Study And Applications Of Zwitterion-based Low-temperature Protection Strategies

Water freezing at subzero temperature can cause dyfunction and even death of cells or organisms,as well as functional deterioration and even failure of water-containing materials or devices,thus affecting human production activities.Hydrophilic zwitterions can easily bind water molecules,depress water freezing point and inhibit ice formation.In this thesis,based on the antifreezing properties of hydrophilic zwitterions,we developed different low-temperature protection strategies and investigated their applications in cell cryopreservation and antifreezing hydrogel-based flexible devices.Cell cryopreservation is fundamentally important to the development and applications of advanced medical examination and treatment.However,the freezing of intracellular and extracelluar water during cryopreservation can cause cell dyfunction and even death.Firstly,for the cryopreservation of red blood cells（RBCs）in whole blood,by combining zwitterionic betaine and membrane stabilizers,this thesis developed a novel cryopreservation solution.The solution could significantly mitigate the cryoinjuries to RBCs in whole blood and achieved about 90%RBC recovery.Besides,after thawing,the solution could be easily removed without causing RBC hemolysis.Secondly,for the cryopreservation of chondrocytes,this thesis developed a novel cryoprotection strategy based on zwitterionic betaine and alginate polymers,and its cryoprotection efficiency to chondrocytes was higher than 90%.More importantly,after thawing,without removing the cryopreservation solution,the freeze-thawed cells could be encapsulated in alginate hydrogels by directly adding Ca²⁺into the thawing cell suspension and maintained their high survival and function for a long time（>14days）,which showed great potential in cartilage repair.Synthetic polymeric hydrogels possess similar high water content and Young’s modulus as cells and tissues,thus are ideal materials for fabricating flexible electronics.However,the ice formation inside hydrogels can cause functional deterioration and even failure of the hydrogel-based devices.In this thesis,novel antifreezing hydrogels were designed and fabricated by introducing zwitterionic cryoprotectants（betaine or proline）and NH₄Cl into Ca-alginate/polyacrylamide hydrogels via a solvent displacement method.The hydrogels could remain unfrozen at-40℃and exhibited stable mechanical flexibility as well as high ionic conductivity（up to 2.72 S/m）,which showed negligible change during 2000 times of bending tests.Besides,they could be applied in flexible pressure or strain sensors working at-40℃.Water evaporation is the major cause for unstable performance and short working life of antifreezing hydrogels.This thesis further fabricated poly（zwitterionic sulfobetaine-co-acrylic acid）/Li Cl hydrogels using free radical polymerization and solvent displacement methods.The hydrogels could remain unfrozen at-80℃over 30days and retain 100%of their water content for 7 days at 25℃with 54%relative humidity.Besides,after vacuum drying,the totally dried hydrogels could spontaneously absorb water molecules from surrounding environments to achieve 100%of self-regeneration.Meanwhile,they could be applied in antifreezing soft sensors for motion detection at low temperature and provided a new strategy to solve the problem of water loss of hydrogel-based sensors.