Ice Nucleation Research Articles

Optimized partial freezing protocol enables 10-day storage of rat livers

Preserving organs at subzero temperatures with halted metabolic activity holds the potential to prolong preservation and expand the donor organ pool for transplant. Our group recently introduced partial freezing, a novel approach in high-subzero storage at -15 °C, enabling 5-day storage of rodent livers through precise control over ice nucleation and unfrozen fraction. However, increased vascular resistance and tissue edema suggested a need for improvements to extend viable preservation. Here, we describe an optimized partial freezing protocol with key optimizations, including an increased concentration of polyethylene glycol (PEG) to enhance membrane stability while minimizing shear stress during cryoprotectant unloading with an acclimation period and a maintained osmotic balance through an increase in bovine serum albumin (BSA). These approaches ensured the viability during preservation and recovery processes, promoting liver function and ensuring optimal preservation. This was evidenced by increased oxygen consumption, decreased vascular resistance, and edema. Ultimately, we show that using the optimized protocol, livers can be stored for 10 days with comparable vascular resistance and lactate levels to 5 days, outperforming the viability of time-matched static cold stored (SCS) livers as the current gold standard. This study represents a significant advancement in expanding organ availability through prolonged preservation, thereby revolutionizing transplant medicine.

Aerosol size distribution properties associated with cold-air outbreaks in the Norwegian Arctic

Abstract. The aerosol particles serving as cloud condensation and ice nuclei contribute to key cloud processes associated with cold-air outbreak (CAO) events but are poorly constrained in climate models due to sparse observations. Here we retrieve aerosol number size distribution modes from measurements at Andenes, Norway, during the Cold-Air Outbreaks in the Marine Boundary Layer Experiment (COMBLE) and at Zeppelin Observatory, approximately 1000 km upwind from Andenes at Svalbard. During CAO events at Andenes, the sea-spray-mode number concentration is correlated with strong over-ocean winds with a mean of 8±4 cm−3 that is 71 % higher than during non-CAO conditions. Additionally, during CAO events at Andenes, the mean Hoppel minimum diameter is 6 nm smaller than during non-CAO conditions, though the estimated supersaturation is lower, and the mean number concentration of particles that likely activated in-cloud is 109±61 cm−3 with no statistically significant difference from the non-CAO mean of 99±66 cm−3. For CAO trajectories between Zeppelin Observatory and Andenes, the upwind-to-downwind change in number concentration is the largest for the accumulation mode with a mean decrease of 93±95 cm−3, likely attributable primarily to precipitation scavenging. These characteristic properties of aerosol number size distributions during CAO events provide guidance for evaluating CAO aerosol–cloud interaction processes in models.

How Porosity Influences the Heterogeneous Ice Nucleation Ability of Secondary Organic Aerosol Particles

AbstractDuring processing in deep convective cloud systems, highly viscous or glassy secondary organic aerosol (SOA) particles can develop a porous structure through a process known as atmospheric freeze‐drying. This structural modification may enhance their heterogeneous ice nucleation ability under cirrus conditions through the pore condensation and freezing mechanism. Pristine, compact SOA particles, on the other hand, are recommended to be treated as ice‐inactive in models. This recommendation also applies to internally mixed particles, where a coating layer of secondary organic matter (SOM) deactivates the intrinsic ice nucleation ability of the core, which may be a mineral dust grain. Ice cloud‐processing may also improve the ice nucleation ability of such a composite particle by inducing structural changes in the coating layer, which can release active sites on the mineral surface. In this work, we investigated the change in the ice nucleation ability of pure SOA particles from the ozonolysis of α‐pinene and two types of internally mixed particles (zeolite and coal fly ash particles coated with SOM) after being subjected to the atmospheric freeze‐drying process simulated in an expansion cloud chamber. For pure α‐pinene SOA, we found only a slight improvement in the ice nucleation ability of the ice cloud‐processed, porous particles compared to their pristine, compact counterparts at 221 and 217 K. In contrast, the zeolite and coal fly ash particles, which were initially deactivated by the organic coating, became significantly more ice‐active after atmospheric freeze‐drying, emphasizing that such composite particles cannot be excluded from model simulations of heterogeneous ice formation.

