The effect of extracellular ice and cryoprotective agents on the water permeability parameters of human sperm plasma membrane during freezing

Freezing of Solute-Laden Aqueous Solutions: Kinetics of Crystallization and Heat- and Mass-Transfer-Limited Model

Following an earlier study, we reexamined the latent heat of fusion during freezing at 5 K/min of twelve different pre-nucleated solute-laden aqueous solutions using a Differential Scanning Calorimeter (DSC) and correlated it with the amount of initially dissolved solids or solutes in the solution. In general, a decrease in DSC-measured heat release (in comparison to that of pure water, 335 mJ/mg) was observed with an increasing fraction of dissolved solids or solutes, as observed in the earlier study. In addition, the kinetics of ice crystallization was also obtained in three representative biological media by performing additional experiments at 1, 5 and 20 K/min. A model of ice crystallization based on the phase diagram of a water–NaCl binary solution and a modified Avrami-like model of kinetics was then developed and fit to the experimental data. Concurrently, a heat and mass transfer model of the freezing of a salt solution in a small container is also presented to account for the effect of the cooling rate as well as the solute concentration on the measured latent of freezing. This diffusion-based model of heat and mass transfer was non-dimensionalized, solved using a numerical scheme and compared with experimental results. The simulation results show that the heat and mass transfer model can predict (± 10%) the experimental results.

Effect of subfreezing storage on the qualities of dough and bread containing pea protein

BACKGROUND

In this paper, -6, -9 and -12 °C were selected as subfreezing temperatures of dough containing pea protein based on the results of low-field nuclear magnetic relaxation time. The effect of storage at subfreezing temperatures on dough properties was then investigated and compared with sample storage at -18 °C.

RESULTS

The pH value, springiness, resilience, cohesiveness of dough and sensory score of bread gradually decreased and the hardness and water loss rate of dough gradually increased with the extension of storage time. However, dough hardness, viscoelasticity and fermentation volume were maintained more effectively in subfreezing storage than in -18 °C storage. The subfreezing temperature could alleviate the damage of gluten network structure in frozen dough by ice crystals and was beneficial in maintaining the elasticity of gluten proteins. The network system of pea protein, gluten protein and starch granules in dough storage at -9 and -12 °C was more tightly connected and the microstructure was similar to that at -18 °C. There was no significant difference between the quality of bread made from the dough stored at subfreezing temperature and that stored at -18 °C for 1-6 weeks, and the preservation effect at -12 °C was closer to that at -18 °C.

CONCLUSION

Subfreezing storage can keep the stability of dough containing pea protein close to traditional frozen storage (-18 °C), which provides a new method for storage and transportation of frozen dough. © 2022 Society of Chemical Industry.

Controlled rate slow freezing with lyoprotective agent to retain the integrity of lipid nanovesicles during lyophilization

We designed a novel lyophilization method using controlled rate slow freezing (CSF) with lyoprotective agent (LPA) to achieve intact lipid nanovesicles after lyophilization. During the freezing step, LPA prevented water supercooling, and the freezing rate was controlled by CSF. Regulating the freezing rate by various liquid media was a crucial determinant of membrane disruption, and isopropanol (freezing rate of 0.933 °C/min) was the optimal medium for the CSF system. Lyophilized lipid nanovesicle using both CSF and LPA retained 92.9% of the core material and had uniform size distributions (Z-average diameter = 133.4 nm, polydispersity index = 0.144), similar to intact vesicles (120.7 nm and 0.159, respectively), after rehydration. Only lyophilized lipid nanovesicle using both CSF and LPA showed no changes in membrane fluidity and polarity. This lyophilization method can be applied to improve storage stability of lipid nanocarriers encapsulating drugs while retaining their original activity.

New Sperm Morphology Analysis in Equids: Trumorph® Vs Eosin-Nigrosin Stain

The evaluation of the male fertility potential is based on the analysis of the basic spermatic characteristics of concentration, motility and morphology. Thus, the study of sperm morphology is a fundamental element in the seminal analysis, but its real meaning has been biased by the techniques used for its evaluation. These techniques involve dehydration phases and subsequent staining, which involves the production of artifacts. The aim of the study is to compare two methods for equid semen morphology evaluation, Trumorph^® using living sperm vs. eosin-nigrosine stain. A total of 49 ejaculates from stallions and donkeys were used. After semen collection and dilution, an aliquot was placed on the slide and introduced in the Trumorph^® device. Then observation was made with a 40x objective and negative phase-contrast microscope. Another aliquot was stained using eosin-nigrosine stain and viewed using 100× magnification. Well-formed sperm were observed, and different abnormalities were identified using Trumorph^®. The use of eosin-nigrosin staining method and Trumorph^® led to the same results and both techniques can be used for stallion and donkey sperm morphological analysis. However, considering the fact that Trumorph^® uses living sperm helps prevent sperm cell alteration during sample preparation. Therefore, Trumorph^® can be a good alternative to the conventional staining method, which provides a quick test on live sperm.

Aseptic capillary vitrification of human spermatozoa: Cryoprotectant-free vs. cryoprotectant-included technologies

The protocol of aseptic cryoprotectant-free vitrification on human spermatozoa is well documented. However, data about the effect of permeable cryoprotectants at this procedure is limited. Presented study aimed to test the aseptic capillary vitrification technologies using permeable cryoprotectant-included or cryoprotectant-free media. Thirty-two normal samples were included and analyzed after vitrification in three different media and thawing. Three treatment groups were formed: Group 1, basic medium; Group 2, basic medium with 0.25 M sucrose; Group 3, basic medium with glycerol. Before plunging into liquid nitrogen, capillaries were filled by 10 μl of spermatozoa suspension and isolated from liquid nitrogen by location in hermetically closed 0.25 ml straws. Progressive motility, plasma membrane integrity, total motility/viability after 24, 48 and 72 h in vitro culture, apoptosis and mitochondrial membrane potential (ΔΨm) were determined after thawing at 42 °C. Progressive motility of spermatozoa in groups 1, 2, 3 was 24.9 ± 1.7%, 34.5 ± 2.8% and 34.0 ± 1.4%, respectively (P_1-2,3<0.05). The plasma membrane integrity of spermatozoa in groups 2 and 3 (48.4 ± 2.9% and 45.5 ± 3.9%, respectively) was higher than in Group 1 (33.3 ± 2.1%, P < 0.05). After 24 h, 48 h and 72 h in vitro culture, the total motility and viability of spermatozoa in Group 1 was significantly lower than Group 2 and Group 3. The apoptosis rate in Group 3 (44.5 ± 3.0%) and Group 2 (47.7 ± 4.1%) were lower than in Group 1 (52.5 ± 4.4%; P < 0.05). ΔΨm rates in Group 3 and Group 2 were higher than in Group 1 (P < 0.05) with no statistical differences between this parameter in Group 2 and Group 3 (P > 0.1). In conclusion, supplementation of medium for aseptic capillary technology for cryoprotectant-free vitrification of human spermatozoa by permeable cryoprotectant does not improve the quality of spermatozoa after warming.

