Enhanced formation of methane hydrate from active ice with high gas uptake.

Gas hydrates provide alternative solutions for gas storage & transportation and gas separation. However, slow formation rate of clathrate hydrate has hindered their commercial development. Here we report a form of porous ice containing an unfrozen solution layer of sodium dodecyl sulfate, here named active ice, which can significantly accelerate gas hydrate formation while generating little heat. It can be readily produced via forming gas hydrates with water containing very low dosage (0.06 wt% or 600 ppm) of surfactant like sodium dodecyl sulfate and dissociating it below the ice point, or by simply mixing ice powder or natural snow with the surfactant. We prove that the active ice can rapidly store gas with high storage capacity up to 185 Vg Vw-1 with heat release of ~18 kJ mol-1 CH4 and the active ice can be easily regenerated by depressurization below the ice point. The active ice undergoes cyclic ice-hydrate-ice phase changes during gas uptake/release, thus removing most critical drawbacks of hydrate-based technologies. Our work provides a green and economic approach to gas storage and gas separation and paves the way to industrial application of hydrate-based technologies.

Study on acoustic properties of hydrate-bearing sediments with reconstructed CO2 hydrate in different layers during CH4 hydrate mining.

Natural gas hydrate (NGH), a clean energy source with huge reserves in nature, and its safe and efficient exploitation fits perfectly with the UN Sustainable Development Goals (SDG-7). However, large-scale NGH decomposition frequently results in subsea landslides, reservoir subsidence, and collapse. In this work, in order to achieve safe and efficient exploitation of NGHs, the stability variation of different reservoir layers by depressurization/intermittent CO2/N2 injection (80:20 mol%, 50:50 mol%) was investigated using acoustic properties (P-wave velocity, elastic modulus), as well as reservoir subsidence under an overburden stress of 10 MPa. The P-wave velocity increased from 1282 m/s to 2778 m/s in the above-reservoir and from 1266 m/s to 2564 m/s in the below-reservoir, significantly increasing reservoir strength after CO2 hydrate formation. The P-wave velocity and elastic modulus in the top reconstructed reservoir were continually decreased by the shear damage of the overlying stress, while they remained stable in the bottom reconstructed reservoir during hydrate mining. However, due to superior pressure-bearing ability of the top CO2 hydrate reservoir, which was lacking in the bottom CO2 hydrate reservoir, the reservoir subsidence was relieved greatly. Despite the stiffness strength of reconstructed reservoir was ensured with CO2/N2 sweeping, the skeletal structure of CH4 hydrate reservoir was destroyed, and only the formation of CO2 hydrate could guarantee the stability of P-wave velocity and elastic modulus which was most beneficial to relieve reservoir subsidence. A large amount of CO2 was used in reservoir reconstruction and CH4 hydrate mining, which achieved the geological storage of CO2 (SDG-13). This work provided a new idea for safe and efficient NGHs mining in the future, and the application of acoustic properties served as a guide for the efficient construction of reconstructed reservoirs and offers credible technical assistance for safe exploitation of NGHs.

Tenofovir Alafenamide for Pregnant Chinese Women With Active Chronic Hepatitis B: A Multicenter Prospective Study.

BACKGROUND & AIMS: Data on long-term tenofovir alafenamide (TAF) therapy for pregnant women with active chronic hepatitis B (CHB) (immune clearance and reactivation phases, currently and previously diagnosed) and their infants are lacking. METHODS: Pregnant women with active CHB treated with TAF and tenofovir disoproxil fumarate (TDF) were enrolled in this multicenter prospective study, and infants received immunoprophylaxis. The primary outcomes were rates of adverse (safety) events in pregnant women and defects in infants and fetuses. The secondary outcomes were virologic responses in pregnant women, infants' safety, hepatitis B surface antigen (HBsAg) status, and growth conditions. RESULTS: One hundred three and 104 pregnant women were enrolled and 102 and 104 infants were born in the TAF and TDF groups, respectively. In the TAF group, the mean age, gestational age, alanine aminotransferase level, and viral loads at treatment initiation were 29.3 years, 1.3 weeks, 122.2 U/L, and 5.1 log10 IU/mL, respectively. TAF was well-tolerated, and the most common adverse event was nausea (29.1%) during a mean of 2 years of treatment. Notably, 1 (1.0%) TAF-treated pregnant woman underwent induced abortion due to noncausal fetal cleft lip and palate. No infants in either group had birth defects. In the TAF group, the hepatitis B e antigen seroconversion rate was 20.7% at postpartum month 6, infants had normal growth parameters, and no infants were positive for HBsAg at 7 months. The TDF group had comparable safety and effectiveness profiles. CONCLUSIONS: TAF administered throughout or beginning in early pregnancy is generally safe and effective for pregnant women with active CHB and their infants.