Molecular dynamics insights into electric Field-Induced heterogeneous ice nucleation

In this study, molecular dynamics simulations on the LAMMPS platform were used to investigate heterogeneous ice nucleation of water molecules based on the TIP4P/Ice-Water molecular model. We have developed a method for calculating electric field force for the TIP4P model, revealing distinct outcomes in the absence and presence of an electric field. In the absence of the electric field, both single and mixed ice structures are observed as final states. In contrast, the introduction of an electric field exclusively leads to the formation of a single ice structure, effectively reducing the energy barrier associated with heterogeneous nucleation. Importantly, this study highlights the significant impact of the electric field, resulting in the controlled formation of a specific ice structure and a pronounced reduction in the energy barrier for non-homogeneous nucleation. These findings provide valuable insights for the freezing industry, offering theoretical guidance for optimizing the freezing process. The developed method for electric field force calculation, specifically tailored to the TIP4P water molecule model, contributes to advancing our understanding of the complex dynamics in ice nucleation and holds promise for practical applications in controlled freezing environments.

Hierarchical assembly and environmental enhancement of bacterial ice nucleators

Bacterial ice nucleating proteins (INPs) are exceptionally effective in promoting the kinetically hindered transition of water to ice. Their efficiency relies on the assembly of INPs into large functional aggregates, with the size of ice nucleation sites determining activity. Experimental freezing spectra have revealed two distinct, defined aggregate sizes, typically classified as class A and C ice nucleators (INs). Despite the importance of INPs and years of extensive research, the precise number of INPs forming the two aggregate classes, and their assembly mechanism have remained enigmatic. Here, we report that bacterial ice nucleation activity emerges from more than two prevailing aggregate species and identify the specific number of INPs responsible for distinct crystallization temperatures. We find that INP dimers constitute class C INs, tetramers class B INs, and hexamers and larger multimers are responsible for the most efficient class A activity. We propose a hierarchical assembly mechanism based on tyrosine interactions for dimers, and electrostatic interactions between INP dimers to produce larger aggregates. This assembly is membrane-assisted: Increasing the bacterial outer membrane fluidity decreases the population of the larger aggregates, while preserving the dimers. Inversely, Dulbecco's Phosphate-Buffered Saline buffer increases the population of multimeric class A and B aggregates 200-fold and endows the bacteria with enhanced stability toward repeated freeze-thaw cycles. Our analysis suggests that the enhancement results from the better alignment of dimers in the negatively charged outer membrane, due to screening of their electrostatic repulsion. This demonstrates significant enhancement of the most potent bacterial INs.

Anomalous behaviour of transport properties in a supercooled water–glycerol mixture

Glycerol acts as a natural cryoprotectant by depressing the temperature of ice nucleation and slowing down the dynamics of water mixtures. In this work, we characterise dynamics – diffusion, viscosity and hydrogen bond dynamics – as well as density anomaly and structure of water mixtures with 1%–50% (w/w) glycerol at low temperatures via molecular dynamics simulations using all-atom and coarse-grained models. Simulations reveal distinct violations of the Stokes–Einstein relation in the low-temperature regime for water and glycerol. Deviations are positive for water at all concentrations, and positive for glycerol in very dilute solutions but turning negative in concentrated ones. The all-atom and coarse-grained models reveal an unexpected crossover in the dynamics of the 1% and 10 % (w/w) glycerol at the lowest simulated temperatures. This crossover manifests in the diffusion coefficients of water and glycerol, as well as in the viscosity and lifetime of hydrogen bonds in water. We interpret that the crossover originates on the opposing dependence with glycerol concentration of the two factors controlling the solutions' slow down: the increase in tetrahedrally coordinated water and the dynamics and clustering of the glycerol molecules. We anticipate that this dynamic crossover will also occur for solution of water with other polyols.

