An in vitro biomechanical comparison of human dermis to a silicone biosimulant material

A major quality of life concern for designers of prosthetics is the look and feel of the limb. Even up close, the limb should look and feel natural. This means covering the underlying mechanical components with a "cosmesis" . This cosmesis should match the skin tone of the patient and the material from which it is constructed should have similar mechanical properties to human skin. The objective of this study was to compare a candidate biosimulant material to cadaveric skin. Skin specimens were harvested from three donors furnished by the Maryland State Anatomy Board. In daily use, the cosmesis material would often be compressed against the hard backing of the case. Thus, to compare the two materials, indentors with eight different tip geometries were driven into samples supported by a flat metal plate. 1.5" square samples were compressed to 40% of their initial thickness at a rate of 0.1 mm/sec using a servohydraulic test machine. Force versus deflection curves were automatically reduced to stiffness and elastic modulus values for each trial using a custom MATLAB algorithm. Results of this study showed that the surrogate material was significantly more compliant than human skin (ANOVA, p<0.05). A secondary, perhaps more interesting result is an estimate of the compressive elastic modulus of human skin. While the properties of human skin in tension and penetration are well documented in the literature, there is a paucity of data on compression of skin against a hard surface. In the broader biomechanics context, this loading modality is observed frequently where skin abuts directly to bone, such as the hands, chest, face, and scalp. The wide range of tests performed in this study estimate the compressive elastic modulus of human skin at 6.8 +/- 2.0 MPa.