(Nanowerk News) Tiny amounts of a nanometer-thin metal-organic layer efficiently protect red blood cells during freezing and thawing, the research team wrote in the journal Applied chemistry have found (“Dimensional Reduction of Metal–Organic Frameworks for Enhanced Red Blood Cell Cryopreservation”).
The nano-coating, made of a metal-organic framework based on hafnium metal, prevents the formation of ice crystals at very low concentrations. This new effective mode of cryoprotection can be used to develop new and more efficient cryoprotectants for the biosciences.
Cryoprotectants prevent the formation of ice crystals when samples are frozen. Growing crystals can damage delicate cell membranes and cell components and disrupt cell integrity. Some solvents or polymers make good cryoprotectants; they prevent the formation of ice crystals by binding to water molecules and disrupting their orderly arrangement during ice formation.
Synthetic chemistry has more tricks up its sleeve to target and influence ice formation in a more effective way. Metal-organic frameworks (MOFs) are three-dimensional crystal networks of metal ions linked by organic ligands. These ligands can be adapted to bind to small molecules such as water, enabling the assembly of water molecules into extremely finely tuned ice crystals.
Wei Zhu of the South China University of Technology in Guangzhou (China) and colleagues have now found that as MOFs based on hafnium and organic ligands become thinner, their ability to bind to and influence water molecules increases, especially as more ligand sites become available. The team therefore developed a method for controlled deconstruction of a three-dimensional metal-organic framework until only two-dimensional thin nano-layers remained.
To test their suitability of hafnium-MOL (MOL stands for metal-organic coating, to distinguish it from three-dimensional MOF) as a cryoprotectant, the team froze red blood cells, a type of cell that needs to be stored in large quantities for medical purposes but is easily destroyed by crystal formation. ice. Compared to hydroxyethyl starch (HES), which is commonly used as a cryoprotectant, MOL hafnium shows excellent cryoprotection at minimal concentrations of less than 0.1%, whereas HES solutions are typically used at concentrations up to 30%.
Zhu and team explain that MOL is very effective because the disordered two-dimensional structure of the ligands that bind to water molecules prevents the formation of nuclei of ordinary ice crystals. The team suggests that dimensionality reduction of MOFs is an interesting new perspective for obtaining highly efficient cryoprotectants.