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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Molecular Dynamics Studies of Structure and Functions of Water-Membrane Interfaces

A large number of essential cellular processes occur at the interfaces between water and membranes. The selectivity and dynamics of these processes are largely determined by the structural and electrical properties of the water-membrane interface. We investigate these properties by the molecular dynamics method. Over the time scales of the simulations, the membrane undergoes fluctuations described by the capillary wave model. These fluctuations produce occasional thinning defects in the membrane which provide effective pathways for passive transport of ions and small molecules across the membrane. Ions moving through the membrane markedly disrupt its structure and allow for significant water penetration into the membrane interior. Selectivity of transport, with respect to ionic charge, is determined by the interfacial electrostatic potential. Many small molecules. of potential significance in catalysis, bioenergetics and pharmacology, are shown to bind to the interface. The energetics and dynamics of this process will be discussed.

Pohorille, Andrew↗
NASA NTRS2001

Corner Wrinkling at a Square Membrane Due to Symmetric Mechanical Loads

Thin-film membrane structures are under consideration for use in many future gossamer spacecraft systems. Examples include sunshields for large aperture telescopes, solar sails, and membrane optics. The development of capabilities for testing and analyzing pre-tensioned, thin film membrane structures is an important and challenging aspect of gossamer spacecraft technology development. This paper presents results from experimental and computational studies performed to characterize the wrinkling behavior of thin-fi[m membranes under mechanical loading. The test article is a 500 mm square membrane subjected to symmetric comer loads. Data is presented for loads ranging from 0.49 N to 4.91 N. The experimental results show that as the load increases the number of wrinkles increases, while the wrinkle amplitude decreases. The computational model uses a finite element implementation of Stein-Hedgepeth membrane wrinkling theory to predict the behavior of the membrane. Comparisons were made with experimental results for the wrinkle angle and wrinkled region. There was reasonably good agreement between the measured wrinkle angle and the predicted directions of the major principle stresses. The shape of the wrinkle region predicted by the finite element model matches that observed in the experiments; however, the size of the predicted region is smaller than that determined in the experiments.

Blandino, Joseph R.↗
NASA NTRS2002

The Effect of Asymmetric Mechanical and Thermal Loading on Membrane Wrinkling

Large, tensioned membranes are being considered for future gossamer spacecraft systems. Examples include sunshields, solar sails, and membrane optics. In many. cases a relatively flat membrane with minimal wrinkling is desired. Developing methods to predict and measure membrane wrinkling is important to the future development of gossamer spacecraft. Numerical and experimental data are presented for a 0.5 m square, tensioned membrane. The membrane is subjected to symmetric and asymmetric mechanical loading. Data are also presented for a symmetrically loaded membrane subjected to spot heating in the center. The numerical model shows good agreement with the experiment for wrinkle angle data. There is. also reasonable agreement for the wrinkled area for both isothermal and elevated temperature tests.

Blandino, Joseph R.↗
NASA NTRS2003

Membrane-Based Functions in the Origin of Cellular Life

How simple membrane peptides performed such essential proto-cellular functions as transport of ions and organic matter across membranes separating the interior of the cell from the environment, capture and utilization of energy, and transduction of environmental signals, is a key question in protobiological evolution. On the basis of detailed, molecular-level computer simulations we investigate how these peptides insert into membranes, self-assemble into higher-order structures and acquire functions. We have studied the insertion of an a-helical peptide containing leucine (L) and serine (S) of the form (LSLLLSL)S into a model membrane. The transmembrane state is metastable, and approximately 15 kcal/mol is required to insert the peptide into the membrane. Investigations of dimers formed by (LSLLLSL)S and glycophorin A demonstrate how the favorable free energy of helix association can offset the unfavorable free energy of insertion, leading to self- assembly of peptide helices in the membrane. An example of a self-assembled structure is the tetrameric transmembrane pore of the influenza virus M2 protein, which is an efficient and selective voltage-gated proton channel. Our simulations explain the gating mechanism and provide guidelines how to reengineering the channel to act as a simple proton pump. In general, emergence of integral membrane proteins appears to be quite feasible and may be easier to envision than the emergence of water-soluble proteins.

