A pioneering experimental investigation of a novel in-situ dynamic characterization of the tensile/compression stress-strain mechanism on human plantar soft tissue

We have conducted the first in-situ and in-vivo dynamic mechanical test on human plantar soft tissue. A dynamic mechanical analysis (DMA)-like device has been invented to perform the in-situ and in-vivo stress-strain tests on living plantar in order to characterize the material mechanism of biological soft tissue, whereas it is nearly impossible to prepare a sample from a living body for classical tests. A series of pioneering tests of tensile/compression on the heel of ten volunteers are reported, with the reference of tests on mimic foot model made by silicon rubber, standard silicon rubber brick sample, and finite elementary analysis. In addition to demonstrating the effectiveness of the device and approach, interesting correlations between the results and clinic data were found, suggesting considerable potential for the invention in future research.

Methods
Test protocol: The volunteer testee put their heel pad on the detection hole, with the point right below the rear end of calcaneus at the center. The detector with suction cup automatically rises and touches the pad, and vacuum is then applied to adjoint the skin. The vacuum degree provided by regular laboratory oil pump is sufficient for the suction without uncomforted feeling reported by testees. The reciprocal tensile/compression is processed for ten seconds (Fig. 1d), with the amplitude of ±2mm and frequency of 2Hz. The amplitude is chosen by observing the regular tensile/compression motion of healthy plantar pad, and the frequency is determined by an empirical limit of human foot usage in common sense. The tests on mimic foot model and brick sample are similar.