Study On The Preparation And Shape Memory Property Of Stimuli-responsive Crosslinked Polymers

Shape memory polymers(SMPs)have potential application in the biomedical fields due to lightweight,high elasticity and good cost-performance.Although SMPs with various functions have been widely reported,many of them are difficult to be applied in the biomedical fields because their trigger temperature is much higher than that of the human body.To solve this problem,preparing human body temperature-or near-infrared(NIR)light-triggered SMPs is an important way.In this work,a series of body temperature-or NIR light-triggered SMPs were prepared through covalent crosslinking and dynamic crosslinking strategies.The shape memory performance,the possible application fields and the possible mechanism of the prepared SMPs were investigated.(1)Poly(2-phenoxy ethyl acrylate-co-acrylamide-co-poly(ethylene glycol)diacrylate)(P(PEA-co-AAm-co-PEGDA))hydrogels containing different amount of PEA were synthesized using PEA and AAm as monomers,and PEGDA-700 as a crosslinker.The composition of the P(PEA-co-AAm-co-PEGDA)hydrogels was analyzed by FTIR,and the result confirmed that the synthesis was successful.The swelling behavior,dynamic thermomechanical property,mechanical property,crystallization behavior,network structure,cytotoxicity and the shape memory performance of the hydrogels were studied by gravimetric analysis,DMA,tensile test,WAXD,SEM,CCK-8 method,and bending recovery test,respectively.The results showed that the hydrogels exhibited considerable mechanical properties with a tensile strength of up to 5.1 ± 0.16 MPa,owing to the synergistic effects of the formed hydrophobic interaction and hydrogen bonding.Besides,the hydrogels exhibited good body temperature-triggered shape memory effect and biocompatibility.The application possibility of the P(PEA-co-AAm-co-PEGDA)hydrogels in embolization materials was studied,and it was found that the hydrogels could respond to human body temperature quickly and recover their shapes within 36 s,which could lead to a rapid block of the blood vessels.The results indicated that the obtained hydrogels have a good application prospect in this field.(2)Macromonomers PEGDA and polytetrahydrofuran diacrylate(PTHFDA)were prepared from biocompatible polyethylene glycol(PEG)and polytetrahydrofuran(PTHF)by esterification reactions,respectively.The structure of the macromonomers was characterized by 1H NMR.Using PEGDA and PTHFDA as monomers and pentaerythritol tetra(3-mercaptopropionate)(PETMP)as a crosslinker,poly(polytetrahydrofuran-co-polyethylene glycol-co-pentaerythritol tetra(3-mercaptopropionate))(P(PTHF-co-PEG-co-PETMP))networks were prepared through thiol-ene click chemistry.The swelling behavior,composition,thermal property,mechanical property and shape memory performance of the polymer networks were studied by gravimetric analysis,FTIR,DSC,tensile test and DMA,respectively.The results showed that PEGDA and PTHFDA were successfully synthesized The swelling behavior,crystallization behavior and shape memory performance of the polymer networks were dependent on the content of the PTHF segment and the PEG segment in the polymer.The reversible strain of the polymers was affected by the pre-stretch strain and temperature.The highest reversible strain of the sample P60-G40 exceeded 23.0%and showed good repeatability.The P60-G40 sample could stalely and reversibly shift between two different shapes by cycling the temperature between-15? and 37?,showing good application prospects in the field such as bionic materials,soft robots,and so on.Additionally,based on the hydrophilicity of the PEG segment and the body temperature-responsiveness of the PTHF segment,the application possibility of the polymers in adjustable esophageal stents was studied,and the result indicated a good application prospect of the polymer networks in this filed.(3)Polycaprolactone diol(PCL-OH)was synthesized and then reacted with hexamethylene diisocyanate(HDI)and dopamine hydrochloride in sequence to synthesize dopamine-terminated polycaprolactone(PCL-Dopa).The structure of the PCL-OH and the PCL-Dopa were characterized by 1H NMR.Fe3O4 NPs modified with oleic acid were prepared by coprecipitation,and the successful preparation was confirmed by XRD,FTIR,DLS and magnetic response analysis.The PCL-Dopa-Fe3O4 crosslinked polymer was prepared by using 10 wt%Fe3O4 NPs and 90 wt%PCL-Dopa.The thermal property,functional groups,morphology,element distribution,thermal stability,photothermal conversion performance,stress relaxation,plasticity and the shape memory behavior of the PCL-Dopa-Fe3O4 crosslinked polymer were studied by DSC,FTIR,SEM,EDS,TGA,NIR light,and DMA,respectively.The results showed that the PCL-OH and PCL-Dopa were successfully synthesized.The formation of crosslinking and the blocking effect of the Fe3O4 NPs could limit the crystallization of the PCL segment in the PCL-Dopa-Fe3O4 crosslinked polymer and reduced its crystallization temperature and melting point.The Fe3O4 NPs were distributed uniformly in the PCL-Dopa-Fe3O4 crosslinked polymer.The prepared PCL-Dopa-Fe3O4 crosslinked polymer exhibited a good photothermal conversion performance,and the surface temperature was depended on the output power of the NIR light.The stress relaxation tests show that the rate and extent of the stress relaxation of the PCL-Dopa-Fe3O4 crosslinked polymer could be significantly accelerated and increased by increasing temperature.The application possibility of the PCL-Dopa-Fe3O4 crosslinked polymer in personalizing vascular stents was explored,and the PCL-Dopa-Fe3O4 crosslinked polymer exhibited good plasticity,NIR light-and thermal-triggered shape memory property,showing a good application prospect of the obtained crosslinked polymer in this filed.(4)Dopamine-terminated PEG(PEG-Dopa)was synthesized by a stepwise reaction of PEG with HDI and dopamine hydrochloride.The structure of the PEG-Dopa was characterized by 1H NMR.The PEG-Dopa-Fe3+crosslinked polymers were prepared through mixing the PEG-Dopa aqueous solution with FeCl3 aqueous solution followed by adjusting the pH to form metal-ligand coordination crosslinking.The reversibility of the coordination bonds in the PEG-Dopa-Fe3+ crosslinked polymer networks was analyzed by using HC1 and EDTA solution treatment.The coordination structure,morphology,element distribution,thermal property,photothermal conversion performance,stress relaxation,plasticity and shape memory behavior of the PEG-Dopa-Fe3+ polymers were studied by UV-vis spectroscopy,Raman spectroscopy,SEM,EDS,DSC,NIR light and DMA,respectively.The results showed that the PEG-Dopa was successfully synthvaized.The tris-catechol-Fe3+ coordination played a dominant role in the construction of the crosslinking points in the PEG-Dopa-Fe3+ polymer networks.The PEG-Dopa-Fe3+ polymers exhibited a considerable photothermal conversion performance,and the surface temperature was significantly depended on the output power of the NIR light.The stress relaxation tests show that the rate and extent of the stress relaxation of the PEG-Dopa-Fe3+ polymers could be significantly accelerated and increased by increasing temperature.The application possibility of the PEG-Dopa-Fe3+ polymers in personalizing vascular stents was explored,and the polymers exhibited good plasticity,NIR light-and thermal-triggered shape memory property,showing a good application prospect of the obtained crosslinked polymers in this filed.