Wilson, Michael A.↗
NASA NTRS2003

Influence of Solutocapillary Convection on Macrovoid Defect Formation in Polymeric Membranes

The focus of this research project involved the dry-cast process for polymeric membrane formation, whereby evaporation of solvent from an initially homogeneous polymer/solvent/ nonsolvent solution results in phase separation and the formation of polymer-rich and polymer-lean phases. Under certain conditions the polymer-lean phase gives rise to very large and usually undesirable, tear-drop-shaped pores (size approx. 10 - 50 microns) termed macrovoids (MVs). Although in many cases the presence of MV pores has deleterious effects on membrane performance, there are a number of innovative applications where the presence of such pores is highly desirable. Although researchers have proposed a variety of mechanisms for MV formation over the past three decades, two main hypotheses are currently favored: one asserts that MV growth can be attributed solely to diffusion (the diffusive growth hypothesis), whereas the other states that solutocapillary convection (the SC hypothesis) at the MV interface contributes to growth. The overall goal of this research was to obtain a more comprehensive understanding of the fundamental mechanism of MV growth. This research incorporates a coupled modeling and experimental approach to test a solutocapillary convection hypothesis for the growth of macrovoid pores in polymeric membranes. Specifically, we utilized a modification of the first principles model developed by two of the PIs (ARG and WBK) for dry-cast CA membranes. For the experimental component, two separate and mutually complementary approaches were used to study MV growth. In the first, membranes cast in a zero-g environment aboard the NASA KC-135 aircraft were compared with those cast on the ground to assess the effect of the buoyancy force on membrane morphology and MV size and shape. In the second approach, videomicroscopy flow visualization (VMFV) was utilized to observe MV formation and growth in real time and to assess the effect of surface tension on the MV growth dynamics. As a result of these fundamental studies, our research group advanced a new hypothesis for MV pore development in polymeric membranes.

Greenberg, Alan R.↗
NASA NTRS2005

A Prototype Actuator Concept for Membrane Boundary Vibration Control

In conjunction with the research in ultra-lightweight deployable spacecraft and membrane structures is an underlying need for shape and vibration control. For thin film membrane structures, fundamental modes of vibration for the membrane can be excited through station keeping, attitude adjustments, orbital maneuvers, or contact with space junk or micrometeorites. In order to maintain structural integrity as well as surface shape contour, which may be essential for inflatable antennas, reflective surfaces, or solar sails; vibration damping is a necessary component. This paper discusses development of an actuator attached at the membrane boundary, containing two types of piezoelectric elements, which can be used to perform active control of vibration from the boundary of a membrane. The actuator is designed to control the membrane out-of-plane displacement and in-plane tension by varying the boundary conditions. Results from an initial experimental evaluation of the concept are presented with bench tests of the actuator alone, and with the actuator connected to a large membrane.

Solter, Micah J.↗
NASA NTRS2007

An Aeroelastic Analysis of a Thin Flexible Membrane

Studies have shown that significant vehicle mass and cost savings are possible with the use of ballutes for aero-capture. Through NASA's In-Space Propulsion program, a preliminary examination of ballute sensitivity to geometry and Reynolds number was conducted, and a single-pass coupling between an aero code and a finite element solver was used to assess the static aeroelastic effects. There remain, however, a variety of open questions regarding the dynamic aeroelastic stability of membrane structures for aero-capture, with the primary challenge being the prediction of the membrane flutter onset. The purpose of this paper is to describe and begin addressing these issues. The paper includes a review of the literature associated with the structural analysis of membranes and membrane utter. Flow/structure analysis coupling and hypersonic flow solver options are also discussed. An approach is proposed for tackling this problem that starts with a relatively simple geometry and develops and evaluates analysis methods and procedures. This preliminary study considers a computationally manageable 2-dimensional problem. The membrane structural models used in the paper include a nonlinear finite-difference model for static and dynamic analysis and a NASTRAN finite element membrane model for nonlinear static and linear normal modes analysis. Both structural models are coupled with a structured compressible flow solver for static aeroelastic analysis. For dynamic aeroelastic analyses, the NASTRAN normal modes are used in the structured compressible flow solver and 3rd order piston theories were used with the finite difference membrane model to simulate utter onset. Results from the various static and dynamic aeroelastic analyses are compared.

