If you have been reading about primary drying and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Last reviewed on 2025-09-27. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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, also called freeze-drying, removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts free water into ice and may also produce a glassy phase. Primary drying then lowers chamber pressure so ice sublimes directly to vapor without passing through a liquid stage. Secondary drying raises the temperature modestly to remove bound water. The result is a porous, dry solid that usually reconstitutes quickly. Each stage influences pore structure, residual moisture, and stability.
The physics of lyophilization depends on phase boundaries and heat and mass transfer. During primary drying, heat supplied to the product must equal the latent heat of sublimation, while water vapor moves through the drying cake to the condenser. If shelf temperature or pressure is set too high, the ice front can exceed the collapse temperature, causing meltback or pore collapse. If conditions are too cold, drying slows and costs rise. Formulation excipients, vial geometry, and freezing rate alter these limits.
Equipment for lyophilization includes a vacuum chamber, temperature-controlled shelves, a condenser, and a vacuum pump. A refrigeration system cools the shelves and condenser below the product's freezing point. Process monitoring often uses Pirani and capacitance manometers, thermocouples, and resistance sensors. Cycle development balances product quality with time and energy use. Some products are annealed during freezing to improve crystallization of bulking agents. Open questions remain about scaling cycles between laboratory, pilot, and production freeze-dryers.
| Property | Value | Notes |
|---|---|---|
| Primary phase change | Sublimation | Ice changes directly to vapor under reduced pressure |
| Typical chamber pressure | 0.01–0.5 mbar (1–50 Pa) | Below the triple point of water; product-specific |
| Typical product temperature during primary drying | −40 °C to −10 °C | Kept below collapse temperature |
| Typical residual moisture | 0.5–3% w/w | Target range varies by formulation and use |
| Common synonyms | Freeze-drying; lyophilisation | Lyophilization is the US spelling |
Lyophilization removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts liquid water into ice and concentrates dissolved solids. Primary drying then lowers chamber pressure so ice changes directly into vapor without passing through a liquid phase. Secondary drying raises the shelf temperature to remove bound water that remains after ice sublimation. The result is a dry, porous structure that can be reconstituted later.
Formulation composition influences whether freeze-drying produces an intact cake or a collapsed mass. Excipients such as sugars and polymers can raise the collapse temperature and provide bulk during drying. The critical temperature for primary drying is often the collapse temperature or the glass transition temperature of the maximally concentrated phase. If the product temperature exceeds this threshold, the frozen matrix may soften and lose structure. Established practice therefore links shelf temperature and chamber pressure to the formulation's thermal properties.
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 situation during Tehuantepecers and Santa Ana wind events are more complicated, as they occur when air rushing southward due to cold air damming east of the Sierra Madre Oriental and Sierra Nevada respectively, is accelerated when it moves through gaps in the terrain. The Santa Ana is further complicated by down-sloped air, or foehn winds, drying out and warming up in the lee of the Sierra Nevada and coastal ranges, leading to a dangerous wildfire situation.
=== Early studies in Prague laboratory === Kopeček's graduate research focused on the kinetics of crosslinking polymerization of hydrophilic esters of methacrylic acid and structural characterization of ensuing hydrogels. This was followed by the investigation of the relationship between the chemical and physical structure of hydrogels and their biocompatibility. This formed the basis for the translation of hydrogels based on crosslinked poly(ethyleneglycol monomethacrylate) into the clinics. The next focus was the design of water-soluble polymer-drug conjugates based on the copolymers of N-(2-hydroxypropyl)methacrylamide (HPMA). Kopeček and coworkers formulated and implemented a comprehensive approach to the problems designing macromolecular conjugates to modulate the pharmacokinetics and tissue localization of therapeutic agents.
The element emanates naturally from the ground, and some building materials, all over the world, wherever traces of uranium or thorium are found, and particularly in regions with soils containing granite or shale, which have a higher concentration of uranium. Not all granitic regions are prone to high emissions of radon. Being a rare gas, it usually migrates freely through faults and fragmented soils, and may accumulate in caves or water. Owing to its very short half-life (four days for 222Rn), radon concentration decreases very quickly when the distance from the production area increases. Radon concentration varies greatly with season and atmospheric conditions. For instance, it has been shown to accumulate in the air if there is a meteorological inversion and little wind. High concentrations of radon can be found in some spring waters and hot springs. The towns of Boulder, Montana; Misasa; Bad Kreuznach, Germany; and the country of Japan have radium-rich springs that emit radon. To be classified as a radon mineral water, radon concentration must be above 2 nCi/L (74 kBq/m3). The activity of radon mineral water reaches 2 MBq/m3 in Merano and 4 MBq/m3 in Lurisia (Italy). Natural radon concentrations in the Earth's atmosphere are so low that radon-rich water in contact with the atmosphere will continually lose radon by volatilization. Hence, ground water has a higher concentration of 222Rn than surface water, because radon is continuously produced by radioactive decay of 226Ra present in rocks.
