Mechanical properties of silica hydrogels prepared and aged at physiological conditions: testing in the compression mode

The mechanical properties for silica hydrogel prepared at physiological conditions are reported in this paper. The mechanical testing was performed in the compression mode determining the mechanical characteristics as a function of aging time in TRIS buffer up to 14 days. In addition to a typically used gradient method for Young’s modulus determination from the stress–strain curves, a new phenomenological model was proposed to describe the experimental data. The mechanical properties were stabilized after 2 days of aging, which was concluded from an increase in Young’s modulus between 90 and 400 kPa, an increase in stress at break between 50 and 100 kPa and by a decrease in relative deformation at break from 0.26 to 0.16. The height of samples was constant in the first three days of aging followed by a decrease by ~20%. Dissolving of silica hydrogel characterized through determination of silica content in TRIS buffer employing the molybdenum method was not found to be responsible for this phenomenon. The phenomenological model is proposed to be used for a reliable evaluation of mechanical properties of silica as well as other hydrogels exhibiting low Young’s modulus.