Scott, Robert C.↗
NASA NTRS2010

Self-Deployable Membrane Structures

Currently existing approaches for deployment of large, ultra-lightweight gossamer structures in space rely typically upon electromechanical mechanisms and mechanically expandable or inflatable booms for deployment and to maintain them in a fully deployed, operational configuration. These support structures, with the associated deployment mechanisms, launch restraints, inflation systems, and controls, can comprise more than 90 percent of the total mass budget. In addition, they significantly increase the stowage volume, cost, and complexity. A CHEM (cold hibernated elastic memory) membrane structure without any deployable mechanism and support booms/structure is deployed by using shape memory and elastic recovery. The use of CHEM micro-foams reinforced with carbon nanotubes is considered for thin-membrane structure applications. In this advanced structural concept, the CHEM membrane structure is warmed up to allow packaging and stowing prior to launch, and then cooled to induce hibernation of the internal restoring forces. In space, the membrane remembers its original shape and size when warmed up. After the internal restoring forces deploy the structure, it is then cooled to achieve rigidization. For this type of structure, the solar radiation could be utilized as the heat energy used for deployment and space ambient temperature for rigidization. The overall simplicity of the CHEM self-deployable membrane is one of its greatest assets. In present approaches to space-deployable structures, the stow age and deployment are difficult and challenging, and introduce a significant risk, heavy mass, and high cost. Simple procedures provided by CHEM membrane greatly simplify the overall end-to-end process for designing, fabricating, deploying, and rigidizing large structures. The CHEM membrane avoids the complexities associated with other methods for deploying and rigidizing structures by eliminating deployable booms, deployment mechanisms, and inflation and control systems that can use up the majority of the mass budget

Sokolowski, Witold M.↗
NASA NTRS2004

Membrane-Based Water Evaporator for a Space Suit

A membrane-based water evaporator has been developed that is intended to serve as a heat-rejection device for a space suit. This evaporator would replace the current sublimator that is sensitive to contamination of its feedwater. The design of the membrane-based evaporator takes advantage of recent advances in hydrophobic micropore membranes to provide robust heat rejection with much less sensitivity to contamination. The low contamination sensitivity allows use of the heat transport loop as feedwater, eliminating the need for the separate feedwater system used for the sublimator. A cross section of the evaporator is shown in the accompanying figure. The space-suit cooling loop water flows into a distribution plenum, through a narrow annulus lined on both sides with a hydrophobic membrane, into an exit plenum, and returns to the space suit. Two perforated metal tubes encase the membranes and provide structural strength. Evaporation at the membrane inner surface dissipates the waste heat from the space suit. The water vapor passes through the membrane, into a steam duct and is vented to the vacuum environment through a back-pressure valve. The back-pressure setting can be adjusted to regulate the heat-rejection rate and the water outlet temperature.

Ungar, Eugene K.↗
NASA NTRS2016

Advanced Supported Liquid Membranes for Carbon Dioxide Control in Cabin Applications

The development of new, robust, life support systems is critical to NASA's continued progress in space exploration. One vital function is maintaining the carbon dioxide (CO2) concentration in the cabin at levels that do not impair the health or performance of the crew. The CO2 removal assembly (CDRA) is the current CO2 control technology on-board the International Space Station (ISS). Although the CDRA has met the needs of the ISS to date, the repeated cycling of the molecular sieve sorbent causes it to break down into small particles that clog filters or generate dust in the cabin. This reduces reliability and increases maintenance requirements. Another approach that has potential advantages over the current system is a membrane that separates CO2 from air. In this approach, cabin air contacts one side of the membrane while other side of the membrane is maintained at low pressure to create a driving force for CO2 transport across the membrane. In this application, the primary power requirement is for the pump that creates the low pressure and then pumps the CO2 to the oxygen recovery system. For such a membrane to be practical, it must have high CO2 permeation rate and excellent selectivity for CO2 over air. Unfortunately, conventional gas separation membranes do not have adequate CO2 permeability and selectivity to meet the needs of this application. However, the required performance could be obtained with a supported liquid membrane (SLM), which consists of a microporous material filled with a liquid that selectively reacts with CO2 over air. In a recently completed Phase II SBIR project, Reaction Systems, Inc. fabricated an SLM that is very close to meeting permeability and selectivity objectives for use in the advanced space suit portable life support system. This paper describes work carried out to evaluate its potential for use in spacecraft cabin application.