Hyperspectral interference tomography of nacre.

Structural characterization of biologically formed materials is essential for understanding biological phenomena and their enviro-nment, and for generating new bio-inspired engineering concepts. For example, nacre-the inner lining of some mollusk shells-encodes local environmental conditions throughout its formation and has exceptional strength due to its nanoscale brick-and-mortar structure. This layered structure, comprising alternating transparent aragonite (CaCO3) tablets and thinner organic polymer layers, also results in stunning interference colors. Existing methods of structural characterization of nacre rely on some form of cross-sectional analysis, such as scanning or transmission electron microscopy or polarization-dependent imaging contrast (PIC) mapping. However, these techniques are destructive and too time- and resource-intensive to analyze large sample areas. Here, we present an all-optical, rapid, and nondestructive imaging technique-hyperspectral interference tomography (HIT)-to spatially map the structural parameters of nacre and other disordered layered materials. We combined hyperspectral imaging with optical-interference modeling to infer the mean tablet thickness and its disorder in nacre across entire mollusk shells from red and rainbow abalone (Haliotis rufescens and Haliotis iris) at various stages of development. We observed that in red abalone, unexpectedly, nacre tablet thickness decreases with age of the mollusk, despite roughly similar appearance of nacre at all ages and positions in the shell. Our rapid, inexpensive, and nondestructive method can be readily applied to in-field studies.

Tenofovir Alafenamide to Prevent Perinatal Hepatitis B Transmission: A Multicenter, Prospective, Observational Study.

BACKGROUND: Few safety and effectiveness results have been published regarding the administration of tenofovir alafenamide fumarate (TAF) during pregnancy for the prevention of mother-to-child transmission (MTCT) of hepatitis B virus (HBV). METHODS: In this multicenter prospective observational study, pregnant women with HBV DNA levels higher than 200 000 IU/mL who received TAF or tenofovir disoproxil fumarate (TDF) from gestational weeks 24-35 to delivery were 1:1 enrolled and followed until postpartum month 6. Infants received immunoprophylaxis. The primary endpoint was the safety of mothers and infants. The secondary endpoint was the hepatitis B surface antigen (HBsAg)-positive rate at 7 months for infants. RESULTS: In total, 116 and 116 mothers were enrolled, and 117 and 116 infants were born, in the TAF and TDF groups, respectively. TAF was well tolerated during a mean treatment duration of 11.0 weeks. The most common maternal adverse event was nausea (19.0%). One (0.9%), 3 (2.6%), and 9 (7.8%) mothers had abnormal alanine aminotransferase levels at delivery and at postpartum months 3 and 6, respectively. The TDF group had safety profiles that were comparable to those of the TAF group. No infants had birth defects in either group. The infants' physical and neurological development at birth and at 7 months in the TAF group were comparable with those in the TDF group. The HBsAg positive rate was 0% at 7 months in all 233 infants. CONCLUSIONS: Antiviral prophylaxis with TAF was determined to be generally safe for both mothers and infants and reduced the MTCT rate to 0%.

X-ray linear dichroic ptychography.

Biominerals such as seashells, coral skeletons, bone, and tooth enamel are optically anisotropic crystalline materials with unique nanoscale and microscale organization that translates into exceptional macroscopic mechanical properties, providing inspiration for engineering new and superior biomimetic structures. Using Seriatopora aculeata coral skeleton as a model, here, we experimentally demonstrate X-ray linear dichroic ptychography and map the c-axis orientations of the aragonite (CaCO3) crystals. Linear dichroic phase imaging at the oxygen K-edge energy shows strong polarization-dependent contrast and reveals the presence of both narrow (<35°) and wide (>35°) c-axis angular spread in the coral samples. These X-ray ptychography results are corroborated by four-dimensional (4D) scanning transmission electron microscopy (STEM) on the same samples. Evidence of co-oriented, but disconnected, corallite subdomains indicates jagged crystal boundaries consistent with formation by amorphous nanoparticle attachment. We expect that the combination of X-ray linear dichroic ptychography and 4D STEM could be an important multimodal tool to study nano-crystallites, interfaces, nucleation, and mineral growth of optically anisotropic materials at multiple length scales.