Impact of Asian Dust on Cirrus Formation Over the Central Pacific: CALIOP‐ and CloudSat‐Observation‐Based Case Studies

AbstractCirrus clouds are of great importance to the global climate, with their net radiative forcing strongly dependent on the microphysical properties that are related to the ice‐nucleating regime. However, the influence of long‐range transport of dust on primary ice formation in cirrus clouds is limitedly understood, specifically over the clean remote ocean regions. Here, two case studies show that transpacific Asian dust can impact the ice formation of cirrus clouds over the central Pacific based on Cloud‐Aerosol Lidar with Orthogonal Polarization and Cloud Profiling Radar (CPR, CloudSat) observations. One case shows a well‐developed horizontally extended cirrus embedded in a pure dust layer, with an average dust‐related ice‐nucleating particle concentration (INPC) of 7 L−1 and 96 L−1 for an ice saturation ratio Si of 1.15 and 1.25, respectively; ice crystal number concentration (ICNC) with diameters >25 and 100 μm (denoted as nice,25 μm and nice,100 μm) are 64 L−1 and 7 L−1, respectively. Another case shows that cirrus clouds with a much smaller horizontal extent appeared in the vicinity of polluted dust, with an average INPC of 42–310 L−1 for the typical higher Si of 1.25–1.35 by considering a tenfold reduction of the ice nucleation efficiency of ice crystals; nice,25 μm and nice,100 μm are 168 L−1 and 20 L−1, respectively. The estimated INPC and ICNC values suggest the dominance of ice formation by dust‐induced heterogeneous nucleation, proving that the long‐range transport of dust toward the upper troposphere and the potential influence on cirrus formation over the central Pacific should be well considered in atmospheric models.

Enhancing Ice Nucleation: The Role of Surface Roughness in Electrofreezing Using Laser Shock Processed Al6061 T6 Electrodes

The present study investigates the impact of the electrode surface roughness on the electrofreezing of water. This research focuses on how the electrode microstructure induced by a laser treatment affects the nucleation and growth of ice crystals under controlled electric fields. For this, electrofreezing experiments of deionized water over electrodes with varying surface roughnesses and crystalline textures were conducted. The electrodes of the Al6061 T6 alloy were microstructured via the Laser Shock Processing (LSP) method. For this purpose, the pulse densities during the LSP process were varied (900, 1600, and 2500 pulses/cm2). The increase in pulse density was correlated to the microstructural features and average roughness of the LSP-treated Al6061 alloy. A wave-like microstructure was induced upon the LSP treatment, with roughnesses between 3.5 and 6 µm at the selected pulse densities. The results indicate that electrode roughness significantly influences the electrofreezing process. Rougher electrodes were found to increase the nucleation temperature, suggesting enhanced ice nucleation activity. These findings are attributed to the increased electric field concentration at the asperities of the rough surfaces and the (111) planes of the Al6061 alloy, which may facilitate the alignment of water molecules and the formation of critical ice nuclei.

Atmospheric Fungal Spore Injection: A Promising Breakthrough for Challenging the Impacts of Climate Change Through Cloud Seeding and Weather Modification

Cloud seeding is a technique used to enhance precipitation in drought-prone areas, support agricultural productivity, ensure water supply for human consumption, improve hydropower generation from dams, lessen hurricanes, cool urban heat, and disperse fog in airports. Growing global population size and climate change are the biggest impetus for weather modification and cloud seeding operations. Currently, salt powders like silver iodide, potassium iodide, sodium chloride, calcium chloride, dry ice (solid carbon dioxide), and liquid propane are widely used as ice nucleating particles for cloud seeding purposes while in natural cloud formation, and precipitation particles from dust storms, mineral dust and biological aerosols (like spores, pollen, bacteria) are the dominant ice nucleators. Having this knowledge on hand and the ubiquitous nature of fungi on the other hand; it is feasible to exploit the ice nucleating ability of fungal spores and use it as potential candidates for cloud seeding and weather modification operations.

Physicochemical properties and their impact on ice nucleation efficiency of respiratory viral RNA and proteins.

