Synthesis and Measurement of Cohesive Mechanics in Polydopamine Nanomembranes

Polydopamine (PDA) is a complex biomimetic material exhibiting advantageous properties of both melanin polymers and biological adhesives. These concomitant features have prompted an increasing interest in exploiting PDA for bioelectronics, smart coatings, and functional membranes. The ability to apply the rich biochemistry of melanins in structurally durable contexts will help accelerate their practical implementation and the design of next-generation materials. Here, this paper presents approaches for manipulating the adhesion and cohesive mechanics of PDA nanomembranes. Visual recording of PDA film delamination from SiO2 substrates reveals accelerated delamination (spanning orders of magnitude from 12 h to 1 min) with increasing pH and monovalent salt concentration. Delamination is retarded for films synthesized from higher dopamine concentrations, and it is completely prevented in the presence of Ca2+. Delaminated nanomembranes exhibit orientation-dependent underwater adhesion to polydimethylsiloxane elastomer. Elastic moduli of PDA nanomembranes are quantified by compressive thin film buckling, and the measured value of 2.0 +/- 0.9 GPa supports compositional simulations of PDA. Crosslinking of primary amines within the nanomembranes by genipin is successful in increasing the modulus to 7.9 +/- 2.5 GPa. These results demonstrate that the adhesive stability and elastic modulus of PDA films/nanomembranes can be controlled by synthesis and postprocessing techniques.