This is a working overview of secondary drying, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2025-12-31 and is reviewed periodically as new material appears.
Quality control for lyophilized products includes appearance, cake structure, reconstitution time, pH, residual moisture, and potency. Residual moisture is a key attribute because excess water can reduce stability, while excessively low moisture may cause structural changes or aggregation in some systems. Stability studies compare real-time and accelerated conditions to estimate shelf life. Analytical methods must be validated for the specific matrix, container, and moisture range. Sterility and container integrity are also monitored for sterile products.
Handling practices aim to prevent moisture ingress and mechanical damage. Vials should remain stoppered and crimped until use, and reconstitution should follow the labeled diluent and volume. Shipping may involve temperature-controlled containers and desiccants, but direct contact between desiccant and product is avoided. Regulatory guidance expects documented storage conditions, excursion assessments, and stability commitments. Open questions remain about how best to predict long-term stability from short accelerated studies for every formulation class.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Typical appearance | White to off-white porous cake or powder | Color and structure vary with formulation. |
| Typical reconstitution time | Seconds to several minutes | Diluent, agitation, and temperature affect rate. |
| Typical storage temperature | 2–8 °C, 15–25 °C, or ≤−20 °C | Product-specific; protect from moisture and light. |
| Typical container closure | Glass vial with rubber stopper and crimp seal | Closure must limit moisture ingress. |
| Typical stability indicator | Residual moisture, potency, and reconstitution time | Monitored throughout shelf life. |
Storage conditions for dried products usually aim to exclude moisture and oxygen. Vials are sealed under vacuum or with an inert gas, and stoppers must maintain a barrier during transport. Temperature recommendations vary; some materials remain stable at room temperature, while others need refrigeration or frozen storage. Humidity control is critical because dried cakes can absorb water rapidly once a container is opened. Desiccant packs and moisture-barrier bags add further protection during shipping.
Quality control also examines cake structure, color, and reconstitution behavior. A collapsed or shrunken cake can indicate a thermal excursion during drying. Analytical methods such as X-ray diffraction, differential scanning calorimetry, and near-infrared spectroscopy can detect crystallinity or moisture distribution. Regulatory expectations focus on validated assays and lot-to-lot consistency. Questions remain about how well accelerated stability tests predict long-term behavior for every formulation. Visual inspection remains common but is subjective without trained reviewers and reference images.
After lyophilization, a product's quality depends on residual moisture, cake appearance, and reconstitution time. Residual moisture is often measured by Karl Fischer titration or thermogravimetric analysis. A low moisture content can slow chemical degradation, but overly dry cakes may be brittle or slow to dissolve. Stability studies track these attributes over months under defined temperature and humidity conditions. Batch records link these measurements to specific process runs and help identify trends before a product fails specification.
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 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.
oryzae can convert both glucose and xylose under aerobic conditions into pure L (+)-lactic acids with by-products such as xylitol, glycerol, ethanol, carbon dioxide and fungal biomass. Endo-xylanase is a key enzyme for xylan depolymerization and was produced by R. oryzae fermentation from different xylan-containing agricultural by-products such as wheat straw, wheat stems, cottons bagasse, hazelnut shells, corn cobs, and oat sawdust. Pectinases are required for extraction and clarification of fruit juices and wines, extraction of oils, flavors and pigmentation from plant material, preparation of cellulose fibers for linen, jute and hemp manufacture as well as, coffee and tea fermentations. R. oryzae can break down starch content in rice plants and therefore shows amylolytic activities. Also, it has been reported to produce extra cellular isoamylase which is used in food industries. Isoamylase was found to saccharify potato starch, arrow root, tamarind kernel, tapioca, and oat. The saccharifying ability of the enzyme is highly applicable in sugar production industries. Proteases, which can be found in R. oryzae are highly useful in commercial industries. For instance, it has increased application in food, pharmaceutical, detergent, leather, tanning industries. It is also involved in silver recovery and peptide synthesis. One strain of R. oryzae was found to secrete alkaline serine protease which shows high pH stability within 3 to 6 and poor thermos-stability. Lipase that is extracted from R. oryzae have been consumed as digestive aids without adverse reactions.
This is relevant for enzymes like pepsin that are active in acidic environments such as the mammalian stomach and lysosomes, but does not significantly apply to intracellular enzymes. In highly basic conditions (pH greater than 10, not normally seen in physiological conditions), the ammonio group is deprotonated to give NH2−CHR−CO−2. Although various definitions of acids and bases are used in chemistry, the only one that is useful for chemistry in aqueous solution is that of Brønsted: an acid is a species that can donate a proton to another species, and a base is one that can accept a proton. This criterion is used to label the groups in the above illustration. The carboxylate side chains of aspartate and glutamate residues are the principal Brønsted bases in proteins. Likewise, lysine, tyrosine and cysteine will typically act as a Brønsted acid. Histidine under these conditions can act both as a Brønsted acid and a base.
