Modeling ultrasound-induced nucleation during cooling crystallization

Cryopreservation of organoids: Strategies, innovation, and future prospects

Organoid technology has demonstrated unique advantages in multidisciplinary fields such as disease research, tumor drug sensitivity, clinical immunity, drug toxicology, and regenerative medicine. It will become the most promising research tool in translational research. However, the long preparation time of organoids and the lack of high-quality cryopreservation methods limit the further application of organoids. Although the high-quality cryopreservation of small-volume biological samples such as cells and embryos has been successfully achieved, the existing cryopreservation methods for organoids still face many bottlenecks. In recent years, with the development of materials science, cryobiology, and interdisciplinary research, many new materials and methods have been applied to cryopreservation. Several new cryopreservation methods have emerged, such as cryoprotectants (CPAs) of natural origin, ice-controlled biomaterials, and rapid rewarming methods. The introduction of these technologies has expanded the research scope of cryopreservation of organoids, provided new approaches and methods for cryopreservation of organoids, and is expected to break through the current technical bottleneck of cryopreservation of organoids. This paper reviews the progress of cryopreservation of organoids in recent years from three aspects: damage factors of cryopreservation of organoids, new protective agents and loading methods, and new technologies of cryopreservation and rewarming.

Spatiotemporal Control of Ice Crystallization in Supercooled Water via an Ultrashort Laser Impulse

Focused irradiation with ultrashort laser pulses realized the fine spatiotemporal control of ice crystallization in supercooled water. An effective multiphoton excitation at the laser focus generated shockwaves and bubbles, which acted as an impulse for inducing ice crystal nucleation. The impulse that was localized close to the laser focus and accompanied by a small temperature elevation allowed the precise position control of ice crystallization and its observation with spatiotemporal resolution of micrometers and microseconds using a microscope. To verify the versatility of this laser method, we also applied it using various aqueous systems (e.g., plant extracts). The systematic study of crystallization probability revealed that laser-induced cavitation bubbles play a crucial role in inducing ice crystal nucleation. This method can be used as a tool for studying ice crystallization dynamics in various natural and biological phenomena.

Numerical simulations for sonochemistry

Numerical simulations for sonochemistry are reviewed including single-bubble sonochemistry, influence of ultrasonic frequency and bubble size, acoustic field, and sonochemical synthesis of nanoparticles. The theoretical model of bubble dynamics including the effect of non-equilibrium chemical reactions inside a bubble has been validated from the study of single-bubble sonochemistry. By the numerical simulations, it has been clarified that there is an optimum bubble temperature for the production of oxidants inside an air bubble such as OH radicals and H2O2 because at higher temperature oxidants are strongly consumed inside a bubble by oxidizing nitrogen. Unsolved problems are also discussed.

Nucleation kinetics for primary, secondary and ultrasound-induced paracetamol crystallization

Investigation into the effect of different nucleation mechanisms on the nucleation rate for paracetamol crystallization in stirred microvials.

A review on possible mechanisms of sonocrystallisation in solution

Sonocrystallisation is the application of ultrasound to the crystallisation process. The benefits obtained by sonication have been widely studied since the beginning of the 20th century and so far it is clear that ultrasound can be a very useful tool for enhancing crystallisation and controlling the properties of the final product. Crystal size, polymorphs, purity, process repeatability and lower induction time are only some of the advantages of sonocrystallisation. Even though the effects of sonication on crystallisation are quite clear, the physical explanation of the phenomena involved is still lacking. Is the presence of cavitation necessary for the process? Or is only the bubbles surface responsible for enhancing crystallisation? Are the strong local increases in pressure and temperature induced by cavitation the main cause of all the observed effects? Or is it the strong turbulence induced in the system instead? Many questions still remain and can only be appreciated with an understanding of the complexity behind the individual processes of crystallisation and acoustic cavitation. Therefore, this review will first summarise the theories behind crystallisation and acoustic cavitation, followed by a description of all the current proposed sonocrystallisation mechanisms, and conclude with an overview on future prospects of sonocrystallisation applications.

