The short version of Sublimation fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2026-06-12. Anything still debated is marked as such rather than presented as settled.
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.
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, 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.
The process generally proceeds in three stages: freezing, primary drying, and secondary drying. During freezing, controlled cooling converts water into ice and may also crystallize or vitrify solutes. In primary drying, the pressure is lowered below the triple point, and heat is supplied so ice sublimes directly to vapor. Secondary drying removes water that remains bound to the solid matrix, yielding a low final water content. Product temperature must stay below the collapse or glass transition temperature to maintain structure. Cycle design therefore balances shelf temperature, chamber pressure, and time.
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.
| Property | Value | Notes |
|---|---|---|
| Common synonyms | Freeze-drying; lyophilisation; cryodesiccation | Regional spelling and historical terms. |
| Primary drying pressure | 0.05-0.5 mbar (5-50 Pa) | Kept below the triple point of water; product-specific. |
| Shelf temperature range | -40 to +40 °C | Freezing, primary, and secondary stages use different set points. |
| Cycle duration | 12-72 hours | Depends on fill volume, formulation, and equipment. |
| Condenser temperature | -50 to -80 °C | Must remain below the product's ice temperature. |
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.
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 is a dehydration process that removes water from a frozen material by sublimation under low pressure. The material is first frozen to convert liquid water into ice. Next, the pressure is reduced below the triple point of water so that ice changes directly into vapor without passing through a liquid phase. This step is called primary drying. The result is a porous solid or cake that retains the original shape of the frozen solution.
After primary drying, secondary drying removes water that remains bound to the material. This stage raises the shelf temperature while maintaining low pressure, which encourages desorption of unfrozen water. Residual moisture can be reduced to a low percentage, improving stability for many products. The process parameters, including freezing rate, shelf temperature, and chamber pressure, influence the final pore structure and reconstitution behavior. Control of these variables helps prevent collapse or meltback during drying.
Silicon is a crystalline solid with a blue-grey metallic lustre. Like boron, it is less dense (at 2.33 g/cm3) than aluminium, and is hard and brittle. It is a relatively unreactive element. According to Rochow, the massive crystalline form (especially if pure) is "remarkably inert to all acids, including hydrofluoric". Less pure silicon, and the powdered form, are variously susceptible to attack by strong or heated acids, as well as by steam and fluorine. Silicon dissolves in hot aqueous alkalis with the evolution of hydrogen, as do metals such as beryllium, aluminium, zinc, gallium or indium. It melts at 1414 °C. Silicon is a semiconductor with an electrical conductivity of 10−4 S•cm−1 and a band gap of about 1.11 eV. When it melts, silicon becomes a reasonable metal with an electrical conductivity of 1.0–1.3 × 104 S•cm−1, similar to that of liquid mercury. The chemistry of silicon is generally nonmetallic (covalent) in nature. It is not known to form a cation. Silicon can form alloys with metals such as iron and copper. It shows fewer tendencies to anionic behaviour than ordinary nonmetals. Its solution chemistry is characterised by the formation of oxyanions. The high strength of the silicon–oxygen bond dominates the chemical behaviour of silicon. Polymeric silicates, built up by tetrahedral SiO4 units sharing their oxygen atoms, are the most abundant and important compounds of silicon. The polymeric borates, comprising linked trigonal and tetrahedral BO3 or BO4 units, are built on similar structural principles.
Promoting absorption of dietary calcium from the gastrointestinal tract. Increasing renal tubular reabsorption of calcium, thus reducing the loss of calcium in the urine. Stimulating release of calcium from bone. For this it acts on the specific type of bone cells referred to as osteoblasts, causing them to release RANKL, which in turn activates osteoclasts. Calcitriol acts in concert with parathyroid hormone (PTH) in all three of these roles. For instance, PTH also indirectly stimulates osteoclasts. However, the main effect of PTH is to increase the rate at which the kidneys excrete inorganic phosphate (Pi), the counterion of Ca2+. The resulting decrease in serum phosphate causes hydroxyapatite (Ca5(PO4)3OH) to dissolve out of bone, thus increasing serum calcium. PTH also stimulates the production of calcitriol (see below). Many of the effects of calcitriol are mediated by its interaction with the calcitriol receptor, also called the vitamin D receptor or VDR. For instance, the unbound inactive form of the calcitriol receptor in intestinal epithelial cells resides in the cytoplasm. When calcitriol binds to the receptor, the ligand-receptor complex translocates to the cell nucleus, where it acts as a transcription factor promoting the expression of a gene encoding a calcium binding protein. The levels of the calcium binding protein increase enabling the cells to actively transport more calcium (Ca2+) from the intestine across the intestinal mucosa into the blood. Alternative, non-genomic pathways may be mediated through either PDIA3 or VDR.
