secondary 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 2026-06-24 and is reviewed periodically as new material appears.
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.
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.
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 synonyms | Freeze-drying; lyophilisation; cryodesiccation | Regional spelling and historical terms. |
| Primary drying pressure | 0.05-0.5 mbar (5-50 Pa) | Kept below the triple point of water; product-specific. |
| Shelf temperature range | -40 to +40 °C | Freezing, primary, and secondary stages use different set points. |
| Cycle duration | 12-72 hours | Depends on fill volume, formulation, and equipment. |
| Condenser temperature | -50 to -80 °C | Must remain below the product's ice temperature. |
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.
Lyophilization is a dehydration process that removes water from a frozen material by sublimation under low pressure. The material is first frozen so that water becomes ice; then the surrounding pressure is lowered below the vapor pressure of ice. Heat is applied gently so ice changes directly to vapor without passing through a bulk liquid phase. The vapor is collected on a cold condenser, leaving a dry porous matrix. This process differs from simple evaporation because the material remains frozen during the main drying stage.
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.
Lyophilization, also known as freeze-drying, is a process that removes water from a material by freezing it and then reducing pressure to allow ice to sublimate directly into vapor. The method begins with a freezing step that solidifies the water content. Next, primary drying lowers the pressure below the triple point of water, enabling sublimation without passing through a liquid phase. A final secondary drying step removes bound water through desorption. This sequence produces a dry, porous cake that can be reconstituted later.
The process relies on the phase diagram of water, where the triple point marks the conditions at which ice, liquid water, and vapor coexist. By maintaining pressure below this point, typically around 0.01 to 0.1 millibar, sublimation becomes the dominant mechanism. Formulations often include excipients such as sugars or polymers that act as lyoprotectants and bulking agents. These additives help preserve the structure of the active ingredient and prevent collapse during drying. The choice of excipient and freezing rate influences the final cake morphology and stability.
Industries use lyophilization for pharmaceuticals, biological products, and food preservation. In the pharmaceutical sector, it extends the shelf life of injectable drugs, vaccines, and proteins that are unstable in aqueous solution. Food manufacturers apply freeze-drying to coffee, fruits, and ready meals to retain flavor and texture. The process is energy-intensive and requires specialized equipment, which limits its use to high-value products. Ongoing research examines how formulation and process parameters affect the quality of the final dried product.
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.
Third and fourth generations In the 1980s, the third and fourth generations of breast prostheses featured shells coated with an elastomer that decreased gel bleed (filler leakage) into the thorax of the woman, which was achieved with thick filler-gels of various viscosities for the different models of prosthetic breast. The designs of the models of breast prostheses are anatomically symmetrical, in accordance with the body type of the woman. The shaped models realistically reproduce the types of breast hemispheres for the corresponding body-types of women. The tapered models of breast prosthesis feature a uniformly textured surface that produces friction to limit the rotation of the breast prosthesis within the implant-socket. Moreover, the round models of breast prosthesis are available in textured-surface models and in smooth-surface models, for when the prosthetic breast is not expected to rotate within the implant-socket.
Sickle cell disease (SCD), also simply called sickle cell, is a group of inherited hemoglobin-related blood disorders. Sickle cell disease is caused by an abnormality in the oxygen-carrying protein haemoglobin found in red blood cells. This leads to the red blood cells adopting an abnormal sickle-like shape under certain circumstances. With this shape, they cannot deform as they pass through capillaries, causing blockages. Problems in sickle cell disease typically begin around 5 to 6 months of age. Several health problems may develop, such as attacks of pain (known as a sickle cell crisis) in joints, anaemia, swelling in the hands and feet, bacterial infections, dizziness and stroke. The probability of severe symptoms, including long-term pain, increases with age. Without treatment, people with sickle cell disease rarely reach adulthood, but with good healthcare, median life expectancy is between 58 and 66 years. All of the major organs are affected by sickle cell disease. The liver, heart, kidneys, lungs, gallbladder, eyes, bones, and joints can be damaged by abnormal sickle cells and their inability to flow through the small blood vessels. Sickle cell disease occurs when a person inherits two abnormal copies of the β-globin gene that make haemoglobin, one from each parent. The abnormal gene generates haemoglobin S (HbS) which changes the properties of red blood cells.
