The measurement of global shortening as a new parameter to evaluate bone specimen response to uniaxial loading: Length change measurement for bone tissue specimens

Mechanical load is nowadays considered one of the factor mainly affecting bone tissue properties, both as architecture and functionality. Mechanotransduction is the capability of cells to translate mechanical stresses into biochemical signals, and several studies performed on mouse models demonstrated that also bone cells show a high responsiveness to mechanical stimuli. To date, bone cells mechanotransduction is mainly investigated in animal models, by the use of organ cultures or directly in vivo, and the actual strains induced by the external loads are measured through the use of micro strain gauges placed on the tibia mid-diaphysis. With the aim of proposing a new parameter to come along with the measurement of the actual strains, we exploited the capability of tibial global shortening to return useful information. We employed an experimental system based on a dual mode actuator/transducer with an adequate force range and a high length resolution to retrieve the small shortening of the bone specimens subjected to uniaxially load. Preliminary results showed that the tibia global shortening has a linear relationship with the increasing load, in the range of force usually used in these studies. In addition, the tibia global shortening showed the capability of gathering the changes occurring in the bone tissue mechanical properties when subjecting the specimens to loading signals of different frequencies. When tested with load signals of a frequency equal or higher than 1 Hz, in fact, the bone specimens showed a more rigid behavior. At 9 N of load, for example, the average value of tibia global shortening measured at 0.1 Hz is, on average, 18 % higher than when measured at all the other tested frequencies.