Cryopreservation of winter-dormant apple buds: II - tissue water status after desiccation at -4C and before further cooling

The established protocol for the cryopreservation of winter-dormant Malus buds requires that stem explants, containing a single, dormant bud are desiccated at -4 degree C, for up to 14 days, to reduce their water content to 25-30 percent of fresh weight. Using three apple cultivars, with known differences in response to cryopreservation, the pattern of evaporative water loss has been characterised, including early freezing events in the bud and cortical tissues that allow further desiccation by water migration to extracellular ice. There were no significant differences between cultivars in this respect or in the proportions of tissue water lost during the desiccation process. Differential Scanning Calorimetry (to -90 degree C) of intact buds indicated that bud tissues of the cultivar with the poorest response to cryopreservation had the highest residual water content at the end of the desiccation process and froze at the highest temperature.     

静电场对红细胞悬液冻结特性的影响

本文以红细胞悬液为研究模型,通过在对其进行慢速冻结的过程中引入静电场,具体研究了静电场对降温过程中红细胞悬液冻结特性的影响。实验结果表明:静电场在一定程度上改变了冰晶的形成与生长特性,抑制了晶核的形成, 使晶枝出现不对称生长,并减缓了冰晶的生长速度,这些影响随着场强的增加而逐渐加强。在较强的静电场的影响下,冰晶明显变粗,最终成为块状,细胞也不再与冰晶分离而是完全融入粗大的冰晶之中,在冻结的末期,细胞不再受到冰晶挤压,从而减少了其所受的机械性损伤。     

Antifreeze glycoproteins from the antarctic fish Dissostichus mawsoni studied by differential scanning calorimetry (DSC) in combination with nanolitre osmometry

This study investigates in detail the freezing events during cooling of solutions of various size classes of antifreeze glycoproteins. Differential scanning calorimetry and nanolitre osmometry were used to observe ice growth at temperatures within the hysteresis gap between the melting point and non-equilibrium freezing point (hysteresis freezing point) of solutions of the various sized antifreeze glycoproteins (AFGPs). The ice growth within the hysteresis gap is presumably due to both the expression of primary or near primary prism planes and also some growth at the basal plane. The binding of the AFGPs to the ice causes a particular ice crystal morphology. With the smaller AFGPs, substantial microscopic ice growth was observed in the form of a hexagonal bipyramids within the hysteresis gap.     

Refining the risk of freezing mortality for antarctic terrestrial microarthropods

In studies of three common, freezing susceptible, Antarctic microarthropods, the springtail Cryptopygus antarcticus and the mites Alaskozetes antarcticus and Halozetes belgicae, we report (i) the consequences on cold tolerance of cooling in contact with water, and (ii) the risk of freezing when held at temperatures above the typical freezing point (measured using standard techniques) for up to 12 h. The springtail showed no change in SCP distribution when in contact with freezing water while, in contrast, the mites showed clear shifts towards decreased cold tolerance, in addition to death of c. 33% of individuals during the freezing of the water. The springtail showed a bimodal SCP distribution, with the population divided into "high"(typically -8 to -12 degree C) and "low" (typically below -20 degree C) groups. Some animals held at temperatures above these values froze, over a timescale between minutes and several hours. These results highlight the danger of equating standard cold tolerance measures with mortality risk under more realistic water and thermal regimes.     

Pellet freezing of in vitro produced bovine embryos using dry ice

In vitro produced bovine embryos were frozen by pellet freezing or vitrification method. In the pellet freezing method, the embryos were cooled on the dry ice and then frozen as pellets. At warming, the pellets were immersed directly into 0.5 M sucrose. The survival rates of blastocysts frozen by the pellet freezing method were higher (P<0.01) in 40% ethylene glycol (EG) than those in the lower concentrations (20 and 30% EG). Higher survival rates of blastocysts frozen by the pellet freezing method were obtained but the development rates did not differ, as compared with those by the vitrification method. There were no significant differences between the pellet freezing and vitrification method in the frequencies of post-thaw survival of hatched blastocysts. These results demonstrate that the pellet freezing method using dry ice can be used successfully for the cryopreservation of blastocysts.     

Freezing transition of interfacial water at room temperature under electric fields

The freezing of liquid water into ice was studied inside a gap of nanometer spacing under the control of electric fields and gap distance. The interfacial water underwent a sudden, reversible phase transition to ice in electric fields of 10(6) V m(-1) at room temperature. The critical field strength for the freezing transition was much weaker than that theoretically predicted for alignment of water dipoles and crystallization into polar cubic ice (>10(9) V m(-1)). This new type of freezing mechanism, occurring in weak electric fields and at room temperature, may have immediate implications for ice formation in diverse natural environments.     