Ice nucleation processes in the earth's atmosphere are critical for cloud formation, radiation, precipitation, and climate change. We investigated the physicochemical properties and ice nucleation potential of selected viral aerosols, including their RNA and proteins, using advanced techniques such as scanning-transmission electron microscopy (S/TEM), small angle X-ray scattering (SAXS), particle analyzers, and a peltier chamber. The experiments revealed that RNA particles obtained from MS2 bacteriophage had a mean freezing point of -13.9 ± 0.3 °C, comparable to the average ice nucleation temperature of global dust particles, which is approximatively -15 °C. RNA from MS2, Influenza, SARS-CoV-1 and SARS-CoV-2 demonstrated average ice nucleation temperatures of -13.9 ± 0.3 °C, -13.7 ± 0.3 °C, -13.7 ± 0.3 °C, and -15.9 ± 0.4 °C, respectively. SAXS analysis indicated a high local crystallinity value of 0.5 of MS2 RNA particles, hinting that high crystalline nature may contribute to their effectiveness as ice nuclei. Dilution experiments show that viral RNA consistently catalyzes ice nucleation. The addition of dust-containing particles, such as Fe2O3, CuO, and TiO2, to MS2 bacteriophage droplets enhanced ice nucleation, as did UV radiation. We herein discuss the implications of this work on ice nucleation and freezing processes.

Kinetic study on the effect of ice nucleation and generation on methane hydrate dissociation below the quadruple point

Natural gas hydrates (NGHs) have captured worldwide attention because of its huge resources and high energy density. Deep depressurization by dropping the pressure below the quadruple point is recognized as a promising exploitation method. However, the impact of ice formation on NGHs dissociation within depressurization is still controversial. Thus, we examine the dissociative behavior of NGHs at low temperature below the quadruple point using a high-pressure reactor. It primarily focuses on how ice formation affects heat and mass transfer, as well as the kinetics of hydrate dissociation. The results indicate that during the hydrate dissociation process, liquid water initially transforms into metastable supercooled water, which then transitions to solid ice under external disturbance. Ice nucleation predominantly occurs in two locations: within the free water phase and on the surface of hydrate particles. A double-edged effect of ice on NGHs dissociation is observed: the latent heat released by ice nucleation and generation could accelerate the hydrate breakdown (positive effect), while the decrease in permeability along with the self-preservation effect from ice formation tends to inhibit the NGHs dissolution (negative effect). In addition, a higher pressure drawdown rate can accelerate both ice nucleation and formation, which in turn shortens the freezing induction time. The increase of water saturation (SA) and the decrease of hydrate saturation (SH) can significantly reduce the mining time and strengthen both the hydrate dissociation rate (QH) and gas production rate (QP). Therefore, hydrate sediments with higher SA or lower SH are more conductive to gas recovery of low-temperature NGHs deposits in permafrost regions.

High cooling rate of 60°C/min around ice nucleation during cryopreservation compromises chicken sperm viability.

The present study compares two protocols for the cryopreservation of chicken semen. Both protocols had an initial low cooling rate in the first step, followed by higher cooling rates around ice nucleation (Protocol 1) or following the dissipation of the latent heat of fusion (Protocol 2) in the second step. Semen ejaculates obtained from 12 roosters were diluted with Rootex with 6% dimethylformamide and frozen following either Protocol 1 (from +5°C to -10°C at 5°C/min and from -10°C to -130°C at 60°C/min) or Protocol 2 (from +5°C to -35°C at 7°C/min and from -35°C to -140°C at 60°C/min). Compared with fresh semen, following both protocols, cryopreservation resulted in reduced post-thaw sperm quality (p < .001). Post-thaw percentage of sperm with an intact plasma membrane was greater using Protocol 2 than Protocol 1 (p < .05). The results suggest that high cooling rates around the time of ice nucleation are not recommendable.

Relevance of Bacteria in Causing Rain and Snow.

