Mechanophores are force-responsive molecules that have the potential to serve as stress sensors in various material systems. This review discusses recent scientific advances and critical challenges facing engineers regarding implementation of mechanophores in polymeric materials.

The adhesion of rough surfaces comprised of dewetted thermoplastic asperities on an elastomer is controlled by changing the applied compressive load.

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and medical devices [4] that must be removed from skin without causing pain. Additionally, many of these applications involve adhesion to nonplanar surfaces that span large areas, implying that scalability is another requirement. Conventional pressure sensitive adhesives (PSAs) satisfy the first requirement. They can sustain large loads due to their ability to flow and establish conformal contact without significant applied pressure. [5] While PSAs require a relatively low threshold pressure for contact formation, there is little to no change in their adhesive response if the applied pressure is above this threshold. These materials are far from ideal as large deformations are required for interfacial separation and, if the adhesive fails cohesively, permanent damage of the interface will limit its reusability and contaminate the target substrate.Significant advances have been made in the development of new adhesive systems. Surface modification, such as patterning with microscopic wrinkles [6][7][8] or fibrillar posts, [9][10][11][12] have been demonstrated to enhance adhesion strength or release with some success. These materials are advantageous as they can be designed with stiffer and more elastic properties relative to PSAs, which can yield switchable [11,12] or even tunable adhesives. [8] However, these surface modification approaches remain limited either by scalability or the inability to be adapted to a diverse range of surface chemistries. A scalable and universal strategy, which enables the modification of any adhesive surface for pressure-tunable adhesion and easy release on a variety of substrate materials and geometries, has yet to be realized. Previously, [13] we presented a new and generalized approach to obtain a material with pressure-tunable adhesion. This new pressure-tunable adhesive (PTA) is a surface patterned material that utilizes polymer thin film dewetting. This phenomenon can be realized in a host of materials, which we leverage here to form selfassembled stiff asperities on an elastomeric substrate to control adhesion. In the present work, we study the adhesive properties of these materials and demonstrate the control of their pressure-tunable behavior by changing the size of the stiff asperities. As thin film dewetting can be designed to occur in various materials systems, we anticipate that our present strategy to generate a patterned adhesive can displace existing surface patterning approaches and be applied over large surface areas.Polymer thin film dewetting is an interfacial phenomenon associated with an energetically favorable breakdown of a polymer film into droplets due to an external thermodynamic driving force such as temperature or solvent annealing. [14] Control of adhesion is important in a host of applications including soft robotics, pick-and-place manufacturing, wearable devices, and transfer printing. While there are adhesive systems with discrete switchability between states of high and low adhesion, achieving continuously variable adhesion strength remains a challe...

Pressure‐Tunable Adhesives In article number 2207337, Chelsea Davis and co‐workers show that pressure‐tunable adhesives (PTAs) demonstrate variable adhesive separation forces depending on the application pressure used to form the interface. PTAs are formed by annealing a polymer film on a silicone surface so that it dewets, forming polygonal clusters. The large gray circle is the flat face of a cylindrical probe about to make contact with the PTA during a probe‐tack adhesion experiment.

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