The short version of secondary drying fits in a sentence. The long version — which is the one that helps — is below.
This page was last updated on 2025-12-21 and is reviewed periodically as new material appears.
Lyophilization is a dehydration process that removes water from a frozen material by sublimation under low pressure. The material is first frozen to convert liquid water into ice. Next, the pressure is reduced below the triple point of water so that ice changes directly into vapor without passing through a liquid phase. This step is called primary drying. The result is a porous solid or cake that retains the original shape of the frozen solution.
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 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.
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.
| Property | Value | Notes |
|---|---|---|
| Common synonyms | Freeze-drying, lyophilisation | Lyophilization is the American spelling; lyophilisation is British |
| Primary drying mechanism | Sublimation of ice | Occurs under vacuum below the triple point |
| Typical chamber pressure | 0.05-0.5 mbar | Range depends on product and equipment |
| Typical shelf temperature during freezing | -40 to -20 °C | Lower temperatures may be used for labile products |
| Resulting product form | Porous cake or powder | Appearance depends on formulation and cycle |
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.
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.
Kipa-Williams enjoyed working with Samson, as they got along well and he believed that showed on-screen as Ari and Mia reconcile. He also praised Barrett and explained how they got the chance to explore their characters' histories together, saying "you'll get to see a softer side of Ari in the way that Sam plays her character. And I think people will be surprised at the father figure that he has forgotten he is, or was." The first test of Ari and Mia's new relationship is his involvement with a criminal gang headed up by Paul (Jack Finsterer), which leads to the kidnapping of Chloe, Nikau, Bella, and Ryder Jackson (Lukas Radovich). Mia decides to leave the Bay with Chloe and tells Ari that she regrets letting him back into her life. Kipa-Williams commented that "Ari is heartbroken – he's faced with losing the love of his life." He sympathised with Mia, who is angry about her daughter being kidnapped. He also pointed out that Mia thought Ari had changed, so it "pains" her to think that he is still the same man who could end up in prison again. As Ari is walking along the road, he calls Chloe before she leaves town, and is struck by a car driven by Paul who then speeds off. Kipa-Williams said Ari is "blindsided" by the attack and described it as "a ruthless hit-and-run". Ari suffers multiple injuries and has to be placed in a medically induced coma due to a bleed on the brain. Following Ari's recovery, writers scripted a pregnancy for Mia after the couple agree to try for a baby.
== Military career == After graduating from the Military Academy, al-Burhan worked in Khartoum, as part of the Sudanese army, and participated in the fighting fronts in the Darfur war and in the Second Sudanese Civil War in South Sudan and other regions. He was regional commander in Darfur. He later traveled to Egypt and then to Jordan to receive training courses in his military field until in 2018 he was appointed commander of the ground forces of the army. Al-Burhan held several positions throughout his career as he began as a soldier with the Border Guard Forces and later became commander of this force before becoming Deputy Chief of Staff of the Ground Forces Operations and then Chief of Staff of the Sudanese Army in February 2018 before he served as Inspector General of the Army for a period of time. By 26 February 2019, during the massive protests that swept the country and demanded the fall of Omar al-Bashir's regime, al-Burhan was elevated to the rank of lieutenant general.
== Effectiveness == Marketing claims that Protadim can prevent or treat cancer are unproven and have been deemed fraudulent by the FDA. Research into use as a treatment for amyotrophic lateral sclerosis is of poor quality, casting doubt on its usefulness for drawing any conclusions about efficacy. In 2011, Harriet A. Hall wrote for Science-Based Medicine that "we simply don't know enough at this point to recommend Protandim for treatment or prevention of any disease, for anti-aging, for making people feel healthier or more energetic, or for anything else".
Sources: en.wikipedia.org
== Interaction with other cells == Within the epidermis keratinocytes are associated with other cell types such as melanocytes and Langerhans cells. Keratinocytes form tight junctions with the nerves of the skin and hold the Langerhans cells and intra-dermal lymphocytes in position within the epidermis. Keratinocytes also modulate the immune system: apart from the above-mentioned antimicrobial peptides and chemokines they are also potent producers of anti-inflammatory mediators such as IL-10 and TGF-β. When activated, they can stimulate cutaneous inflammation and Langerhans cell activation via TNFα and IL-1β secretion. Keratinocytes contribute to protecting the body from ultraviolet radiation (UVR) by taking up melanosomes, vesicles containing the endogenous photoprotectant melanin, from epidermal melanocytes. Each melanocyte in the epidermis has several dendrites that stretch out to connect it with many keratinocytes. The melanin is then stored within keratinocytes and melanocytes in the perinuclear area as supranuclear "caps", where it protects the DNA from UVR-induced damage.
==== Chain conformation ==== The space occupied by a polymer molecule is generally expressed in terms of radius of gyration, which is an average distance from the center of mass of the chain to the chain itself. Alternatively, it may be expressed in terms of pervaded volume, which is the volume spanned by the polymer chain and scales with the cube of the radius of gyration. The simplest theoretical models for polymers in the molten, amorphous state are ideal chains. The random-coil (ideal-chain) conformation of linear polymer chains in the melt was experimentally confirmed in the 1970s using small-angle neutron scattering (SANS), as soon as the first SANS diffractometers became available, and this result is considered one of the landmark achievements in polymer physics.
