Bio-Inspired Dry Adhesives

The proposed project will develop bio-inspired adhesives for reliable and convenient sealing of full-facepiece respiratory masks against skin. Conventional pressure-sensitive adhesives rely on a liquid-like fluidity to establish molecular-scale contact against rough surfaces. While this contact mechanism limits their versatility and stability, they exhibit desirable long-range deformations which benefit adhesion capacity. Nature, on the other hand, relies on the conformability of fibrillar structures as a more versatile means of establishing massive molecular-scale contacts against rough surfaces. This mechanism relies on van der Waals interactions as well as the capillary effect for adhesion to dry and wet surfaces, and offers the potential to accommodate micro-scale obstacles (e.g., dust particles and hair). Extensive efforts devoted to the development of biomimetic adhesives, however, have not yet produced commercially viable end products. While synthetic fibrillar structures (based on carbon nanotube or polymer fibril arrays) can desirably adapt to the global surface roughness, the fibril tips lack the ability to adapt to the local surface roughness. Recent work has confirmed that modification of fibril tips for enhancing their conformability benefits the adhesion capacity; such refined fibrillar arrays, however, still lack the adhesion qualities and the scalability needed for commercial success. We propose to optimize the design of polymer fibrillar arrays and refine the fibril tips using conformable polymers which are highly crosslinked varieties of today’s pressure-sensitive adhesives. This design relies on the conformability of the fibrillar structure and the pressure-sensitive features of fibril tips to adapt to global and local roughness, respectively. The complementary action of these two adhesion mechanisms promises to overcome the drawbacks experienced by each of them when used individually. Biocompatible polymer fibrillar arrays provide a versatile and economical basis for development of the new bio-inspired adhesives; modification of the fibril tips can be accomplished using a simple “inking & printing” method. The proposed Phase I project will: (i) define the performance requirements of adhesives for sealing full-facepiece respiratory masks; (ii) design bio-inspired adhesives which meet the targeted performance requirements in application to dry and wet skin in the presence of hair; (iii) fabricate bio-inspired adhesives, and evaluate their performance against dry and wet synthetic substitutes for skin; and (iv) develop refined models of bio-inspired adhesives, and assess their potential to meet the requirements for sealing full-facepiece respiratory masks against skin. Efforts in Phase I Option will be devoted to fabricating second-generation bio-inspired adhesives, verifying their improved performance, and identifying aspect of design which require further refinement.