The Earth's climate is influenced by both natural phenomena (solar fluctuations, oceanic patterns, volcanic eruptions, and tectonic movements) and human activities (deforestation, CO and CO2 emissions, and desertification), all of which contribute to ongoing climate change and the resulting global warming. However, human actions are a major factor in exacerbating global warming and amplifying its adverse impacts worldwide. . With rising temperatures, water evaporation from water bodies and soils intensifies, leading to heightened water scarcity, particularly in drought-prone regions. This scarcity compounds rainfall deficits, posing significant challenges. Precipitation, essential for the biosphere's hydrological cycle, replenishes much of the world's freshwater. It occurs when condensed water vapor in the atmosphere falls back to Earth as rain, drizzle, sleet, graupel, hail, or snow due to gravity. Literature highlights the indispensable role of bacterial populations in this process, termed bio-precipitation. This phenomenon begins with bacterial colonization on plant surfaces, with colonies subsequently dispersed into the atmosphere by winds, triggering ice crystal formation. Through their ice nucleating property, these bacteria facilitate the growth of larger ice crystals, which eventually melt and precipitate as rain or snow. This mechanism aids in nutrient transfer from clouds to soil or vegetation. Pseudomonas syringae stands out as the most notable microorganism exhibiting this ice-nucleation property, serving as the primary source of ice nucleators driving bio-precipitation. Despite limited literature on "rain and snow-causing bacteria," this review comprehensively explores the conceptual background of bio-precipitation, the involved bioprocesses, and the critical role of bacteria like P. syringae, offering insights into future research directions.

Functionalisation of the Aluminium Surface by CuCl2 Chemical Etching and Perfluoro Silane Grafting: Enhanced Corrosion Protection and Improved Anti-Icing Behaviour

This study aimed to prepare a facile hierarchical aluminium surface using a two-step process consisting of chemical etching in selected concentrations of CuCl2 solution and surface grafting through immersion in an ethanol solution containing 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane. The goal was to achieve superhydrophobic characteristics on the aluminium surface, including enhanced corrosion resistance, efficient self-cleaning ability, and improved anti-icing performance. The surface characterisation of the untreated aluminium and treated in CuCl2 solutions of different concentrations was performed using contact profilometry, optical tensiometry, and scanning electron microscopy coupled with energy dispersive spectroscopy to determine the surface topography, wettability, morphology, and surface composition. The corrosion properties were evaluated using potentiodynamic measurements in simulated acid rain solution and salt-spray test according to ASTM B117-22. In addition, self-cleaning and anti-icing tests were performed on superhydrophobic surfaces prepared under optimal conditions. The results showed that the nano-/micro-structured etched aluminium surface with an optimal 0.5 M concentration of CuCl2 grafted with a perfluoroalkyl silane film achieved superhydrophobic characteristics, with water droplets exhibiting efficient corrosion protection, self-cleaning ability, and improved anti-icing performance with decreased ice nucleation temperature and up to 545% increased freezing delay.

Observational evidence of the association between aerosol properties and lightning characteristics in the Indian subcontinent

Abstract Lightning is a leading cause of natural disaster-related mortality in the Indian Subcontinent. Currently, there is a lack of observational evidence supporting the role of aerosol composition in modulating lightning intensity and trends in this region. In this study, we analyzed satellite and reanalysis datasets to examine the association between aerosol properties and lightning intensity over three contrasting geographic regions of Indian subcontinent during the premonsoon season (1998-2022). By comparing lightning and non-lightning days, we found a 0.1 unit increase in total aerosol optical depth specifically on lightning days in all three study areas. Additionally, we observed that the aerosol composition of a region influences convective activity. The presence of dust alongside fine aerosols acts as efficient ice nuclei, thereby stimulating lightning activity in all three regions. Therefore, considering aerosol composition together with local meteorology is essential for accurately predicting lightning flash rates in a region.

Supercooling preservation of vascularized composite allografts through CPA optimization, thermal tracking, and stepwise loading techniques

Vascularized composite allografts (VCAs) present unique challenges in transplant medicine, owing to their complex structure and vulnerability to ischemic injury. Innovative preservation techniques are crucial for extending the viability of these grafts, from procurement to transplantation. This study addresses these challenges by integrating cryoprotectant agent (CPA) optimization, advanced thermal tracking, and stepwise CPA loading strategies within an ex vivo rodent model. CPA optimization focused on various combinations, identifying those that effectively suppress ice nucleation while mitigating cytotoxicity. Thermal dynamics were monitored using invasive thermocouples and non-invasive FLIR imaging, yielding detailed temperature profiles crucial for managing warm ischemia time and optimizing cooling rates. The efficacy of stepwise CPA loading versus conventional flush protocols demonstrated that stepwise (un)loading significantly improved arterial resistance and weight change outcomes. In summary, this study presents comprehensive advancements in VCA preservation strategies, combining CPA optimization, precise thermal monitoring, and stepwise loading techniques. These findings hold potential implications for refining transplantation protocols and improving graft viability in VCA transplantation.

