Stick-slip Dynamics in Penetration Experiments on Simulated Regolith

The surfaces of many planetary bodies, including asteroids and small moons, are covered with dust to pebble-sized regolith held weakly to the surface by gravity and contact forces. Understanding the reaction of regolith to an external perturbation will allow for instruments, including sensors and anchoring mechanisms for use on such surfaces, to implement optimized design principles. We analyze the behavior of a flexible probe inserted into loose regolith simulant as a function of probe speed and ambient gravitational acceleration to explore the relevant dynamics. The EMPANADA experiment (Ejecta-Minimizing Protocols for Applications Needing Anchoring or Digging on Asteroids) flew on several parabolic flights. It employs a classic granular physics technique, photoelasticity, to quantify the dynamics of a flexible probe during its insertion into a system of bi-disperse, centimeter-sized model grains. We identify the force chain structure throughout the system during probe insertion at a variety of speeds and for four different levels of gravity: terrestrial, Martian, lunar, and microgravity. We identify discrete, stick-slip failure events that increase in frequency as a function of the gravitational acceleration. In microgravity environments, stick-slip behaviors are negligible, and we find that faster probe insertion can suppress stick-slip behaviors where they are present. We conclude that the mechanical response of regolith on rubble-pile asteroids is likely quite distinct from that found on larger planetary objects, and scaling terrestrial experiments to microgravity conditions may not capture the full physical dynamics.

Scalable Batch Fabrication of Ultrathin Flexible Neural Probes using Bioresorbable Silk Layer

Flexible deep brain probes have been the focus of many research works and aims at achieving better compliance with the surrounding brain tissue while maintaining minimal rejection. Strategies have been explored to find the best way to implant a flexible probe in the brain, while maintaining its flexibility once positioned in the cortex. Here, we present a novel and versatile scalable batch fabrication approach to deliver ultra-thin and flexible penetrating neural probe consisting of a silk-parylene bilayer. The biodegradable silk layer provides a temporary and programmable stiffener to ensure ease of insertion of the ultrathin parylene-based flexible devices. The innovative and yet robust batch fabrication technology allows complete design freedom of the neural probe in terms of materials, size, shape and thickness. These results provide a novel technological solution for implanting ultra-flexible and ultrathin devices, which possesses great potential for brain research.

Probing regolith-covered surfaces in low gravity

The surfaces of many planetary bodies, including asteroids, moons, and planets, are composed of rubble-like grains held together by varying levels of gravitational attraction and cohesive forces. Future instrumentation for operation on, and interacting with, such surfaces will require efficient and effective design principles and methods of testing. Here we present results from the EMPANADA experiment (Ejecta-Minimizing Protocols for Applications Needing Anchoring or Digging on Asteroids) which flew on several reduced gravity parabolic flights. EMPANADA studies the effects of the insertion of a flexible probe into a granular medium as a function of ambient gravity. This is done for an idealized 2D system as well as a more realistic 3D sample. To quantify the dynamics inside the 2D granular material we employ photoelasticity to identify the grain-scale forces throughout the system, while in 3D experiments we use simulated regolith. Experiments were conducted at three different levels of gravity: martian, lunar, and microgravity. In this work, we demonstrate that the photoelastic technique provides results that complement traditional load cell measurements in the 2D sample, and show that the idealized system exhibits similar behaviour to the more realistic 3D sample. We note that the presence of discrete, stick-slip failure events depends on the gravitational acceleration.

Double-layer flexible neuronal probe with closely spaced electrodes for high-density in-vivo brain recordings

Flexible probes for brain activity recordings are an attractive emerging approach that reduces mechanical mismatch between probe and neuronal tissue, thus minimizing the risk of brain damage or glial scaring. Although promising, flexible probes still present some technical challenges namely: i) how to overcome probe buckling during brain insertion given its intrinsically low mechanical rigidity; ii) how to fabricate closely spaced electrode configurations for high density recordings by standard lithography techniques in the flexible substrate. Here, we present a new flexible probe based solely on standard and low-cost lithography processes, which has closely spaced 10 μm diameter gold electrode sites on a polyimide substrate with inter-site distances of only 5 μm. By using a double-layer design and fabrication approach we were able to accommodate closely spaced electrode sites at two different depths from probe surface while also providing additional stiffening, just sufficient to prevent probe buckling during brain insertion. Detailed probe characterization through metrology of structural and electrical properties and chemical composition analysis, as well as functional assessment through in vivo high-density recordings of neuronal activity in the mouse cortex, confirmed the viability of this new fabrication approach and that this probe can be used for obtaining high quality brain recordings with excellent signal-to-noise ratio (SNR).

Morphofunctional characteristics of mouse (Mus musculus musculus) liver on the application of various doses of nanostructural sapropel

The liver is considered to be the main organ in the processes of regulating metabolism, neutralizing toxins and maintaining the constancy of the internal environment of the body. The goal of the research was to study the morphofunctional state of the liver under the effect of different concentrations of nanostructured sapropel. The experiments were carried out on non-linear (outbred) white mice weighing 24.9 ± 1.8 g. Twelve mature males were allotted to four groups. Mice of the experimental groups I, II and III intragastrically through the atraumatic flexible probe were once injected with nanostructured sapropel (particle size of 45.0–180.0 nm) in the following doses: lethal – 3.0 g/kg of the body weight; toxic – 1.8 g/kg of the body weight and safe – 0.6 g/kg of the body weight. Mice of group IV served as a control one and received deionized water in the same way. The choice of liver as the organ for analyzing is justified by the fact that the liver did not have direct contact with sapropel nanoparticles in the process of its intragastric administration into the body of white mice. Four hours after the introduction of nanostructured sapropel, three mice from each group were killed by cervical dislocation. After preparation and staining with hematoxylin and eosin, identical pieces of the liver were evaluated using light microscopy. Histological studies have established that the introduction of a lethal dose of nanostructured sapropel caused hemodynamic vascular disorders; focal necrosis and necrobiosis of hepatocytes were also observed in the research. Furthermore, the research noted a migration of reticuloendotheliocytes to the centrolobular regions of the lobules and enhancement of their activity. The microstructure of the liver when introducing a toxic dose of nanostructured sapropel was characterized by moderate plethora of sinusoidal capillaries, deformation of hepatocytes, focal destruction with the development of karyopiknosis, karyorhexis and karyolysis. The study revealed the activation of reticuloendothelial cells. Liver histology when introducing a safe dose of nanostructured sapropel was characterized by the preservation of the integrity of the structural elements, polyploid (two- and multi-core) hepatocytes were identified in the periportal part of the lobes. The changes in the structural and functional state of the mice liver were found to be depending on the dose of the nanostructured sapropel.