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Cryobiology is the branch of biology that studies the effects of low on living things within Earth's cryosphere or in science. The word cryobiology is derived from the Greek words κρῧος kryos, "cold", βίος bios, "life", and λόγος logos, "word". In practice, cryobiology is the study of biological material or systems at temperatures below normal. Materials or systems studied may include , cells, tissues, organs, or whole . Temperatures may range from moderately Hypothermia conditions to cryogenic temperatures.
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The larvae of Haemonchus contortus, a nematode, can survive 44 weeks frozen at -196 °C.
Other vertebrates that survive at body temperatures below 0 °C include painted turtles ( Chrysemys picta), gray tree frogs ( Hyla versicolor), Moor frog (Rana arvalis), ( Terrapene carolina - 48 hours at -2 °C), spring peeper ( Pseudacris crucifer), ( Thamnophis sirtalis- 24 hours at -1.5 °C), the chorus frog ( Pseudacris triseriata), Siberian salamander ( Salamandrella keyserlingii - 24 hours at -15.3 °C), European common lizard ( Lacerta vivipara) and Antarctic fish such as Pagothenia borchgrevinki. Antifreeze proteins cloned from such fish have been used to confer frost-resistance on Transgenesis plants.
Hibernating Arctic ground squirrels may have abdominal temperatures as low as −2.9 °C (26.8 °F), maintaining subzero abdominal temperatures for more than three weeks at a time, although the temperatures at the head and neck remain at 0 °C or above.
In 1949, bull semen was cryopreservation for the first time by a team of scientists led by Christopher Polge.C. Polge, AU Smith, AS Parkes, Revival of spermatozoa Effective vitrification and dehydration at low temperatures Nature, 164 (1949), p. 666 This led to a much wider use of cryopreservation today, with many organs, tissues and cells routinely stored at low . Large organs such as are usually stored and transported, for short times only, at cool but not freezing temperatures for Organ transplant. Cell suspensions (like blood and semen) and thin tissue sections can sometimes be stored almost indefinitely in liquid nitrogen temperature (cryopreservation). Human sperm, eggs, and are routinely stored in fertility research and treatments. Controlled-rate and slow freezing are well established techniques pioneered in the early 1970s which enabled the first human embryo frozen birth (Zoe Leyland) in 1984. Since then, machines that freeze biological samples using programmable steps, or controlled rates, have been used all over the world for human, animal, and cell biology – 'freezing down' a sample to better preserve it for eventual thawing, before it is deep frozen, or cryopreserved, in liquid nitrogen. Such machines are used for freezing oocytes, skin, blood products, embryo, sperm, stem cells, and general tissue preservation in hospitals, veterinary practices, and research labs. The number of live births from 'slow frozen' embryos is some 300,000 to 400,000 or 20% of the estimated 3 million in vitro fertilized births. Dr Christopher Chen, Australia, reported the world’s first pregnancy using slow-frozen oocytes from a British controlled-rate freezer in 1986.
Cryosurgery (intended and controlled tissue destruction by ice formation) was carried out by James Arnott in 1845 in an operation on a patient with cancer.
A rule of thumb in hypothermic storage is that every 10 °C reduction in temperature is accompanied by a 50% decrease in Aerobic exercise. Although hibernating animals have adapted mechanisms to avoid Metabolism associated with hypothermia, hypothermic organs, and tissues being maintained for transplantation require special preservation solutions to counter acidosis, depressed sodium pump activity. and increased intracellular calcium. Special organ preservation solutions such as Viaspan (University of Wisconsin solution), HTK, and Celsior have been designed for this purpose. These solutions also contain ingredients to minimize damage by free radicals, prevent edema, compensate for ATP loss, etc.
Cryopreservation of cells is guided by the "two-factor hypothesis" of American cryobiologist Peter Mazur, which states that excessively rapid cooling kills cells by intracellular ice formation and excessively slow cooling kills cells by either electrolyte toxicity or mechanical crushing. During slow cooling, ice forms extracellularly, causing water to osmosis leave cells, thereby dehydration them. Intracellular ice can be much more damaging than extracellular ice.
