Primary drying raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
This page was last updated on 2025-10-05 and is reviewed periodically as new material appears.
A typical cycle begins with freezing, sometimes including an annealing step to control ice crystal size. Freezing conditions influence the pore network that later allows vapor escape. During primary drying, shelf temperature and chamber pressure are set so heat enters the product while its temperature stays below the collapse or eutectic point. Secondary drying then raises the shelf temperature to desorb bound water and lower residual moisture. Cycle design depends on formulation, fill volume, container type, and equipment capability.
The physics of lyophilization couples heat transfer, mass transfer, and phase behavior. Sublimation requires a vapor pressure difference between the ice front and the chamber, and the dried layer adds resistance to vapor flow. Amorphous formulations are characterized by a glass transition temperature of the maximally freeze-concentrated solute, often denoted Tg'. Crystalline bulking agents can provide structure, while amorphous excipients stabilize labile components. Open questions remain about spatial heterogeneity, edge effects, and how laboratory cycles scale to production.
Lyophilization is a drying process in which a solvent, usually water, is removed from a frozen material by sublimation under reduced pressure. The material is first solidified, then placed under vacuum so that ice transitions directly to vapor without a bulk liquid phase. This approach suits heat-sensitive substances that would degrade during conventional evaporation. Primary drying removes unbound ice, while secondary drying reduces water that remains adsorbed to the solid matrix. The result is a porous, lightweight solid that can be reconstituted later.
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.
Lyophilization removes water by freezing a material and then lowering pressure so ice changes directly to vapor. The process relies on sublimation, the phase transition from solid to gas without an intermediate liquid state. Because the material remains frozen during primary drying, the structure often stays porous. This porous matrix can rehydrate quickly when water is added back. The low pressure also allows vapor to leave the solid matrix without boiling.
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.
| Property | Value | Notes |
|---|---|---|
| Physical state | Solid, porous cake or powder | Depends on formulation and container |
| Typical storage temperature | 2–25 °C, protected from moisture | Some materials require colder conditions |
| Solubility class | Usually readily soluble after reconstitution | Not an intrinsic chemical property |
| Common analytical method | Karl Fischer titration | Used for residual moisture |
| Common synonyms | Freeze-drying; lyophilisation | Lyophilisation is a spelling variant |
The process usually has three stages: freezing, primary drying, and secondary drying. Freezing sets the ice crystal structure and can determine pore size in the final cake. Primary drying removes free ice by sublimation at low pressure and low shelf temperature. Secondary drying removes bound water by raising the shelf temperature, although some water may remain as part of the solid. Cycle parameters depend on formulation, fill volume, vial type, and equipment performance.
The physical chemistry of freezing influences whether a formulation forms an amorphous glass or a crystalline solid. Amorphous systems can collapse if product temperature rises above the glass transition temperature of the freeze concentrate. Crystalline systems may show eutectic melting, where ice and solute melt together at a fixed temperature. Formulators add bulking agents, lyoprotectants, and buffers to preserve structure and biological activity. The optimum cycle keeps product temperature below critical thresholds during primary drying while allowing efficient sublimation.
Secondary drying removes bound water that remains after ice sublimation. Shelf temperature is raised gradually while pressure remains low, reducing water content to a target range. Over-drying can cause brittleness or electrostatic issues, while under-drying affects stability. The endpoint is often judged by pressure rise tests, temperature measurements, or water content analysis. Scale-up depends on matching heat and mass transfer across equipment sizes. Small changes in shelf temperature or pressure can alter cycle length substantially.
Lyophilization, or freeze-drying, removes water from a material by freezing it and then lowering pressure so ice changes directly to vapor. The process relies on sublimation, the phase transition from solid to gas without an intervening liquid state. It is used for heat-sensitive materials that would degrade in conventional drying. The three stages are freezing, primary drying, and secondary drying, each with distinct temperature and pressure requirements. In practice, cycle design balances these variables.
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.