Measurement report: The Fifth International Workshop on Ice Nucleation phase 1 (FIN-01): intercomparison of single-particle mass spectrometers

Abstract. Knowledge of the chemical composition and mixing state of aerosols at a single-particle level is critical for gaining insights into atmospheric processes. One common tool to make these measurements is single-particle mass spectrometry. There remains a need to compare the performance of different single-particle mass spectrometers (SPMSs). An intercomparison of SPMSs was conducted at the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) chamber at the Karlsruhe Institute of Technology (KIT) in November 2014, as part of the first phase of the Fifth International Workshop on Ice Nucleation (FIN-01). In this paper we compare size distributions and mass spectra of atmospherically relevant particle types measured by five SPMSs. These include different minerals, desert and soil dusts, soot, bioaerosol (Snomax; protein granule), secondary organic aerosol (SOA), and SOA-coated mineral particles. Most SPMSs reported similar vacuum aerodynamic diameter (dva) within typical instrumental ranges from ∼100–200 nm (lower limit) to ∼2–3 µm (upper limit). In general, all SPMSs exhibited a wide dynamic range (up to ∼103) and high signal-to-noise ratio (up to ∼104) in mass spectra. Common spectral features with small diversities in mass spectra were found with high average Pearson's correlation coefficients, i.e., for average positive spectra ravg-pos=0.74 ± 0.12 and average negative spectra ravg-neg=0.67 ± 0.22. We found that instrument-specific detection efficiency (DE) was more dependent on particle size than particle type, and particle identification favored the use of bipolar, rather than monopolar, instruments. Particle classification from “blind experiments” showed that all instruments differentiated SOA, soot, and soil dust and detected subtle changes in the particle internal mixing but had difficulties differentiating among specific mineral types and dusts. This study helps to further understand the capabilities and limitations of the single-particle mass spectrometry technique in general and the specific performance of the instrument in characterizing atmospheric aerosol particles.

Two state model for the ML-BOP potential

The coarse-grained machine-learning derived ML-BOP model [Chan et al., Nature Commun. 10, 379 (2019)] provides a monoatomic representation of the water-water interaction potential in which orientational interactions are included as three-body contributions. Despite its simplicity, the model reproduces the phase diagram of water and its anomalies. Here, we show that a two-state Gibbs free energy expression – fitted simultaneously on the temperature and pressure dependence of the density and internal energy – predicts the existence of a liquid–liquid critical point, with critical parameters consistent with previous estimates. We also show that in this model: (i) while the low density liquid is pre-empted by crystal nucleation, the high-density liquid and its spinodal are accessible in numerical studies down to 100 K; (ii) crystallisation requires the presence of a local low density region. Thus, for densities larger than the critical density, spinodal decomposition (or nucleation of the low-density liquid) is a pre-requisite for ice nucleation.

Modeling homogeneous ice nucleation from drop-freezing experiments: impact of droplet volume dispersion and cooling rates

Modeling homogeneous ice nucleation from drop-freezing experiments: impact of droplet volume dispersion and cooling rates

Simulated contrail-processed aviation soot aerosols are poor ice-nucleating particles at cirrus temperatures

Abstract. Aviation soot surrogates processed in contrails are believed to become potent ice nuclei at cirrus temperatures. This is not verified for real aviation soot, which can have vastly different physico-chemical properties. Here, we sampled soot particles from in-use commercial aircraft engines and quantified the effect of contrail processing on their ice nucleation ability at T&lt; 228 K. We show that aviation soot becomes compacted upon contrail processing, but that does not change their ice nucleation ability in contrast to other soot types. The presence of H2SO4 condensed in soot pores, the highly fused nature of the soot primary particles and their arrangement are what limit the volume of pores generated upon contrail processing, in turn limiting sites for ice nucleation. Furthermore, we hypothesized that contrail-processed aviation soot particles emitted from alternative jet fuel would also be poor ice-nucleating particles if their emission sizes remain small (&lt; 150 nm).