Antisolvent Sonocrystallisation of Sodium Chloride and the Evaluation of the Ultrasound Energy Using Modified Classical Nucleation Theory

The crystal nucleation rate of sodium chloride in ethanol was investigated by measuring the induction time at various supersaturation ratios under silent and ultrasound irradiation at frequencies between 22 and 500 kHz. Under silent conditions, the data follows the classical nucleation theory showing both the homogeneous and heterogeneous regions and giving an interfacial surface tension of 31.0 mN m−2. Sonication led to a non-linearity in the data and was fitted by a modified classical nucleation theory to account for the additional free energy being supplemented by sonication. For 98 kHz, this free energy increased from 1.33 × 108 to 1.90 × 108 J m−3 for sonication powers of 2 to 15 W, respectively. It is speculated that the energy was supplemented by the localised bubble collapses and collisions. Increasing the frequency from 22 to 500 kHz revealed that a minimum induction time was obtained at frequencies between 44 and 98 kHz, which has been attributed to the overall collapse intensity being the strongest at these frequencies.

Constructing regions of attainable sizes and achieving target size distribution in a batch cooling sonocrystallization process

The application of ultrasound to a crystallization process has several interesting benefits. The temperature of the crystallizer increases during ultrasonication and this makes it difficult for the temperature controller of the crystallizer to track a set temperature trajectory precisely. It is thus necessary to model this temperature rise and the temperature-trajectory tracking ability of the crystallizer controller to perform model-based dynamic optimization for a given cooling sonocrystallization set-up. In our previous study, we reported a mathematical model based on population balance framework for a batch cooling sonocrystallization of l-asparagine monohydrate (LAM). Here we extend the previous model by including energy balance equations and a Generic Model Control algorithm to simulate the temperature controller of the crystallizer that tracks a cooling profile during crystallization. The improved model yields very good closed-loop prediction and is conveniently used for studies related to particle engineering by optimization. First, the model is used to determine the regions of attainable particle sizes for LAM batch cooling sonocrystallization process by solving appropriate dynamic optimization problems. Then the model is used to determine optimal operating conditions for achieving a target crystal size distribution. The experimental evidence clearly demonstrates the efficiency of the particle engineering approach by optimization.

Numerical simulations of sonochemical production and oriented aggregation of BaTiO3 nanocrystals

Numerical simulations of sonochemical production and oriented attachment of BaTiO₃ nanocrystals are performed in aqueous solution with pH 14. It is suggested that most significant effect of ultrasound is the dissolution of Ti-based gel in aqueous solution. It results in the dissolution-precipitation mechanism in the production of BaTiO₃ nanoparticles, while with mechanical stirring without ultrasound it is the in situ mechanism that BaTiO₃ is gradually formed on Ti-based gel. The oriented attachment of spherical BaTiO₃ nanocrystals occurs by van der Waals torque (Casimir torque). Large aggregates of nanocrystals do not attach with each other as the repulsive double layer interaction is stronger for larger aggregates. For smaller spherical nanocrystals, the alignment of the crystal axes is less accurate due to more significant rotational Brownian motion of the nanocrystals.

Sono-crystallization kinetics of K2SO4: Estimation of nucleation, growth, breakage and agglomeration kinetics

Application of ultrasound in crystallization has showed improved process characteristics. Although several attempts have been made in the past to study the sono-crystallization kinetics, only nucleation and crystal growth were considered, neglecting breakage and agglomeration of crystals. In this study, an attempt is made for the estimation of the kinetic parameters of all the phenomena occurring simultaneously during sono-crystallization. For this, both conventional and ultrasonic crystallization of K₂SO₄-water system has been reported. Sono-crystallization experiments were carried out using ultrasonic horn operating at 20 kHz frequency. Reduction in the induction time, reduction in metastable zone width (MSZW), narrowing of crystal size distribution (CSD) were the key observations of sono-crystallization experiments. Population balance equations (PBE) were used to model the crystallization system and the various kinetic parameters have been estimated. The kinetic parameters obtained for conventional crystallization and sonocrystallization were compared. The estimated parameters suggest an increase in nucleation and breakage rate during sono-crystallization. Growth rates were observed to be of the same order of magnitude for both conventional and sonocrystallization. While agglomeration during sono-crystallization was found to be negligible.

The role of ultrasound in pharmaceutical production: sonocrystallization

Objectives

The main aim of this review was to develop a critical discussion of the key role ultrasound (US) can play on the production of active pharmaceutical ingredients (APIs) by discussing the versatile effect this type of energy produces.

