Primary drying is one of those subjects where the details matter more than the headlines. This page pulls together the background, the mechanisms, and the practical points readers ask about most.
Last reviewed on 2025-12-08. Where a claim depends on a specific study, the study is described rather than over-claimed.
A typical cycle begins with freezing, which fixes the material into a solid and determines ice crystal size. Primary drying then raises heat under vacuum so ice sublimes, often near or below the collapse temperature of the formulation. Secondary drying removes bound water that remains after ice is gone, usually by gently warming the product. Each stage balances heat input against pressure to avoid melting or structural damage. Temperature probes and pressure sensors guide the transition between stages.
In practice, lyophilization is slower and more energy intensive than simple drying. Cycle times can range from hours to several days depending on load, container, and formulation. Amorphous materials may require excipients that help preserve structure during freezing and drying. The method is widely used for biological materials, pharmaceuticals, and foods where heat drying would cause unacceptable change. Open questions remain about scaling cycles between laboratory and production equipment, and this gap affects technology transfer.
Freeze-drying is distinct from simple evaporation and from spray drying. Evaporation removes water at temperatures above freezing, while spray drying rapidly dries droplets in a heated gas stream. Lyophilization avoids high temperatures, which can be useful for heat-sensitive materials such as proteins, vaccines, and some foods. The porous cake produced by sublimation dissolves or rehydrates more quickly than a dense dried mass. Not all materials tolerate freezing or the pH shifts that can occur as solutes concentrate during ice formation.
Lyophilization removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts liquid water into ice and fixes the structure of the sample. After freezing, primary drying lowers pressure so ice changes directly to vapor without passing through a liquid phase. Secondary drying then removes bound water that remains after ice sublimation. The result is a dry, porous solid that often retains its original shape.
The low pressure used during drying allows water vapor to move from the ice surface to a cold condenser. Energy supplied as heat drives sublimation but must stay below the collapse temperature of the frozen matrix. If the product becomes too warm, the frozen structure may soften or melt, reducing pore formation and slowing drying. Formulations often include bulking agents, stabilizers, or buffers to support a rigid cake. The final moisture content depends on formulation, freezing rate, and the length of secondary drying.
| Property | Value | Notes |
|---|---|---|
| Common synonym | Freeze-drying | Same dehydration operation |
| Typical vacuum | 10-100 Pa | Pressure during primary drying |
| Primary drying temperature | -40 to -10 °C | Below collapse temperature for many formulations |
| Cycle duration | 12-72 hours | Varies with load, container, and formulation |
| Key phase change | Sublimation | Solid ice to water vapor |
After primary drying, secondary drying removes water that remains bound to the material. This stage raises the shelf temperature while maintaining low pressure, which encourages desorption of unfrozen water. Residual moisture can be reduced to a low percentage, improving stability for many products. The process parameters, including freezing rate, shelf temperature, and chamber pressure, influence the final pore structure and reconstitution behavior. Control of these variables helps prevent collapse or meltback during drying.
A formulation often contains excipients that protect the active ingredient during freezing and drying. Bulking agents provide structure, while lyoprotectants stabilize sensitive molecules. The freezing step can produce ice crystals whose size and distribution affect the drying rate, and cycle design includes freezing, annealing, and drying phases. If the product temperature rises above a critical value, the cake may collapse or lose its porous structure. Successful lyophilization therefore depends on the interaction between formulation, equipment, and cycle design.
Lyophilization, also called freeze-drying, is a dehydration process in which a solvent, usually water, is frozen and then removed by sublimation under reduced pressure. The method preserves heat-sensitive materials that would degrade in conventional drying. Large-scale use grew during the mid-twentieth century for blood plasma and antibiotics, and it later expanded to vaccines, enzymes, foods, and advanced materials. The process produces a dry, porous solid that usually reconstitutes rapidly. It is distinct from simple evaporation because the solvent bypasses the liquid phase during primary removal.
The process generally proceeds in three stages: freezing, primary drying, and secondary drying. During freezing, controlled cooling converts water into ice and may also crystallize or vitrify solutes. In primary drying, the pressure is lowered below the triple point, and heat is supplied so ice sublimes directly to vapor. Secondary drying removes water that remains bound to the solid matrix, yielding a low final water content. Product temperature must stay below the collapse or glass transition temperature to maintain structure. Cycle design therefore balances shelf temperature, chamber pressure, and time.
