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 2025-12-27. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
Quality assessment of a lyophilized product includes cake appearance, residual moisture, reconstitution time, and container closure integrity. A uniform, porous cake suggests that freezing and drying stayed within the formulation's design space. Cracks, shrinkage, meltback, or a glassy film can indicate thermal abuse or a formulation problem. Analysts also test for subvisible particles and sterility when the product requires those specifications. Visual inspection alone cannot confirm biological activity or chemical stability, so it is combined with analytical methods.
Stability programs monitor lyophilized products under defined temperature and humidity conditions over time. Real-time studies at recommended storage conditions are the reference, while accelerated studies provide early signals of degradation pathways. Because a dry cake can still undergo oxidation, hydrolysis, or aggregation, stability depends on residual moisture, excipients, and container headspace. Open questions include how best to predict long-term stability from short accelerated runs and how vial-to-vial variability affects shelf life. Current guidance treats these predictions as product-specific rather than universally generalizable.
| 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 |
Freeze-drying is used for materials whose activity or structure depends on low temperature and low water content. Examples include certain biologics, diagnostic reagents, starter cultures, coffee, and porous inorganic precursors. The dried product forms a cake whose porosity aids rapid wetting and dissolution. Main drawbacks are high energy use, long cycle times, and sensitivity to formulation and equipment variation. Questions remain about how freezing rates and ice morphology affect batch uniformity, especially when moving from laboratory to production scale.
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.
Stability studies examine how temperature, humidity, and time influence a lyophilized product. Accelerated conditions provide early information about degradation pathways, while long-term studies support shelf-life claims. The glass transition temperature of the dried formulation can indicate its physical stability, and storage above this temperature may increase molecular mobility and lead to collapse or aggregation. Container closure integrity also matters because moisture or oxygen ingress can degrade the product, so vial stoppers and seals are part of the quality system.
Handling and storage practices aim to keep the cake intact and dry. Vials are typically stored upright at controlled temperatures, often between 2 °C and 8 °C or at -20 °C for longer-term use. Reconstitution involves adding a suitable diluent and gently mixing until the solid dissolves. Shaking or rapid injection of diluent can create foam or damage sensitive molecules. Once reconstituted, the product may require refrigeration and use within a defined period.
==== Estrogen receptors ==== In addition to its affinity for the androgen receptor, DHEA has also been found to bind to (and activate) the ERα and ERβ estrogen receptors with Ki values of 1.1 μM and 0.5 μM, respectively, and EC50 values of >1 μM and 200 nM, respectively. Though it was found to be a partial agonist of the ERα with a maximal efficacy of 30–70%, the concentrations required for this degree of activation make it unlikely that the activity of DHEA at this receptor is physiologically meaningful. Remarkably however, DHEA acts as a full agonist of the ERβ with a maximal response similar to or actually slightly greater than that of estradiol, and its levels in circulation and local tissues in the human body are high enough to activate the receptor to the same degree as that seen with circulating estradiol levels at somewhat higher than their maximal, non-ovulatory concentrations; indeed, when combined with estradiol with both at levels equivalent to those of their physiological concentrations, overall activation of the ERβ was doubled.
== Medical uses == Vardenafil's indications and contraindications are the same as with other PDE5 inhibitors; it is closely related in function to sildenafil citrate (Viagra) and tadalafil (Cialis). The difference between the vardenafil molecule and sildenafil citrate is a nitrogen atom's position and the change of sildenafil's piperazine ring methyl group to an ethyl group. Tadalafil is structurally different from both sildenafil and vardenafil. Vardenafil's relatively short effective time is comparable to but somewhat longer than sildenafil's. Despite the structural differences between vardenafil and sildenafil, they both show similar ocular side effects due to their similar selectivity overlap with PDE6, an enzyme found in the eye. Beyond its indications for erectile dysfunction, vardenafil may be effective in the treatment of premature ejaculation, where it may significantly increase the time from penetration to ejaculation.
== State of the industry == Irradiation has been approved by many countries. For example, in the U.S. and Canada, food irradiation has existed for decades. Food irradiation is used commercially and volumes are in general increasing at a slow rate, even in the European Union where all member countries allow the irradiation of dried herbs spices and vegetable seasonings, but only a few allow other foods to be sold as irradiated. Although there are some consumers who choose not to purchase irradiated food, a sufficient market has existed for retailers to have continuously stocked irradiated products for years. When labelled irradiated food is offered for retail sale, consumers buy and re-purchase it, indicating a market for irradiated foods, although there is a continuing need for consumer education. Food scientists have concluded that any fresh or frozen food undergoing irradiation at specified doses is safe to consume, with some 60 countries using irradiation to maintain quality in their food supply.
