The short version of primary drying fits in a sentence. The long version — which is the one that helps — is below.
This page was last updated on 2025-09-13 and is reviewed periodically as new material appears.
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.
Industries use lyophilization for pharmaceuticals, biological products, and food preservation. In the pharmaceutical sector, it extends the shelf life of injectable drugs, vaccines, and proteins that are unstable in aqueous solution. Food manufacturers apply freeze-drying to coffee, fruits, and ready meals to retain flavor and texture. The process is energy-intensive and requires specialized equipment, which limits its use to high-value products. Ongoing research examines how formulation and process parameters affect the quality of the final dried product.
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.
| 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 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.
The physics of lyophilization couples heat transfer, mass transfer, and phase behavior. Sublimation requires a vapor pressure difference between the ice front and the chamber, and the dried layer adds resistance to vapor flow. Amorphous formulations are characterized by a glass transition temperature of the maximally freeze-concentrated solute, often denoted Tg'. Crystalline bulking agents can provide structure, while amorphous excipients stabilize labile components. Open questions remain about spatial heterogeneity, edge effects, and how laboratory cycles scale to production.
Lyophilization is a drying process in which a solvent, usually water, is removed from a frozen material by sublimation under reduced pressure. The material is first solidified, then placed under vacuum so that ice transitions directly to vapor without a bulk liquid phase. This approach suits heat-sensitive substances that would degrade during conventional evaporation. Primary drying removes unbound ice, while secondary drying reduces water that remains adsorbed to the solid matrix. The result is a porous, lightweight solid that can be reconstituted later.
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 by freezing a material and then lowering pressure so ice changes directly to vapor. The process relies on sublimation, the phase transition from solid to gas without an intermediate liquid state. Because the material remains frozen during primary drying, the structure often stays porous. This porous matrix can rehydrate quickly when water is added back. The low pressure also allows vapor to leave the solid matrix without boiling.
{\displaystyle \Delta _{^{12}CH_{2}D_{2}}={\left({\frac {0.183798}{T}}\right)}-{\left({\frac {785.483}{T^{2}}}\right)}+\left({\frac {1056280.0}{T^{3}}}\right)+\left({\frac {9.37307\times 10^{7}}{T^{4}}}\right)-\left({\frac {8.919480\times 10^{10}}{T^{5}}}\right)+\left({\frac {9.901730\times 10^{12}}{T^{6}}}\right)}
characterizes the potential for initial spread of an infectious person in a naive population, assuming the change in the susceptible population is negligible during the initial spread. A linear system of ODEs can always be described by a matrix. So, the next step is to construct a linear positive operator that provides the next generation of infected people when applied to the present generation. Note that this operator (matrix) is responsible for the number of infected people, not all the compartments. Iteration of this operator describes the initial progression of infection within the heterogeneous population. So comparing the spectral radius of this operator to unity determines whether the generations of infected people grow or not.
Countries have differing standards for grading honey. In the US, honey grading is performed voluntarily based upon USDA standards. USDA offers inspection and grading "as on-line (in-plant) or lot inspection...upon application, on a fee-for-service basis." Honey is graded based upon a number of factors, including water content, flavor and aroma, absence of defects, and clarity. Honey is also classified by color, though it is not a factor in the grading scale. The USDA honey grade scale is:
== Menu and themes == Zaxbys is a fast casual restaurant offering Chicken Fingerz, chicken wings, fried shrimp, sandwiches, and salads. Dipping sauces are offered with chicken finger orders, and range from mild, to the moderate "Zax Sauce", to the intensely hot "Nuclear". Dining rooms at Zaxbys restaurants are decorated with assorted whimsical objects and signs, which often vary in theme by location and region. Some locations in college towns feature objects and decorations related to the local university. Similarly, citrus-industry themed decorations line the walls at a location in Orlando, Florida.
=== Cyclic peptide binders Screening === Cyclic peptides can be successfully displayed on bacterial cell surface. By DNA randomization millions of cyclic peptides displayed on cell surface can be screened against a protein target using high-throughput FACS.
