Long-duration Exploration Missions Research Articles

Simulated neutron dose for two cell culture configurations

One of the major hurdles for long duration interplanetary space missions is space radiation-induced carcinogenesis. The need for early identification of relevant biomarkers of elevated space radiation risk is crucial for ensuring the health of astronauts after returning from long-duration exploration missions. The longer the duration of the mission the more the risk of space-radiation induced carcinogenesis increases. It is vital to have an accurate understanding of the absorbed dose to sensitive cells comprising the liver and colon cell models for identifying biomarkers that should be further investigated in more human-like systems exposed to space-like radiation. The specific liver and colon cell lines were chosen to build on previous experience with them, to establish a proof of concept for investigation of individual variability impact on biomarkers. Monte Carlo N-Particle transport code 6.2 was used in the simulation of two-dimensional and three-dimensional cell cultures exposed to deuterium-tritium fusion neutrons. Fast neutrons were chosen as most space neutron dose is delivered by neutrons with energy greater than 100MeV. Deuterium-tritium fusion neutrons posses the greatest possible neutron energy outside of large accelerator facilities. Deuterium-tritium neutron-induced charged particles closely resemble the high-LET portion of the GCR spectrum. The absorbed dose was recorded over the cell layer (target volume) using an F6 tally in MCNP. From foil activation analysis, the experimental source strength of 7.65 × 107 neutrons s−1 was used to determine the absorbed dose rate to the cells which ranged from 4.66 to 4.84 mGy h−1. This simulated dose rate will be used to determine the total dose received by the cells in experiments conducted to identify biomarkers related to increased risk of carcinogenesis from fast neutron exposure.

Potential Biomarkers of Resilience to Microgravity Hazards in Astronauts.

Space exploration exposes astronauts to the unique environment of microgravity, which poses significant health challenges. Identifying biomarkers that can predict an individual's resilience to the stressors of microgravity holds great promise for optimizing astronaut selection and developing personalized countermeasures. This narrative review examines the principal health risks associated with microgravity and explores potential biomarkers indicative of resilience. The biomarkers being evaluated represent a broad spectrum of physiological domains, including musculoskeletal, neurological, immunological, gastrointestinal, cardiovascular, and cutaneous systems. Earth-based microgravity analogs, such as dry immersion and head-down tilt bed rest, may provide valuable platforms to validate candidate biomarkers. However, biomarker sensitivity and specificity must be further evaluated to ensure efficacy and reliability. Establishing a panel of biomarkers predictive of resilience to microgravity-induced health risks would significantly enhance astronaut health and mission success, especially for long-duration exploration missions. Insights gained may also translate to health conditions on Earth characterized by reduced physical activity and mechanical loading.

Selective Serotonin Reuptake Inhibitors and Other Treatment Modalities for Deep Space Missions.

INTRODUCTION: As humankind ventures further into the depths of space, planning is already underway for long-duration exploration missions that will test the bounds of human performance. Deep space travel will include added risk related to stressors from the isolated, confined, and extreme environment that lies outside the boundaries of low Earth orbit. Currently, selective serotonin reuptake inhibitors (SSRIs) are considered the standard of care for many mental health diagnoses, including anxiety and depression; however, SSRIs are also associated with several undesired side effects. The utility of nonpharmacological therapies for the management of behavioral health conditions has not yet been fully explored.METHODS: A comprehensive literature search was performed using PubMed. Relevant articles pertaining to the psychological impacts of isolated, confined, and extreme environments, use of SSRIs in spaceflight, side effects associated with SSRIs, and nonpharmacological treatments for anxiety and depression were reviewed. Over 70 studies were reviewed in total.RESULTS: Reduced bone mineral density, impaired hemostatic function, significant individual variability resulting from gene polymorphisms, and drug-drug interactions are well described adverse effects of SSRIs that may complicate their operational use in the deep space environment. Four alternative therapies for the treatment of anxiety and depression may show promise for long duration missions.DISCUSSION: Although SSRIs have long been considered standard of care treatment for many behavioral health conditions, we cannot trivialize the risk that prolonged pharmacological therapy may pose. The need to mitigate these risks by exploring alternative therapies has never been more relevant.El-Khoury BB, Ray KL, Altchuler SI, Reichard JF, Dukes CH. Selective serotonin reuptake inhibitors and other treatment modalities for deep space missions. Aerosp Med Hum Perform. 2023; 94(11):843-851.

