Preparation,Structures And Properties Of Multi-urea Based Strong Supramolecular Hydrogel And Elastic Macroporous Polyacrylamide Chemical Hydrogel

Over the past decades,high strength hydrogels have received growing interest due to their great potential for extended use in load-bearing soft tissues such as tendon,cartilage,and blood vessels,ect.However,most of the reported strong and tough hydrogels were prepared by in-situ solution（co）polymerization within special mould and were chemically cross-linked,and thus its shape was set at the time of gelation.Strong,tough and recyclable hydrogels in different forms that can be generated by different methods according to different practical applications still remain an intrinsic bottleneck.In view of this,in this work,we are aiming to introduce multi-urea linkages into the backbone of linear polyurethane-urea（PUU）copolymers.Various manufacturing methods（such as solution casting,thermo-compression,electro-spinning,wet-spinning,microfluidic spinning,etc.）were applied to prepare ultra-strong hydrogels or stretchable hydrogel fibers with nano-,micro-or macro-scale diameters.Moreover,the linear copolymers could also be easily recycled.Biocompatible and bioactive hydroxyapatite（HAp）nanocrystals hybrid hydrogel films still show comparable mechanical strength with the pristine hydrogels.The hybrid strong and tough hydrogel will greatly enhance its application in load bearing biomaterial market.Main contents of this thesis are as follows:1.Firstly,multi-urea segmented polyurethane-urea（PUU）copolymers were synthesized by a“one-pot with two-step”method.GPC results demonstrated that high molecular weight linear PUU copolymers were successfully synthesized.The results of FT-IR revealed that the existence of hydrophobic multi-urea linkages in the backbone of the copolymers greatly enhanced the H-bonding interaction of the PUU copolymers.TGA results showed that the obtained copolymers have good thermal stability.2.The synthesized PUU copolymers were then transformed into supramolecular hydrogels by solution-casting method.The obtained the PUU supramolecular hydrogels show superior mechanical strength with 2-14 MPa tensile strength,600-1400%elongation at break,0.5-6 MPa tensile modulus,10-60 MJ m^-3 extremely high toughness and 35 kPa-180 kPa storage modulus.These hydrogels also show relative high equilibrium water content（55%-75%）.Due to the linear character of the multi-urea linkage segmented PUU copolymers,various manufacture approaches,including compression molding,solution casting and spinning methods can be used to yield macroscopic hydrogel films or fibers with diameters ranging from macro-,micro-to nanoscale.Moreover,electronic spinning fibrous hydrogel film and the wet-spinning macro-scale hydrogel fiber also exhibited excellent stretchable ability.Biocompatible and bioactive hydroxyapatite（HAp）nanocrystals hybrid hydrogel films still show¹000%elongation at break with tensile strength up to⁵ MPa.In addition,the present material can also be easily recycled from either the fully swelling or the dehydrated hydrogel for further processing or regeneration without scarifying their mechanical performance.3.On the other hand,macroporous hydrogels,which are often made by cryo-gelation technique and named as cryogels,have great potential applications in cell culture scaffold,cell separation matrix,drug delivery and tissue engineering materials,etc.due to their special interconnected pores,tissue-like elasticity and fast stimuli-sensitive response.However,most reported macroporous cryogels are still lack of stretch ability.Based on the reactive micelle copolymerization method developed in our group for preparing highly resilient and stretchable hydrogels,stretchable and elastic macroporous polyacrylamide（PAM）cryogels were successfully prepared by using polymerizable polyurethane macromolecular surfactant as the multi-functional crosslinker.Moreover,different influence factors on the macroporous structure of the polyacrylamide cryogels were studied and characterized.