前列腺低温微创治疗及器件的研究

利用低温冷冻破坏前列腺增生或肿瘤组织治疗疾病具有许多的优点,如出血少、痛苦小,有时甚至不需要麻醉。前列腺冷冻术可采用两种方法,即穿刺式和接触式。穿刺式就是将探针直接插入病灶组织中心,予以冷冻,主要用于较小的病灶;接触式就是将探针冷冻区接触病灶组织表面予以冷冻,主要用于较小的前列腺增生或不规则的肿瘤等,有时也可将二者结合使用。冷冻术最大的优点还在于可防止肿瘤细胞的扩散。文中详细介绍前列腺冷冻治疗的机理、冷冻探针的结构特点及临床应用效果。     

覆冰垂直粘结强度的测试研究

本文利用自行设计的新型表面覆冰垂直粘结强度测试装置,测试了不同材料表面的覆冰垂直粘结强度,并探讨了基体表面粗糙度、冻冰时间、冰层厚度、冻冰温度等因素对同一材料表面覆冰垂直粘结强度的影响。结果发现,覆冰垂直粘结强度随着材料表面粗糙度增加而增大,随着冰冻温度的升高而降低。而冻冰时间与冰层厚度对覆冰垂直粘结强度的影响较为复杂。     

Larch (Larix kaempferi) xylem parenchyma cells respond to subfreezing temperature by deep supercooling

In previous studies, xylem parenchyma cells (XPCs) in the boreal softwood species larch, which has thick and rigid walls similar to those of XPCs in boreal hardwood species, were shown to respond to subfreezing temperature by deep supercooling during summer but change their freezing behavior to extracellular freezing during winter. In this study, we re-examined freezing behavior of XPCs in larch by observation of deep etching of frozen samples as well as observation of re-warmed samples after freezing using a cryo-scanning electron microscope. The results showed that XPCs in larch adapts to subfreezing temperature by deep supercooling throughout all seasons. Such freezing behavior is the same as that of XPCs in boreal hardwood species.     

细胞尺度冰晶生长行为的相场数值模拟

细胞尺度的冻结损伤机制是实施低温手术及生物材料低温保存的关键,本文围绕低温条件下的微尺度冻结问题,应用相场模型对冰晶的形成过程进行了数值模拟,明确了相场模型相关重要参数的确定方法,并最终得到各向同性条件下,二维平面内冰晶的生长过程及其生长特点.     

有限厚度冻冰相变过程的传热研究

1前言确定相界面的瞬态位置是求解冻冰相变问题的重要部分。目前对于有限区域相变问题还没有可靠的精确解[1]。冻冰过程最简单分析方法是忽略固液两相的显热变化，建立相界面移动的准稳态传热关系式，近似预测固一液相变位置[2-4]。本文将考虑液、固相中显热的变化，对有限厚平板冻冰过程，采用精确解与积分解相结合的方法，分析冰层冻结过程中的固一液相界面、边界热流密度和贮入固、液相内的冷量随冻冰时间的变化规律。2物理一数学模型分析该研究的问题是一块贮冷板的两侧面直接与一个低温蒸发器直接接触，使贮冷板内冻冰贮冷。通常蒸发器…     

Direct cryopreservation of winter buds of nine cultivars of blackcurrant (Ribes nigrum L)

Direct cryopreservation of overwintering, dormant buds has been applied to nine blackcurrant cultivars, using a 7 day dehydration period at c.-20° C before plunging directly into liquid nitrogen. The buds on shoots thawed from -20° C showed normal development simply by standing them in water and all the cultivars could be successfully recovered (> 58%) by grafting. None of the shoots thawed from liquid nitrogen showed any development after standing in water and all of the grafts failed. Shoots thawed from liquid nitrogen showed significant damage to xylem transport, and the cortical tissues necessary fro successful grafting showed significant loss of membrane semipermeability. However, buds excised from shoots immediately after thawing from liquid nitrogen were viable and could be recovered using in vitro culture. Survival ranged from 88 to 55%, depending upon cultivar.     

In situ investigation of ice formation on surfaces with representative wettability

In this work, we have prepared a series of samples with five representative surface wettabilities: i.e. superhydrophilic, hydrophilic, critical, hydrophobic and superhydrophobic. These samples were in situ observed the freezing process of water droplets on clean and artificially contaminated surfaces to investigate the relationship between surface wettability and ice formation. Ice accretion was also tested by spraying supercooled water to samples at different horizontal inclination angles (HIA). Surface topography was proved to be essential to the icing through heterogeneous nucleation. However, the correlation between surface wettability and ice formation was not observed. Finally, we found that the superhydrophobic surface clearly exhibited reduced ice accumulation in the initial stage of ice formation associated with the lower sliding angle (SA) of water droplets.     