While the Arrhenius concept is useful for describing many reactions, it is also quite limited in its scope. In 1923, chemists Johannes Nicolaus Brønsted and Thomas Martin Lowry independently recognized that acid–base reactions involve the transfer of a proton. A Brønsted–Lowry acid (or simply Brønsted acid) is a species that donates a proton to a Brønsted–Lowry base. Brønsted–Lowry acid–base theory has several advantages over Arrhenius theory. Consider the following reactions of acetic acid (CH3COOH), the organic acid that gives vinegar its characteristic taste:
==== Pit closures ==== Heseltine's responsibilities also included Energy, as the separate Energy ministry was abolished. Electricity companies now decided on their own contracts, rather than being obliged by the government to choose British coal. With plans being made for the privatisation of British Coal, on 13 October 1992 Heseltine and British Coal both separately announced that 31 of British Coal's 50 pits were to close, with the loss of 30,000 jobs. Most of the detailed work had been done by the minister of state Tim Eggar. Many of the mines in Nottinghamshire that had continued working during the 1984–1985 strike were to close. Although this policy was seen by the Nottinghamshire miners as a betrayal, there was hardly any organised resistance to the programme. The government stated that since the pits were losing money they could be sustained only through unjustifiable government subsidies. Mine supporters pointed to the mines' high productivity rates and to the fact that their monetary losses were due to the large subsidies that other European nations were giving to their coal industries. An early leak had seen little reaction but Heseltine was taken aback by the public anger. Over 100 pits had closed since the 1984–1985 strike. The closures were to be rushed because the Treasury, under pressure from Major, had agreed to make money for generous redundancy settlements available only in the 1992–1993 fiscal year.
== Methods to screen protein–protein interactions == Though there are many methods to detect protein–protein interactions, the majority of these methods—such as co-immunoprecipitation, fluorescence resonance energy transfer (FRET) and dual polarisation interferometry—are not screening approaches.
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The pancreatic islets or islets of Langerhans are the regions of the pancreas that contain its endocrine cells (hormone-producing cells), discovered in 1869 by German pathological anatomist Paul Langerhans. The pancreatic islets constitute 1–2% of the pancreas volume and receive 10–15% of its blood flow. The pancreatic islets are arranged in density routes throughout the human pancreas, and are important in the metabolism of glucose.
Complications were observed in each of the leucotomy patients and included: "increased temperature, vomiting, bladder and bowel incontinence, diarrhea, and ocular affections such as ptosis and nystagmus, as well as psychological effects such as apathy, akinesia, lethargy, timing, and local disorientation, kleptomania, and abnormal sensations of hunger". Moniz asserted that these effects were transitory and, according to his published assessment, the outcome for these first twenty patients was that 35%, or seven cases, improved significantly, another 35% were somewhat improved and the remaining 30% (six cases) were unchanged. There were no deaths and he did not consider that any patients had deteriorated following leucotomy.
== Structure == The prostate is an exocrine gland of the male reproductive system. In adults, it is about the size of a walnut, and has an average weight of about 11 grams (0.39 oz), usually ranging between 7 and 16 grams (0.25–0.56 oz). The prostate is located in the pelvis. It sits below the urinary bladder and surrounds the urethra. The part of the urethra passing through it is called the prostatic urethra, which joins with the two ejaculatory ducts. The prostate is covered in a surface called the prostatic capsule or prostatic fascia. The internal structure of the prostate has been described using both lobes and zones. Because of the variation in descriptions and definitions of lobes, the zone classification is used more predominantly. The prostate has been described as consisting of three or four zones. Zones are more typically able to be seen on histology, or in medical imaging, such as ultrasound or MRI.
