Polyvinylpyrrolidone (PVP) mitigates the damaging effects of intracellular ice formation in adult stem cells

A High-Resolution Microscopy System for Biological Studies of Cold-Adapted Species Under Physiological Conditions

The Antarctic seabed harbors significant biodiversity, and almost 90% of oceanic environments are permanently below 5 °C (i.e., deep sea and polar regions). However, organisms whose entire lifecycle occurs around 0 °C are understudied, leaving this large and diverse proportion of the global biome poorly understood. To address this question at the cellular level, tools are required for high-resolution imaging of biological systems under physiological conditions. This poses severe technical challenges. High-resolution imaging objectives require short working distances and immersion media, causing rapid heat transfer from the microscope to the sample. This affects the viability of live specimens and the interpretability of results. Here, we present a method for high-fidelity imaging of live biological samples at temperatures of around, or below, 0 °C. It relies on hardware additions to traditional microscopy, namely as a cooling collar, 10% ethanol as an immersion medium, and nitrogen flow to reduce condensation It can be straightforwardly implemented on different microscopy modalities, including super-resolution imaging. The method is demonstrated in live cell cultures derived from Antarctic fish and highlights the need to maintain physiological conditions for these fragile samples. Future applications include evolutionary biology, biophysics and biotechnology.

Effects of Decade Long Freezing Storage on Adipose Derived Stem Cells Functionality

Over the last decade and half, the optimization of cryopreservation for adipose tissue derived stromal/stem cells (ASCs) especially in determining the optimal combination of cryoprotectant type, cooling rate, and thawing rate have been extensively studied. In this study, we examined the functionality of ASCs that have been frozen-stored for more than 10 years denoted as long-term freezing, frozen within the last 3 to 7 years denoted as short-term freezing and compared their response with fresh ASCs. The mean post-thaw viability for long-term frozen group was 78% whereas for short-term frozen group 79% with no significant differences between the two groups. The flow cytometry evaluation of stromal surface markers, CD29, CD90, CD105, CD44, and CD73 indicated the expression (above 95%) in passages P1-P4 in all of the frozen-thawed ASC groups and fresh ASCs whereas the hematopoietic markers CD31, CD34, CD45, and CD146 were expressed extremely low (below 2%) within both the frozen-thawed and fresh cell groups. Quantitative real time polymerase chain reaction (qPCR) analysis revealed some differences between the osteogenic gene expression of long-term frozen group in comparison to fresh ASCs. Intriguingly, one group of cells from the short-term frozen group exhibited remarkably higher expression of osteogenic genes in comparison to fresh ASCs. The adipogenic differentiation potential remained virtually unchanged between all of the frozen-thawed groups and the fresh ASCs. Long-term cryopreservation of ASCs, in general, has a somewhat negative impact on the osteogenic potential of ASCs, especially as it relates to the decrease in osteopontin gene expression but not significantly so with respect to RUNX2 and osteonectin gene expressions. However, the adipogenic potential, post thaw viability, and immunophenotype characteristics remain relatively intact between all the groups.

Adult multipotent stromal cell cryopreservation: Pluses and pitfalls

Study and clinical testing of adult multipotent stromal cells (MSCs) are central to progressive improvements in veterinary regenerative medicine. Inherent limitations to long-term culture preclude use for storage. Until cell line creation from primary isolates becomes routine, MSC stasis at cryogenic temperatures is required for this purpose. Many protocols and reagents, including cryoprotectants, used for veterinary MSCs are derived from those for human and rodent cells. Dissimilarities in cryopreservation strategies play a role in variable MSC behaviors. Familiarity with contemporary cryopreservation reagents and processes is essential to an appreciation of their impact on MSC survival and post-cryopreservation behavior. In addition to these points, this review includes a brief history and description of current veterinary stem cell regulation.

Measurement of the biophysical properties of porcine adipose-derived stem cells by a microperfusion system

Adipose-derived stem cells (ADSCs), which are an accessible source of adult stem cells with capacities for self-renewal and differentiation into various cell types, have a promising potential in tissue engineering and regenerative medicine strategies. To meet the clinical demand for ADSCs, cryopreservation has been applied for long-term ADSC preservation. To optimize the addition, removal, freezing, and thawing of cryoprotective agents (CPAs) applied to ADSCs, we measured the transport properties of porcine ADSCs (pADSCs). The cell responses of pADSCs to hypertonic phosphate-buffered saline and common CPAs, dimethyl sulfoxide, ethylene glycol, and glycerol were measured by a microperfusion system at temperatures of 28, 18, 8, and -2°C. We determined the osmotically inactive cell volume (Vb), hydraulic conductivity (Lp), and CPA permeability (Ps) at various temperatures in a two-parameter model. Then, we quantitatively analyzed the effect of temperature on the transport properties of the pADSC membrane. Biophysical parameters were used to optimize CPA addition, removal, and freezing processes to minimize excessive shrinkage of pADSCs during cryopreservation. The biophysical properties of pADSCs have a great potential for effective optimization of cryopreservation procedures.

A numerical study on distributions during cryoprotectant loading caused by laminar flow in a microchannel

In this work, we conduct a computational study on the loading of cryoprotective agents into cells in preparation for cryopreservation. The advantages of microfluidics in cryopreserving cells include control of fluid flow parameters for reliable cryoprotectant loading and reproducible streamlined processing of samples. A 0.25 m long, three inlet T-junction microchannel serves as an idealized environment for this process. The flow field and concentration distribution are determined from a computational fluid dynamics study and cells are tracked as inert particles in a Lagrangian frame. These particles are not confined to streamlines but can migrate laterally due to the Segre-Sildeberg effect for particles in a shear flow. During this tracking, the local concentration field surrounding the cell is monitored. This data are used as input into the Kedem-Katchalsky equations to numerically study passive solute transport across the cell membrane. As a result of the laminar flow, each cell has a unique pathline in the flow field resulting in different residence times and a unique external concentration field along its path. However, in most previous studies, the effect of a spatially varying concentration field on the transport across the cell membrane is ignored. The dynamics of this process are investigated for a population of cells released from the inlet. Using dimensional analysis, we find a governing parameter α, which is the ratio of the time scale for membrane transport to the average residence time in the channel. For [Formula: see text], cryoprotectant loading is completed to within 5% of the target concentration for all of the cells. However, for [Formula: see text], we find the population of cells does not achieve complete loading and there is a distribution of intracellular cryoprotective agent concentration amongst the population. Further increasing α beyond a value of 2 leads to negligible cryoprotectant loading. These simulations on populations of cells may lead to improved microfluidic cryopreservation protocols where more consistent cryoprotective agent loading and freezing can be achieved, thus increasing cell survival.