For red blood cells, the optimum cooling rate is very rapid (nearly 100 °C per second), whereas for the optimum cooling rate is very slow (1 °C per minute). Cryoprotectants, such as dimethyl sulfoxide and glycerol, are used to protect cells from freezing. A variety of cell types are protected by 10% dimethyl sulfoxide. Cryobiologists attempt to optimize cryoprotectant concentration (minimizing both ice formation and toxicity) and cooling rate. Cells may be cooled at an optimum rate to a temperature between −30 and −40 °C before being plunged into liquid nitrogen.
Slow cooling methods rely on the fact that cells contain few Nucleation agents, but contain naturally occurring vitrifying substances that can prevent ice formation in cells that have been moderately dehydrated. Some cryobiologists are seeking mixtures of cryoprotectants for full vitrification (zero ice formation) in preservation of cells, tissues, and organs. Vitrification methods pose a challenge in the requirement to search for cryoprotectant mixtures that can minimize toxicity.
Cryopreservation in humans with regards to infertility involves preservation of embryos, sperm, or oocytes via freezing. Conception, in vitro, is attempted when the sperm is thawed and introduced to the 'fresh' eggs, the frozen eggs are thawed and sperm is placed with the eggs and together they are placed back into the uterus or a frozen embryo is introduced to the uterus. Vitrification has flaws and is not as reliable or proven as freezing fertilized sperm, eggs, or embryos as traditional slow freezing methods because eggs alone are extremely sensitive to temperature. Many researchers are also freezing ovarian tissue in conjunction with the eggs in hopes that the ovarian tissue can be transplanted back into the uterus, stimulating normal ovulation cycles. In 2004, Donnez of Louvain in Belgium reported the first successful ovarian birth from frozen ovarian tissue. In 1997, samples of ovarian cortex were taken from a woman with Hodgkin's lymphoma and cryopreserved in a (Planer, UK) controlled-rate freezer and then stored in liquid nitrogen. Chemotherapy was initiated after the patient had premature ovarian failure. In 2003, after freeze-thawing, orthotopic autotransplantation of ovarian cortical tissue was done by laparoscopy and after five months, reimplantation signs indicated recovery of regular ovulatory cycles. Eleven months after reimplantation, a viable intrauterine pregnancy was confirmed, which resulted in the first such live birth – a girl named Tamara.
Therapeutic hypothermia, e.g. during heart surgery on a "cold" heart (generated by cold perfusion without any ice formation) allows for much longer operations and improves recovery rates for patients.
The Society for Low Temperature Biology was founded in 1964 and became a registered charity in 2003(Charity Commission for England & Wales No. 1099747) with the purpose of promoting research into the effects of low temperatures on all types of organisms and their constituent cells, tissues, and organs. As of 2006, the society had around 130 (mostly British and European) members and holds at least one annual general meeting. The program usually includes both a symposium on a topical subject and a session of free communications on any aspect of low-temperature biology. Recent symposia have included long-term stability, preservation of aquatic organisms, cryopreservation of embryos and , preservation of plants, low-temperature microscopy, vitrification (glass formation of aqueous systems during cooling), freeze drying and tissue banking. Members are informed through the Society Newsletter, which is presently published three times a year.
Cryo Letters is an independent UK-based rapid communication journal which publishes papers on the effects produced by low temperatures on a wide variety of biophysical and biological processes, or studies involving low-temperature techniques in the investigation of biological and ecological topics.
Biopreservation and Biobanking (formerly Cell Preservation Technology) is a peer-reviewed quarterly scientific journal published by Mary Ann Liebert, Inc. dedicated to the diverse spectrum of preservation technologies including cryopreservation, dry-state (anhydrobiosis), and glassy-state and hypothermic maintenance. Cell Preservation Technology has been renamed Biopreservation and Biobanking and is the official journal of International Society for Biological and Environmental Repositories.
Problems of Cryobiology and Cryomedicine (formerly 'Kriobiologiya' (1985-1990) and 'Problems of Cryobiology'(1991-2012) ) published by Institute for Problems of Cryobiology and Cryomedicine. The journal covers all topics related to low temperature biology, medicine and engineering.
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