In vivo adhesive behavior of human facial skin by a modified indentation test

A better understanding of the adhesive behavior of human facial skin is important for dermatological or cosmetic applications. For their in vivo experimental characterization and analysis, the indentation test is an effective and widely used method. In this study, our independently developed transparent indenter and curved surface optical imaging technique are improved, by which the contact area of facial skin can be in vivo and in situ obtained during an indentation test. Thanks to the modified indentation technique, the real contact radii of human facial skin under different conditions (normal, as-moistened, moistened after 30 min) are obtained, and their adhesive behavior is studied. Moreover, we modify the classical elastic adhesion theory (JKR theory) based on the Neo-hookean model considering the fact that the hyperelastic model is usually more appropriate for skin research. It is evidenced that the adhesion properties highly influence the contact area as well as the adhesive force/energy, and our modified hyperelastic adhesion theoretical model shows a better agreement with the experimental values of contact radius under each condition.