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| Photo of liver processed in LTVEP, taken in the electron microscope. The tissues section was not stained, so the density of the organelles is the original one. The Middle of the cell is occupied by the cell nucleus, and nucleoli can be easily seen in the 5 o'clock position. Also, nuclear pores and double nuclear membranes can be seen. Numerous dark spots in the cell are mitochondria. In the 4 o´clock position, outside the nucleus, the rough endoplasmic reticulum can be easily discerned. |
Low-temperature vacuum embedding process (often associated with LTVEP) is a specialized tissue processing technique designed to dehydrate and embed biological samples—such as donor corneas or research tissue—without the damaging effects of high heat or chemical fixation. The apparatus and the process were developed by Dr. Romuald (Roman) Wróblewski at Karolinska Institute in Stockholm.
Core Process Characteristics:
- Temperature & Vacuum: The technique uses a vacuum in a freeze-dryer to manipulate the boiling point of water, allowing tissue to dehydrate at low temperatures. To prevent freezing damage, the vacuum pressure is typically managed to stay above a certain threshold (e.g., >1.5 mbar).
- Low-Temperature Vacuum Embedding Process (LTVEP) was often used with specialized resins that, after dehydration in the specialized freeze-dryer, allow infiltration and polymerization at sub-zero temperatures, sometimes as low as -60°C, to preserve ultrastructure. During the entire procedure, freeze-drying, infiltration by low viscosity resins, and polymerization, the tissue is kept in the same tube in the freeze-dryer. First, after the polymerisation using UV-light at low temperature, the sample is allowed to reach room temperature.
Key Advantages:
- Excellent Structural Preservation: Prevents shrinkage, brittleness, and hardening caused by overheating.
- Biological Integrity: Maintains the biological characteristics of tissues, including extracellular matrix structures.
- Bio-molecule Preservation: Ideal for preserving DNA, RNA, and proteins, often allowing for fresh tissue transportation.
- Sterilization & Stability: Enables long-term, room-temperature storage of all biological tissues.
- Immunoreactivity: Preserves antigens, making the tissue suitable for subsequent immunogold labeling in electron microscopy
