Study On Hydrogels With High Machenical Strength And Low Frictional Behavior

Hydrogels is the suitable material as the replacement of cartilages and tissues because of their low friction and frictional coefficient which is much lower than the hard solids. And the double network hydrogels, with high machenical properity, become ths best replacement of the cartilages and tissues. In this paper, the PAMPS-PAAm hydrogels were synthesised by UV photoinitiated polymerization, and the cross-linking degrees of the two networks both are different respectively. Taking the tests to invetigate the influence of cross-linking degree on PAMPS-PAAm DN hydrogels'tensile-strength and tear-strength, and testing the compressing strength of PAAm hydrogels. By measuring the equilibrium swelling ratios of these hydrogels, observing the morphologies of the inner network structures,and studying the dynamic mechanical poperties under the different temperitures and frequencies to analyse the mechanism of the PAMPS-PAAm hydrogels'high mechanical porperity. Meanwhile, investgating the influence of different loadings and temperatures on their frictional coefficients, studying the hydrogels'various frictional behaviors under different velocities, then analyzing this non-linear relationship between velocities and frictional coefficients, and at last, basing on repulsion-adsorption model to invetigate the hydrogels'frictional behavior on different substrates.It reveals that the tensile-strength of PAMPS-PAAm hydrogels increase with increasing of the first or/and second network's cross-linking degree, even when the equilibrium swelling ratio is 8, the tensile-strength can reach 1 MPa. When the hydrogel has the composition of PAMPS-PAAm 1-4-0.1+2-0.01-0.01,"necking"appears during the procession of stretching. According to the tearing tests, their tear-strength depends on the first network'structure. For the PAAm hydrogels, with the increasing of cross-linking degree, the compressive strength increases, Mc decreases, andχ1changes. The morphologies of PAMPS-PAAm dry gels reveal the second network structure making the hydrogels get the higher mechanical strength, because the networks of hydrogels become more stable and the cells'distribution become more uniform.When the sliding velocity is 100mm/min, loading is 2N and the temperature is 37℃, the frictional coefficient of PAMPS-PAAm (1-4-0.1+2-0.01-0.01) hydrol sliding on the steel is 0.01, which is much less than the frictional coefficient of solids(>1). The hydrogels'frictional coefficient increases with the increasing of temperature and loading. When the sliding velocity is low, frictional coefficient mainly comes from the elastic resistance of the polymer chains which adhere on the substrate; and when the sliding velocity is high, it mainly comes from the fluid resistance of water dynamic layer between the hydrogel and substrate. The frictional coefficient is less than the two situations when the sliding velocity is the intermediate value, because of the water lubrication layer. Comparing the frictional coefficients of the hydrogels sliding on these substrates, that is PTFE, Steel, PET, Glass, the results show that the hydrogels sliding on the hydrophilic substrates follows the absorption model, but when they slid on the the hydrohobic substrate, the repulsion phenomennon should be deeper studied.