Applying nanotechnology to cryopreservation studies: Status and future

Abstract

Currently, cryopreservation is considered as one of the most effective methods for preserving biological samples, such as biological molecules, cells, tissues and organs. Cryopreservation of cells has been studied a lot and attracts most interests. The conventional cell cryopreservation technique has a few limitations, including the cytotoxicity of the high concentrations of cryoprotective agents, osmotic stress caused by adding and removing of the protectants, uncontrolled formation and growth of ice during freezing process, ice recrystallization due to not rapid enough warming rate during rewarming process and so on. Nanotechnology has been more and more widely applied in the research of cryobiology field. The nanoparticles own characteristics of quantum size effect, surface effect, small size effect and macroscopic quantum tunneling effect. Among them, magnetic nanoparticles (mainly iron oxide nanoparticles) are one of the most common used nanomaterials, due to their excellent particle size controllability, biocompatibility and biodegradation, surface modifiability and intrinsic magnetic response. It has been expected that the nanotechnology will solve the current bottleneck problems for cryopreservation, as well as bring new ideas for expanding the research area of cryobiology. This article mainly reviews the recent research status concerned with applying the nanotechnology to the cryopreservation studies. It has been reported that loading nanoparticles in cryoprotectant solutions will affect the membrane hydraulic permeability parameters and volume response of cells, therefore, by fitting the parameters with proper model and predicting the cell volume change, the adding and removing process of the cryoprotective agents can be optimized to reduce the osmotic stress to cells. Moreover, nanoparticles are found to be able to change the thermal and physical properties of the cryoprotectants, e.g., specific heat, viscosity, nucleation and vitrification temperatures. As a result, the ice formation and growth can be regulated, and the freezing/cooling efficiency is largely improved. Furthermore, it has been shown that the magnetic induction heating effect of magnetic nanoparticles can provide a rapid enough warming rate under electrical and magnetic field, which avoids the ice recrystallization and rewarms the frozen samples uniformly with high efficiency. Besides, the nanotechnology has more applications such as the nanoparticles can bring the impermeable protectants into cells, increase the tolerance of organs to oxidative stress during cryopreservation and so on. The further studies to be done in future are also discussed: (1) The functionality of nanomaterials, e.g., the biocompatibility, including the toxicity of the nanomaterials, the effects and reactions of adding the different kinds of nanomaterials to organisms and so on; (2) removing the nanomaterials from the biological samples after cryopreservation is one challenge when applying the nanotechnology, the questions like how to remove the nanoparticles with minimum damages, whether the nanoparticles can be completely cleaned and how to detect the rest of them need to be considered; (3) the properties of nanomaterials during freezing and rewarming process, such as mechanisms of heat and mass transfer, thermodynamics concerned with ice nucleation and formation; (4) developing the optimized cryopreservation protocols according to the practical clinical uses is also of great importance. Hopefully, the application of the nanotechnology will achieve new breakthroughs in cryopreservation field, and the advancement benefits mankind and promotes the development of clinical medicine.