"Patent Pending". FBI: Most Wanted. Season 4. Episode 6. 15 November 2022. CBS. "Via Negativa". The X-Files. Season 8. Episode 7. 17 December 2000. Fox Broadcasting Company. "Getting Off". CSI: Crime Scene Investigation. Season 4. Episode 16. 26 February 2004. CBS. "Users". Law & Order: Special Victims Unit. Season 11. Episode 7. 4 November 2009. NBC. "Echoes". Nikita. Season 1. Episode 16. 24 February 2011. The CW Television Network. "One Last Time". Homeland (TV series). Season 3. Episode 9. 24 November 2013. Showtime. "Bon Voyage". Graceland (TV series). Season 3. Episode 7. 6 August 2015. USA Network.
Sources: en.wikipedia.org
=== Metabolism === The hepatic metabolism of hexobarbital (HB) can be divided into different pathways all forming different metabolites. The S(+) enantiomer of HB preferentially metabolizes into β-3'-hydroxyhexobarbital and the R(-) enantiomer preferentially metabolizes into α-3'-hydroxyhexobarbital, the reaction thus is stereoselective. Both enantiomers, however, form both α- and β-isomers. In total four enantiomers for 3'-hydroxyhexobarbital (3HHB) can be metabolized. This reaction is catalyzed by a cytochrome P450, CYP2B1. All 3HHB isomers formed can undergo further metabolism via glucuronidation or dehydrogenation. If 3HHB undergoes a glucuronidation reaction, via UDP-glucuronosyl transferases (UGTs), it is readily excreted. 3HHB can also undergo dehydrogenation, forming a reactive ketone, 3'-oxohexobarbital (3OHB). The biotransformation of 3HHB into 3OHB is via the enzyme 3HHB dehydrogenase (3HBD), a NAD(P)+ linked oxidation. This enzyme is part of the aldo-keto reductase (AKR) superfamily. In humans, 3HBD has a high preference for NAD+. These reactions are also stereospecific, the R(-) conformation preferentially forms 3OHB as 3HBD has the highest activity for this enantiomer in both alpha and beta form. New evidence proved the further metabolism of 3OHB into 1,5-dimethylbarbituric acid and a cyclohexenone glutathione adduct. This biotransformation step takes place via an epoxide-diol mechanism. The formation of a reactive epoxide, leads to the formation of the compounds mentioned.
In his first semester, Pauling registered for two courses in chemistry, two in mathematics, mechanical drawing, introduction to mining and use of explosives, modern English prose, gymnastics and military drill. His roommate was childhood pal and lifelong best friend Lloyd Jeffress. He was active in campus life and founded the school's chapter of the Delta Upsilon fraternity. After his second year, he planned to take a job in Portland to help support his mother. The college offered him a position teaching quantitative analysis, a course he had just finished taking himself. He worked forty hours a week in the laboratory and classroom and earned US$100 a month (equivalent to US$1,600 in 2025), enabling him to continue his studies. In his last two years at school, Pauling became aware of the work of Gilbert N. Lewis and Irving Langmuir on the electronic structure of atoms and their bonding to form molecules. He decided to focus his research on how the physical and chemical properties of substances are related to the structure of the atoms of which they are composed, becoming one of the founders of the new science of quantum chemistry. Engineering professor Samuel Graf (1887–1966) selected Pauling to be his teaching assistant in a mechanics and materials course. During the winter of his senior year, Pauling taught a chemistry course for home economics majors. It was in one of these classes that Pauling met his future wife, Ava Helen Miller. In 1922, Pauling graduated with a degree in chemical engineering.
Historically, American black bears occupied the majority of North America's forested regions. Today, they are primarily limited to sparsely settled, forested areas. American black bears currently inhabit much of their original Canadian range, though they seldom occur in the southern farmlands of Alberta, Saskatchewan and Manitoba; they have been extirpated on Prince Edward Island since 1937. Surveys taken in the mid-1990s found the Canadian black bear population to be between 396,000 and 476,000 in seven provinces; this estimate excludes populations in New Brunswick, the Northwest Territories, Nova Scotia and Saskatchewan. All provinces indicated stable populations of American black bears over the 2000s. The current range in the United States is constant throughout most of the Northeast and within the Appalachian Mountains almost continuously from Maine to northern Georgia, the northern Midwest, the Rocky Mountain region, the West Coast and Alaska. However, it becomes increasingly fragmented or absent in other regions. Despite this, American black bears in those areas seem to have expanded their range in recent decades, such as with sightings in Ohio, Illinois, southern Indiana, and western Nebraska. Sightings of itinerant black bears in the Driftless Area of southeastern Minnesota, northeastern Iowa, and southwestern Wisconsin are common.