Methods

The different crystallization techniques that can be assisted and improved by US are discussed in the light of the available US devices and the effect pursued by application of US energy. Simple and complex analytical methods to monitor API changes are also discussed.

Key findings

The countless achievements of API US-assisted production are summarized in a table, and outstanding effects such as narrower particle size distribution; decreased particle size, induction time, metastable zone and supersaturation levels; or a solubility increase are critically discussed.

Conclusions

The indisputable advantages of sonocrystallization over other ways of API production have been supported on multiple examples, and pending goals in this field (clarify the effect of US frequency on crystallization, know the mechanism of sonocrystallization, determine potential degradation owing to US energy, avoid calculation of the process yield by determining the concentration of the target drug remaining in the solution, etc.) should be achieved.

Theoretical model of ice nucleation induced by inertial acoustic cavitation. Part 2: Number of ice nuclei generated by a single bubble

In the preceding paper (part 1), the pressure and temperature fields close to a bubble undergoing inertial acoustic cavitation were presented. It was shown that extremely high liquid water pressures but quite moderate temperatures were attained near the bubble wall just after the collapse providing the necessary conditions for ice nucleation. In this paper (part 2), the nucleation rate and the nuclei number generated by a single collapsing bubble were determined. The calculations were performed for different driving acoustic pressures, liquid ambient temperatures and bubble initial radius. An optimal acoustic pressure range and a nucleation temperature threshold as function of bubble radius were determined. The capability of moderate power ultrasound to trigger ice nucleation at low undercooling level and for a wide distribution of bubble sizes has thus been assessed on the theoretical ground.

A novel sonochemical synthesis of antlerite nanorods

Antlerite - Cu3(OH)4SO4 was prepared, for the first time, by the sonochemical method from an aqueous solution of CuSO4, without any additives. The source of OH(-) is a result of protonation of SO4(2-) forming HSO4(-) and OH(-). The extreme local conditions inside the cavity that are developed during the bubble collapse (pressure is above 1000atm and the temperature is higher than 5000K) lead to the formation of the crystalline mineral. A suggested mechanism for the mineral formation is proposed. Due to the collapse of the bubbles, the distances between the opposite charge Cu(2+) and SO4(2-) ions is shortened and a crystallization process is initiated. In addition, the reaction is a one-step process with short irradiation time of less than 30min. The chemo-physical analysis of the sonochemically obtained product has revealed the presence of single phase antlerite nanorods.

Sonocrystallization and sonofragmentation

The application of ultrasound to crystallization (i.e., sonocrystallization) can dramatically affect the properties of the crystalline products. Sonocrystallization induces rapid nucleation that generally yields smaller crystals of a more narrow size distribution compared to quiescent crystallizations. The mechanism by which ultrasound induces nucleation remains unclear although reports show the potential contributions of shockwaves and increases in heterogeneous nucleation. In addition, the fragmentation of molecular crystals during ultrasonic irradiation is an emerging aspect of sonocrystallization and nucleation. Decoupling experiments were performed to confirm that interactions between shockwaves and crystals are the main contributors to crystal breakage. In this review, we build upon previous studies and emphasize the effects of ultrasound on the crystallization of organic molecules. Recent work on the applications of sonocrystallized materials in pharmaceutics and materials science are also discussed.

Ultrasonic irradiation effects on electrochemical synthesis of ZnO nanostructures

In the present article, electrochemical synthesis of ZnO nanostructures in presence of ultrasonic irradiation is investigated. The ultrasonic bath use for synthesis is calibrated using hydrophone method so that its frequency and acoustic power were obtained. From the results of the experimentation the role of ultrasonic irradiation in synthesis of ZnO nanoparticles is discussed. Diameter of the ZnO nanoparticles produced in the electrolyte was compared and investigated in absence and presence of the ultrasonic irradiation utilizing UV-visible photo-spectrometer. Then electrodeposited ZnO layer on the ITO glass as cathode's surface in absence and presence of the ultrasonic irradiation were studied by UV-visible photo-spectrometer and field emission scanning electron microscopy (FE-SEM) and the results were compared. FE-SEM micrographs show, higher growth of nanosheets on the cathode electrode in presence of ultrasonic irradiation. Experiment shows synthesis of ZnO nanoparticles in presence of the ultrasonic irradiation happen 10 times faster.