Crystal nucleation and growth of spherulites demonstrated by coral skeletons and phase-field simulations.

Spherulites are radial distributions of acicular crystals, common in biogenic, geologic, and synthetic systems, yet exactly how spherulitic crystals nucleate and grow is still poorly understood. To investigate these processes in more detail, we chose scleractinian corals as a model system, because they are well known to form their skeletons from aragonite (CaCO3) spherulites, and because a comparative study of crystal structures across coral species has not been performed previously. We observed that all 12 diverse coral species analyzed here exhibit plumose spherulites in their skeletons, with well-defined centers of calcification (CoCs), and crystalline fibers radiating from them. In 7 of the 12 species, we observed a skeletal structural motif not observed previously: randomly oriented, equant crystals, which we termed "sprinkles". In Acropora pharaonis, these sprinkles are localized at the CoCs, while in 6 other species, sprinkles are either layered at the growth front (GF) of the spherulites, or randomly distributed. At the nano- and micro-scale, coral skeletons fill space as much as single crystals of aragonite. Based on these observations, we tentatively propose a spherulite formation mechanism in which growth front nucleation (GFN) of randomly oriented sprinkles, competition for space, and coarsening produce spherulites, rather than the previously assumed slightly misoriented nucleations termed "non-crystallographic branching". Phase-field simulations support this mechanism, and, using a minimal set of thermodynamic parameters, are able to reproduce all of the microstructural variation observed experimentally in all of the investigated coral skeletons. Beyond coral skeletons, other spherulitic systems, from aspirin to semicrystalline polymers and chocolate, may also form according to the mechanism for spherulite formation proposed here. STATEMENT OF SIGNIFICANCE: Understanding the fundamental mechanisms of spherulite nucleation and growth has broad ranging applications in the fields of metallurgy, polymers, food science, and pharmaceutical production. Using the skeletons of reef-building corals as a model system for investigating these processes, we propose a new spherulite growth mechanism that can not only explain the micro-structural diversity observed in distantly related coral species, but may point to a universal growth mechanism in a wide range of biologically and technologically relevant spherulitic materials systems.

From particle attachment to space-filling coral skeletons.

Reef-building corals and their aragonite (CaCO3) skeletons support entire reef ecosystems, yet their formation mechanism is poorly understood. Here we used synchrotron spectromicroscopy to observe the nanoscale mineralogy of fresh, forming skeletons from six species spanning all reef-forming coral morphologies: Branching, encrusting, massive, and table. In all species, hydrated and anhydrous amorphous calcium carbonate nanoparticles were precursors for skeletal growth, as previously observed in a single species. The amorphous precursors here were observed in tissue, between tissue and skeleton, and at growth fronts of the skeleton, within a low-density nano- or microporous layer varying in thickness from 7 to 20 µm. Brunauer-Emmett-Teller measurements, however, indicated that the mature skeletons at the microscale were space-filling, comparable to single crystals of geologic aragonite. Nanoparticles alone can never fill space completely, thus ion-by-ion filling must be invoked to fill interstitial pores. Such ion-by-ion diffusion and attachment may occur from the supersaturated calcifying fluid known to exist in corals, or from a dense liquid precursor, observed in synthetic systems but never in biogenic ones. Concomitant particle attachment and ion-by-ion filling was previously observed in synthetic calcite rhombohedra, but never in aragonite pseudohexagonal prisms, synthetic or biogenic, as observed here. Models for biomineral growth, isotope incorporation, and coral skeletons' resilience to ocean warming and acidification must take into account the dual formation mechanism, including particle attachment and ion-by-ion space filling.

Biomineral armor in leaf-cutter ants.

Although calcareous anatomical structures have evolved in diverse animal groups, such structures have been unknown in insects. Here, we report the discovery of high-magnesium calcite [CaMg(CO3)2] armor overlaying the exoskeletons of major workers of the leaf-cutter ant Acromyrmex echinatior. Live-rearing and in vitro synthesis experiments indicate that the biomineral layer accumulates rapidly as ant workers mature, that the layer is continuously distributed, covering nearly the entire integument, and that the ant epicuticle catalyzes biomineral nucleation and growth. In situ nanoindentation demonstrates that the biomineral layer significantly hardens the exoskeleton. Increased survival of ant workers with biomineralized exoskeletons during aggressive encounters with other ants and reduced infection by entomopathogenic fungi demonstrate the protective role of the biomineral layer. The discovery of biogenic high-magnesium calcite in the relatively well-studied leaf-cutting ants suggests that calcareous biominerals enriched in magnesium may be more common in metazoans than previously recognized.

