Porous cake 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 2025-11-04. Where a claim depends on a specific study, the study is described rather than over-claimed.
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 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.
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.
Lyophilization, or freeze-drying, removes water from a material by freezing it and then lowering pressure so ice changes directly to vapor. The process relies on sublimation, the phase transition from solid to gas without an intervening liquid state. It is used for heat-sensitive materials that would degrade in conventional drying. The three stages are freezing, primary drying, and secondary drying, each with distinct temperature and pressure requirements. In practice, cycle design balances these variables.
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.
| 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. |
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.
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 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.
Equipment for lyophilization includes a vacuum chamber, temperature-controlled shelves, a condenser, and a vacuum pump. A refrigeration system cools the shelves and condenser below the product's freezing point. Process monitoring often uses Pirani and capacitance manometers, thermocouples, and resistance sensors. Cycle development balances product quality with time and energy use. Some products are annealed during freezing to improve crystallization of bulking agents. Open questions remain about scaling cycles between laboratory, pilot, and production freeze-dryers.
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.
=== Bibliography === Jamaluddin, Ahmad Badawi (2007). PENGGUNAAN UBATAN TRADISIONAL DI PASAR TAMU DAN PASAR BESAR DAERAH TAWAU, SABAH: SATU TINJAUAN [USE OF TRADITIONAL MEDICINE IN WEEKLY MARKET AND MAIN MARKET IN TAWAU DISTRICT, SABAH: A REVIEW] (PDF). Conservation Biology Program School of Science and Technology (Thesis) (in Malay). pp. 1–27. Archived (PDF) from the original on 2 June 2025. Retrieved 2 June 2025 – via Universiti Malaysia Kelantan. Kustiariyah (2007). "TERIPANG SEBAGAI SUMBER PANGAN DAN BIOAKTIF" [SEA CUCUMBER AS A FOOD AND BIOACTIVE SOURCE]. Indonesian Journal of Aquatic Product Technology [Buletin Teknologi Hasil Perikanan] (in Indonesian). X (1): 1–8. Archived from the original on 1 June 2025. Damaiyanti, Dian Widya (2015). "Karakterisasi Esktrak Air Teripang Emas (Stichopus hermanii)" [Characterization Of Water Extract Gold Sea Cucumber (Stichopus hermanii)]. Denta (Jurnal Kedokteran Gigi) (in Indonesian). 9 (1): 1–8. ISSN 1907-5987. Archived from the original on 2 June 2025. Text is licensed by DENTA (Journal Kedokteran Gigi) under CC BY-NC-SA 4.0 Vaitilingon, Devarajen; Smith, Stuart; Watson, Guy; Miller, Tim; Alattas, Syed; Ong Hock, Keat; Zainoddin, Jamari; Zaidnuddin, Ilias; Azhar, Hamzah (2016). "Sea cucumber hatchery seed production in Malaysia: From research and development, to pilot-scale production of the sandfish Holothuria scabra" (PDF). SPC Beche-de-mer Information Bulletin (36): 67–75. Archived from the original (PDF) on 16 May 2021 – via Sustainable Aquaculture Research & Development (Mauritius).
In some cases, certain device geometries are preferred, for example a flow focusing junction was used to encapsulate bacteria in agarose microparticles. Multiple emulsions are of interest for pharmaceutical and cosmetic applications and are formed using two consecutive flow focusing junctions. More complicated particles can also be synthesized such as Janus particles, which have surfaces with two or more distinct physical properties. Some examples of the increasing application of gel particles include drug delivery, biomedical applications, and tissue engineering, and many of these applications require monodisperse particles where a microfluidics-based approach is preferred. Bulk emulsification methods are still relevant, though, since not all applications require uniform microparticles. The future of microfluidic synthesis of gels may lie in developing techniques to create bulk amounts of these uniform particles in order to make them more commercially/industrially available. Recent developments in droplet microfluidics have also allowed for in situ synthesis of hydrogel fibers containing aqueous droplets with controlled morphology. Hydrogel fibers provide an intriguing option for biocompatible material for drug delivery and bioprinting of materials that can mimic the behavior of an extracellular matrix. This microfluidic method differs from the traditional wet-spinning synthesis route through the use of aqueous droplets in an immiscible oil stream rather than the extrusion of a bulk solution of the same composition mixed off site.
William Nathaniel Phillips (born September 23, 1964) is an American entrepreneur and author. He wrote Body for Life: 12 Weeks to Mental and Physical Strength with Mike D'Orso. He is also the author of Eating for Life and the founder and former editor in chief of Muscle Media magazine and the former CEO of EAS, a performance nutritional supplement company. Other books that Phillips has authored are Anabolic Reference Guide, The Natural Supplement Review, and Transformation: The Mindset You Need. The Body You Want. The Life You Deserve. Phillips made a promotional movie called Body of Work which was filmed in Las Vegas, Nevada and chronicled the first EAS Challenge.
