arXiv subjects

Dmytro Dedovets

Publications and source records attributed to Dmytro Dedovets.

5 recordsLinked to original sources

arXiv2020

Unveiling cells' local environment during cryopreservation by correlative in situ spatial and thermal analyses

Cryopreservation is the only fully established procedure to extend the lifespan of living cells and tissues, a key to activities spanning from fundamental biology to clinical practice. Despite its prevalence and impact, central aspects of cryopreservation, such as the cell's physico-chemical environment during freezing, remain elusive. Here we address that question by coupling in situ microscopic directional freezing to visualize cells and their surroundings during freezing with the freezing medium phase diagram. We extract the freezing medium spatial distribution in cryopreservation, providing a tool to describe the cell vicinity at any point during freezing. We show that two major events define the cells' local environment over time: the interaction with the moving ice front and with the vitreous moving front - a term we introduce here. Our correlative strategy may be applied to cells relevant in clinical research and practice, and help designing new cryoprotective media based on local physico-chemical cues.

physics.bio-ph↗

arXiv2019

Solute effects in confined freezing

The presence of liquid water in frozen media impacts the strength of soils, the growth of frost heave, plant life and microbial activities, or the durability of infrastructures in cold regions. If the effect of confinement on freezing is well known, water is never pure and solutes depressing the freezing point are naturally found. Moreover, the combination of confinement and solute is poorly understood. We imaged the freezing dynamics of water in a model porous medium with various salt (KCl) concentrations. We showed that the freezing front, initially heterogeneous due to confinement, drives salt enrichment in the remaining liquid, further depressing its freezing point. Confinement and solute have a synergistic effect that results in much larger mushy layers and greater freezing point depression. These results should help understand the distribution of water in frozen porous media, solute precipitation and redistribution in soils, and cryo-tolerance of construction materials and organisms.

cond-mat.soft↗

arXiv2018

Five-dimensional imaging of freezing emulsions with solute effects

The interaction of objects with a moving solidification front is a common feature of many industrial and natural processes such as metal processing, the growth of single-crystals, the cryopreservation of cells, or the formation of sea ice. Solidification fronts interact with objects with different outcomes, from the total rejection to their complete engulfment. We image the freezing of emulsions in 5D (space, time, and solute concentration) with confocal microscopy. We show the solute induces long-range interactions that determine the solidification microstructure. The local increase of solute concentration enhances premelting, which controls the engulfment of droplets by the front and the evolution of grain boundaries. Freezing emulsions may be a good analogue of many solidification systems where objects interact with a solidification interface.

cond-mat.mtrl-sci↗

arXiv2017

A temperature-controlled stage for laser scanning confocal microscopy and case studies in chemistry of materials

If confocal microscopy is an ubiquitous tool in life science, its applications in chemistry and materials science are still, in comparison, very limited. Of particular interest in these domains is the use of confocal microscopy to investigate temperature-dependent phenomena such as self-assembly, diffusio- or thermophoresis, or crystal growth. Several hurdles must be solved to develop a temperature-controlled stage for laser scanning confocal microscopy, in particular regarding the influence of an elevated temperature gradient close to the microscope objective, which most people try very hard to avoid. Here we report the design of a temperature-controlled stage able to generate stable temperature gradients in both positive and negative temperature range and does not require use of liquid nitrogen. Our setup provides an excellent control of the temperature gradient, which can be coupled with a controlled displacement of the sample, making it useful in particular for a variety of solidification, chemistry, and interfacial problems. We illustrate the benefits of our setup with several case studies of interest in chemistry and materials science: the 3D real-time imaging of ice growth, the segregation of hard particles by growing crystals, the freezing behaviour of single emulsions, the self-shaping of oil droplets upon cooling, and the self-assembly of amphiphile molecules into helical structures. These results show how confocal microscopy coupled with a temperature-controlled stage is a welcome addition to the toolkit of chemists and materials scientists.

cond-mat.soft↗

arXiv2017

Multiphase imaging of freezing particle suspensions by confocal microscopy

Ice-templating is a well-established processing route for porous ceramics. Because of the structure/properties relationships, it is essential to better understand and control the solidification microstructures. Ice-templating is based on the segregation and concentration of particles by growing ice crystals. What we understand so far of the process is based on either observations by optical or X-ray imaging techniques, or on the characterization of ice-templated materials. However, in situ observations at particle-scale are still missing. Here we show that confocal microscopy can provide multiphase imaging of ice growth and the segregation and organization of particles. We illustrate the benefits of our approach with the observation of particles and pore ice in the frozen structure, the dynamic evolution of the freeze front morphology, and the impact of PVA addition on the solidification microstructures. These results prove in particular the importance of controlling both the temperature gradient and the growth rate during ice-templating.

cond-mat.soft↗