Minimally Invasive Micro-Indentation: mapping tissue mechanics at the tip of an 18G needle (vol 7, 2017)

Upon contact with the tissue, the feedback-controlled piezoelectric transducer moved the probe forward (thus bending the cantilever) until a predefined value for the applied load (~300) by the cantilever was reached. This load was kept stable for at least 60 s to allow for dissipation of the tissue. Afterwards, the load was oscillated sequentially (amplitude ~10) for a finite number of increasing frequencies (5 periods each), logarithmically spaced between 0.05 Hz (0.5 Hz for the NP measurements) and 10 Hz. During all indentations it was ensured that the indentation depth stayed within the linear viscoelastic regime and that indentation depth was much smaller than the bead radius (the maximum static indentation depth was 40).