== Epidemiology == Sack–Barabas syndrome is rare and has an estimated prevalence of 1 in 100,000 to 200,000. The initial clinical manifestation of vascular problems in patients with SBS is early, about 25% have their first symptoms at age 20 and more than 80% of patients have had at least one complication by the age of 40. The median survival for one study of SBS patients was only 48 years.
=== Controversies on the nature and reality of fibromyalgia === In the past, fibromyalgia was a disputed diagnosis. Rheumatologist Frederick Wolfe, lead author of the 1990 paper that first defined the diagnostic guidelines for fibromyalgia, stated in 2008 that he believed it "clearly" was not a disease but instead a physical response to depression and stress. In 2013, Wolfe added that its causes "are controversial in a sense" and "there are many factors that produce these symptoms – some are psychological and some are physical and it does exist on a continuum." Some members of the medical community did not consider fibromyalgia a disease because of a lack of abnormalities on physical examination and the absence of objective diagnostic tests. In the past, some psychiatrists viewed fibromyalgia as a type of affective disorder, or a somatic symptom disorder. These controversies did not engage healthcare specialists alone; some patients objected to fibromyalgia being described in purely somatic terms. As of 2022, neurologists and pain specialists tended to view fibromyalgia as a real pathology. It was mostly seen as due to dysfunction of muscles and connective tissue as well as functional abnormalities in the central nervous system. Rheumatologists defined the syndrome in the context of "central sensitization" – heightened brain response to normal stimuli in the absence of disorders of the muscles, joints, or connective tissues.
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Schwartz–Jampel syndrome (SJS, also known as chondrodystrophic myotonia) is a rare genetic disease caused by a mutation in the perlecan gene (HSPG2) which causes osteochondrodysplasia associated with myotonia. Most people with Schwartz–Jampel syndrome have a nearly normal life expectancy.
The party was named the Centre Party due to the fact that in Parliament the Catholics sat between the Liberals on the left and the Conservatives on the right as opposed to the party adhering to centrism in the modern context. Also in other German states Catholic parties were formed, cooperating with the Prussian Centre Party in the Reichstag:
=== In popular culture === The movie A Civil Action, starring John Travolta, was based on the Grace groundwater contamination lawsuits in Woburn, Massachusetts. The PBS television show P.O.V., which highlights independent films, in August 2007 premiered the movie Libby, Montana which documents the thousands of people in Libby, Montana, that have been exposed to and are suffering the effects of asbestos exposure. The show also discusses the criminal indictments of many Grace executives for covering up asbestos related illnesses and deaths. PBS also aired Dust to Dust, a documentary produced by Michael Brown Productions, Inc. in 2002. Dust to Dust reports on the more than 200 people who have died from asbestos exposure in Libby, Montana. The film focuses on the plights of several of these individuals and the damage done over almost 30 years while the mine was operated by W. R. Grace. NPR aired a piece on All Things Considered discussing the criminal charges against W. R. Grace. A U.S. attorney general alleges that the company and managers of the mine in Libby, Montana, knew about the dangers of the asbestos they were dumping into the air for over 20 years. On February 19, 2008, the NPR-produced radio show Here and Now broadcast a story about the film Libby, Montana, which details the asbestos contamination in the town of that name. On April 22, 2009, the television and radio program Democracy Now! broadcast two segments on the trial of W. R. Grace and some of its employees related to the asbestos contamination in Libby, Montana.
==== Tumors ==== Testicular tumors such as Leydig cell tumors, Sertoli cell tumors (such as in Peutz–Jeghers syndrome) and hCG-secreting choriocarcinoma may result in rapid-onset gynecomastia by causing excess production of estrogen. Other tumors such as adrenal tumors, pituitary gland tumors (such as a prolactinoma), or lung cancer, can produce hormones that alter the male–female hormone balance and cause gynecomastia. Individuals with prostate cancer who are treated with androgen deprivation therapy may experience gynecomastia.
