How the Viscoelastic and Sweat-Absorbing Properties of Skin Adhesives Affect Their Performance during Perspiration

Maintaining adhesion on human skin during perspiration is challenging and may result in undesired detachment. Improvements in the performance are generally made by adjustments in the adhesive composition, which simultaneously changes the viscoelastic properties, sweat absorption capabilities, and peel adhesion. To aid the design of skin adhesives for prolonged wear, we systematically investigate the impact of the viscoelastic properties and the sweat absorption capabilities during perspiration. Therefore, four skin adhesives are designed with a stepwise variation in one of the properties at a time to decouple the different effects. A perspiration simulator is used during the study to ensure well-defined and reproducible perspiration conditions. Depending on the sweating pressure and the adhesive formulation, different failure mechanisms are observed. The sweating pressure delaminates the non-absorbing adhesives and causes adhesive failure. Thereby, viscoelastic flow and subsequent cavity growth occur if the sweating pressure overcomes the mechanical strength of the adhesive, while elastic detachment is observed otherwise. The addition of absorbing components results in a pressure relief and thus enables the maintenance of adhesion over prolonged periods. However, the absorption of sweat weakens the mechanical integrity of the adhesive and causes cohesively dominated failure during peel. These findings are also supported by the behavior of the adhesives on human skin before and after perspiration. This shows that the design of skin adhesives requires an intricate balance between viscoelasticity and sweat absorption in order to maintain adhesion during perspiration.