sublimation is one of those subjects where the details matter more than the headlines. This page pulls together the background, the mechanisms, and the practical points readers ask about most.
Last reviewed on 2026-08-01. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
A formulation often contains excipients that protect the active ingredient during freezing and drying. Bulking agents provide structure, while lyoprotectants stabilize sensitive molecules. The freezing step can produce ice crystals whose size and distribution affect the drying rate, and cycle design includes freezing, annealing, and drying phases. If the product temperature rises above a critical value, the cake may collapse or lose its porous structure. Successful lyophilization therefore depends on the interaction between formulation, equipment, and cycle design.
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.
| Property | Value | Notes |
|---|---|---|
| Common name | Freeze-drying | Process removes water by sublimation under vacuum. |
| Typical primary drying shelf temperature | -40 C to -10 C | Set below the formulation's collapse temperature. |
| Typical chamber pressure | 0.05-0.3 mbar | Low pressure allows ice to sublime below its triple point. |
| Water content after drying | 0.5-3% by weight | Higher values may reduce storage stability for some materials. |
| Key thermal parameter | Collapse temperature | Measured by freeze-drying microscopy or differential scanning calorimetry. |
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, 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.
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.
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.
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, 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.
After meeting threshold concentration, transmembrane histidine kinases are activated via binding of corresponding peptides. Regulator proteins in turn are phosphorylated by the activated kinases, thereby inducing competency gene expression. Such genes produce proteins responsible for inducing DNA transformation.
Aberrant basal cell carcinoma Acanthoma fissuratum (granuloma fissuratum, spectacle frame acanthoma) Acrospiroma (clear cell hidradenoma, dermal duct tumor, hidroacanthoma simplex, nodular hidradenoma, poroma) Actinic keratosis (senile keratosis, solar keratosis) Adenoid squamous cell carcinoma (pseudoglandular squamous cell carcinoma) Aggressive digital papillary adenocarcinoma (digital papillary adenocarcinoma, papillary adenoma) Apocrine gland carcinoma Apocrine nevus Arsenical keratosis Atrophic actinic keratosis Balanitis plasmacellularis (balanoposthitis chronica circumscripta plasmacellularis, balanitis circumscripta plasmacellularis, plasma cell balanitis, plasma cell vulvitis, vulvitis circumscripta plasmacellularis, Zoon's balanitis, Zoon's erythroplasia, Zoon's vulvitis) Basal cell carcinoma Basaloid follicular hamartoma Basaloid squamous cell carcinoma Birt–Hogg–Dubé syndrome Bowen's disease (squamous cell carcinoma in situ) Brooke–Fordyce syndrome Ceruminoma Cicatricial basal cell carcinoma (morpheaform basal cell carcinoma, morphoeic basal cell carcinoma) Ciliated cyst of the vulva (cutaneous Müllerian cyst, paramesonephric mucinous cyst of the vulva) Clear cell acanthoma (acanthome cellules claires of Degos and Civatte, Degos acanthoma, pale cell acanthoma) Clear cell squamous cell carcinoma (clear cell carcinoma of the skin) Chronic scar keratosis (chronic cicatrix keratosis) Clonal seborrheic keratosis Common seborrheic keratosis (basal cell papilloma, solid seborrheic keratosis) Cowden syndrome (Cowden's disease, multiple hamartoma syndrome) Cutaneous ciliated cyst Cutaneous columnar cyst Cutaneous horn (Cornu cutaneum) Cystic basal cell carcinoma Dermal eccrine cylindroma (cylindroma) Dermatosis papulosa nigra Desmoplastic trichoepithelioma Dilated pore (dilated pore of Winer) Eccrine carcinoma (syringoid carcinoma) Eccrine nevus Epidermal cyst (epidermal inclusion cyst, epidermoid cyst, infundibular cyst, keratin cyst) Epidermal nevus syndrome (Feuerstein and Mims syndrome, Solomon's syndrome) Epidermolytic acanthoma Epithelioma cuniculatum (Ackerman tumor, carcinoma cuniculatum) Eruptive vellus hair cyst Erythroplasia of Queyrat Extramammary Paget's disease Fibroepithelioma Fibroepithelioma of Pinkus Fibrofolliculoma Follicular hybrid cyst (Hybrid cyst) Folliculosebaceous-apocrine hamartoma (follicular-apocrine hamartoma) Folliculosebaceous cystic hamartoma Generalized eruptive keratoacanthoma (generalized eruptive keratoacanthoma of Grzybowski) Giant solitary trichoepithelioma Hidradenoma Hidradenocarcinoma Hidrocystoma (cystadenoma, Moll's gland cyst, sudoriferous cyst) Hydrocarbon keratosis (pitch keratosis, tar keratosis, tar wart) Hyperkeratosis lenticularis perstans (Flegel's disease) Hyperkeratosis of the nipple and areola Hyperkeratotic actinic keratosis Ichthyosis hystrix (ichthyosis hystrix gravior type Lambert, porcupine man, systematized verrucous nevus) Ichthyosis hystrix of Curth–Macklin Infiltrative basal cell carcinoma Inflammatory