Adequacy of in-mission training to treat tibial shaft fractures in mars analogue testing

Long bone fractures are a concern in long-duration exploration missions (LDEM) where crew autonomy will exceed the current Low Earth Orbit paradigm. Current crew selection assumptions require extensive complete training and competency testing prior to flight for off-nominal situations. Analogue astronauts (n = 6) can be quickly trained to address a single fracture pattern and then competently perform the repair procedure. An easy-to-use external fixation (EZExFix) was employed to repair artificial tibial shaft fractures during an inhabited mission at the Mars Desert Research Station (Utah, USA). Bone repair safety zones were respected (23/24), participants achieved 79.2% repair success, and median completion time was 50.04 min. Just-in-time training in-mission was sufficient to become autonomous without pre-mission medical/surgical/mechanical education, regardless of learning conditions (p > 0.05). Similar techniques could be used in LDEM to increase astronauts’ autonomy in traumatic injury treatment and lower skill competency requirements used in crew selection.

Enabling astronaut self-scheduling using a robust advanced modelling and scheduling system: An assessment during a Mars analogue mission

Human long duration exploration missions (LDEMs) raise a number of technological challenges. This paper addresses the question of the crew autonomy: as the distances increase, the communication delays and constraints tend to prevent the astronauts from being monitored and supported by a real time ground control. Eventually, future planetary missions will necessarily require a form of astronaut self-scheduling. We study the usage of a computer decision-support tool by a crew of analog astronauts, during a Mars simulation mission conducted at the Mars Desert Research Station (MDRS, Mars Society) in Utah. The proposed tool, called Romie, belongs to the new category of Robust Advanced Modelling and Scheduling (RAMS) systems. It allows the crew members (i) to visually model their scientific objectives and constraints, (ii) to compute near-optimal operational schedules while taking uncertainty into account, (iii) to monitor the execution of past and current activities, and (iv) to modify scientific objectives/constraints w.r.t. unforeseen events and opportunistic science. In this study, we empirically measure how the astronauts, who are novice planners, perform at using such a tool when self-scheduling under the realistic assumptions of a simulated Martian planetary habitat.

Effect of Explanations in AI-Assisted Anomaly Treatment for Human Spaceflight Missions

Artificial Intelligence (AI) agents have the potential to play a critical role in human spaceflight by being the first point of contact for astronauts during emergencies in a long duration spaceflight mission, when communication delays with the Mission Control Crew (MCC) become longer and more frequent. Sharing some of tasks done by the MCC with an on-board AI agent that can provide assistance with treating in-flight anomalies gives the crew more autonomy and allows them to respond faster and more safely to emergencies, or focus on other critical aspects of their mission. For this technology to succeed in this role, providing accurate diagnoses for the anomalies encountered is obviously important. However, providing explanations for those recommendations may also be a critical factor to help establish trust and increase the likelihood of the crew actually following the agent’s recommendations. This paper evaluates the effects of explanations on crew performance, trust in automation, mental workload, and situational awareness in the context of anomaly resolution tasks. We conduct a study where subjects subjects work with the AI agent on various simulated anomaly scenarios. They are provided by the agent with a diagnosis and recommendation with no explanations in one session and with explanations for its diagnosis in the other session. We measure the effects of the explanations on Trust in Automation, Situational Awareness, Performance, and Workload. We discuss our findings and provide design recommendations for AI agents in the context of anomaly treatment in Long Duration Exploration Missions (LDEM).

The impact of digital scents on behavioral health in a restorative virtual reality environment