Water-transport and intracellular ice formation of human adipose-derived stem cells during freezing

The key to optimizing the cryopreservation strategy of human adipose-derived stem cells (hADSCs) is to identify the biophysical characteristics during freezing. Systematic freezing experiments were conducted under a cryo-microscope system to investigate the cryoinjury mechanism for hADSCs at different cooling rates. By simultaneously fitting morphological change data to the water-transport equation at 5, 10 and 20 °C/min, the plasma membrane hydraulic conductivity, L_pg, and activation energy, E_Lp, were determined. Moreover, the optimal cooling rate was also predicted by using mathematical model methods. Additionally, the surface-catalyzed nucleation (SCN) parameters were calculated by fitting in numerical models, Ω₀^SCN and k₀^SCN were determined at cooling rates of 30, 45 and 60 °C/min. These results may provide potential application value for cryopreservation of hADSCs.

Cryoprotective role of organic Zn and Cu supplementation in goats (Capra hircus) diet

The current study focused on cryopreservation and assessment of characters of post-thaw semen of indigenous Osmanabadi bucks maintained with standard diet, supplemented with different concentrations of organic zinc (Zn), copper (Cu) or in combination, for a period of 180 days. The different doses of organic Zn and Cu were fed per kg DM basis, Zn groups (low: Zn20, medium: Zn40 and high: Zn60), Cu groups: (low: Cu12.5, medium: Cu25 and high: Cu37.5) and combination of Zn + Cu groups (low: Zn20 + Cu12.5, medium: Zn40 + Cu25 and high: Zn60 + Cu37.5) respectively. The control group bucks were maintained mainly on the basal diet without any additional mineral supplementation. Two hundred and forty (240) semen samples were collected from 40 bucks aged 11 months, through electro ejaculator method, processed and analysed for sperm quality parameters both at pre freeze and post-thaw stage. The semen samples were diluted in Tris egg yolk extender, cooled and equilibrated for 4 h at 5 °C, cryopreserved using programmable freezer (PLANER Kryo 360-1.7) and stored at -196 °C. The organic trace minerals (Zn, Cu and Zn + Cu) protected the spermatozoa against the cryoinjury and maintained higher post-thaw semen parameters except in high Zn group. Additional feeding of organic Cu and Zn to bucks had a protective role and resulted in higher sperm liveability, plasma membrane and acrosome integrities, motility and velocity and reduced oxidative stress in supplemented goats (P < 0.05).

The effects of storing and transporting cryopreserved semen samples on dry ice

Objective

This study aimed to test the effects on sperm viability of transporting cryopreserved semen samples on dry ice.

Methods

Twenty normozoospermic semen samples were cryopreserved and divided into five groups. The samples in Group 1 were immersed in liquid nitrogen throughout the experiment in cryogenic storage tanks; the cryopreserved straws in Group 2 were placed in a Styrofoam box containing dry ice and kept under these conditions for 48 hours; the samples in Group 3 were kept for 48 hours on dry ice under the same conditions as the Group 2 samples, and were then moved to a storage tank filled with liquid nitrogen; Group 4 samples were also kept for 48 hours in dry ice storage, and the Styrofoam box containing the samples was shipped by plane to assess the effects of shipping; the samples in Group 5 were shipped together with the Group 4 samples and were placed in a storage tank with liquid nitrogen after spending 48 hours stored on dry ice. After thawing, sperm parameters were analyzed for viability, vitality, and motility; spermatozoa were also tested for mitochondrial activity.

Results

Significant decreases in motility recovery rates (P=0.01) and vitality (P=0.001) were observed in all groups when compared to the control group. Mitochondrial activity was significantly decreased only in Group 5 (P=0.04), as evidenced by greater numbers of sperm cells not stained by reagent 3,3'-diaminobenzidine.

Conclusions

Transportation did not affect the quality of cryopreserved semen samples, but dry ice as a means to preserve the samples during transportation had detrimental effects upon the sperm parameters assessed in this study.

Evaluation of the Efficiency of Two Different Freezing Media and Two Different Protocols to Preserve Human Spermatozoa from Cryoinjury

It is universally recognized that cryopreservation impairs sperm quality. In order to improve postthawing sperm survival and motility, media of different composition and different protocols have been proposed. However, no clear evidence is available to understand which are the most efficient protocol and medium for sperm cryopreservation. The present study evaluates the efficiency of two different cryopreservation protocols and two common freezing media (FM) containing different cryoprotectants (CPs), TEST Yolk Buffer (TYB) and Sperm Freeze (SF), to preserve human sperm quality. Our data suggest that TYB is better than SF both in terms of postthaw viability and in terms of progressive motility, while the direct addition of FM to the sperm sample resulted in the most efficient protocol in terms of postthaw viability but not in terms of progressive motility.

Comparative Study on Two Different Methods for Determination of Hydraulic Conductivity of HeLa Cells During Freezing

BACKGROUND

The measurement of hydraulic conductivity of the cell membrane is very important for optimizing the protocol of cryopreservation and cryosurgery. There are two different methods using differential scanning calorimetry (DSC) to measure the freezing response of cells and tissues. Devireddy et al. presented the slow-fast-slow (SFS) cooling method, in which the difference of the heat release during the freezing process between the osmotically active and inactive cells is used to obtain the cell membrane hydraulic conductivity and activation energy. Luo et al. simplified the procedure and introduced the single-slow (SS) cooling protocol, which requires only one cooling process although different cytocrits are required for the determination of the membrane transport properties. To the best of our knowledge, there is still a lack of comparison of experimental processes and requirements for experimental conditions between these two methods. This study made a systematic comparison between these two methods from the aforementioned aspects in detail.

METHODS

The SFS and SS cooling methods mentioned earlier were utilized to obtain the reference hydraulic conductivity (L_pg) and activation energy (E_Lp) of HeLa cells by fitting the model to DSC data.

RESULTS

With the SFS method, it was determined that L_pg = 0.10 μm/(min·atm) and E_Lp = 22.9 kcal/mol; whereas the results obtained by the SS cooling method showed that L_pg = 0.10 μm/(min·atm) and E_Lp = 23.6 kcal/mol.

CONCLUSIONS

The results indicated that the values of the water transport parameters measured by two methods were comparable. In other words, the two parameters can be obtained by comparing the heat releases between two slow cooling processes of the same sample according to the SFS method. However, the SS method required analyzing heat releases of samples with different cytocrits. Thus, more experimental time was required.

Standards in reporting cryopreserved donor sperm characteristics: should they be reported post-thaw or post-wash?

