Mechanically-excited surface waves on soft gels

Mechanically-excited Faraday waves appear as surface patterns on soft agarose gels. We experimentally quantify the dispersion relationship of these waves for frequencies ranging from 40Hz to 200Hz and over a range of shear modulus where the surface energy (capillarity) is comparable to the elastic energy of the solid. Rayleigh waves and capillary-gravity waves are recovered as limiting cases. Non-dispersive Rayleigh waves are observed on stiffer gels above a critical shear modulus. For our softest gels, we find that surface tension affects the dispersion relationship. Gravitational forces appear through the self-weight of the gel and are also important. We show the experimental data fits well to a proposed dispersion relationship. Our results are highly relevant to cell printing and tissue engineering technologies which utilize bioinks driven to pinchoff.