Research On Preparation And Properties Of PH/Thermo-Responsive And Self-repairing Hydrogel

Hydrogels are soft and hydrated materials similar as biological systems having potential applications in biomedical engineering and related fields.Hydrogels may differ in chemistry,architecture and function,and strategies to develop tough hydrogels with chemical,physical or the combined mechanism crosslinks are reliable,but it is still a great challenge to coalesce several properties in one system.We designed a methodology that the assembly of benzaldehyde-terminated PF127 and acylhydrazine-terminated three-armed PEG in buffer could build a hydrogel,existing two energy dissipative units,PF127 micelles and acylhydrazone bonds.This dissertation systematically explored self-repairing and dual pH and thermal responsive characteristics,as well as 3D printing property of the hydrogel by the combination use of particle analysis system,Fourier-Transform infrared spectroscopy measurement,swelling behaviors,tensile and rheological tests as well as 3D printing technique.According to the p H/thermo-responsive characteristics depicted,the mechanism were discussed profoundly.The dynamic character of both acylhydrazone bonds and micelles entrusted the selfrepairing ability about 90% of its initial strength within 24 h to this hydrogel.Note that the acylhydrazone bond used here belongs to a class of dynamic covalent chemistry,which is mainly sensitive to pH value,formed through the reaction of active acylhydrazine and benzaldehyde group.And it was more favorable for pH 6.0 to form acylhydrazone bonds than that of other pH values.Therefore,the pH 6.0 could decline the swelling ratio of the hydrogel and increase its toughness.On the other hand,benzaldehyde-terminated PF127 is a thermoresponsive triblock copolymer,the net interactions between PPO blocks and water change with temperature,forming temperature sensitive micelles.As the temperature increases,the number of micelles increased generally,and micelles showed multiple size distribution eventually.Therefore,the increasing temperature resulted that the swelling ratio decreased significantly,while the toughness got remarkable.The impact of temperature on the micelles and pH values on acylhydrazone bonds have made this hydrogel a remarkable dual thermal and pH responsive material.Based on thermal-responsiveness,a pneumatically extruder-based 3D printing technique was conducted to fabricate complex constructs of good shape fidelity,showing perfect printability of this hydrogel.Apart from this,this hydrogel could stretch up to 120 times and its toughness could reach up to 1600 kPa.Accordingly,we speculate it may achieve significant breakthroughs if this remarkable hydrogel is used in biomedical related fields,especially in tissue engineering.