Astronauts on long-duration missions are at an increased risk of developing adverse behavioral conditions due to prolonged periods in isolated, confined, and extreme (ICE) environments. Sleep loss, sensory deprivation and monotony, and loss in social connectedness can further exacerbate their conditions and decrement performance, thus jeopardizing mission success. Future missions will require crews to travel distances that make current countermeasures increasingly difficult, as they rely on proximity to Earth. We have developed a multi-sensory virtual reality (VR) environment as a potential tool to maintain the long-term behavioral health of astronauts. We conducted a within-subjects study (N = 10) to compare the effectiveness of our VR environment with and without the incorporation of digital scents. Prior to the VR experience, subjects completed a public speaking task to elevate stress levels and emulate the stressful conditions that astronauts might encounter on a mission. The virtual nature environment features a small, forested area with localized scents that are dispersed based on the user's location in the VR environment. For example, floral scents were emitted when the user was near the field of flowers. The Positive and Negative Affect Schedule (PANAS) and the 6-item State-Trait Anxiety Inventory (STAI-6) questionnaires were administered to record subjective data on the participant's state affect and anxiety throughout the experiment. Participants reported significantly lower STAI-6 scores after the VR experience when scents were present than in the control condition (p = 0.03). Compared to the stressed state, PANAS Negative Affect (p = 0.003) and STAI-6 (p = 0.001) scores decreased after the VR with scents condition. STAI-6 scores (p = 0.013) also decreased from baseline when olfactory stimuli were added. These results suggest that the addition of olfactory stimuli to the VR environment aided in reducing negative affect and state anxiety levels. In addition, our results indicate that the use of multisensory VR environments are a promising countermeasure to support behavioral health during long-duration exploration missions.

Isolation and confinement due to the COVID-19 pandemic: Lessons for human spaceflight

BackgroundAstronauts live and work in isolated, confined, extreme (ICE) environments that create both high stress and the need for high performance. The COVID-19 pandemic created ICE-like conditions across the globe by confining people to their homes under the ever-present threat of disease. Our goal is to understand the impact of prior experience in ICE on coping, using the pandemic as a pseudo space analog environment. MethodsWe administered a survey three times with 7 days between administrations. A total of 82 participants completed all three survey sessions, and these participants were divided into three groups for analysis. The first group is those with prior experience in an ICE environment (n = 17; 7F/10 M), the second is those aged 30–55 with a master's or doctoral degree and without prior experience (n = 22; 10F/12 M), and the third is the general population (n = 43; 27F/16 M). Linear mixed models were used for statistical analysis of the results, given the unequal sample sizes. ResultsThe experienced group did not show healthier mental health scores than the astronaut-like group, but both groups displayed higher scores than the general population. However, work productivity scores for the experienced group were higher on average than the other two groups. DiscussionResults suggest that prior experience in ICE may improve the capability to maintain productivity—corresponding to the idea of resilience. However, experience may not improve mental health maintenance, suggesting that other approaches are needed to prepare astronauts for the mental health stressors of long-duration exploration missions.

Assessment of Spaceflight Medical Conditions’ and Treatments’ Potential Impacts on Behavioral Health and Performance

Long-duration space exploration missions will pose significant risks to the physical and behavioral health and performance of the crew. We documented the presence and frequency of (1) behavioral health and performance (BHP)-relevant symptoms for each condition in NASA's Exploration Medical Conditions List (EMCL), (2) the BHP-relevant effects of applicable medical treatments in the current International Space Station (ISS) On-Orbit Medication List, (3) the breadth of potential BHP impacts of spaceflight medical treatments, and (4) the likelihood of adverse BHP effects of treating spaceflight medical conditions. BHP symptoms and effects were categorized by the six neurobehavioral domains of the National Institute of Mental Health's Research Domain Criteria (RDoC) framework. Including the cognitive effects of acute and chronic pain (e.g., attention, memory), 94% of spaceflight medical conditions include symptoms relevant to Cognitive Systems (e.g., attention deficits, confusion, psychosis), 36% include symptoms relevant to Negative Valence Systems (e.g., anxiety), 32% include symptoms relevant to Arousal and Regulatory Systems (e.g., sleep disturbances), 22% include symptoms relevant to Sensorimotor Systems (e.g., dizziness), 19% include symptoms relevant to Positive Valence Systems (e.g., mania), and 11% include symptoms relevant to Social Processes (e.g., social withdrawal). Only 2% of spaceflight medical conditions have no documented BHP symptoms. Of the spaceflight medical treatments, 63% affect Arousal and Regulatory Systems, 60% affect Sensorimotor Systems, 59% affect Cognitive Systems, 53% affect Negative Valence Systems, 38% affect Positive Valence Systems, and 31% affect Social Processes. The breadth of potential BHP impacts was bimodal, in that 27% of spaceflight medical treatments had no documented BHP effects; however, 27% of treatments may produce adverse effects across all six neurobehavioral domains. Historical prevalence data on medical conditions, symptoms, and complaints from 14 years of International Space Station operations coupled with documented BHP effects of recommended treatments indicates the potential for up to 481 adverse BHP effects of spaceflight medical treatments per person-year. Assessing the potential BHP impacts of spaceflight medical conditions and their treatments highlights the interactive nature of operational risks, and can provide an enhanced evidence base to support integrated research and countermeasure development strategies for long-duration exploration missions.

