SBIR-STTR Award

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.

Keywords:
Bio-Inspired Adhesives; Pressure-Sensitive Adhesives; Seal Leakage; Respiratory Protective Masks; Skin; Roughness; Sweat.

A new generation of bio-inspired adhesives is under development for controlling the face-seal leakage in respirator masks. While conventional pressure-sensitive adhesives rely on liquid-like fluidity under pressure to adapt to surface roughness, biological adhesion mechanisms employed by gecko, spider and insects rely upon the compliance of a fibrillar array to accommodate surface roughness for magnifying molecular-scale contacts. The fibrillar nature of biological adhesives distinguishes them from conventional pressure-sensitive adhesives in terms of adhesion to wet surfaces via capillary action, self-cleaning, stability under repeated use and in severe conditions, the ability to accommodate facial hair, dirt and skin irregularities, and removability. Bio-inspired adhesives, however, cannot match some key qualities of pressure-sensitive adhesives, including ductility and energy absorption capacity (reliability and immunity to excess size effect), density of the interface (sealing qualities), and accommodation of local (sub-micron-scale) roughness (adhesion capacity). Our approach makes complementary use of patterned bio-inspired adhesives and highly stable variations of pressure-sensitive adhesives to combine their corresponding advantages in a new generation of bio-inspired adhesives. The integrated theoretical/experimental work of Phase I project verified the balanced qualities and the commercial promise of the new bio-inspired adhesives. The proposed Phase II project will build upon the Phase I accomplishments towards full development and optimization of the new bio-inspired adhesives, their integration into the peripheral seal of full-facepiece respirator masks, thorough evaluation of the corresponding benefits to the face-seal leak resistance of respirators, and assessment of the commercial potential of the technology in application to respirator masks and also in other fields of application.

Keywords:
Bio-Inspired Adhesives, Pressure-Sensitive Adhesives, Elastomers, Fibrillar Arrays, Fibril Tip Modification, Respirator Masks, Peripheral Seals, Face-Seal Leakage.