Freezing rate affects the survival of a short-term freezing stress in Panagrolaimus davidi, an Antarctic nematode that survives intracellular freezing

The ability of the Antarctic nematode Panagrolaimus davidi to survive a short-term freezing stress depended upon the rate of freezing of its surroundings, measured as the duration of the sample exotherm. The freezing rate increased as the sample volume and freezing temperature decreased and resulted in fewer nematodes surviving. This appears to be due to the greater risk of physical damage by ice crystal growth at high freezing rates. Once frozen the nematodes will then survive exposure to lower temperatures. The environment of the nematode is likely to produce the slow rate of freezing of its surroundings that is necessary for its survival.     

Ice can penetrate invertebrate tissues via paracellular pathways

Ice-cell interactions especially the question whether and how ice crystals invade tissues and organs during freezing were examined in small transparent organs (salivary glands) in which many structural details remained visible despite of freeze-induced cell darkening. In most glands no invasion of ice into the lumen was observed since ice dendrites stopped growing after touching the gland. Here I report that in rare cases a so far unknown type of ice crystals developed which aggressively pushed against cell membranes before invading the gland via paracellular pathways (septate junctions). Aggressive ice crystals were also observed within a salivary gland cell which deformed and finally invaded the nucleus. In cell strands it was observed that intracellular freezing is indeed a two-step event in which ice developed in cytoplasm several seconds before invading the nucleus.     

Evaluation of the ice ratio formed during quasi-adiabatic pressure shift freezing

Abstract

Pressure shift freezing consists in cooling a biological substance (mainly containing water) under pressure without phase change followed by a sudden release of the pressure. The high supercooling obtained during the quasi adiabatic depressurisation permits to achieve a rapid and uniform ice nucleation. The ice fraction formed during the pressure release of a sample of pure water has been calculated using a mathematical model. In addition, this fraction was experimentally evaluated by isothermal calorimetry. The calculations and measurements were carried out at 3 different initial points of the ice I melting curve. A relatively good agreement is observed between the experimental and calculated ice ratio which were between 0.117 and 0.402 (kg ice/kg ice-water mixture) for an initial temperature-pressure values of -10°C/1 15 MPa and -21°C/210 MPa respectively.     

Fast radial NMR microimaging studies of the freezing of extruded pasta

Fast radial NMR microimaging protocols are presented for studying time dependent profiles of unfrozen water and ice during the freezing of extruded pasta (spaghetti). The radial imaging profiles of unfrozen water are analysed with an approximate analytic solution based on a generalized Plank model of freezing as well as by a more exact numerical simulation. The potential of the imaging technique for studying freezing kinetics in other food materials is discussed.     

Kinetics of freezing of an oil-in-water emulsion by pressure release. Impact on ice crystals and oil droplets

Abstract

Pressure release freezing (PRF) of an oil-in-water emulsion is studied. The characteristics of ice crystals as a function of freezing process is studied.     

An experimental investigation into the icing and melting process of a water droplet impinging onto a superhydrophobic surface

The freezing and melting process of a small water droplet on a superhydrophobic cold surface was investigated using the Laser Induced Fluorescence (LIF) technique. The superhydrophobic surface was prepared using a sol-gel method on a red copper test plate. From the obtained fluorescence images, the phase transition characteristics during the freezing and melting process of a water droplet were clearly observed. It was found that, at the beginning of the droplet freezing process, liquid water turned into ice at a very fast rate. Such phase transition process decreased gradually with time and the volume of frozen ice approached a constant value at the end of the icing process. In addition, the freezing time was found to reduce with the decrease of the test plate temperature. Besides, when the test plate temperature is relatively high, the effect of droplet volume on the freezing time is very significant. Over all, we provide some tentative insights into the microphysical process related to the icing and melting process of water droplets.     

基于ZigBee的高速公路结冰信息检测系统的设计

针对高速公路上结冰状况仅靠驾驶员观察易导致事故的现状,根据结冰温度和冰的导电性,并结合光在冰层中的传播特性,提出一种利用ZigBee技术的新型的高速公路路面结冰信息检测系统。该系统以楔形光纤作为光的传播媒介,通过采集光纤内光强的变化,结合温度和阻值的大小来融合出高速公路上冰的冰厚和冰型。介绍温度、阻值和光强等采集模块的设计原理,及实验测试环境的实现。经过验证,该系统可有效检测出路面的冰厚和冰型。