Effects of hydration water on bioresponsiveness of polymer interfaces revealed by analysis of linear and cyclic polymer-grafted substrates†

Given that the hydration water of polymer matrices may differ from that of outermost polymer surfaces, processes at biomaterial–biofluid interfaces and role of hydration water therein cannot be adequately examined using most conventional characterization methods. To bridge this gap, a gold substrate was herein modified with linear and cyclic poly(2-methoxyethyl acrylate) to prepare gl-PMEA and gc-PMEA surfaces, respectively, as models for the outermost surfaces of blood-contacting medical devices. Both surfaces suppressed the adhesion of human platelets but differed in the adhesion behaviors of normal and tumor cells despite having the same areal density of fixed-end units. The surfaces were analyzed using quartz crystal microbalance (QCM), frequency modulation atomic force microscopy (FM-AFM), and X-ray emission spectroscopy (XES) measurements under wet conditions to clarify the relationship between bioresponsivity and hydration water. QCM measurements provided evidence that both grafted-PMEA were hydrated. FM-AFM observations revealed that the swelling layer was thicker for gc-PMEA. To rationalize the differences in the surface hydration states, we performed XES measurements under conditions enabling control over the number of hydration water molecules. In the low-water-content region, hydrogen bonds or interactions between water molecules developed in the vicinity of gl-PMEA but not gc-PMEA. Thus, the initial hydration behavior of the gc-PMEA surface, which promoted intermediate water formation, was different from that of the gl-PMEA surface. The results suggested that the adjustment and optimization of the hydration state of outermost biomaterial surfaces enable the control of bioresponsivity, including the selective isolation of tumor cells.