Commentary Open Access

Highlights on Gravity Research

Abstract

Throughout our lives, we are pulled down by a force. It follows us everywhere: in the mountains, underground in caves, on the street, on the bus, and on the plane. It cannot be protected in the same way that electric and magnetic fields can. It is not like electricity in that it cannot be turned off or on. Gravity is this force. The cause of gravity, according to Isaac Newton, is mass. Any mass-carrying body attracts other mass-carrying bodies [1]. The attraction force is related to the product of masses and inversely proportional to the square of the distance between bodies. The Newton gravity law is useful for calculating planet orbits and in everyday life. “Microgravity” isn't a science, as some presume, but a specific environment where science is often performed. The most reason behind performing basic sciences under such microgravity, free fall, or conditions of near weightlessness is indeed that the load is far away from the mass. This leads to less mechanical stress within a system, less or nearly no convection, reduced pressure differences within a system, etc. In such an environment, one also can observe phenomena that are otherwise obscured or blurred when studied during a field, like thermo-capillary Bénard-Marangoni convection or surface-tension-dominated Gibbs-Marangoni convections, capillary flows, juncture phenomena, and lots of more related issues in physical sciences and engineering. Items of study include colloids, emulsions, foams, liquid crystals, dusty plasmas, flames/combustion or granular material, and also elementary particle physics, e.g., Bose-Einstein condensates, or more bulk processes, like alloy solidification. Albert Einstein was of the opinion that this was not the case. Gravity did not fit into his theory of relativity as a force. As a result, he assumed that gravity is a curvature of space rather than a force. Curvature is caused by mass. Extensive studies of how light bends near the Sun revealed that space is really curved. Nonetheless, we experience the force of gravity on a daily basis, which we must fight when lifting large objects. We are oblivious to the curvature of space. We have operational sciences where we have to deal with the microgravity environment, in addition to basic sciences where we employ the microgravity environment. In operational sciences, also known as applied sciences, one must build and apply methods for both physical and biological sciences sectors that make it easier to live in such a setting. For example, all fluidic and two-phase systems must function without the sedimenting effect of gravity in all types of fluid-filled systems in space stations, as well as in fuel tanks for other satellites [2]. Additionally, individuals must be prepared to work in a free-falling system in the future. However, when it comes to human health, the latter poses major issues. Many so-called "countermeasures" have been devised to prevent human physiology from entering a state. Disorders like osteoporosis and sarcopenia, cardiovascular deconditioning, impaired cognitive performance, Spaceflight Associated Neuro-ocular Syndrome (SANS), reduced immune sensitivity, renal stones, loss of quality and duration of sleep, lower back pain, post-flight balance and coordination issues, and orthostatic intolerance or spinal compression with intervertebral disc damage are all seen in cosmonauts, astronauts, and taikonauts. Some might question if the present lack of proper microgravity therapies is compliant with ethical labor and legal standards. This new journal would even be available to receive manuscripts concerning the event and test of instruments concerning the mitigation or full “recovery” of chronic microgravity and gravity transitions. Besides, for instance, high-impact training or Lower Body Negative Pressure (LBNP) devices we'd explore the appliance of centrifuges to truly generate in-flight artificial gravity. Short arm systems are the foremost obvious ones, although such systems generate a steep body gradient of gravity, and not all organs could also be exposed to a sufficient gravity level. One can also check out rotating the entire spacecraft. In such systems, there's a more evenly distributed gravity level, and therefore the subjects are chronically exposed to the synthetic gravity like on Earth. However, such systems require understanding on long duration rotation for both humans and engineering. Ground- based facilities might be wont to address such in-flight-related questions at an equivalent time as they address the utilization of systems for health care (e.g., aging and obesity) and athletics-related applications. The impact of gravity on small, low-mass systems remains puzzling. Quite half a century ago, Pollard published a paper indicating that, from a biophysics point of view, weightlessness isn't expected to possess a big effect at the extent of one cell. Possible “gravisensors” during a non-specialized cell could be the mitochondria or the nucleolus. Later, Todd (1989) and Albrecht- Buehler (1991) published interesting papers, which are still quite relevant, addressing a series of forces that are involved at a little scale cellular level and compared them to the force of gravity at that micro scale [3]. Therefore, although there are numerous experiments in space and on the bottom showing the effect of gravity, or the shortage thereof, on cells, the particular sensing mechanism in non-specialized cells has yet to be described. In an in-vitro model monolayer single cell with a diameter of 10 μm, the gravitational energy of a clear weight of 0.5 pN at a mean distance of the radius (5 μm) above rock bottom point of the cell is ~500 kT, where k is Boltzmann's constant, and T is temperature. These are small forces and energies compared to other intra- and extra-cellular forces. Instruments such as femtosecond lasers, microscopes with improved imaging modalities such as FLIM or FRET, atomic force microscopes, optical tweezers, or micro-aspiration techniques, especially in non-specialized cells, could play a significant role in the quest for a gravity mechanosensory. Systems like the FLUMIAS, the sunshine Microscopy Module, or the JAXA microscope adapted plate readers or equivalents, which could be quite illustrative regarding molecular conformational changes or interactions, e.g., with plate readers or the Nano Racks plate reader, micro-NMR systems, or specific in vivo probes that reflect biophysical properties in molecules based on their extra-molecular environment. Numerous studies are performed to explore the effect of weight or near weightlessness on cells. These studies are, partially pushed by contemporary techniques, focused on the genetic effects, although this is often moving more and more toward proteomics/metabolomics and therefore the actual physiology, while it's possible that adapted phenotypes or sometimes pathological changes are often noted. Of these findings are within the area of mechano-transduction and mechano-adaptation, while the grail and grand challenge during this field would be to spot a gravisensor (if such a thing exists). Most of the effects reported from altered gravity research in cell biology should start, at some point, with a mechanical, conformational, or frequency change within the system. It’s this gravi- or mechano-sensor that ought to be identified. More advanced in-flight research opportunities and technologies are required for this, which is analogous to what's utilized in the sector of biomechanics, especially in molecular, cellular, and tissue biomechanics, but also on an organ and organism level.

Scarlett H

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