The first sizeable batch of Boer prisoners taken by the British consisted of those captured at the Battle of Elandslaagte on 21 October 1899. Initially, these POWs were held on troopships in Simons Bay until POW camps in Cape Town and Simonstown were completed. In total, six prisoner of war camps would be set up in South Africa. As numbers grew, the British decided they did not want them kept locally. The capture of 4000 POWs in February 1900 was a key event, which made the British realise they could not accommodate all POWs in South Africa. The British feared they could be freed by sympathetic locals. Moreover, they already had trouble supplying their troops and did not want the added burden of sending supplies for the POWs. Britain therefore sent many POWs overseas. Around 31 prisoner of war camps were consequently set up in British colonies overseas during the war. The first overseas (off African mainland) camps were opened in Saint Helena, which ultimately received about 5,000 POWs. About 5,000 POWs were sent to Ceylon. Other POWs were sent to Bermuda and India.
=== Sa–Sc === Margarita Salas (1938–2019). Spanish biochemist at the Spanish National Research Council. Known for work on DNA replication. First woman elected to the Royal Spanish Academy. Wolfram Saenger (1939–2026). German biochemist and protein crystallographer at the Free University of Berlin, known for work on membrane proteins and protein-nucleic acid complexes. Member Natl. Acad. Sci. USA Frederick Sanger FRS (1918–2013). British biochemist at Cambridge University, known for advances in sequencing proteins and nucleic acids. Nobel prizes in Chemistry (1958, 1980). Foreign Associate Natl. Acad. Sci. USA. Albert Schatz (1920–2005). American microbiologist and science educator at Temple University, the discoverer of the antibiotic streptomycin. Paul Schimmel (b. 1940). American biochemist at the Scripps Research Institute, who developed methods of nucleic acid sequencing and coauthored (with Charles Cantor) the very influential three-volume book Biophysical Chemistry. Member Natl. Acad. Sci. USA Rudolph Schoenheimer (1898–1941). German-American biochemist at Columbia, pioneer of radioactive tagging of molecules. Stefan Schuster (b. 1961). German biophysicist at the University of Jena, pioneer in metabolic control analysis and metabolic pathway analysis. Rose Scott-Moncrieff (1903–1991). British biochemical geneticist at the University of Cambridge.
Muhammad, Naseem; Tsai, Peter S.; Lauback, Ronald G. (1982). "High-Pressure Liquid Chromatography Assay for Dane Salt Potassium (-)-N-(1-Methoxycarbonylpropene-2yl)-p-hydroxyphenylglycine". Journal of Liquid Chromatography. 5 (7): 1349–1355. doi:10.1080/01483918208067593. Lauback, Ronald (1984). "Specific High-Performance Liquid Chromatographic Determination of Ampicillin in Bulks, Injectables, Capsules, and Oral Suspensions by Reverse-Phase Ion-Pair Chromatography". Journal of Liquid Chromatography. 7 (6): 1243–1265. doi:10.1080/01483918408074041. Ron Lauback retired in July 2014 from Hanford Pharmaceuticals, based out of Syracuse, New York. He was Vice President of Science from 2007 to 2014.
=== President of the Royal Society === One of the most prestigious institutions in the UK was the Royal Society. Mellanby put Florey's name forward for membership in 1937, but at that time it accepted only twenty new members each year. He was elected a fellow in 1941. The Royal Society was governed by a council of twenty-one fellows, and Florey served on the council from 1942 to 1943, and again from 1951 to 1953, when he was vice president. He received the Royal Society's Royal Medal in 1951 and its Copley Medal in 1957. By custom, the president of the Royal Society served for five years, and the position alternated between the mathematical and physical sciences, and the biological sciences, so Florey was eligible in 1960. Since the president was a public figure, his private life had to be beyond reproach, which was a sore point due to his relationship with Margaret Jennings.
Actinium (89Ac) has no stable isotopes and no characteristic terrestrial isotopic composition, thus a standard atomic weight cannot be given. There are 34 known isotopes, from 203Ac to 236Ac, and 9 isomers. Three isotopes are found in nature, 225Ac, 227Ac and 228Ac, as intermediate decay products of, respectively, 237Np, 235U, and 232Th. 228Ac and 225Ac are extremely rare, so almost all natural actinium is 227Ac. The most stable isotopes are 227Ac with a half-life of 21.772 years, 225Ac with a half-life of 9.919 days, and 226Ac with a half-life of 29.37 hours. All other isotopes have half-lives under seven hours, and most under a minute. The shortest-lived known isotope is 217Ac with a half-life of 69 ns. Purified 227Ac comes into equilibrium with its decay products (mainly 227Th and 223Ra) after 185 days.
