A Constitutive Model to Characterize In Vivo Human Palmar Tissue.

In vivo characteristics of palmar soft tissue can be used to improve the accuracy of human models to explore and simulate a range of contact scenarios. Tissue characteristics can help to assess injury prevention strategies and designing technologies that depend on quantified physical contacts such as prosthetics, wearables, and assistive devices. In this study, a simplified quasi-linear viscoelastic (QLV) model was developed to quantify large deformation, in vivo soft tissue relaxation characteristics of the palm. We conducted relaxation tests on 11 young adults (6 males, 5 females, 18 < age < 30, mean age: 25 ± 4 yr) and 9 older adults (6 males, 3 females, age > 50, mean age: 61.5 ± 11.5 yr) using a 3 mm indenter to a depth of 50% of each participant's soft tissue thickness. The relaxation parameters of the QLV model were found to differ with age and sex, emphasizing the importance of using targeted material models to represent palmar soft tissue mechanics. Older adults showed on average 2.3-fold longer relaxation time constant compared to younger adults. It took 1.2-fold longer for young males to reach equilibrium than for young females; however, young females had a higher level of relaxation (36%) than young males (33%). Differences in specific QLV model parameters, P1, P2, and α were also found between age and sex groups. QLV characteristics differentiated by age and sex, add biofidelity to computational models which can provide a better representation of the diversity of tissue properties in the population.