Wickham, David T.↗
NASA NTRS2016

Advanced Supported Liquid Membranes for Carbon Dioxide Control in Cabin Applications

The development of new, robust, life support systems is critical to NASA's continued progress in space exploration. One vital function is maintaining the carbon dioxide (CO2) concentration in the cabin at levels that do not impair the health or performance of the crew. The carbon dioxide removal assembly (CDRA) is the current CO2 control technology on-board the International Space Station (ISS). Although the CDRA has met the needs of the ISS to date, the repeated cycling of the molecular sieve sorbent causes it to break down into small particles that clog filters or generate dust in the cabin. This reduces reliability and increases maintenance requirements. Another approach that has potential advantages over the current system is a membrane that separates CO2 from air. In this approach, cabin air contacts one side of the membrane while other side of the membrane is maintained at low pressure to create a driving force for CO2 transport across the membrane. In this application, the primary power requirement is for the pump that creates the low pressure and then pumps the CO2 to the oxygen recovery system. For such a membrane to be practical, it must have high CO2 permeation rate and excellent selectivity for CO2 over air. Unfortunately, conventional gas separation membranes do not have adequate CO2 permeability and selectivity to meet the needs of this application. However, the required performance could be obtained with a supported liquid membrane (SLM), which consists of a microporous material filled with a liquid that selectively reacts with CO2 over air. In a recently completed Phase II SBIR project, Reaction Systems, Inc. fabricated an SLM that is very close to meeting permeability and selectivity objectives for use in the Portable Life Support System (PLSS). This paper describes work carried out to evaluate its potential for use in the cabin.

Wickham, David T.↗
NASA NTRS2016

Testing of Synthetic Biological Membranes for Forward Osmosis Applications

Commercially available forward osmosis membranes have been extensively tested for human space flight wastewater treatment. Despite the improvements achieved in the last decades, there is still a challenge to produce reliable membranes with anti-fouling properties, chemical resistance, and high flux and selectivity. Synthetic biological membranes that mimic the ones present in nature, which underwent millions of years of evolution, represent a potential solution for further development and progress in membrane technology. Biomimetic forward osmosis membranes based on a polymeric support filter and coated with surfactant multilayers have been engineered to investigate how different manufacturing processes impact the performance and structure of the membrane. However, initial results of the first generation prototype membranes tests reveal a high scatter in the data, due to the current testing apparatus set up. The testing apparatus has been upgraded to improve data collection, reduce errors, and to allow higher control of the testing process.

Forward osmosis↗
NASA NTRS2015

Space Technology Game Changing Development: Synthetic Biological Membrane

The goal of this project is to use synthetic biology techniques to develop biomimetic FO membranes that can self-repair when exposed to chemical and physical damage, as well as radiation and fouling. The self-repair capability is derived from the regenerative characteristics of living systems. Ultimately, this living membrane will be used to extend the operating life and improve the performance of membrane-based life support systems currently being used by NASA.Biological membranes are primarily composed of lipid bilayers. Lipids are organic compounds that, due to their polar hydrophobic fatty acid tails per lipid molecule, are able to self-assemble spontaneously. The lipid bilayer acts as a selective barrier, letting only specific molecules cross the membrane. Recent research into membranes for Next Generation Life Support (NGLS) applications has identified a type of FO membrane that can function as a biomimetic structure.

Flynn, Michael↗
NASA NTRS2003

Intracellular localization of a group II chaperonin indicates a membrane-related function

Chaperonins are protein complexes that are believed to function as part of a protein folding system in the cytoplasm of the cell. We observed, however, that the group II chaperonins known as rosettasomes in the hyperthermophilic archaeon Sulfolobus shibatae, are not cytoplasmic but membrane associated. This association was observed in cultures grown at 60 degrees C and 76 degrees C or heat-shocked at 85 degrees C by using immunofluorescence microscopy and in thick sections of rapidly frozen cells grown at 76 degrees C by using immunogold electron microscopy. We observed that increased abundance of rosettasomes after heat shock correlated with decreased membrane permeability at lethal temperature (92 degrees C). This change in permeability was not seen in cells heat-shocked in the presence of the amino acid analogue azetidine 2-carboxylic acid, indicating functional protein synthesis influences permeability. Azetidine experiments also indicated that observed heat-induced changes in lipid composition in S. shibatae could not account for changes in membrane permeability. Rosettasomes purified from cultures grown at 60 degrees C and 76 degrees C or heat-shocked at 85 degrees C bind to liposomes made from either the bipolar tetraether lipids of Sulfolobus or a variety of artificial lipid mixtures. The presence of rosettasomes did not significantly change the transition temperature of liposomes, as indicated by differential scanning calorimetry, or the proton permeability of liposomes, as indicated by pyranine fluorescence. We propose that these group II chaperonins function as a structural element in the natural membrane based on their intracellular location, the correlation between their functional abundance and membrane permeability, and their potential distribution on the membrane surface.