Sources: en.wikipedia.org
== Positive feedback loops == For many intracrines, once they stimulate the upregulation of a gene, a positive feedback loop is initiated. The intracrine promotes cell proliferation and stimulates further intracellular signaling, leading to increased synthesis and release of the intracrine itself, thereby reinforcing the loop. In multicellular organisms, an intracrine may also be secreted, causing neighboring cells to proliferate and enter a similar positive feedback loop. This mechanism results in a coordinated response that contributes to tissue growth and development.
== Notable people == Pope Pius I is believed to have been born at Aquileia during the late first century. Saint Chrysogonus was martyred here in the beginning of the fourth century. Licia Kokocinski - Australian politician
=== Current === There are currently 67 territorial authorities. Before the Auckland Council "super merge" in November 2010, there were 73 territorial authorities. Before the Banks Peninsula District Council merged with the Christchurch City Council in 2006, there were 74 territorial authorities.
In 1991, Japanese scientists created the first milk-based ACE inhibitor, in the form of a fermented milk drink, using specific cultures to liberate the tripeptide isoleucine-proline-proline (IPP) from the dairy protein. Valine-proline-proline (VPP) is also liberated in this process—another milk tripeptide with a very similar chemical structure to IPP. Together, these peptides are now often referred to as lactotripeptides. In 1996, the first human study confirmed the blood pressure-lowering effect of IPP in fermented milk. Although twice the amount of VPP is needed to achieve the same ACE-inhibiting activity as the originally discovered IPP, VPP also is assumed to add to the total blood pressure lowering effect. Since the first lactotripeptides discovery, more than 20 human clinical trials have been conducted in many different countries.
Sources: en.wikipedia.org
== Disorders and conditions == Numerous reports have been published indicating that the glutamate/GABA–glutamine cycle is compromised in a variety of neurological disorders and conditions. Biopsies of sclerotic hippocampus tissue from human subjects with epilepsy have shown decreased glutamate–glutamine cycling. Another pathology in which the glutamate/GABA–glutamine cycle might be compromised is Alzheimer's disease; NMR spectroscopy showed decreased glutamate neurotransmission activity and TCA cycling rate in patients with Alzheimer's disease. Hyperammonemia in the brain, typically occurring as a secondary complication of primary liver disease and known as hepatic encephalopathy, is a condition that affects glutamate/GABA–glutamine cycling in the brain. Current research into autism also indicates potential roles for glutamate, glutamine, and/or GABA in autistic spectrum disorders.
== Doubts about existence == In October 2011 the Journal of Strategic Studies, a leading journal in that field, published an article by Thomas Rid, "Cyber War Will Not Take Place" which argued that all politically motivated cyber attacks are merely sophisticated versions of sabotage, espionage, or subversion – and that it is unlikely that cyber war will occur in the future.
Mahmoud Reza Banki (Persian: محمودرضا بانکی; born 1976) is an Iranian-American scientist, management consultant and business executive. Born in Tehran, Iran, Banki immigrated to the US to attend college and became a naturalized US citizen in the 1990s. In January 2010, Banki was arrested and charged with violating US sanctions against Iran by the United States Attorney's office in New York City. Ultimately Banki won his case on appeal, and it was permanently closed in July 2012. Banki spoke about his case at a TED Talk in 2014, presenting a case for change in criminal justice. As of 2015 a documentary film about the case was being made. In The Moth podcast released January 2017, Banki spoke to the personal toll of the ordeal. Banki has also spoken before various audiences for the cause of improving the criminal justice system. As of 2022, Banki was Chief Financial Officer and Chief Strategy Officer at leading streaming company Tubi. On January 20, 2021, Banki received a full and unconditional pardon from the President of the United States. He was the CFO of X Corp. between November 2024 and October 2025.
Sources: en.wikipedia.org
Primary drying removes ice by sublimation under vacuum. Secondary drying removes water that is bound to the material, often by warming the product after most ice has left. Both stages occur below temperatures that would cause unwanted melting.
Sublimation requires the solvent to remain solid so vapor leaves without passing through a liquid phase. If the product melts, the porous structure can collapse and drying becomes uneven. Maintaining frozen conditions preserves the intended physical form.
No, freeze-drying is a dehydration method, not a sterilization step. It can reduce water activity and limit microbial growth during storage, but it does not reliably kill microbes or remove endotoxins. Sterility must come from separate validated processes.
Lyophilization relies on sublimation, so water moves from solid ice to vapor without becoming liquid. The material is frozen, pressure is reduced, and controlled heat is supplied. Vapor is captured on a cold condenser, leaving a dry porous solid.