Preparation And Characterization Of Poly (N-isopropyl Acrylamide) Organic And Inorganic Composite Hydrogels

Articular cartilage was a complex active connective tissue on the surface of bone.It's hardly to repair itself if it damaged,and there was no effective treatment in clinic.Poly N-isopropylacrylamide?PNIPA?hydrogel was widely used in tissue engineering due to its biocompatibility and the lower critical solution temperature?LCST?which approaching the human physiological temperature.PNIPA hydrogel was a potential ideal material for cartilage scaffolds.However,the traditional chemical crosslinking PNIPA hydrogel had no phase change and injectability.Morever,the application and development of linear PNIPA hydrogel were greatly limited by its poor mechanical strength,slow response to external stimuli.In this paper,a series of organic-inorganic composite hydrogels with excellent properties and rapid response rate were prepared with nano-hydroxyapatite?nano-HA?and layered double hydroxides?LDHs?as inorganic crosslinkers.The research content of this paper consists of the following two parts:I.Preparation and study of high strength injectable thermosensitive hydrogel based on PNIPA/HA.?1?Nano-HA was prepared through coprecipitation method with?NH₄?₂HPO₄ and Ca?NO₃?₂ as precursors,added and changed the contents of PVP-K30.Nano-HA was characterized by particle size analyzer,FTIR,XRD,SEM and TGA.The results show that when the PVP-K30 content was 2 wt.%,nano-HA had largest axial diameter ratio and the narrowest particle size distribution which was about 350 nm.Nano-HA was a rod-like structure with single crystal.The thermal stability of nano-HA was well.?2?A series of PNIPA/HA composite hydrogels were prepared by free radical polymerization using NIPA as monomer,KPS as initiator,TEMED as accelerator,and nano-HA as crosslinking agent.The structure and thermomechanical properties of PNIPA/HA composite hydrogels were analyzed by FTIR,SEM,TGA,DSC,rheological analysis and hemolysis experiments.The results show that the PNIPA/HA hydrogels existed a phase transition from sol to gel,and the LCST was about 33°C.PNIPA/HA hydrogel was a non-hemolytic material with regular pore structure and good thermal stability.It had a wide linear viscoelastic region at 25°C,and the storage modulus G'was always larger than the loss modulus G''.When the temperature was above 33°C,the G'and G''of the hydrogels increase considerably,and the maximum of G'was about 24 kPa.The hydrogel was a non-Newtonian fluid with shear thinning properties and injectability.It had good application potential in cartilage tissue engineering scaffolds.II.Preparation and study of high strength and fast response thermosensitive hydrogels based on poly PNIPA/LDHs/HA.A series of PNIPA/LDHs/HA composite hydrogels were prepared to improve the injectability of PNIPA/HA hydrogels because of the high G'and poor fluidity at low temperature.?1?Mg-Al-LDHs was prepared by steady-state precipitation with Mg?NO₃?₂ and Al?NO₃?₃ as precursors,and the initial raw material ratio n[Mg]:n[Al]=3:1 with the pH=10.The LDHs crystals were characterized by FTIR,SEM,XRD and TGA.The results show that the LDHs crystals displayed a characteristic hexagonal sheet structure with a particle size of about 80 nm.It has uniform particle size,single crystal form and good thermal stability.?2?A series of PNIPA/LDHs/HA composite hydrogels were prepared by free radical polymerization using NIPA as monomer,KPS as initiator,TEMED as accelerator,nano-HA and LDHs as crosslinking agent.The structure and thermomechanical properties of PNIPA/LDHs/HA composite hydrogels were analyzed by FTIR,SEM,TGA,DSC,swelling/deswelling,rheological and hemolysis experiments.The results show that the addition of LDHs had no significant effect on the LCST and thermal stability of PNIPA hydrogels.PNIPA/LDHs/HA hydrogels had reversible swelling and deswelling properties.The rheological tests shown that the G”of PNIPA/LDHs/HA hydrogels is always greater than G',which indicated that the hydrogels were mainly liquid and fluidity.When the temperature was about the LCST,the G'increases rapidly.The maximum modulus of PNIPA/HA hydrogels was about 4.8 times,98 times that of PNIPA/LDHs hydrogels.These indicated that the addition of LDHs greatly improved the fluidity of composite hydrogels at low temperature,and greatly improved the hydrogel modulus after phase transformation,which was beneficial to obtain an injectable hydrogel system with high mechanical strength.It showed that the electrostatic attraction between the oppositely charged nanoparticles would produce good synergistic enhancement effect with hydrogen bonding.The obtained PNIPA/LDHs/HA hydrogels would have broad application prospects in tissue engineering and other fields.