In order to collect data from human subjects, institutional review board (IRB) approval must be obtained. At MIT, this is also referred to as the Committee on the Use of Humans as Experimental Subjects (COUHES).
An application was completed and submitted last week, which described the relevant personnel, funding sources, experimental protocol, potential risks to the participants, possible benefits, and other relevant information about the study. In addition, a consent form was drafted for submission with the COUHES application. This document provides information to the experiment participants, and they are required to sign the consent form before participating in the experiment.
The Skinsuit is a skin-tight garment made of elastic material which provides skin compression and vertical loading on the body. Prior to any experiments, the subject will be sized for a custom Skinsuit. Detailed body measurements will be obtained manually with a soft tape measure or using a 3D body scanner. A suit will be custom fabricated based on these measurements.
During the experimental procedure, the subject will be asked to perform simple body movements (e.g. arm flexion or extension) while wearing several wearable sensing systems. This may include 1) surface electromyography sensors adhered to the skin and 2) pressure sensors on the skin and in the soles of the subject's shoes. Medical tape may be used to secure sensors to the skin. Video may also be recorded while the subject is performing the task, and brightly colored tape will be used to mark key landmarks on the participant's body. The subject may be prompted with qualitative survey questions before and after each trial, asking about their perception and disorientation during the experiment.
The experimental protocol will include an unsuited condition (i.e. non-specific clothing or tight-fitting athletic wear). There may be 1 to 2 suited conditions in which the subject will wear the Skinsuit (with or without Skinsuit stirrups disconnected). Trials may occur during multiple environmental conditions including 1-G, microgravity, and partial gravity. In any combination of the above conditions and environments, the subject may also be blindfolded or allowed full vision. The same activity (i.e. simple body movements while data is recorded from body-worn sensors and, if needed, video) will be performed in each condition/environment.
The participant will be asked to wear tight-fitting athletic wear under the Skinsuit to ensure modesty when donning and doffing the suit during the Zero-G flight.
For the flight tests: The subject will arrive in Pease, New Hampshire for the parabolic flight with Zero Gravity Corporation (ZGC). The subject will be offered an optional dose of over-the-counter scopolamine to counteract possible effects of nausea in microgravity. The flight will consist of about 20 cycles of flight profile. A flight profile will consist of a period of hypergravity and a period of microgravity (or partial gravity). During the phase of microgravity (or partial gravity), which will last approximately 20 seconds, the subject will perform the previously mentioned activity (i.e. simple body movements while data is recorded from body-worn sensors and, if needed, video) during suited and unsuited conditions. During the hypergravity periods, the subject will stop all experimental activity and rest. This will minimize the chance of nausea due to motion in dynamic gravity environments.
During pre- and post- flight tests the subject will again perform simple body movements while data is recorded from body-worn sensors. These pre- and post-flight test sessions will take a maximum of 2 hours and will take place in the Human Systems Laboratory at MIT.
One risk of this study is short-term exposure to a microgravity environment. To minimize the risks of microgravity, the subject will be trained on best practices in microgravity through the MAS.S66 course and the instruction of the Zero-G Corporation. The subject will also be offered an optional dose of scopolamine to reduce the likelihood of nausea in flight. During hypergravity periods the subject may rest in a static position, reducing the likelihood of nausea. Some minimal discomfort may be associated with the compression and loading of the Skinsuit garment. The participant will don the Skinsuit prior to flight to decide if the suit is comfortable enough to wear for multiple hours. The participant may also doff the Skinsuit at any time if it becomes too uncomfortable. There may also be minimal risks/discomforts associated with surface electromyography, including minor irritation to the skin.
A more detailed experimental protocol will be refined over the next month. This will include trial/condition order and decisions regarding the use of blindfolded trials and qualitative surveys.
A 100% PrimeflexTM woven fabric has been selected for the Skinsuit. PrimeflexTM is composed of two types of polyester PET (polyethylene terephthalate) and PTT (polytrimethylene terephthalate), which provide bi-component stretch with high recovery forces. Different fabric structures (knitting, weaving, yarn density, etc.) can be used with the Primeflex material and will influence the mechanical properties.
The fabric selected for the current Skinsuit is slightly transparent due to a low gsm (grams per square metre). Despite the transparency, the fabric performs favorable in its strain-tension profile and durability tests. To resolve the problem of transparency, an underlayer will be required while wearing the Skinsuit.
Several additional materials will be used for the Skinsuit; and most have been pre-selected during previous Skinsuit prototype developing. All materials are listed in the table below.
The timeline for suit fabrication has been confirmed in the table below.
Material testing is ongoing for the longer-duration durability tests. Some initial results are included below. The provided results indicate the percent decrease in tension after the test. For the tension relaxation tests, the samples are stretched to the maximum expected Skinsuit tension (500N/m in x-direction, and 2000N/m in y-direction) and held for 30 min to 8 hours. For cycle testing, the the samples are stretched to the maximum expected Skinsuit tension over 100 cycles.