Short-term Peginterferon-Induced High Functional Cure Rate in Inactive Chronic Hepatitis B Virus Carriers With Low Surface Antigen Levels.

BACKGROUND: None of the current guidelines recommend antiviral therapy for inactive hepatitis B virus (HBV) carriers (IHCs). METHODS: In this real-world, multicenter, nonrandomized study, 32 participants meeting the inclusion criteria were enrolled 1:1 for treatment with peginterferon α-2b or monitoring without treatment based on participant preference. The expected treatment duration was 48 weeks. The primary end point was hepatitis B surface antigen (HBsAg) loss. The HBV vaccine could be injected after HBsAg loss. RESULTS: All patients had HBsAg levels of <20 IU/mL. The mean baseline HBsAg levels were 6.6 IU/mL and 5.8 IU/mL in the treated and untreated groups, respectively. Fifteen (93.8%) participants achieved HBsAg loss, 5 obtained HBsAg seroconversion after undergoing a mean of 19.7 weeks of therapy in the treated group, and no one in the follow-up group achieved HBsAg loss during a mean follow-up time of 12.6 months (P < .0001). Generally, the therapy was well tolerated. Nine of 11 individuals who exhibited HBsAg loss benefited from receiving the HBV vaccine. CONCLUSIONS: This study provides justification for further studies of short-course peginterferon α-2b for the functional cure of IHCs with low HBsAg levels. Additionally, HBV vaccine injection is beneficial after interferon-induced HBsAg loss.

Adsorption-Hydration Sequence Method for Methane Storage in Porous Material Slurry.

Porous materials are deemed to be capable for promoting hydrate formation, while for the purpose of hydrate-based gas storage, those systems containing porous materials often cannot meet the requirement of high storage density. To increase the storage density, an adsorption-hydration sequence method was designed and systematically examined in this study. Methane storage and release in ZIF-8 slurries and fixed beds were investigated. The ZIF-8 retained 98.62%, while the activated carbon lost 62.17% of their adsorption capacities in slurry. In ZIF-8 fixed beds, methane storage density of 127.41 V/Vbed was acquired, while the gas loss during depressurization accounted for 21.50% of the gas uptake. In the ZIF-8 slurry, the storage density was effectively increased with the adsorption-hydration sequence method, and the gas loss during depressurization was much smaller than that in fixed beds. In the slurry, the gas uptake and gas loss decreased with the decrease of the chilling temperature. The largest gas uptake and storage density of 78.84 mmol and 133.59 V/Vbed were acquired in the slurry with ZIF-8 content of 40 wt.% at 268.15 K, meanwhile, the gas loss just accounted for 14.04% of the gas uptake. Self-preservation effect was observed in the slurry, and the temperature for the slowest gas release was found to be 263.15 K, while the release ratio at 10 h reached to 43.42%. By increasing the back pressure, the gas release rate could be effectively controlled. The gas release ratio at 1.1 MPa at 10 h was just 11.08%. The results showed that the application of adsorption-hydration sequence method in ZIF-8 slurry is a prospective manner for gas transportation.

Coral acid rich protein selects vaterite polymorph in vitro.

Corals and other biomineralizing organisms use proteins and other molecules to form different crystalline polymorphs and biomineral structures. In corals, it's been suggested that proteins such as Coral Acid Rich Proteins (CARPs) play a major role in the polymorph selection of their calcium carbonate (CaCO3) aragonite exoskeleton. To date, four CARPs (1-4) have been characterized: each with a different amino acid composition and different temporal and spatial expression patterns during coral developmental stages. Interestingly, CARP3 is able to alter crystallization pathways in vitro, yet its function in this process remains enigmatic. To better understand the CARP3 function, we performed two independent in vitro CaCO3 polymorph selection experiments using purified recombinant CARP3 at different concentrations and at low or zero Mg2+ concentration. Our results show that, in the absence of Mg2+, CARP3 selects for the vaterite polymorph and inhibits calcite. However, in the presence of a low concentration of Mg2+ and CARP3 both Mg-calcite and vaterite are formed, with the relative amount of Mg-calcite increasing with CARP3 concentration. In all conditions, CARP3 did not select for the aragonite polymorph, which is the polymorph associated to CARP3 in vivo, even in the presence of Mg2+ (Mg:Ca molar ratio equal to 1). These results further emphasize the importance of Mg:Ca molar ratios similar to that in seawater (Mg:Ca equal to 5) and the activity of the biological system in a aragonite polymorph selection in coral skeleton formation.

