The Preparation And Properties Of PH-responsive Microgel

pH-responsive microgels can occur the volume change at different pH values,the high concentration of microgel dispersions can form gel with good biological compatibility and certain mechanical strength by control the pH value.The gel can transform the injectable material,when it enters the organism form gel with mechanical strength in high pH value.Microgels have a great application potential in the tissue engineering scaffolds 'material due to its unique properties,with has became the present research focus.Methyl methacrylate(MMA),hydroxyethyl methacrylate(HEMA)and methacrylic acid(MAA)were used as comonomers.Ethyleneglycol dimethacrylate(EGDMA)was used as crosslinker,dodecyl sulfate was used as emulsifier and ammonium persulfate as initiator.The poly(MMA/MAA/HEMA)microgel were prepared by semi-continuous seeded emulsion and pre-emulsification emulsion polymerization.The polymerization was determined according to the gel rate.The chemical structure and morphology of microgels were characterized through Fourier Transform Infra Red Spectrophotometer(FTIR)and Transmission Electron Microscope(TEM);the particle size and distribution of microgel characterized by dynamic light scattering(DLS);some factors affecting the particle size were studied,such as initiator and emulsifier content,the best emulsifier content was determined combined with the emulsion stability.The property of microgel(nMMA:nMAA:nHEMA=2:1:1)was most stable when the concentration of initiator and emulsifier were 1 wt%and 2 wt%respectively.The photos by TEM showed that the microgel was core-shell structure and diameter of microgel was 90 nm.The carboxyl content of microgel(nMMA:nMAA:nHEMA=2:1:1)was 25 wt%which approach to the actual value 26 wt%,and its pKa was 6.75.The pH sensitive behaviour and the swelling property were investigated by UV-Vis sepctrophotomrtry(UV-Vis)and Dynamic Light Scattering(DLS),the equilibrium swelling time of microgel was Measured,and the turbidity of microgel dispersion were studied in different salt concentrations.The results show that the microgel particles in the medium water can quickly reach the swelling equilibrium.The turbidity of microgel dispersions performanced difference at different pH,and the absorbance of microgel dispersions changed at pKa.The hydrodynamic diameter of microgel was from 180 nm into 1100 nm in different pH.These results suggest that the microgel has a good pH response and swelling properties,the maximum swelling ratio of microgel can up to 180.The turbidity of microgel changed obviously at different salt concentrations.The swelling of microgel has been shielded in sodium chloride solution.The microgel dispersion began to flocculation when the sodium ion concentration higher than 0.19 mol/L.Micogels with different contents of HEMA were prepared,a series of phase diagrams were researched by tube inversion measyrements.The results show that the critical minimum concentration increased and critical maximum pH decreased when the dispersion gelatinized.The mechanical strength of microgel dispersions transformed to colloidal gels were investigated by Lamina rheometer.It shows that storage modulus of gels increase with increasing HEMA contents and the introduction of hydroxyl increased hydrogen bonding combining site,the important factor of network structure stability and mechanical gel strength is hydrogen bonding.The storage modulus decreased with increasing temperature.The storage modulus of colloidal gel(nMMA:nMAA:nHEMA=2:1:1,15 wt%)is the best which reached 20000Pa.