**Testing results updated 10/28/2020
The system block diagram is included in Figure 6. This primarily includes two sensor systems connected to a laptop: the Novel Pressure Sensor System and the Delsys Electromyography (EMG) System. A GoPro will be used for motion capture, but is not connected to the laptop.
The concept of operation is included below.
Set up tripod and GoPro
Secure laptop and instrumentation boxes, plug in USBs, tape down wires, plug in laptop
Attach EMG sensors
Don shoes with insole sensors, secure Novel box on waist belt
Open LabView and Novel software
Ensure Novel Bluetooth is connected
Test setup with a short recording
Mark participant’s target location with tape, measure distance from GoPro tripod
* It would be ideal to use the first few cycles for acclimation and some data collection, the second 5 cycles for suited protocol, the third 5 cycles for suited protocol with stirrups disconnected, the fourth 5 cycles for unsuited protocol. However, I am unsure if I will be able to doff the suit during the shorter period of level flight.
**Update: A 10 minute period of level flight will be added after parabola #15 to allow for suit doffing.
Close LabView and Novel software
Stope recording of GoPro
Remove sensors and put away into cases
I have completed preliminary tensile testing for nine fabric candidates for the Skinsuit. The Jumbo Spandex and Elastot are previously used Skinsuit materials. The Navy Kinetic, Black Primeflex, and Gray Primeflex are new materials sourced from an industry collaborator. The remaining four fabrics are commercially available fabrics with various compositions (mostly spandex blends). Testing will continue this week as I perform longer-duration durability tests.
In Figure 5, the primary goal is to identify the bidirectional behavior of the fabric and determine if the fabric can provide the required range of tension. Some fabrics can be eliminated immediately, including the Black Performance Spandex/Cotton, the Gray Superflex Compression Spandex, the Red Ember Ponte Knit, and the 2020 Jumbo Spandex. These fabrics do not reach the required range for neither axial nor circumferential tension within a reasonable level of strain (arbitrarily set at 150% strain). Additionally, the Navy Ponte Knit and the 2020 Elastot do not reach the required ranges for axial tension, despite satisfying the circumferential requirements. While the 2020 Elastot and Jumbo Spandex samples appear to be insufficent, their previous results (plotted for reference) provided much larger levels of tension. This is likely due to differences between fabric batches and potentially difference sourcing methods.
This analysis eliminates all of the commercially available fabrics, leaving the three new materials sourced from our industry partner. This is supported by cycles testing in Figures 5 and 6. One limitation in this testing procedures was the small sample gauge length. A larger gauge length will be used in later testing sessions for comparison.
The cycle testing in Figures 6 and 7 show a large deformation after the 1st cycle in most fabrics, but behavior is fairly consistent over the following four trials for the three candidate fabrics. Hysteresis is also quite low in these samples compared to the commercially available fabrics.
I have performed an initial literature review of the sensorimotor effects of spaceflight, which will be expanded upon in later work. Balance, posture, and movement rely on inputs from several physiological sensors (Figure 4). In microgravity, the sensor stimuli are significantly altered. The otolith organs are particularly affected by the loss of their primary stimulus: gravity. Additionally, pressure is no longer applied to the soles of the feet and axial mechanical loading is not applied to the body. The body likely adapts to these changes by altering the gain and sensitivity of some sensors. The integration centers may rely more on visual inputs in microgravity to compensate . Upon return to Earth, phsyiological adaptations during spaceflight can result in ataxia, disorientation, and posture and locomotion impairment .
A large majority of the research in spaceflight neuroscience focuses on the vestibular system (inner ear), as this is most relevant for space sickness and rapid adaptations to gravity changes (~3 days, but potentially weeks to months for full adaptation). In this case, “sensorimotor effects” refer to the sensory inputs from vestibular organs and how they can affect movement. In the scope of the Skinsuit project, we are interested in position- and loading-related sensorimotor effects. The effect of vestibular adaptations is likely of greater magnitude and thus, appears to dominate the literature in space neuroscience and our understanding of sensorimotor changes in microgravity. Wearable devices cannot reintroduce the gravito-inertial forces to affect the vestibular system, but they can provide foot pressure and skin pressure, perhaps restoring stimuli for mechanoreceptors, proprioception processes, and certain motor control strategies.
Unloading in microgravity affects body load receptors  and causes changes in proprioception . In combination with adaptations in the vestibular system, these sensorimotor adaptations may affect posture, locomotion, balance upon return to Earth . English et al. detail the use of exercise countermeasures to re-introduce body loading and maintain some of the typical afferent feedback required for locomotion and other movements . In addition to exercise, studies suggest that foot pressure or plantar stimulation in microgravity may enhance neuromuscular activation and prevent neuromuscular degradation ,. For example, studies show that muscle activation patterns change in microgravity relative to preflight measurements . Layne et al. used an arm raising movement which is known to involve whole-body coordination, with muscle activation in the lower limbs and postural muscles in addition to the arms. This effect is decreased in microgravity. By re-introducing foot pressure in microgravity using special pneumatic shoes, muscle activation in the lower limbs was enhanced during arm raises compared to a control condition with no foot pressure . These studies were largely performed by Layne in the 1990s (often in collaboration with Kozlovskaya from the Russian Institute for Biomedical Problems). While these papers seem to be commonly cited for changes in motor control strategies, I have yet to find any recent publications with similar experiments. Additionally, there is likely much more that needs to be understood following Layne’s work. Layne et al.’s results stated there was “enhanced” neuromuscular activity. This described the higher levels of activity with foot pressure and the earlier onset of muscle activity. However, the control in this study was microgravity without foot pressure. Results were not compared to 1-G data.
