Cryoprotective

Cryoprotective refers to substances or strategies used to protect biological materials from damage during freezing and cryopreservation. Cryoprotective agents (CPAs) are chemicals that reduce ice formation, limit osmotic and chemical stress, and help maintain viability of cells, tissues, or organs at low temperatures.

CPAs can be broadly categorized as permeating and non-permeating. Permeating CPAs, such as glycerol, dimethyl sulfoxide (DMSO), ethylene glycol, and propylene glycol, enter cells and help reduce ice crystal formation inside, while also contributing to osmotic balance. Non-permeating CPAs, including sugars like sucrose and trehalose, act outside cells to draw water out, promote dehydration, and stabilize membranes. Some CPAs function through vitrification, a glass-like solidification that avoids ice crystal formation by using high CPA concentrations and rapid cooling.

Commonly used CPAs include glycerol, DMSO, and ethylene glycol for various cell types and organisms, as well as trehalose and sucrose for extracellular protection. Cryopreservation applications span sperm, oocytes, embryos, blood products, cell lines, and tissue samples, with protocols differing for slow freezing versus vitrification. The choice and concentration of CPAs depend on the material, desired cooling rate, and downstream applications.

Risks and considerations include CPA toxicity, osmotic stress during addition and removal, and the need for careful optimization of protocols. After thawing, CPAs are often diluted or removed to restore normal physiology, and residual CPA effects can influence viability. Regulatory and safety considerations guide clinical and research use of cryoprotective agents.