An increase in the reliance on imported donor samples has been the consequence of a continued shortage of UK donors. Disputes can arise between suppliers and purchasers if the sperm quality is not as expected, yet there appears to be no requirement for the standardization of methods for sperm processing or analysis. Following analysis of 102 donor intrauterine insemination cycles, this study demonstrates that the motile sperm concentration is significantly (P < 0.05) reduced after the necessary removal of cryoprotectant before insemination. Suppliers of donor spermatozoa should therefore provide information on standards used for sperm assessment and whether analysis is performed before or after washing in order that purchasers are better informed about the quality of the end product they are committed to buying.

Determination of the Membrane Permeability to Water of Human Vaginal Mucosal Immune Cells at Subzero Temperatures Using Differential Scanning Calorimetry

To study mucosal immunity and conduct HIV vaccine trials, it is important to be able to cryopreserve mucosal specimens and recover them in functional viable form. Obtaining a good recovery depends, in part, on cooling the cells at the appropriate rate, which is determined by the rate of water transport across the cell membrane during the cooling process. In this study, the cell membrane permeabilities to water at subzero temperatures of human vaginal mucosal T cells and macrophages were measured using the differential scanning calorimetry method proposed by Devireddy et al. in 1998. Thermal histograms were measured before and after cell lysis using a Slow-Fast-Fast-Slow cooling program. The difference between the thermal histograms of the live intact cells and the dead lysed cells was used to calculate the temperature-dependent cell membrane permeability at subzero temperatures, which was assumed to follow the Arrhenius relationship, [Formula: see text], where Lpg is the permeability to water at the reference temperature (273.15 K). The results showed that Lpg = 0.0209 ± 0.0108 μm/atm/min and Ea = 41.5 ± 11.4 kcal/mol for T cells and Lpg = 0.0198 ± 0.0102 μm/atm/min and Ea = 38.2 ± 10.4 kcal/mol for macrophages, respectively, in the range 0°C to -40°C (mean ± standard deviation). Theoretical simulations predicted that the optimal cooling rate for both T cells and macrophages was about -3°C/min, which was proven by preliminary immune cell cryopreservation experiments.

Use of high concentrations of dimethyl sulfoxide for cryopreservation of HepG2 cells adhered to glass and polydimethylsiloxane matrices

Animal cells are generally cryopreserved in cryovials in a cell suspension state containing 5%-10% v/v dimethyl sulfoxide (DMSO) used as a cryoprotective agent. However, cryopreservation of cells in an attached state has not been intensively studied, and the effective freezing solution remains unknown. Here we determined the suitable DMSO concentration for the cryopreservation of human hepatoma HepG2 cells attached to glass and polydimethylsiloxane (PDMS) matrices coated with poly-l-lysine. With the use of the glass matrix, the rate of cell adhesion increased with the DMSO concentration up to 30% v/v in the freezing solution. In contrast, the cell-adhesion rate remained constant in the case of the PDMS matrix irrespective of the DMSO concentration between 10% v/v and 30% v/v. The viability of post-thawed cells attached to glass or PDMS matrix was also investigated. The viability was highest at the DMSO concentration of 20% v/v in the freezing solution. The DMSO concentration of 30% v/v, however, had a cytotoxic effect on the cell viability. Thus, the 20% v/v DMSO concentration was found to be most suitable for the cryopreservation of HepG2 cells in the attached state. This dose is high compared to the DMSO concentration used for the cryopreservation of cells in the suspended state.

Calorimetric analysis of cryopreservation and freeze-drying formulations

Differential scanning calorimetry (DSC) is a commonly used thermal analysis technique in cryopreservation and freeze-drying research. It has been used to investigate crystallization, eutectic formation, glass transition, devitrification, recrystallization, melting, polymorphism, molecular relaxation, phase separation, water transport, thermochemistry, and kinetics of complex reactions (e.g., protein denaturation). Such information can be used for the optimization of protective formulations and process protocols. This chapter gives an introduction to beginners who are less familiar with this technique. It covers the instrument and its basic principles, followed by a discussion of the methods as well as examples of specific applications.

The effect of solution nonideality on modeling transmembrane water transport and diffusion-limited intracellular ice formation during cryopreservation

A new model was developed to predict transmembrane water transport and diffusion-limited ice formation in cells during freezing without the ideal-solution assumption that has been used in previous models. The model was applied to predict cell dehydration and intracellular ice formation (IIF) during cryopreservation of mouse oocytes and bovine carotid artery endothelial cells in aqueous sodium chloride (NaCl) solution with glycerol as the cryoprotectant or cryoprotective agent. A comparison of the predictions between the present model and the previously reported models indicated that the ideal-solution assumption results in under-prediction of the amount of intracellular ice at slow cooling rates (<50 K/min). In addition, the lower critical cooling rates for IIF that is lethal to cells predicted by the present model were much lower than those estimated with the ideal-solution assumption. This study represents the first investigation on how accounting for solution nonideality in modeling water transport across the cell membrane could affect the prediction of diffusion-limited ice formation in biological cells during freezing. Future studies are warranted to look at other assumptions alongside nonideality to further develop the model as a useful tool for optimizing the protocol of cell cryopreservation for practical applications.

High-resolution multiphoton cryomicroscopy

An ultracompact high-resolution multiphoton cryomicroscope with a femtosecond near infrared fiber laser has been utilized to study the cellular autofluorescence during freezing and thawing of cells. Cooling resulted in an increase of the intracellular fluorescence intensity followed by morphological modifications at temperatures below -10 °C, depending on the application of the cryoprotectant DMSO and the cooling rate. Furthermore, fluorescence lifetime imaging revealed an increase of the mean lifetime with a decrease in temperature. Non-destructive, label-free optical biopsies of biomaterial in ice can be obtained with sub-20 mW mean powers.

Freezing injury: the special case of the sperm cell

The cellular damage that spermatozoa encounter at rapid rates of cooling has often been attributed to the formation of intracellular ice although no convincing evidence of intracellular ice formation has ever been obtained. We demonstrate that the high intracellular protein content together with the osmotic shrinkage associated with extracellular ice formation leads to intracellular vitrification of spermatozoa during cooling. At rapid rates of cooling the cell damage to spermatozoa is a result of an osmotic imbalance encountered during thawing, not intracellular ice formation. The osmotic imbalance occurs at rapid cooling rates due to a diffusion limited ice crystallisation in the extracellular fluid, i.e. the amount of ice forming during the cooling is less than expected from the equilibrium phase diagram. This explanation allows insights into other aspects of the cryobiology of spermatozoa and it is anticipated that this understanding will lead to specific improved methods of conventional cryopreservation for mammalian spermatozoa. It is also likely that this model will be relevant to the development of novel technologies for sperm preservation including vitrification and freeze drying.

