Sublimation comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Updated 2026-08-01. Numbers and descriptions here follow the published literature rather than marketing material.
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.
Stability of a lyophilized solid depends on water content, temperature, and the physical state of the formulation. Amorphous products may slowly absorb moisture and drop below their glass transition temperature, causing collapse or crystallization. Some proteins and peptides can aggregate even in a dry state, especially when exposed to heat or moisture. Accelerated stability studies at elevated temperature and humidity help estimate shelf life, but real-time data remain the basis for expiration dating.
After drying, a lyophilized product is usually sealed under vacuum or an inert gas to limit moisture and oxygen exposure. The container closure system matters because stoppers and seals can allow moisture ingress over time. Storage conditions are selected from stability studies that track potency, cake appearance, and reconstitution behavior. Many freeze-dried materials are kept at controlled room temperature, while some require refrigeration or protection from light.
Quality control for freeze-dried forms includes visual inspection, water content measurement, and reconstitution time. A satisfactory cake is typically uniform, porous, and intact, although minor shrinkage or cracking may be acceptable if specifications allow. Karl Fischer titration, thermal gravimetric analysis, and near-infrared spectroscopy are used to measure water content. Reconstitution is assessed by adding a specified diluent and recording the time and ease of dissolution. Microbiological and particulate tests are added when the product is sterile or intended for injection.
| Property | Value | Notes |
|---|---|---|
| Common synonym | Freeze-drying | Same dehydration operation |
| Typical vacuum | 10-100 Pa | Pressure during primary drying |
| Primary drying temperature | -40 to -10 °C | Below collapse temperature for many formulations |
| Cycle duration | 12-72 hours | Varies with load, container, and formulation |
| Key phase change | Sublimation | Solid ice to water vapor |
Formulation composition influences whether freeze-drying produces an intact cake or a collapsed mass. Excipients such as sugars and polymers can raise the collapse temperature and provide bulk during drying. The critical temperature for primary drying is often the collapse temperature or the glass transition temperature of the maximally concentrated phase. If the product temperature exceeds this threshold, the frozen matrix may soften and lose structure. Established practice therefore links shelf temperature and chamber pressure to the formulation's thermal properties.
The physics of freeze-drying couples heat transfer, mass transfer, and phase change. Heat supplied through the shelf must reach the sublimation front without melting the ice or degrading the product. Water vapor then travels through the already dried layer and leaves the chamber, where low pressure and cold traps keep it from returning. The dried layer acts as a resistance to vapor flow, so drying rate changes as the front recedes. Open questions remain about how pore structure and formulation heterogeneity affect drying uniformity at larger scales.
Lyophilization removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts liquid water into ice and concentrates dissolved solids. Primary drying then lowers chamber pressure so ice changes directly into vapor without passing through a liquid phase. Secondary drying raises the shelf temperature to remove bound water that remains after ice sublimation. The result is a dry, porous structure that can be reconstituted later.
Lyophilized products are typically hygroscopic and require protection from moisture during storage. Manufacturers seal them in glass vials, often under vacuum or an inert gas such as nitrogen. The container closure system, including the stopper and crimp seal, must prevent water vapor ingress. Storage temperature varies from controlled room temperature to refrigerated or frozen conditions, depending on the formulation. Humidity-controlled environments are essential because even brief exposure to ambient air can degrade the product.
Stability of a lyophilized product depends on its glass transition temperature, the temperature at which the amorphous cake transitions from a glassy to a rubbery state. Storage below this temperature minimizes molecular mobility and slows chemical degradation. If the storage temperature exceeds the glass transition temperature, the cake may collapse, shrink, or become sticky. Accelerated stability studies at elevated temperatures and humidity help predict shelf life, but they do not always reflect real-time behavior. Residual moisture content also plays a critical role in long-term stability.
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.
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.
==== M ==== Mackerel – is dried in Greece, Turkey and Cyprus; this product is called "çiroz" in Turkey. Maldives fish – cured tuna fish traditionally produced in Maldives. It is a staple of the Maldivian cuisine, as well as of the Sri Lankan cuisine, and in the past it was one of the main exports from Maldives to Sri Lanka. Meat floss – a Chinese dried and powdered meat product. Mojama – a Spanish delicacy consisting of filleted salt-cured tuna, made using the loins of the tuna.
==== Skin conditions ==== UV rays also treat certain skin conditions. Modern phototherapy has been used to successfully treat psoriasis, eczema, jaundice, vitiligo, atopic dermatitis, and localized scleroderma. In addition, UV radiation, in particular UVB radiation, has been shown to induce cell cycle arrest in keratinocytes, the most common type of skin cell. As such, sunlight therapy can be a candidate for treatment of conditions such as psoriasis and exfoliative cheilitis, conditions in which skin cells divide more rapidly than usual or necessary.
Extracts of the adrenal gland were first obtained by Polish physiologist Napoleon Cybulski in 1895. These extracts, which he called nadnerczyna ("adrenalin"), contained adrenaline and other catecholamines. American ophthalmologist William H. Bates discovered adrenaline's usage for eye surgeries prior to 20 April 1896. In 1897, John Jacob Abel (1857–1938), the father of modern pharmacology, found a natural substance produced by the adrenal glands that he named epinephrine. The first hormone to be identified, it remains a crucial, first-line treatment for cardiac arrests, severe allergic reactions, and other conditions. In 1901, Jokichi Takamine successfully isolated and purified the hormone from the adrenal glands of sheep and oxen. Adrenaline was first synthesized in the laboratory by Friedrich Stolz and Henry Drysdale Dakin, independently, in 1904. Although secretin is mentioned as the first hormone, adrenaline is the first hormone since the discovery of the activity of adrenal extract on blood pressure was observed in 1895 before that of secretin in 1902. In 1895, George Oliver (1841–1915), a general practitioner in North Yorkshire, and Edward Albert Schäfer (1850–1935), a physiologist at University College of London published a paper about the active component of adrenal gland extract causing the increase in blood pressure and heart rate was from the medulla, but not the cortex of the adrenal gland.