Sources: en.wikipedia.org
=== Nordic countries === Norway was the first country in the world to outlaw beak trimming in 1974, followed by Finland in 1986 and Sweden in 1988. Beak trimming was subsequently phased out in Denmark in two stages: in 2013 for the enriched cage system and in 2014 for aviary and free range systems.
== External links == Clinical trial number NCT03422653 for "A Study to Evaluate the Safety and Efficacy of CR845 in Hemodialysis Patients With Moderate-to-Severe Pruritus (KALM-1)" at ClinicalTrials.gov Clinical trial number NCT03636269 for "CR845-CLIN3103: A Global Study to Evaluate the Safety and Efficacy of CR845 in Hemodialysis Patients With Moderate-to-Severe Pruritus (KALM-2)" at ClinicalTrials.gov
Both Agincourt Collegiate Institute and R. H. King Academy claim to be the oldest secondary schools in the district. Agincourt Collegiate Institute (the former Agincourt Continuation School) opened in 1915. It became a high school in 1954. R. H. King Academy opened in 1922 as the Scarborough High School being the first high school in the Scarborough area at that time, and became a collegiate in 1930. Four public school boards operate primary and secondary schools in the district: Conseil scolaire catholique MonAvenir (CSCM), Conseil scolaire Viamonde (CSV), the Toronto Catholic District School Board (TCDSB), and the Toronto District School Board (TDSB). CSV and TDSB operate as secular public school boards, the former operating French first language institutiona, whereas the latter operates English first language institutions. The other two school boards, CSCM and TCDSB, operate as public separate school boards, the former operating French first-language separate schools, the latter operating English first-language separate schools. As of 2008, there are 28 secondary schools in Scarborough. In addition to primary and secondary schools, two post-secondary institutions are located in Scarborough. The University of Toronto maintains a Scarborough campus, established in 1964, which has an enrolment of more than 15,000 students as of 2024. Centennial College was opened in 1966. It was the first vocational college to open in Ontario. Starting from one campus in Warden Woods, it grew to three campuses across Scarborough (and two others located in East York and North York).
Sources: en.wikipedia.org
== Occurrence == Chymosin is found in a wide range of tetrapods, although it is best known to be produced by ruminant animals in the lining of the abomasum. Chymosin is produced by gastric chief cells in newborn mammals to curdle the milk they ingest, allowing a longer residence in the bowels and better absorption. Non-ruminant species that produce chymosin include pigs, cats, seals, and chicks. One study reported finding a chymosin-like enzyme in some human infants, but others have failed to replicate this finding. Humans have a pseudogene for chymosin that does not generate a protein, found on chromosome 1. Humans have other proteins to digest milk, such as pepsin and lipase. In addition to the primate lineage leading up to humans, some other mammals have also lost the chymosin gene.
=== Caucus memberships === Sanders was only the third senator from Vermont to caucus with the Democrats, after Jeffords and Leahy. His caucusing with the Democrats gave them a 51–49 majority in the Senate during the 110th Congress in 2007–08. The Democrats needed 51 seats to control the Senate because Vice President Dick Cheney would likely have broken potential ties in favor of the Republicans. He is a member of the following caucuses:
==== Grafting to ==== Grafting to approach which is the most common and straightforward methodology refers to directly attaching the synthetic polymers to the target protein. This technique can be engineered for site-specific or random conjugation and, when compared to other conjugation methods, provides simple and thorough characterization of polymer before conjugation. And when using this method, the protein remains unaffected by polymerization methods.
Sources: en.wikipedia.org
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.
The process has three main stages: freezing, primary drying, and secondary drying. Freezing sets the ice structure, primary drying removes free ice, and secondary drying removes bound water. Each stage uses specific temperature, pressure, and time settings.
No, it is a drying method rather than a sterilization method. Removing water can limit microbial growth, but it does not reliably kill microorganisms. Sterility must come from separate steps such as filtration, heat treatment, or aseptic processing.
Simple drying usually removes water by evaporation from a liquid or solid, often with heat. Lyophilization first freezes the material and then removes ice by sublimation under vacuum. This avoids prolonged exposure to liquid water and high temperatures.