Air Cavitation in Gel

              This video shows a typical cavitation event in a hydrogel where the pressure at the tip of the syringe needle is increased via a syringe pump compressing the air in the system.  As you can see, there is little to no cavity expansion before the critical point is reached and within less than 200 ms, an instability occurs in the form of a cavitation.  The pressure at which the cavitation occurs, P, can be directly related to the modulus of the material, where the P ~ 5E/6, where E is the linear modulus.