== Principles == Proximity labeling relies on a labeling enzyme that can biotinylate nearby biomolecules promiscuously. Biotin labeling can be achieved through several different methods, depending on the species of labeling enzyme. BioID and TurboID rely on exogenous biotin supplementation; APEX and APEX2 utilize exogenous biotin phenol and hydrogen peroxide.
Sources: en.wikipedia.org
In 1800, France built Nautilus, a human-powered submarine designed by American Robert Fulton. They gave up on the experiment in 1804, as did the British, when they reconsidered Fulton's submarine design. In 1850, Wilhelm Bauer's Brandtaucher was built in Germany. It remains the oldest known surviving submarine in the world. In 1864, late in the American Civil War, the Confederate navy's H. L. Hunley became the first military submarine to sink an enemy vessel, the Union sloop-of-war USS Housatonic, using a gun-powder-filled keg on a spar as a torpedo charge. The Hunley also sank. The explosion's shock waves may have killed its crew instantly, preventing them from pumping the bilge or propelling the submarine. In 1866, Sub Marine Explorer was the first submarine to successfully dive, cruise underwater, and resurface under the crew's control. The design by German American Julius H. Kroehl (in German, Kröhl) incorporated elements that are still used in modern submarines. In 1866, Flach was built at the Chilean government's request by Karl Flach, a German engineer and immigrant. It was the fifth submarine built in the world and, along with a second submarine, was intended to defend the port of Valparaíso against attack by the Spanish Navy during the Chincha Islands War.
Nanoghosts are nanosized vesicles containing a chosen drug delivery payload manufactured from extracted leukocyte membranes with the cell cytoplasm content removed. The use of biological membranes serves to mask the particles from the immune system to reduce the likelihood of an immunogenic response, as well as to extend circulation of the particles in the blood. They are produced by homogenizing the cells to remove the cytosol, and then sonicating the empty cell membranes to create nanoghosts between 100 and 200 nm in diameter. Membranes used to make nanoghosts harvested form red blood cells have been shown to circulate for about 120 days and avoid phagocytotic cells. Neutrophil based nanoghosts retain the chemotaxis capacity of neutrophils to sites of inflammation, which encourages tumor targeting. NK based nanoghosts exhibit metastatic cancer targeting behavior. Monocyte based nanoghosts are effective at infiltrating the tumor microenvironment. Mesenchymal stem cell derived nanoghosts exhibit cancer targeting properties.
The use of additional manipulation tools may be needed to organize 3D co-cultures into a configuration similar enough to native tissue architecture. Endothelial cells (PEC), smooth muscle cells (SMC), fibroblasts (PF), and epithelial cells (EpiC) cultured through magnetic levitation can be sequentially layered in a drag-and-drop manner to create bronchioles that maintain phenotype and induce extracellular matrix formation. Below is a list of cell types (primary and cell lines) that have been successfully cultured by the magnetic levitation method.
==== Legal challenges ==== In Glossip v. Gross, attorneys for three Oklahoma inmates argued that midazolam could not achieve the level of unconsciousness required for surgery, meaning severe pain and suffering was likely. They argued that midazolam was cruel and unusual punishment and thus contrary to the Eighth Amendment to the United States Constitution. In June 2015, the U.S. Supreme Court ruled that they had failed to prove that midazolam was cruel and unusual when compared to known, available alternatives. The state of Nevada is also known to use midazolam in execution procedures. In July 2018, one of the manufacturers accused state officials of obtaining the medication under pretences. This incident was the first time a drug company successfully, though temporarily, halted an execution. A previous attempt in 2017, to halt an execution in the state of Arizona by another drug manufacturer was not successful.
== Selection == In order to ensure growth of only transformed bacteria (which carry the desired plasmids to be harvested), a marker gene is used in the destination vector for selection. Typical marker genes are for antibiotic resistance or nutrient biosynthesis. So, for example, the "marker gene" could be for resistance to the antibiotic ampicillin. If the bacteria that were supposed to pick up the desired plasmid had picked up the desired gene then they would also contain the "marker gene". Now the bacteria that picked up the plasmid would be able to grow in ampicillin whereas the bacteria that did not pick up the desired plasmid would still be vulnerable to destruction by the ampicillin. Therefore, successfully transformed bacteria would be "selected."
Sources: en.wikipedia.org
Collapse occurs when the product temperature rises above its collapse or eutectic temperature during drying. The frozen matrix loses structure, producing a shrunken or melted appearance. This can slow reconstitution and may affect stability.
Karl Fischer titration is a common method, along with loss on drying and thermogravimetric analysis. Each method has different sensitivity and sample requirements. Results should be interpreted with the product's formulation and container in mind.
No. Lyophilization removes water but is not a sterilization step. Sterile products are typically filtered and filled aseptically before freezing, and container closure integrity is maintained afterward.
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.