Marijuana use is also linked to other substance use disorders including nicotine addiction." It also reported that "These findings are consistent with the idea of marijuana as a "gateway drug". However, the majority of people who use marijuana do not go on to use other, "harder" substances. Also, cross-sensitization is not unique to marijuana. Alcohol and nicotine also prime the brain for a heightened response to other drugs and are, like marijuana, also typically used before a person progresses to other, more harmful substances."
== Causes == The American Cancer Society noted that several factors contributed to escalating nationwide drug shortages, which included decreased or restricted drug manufacturing capacity, increased drug demands coupled with corresponding shortages in supplies, and lower profit margins for several generic drugs decreasing corporate desires towards creating surpluses. The organization also noted that the Food and Drug Administration's means to prevent drug shortages were fundamentally centered around contact with the drug manufacturers involved, giving early warnings that requested them to increase production instead of directly pushing for specific drug quotas. The ASHP reported that one of the main causes of continuous severe shortages was due to "extreme price competition" between generic drug manufacturers. Challenges to quick-enough production of high-quality medications coupled with possible supply chain disruptions pushed many of these companies to shift their manufacturing to producing drugs with higher profit margins, with some completely stopping production of less lucrative drugs. The organization also pointed out the role that difficult and multi-year federal regulatory approval processes for new manufacturers played in lowering the number of new drug manufacturers and resulting supply decreases. Generic drug user fees noted in section 506C(g) of the Federal Food Drug and Cosmetics Act further made it difficult for companies to keep their businesses profitable. U.S.
Hyperpolarization A change in a cell’s membrane potential that makes it more negative, decreasing the likelihood of firing an action potential. Hypoglossal nerve (Cranial Nerve XII) A cranial nerve responsible for controlling the muscles of the tongue. Damage can cause slurred speech and difficulty swallowing. Hypothalamus A region of the brain below the thalamus that regulates homeostatic functions such as hunger, thirst, body temperature, and circadian rhythms. It controls the pituitary gland and links the nervous and endocrine systems.
During the Allied occupation of Germany after World War II, internal borders were redrawn by the Allied military governments. New states were established in all four zones of occupation: Bremen, Hesse, Württemberg-Baden, and Bavaria in the American zone; Hamburg, Schleswig-Holstein, Lower Saxony, and North Rhine-Westphalia in the British zone; Rhineland-Palatinate, Baden, Württemberg-Hohenzollern and the Saarland – which later received a special status – in the French zone; Mecklenburg(-Vorpommern), Brandenburg, Saxony, Saxony-Anhalt, and Thuringia in the Soviet zone. No single state comprised more than 30% of either population or territory; this was intended to prevent any one state from being as dominant within Germany as Prussia had been in the past. Initially, only seven of the pre-War states remained: Baden (in part), Bavaria (reduced in size), Bremen, Hamburg, Hesse (enlarged), Saxony, and Thuringia. The states with hyphenated names, such as Rhineland-Palatinate, North Rhine-Westphalia, and Saxony-Anhalt, owed their existence to the occupation powers and were created out of mergers of former Prussian provinces and smaller states. Former German territory that lay east of the Oder-Neisse line fell under either Polish or Soviet administration but attempts were made at least symbolically not to abandon sovereignty well into the 1960s.
According to the UN Department of Economic and Social Affairs, Pakistan has the sixth-largest diaspora globally. Approximately 7 million Pakistanis reside abroad, mainly in the Middle East, Europe, and North America. Pakistan ranks 10th globally for remittances sent home. Saudi Arabia is the largest source of remittances, contributing $5.9 billion as of 2016. The term Overseas Pakistani is officially recognised by the Government of Pakistan, with the Ministry of Overseas Pakistanis and Human Resource Development addressing their needs, welfare, and issues. Overseas Pakistanis constitute the second-largest source of foreign exchange remittances to Pakistan, with remittances increasing by over 100% from US$8.9 billion in 2009–10 to US$19.9 billion in 2015–16.
