The Effect Of Nanoparticles On Thermodynamic Parameters Of Cryoprotective Agents

As the reason of the destructive effect of extracellular ice formationcryopreservation by freezing fails to provide effective protection to tissues or organs.Vitrification was developed as an alternative to freezing to solve the problems of humanorgan cryopreservation. Vitrification is essentially the solidification of a supercooledliquid by adjusting the composition, cooling rate, and sometimes pressure to avoidcrystallization. Relatively high concentrations of cryoprotective agents (CPAs) arerequired to achieve a glassy state and relatively fast cooling and warming rates arerequired to avoid damage associated with ice crystallization. These rapid cooling ratesmay not be possible to achieve as the size of biomaterials become larger.Modern nanotechnology provides new challenges and opportunities forthermo-science. Nano-CPAs are a new type of heat transfer carriers by suspendingnanoscaled metallic or nonmetallic particles in base CAPs. Nano-CPAs are expected toexhibit heat transfer properties superior to those of conventional heat transfer fluids.Thepurpose of this paper is to study experimentally and theoretically the enhancement ofnanoparticles to the heat transfer of nano-CAPs, as following:1. Preparation and stability of nano-CPAs. This paper presents a preparationmethod of nano-CPAs by directly mixing nanoscaled powders into base CPAsfluids. Some auxiliary dispersants are necessary to obtain the even distributedand stabilized suspensions. With this method, several types of CPAs ofdifferent volume fraction have been prepared. The stability and evenness ofsuspensions were evaluated using the TEM photographs. Some factorsinfluencing the stability and evenness of nano-CPAs, such as the property ofbase CPAs fluid, the dimension and the property of nanoparticles, arediscussed.2. To study the effects of the nanoparticles on thermodynamic parameter of PVPcryoprotectant solutions, the DSC were used to measure of the PVP solutionswith/without nanoparticiles in the paper. Consider the result shows that thespecific heat decreases with the increasing of the concentration ofnanoparticles. The paper takes the explanation about this phenomenon by theinteraction between the nanoparticles and solution.3. In order to investigate the subcooling efficiency of nanoparticles as nucleation agents in cryoprotectant solutions at cryogenic temperatures, the frozenparameters of these solutions with different concentrations of HAnanoparticles were measured by using differential scanning calorimetric. Theresults indicate that the variation of supercooling does not change significantlyin the concentration range of0%to15%. However, when the concentration ofthe solution is higher than15%, the nanoparticles can significantly improvethe nucleation temperature of the solution. Experimental results also show thatsupercooling temperature increase with the increment of nanoparticles’ sizeand concentration.4. In order to investigate the effects of Nanoparticles on the vitrification ofCryprotective agent solutions at cryogenic temperatures, the vitrification anddevitrification temperature of these solutions with different particle size andconcentrations of HA nanoparticles w ere measured by differential scanningcalorimeter (DSC). Experimental results indicate that the vitrification can besignificantly affected by nanoparticles. And with the mass fraction ofnanometer particles increasing, the vitrification and devitrification temperatureof solutions significantly reduced. Different effects of Nanoparticles on thevitrification are affected by different particle size. The effects of40nmHAnanoparticles are the most obvious. And the vitrification stability of solutionsis the minimum.