The discovery of penicillin was one of the most important scientific discoveries in the history of medicine. Ancient societies used moulds to treat infections and in the following centuries many people observed the inhibition of bacterial growth by moulds. While working at St Mary's Hospital in London in 1928, Scottish physician Alexander Fleming was the first to experimentally demonstrate that a Penicillium mould secretes an antibacterial substance, which he named "penicillin". The mould was found to be a variant of Penicillium notatum (now called Penicillium rubens), a contaminant of a bacterial culture in his laboratory. The work on penicillin at St Mary's ended in 1929. In 1939, a team of scientists at the Sir William Dunn School of Pathology at the University of Oxford, led by Howard Florey that included Edward Abraham, Ernst Chain, Jean Orr-Ewing, Arthur Gardner, Norman Heatley and Margaret Jennings, began researching penicillin. They devised a method for cultivating the mould, as well as extracting, purifying and storing penicillin from it. They created an assay for measuring its purity. They carried out experiments with animals to determine penicillin's safety and effectiveness before conducting clinical trials and field tests. They derived its chemical formula and determined how it works. The private sector and the United States Department of Agriculture located and produced new strains and developed mass production techniques. Penicillin became an important part of the Allied war effort in the Second World War, saving the lives of thousands of soldiers.
Sources: en.wikipedia.org
Strained cyclooctenes and other activated alkenes react with tetrazines in an inverse electron-demand Diels-Alder reaction followed by a retro [4+2] cycloaddition (see figure). Three-membered and four-membered cycloalkenes, due to their high ring strain, also make ideal alkene substrates. Similar to other [4+2] cycloadditions, electron-donating substituents on the dienophile and electron-withdrawing substituents on the diene accelerate the inverse-demand Diels-Alder reaction. The diene, the tetrazine, by virtue of having the additional nitrogens, is a good diene for this reaction. The dienophile, the activated alkene, may often be attached to electron-donating alkyl groups on target molecules, thus making the dienophile more suitable for the reaction.
== Management == There is no standard course of treatment to slow or stop the progression of the disease as of 2019. sIBM patients do not reliably respond to anti-inflammatory, immunosuppressant, or immunomodulatory medications. Most of disease management is supportive care. Prevention of falls is an important consideration. There is no consensus on exercise guidelines; however, physical therapy is recommended to teach the patient a home exercise program, to teach how to compensate during mobility-gait training with an assistive device, transfers and bed mobility. An exercise regimen preferentially minimizes a patient's risk of injury and corresponds to the patient's goals.
Mahathir was born at his parents' home in a poor neighbourhood at Lorong Kilang Ais, Alor Setar, in the capital of the Malay sultanate of Kedah under a British protectorate, on 10 July 1925. He was the first prime minister who was not born into the aristocracy or a prominent religious or political family. Mahathir's mother, Wan Tempawan Wan Hanapi, was a Malay from Kedah. His father, Mohamad Iskandar, was from Penang of Malay and Indian descent. Mahathir's paternal grandfather had come from Kerala, British India. Some claim that Mahathir's facial features resemble those of Kerala Chief Minister Pinarayi Vijayan, although they are not related. Mohamad Iskandar was the principal of an English-medium secondary school, whose lower-middle-class status meant his daughters were unable to enrol in a secondary school. Wan Tempawan Wan Hanapi had only distant relations to members of Kedah's royalty. Both had been married previously. Mahathir was born with six half-siblings and two full-siblings. His childhood home, with a single shared bedroom and no electricity supply, was later converted to a tourist attraction and opened to the public. During his childhood, Mahathir enjoyed playing snakes and ladders and demonstrated multiple creative talents, including playing the trumpet, interior decorating, and engaging in crafts and carpentry work. He once shared that he was bullied in his youth, recalling how he sold balloons for a small profit but was forced by a stronger peer to use his earnings to buy food for him.