=== Use in water treatment === Nelumbo nucifera shows high potential for usage in wastewater treatment removing polluting compounds and heavy metals. It is able to grow in variable water conditions and in low light intensity. Various studies show the successful use of N. nucifera to counteract water eutrophication. The leaves of the floating lotus reduce sunlight reaching the lower part of the water. This suppresses algae growth in N. nucifera aquatic systems and thus, the oxygen content is up to 20% higher than in other aquatic plant systems. Due to intense agricultural practices, nitrogen and phosphorus pollution are major problems in aquatic systems. N. nucifera is able to assimilate a higher content of phosphorus than aquatic plants currently used for water remediation (such as water hyacinth). It also assimilates nitrogen ("denitrification") and creates a habitat for bacterial growth in the water body. Through rhizofiltration, heavy metals – including arsenic, copper, and cadmium – can be removed efficiently from the water. The results observed are impressive showing 96% of copper and 85% cadmium metals removed after a seven-day incubation period. The accumulation of heavy metals doesn't show morphological symptoms of metal toxicity; however, the rhizome quality for human consumption needs further study.
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For Reynolds number greater than 4000, the flow is turbulent; the resistance to flow follows the Darcy–Weisbach equation: it is proportional to the square of the mean flow velocity. Over a domain of many orders of magnitude of Re (4000 < Re < 108), the friction factor varies less than one order of magnitude (0.006 < fD < 0.06). Within the turbulent flow regime, the nature of the flow can be further divided into a regime where the pipe wall is effectively smooth, and one where its roughness height is salient.
== Description == The blue mackerel typically reaches 30 cm (12 in) in fork length. It can reach 44 cm (17 in) in fork length and 1.4 kg (3.1 lb) in weight. Mackerels have a round body that narrows into the tail after the second dorsal fin, similar to a tuna fish. Blue mackerel are often mistaken for chub mackerel. In fact, blue mackerel were believed to be a subspecies of chub mackerel until the late 1980s. Though they are both in the same genus (Scomber), blue mackerel set themselves apart by differing structural genes than those of the chub mackerel. Other, more obvious, characteristics set these two apart, like the longer anal spine of the blue mackerel, and the amount of spines on the first dorsal fin.
=== Calibration === Continuous glucose monitoring systems do not always produce readings identical to those obtained through fingerstick blood glucose testing. Differences between CGM and fingerstick values are expected due to physiological and technical factors, including the lag time between glucose levels in interstitial fluid and those in capillary blood. While the Dexcom G7 has a reported MARD of approximately 8.2%, variations of up to 20% between CGM and fingerstick readings are considered within the normal accuracy range. These differences are particularly noticeable during periods of rapid glucose change, such as after meals, physical activity, or insulin administration. As a result, CGM readings are most reliable when glucose levels are stable, and discrepancies may occur during times of fluctuation. There is an option to calibrate using a blood glucose reading taken from another device such as a blood glucose meter that uses a fingerstick lancing device, but it is not mandatory on any currently available Dexcom CGMs. The "20 rule" (or 20/20 rule) is commonly used to assess the accuracy of the CGM. If the difference between the Dexcom G6 or G7 reading and the fingerstick blood glucose meter value is within 20% (or 20 mg/dL when glucose levels are under 80 mg/dL), the sensor is operating within its expected error margin. While CGM and meter readings may not match exactly, they should generally fall within this acceptable range, especially when glucose levels are stable.
Sources: en.wikipedia.org
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.
Reduced pressure lowers the boiling point of water and allows ice to sublime at temperatures below freezing. It also helps remove water vapor from the product toward the condenser. The exact pressure is chosen to stay below the triple point of water.
No. Materials with low solids content or high volatile solvents may form weak or collapsed cakes. Some proteins and cells require stabilizers to survive freezing and drying stresses. Feasibility depends on formulation and process design.
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.