Hydrotalcite-based Double-network Nanocomposite Hydrogels:design,Synthesis And Performance Studies

Nanocomposite hydrogels are superior to traditional hydrogels in mechanical properties and are therefore receiving more and more attention.Most of the nanocomposite hydrogels have been reported to be prepared by one-step in-situ polymerization.The weak van der Waals forces and hydrogen bonds between the nanomaterials and the polymer chains make the nanoparticles easily lose during long-term use.The hydrogel is poor in stability and the crosslinking point is easily broken.In view of the above problems,we report here a new type of double-network hydrogels based on tri(hydroxymethyl)aminomethane modified layered double hydroxides(Tris-LDHs).The first network of the hydrogel is formed by Schiff Base reaction between the oxidized dextran and Tris-LDHs.While the second network is constructed by introducing sodium 2-acryl amido-2-methylpropane sulfate(AMPS-Na)and acrylamide(AM)/N-iso propyl-acrylamide(NIPA)monomers via electrostatic and hydrogen bonding interactions,repectively.The mechanical properties of the resulting double-network nanocomposite hydrogels are systematically studied,and the on-demand drug delivery of the NIPA hydrogels is investigated in detail as well.The contents of this thesis are as follows:1.By using the Schiff Base reaction,amino-containing Tris-LDHs are decorated onto the oxided dextran(ODex)to help stabilize the inorganic nanosheets in water.The resulting complex has been fully characterized by techniques such as NMR,XPS,FT-IR,XRD,etc.The second network of the hydrogel is generated by free radical polymerization of AMPS-Na and AM monomers in the mother liquor of the first network.The effects of the monomers and ODex on hydrogel morphology,swellability,and mechanical properties are explored by finely tuning the AMPS-Na/AM ratio,and the amount of ODex.Our results show that with the incorporation of AMPS-Na monomers,the hydrogel possesses a fracture strain as high as 3000%,compressive stress of 10.81 MPa,and swelling ratio of 1140.In addition,polarized optical microscopy measurements demonstrate that the LDH nanosheets are uniaxially oriented,and the hydrogel shows anisotropic color changing upon stretching.These results lay a good foundation for the application of LDH-based hydrogels in tissue engineering.2.By replacing AM monomers with NIP A,a thermo-responsive LDH-based hydrogels is prepared.A series of characterizations have been adopted to investigate the morphology,structure,response performance,mechanical and drug-releasing properties of the hydrogel.It is found that the addition of ODex and AMPS can significantly shorten the response time of the hydrogel.And drug-releasing experiments under the physio-logical conditions reveal that ODex and AMPS can help to increase the loading amounts and release rate of drugs such as anionic naproxen,neutral ciprofloxacin,and cationic methylene blue.The releasing ratio can even reach 80%by optimizing the dosage of ODex and AMPS.Therefore,we provide here a controllable pathway for on-demand drug delivery using hydrogels as carriers.