Designing Procedure Execution Tools with Emerging Technologies for Future Astronauts

NASA’s human spaceflight efforts are moving towards long-duration exploration missions requiring asynchronous communication between onboard crew and an increasingly remote ground support. In current missions aboard the International Space Station, there is a near real-time communication loop between Mission Control Center and astronauts. This communication is essential today to support operations, maintenance, and science requirements onboard, without which many tasks would no longer be feasible. As NASA takes the next leap into a new era of human space exploration, new methods and tools compensating for the lack of continuous, real-time communication must be explored. The Human-Computer Interaction Group at NASA Ames Research Center has been investigating emerging technologies and their applicability to increase crew autonomy in missions beyond low Earth orbit. Interactions using augmented reality and the Internet of Things have been researched as possibilities to facilitate usability within procedure execution operations. This paper outlines four research efforts that included technology demonstrations and usability studies with prototype procedure tools implementing emerging technologies. The studies address habitat feedback integration, analogous procedure testing, task completion management, and crew training. Through these technology demonstrations and usability studies, we find that low- to medium-fidelity prototypes, evaluated early in the design process, are both effective for garnering stakeholder buy-in and developing requirements for future systems. In this paper, we present the findings of the usability studies for each project and discuss ways in which these emerging technologies can be integrated into future human spaceflight operations.

Wearable 3-Lead Electrocardiogram Placement Model for Fleet Sizing of Medical Devices.

BACKGROUND: Electrocardiography (ECG) provides valuable information on astronaut physiological and psychological health. ECG monitoring has been conducted during crewed missions since the beginning of human spaceflight and will continue during astronauts upcoming long-duration exploration missions (LDEMs) in support of automated health monitoring systems. ECG monitoring is traditionally performed in clinical environments with single-use, adhesive electrodes in a 3, 6, or 12-lead configuration placed by a trained clinician. In the space exploration environment, astronauts self-place electrodes without professional assistance. Wearable ECG systems are an attractive option for automated health monitoring, but electrode placement has not been quantified to a high enough degree to avoid artifacts within the data due to position changes. This variability presents challenges for physician-limited, autonomous health monitoring, so quantifying electrode placement is key in the development of reliable, wearable ECG monitoring systems.METHODS: We present a method of quantifying electrode placement for 3-lead, chest-mounted ECG using easy-to-measure, two-dimensional chest measurements.RESULTS: We find that male and female dimensions require different electrode positioning computations, but there is overlap in positioning between men and women. The distribution of electrodes vertical positions is wider than their horizontal positions.DISCUSSION: These results can be translated directly to ECG wearable design for the individual and for the size range and adjustability required for the astronaut fleet. Implementation of this method will improve the reliability in placement and fit of future wearables, increasing comfort and usability of these systems and subsequently augmenting autonomous health monitoring capabilities for exploration medicine.Arquilla K, Leary S, Webb AK, Anderson AP. Wearable 3-lead electrocardiogram placement model for fleet sizing of medical devices. Aerosp Med Hum Perform. 2020; 91(11):868875.

Communication in the Spaceflight Multi-Team System: Training and Technology Recommendations to Support Boundary Spanners

Long-duration exploration missions (LDEMs) in space rely on the coordinated efforts of a large, dynamic, and global multi-team system (MTS) that crosses organizational, geographic, cultural, and temporal boundaries. A key role in the spaceflight MTS is the leader who connects or spans the boundaries between distinct teams and supports the development of team cognition. The purpose of the present paper is to provide recommendations on how to train “boundary spanner” leaders and the tools they use to coordinate and communicate with teams in the context of a LDEM MTS. To this end, we address four specific questions focused on 1) how the MTS will change for future missions, 2) identifying the primary boundary spanners, 3) identifying the key attitudes, behaviors, and cognitions (ABCs) for effective boundary spanners, and 4) communication technologies to support the development of team cognition in the MTS. Results indicate six critical boundary spanner roles in the NASA Mission Control Center and 12 ABCs that should be trained. We conclude with concrete recommendations for NASA and its partners to empirically test different training approaches and commercial task management tools the MTS can use to improve communication efficiency and accuracy.

