Piezoelectric Micro Probe Device for Mechanical Stimulation and Its Detection for Living Cells

As one of the cellular responses to external mechanical stimulation, it is presumable that the cell adjusts the cytoskeletal mechanical strength globally as well as locally. However, methodologies to validate the hypothesis are extremely limited and expensive. In this study, a new micro probe device, utilizing dynamic response of a piezoelectric vibrator, is developed, which works not only as a sensor to evaluate local stiffness, but also as an actuator to enforce local mechanical stimulation onto cultured living adhesive cells. The second mode of vibration of a beam vibrator with clamped-free boundary condition is utilized because of its stability and large vibration displacement at the vibrating free end. In order to excite the second mode of vibration, a stainless-steel plate was used for the vibrator. Two pieces of piezoelectric ceramics, one for excitation and the other for detection, are bonded onto the vibrator. In order to have contact with a minute living cell and to enhance sensing capability, a newly designed microprobe having stepped cross section was set at the free end of the vibrator. The experimental setup consists the developed micro probe device, two FFT analyzers to drive the micro probe device sensing and actuation function, a three-dimensional micromanipulator to operate the micro probe device, an inverted phase contrast microscope and some assisting devices. Focusing on an osteoblastic feature, which is sensitive to external mechanical stimuli, normal human osteoblast (NHOst) was chosen as a specimen. As the result of the experiment, depending on the cytoskeletal condition, the cell showed different behaviors against vibration stimulations with same amplitude but different frequency. This suggests that the overall actin cytoskeleton has an importance to initiate the local cellular response.