Cell Membrane/physiology/ultrastructure↗
NASA NTRS1994

Permeability of membranes to amino acids and modified amino acids: mechanisms involved in translocation

The amino acid permeability of membranes is of interest because they are one of the key solutes involved in cell function. Membrane permeability coefficients (P) for amino acid classes, including neutral, polar, hydrophobic, and charged species, have been measured and compared using a variety of techniques. Decreasing lipid chain length increased permeability slightly (5-fold), while variations in pH had only minor effects on the permeability coefficients of the amino acids tested in liposomes. Increasing the membrane surface charge increased the permeability of amino acids of the opposite charge, while increasing the cholesterol content decreased membrane permeability. The permeability coefficients for most amino acids tested were surprisingly similar to those previously measured for monovalent cations such as sodium and potassium (approximately 10(-12)-10(-13) cm s-1). This observation suggests that the permeation rates for the neutral, polar and charged amino acids are controlled by bilayer fluctuations and transient defects, rather than partition coefficients and Born energy barriers. Hydrophobic amino acids were 10(2) more permeable than the hydrophilic forms, reflecting their increased partition coefficient values. External pH had dramatic effects on the permeation rates for the modified amino acid lysine methyl ester in response to transmembrane pH gradients. It was established that lysine methyl ester and other modified short peptides permeate rapidly (P = 10(-2) cm s-1) as neutral (deprotonated) molecules. It was also shown that charge distributions dramatically alter permeation rates for modified di-peptides. These results may relate to the movement of peptides through membranes during protein translocation and to the origin of cellular membrane transport on the early Earth.

Review↗
NASA NTRS1996

Mechanism of unassisted ion transport across membrane bilayers

To establish how charged species move from water to the nonpolar membrane interior and to determine the energetic and structural effects accompanying this process, we performed molecular dynamics simulations of the transport of Na+ and Cl- across a lipid bilayer located between two water lamellae. The total length of molecular dynamics trajectories generated for each ion was 10 ns. Our simulations demonstrate that permeation of ions into the membrane is accompanied by the formation of deep, asymmetric thinning defects in the bilayer, whereby polar lipid head groups and water penetrate the nonpolar membrane interior. Once the ion crosses the midplane of the bilayer the deformation "switches sides"; the initial defect slowly relaxes, and a defect forms in the outgoing side of the bilayer. As a result, the ion remains well solvated during the process; the total number of oxygen atoms from water and lipid head groups in the first solvation shell remains constant. A similar membrane deformation is formed when the ion is instantaneously inserted into the interior of the bilayer. The formation of defects considerably lowers the free energy barrier to transfer of the ion across the bilayer and, consequently, increases the permeabilities of the membrane to ions, compared to the rigid, planar structure, by approximately 14 orders of magnitude. Our results have implications for drug delivery using liposomes and peptide insertion into membranes.

NASA Discipline Exobiology↗
NASA NTRS2006

Dynamic Analysis of Large In-Space Deployable Membrane Antennas

This paper presents a vibration analysis of an eight-meter diameter membrane reflectarray antenna, which is composed of a thin membrane and a deployable frame. This analysis process has two main steps. In the first step, a two-variable-parameter (2-VP) membrane model is developed to determine the in-plane stress distribution of the membrane due to pre-tensioning, which eventually yields the differential stiffness of the membrane. In the second step, the obtained differential stiffness is incorporated in a dynamic equation governing the transverse vibration of the membrane-frame assembly. This dynamic equation is then solved by a semi-analytical method, called the Distributed Transfer Function Method (DTFM), which produces the natural frequencies and mode shapes of the antenna. The combination of the 2-VP model and the DTFM provides an accurate prediction of the in-plane stress distribution and modes of vibration for the antenna.

vibrations↗
NASA NTRS1974

Water vapor diffusion membrane development

The phase separator component used as a membrane in the vapor diffusion process (VRD) for the recovery of potable water from urine on manned space missions of extended duration was investigated, with particular emphasis on cation-selective membranes because of their noted mechanical strength, superior resistance to acids, oxidants, and germicides, and their potential resistance to organic foulants. Two of the membranes were tested for 700 hours continuously, and were selected on the basis of criteria deemed important to an effective water reclamation system onboard spacecraft. The samples of urine were successfully processed by removing 93 percent of their water content in 70 hours using the selected membranes. Pretreatment with an acid-oxidant formulation improved product quality. Cation exchange membranes were shown to possess superior mechanical strength and chemical resistance, as compared to cellulosic membranes.

Tan, M. K.↗