Segmental interpolating spectra for solar particle events and in situ validation

It is a delicate task to accurately assess the impact of solar particle events (SPEs) on future long-duration human exploration missions. In the past, researchers have used several functional forms to fit satellite data for radiation exposure estimation. In this work we present a segmental power law interpolating algorithm to stream satellite data and get time series of proton spectra, which can be used to derive dosimetric quantities for any short period during which a single SPE or multiple SPEs occur. Directly using the corrected High Energy Proton and Alpha Detector fluxes of GOES, this method interpolates the intensity spectrum of a typical SPE to hundreds of MeV and extrapolates to the GeV level as long as sufficient particles are recorded in the high-energy sensors. The high-energy branch of the May 2012 SPE is consistent with the Band functional fitting, which is calibrated with ground level measurement. Modeling simulations indicate that the input spectrum of an SPE beyond 100 MeV is the major contributor for dose estimation behind the normal shielding thickness of spacecraft. Applying this method to the three SPEs that occurred in 2012 generates results consistent with two sets of in situ measurements, demonstrating that this approach could be a way to perform real-time dose estimation. This work also indicates that the galactic cosmic ray dose rate is important for accurately modeling the temporal profile of radiation exposure during an SPE.

Lessons from a Space Analog on Adaptation for Long-Duration Exploration Missions.

Exploration missions to asteroids and Mars will bring new challenges associated with communication delays and more autonomy for crews. Mission safety and success will rely on how well the entire system, from technology to the human elements, is adaptable and resilient to disruptive, novel, or potentially catastrophic events. The recent NASA Extreme Environment Missions Operations (NEEMO) 20 mission highlighted this need and produced valuable "lessons learned" that will inform future research on team adaptation and resilience. A team of NASA, industry, and academic members used an iterative process to design a tripod shaped structure, called the CORAL Tower, for two astronauts to assemble underwater with minimal tools. The team also developed assembly procedures, administered training to the crew, and provided support during the mission. During the design, training, and assembly of the Tower, the team learned first-hand how adaptation in extreme environments depends on incremental testing, thorough procedures and contingency plans that predict possible failure scenarios, and effective team adaptation and resiliency for the crew and support personnel. Findings from NEEMO 20 provide direction on the design and testing process for future space systems and crews to maximize adaptation. This experience also underscored the need for more research on team adaptation, particularly how input and process factors affect adaption outcomes, the team adaptation iterative process, and new ways to measure the adaptation process.

Chemical Potency and Degradation Products of Medications Stored Over 550 Earth Days at the International Space Station.

Medications degrade over time, and degradation is hastened by extreme storage conditions. Current procedures ensure that medications aboard the International Space Station (ISS) are restocked before their expiration dates, but resupply may not be possible on future long-duration exploration missions. For this reason, medications stored on the ISS were returned to Earth for analysis. This was an opportunistic, observational pilot-scale investigation to test the hypothesis that ISS-aging does not cause unusual degradation. Nine medications were analyzed for active pharmaceutical ingredient (API) content and degradant amounts; results were compared to 2012 United States Pharmacopeia (USP) requirements. The medications were two sleep aids, two antihistamines/decongestants, three pain relievers, an antidiarrheal, and an alertness medication. Because the samples were obtained opportunistically from unused medical supplies, each medication was available at only 1 time point and no control samples (samples aged for a similar period on Earth) were available. One medication met USP requirements 5months after its expiration date. Four of the nine (44% of those tested) medications tested met USP requirements 8months post expiration. Another three medications (33%) met USP guidelines 2-3months before expiration. One compound, a dietary supplement used as a sleep aid, failed to meet USP requirements at 11months post expiration. No unusual degradation products were identified. Limited, evidence-based extension of medication shelf-lives may be possible and would be useful in preparation for lengthy exploration missions. Only analysis of flight-aged samples compared to appropriately matched ground controls will permit determination of the spaceflight environment on medication stability.