The hidden structure of human enamel.

Enamel is the hardest and most resilient tissue in the human body. Enamel includes morphologically aligned, parallel, ∼50 nm wide, microns-long nanocrystals, bundled either into 5-µm-wide rods or their space-filling interrod. The orientation of enamel crystals, however, is poorly understood. Here we show that the crystalline c-axes are homogenously oriented in interrod crystals across most of the enamel layer thickness. Within each rod crystals are not co-oriented with one another or with the long axis of the rod, as previously assumed: the c-axes of adjacent nanocrystals are most frequently mis-oriented by 1°-30°, and this orientation within each rod gradually changes, with an overall angle spread that is never zero, but varies between 30°-90° within one rod. Molecular dynamics simulations demonstrate that the observed mis-orientations of adjacent crystals induce crack deflection. This toughening mechanism contributes to the unique resilience of enamel, which lasts a lifetime under extreme physical and chemical challenges.

Biomineralization by particle attachment in early animals.

Crystallization by particle attachment (CPA) of amorphous precursors has been demonstrated in modern biomineralized skeletons across a broad phylogenetic range of animals. Precisely the same precursors, hydrated (ACC-H2O) and anhydrous calcium carbonate (ACC), have been observed spectromicroscopically in echinoderms, mollusks, and cnidarians, phyla drawn from the 3 major clades of eumetazoans. Scanning electron microscopy (SEM) here also shows evidence of CPA in tunicate chordates. This is surprising, as species in these clades have no common ancestor that formed a mineralized skeleton and appear to have evolved carbonate biomineralization independently millions of years after their late Neoproterozoic divergence. Here we correlate the occurrence of CPA from ACC precursor particles with nanoparticulate fabric and then use the latter to investigate the antiquity of the former. SEM images of early biominerals from Ediacaran and Cambrian shelly fossils show that these early calcifiers used attachment of ACC particles to form their biominerals. The convergent evolution of biomineral CPA may have been dictated by the same thermodynamics and kinetics as we observe today.

Structure Prior Constrained Estimation of Human Cardiac Diffusion Tensors.

OBJECTIVE: The purpose of this paper is to increase the accuracy of human cardiac diffusion tensor (DT) estimation in diffusion magnetic resonance imaging (dMRI) with a few diffusion gradient directions. METHODS: A structure prior constrained (SPC) method is proposed. The method consists in introducing two regularizers in the conventional nonlinear least squares estimator. The two regularizers penalize the dissimilarity between neighboring DTs and the difference between estimated and prior fiber orientations, respectively. A novel numerical solution is presented to ensure the positive definite estimation. RESULTS: Experiments on ex vivo human cardiac data show that the SPC method is able to well estimate DTs at most voxels, and is superior to state-of-the-art methods in terms of the mean errors of principal eigenvector, second eigenvector, helix angle, transverse angle, fractional anisotropy, and mean diffusivity. CONCLUSION: The SPC method is a practical and reliable alternative to current denoising- or regularization-based methods for the estimation of human cardiac DT. SIGNIFICANCE: The SPC method is able to accurately estimate human cardiac DTs in dMRI with a few diffusion gradient directions.

A hydrated crystalline calcium carbonate phase: Calcium carbonate hemihydrate.

As one of the most abundant materials in the world, calcium carbonate, CaCO3, is the main constituent of the skeletons and shells of various marine organisms. It is used in the cement industry and plays a crucial role in the global carbon cycle and formation of sedimentary rocks. For more than a century, only three polymorphs of pure CaCO3-calcite, aragonite, and vaterite-were known to exist at ambient conditions, as well as two hydrated crystal phases, monohydrocalcite (CaCO3·1H2O) and ikaite (CaCO3·6H2O). While investigating the role of magnesium ions in crystallization pathways of amorphous calcium carbonate, we unexpectedly discovered an unknown crystalline phase, hemihydrate CaCO3·½H2O, with monoclinic structure. This discovery may have important implications in biomineralization, geology, and industrial processes based on hydration of CaCO3.

Growth and regrowth of adult sea urchin spines involve hydrated and anhydrous amorphous calcium carbonate precursors.