Novel Approaches to the Cryopreservation of Human Spermatozoa: History and Development of the Spermatozoa Vitrification Technology

Cryobiology is very intensively applied in reproductive and veterinary medicine for preservation of gametes, embryos and reproductive tissues. Sub-zero temperatures combined with appropriate cryoprotective agents preserve the physiological and reproductive functions of the cells making long-term storage possible without loss of viability. With the use of cryoprotective agents it has become possible to develop cryopreservation techniques, such as the slow conventional freezing and vitrification that are in use in the present times. In slow controlled-rate conventional freezing extracellular ice crystals are formed whereas in vitrification no ice crystals are formed. Glass formation is compatible with the survival of the cell and the preservation of its intracellular structures provided the type(s) and concentrations of cryoprotectant used are not chemo- or osmotoxic. However, irrespective of the type of cooling method employed the cryosurvival of cells and tissues is influenced by the size and maturity of cells, amounts of intracellular water, quality and quantity of intracellular lipids, type of cells, their function and morphology. The intracellular milieu of cryopreserved cells and tissues remain less understood. The application of nanotechnology may help reveal and help advance our knowledge of the cryobiological principles involved in cryosurvival. At this moment the methods of cryopreservation that merit further investigation are vitrification and lyophilization. Vitrification is cheap if reagents are prepared in-house and the procedure can be performed rapidly. It has been successfully applied for gametes and embryos (of different stages of development), and reproductive cells/tissues, somatic cells and stem cells. However, vitrification is more demanding technically and requires operation and storage at sub-zero temperatures. On the other hand lyophilization deserves further investigation because it is a cheaper form of cryopreservation that may enable cryostorage at less demanding temperatures of 4°C and may even allow transport at ambient temperature. These possibilities are explored in this review.

Do physical forces contribute to cryodamage?

To achieve the ultimate goal of both cryosurgery and cryopreservation, a thorough understanding of the processes responsible for cell and tissue damage is desired. The general belief is that cells are damaged primarily due to osmotic effects at slow cooling rates and intracellular ice formation at high cooling rates, together termed the "two factor theory." The present study deals with a third, largely ignored component--mechanical damage. Using pooled bull sperm cells as a model and directional freezing in large volumes, samples were frozen in the presence or absence of glass balls of three different diameters: 70-110, 250-500, and 1,000-1,250 microm, as a means of altering the surface area with which the cells come in contact. Post-thaw evaluation included motility at 0 h and after 3 h at 37 degrees C, viability, acrosome integrity, and hypoosmotic swelling test. Interactions among glass balls, sperm cells, and ice crystals were observed by directional freezing cryomicroscopy. Intra-container pressure in relation to volume was also evaluated. The series of studies presented here indicate that the higher the surface area with which the cells come in contact, the greater the damage, possibly because the cells are squeezed between the ice crystals and the surface. We further demonstrate that with a decrease in volume, and thus increase in surface area-to-volume ratio, the intra-container pressure during freezing increases. It is suggested that large volume freezing, given that heat dissipation is solved, will inflict less cryodamage to the cells than the current practice of small volume freezing.

Comparison of the permeability properties and post-thaw motility of ejaculated and epididymal bovine spermatozoa

There are very few experimental reports on the comparative water transport (membrane permeability) characteristics of ejaculated and epididymal mammalian spermatozoa during freezing. In the present study, we report the effects of cooling ejaculated and epididymal bovine sperm from the same males with and without the presence of a cryoprotective agent, glycerol. Water transport data during freezing of ejaculated and epididymal bovine sperm suspensions were obtained at a cooling rate of 20 degrees C/min under two different conditions: (1) in the absence of any cryoprotective agents, CPAs and, (2) in the presence of 0.7 M glycerol. Using values published in the literature, we modeled the spermatozoa as a cylinder of length 39.8 microm and a radius of 0.4 microm with an osmotically inactive cell volume, V(b), of 0.61 V(o), where V(o) is the isotonic cell volume. The subzero water transport response is analyzed to determine the variables governing the rate of water loss during cooling of bovine spermatozoa, i.e. the membrane permeability parameters (reference membrane permeability, L(pg) and activation energy, E(Lp)). The predicted best-fit permeability parameters ranged from, L(pg)=0.021-0.038 microm/min-atm and E(Lp)=27.8-41.1 kcal/mol. The subzero water transport response and consequently the subzero water transport parameters are not significantly different between the ejaculated and epididymal bovine spermatozoa under corresponding cooling conditions. If this observation is found to be more generally valid for other mammalian species as well, then in the future the sperm extracted from the testes of a postmortem male could be optimally cryopreserved using procedures similar to those derived for ejaculated sperm.

Cellular biophysics during freezing of rat and mouse sperm predicts post-thaw motility

Though cryopreservation of mouse sperm yields good survival and motility after thawing, cryopreservation of rat sperm remains a challenge. This study was designed to evaluate the biophysics (membrane permeability) of rat in comparison to mouse to better understand the cooling rate response that contributes to cryopreservation success or failure in these two sperm types. In order to extract subzero membrane hydraulic permeability in the presence of ice, a differential scanning calorimeter (DSC) method was used. By analyzing rat and mouse sperm frozen at 5 degrees C/min and 20 degrees C/min, heat release signatures characteristic of each sperm type were obtained and correlated to cellular dehydration. The dehydration response was then fit to a model of cellular water transport (dehydration) by adjusting cell-specific biophysical (membrane hydraulic permeability) parameters L(pg) and E(Lp). A "combined fit" (to 5 degrees C/min and 20 degrees C/min data) for rat sperm in Biggers-Whitten-Whittingham media yielded L(pg) = 0.007 microm min(-1) atm(-1) and E(Lp) = 17.8 kcal/mol, and in egg yolk cryopreservation media yielded L(pg) = 0.005 microm min(-1) atm(-1) and E(Lp) = 14.3 kcal/mol. These parameters, especially the activation energy, were found to be lower than previously published parameters for mouse sperm. In addition, the biophysical responses in mouse and rat sperm were shown to depend on the constituents of the cryopreservation media, in particular egg yolk and glycerol. Using these parameters, optimal cooling rates for cryopreservation were predicted for each sperm based on a criteria of 5%-15% normalized cell water at -30 degrees C during freezing in cryopreservation media. These predicted rates range from 53 degrees C/min to 70 degrees C/min and from 28 degrees C/min to 36 degrees C/min in rat and mouse, respectively. These predictions were validated by comparison to experimentally determined cryopreservation outcomes, in this case based on motility. Maximum motility was obtained with freezing rates between 50 degrees C/min and 80 degrees C/min for rat and at 20 degrees C/min with a sharp drop at 50 degrees C/min for mouse. In summary, DSC experiments on mouse and rat sperm yielded a difference in membrane permeability parameters in the two sperm types that, when implemented in a biophysical model of water transport, reasonably predict different optimal cooling rate outcomes for each sperm after cryopreservation.