Cannabis strains is a popular name to refer to plant varieties of the monospecific genus Cannabis sativa L.. They are either pure or hybrid varieties of the plant, which encompasses various sub-species C. sativa, C. indica, and C. ruderalis. Varieties are developed to intensify specific characteristics of the plant, or to differentiate the strain for the purposes of marketing or to make it more effective as a drug. Variety names are typically chosen by their growers, and often reflect properties of the plant such as taste, color, smell, or the origin of the variety. The Cannabis strains referred to in this article are primarily those varieties with recreational and medicinal use. These varieties have been cultivated to contain a high percentage of cannabinoids. Several varieties of cannabis, known as hemp, have a very low cannabinoid content, and are instead grown for their fiber and seed. Due to the legal status of the plant in many jurisdictions, Cannabis plant varieties are at high risk of biopiracy.
=== Immigration === The vast majority of the district's population is composed of immigrants who have arrived in the last five decades, and their descendants. In 2016, 56.6% of residents were foreign-born. The immigrant population has created vibrant multicultural locales in various areas. One of the more notable among these is the heavy concentration of Chinese businesses and restaurants in the Agincourt neighbourhood. Many of Scarborough's main arteries, including segments of Kingston Road, Eglinton Avenue East and Lawrence Avenue East, feature Caribbean, Chinese, African, and Indian restaurants and shops, as well as businesses representing the other ethnic groups in the area.
Sources: en.wikipedia.org
But its first session only materialised in 1869 when, after the 1866 Prussian annexation of the Kingdom of Hanover, the Hanoverian Lutherans desired a representative body separate from Prussian rule, though it was restricted to Lutheran matters only. After the Prussian conquest in 1866, on 19 September 1866, the day before the official Prussian annexation took place and with the last summus episcopus, King George V of Hanover, in exile, the Kingdom's six consistories joined to form today's still-existing church body, the Lutheran State Church of Hanover. An all-Hanoverian consistory, the Landeskonsistorium (state consistory), was formed with representatives from the regional consistories. While the Calvinist congregations in formerly-Prussian East Frisia had a common roof organisation with the Lutherans there ("Coetus") and the Reformed Church in the former County of Bentheim, then being the state church, had fully established church bodies for Bentheim only (German: Königlich-Großbrittanisch-Hannoverscher Ober-Kirchenrath, English: Royal British-Hanoverian Supreme Church Council), the Calvinist congregations elsewhere in Hanover were in a somewhat sorry state. However, some Calvinist congregations of Huguenot origin were organised in the Lower Saxon Confederation (German: Niedersächsische Konföderation). The Lutheran church, being the state church of Hanover, also supervised the Calvinist diaspora parishes outside East Frisia and Bentheim.
== Safety == SOCl2 is highly reactive, releasing hydrochloric acid and sulfur dioxide upon contact with water and alcohols. Inhalation can cause pulmonary edema. It is also a controlled substance under the Chemical Weapons Convention, where it is listed as a Schedule 3 substance, since it is used in the manufacture of G-series nerve agents and the Meyer and Meyer–Clarke methods of producing sulfur-based mustard gases.
Such simulations are currently able to unfold and refold small proteins (<150 amino acids residues) in equilibrium and predict how mutations affect folding kinetics and stability. In 2020 a team of researchers that used AlphaFold, an artificial intelligence (AI) protein structure prediction program developed by DeepMind placed first in CASP, a long-standing structure prediction contest. The team achieved a level of accuracy much higher than any other group. It scored above 90% for around two-thirds of the proteins in CASP's global distance test (GDT), a test that measures the degree of similarity between the structure predicted by a computational program, and the empirical structure determined experimentally in a lab. A score of 100 is considered a complete match, within the distance cutoff used for calculating GDT. AlphaFold's protein structure prediction results at CASP were described as "transformational" and "astounding". Some researchers noted that the accuracy is not high enough for a third of its predictions, and that it does not reveal the physical mechanism of protein folding for the protein folding problem to be considered solved. Nevertheless, it is considered a significant achievement in computational biology and great progress towards a decades-old grand challenge of biology, predicting the structure of proteins.
The needle may cut small pieces of rubber from the septum as it injects sample through it. These can block the needle and prevent the syringe filling the next time it is used. It may not be obvious that this has happened. A fraction of the sample may get trapped in the rubber, to be released during subsequent injections. This can give rise to ghost peaks in the chromatogram. There may be selective loss of the more volatile components of the sample by evaporation from the tip of the needle.
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.
Many dried cakes are hygroscopic and can adsorb water during storage or handling. Absorbed moisture may lower the glass transition temperature and promote chemical reactions. Sealed packaging and controlled humidity reduce this risk.