Sources: en.wikipedia.org
== Research == BPC-157 was discovered by Predrag Sikiric, a researcher in Zagreb, Croatia who published it in 1993 in Journal of Physiology, Paris. Pre-clinical research has indicated that BPC-157 may have cytoprotective, neuroprotective, and anti-inflammatory effects, and may also accelerate tissue and organ healing. This substance is sometimes used in functional medicine despite not being approved by any drug regulatory agency. The compound promotes angiogenesis and as a result has some concerns over cancer promotion. As of 2022, the peptide has been banned by the World Anti-Doping Agency under the S0 category of non-exempt substances. BPC-157 has been widely used both by athletes and among the general public, mainly for recovery from injury or stimulating healing in chronic conditions, but there is as yet only very limited human trial data on efficacy and only a few preliminary safety studies. Human studies of BPC-157 remain scarce; a 2025 literature review identified limited clinical evidence, including a retrospective study of 12 patients with knee pain and a Phase I trial in healthy volunteers whose results were not submitted. Use of BPC-157 is discouraged by health authorities and it has been controlled as a prescription medicine in several jurisdictions such as New Zealand and Australia, despite not actually being available for prescription.
==== Reduction ==== Reduction of the carbonyl groups of chiral 2,5-diketopiperazine with lithium aluminium hydride (LiAlH4) cleanly gives the corresponding chiral piperazines. For example, cyclo(L-Phe-L-Phe) 1 gives the chiral piperazine (2S,5S)-dibenzylpiperazine 2.
This harder to crush formulation was put into production in 2012 in an effort to reduce the risk of abuse from snorting the crushed up pill. However, opioid abusers circumvented this issue by finding a way to dissolve and inject the drug. The extent of this outbreak has garnered the attention of both the CDC and FDA. The CDC opened a larger investigation into all disease outbreaks involving Opana ER, focusing on the incidence of thrombotic thrombocytopenic purpura (TTP)-like illness in the 2012 Tennessee outbreak, as well as the 2015 HIV outbreak in Indiana. The FDA launched a post-marketing safety study regarding the reformulation of Opana ER in 2012 and the Indiana state government helped fund another study exploring the link between HIV infection and injection use of oxymorphone in Indiana from 2014 to 2015. The results of these studies found that the reformulation of Opana to a hard to crush tablet unintentionally increased the risk of transmission of acquired blood borne infections because opioid abusers switched from using the drug through the nasal route to injection. This epidemic caused the risk of acquiring a blood borne infection with the use of injectable opioids to increase in comparison to the risk of acquiring an infection when using injectable heroin or cocaine. In June 2017, faced with the public health crisis, the opioid epidemic, the FDA asked Endo Pharmaceuticals to "remove its opioid pain medication, reformulated Opana ER (oxymorphone hydrochloride), from the market".
branched-chain-amino-acid+transaminase at the U.S. National Library of Medicine Medical Subject Headings (MeSH) "RCSB Protein Data Bank - Structure Summary for 3DTF - Structural analysis of mycobacterial branched chain aminotransferase- implications for inhibitor design".
Sources: en.wikipedia.org
=== Etymology === The word "mesentery" and its Neo-Latin equivalent mesenterium () use the combining forms mes- + enteron, ultimately from ancient Greek μεσέντερον (mesenteron), from μέσος (mésos, "middle") + ἔντερον (énteron, "gut"), yielding "mid-intestine" or "midgut". The adjectival form is "mesenteric" ().
