Development and mechanical validation of an in vitro system for bone cell vibration loading

Vibration loading, both low magnitude and high magnitude at high frequency, has been demonstrated to have an anabolic effect on bone cells. The study of the mechanotransduction, the process by which mechanical loadings are detected by cells and converted in a chemical signal, is made accessible through the use of in vitro loading system. The aim of an in vitro loading system is to recreate the forces acting in the cell microenvironment. The goal of this study was to develop and mechanically validate a vibration loading system able to engender sinusoidal vertical vibration at different combinations of magnitude (0.3 g, 1 g, and 3 g) and frequency (30 Hz, 60 Hz and 90 Hz). A system like this can be therefore employed to study cell response to high and low magnitudes at high frequencies, thus providing a comprehensive evaluation of bone cell mechanotransduction. The mechanical validation, that is the characterization of the right loading input to the system to obtain the desired stimulation on cell culture, was performed in two different methods: open-loop and closed-loop mode. The results obtained in the open-loop mode showed a good intra-day repeatability of the measurements with values of index of dispersion always lower than 0.6%. While in the closed-loop mode a systematic search was implemented to reach the optimal amplitude stimulation. The vibration signals acquired on long-term test following the systematic search showed a good stability with index of dispersion always lower than 1%. Following the mechanical validation, the system was used to stimulate osteoblast like cells (Saos-2) with vibration loading of nine combinations of magnitude and frequency and the cell proliferation was studied 24h after the treatment by cell counting. Our preliminary results showed that no alterations in the proliferation were induced by 90 Hz vibration loading. On the other hand, small modulations in the proliferation were reported for lower stimulation frequency, being statistically significant when using 0.3 g of amplitude at 30 Hz.