freeze-drying 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.
Last reviewed on 2026-08-01. Where a claim depends on a specific study, the study is described rather than over-claimed.
Freezing determines ice crystal structure and pore size, which affect drying speed and product uniformity. Rapid freezing creates small crystals, while slow freezing creates larger crystals and often faster sublimation. During primary drying, chamber pressure is held below the vapor pressure of ice, and shelf temperature supplies heat for sublimation. The ice front recedes, leaving a porous matrix. Thermal limits such as collapse and eutectic temperatures set safe boundaries for formulation. These limits vary with solute composition and concentration.
Secondary drying removes bound water that remains after ice sublimation. Shelf temperature is raised gradually while pressure remains low, reducing water content to a target range. Over-drying can cause brittleness or electrostatic issues, while under-drying affects stability. The endpoint is often judged by pressure rise tests, temperature measurements, or water content analysis. Scale-up depends on matching heat and mass transfer across equipment sizes. Small changes in shelf temperature or pressure can alter cycle length substantially.
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 |
|---|---|---|
| Process name | Lyophilization or freeze-drying | Both terms appear in technical standards and literature. |
| Phase transition | Sublimation | Solid ice becomes vapor without a liquid step. |
| Typical chamber pressure | 0.05-0.5 mbar | Range depends on product temperature and equipment. |
| Typical product temperature | -40 °C to -10 °C | Measured during primary drying; formulation sets limits. |
| Water content after drying | 0.5-3% w/w | Target varies by material and stability needs. |
Freezing is the first stage and sets the ice structure that later becomes the pore network. The formulation is cooled below its freezing point, often with a controlled ramp, and solutes concentrate as ice forms. Primary drying then lowers chamber pressure and supplies heat to sublime the ice. The product temperature must stay below its collapse or eutectic temperature to prevent structural loss. Secondary drying raises the temperature modestly to remove bound water and achieve a low residual moisture.
A freeze-dryer consists of a vacuum chamber, temperature-controlled shelves, a condenser, and a vacuum pump. Vials, ampoules, or bulk trays hold the product during the cycle. The condenser traps water vapor as ice at a temperature lower than the product. Cycle development balances shelf temperature, chamber pressure, and time. Scale-up can be difficult because heat and mass transfer change with equipment size, so process analytical tools and conservative validation are often used.
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.
Trypsinogen () is the precursor form (or zymogen) of trypsin, a digestive enzyme. It is produced by the pancreas and found in pancreatic juice, along with amylase, lipase, and chymotrypsinogen. It is cleaved to its active form, trypsin, by enteropeptidase, which is found in the intestinal mucosa. Once activated, the trypsin can cleave more trypsinogen into trypsin, a process called autoactivation. Trypsin cleaves the peptide bond on the carboxyl side of basic amino acids such as arginine and lysine.
Starfish have been used in reproductive and developmental studies. Female starfish produce large numbers of oocytes that are easily isolated; these can be stored in a pre-meiosis phase and stimulated to complete division by the use of 1-methyladenine. Starfish oocytes are well suited for this research as they are easy to handle, can be maintained in sea water at room temperature, are transparent, and develop quickly. Asterina pectinifera, used as a model organism for this purpose, is resilient and easy to breed and maintain in the laboratory. Another area of research is the ability of starfish to regenerate lost body parts. The stem cells of adult humans are incapable of much differentiation and understanding the regrowth, repair and cloning processes in starfish may have implications for human medicine. Starfish have an unusual ability to displace foreign objects from their bodies, which makes them difficult to tag for research tracking purposes.
=== Whistleblower retaliation lawsuit === In 2013, Bio-Rad's general counsel of 25 years, Sanford Wadler, followed internal whistleblowing procedures by reporting suspected bribery to Bio-Rad's audit committee, believing Bio-Rad had falsified books and records. The company fired him for making this report, which the courts found to amount to California common law wrongful discharge in violation of public policy. In 2017, a federal jury awarded Wadler with a $10.9 million settlement. This was appealed by Bio-Rad, and in 2019 the US appeals court reduced this to $7.96 million, plus $3.5 million in attorneys' fees and costs.
=== Tumor detection === In cancer research, colloidal gold can be used to target tumors and provide detection using SERS (surface enhanced Raman spectroscopy) in vivo. These gold nanoparticles are surrounded with Raman reporters, which provide light emission that is over 200 times brighter than quantum dots. It was found that the Raman reporters were stabilized when the nanoparticles were encapsulated with a thiol-modified polyethylene glycol coat. This allows for compatibility and circulation in vivo. To specifically target tumor cells, the polyethylenegylated gold particles are conjugated with an antibody (or an antibody fragment such as scFv), against, e.g. epidermal growth factor receptor, which is sometimes overexpressed in cells of certain cancer types. Using SERS, these pegylated gold nanoparticles can then detect the location of the tumor. Gold nanoparticles accumulate in tumors, due to the leakiness of tumor vasculature, and can be used as contrast agents for enhanced imaging in a time-resolved optical tomography system using short-pulse lasers for skin cancer detection in mouse model. It is found that intravenously administered spherical gold nanoparticles broadened the temporal profile of reflected optical signals and enhanced the contrast between surrounding normal tissue and tumors.