Determination of the water permeability (Lp) of mouse oocytes at -25 degrees C and its activation energy at subzero temperatures

Typically, subzero permeability measurements are experimentally difficult and infrequently reported. Here we report an approach we have applied to mouse oocytes. Interrupted cooling involves rapidly cooling oocytes (50 degrees C/min) to an intermediate temperature above the intracellular nucleation zone, holding them for up to 40 min while they dehydrate, and then rapidly cooling them to -70 degrees C or below. If the intermediate holding temperature and holding time are well chosen, high post thaw survival of the oocytes is possible because the freezable water is removed during the hold. The length of time required for the exit of the freezable water allows the water permeability at that temperature to be determined. These experiments used 1.5M ethylene glycol in PBS and included a transient hold of 2 min for equilibration at -10 degrees C, just below the extracellar ice formation temperature. We obtain an Lp=1.8 x 10(-3)microm min(-1)atm(-1) at -25 degrees C based on a hold time of 30 min yielding 80% survival and the premise that most of the freezable water is removed during the 30 min hold. If we assume that the water permeability is a continuous function of temperature and that its Ea changes at 0 degrees C, we obtain a subzero Ea of 21 kcal/mol; higher than the suprazero value of 14 kcal/mol. A number of assumptions are required for these water loss calculations and the resulting value of Lp can vary by up to a factor of 2, depending on the choices make.

Rapidly cooled horse spermatozoa: Loss of viability is due to osmotic imbalance during thawing, not intracellular ice formation

The cellular damage that spermatozoa encounter at rapid rates of cooling has often been attributed to the formation of intracellular ice. However, no direct evidence of intracellular ice has been presented. An alternative mechanism has been proposed by Morris (2006) that cell damage is a result of an osmotic imbalance encountered during thawing. This paper examines whether intracellular ice forms during rapid cooling or if an alternative mechanism is present. Horse spermatozoa were cooled at a range of cooling rates from 0.3 to 3,000 degrees C/min in the presence of a cryoprotectant. The ultrastructure of the samples was examined by Cryo Scanning Electron Microscopy (CryoSEM) and freeze substitution, to determine whether intracellular ice formed and to examine alternative mechanisms of cell injury during rapid cooling. No intracellular ice formation was detected at any cooling rate. Differential scanning Calorimetry (DSC) was employed to examine the amount of ice formed at different rate of cooling. It is concluded that cell damage to horse spermatozoa, at cooling rates of up to 3,000 degrees C/min, is not caused by intracellular ice formation. Spermatozoa that have been cooled at high rates are subjected to an osmotic shock when they are thawed.

Infrared image to evaluate the selective (directional) freezing due to localized injection of thermally important solutions

Cryosurgery is a minimally invasive surgical technique that employs the destructive effect of freezing to eradicate benign or malignant tumors which are difficult or even impossible to be extirpated by conventional surgery. Recently, we proposed a method for flexibly controlling the freezing scale during cryosurgery by percutaneously injecting thermally important functional solutions into the target tissues. This method can also help modify the direction of the iceball formation which is desirable for a successful cryosurgery for treating tumors with complex anatomical structure. To evaluate the effect of controlling the size, shape and direction of the iceball formation by injecting solutions with specific thermal properties into the target tissues, a medical infrared thermometer was introduced in this paper to map the temperature profile over the whole surface above the treated area. The cryosurgical procedure was performed using a minimally invasive cryoprobe cooled by liquid nitrogen in order to obtain a deep regional freezing. Meanwhile, one thermocouple was also amounted in the tip of the probe to record the transient temperature in order to detect the freezing and thawing effect on the tissues. The obtained infrared image was applied to monitor and evaluate the whole process. Simulation experiments on biological tissues (fresh pork and liver) were performed in vitro and four different liquids were injected into the test materials, which were distilled water, an aqueous suspension of aluminum nano-particles in water, ethanol and a 10% solution of the cryoprotective agent dimethylsulfoxide, (Me2SO), respectively. It was clearly demonstrated that the localized injection of an appropriate solution could effectively regulate the tumor-killing area via directional freezing. The study also suggested that infrared imaging can be used as an effective way to monitor and evaluate the selective freezing process, which will provide important information to help enhance fr- eezing damage to the target diseased tissues while preserving the normal tissues from injury.

Significant variability among bulls in the sperm membrane permeability for water and glycerol: Possible implications for semen freezing protocols for individual males

The aim of this study was to test the hypothesis that bulls have significant intra-individual differences in the hydraulic conductivity (L(p)) and permeability coefficient for glycerol (P(s)) of the sperm cell membrane. The permeability parameters were determined at 22, 10, and 0 degrees C of sperm from 7 Holstein Frisian artificial insemination (AI) bulls, using four ejaculates per bull. A stopped-flow approach was applied to provide temporal resolution sufficient to measure rapid cell volume changes under anisosmotic conditions in the absence or presence of glycerol. This technique utilizes a concentration-dependent self-quenching entrapped fluorophore. The resulting cell volume changes were used in three-parameter fitting calculations to compute L(p) in the absence glycerol, and L(p) in the presence of glycerol (L(p)(gly)) and P(s). Averaged over all bulls, L(p) in the absence of glycerol was 0.28+/-0.01, 0.15+/-0.01 and 0.10+/-0.01 microm min(-1)atm(-1) (mean+/-SD) at 22, 10 and 0 degrees C, respectively, yielding an Arrhenius activation energy (E(a)) of 7.39 kcal/mol. The average L(p)(gly) value at 22 degrees C, was 3.8 times lower than L(p) in the absence of glycerol (P<0.05). L(p)(gly), P(s), and the reflection coefficient (sigma) at 22 degrees C were 0.073+/-0.015 microm min(-1)atm(-1), 0.80+/-0.33 x 10(-3)cm min(-1), and 0.92+/-0.10 (mean+/-SD), respectively. Subsequent experiments were performed at 10 and 0 degrees C. Activation energies for L(p)(gly) and P(s) were 10.08 and 8.77 kcal/mol, respectively. The significant differences between individual bulls in L(p) and P(s) indicate that individual males may require individual adjustments of the cooling protocol. Application of these data in a theoretical model to simulate the osmotic events during freezing resulted in predicted optimal cooling rates in the range of published empirical values.

Effect of antibiotics on thermodynamic properties of freezing media in rabbit species: A first calorimetric approach

Semen freezing is an effective and safe solution for the cryopreservation of animal genetic resources and for the diffusion of the genetic progress. Actually, these techniques are not yet under control for the rabbit species partly because methods are not clearly defined. Thus, the aim of this work is to study the effect of antibiotics (Penicillin G, Streptomycin) routinely used in freezing semen on the thermodynamic properties of freezing media mainly used in rabbit species. Measurements realized by differential scanning calorimetry show that these antibiotics may change the temperature of crystallization and the quantity of ice formed in the freezing media considered. Our calorimetric approach underlined that the composition and the properties of the cryoprotective solutions should be studied more precisely.

