Primary drying raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
Reviewed 2025-09-03. Anything still debated is marked as such rather than presented as settled.
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.
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, 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.
| Property | Value | Notes |
|---|---|---|
| Common synonyms | Freeze-drying, lyophilisation | Lyophilisation is the British spelling; the process is not simple evaporation. |
| Primary drying pressure | 0.05–0.3 mbar | Pressure must remain below the vapor pressure of ice at the product temperature. |
| Sublimation temperature | Below 0 °C | Ice changes directly to vapor while the product remains frozen. |
| Typical shelf temperature | −40 to −10 °C | Exact setting depends on formulation critical temperature and equipment. |
| Cycle duration | 12–72 hours | Time varies with fill volume, formulation, and dryer performance. |
Lyophilization is a dehydration technique in which a product is frozen and the solvent is removed under reduced pressure. The low pressure allows ice to sublimate directly into vapor without passing through a bulk liquid phase. This differs from conventional drying, where heat drives evaporation and can damage heat-sensitive structures. The process is used for biological materials, pharmaceutical formulations, and some foods. Its main advantage is preservation of porous structure and rapid reconstitution.
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 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.
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.
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.
Produced by Charles Konowal, directed by Stephen Low, made by Uden Associates and National Film Board of Canada 27 August Little by Little, about Eric Drexler and nanotechnology. Produced by David Kennard, directed by Karl Sabbagh, made by InCA 3 September Woomera, a rocket base for over 30 years; set up by Sir John Events; rockets arrived in 1949, and the Australian Security Intelligence Organisation (ASIO) needed to be set up as sensitive information had leaked to the Soviets; the Weapons Research Establishment was set up at Edinburgh, South Australia, which is now largely RAAF Base Edinburgh; the GAF Jindivik target drone was developed in 1952; up to 6 or 7 guided missiles would be launched per day; the Malkara and Stanley Schatzel (1924-2015), technical director from 1970 to 1989 for Hawker Siddeley Dynamics; the drop of the Blue Danube by No.
=== Monitoring drug-related alterations in metabolic pathways === The second major application of pharmacometabolomics is the analysis of a patient's metabolic profile following the administration of a specific therapy. This process is often secondary to a pre-treatment metabolic analysis, allowing for the comparison of pre- and post-treatment metabolite concentrations. This allows for the identification of the metabolic processes and pathways that are being altered by the treatment either intentionally as a designated target of the compound, or unintentionally as a side effect. Furthermore, the concentration and variety of metabolites produced from the compound itself can also be identified, providing information on the rate of metabolism and potentially leading to development of a related compound with increased efficacy or decreased side effects. An example of this approach was used to investigate the effect of several antipsychotic drugs on lipid metabolism in patients treated for schizophrenia. It was hypothesized that these antipsychotic drugs may be altering lipid metabolism in treated patients with schizophrenia, contributing to the weight gain and hypertriglyceridemia. The study monitored lipid metabolites in patients both before and after treatment with antipsychotics. The compiled pre- and post-treatment profiles were then compared to examine the effect of these compounds on lipid metabolism.
is the recovery rate constant in the unit fraction of a person recovered per day per infected person, when time is in unit day. This model was for the first time proposed by William Ogilvy Kermack and Anderson Gray McKendrick as a special case of what we now call Kermack–McKendrick theory, and followed work McKendrick had done with Ronald Ross. This system is non-linear, however it is possible to derive its analytic solution in implicit form. Firstly note that from:
Sources: en.wikipedia.org
== Education == Bewley completed a Ph.D. from University of California, San Diego in 1995. Her dissertation was titled New antifungal and cytotoxic cyclic peptides and studies of the bacterial symbionts of lithistid sponges. Bewley's doctoral advisor was D. John Faulkner.
=== Chemical and electrochemical techniques === Conversion coating Autophoretic, the registered trade name of a proprietary series of auto-depositing coatings specifically for ferrous metal substrates Anodising Chromate conversion coating Plasma electrolytic oxidation Phosphate (coating) Ion beam mixing Pickled and oiled, a type of plate steel coating Plating Electroless plating nickel plating coating using a different material to preserve mechanical properties Electroplating
Molecular clocks have caused controversy due to the dates they derive for events such as explosive radiations seen after extinction events like the Cambrian explosion and the radiations of mammals and birds. Two-fold differences exist in dates derived from molecular clocks and the fossil record. While some paleontologists argue that molecular clocks are systemically inaccurate, others attribute the discrepancies to lack of robust fossil data and bias in sampling. While not without constancy and discrepancies with the fossil record, the data from molecular clocks have shown how evolution is dominated by the mechanisms of a neutral model and is less influenced by the action of natural selection.