Kozlovskaya et al. suggest that the Penguin Suit, another countermeasure suit and the precursor to the Skinsuit, may produce sensorimotor effects, specifically the restoration of mechanoreceptors in the skin and muscles . However, this comment is not supported with any quantitative evidence or references to the literature.
Another note from the literature mentions that there is currently no adequate analog for sensorimotor adaptations. While this statement was made primarily in regards to the vestibular system, it seems accurate for mechanical load sensors as well . Even in bed rest analogs or body-weight suspension there is a the constant force of gravity on the body and body-load receptors.
The mechanical properties of the Skinsuit fabric will depend on yarn and fabric structure (knit structure, density, thickness, etc.). Different mechanical properties are required in the axial and circumferential directions to apply appropriate loading levels to the body.
The material will provide forces between 100 N/m and 2000 N/m in the axial direction with strains less than 150%
The material will have a <10% change in expected force in the axial direction over 100 cycles to 2000 N/m.
The material will provide forces between 50 N/m and 500 N/m in the circumferential direction with strains less than 150%
The material will have a <10% change in expected force in the circumferential direction over 100 cycles to 500 N/m.
The material will have low stiffness in the circumferential direction to accommodate donning/doffing and small changes in circumference.
The material will be:
Breathable / Moisture-wicking (i.e. appropriate for exercising)
Opaque (There were some problems in previous suits with see-through fabric.)
Antimicrobial (Can be implemented in later prototypes. Laundry is not available on the ISS.)
Previously Used Materials
The Gravity Loading Countermeasure Skinsuit (or “Skinsuit”) is an intravehicular activity suit for astronauts that has been developed to simulate the effects of Earth gravity. The Skinsuit produces a static load from the shoulders to the feet with elastic material in the form of a skin-tight wearable suit ,. This wearable system is intended to supplement exercise during future missions to the moon and Mars (where space for large exercise equipment may be unavailable) and to further attenuate microgravity-induced physiological effects in current ISS mission scenarios. The Skinsuit targets multiple physiological systems, aiming to mitigate bone loss, muscle loss, and spinal elongation. Additionally, the Skinsuit may provide benefits to the sensorimotor system, which have not been tested in previous studies. The sensorimotor effects of microgravity are difficult to simulate on Earth, even in bed rest analogs or body-weight suspension, due to the constant force of gravity on the body and body-load receptors. The goal of this project is to use the microgravity afforded by a parabolic flight to explore a research question: Can the Skinsuit restore sensorimotor functions that are typically altered in microgravity?
Microgravity unloading affects body-load receptors, such as mechanoreceptors in the skin and muscles. In combination with adaptations in the vestibular system, sensorimotor adaptations may affect posture, locomotion, balance, and proprioception upon return to Earth . Muscle activation patterns are known to change in microgravity relative to preflight measurements, including, for example, decreased preparatory muscle activation in the lower limbs, and such changes have been observed in the time scale of parabolic flights ,. Layne et al. have shown that re-introducing foot pressure in microgravity enhances muscle activation in the lower limbs during arm raises compared to a control condition with no foot pressure . Therefore, foot pressure, which is provided by the Skinsuit, may attenuate neuromuscular degradation and partially restore 1-G motor control strategies.
Several Skinsuit versions have been developed over the past decade with various design modifications (Figure 1). Previous Skinsuit experiments, including ground experiments, one parabolic flight, and ISS flights, have primarily studied operational feasibility, loading magnitude, and spinal elongation attenuation. The investigation of sensorimotor effects and microgravity EMG patterns associated with the Skinsuit is novel.
In parallel to developing an experimental protocol to answer questions about physiology, I plan to design and fabricate the next-generation Skinsuit as part of my thesis work, with improved materials and an integrated platform for wearable technology to create the first “smart” Skinsuit  (Figure 2). In order to meet the December deadline for this course, I anticipate that I may use an un-instrumented Skinsuit or an earlier version of the Skinsuit for the parabolic flight. The experimental protocol will be considered over the course of the semester, and measurables may include electromyography (EMG), kinematics, and foot pressure. As a preliminary experimental protocol, the participant could perform arm movements with and without the Skinsuit for comparison to typical 1-G muscle activation patterns or postural control strategies.
This work aims to characterize the function and physiological effects of the Skinsuit and may elucidate short-term changes in human sensorimotor function in microgravity. Research outputs will include academic publications and inclusion in my Ph.D. thesis. Overall, the proposed work would support the goal of the Skinsuit project in enabling humans to adapt to multiple levels of gravity, bringing us one step closer to long-term space habitation.