Sublimation raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
Reviewed 2026-06-20. Anything still debated is marked as such rather than presented as settled.
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.
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.
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.
Reconstitution involves adding a suitable diluent, often sterile water or a buffer, to the dried cake. Gentle swirling or inversion helps dissolve the material without creating excessive foam. The time required for complete dissolution can range from seconds to several minutes and depends on the cake structure and the diluent. Improper reconstitution, such as vigorous shaking or using the wrong diluent, can cause protein aggregation or loss of activity. After reconstitution, the product may have a limited shelf life and should be used according to its labeling.
| 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. |
Freeze-drying is used for materials whose activity or structure depends on low temperature and low water content. Examples include certain biologics, diagnostic reagents, starter cultures, coffee, and porous inorganic precursors. The dried product forms a cake whose porosity aids rapid wetting and dissolution. Main drawbacks are high energy use, long cycle times, and sensitivity to formulation and equipment variation. Questions remain about how freezing rates and ice morphology affect batch uniformity, especially when moving from laboratory to production scale.
Lyophilization, also called freeze-drying, is a dehydration process in which a solvent, usually water, is frozen and then removed by sublimation under reduced pressure. The method preserves heat-sensitive materials that would degrade in conventional drying. Large-scale use grew during the mid-twentieth century for blood plasma and antibiotics, and it later expanded to vaccines, enzymes, foods, and advanced materials. The process produces a dry, porous solid that usually reconstitutes rapidly. It is distinct from simple evaporation because the solvent bypasses the liquid phase during primary removal.
Quality control for lyophilized materials examines appearance, reconstitution time, residual moisture, and mechanical integrity. An acceptable cake is usually uniform and porous, though appearance alone does not prove stability. Karl Fischer titration is a common method for water content, while differential scanning calorimetry can reveal glass transition events. Stability studies track potency, aggregation, and moisture over time under defined temperature and humidity conditions. Specifications are product-specific and may include sterility and endotoxin tests for sterile preparations.
Misconceptions about lyophilization include the idea that dried products are indefinitely stable or that vacuum sealing eliminates all degradation. Chemical reactions can continue in the solid state, and some proteins lose activity even at low moisture. Another misconception is that any freeze-dryer cycle can be scaled by time alone; heat and mass transfer differ with equipment and load. Open questions remain about predicting long-term stability from short accelerated studies, particularly for amorphous formulations. Real-time stability data remain the standard for shelf-life assignment.
==== Double-derivatization methods ==== Either the enantiomer of the substrate is derivatized with two enantiomers of the CDA or both enantiomers of the substrate are derivatized with one enantiomer of the CDA. Two diastereomers form in both cases and the chemical shifts of their nuclei are evaluated to assign the configuration of the substrate.
=== Clinical applications === Thymosin β4 has been tested in multicenter trials sponsored jointly by RegeneRx Biopharmaceuticals Inc (Rockville, MD, USA) and Sigma Tau (Pomezia, Italy) in the United States and Europe in patients with bed sores, ulcers caused by venostasis, and Epidermolysis bullosa simplex and was found to accelerate bed sore and stasis ulcer repair by one month. It has also been tested in patients with chronic neurotrophic corneal epithelial defects and found to promote repair. Thymosin β15 : Levels of human thymosin β15 in urine have shown promise as a diagnostic marker for prostate cancer which is sensitive to potential aggressiveness of the tumour
Many psychoactive drugs can be or have been specifically designed for sublingual administration, including barbiturates, benzodiazepines, opioid analgesics with poor gastrointestinal bioavailability, LSD blotters, coca leaves, some hallucinogens. This route of administration is activated when chewing some forms of smokeless tobacco (e.g. dipping tobacco, snus). intrarectal ("plugging"): administering into the rectum, most water-soluble drugs can be used this way. smoking (see also the section below): tobacco, cannabis, opium, crystal meth, phencyclidine, crack cocaine, and heroin (diamorphine as freebase) known as chasing the dragon. transdermal patches with prescription drugs: e.g. methylphenidate (Daytrana) and fentanyl. Many drugs are taken through various routes. Intravenous route is the most efficient, but also one of the most dangerous. Nasal, rectal, inhalation and smoking are safer. The oral route is one of the safest and most comfortable, but for some drugs has poorer bioavailability.
