Synthesis And Properties Of Stimuli-responsive Intelligent Hydrogel

Stimuli-responsive intelligent polymer hydrogels as soft and wet three-dimensional cross-linked networks materials can convert external stimuli such as temperature,p H,electric fields,magnetic fields and near infrared lasers into volume change and other characteristics.These hydrogels have been investigated due to their exceptionally promising potential in a wide range of applications,such as drug delivery,wound healing,tissue engineering,actuators,etc.It is well known that the traditional Poly（N-isopropylacrylamide）（PNIPAm）hydrogel’s volume phase transition temperature is close to human body temperature due to their hydrophilic amide group and hydrophobic isopropyl group,it has been shown to be useful in soft actuators,optical switches,wound dressings and drug delivery.In this paper,the composite hydrogel（P（AMPS-NIPAm）/CS）was prepared by radical copolymerization with NIPAm,2-acrylamido-2-methylpropanesulfonic acid（AMPS）and chitosan（CS）as raw materials.By balancing the mass ratio between NIPAm,AMPS and CS,the optimal feed ratio of the P（AMPS-NIPAm）/CS hydrogel with high mechanical properties and effective self-healing properties is determined,and its temperature sensitivity,swelling property,mechanical strength and self-healing properties were studied.Afterwards,we introduced acrylamide（AM）into the P（AMPS-NIPAm）/CS hydrogel system to synthesize a bilayer hydrogel（BLGEL）.The freeze-thaw bilayer hydrogel（F-BLGEL）was obtained after freeze-thaw treatment of the BLGEL hydrogel.The deformation-recovery and shape memory abilities could be simply realized by adjusting the temperature of solution and geometry parameters of the F-BLGEL hydrogel.Moreover,the driving shape transformation mechanisms of F-BLGEL hydrogel were discussed,and excellent anti-fatigue performance was also confirmed by repeated deformation and load-bearing.1.For different formulations of the synthesized P（AMPS-NIPAm）/CS hydrogel samples,the solid content was maintained at 20%.The mechanical strength of P（AMPS-NIPAm）/CS hydrogel is the highest when the mass ratio of（AMPS+CS）/NIPAm is 0.6:1.When the mass ratios of AMPS/CS are between 1:1 and1.8:1,the self-healing properties of hydrogels are the best.2.The mass ratio of AMPS/CS has significant influence on the temperature sensitivity of hydrogel.The LCSTs of AMPS/CS-1.2:1,AMPS/CS-1.4:1,and AMPS/CS-1.6:1hydrogel were around 16℃,37℃,and 58℃,respectively.AMPS/CS-1.8:1 hydrogel was not temperature-sensitive.3.The AMPS/CS-1.4:1 hydrogel’s network is more regular,its swelling rate is the fastest.The equilibrium swelling ratios of AMPS/CS-1.2:1,AMPS/CS-1.4:1,AMPS/CS-1.6:1 and AMPS/CS-1.8:1 were 4.99,30.33,122.13 and 178.53 g/g,respectively.4.The hydrogels with different proportions of AMPS/CS showed favorable properties with tensile fracture strength ranging from 87 KPa to 95 KPa,the elongations at break from 200%to 235%.Crosslinking density also has a significant impact on material properties.The maximum compression strength is 4.0 KPa at AMPS/CS-1.4:1.5.The self-healing efficiencies were 81.74%,98.51%,65.01%and 77.34%when the mass ratios of AMPS/CS were 1.2:1,1.4:1,1.6:1,and 1.8:1,respectively.Among them,AMPS/CS-1.4:1 hydrogel had excellent self-healing properties.6.The bending deformation-recovery process of the bilayer hydrogel（BLGEL）is related to the thickness ratio of the two-layer hydrogel.The deformation angles increase quickly to almost 360^o within 6 min,7 min and 16 min,and complete recovery occurs at 30 ^oC in 160 min,70 min and 45 min when the thickness ratios of top layer to bottom layer were 0.5:1,1.0:1 and 1.5:1,respectively.7.The BLGEL hydrogel has excellent structural stability and robust mechanical property.BLGEL hydrogel can tolerate extreme external conditions such as long-term freezing at-18℃（three months）and long-term soaking in deionized water（three months）.BLGEL hydrogel can still maintain structural integrity without any interface delamination,indicating that there is strong interface adhesion between the two layers.8.The F-BLGEL_0.5:1,F-BLGEL_1.0:1 and F-BLGEL_1.5:1 hydrogels generated a superfast self-bending movement and formed rolls with a bending angle of 360^o in just30 s,30s and 90s,respectively.Obviously,compared with the BLGEL hydrogels,the times required for the F-BLGEL hydrogels deform to 360^o were shortened by 92%,93%and 91%,respectively.9.The deformation recovery degree of F-BLGEL_1.0:1 hydrogel can be precisely controlled.10.The F-BLGEL hydrogel has excellent fatigue resistance in the five-cycle test.After deformation,F-BLGEL_1.0:1 hydrogel can bear the object that is 25 times the weight of the dry hydrogel,and readily and repeatedly lifted up to 1.2 cm and lasted for at least 2 h.11.As an intelligent and controllable deformation material,F-BLGEL hydrogel is an ideal material for building an intelligent water temperature alarm switch.