Cryopreservation involves preserving biological materials by cooling them to extremely low temperatures. This process halts biological activity, including metabolic processes and chemical reactions, without damaging cells or tissues. Precise temperature control is essential for successful, long-term storage of biological samples.
How Extreme Cold Affects Living Matter
Cooling biological materials slows or stops metabolic processes, preventing degradation. Freezing, however, presents a challenge: ice crystal formation within cells and tissues. As temperatures drop, water inside and outside cells freezes. Extracellular ice can cause damage, but intracellular ice formation is more concerning.
Ice crystals can puncture cell membranes and disrupt cellular structures, including the spindle apparatus and cytoskeleton. This mechanical damage is a key challenge in cryopreservation. As ice crystals form, they consist of nearly pure water, concentrating solutes and cryoprotective agents in the remaining unfrozen solution. This increased solute concentration can lead to osmotic shock and dehydration, further damaging cells. Careful temperature control helps mitigate these damaging effects.
Specific Temperatures Used in Cryopreservation
Cryopreservation relies on reaching and maintaining specific cryogenic temperatures for biological stability. The standard temperature for deep cryopreservation is approximately -196°C (-321°F), achieved by storing samples in liquid nitrogen. This temperature is below the glass transition temperature of water, which typically ranges from -121°C to -137°C for biological solutions.
Below the glass transition temperature, any remaining unfrozen water vitrifies, forming an amorphous, glass-like solid rather than crystallizing. This vitrification prevents the formation and growth of damaging ice crystals. At -196°C, all biological activity and chemical reactions stop, allowing for long storage times. While some materials may be stored at higher temperatures, such as -80°C, these conditions only slow biological processes, and cellular changes can still accumulate.
Methods for Achieving and Maintaining Cryogenic Temperatures
Achieving and maintaining ultra-low temperatures for cryopreservation involves specific cooling strategies and specialized equipment. Two main cooling methods are controlled slow freezing and vitrification. Controlled slow freezing involves a gradual temperature reduction, often using programmable freezers, to allow water to move out of cells and cryoprotectants to penetrate. This method aims to manage ice crystal formation and minimize damage.
Vitrification involves rapid cooling to bypass ice crystal formation, solidifying the biological material into a glass-like state. This technique often uses higher concentrations of cryoprotective agents and relies on rapid cooling rates, sometimes achieved by plunging samples directly into liquid nitrogen. Equipment includes controlled-rate freezers that precisely regulate cooling rates, and liquid nitrogen storage dewars for long-term preservation at -196°C. Precise temperature regulation throughout cooling and storage is crucial for successful cryopreservation.
What is Preserved Through Cryogenic Temperatures
Cryogenic temperatures allow for the preservation of a diverse range of biological materials, safeguarding their viability and functionality for extended periods. This includes various types of cells, such as stem cells, blood cells, sperm, and eggs. Tissues like skin, heart valves, and ovarian tissues are also routinely preserved. More complex biological structures, such as embryos and seeds for gene banks, are successfully maintained.
The ability to preserve these materials has significance across medicine, research, and conservation. It supports fertility treatments, enables cell and organ transplantation, and facilitates long-term storage of valuable cell lines for scientific investigations and drug development. Cryopreservation provides a stable means to transport samples, create biobanks, and protect genetic integrity.