Hygroscopy of Single‐Stranded DNA Nano‐Brushes: Atomic Workings of its Hydration‐Induced Deformation

Hydration control of structure and mechanical properties is a process widely exploited in living organisms for key biological functions and, most recently, also in man-made smart materials. Here, the challenge of unveiling the underlying atomistic mechanisms of this phenomenon using all-atom Molecular Dynamics (MD) simulations to model the hygroscopic properties of polymer-brushes composed by single-stranded DNA (ssDNA) molecules is faced. The simulations identify three swelling regimes with a markedly different mechanical response. This evolution is produced by the competition between the formation of additional water-ssDNA and water-water hydrogen bonds, in a subtle interplay with the co-evolving structure of the ssDNA SAM. This cooperative interaction between conformational and hydration degrees of freedom should be applicable to other polymer brushes and related hydrogen-bonded systems. The results have direct implications for the use of ssDNA SAMs as sequencing devices, explaining the crucial role of the polymer-brush density in the SAM collective response to hydration, and for the alternative design of hygroscopic materials, that exploit the extreme hygroscopic power of biological polymers like ssDNA brushes.