Preparation And Properties Research Of The Thermally Respensive Shape Memory Hydrogels Based On Hydrogen Bonding

Shape memory hydrogel(SMH)are intelligent multi-functional hydrogel,which have the ability to “memorize” a macroscopic(permanent)shape,can be manipulated and “fixed” to a temporary shape under certain conditions,and then later relax to the original,that combine with the intelligence of shape memory material and the softness,biocompatibility of the hydrogel,have a huge development space in biomedical fields the present and future.Due to the high water content of hydrogels,more of the covalent or non-covalent chemical,such as hydrophobic association,metal-ligand,dipole-dipole,the role of subject and object,hydrogen bonding and so on,are often used to design the shape memory,hydrogel.Among them,hydrogen bonding action as an important force in the organism,get more attention and research.In this paper,we designed and attempted to prepare the shape memory hydrogel by hydrogen bonding.Polyvinyl alcohol(PVA)contains many hydroxyl groups,which should be qualified to make SMHs.In this paper,polyvinyl alcohol hydrogels were first prepared by means of the simple chemical cross-linking and the hydrogen bonding formed between the chains of polyvinyl alcohol were used as the reversible phases attempting to enable the shape memory function and found that the temporary shape of the PVA hydrogel can not be fixed in this case.So,the PVA hydrogel was further subjected to the "freezing-thawing" treatment to promote the formation of the hydrogen bonding,giving rise to a "microcrystalline" region,as a consequense,the shape memory PVA hydrogel was obtained;The effects of crosslinker concentration on the mechanical properties of hydrogels were discussed,In addition,carbon dots was prepared via a simple "one pot " method using chitosan as carbon source and the hydrogel with the dual functions of fluorescence and shape memory was obtained as well by introducing carbon nanodots into the shape memory PVA hydrogel at a suitable crosslinker concentration;The hybrid hydrogel exhibited strong fluorescence emission at the excitation wavelength of 380 nm and its shape fixing(Rf)and the recovery ratio(Rr)are be able to reach > 90% when the PVA mass fraction was 25%,the freezing time was 6h,the crosslinker concentration was 0.25%;the fixing ratio of hydrogel will increase when the number of times of "freezing-thawing" are increasd.In order to achieve stronger hydrogen bonging interaction for shape memory hydrogel,the 2-amino-4-hydroxy-6-methylpyrimidone(MIS)and 2-Isocyanatoethyl methacrylate(ICEMA)were used to prepare 2-ureido-4[1H]-pyrimidinone methacrylate(UPyMA),which can form a strong quadruple hydrogen bonding between molecular;then UPyMA,N'Ndimethylacrylamide(DMA)and N'N-dimethylene bisacrylamide(MBA)were used to prepare the thermally responsive shape memory hydrogel through the free random copolymerization.The structure of 2-ureido-4[1H]-pyrimidinone methacrylate(UPyMA)was characterized by Fourier Transform Infrared spectroscopy(FTIR)and 1H-NMR spectrum.The effect of crosslinker concentration on shape memory properties was discussed preliminary;The effects of UPyMA content on the water content,mechanical strength and shape memory properties of the hydrogel were discussed in detail when the cross-linking agent mass fraction is 4%.When the mass fraction of UPyMA is 50%,the water content at equilibrium is 50%.With the increase of UPyMA content,the number of hydrogen bonding increases and the fixation rate increases.When the mass fraction is 50%,the fixation ratio and recovery ratio are more than 90%;The effects of temperature on the fixing ratio(Rf)and recovery ratio(Rr)of shape memory were also discussed,the higher the transition temperature,the higher the fixing ratio;the lower the fixed temperature,the higher the fixing ratio at the same deformation temperature.For thermally responsive shape memory materials,in addition to the direct heating,light is another unique alternative to induce heat generation to stimulate shape recovery of shape memory polymers.Through the UV-visible-near-infrared analysis,a strong absorption band centered at ~1454nm of water was found,and the solid laser equipment with the corresponding wavelength(1467.6nm)is custom-made.The water was used as the photo-thermal conversion material to induce heat and stimulate the shape recovery of the hydrogel.The effect of the laser power on the hydrogel temperature was discussed,for the same hydrogel,the greater the power,the faster the hydrogel temperature increasing during the same time;The effect of the water content on the hydrogel temperature also was discussed,When the recovery ratio was 50%,the irradiation time increased with the increase of UPyMA content(20%,30%,40%,50%),which were 30 s,50s,62 s and 87 s respectively.The time required to return to the original shape increases with the increase of UPyMA content,which were 60 s,90s,105 s and 150 s respectively.