In various mineralizing marine organisms, calcite or aragonite crystals form through the initial deposition of amorphous calcium carbonate (ACC) phases with different hydration levels. Using X-ray PhotoEmission Electron spectroMicroscopy (X-PEEM), ACCs with varied spectroscopic signatures were previously identified. In particular, ACC type I and II were recognized in embryonic sea urchin spicules. ACC type I was assigned to hydrated ACC based on spectral similarity with synthetic hydrated ACC. However, the identity of ACC type II has never been unequivocally determined experimentally. In the present study we show that synthetic anhydrous ACC and ACC type II identified here in sea urchin spines, have similar Ca L 2,3-edge spectra. Moreover, using X-PEEM chemical mapping, we revealed the presence of ACC-H2O and anhydrous ACC in growing stereom and septa regions of sea urchin spines, supporting their role as precursor phases in both structures. However, the distribution and the abundance of the two ACC phases differ substantially between the two growing structures, suggesting a variation in the crystal growth mechanism; in particular, ACC dehydration, in the two-step reaction ACC-H2O → ACC → calcite, presents different kinetics, which are proposed to be controlled biologically.

X-ray Linear Dichroism in Apatite.

The recent observation in parrotfish teeth of X-ray linear dichroism motivated an in-depth investigation into this spectroscopic effect in various apatite crystals, including geologic hydroxyapatite (Ca5(PO4)3OH), fluorapatite (Ca5(PO4)3F), and their biogenic counterparts in human bone, mouse enamel, and in parrotfish bone, dentin, and enameloid, the equivalent of dental enamel in certain fish. These data are important because they now enable visualization of the nano- to microscale structure of apatite crystals in teeth and bone. Polarization-dependent imaging contrast (PIC) maps of lamellar bone, obtained with a new method that minimizes space-charge and charging effects, show the expected rotating apatite crystal orientations. PIC maps of mouse enamel reveal a complex arrangement of hydroxyapatite crystals perpendicular to the dentin-enamel junction, with rods arranged in a decussation pattern in inner enamel and nearly parallel to one another in outer enamel. In both inner and outer enamel crystal c-axes are not always aligned with the rod elongation direction.

Influence of parameter accuracy on pharmacokinetic analysis of hyperpolarized pyruvate.

PURPOSE: To explore the effects of noise and error on kinetic analyses of tumor metabolism using hyperpolarized [1-13 C] pyruvate. METHODS: Numerical simulations were performed to systematically investigate the effects of noise, the number of unknowns, and error in kinetic parameter estimates on kinetic analysis of the apparent rate of chemical conversion from hyperpolarized pyruvate to lactate (kPL ). A pharmacokinetic model with two physical and two chemical pools of hyperpolarized spins was used to generate and analyze the synthetic data. RESULTS: The reproducibility of kPL estimates worsened quickly when peak signal-to-noise ratio for hyperpolarized pyruvate was below approximately 20. The accuracy of kPL estimates was most sensitive to errors in high excitation angles, the vascular blood volume fraction (vb ), and the rate of pyruvate extravasation (kve ), and was least sensitive to errors in the T1 of pyruvate. When vb and/or kve were fit as additional unknowns, the accuracy of kPL estimates suffered, and when the vascular input function of pyruvate was also fit, the reproducibility of kPL estimates worsened. CONCLUSIONS: The accuracy and precision of kPL estimates improve substantially for peak signal-to-noise ratio above approximately 20. Accurate estimates of perfusion parameters (combinations of vb , kve , and the pyruvate vascular input function) and transmit calibration at high excitation angles have the greatest effect on the accuracy of kinetic analyses. Magn Reson Med 79:3239-3248, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Coherently aligned nanoparticles within a biogenic single crystal: A biological prestressing strategy.

In contrast to synthetic materials, materials produced by organisms are formed in ambient conditions and with a limited selection of elements. Nevertheless, living organisms reveal elegant strategies for achieving specific functions, ranging from skeletal support to mastication, from sensors and defensive tools to optical function. Using state-of-the-art characterization techniques, we present a biostrategy for strengthening and toughening the otherwise brittle calcite optical lenses found in the brittlestar Ophiocoma wendtii This intriguing process uses coherent nanoprecipitates to induce compressive stresses on the host matrix, functionally resembling the Guinier-Preston zones known in classical metallurgy. We believe that these calcitic nanoparticles, being rich in magnesium, segregate during or just after transformation from amorphous to crystalline phase, similarly to segregation behavior from a supersaturated quenched alloy.