Accuracy and reliability of a dynamic biomechanical skin measurement probe for the analysis of stiffness and viscoelasticity

Mechanical behavior of full-thickness burn human skin is rate-independent

Skin tissue is recognized to exhibit rate-dependent mechanical behavior under various loading conditions. Here, we report that the full-thickness burn human skin exhibits rate-independent behavior under uniaxial tensile loading conditions. Mechanical properties, namely, ultimate tensile stress, ultimate tensile strain, and toughness, and parameters of Veronda-Westmann hyperelastic material law were assessed via uniaxial tensile tests. Univariate hypothesis testing yielded no significant difference (p > 0.01) in the distributions of these properties for skin samples loaded at three different rates of 0.3 mm/s, 2 mm/s, and 8 mm/s. Multivariate multiclass classification, employing a logistic regression model, failed to effectively discriminate samples loaded at the aforementioned rates, with a classification accuracy of only 40%. The median values for ultimate tensile stress, ultimate tensile strain, and toughness are computed as 1.73 MPa, 1.69, and 1.38 MPa, respectively. The findings of this study hold considerable significance for the refinement of burn care training protocols and treatment planning, shedding new light on the unique, rate-independent behavior of burn skin.

Radiation cross-linked gelatin/sodium alginate/carboxymethylcellulose sodium hydrogel for the application as debridement glue paste

Autolytic debridement can accelerate wound healing by removing necrotic tissue. A hydrogel was fabricated from an aqueous solution of gelatin, sodium alginate and carboxymethylcellulose sodium by radiation-induced cross-linking at room temperature, which was aiming at the application of debridement glue paste. The swelling ratio of the debridement glue paste is 30 times to its dry weight, when the weight ratio of gelatin/sodium alginate/carboxymethylcellulose sodium was 2:2:2 and the absorbed dose was 20 kGy, with dose rate of 20 Gy/min. The extrusion and compressive assay have confirmed that it possessed stable mechanical strength, and the weight ratio had little effect on the molecular structure by FTIR and TGA. Cell culture experiments demonstrated the debridement glue pastes with the cytotoxicity of grade 0 or 1 (biosafe). The debridement glue paste group could remove the necrotic tissue within 4 days and showed complete wound healing within 18 days; comparatively, the control group without treatment removed the necrotic tissue within 10 days and showed complete wound healing within 26 days in animal experiments using rabbit scald model. Histologic analysis exhibited that more granulation tissue was observed in debridement glue paste. The result of this study suggested that debridement glue pastes had excellent biocompatibility, could selectively remove necrotic tissue, induced granulation tissue formation and accelerated the wound healing.

Strain rate and anisotropy effects on the tensile failure characteristics of human skin

The anisotropic failure characteristics of human skin are relatively unknown at strain rates typical in impact biomechanics. This study reports the results of an experimental protocol to quantify the effect of dynamic strain rates and the effect of sample orientation with respect to the Langer lines. Uniaxial tensile tests were carried out at three strain rates (0.06s(-1), 53s(-1), and 167s(-1)) on 33 test samples excised from the back of a fresh cadaver. The mean ultimate tensile stress, mean elastic modulus and mean strain energy increased with increasing strain rates. While the stretch ratio at ultimate tensile stress was not affected by the strain rate, it was influenced by the orientation of the samples (parallel and perpendicular to the Langer lines. The orientation of the sample also had a strong influence on the ultimate tensile stress, with a mean value of 28.0 ± 5.7 MPa for parallel samples, and 15.6 ± 5.2 MPa for perpendicular samples, and on the elastic modulus, with corresponding mean values of 160.8 MPa ± 53.2 MPa and 70.6 MPa ± 59.5 MPa. The study also pointed out the difficulties in controlling the effective applied strain rate in dynamic characterization of soft tissue and the resulting abnormal stress-strain relationships. Finally, data collected in this study can be used to develop constitutive models where high loading rates are of primary interest.

Measuring Lifting Forces in Rock Climbing: Effect of Hold Size and Fingertip Structure

This study investigates the hypothesis that shallow edge lifting force in high-level rock climbers is more strongly related to fingertip soft tissue anatomy than to absolute strength or strength to body mass ratio. Fifteen experienced climbers performed repeated maximal single hand lifting exercises on rectangular sandstone edges of depth 2.8, 4.3, 5.8, 7.3, and 12.5 mm while standing on a force measurement platform. Fingertip soft tissue dimensions were assessed by ultrasound imaging. Shallow edge (2.8 and 4.3 mm) lifting force, in newtons or body mass normalized, was uncorrelated with deep edge (12.5 mm) lifting force (r< .1). There was a positive correlation (r= .65,p< .05) between lifting force in newtons at 2.8 mm edge depth and tip of bone to tip of finger pulp measurement (r< .37 at other edge depths). The results confirm the common perception that maximum lifting force on a deep edge (“strength”) does not predict maximum force production on very shallow edges. It is suggested that increased fingertip pulp dimension or plasticity may enable increased deformation of the fingertip, increasing the skin to rock contact area on very shallow edges, and thus increase the limit of force production. The study also confirmed previous assumptions of left/right force symmetry in climbers.