=== True cobras === The cobras (Naja spp.) are a medically important group of snakes due to the number of bites and fatalities they cause across their geographical range. The genus Naja consists of 20 to 22 species, but has undergone several taxonomic revisions in recent years, so sources vary greatly. They range throughout Africa (including some parts of the Sahara where Naja haje can be found), Southwest Asia, Central Asia, South Asia, East Asia, and Southeast Asia. The most recent revision, listed 28 species after the synonymisation of Boulengerina and Paranaja with Naja. But unlike some other members of the family Elapidae (the species of the genus Bungarus, genus Oxyuranus, genus Pseudohaje, and especially genus Dendroaspis), half of the bites by many species of both African and Asian origin of the genus Naja are "dry bites" (a dry bite is a bite by a venomous snake in which no venom is released). Roughly 45–50% of bites by most cobra species are dry bites and thus don't cause envenomation. Some of the species that are known and documented to deliver dry bites in a majority of cases include Naja naja, Naja kaouthia, Naja sputatrix, Naja siamensis, Naja haje, Naja annulifera, Naja anchietae, and Naja nigricollis. Some species will inject venom in the majority of their bites, but still deliver high number of dry bites (40–45%) include: Naja sumatrana, Naja melanoleuca, Naja atra, Naja mossambica and Naja katiensis. Within this genus, there are a few species in which dry bites are very rare. Envenoming occurs in at least 75–80% of bite cases involving these species.
ketogenic diet (KD) – usually less than 50 grams of carbohydrates per day (assuming total intake of 2,000 calories). very low-calorie ketogenic diet (VLCKD) – same as KD, but limits total calories to a maximum of 800 calories per day. ketogenic low-carbohydrate high-fat diet (K-LCHF) – same as KD, with the additional restriction of 60 to 80% of calories coming from fat. modified Atkins diet (MAD) – fewer carbohydrates than K-LCHF (less than 10 grams per day), and encourages high-fat foods without specifying a specific required amount. A very low calorie ketogenic diet that is high in fat but low in protein is an effective means for weight loss in those who are overweight or obese, yielding an average weight loss of 10 kg over four weeks, with maintenance of the weight loss for up to two years. However, concerns about serum sodium levels led researchers to propose the diet only be used in "selected" people, and under strict medical supervision. In 2021 the American Heart Association issued a scientific statement on dietary guidance to improve cardiovascular health which noted that "there is insufficient evidence to support any existing popular or fad diets such as the ketogenic diet and intermittent fasting to promote heart health".
Higher temperatures accelerate germination, with 23 °C (73 °F) promoting faster colony formation than 19 °C (66 °F). Light exposure is unnecessary for early fungal growth—cultures in darkness develop healthier, more extensive mycelial networks. Developing mycobiont morphology provides insights into early symbiosis. In vitro, X. parietina forms septate, branched hyphae, which later develop into lobed structures, resembling early lichen thalli. Scanning electron microscopy reveals a dense, interwoven hyphal network, potentially facilitating photobiont interactions during natural lichenization. These adaptations support X. parietina's regenerative ability and symbiotic establishment across varied environments. Although X. parietina lacks specialized vegetative propagules, it has a regenerative capacity that enhances its ecological success. Older, apothecia-covered thalli detach along drought-induced cracks, while younger margins remain attached. When fragments land on suitable substrates, they regenerate new lobes along wound margins, acting as natural propagules. Field studies show a 150% laminal size increase in just 13 months in regenerating thalli. In a five-year experiment, X. parietina maintained 50% substrate coverage, despite losing 90% of its initial thallus area, as regrowth compensated for these losses. Total turnover (growth + loss) exceeded 170%, highlighting its dynamic life cycle.
In March 2014, the IOC Disciplinary Commission decided that Bäckström would be awarded the silver medal. In January 2015 Bäckström, the IOC, WADA and the IIHF agreed to a settlement in which he accepted a reprimand but was cleared of attempting to enhance his performance.
Sources: en.wikipedia.org
Freezing only converts liquid to solid. Lyophilization adds vacuum and controlled warming so frozen solvent sublimes, leaving a dry porous solid. The two steps are related but not interchangeable.
Reduced pressure keeps the solvent below its triple point, allowing ice to become vapor without melting. Vacuum also helps remove water vapor from the product chamber. The exact pressure is chosen with the formulation and equipment.
Residual moisture is water that remains in the dried solid after secondary drying. It is often measured by Karl Fischer titration, near-infrared spectroscopy, or thermogravimetry. Acceptable levels depend on the material and its stability profile.
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.