Quantitative Dynamic AFM Hydration-Adsorption Design for Hygroscopic and Bio-Compatible Polymeric Nanofibers

Abstract

Nanomechanical properties of bio-compatible polymers play crucial roles in tissue engineering scaffolds and filtration devices. The hygro-mechanical properties of those fibers have been mostly studied from a very coarse perspective, reaching a micrometer-scale. However, at the nanoscale the mechanical response of polymeric fibers becomes more challenging due to both experimental-theoretical limitations. In particular, the environment-mediated mechanical response of polymer-fibers demands advanced models that consider sub-nanometric changes in the local structure of water-intercalated with single-polymer-chains. Herein, atomic force-microscopy (AFM) experiments, analytical theory, and simulations are combined to determine the elastic properties of the nanofibers as a function of relative humidity. The effect of morphological changes from the adsorbed water-layer, and an ensemble of inter-chain interaction strength and morphological changes at peak-forces are explored. For the polyvinyl-alcohol (PVA) nanofibers, considerable differences are found, which are strongly dependent on the molecular signatures of hydration-adsorption at a polymer-chain level. Here, the semi-empirical model plays a key role in properly interpreting experiments by evaluating only a few observables, the height, phase (dissipation), and alternatively the force-distance curves. Beyond the semi-empirical model, an analytical approach to calculate the peak-forces of hygroscopic materials is featured, which enables on-the-fly characterization of the samples, and thus the interactive adjustment of operational-parameters.