Sources: en.wikipedia.org
In 2009, the Justice Department reported that Mexican drug cartels distribute drugs in nearly 200 cities across the United States, including Los Angeles, Chicago, and Atlanta. Gang-related activity and violence has increased along the U.S. Southwest border region, as U.S.-based gangs act as enforcers for Mexican drug cartels. In October 2025, Mexican cartels are issuing bounties up to $50,000 for a hit on ICE and CBP agents according to the Department of Homeland Security.
== Pharmacological modulation == Neutral endopeptidase (NEP) also known as neprilysin is the enzyme that metabolizes natriuretic peptides. Several inhibitors of NEP are currently being developed to treat disorders ranging from hypertension to heart failure. Most of them are dual inhibitors (NEP and ACE). In 2014, PARADIGM-HF study was published in NEJM. This study considered as a landmark study in treatment of heart failure. The study was double blinded; compared LCZ696 versus enalapril in patients with heart failure. The study showed lower all cause mortality, cardiovascular mortality and hospitalization in LCZ696 arm. Omapatrilat (dual inhibitor of NEP and angiotensin-converting enzyme) developed by BMS did not receive FDA approval due to angioedema safety concerns. Other dual inhibitors of NEP with ACE/angiotensin receptor are (in 2003) being developed by pharmaceutical companies.
Artocarpus is a genus of approximately 60 trees and shrubs of Southeast Asian and Pacific origin, belonging to the mulberry family, Moraceae. Most species of Artocarpus are restricted to Southeast Asia; a few cultivated species are more widely distributed, especially A. altilis (breadfruit) and A. heterophyllus (jackfruit), which are cultivated throughout the tropics.
=== Hierarchical structure === While the secondary structures are determined by energy state and hydrogen bonds formed between amino acids, hierarchical structures are determined by the hydrophobicity of the peptide. Exon 1 encoded peptide is mainly hydrophilic, and is more extended when immersed in water. In contrast, exon 3 encoded peptide contains both hydrophobic and hydrophilic blocks, suggesting the formation of micelles, where the hydrophobic block will cluster on the inside with the hydrophilic portion surrounding it. Thus, a single complete resilin protein, when immersed in water, takes on the structure in which exon 1 encoded segment extends out from the micelle exon 3 encoded peptide forms. Once resilin is transferred to the outside of the cell, their exon 2 encoded peptides, the chitin binding segments, bind to chitin. Meanwhile, di- or tri-tyrosine crosslinking is formed by oxidative coupling, mediated by peroxidase, between tyrosine residuals. Like other elastomeric proteins, the degree of cross linking in resilin is low, which ensures the low stiffness and high resilience. Cross linked peptides encoded by exon 1 have a resilience greater than 93%, while that encoded by exon 3 has a resilience of 86%. In addition, natural resilin has a resilience of 92%, similar to that of exon 1, suggesting again that exon 1 may play a more important role in the elastic property of resilin.
Sources: en.wikipedia.org
The main change is sublimation, in which ice becomes water vapor without melting into liquid water. This occurs when the chamber pressure is held below the vapor pressure of ice while mild heat is supplied. The result is a dry, porous solid that retains much of its original shape.
Freezing determines ice crystal size, solute distribution, and the pore network left after drying. A slow or fast freezing rate can produce different cake structures and affect reconstitution. It also sets whether the formulation follows an amorphous or crystalline drying path.
It removes most free water during primary drying and part of the bound water during secondary drying. A small residual moisture content often remains and is specified for each product. Complete removal is generally neither practical nor desirable for stability.
Conventional drying uses heat to evaporate water from a material, while lyophilization freezes the material and removes water by sublimation under vacuum. This avoids the liquid phase and reduces thermal damage to sensitive substances. The result is a porous cake that reconstitutes quickly.