== War period, 1938–1945 == When the committee was outlawed in September 1937, six of its members were deported, its president Amin al-Husayni managed to escape arrest and went into exile in Beirut. Jamal al-Husayni escaped to Syria. Three other members were deported to the Seychelles, and other members moved into voluntary exile in neighbouring countries. Al-Hadi, who was out of the country at the time, was not allowed to return. Membership of the outlawed committee had dwindled to Jamal al-Husayni (acting chairperson), Husayn al-Khalidi (secretary), Ahmed Hilmi Pasha and Emil Ghuri. For all practical purposes, the committee ceased to exist, however, this brought little change in the structure of Arab political life and the Palestinian revolt continued. With the indications of a new European war on the horizon, and in an endeavor to resolve the inter-communal issues in Palestine, the British government proposed in late 1938 a conference in London of the two Palestinian communities. Some Arab leaders welcomed the proposed London Conference but indicated that the British would need to deal with the disbanded Arab Higher Committee and with Amin al-Husayni. On 23 November 1938, the Colonial Secretary, Malcolm MacDonald, repeated his refusal to allow Amin al-Husayni to be a delegate, but was willing to allow the five Palestinian leaders held in the Seychelles to take part in the conference.
Sources: en.wikipedia.org
==== Fatty acids ==== There has been a growing interest in the role of long-chain omega-3 polyunsaturated fatty acids to reduce inflammation and alleviate the symptoms of RA. Metabolism of omega-3 polyunsaturated fatty acids produces docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), which inhibit pro-inflammatory eicosanoids and cytokines (TNF-a, IL-1b, and IL-6), decreasing both lymphocyte proliferation and reactive oxygen species. These studies showed evidence for significant clinical improvements on RA in inflammatory status and articular index. Gamma-linolenic acid, an omega-6 fatty acid, may reduce pain, tender joint count, and stiffness, and is generally safe. For omega-3 polyunsaturated fatty acids (found in fish oil, flax oil and hemp oil), a meta-analysis reported a favorable effect on pain, although confidence in the effect was considered moderate. The same review reported less inflammation but no difference in joint function. A review examined the effect of marine oil omega-3 fatty acids on pro-inflammatory eicosanoid concentrations; leukotriene4 (LTB4) was lowered in people with rheumatoid arthritis but not in those with non-autoimmune chronic diseases. Fish consumption has no association with RA. A fourth review limited inclusion to trials in which people eat ≥2.7 g/day for more than three months. The use of pain relief medication was decreased, but improvements in tender or swollen joints, morning stiffness, and physical function were unchanged.
=== Temperature === Conversion of both CO and CO2 to CH4 starts at a catalyst temperature below 300°C, but the conversion is incomplete and peak tailing is evident. At around 340°C, conversion is complete, as indicated by area measurements, but some tailing limits the peak height. At 360-380°C, tailing is eliminated and there is little change in peak height up to 400°C. Operating temperatures for various methanizers range from 350-400°C. Although carbonization of CO has been reported at temperatures above 350°, it is rather a rare phenomenon.
== Classification of fuzzy complexes == Structural ambiguity in protein complexes covers a wide spectrum. In a polymorphic complex, the protein adopts two or more different conformations upon binding to the same partner, and these conformations can be resolved. Clamp, flanking and random complexes are dynamic, where ambiguous conformations interchange with each other and cannot be resolved. Interactions in fuzzy complexes are usually mediated by short motifs. Flanking regions are tolerant to sequence changes as long as the amino acid composition is maintained, for example in case of linker histone C-terminal domains and H4 histone N-terminal domains.
A crystal structure of the serotonin 5-HT2B receptor bound to LSD reveals an extracellular loop that forms a "lid" over the diethylamide end of the binding cavity and "traps" LSD in the binding pocket, which explains the slow rate of LSD unbinding from serotonin receptors. The related lysergamide lysergic acid amide (LSA) that lacks the diethylamide moiety is far less potent in comparison. Moreover, a specific residue in the binding pocket is partially responsible for the prolonged action of LSD, and this residue is found in the human protein but not in the receptors of rodents. LSD is an extraordinarily potent psychoactive drug and is among the most potent psychedelics known in humans. The very high potency of LSD in producing psychedelic-like effects is also the case in animals, including rodents and monkeys. It is unclear why LSD is so potent. The affinity and activational potency of LSD at the human serotonin 5-HT2A receptor in vitro is unremarkable compared to other psychedelics such as DOI and DOB. There is no evidence for its greater potency being related to pharmacokinetics or metabolism. It appears that the N,N-diethylamide moiety of LSD fits into a sterically constrained region of the serotonin 5-HT2A receptor that specifically accommodates this moiety. LSD, like other psychedelics, has been found to increase the expression of genes related to synaptic plasticity and hence to have psychoplastogenic effects. This appears to be mediated by serotonin 5-HT2A receptor agonism.
Sources: en.wikipedia.org
Conventional drying uses heat to evaporate liquid water, often at temperatures that can degrade sensitive materials. Lyophilization freezes the material first and then removes water by sublimation under vacuum. This avoids prolonged exposure to liquid water and high heat.
Lowering pressure reduces the boiling point of water and allows ice to sublimate at temperatures below freezing. Vacuum also limits convective heat transfer, so heat is usually supplied by shelves or radiation. The pressure must stay below the vapor pressure of ice at the product temperature.
The cycle typically includes freezing, primary drying, and secondary drying. Freezing solidifies water and sets the pore structure; primary drying removes bulk ice; secondary drying removes bound water. Some cycles add annealing or pre-freezing steps.
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.