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.