==== EPS in building construction ==== Sheets of EPS are commonly packaged as rigid panels (common in Europe is a size of 100 cm x 50 cm, usually depending on an intended type of connection and glue techniques, it is, in fact, 99.5 cm x 49.5 cm or 98 cm x 48 cm; less common is 120 x 60 cm; size 4 by 8 ft (1.2 by 2.4 m) or 2 by 8 ft (0.61 by 2.44 m) in the United States). Common thicknesses are from 10 mm to 500 mm. Many customizations, additives, and thin additional external layers on one or both sides are often added to help with various properties. An example of this is lamination with cement board to form a structural insulated panel. Thermal conductivity is measured according to EN 12667. Typical values range from 0.032 to 0.038 W/(m⋅K) depending on the density of the EPS board. The value of 0.038 W/(m⋅K) was obtained at 15 kg/m3 while the value of 0.032 W/(m⋅K) was obtained at 40 kg/m3 according to the datasheet of K-710 from StyroChem Finland. Adding fillers (graphites, aluminum, or carbons) has allowed the thermal conductivity of EPS to reach around 0.030–0.034 W/(m⋅K) (as low as 0.029 W/(m⋅K)) and as such has a grey/black color which distinguishes it from standard EPS. Several EPS producers have produced a variety of these increased thermal resistance EPS usage for this product in the UK and EU. Water vapor diffusion resistance (μ) of EPS is around 30–70. ICC-ES (International Code Council Evaluation Service) requires EPS boards used in building construction meet ASTM C578 requirements.
Sources: en.wikipedia.org
Duterte campaigned for decentralization and a shift to a federal government during the 2016 presidential election. In an October 2014 forum organized by Federal Movement for a Better Philippines in Cebu City prior to joining the presidential race, the then-mayor of Davao City called for the creation of two federal states for Moro people as a solution to the problems besetting Mindanao. Mayor Duterte said that Nur Misuari and his Moro National Liberation Front do not see eye-to-eye with the Moro Islamic Liberation Front which the administration of President Benigno Aquino III had inked a peace deal with. He also said that the "template of the Bangsamoro Basic Law is federal", but what is granted to the Bangsamoro should also be granted to other Moro groups and other regions in the country. In a dialogue with the Makati Business Club prior to the elections, Duterte said he is open to "toning down the Constitution" to accommodate more foreign investors to the Philippines. He also said he is open to up to 70 percent foreign ownership of businesses in the country and foreign lease of lands up to 60 years, but will "leave it to Congress to decide".
In May 2023, Peña announced the intention to move the Paraguayan embassy in Israel from Tel Aviv to Jerusalem. That measure had previously been taken by Horacio Cartes in 2018, but reversed by Mario Abdo Benítez later that same year, causing Israel to close its embassy in Asunción. According to Paraguayan foreign minister Rubén Ramírez Lezcano, the Israeli embassy in Paraguay was expected to reopen in July 2024. After the outbreak of the war between Israel and Gaza in October 2023, Peña's government adopted a strongly pro-Israel stance, with Paraguay abstaining or voting against several United Nations resolutions calling for a cessation of hostilities between Israel and Hamas, including a vote recognizing Palestine as a legitimate state, in which Paraguay abstained. Likewise, Paraguay opposed the South African case before the International Court of Justice against Israel, in which the former accused the latter of committing genocide in the Gaza Strip, and also opposed the intention of Karim Khan, chief prosecutor of the International Criminal Court, to issue international arrest warrants against Israeli prime minister Benjamin Netanyahu and his defense minister Yoav Gallant, calling it "incorrect". In public statements, Peña has argued that support for Israel goes beyond his personal view and represents, in his words, "a message from the entire Paraguayan nation", appealing to a historical and political affinity between the two countries.
Pessary – This is a removable device inserted into the vagina to support the anterior vaginal wall. Pessaries come in many different shapes and sizes. Vaginal pessaries can immediately relieve prolapse and prolapse-related symptoms. There are sometimes complications with the use of a pessary. Pelvic floor muscle therapy – Pelvic floor exercises to strengthen vaginal support can be of benefit. Specialized physical therapy can be prescribed to help strengthen the pelvic floor muscles. Dietary changes – Ingesting high fiber foods will aid in promoting bowel movements. Estrogen – intravaginal administration helps to prevent pelvic muscle atrophy
==== Creatine ==== The amino acid creatine, commonly used as a supplement to improve the performance of bodybuilders, has been studied for its potential antidepressant properties. A review found that creatine "has the potential to improve these disruptions [of brain metabolism] in some patients, and early clinical trials indicate that it may have efficacy as an antidepressant agent." Studies on mice have found that the antidepressant effects of creatine can be blocked by dopamine receptor antagonists such as haloperidol, suggesting that the drug acts on dopamine pathways.
Three enzymes present in different organisms and tissues are known to catalyse the oxidation of the pyrrole ring in tryptophan, giving the N-formyl deriative which is subsequently hydrolysed to kynurenine. These are tryptophan dioxygenase, indoleamine 2,3-dioxygenase and indoleamine 2,3-dioxygenase 2.
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.
Lyophilized products should be stored in airtight containers, protected from moisture and light, at the temperature specified by the manufacturer. Many require refrigeration at 2–8 °C, while some need frozen storage. Always check the product label for specific conditions.