Ultrasonication as a potential tool to predict solute crystallization in freeze-concentrates

PURPOSE

We hypothesize that ultrasonication can accelerate solute crystallization in freeze-concentrates. Our objective is to demonstrate ultrasonication as a potential predictive tool for evaluating physical stability of excipients in frozen solutions.

METHODS

The crystallization tendencies of lyoprotectants (trehalose, sucrose), carboxylic acid buffers (citric, tartaric, malic, and acetic) and an amino acid buffer (histidine HCl) were studied. Aqueous solutions of buffers, lyoprotectants and mixtures of the two were cooled from room temperature to -20°C and sonicated to induce solute crystallization. The crystallized phases were identified by X-ray diffractometry (laboratory or synchrotron source).

RESULTS

Sonication accelerated crystallization of trehalose dihydrate in frozen trehalose solutions. Sonication also enhanced solute crystallization in tartaric (200 mM; pH 5), citric (200 mM pH 4) and malic (200 mM; pH 4) acid buffers. At lower buffer concentrations, longer annealing times following sonication were required to facilitate solute crystallization. The time for crystallization of histidine HCl progressively increased as a function of sucrose concentration. The insonation period required to effect crystallization also increased with sucrose concentration.

CONCLUSIONS

Sonication can substantially accelerate solute crystallization in the freeze-concentrate. Ultrasonication may be useful in assessing the crystallization tendency of formulation constituents used in long term frozen storage and freeze-drying.

Forming nanoparticles of water-soluble ionic molecules and embedding them into polymer and glass substrates

This work describes a general method for the preparation of salt nanoparticles (NPs) made from an aqueous solution of ionic compounds (NaCl, CuSO(4) and KI). These nanoparticles were created by the application of ultrasonic waves to the aqueous solutions of these salts. When the sonication was carried out in the presence of a glass microscope slide, a parylene-coated glass slide, or a silicon wafer the ionic NPs were embedded in these substrates by a one-step, ultrasound-assisted procedure. Optimization of the coating process resulted in homogeneous distributions of nanocrystals, 30 nm in size, on the surfaces of the substrates. The morphology and structure of each of the coatings were characterized by physical and chemical methods, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). After 24 h of leaching into water the nanoparticles of the inorganic salts were still present on the slides, and complete leaching of nanoparticles occurred only after 96 h. A mechanism of the ultrasound-assisted coating is proposed.

Numerical simulations of sonochemical production of BaTiO3 nanoparticles

Numerical simulations of sonochemical production of nanoparticles have been performed for the first time under the experimental condition of Dang et al. [Jpn. J. Appl. Phys. 48 (2009) 09KC02] on the production of BaTiO(3). The results of the numerical simulations have suggested that only primary particles aggregate with other particles. It is also shown that larger aggregates are produced for lower initial concentration of BaCl(2) and TiCl(4). This is caused by longer reaction time as the reaction rate is lower for lower concentration and by lower viscosity which results in higher rate of aggregation.

Investigations in the physical mechanism of sonocrystallization

This paper addresses the issue of mechanistic aspects of sonocrystallization with approach of coupling experiments with simulations of bubble dynamics. The major experimental result of our study is that, as compared to a mechanically agitated crystallization system, the dominant crystal size (or median) of the crystal size distribution (CSD) of sonocrystallization systems is smaller, but span of CSD is larger. The CSD is influenced by nucleation rate and growth rate. The nature of convection in the medium is found to be the crucial factor. In a mechanically agitated system, uniform velocity field prevails in crystallization volume, due to which both dominant crystal size and span of CSD reduce. The convection in a sonicated system is of a different kind. This convection has two components, viz. microturbulence (or micro-convection), which is continuous oscillatory motion of liquid induced by radial motion of cavitation bubble, and shock waves, which are discrete, high pressure amplitude waves emitted by the bubble. These components have different impact on crystallization process due to their nature. Shock waves increase the nucleation rate and microtubulence governs growth of the nuclei. However, the effect of shock waves is more marked than microturbulence (or micro-convection). Nucleation rate shows an order of magnitude rise with sonication, while growth rate (and hence the dominant crystal size) reduces with sonication as compared to the mechanically agitated system.