An indentation apparatus for evaluating discomfort and pain thresholds in conjunction with mechanical properties of foot tissue in vivo

The mechanical properties of human foot tissue in vivo as well as di scomfort and pain th resholds are important for various applications. In this study, an apparatus for measur- ing the d iscomfort and pain th resholds and the mechanical properties of hu man t issues is presen ted. The apparatus employs a stepper motor that controls the indentation speed, as well as a load ce ll and potentiometer that determine the corre- sponding reaction force and tissue deformation (displacement), respectively. A LabVIEW progr am (Lab VIEW 8, Natio nal Instruments Corporation; Austin, Texas) was developed to con- trol the indentation via a dat a acquisition card. The apparatus can accommodate indentor displacements up to 35 mm and can im part forces up to 150 N at a controlled indentation speed in the range of 0 to 10 mm/s. Tests showed that the displacement measurement error is 0.17 mm in the nominal range (0.5% in the full scale) and the mea surement error of force is 1.6 N in the nominal range (1.1% in the full scale). Experimental results indicate that the apparatus is reliable and flexible for measur- ing the mechanical properties of foot tissue in vivo in conjunc- tion with pain and discomfort thresholds.