Over-Expression of FT1 in Plum (Prunus domestica) Results in Phenotypes Compatible with Spaceflight: A Potential New Candidate Crop for Bioregenerative Life Support Systems

ABSTRACT Tree fruits (e.g., apples, plums, cherries) are appealing constituents of a crew menu for long-duration exploration missions (i.e., Mars), both in terms of their nutritive and menu diversity contributions. Although appealing, tree fruit species have long been precluded as candidate crops for use in plant-based bioregenerative life support system designs based on their large crown architecture, prolonged juvenile phase, and phenological constraints. Recent advances by researchers at the United States Department of Agriculture (USDA) have led to the development of plum (Prunus domestica) trees ectopically over-expressing the Flowering Locus T-1 (FT1) gene from Populus trichocarpa (poplar). The transformed plants exhibit atypical phenotypes that seemingly eliminate the aforementioned obstacles to spaceflight. Here we demonstrate the FT1 expression system (FasTrack) and the resultant dwarf growth habits, early flowering, and continuous fruit production. The potential contribution of P. domestica as a countermeasure to microgravity-induced bone loss is also discussed.

Individual Differences in Attentional Deficits and Dopaminergic Protein Levels following Exposure to Proton Radiation

To assess the possible neurobehavioral performance risks to astronauts from living in a space radiation environment during long-duration exploration missions, the effects of head-only proton irradiation (150 MeV/n) at low levels (25-50 cGy, approximating an astronaut's exposure during a 2-year planetary mission) were examined in adult male Long-Evans rats performing an analog of the human psychomotor vigilance test (PVT). The rodent version of PVT or rPVT tracks performance variables analogous to the human PVT, including selective attention/inattention, inhibitory control ("impulsivity") and psychomotor speed. Exposure to head-only proton radiation (25, 50, 100 or 200 cGy) disrupted rPVT performance (i.e., decreased accuracy, increased premature responding, elevated lapses in attention and slowed reaction times) over the 250 day testing period. However, the performance decrements only occurred in a subgroup of animals at each exposure level, that is, the severity of the rPVT performance deficit was unrelated to proton exposure level. Analysis of brain tissue from irradiated and control rats indicated that only rats with rPVT performance deficits displayed changes in the levels of the dopamine transporter and, to a lesser extent, the D₂ receptor. Additional animals trained to perform a line discrimination task measuring basic and reversal learning showed no behavioral effects over the same exposure levels, suggesting a specificity of the proton exposure effects to attentional deficits and supporting the rPVT as a sensitive neurobehavioral assay.

NASA’s Human System Risk Management Approach and Its Applicability to Commercial Spaceflight

As planning continues for commercial spaceflight, attention is turned to NASA to assess whether its human system risk management approach can be applied to mitigate the risks associated with commercial suborbital and orbital flights. NASA uses a variety of methods to assess the risks to the human system based on their likelihood and consequences. In this article, we review these methods and categorize the risks in the system as "definite," "possible," or "least" concern for commercial spaceflight. As with career astronauts, these risks will be primarily mitigated by screening and environmental control. Despite its focus on long-duration exploration missions, NASA's human system risk management approach can serve as a preliminary knowledge base to help medical planners prepare for commercial spaceflights.

Transforming the operations paradigm of space exploration

The international space community has become comfortable over the years with a model of operations based on verbal delegation of operations control from a mission control center based on Earth. This model requires near-constant telemetry regarding the status of the vehicle, as well as tasks on-board. The future long-duration exploration missions being considered will require significant changes in this operational paradigm, adjusting to situational realities, capitalizing on the evolution that has occurred in vehicle autonomous health management, and maximizing the time crew members can devote to exploration.

Surface Modification Technologies for Durable Space Polymers

AbstractMany polymers, paints, and organic-based materials exposed to the space environment undergo dramatic changes and irreversible degradation of physical and functional characteristics. While many protective approaches, including protective coatings and mechanical metal foil wrapping or cladding—especially for synthesized bulk materials, are used to reduce the effects of the space environment, the protection of such materials in space remains a major challenge, especially for future long-duration exploration missions or permanent space stations. In addition to the traditional approaches, surface modification processes are used increasingly to protect or to impart new properties to materials used in the space environment. This article presents a brief overview of the present situation in the field of surface modification of space materials. A number of surface modification solutions that differ from the traditional protective coating approaches are discussed that change the surface properties of treated materials, thus protecting them from the hazards of low Earth orbit and geostationary orbit environments or imparting new functional properties. Examples of their testing, characterization, and applications are provided.