Targeted Tuning of Interactive Forces by Engineering of Molecular Bonds in Series and Parallel Using Peptide-Based Adhesives.

Polymer-mediated adhesion plays a major role for both technical glues and biological processes like self-assembly or biorecognition. In contrast to engineering systems, adhesive strength in biological systems is precisely tuned via well-adjusted arrangement of individual bonds. How adhesion may be engineered by arrangement of individual bonds is however not yet well-understood. Here we show how the number of bonds in series and parallel can significantly influence adhesion forces using specifically designed surface-bridging peptides. We directly measure how adhesion forces between -COOH and -NH2 functionalized surfaces across aqueous media vary as a function of the number of bonds in parallel. We also introduce surface bridging peptide sequences that are similarly end-functionalized with amines and carboxylic acid. Compared to single molecular junctions, adhesive strength mediated by these surface bridging peptides decreases by a factor of 2 for adhesive junctions that consist of two acid/base bonds in series. Furthermore, adhesive strength varies with the density of bonds in parallel. For dense systems, we observe that the formation of a bridging peptide monolayer is sterically hindered and therefore adhesion is further reduced significantly by 20%. Our results unravel how the arrangement of individual bonds in an adhesive junction allows for a wide tuning of adhesive strength on the basis of utilizing just one single specific bond. As such, for peptide adhesives it is essential to consider bonds in parallel in a wide range of applications where both high adhesion and triggered release of adhesive bonds is essential.