Easy removal of pressure sensitive adhesives for skin applications

There are two essential requirements of medical pressure sensitive adhesives: that they should stick firmly to a difficult substrate (skin) and that they should be easily and cleanly removed from that substrate when desired. These requirements would seem to be in conflict: a high peel force usually signals the ability to stick firmly, while a low force is needed when removing dressings by peeling. A number of ways have been considered to resolve this conflict. These may be divided into two broad categories: those that make the best of existing pressure sensitive adhesives technology, broadly taking a physical approach, and those that introduce novel chemistry into the process. Physical approaches consider such details as the dependence of peel force on peel angle, peel rate, backing materials, the deformation of the skin during peeling and use of barrier films and solvents. As an alternative to simply making the best of the physics of the peeling process, various workers have devised chemical systems for making the adhesive less strongly adhering at the time of removal. These systems usually consist of introducing a 'switch' mechanism into a strongly adhering adhesive so that its adherence may be reduced significantly at the time of removal by operation of the 'switch'. Means of activating the 'switch' include: heat (warming or cooling), application of water via an absorbent backing and exposure to visible light. These may produce physical or chemical changes in the adhesive. While these approaches bring benefits to patients, consideration of the science behind them is leading to an enhanced understanding of the peeling process. (C) 2001 Elsevier Science Ltd. All rights reserved.