Estimation of living tissue constitutive law is needed for patient-specific simulations during surgery. However, this task remains very challenging. The device used for characterisation must undergo sterilisation and must give real-time results to characterise tissues that can only be accessed in the operating room (e.g. brain tissues). This paper presents the light aspiration device for in vivo soft tissue characterisation (LASTIC) device that was designed to fulfil these expectations. The paper compares the axisymmetric 2D model with a 3D model of LASTIC's aspiration procedure.