The high viscosity encountered during freezing in glycerol solutions: Effects on cryopreservation

The objective of this study was to determine the viscosity of the residual unfrozen solution that cells are exposed to during freezing in the presence of glycerol and use this to interpret some key aspects of cryopreservation. The viscosity of the glycerol-water binary system exceeded 1000 cP at -40 degrees C, whilst the viscosity of the ternary system, glycerol-water-NaCl, exceeded 100,000 cP at -55 degrees C. The effect of these high viscosities on the diffusion of water at a constant temperature during freezing and during cooling at different linear rates has been estimated. At rates of cooling faster than 100 degrees C min(-1) the diffusion distance during freezing was calculated to be less than 15 microm. Validation of the diffusion calculations was confirmed by examination of the ultrastructure of the freeze concentrated matrix in samples prepared at a range of cooling rates. At a critical rate of cooling, water diffusion becomes limited by the high viscosity and two phenomena, of relevance to cryobiology, occur: (1) the composition of the freeze concentrated matrix around cells deviates from that of the equilibrium phase diagram; and (2) the osmotic loss of water from cells is restricted. These factors are of particular relevance to an understanding of the response of cells such as spermatozoa, red blood cells, and bacteria cooled rapidly with glycerol as cryoprotectant.

Effect of glycerol and cholesterol-loaded cyclodextrin on freezing-induced water loss in bovine spermatozoa

Recent experimental data show that incubating bovine sperm with cholesterol-loaded cyclodextrin (CLC) before cryopreservation increases the percentages of motile and viable cells recovered after freezing and thawing, compared with control sperm. In the present study, we report the effect of incubating bovine sperm with CLC on the subzero water transport response and the membrane permeability parameters (reference membrane permeability (Lpg) and activation energy (ELp)). Water transport data during freezing of bovine sperm cell suspensions were obtained at a cooling rate of 20 °C/min under three different conditions: 1. in the absence of cryoprotective agents (CPAs); 2. in the presence of 0.7 M glycerol; and 3. in the presence of 1.5 mg/ml CLC and 0.7 M glycerol. With previously published values, the bovine sperm cell was modeled as a cylinder of length 39.8 μm and radius 0.4 μm, with osmotically inactive cell volume (Vb) of 0.61Vo, whereVois the isotonic cell volume. By fitting a model of water transport to the experimentally obtained data, the best-fit water transport parameters (LpgandELp) were determined. The predicted best-fit permeability parameters ranged fromLpg= 0.02 to 0.036 μm/min-atm andELp= 26.4 to 42.1 kcal/mol. These subzero water transport parameters are significantly different from the suprazero membrane permeability values (obtained in the absence of extracellular ice) reported in the literature. Calculations made of the theoretical response of bovine spermatozoa at subzero temperatures suggest that the optimal cooling rate to cryopreserve bovine spermatozoa is 45–60 °C/min, agreeing quite closely with experimentally determined rates of freezing bovine spermatozoa.

Rapidly cooled human sperm: no evidence of intracellular ice formation

BACKGROUND

The cellular damage that human spermatozoa encounter at rapid rates of cooling has often been attributed to the formation of intracellular ice. However, no direct evidence of intracellular ice has been presented. Alternatively, the cell damage may be the result of an osmotic imbalance encountered during thawing. This article examines whether intracellular ice forms during rapid cooling or if an alternative mechanism is present.

METHODS

In this study, human spermatozoa were cooled at a range of cooling rates from 0.3 to 3000 degrees C/min. The ultrastructure of the samples was examined by cryo scanning electron microscopy and freeze substitution to determine whether intracellular ice formed during rapid cooling and to examine alternative mechanisms of cell injury during rapid cooling.

RESULTS

No intracellular ice formation was detected at any cooling rate. Freeze substitution of cells that had been cooled at 3000 degrees C/min and then slowly warmed showed that the cells had become plasmolysed and had evidence of membrane damage.

CONCLUSIONS

Cell damage to human spermatozoa, at cooling rates of up to 3000 degrees C/min, is not caused by intracellular ice formation. Spermatozoa that have been cooled at high rates are subjected to an osmotic shock when they are thawed.

Transport phenomena during freezing of adipose tissue derived adult stem cells

In the present study a well-established differential scanning calorimeter (DSC) technique is used to measure the water transport phenomena during freezing of stromal vascular fraction (SVF) and adipose tissue derived adult stem (ADAS) cells at different passages (Passages 0 and 2). Volumetric shrinkage during freezing of adipose derived cells was obtained at a cooling rate of 20 degrees C/min in the presence of extracellular ice and two different, commonly used, cryoprotective agents, CPAs (10% DMSO and 10% Glycerol). The adipose derived cells were modeled as spheres of 50 microm diameter with an osmotically inactive volume (Vb) of 0.6Vo, where Vo is the isotonic cell volume. By fitting a model of water transport to the experimentally obtained volumetric shrinkage data, the "best-fit" membrane permeability parameters (reference membrane permeability to water, Lpg or Lpg[cpa] and the activation energy, ELp or ELp[cpa]) were determined. The "best-fit" membrane permeability parameters for adipose derived cells in the absence and presence of CPAs ranged from: Lpg=23.1-111.5x10(-15) m3/Ns (0.135-0.652 microm/min-atm) and ELp=43.1-168.8 kJ/mol (9.7-40.4 kcal/mol). Numerical simulations of water transport were then performed under a variety of cooling rates (5-100 degrees C/min) using the experimentally determined membrane permeability parameters. And finally, the simulation results were analyzed to predict the optimal rates of freezing adipose derived cells in the presence and absence of CPAs.

A simplified procedure to determine the optimal rate of freezing biological systems

The effect of several cell-level parameters on the predicted optimal cooling rate B(opt) of an arbitrary biological system has been studied using a well-defined water transport model. An extensive investigation of the water transport model revealed three key cell level parameters: reference permeability of the membrane to water L(pg), apparent activation energy E(Lp), and the ratio of the available surface area for water transport to the initial volume of intracellular water (SA/WV). We defined B(opt) as the "highest" cooling rate at which a predefined percent of the initial water volume is trapped inside the cell (values ranging from 5% to 80%) at a predefined end temperature (values ranging from -5 degrees C to -40 degrees C). Irrespective of the choice of the percent of initial water volume trapped and the end temperature, an exact and linear relationship exists between L(pg), SA/WV, and B(opt0. However, a nonlinear and inverse relationship is found between E(Lp) and B(opt). Remarkably, for a variety of biological systems a comparison of the published experimentally determined values of B(opt) agreed quite closely with numerically predicted B(opt) values when the model assumed 5% of initial water is trapped inside the cell at a temperature of -15 degrees C. This close agreement between the experimental and model predicted optimal cooling rates is used to develop a generic optimal cooling rate chart and a generic optimal cooling rate equation that greatly simplifies the prediction of the optimal rate of freezing of biological systems.

