists of low molecular-weight polypropylene carbonate , poly­(ethylene oxide) (PEO), and lithium salt. Rheological experiments indicate that ABL is viscoelastic and that it flows with a higher viscosity compared to PEO-only SPE. ABL also has higher ionic conductivity than PEO-only SPE. In the presence of ABL, the interface resistance of the Li/ABL/SPE/LiFePO4 battery only increased 20% after 150 cycles, whereas that of the battery without ABL increased by 117%. In addition, because ABL makes a good solid–solid interface contact between the Li metal anode and SPE, the battery with ABL delivered an initial discharge specific capacity of >110 mA·h/g, which is nearly twice that of the battery without ABL, which is 60 mA·h/g. Moreover, ABL is able to maintain electrode–electrolyte interfacial contact during battery cycling, which stabilizes the battery Coulombic efficiency.

Fire ant aggregations are active materials composed of individual constituents that are able to transform internal energy into work. We find using rheology and direct visualization that the aggregation undergoes activity cycles that affect the mechanical properties of the system. When the activity is high, the aggregation approximately equally stores and dissipates energy, it is more homogeneous, and exerts a high outward force. When the activity is low, the aggregation is predominantly elastic, it is more heterogeneous, and it exerts a small outward force. We rationalize our results using a simple kinetic model where the number of active ants within the aggregation is the essential quantity.