== Excipient == Excipient has a significant impact on the final product performance, manufacturability, and stability. Therefore, the selection of excipients has to be carefully considered during topical cream formulation design.
Sources: en.wikipedia.org
Furthermore, possible recognition sequences for furin (a major physiological protease) cleavage sites have been found in both amino-terminal NC1 domain and carboxyl-terminal NC4 domain of each one of these collagens. The activity of this protease is vital to explain the origin of the two forms that collagen types XIII, XXIII and XXV can adopt.
Indium is a shiny silvery-white, highly ductile post-transition metal with a bright luster. It is so soft (Mohs hardness 1.2) that it can be cut with a knife or be bitten into by human teeth. Indium also leaves a visible line like a pencil when rubbed on paper. It is a member of group 13 on the periodic table and its properties are mostly intermediate between its vertical neighbors gallium and thallium. As with tin, a high-pitched cry is heard when indium is bent – a crackling sound due to crystal twinning. Like gallium, indium is able to wet glass and has a low melting point, 156.60 °C (313.88 °F); higher than its lighter homologue, gallium, but lower than its heavier homologue, thallium, and lower than tin.< The boiling point is 2072 °C (3762 °F), higher than that of thallium, but lower than gallium, conversely to the general trend of melting points, but similarly to the trends down the other post-transition metal groups because of the weakness of the metallic bonding with few electrons delocalized. The density of indium, 7.31 g/cm3, is also greater than gallium, but lower than thallium. Below the critical temperature, 3.41 K, indium becomes a superconductor. Indium crystallizes in the body-centered tetragonal crystal system in the space group I4/mmm (lattice parameters: a = 325 pm, c = 495 pm): this is a slightly distorted face-centered cubic structure, where each indium atom has four neighbours at 324 pm distance and eight neighbours slightly further (336 pm).
== Mechanism of action == Imipenem/cilastatin has the ability to kill a wide variety of bacteria. Imipenem is the active antibiotic agent and works by interfering with their ability to form cell walls, so the bacteria break up and die. Imipenem is rapidly degraded by the renal enzyme dehydropeptidase if administered alone (making it less effective); the metabolites can cause kidney damage. Imipenem is a broad-spectrum betalactam antibiotic used for severe bacterial infections caused by susceptible organisms. Because imipenem is rapidly inactivated by renal dehydropeptidase I, it is given in combination with cilastatin, a DHP-I inhibitor which increases half-life and tissue penetration of imipenem. Imipenem/cilastatin, like other carbapenems, binds to bacterial penicillin-binding proteins and interferes with bacterial cell wall integrity and synthesis. It has activity against many aerobic and anaerobic Gram-positive and Gram-negative organisms, including Staphylococcus aureus, Streptococcus pyogenes, S. agalactiae, S. viridans- group streptococci, Enterococcus faecalis, Pseudomonas aeruginosa, Escherichia coli, Proteus mirabilis, Bacteroides fragilis and Peptostreptococcus species. Imipenem/cilastatin was approved for use in the United States in 1985. Imipenem/cilastatin is indicated for the treatment of severe or complicated skin, tissue, joint, respiratory tract, intra-abdominal, urinary tract and urogenital infections, but not meningitis (as it does not pass through the blood brain barrier), endocarditis, and sepsis due to susceptible organisms.
Sources: en.wikipedia.org
Simple drying usually removes water by evaporation from a liquid or solid, often with heat. Lyophilization first freezes the material and then removes ice by sublimation under vacuum. This avoids prolonged exposure to liquid water and high temperatures.
Reduced pressure lowers the boiling point of water and allows ice to sublime at temperatures below freezing. It also helps remove water vapor from the product toward the condenser. The exact pressure is chosen to stay below the triple point of water.
No. Materials with low solids content or high volatile solvents may form weak or collapsed cakes. Some proteins and cells require stabilizers to survive freezing and drying stresses. Feasibility depends on formulation and process design.
Yes. Lyophilization and freeze-drying are synonyms for the same vacuum-assisted sublimation process. The term lyophilization is more common in pharmaceutical and laboratory settings, while freeze-drying is widely used in food and general contexts.