A theoretically estimated optimal cooling rate for the cryopreservation of sperm cells from a live-bearing fish, the green swordtail Xiphophorus helleri

Sperm cryopreservation of live-bearing fishes, such as those of the genus Xiphophorus is only beginning to be studied, although these fishes are valuable models for biomedical research and are commercially raised as ornamental fish for use in aquariums. To explore optimization of techniques for sperm cryopreservation of these fishes, this study measured the volumetric shrinkage response during freezing of sperm cells of Xiphophorus helleri by use of a shape-independent differential scanning calorimeter (DSC) technique. Volumetric shrinkage during freezing of X. helleri sperm cell suspensions was obtained in the presence of extracellular ice at a cooling rate of 20 degrees C/min in three different media: (1) Hanks' balanced salt solution (HBSS) without cryoprotective agents (CPAs); (2) HBSS with 14% (v/v) glycerol; and (3) HBSS with 10% (v/v) dimethyl sulfoxide (DMSO). The sperm cell was modeled as a cylinder of 33.3 microm in length and 0.59 microm in diameter with an osmotically inactive cell volume (V(b)) of 0.6V(o), where V(o) is the isotonic or initial cell volume. By fitting a model of water transport to the experimentally determined volumetric shrinkage data, the best-fit membrane permeability parameters (reference membrane permeability to water, L(pg) or L(pg)[cpa] and the activation energy, E(Lp) or E(Lp)[cpa]) of the Xiphophorus helleri sperm cell membrane were determined. The best-fit membrane permeability parameters at 20 degrees C/min in the absence of CPAs were: L(pg)=0.776 x 10(-15)m3/Ns (0.0046 microm/min atm), and E(Lp)=50.1 kJ/mol (11.97 kcal/mol) (R2=0.997). The corresponding parameters in the presence of 14% glycerol were L(pg)[cpa]=1.063 x 10(-15)m3/Ns (0.0063 microm/min atm), and E(Lp)[cpa]=83.81 kJ/mol (20.04 kcal/mol) (R2=0.997). The parameters in the presence of 10% DMSO were L(pg)[cpa]=1.4 x 10(-15)m3/Ns (0.0083 microm/min atm), and E(Lp)[cpa]=90.96 kJ/mol (21.75 kcal/mol) (R2=0.996). Parameters obtained in this study suggested that the optimal rate of cooling for X. helleri sperm cells in the presence of CPAs ranged from 20 to 35 degrees C/min and were in close agreement with recently published, empirically determined optimal cooling rates.

Selective freezing of target biological tissues after injection of solutions with specific thermal properties

Cryosurgery is a minimally invasive surgical technique that employs the destructive effect of freezing to eradicate undesirable tissues. This paper proposes a flexible method to control the size and shape of the iceball by injecting solutions with specific thermal properties into the target tissues, to enhance freezing damage to the diseased tissues while preserving the normal tissues from injury. The cryosurgical procedure was performed using a minimally invasive cryoprobe cooled by liquid nitrogen (LN2) to obtain deep regional freezing. Several needle thermocouples were applied simultaneously to record the transient temperature to detect the freezing effect on the tissues. Simulation experiments on biological tissue (fresh pork) were performed in vitro and four different liquids were injected into the test materials; these were distilled water, an aqueous suspension of aluminum nanoparticles in water, ethanol, and a 10% solution of the cryoprotective agent dimethyl sulfoxide (Me2SO). The experimental results demonstrate that the localized injection of an appropriate solution could enhance the tumor-killing effect without altering the freezing conditions. The study also suggests the potential value of combining cryosurgery with other therapeutic methods, such as electrical, chemical, and thermal treatments, to develop new clinical modalities in the near future.

Variation in the Membrane Transport Properties and Predicted Optimal Rates of Freezing for Spermatozoa of Diploid and Tetraploid Pacific Oyster, Crassostrea gigas1

In the present study, a shape-independent differential scanning calorimeter (DSC) technique was used to measure the dehydration response during freezing of sperm cells from diploid and tetraploid Pacific oysters, Crassostrea gigas. This represents the first application of the DSC technique to sperm cells from nonmammalian species. Volumetric shrinkage during freezing of oyster sperm cell suspensions was obtained at cooling rates of 5 and 20 degrees C/min in the presence of extracellular ice and 8% (v/v) concentration of dimethyl sulfoxide (DMSO), a commonly used cryoprotective agent (CPA). Using previously published data, sperm cells from diploid oysters were modeled as a two-compartment "ball-on-stick" model with a "ball" 1.66 microm in diameter and a "stick" 41 microm in length and 0.14 microm wide. Similarly, sperm cells of tetraploid oysters were modeled with a "ball" 2.14 microm in diameter and a "stick" 53 microm in length and 0.17 microm wide. Sperm cells of both ploidy levels were assumed to have an osmotically inactive cell volume, Vb, of 0.6 Vo, where Vo is the isotonic (or initial) cell volume. By fitting a model of water transport to the experimentally obtained volumetric shrinkage data, the best-fit membrane permeability parameters (Lpg and ELp) were determined. The combined-best-fit membrane permeability parameters at 5 and 20 degrees C/min for haploid sperm cells (or cells from diploid Pacific oysters) in the absence of CPAs were: Lpg = 0.30 x 10(-15) m(3)/Ns (0.0017 microm/min-atm) and ELp = 41.0 kJ/mole (9.8 kcal/mole). The corresponding parameters in the presence of 8% DMSO were: Lpg[cpa] = 0.27 x 10(-15) m(3)/Ns (0.0015 microm/min-atm) and ELp[cpa] = 38.0 kJ/mole (9.1 kcal/mole). Similarly, the combined-best-fit membrane permeability parameters at 5 and 20 degrees C/min for diploid sperm cells (or cells from tetraploid Pacific oysters) in the absence of CPAs were: Lpg = 0.34 x 10(-15) m(3)/Ns (0.0019 microm/min-atm) and ELp = 29.7 kJ/mole (7.1 kcal/mole). The corresponding parameters in the presence of 8% DMSO were: Lpg[cpa] = 0.34 x 10(-15) m(3)/Ns (0.0019 microm/min-atm) and ELp[cpa] = 37.6 kJ/mole (9.0 kcal/mole). The parameters obtained in this study suggest that optimal rates of cooling for Pacific oyster sperm cells range from 40 to 70 degrees C/min. These theoretical cooling rates are in close conformity with empirically determined optimal rates of cooling sperm cells from Pacific oysters, C. gigas.

