Preparation And Application Of NIR Responsive PNIPAM Nanocomposite Hydrogel

As a typical thermosensitive hydrogel,poly-N-isopropylacrylamide（PNIPAM）hydrogel has a volume phase transition temperature（VPTT）close to human body temperature,so it has received extensive attention in the field of biomedical materials.The photothermal conversion reagent is a material that can convert light into heat.Combining the photothermal reagent with PNIPAM can construct a photo-responsive hydrogel.Compared with thermal stimulation,light can be turned on and off faster,and the operation is convenient.Accurately realize fixed-point timing control.Graphene is a photothermal reagent with excellent performance.This material can convert near-infrared light（NIR）into heat.Compared with other wavelength light sources,NIR light sources have a deeper incidence depth and are less harmful.In addition,Fe₃O₄ nanoparticles can not only convert NIR into heat,but also impart magnetic properties to the hydrogel.In addition,the mechanical properties of PNIPAM hydrogels are also a direction that many researchers pays attention to.Different cross-linking methods give PNIPAM hydrogels different mechanical properties.Laponite nanomaterials are considered to be one of the best physical crosslinking agents in the preparation of PNIPAM hydrogels.In this work,N,N’-methylene bisacrylamide（BIS）or Laponite is used as the crosslinking agent,and graphene oxide（GO）or Fe₃O₄ is used as the functional component,prepared by in-situ free radical polymerization.Near-infrared light responds to PNIPAM hydrogel,and its related properties and application have been preliminary explored.The main content and results of this work are as follows:（1）Using NIPAM as the monomer,BIS as the chemical crosslinking agent,and introducing GO as the photothermal conversion reagent,the accelerator N,N,N’,N’-tetramethylethylenediamine（TMEDA）and initiator are used.Under the action of potassium sulfate（K₂S₂O₈,KPS）,BIS-PNIPAM/GO hydrogels with both temperature sensitivity and photothermal properties were prepared by free radical polymerization.The effect of BIS content on the fracture extension of BIS-PNIPAM hydrogels was investigated.The influence of length rate and tensile strength,and the influence of GO content on the related properties of BIS-PNIPAM/GO hydrogels,and then a series of characterizations on the tensile properties,photothermal properties,and microscopic morphology of the hydrogels.The results show that when the dosage of BIS is 0.6 mg/m L,the elongation at break and the tensile strength of BIS-PNIPAM hydrogel reach the maximum,which are 2447.81%and121.43 KPa,respectively;when the content of GO（Based on monomer,the same below）,the mechanical properties of the composite hydrogel prepared at 0.53%are the best,and its tensile strength can reach 30 KPa or more;then the VPTT and NIR of the composite hydrogel are characterized,Finally,the photothermal effect of the optimal content of BIS-PNIPAM/GO-0.53hydrogel is studied.The VPTT of BIS-PNIPAM/GO-0.53 hydrogel is about 34℃;under NIR irradiation,BIS-PNIPAM/GO-0.53 hydrogel can be heated from 24.9℃to 52.6℃within 5 minutes,the temperature increased by 27.7℃;due to the temperature sensitivity and photothermal effect of BIS-PNIPAM/GO-0.53 hydrogel,it shows that the hydrogel is in NIR non-contact light control to achieve the potential of material driving.（2）Using Laponite as the crosslinking agent and GO as the light-to-heat conversion factor,NIR-responsive Laponite-PNIPAM/GO hydrogels were prepared by in-situ polymerization of NIPAM.The effect of Laponite content on the elongation at break and tensile strength of Laponite-PNIPAM hydrogel was investigated,and the effect of GO content on the related properties of Laponite-PNIPAM/GO hydrogel was investigated.The VPTT and NIR responsiveness of the prepared hydrogel were characterized,and the application of Laponite-PNIPAM/GO hydrogel in light-controlled fluid switch and light-controlled desorption was explored.The results show that the introduction of GO can enhance the mechanical properties of the hydrogel.When the content of Laponite and GO are 12.0%and 0.21%,respectively,the Laponite-PNIPAM/GO-12.0-0.21 hydrogel has higher strength and Good toughness,the tensile strength is 123.98 KPa,and the elongation at break can reach 1181%.The VPTT of Laponite-PNIPAM/GO-12.0-0.21 hydrogel is around 36℃;under NIR irradiation,the Laponite-PNIPAM/GO-12.0-0.21 hydrogel can be heated from 20.3℃to48.5℃in 5 minutes,and the temperature rises by 28.2℃.Because of its temperature sensitivity and photothermal effect,it has demonstrated its potential as a light-controlled fluid switch and light-controlled desorption.（3）In order to endow the hydrogel magnetic properties,the Fe₃O₄@Laponite nanoparticles were prepared,and then Fe₃O₄@Laponite and Laponite were used as the crossing agents to prepare the magnetic hydgrogel（Fe₃O₄@Laponite-Laponite/PNIPAM）.The effects of Laponite and Fe₃O₄@Laponite content on the elongation at break and tensile strength of hydrogels were investigated.Afterwards,the VPTT and NIR responsiveness of the prepared hydrogels were also characterized,and Fe₃O₄@Laponite-Laponite/PNIPAM was hydraulically coagulated.The application of glue in the light-controlled fluid switch in the controlled release of drugs has been initially explored.The results show that when the content of Fe₃O₄@Laponite nanoparticles is 6.8%and the content of Laponite is 8.0%,the mechanical properties of the prepared composite hydrogel are the best,the elongation at break is 1452.83%,and the tensile strength is 63.04 KPa;The VPTT of Fe₃O₄@Laponite-Laponite/PNIPAM hydrogel is around 36℃;in addition,under NIR irradiation,Fe₃O₄@Laponite-Laponite/PNIPAM hydrogel can heat up from 20.5℃to 55.8℃within 5 minutes,and the temperature rises by 35.3℃;Due to the temperature sensitivity and magnetocaloric effect of Fe₃O₄@Laponite-Laponite/PNIPAM hydrogel,the magnet light-controlled fluid switch valve has shown potential in the controlled release of drugs.