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At that time, the drug had not been discontinued and was considered a treatment for hereditary angioedema. In March 2009, Lundbeck purchased Ovation In 2010, Lundbeck withdrew stanozolol from the market in the US; as of 2014 no other company is marketing stanozolol as a pharmaceutical drug in the US but it can be obtained via a compounding pharmacy. Pfizer had marketed stanozolol as a veterinary drug; in 2013 Pfizer spun off its veterinary business to Zoetis and in 2014 Pfizer transferred the authorizations to market injectable and tablet forms of stanozolol as a veterinary drug to Zoetis. It is used in veterinary medicine as an adjunct in the management of wasting diseases, to stimulate the formation of red blood cells, arouse appetite, and promote weight gain, but the evidence for these uses is weak. It is used as a performance-enhancing drug in race horses. Its side effects include weight gain, water retention, and difficulty eliminating nitrogen-based waste products and it is toxic to the liver, especially in cats. Because it may promote the growth of tumors, it is contraindicated in dogs with enlarged prostates. Stanozolol and other AAS were commonly used to treat hereditary angioedema attacks, until several drugs were brought to market specifically for treatment of that disease, the first in 2009: Cinryze, Berinert, ecallantide (Kalbitor), icatibant (Firazyr) and Ruconest. Stanozolol is still used long-term to reduce the frequency of severity of attacks.
6 May At 00:35 the 2nd Battalion, 8th Cavalry Regiment and 2nd Battalion, 19th Artillery Regiment in a night defensive position at Firebase Carolyn (11.547°N 106.167°E / 11.547; 106.167) 7 miles (11 km) south of Katum was attacked. The contact continued until 06:00 when the PAVN withdrew leaving 101 dead and 29 captured and 47 individual and 23 crew-served weapons captured; U.S. losses were nine killed. A CH-47 carrying 83 persons crashed 3 miles (4.8 km) southwest of Phước Vĩnh Base Camp, killing 40 of those on board.
== Controversies == In May, 2014, it was announced that The Psychemedics Corporation would be providing hair testing services to three private Cleveland-area schools. Journalists quickly noted a severe conflict of interest, as James Kubacki, Principal of St. Edward's High School, is the brother of Raymond Kubacki, CEO of The Psychemedics Corporation. The Plain Dealer noted that this fact was not disclosed to parents, revealing that it "wasn't stated at the institution-wide meetings to discuss with students their soon-to-be-curtailed privacy." This is not the first time that The Psychemedics Corporation has been scrutinized for questionable business tactics, having previously hired the high ranking employees of their clients. "Dr. George Elder, a principal for decades, says he instituted drug testing for all students and faculty members at his school. Now he's Psychemedics vice president and pitchman."
== Uses == TCFH itself is a common reagent used in the preparation of uronium and guanidinium salts used for amide bond formation and peptide synthesis, such as HATU. Amide bond formation with TCFH can be performed in a wide range of organic solvents, most commonly acetonitrile, but also water and in the solid state. Reactions typically require an added Brønsted base, and a wide range can be employed including N,N-diisopropylethylamine (DIPEA). In reactions of carboxylic acids with TCFH and a weakly Lewis basic amine like DIPEA, formation of an acid chloride or anhydride as the active acylating agent occurs. Use of N-methylimidazole (NMI) as a base, with both Brønsted and Lewis basic properties, provides some unique advantages. Reactions of carboxylic acids with TCFH and a strongly Lewis basic amine like NMI lead to in situ formation of an N-acyl imidazolium ion (NAI) as the active acylating agent.
A κ-opioid receptor agonist, or simply KOR agonist or kappa agonist, is a drug which acts as an agonist of the κ-opioid receptor (KOR), the target of the endogenous dynorphin peptides such as dynorphin A and one of several types of opioid receptors. They can variably produce hallucinogenic effects, pro-depressive and dysphoric effects, sedation, analgesic effects, antipruritic (anti-itch) effects, and anti-addictive effects, among others. Due to their various effects, KOR agonists are used for a variety of medical uses and for other purposes. Salvinorin A is a highly potent and selective KOR agonist and hallucinogen found in Salvia divinorum (diviner's sage) which has been used as an entheogen by the Mazatec people of Mexico and as a recreational drug elsewhere. The psychoactive and other effects of salvinorin A have been evaluated in clinical studies. The non-selective opioid receptor antagonist naltrexone blocks the effects of salvinorin A. Synthetic analogues with greater potency and/or duration include salvinorin B methoxymethyl ether (2-MMSB) and salvinorin B ethoxymethyl ether (2-EMSB). The irreversible G protein-biased agonist RB-64 (22-thiocyanatosalvinorin A) has unknown psychoactivity. Nalorphine (N-allylnormorphine; Lethidrone; Nalline) was an early opioid antagonist used to reverse opioid overdose which acts as a dual μ-opioid receptor (MOR) agonist–antagonist and KOR agonist and was superseded by other drugs like naloxone due to producing dysphoria and hallucinogenic effects among other drawbacks.
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 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.