Sikhs were the first Indian immigrants to Belize (not counting indentured workers), and the former Chief Justice of Belize George Singh was the son of a Sikh immigrant, there was also a Sikh cabinet minister. Belize's Muslim population dates from the 1980s. Muslims numbered 577 in 2010 according to the official statistics, accounting for 0.16 per cent of the population.
Sources: en.wikipedia.org
SR-17018, also known informally as SR-17 or just SR and as 5,6-dichloro-desmethylchlorphine, is an atypical opioid receptor modulator with unusual actions and effects. It acts as a biased partial agonist of the μ-opioid receptor (MOR), showing strong selectivity for activation of G protein signaling over β-arrestin2 recruitment at this receptor. In addition, the drug appears to also act as a MOR positive allosteric modulator, with this possibly being its primary action. Unlike conventional opioids such as morphine and fentanyl, SR-17018 produces robust analgesic effects in rodents with very little respiratory depression and with much less analgesic tolerance. Moreover, substitution of conventional opioids like morphine with SR-17018 can reverse analgesic tolerance and suppress withdrawal symptoms in rodents. However, conflicting findings exist in terms of analgesic tolerance and respiratory depression. The drug has not been formally studied in humans. SR-17018 was first described in the scientific literature by Laura Bohn and colleagues in 2017. It was encountered online as a novel designer drug by 2023. Subsequently, discussion of SR-17018 on the social media website Reddit dramatically increased in 2024. Although technically a designer opioid, SR-17018 is said to have very different effects from other opioids, for instance producing minimal euphoria. Rather than being used recreationally itself, SR-17018 is typically employed by users to prevent opioid withdrawal symptoms and facilitate opioid discontinuation in the context of opioid dependence.
== History == Remimazolam was approved for medical use in the United States in July 2020. The U.S. Food and Drug Administration (FDA) approved remimazolam based on evidence from three clinical trials (Trial 1/NCT02290873, Trial 2/NCT02296892 and Trial 3/NCT02532647) in adults undergoing short procedures. Trials were conducted at 32 sites in the United States. Trials 1 and 3 were conducted in participants undergoing colonoscopy and Trial 2 was conducted in participants undergoing bronchoscopy procedures. In the trials, participants were randomly divided in three groups: one group received remimazolam, one group received placebo and one group received midazolam (similar, but approved drug). In the first two groups, neither participants nor investigators knew which medications were given and participants could also receive midazolam as a rescue drug when needed for sedation. In the third group, all participants received midazolam only Additionally, in all three trials participants received a medication for pain control Trials 1 and 2 compared participants who received remimazolam to participants in the other two groups, measuring the success of sedation with the set of pre-determined criteria. Data from Trial 3 were used primarily to assess the side effects of remimazolam when multiple dosing is used.
The findings of drug discrimination tests suggest that 5-HTP has a more complex or compound discriminative stimulus compared to other agents like LSD and that its stimulus properties may not be readily explained by either the serotonin 5-HT1 or 5-HT2 receptors alone. Instead, a combination of actions at these and/or other receptors may be involved in its stimulus effects.
Lockheed implemented it into the L-1011 TriStar in 1973 at the request of Pacific Southwest Airlines (who used the baggage compartment as an entertainment lounge) and possibly also to suit potential Soviet buyers (see below). In October 1967, the Soviet government approved a Ministry of Civil Aviation (Aeroflot) specification for an aerobus. This called for 350 seats and a range of 3,600 kilometres (1,900 nautical miles) with a 40-tonne payload or 5,800 km (3,100 nmi) with seats taken but no freight. The airliner had to operate from smaller airports (classified as Klass "B" and "V" [Russian: класс "Б", "В"] or "Class B/C" by the Soviets) 2,600-metre (8,500 ft) runways. In the second half of the 1960s, OKB-240 (as the Ilyushin bureau was formally known) was restoring positions lost (with Yakovlev, in favour of Tupolev and Antonov) during the Khrushchev era and was well placed to secure design of the aerobus. When the Soviet cabinet's defence industry committee promoted the Aeroflot specification on September 8, 1969, to a preliminary project, (Russian: аванпроект; transliterated: avanproyekt), it entrusted it to Ilyushin. The bureau received specific operational requirements for the aerobus on February 22, 1970. In developing the concept which had been agreed, Ilyushin faced four challenges: configuration (layout or "shape"), powerplant, automation (avionics) and manufacturing capacity.
Sources: en.wikipedia.org
Lyophilization removes water by sublimation from a frozen material, while evaporation changes liquid water into vapor. The low-pressure freezing step avoids the liquid phase and can preserve heat-sensitive structures.
Vacuum lowers the pressure below the triple point of water, allowing ice to sublimate directly into vapor. It also helps remove water vapor from the product chamber and shortens primary drying.
Many aqueous solutions and suspensions can be freeze-dried, but some formulations collapse or do not form a stable cake. The process requires careful formulation and cycle development.
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.