=== Core layer === The core of an aquasome can be made from either ceramic or polymeric materials. Examples of such polymers include acrylates and gelatin. However, because ceramic materials are more ordered due to their naturally occurring crystalline structure, they are more often preferred as the material type for the core. Some of the most common ceramic materials used in the formation of an aquasome core include tin oxide, calcium phosphate, and even diamond. Another characteristic that ceramic materials provide is enhanced binding of the carbohydrate layer due to the high surface energy present on the orderly surface. The binding affinity of the carbohydrate layer also reduces surface tension for its bond to the ceramic core. The first aquasomes fabricated with a nanocrystalline core using ceramic material are detailed in Kossovsky et al. in 1996. Calcium phosphate ceramic nanoparticles (brushite) were first prepared via the method of solution precipitation and sonication. Precipitation methods are the most common techniques employed when synthesizing the core of an aquasome as they offer control over the homogeneity and purity of the precipitated products, which are important design features in the core structure. Once the cores are prepared, they are separated by centrifugation and then washed to remove any salt byproducts from the solution precipitation process. Finally, the washed cores are passed through a Millipore filter to selectively isolate core particles of a certain size.
Likewise, in eukaryotes the maintenance of telomeres involves copying of an RNA template that is a constituent part of the telomerase ribonucleoprotein enzyme. Another cellular organelle, the vault, includes a ribonucleoprotein component, although the function of this organelle remains to be elucidated.
Sources: en.wikipedia.org
2-, alpha-, or α-amino acids have the generic formula H2NCHRCOOH in most cases, where R is an organic substituent known as a "side chain". Of the many hundreds of described amino acids, 22 are proteinogenic ("protein-building"). It is these 22 compounds that combine to give a vast array of peptides and proteins assembled by ribosomes. Non-proteinogenic amino acids may arise through nonribosomal peptide synthesis. Modified amino acids, by contrast, typically result from post-translational modification.
==== Radio and podcasts ==== "Sink or Swim. Act Two. I'm Not a Doctor, But I Play One at the Holiday Inn.". This American Life. Episode 321. 1 December 2006. — A former heroin addict realizes that he wants to help other addicts kick their habits. The problem is, he wants to do this using a hallucinogenic drug – ibogaine – that is completely illegal, and which requires medical expertise he doesn't have. In January 2025, former Texas Governor Rick Perry and W. Bryan Hubbard, appeared on The Joe Rogan Experience. The trio discussed advances in public policy towards ibogaine and eventual FDA clinical trials. Hubbard was the former chairman and executive director of the Kentucky Opioid Abatement Advisory Commission until he was asked to resign in December 2023. Since 2024, Hubbard has continued his campaign outside Kentucky and now works with the REID Foundation as the executive director of the American Ibogaine Initiative.
=== Raw donkey milk === After collection, donkey milk is cooled to refrigeration temperature. Raw milk can be kept for 3 days at refrigerator temperature starting from the day of milking. To prolong conservation, raw milk can be frozen for up to 2–3 months. In any case, it must be thawed in the refrigerator and pasteurized before use. EU regulations dictate that it must be pasteurized before being used, i.e. it must be heated up to about 90 °C for at least 2 minutes.
"I believe that all the power of the supreme being is not enough to liberate that despicable country (Peru): only Bolívar, supported by force, can do it." It is also known that San Martín wanted the disputed territory of Upper Peru, administered since 1810 by the Viceroyalty of Peru, to be handed over to the United Provinces of the Río de la Plata, which, although it would be somewhat predictable on his part (because it was an Argentine) in the exercise of a realpolitik, on the other hand it would be a sign of anti-Peruvianism on his part in the face of vague promises that he made to warlords, like Andrés de Santa Cruz, over the territory. Given this, he was allegedly accused of being dishonest with his ambiguous promises that he gave to Peruvian politicians who supported his government, since the Protectorate of San Martín de facto controlled the Atacama Party and was also claiming part of the territories of the current La Paz and Pando. That ended up generating a climate of mistrust, where the praises and praise of the Peruvians to the Liberator would have been apparent, in the midst of hostilities towards the Argentine caudillo. In the secret session of the Peruvian Congress, on September 27, 1822, suspicion and fear were expressed that San Martín tried to seize the provinces of Upper Peru, Arequipa and Cuzco.
Sources: en.wikipedia.org
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.
Sublimation requires the solvent to remain solid so vapor leaves without passing through a liquid phase. If the product melts, the porous structure can collapse and drying becomes uneven. Maintaining frozen conditions preserves the intended physical form.
No, freeze-drying is a dehydration method, not a sterilization step. It can reduce water activity and limit microbial growth during storage, but it does not reliably kill microbes or remove endotoxins. Sterility must come from separate validated processes.
Sealed vials or containers should be kept at the temperature specified by stability data, often controlled room temperature or 2–8 °C. Moisture and oxygen barriers are important because both can degrade sensitive materials. Opened containers may need immediate use or protection from ambient humidity.