Mechanical Characterization Of Hydrogels Using A Novel Micromanipulationrig

Hydrogels has a wide applications,such as slowly released drugs,tissue engineering and scaffold engineering.In thesis a novel micromanipulation rig is applied to mechanically characterize whey protein isolate(WPI)hydrogels.Three indenters,whose diameters are 0.2~1 mm,are applied to indent WPI hydrogels,which are submerged in 0.1~0.6 M NaCl solution until equilibrium before tests.It shows that the calculated shear modulus does not change significantly with indenter sizes.When [NaCl] is lower than 0.2M,the shear modulus changes significant with [NaCl].When [NaCl] is higher than 0.2M,shear modulus does not change significantly.Due to the visco relaxation,the force keeps relaxing and no constant force is achieved in a long term.Poroviscoelasticity fitting choosing the minimum MSE corresponding time as the final relaxation time shows that the diffusivity do not change significantly for different indenters.For visco properties,relaxation time and extent for 1mm is significantly higher than 0.2 and 0.5 mm indenters,which is mainly due to numerical fitting.For WPI hydrogels with 0.15 M NaCl inside swollen in 0.15 M NaCl solution until equilibrium,indentation and relaxation experiments with micromanipulation rig shows that the indentation force versus displacement curve is not completely linear due to the relaxation during indentation.After indentation there is a sharp decline of the force,which will keep decreasing in a long term and no constant force is achieved,mainly due to visco relaxation.WPI hydrogel indentations in dynamic swelling show that at low pH swelling,the shear modulus gradient in time scale is obvious but not in indentation depth scale.At high pH dynamic swelling,the shear modulus decrease shapely in the initial dynamic swelling and later on the shear modulus gradients in time scale will not be obvious.At low pH there exists a weak layer between the hard gel and the solution.In this weak layer indentation,no force is found.The thickness of the weak layer keeps nearly constant.WPI hydrogels dynamic swelling in water shows the swelling will not stop and the shear modulus will keep decraeasing,and its gradient in time scale is becoming smaller and smaller.