Subzero water transport characteristics of boar spermatozoa confirm observed optimal cooling rates

Incomplete understanding of the water transport parameters (reference membrane permeability, L(pg), and activation energy, E(Lp)) during freezing in the presence of extracellular ice and cryoprotective agents (CPAs) is one of the main limiting factors in reconciling the difference between the numerically predicted value and the experimentally determined optimal rates of freezing in boar (and in general mammalian) gametes. In the present study, a shape-independent differential scanning calorimeter (DSC) technique was used to measure the water transport during freezing of boar spermatozoa. Water transport data during freezing of boar sperm cell suspensions were obtained at cooling rates of 5 and 20 degrees C/min in the presence of extracellular ice and 6% (v/v) glycerol. Using previously published values, the boar sperm cell was modeled as a cylinder of length 80.1 microm and a radius of 0.31 microm with an osmotically inactive cell volume, V(b), of 0.6 V(o), where V(o) is the isotonic cell volume. By fitting a model of water transport to the experimentally obtained data, the best-fit water transport parameters (L(pg) and E(Lp)) were determined. The "combined-best-fit" parameters at 5 and 20 degrees C/min for boar spermatozoa in the presence of extracellular ice are: L(pg) = 3.6 x 10(-15) m(3)/N. s (0.02 microm/min-atm) and E(Lp) = 122.5 kJ/mole (29.3 kcal/mole) (R(2) = 0.99); and the corresponding parameters in the presence of extracellular ice and glycerol are: L(pg)[cpa] = 0.90 x 10(-15) m(3)/N. s (0.005 microm/min-atm) and E(Lp)[cpa] = 75.7 kJ/mole (18.1 kcal/mole) (R(2) = 0.99). The water transport parameters obtained in the present study are significantly different from previously published parameters for boar and other mammalian spermatozoa obtained at suprazero temperatures and at subzero temperatures in the absence of extracellular ice. The theoretically predicted optimal rates of freezing using the new parameters ( approximately 30 degrees C/min) are in close agreement with previously published but experimentally determined optimal cooling rates. This analysis reconciles a long-standing difference between theoretically predicted and experimentally determined optimal cooling rates for boar spermatozoa.

Cryopreservation of Collagen-Based Tissue Equivalents. II. Improved Freezing in the Presence of Cryoprotective Agents

In Part I of this study we determined an optimal cooling rate for cryopreservation of collagen-based tissue equivalents (TEs) that preserves both the postthaw cell viability and mechanical properties, but results in tissue contraction and an overall loss of opacity. The empirically determined optimal cooling rate (5 degrees C/min) was obtained in a freezing medium consisting solely of phosphate-buffered saline (PBS) at physiological concentration (1x). In the present study we report the effect of freezing on TEs in the presence of PBS and two cryoprotective agents (CPAs) (glycerol and dimethyl sulfoxide [Me(2)SO]), at two different concentrations (0.5 and 1.0 M), to two different end temperatures (-80 and -160 degrees C), at a cooling rate of 5 degrees C/min. The controlled rate freezing experiments, postthaw cell viability, and mechanical property measurements were performed as described in Part I of this study. In addition to studying the effect of CPAs on the postthaw properties of TEs, we also investigated (1). the effect of freezing TEs attached to the substrate (as opposed to detached and floating in medium) to determine differences when freezing TEs subject to static mechanical stress via a mechanical constraint to contraction; (2). the effect of freezing glutaraldehyde-fixed TEs to determine differences in freezing-mediated damage to the microstructure; and (3). the effect of freezing more mature TEs that were incubated for 4 weeks in growth factor-supplemented medium as opposed to 2 weeks in basal medium. All TEs frozen at 5 degrees C/min to -80 degrees C in the presence of 0.5 M glycerol or Me(2)SO in PBS were found to be optimally cryopreserved in terms of maintaining opacity and structure as well as cell viability and mechanical properties as compared with unfrozen TEs. The postthaw mechanical properties were adversely affected by freezing to the lower end temperature of -160 degrees C in the presence of CPAs, with the samples frozen in the 1.0 M concentration of CPAs exhibiting a total loss of structural integrity on thawing. Furthermore, TEs frozen attached to the substrate showed decreased opacity and significant contraction as compared with TEs frozen detached from the substrate, as did cross-linked samples frozen without CPA.

Cryopreservation of canine spermatozoa: theoretical prediction of optimal cooling rates in the presence and absence of cryoprotective agents

In the present study a shape independent differential scanning calorimeter (DSC) technique was used to measure the dehydration response during freezing of ejaculated canine sperm cells. Volumetric shrinkage during freezing of canine sperm cell suspensions was obtained at cooling rates of 5 and 10 degrees C/min in the presence of extracellular ice and CPAs (6 different combinations of freezing media were used, ranging from a media with no CPAs, and those with 0.5%, 3%, and 6% glycerol and with 0.5% and 3% Me(2)SO). Using previously published data, the canine sperm cell was modeled as a cylinder of length 105.7mum and a radius of 0.32mum with an osmotically inactive cell volume, V(b), of 0.6 V(o), where V(o) is the isotonic cell volume. By fitting a model of water transport to the experimentally obtained volumetric shrinkage data the best fit membrane permeability parameters (L(pg) and E(Lp)) were determined. The "combined best fit" membrane permeability parameters at 5 and 10 degrees C/min for canine sperm cells in the absence of CPAs are: L(pg)=0.52x10(-15)m(3)/Ns (0.0029mum/min-atm) and E(Lp)=64.0kJ/mol (15.3kcal/mol) (R(2)=0.99); and the corresponding parameters in the presence of CPAs ranged from L(pg)[cpa]=0.46 to 0.53x10(-15) m(3)/Ns (0.0027-0.0031mum/min-atm) and E(Lp)[cpa]=46.4-56.0kJ/mol (11.1-13.4kcal/mol). These parameters are significantly different than previously published parameters for canine and other mammalian sperm obtained at suprazero temperatures and at subzero temperatures in the absence of extracellular ice. The parameters obtained in this study also suggest that optimal rates of freezing canine sperm cells ranges from 10 to 30 degrees C/min; these theoretical cooling rates are found to be in close conformity with previously published but empirically determined optimal cooling rates.

A new development in the cryopreservation of sperm

Recent developments in in vitro fertilization have made it necessary to develop better methods for sperm cryopreservation. This article sets out the cryobiological and physical background relevant to sperm cryopreservation together with some new observations on the morphology of sperm in the frozen state. It also provides new data and analysis using a recently developed improved method of cryopreservation.

Cryopreservation of human sperm

Freezing of human sperm is considered a routine procedure in assisted reproductive technology (ART) laboratories. This article considers various aspects of cryopreservation of human sperm. Human sperm show a specific cryophysical behaviour and different sperm freezing protocols have been developed to avoid damage to the sperm cells. The damage can range from impaired motility and reduced viability to damage to the cellular organelles and effects at the molecular level, resulting in an impaired fertilizing potential. As testicular sperm are immature and only a small number can be retrieved, special techniques are required for successful freezing and thawing of these samples. Banking of human sperm has to be performed in a safe and controlled way and different guidelines are necessary to ensure that this is achieved.