Sources: en.wikipedia.org
=== Occurrence in animals === Numerous arthropods (Arthropoda) contain cyanogenic (hydrogen cyanide-releasing) nitrile compounds, including centipedes (Chilopoda), bipedes (Diplopoda), beetles (Hemiptera), beetles (Coleoptera), and butterflies (Lepidoptera). The gooseberry moth (Abraxas grossulariata) contains the nitrile-bearing glycoside sarmentosin, which likely functions in defense. Sarmentosin is also present in several species of the genus Parnassius. Several species of glass-winged bug (including Jadera haematoloma) contain cyanolipids or cardiospermine, which they may acquire from their host plants through sequestration of toxins, i.e., uptake and storage. Six-spotted damselflies are butterflies capable of both sequestering the cyanogenic glycosides linamarin and lotaustralin from their host plants and synthesizing them de novo. Other species of the same genus (Zygaena), such as the Marsh Hornwort, also contain cyanogenic glycosides. The defensive secretion of the centipede Himantarium gabrielis contains benzoyl cyanide, phenylacetonitrile, mandelonitrile (benzaldehyde cyanohydrin), and mandelonitrile benzoate. Phenylacetonitrile also functions as a hormone in the desert locust (Schistocerca gregaria). In various tapeworms (Polydesmida), the defensive secretion likewise contains benzoyl cyanide. The mite species Oribatula tibialis (order horn mite, Oribatida) contains mandelonitrile hexanoate. Hydrogen cyanide also occurs in arthropods as a degradation product of cyanogenic compounds.
An ointment is a homogeneous, viscous, semi-solid preparation; most commonly a greasy, thick water-in-oil emulsion (80% oil, 20% water) having a high viscosity, that is intended for external application to the skin or mucous membranes. Ointments have a water number that defines the maximum amount of water that they can contain. They are used as emollients or for the application of active ingredients to the skin for protective, therapeutic, or prophylactic purposes and where a degree of occlusion is desired. Ointments are used topically on a variety of body surfaces. These include the skin and the mucous membranes of the eye (an eye ointment), chest, vulva, anus, and nose. An ointment may or may not be medicated. Ointments are usually very moisturizing, and good for dry skin. They have a low risk of sensitization due to having few ingredients beyond the base oil or fat, and low irritation risk. There is typically little variability between brands of drugs. They are often disliked by patients due to greasiness. The vehicle of an ointment is known as the ointment base. The choice of a base depends upon the clinical indication for the ointment. The different types of ointment bases are:
=== Hair growth === Dermal macrophages are the essential component of the hair follicle immune system. They generally facilitate hair growth. There are three steps of hair growth: anagen, catagen, and telogen. During catagen, dermal macrophages' population decreases progressively when the hair grows. The number of dermal macrophages in hair follicles reaches a minimum during telogen (resting state) and increases during anagen (beginning of another growth cycle). In rodents, perifollicular macrophages can actively remove collagen fibres around the follicles via phagocytosis. This phenomenon might contribute to remodelling the follicular composition during anagen when dermal macrophages prevent the activation of follicular stem cells, thereby preventing entry to catagen, a process in which hair stops growing. Hence, dermal macrophages facilitate the growth of the hair by preventing the halt of the growth process and its regression. When under physical stress, the release of CCL2 (cytokine) in the hair follicle induces the infiltration of macrophages. The infiltrated macrophages mainly express an M1 phenotype, which are pro-inflammatory macrophages that could trigger apoptosis of cells in the follicle by their upregulation of pro-inflammatory cytokines such as TNF-a. However, TNF-a is a major factor facilitating hair regeneration by promoting various pathways' signalling (Wnt, NF-κB pathway). Dermal macrophages could also contribute to hair regeneration by skewing towards the anti-inflammatory phenotype (M2) under minor stress.
=== Copyright === Existing food products in the market such as chocolates in various shapes could easily be scanned and the obtained 3D models could be used to replicate those products. These 3D models could then be disseminated via Internet leading to copyright infringement. There are laws regulating copyright issues but it is not clear whether they will be sufficient to cover all aspects of a field like 3D food printing.
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.
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.