linear verrucous epidermal nevus Inverted follicular keratosis Irritated seborrheic keratosis (basosquamous cell acanthoma, inflamed seborrheic keratosis) Isthmicoma (infundibuloma, tumor of the follicular infundibulum) Juvenile myelomonocytic leukemia Keratin implantation cyst Keratoacanthoma Keratoacanthoma centrifugum marginatum Large cell acanthoma Lichenoid actinic keratosis Lichenoid keratosis (benign lichenoid keratosis, lichen planus-like keratosis, solitary lichen planus, solitary lichenoid keratosis) Linear verrucous epidermal nevus (linear epidermal nevus, verrucous epidermal nevus) Malignant acrospiroma (spiradenocarcinoma) Malignant mixed tumor (malignant chondroid syringoma) Malignant trichilemmal cyst Mantleoma Marjolin's ulcer Melanoacanthoma (pigmented seborrheic keratosis) Merkel cell carcinoma (cutaneous apudoma, primary neuroendocrine carcinoma of the skin, primary small cell carcinoma of the skin, trabecular carcinoma of the skin) Microcystic adnexal carcinoma (sclerosing sweat duct carcinoma) Micronodular basal cell carcinoma Milia en plaque Milium Mixed tumor (chondroid syringoma) Mucinous carcinoma Mucinous nevus (nevus mucinosus) Muir–Torre syndrome Multiple familial trichoepithelioma (Brooke–Spiegler syndrome, epithelioma adenoides cysticum) Multiple keratoacanthomas (Ferguson–Smith syndrome, Ferguson-Smith type of multiple self-healing keratoacanthomas, multiple keratoacanthomas of the Ferguson–Smith type) Multiple minute digitate hyperkeratosis (digitate keratoses, disseminated spiked hyperkeratosis, familial disseminated piliform hyperkeratosis, minute aggregate keratosis) Nevoid basal cell carcinoma syndrome (basal cell nevus syndrome, Gorlin syndrome, Gorlin–Goltz syndrome) Nevus comedonicus (comedo nevus) Nevus comedonicus syndrome Nevus sebaceous (nevus sebaceous of Jadassohn, organoid nevus) Nevus unius lateris Nodular basal cell carcinoma (classic basal cell carcinoma) Paget's disease of the breast Papillary eccrine adenoma (tubular apocrine adenoma) Papillary hidradenoma (hidradenoma papilliferum) Papillomatosis cutis carcinoides (Gottron's carcinoid papillomatosis, papillomatosis cutis carcinoides of Gottron–Eisenlohr) Patch blue nevus (acquired dermal melanocytosis, dermal melanocyte hamartoma) Perifollicular fibroma Phakomatosis pigmentokeratotica Pigmented actinic keratosis Pigmented basal cell carcinoma Pigmented hairy epidermal nevus syndrome Pilar sheath acanthoma Pilonidal sinus (Barber's interdigital pilonidal sinus, pilonidal cyst, pilonidal disease) Porocarcinoma (malignant poroma, eccrine porocarcinoma) Polypoid basal cell carcinoma Pore-like basal cell carcinoma Primary cutaneous adenoid cystic carcinoma Proliferating epidermoid cyst (proliferating epithelial cyst) Proliferating trichilemmal cyst (pilar tumor, proliferating follicular cystic neoplasm, proliferating pilar tumor, proliferating trichilemmal tumor) Pseudocyst of the auricle (auricular endochondrial pseudocyst, cystic chondromalacia, endochondral pseudocyst, intracartilaginous cyst) Pseudoepitheliomatous keratotic and micaceous balanitis PUVA keratosis Rasmussen syndrome Reactional keratosis Reticulated seborrheic keratosis (adenoid seborrheic keratosis) Rodent ulcer (Jacobi ulcer) Schimmelpenning syndrome (Schimmelpenning–Feuerstein–Mims syndrome) Sebaceoma (sebaceous epithelioma) Sebaceous adenoma Sebaceous carcinoma Sebaceous hyperplasia Sebaceous nevus syndrome Seboacanthoma Seborrheic keratosis (seborrheic verruca, senile wart) Seborrheic keratosis with squamous atypia Signet-ring cell squamous cell carcinoma Solitary keratoacanthoma (subungual keratoacanthoma) Solitary trichoepithelioma Spindle cell squamous cell carcinoma (spindle cell carcinoma) Spiradenoma Squamous cell carcinoma Steatocystoma multiplex (epidermal polycystic disease, sebocystomatosis) Steatocystoma simplex (simple sebaceous duct cyst, solitary steatocystoma) Stucco keratosis (digitate seborrheic keratosis, hyperkeratotic seborrheic keratosis, keratosis alba, serrated seborrheic keratosis, verrucous seborrheic keratosis) Superficial basal cell carcinoma (superficial multicentric basal cell carcinoma) Syringadenoma papilliferum (syringocystadenoma papilliferum) Syringofibroadenoma (acrosyringeal nevus of Weedon and Lewis) Syringoma Systematized epidermal nevus Thermal keratosis Trichilemmal carcinoma Trichilemmal cyst (isthmus-catagen cyst, pilar cyst) Trichilemmoma Trichoadenoma (trichoadenoma of Nikolowski) Trichoblastoma Trichoblastic fibroma Trichodiscoma Trichofolliculoma Unilateral palmoplantar verrucous nevus Urethral caruncle Verrucous carcinoma Verrucous cyst (cystic papilloma) Viral keratosis Warty dyskeratoma (isolated dyskeratosis follicularis) Waxy keratosis of childhood (kerinokeratosis papulosa) Zoon's vulvitis Zosteriform speckled lentiginous nevus
