Everything below concerns Secondary drying. We keep the language plain, cite what the science says, and separate well-supported claims from open questions.
Last reviewed on 2026-04-28. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
After lyophilization, the dried product is often sealed under vacuum or an inert gas to limit moisture and oxygen exposure. Vials, stoppers, and seals must maintain their barrier throughout shelf life. Storage temperature depends on product sensitivity: some cakes tolerate controlled room temperature, while labile biologics require refrigeration. Humidity is a critical variable because dried cakes are hygroscopic and can absorb water when exposed to air. Handling procedures therefore limit open-vial time and use desiccated environments for sampling.
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.
| Property | Value | Notes |
|---|---|---|
| Process name | Lyophilization or freeze-drying | Both terms appear in technical standards and literature. |
| Phase transition | Sublimation | Solid ice becomes vapor without a liquid step. |
| Typical chamber pressure | 0.05-0.5 mbar | Range depends on product temperature and equipment. |
| Typical product temperature | -40 °C to -10 °C | Measured during primary drying; formulation sets limits. |
| Water content after drying | 0.5-3% w/w | Target varies by material and stability needs. |
Netter, Frank H. (1987), Musculoskeletal system: anatomy, physiology, and metabolic disorders, Summit, New Jersey: Ciba-Geigy Corporation Jaffe, N.; et al. (2009). Pediatric and Adolescent Osteosarcoma. New York: Springer. ISBN 978-1-4419-0283-2.
The part instead went to Martin Landau. Culp co-starred in The Greatest American Hero as tough veteran FBI Special Agent Bill Maxwell, who teams up with a high-school teacher who receives superpowers from extraterrestrials. He wrote and directed the second-season finale episode "Lilacs, Mr. Maxwell", with free rein to do the episode as he saw fit. The show lasted three years from 1981 to 1983. He reprised the role in the spin-off pilot The Greatest American Heroine. During that time, Culp was rumored to replace Larry Hagman as J. R. Ewing in Dallas. However, Culp firmly denied this, insisting he would never leave his role as Bill Maxwell. Culp reunited with Cosby on The Cosby Show in the episode "Bald and Beautiful" (1987), playing Dr. Cliff Huxtable's old friend Scott Kelly. The name was a combination of their I Spy characters' names. In I Spy Returns (1994), a nostalgic television movie, Culp and Cosby reprised their roles as Robinson and Scott for the first time since 1968. Culp and Cosby reunited one last time on the television show Cosby in an episode entitled "My Spy" (1999), in which Cosby's character, Hilton Lucas, dreams he is Alexander Scott on a mission with Kelly Robinson. Culp appeared on episodes of other television programs, including The Golden Girls where he played Simon, Blanche's beau, in the episode titled "Like the Beep Beep Beep of My Tom Tom" (1990), as well as Murder, She Wrote, Matlock, Who's the Boss?, Dr. Quinn, Medicine Woman, The Nanny, and Wings.
== Medical uses == Imipenem/cilastatin is used for lower respiratory tract infections, urinary tract infections, intra-abdominal infections, gynecologic infections, bacterial sepsis, bone and joint infections, skin and skin structure infections, endocarditis and polymicrobic infections. It is a broad-spectrum beta-lactam containing equal quantities of imipenem and cilastatin.
Sources: en.wikipedia.org
=== Deaths === Combined consumption of U-47700 with fentanyl and flubromazepam caused one fatality each in Belgium and Germany, respectively. One death was reported in Ireland and another one in Italy. 17 opioid overdoses and several deaths in the United States had initially been associated with U-47700 in April 2016. As of September 2016 at least 15 fatalities were confirmed. By December 2017, at least 46 fatalities had been associated with the use of U-47700. U-47700 was found in combination with fentanyl during the autopsy of the American artist Prince in 2016.
=== IARW === The International Association of Refrigerated Warehouses (IARW) was founded in 1891. It was created when a group of conventional (non-refrigerated) warehouse owners began sharing knowledge about storing perishable food. As perishable food storage is complex, this organization soon became known industry-wide for their expertise about temperature controlled storage facilities. IARW's goals and activities broadened over the years. In addition to collecting information and encouraging the exchange of ideas, the association promoted efficiency in distribution, aids members in adopting new technology, advises legislators on behalf of the food industry, assists members in complying with U.S. and international regulations, and participates in alliances with international organizations to build an efficient world food logistics community. All active members of IARW are also members and beneficiaries of the work of The World Food Logistics Organization (WFLO).
Rope bridges were an integral part of the Inca road system. "Five centuries ago, the Andes were strung with suspension bridges. By some estimates there were as many as 200 of them." As pictured to the right, these structures were used to connect two land masses, allowing for the flow of ideas, goods, people, animals, etc. across the Incan empire. "The Inca suspension bridges achieved clear spans of at least 150 feet, probably much greater. This was a longer span than any European masonry bridges at the time." Since the Incan people did not use wheeled vehicles, most traveled by foot and/or used animals to help in the transporting of goods.
Sources: en.wikipedia.org
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.
Lowering pressure reduces the boiling point of water and allows ice to sublimate at temperatures below freezing. Vacuum also limits convective heat transfer, so heat is usually supplied by shelves or radiation. The pressure must stay below the vapor pressure of ice at the product temperature.
The cycle typically includes freezing, primary drying, and secondary drying. Freezing solidifies water and sets the pore structure; primary drying removes bulk ice; secondary drying removes bound water. Some cycles add annealing or pre-freezing steps.
No. Freeze-drying removes water but does not reliably kill microorganisms. Sterile lyophilized products are typically prepared aseptically before freezing or are sterilized by a validated method. Microbial control depends on the entire manufacturing process.