Research On The Relationship Between Mechanical Properties And Structure Of DNA Supramolecular Hydrogels And Its Applications

The extracellular matrix(ECM)is the three-dimensional environment for living cells.Hydrogels have similar physical and chemical properties to the extracellular matrix,which provide mechanical support and nutrient for cells.DNA supramolecular hydrogels have important applications in cell culture because of their designability,tunable mechanical strength,good biocompatibility,and good permeability.Mechanical properties are crucial for DNA hydrogels.The regulation and mechanism of their mechanical properties needs further understanding.Here we focus on the mechanical properties of DNA supramolecular hydrogels,including the regulation of hydrogel mechanical strength,the mechanism of backbone rigidity on hydrogel mechanical properties,and the application of doublenetwork hydrogels in three-dimensional cell imaging.First,by integrating aptamer sequence into the three-dimensional DNA network,we designed and constructed an ATP-responsive DNA supramolecular hydrogel.Through the addition of ATP,which specifically binds the aptamer,the mechanical strength of the DNA supramolecular hydrogel can be enhanced in situ.The mechanical strength of the hydrogel showed a clear dependence on the ATP concentration.Adding fully complementary single strands of aptamers can further increase the hydrogel mechanical strength.Therefore,we successfully tuned the the mechanical strength of DNA supramolecular hydrogels in three phases.By comparing the three states,we find that the rigidity of the backbone is an important factor affecting the mechanical strength of the hydrogel.Then we used dynamic-light-scattering-based microrheology to characterize the mechanical properties of DNA hydrogels with different backbone rigidity and investigate the mechanisms that influences the mechanical properties of the bulk materials.We found that the system with rigid backbone has increased viscosity during cooling,which shows a clear gelation process.The system with flexible backbone has lower viscosity as the temperature decreases.By calculating the energy change of the process and combining with the coarse-grained model simulation results,we found that a ring structure was formed in the flexible backbone system,which lowered the binding valence and lead to a cluster fluid.Thus,we revealed the mechanism of backbone rigidity on the gelation process and mechanical properties of DNA hydrogels.Finally,to solve the problem that DNA supramolecular hydrogels collapse during in situ staining and imaging after 3D cell culture,we developed a strategy to build doublenetwork hydrogels by in situ formation of covalent second network in DNA supramolecular hydrogels.By optimizing the cross-linking ratio of polyacrylamide/BIS and polymerizing in situ,we successfully constructed DNA-polyacrylamide doublenetwork hydrogels.The doublenetwork hydrogels showed enhanced mechanical strength and good stability.By introducing AAm/BIS monomers to DNA hydrogels after cell culture and forming a second network through in situ polymerization,the cells can be immobilized three-dimensionally for immunostaining and imaging.