Other advantages of the NPT approach are that it is fast and convenient, usually less painful, and offers, in home use, the ability for patients to measure their own INRs when required. Among its problems are that quite a steady hand is needed to deliver the blood to the exact spot, that some patients find the finger-pricking difficult, and that the cost of the test strips must also be taken into account. In the UK these are available on prescription so that elderly and unwaged people will not pay for them and others will pay only a standard prescription charge, which at the moment represents only about 20% of the retail price of the strips. In the US, NPT in the home is currently reimbursed by Medicare for patients with mechanical heart valves, while private insurers may cover for other indications. Medicare is now covering home testing for patients with chronic atrial fibrillation. Home testing requires a doctor's prescription and that the meter and supplies are obtained from a Medicare-approved Independent Diagnostic Testing Facility (IDTF). There is some evidence to suggest that NPT may be less accurate for certain patients, for example those who have the lupus anticoagulant.
== Function == The protein encoded by the CALCRL gene is a G protein-coupled receptor related to the calcitonin receptor. CALCRL is linked to one of three single transmembrane domain receptor activity-modifying proteins (RAMPs) that are essential for functional activity. The association of CALCRL with different RAMP proteins produces different receptors:
=== Classification === Scleroderma is characterised by the appearance of circumscribed or diffuse, hard, smooth, ivory-colored areas that are immobile and which give the appearance of hidebound skin, a disease occurring in both localised and systemic forms:
Sources: en.wikipedia.org
where [A] is the concentration of A, etc., is independent of the analytical concentration of the reactants. For this reason, equilibrium constants for solutions are usually determined in media of high ionic strength. Kc varies with ionic strength, temperature and pressure (or volume). Likewise Kp for gases depends on partial pressure. These constants are easier to measure and encountered in high-school chemistry courses.
21 April In one of the first Fragging incidents of the war, a grenade was thrown into the office of K Company, 9th Marine Regiment, at Quảng Trị Combat Base, killing First Lieutenant Robert T. Rohweller. Private Reginald F. Smith pleaded guilty to the premeditated murder and was sentenced to 40 years' imprisonment; he died in custody on 25 June 1982.
== Professional membership == American Association of Clinical Chemistry (AACC) Academy Fellow of AACC American Society of Clinical Pathology (ASCP) International Society on Thrombosis and Haemostasis (ISTH) Korean Society for Biochemistry and Molecular Biology
==== Encoded combinatorial libraries ==== When dealing with a non-peptide organic libraries library, it is not as simple to determine the identity of the content of a bead as in the case of a peptide one. In order to circumvent this difficulty, methods have been developed to attach molecules that encode the structure of the compound formed in the bead to the beads, in parallel with the synthesis of the library. Ohlmeyer and his colleagues published a binary encoding method. They used mixtures of 18 tagging molecules that, after cleaving them from the beads, could be identified by Electron Capture Gas Chromatography. Sarkar et al. describe chiral oligomers of pentenoic amides (COPAs) that can be used to construct mass encoded OBOC libraries. Kerr et al. introduced an innovative encoding method. An orthogonally protected removable bifunctional linker was attached to the beads. One end of the linker was used to attach the non-natural building blocks of the library, while encoding amino acid triplets were linked to the other end. The building blocks were non-natural amino acids and the series of their encoding amino acid triplets could be determined by Edman degradation. The important aspect of this kind of encoding was the possibility to cleave down from the beads the library members together with their attached encoding tags forming a soluble library. The same approach was used by Nikolajev et al. for encoding with peptides. In 1992, Brenner and Lerner introduced DNA sequences to encode the beads of the solid support that proved to be the most successful encoding method.
Sources: en.wikipedia.org
Primary drying removes ice by sublimation at low pressure and low shelf temperature. Secondary drying removes bound water by raising the shelf temperature, often under the same vacuum. The two stages differ in the water state being removed.
Freezing determines ice crystal size, pore structure, and the concentration of solutes in remaining liquid. Faster freezing generally creates smaller ice crystals and a denser dried matrix. These features affect drying rate and reconstitution behavior.
Lyophilization reduces water content but usually leaves a small amount of water in the dried material. Some water remains bound to solids or trapped in the dried matrix. Very low water targets can require extended secondary drying, which may alter product stability.
Lyophilization removes water by sublimation from a frozen material, while evaporation changes liquid water into vapor. The low-pressure freezing step avoids the liquid phase and can preserve heat-sensitive structures.